Power generation from cold energy...iii Abstract This document reviews different methods to take...

BACHELOR’S THESIS

Power generation from cold energy

Faculty of Engineering

IREXC10015 International student research project

Student: Rubio del Amor, Jose Antonio

Student number: B18INT02

Bachelor’s degree: Mechanical Engineering

Supervisor: Olav Aaker

Fredrikstad, June 2018

iii

Abstract

This document reviews different methods to take advantage of the LNG cold energy. It is

proposed a system where an Organic Rankine Cycle and the direct expansion of the

natural gas are combined to increase the thermal efficiency of the LNG regasification

process. It also suggested the utilization of low-grade waste heat to improve the

performance. After the theoretical approach, the results are intended to be applied to an

actual case of small size. Some guidelines for the components and working parameters

selection are proposed as well. It can be concluded that for a system of this type, the

turbine is the most expensive element. Therefore, the working parameters should be

adapted to it. Additionally, it has been suggested some alternatives to design a minimum

viable setup. Finally, it can be drawn the possibility to obtain 39 kW·h/tonLNG from the

analysis of a proposed case.

v

Acknowledgments

The completion of a degree is not something that a single person achieves. I would

therefore like to mention certain people as a sign of gratitude:

First of all, thanks to my parents and siblings for believing in me and investing

in my education.

Thanks to the Østfold University College and especially to Olav Aaker who has

overseen my work.

Thanks to the Universidad Politécnica de Cartagena and to all the professors

from whom I have learned something.

And finally, thanks to my colleagues with whom I have lived this engineering

adventure and with whom I have learned the really important things.

vii

List of contents

Abstract ............................................................................................................................ iii

List of contents ............................................................................................................... vii

List of Figures .................................................................................................................. ix

List of tables ..................................................................................................................... x

Presentation ..................................................................................................................... xi

Nomenclature.................................................................................................................. xii

1. Introduction .............................................................................................................. 1

1.1 Topic and problem statement. ............................................................................ 1

1.2 Objectives .......................................................................................................... 4

1.3 Background ........................................................................................................ 4

1.4 Overview of the document ................................................................................. 5

2. Theoretical framework ............................................................................................. 6

2.1 Natural Gas ........................................................................................................ 6

2.2 NG direct expansion .......................................................................................... 7

2.3 Carnot cycle ....................................................................................................... 8

2.4 Stirling cycle ...................................................................................................... 9

2.5 Rankine cycle ..................................................................................................... 9

2.6 Brayton cycle ................................................................................................... 10

2.7 Kalina cycle ..................................................................................................... 10

3. Methodology ........................................................................................................... 11

4. Revised literature .................................................................................................... 12

5. Suggested solutions ................................................................................................ 14

5.1 Direct Turbo Expansion ................................................................................... 14

5.2 ORC with low-grade waste heat as heat source and direct NG expansion ...... 14

6. Theoretical analysis ................................................................................................ 16

6.1 Direct NG Expansion ....................................................................................... 16

6.1.1 Conceptual design ......................................................................................... 16

6.1.2 Thermodynamic analysis ............................................................................... 17

6.1.3 Efficiency....................................................................................................... 18

6.2 ORC with low-grade waste heat as heat source and Direct NG Expansion ......... 20

6.2.1 Conceptual design ......................................................................................... 20

6.2.2 Working fluid ................................................................................................ 22

6.2.3 Thermodynamic analysis ............................................................................... 25

viii

6.2.4 Efficiency....................................................................................................... 27

7. Selection of real components .................................................................................. 29

7.1 Selection of the pumps ..................................................................................... 29

7.2 Selection of the heat exchangers ...................................................................... 29

7.3 Selection of the turbines .................................................................................. 30

8. Investment analysis ................................................................................................ 31

9. Minimum Viable Design ........................................................................................ 32

10. Simulation of an actual application ..................................................................... 33

11. Future ................................................................................................................... 40

12. Conclusions. ........................................................................................................ 41

References ...................................................................................................................... 42

Appendix 1: List of suppliers ......................................................................................... 46

ix

List of Figures

Figure 1. World Energy Supply. Enerdata, 2016. ............................................................ 1

Figure 2. LNG terminal in Øra from the company Skangas. Google Maps, 2018. .......... 2

Figure 3. LNG terminal in Øra from the company Skangas. Google Maps, 2018. .......... 2

Figure 4. Diagram h-s for methane, EES. [17] ................................................................. 7

Figure 5. Comparison of reservoir temperatures on Carnot Engines. .............................. 9

Figure 6. Thermoacoustic Stirling Engine. Wang, Dubey, Choo, Duan, 2017. ............. 12

Figure 7. Direct NG expansion configuration. ............................................................... 16

Figure 8. Approximate LNG thermodynamic cycle. EES, 2018. ................................... 18

Figure 9. Increasing the efficiency, lowering the outlet pressure. EES, 2018................ 19

Figure 10. Increasing efficiency, increasing gas temperature. EES, 2018. .................... 19

Figure 11. ORC with low-grade waste heat as heat source and direct NG expansion

configuration. .................................................................................................................. 21

Figure 12. P-T diagram for Carbon Dioxide. Wikipedia. ............................................... 24

Figure 13. Approximate propane thermodynamic cycle. EES, 2018. ............................ 25

Figure 14. Comparison between different working pressures. EES, 2018. .................... 28

Figure 15. Representation of the system. ....................................................................... 34

Figure 16. Propane thermodynamic cycle. ..................................................................... 34

Figure 17. LNG thermodynamic cycle. .......................................................................... 35

x

List of tables

Table 1. LNG composition. Skangas 2018. ...................................................................... 3

Table 2. Physical, safety and environmental data for preselected working fluids. M.

Romero Gómez et al. / Renewable and Sustainable Energy Reviews 38 (2014) 781–795

........................................................................................................................................ 23

Table 3. Working fluids price. Chem-space, 2018. ........................................................ 24

Table 4. Propane data at the different stages of the process. .......................................... 35

Table 5. LNG data at the different stages of the process. ............................................... 35

Table 6. Heat source data at the different stages of the process. ................................... 35

xi

Presentation

This project has been carried out by the student Jose Antonio Rubio del Amor. He is a

mechanical engineering student from the Technical University of Cartagena (Spain). In

the years 2017-2018, he is enjoying the Erasmus scholarship in the Østfold University

College (Norway).

The realization of the project is part of the fourth year of studies and it is considered the

bachelor thesis for the Mechanical Engineering bachelor’s degree. Its main topic is the

recovering of energy from the Liquified Natural Gas and it is supervised by Mr. Olav

Aaker.

The motivation of the project is the desire to learn how to manage the limited resources

that exist in the world. Concern for the environment is increasing every day, so it is

important to research systems that reduce the impact that humans have on nature. The

development of sustainable technologies and the optimization of the use of fossil fuels

are the main motivations.

xii

Nomenclature

Abbreviatures

ASHRAE American Society of Heating,

Refrigerating and Air-Conditioning

Engineers

ATEX Atmosphères Explosibles

BC Brayton Cycle

EES Engineering Equations Solver

GWP Global Warming Potential

LNG Liquified Natural Gas

NG Natural Gas

ODP Ozone Depletion Potential

ORC Organic Rankine Cycle

R Refrigerant

RC Rankine Cycle

Units

$ United States dollars

€ euro

bcm billion cubic meter

g gram

h hour

K Kelvin degree

kJ kilojoule

kW kilowatt

m3 cubic meter

Nm3 Normal cubic meter

ºC Celsius degree

s second

USD United States dollars

Variables

m mass

q heat flow

h enthalpy

s entropy

T temperature

w work

Greek letters

Δ differential

η efficiency

Ψ exergy

Subscripts

0 equilibrium state

H hot

C cold

in input

turb turbine

out output

Power generation from cold energy Introduction

1

1. Introduction

1.1 Topic and problem statement.

Natural Gas (NG) is one of the cleanest fossil fuels and it has the lowest carbon footprint.

It produces 400 gCO2 per kilowatt-hour generated while the coal (anthracite) produces

around 860 gCO2/kWh and the diesel oil 700 gCO2/kWh [1].

Figure 1. World Energy Supply. Enerdata, 2016.

Nowadays, NG produces around 21% of world energy supply. Its consumption has been

increasing annually being higher than 3.500 bcm in 2016. Norway produced 120 bcm in

2016 being the seventh largest producer in the world [2]. Despite it produces almost all

its electric power by hydraulic power plants, also 6,25 bcm of NG were consumed in 2016

[2] for industrial purposes mainly [3].

Natural gas reserves are distributed around the world. Although most of the production is

transported by pipelines, when the distance between the production and the consumption

place is too long, it is necessary to liquify the NG and transport it by ship in its cryogenic

form. This is an advantage for the consumer countries because they do not depend on just

one supplier. It is expected that almost 50% of European NG demand will be supplied in

its liquid form by 2035 [4].

Liquified Natural Gas is produced by cryogenic refrigeration of NG and it is the most

expensive process in the NG supply chain. It is estimated that producing one ton of LNG

consumes around 850 kWh of electric energy [5]. Therefore, it is more expensive the NG

that it comes in liquid state than the NG that comes directly by pipelines [6]. For that

reason, it is interesting to recover part of the invested energy in the liquefaction process.

It is necessary to regasify the LNG before it is consumed. There are more than 117 LNG

regasification terminals around the world [7] of which just a few of them recover some

energy from the process. It usual to use sea water as heat source to regasify the LNG but

also ambient air. In any case, almost all the cold energy stored in the LNG is lost in the

surroundings.

This situation becomes a huge problem in a world where the NG consumption is

increasing annually and at the same time, the people are concerned about the environment.

21% Gas


2

It is necessary to develop a technology to increase the efficiency of the NG supply chain

and thereby reduce the environmental impact of this fuel.

Is it possible to generate electric power from the LNG cold energy? Is it possible to use

the cold for side processes instead of developing more complex refrigeration systems?

Would it be possible to turn the situation around and reduce the costs of using LNG?

These are some questions that will be answered in this document.

Finally, it is described an actual LNG regasification plant as introduction of the problem.

A small LNG regasification plant from the company Skangas is taken as an example [8].

Figure 2. LNG terminal in Øra from the company Skangas. Google Maps, 2018.

The receiving terminal is situated in Øra (Fredrikstad), in the south of Norway. It is close

to the sea in order to receive the fuel transported by LNG carriers weekly. It is sent directly

from the liquefaction plant of the company. In Øra there are two objectives. The first one

is to regasify part of the LNG and supply a NG network for the surrounding industries.

The second one is to refill some trucks and transport the LNG to more distant customers.

Most of the information described below has been obtained through communication with

several terminal managers.

This terminal has the capacity to store 6.415 m3 of LNG in nine different tanks. All the

tanks are connected between each other and they keep the LNG at -162 ºC and

atmospheric pressure approximately.

Figure 3. LNG terminal in Øra from the company Skangas. Google Maps, 2018.


3

There are twelve vaporizers but just six of them work at the same time. This is because

the vaporizers generate ice around them and the efficiency decreases so it is necessary to

switch with the other six until the ice is melted. The working principle is that the LNG

flow crosses through small diameter pipelines for a long distance. So there is a huge

surface where the energy exchange is favored between the LNG and the air of the

surroundings. Each vaporizer can stand 40 bar and they are designed to work in a range

of temperatures between -196 ºC and 50 ºC.

The flow rate for the regasification process is very seasonal but there is an average around

2,5-3 tons per hour (0,7-0,8 kg/s).

After the regasification, the NG is at 3 bar and ambient temperature except when ambient

temperature is below 5 ºC that the gas is heated before the distribution. For safety reasons,

a chemical compound is added to the NG in order to detect leakages due to it is colorless

and odorless. Henceforth, 3 bar is considered as distribution pressure for all the analyses

despite it could be different depending on the gas network.

In this case, there is not a pump to set a working pressure and a flow rate. It depends on

the customers demand. Also, it is important to note that the vaporizers work with air from

the surrounding, so any cold energy is recovered in the process.

LNG usually has a density of 443,8 kg/m3 at -159,4 ºC or in gas form 0,774 kg/Nm3

according to SkanGas analysis. The typical values for the composition are showed below

but they can vary depending on the composition of the feed gas as well as the operational

parameters in the liquefaction plant.

Table 1. LNG composition. Skangas 2018.

Taking the Øra LNG receiving terminal as an example, it is seen a simple process. It

would be possible to modify the LNG regasification chain to implement an electric power

generation system without increasing complexity? This one and other objectives of this

document are described in the following section.

Typical composition Mol (%) Weight (%)

N2 0,35 0,56

CH4 92,10 85,42

C2H6 6,64 11,55

C3H8 0,76 1,94

Others 0,15 0,53


4

1.2 Objectives

The aim of this work is to showcase the importance of recover the cold energy from the

LNG to generate electric power.

It is necessary to understand some other concepts to achieve the main objective. Some

other task to be carried out are:

• To understand and to analyze the LNG regasification process.

• To research some possible uses for cold energy.

• To understand and to analyze different technologies to recover cold energy.

• To propose a viable solution to increase efficiency in the NG supply chain.

Carry out a theoretical thermodynamic study of it.

• To design an experimental plant that is able to generate electric power at the

same time that regasify the LNG. To calculate its efficiency, its cost and the

investment recovery time. The solution proposed will be for a small

experimental terminal, being planned the implementation in a small

regasification plant where the LNG flow is not very large.

• To comment the technologies that is necessary to develop in order to optimize

the NG use in the future.

Also, from the academic point of view there are some objectives to be achieved with this

work:

• To learn how to organize the working load in a certain time period.

• To learn how to obtain technical information from reliable sources.

• To learn how to reference the work of others.

• To learn how to find data and statistics and present them in a clear and easy to

understand way.

• To learn how to make a thermodynamic analysis of an energy process.

• To learn how to apply theoretical results to actual cases.

1.3 Background

The first LNG regasification plant was built around 1969 in Spain [7]. However, it was

not until ten years later that Osaka Gas started operating the first LNG regasification plant

with power generation in Japan [9].

There are not too many LNG receiving terminal with power generation capacity but those

that do have it, it seems that they use a Rankine cycle, Direct NG expansion or both. In

this section, a summary of the LNG receiving terminals with exergy recovery is given but

also there is a detailed list of cryogenic power plants in Review of thermal cycles

exploiting the exergy of liquefied natural gas in the regasification process [10].


5

In conventional plants, the exergy is transferred to the sea water or another fluid as the

heat source. It is usually to find three gasification systems:

• Open rack vaporizers (ORV) with sea water.

• Submerged combustion vaporizers (SCV)

• Vaporizers that use air as heat source.

On the other hand, as it has been said the first LNG regasification plant with power

generation was started in 1979 in Japan with a 1.450 kW propane Rankine cycle (RC).

Nowadays, Japan still being the country with more LNG exergy exploitation and the

company Osaka Gas has the record of LNG exergy usage [11].

In Europe, the pioneer was the company Enagas in Spain with a 4,5 MW RC using sea

water as heat source [12]. It is operating since 2013 and the same company is planning to

install a NG direct expansion system of 5,5 MW in its Barcelona terminal. In France,

there is a synergy between the companies Fos-Tokin and Air Liquide to improve the

efficiency of both processes [13]. It is known that other European terminals use waste

heat in the LNG regasification process to decrease the environmental impact in the sea

water temperature, but they do not improve its efficiency at all [10]. To conclude, there

is in Puerto Rico an example that integrate the LNG as heat sink of a combined cycle

power plant [10].

Nevertheless, each terminal should carry out a technical-economic study to determine the

feasibility of an exergy recovery system due to not always the theoretical concepts are

profitable.

1.4 Overview of the document

The document is organized as follow: Section 1 introduces the problem of the actual LNG

industry, Section 2 analyses the theoretical aspect of LNG exergy exploitation and it

introduces some suitable technologies to do it, in Section 3 is explained how the project

has been developed, Section 4 is an overview of the papers carried out until the present,

Section 5 suggests suitable solutions to the problem and in Section 6, they are analyzed

theoretically. Section 7 it is about the selection of the appropriate components for the

installation, Section 8 is an economic analysis, Section 9 propose a Minimum Viable

Design for an installation, Section 10 analyses an actual case and Section 10 tries to set

some guidelines to the future. Finally, some conclusions are drawn from the work done.

Power generation from cold energy Theoretical framework

6

2. Theoretical framework

The concepts from the book Thermodynamics an engineering approach [14] have been

applied to the theoretical calculations in this section. On the other hand, the characteristics

of the fluids have been obtained from the software Engineering Equations Solver.

2.1 Natural Gas

NG is a colorless and non-toxic gas consisting mainly in hydrogen and carbon. It is

liquified when it reaches -162 ºC approximately. It is usually stored at some degrees

below that temperature and at atmospheric pressure. When natural gas is liquefied, its

volume decreases about 600 times, making it much more suitable for transportation [15].

To obtain LNG, it is necessary around 1370 kJ/kgLNG [16], a huge quantity that it is not

recovered currently in the regasification process. In the following paragraph, it is

discussed how much of that energy is possible to recover when the LNG becomes gas

again.

Exergy is the work potential of a certain system that is in disequilibrium with the reference

environment. And environment is the region around the system that it is not affected by

any process, so it keeps constant its properties [14].

How much exergy is there inside the LNG? The exergy available is considered to be

chemical and physical due to the kinetic and potential energy are insignificant compared

to the previous ones. The chemical energy is not used in the regasification process.

Therefore, it is the physical energy where the system will take advantage from. It would

be correct to say that the system exergy comes from an imbalance of the pressure and the

temperature between the LNG and the environment.

On the other hand, there are two different ways to exploit that exergy. It would be possible

to take advantage of that exergy in a thermal way using the cold for a refrigeration

application for example or generating a heat sink for a thermodynamic cycle.

Furthermore, the mechanical way to generate electric power can only be recovered

through the direct expansion of NG.

In order to calculate the potential work of the LNG, some assumptions are taken:

• The LNG is considered pure methane.

• The initial conditions are -162 ºC and 1 bar.

• The required NG distribution pressure is 3 bar.

• The environment conditions are 10 ºC and 1 bar.

Therefore, in this regasification process, the NG properties at the outlet will be 10 ºC and

3 bar. Also, it is known that the exergy change of a fluid stream as it undergoes a process

from state 1 to state 2 becomes [14].

∆𝛹 = (ℎ1 − ℎ2) + 𝑇0(𝑠2 − 𝑠1) (1)


7

Where

ℎ1 = −912,7 𝑘𝐽

𝑘𝑔

ℎ2 = −36,34 𝑘𝐽

𝑘𝑔

𝑠1 = −6,693 𝑘𝐽

𝑘𝑔 · 𝐾

𝑠2 = −0,6847 𝑘𝐽

𝑘𝑔 · 𝐾

𝑇0 = 10 º𝐶 = 283 𝐾

Therefore,

∆𝛹 = 824 𝑘𝐽

𝑘𝑔

The total LNG exergy is 984,53 kJ/kg. That means that taking the NG at the required

distribution conditions, the process would be able to recover around 83,71 % of the total

exergy.

Figure 4. Diagram h-s for methane, EES. [17]

2.2 NG direct expansion

NG expansion in an open cycle is the most inefficient way to exploit its exergy. Despite

it is the straightforward system, almost all the exergy would go to the heat source without


8

take advantage of it. It would be necessary to pump the LNG at a higher pressure than the

required for the distribution and then, the NG it is expanded in a turbine that transforms

just the mechanical exergy in electric power. It is in that moment when NG gets the

distribution pressure. Also, it must be noticed that it would be necessary to heat the NG

again because the temperature would be below ambient temperature at the turbine outlet.

Nevertheless, this process may be of interest in small regasification plants due to its

simplicity and low maintenance.

2.3 Carnot cycle

It is known that a heat engine is a cyclic device where the working fluid return to its initial

state at the end of each cycle. Work is done by the working fluid in one stage of the cycle

and on the fluid in other stage. The difference between this two works is the useful energy

that is possible to extract from the system. The efficiency of a cycle depends on the

processes that make it up. Therefore, the cycles with higher efficiency are the ones that

consists of reversible processes.

Reversible processes do not exist in the practice. However, reversible cycles set upper

limits on the performance of real cycles and they allow a better comparison between

actual heat engines.

A well-known reversible cycle is the Carnot cycle [14]. It consists in four reversible

processes that are:

1-2 Reversible Isothermal Expansion

2-3 Reversible Adiabatic Expansion

3-4 Reversible Isothermal Compression

4-1 Reversible Adiabatic Compression

Due to the nature of these processes, it can be observed that to develop such a cycle, an

energy source is needed to exchange energy with it.

It has been said that it does not exist in practice, so where are the limits?

The main restriction is that irreversible processes cannot be carried out, for example, there

is always friction. Another limit comes from the second law of thermodynamic and it says

that a heat engine cannot operate by exchanging energy with a single reservoir. Also,

there are two Carnot principles:

1. The efficiency of an irreversible heat engine is always less than the efficiency of

a reversible one operating between the same two reservoirs.

2. The efficiencies of all reversible heat engines operating between the same two

reservoirs are the same.

It has been said that is impossible to build a Carnot heat engine because there are not

reversible processes in the real world. But it is a good model to compare the maximum

efficiency between two energy reservoirs due to there are not others cycles with higher

efficiencies. Add that it is only necessary to know the temperature of both reservoirs

without knowing what is happening between them.


9

Besides the very low temperature of LNG provides a really valuable situation. Not just

from the exergetic point of view, it is because from the Carnot efficiency equation it can

be deduced that the temperature of the cold focus is crucial for thermodynamic cycles,

even more than the hot focus.

In the following figure are compared to thermodynamic cycles with the same temperature

differential between the heat source and the sink. However, the efficiency of the cycle is

considerably higher if the temperature differential is below 0 ºC. That means that it is

more worthwhile to invest effort in reducing the temperature of the cold reservoir than in

increasing the temperature of the hot one.

Figure 5. Comparison of reservoir temperatures on Carnot Engines.

2.4 Stirling cycle

Another system that involves an isothermal heat-addition process is the Stirling cycle.

The difference with the Carnot cycle is that the two isentropic processes are replaced by

two constant-volume regeneration processes. Regeneration in a cycle happens when the

heat is transferred to an energy storage device (regenerator) in one stage and that heat is

recovered in other stage of the process [14].

Nowadays, the application of the Stirling cycle to actual applications requires a quite

innovative hardware. Stirling engines are heavy and complicated and as their use is not

very widespread, they are expensive [17] [18] [19].

Stirling engines are quite interesting due to its good efficiency and the fact that the main

important parameter is the temperature differential between reservoirs, not much more.

Nevertheless, it seems that it is necessary to wait some time until the hardware is totally

developed [20].

It is not going to go deeper into this cycle, but it has been introduced as some studies that

apply its technology to the LNG regasification process will be described in following

sections.

2.5 Rankine cycle

The ideal RC [14] does not involve any internal irreversibilities. It is a cycle where the

working fluid is superheated in the hot side and it is totally condensed in the cold one.

RC consists of four different stages:


10

1-2 Isentropic compression in a pump

2-3 Constant pressure heat addition in a boiler

3-4 Isentropic expansion in a turbine

4-1 Constant pressure heat rejection in a condenser

The most interesting point of this cycle is the possibility to choose between hundreds of

working fluids. Each one has different properties so always there is one that fits to the

application.

In the regasification process, the low temperature of the LNG is used as heat sink to

condense the working fluid in the stage 4-1 of the RC. Therefore, the LNG exergy is not

used directly to generate electric power, but it is used to create a proper temperature

differential for the heat engine.

An Organic Rankine Cycle (ORC) differs from regular RC basically in that the first one

uses an organic fluid as working fluid.

2.6 Brayton cycle

It is quite similar to the RC. The main difference is that the working fluid is still gas state

through all the cycle [14]. For that reason, Brayton cycle (BC) is used when the

temperature of the heat source is very high. Sometimes, to increase the efficiency of

thermal processes, BC and RC are combined. The cold side of the Brayton cycle is used

as heat source in the boiler of the Rankine cycle due to that temperature still being useful

if the right working fluid is selected [10].

2.7 Kalina cycle

The choice of the working fluid is what make the difference with the RC. Kalina cycle

uses a mixture of two fluid (usually ammonia-water) with different boiling temperatures.

This allow a better heat absorption because the temperature is not uniform during the

phase change. It is useful because the temperature profile of the mixture is closer to the

heat source temperature so the exergetic efficiency improve. This cycle is a little bit more

complex due to the necessity to install a separator before the condenser [21], it has a

limited efficiency due to the limited temperature range of the mixture and there are no

actual plants implemented. Despite that, it still being an interesting solution when there

are the right conditions [10].

Power generation from cold energy Methodology

11

3. Methodology

Following this paragraph, it possible to see the guidelines to face almost every

engineering problem. Guidelines that are followed in this project until the third stage of

the diagram.

In order to state the problem, it has been studied several previous works from different

researchers. Mainly, the book Thermodynamics: an engineering approach [14] has been

used to carry out the thermodynamic analyses obtaining data from the software EES.

Finally, in order to apply the theory to a real system, the information has been searched

on the web, it has been reviewed different brochures and different companies have been

contacted.

Power generation from cold energy Revised literature

12

4. Revised literature

Before deciding which system is the most suitable for an experimental plant, numerous

previous papers have been reviewed and research has been carried out into which

technologies are currently being used in the world.

A selection of the most interesting papers for the LNG industry is described in the

following paragraphs:

• In the Nanyang Technological University (Singapore), it was made a complete

review about all the cold utilization systems of LNG in 2017 [22]. As conclusion,

it is said that the LNG cold energy can be utilized in the different processes such

as power generation, air separation, CO2 capture, desalination, etc. But one of the

more common uses is the power generation using a combination between a RC

and Direct NG expansion. Also, it is noted that it is possible to obtain better

efficiencies with higher working pressures.

• In another study from the Silesian University of Technology (Poland), the Stirling

cycle applied to the LNG is analyzed in a theoretical way. One of the main

conclusion is “it can be noticed that the obtained values of exergy efficiency are

smaller than efficiencies obtained for the system based on the RC”. However, they

add that a Stirling engine would be easier to build [23].

• Also, in the Nanyang Technological University, there are researcher trying to

develop a real Stirling engine. It is called thermoacoustic Stirling electric

generator and it seems to be capable of generating 2,3 kW of electric power with

an exergy efficiency around 25,3 % when the cold and hot ends are maintained at

-163 ºC and 227 ºC. In a near future, they will build an experimental setup to

verify the concept and the predictions [24].

Figure 6. Thermoacoustic Stirling Engine. Wang, Dubey, Choo, Duan, 2017.

Power generation from cold energy Revised literature

13

• It is not just the power generation what it is an interesting application to recover

the cold. In the Universitat Rovira I Virgili (Spain), it is proposed a recovery

system for polygeneration applications. They suggest using the cold to several

purposes at the same time as air conditioning, food preservation, seawater

desalination, frozen food storage, dry ice production, cryogenic CO2 capture, air

separation, etc. The proposed plant achieves an equivalent energy saving of 81,1

kW·h/tonLNG [25].

• Finally, one of the most revealing studies is carried out in the University of A

Coruña. It is a comparison between different thermal cycles to exploit the LNG

exergy. Its conclusions are that a single RC is the best option when it is available

the environment or a low-grade waste heat as heat source while the BC is more

appropriate when and intermediate grade source is available. In case that it is

possible to use a high temperature heat source, the combination of RC, BC and

direct NG expansion is the best system to achieve the best efficiency [10].

• There are much more studies regarding how to take advantage of the LNG exergy.

They analyze different thermal cycles, several parameters, optimal temperature

differential, etc. It is not commented in this section but most of them are shown

in the bibliography.

Before moving on to the next section, point out that all studies are focused in huge

regasification plant with very high LNG flow rate. In this case, there are other parameters

to take into account due to it will be an experimental setup.

Power generation from cold energy Suggested solutions

14

5. Suggested solutions

5.1 Direct Turbo Expansion

The first suggested configuration is a cycle where electric power is generated by an

isentropic expansion in a turbine. The working fluid is the NG itself. NG must have

certain distribution conditions at the outlet of the cycle, so the rest of parameters should

be adapted to those values.

A low-grade waste heat will be used as heat source to increase the internal energy of the

NG before it goes into the turbine. Then, the same heat flow will establish the distribution

conditions of the NG at the outlet of the system. Also, heat from the surroundings will be

used to set the NG at ambient temperature before it draws energy from the low-grade

waste heat.

The elements of the circuit are:

• A LNG storage tank that supply the working fluid at -162 ºC and 1 bar

approximately.

• A pump that increases the LNG pressure in an isentropic process above the

distribution pressure.

• A turbine that generates electric power decreasing the pressure and temperature

of the NG.

• Different types of heat exchangers depending on the temperature and pressure of

the fluids.

In order to simplify the requirements of the system, it is possible to use the same

configuration but removing the low-grade waste heat. In that case the heat source should

be the surroundings. Consequently, the electric power generated by the turbine will be

less. Also, it would be necessary to consider that usually there is a low ambient

temperature in Norway and it possible that the NG does not get the required conditions

for the distribution or NG temperature could be too low at the outlet of the turbine, so this

cannot withstand it.

5.2 ORC with low-grade waste heat as heat source and direct NG

expansion

The main process to produce electric power still being an isentropic expansion as in the

first configuration. But there are some differences.

It is suggested an Organic Rankine Cycle complemented by a direct expansion of the NG.

In this case, there are two isolated circuits. An organic fluid will go through the Rankine

cycle producing most of the electric power. In this first circuit, a low-grade waste heat is

the heat source and the LNG works as heat sink. The second one, it is the LNG

regasification circuit. But the low-grade waste heat still being useful after the Rankine

cycle, so it is possible to increase a little bit the NG temperature and then it generates

some extra electric power in another turbine.

The elements for the LNG regasification circuit are the same as in the first suggestion.

Power generation from cold energy Suggested solutions

15

The elements for the Rankine cycle are:

• An organic working fluid.

• A pump to increase the pressure of the working fluid in an isentropic compression.

• A turbine that will generate electric power while the working fluid is expanding

in an isentropic process.

• A boiler where the working fluid becomes gas.

• A heat exchanger where the fluid raises its temperature.

• A condenser where the working fluid becomes liquid.

It is possible to simplify the process in two different ways. The first one would be

removing the NG expansion. The second one would be using the surroundings as heat

source, but there are cons that have already been mentioned in the first suggestion.

Power generation from cold energy Theoretical analysis

16

6. Theoretical analysis

6.1 Direct NG Expansion

6.1.1 Conceptual design

The conceptual design of this configuration is like a Rankine cycle but with an open

circuit. As it is shown in the figure below, the fluid will go through five stages and its

properties will be analyzed in six different points.

Figure 7. Direct NG expansion configuration.

The five stages of the process are:


2-3 Vaporization in a heat exchanger

3-4 Constant pressure heat addition in a heat exchanger


5-6 Constant pressure heat addition in a heat exchanger

The detailed processes that the NG will go through are described in the following

paragraph.

First, there is LNG at -162 ºC and 1 bar, then a pump set the flow rate and the pressure of

the fluid in an isentropic compression. After that, the LNG vaporizes in a heat exchanger

taking energy from the surroundings until it gets ambient temperature. On the next stage,

the NG increases its enthalpy absorbing energy from the low-grade waste heat. In that

moment, it is ready to go into the turbine where rotational movement is generated in an

isentropic expansion. When the NG goes out of the turbine, its conditions probably should

be adjusted to the required temperature and pressure for the distribution. Therefore, there

is a final heat exchanger to that purpose.

Before the analysis, some considerations are assumed:

• The flow is constant and the parameters of the working fluid in each location do

not change with the time.


17

• All components are well insulated.

• The LNG is assumed to be pure methane.

• Pressure drop and heat lost in pipe lines are not taken into account.

• There is 100 % vapor at the turbine outlet to avoid erosion.

• The distribution parameters of NG are 3 bar and 5 ºC

• Ambient temperature is 10 ºC.

• Compressions and expansions are isentropic.

• Turbines are able to withstand –10 ºC as minimum temperature.

6.1.2 Thermodynamic analysis

In this section, energy balances for each stage are shown.


��𝑝𝑢𝑚𝑝,𝑖𝑛 = ��𝐿𝑁𝐺(ℎ2 − ℎ1) (2)

Where

ℎ2 = ℎ1 + (

ℎ𝑠2 − ℎ1

𝜂𝑝𝑢𝑚𝑝) (3)

2-3 Vaporization in a heat exchanger

��𝑖𝑛1 = ��𝐿𝑁𝐺(ℎ3 − ℎ2) (4)

3-4 Temperature rise in a heat exchanger

��𝑖𝑛2 = ��𝐿𝑁𝐺(ℎ4 − ℎ3)


��𝑡𝑢𝑟𝑏,𝑜𝑢𝑡 = ��𝐿𝑁𝐺(ℎ4 − ℎ5) (5)

Where

ℎ5 = ℎ4 − 𝜂𝑡𝑢𝑟𝑏(ℎ4 − ℎ𝑠5) (6)

5-6 Temperature rise in a heat exchanger

��𝑖𝑛3 = ��𝐿𝑁𝐺(ℎ6 − ℎ5)

The net electricity produced is

��𝑛𝑒𝑡 = ��𝑡𝑢𝑟𝑏,𝑜𝑢𝑡 − ��𝑝𝑢𝑚𝑝,𝑖𝑛 (7)


18

And the thermal efficiency

𝜂 =

��𝑛𝑒𝑡

��𝑖𝑛2 + ��𝑖𝑛3 (8)

Just these two inputs of heat are taken due to the heat from the surroundings (��𝑖𝑛1) is

considered unlimited and free.

It is possible to see an approximately representation of the process in the figure below:

Figure 8. Approximate LNG thermodynamic cycle. EES, 2018.

6.1.3 Efficiency

Based on theory, there are three different ways to increase the efficiency of the process

[14]. Each of them will be analyzed according to this application and considering the

process similar to a Rankine cycle open circuit.

Lowering the pressure at the turbine outlet

Lowering that pressure automatically the temperature of the fluid decreases providing a

wider range of energy extraction to the turbine. Theoretically, the limit would be the

pressure at what the gas reaches the saturated state due to the condensation inside the

turbine is not good for the materials. However, in this application the limit is at 3 bar

because it is the NG distribution pressure [8] so it is a mandatory condition. That concept

is easy to understand in the T-s diagram, if the pressure decreases until 1 bar instead 3 bar

(green line), the power output increases.


19

Figure 9. Increasing the efficiency, lowering the outlet pressure. EES, 2018.

Superheating the NG to high temperatures

The average temperature at what the working fluid is vaporized can increase without the

necessity of increase the heat exchanger pressure. Doing this variation, a higher efficiency

is achieved because the net work improves. At the same time, the temperature at the

turbine outlet increases so for this application it is really interesting due to the turbine

probably could not withstand excessive low temperatures. Therefore, the limit is in the

heat source temperature. It is possible to increase the fluid temperature as high as the low-

grade waste heat allows it. This concept is shown in the figure below.

Figure 10. Increasing efficiency, increasing gas temperature. EES, 2018.


20

Increasing the vaporizer pressure

Actually, this is another way to increase the gas temperature. Increasing the pressure in

the heat exchanger requires a higher temperature to vaporize the fluid so theoretically it

is the same principle. For this application, the limit would be again the temperature of the

heat source but also the pressure limits in the heat exchanger. A higher pressure

differential in the pump means a higher cost as well. Therefore, the second way to increase

the system efficiency seems to be the most appropriate.

6.2 ORC with low-grade waste heat as heat source and Direct NG Expansion

6.2.1 Conceptual design

The conceptual design for the LNG regasification circuit is quite similar to the first

configuration design. The main difference is that the first heat exchanger in this system

is at the same time the condenser for the RC and the evaporator for the LNG. It means

that the LNG works as heat sink for the ORC.

As the theory says, the working fluid in the Rankine cycle go through four different

stages. However, the fluid will be analyzed in five different points due to the vaporization

has been split in two stages.

The five stages of the process are:


2-3 Constant pressure heat addition from the surroundings.

3-4 Constant pressure heat addition from the heat source.

4-5 Isentropic expansion in a turbine.

5-1 Constant pressure heat rejection in a condenser.


21

Figure 11. ORC with low-grade waste heat as heat source and direct NG expansion configuration.

The detailed processes that the working fluid will go through are described in the

following paragraph.

First, the working fluid raises its pressure in the pump increasing at the same time its

temperature and fixing a certain flow rate. After that, the vaporization starts in the boiler

thanks to the addition of energy from the surroundings. Then, energy is taken from the

heat source. If the energy to vaporize the fluid is directly taken from the waste heat, its

temperature would decrease before it is really useful. When the fluid has the required

characteristics, it goes into the turbine to generate electric power. At the turbine outlet the

fluid is almost saturated gas so in the final stage, the working fluid becomes liquid again

and the process is restarted.

Before the analysis, some considerations are assumed:







• The distribution parameters of NG are 3 bar and 5 ºC



• Turbines are able to withstand –10 ºC as minimum temperature.


22

6.2.2 Working fluid

One of the most important decisions in this configuration is the working fluid. It should

have adequate physical properties that perform well to the RC application and chemical

stability in the selected temperature range.

There are different approaches to asses which fluid is the most suitable. The best decision

depends on the operating conditions, environmental impact, toxicity and flammability

level, system efficiency and economic viability.

▪ Considering the operating conditions, the fluid must have a low freezing point and

thermal stability at medium high temperatures. The freezing point indicates the

minimum working temperature and the thermal stability ensures that it will not

auto-ignite when it is close to the heat source. Also, it is important to take into

account that it is not interesting to work with temperatures that allow the

condensation below atmospheric pressure because external air could get into the

circuit. Thereby, the air moisture could freeze or flammable compounds could

explode.

▪ In order to reduce the flow rate, and therefore the electric power consumed in the

pump it would be interesting a working fluid with a high specific heat and a low

specific volume, so with that characteristics it is able to absorb a greater quantity

of energy.

▪ Nowadays, the environment is one of the most worrying aspect for the society.

After some recent international agreements, the use of most fluorinated

greenhouse gases is strictly regulated. Therefore, the environmental impact will

be a basic criterion to decide which fluid is used in the RC. There are three main

parameters to compare which fluid is more harmful to the environment:

• Global Warming Potential (GWP) means “the climatic warming potential

of a greenhouse gas relative to that of carbon dioxide (CO2), calculated in

terms of the 100-years warming potential of one kilogram of a greenhouse

gas relative to one kilogram of CO2” [26].

• Ozone Depletion Potential (ODP) means the relative risk to harm the

ozone layer of the atmosphere. The potential 1 is fixed for the compound

trichlorofluoromethane (R-11). Therefore, one compound with a potential

of 0,05 it is less dangerous for the ozone layer. Several countries created

the Montreal Protocol in 1987 to regulate the depletion of the ozone layer.

Since that moment, many compounds (most of them are refrigerants) have

been replaced to less harmful alternatives. Nowadays, in developed

countries it is not common, even illegal, the use of certain chemical

elements due to this protocol.

• Atmospheric lifetime is the amount of years that a greenhouse gas still in

the atmosphere before it is demoted.

▪ Safety is an important parameter in this system. It is use the ASHRAE

classification to determine the fluid hazard level. The fluid should not be toxic,

explosive, flammable or corrosive. According to the ASHRAE classification, the


23

letters A or B mean less or more toxicity at a certain concentration respectively.

The numbers from 1 to 3 indicate the flammability potential being one less

potential and three more potential.

▪ In general, if a gas is popular and abundant, it is cheaper than other less common

alternatives, so the price and the availability is an important factor as well.

After a first selection, five fluids have been proposed as potential candidates. All of them

are pure substances. However, zeotropic mixtures are quite common in this kind of

applications. A zeotropic mixture (two or more compounds with different boiling

temperatures) allows a reduction of the irreversibilities in the heat transfer process. There

are some references where a mixture of ammonia-water or methane-ethane are used with

good efficiency results [27].

Table 2. Physical, safety and environmental data for preselected working fluids. M. Romero Gómez et al. / Renewable

and Sustainable Energy Reviews 38 (2014) 781–795

ASHRAE

Number

Molecular

Formula

Atmospheric

Lifetime

(years)

ODP GWP

100-yr

Safety

Group

Normal

Boiling

Temperature

(ºC)

Critical

Temperature

(ºC)

Critical

Pressure

(bar)

R-23 CHF3 270,0 0 12000 A1 -82,09 26,14 48,32

R-134a C2H2F4 14,0 0 1100 A1 -26,07 101,06 40,59

R-32 CH2F2 4,9 0 550 A2 -51,65 78,10 57,82

Propane C3H8 0,5 0 3,3 A3 -42,11 96,74 42,51

Carbon

dioxide CO2 95,0 0 1 A1 - 30,98 73,77

Trifluoroiodo-

methane CF3I Days 0 <1 A1 -21,85 123,29 39,53

To decide which fluid is used between the five above, it is commented the cons of each

one in the following paragraph:

▪ Refrigerant-23

It would be a good fluid to perform in a RC when the temperature of the heat source is

quite low. For example, when the heat source is at ambient temperature. The main

problem is that in those cases, the temperature of the fluid is too low at the turbine outlet,

so it is necessary to provide the system with better elements to withstand the temperature

and that means a more expensive turbine. In these suggestions, the R-134a and R-32

performance are similar, and they have less environmental impact as it is shown in the

table.

▪ Refrigerant-134a

It is one of the most popular refrigerants for domestic use. It is used for several

applications and its properties are widely known. However, recent regulations suggest

that it will be replaced for the R-32 because its environmental impact still being high.

▪ Refrigerant-32

It has similar properties to R-134a so the performance will be almost equal. The negative

point is that the flammability risk is higher. However, it is less harmful to the

environment.


24

▪ Propane

It is one of the least polluting gases of the table and its properties are close to the R-32.

The main cons of this fluid would be the high flammability risk because it is classified as

A3.

▪ Carbon dioxide

The main problem to work with CO2 is that its working pressure is too high for an

experimental purpose. It becomes liquid and even solid easily at low temperatures if the

pressure has not increased. It is used in some industrial process as refrigerant being dry

ice but it is not suitable in this process.

Figure 12. P-T diagram for Carbon Dioxide. Wikipedia.

▪ Trifluoroiodomethane

It seems to be the most suitable one. Almost, it has not environmental impact. Its

properties are quite similar to R-134a. And it is classified as non-toxic gas and low

flammability potential. The negative point would be the instability of the compound in

contact with water. However, it should not be a problem in a closed circuit.

It is compared the price of each fluid in the table below. It is possible to see that the most

polluting fluids are the cheapest one as well.

Table 3. Working fluids price. Chem-space, 2018.

For the following analysis, it has been chosen the propane as working fluid for the ORC.

However, it would be possible to make a more accurate process of selection, but it is not

the purpose of this work. Propane has the right characteristics, it is a well-known

substance, it is not toxic, the price is not too high and it is environmentally friendly. As it

ASHRAE Number Molecular Formula Approximate price

($/100g)

R-134a C2H2F4 155

R-23 CHF3 173

Propane C3H8 200

Trifluoroiodomethane CF3I 343

R-32 CH2F2 444

Carbon dioxide CO2 4300* *Note: It has not been found a 100 g supply so that price it is calculated from another package size


25

has been said, the main problem is the necessity of a good manipulation due to his

flammability potential.

6.2.3 Thermodynamic analysis

In this section, energy balances for each stage are shown. Both circuits are differenced.

a) Organic Rankine Cycle

Figure 13. Approximate propane thermodynamic cycle. EES, 2018.

In the plot above, it is represented an approximate T-s diagram for the process.


��𝑝𝑢𝑚𝑝,𝑖𝑛1 = ��𝐶3𝐻8(ℎ2 − ℎ1)

Where

ℎ2 = ℎ1 + (ℎ𝑠2 − ℎ1

𝜂𝑝𝑢𝑚𝑝)

2-3 Constant pressure heat addition from the surroundings.

��𝑖𝑛1,ORC = ��𝐶3𝐻8(ℎ3 − ℎ2)

3-4 Constant pressure heat addition from the heat source.

��𝑖𝑛2,ORC = ��𝐶3𝐻8(ℎ4 − ℎ3)

4-5 Isentropic expansion in a turbine.

��𝑡𝑢𝑟𝑏,𝑜𝑢𝑡1 = ��𝐶3𝐻8(ℎ4 − ℎ5)

Where

ℎ5 = ℎ4 − 𝜂𝑡𝑢𝑟𝑏(ℎ4 − ℎ𝑠5)



26

��𝑜𝑢𝑡 = ��𝐶3𝐻8(ℎ5 − ℎ1)


��𝑛𝑒𝑡1 = ��𝑡𝑢𝑟𝑏,𝑜𝑢𝑡1 − ��𝑝𝑢𝑚𝑝,𝑖𝑛1


𝜂𝑂𝑅𝐶 =��𝑛𝑒𝑡1

��𝑖𝑛2

b) LNG regasification process


��𝑝𝑢𝑚𝑝,𝑖𝑛2 = ��𝐿𝑁𝐺(ℎ2 − ℎ1)

Where

ℎ2 = ℎ1 + (ℎ𝑠2 − ℎ1

𝜂𝑝𝑢𝑚𝑝)

2-3 Constant pressure heat addition

��𝑖𝑛1 = ��𝐿𝑁𝐺(ℎ3 − ℎ2)


��𝑖𝑛2 = ��𝐿𝑁𝐺(ℎ4 − ℎ3)


��𝑖𝑛3 = ��𝐿𝑁𝐺(ℎ5 − ℎ4)


��𝑡𝑢𝑟𝑏,𝑜𝑢𝑡2 = ��𝐿𝑁𝐺(ℎ5 − ℎ6)

Where

ℎ5 = ℎ4 − 𝜂𝑡𝑢𝑟𝑏(ℎ4 − ℎ𝑠5)


��𝑖𝑛4 = ��𝐿𝑁𝐺(ℎ7 − ℎ6)


��𝑛𝑒𝑡2 = ��𝑡𝑢𝑟𝑏,𝑜𝑢𝑡2 − ��𝑝𝑢𝑚𝑝,𝑖𝑛2


27


𝜂𝐿𝑁𝐺 =��𝑛𝑒𝑡2

��𝑖𝑛3 + ��𝑖𝑛4

The overall thermal efficiency

𝜂𝐿𝑁𝐺 =

��𝑛𝑒𝑡1 + ��𝑛𝑒𝑡2

��𝑖𝑛2,𝑂𝑅𝐶 + ��𝑖𝑛3 + ��𝑖𝑛4 (9)

6.2.4 Efficiency

The same theoretical concepts than in 6.1.3 work here. Additionally, it is represented the

process efficiency in function of its pressure in the vaporizer for this configuration.

Consequently, the efficiency is the overall thermal efficiency of the system. The data is

taken from the software EES and represented in a Excel plot. In order to acquire the data,

some conditions have been assumed as:

• LNG is at -162 ºC and 1 bar.


• NG distribution parameters are 5 ºC and 3 bar.

• The working fluid in the ORC is propane.

• Both pressures, ORC and LNG, are the same at the vaporizer.

• The fluid is at -10 ºC at the turbine outlet.

• Flow rate is 1 kg/s for both fluids.

• The heat source temperature is not limited.

• Just the heat absorbed from the heat source is taken into account to

calculate the efficiency because it is assumed that the surroundings supply

unlimited and free heat until the fluid gets temperature equilibrium.


• The flow is constant and the parameters of the working fluid in each

location do not change with the time.




• Turboexpanders can withstand -10 ºC as minimum temperature.


28

Figure 14. Comparison between different working pressures. EES, 2018.

What can be extracted from that data representation? As the pressure in the vaporizer is

higher, the rest of parameters increase. It is required a higher amount of heat to perform

the process but also the extracted work is higher. To illustrate this with numbers, when

the pressure is 20 bar, it is required 30 % more heat than when the pressure is 10 bar.

However, it is produced around 76 % more net work. Increasing the efficiency a 46 %.

Therefore, the conclusion is that the pressure should be settled as high as possible, as high

as the real turbine still performing well and the low-grade waste heat can supply energy.

This conclusion can be applied to both circuit.

Power generation from cold energy Selection of real components

29

7. Selection of real components

Despite the analyses carried out, it is now important to select the components so that the

system operates with an efficiency similar to the calculated one. The total efficiency of

the process is the most important variable to control. However, the initial investment in

the construction of the system plays an important role. In this section, some notable

features are described for the main components: pump, heat exchangers and turbine. As

it has been said, the size of the elements is based on a small application due to the

experimental purpose.

7.1 Selection of the pumps

The suitable pump for this kind of process should meet some requirements:

• It is really important the isentropic efficiency even more than in a regular process

because the electric power consumption is directly taken from what the turbine is

generating. So, it has a significant impact in the net power and the cycle efficiency.

• A perfect seal is absolutely mandatory due to the explosive nature of the working

fluids. For the propane and the methane, the environmental impact of a small

leakage is not dramatic but still being harmful. Additionally, it has an economic

cost. Therefore, to certify the safety of the component, the optimum pump would

be one that complies with the ATEX regulation.

• In order to avoid cavitation issues, a low net positive suction would be required.

• Finally, the condition that will probably determine the validity of the component

will be the resistance to low temperatures. It necessary a pump designed to

withstand cryogenic purposes. Even more important for the LNG than for the

propane.

There are different types of pumps but not all of them are suitable for every applications.

In this case, it is necessary a low flow rate and a high-pressure differential so volumetric

pumps are the most adapted. Although, there is a wide variety of volumetric pumps

available as gear, piston, vane, diaphragm, etc. It seems that multidiaphragm pumps are

the most interesting ones. Anyway, it should be deeply analyzed to fulfill every condition.

7.2 Selection of the heat exchangers

The selection of one or another heat exchanger depends on several aspects as the hot and

cold fluids physical state, the maximum pressure, the flow rate, tolerable temperatures,

corrosion resistance, heat transfer capacity, etc. For this application, most of the heat

exchangers will be gas to gas type except the ORC condenser and the LNG and ORC

vaporizer where it will be liquid at the inlet and gas at the outlet. No further information

is given about heat exchangers as they will generally be easier to select than pumps and

turbines. Therefore, it would be carried out after they determine certain working

conditions.

Power generation from cold energy Selection of real components

30

7.3 Selection of the turbines

Looking for the most suitable turbine to generate electric power, it has been found than

this component is the most expensive of the whole process as well as the most important.

Therefore, all the parameters must be set to achieve maximum efficiency in the turbine.

Situation that will increase its useful life and decrease the maintenance required. In

general, all the requirements described in the section of the pumps selection are valid for

the turbine, so it will not be repeated.

Nevertheless, if regular turboexpanders are expensive, small turboexpanders even have a

higher cost. Companies usually do not have a small turbine full production, so they work

when a customer ask for. This allows a better adaptation to the application at the expense

of the price increase. If certain special conditions (cold, explosive fluid…) are added as

in this case, the offer is considerably reduced. Also, it has been noticed that the price per

kilowatt increase as the power of the model decreases.

As a cheaper alternative, it has been found a reference [28] where it is suggested the use

of a usual turbocharger. The cost is much lower than the turbine price, but its reliability

cannot be compared. Anyway, it could be an interesting option in an experimental setup

where the environment is controlled.

In another source [29], it is said that scroll expanders are the most suitable machines for

applications under 10 kW. Also, it is mentioned that the widespread use of scroll

machines as compressors makes them available at low cost and they can be expanders

with just a few modifications.

In order to create an own vision, some companies in the sector have been consulted about

the cost of the turbines that they manufacture. These data will be discussed in the

following section.

Power generation from cold energy Investment analysis

31

8. Investment analysis

The turbines are the components with the highest cost, so the analysis focuses on their

study. The relative cost of the other components can be consulted in the following

reference [29]. This project does not go into this issue further because it all depends on

the choice of the turbine, any conclusions drawn would vary significantly if it is decided

to install one type of turbine or another.

The German company DEPRAG has developed the called Green Energy Turbine

precisely thinking on applications like this one. They have a wide catalog with expanders

between 1 to 120 kW. However, the only one with the ATEX certificate is the 60 kW

turbine. That model costs around 45.000 € including development, generator and greasing

unit. This implies an approximate cost of 750 €/kW. As it has been said, smaller models

would have a higher relative price.

On the other hand, there is an American screw expanders manufacturer called Air

Squared. They also have several models. They quote the E22H038A-SH 5 kW model in

21.950 USD including the generator. What means a price of 4.390 $/kW. Considerably,

a higher cost than the previous turbine. However, the absolute cost is lower when

considering designing an experimental plant.

Considering the use of turbochargers, there is a wide offer that approximately goes

between 600 – 1000 €/kW without the generator. This would be the lowest absolute cost

for the experimental setup.

In order to make a comparison with turbines normally used in the energy sector, an expert

has been asked. The customer service manager of L. A. Turbine states that turboexpanders

are not cost effective below 1 MW output of electricity. Costing that kind of turbines

around 1.200 $/kW (> 1 MW turbines).

Additionally, it is interesting to mention the French company Enogia. They manufacture

a 10 kW ORC ready to use with a cost of 36.000 €. This means 3.600 €/kW including

evaporator, condenser, pump, expander and generator. However, it is not designed for

cold applications.

Power generation from cold energy Minimum Viable Design

32

9. Minimum Viable Design

Based on the theory of a Minimum Viable Product, it is possible to suggest a Minimum

Viable Design. It consists of implementing a system with the minimum features necessary

to fulfill the requirements at an early stage of the development. In this way, feedback is

obtained on its operation, indicating the correct way to improve small aspects of the

design until the optimum system is obtained. In addition, it is the only way to obtain an

experimental product that provides a lot of information for its development without the

necessity of a large initial investment. A Minimum Viable Design should be valuable

enough to be worth a first investment, it should demonstrate enough benefits to retain

early users and it should provide a constant feedback of valuable information [30] [31].

Some suggestions are made in this section based on previous information:

• The minimum absolute cost is obtained providing the system with the smallest

available elements. Therefore, it would be necessary the selection of a turbine

with an electrical output around 1 kW. It is not just because the price is lower,

also it is because the rest of the components as the pump, pipelines, heat

exchangers or valves will have smaller sizes. The system could start just with the

direct NG expansion focusing the energy of the heat source in the LNG. After this

process is optimized, the ORC could be adapted to that parameters. If it is possible

to develop the system to obtain a significant amount of energy per ton of LNG, it

can be resized for larger applications.

• On the other hand, it has been suggested the used of regular turbochargers. Due

to these elements are not usually applied in this kind of process, it would be

necessary to adapt it to work with explosive substances such as NG. But

turbochargers are less expensive than the rest of turboexpanders, so they could be

analyzed in small size setup to optimize its use and determine the best range of

temperatures, pressures, etc. Then it could be adapted the process to the working

conditions implementing a circuit in cascade configuration, parallel, etc. Despite

the acquisition cost is lower, probably the development and optimization process

would take more time and effort.

Power generation from cold energy Simulation of an actual application

33

10. Simulation of an actual application

In order to involve all the concepts mentioned previously, a real situation will be supposed

to analyze the actual process in a LNG regasification terminal. Two 60 kW

turboexpanders will be used because they have the lowest cost per kW in a combination

of an ORC and a NG direct expansion. This will require a series of conditions to be

properly specified. The cost of such a terminal will serve as an upper limit as it is known

that it is possible to design an experimental plant for a lower price. Only the elements that

are not required in a regular regasification terminal will be considered to estimate the

cost.

The assumptions and decisions used in the analysis are listed below:

• LNG is at -162 ºC and 1 bar.

• The working fluid in the ORC is propane.

• Both fluids are at 10 bar at the outlet of the pumps.

• NG distribution parameters are 5 ºC and 3 bar.


• The low-grade waste heat is regular air at 200 ºC.

• The tolerance of the heat exchangers where the waste heat is involved is 20 ºC.

This means that the waste heat must be at the outlet at least 20 ºC above the

working fluid.








• The isentropic efficiency of the components is 50 %.

• Turboexpanders can withstand -10 ºC as minimum temperature.

• The flow rate of methane and propane is set to 0,85 kg/s and 1 kg/s respectively.

Therefore, turbines are supposed to allow these flows.

• The surroundings supply unlimited and free heat until the fluid gets temperature

equilibrium.


34

First of all, in the figure below it is shown the representation of the system.

Figure 15. Representation of the system.

Then, it is represented the thermodynamic cycle of each fluid, being marked in the

diagram each characteristic point of the process. All the thermodynamic properties of the

fluids as well as the T-s diagrams are taken from the software of the company F-Chart

called EES. Also, that thermodynamics properties are shown in the tables below.

Figure 16. Propane thermodynamic cycle.


35

Table 4. Propane data at the different stages of the process.

Propane

Temperature (ºC) Pressure (bar) Enthalpy (kJ/kg) Entropy (kJ/kg·K) Volume (kg/m3)

1 -45 1 93,50 0,58 584,80

2 -45 10 95,03 0,58 585,50

3 10 10 225,70 1,09 515,50

4 100 10 752,90 2,80 15,48

5 16 1 615,70 2,80 1,87

Figure 17. LNG thermodynamic cycle.

Table 5. LNG data at the different stages of the process.

LNG

Temperature

(ºC)

Pressure

(bar)

Enthalpy

(kJ/kg)

Entropy

(kJ/kg·K)

Volume

(kg/m3)

1 -162 1 -912,70 -6,69 423,10

2 -162 10 -910,60 -6,69 423,60

3 -65 10 -212,2 -2,018 9,84

4 10 10 -43,92 -1,33 6,96

5 93 10 151,50 -0,72 5,30

6 5 3 -47,39 -0,72 2,10

Table 6. Heat source data at the different stages of the process.

Air

Temperature

(ºC)

Pressure

(bar)

Enthalpy

(kJ/kg)

Entropy

(kJ/kg·K)

Volume

(kg/m3)

1 200 1 475,70 7,33 0,74

2 139,2 1 413,72 7,19 0,85

3 120 1 394,20 7,14 0,89


36

Subsequently, all the energy transfers of the system are calculated as it is described in

previous sections. First for the ORC, second for the NG expansion and third for the low-

grade waste heat.

a) ORC

1-2 Isentropic compression in the pump

��𝑝𝑢𝑚𝑝,𝑖𝑛1 = ��𝐶3𝐻8(ℎ2 − ℎ1) = 1

𝑘𝑔

𝑠· (96,56 − 93,5)

𝑘𝐽

𝑘𝑔= 3,06

𝑘𝐽

𝑠

Where

ℎ2 = ℎ1 + (ℎ𝑠2 − ℎ1

𝜂𝑝𝑢𝑚𝑝) = 93,5

𝑘𝐽

𝑘𝑔+ (

95,03 − 93,5

0,5)

𝑘𝐽

𝑔= 96,56

𝑘𝐽

𝑘𝑔

2-3 Constant pressure heat addition from the surroundings

��𝑖𝑛1,𝑂𝑅𝐶 = ��𝐶3𝐻8(ℎ3 − ℎ2) = 1

𝑘𝑔

𝑠· (225,7 − 96,56)

𝑘𝐽

𝑘𝑔= 129,14

𝑘𝐽

𝑠

3-4 Constant pressure heat addition from the heat source

��𝑖𝑛2,𝑂𝑅𝐶 = ��𝐶3𝐻8(ℎ4 − ℎ3) = 1

𝑘𝑔

𝑠· (752,9 − 225,7)

𝑘𝐽

𝑘𝑔= 527,2

𝑘𝐽

𝑠

4-5 Isentropic expansion in the turboexpander.

��𝑡𝑢𝑟𝑏,𝑜𝑢𝑡1 = ��𝐶3𝐻8(ℎ4 − ℎ5) = 1

𝑘𝑔

𝑠· (752,9 − 684,3)

𝑘𝐽

𝑘𝑔= 68,6

𝑘𝐽

𝑠

Where

ℎ5 = ℎ4 − 𝜂𝑡𝑢𝑟𝑏 · (ℎ4 − ℎ𝑠5) = 752,9𝑘𝐽

𝑘𝑔− 0,5 · (752,9 − 615,7)

𝑘𝐽

𝑔= 684,3

𝑘𝐽

𝑘𝑔


��𝑜𝑢𝑡,𝑂𝑅𝐶 = ��𝐶3𝐻8(ℎ5 − ℎ1) = 1

𝑘𝑔

𝑠· (684,3 − 93,5)

𝑘𝐽

𝑘𝑔= 590,8

𝑘𝐽

𝑠


��𝑛𝑒𝑡,𝑂𝑅𝐶 = ��𝑡𝑢𝑟𝑏,𝑜𝑢𝑡1 − ��𝑝𝑢𝑚𝑝,𝑖𝑛1 = (68,6 − 3,06)𝑘𝐽

𝑠= 65,54

𝑘𝐽

𝑠


37



��𝑖𝑛2,𝑂𝑅𝐶=

65,54𝑘𝐽𝑠

527,2𝑘𝐽𝑠

= 12,43 %

It is taken just the heat addition from the low-grade waste heat because the first energy

addition is from the surroundings and it is free and unlimited.

b) LNG Direct Expansion

1-2 Isentropic compression in the pump

��𝑝𝑢𝑚𝑝,𝑖𝑛2 = ��𝐿𝑁𝐺(ℎ2 − ℎ1) = 0,85𝑘𝑔

𝑠· (−908,5 + 912,7)

𝑘𝐽

𝑘𝑔= 3,57

𝑘𝐽

𝑠

Where

ℎ2 = ℎ1 + (ℎ𝑠2 − ℎ1

𝜂𝑝𝑢𝑚𝑝) = −912,7

𝑘𝐽

𝑘𝑔+ (

−910,6 + 912,7

0,5)

𝑘𝐽

𝑔= −908,5

𝑘𝐽

𝑘𝑔

2-3 Constant pressure heat addition from ORC

��𝑖𝑛1,𝐿𝑁𝐺 = ��𝐿𝑁𝐺(ℎ3 − ℎ2) = 0,85𝑘𝑔

𝑠· (−212,2 + 908,5)

𝑘𝐽

𝑘𝑔≈ 590,8

𝑘𝐽

𝑠

Actually, in this equation it is calculated the minimum LNG flow rate because two

conditions influence here. It is considered that it must be at least 20 ºC of difference

between fluids in the heat exchangers and the heat rejected in the ORC must be absorbed

by the LNG.

3-4 Constant pressure heat addition from the surroundings

��𝑖𝑛2,𝐿𝑁𝐺 = ��𝐿𝑁𝐺(ℎ4 − ℎ3) = 0,85𝑘𝑔

𝑠· (−43,92 + 212,2)

𝑘𝐽

𝑘𝑔= 143,038

𝑘𝐽

𝑠

4-5 Constant pressure heat addition from the heat source

��𝑖𝑛3,𝐿𝑁𝐺 = ��𝐿𝑁𝐺(ℎ5 − ℎ4) = 0,85𝑘𝑔

𝑠· (151,5 + 43,92)

𝑘𝐽

𝑘𝑔= 166,107

𝑘𝐽

𝑠

5-6 Isentropic expansion in the turboexpander.

��𝑡𝑢𝑟𝑏,𝑜𝑢𝑡2 = ��𝐿𝑁𝐺(ℎ5 − ℎ6) = 0,85𝑘𝑔

𝑠· (151,5 − 52,055)

𝑘𝐽

𝑘𝑔= 84,528

𝑘𝐽

𝑠

Where

ℎ6 = ℎ5 − 𝜂𝑡𝑢𝑟𝑏 · (ℎ5 − ℎ𝑠6) = 151,5𝑘𝐽

𝑘𝑔− 0,5 · (151,5 + 47,39)

𝑘𝐽

𝑔= 52,055

𝑘𝐽

𝑘𝑔


38

Clearly, this is far from the reality because the output of the turbine should be around 60

kW. If it is obtained 85 kW, it is because working at that conditions the turbine would

have a really bad efficiency, so it is possible to decrease the LNG pressure and

temperature in order to optimize the process. Also, it is possible to use a more powerful

turboexpander. It is not calculated again in this document because the actual working

parameters for the best performance of the turbine are not known. But it would proceed

in a similar pattern.


��𝑛𝑒𝑡,𝐿𝑁𝐺 = ��𝑡𝑢𝑟𝑏,𝑜𝑢𝑡2 − ��𝑝𝑢𝑚𝑝,𝑖𝑛2 = (84,528 − 3,57)𝑘𝐽

𝑠= 80,958

𝑘𝐽

𝑠



��𝑖𝑛3,𝐿𝑁𝐺=

80,958𝑘𝐽𝑠

166,107𝑘𝐽𝑠

= 48,74 %

It would be around 36 % with a 60 kW electricity output.

c) Low-grade waste heat

First of all, it is necessary to calculate the minimum air flow rate.

��𝑎𝑖𝑟(ℎ1 − ℎ3) = (��𝑖𝑛2,𝑂𝑅𝐶 + ��𝑖𝑛3,𝐿𝑁𝐺)

��𝑎𝑖𝑟 = 8,507 𝑘𝑔

𝑠

1-2 Constant pressure heat rejection to the ORC

��𝑜𝑢𝑡1,𝐴𝑖𝑟 = ��𝑎𝑖𝑟(ℎ1 − ℎ2) = 8,507𝑘𝑔

𝑠· (475,7 − 413,72)

𝑘𝐽

𝑘𝑔= 527,2

𝑘𝐽

𝑠

2-3 Constant pressure heat rejection to the LNG

��𝑜𝑢𝑡2,𝐴𝑖𝑟 = ��𝑎𝑖𝑟(ℎ2 − ℎ3) = 8,507𝑘𝑔

𝑠· (413,72 − 394,2)

𝑘𝐽

𝑘𝑔≅ 166,107

𝑘𝐽

𝑠

What can be drawn from these calculations? Despite the waste heat flow rate is quite high,

if two 60 kW turboexpanders are used in a combination of ORC and NG direct expansion

it is possible to obtain around the 17 % of the total LNG exergy and the overall thermal

efficiency of the process is around 17 % as well. It is not a bad result, but it could be

improved knowing the actual characteristic of the used components.

Finally, it is calculated the investment recovery time just for the turbines because they are

the more expensive element of the process. It is taken as reference the average electricity

price of 2018 from the organization Nordpool [30]. The cost for two 60 kW turbines from

the company DEPRAG is 91.340 € including the two electricity generators and two

greasing units. It is supposed a working period of 8 hours per day and 365 days per year


39

with 120 kW of electric power generation. If it is obtained 37,9 €/MWh [30], the total

investment recovery time is approximately 7 years just for the turbines. Based on the

LNG flow, the production is around 39,22 kW·h/tonLNG meanwhile the average in the

Japanese plants is 37 kW·h/tonLNG [10].

Power generation from cold energy Future

40

11. Future

Working on this project it has been identified some techno-economic constraints which

will be described below, and which could be the basis for future works.

The technology for micro turboexpanders is not fully developed. There is not much

supply in the market, so the working parameters do not cover a wide range. When the

application requires certain special features, the selection of components becomes

difficult. In addition, the price of these components is quite high when it involves a small

application. The development of a simple and easy to manufacture turbine or one that can

be manufactured automatically would make a difference in the future. It could be

interesting not only for LNG related applications but also for energy recovery from

exhaust gases of any kind.

It has been briefly commented before, Stirling cycles have a huge potential in applications

like this one, where two sides at different temperatures are generated naturally. Based on

the mentioned papers, a Stirling machine capable of generate electric power would be a

simple way to take advantage of the cold. It will not be necessary pumps, turbines or any

other element. Consequently, the maintenance would be reduced as well. Technical

difficulties and the low efficiency achieved in the regenerator is what is slowing down

the development of this kind of machines.

Another interesting advancement would be a safe and eco-friendly working fluid for

ORC. If there is available a fluid which leakages does not matter with, some decisions

are avoided. Another option, it is to control the environment reducing the oxygen to avoid

explosion and filtering the air to recover the harmful substances to the atmosphere.

Something which is probably under active investigation is the way to achieve unlimited

and natural low-temperature heat sources at a very low price. Solar and geothermal energy

are fields that will be widely used in the future for that purpose.

Finally, the efficiency of the process depends on many variables and it changes with the

modification of any of them. It would be interesting to develop a system that allows the

efficiency of the process to be easily calculated according to the specific characteristics

of each application. This would be useful as each regasification plant changes the

distribution pressure, the NG demand, the supply period, etc...

41

12. Conclusions.

Through this work, it is concluded that the extraction of energy from the LNG

regasification process for the purpose of generating electric power is perfectly feasible.

Certain technologies for this purpose are already developed and applied in large

regasification terminals. The fact that this project is focused on a small plant increases

the cost per kilowatt of the plant because there is not much demand for the necessary

components in the market. These components are usually manufactured on request.

Therefore, it is difficult to estimate the total cost of the installation without carrying out

an actual construction project and setting certain parameters in advance. Also, it is

deduced that the construction of an experimental plant would not give economic benefits

in a short time period but it could be really interesting for scientific purposes. As the NG

demand increase, it seems that the investment recovery time decrease due to the expenses

are mainly at the beginning of the system implementation and not during its use.

As for the system to be implemented, it can be concluded that the combination of an ORC

and a NG direct expansion is the most optimal configuration. It is also possible to adapt

this configuration according to certain characteristics determined by each application,

such as the temperature of the heat source or the flow rate of LNG. With this system the

greatest possible exergy is extracted because it is exploited in a thermal and physical way.

In addition, numerous scientific papers have been found on the same subject and they

compare many of the conditions to which the system can be subjected, such as the use of

different working fluids, different thermodynamic cycles, the placement of a turbine or

several in a row, etc...

Finally, it is concluded that NG, and in particular LNG, will be one of the fossil fuels that

will survive the longest in an increasingly environmentally friendly world due to its clean

combustion.

42

References

[1] International Energy Agency, "CO2 emissions from fuel combustion," 2017. [Online].

Available:

http://www.iea.org/publications/freepublications/publication/CO2EmissionsfromFuel

CombustionHighlights2017.pdf.

[2] Enerdata, "Global Energy Statistical Yearbook 2017," 2017. [Online]. Available:

https://yearbook.enerdata.net/natural-gas/world-natural-gas-production-statistics.html.

[3] Statistics Norway, "Production and consumption of energy, energy balance," 28 June

2017. [Online]. Available: https://www.ssb.no/en/energi-og-

industri/statistikker/energibalanse/aar-forelopige.

[4] BP, "BP Energy Outlook 2017," 2017. [Online]. Available:

https://www.bp.com/content/dam/bp/pdf/energy-economics/energy-outlook-2017/bp-

energy-outlook-2017.pdf.

[5] H. Liu y L. You, «Characteristics and applications of the cold heat exergy of liquified

natural gas,» Energy Conversion & Management, pp. 40:1515-25, 1999.

[6] U.S. Energy Information Administration, «Natural Gas Prices,» 30 3 2018. [En línea].

Available: https://www.eia.gov/dnav/ng/ng_pri_sum_dcu_nus_a.htm.

[7] International Gas Union, "2017 World LNG Report," 2017. [Online]. Available:

http://www.igu.org/sites/default/files/node-document-field_file/103419-

World_IGU_Report_no%20crops.pdf. [Accessed 30 4 2018].

[8] Skangas, "Skangas terminal, Øra," [Online]. Available:

https://www.skangas.com/supply-chain/terminals--plants/skangas-terminal-ora/.

[Accessed 2018].

[9] Osaka Gas, "Cryogenic power generation system recovering LNG's cryogenic energy

and generating power for energy and CO2 emission savings," 2017. [Online].

Available: https://www.osakagas.co.jp/en/rd/technical/1198907_6995.html#anchor3.

[Accessed 01 05 2018].

[10] M. Romero Gómez, R. Ferreiro García, J. Romero Gómez y J. Carbia Carril, «Review

of thermal cycles exploiting the exergy of liquified natural gas in the regasification

process,» Renewable and Sustainable Energy Reviews, vol. 38, pp. 781-795, 2014.

[11] T. Otsuka, "Evolution of a LNG terminal: Senboku Terminal of Osaka Gas,"

International gas union world gas coference papers, vol. 5, pp. 2617-2630, 2006.

[12] J. C. Sánchez-Izquierdo and L. C. Gutiérrez Pérez, "Electricity generation in Enagas

regasifying plant in Palos de la Frontera (Huelva)," Futurenergy, vol. 5, pp. 31-35,

2013.

43

[13] Elengy, [Online]. Available: https://www.elengy.com/en/.

[14] Y. A. Cengel and M. A. Boles, Thermodynamics an engineering approach, New York:

McGraw-Hill, 2011.

[15] Shell, "LIQUEFIED NATURAL GAS (LNG)," [Online]. Available:

https://www.shell.com/energy-and-innovation/natural-gas/liquefied-natural-gas-

lng.html.

[16] M. S. Khan and M. Lee, "Design optimization of single mixed refrigerant natural gas

liquefaction process using the particle swarm paradigm with nonlinear constraints,"

Energy, vol. 49, pp. 146-155, 2013.

[17] D. A. Trayser and J. A. Eibling, "A 50-watt portable generator employing a solar-

powered stirling engine," Solar Energy, vol. 11, pp. 153-159, 1967.

[18] T. Li, D. Tang, Z. Li, J. Du, T. Zhou and Y. Jia, "Development and test of a Stirling

engine driven by waste gases for the micro-CHP system," Applied Thermal

Engineering, Vols. 33-34, pp. 119-123, 2012.

[19] C. Cinar, F. Aksoy, H. Solmaz, E. Yilmaz and A. Uyumaz, "Manufacturing and testing

of an α-type Stirling engine," Applied Thermal Engineering, vol. 130, pp. 1373-1379,

2018.

[20] K. Oshima, Y. Ishizaki, M. Kamiyama and M. Okuda, "The utilization of LH2 and

LNG cold for generation of electric power by a cryogenic type stirling engine,"

Cryogenics, vol. 18, pp. 617-620, 1978.

[21] Imajey Consulting Engineers, "Kalina Cycle Power Plant," learnengineering, [Online].

Available: http://www.learnengineering.org/2013/01/kalina-cycle-power-plant.html.

[Accessed 2018].

[22] B. B. Kanbur, L. Xiang, S. Dubey, F. H. Choo and F. Duan, "Cold Utilization systems

of LNG: A review," Renewable and Sustainable Energy Reviews, vol. 79, pp. 1171-

1188, 2017.

[23] I. Szczygiel, W. Stanek and J. Szargut, "Application of the Stirling engine driven with

cryogenic exergy of LNG (liquified natural gas) for the production of electricity,"

Energy, vol. 105, pp. 25-31, 2016.

[24] K. Wang, S. Dubey, F. H. Choo and F. Duan, "Thermoacoustic Stirling power

generation from LNG cold energy and low-temperature waste heat," Energy, vol. 127,

pp. 280-290, 2017.

[25] A. Atienza-Márquez, J. C. Bruno and A. Coronas, "Cold recovery from LNG-

regasification for polygeneration applications," Applied Thermal Engineering, vol.

132, pp. 463-478, 2018.

44

[26] European Union, "REGULATION (EU) No 517/2014 OF THE EUROPEAN

PARLIAMENT AND OF THE COUNCIL," 2014. [Online]. Available: http://eur-

lex.europa.eu/legal-content/EN/TXT/?uri=uriserv:OJ.L_.2014.150.01.0195.01.ENG.

[27] A. H. Mosaffa, N. H. Mokarram and L. G. Farshi, "Thermoeconomic analysis of a new

combination of ammonia/water power generation cycle with GT-MHR cycle and LNG

cryogenic exergy," Applied Thermal Engineering, vol. 124, pp. 1343-1353, 2017.

[28] D. Meyer, C. Wong, F. Engel and S. Krumdieck, "DESIGN AND BUILD OF A 1

KILOWATT ORGANIC RANKINE CYCLE," 20 November 2013. [Online].

Available: https://www.geothermal-

energy.org/pdf/IGAstandard/NZGW/2013/Meyer_Final.pdf. [Accessed 2018].

[29] E. Georges and S. Declaye, "Design of a small-scale organic Rankine cycle,"

International Journal of Low-Carbon Technologies, 12 May 2013.

[30] Techopedia, "Minimum Viable Product (MVP)," [Online]. Available:

https://www.techopedia.com/definition/27809/minimum-viable-product-mvp.

[Accessed 2018].

[31] E. Ries, "What is the minimum viable product?," Venture Hacks, 2009. [Online].

Available: http://venturehacks.com/articles/minimum-viable-product. [Accessed

2018].

[32] NORDPOOL, [Online]. Available: https://www.nordpoolgroup.com/. [Accessed 11

May 2018].

[33] Y. Liu and K. Guo, "A novel cryogenic power cycle for LNG cold energy recovery,"

Energy, vol. 36, pp. 2828-2833, 2011.

[34] K. H. Kim y K. C. Kim, «Thermodynamic performance analysis of a combined power

cycle using low grade heat source and LNG cold energy,» Applied Thermal

Engineering, vol. 70, pp. 50-60, 2014.

[35] M. Romero Gómez, R. Ferreiro García, J. Romero Gómez and J. Carbia Carril,

"Thermodynamic analysis of a Brayton cycle and Rankine cycle arranged in series

exploiting the cold exergy of LNG," Energy, vol. 66, pp. 927-937, 2014.

[36] H. Dong, L. Zhao, S. Zhang, A. Wang and J. Cai, "Using cryogenic exergy of liquefied

natural gas for electricity production with the Stirling cycle," Energy, vol. 63, pp. 10-

18, 2013.

[37] A. Franco and C. Casarosa, "Thermodynamic analysis of direct expansion

configurations for electricity production by LNG cold energy recovery," Applied

Thermal Engineering, vol. 78, pp. 649-657, 2015.

[38] M. Gómez Romero, J. Gómez Romero, L. M. López-González y L. M. López-Ochoa,

«Thermodynamic analysis of a novel power plant with LNG cold exergy exploitation

and CO2 capture,» Energy, vol. 105, pp. 32-44, 2016.

45

[39] R. Ferreiro García, J. Carbia Carril, J. Romero Gomez and M. Romero Gomez,

"Combined cascaded Rankine and direct expander based power units using LNG cold

as heat sink in LNG regasification," Energy, vol. 105, pp. 16-24, 2016.

[40] R. Ferreiro García, J. Carbia Carril, J. Romero Gómez and M. Romero Gómez, "Power

plant based on three series Rankine cycles combined with a direct expander usin LNG

cold as heat sink," Energy Conversion and Management, vol. 101, pp. 285-294, 2015.

[41] I. H. Choi, S. Lee, Y. Seo and D. Chang, "Analysis and optimization of cascade

Rankine cycle for liquefied natural gas cold energy recovery," Energy, vol. 61, pp. 179-

195, 2013.

[42] J. Bao, Y. Lin, R. Zhang, N. Zhang and G. He, "Effects of stage number of condensing

process on the power generation systems for LNG cold energy recovery," Applied

Thermal Engineering, vol. 126, pp. 566-582, 2017.

[43] I. Lee, J. Park and I. Moon, "Conceptual design and exergy analysis of combined

cryogenic energy storage and LNG regasification processes: Cold and power

integration," Energy, vol. 140, pp. 106-115, 2017.

[44] J. Szargut and I. Szczygiel, "Utilization of the cryogenic exergy of liquid natural gas

(LNG) for the production of electricity," Energy, vol. 34, pp. 827-837, 2009.

[45] L. Tomkow and M. Cholewinski, "Improvement of the LNG (liquid natural gas)

regasification efficiency by utilizing the cold exergy with a coupled absortion - ORC

(organic Rankine cycle)," Energy, vol. 87, pp. 645-653, 2015.

46

Appendix 1: List of suppliers It is possible to find in this appendix a list of suppliers for different element related to

LNG. In general, there are companies that they have been interesting or directly useful to

the execution of this project. It is organized in three headings, the first one is for small

size turbines. The second one for small size ORC, companies developing ORC capable

to produce energy from waste heat in a really compact space. In the last one are included

companies directly related with LNG, they use to distribute or manufacture elements for

cryogenic use or, on the other hand, they have the knowledge and the experience to

implement cryogenic systems.

• Turbines

▪ DEPRAG

They have available turbines with a power output between 1 kW to 120

kW to recover waste energy sources.

Germany

+49 9621/371-0

[email protected]

www.deprag.com

▪ Air Squared

They develop scroll expanders with a power output between 1 kW and 10

kW. They develop micro ORC as well.

USA

+1(303) 466-2669

[email protected]

www.airsquared.com

▪ Honeywell

They manufacture turboexpanders of medium size with an electrical output

between 160 kW to 550 kW. Also, a wide variety of turbochargers.

Europe

www.honeywell.com

▪ G – Team

Small and medium sizes for steam turbines available.

0042 605 236 642

Czech Republic

[email protected]

mailto:[email protected]

http://www.deprag.com/


http://www.airsquared.com/

http://www.honeywell.com/


47

www.steamturbo.com

▪ Infinity Turbine

It is a platform with open turbine designs. Free to download.

USA

(720) 541-9113

[email protected]

www.infinityturbine.com

▪ Electratherm

They manufacture some power generators for waste heat.

USA

1(877) 883-7101

[email protected]

www.electratherm.com

▪ Svenska Rotor Maskiner

They are specialized in Twin Screw Expanders.

Sweden

+46 8 466 45 00

[email protected]

www.svenskarotormaskiner.com

▪ CryoBridge

They manufacture small size turbines suitable for cryogenic applications.

USA

+1(614) 316-4367

[email protected]

www.cryobridge.com

http://www.steamturbo.com/


http://www.infinityturbine.com/


http://www.electratherm.com/


http://www.svenskarotormaskiner.com/


http://www.cryobridge.com/

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• Organic Rankine Cycles

▪ Air Squared

They develop scroll expanders with a power output between 1 kW and 10 kW.

They develop micro ORC as well.

USA

+1(303) 466-2669

[email protected]

www.airsquared.com

▪ ENOGIA

It is an expert company in thermodynamic systems. They manufacture ORC

with electrical power output between 5 kW to 100 kW.

France

(+33) 484 25 60 17

[email protected]

www.enogia.com

▪ Enerbasque

This company is developing an experimental setup for scientific purposes with

ORC systems.

Spain

+34 945 23 22 80

[email protected]

www.enerbasque.com

▪ Micropower Europe (Capstone)

They manufacture an ORC with 125 kW of electric output for waste heat.

Spain

93 514 93 02

[email protected]

micropowereurope.com


http://www.airsquared.com/


http://www.enogia.com/


http://www.enerbasque.com/


49

• LNG related companies

▪ CHART Industries

Europe

+1 800 371 33 03

[email protected]

www.chartindustries.com

▪ Clean Energy

USA

+1 (888) 732-6487

[email protected]

www.cleanenergyfuels.com

▪ Wärtsilä

Finland

+358 10 709 0000

www.wartsila.com

▪ Technip FMC

United Kingdom

+44 (0) 203 429 3950

www.technipfmc.com

▪ Linde

Germany

+49 89 7445-3434

www.linde-engineering.com

▪ Air Products and Chemicals

USA

+1-610-481-4861

[email protected]

www.airproducts.com


http://www.chartindustries.com/


http://www.cleanenergyfuels.com/

http://www.wartsila.com/

http://www.technipfmc.com/

http://www.linde-engineering.com/


http://www.airproducts.com/

50

▪ Cryoquip

Europe

+44-1227-714350

[email protected]

www.cryoquip.com

▪ Welker

USA

281 491 2331

[email protected]

www.welker.com


http://www.cryoquip.com/


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