HIGH EFFICIENT INDUSTRIAL PROCESSES INCLUDING CARBON CAPTURE (CC) - FIELD TESTS

S. Martini, M. Kleinhappl, J. Zeisler

Bioenergy 2020+ GmbH

Inffeldgasse 21b, 8010 Graz, Austria

ABSTRACT: In large scale industrial processes, such as iron production, or in gasification based process chains

(coal/biomass to synthesis gas, fuel, or power, etc.), the separation of CO2 (Carbon Capture - CC) can lead to

ecological and procedural benefits. Chemical absorption of CO2 is a well proved technology for CC with

comparatively low electrical energy demand. However, the high heat demand, absorption kinetics, CO2 capacity and

sorbent degradation are limiting factors for the industrial application. Further investigation and development of

sorbent-solutions in relation to specific gas conditions are necessary for optimisation. For testing different sorbent-

solutions a mobile test plant was designed and built up. Focus of this work was the evaluation of process key data for

CC in blast furnace gas under real conditions. The tests have been carried out continuously up to 300 hours. Aqueous

monoethanol-amine (MEA), diethanol-amine (DEA) and methyl-diethanol-amine (MDEA) solutions have been

investigated. Detailed analyses of the process gas, analyses of used liquids (chemical properties, degradation

products) and the examination of process data lead to further development in process design, control strategies for

specific applications and give routes for an efficient implementation of CC to increase the benefit in the overall

process chain.

Keywords: carbon capture, CO2 removal, amine scrubbing, chemical absorption

1 INTRODUCTION

A feasible short- and middle-term measure to reduce

the emission of CO2 is the so called Carbon Capture (CC)

in large scale industrial processes. Thereby CO2 is

separated from a gas stream, which can be of different

origin: flue gas, product gas of gasification processes,

blast furnace gas, biogas of fermentation plants or any

other process gas. Therefore also the gas properties can

differ a lot (O2/O2-free, low/high CO2-content,

atm./pressurised, impurities). After the separation, CO2

can be further utilised (CCU) or has to be stored (CCS).

There are several approaches of CO2-utilisation as a

carbon-source (production of chemicals, chemical energy

storage) but still efficient concepts to recycle high

amounts of CO2 have to be further developed. Options

for CCU are, for example, given in [1] and [2].

In general there are three feasible integration

strategies: the post-combustion-process, the oxyfuel-

process and the processes-integrated CC (including pre-

combustion CC). A short explanation of the different

strategies is given in [3].

1.1 Benefits of Carbon Capture

Beside ecological benefits, the integration of CC in

existing or new plants (process-integrated CC) can lead

to procedural advantages [3]. Ecological and procedural

advantages of CC can be:

• emission reduction and energy recovery

• saving primary resources due CO2 recycling

• increase of calorific value of process gases

• volume flow reduction

• decrease of CO2 partial pressure

• benefits in following catalytic conversion

steps, including e.g. complete recovery of

sulphur

In the thermo chemical conversion process of solid

biomass, for example, the lowered CO2-partial pressure

gives essential benefits in subsequent catalytic processes

(synthesis applications).

Due to large energetic demands, the CC-step often

leads to a decrease of overall efficiency. Therefore a

process-tailored CC-technology has to be found for each

application, as well as a reasoned implementation

strategy.

1.2 Carbon Capture technologies In general for the removal of CO2 there are different

principles conceivable. Some of them are already

successfully applied in industrial plants. At the treatment

of fermentation-derived biogas for grid-injection, for

example, adsorptive processes, like PSA (Pressure Swing

Adsorption), wet pressure scrubbing and membrane

technologies are preferred [4] [5] [6].

For the treatment of natural gas, synthesis gas or coal

gasification gas for clean gas applications (ammonia

synthesis, Fischer-Tropsch synthesis, acetylene

recovery), physical absorption processes (Selexol,

Rectisol, Purisol, etc.) are state of technology. Thereby

very low residual CO2-concentration at high electrical

energy demand (compression work) can be achieved [7]

[8] [9].

Beside physical methods, the chemical absorption is a

well proved technology for CO2 removal. Alkanolamine-

based aqueous solutions (MEA, DEA) are currently the

most favoured sorbents for chemi-sorptive acid gas

removal. The high amount of energy, which is needed in

the desorption step (thermal energy) and occurring

degradation effects are limiting factors for the industrial

realisation.

2 BASICS AND METHODOLOGY

2.1 Principles of chemical absorption of CO2

The CO2-containing process gas has to be in contact

with a liquid sorbent-solution. CO2 is transferred by

physical and chemical absorption mechanisms into the

solution and is so separated from the main gas stream. In

a second step the bound CO2 is stripped out with steam

by increasing the temperature level in the desorption step.

The so regenerated sorbent solution can be used for CO2

absorption again (absorption-desorption-cycle-process).

The most important reactions in the CO2-absorption

process in amine-solutions are the dissociation of CO2

(1), the protonation of the alkanolamin (2) and in case of

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primary (MEA) and secondary (DEA) amines the

formation of carbamates (3).

Dissociation of CO2:

CO2 + H2O � HCO3- + H+ (1)

Protonation of alkanolamine:

R-N-H2 + H+ � R-N-H3+ (2)

Carbamate formation (only primary and secondary

alkanolamines:

R-N-H2 + CO2 � R-N-HCOO- + H+ (3)

Detailed description of mechanisms in chemical

absorption processes are shown in [10], [11] and [12].

2.2 Selection of the appropriate amine-solution

The different alkanolamines distinguish in there

chemical properties: absorption capacity, ability for CO2

desorption, kinetics of absorption and desorption

reactions [13]. MEA and DEA show very fast reaction

kinetics and high capacity for CO2 absorption.

Due to its high selectivity for H2S absorption, and

comparatively slow reaction kinetics with CO2, MDEA is

mostly not considered as sorbent for CO2 removal.

However, a number of advantages make the tertiary

alkanolamine interesting even for the removal of large

amounts of CO2. [11] has listed following benefits of

MDEA as CO2-sorbent:

• High amine-concentration in solution

• High acid gas loading

• Low corrosion

• Slow degradation rates

• Lower heats of reaction (in comparison to MEA,

DEA)

• Low vapour pressure and solution losses

The choice of amines (or of mixtures of amines) for

the specific application (gas condition, quality

requirements) is a mayor factor for an optimised CO2-

removal operation (separation efficiency, heat duty,

sorbent degradation) [14]. Detailed investigations

considering corrosion effects caused by alkanolamine

solutions in treatment plants were made by [15]. It is

shown, that a 30 %-MEA-solution leads to a ten time

higher corrosion rate than a 50 %-MDEA-solution (all

saturated with CO2 at temperatures of 99 °C).

2.3 Operational key data

All these factors are influencing the two most

important key data for the process: the separation

efficiency, ηCC (4) and the specific heat duty, qdes (5).

inputm

separm

CO

CO

CC

2

2.

&

&=η (4)

.2separm

Qq

CO

Heatdes

&

&

= (5)

For the industrial application further properties of

sorbents are important. Viscosity, corrosiveness, thermal

and chemical stability (formation of degradation

products), toxicity and costs have to be considered.

2.4 Technology

The plant is designed for a gas flow of 10 to 30 m³/h

(usc). The simplified scheme is shown in Figure 1. It

consists of an optional pre-scrubber (T1) and the

absorption-desorption cycle unit. The contacting of the

gas and the sorbent solution is realised via a one-stage

packed column (T2) with an active height of 4 meters.

The CO2-rich solution is taken out of the bottom tank

of the absorber (T3) and is then conducted - passing a

heat recovery unit - to the desorption unit. The desorption

step consists of a reboiler tank with a fitted stripping

column (packed column), where the CO2 is stripped out

of the liquid sorbent with steam.

Figure 1: Scheme of mobile CC test plant; shown in [3].

Figure 2: Mobile test plant for CO2-separation from

process gas; here situated at Linz, Austria, [3].

Automation including remote monitoring allows the

realisation of long-term tests. A detailed description of

20th European Biomass Conference and Exhibition, 18-22 June 2012, Milan, Italy

1128

the test plant is given in [3].

2.5 Test execution program

The data of the small-scale test operation of chemical

absorption under real gas conditions should deliver the

basis for CC integration in high efficient industrial

conversion processes. Long-term test series with oxygen-

free process gas with a high CO2-fraction of 22 vol%

(blast furnace gas) were carried out. Next to the reference

sorbent-solutions (20 mass% and 30 mass%-MEA and

30 mass%-DEA), diverse mixtures of MDEA and MEA

have been tested. Thereby the total content of amine (sum

of MDEA and MEA) was always kept to 50 mass%.

Operational settings and the concentration of the tested

sorbent-solutions are listed in Table I. To make operation

points of different sorbent-solutions comparable, a target

separation rate was defined (range of 75 to 95 %), gas to

liquid ratio was adjusted to minimise the heat duty.

All sorbent-solutions have been tested for more than

200 hours, which is related to a number of absorption-

desorption-cycles of about 200.

Table I: Key data of test program.

MEA DEA MDEA + MEA

Aqueous sorbent

solution [mass%] 20/30 30 45/40/30* 5/10/20*

Crude gas CO2-

concentr. [vol%] 21 - 23

Test duration [h] 175+256 180 300

Gas flow [m³/h] 9 - 30 9 - 20 14 - 21

Sorbent flow [l/h] 115 - 300 120 - 260 180 - 260

Numbers of cycles 200 + 233 220 367

Separation rate [%] 75 - 95 75 - 95 75 - 95

all parameters under standard conditions

* Total amine (MDEA+MEA) constant 50 mass%

2.6 Measurements, sampling and analyses

To evaluate the process performance extensive gas

and liquid analyses have been done besides continuous

monitoring of all relevant process parameters. Main gas

components (CO2, CO, H2, CH4 and O2 as control value)

were registered at three measuring points (before, in the

middle and after treatment). Gas impurities, like H2S,

HCN, NH3, HCl and residual particulate matter, were

detected via periodical sampling and analyses according

to standardised methods, see also [3] and [16].

Liquid analyses deliver information about the CO2-

content of tested sorbents (loaded and lean), the loss of

active amines and also the presence of degradation

products after sorbent utilisation. For the determination

of typical degradation products, like oxazolidone,

HEIDA, HEEDA, or N,N-di(2-hydroxyethyl)urea,

special HPLC-methods have been developed and

validated. Detailed description of applied methods of

sampling and analysis can be found in [16].

3 RESULTS

Best performance was achieved with 30 %-MEA-

solution: specific heat duty, qDes 3,250 kJ/kg CO2 at 80 %

separation efficiency.

To achieve comparable efficiencies in the tests with

20 %-MEA the specific heat duty is about 25 % higher.

This can be explained by the higher required liquid to gas

ratio at 20 %-MEA (9 to 11 l/m³ for 20%-MEA and 6 to

8 l/m³ for 30 %-MEA).

In Figure 3 the development of CO2-concentration

during a typical parameter variation (sorbent and gas

flow) is shown for the 30 %-MEA-solution.

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

27.06.

00:00

27.06.

12:00

28.06.

00:00

28.06.

12:00

29.06.

00:00

29.06.

12:00

30.06.

00:00

30.06.

12:00

01.07.

00:00

01.07.

12:00

time

CO2-concentration [vol%

]

0

50

100

150

200

250

300

350

400

flow [l/h], [m³/h, usc]

liquid flow

gas flow

MEA 30%

desorption pressure: 1,8 bar

absorber in

absorber

middle

absorber out

A FB

CD

E

Figure 3: CO2-concentration under variation of sorbent

and gas flow, 30 %-MEA-solution.

To determine the limits of the absorption column

(geometry-retention time-absorption kinetics) the gas

flow and related sorbent flow (constant liquid to gas

ratio, Vl/Vg=6.7 l/m³) was increased (from point A: ηCC =

80 %; qDes=3,300 kJ/kg in Figure 3). For a gas flow

greater 22 m³/h the separation efficiency limit of 80 %

could not be achieved any more (B: ηCC = 65 %;

qDes=4,400 kJ/kg). An increase of the sorbent flow

(operation point C: Vl/Vg=8.5 l/m³) leads to a higher ηCC

of 92 %, but also a higher specific heat duty (qDes=3,700

kJ/kg). Lowering again the liquid sorbent flow at constant

gas flow (points D, E and F) leads to a slight decrease of

the separation efficiency and lower heat demand in the

desorption process. The operation at point F was carried

out at exactly the same settings like A - also the same

efficiency and heat demand were detected.

In Figure 4 the key parameters, liquid to gas ratio

over specific heat duty (left) and over separation

efficiency (right) for different tested sorbent-solutions are

illustrated. Each dot in the figure represents a working

point, averaged over 4 hours steady condition.

The addition of 30 %-MDEA to the 20 % MEA-

solution leads to a decrease of the energy demand of

about 10 %.

Figure 4: Liquid to gas ratio over specific heat duty (left)

and over separation efficiency (right) for different tested

sorbent-solutions.

Figure 5 shows the specific heat duty over liquid to

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gas ratio for the tested amine-blends, MDEA/MEA (ratio:

45/5; 40/10; 30/20). Applying pure aqueous MDEA-

solution no comparable results were achieved (ηCC

always <75 %, not shown).

For solutions with low concentration of MEA

(5 mass%) a comparatively high liquid to gas ratio (15 to

16 l/m³) was necessary to obtain the desired separation

efficiency of 80 %. A related specific heat duty of

5,300 kJ/kg was detected, which is about 40 % higher

than the blend with 20 mass% MEA (qDes=3,800 kJ/kg).

3.000

3.500

4.000

4.500

5.000

5.500

6.000

8 9 10 11 12 13 14 15 16 17

liquid to gas ratio [l/m³]

qdes, specific heat duty [kJ/kg CO2]

desorption pressure: 1,8 bar

separation efficiency: 86 to 90% MDEA/MEA - 45/5

MDEA/MEA - 40/10

MDEA/MEA - 30/20

Figure 5: Specific heat duty over liquid to gas ratio for

the tested amine-blends.

Further results of 20 %-MEA-solution and DEA-

solutions have already been shown in [3].

Significant differences were observed in the CO2-

capacity of sorbents: Table II shows the detected CO2-

concentrations in the tested solutions.

Table II: CO2-concentrations in sorbent solution in [g/l].

CO2-rich

solution

CO2-lean

solution ∆∆∆∆c

MEA 30% 115 - 132 59 – 82 38 - 55

DEA 30% 34 – 44 8.5 – 19 18 - 26

MEA 20%

+MDEA30% 72 - 75 38 – 41 32 - 47

The determined maximal loads per mol active amine

(α) for all MEA solutions were close to equilibrium (0.53

– 0.62 mol/mol), whereas for DEA-solution only about

75 % (0.35 mol/mol) of equilibrium-concentration was

detected.

During the MEA and MDEA operation no procedural

degradation effects, (decrease of efficiency, increase of

energy demands) were detected. Analysis of the applied

MEA-solutions confirmed that no typical degradation

products (oxazolidone, HEIDA, HEEDA, N,N-di(2-

hydroxy-ethyl)urea) have been formed during the

process. As an example a HPLC-chromatogram of a

sampled MEA-solution after 400 hours of operation is

shown in Figure 6. No peak at oxazolidone-retention time

(compare dotted line - spiked sample) was detectable.

min2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5

mAU

0

10

20

30

40

3.138

3.998

4.254

3.383

min2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5

mAU

0

10

20

30

40

3.138

3.998

4.254

3.383

Figure 6: HPLC-analysis of used sorbent (30 mass%-

MEA): dotted line = 200 mg/l-oxazolidone-spiked

sample; oxazolidone-peak in circle; blue line at bottom:

sample only.

4 OUTLOOK

For specific industrial process chains the gained

operational experience in CO2 separation forms the basis

of an optimised process design: from the integration

strategy, the selection of sorbent solutions, the control

strategy to the optimised operating point.

After the separation step, the further handling of CO2

is an essential issue to be focused on. The storage via

sequestration (CCS) can only be a temporary solution of

the CO2-problem. Enhanced oil/gas recovery and

simultaneous CO2 permanent-storage is currently one of

the favoured options. Further there is a great potential for

CO2 as a substantial C1-source for the production of bulk

and fine chemicals (e.g. urea, salicylic acid, polymers) or

chemical energy storage (via methane, methanol). A

small amount, which has the potential to be enhanced, is

already used as industrial gas as fire extinguisher,

refrigerant, or in beverage/food industry. A recent field of

research for CO2 utilisation is the biological conversion

(artificial photosynthesis, micro algae), which can

produce biomass, but also more valued products, such as

fuels, or biodegradable plastics.

The potentials for the different possibilities to

mitigate the CO2 emission (CCS, CCU) have to be

studied in the context of the regional and procedural

situation for each industrial application.

5 REFERENCES

[1] VCI, DECHEMA, Positionspapier, Verwertung und

Speicherung von CO2 (2009)

[2] Specht M, Baumgart F, Feigl B, Speicherung von

Bioenergie und erneuerbarem Strom im Erdgasnetz.

FVEE Jahrestagung (2009)

[3] S. Martini, M. Kleinhappl, J. Zeisler, Further

Perspectives Of Biomass Gasification Including

Carbon Capture (Cc); Investigation Of Suitable

Technologies, Proceeding, 19th European Biomass

Conference and Exhibition, Berlin (2011)

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of Biogas, Task 24: Energy from biological

conversion of organic waste (1999)

[5] Richter U, Aufbereitung von Biogas mit

Druckwasserwaesche, EuroHeat&Power 37, Heft 7-

8 (2008)

[6] Miltner M, Makaruk A, Harasek M. Application of

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Experiences of Feeding Biomethane into the

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Austrian Gas Grid proceeding, 16th European

Biomass Conference and Exhibition, Valencia

(2008)

[7] R. Roschitz , W. Stutterecker, M. Kleinhappl, N.

Machan, J. Draxler, Treatment Of Fuel Gas To Gain

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Berlin (2007)

[8] A. Ohle, CO2-Abtrennung aus Gasströmen durch

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[11] J. C. Polarsek et. al., Using Mixed Amine Solutions

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[12] Z. Aliabadi et. al., Using Mixed Amine Solutions for

Gas Sweretening, World Academy of Science,

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[13] A. Jamal; Kinetics of carbon dioxide absorption and

desorption in aqueous alkanolamine solutions using

a novel hemispherical contactor—Experimental

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[14] H. R. Khakdaman et. al., Revamping of Gas

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[15] M. S. DuPart, T.R. Bacon, D.J. Edwards,

Understanding orrosion in Alkanolamine Gas

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6 ACKNOWLEDGEMENTS

We gratefully thank our company partner voestalpine

AG (Bürgler T, Rummer B, Rummetshofer T) and our

colleagues from Bioenergy 2020+ for successful co-

working.

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