Executive Summary

In September of 2004, the ALPHA Consultancy entered into a bidding agreement to design a Methanol Production plant with special requirements to produce methanol from Syngas, using natural gas. The following outlines the major factors being considered and the investment cost necessary for the plant to be manufactured.

With the availability of 99% purity natural gas the Syngas is to be produced using gas via steam reforming process. Under a required production of 1000 tonne per year this method of Syngas was deemed most suitable as alternative methods involves air purifiers, which are more suited for methanol production capacities above 2500 tonnes per year.

The table shows a Financial Summary of the major results from the design of the process.

Natural Gas Cost 37483 x 50 £ 1836630 h-1Yearly Operation 300 days 7200 hrs

Daily Cost 1604500/7200 £230

Total Variable cost £ 15454965Fixed CostInsurance 1% fixed capital £ 372035Total Fixed cost £ 6132567

Direct production cost £17640983 + £ 6,132,567 £231,773,550

Price of Methanol £158.34/tonne

Sales revenue £158.34 x 1000 x 300 £47,502,000Profit Sales revenue – direct production cost = £23,728,540

Profit = 47 502 000 – 15 454 965 = £ 23, 728,450

The basis of producing methanol from Syngas is to be using a multi tubular isothermal reactor. This reactor would operate at low temperatures and pressure with the use of Cu/Zn/AL2O3/CrO as catalyst. This method of methanol production is a modern process which would give up to a conversion of 85% CO, which determines the actual amount of Methanol produced. Shell and tube reactors were chosen because the reactions are exothermic.  Therefore heat needs to be removed from the reaction system.  Shell and tube reactors not only allow heat to be removed from the process by circulating a cooling medium on the shell side of the reactor, but also reduce hot spot formation in the reactor.   In the shell and tube reactors, process fluid flows through the tubes while cooling fluid, saturated water, which is boiling to saturated steam, flows through the shell.

The main issue of environmental effect of methanol is the production and removal of carbon dioxide. The Alpha Consultancy is proposing to inject the carbon dioxide into the ground. This requires very extensive research and we are in the process of seeing it through.

Table of ContentsPage

1. Introduction 3

2. HYSIS – Process Simulation 4-6

3. Energy Recovery 7-9

4 Methanol Reactor Design 10

5. Chemical Engineering Design 10-19

6. Mechanical Design 20-23

7. Process Control and Instrumentation 24-26

8. HAZOP 27-29

9. Cost Estimation and Economic Appraisal 30-32

10. Critical Review 33-34

11. Reference 35

12. Appendix 36

Phase1 ReportPhase 2 ReportPhase 3ReportHYSIS material and Energy Balance

Introduction

Phase 4 of the design report represents the last in a series of 4 reports on the design of the Alpha Consultancy Methanol Plant. The previous covered aspects of design routine, the methanol market, environmental issues and sustainability. Phase 4 is a summary of the entire report as well as detail reports on the methanol reactor design, simulation of process using HYSIS and a final cost estimation appraisal.

The major part of the entire process is the reactors, this is where initially Syngas is produced in the process, and secondly where methanol is produced. This report will cover all the aspects considered when designing a methanol reactor, with special interest in the multi-tubular isothermal methanol reactor.Issues of both chemical and mechanical design are covered as well as cooling medium for the reactor.

Also covered in this report is a detailed Hazard Analysis Syngas reformer. It is necessary fro a standard as well as management point of view to understand the steps taken in analyzing a process for risks and hazards to estimate any unforeseeable accident. This detailed study gives more depth to process control, which is also considered in this report fort the Methanol Synthesis reactor.

HYSIS

In the modern methanol and other chemical industries, the initially process flow of a plant is usually defined by simulation packages, and other control software packages. The use of simulation packages in chemical plants over the past 3 decades has grown rapidly and more companies buy into the idea each day. Simulation packages do as the term suggests, simulates and put an actual process into theoretical operation. With these packages getting more user friendly and capable to do more than normal, simulation packages can set up an entire production with a few user specified variable. User knowledge is always the key however as all simulation package can only give an output, based on an input.HYSIS, a user-friendly computer software package developed by Hyprotech is one of these packages;The goal of programs like HYSYS is to provide users with the capability to design an entire process as completely and accurately as possible. In the ALPHA Consultancy, HYSIS was used to do a simulation and design with reference to hand calculations that were done in phase 2 of these reports.

PFD

The two main areas of methanol production are the Syngas production and methanol synthesis. These were the only two areas in the process where reaction actually occurred. Unlike the hand calculation, only some basis had to be specified for HYSIS, these including components, reaction equations with appropriate stoichiometry, reaction type and where necessary process conditions. The first obvious difference was the principle by which HYSIS does the calculations. Gibbs free is the basis of its calculations, and because of this showed a difference in calculated conditions. The Peng-Robinson SV basis of fluid package was chosen since the PRSV is a two-fold modification of the PR equation of state that extends the application of the original PR method for highly non-ideal systems, even though ideality was assumed for much part of the phase 2 report calculations.

Syngas was produced with the use of an equilibrium reactor, as the basis for the production was, (Fro phase2) defined by an equilibrium relationship between the CO and steam reaction, with the water gas shift reaction.

Methanol synthesis reactor was of the converter type. For this reactor the reaction and conversion had to be defined in the reaction manager in HYSIS. This type of reactor was chosen because detailed knowledge was obtained prior to simulation and data was collected for specific conversion of CO and CO2 to methanol.

Fig 7 – Process Flow Diagram ‘ALPHA Methanol Process’

Fig 7 shows the final PFD of the methanol production process simulated through the HYSISTM, simulation package. From Phase2 in these reports, the inlet ratio of CO to steam was found to be 3:1, and a SET block was use to set this ratio. The SET operation set the value of one stream variable (the independent variable) to meet a required ratio (the dependent variable) in another stream or operation. Table 7 gives a short description to some the major units and streams in the PFD.

APLHA©2005HYSIS METHANOL PRODUCTIONPROCESS.

Table 8 – HYSIS equipment unit and streams explained.

Unit/ Streams

MIX-1 Mixer used to mix the process flow water with the treated and recycled water from the process

HTR-1 Heater used to raise the temperature of the process water to form steam

SET-1 Used to set the inlet flow of steam to 3 times the molar flow rate of natural gas

n.gas Raw methane feed, of 99% purity at ambient temperature and pressure at a flow rate of at 2000kgmol/hr

p.water Pure uncontaminated water at 2O˚C and ambient pressure

MIX-2 Mixer used to mix steam and natural gas before entry into the steam reformer.

HX-1 Heat Exchanger, which exchanges heat between the cold, feed mixture of natural gas and steam with hot outlet syngas. Beyond HX-1 also would be an array of heat exchangers, which are responsible for adequately exchanging heat while making HP, MP and LP steam from the useful energy from the reactor.

RX-100 Steam Reformer, in the form of an equilibrium reactor, where 1st set of reaction occurs in the process. Produces syngas at very high temperature and low pressure. Reaction highly endothermic so a considerable amount of energy is needed to drive reaction.

CLR-1 Representing a series of heat exchangers and cooling system, the purpose of the cooler is to bring the temperature of stream from reformer, under a temperature (60˚C), suitable for water separation.

SEP -1 Separator used to condense the gas mixture; so as much water can be removed from the process as possible. Water is very corrosive to compressors etc.

x27 Stream x27 is the recycled stream, of gases rich in CO concentration, used to improve the efficiency of the process, by recombining with fresh feed before entering the synthesis reactor.

RX-200 In the form of a converter reactor, this is where methanol is produced from high pressure (70bars), low temperature (260˚C) reactions of CO 2, CO and H2. Reaction highly exothermic.

MIX-100 The mixing of the fresh feed and recycled feed to the synthesis reactor.

CMPR-1 The compressor increases the pressure of the reactor inlet feed to the reactor operating pressure 70bars. Also a representation of compressors in series as one compressor would need too much of an unrealistic volume to yield correct pressure increase.

HX-2 Also used to decrease the temperature of the exit stream from the reactor, this set of heat exchangers also produces LP steam with the useful energy from the reactor.

Sep 2 To obtain gas for recycling, the separator maintained at a pressure and temperature below BP of methanol, so the gases could evaporate and be recycled, while the stream rich methanol concentration is distilled for purification.

HYSIS

Selected HYSIS simulated data comparison with results from PHASE 1, Hand Calculated results.

Units Phase-1 Report

HYSIS Simulated

Inlet Natural Gas Molar Flow (kgmol/hr) 1803 2000Inlet Steam Molar Flow (kgmol/hr) 5410 6000CH4: Steam Ratio - 3 : 1 3 : 1CH4 conversion % 85 94Reformer Temperature K 1273 1273Reformer Pressure bar 16 16CO: H2 ratio in Synthesis Reactor Inlet - 15 : 1 3.6 : 1Reactor Temperature K 533 533Reactor Pressure bar 100 70CO conversion in synthesis reactor % 74 77CO2 conversion % 5 0Methanol Production Kgmol/hr 995 1340Overall Energy usage KJ/hr 5.74E+09 2.29E+09

From the above data comparison it can be seen that the HYSIS package, through optimization produced on average more methanol than using hand calculations. The principles and basis for the HYSIS calculations has to be taken into account as well as the nature by which optimizations are done. For e.g., the inlet pressure of the reactor was varied, and by hand calculations this would take a very long time to examine the effect on methanol production and other downstream processes. With added units also, the heat flow throughout the process was almost halved comparing with that of the phase 1 calculation.

Energy Recovery

The area of Syngas production produced a considerable amount of heat, and this was seen as major source of energy recovery for the Alpha Consultancy. The heat from the exiting feed stream from the reformer is cooled through a series of heat exchangers. These exchangers use the useful heat from in the stream to produce HP, IP and LP steam.

Methanol Reactor Design

Methanol synthesis is believed a combination of two exothermic reactions, namely conversion of CO via the water gas shift reaction to CO2 followed by hydrogenation of CO2 to methanol.

CO + H2O ↔ H2 + CO2 ∆H298 = -41.2 KJmol-1 -1-CO2 + 3H2 ↔CH3OH + H2O ∆H298 = -49.5 KJmol-1 -2-

These two reactions will be considered for the major unit design of an Isothermal Multi-tubular Methanol Synthesis Reactor.

Design Approach

Kinetics

Various personnel have studied the complex chain reaction of the methanol synthesis process over the years and many theories have been made for the actual rate kinetic equations that correctly define the mechanism.

Bussche and Froment (Journal of Coal and Petroleum, 1996) have reported a proposed model of the kinetic relationship based on production of methanol in the presence of high selective Cu/ZnO/Al2O3 catalyst, which permits operation at lower pressure than classic pressure process.

The proposed model takes into consideration only reaction from carbon dioxide and inverse water-gas shift reaction, the two also been considered for ALPHA methanol synthesis reactor design.

CO + H2O ↔ H2 + CO2 -1-CO2 + 3H2 ↔CH3OH + H2O -2-

Bussche and Froment showed that for the rate of methanol synthesis and the inverse water gas shift reaction the following expressions are accepted:

-3-And,

-4-

Where;

5 -12

These reaction and equilibrium constant were based on detailed research, which spanned across companies institutions, and have had the credibility authorization from world-renowned researchers. Buscche and Froment proposal was based on combined the work of past research models, their own laboratory data and detailed researches.Buscche and Froment.

Using Eqn 5-12 the following values of pi, k1, k2, k3, k4, k5, Ke1, and Ke2 at various reactor temperatures are given below.Table 1 – Values of Rate Constants at various Temperatures

Rate of reaction obtained from equations 3 and 4.Fig 1 – Graph of Temperature Effect on Rate of Methanol Formation

T (K) R1(CH3OH) R2(RWGS)

500 7.1E-06 5.77E+16520 2.1E-05 5.898E+16530 2.7E-05 5.442E+16540 2.9E-05 4.717E+16550 2.9E-05 3.875E+16560 2.8E-05 3.056E+16570 2.6E-05 2.345E+16580 2.3E-05 1.771E+16590 2.1E-05 1.328E+16600 1.9E-05 9.945E+15630 1.4E-05 4.259E+15670 9.2E-06 1.501E+15700 6.9E-06 7.363E+14720 5.8E-06 4.726E+14

R(MeOH) Varaition w ith Temperature

0

0.00001

0.00002

0.00003

0.00004

450 500 550 600 650 700 750

Temperature (K)

Rxn

Rate

(r)/k

gmol/

hr

Fig1 shows the variation MeOH formation rate with temperature. Beyond 530-540K, the reaction rate slows and is an indication of the shift in conversion of Co2 being produced while the methanol being produced decreases in the reaction. From this evidence the reactor temperature of 530K, was confirmed as an ideal temperature to be used with the Bussche kinetic model. Equilibrium ConstantsAlthough obtained from the Bussche model of methanol reaction kinetics, the aim is the understand the validity of the rate constants proposed, by calculating the Equilibrium constant of the Reverse Water Gas shift Reaction from the Gibbs Energy model.The equilibrium constants Kp1 (RWGSR) and Kp2 (MeOH) are carried with the use of Gibbs Energy Relationship and Hoff’s Law.

-13-

-14-

(Hoff’s Equation) 15

∆H298, ∆S298 obtained from ‘Chemical Properties Handbook by Yaws, C.L, 1999 McGraw Hill’.From 13, we obtain ∆G298, and 14, we obtain values for ln K.

Table-2. Calculated Values

From Hoff’s equation (15), values were obtained for the equilibrium constants, Kp1 and Kp2 at different range of temperatures, and specifically at the ALPHA methanol synthesis reactor temperature and pressure. (530°C and 70 bars)

Table-3 shows the K values obtained for the RWGSR (Reverse Water Gas Shift Reaction) compared with values using Bussche Kinetic Model.

Conversions

298 298 298R R RH T S G

298

298298

1 1RHln K ln K ( )

RT T T

The equilibrium constant Kp can be expressed as the product of the equilibrium constant Ky in terms of mole fractions and a function of pressure, i.e. Kp = Ky∏PT

∑νi. Equilibrium expression can be set up in terms of mole fractions у i, in terms of ni, since уi = ni /nT for a system of j reactions having an equilibrium extent xj:

ni = nio + ∑νij xj -16-

The initial model I started preparing for the design of the reactor consisted of both the reverse water gas shift reaction as well as the decomposition of carbon dioxide to methanol. For both reactions being considered for the design, theses are the number of moles of each species at any time in the reaction, representing the extent of reaction in both equations:

nCO = nCO°- x1 -17-nH2O = nH2O° - x1 + x2 -18-nH2 = nH2° + x1 – 3x2 -19-nCO2 = nCO2° - x1 – x2 -20-nCH3OH = nCH3OH°+ x2 -21-nT = nT – 2x2 -22-

An equation can now be written for the equilibrium expression in terms of the number of moles, equilibrium constant K in terms mole fractions, and correction for non-ideality.

Kprwgsr = (nCO2 nH2)/ nH2O nCO Ky1 -23-KpMEOH = (nCH3OH nH2O nT

2)/ nCO2 nH23 PT

2 Ky2 -24-

Substituting for number of moles of each species in terms of initial moles and extents of reactions from equations 17-22, into equations 23 and 24, sets up simultaneous equations with x1 and x2 as unknowns.

Kprwgsr = (nH2° + x1 – 3x2) (nCO2° - x1 – x2) / (nCO°- x1) (nH2O° - x1 + x2) -25-KpMEOH = (nCH3OH°+ x2) (nH2O° - x1 + x2) (nT-2x2)2 / (nCO2° - x1 – x2) (nH2° + x1 – 3x2)3 PT

2 - 26-

Inlet mole ratio, obtained from HYSIS. Table 4 – Values Obtained fron Hysis Simulation Basis Species Mol Fraction # MolesH2O 0.105 1067.86CH4 0.002 20.34CO2 0.047 478.03H2 0.631 6417.27CH3OH 0.044 447.5CO 0.171 1739.03Total 1 10170.03

Using Kp values from Table 1, initial no of moles and total no. of moles, and total pressure we can substitute into equations 25 and 26, to obtain expressions with only x1

and x2 as unknowns. Values of Ky1 & Ky2 were obtained from generalized fugacity tables (Perrys).

Substituting values of moles from table 4, Kp constants, and Ky, the following expressions are found.

At 530˚C

Where x1= x and x2 = y

-27-

-28-

When solved using Math Cad at 530K, the following values of y and x, were obtained.

By definition of conversion: Xi = (ni° – ni) / ni° -29-XCO = x/nCO°XCO2 = (x+y)/nCO2°

The inconsistency in this approach was a matter of complexity than feasibility. Both reactions affect the rate and extent of reaction on the other, but a mathematical model has to be developed to integrate both equations with respect to the conversion, and later in the model this proved to be very difficult. The conversions in CO and CO2 were found, but to obtain corresponding reaction rates at other conversions would involve very complex mathematics. This would have being the better approach, as the direct relationship on both reactions and their effect on reactor sizing would be more acceptable in practice.

Addition Reaction Approach

Form the reaction rate data in Fig1, it was observed that the rate of the Reverse water gas shift reaction happens much quicker than the Methanol formation reaction and therefore would suggest the reaction-forming methanol is the rate-limiting step. This kinetic concept was also highlighted by Bussche and Froment. With this theory the overall assumption is made that the Methanol forming from CO2 is the actual controlling step. To include an overall mechanism, which would be a better but simpler mechanism, the reverse water gas shift reactions and the CO2 decomposition to methanol, are added to form one reaction. This way, the actual conversion of carbon monoxide to methanol is observed rather than, every other short reaction.In the methanol synthesis industry, very complex relationships on the mechanism and action of one reaction on the other are considered (Journal of Advanced Catalysis). It is important to pinpoint that the RWGSR occurs very quickly, but does have some effect on the sizing of the reactor. That is the reason why, for the purpose of reactor design, a

combination of both equations, which present a more simplistic design, will be considered.

Recall:

CO + H2O ↔ H2 + CO2 ∆H298 = -41.2 KJmol-1 -1-CO2 + 3H2 ↔CH3OH + H2O ∆H298 = -49.5 KJmol-1 -2-

Combining both equations gives the following

CO + 2H2 ↔CH3OH ∆H298 = -90.6 KJmol-1

The equilibrium expression for this reaction can be written as follows can be written

KpMEOH = (nCH3OH nT2)/ nCO nH2

2 PT2 Ky2 -30-

From mass balance the following is obtained.

nCH3OH = nCH3OHº + x -31-

nCO = nCOº -x -32-

nH2 = nH2º - 2x -33-

nT = nTº-2x -34-

Substituting equations 31-34 into equation 30 yields:

KpMEOH = (nCH3OH°+ x) (nT

º – 2x) 2 / (nCO° - x) (nH2° -2x) 3 PT

2Ky2 -35-

From the Bussche Model of Kinetic equations, KpMEOH is found over a range of reactor temperature at 70 bars, using equation 11.

Kp,1 = 10 3066/533 – 10.592 -36-Kp,1 = .00056356 -37-

Using this value of Kp for the Ke,CH3OH at 530K and 70bars, and equation 35, the extent of reaction was calculated in Excel.

0.074324 = (447.5 + x) (nTº

– 2x) 2 / (1739.3 - x) (6417.27 -2x) 3 702 *0.7 -38-

The overall extent showed a value of x to be 1738.98. The conversion associated with this extent in reaction was calculated for carbon monoxide.

This figure represents entire conversion, but the time this would take would not be economically feasible, therefore backward-calculations were doing using equation 38 to specify conversions for reactor actual conversions, so values of Kp can be obtained to specify at what rate this would occur.

Using the Goal-Seek function in Excel, the following values were obtained for extent of reaction and Equilibrium constants.

This was done by specifying a conversion with the associated extent of reaction calculated from equation 29, and setting predicted values so new extent of conversions and Kp values could be obtained.Equation 3 was then used to obtain, the reaction rate corresponding to the respective conversions.

Table 5 – Data Obtained Through Excel Goal Seek Function

Rxn rate Kp Xxnt rctn Conversion - XCO

2046529.51 1.1003E-05 1652.08 0.95802521.36 4.7092E-06 1565.13 0.90448474.48 2.7020E-06 1478.18 0.85287223.10 1.7518E-06 1391.22 0.80197975.97 1.2157E-06 1304.27 0.75142906.67 8.8130E-07 1217.32 0.70106465.46 6.5842E-07 1130.37 0.6581139.77 5.0278E-07 1043.42 0.6062886.43 3.9023E-07 956.47 0.5549354.11 3.0658E-07 869.52 0.5039093.07 2.4303E-07 782.56 0.4531167.62 1.9388E-07 695.61 0.4024951.21 1.5529E-07 608.66 0.3520011.36 1.2459E-07 521.71 0.3016041.92 9.9909E-08 434.76 0.2512821.36 7.9871E-08 347.81 0.2010186.39 6.3470E-08 260.85 0.158014.68 4.9947E-08 173.90 0.104710.43 3.8726E-08 86.95 0.05

Reactor/Catalyst Volume

Since for a plug flow reactor, the volume can be found from defining molar flow rate reaction rate, and conversion. The basic design equation for ideal plug flow is utilized.

-39-One of the most important applications of this design equation is the determination of reactor volume and in this special case of a catalytic reactor, catalyst volume.

With the defined values of conversion and rate of reaction in Table5, a graph corresponding to the function expressed in equation 39, can be plotted.The area under the graph within a specified conversion would relate to V/F0, F0 being the inlet molar flow rate to the reactor, obtained from HYSIS and V’ corresponding to the volume of the reactor and catalyst volume.

Fig2- Graph Plot to Obtain Reactor Volume

As observed from the graph above, the volume necessary for an almost complete conversion would not be economically feasible. For the reactor design therefore an industrial practiced conversion of 50-70%, is used. With a desired 54% of conversion, the aim was then to obtain the desired reactor volume, the residence time, the number and arrangement of pipes, the catalyst weight and the pressure drop across the catalyst bed.

Using the method of counting the squares, the volume of reactor obtained from Fig2, was calculated.Assumption – The molar flow rate of would expect to change during the reaction, but for simplistic design and this is assumed to be constant.

Volume of each square = .02 × 200 = 4m3/kgmolsF0 = 1.07E+04 kgmol/hr=2.885 kgmol/s

Number of squares counted = 30Volume of Reactor, V = 30×4×2.885 = 339m3

Residence TimeTo obtain the residence time θ, for the plug flow reactor the equation 40 is used.θplug = F0 ∫xco dxCO/-rAν(1+εAxA) -40-Assuming ideal gas behaviour:PV = nRT, P/RT = n/V, n/V = C, C = P/RT or Ci = yiP/RTAt 70 bars and Temp of 530 KCCO = (0.171×70, 00,000) / (8.314×530) = 270 kgmol/m3

εA = Expansion coefficient, = 1/Tν = Space Velocity = F0/CCO

Graph of Reaction rate vs CO conversion

0.00

1000.00

2000.00

3000.00

4000.00

5000.00

6000.00

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Conversion

Rat

e (-

1/R

A)

= V/FO

Vol. of squares (area under graph at 55% conversion = 30 × 4(area of unit square) = 120 m3s/kgmolVol. of Reactor = 120 m3s/kgmol × F0 = (120 × 2.825)Vol. of Reactor = 339 ~ 340 m3

εA = 1/T = 1/533 = .001876K-1

ν = F0/CCO = 2.825/270 = 0.01403 m3/s

Equation 40 now becomes;

θplug = F0 ∫xco dxCO/-rCO .0104(1+.001867xCO) -41-

The integral of this graph was found graphically. Fig 3 shows the graph and the corresponding area, which relates directly to the residence time.

Volume of each square = .02 ×100000 = 2000 kgmol/sF0 = 1.07E+04 kgmol/hr=2.825 kgmol/s

Number of squares counted = 4Residence Time = 2000×4×2.885 = 28350 sec = 7.84 hr

Catalyst Weight

Bulk densities (ρb) of Cu/Zn/Al2O3 catalysts are typically 1.1 – 1.4 gcm-3, (Fundamentals of Industrial Catalytic Processes pg 276).

ρb for design purpose is 1.2 gcm-3 = 1200kg/m3

Mass of catalyst therefore = ρb × catalysis volumeMass of catalyst therefore = 1200 × 339 = 406800 kg

Graphical Solution of Reactor Residence Time

0

1000000

2000000

3000000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Conversion

Rat

e(km

ol/s

2)

= T / F 0

θ p l u g = F 0 ?x c o d x C O / - r C O . 0 1 0 4 ( 1 + . 0 0 1 8 6 7 x C O )

Graphical Solution of Reactor Residence Time

0

1000000

2000000

3000000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Conversion

Rat

e(km

ol/s

2)

= T / F 0

θ p l u g = F 0 ?x c o d x C O / - r C O . 0 1 0 4 ( 1 + . 0 0 1 8 6 7 x C O )

Coolant Requirements

The reactor tubes are to be cooled using boiling water, produced from a boiling water tank, mounted near the top of the reactor. The flow rate of boiling water required for this purpose is calculated by dividing the required duty of the reactor by the latent heat of vaporization for steam at 10 bars. The concept of cooling in the reactor is brought about by the difference in temperature of the boiling water and reactor tubes. A driving force is therefore created which removes heat from the reactor tubes to the boiling water creating LP steam at 280˚C

Table7- THERM EXCEL physical data of water

Absolutepressure

Boiling point

Specific volume (steam)

Density (steam)

Specific enthalpy of liquid water (sensible

heat)

Specific enthalpy of steam

(total heat)

Latent heat of vaporization

Specific heat

Dynamic viscosity

bar °C m3/kg kg/m3 kj/kg Kcal/kg kj/kg Kcal/kg kj/kg Kcal/kg kj/kg kg/m.s

2 120.23 0.885 1.129 504.71 120.55 2706.29 646.39 2201.59 525.84 2.1208 0.000013

The required duty of the reactor is given by Q = mλ + mcpΔT -43-Where λ = latent heat of vaporizationm = mass flow rate of boiling watercp = specific heat capacityΔT = change in temperature of coolantAlso obtained from Hysis, Q = -3.878E+04 kWQ = -38.78 MW

From table above, the inlet water is to be maintained at 120˚C, at boiling, and 2 bar. At these conditions the latent heat of vaporization is 2201.59 kJ/kg, and heat capacity. The assumed outlet coolant temperature is 280˚C. This temperature provides a reasonable log mean driving force for heat transfer. The mass flow rate of the boiling water is calculated as follows: From equation 43, m = Q [λ + cp(T2-T1)]

Substituting, m = 3.878E+04 [2201.59 + 2.1208(280 – 120)m = 2.54 kg/sor,m = 9146.844 kg/h

Reactor Tubes

Since the reactor tubes will be in contact with carbon monoxide methane, and a small quantity of water during normal operations, the tubes is constructed of stainless steel (304).  To obtain the number of reactor tubes, with the corresponding pressure drops, and tube diameter, a spreadsheet was used to timely calculate the pressure drop in pipes of different length corresponding to the reactor volume.

Erguns equation was used to calculate the pressure drop.

Where,

-42-

∆P = Pressure dropε = porosityρg = gas density, kg/m3Ug = gas apparent velocity, m/sde = ekvivalent diameter of catalyst pellet, mνg = kinematics gas viscosityz = length of the reactorTable 6 – Iterative Pressure Drop Optimization - Excel

From the iterative length and pressure drop, the tube dimensions chose is below.Reactor Length = 5mInternal Tube Diameter = 0.15mNo. Of tubes = 3850Diameter of catalyst pellet = 0.01mPressure Drop in Reactor Tubes (70 bars) = 2 bars

The pipe thickness is calculated from the British Standard (Coulson and Richardson Vol 6)

or -43-

Where P = internal pressure, bard = pipe outside diameter, mmid = pipe inside diameter, mmb = design stress at working temperature, N/mm2

Design stress found for stainless steal 304, at reactor temperature of 260˚C. bst st304 (260˚C) = 110 N/mm2, et al. (…)

From equation 44, thickness‘t’ obtained, is shown below.

t = [70 * 150]/[20*110]t = 4.77 ~ 5mm

Outside diameter of tubes = 160 mm or 0.16m

Diameter across reactor bed = (Martyn) -45-

Assumed packing efficiency = 95%Pitch, from data (Coulson and Richardson) should be at least 1.25 length of the tube outside diameter. Assuming pitch of 1.6 the length of the tubes, the diameter across the bed is calculated as follows,D = √ ((4/∏)*3850*(1.25*0.15)2)/0.95) = 14.4 m

For reactor length, the height of reactor shell based on maintenance area and catalyst entry area is estimated 3.3 times the height of the reactor tubes. Since the reactor tube height calculated was 5m, the resulting shell height is 16.5m.

The reactor is to be constructed of carbon steel with a 1.25 corrosion allowance.  Carbon steel is cheap and can easily withstand the pressures and temperatures required for the shell side of the reactor.  During normal operations, the only fluid to come in contact with the reactor shell will be industrial water.

The wall thickness can be specified in accordance with 1AS1210 for class 1 pressure-vessel, using an equation based on circumferential difference.

1 Australian Standards 1210

-46-Where;t = minimum shell wall thickness (mm)D = Shell inside diameterP = Design Pressure MPaf = Tensile strength of carbon steel et al. n = joint efficiency

D for shell diameter is estimated to be at least 1.1 times the diameter across the tubes cross-section.This gives: 1.*14.4 = 15.4mJoint efficiency estimated to be 100%Tensile stress of carbon steel (304) = (290) N/mm2

Substituting into equation. 46, t is:

= 37mm

Shell HeadsThe Reactor shell will be closed with a hemispherical head. This is the strongest shape, and used generally for high pressures. (Coulson and Richardson Volume 6)Thickness of hemispherical head using rule of thumb which states it should be at least 7/17 the thickness of the shell. (Brownell and Young 1959)Thickness = 7/17 * 37 = 15mmSupportThe reactor is to be supported by four (4) saddles at the bottom of the reactor, equal distance apart.

Fig4. Mechanical Design -Schematic

PROCESS CONTROL AND INSTRUMENTATION

Tube inner dia 0.15m

Catalyst pellet dia 0.05m

Reactor length (16.5m)

Tube outer dia 0.0.2m

No. of Tubes 3850

Tube length 5m

Diameter across Bed (14.4m)

Shell inner dia 15.4m

Shell thickness 37mm

REACTOR

MECHANICAL DESIGN

Tight process control of the reactor temperature is essential in order to maintain isothermal conditions, and product quality. A control system is established to regulate the flow of coolant through the reactor shell. The system consists of 5 control loops with control 1). The reactor feed rate; 2) the reactor outlet temperature; 3) the coolant temperature; 4) the water tank level and 5); the pressure of the steam stream. A simple PI controller is used to control the feed stream rate. Set-point ramping will be used to smooth changes to the reactor feed. If the flow rate increases the flow rate of the outlet stream (product) will increase the remove any excess build up of feed, and hence temperature and pressure in the reactor.A feedback-feed forward controller will be used to control the reactor outlet temperature. Feed forward control actions will be utilized to detect changes in the reactor feed rate before they impact on the temperature control loop, with the flow rate of coolant changing with respect to reactor outlet temperature.The coolant supply temperature to the reactor will be controlled via the water flow from the boiling feed tank. An increase in temperature of the coolant will automatically cause the flow from the water tank to decrease.Another feedback-feed forward controller will be used to maintain the level of water in the boiling tank. This controller will maintain the correct level by monitoring the boiling water production rate from addition of steam inlet flow rate and process water inlet flow rate to the tank.Pressure indicators are placed at the inlet and outlet of the gas streams to provide a continuous record of the pressure drop over the catalyst, and to detect any abnormal pressure build ups. Temperature indicators are positioned at several positions along the reactor tubes to monitor the temperature profile and the peak temperature. Temperature indicators are also inserted to monitor the coolant. The entire system will also be fitted with alarms to warn of any excess or malfunction in process variables and control.

The diagram in Fig 8 illustrates the process control scheme discussed above.

Fig8 – Reactor Control Scheme

FEED

TI

TI

TI

BOILING WATER

FC

PI

FCTC

FC

TI

REACTOR

TC

PROCESS WATER

BOILING TANKSTEAM

FC

PC

MP STEAM

PRODUCTS

LCFC

PI

PROCESS WATER

FC

CONTROL SCHEME FOR REACTOR

HAZOPThe unit chosen by the Alpha Consultancy for Hazard Analysis is the reformer reactor. Hazards analysis are very important in engineering design as this is where unforeseen process hazards are identified which could cause major accidents. In compliance with the British Heal Standards, the hazard analysis on the Alpha reformer is detailed below, with the addition of a Fault Tree Analysis which outlines the route of unforeseeable accidents.

HAZOPALPHA CONSULTANCY LIMITED

Pre-heated inlet (600 o C, 16bar)

Guide Deviation Possible Causes Consequences Action Required

None No Flow 1.Wrong routing

2.Isolation in error

3.Line fracture a) Institute regular patrolling & inspection of transfer line

4.Equipment failure (control valve, isolation valve e.t.c) No feed in the reactor, Material loss

5.Blockage Pump overheats b) Maintenance of control valves & instrumentations

More Of More Flow 6.Exchanger tube leaks

7.Control faults Covered by b)

8.More quantity Increased in temperature, build up of materials in the reactor c) Regular checks

9.Increased pumping capacity Less conversion of

10.Increased suction pressure reactants in the reactor Covered by b)

More Pressure 11.Thermal expansion Line fracture or flange leak d) Install thermal expansion relief on valve section

12.Isolation in error with pump running Line subjected to full pump delivery e) Install kick-back on pumps

More Temperature 13.Ambient conditions Deactivation of catalyst Covered by c)

14.Higher energy from machines High risk of thermal runaway due to high energy demand Covered by b), f) emergency shutdown procedures

15.Cooling water failure Less conversion of reactants in reactor Covered by c)

Less Of Less Flow 16.Leaking line Material loss adjacent to public highway Covered by a)

17.Defective Pump Reduced output Covered by b)

Less Temperature 18.Ambient conditions Deactivation of catalyst Covered by c)

Guide Deviation Possible Causes Consequences Action Required

None No Flow 19.Transfer line fracture Covered by a)

20.Blockage No feed in the reactor, Material loss

More Of More Flow 21.Failure operation of valves Ruptured vessel g) Install high level alarm and locking off procedure for control valves.

More Pressure 22. As for 21. As for 21. Undesired reactions might occur Covered by g) and c)

More Temperature 23. Thermal runaway As for 21. Risk of explosion Covered by f), h) Immediate evacuation

Less Of Less Pressure 24. Vacuum conditions Less conversion in reactor

25. Condensation As for 24. Covered by b)

26. Vessel drainage Material loss, undesired reaction might occur Covered by c)

Less Temperature 27. As for 13. As for 13. Covered by c)

Part Of Lower Ratios 28. As for 21. Low Syngas formation i) check ratios for optimum Syngas formation

More than Higher Ratios 29. As for 21 High formation of CO2 Covered by i)

As well as Impurities 30. Sulphur in raw materials Poison to catalyst Covered by c)

Other Maintenance 31. Coke formation Accumulation in reactor Covered by f)

Table ()Steam reformer Outlet (1000oC 16bar)

Guide Deviation Possible Causes Consequences Action Required

None No flow 32. Vessel Rupture Material loss to atmosphere

3. As for 3. As for 32.

34. Outlet line blockage As for 32. Covered by f),h)

More Of More Flow 35. As for 6.

36. As for 7. Covered by b)

37. As for 8. As for 8. Covered by c)

More Pressure

FAULT TREE ANALYSIS

Reactor Explodes

Damage to reactor

Physical damage to reactor

Thermal damage to reactor

Mechanical damage to reactor

Reactor runs outOf control

Thermal runaway FirePiping failure Valve failure Sparks Leakage

Explosive power damage

to reactor

Poor design of Heat removal

Inadequate Training

Inadequate control& safety systems

Mechanical failure Technical failure

FINAL COSTING & COMMERCIAL RISK ASSESMENT

The following calculation describes the entire cost associated with the start up of the ALPHA methanol plant if the proposal goes through. For a number of unit and operation pricing, the Chemical Engineering Cost Index was used to find the modern cost in pound sterling. The flow rates were obtained from HYSIS, as the optimized process.

Major EquipmentQuantity £Total

Reactor 2 450000 900000Heat Exchanger 15 34000 510000Cooler 2 654709 1309418Compressor 1 4150741 4150740Heater 2 282487 564974Separator 4 6032 24128Mixer 2 6190 12380Distillation column 1 74709 74709

Total (£) 7546349

Estimation of Fixed Capital CostItem PCE 7546349Equipment erection 0.4 3018540Piping 0.7 5282444Instrumentation 0.2 1509270Electrical 0.1 754634.9Buildings, process 0.15 1131952Utilities 0.5 3773175Storages 0.15 1131952Site development 0.05 377317.5ancillary Buildings 0.15 1131952

Total (£) 25657587

Total Physical Plant Cost PCE25657587

Design and Engineering 0.3 7697276Contractor's Fee 0.05 1282879Contingency 0.1 2565759

Total (£) 1.45 37203501

working capital 5% 0.05 1860175Total investment required for project Total (£) 39063676

Variable Cost

RAW MATERIALS COST

Methane £50/kg

Flow rates obtained from HYSISCH4 mass flow rate 40000 kg h-1

CH4 Cost 37483 x 50 £ 1836630 h-1Yearly Operation 300 days 7200 hrs

Daily Cost 1604500/7200 £230

Maintenance Cost 5 % of fixed capital cost 37203501 × 0.05 £ 1860175.05

Miscellaneous Materials Material

10 % of maintenance cost 0.1 × 1860175.05

£186018

UTILITIESSteam mass flow rate 108100 kgh-1 £7/tonne

Therefore steam cost 7200x (108100/1000) x 7 £ 5448240

Cooling water 62260 kg/h 1 .5p/tonne

Cost 1.5/100 x 62260/1000 x 7200 £ 6725

Power total ( HYSIS) 384942 kW 1.2p/MJ

1.2/100 ×300×9238608 £ 10,732,360Total Variable cost £ 15454965Fixed CostMaintenance 37203501 x 0.05 £1860180

Operating labor Assumed £ 100000

Plant overheads 50 % of Operating labor £ 50000

Laboratory 30 % of Operating labor £ 30000Capital changes 10 % fixed capital £ 3720352Insurance 1% fixed capital £ 372035Total Fixed cost £ 6132567

Direct production cost £17640983 + £ 6,132,567 £231,773,550

Price of Methanol £158.34/tonne

Sales revenue £158.34 x 1000 x 300 £47,502,000Profit Sales revenue – direct production cost = £23,728,540

If we were to assume that the electricity bill is 10 million therefore new var cost = 15454965 pounds

Profit = 47 502 000 – 15 454 965 = £ 23, 728,450

CRITICAL REVIEW

Methanol production in the modern era is a challenge for industries worldwide.

Throughout the design of the Alpha Methanol Plant, from phase 1-4, these challenges at a minute glimpse were observed. With the ALPHA Consultancy initial selection for methanol production down to steam reforming and low temperature, high pressure conditions for methanol production, the process was designed to facilitate a production capacity of 1000 tonnes of methanol per year. The plant to be located in South Cambridgeshire would in actuality not be economically feasible to compete, on either a European or International level in the methanol market. The prime locations from research are areas close to the sea for transportation purposes, areas close to natural gas resources, areas where mass methanol is required and most importantly areas where the maintenance, labor and operation cost is cheap. Cambridge, and in fact nowhere in the UK, qualifies on these basis.With an annual profit of just over £23 million, the venture to invest in the plant would be economically beneficial and would be more profitable than fixing money in a bank account. With other competitors operating at lower costs, and having secure major contract for product, the competition would probably be a huge driver in investment.The choice of Syngas production is also one of great importance in the Alpha methanol production, and using steam reforming as the most economically feasible method to generate steam was considered. Of all the methanol plants worldwide only very few has capacities below 1500 tonnes per year. Mega methanol plant structures are considered because other means of producing Syngas then becomes feasible. These include the partial oxidation method and auto thermal methods. A larger plant can facilitate additional components which could in turn do more for a process financially than smaller plants.

There has not been much discussion of the pollutants that are associated with methanol production. The most harmful situation identified by Alpha Methanol Plant is carbon dioxide being emitted into the atmosphere. With our total dedication to abide with the Protocol Agreement and British Air regulation, our aim is to reduce the emission of carbon dioxide through large scale research and development. In Sweden, the latest approach to discharge carbon dioxide was to inject the gas in the earth, and scientist has proved this harmless. As a promoter on science and new technology the Alpha Consultancy approach the issues of carbon dioxide in a similar mode, by effective research and development.

For process simulation, the package chosen was HYSIS. The practicality of the HYSIS package is extensive and used industrially. The difference in results from the HYSIS package and hand calculation was down to the basis of calculations. The calculations within the HYSIS package are deemed more consistent as the PRSV basis of component calculation was used, while several methods and assumptions were used in the hand calculation. Because of this the nature in the difference in the results were observed.

The methanol synthesis type reactor used was a multi-tubular isothermal reactor. The challenges most encountered by this type of reactor is temperature control, since it is meant to be a kept at constant temperature throughout its operation. The Alpha Consultancy methanol reactor was designed based on kinetics and reaction approach to equilibrium. From research however I most case this is done on the principle heat balance rather than reaction kinetics.

Obtaining data to follow through with the design of the reactor was almost impossible to obtain, as that would be a very confidential issue. Where the relevant data could not de found, assumptions were made and clearly marked. All the calculated data found for the reactor design seemed to go in similarity with theory except for the reactor width compared with its height. The reactor height and width obtained were 14 and 17m respectively. It was expected that the height would be least 50% greater than the width but, other sources shows these dimensions area acceptable, especially in areas of high pressure reaction. The structure would prevent environmental effects such as high wind and ‘sight blockage’ issues. After designing the reactor it was observed that newer processes of temperature control are now being adapted by methanol production plants. Of great interest is the method of using steam to control the temperature of the reactor. This ‘in theory’ gives a better control of the temperature of the reactor, but other issues would have to be considered.

Reference

1. Fundamentals of Industrial Catalytic Processes, Farrauto and Bartholomew, 1997

2. Journal of Petroleum and Coal, Vol. 43, 1, 31-343. Journal of Catalysis, 161, pp 1-10, 1996 4. Chemical Properties Handbook by Yaws, C.L, 1999 McGraw Hill5. Perry’s Chemical Engineers’ Handbook, 6th Edition, Green, D.W, 19846. Chemical Engineering Volume 3, Coulson and Richardson, 19717. http://www.thermexcel.com/english/tables/vap_eau.htm 8. Chemical Engineering Design Project, Martyn S. Ray and Martin. G Sneesby9. Chemical Engineering Design, Volume 6, Coulson and Richardson,10. (Chinchem 1998, Lieu 1984, Klier, 1982).