Capacity increase carbon monoxide plant GEP: Pre-study G- groep 1993

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Technische Universiteit Delft

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FVO Nr 2990

VERTROUWELIJK

Vakgroep Chemische Prcestechnologie

Verslag van A.Doeswijk en H.Vonk

I Pre - study G - groep 1993

Capacity increase carbon monoxide plant GEP

opdrachtdatum 16 sept. 1992 verslagdatum 9 dec. 1992

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?~e-scuày capacity increase GEP CO plant

SUMMARY.

This report is a pre-study for the G-groep of february 1993. The goal of this study is to answer the request of General

Electric Plastics if i t ' s possible to reach a capacity increase

of 20 % for the carbon monoxide plant.

Carbon monoxide is an intermediate in the product ion of different plastics and is produced by steam reforming of natura 1 gas. The

carbon monoxide in the process stream from the reformer is

recovered by drying and cryogenic separation.

In this report the possibilities for the capacity increase are discussed. The subjects of main interest appeared to be:

*

N2 removal from natura 1 gas.

The nitrogen contents have a large influence on the recovery of CO in the cold box. Removal of N2 from the

feed improves this latter separation.

*

use of other feedstocks or extra recycling streams

*

change in the reformer section (pre-reformerl

*

use of other CO recovery processes (COSORB) .

The COSORB process separate CO with a high purity from the N₂ containig process stream.

These subjects are described in more detail and recommendations for the G-groep have been made.

the capaclty data tor the CO Plant:

CO Plant t: CO .... N₂ pure CO

CO

Plant 11: CO ... N₂ pure CO dealgn capactty tJh 0.95 0.86 1.37 1.23

actua.

capaclty tIh 1.0 0.90 1.4 1.26

required

capacity tJh 1.20 1.080 1.68 1.512

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?re-sc.uày capacl t:y increase GEP

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CONTENTS. l . 2 . 3 . 4. 5 . 6. 7. 8. 9. 10. PAGE INTRODUCTION

DESCRIPTION OF THE PROJECT

A SURVEY OF THE CARBON MONOXIDE PLANT TWO CARBON FORMATION

DIFFERENT OPTIONS

5.1 N₂-REMOVAL FROM NATURAL GAS

5.2 THE PPO OFF GAS AS AN ALTERNATIVE FEEDSTREAM 5.3 DIFFERENT FEEDSTREAMS TO THE REFORMER

5.4 CO RECOVERY OF THE REFORMER GAS STREAM REFORMER SECTION

ECONOMIC EVALUATION OF CO PRODUCTION.

DISCUSSION AND INSTRUCTIONS TO THE G-GROUP REFERENCES 3 5 6 10 12 25 26 27 29 APPENDICES 1 BLOCK SCHEME WITH STREAMS AND CONDITIONS

2 PHYSICAL PROPERTIES

3 KICK-OFF MEETING FOR G-STUDY 4 Feedstock alternatives for CO PLAlIT

Cast data for utilities

5 Feedstack alternatives for CO PLANT Check list for confidential information

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?~e-scuày capaclcy ir.crease GEP

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planc page 3

1. INTRODUCTION

In Bergen op Zoom General Electric Plastics produces carbon monoxide in two production plants. The carbon monoxide is

produced by steam reforming of natural gas over a nickel based catalyst ( 850°C ,10.5 bar). The next step in the production of carbon monoxide lS purification of the process gas. The purification steps are carbon dioxide removal, drying and cryogenic separation of methane, carbon monoxide and hydrogen. For a detailled description of the process is referred to chapter 2. The produced carbon monoxide contains an amount of nitrogen. The molair ratio carbon monoxide/nitrogen in the end product is 9/1. The nitrogen is hardly separated of carbon monoxide in the cryogenic separation step.

The goal of the G-group is to investigate if it is possible to lncrease the capacity by 20 %

In this report the possibilities to realise this capacity increase are discussed. The report contains recommendations which are shortly noted in this introduction.

*

The removal of nitrogen somewhere in the process for example the removal of nitrogen from natura 1 gas.

*

Changing the process stream to the reformer or other parts in the plant by recycling or adding up new streams.

For example using the off gas of the polyphenylene-oxide (PPO) plant which contains mainly hydrogen, carbon monoxide and methane.

*

Introducing another carbon monoxide recovery process. The COSORB process can separate carbon monoxide from the

process gas containing nitrogen and hydrogene For this study of the capacity increase, one can use the

information of the carbon monoxide plant number two of General Electric Plastics [lit.l].

The production capacity of this carbon monoxide plant is 1.4 ton per hour carbon monoxide and nitrogen.

There is no information available about the other production plant but that this plant (number one) has a capacity of 1.0 ton per hour. The carbon monoxide plant number two is newer than the plant number one and the study of the capacity increase is based on plant number two.

The industrial preparation of carbon monoxide was increased during the seventies (oil crisis). Carbon monoxide is an alternative feedstock for the petrochemical based feedstocks for the production of bulk chemicals or fine chemicais. There are a lot of investigations to the production possibilities of carbon monoxide.

The produced carbon monoxide is an intermediate. Carbon monoxide is converted into phosgene which could be used for production of polyurethane foam plastics. Another application of carbon monoxide is the production of methanol from syngas (CO and H2) •

Formic acid and acetic acid are also produced from carbon monoxide. These acids are used in the paper and textile industry.

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?re-scudy capacity increase GEP CO planc page 4 GEP however uses it for the production of polycarbonate.

In genera 1 eighty percent of the manufacturing costs are the cost of the manufacturing carbon monoxide. Although this is not the case for the preparation of phosgene because of the even higher C1₂ costs it remains important to have a thorough investigation of carbon monoxide production.

Risk and safety.

The produetion of CO should be applied with care beeause CO is a toxie and highly inflammabie component but is almost inert under mild conditions. Also H₂ and CH₄ are highly flammable so care should be taken. Other subjects whieh could be dangerous are high-pressure applications. These problems should be solved during the design phase.

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?~e-stuày capacity increase GEP CO planc page 5

2. DESCRIPTION OF THE PROJECT.

As said in the introduction, the production of CO is important

for the production of monomers. GEP has two plants that produce CO. Plant number one produces 1.0 tons/day while plant number two

produces 1.4 tons/day. The goal of the G-group is to investigate if it/s possible to improve this production process. To reach

this goal, the G-group, existing of 17 or 18 students (6 chemical engineering / 12 mechanical engineering) is split into smaller groups. Each group looks af ter a particular part of the process

and try to find out what are.the problems when a higher capacity

is needed, and how to solve these problem. The subjects that are being studied are being described in the next chapters.

It should be noted that only data of the second CO plant is available. The capacity of the first plant is considered to behave the same way as the second.

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Pre-study capacity increase GEP

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3. A SURVEY OF THE CARBON MONOXIDE PLANT TWO

The information of the carbon monoxide (CO) plant number two is

released by General Electric Plastics (GEP) for the G-study

[lit.l). The information contains descriptions of every part of

the process. For each part of the process there is a process flow

diagram available. These diagrams contain information of the temperature, pressure and composition of the different streams.

In this chapter the information of GEP is summerized and the most

important aspects are pointed out.

The block scheme of the carbon monoxide production process is

reported in figure 1. In appendix 1 the streanmumbers are

tabulated (temperature, pressure and composition) .

With the aid of this block scheme the process is described. The feed which is used for the product ion of CO is Dutch natural gas (tabie 1 gives the composition of natura I gas). The

composition and the physical properties of natura I gas are

described in a book published by the Nederlandse Gasunie [lit.2)

table 1: Average composition of natural gas.

Component Formula _{n i} % (mol) gi % (mass)

methane CH4 81.29 69.97 ethane C2H6 2.87 4.63 propane C3Hs 0.38 0.90 butane C4H10 0.15 0.47 pentane CSH12 0.04 0.16 hexane C6H14 0.05 0.23 nitrogen N2 14.32 21. 52 oxygen O2 0.01 0.02 carbon monoxide CO2 0.89 2.10 100 100 DESULPHURISATION

If no recycled hydrogen lS added to the natural gas feedstream

then the gas stream goes to a carbon bed desulphurizer to remove the sulphur compounds.

The natural gas stream follows another desulphurisation route

when recycled hydrogen is available (maximum vol % H2 in the

feedstream is 10 %).

Then the feed is transported through a cobalt-molybdenum catalyst bed (COMOX). In this bed the sulphur compounds are converted in

H2S. In a zinc oxide reactor H2S is adsorbed.

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?re-stuày capacity increase GEP CO planc page 7

The feedstream to the reformer must be free of sulphur because sulphur poisons the nickel oxide catalyst in the reformer.

The feedstream to the reformer exist of four separate streams:

*

Desulphurized natural gas with or without recycled hydrogen.

* Recycled

co

? from the

co

? removal section.

*

Recycled tail gas from the CO recovery section. This stream

is mixed with the above mentioned CO" stream.

* Process steam which is manufactured in the unit.

The most important reactions which occur in the reformer are the

following ones

<=> CO + 3 H2 endothermic

<=> 2 CO + 2 H2 endothermic

(1 )

(2 )

Besides these two reactions another reaction occurs, this is the

exothermic watergas shift reaction, and could be related as

reaction (1) minus (2).

exothermic (3 )

The overall reaction is endothermic and favoured at high

temperature (in this plant the reformer outlet temperature is 860°C). The reaction system needs energy for the endothermie reactions, this energy is provided by side wall mounted burners. The heat is transferred by radiation and convection to the process gas in the catalyst tubes. The burners are started up

with natura 1 gas and when H₂-rich gas from the CO recovery unit

is availible natura 1 gas is replaced by the H₂-rich gas.

The process gas composition leaving the reformer is dependent on

the next parameters :

* The reformer outlet temperature and pressure. The out let

pressure could be adapted to the pressure level in the CO purification step.

*

The steam/carbon ratio. An excess of steam is transported to

the reformer. This amount of steam is higher than the stoichiometrie requirements.

It improves the CH4-conversion and decreases the carbon

lay-down on the catalyst.

*

The CO product ion can be improved when the CO2 from the CO2

removal unit is recycled to the reformer. The CO2/carbon

ratio can not be excessive because the CO₂ recovery and

recycling cost would become too expensive. Also an

excess of CO2

in the reformer is not favourable for the energy needed in the reformer.

The information of GEP [lit.1] describes a method for the

calculation of the CO₂/C- and the steam/C-ratio from the process

gas composition leaving the reformer.

The prevention of the carbon deposition on the catalyst and the reactor wall is an important issue.

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?re-stuày capaclty increase GEP CO plant page 8

In the reformer the steam to carbon ratio should stay above a

certain minimum value because of the carbon deposition

tendencies.

When the capacity of catalyst decreases, the methane

concentration in the reformer outlet stream increases.

The reformer outlet should always be operated with the methane slip as master parameter.

The reformer outlet temperature is decreased in two cooling steps to a temperature of 40°C. The condensated steam is almost

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?re-scudy capaclcy lncrease GEP C~ planc page 9

CO2 REMOVAL AND RECOVERY (MBA SECTION)

In the MEA section the CO, is removed from the process gas.

The process gas is counter currently transported through an

absorption column with a monoethanolamine (MEA) stream at a

temperature of 40°C. The CO2 reacts with MEA according to the next reaction :

The CO2 rich MEA solution is transported to the MEA stripper. The

CO2 can be released from the solution at low pressure and a

temperature of 120°C. The CO2 stream flows to the compressor

where it is compressed and recycled to the reformer.

The process gas is compressed in a compressor and transported to

the process gas drying unit where the temperature is reduced to

35°C. The formed condensate is separated (gas liquid separator) .

In the last step of the drying unit the process gas is

transported to a set of mole sieve beds. The process gas leaving the drying unit contains water and carbon dioxide at a level of

0.1 ppm volume.

Water and carbon dioxide would cause clogging problems in the cold box if their concentrations are higher than the above mentioned level.

CARBON MONOXIDE RECOVERY

The process gas coming from the drying unit contains H₂, CO, N₂

and CH4 • The next step is the cryogenic separation (Linde cold

box) of carbon monoxide. This separation/purification step is

based on the difference in boiling points of CO and H2 + CH4 (see

physical properties appendix 2)

The process gas is cooled to a temperature of -203/-193°C by heat exchangers. For this process, the required refrigeration can be

obtained by H2 expansion and a CO recycle loop (for example the

process gas is precooled against the outgoing separation

products). The cold box consists of condensators, flash drums,

CO/CH4 splitters and a CO wash column.

A disadvantage of the cryogenic process is that the nitrogen present in the process gas can' t be completely separated from the carbon monoxide. The reason for this problem is that carbon monoxide and nitrogen have close physical properties (e.g.

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Pre-stuày capacity lncrease GEP CO planc page 10

4. CARBON FORMATION.

Carbon formation is an undesired side reaction at the reformer section. It I S undesired because the formed coke pOlosons the

catalyst so a lower conversion could be obtained. The meant reactions are as follows:

- CH₄ + CO₂ <==> 2 C + 2 H20 - CO + H₂ <==> C + H20 - CH4 <==> C + 2 H2 - 2 CO <==> C + CO2 (5) (6) (7 ) (8)

The effect of different process parameters on the coke formation have been analyzed and are being discussed below.

outlet pressure.

Operating the process at lower pressure levels reduces the feedstock consumption and minimizes the risk of carbon lay-down. The pressure in the reformer however is also dependent on the required pressure in the CO recovery section. An optimum should be chosen.

OUtlet temperature.

Because the reforming reactions are endothermic they are applied at high temperatures to improve the convers ion . The maximum temperature is dependent on the construction materiais. Also the coke formation increases at higher temperatures due to the thermodynamics of these reactions.

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?re-scudy capaclcy lncrease GEP CO planc page 11

Steam/carbon ratio

This parameter is used to optimize the heat balance of the plant. Excess steam is used to avoid carbon depsition and to improve the methane conversion. On the other hand a low steam/carbon ratio should be taken to improve the CO product ion and to minimize the

CO2 formation. As limit is taken the ratio at which the

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?re-scudy capaclcy lncrease GEP C8 planc page 12

5. DIFFERENT OPTIONS.

5.1 N₂-REMOVAL FROM NATURAL GAS.

The source of the feed is Dutch natural gas. This gas contains

about 14 % (vol.) inert nitrogen. Because the nitrogen is inert

it's a superfluous component. When i t could be removed this part

can be replaced by using more feedstock.

There are many different separation methods available of which

the best should be chosen. The following part mentions these

methods and some specific properties.

5.1.1. Cryogenic separation.

There are different cryogenic methods for the nitrogen-removal.

One of them i s described by Martin Streich [lit.3]

The temperature for this separation is 175°K. The process takes

use of three columns. The first one is a CO~-column in which the

cooled gas is separated into two fractions: These fractions are

expanded into a medium pressure column at the same temperature. The bottom product is medium pressure natural gas. The top product (containing nitrogen and wash-methane) is fed in a low pressure column where the nitrogen is removed by distillation. The other fraction is low pressure natural gas. The recovery of this process is 99.9 % (methane) at a purity of 90.7 % for the medium pressure stream and 98.0 % for the low pressure natural

gas stream. This result lS influenced by the numher of

components. The more components the worse this method is.

Another process is the Linde coldbox [lit.4]. The contents of

this process is more or less the same as the former process. Here

a recovery of 99.9 % is reached with purities of 94.7 % (low

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?re-scudy capacity increase GEP CO plant page 13

5.1.2. Adsorption

This method is an easy one. The natural gas is fed in an adsorption-column where it is adsorbed. Shivaji Sircar used this method for separation of high-purity hydrogen [lit. 5]. The diluted adsorbent is regenerated in the same column by changing

the conditions like temperature and pressure. When the separation ~s executed by varying the pressure we speak of pressure swing adsorption (PSA). To use this method it is

important to know the kinetics of adsorption and desorption, because they determine the adsorption and desorption time. A computer program controls the process by opening and closing valves af ter some specific times (time necessary for adsorption, desorption, depressurization and pressurization). R.Jasra describes this method in more detail [lit. 6] . Adsorbents applied are zeolite molecular sieves and carbon molecular sieves. In case of zeolites there' s also a difference in adsorption kinetics

among the different zeolites. For instanee the separation in

molecular sieve 5A is achieved due to equilibrium selectivity,

whereas for zeolite clinoptilolite, separation is due to the difference in the diffusion rates of CH4 and N2 into the adsorbent.

Frankiewicz and Donnelly [lit. 7] say the clinoptilolite adsorption reaches a recovery of 90-95 % The separations costs were found to be $ 0.35/106 _{Btu (fl. 2,03/MW) for the larger} plant (2.0*106 _SCF/day

₌

_5.66*104 _m3_{/day) and $ 1.20/10}6 _Btu

(fl. 6,96/MW) for the smaller one (20.0*106 _SCF/day

₌

_5.66*105 m3

/day). This corresponds to an economie profitable process for the small plant compared to the cryogenic process. The carbon molecular sieves may compete as weil with the cryogenic process if a suitable sorbent is available commercially. Presently no such adsorbents have been developed for CH4/N2 separation.

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?re-scudy capacity increase GEP

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5.1.3. Membrane

This process is an important option for future applications. The best method nowadays for CH₄ recovery from natural gases is separation on composite membranes. An advantage of the membranes is that also H₂S, CO₂ and H₂0 are removed with the nitrogen. The polymerie composite membrane is prepared from polyolefins (e.g. polypropylene) and the po rous space being packed with 10-80 wt

% alkanol polysiloxane membrane. The thickness of the polymerie membrane is preferably 0.1-20 ~. The driving force for this process is the gradient of concentration which could be influenced by the pressure in the vessel (e. g. reversed osmosis) .

Advantages of membrane processes are the low energy costs, mild conditions and low capital costs. Disadvantages however are the

(relatively) low selectivity and slow transfer rate.

5.1.4. Absorption

This method is very suitable for separation of one specific component. The absorbent is a large molecule that forms complexes with the desired component. Unfortunately no such absorbents are present yet for the separation of N₂ from natural gas.

5.1.5. Large scale chromatography

The procedure is the same as in an ordinary GLC; the difference in interaction between components in the mobile phase with the stationary phase results in different residence times and so the components can be caught separately. The purity and recovery are

very high in this process, but the low capacity makes this process undesirable for large scale applications.

To have a good indication which of these before mentioned processes is preferred some important design parameters have been compared. These parameters are capacity, selectivity, recovery and application (based on economie values), and are reported in table 2.

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?re-scudy capacicy increase GEP CO planc page 15

table 2: comparison of different separation methodes for the separation of nitrogen from natura 1 gas.

separation capacity selectivity recovery applicability mechode cryogenic +++ ++ +++ +++ adsorption +++ + + + carbon molsieve zeolite ++ + ++ + molsieve membrane ++ + + + absorption 0 0 0 0 chromato- 0 +++ +++ 0 graphy

o

=

bad, +

=

moderate, ++

=

reasonable, +++

=

good.

It's clear that still the cryogenic process is used. The other methods could be future applications.

As said before the removed nitrogen can be replaced by more feedstock. This changing in the feed has great influences on the entire process. First of all the changing composition provides a new equilibrium in the reformer section. The heat balance of

the reformer changes too due to the changed heat capacity of the feed. This might have it's influence on the temperature.

Because of the nearly equal physical properties of carbon monoxide and nitrogen the recovery of CO is difficult in the cryogenic separation. A bigger contents of N, leads to a smaller recovery of CO, so removal of N₂ improves the final separation section.

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-)3.ae 16 5.2. THE PPO OFF GAS AS AM ALTERNATIVE FEEDSTREAM

The PPO off gas is not generated in the carbon monoxide plant but during the production of polyphenylene-oxide.

Normally the off gas is sent to an incinerator for combustion. The heat produced by combustion is not used.

For the carbon monoxide plant there are some possibilities to use

this off gas stream :

* burner gas (fuel) for the reformer of the CO plant.

* as feedstock to the reformer or for another unit of the process.

The amount of PPO off gas produced is 1600 ton per year [lit.1]. The produced PPO off gas doesn't have a constant composition. In table 3 the average composition of the PPO off gas is reported. Table 3: Average composition PPO off gas.

Component formula Xi % (vol)

hydrogen carbon monoxide methane carbon dioxide nitrogen byproducts

The byproducts in the PPO off gas components. With GCMS-analysis these The main components in the byproduct cyclo-alkanes and aromatics.

H₂ 50 CO 18 CH4 14 CO2 9 N2 6 3

(tabie 3) contain a lot of components were identified. are alkenes, cyclo-alkenes,

The off gas can be used as burner gas for the heating of the reformer. The amount off gas is expressed in equivalent m3

natural gas per ton off gas. This expression makes it easier to compare the results (1 ton off gas is equivalent to 750 m3 _{natura 1 gas). If i t}

is used as burner gas the yearly savings are 1.2 million m3 _natural

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gas (when ehe price or naeural gas is fl. 0.19 per m' , this means

savlngs of fl. 228000. - ) . In the burner the natura 1 gas is

replaced by recycled hydrogen af ter the plant is started up.

The off gas can be used as an extra feedstream to the CO plant.

If the CO plant operates 8000 hour per year, there is an off gas

stream available of 200 kg/ho

The off gas stream contains 18 vol % CO (see table 4). Using

this as an extra stream carbon monoxide, the stream is supplied to the process gas which leaves the reformer (stream number 9 in

the block scheme figure 1, stream number 211 in flow sheet GEP) .

The composition of the process gas af ter the cooling step (stream

number 9/211) is comparable with the PPO off gas stream. In table 4 these two streams are compared.

Table 4: Composition off gas stream and stream number 9/211 .

Component Formula PPO off gas stream 9/211

Hydrogen H2 50 vol % 60.0 mol %

Carbon

monoxide CO 18 vol % 21.4 mol %

methane CH4 14 vol % 1.7 mol %

Carbon

dioxide CO₂ 9 vol % 12.5 mol %

Nitrogen N₂ 6 vol % 3.6 mol %

Byproducts 3 vol % 0.8 mol %

At standard temperature and pressure the volume and molair

percentages are almost the same for a gas. The process stream

(number 9/211) is not at standard conditions but the assumption

is made that the two percentages are the same.

It is difficult to convert the PPO off gas volume percentage in molar percentage because the circumstances of the PPO off gas

(P, Tand density) are not known.

The mass flow of the PPO off gas ( 200 kg/h when the CO plant operates 8000 hours per year) is small compared with the process gas (number 9/211). The mass flow from the reformer is 3535,1

kg/h so the mass percentage of the off gas is 5.4 %.

The percentage methane in the PPO off gas is larger than in the process gas leaving the reformer . The amount methane is separeted from the carbon monoxide stream in the CO recovery unit so the extra amount methane isn't aproblem.

Methane is recycled to the reformer (tail gas) so the methane in the off gas is converted in the reformer.

Another possibility for the PPO off gas is adding this stream directly to the reformer using the amount of methane in this stream. The CO in the PPO off gas stream influences the

convers ion of methane in the reformer . The amount is small compared to the total stream entering the reformer so the influence on the end composition leaving the reformer is small. The PPO off gas contains 3 volume percent oiefins, cyclo alkanes

and aromatics. Higher hydrocarbons (cyclo alkanes) have a

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:;age i8 reactions occur at lower temperacures.

The olefins in t he reformer are hydrogenaceà wich a part of the recycled hydrogen. This causes a temperature rise over the catalyst which isn't favourable for the reformer operation. The influence of the olefins and the cyclo alkancs isn't great because their concentration in the reformer is low.

The PPO off gas flow changes the process parameters which

influence the performance of the reformer (steam/ carbon ratio and

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page 19

5.3. DIFFERENT PROCESS ROUTES

There are some alternatives for the feedstream to the reformer. In this chapter these alternatives are discussed.

5.3.1. Different feedstocks

The ideal composition of the feedstream to the reformer is a feedstream without nitrogen because most of the nitrogen is not

separated from the carbon monoxide in c~e cold box (Linde). The

possibilities of nitrogen separation from the feedstream are discussed in chapter 5.1 .

Also the presence of higher hydrocarbons in the feedstream is advantageous for the reformer operation. The carbon hydrogen ratio (C/H) for hydrocarbons as propane and butane is higher than for natural gas. Complete conversion of propane and butane occurs at a lower temperature so the heat requirement is lower at an equivalent production rate of carbon monoxide.

Liquefied propane gas (LPG) is excluded as feedstream to the

reformer for security reasons. The transport of LPG to the carbon

monoxide plant is too dangerous for this location. This problem

is also valid for LNG, but it isn't delivered by the Gas Unie.

A wide variety of hydrocarbons could be used as feedstock for the

reformer. Examples are natural gas, LPG, naphta, heavy oils and

coal, these are the conventional sources. Each feedstock has

different reforming technologies.

partial oxidation of hydrocarbons

Hydrocarbons (natural gas, naphta and heavy oils) can be partial oxidized by using oxygen. This process doesn't make use of a catalyst and the operating cost is depending on the availability of oxygen.

If oxygen is available at low cost than partial oxidation can be attractive for heavy hydrocarbons.

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--- --- - - . _ - - - -- - - . page 20 Autothermal reforming

Autothermal reforming is a combination of steam reforming and partial oxidation in one single reactor. The heat required for the endothermic reforming (catalytic) of natural gas or naphta is supplied by simultaneous exothermic partial combustion.

The partial combustion with oxygen of the hydrocarbons also

produces carbon monoxide.

Coal gasification

The coal lS gasified with steam and oxygen at elevated

temperature (fluidized bed, entrained bed or fixed bed) .

Coal is a cheap feedstock, but is only favourable for plants with

large capacities. Coal gasification isn't an attractive process

for smallor medium size

co

plants.

The three above mentioned reforming technologies can' t take place in the reformer of GEP. In this reformer natural gas is reacting

with steam (steam reforming) .. If other feedstocks are available

at lower cost at the production location then the reformer unit

needs to be changed.

The non conventional sources are

co

containing gas streams from

the chemicalor steel industry. These gas streams are called off gasses. The non conventional sources are not going to the reformer because these streams already contain CO. Only the separation step will be applied.

Sulphur passivated steam reforming.

The feedgas (for example natura 1 gas) contains sulphur compounds, these sulphur compounds have to be removed from the feedgas (less than 0.25 ppm (weight) of sulphur). The carbon monoxide plant of

General Electric Plastics contains a hydro-desulphurizer.

The sulphur compounds have to be removed from the feedgas stream .

because these compounds poison the reformer catalyst. Haldor Topsoe [lit.8] has developed a sulpur passivated

reformer which eliminates carbon formation during steam reforming by using a partially poisoned catalyst (SPARG process) .

In this process the natural gas may contain some sulphur

com-pounds. The sulphur blocks the catalyst sites which are

responsible for the formation of carbon. This reformer can operate free of carbon format ion at conditions that would otherwise results in carbon formation.

The plant capacity of the SPARG process is big enough in relation to the carbon monoxide plant of GEP. The existing plant can be revamped which results in a product gas containing a higher carbon monoxide/hydrogen ratio.

The operation costs of the SPARG process are 15-20 % lower

compared with the conventional process.

5.3.2. New recycling streams

The Calcor process [lit.9] developed by Caloric GmbH has almost

the same plant configuration as the

co

plant of GEP.

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page 21

!:'erormer burners (rlue gas ) is transporteà to a CO~ recovery unit. The Calcor process contains two CO~ absorber cowers, one for the flue gas and one for the process gas from the reformer. The recycled CO₂ stream to the reformer is greater compared with a process without a flue gas recycle stream. A higher CO2/C ratio

results in a higher CO conversion but the CO2 recovery costs

become greater with an increasing CO2 recycling stream.

The Calcor process produces CO with an extra CO2 stream recovered

from the flue gas (C02 reforming process) In a CO2 reforming

process the next reaction is important

(9 )

The molar ratio of CO and H₂ obtained by this reaction is higher than the ratio obtained by steam reforming (CO/H₂

=

3)

Other imported sources of cheap CO₂ are, for example, plants for the production of NH) and ethylene oxide.

It's of course also possile to use pure COl as feedstock for the reformer when no recyclce streams are available or when they are too smalle

According R.V.Green [lit.10] the reforming process can be

improved if the hydrogen rich gas from the CO recovery unit is recycled to the reformer. Larger quantities of CO relative to the H2 produced can be realized. In the CO plant of GEP this hydrogen rich gas stream is used as fuel for the reformer burners.

In the improved process also the CO₂ stream must be recycled to the reformer.

For every mole hydrogen in the recycle stream at least one mole carbon dioxide must be added.

The stoichiometric balance of hydrogen and carbon dioxide gives the following reaction in the reformer:

(10)

According to this reaction an amount of steam 1S generated in the

reformer. In the CO plant of GEP the molar ratio of steam to natura 1 gas is 3.2 and in the improved process the ratio can be reduced to one.

Also an amount of CO is generated so the feedstock of natura 1 gas can also be reduced.

The configuration of the carbon monoxide plant of GEP needs no special adaptations. The required modifications are the flow streams to the reformer and the addition of the hydrogen recycle stream.

The carbon monoxide plant of GEP has the following recycle streams:

*

*

=

1313.5 kg/h

=

=

16.9 kg/h

=

29.85 kmol/h 8.45 kmol/h The hydrogen-rich fuel gas contains mainly H2 :

*

= 243 .2 kg/h = 121.6 kmol/h

The hydrogen-rich fuel gas contains too much hydrogen 1n relation

with the recycled CO₂ stream. If all of the hydrogen is recycled

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rage 22

Kmol/h is needed for the stoichiometrie requirements.

This stream could be flue gas Erom the reformer burners (see Calcor process) or another plant, but the whole recycled hydrogen and carbon dioxide stream isprobably too la.:?:"qe for the reformer . Another thing to notice is that when hydrogen is used as burner gas no CO2 is produced. The question is how large the recycled

hydrogen stream could beo

The alternatives described in this chapter change the major process parameters. These process parameters influence the performance of the reformer.

The most important parameters have already been mentioned in the text (steam/carbon ratio, CO,/carbon ratio etc.).

The reaction conditions (pressure and temperature) in the reformer are changing when recycling streams change. The influences of differences in the recycling streams on the process need to be known for a good understanding of the process.

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page 23

5.4. CO RECOVERY OF REFORMER GAS STREAM.

Af ter the reformer section it's necessary to separate the CO from the other gases. As was the case with the nitrogen removal from natural gas, also for this separation different methods are

available. The reformer gasstream contains N2, H20, CO, CO2 , H2

and CH4 • Specially the separation of N2 and CO is <iifficult

because of their approaching physical properties. The possible methods for the separation are being described below.

5.4.1. Cryogenic

This process is in practice the same as for the removal of nitrogen from natural gas. The difference is that here more

components are present. The CO₂ and H₂0 must be removed because

they would freeze in the cold box and so give clogging problems.

Af ter this is done the stream is cooled to 700_{K (just below the}

condensation temperature of CO and above the condensation

temperature of N2) • Now distillation is applied, which results in

a stream containing relatively much CO compared to N2 and a

hydrogen rich stream. This hydrogen stream is not pure enough to be sold, and that's why it's used as burner gas. The main stream

is separated in a recycle stream and a CO/N2 (9:1) stream. More

extensive descriptions are given in Ullmann [lit.11] and a KTI artiele [lit.12].

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5.4.2. Complexation with ammoniacal copper liquor.

CO is absorbed to a Copper(I) salt solution. BASF developed a

process using aqueous ammonia solutions of copper carbonate,

acetate, lactate or a mixture of these. The occurring

complexation lS:

<==> [Cu (NH3 ) 3 (CO) ]. (11)

The equilibrium of the complex is highly dependent on the

temperature, pressure and acidity of the medium. So changing

these parameters makes it possible to separate CO. This process is not very specific due to the unstable complex. The high

corrosion rate is another disadvantage, and thus this process is

seldom applied.

5.4.3. COSORB

This process is based on the similar principle of the copper

liquor complexation. The absorbent here is a copper(I)

organometallic complex in an organic solvent (preferably CuA1C14

in toluene). Advantages are the lower corrosion rate and higher CO purity. Compared to the cryogenic process the main advantage is that nitrogen can be separated selectively. On the other hand this process is more sensible for impuri ties (S02' H2S, COS, etc. ). Careful purification is therefore required. Haase and Walker [lit.13] say that operating costs are competitive with the cryogenic unit. Capital investments however are significantly lower and become even more favourable at higher nitrogen contents of the feed.

When the purity of the CO is of minor importance also separation via membranes or pressure swin9 adsorption could be applied. The CO plant is still using the cryogenic separation although the

COSORB process might be better . This is depending on the

compositions. Different compositions studies should be done to compare these two most important processes. A higher CO recovery also improves the purity of the hydrogen-rich and tailgas streams. This means a lower recycle so a higher natural gas strearn could be inserted in the reformer.

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aoe 25 6. REFORMER SECTION.

An important thing to look af ter is the reformer where the

reaction occurs. For higher throughputs i t ' s important to know

whether the reaction is transport limitated or reaction

limitated. Reaction limitation means that a higher throughput yields a higher CO production (at same residence time). To improve the reaction section some possibilities have been proposed. One of the first decisions to be made in the design is

the mode of firing to be employed. A number of possibilities are

available, namely:

*

Side-fired

*

Top-fired

*

Terrace-fired

*

Bottom-fired

*

Different catalysts

These firing-methods are explained in more detail by Johansen e.a. [lit.14]. This article also describes the use of a potformer

and a gas heated reformer (GHR). The optimal heat flux

distribution in these reformers makes the process energetically more efficient. The heat balance could even be improved by combination of these reactors with a reformer. In the pre-reformer part of the reaction takes place. The necessary energy for this reaction is provided by the sensible heat of the stream. The adiabatic behaviour of the reformer results in a temperature

drop of 60-80oC. Af ter this section the stream is reheated to the

original temperature, and fed in the original reformer. Because already a part of the reaction has occurred the thermal load is

lower. Integration of the two reformers makes the process

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:toe 26

7. ECONOMIC EVALUATION OF CO PRODUCTION.

Because CO is an intermediate for many chemicais, it's important

to know the factors that influence the cost of the CO production.

The greatest influence on the manufacturing costs are obtained by the following factors:

*

capacity of plant

*

costs and nature of feedstocks used.

* H2/CO requirements

Optimal combination of feedstock and plant capacity obtain the

lowest cost. Unfortunately the desired feedstock isn't always available at the planned location, so new optimum calculations

should be made.

The different methods of CO production all result in other costs.

The lowest costs are obtained by CO2 reforming of natural gas.

The necessary CO2 is obtained from off gases of other processes

(e.g. H2, NH3, ethylene oxide production) . If the required CO2 is

not available other methods should be applied. These alternatives

are already described in chapter 4.3. If also H2 is demanded the

optimal production costs of the different processes change. Here a high HjCO ratio gives min-imal costs.

The asumptions made with regard to the costs can change during the service life of the plant. The greatest effect on these costs are exerted by changes in:

*

availability and prices of feedstocks

*

rate of capacity and service life of the plant.

if high capacity is applied (more than 10,000 Nm3_{/h CO), partial}

oxidation of petroleum coke appear to be the best economical option.

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8. DISCUSSION AND INSTRUCTIONS TO THE G-GROUP.

Af ter a thorough study for improvement of the

co

plant, the

following things appeared to be interesting to investigate:

1 .

2.

3 •

4.

5.

nitrogen removal of natural gas.

What's the influence of different nitrogen contents ~n the

feedstream to the reformer on the purity of the CO product

stream ? Is the nitrogen removal economie favourable ? If

this is true, what's the optimal removal of it ? comparison of the COSORB process with the traditional cryogenic process for CO separation.

In the cryogenic and COSORB processes, separation of the process gas gives the CO product stream. The composition of the product stream differs with the method of separation.

How does the product stream composition change with

different feedstreams to the reformer (flexibility) ? What

are the advantages and disadvantages of these processes ? using the PPO off gas as feed for CO separation.

Which place in the plant is the best to insert this PPO off

gas (before or af ter the reformer) ? Is i t favourable to

use this PPO off gas at this manner or is it better to use it as burner gas ?

influence of feed composition on CO product ion in reformer.

Changing composition leads to another CO production. What's

the optimal CO2 insertion and how could we approach this

composition ? Could other process conditions be used

because of the changed feed ?

changing the reformer section.

Can the feed rate be increased with other reformer types? What are the advantages of new reformers ?

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6 . rage 28

integration of all before mentioned processes.

In the flowsheet sections could influence on the

program (ASPEN PLUS) the knowledge of all be integrated to simulate what's the entire CO production.

7. are there any brand new process options ?

To have a global review of the process, in this report the presumption is made that all sections ln the entire process operate at their maximum capacity. In practice this presumption is not true. This can be verified when the data of the apparates is demanded from GEP. With these data it's possible to determine what's the bottleneck in the production of CO.

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9. REFERENCES

[1] Design and operating manual carbon monoxide plant (number two) General Electric Plastics,KTI.

[2] Geerssen,T.M.,Physical properties of natural aases gases.Groningen,1988.

[3] Streich,M., 'N₂ removal from natural gas' .Hydrocarbon Processing 49(1970),86-88.

[4] Linde AG, , Nitrogen removal' .Hydrocarbon Processing 61(1) (1982) ,107.

[5] Sircar,S., , Product ion of hydrogen and ammonia synthesis gas by pressure swing adsorption' .Separation science and

technology,25(1990) ,1087-1090.

[6] Jasra,R.V.,Choudary,N.V.,Bhat,S.G.T., 'Separation of gases by pressure swing adsorption' .Separation science and

technology,26(1991),885-930.

[7] Whyte,T.E., Yon,C.M. ,Wagener, E.H., Industrial Gas Seoaration. Washington,D.C.,1983.

[8] Dibbern,H.C.,Olesen,P.,Rostrup-Nielsen,J.R.,Tottrup,P.B., Udengaard,N.R., 'Make low H₂/CO syngas using sulfur

passivated reforming' . Hydrocarbon Processing 65(1) (1986) ,71-74.

[9] Calorie GmbH, 'Calcor' .Hydrocarbon processing 69(1) (1990),73.

[10] Green,R.V.,U.S. US 3,943,236(1976).

[11] Ledon,H.,Ullmann's Encyclopedia of Industrial Chemistry.4th edition Volume A5(1992) ,203-214. [12] Carbon monoxide production technologies,KTI.

[13] Haase,D.J.,Walker,D.G., 'The COSORB process' .Chemical Engineering Progress 70(1974).

[14] Johansen, T. , Raghuraman, K. S. , Hackett, L .A. , , Trends in hydrogen plant design' . Hydrocarbon Processing (august 1992) ,119-127.

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APPENDICES

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-~ H2S

@

C02' TAll GAS REMOVAl STEM-I

6i>

-

-.

C02 COMPRESSION

®

BOILER FEED WATER

(iS)

HEAT

@

~----_._- -RECOVERY -0

@

::0

@

R m

®

®

1/1 C02 1/1 1/1 -1 m - -:I> 3:

Cl)

_®

®

@

DESULPHU- C02 RECYCLE REFORMING (ooll N.J

P .

HYDROGEN RIZATION

®

-' _REMOVAl ~

Q)

~@

NATURAl GAS HYDROGEN RICH GAS FUEL

FUEL _.-. _. . ... _-- -

_.-®

@

_@)

G)

:i\l[NCH

~

~

BLOeK SCHEME CO PLANT

n

NATURAL GAS

€t!0

-@

PROCESS

-

..

GAS

--

.

COMPRESSION

- -

--@

rAil GAS

®

CARBON PROCESS GAS

..

MONOXIDE DRYING RECOVERY

r-ï

I I ~

®

n

@

@

0 HY

-::0 RIC m n -< n r m

®

CARBON I+-- MONOXIDE COMPRESSION

@

CARBON MONOXID ROGEN

--..

H GAS

®

---

E!lock .2d~~ (6-DÎ~;rlL---·--···--·· ··"

.. ··

·

.. ·

·

.'.

str fQ/\1 fl.U1 lU11w\ st r E-Cul1 f'Wl1 Q; 1 pfl?MJff [h:u:. )

Tenp

[oe)

2 3 Y 5 b

t

Q j 10 11 12 13 1'1 15' 16

'1

,8

'1

10 11 n

n

2'1 1S 2b 2J lS

l'

201 lO IS 202 20.& 120 ,103

'1,5

400 20$ _2U

I,-g;;:;

₁₁₀ 20'1 I~,b ~O 20} 1'i.0 ~(j1 208 10.5

860

10

₃

10.0 180 211

_'

_.Lf

40 211 ~.3 ~o

liS O,S' /.jo

llf

1,0 31 21b .. o,S 'JO 21

₁

15,2 ~o 251 16.0 IO~ 25't 22,l. 220 255 2l.l 210

lób

2.5

ja

2t~

_11·1

35

1n

11,1 35 lU

_l'T

11-21l [A"r~1' flOW) 1.0 ~o 226

a.ó

35' n5

B,b

35 22~ 1.0 31

n8

3.5 2)

1

jQQIJ:lltlhIJ'1 2.D 2") c.:GI I 1

211

200 '1,3 108 253 26,0 104 ~h

-IO,~ 10

,1

&.2 I b,j 300.5 3005 JOO,S' 300.1 0,'1

s,ef

b,l 6,l . -300.1 ljB,l 2~ I, ~ lY3,1 -2j2,5 51.1

-.. .' .. ...•.... _ .. ~ .. (o;,.;~t5[~~ I h )

CO

C(\

Nt Ol

CH,!

(lH b

C

j

Ha

('( . ._ -

--

20.8 213.'-1 0.2 6j2, 1 1i5'.5 ~'1 ~

2.r

-

2.1 - · - -2.5 20,8 2/5'.] 0,1 b~;q '15.5'

a,t

y

199,14

1~/3.s 2j,~ . 6~'1 _· 201·1 133'3 1'15,4 -

1

61,4 '15',5 &.} 4

l'ijB.' 13&'o.b 2~S.'1 - 6~i.1 .

1~,O,1 n6b,6 ~'tS,'t - ÓJ.1 11j~8,1 1380,6 2~S,1j - 6~.1 ''1~6.o OS 2'15", I -

&j,o

1,0 1313,S' 0.3 0,1

191,3

- 23,'1 - W,b ISj,4 13/J,5' 2:),8 -

bcY,1

· 'j',~ 1311,5' lj,8 - M,} - -- · - - - - -- - _- - · -- - . . - - -- ·

-

- - ·

-,~~6,o O,S l ~S', 1

-

bj,o

1'1Bp - 2~3,

t

bB,b - ·

56.t

- 50.1 .. _{- ·} bS',b O,S' 5'1,) O,~ · 1l11.~

.

-

15l,b

-na,b

_-

3QO -l'i bo, 1 ·

183

,

6

b8,l

- (x).1 11.'f · 10,6 ·

-

-

- - · ~ .

-

-

- . _-

_-

_..

~.IC,H"

(,H.

mA

.

H,O

jH.L

3 1.5 2,3 - - 9t3~J.'1 ,3 I \,5 I 2.3 I - I

--

'211

f_,l

'Jl

,3 l,S

I

2,3

I

bPj.1

,lJra,o

'WP.6 - , 31,4 ~1·j 2& 2& J,

1

- ,ÓI83., 5jJ6,5 - '31

QJ

~lb',2

1.

8 15',Lf I 100'1, t9 7.p'5'.1 1621.3 5351, } 535/,1 HcYb.3 3515.1

2'

38,6 134'1,3 301,1 1b'i$,b 1621.11 b/a3,j 5j36,5 J<t},y '12&1,2. 21f~ ,5' ,zOn, cP 3'1&,1

1,"1

36j, 0 IJ~b,f 5f11,(j 13}5',0 26J,1 /6'13,

t

411.5

13

Lf 1&'1(,.1 ~81 ,,J )I td td ~

~

H ~

....

tij t"' o n ~ CIl n =x:

fi

~

o

~ n o td t"'

~

t-3 H H

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APPENDIX 2: PHYSICAL PROPERTIES.

tabel Comp. CO CH4 N2 CO2 H2 H20

physical properties of most important components influencing the process.

Molar Melting Boiling Density weight point [OC] point [ °C] [gIl]

28.01 -199 -191. 5 1.2500 16.04 -182 -164 0.466-164 28.013 -209.86 -195.8 O.

sosr

l9S .S 44.01 -56.65.2 alm. -7 S . 5,ubl. _1.56-79 2.016 -259.34 -252.8 0.OS99 18.02 0.00 100.00 0.916So

For natural gas the properties are tabulated in the book of the Gas Unie [lit.2].

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GE PLASTICS

,

AppetJOlx 3

Page' of 3 Rel.:

Project:

_{TU Delft "G-Opdracht"}

1 04205/M I0020/MVOB

MINUTES OF

MEETING

Date held _{Date issued Place held}

September 16, 1992 _{September 21, 1992 BOZ}

Subject _{Kick-oft meeting for study: Feed Gas Alternatives tor}

CO Plant partlelpants: J. Grlevink (TUD)

F. Meijer (TUD) ~. OIUjiC#(TUJ») Dlstrlbullon: _Participants R. Hoogeveen L. de Smet

S.

Vriens J. v.d. Heijkant

R.

Sato

V.

MatthelJ N. Verstoep P. MatthijSsen O. Tant D. Hoogwater (TUD) Recordad by

V.

Matthelj

--.

.

--. ---~---_r_'---1. .l.nl!:qguction

As part of their study a team of _{Chemical and Mechanical}

Engin99~ing st:;d~nts 'Nil! _{(re)design a plant or plant section; this is}

called

a "G-OpdraCht",

2.

GEP

subject

GEP has definad the subject: "feed gas alternativ9s _{for CO plant".} Reasons:

CO

plant capacity iS _{a bottleneck for}

_PC

_{Aesin plant stretch;}

CO plant feed _{gas quality directly influences its capacity;}

Alternatl_{ve feed gas stream (from PPD Manomar Plant) might}

glve additionaJ productivity.

To ba studled:

N₂ removal from _{natural gas: processes available;}

Monomer off·gas quantities and influence of impur:ties; Mass/energy balances and flow schemes;

Proc~ss controls, reliability _{and safety aspects:}

Equipment lay-out and co st estimate.

ACOON REOUIRED 8V

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-_

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__

. 2. Continued

For tha two CO plants, CO

I and

CO 11, the raquired

output

capacities (aftar

stretch)

would ba: 1.2 tlh

lor

CO

land 1.68 tlh for CO 11, 1.88 t/h tata!.

This

output capacity

is CO

+

N₂ SO

if

N₂

can

be

separated out of

the

feed

gas

ttlen

thare

is a direct CO capacity banafit.

3.

Basic

data

Handed over to TUD:

- KTI,

litarature raferenca

about

general CO production;

-

PFO's of

CO

I

and

CO

11

plant; - PFD's of PPO Monomer plant;

- Memo on PPO Monomar off-gas quantities;

- KTI process description of CO 11 plant. Notes:

- CO I mass balance

on

PFD is in kmol/h;

CO 11 mass balance is in

kg/ho

- LPG

may

not ba used as feedstock for the CO plant bacausa of safety reasons (i10 LPG storage in vicinity of site allowed).

4. Timing, actions

In 30 and 4Q '992 two Chemical students wiJl prepare a Basis For

Design; start waek 39. '

Then,

starting February 1993, during 12 weeks

a

group

of

3-4 Chemical and 12-14 Mechanical Engineering students wiJl use this

Basis For Design to make a detailed design, lay-out, cost estimate. etc.

For the detailed design phase

of

the study TUD should appoint one

or two persons of ttle group as contacts to

GEP.

Main GEP-contact iS V. Mattheij.

In February 1993, in the kick-oft meeting for detailed design. GEP will give an introduction about BOZ site and processes;

ca.

3-4 waeks aftar that GEP will organisa a CO plant tour for the group. Finally, at finish of detailed design (ca. May 1993) GEP will set

up

a BOZ site excursion + group lunch.

Page 2 of 3 104205/MI00201MvdB ACTION REaUIRED BV TUD TUD

VM

VM

VM

•

_I

I

I

I

I

I

I

I

I

I

I

I

,

I

:

1

I

I

I

I

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4. Contjnue~

Further

actlons:

Project language English (strongly preferred by GEP);

Process calculations by computer: fjnal calculations should preferably ba done in Aspen

+;

For detailed design phase GE? to teil TUD which economical calculation method (OCRR) and which utilities costs ara to ba used;

During deta!led design phase there

wil!

ba weekly progress meetings in Dalft on Monday afternoons, 14:00 h.

HM wil! expedita secrecy agreement through D. Hoogwater (usa

same

GEP

draft

as

_{for "alectrostatic blending research"}

project). Page 3 of 3 , 04205/M I0020/MvdB ACTION REQUIRED

BV

TUD

TUD

VM

TUD, VM

HM,DH