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CO through CO2Reforming

The Calcor Standard and Calcor Economy

ProcessesBy ST. C. TEUNER, P. NEUMANN and F. VON LINDE*

ABSTRACTCarbon monoxide is required as feed forthe production of many chemicals. Due

to its toxicity transportation of pressurized COis limited. This fact and economical aspects re-sult in on-site production of carbon monoxide.An economic process to generate high purityCO through CO2reforming (Calcor process) isdescribed below. The costs for on-site producti-on are presented considering the different COgenerating processes and available CO purifi-cation technologies.

1INTRODUCTIONCarbon monoxide is an importantfeed for the production of many pro-

ducts or intermediates such as organicacids, phosgene, polycarbonates and agri-cultural chemicals. In most cases the ma-

nufacturing cost of these chemicals is di-rectlydeterminedbytheproductioncostofcarbon monoxide.The common source for CO is syngas fromreforming or from the partial oxidation ofhydrocarbons. Unlike hydrogen, the trans-portation of CO is a sensitivesafety subjectdue to its toxicity. This fact and economicaspects favour the on-site production ofcarbon monoxide.

2

AVAILABLE PROCESSESAn overview of available processes

for CO generation is given in [1]. Thesignificant processes for the production ofCO are the non-catalytic partial oxidationof hydrocarbons with oxygen for quanti-ties of typically above 5000 Nm/h CO, orthe catalytic reforming of hydrocarbons,applicable also for small carbon monoxiderequirements.With the common reforming process, car-bon monoxide is produced by steam refor-ming of a hydrocarbon (e. g. natural gas)mixed with recycled CO2at high tempera-

tures and high pres-sures in the presen-ce of catalysts, follo-wed by a pressureswing adsorption(PSA) unit and/or alow temperaturepurification (coldbox) for the purifi-cation of carbon monoxide, depending onthe quality required.Steam reforming with CO2recycle yields asyngaswithatypicalH2 :COratioof2.8:1,whereby hydrogen as the dominant com-ponent represents a by-product.The typical H2/CO ratio for the main COgenerating processes, when using naturalgas as feedstock, is shown in Table 1.In the Calcor process, steam is totally sub-stitutedby CO2,resultinginaH2 :COratio

of 0.42 : 1. The reduction of by-productsand the high concentration of CO reducethe specific requirement of utilities and of-fer substantial advantages in the selectionof purification technologies.High purity carbon monoxide is required,if the CO is used for the production ofphosgene as an intermediate for thepolycarbonate production. CH4 and H2will form CCl4and HCl as impurities of

phosgene, which would result in an im-paired quality ofthe polycarbonate or inanadditional phosgene purification step.Typically an impurity of CH4lower than20 vpmis acceptable for phosgene produc-tion. Therefore a process design with smallCH4impurities in the CO will be advanta-geous. Only the Calcor process meets thisrequirementwithoutan additionalCH4 re-moval. As a result, the Calcor process formost applications needs only a membrane

for the CO purification instead of a coldbox which is much more cost-intensive.

2.1 The Calcor Standard processThe Calcor Standard process (Fig. 1) is de-signed to operate under low pressure. Theprocess itself is a catalytic reforming pro-cess at high temperatures. To protect thecatalyst, the feed has to be desulphurized.After pre-heating and mixing with hydro-

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0179-3187/01/III 2001 URBAN-VERLAG Hamburg/Wien GmbH

*Dipl.-Ing. Stefan C. Teuner, Dr.-Ing. Peter Neumann, Dr.Florian von Linde, Caloric Anlagenbau GmbH, Graefelfingnear Munich, Germany (E-Mail: peter.neumann@calo-ric.de)

Table 1 Typical H2/CO ratio and CH4 content for the main CO generating

processes

Steam reforming Partial oxidation CALCOR process

with CO2 recycle

H2/ CO ratio 2.8 : 1 1.8 : 1 0.42 : 1CH4 content 3 Vol.-% 0.4 Vol.-% 0.0005 Vol.-%

Fig. 1 Simplified flow sheet for Calcor Standard process

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gen,the feedis sentto a sulphur removal inwhich the sulphur compounds are hydro-genated and adsorbed in a ZnO-layer. Thedesulphurized feed is then mixed withCO2and pre-heated again by utilizing ap-propriateamount of theflue gasheat,priorto entering the reformer. Whilst passingthe reformer tubes, which are filled with

catalysts of different activities and shapes,the mixture of CO2and feed is convertedinto a syngas consisting of carbon monoxi-de together with H2, CO2, H2O and tracesofCH4. Theheat forthis endothermic reac-tion is provided by a high-velocity burner,which burns fuel and tail gas from the COpurification unit.After leaving the reformer, the syngas iscooledto ambient temperature prior to un-

dergoing the CO2removal and reco-very. In this processstep, the CO2 fromthe reformer fluegas as well as theCO2 from the syn-gas are absorbed in

packed towers atambient temperatu-re by a caustic solu-tion (e. g. MEA,MDEA or DGA).In a stripper, theCO2 is separatedfrom the scrubbing liquid and recycled tothe reforming process. The syngas, whichnow typically consists of 70% by vol. CO

and 30% by vol. H2and still carries tracesof CO2and CH4, enters the CO purificati-on step.Dependingupon theCO purityrequired,alow-temperature process or semi-perme-able membrane process may be applied(Table 2).

2.2 The Calcor Economy processIn the Economy version of the Calcor pro-cess, the CO2recovery part is deleted andimported CO2is used instead of recoveredCO2 (Fig. 2). The selective properties ofmembranes make it possible to simultane-ously separate H2and CO2from the COproduct, which results in a simplified de-sign of the Calcor process. The tail gaswhich is separated in the first stage of themembrane is utilized as fuel for the burnerat the reformer and also for feed make up.The permeate of the second stage of themembrane is recycledto thesuction side ofthecompressorduetoitshighCOcontent.

3CALCOR PROCESS ECONOMYWith the recovery of the CO2fromthe reformer flue gas as well as from

thesyngas, theCalcor Standardprocessge-nerates almost 1 CO molecule out of everyC-atom imported into the process as feedandfuel.Thus,a carbonyieldof 9799% al-most reaches the theoretical maximum.The production of one ton CO requires eit-her 816 Nm natural gas (calculated as100% CH4), or 531 kg LPG as the main uti-

lity.With decreasing plant capacity, the costsfor utilities and energy become less andless significant, whereas thecosts of depre-ciation and interest on the investment do-minate.For plants with a capacity of approximate-ly 200 Nm/h CO and downwards, the sa-vingin investmentmore thancompensatesfor the additional costs of imported CO2required by the Calcor Economy process(Fig. 3).

3.1 Production costs

The production costs for the on-site pro-duction of CO are shown in Fig. 3. They in-clude the costs for depreciation and inte-rest on the capital investment, utilities,manpower and maintenance.

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Table 2 Typical CO purity using different process combinations

Product composition, CO H2 CO2 CH4 N2*)

Vol.-%

Calcor Standard with low temperature purification

99.98 1 vpm 0 1 vpm 0,015

Calcor Standard with membrane purification

99.47 0.5 0.01 15 vpm 0.01

Calcor Economy with membrane purification99.25

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For utilities used in the process, the follo-wing costs were assumed for calculationpurposes: natural gas: US$ 0.11/Nm LPG: US$ 164/t electric energy: US$ 0.064/kWh carbon dioxide: US$ 120/t cooling water: US$ 0.066/m

boiler feed water: US$ 1/m import steam: US$ 11/t.Apart from the costs for utilities and ener-gy, thefollowing factors were takeninto ac-countinthecalculationoftheprimecosts: operating hours: 8,600 p.a. annuity: depreciation of the investment

costs over 10 years interest rate: 6% maintenance: 2.5% of the investment

costs p. a. personnel: US$ 24,000 per man year.

3.2 CO purityThe available CO purity depends on theprocess selected and the purification tech-nology applied. Table 2 shows typical COqualities for three process combinations.Nowadays CO qualities between 99.25%and 99.98% can be achieved. Due to the in-novative potential of membranes, it is ex-pected that the CO purity achievable bymembraneswill increasein thenearfuture.

3.3 H2 by-productThe tail gas from the purification step re-presents a H2-rich stream. By using a com-pressor and a pressure swing adsorptionunit (PSA), 37 Nm pure H2can be made

available with each 100 Nm CO product.

3.4 CO2 EmissionsGenerating CO from CO2and hydrocar-bons follows an endothermic reaction. Atcatalytic reforming, the required energy isprovided by burners. Consequently theplants emit flue gas to the atmosphere. Asan approximation, the specific CO2emis-sions related to 1 ton CO product are:

15 kg CO2 for Calcor Standard,1240 kg CO2 for Calcor Economy

(import CO2notconsidered),

minus 360 kg CO2 for Calcor Economy(emitted CO2minusimported CO2),

1785 kg CO2 for steam reformerwith CO2recycle.

LITERATURE

[1] H. H. Gunardson, J. M. Abrardo: ProduceCO-rich synthesis gas. Hydrocarbon proces-sing, April 1999, pp 8793.

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