氢的成本核算.pdf

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1、R.E.Stoll and F.von Linde,Caloric AnlagenbauGmbH,Graefelfing,GermanyHydrogen is a commonly found element.Formany petrochemical/chemical products,it isconsumed as a process reactant or fuel.Currently,the global annual hydrogen demand isapproximately 50 million tons(550 billion Nm3).Bulk petrochemical

2、sammonia and methanoland processing/refining of gasoline consume nearlytwo thirds of the annual hydrogen demand.Thesefacilities typically have hydrogen requirements up to250,000 Nm3/h.The remaining hydrogen demand isdirected to many different process industries inclu-ding:fats and oils processing,ch

3、emicals,pharmaceu-ticals,metallurgy,semiconductor production andaerospace industries.Growing demand.The hydrocarbon processing indus-tries(HPI)are expanding their demand for hydrogen.Operating facilities can either buy hydrogen(H2)orproduce it.When manufacturing hydrogen for indi-vidual needs,severa

4、l significant processes can producehydrogen in quantities ranging from 50 to 4,000 Nm3/h.The technologies include:electrolysis of water,steamreforming and methanol cracking.With several diffe-ring options,operating facilities must consider whichprocess is most cost-effective.Besides capital invest-m

5、ent,operating costs and primary energy require-ments should be evaluated by decision-makers.Se-veral examples highlight key factors to consider whendetermining H2supply requirements.Electrolysis.In the electrolysis process(Fig.1),wateris split according to the principle of:H2O+electric energy H2+12O

6、2In this process,H2is gained at the cathode with apurity of virtually 100%at atmospheric pressure;thecontaminates are oxygen and water vapor.The utili-ties used in the process are electricity and deminera-lized water.Depending on size,type and condition of the plant,the energy requirement to produce

7、 1 Nm3of H2by elec-trolysis ranges between of 4.2 to 5 kWh.Assuming anaverage efficiency in generation and distribution of elec-tric power from natural gas,the primary energy equi-valent is approximately 1.3 Nm3 methane per 1 Nm3 H2.Oxygen is a byproduct of electrolytic dissociation of water;with ha

8、lf the volume of H2 oxygen is gained at the anode.Steam reforming.The dominate steam-reformingprocesses convert natural gas,LPG or naphtha,withwater vapor in the presence of a nickel catalyst,into ahydrogen-rich synthesis gas.The process reaction is:CnHm+H2O H2+CO+CO2+CH4+H2Oat a temperature of 800C

9、900C and a typical pressureof 1025 bar.The classic steam-reforming process with externalheat supply(Figs.2 and 3)requires 0.46 Nm3methaneper Nm3H2.Steam is a process byproduct.After con-sidering the additional energy requirement for electricdrivers and the bonus of 73 Nm3methane/ton ofexported steam

10、,the primary energy requirement is esti-mated at 0.40 Nm3methane for each Nm3of pure H2.New“low-temperature”steam-reforming processescan offer advantages for smaller H2users.The expenseto import steam is compensated by lower feed and fuelconsumption,and substantially reduces investment costs.Methano

11、l cracking.At significantly lower tempera-tures than in the steam-reforming process,theHydrogenwhat are the costs?HPI operating facilities have manychoices on how to meet their risingdemand for H2;here are several optionsPLANT UTILITIES42HYDROCARBON PROCESSING/DECEMBER 2000Fig.1.Simplified process f

12、low sheet for electrolysis.HYDROCARBON PROCESSING/DECEMBER 200043methanol-cracking process splits methanol and steamin the presence of a copper-zinc catalyst(Figs.4 and 5).The process reaction is:CH3OH+H2O H2+CO2+CO+H2O at temperatures between 250C300C and a typicalpressure of 1025 bar.To produce 1

13、Nm3of H2,approximately 0.65 kg ofmethanol is required.Considering the energy require-ment for electrical drivers and that 0.875 Nm3methane is required to produce 1 kg methanol,the pri-mary energy balance for the methanol-cracking pro-cess is 0.59 Nm3methane per Nm3pure H2.Hydrogen purification.The r

14、emoval of O2and watervapor contaminates from hydrogen produced by electrolysis requires a catalytic DeOxo(to convert O2+2H22H2O)and a dryer for the subsequent watervapor removal(Fig.1).The catalytic reforming processesprovide a syngas with approximately 75 vol%H2(drybasis)at elevated pressure.Pressu

15、re-swing adsorption(PSA)process can produce a purified H2with a typicalpurity of 99.999 vol%.In PSA,the nonhydrogen gasesof the syngas are adsorbed at the elevated pressure onactivated carbon and molecular sieves.By expandingthe adsorber vessel to almost atmospheric pressure,these nonhydrogen gases

16、are desorbed and returned tothe reformer as auxiliary fuel(Figs.2 and 4).CO2emissions.Isolating H2from water or hydrocar-bons follows an endothermic reaction.For steam refor-ming and methanol cracking,burners provide the requiredenergy.Consequently,these plants emit flue gas to atmos-phere.Using ele

17、ctric power only,the water electrolysisprocess is free of CO2emissions at the site,but the cor-responding emissions are relocated to the power ge-nerating facility as it processes electricity from fossilfuels.As an approximation,the specific CO2emissionscan be related to these primary energy require

18、ments:Electrolysis2.6 kg CO2/Nm3H2Steam reforming0.8 kg CO2/Nm3H2Methanol cracking 1.2 kg CO2/Nm3H2Cost of investment.The various processes and ope-rating conditions of electrolysis,steam reforming andmethanol cracking have diverse investment costs,Fig.2.Simplified process flow sheet for steam refor

19、ming.Fig.4.Simplified process flow sheet for methanol cracking.Fig.5.Methanol cracker with PSA.Fig.3.Steam reformer with PSA.whereby proportional costs vary with plant capacity.For plant capacities of 250 to 1,000 Nm3/h H2 with asupply pressure of 16 bar g,Table 1 lists the relation ofinvestment cos

20、ts for the processes described.Production costs.Fig.6 lists the production costs for on-site H2.These expenses include depreciation and in-terest on the capital investment,utilities,manpowerand maintenance.Since market prices for naturalgas and methanol vary considerably and depend onlocation and su

21、pply quantities,the production costsfor hydrogen are shown for typical prices.If LPG or naph-tha is used instead of natural gas in the steam-refor-ming process,0.78 kg LPG or 0.84 kg naphtha may beset against 1 Nm3 methane.For the other processingutilities,the following costs were assumed for calcul

22、a-tion purposes:Electric energy 0.04 U.S.$/kWhWater,demineralized 1.10 U.S.$/m3Water,cooling 0.07 U.S.$/m3Apart from the costs for utilities and energy,thesefactors were taken into account in the calculation ofthe production costs:Operating hours,annual 8,600Annuity depreciation of the invest-ment c

23、osts over 10 yearsInterest rate 6%Maintenance 2.0%of the investmentcosts annuallyPersonnel 39,000 U.S.$/man yearThe typical energy requirement of 4.6 kWh/Nm3 H2by elctrolysis results in the highest operating costs,thus,limits their share of total H2 production to lessthan 1%.With decreasing plant ca

24、pacity,however,thecosts for utilities and energy become less significant,whereas the costs of depreciation and interest on theinvestment dominate.The influence of annuity on the production costs for H2 production also becomes clear when comparinghigh-temperature/low-temperature steam-reformingand me

25、thanol-cracking processes.Based on the priceof 0.12 U.S.$/Nm3 natural gas(NG)and 160 U.S.$/tonmethanol,the lower investment costs for low-tem-perature steam-reforming and methanol-crackingplants lower production costs for plant capacities upto approximately 300 Nm3/h H2.The break-even pointmay shift

26、 substantially with changing utility costs,andmust be calculated for each site-specific case.Fig.7 presents the total annual costs for on-site H2production for each process and the cost calculations.Inonly one year,the difference in production costs of thedifferent processes can exceed total investm

27、ent costs.Purchasing hydrogen.An alternative to on-site pro-duction may be the purchase of H2.The expenses,whichhave to be added to the production costs on the suppliersside,are frequently incurred for hydrogen purification,compression or liquefaction and transportation costs.Also,the consumer must

28、consider suppliers generalcosts and profit.Typically,H2 is supplied as a gas inhigh-pressure cylinders by truck or trailer.At a sto-rage pressure of 200 bar,the transport volume is 5,560Nm3=500 kg H2at a total transport weight of 40 tons.For comparison,H2generated from a methanol sup-ply at the same

29、 total transport weight is around 40,000Nm3=3,600 kg H2.The additional costs incurred by theHYDROCARBON PROCESSING/DECEMBER 200045Table 1:Cost of investmentCapacity250 Nm3/h1,000 Nm3/hSteam reforming100%100%Low-temp.steam reforming71%70%Methanol cracking79%74%Electrolysis65%154%0.9000.8000.7000.6000

30、.5000.4000.3000.2000.1000.000Costs U.S.$/Nm3Fig.6.Production costs per Nm3 H2Fig.7.Annual production costs of H2.supplier for treatment,transportation and storage of H2at the consumers facility are economical only in caseof low or occasional requirements.Since the price varies considerably,depending

31、 on supply source and transport distance,a general market price for purchased hydro-gen cannot be quoted.The decision between on-site pro-duction and purchasing of H2 must be made by com-paring the production costs shown in Figs.6 and 7 andthe most favorable offer obtained for the supply of H2.Raine

32、r E.Stoll is project and sales mana-ger at Caloric Anlagenbau GmbH,Graefel-fing,Germany.He has worked for the com-company for more than three years.Prior toCaloric,Mr.Stoll has 16 years of experienceas project and sales manager with Schmidt-Bretten and Krauss Maffei Verfahrenstechnik.Mr.Stoll holds

33、an MSc degree in processengineering from the Technical College ofMannheim.Florian von Linde is president of CaloricAnlagenbau GmbH,Graefelfing,Germany.Previously,he worked as sales engineer forCaloric and for Lenzing AG,Lenzing Technik,Austria.Dr.von Linde holds an MSc degree inchemical engineering from the Technical Uni-versity of Munich and a PhD in chemical engi-neering from the Technical University of Graz.