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ECONOMICS OF PRODUCING METHANOL FROM COALB Y ENTRAINED AND FLUIDIZED-BED GASIFIERS

William C . Morel and Yong J ai YimU . S . Department of the I nteri or, Bureau of M inesProcess Evaluation Office--MMRO

P.O. Box 880Morgantown, West V i rgini a 26505Methanol i s one of several l i qui d fuel s being considered as a supplement t ohelp al l evi ate increasing gasol ine requirements, the anticipated curtail ment of theavai l abi l i ty of domestic crude oi l and natural gas, and the steadi l y increasingcost of foreign crude.lower a i r requirement f or combustion, so some modif ications wi l l be required i n the

carburetor design.taini ng about 10 percent methanol. Coal i s being considered as an alternative rawmaterial for the production of methanol owing to the apparent depletion of naturalgas supplies.An economic evaluation of methanol production from coal synthesis gas basedon a 5,000-ton-per-day capaci ty i s presented. Two coal gasi f i cati on systems ar econsidered--entrained and Synthane (a fluid-bed process).diagram showing major uni ts in these two processes.J anuary 1976 cost indexes. Average sel l i ng pr ices of the gas were determined byusing DC F rates of 12, 15, and 20 percent at various coal costs.f actors are included during the l i f e of the pl ant.ti ons have been incorporated. Some of the economic and techni cal detai l s areincluded for the two systems.

Methanol has one-half the heating value of gasol ine and aPresent-day carburetors can operate with a gasoline fuel con-

Figure 1 i s a blockNo inf lation

The estimates are based onPollution abatement considera-

ENTRAINED GASIFICATIONIn thi s system methanol i s produced from synthesi s gas prepared by entrainedFigure 2 i s a flow dia-1. Coal preparation, which includes crushing, screening, si zi ng, and drying of2. Entrained oxygen-coal gasi f i cati on a t 30 atmospheres wi th a 2,400" F outlet3. A dust removal uni t removes the entrai ned dust from the synthesis gas w i t h

gasi f i cati on of Pi ttsburgh seam coal a t 30 atmospheres. ( 1 )gram of the process and includes the following steps:the run-of-mine coal (not shown on f igure 2).gas temperature.cyclone separators,before i t enters the waste heat recovery uni t where steam requi redin the gasi f i cati on and sh i f t conversion uni ts i s produced.flows through an electrostatic precipitator for residual dust removal.

Shift conversion of the clean synthesis gas to a H2:CO rat io o f 2.3:l in thepresence of sulfur-resistant catalyst.puri f ication uni t i s produced i n the heat recovery system fol lowing the sh i f t con-verters. The hot-carbonate purification u n i t , which reduces the COP content to 2.8percent and removes essenti al l y al l of the H2S and COS. (2)f or removal of resi dual sul fur compounds.6. The low-pressure methanol synthesi s system, operating a t 570" F and 1,470psia and uti l i z i ng a copper-based catal yst.I t i s assumed that approximately 15 percent of the total H2 and CO entering theconverte'r i s synthesized to methanol. The design of the converters was based on agas space velocity of 10,000 v / v / h . (3) The thermal efficiency of the plant i s 46.5percent, based on a gross heating,value of coal at 13,400 B t u per pound and methanolat 10,259 B tu per pound.

Gasi f ier volume was based on a 2.5-second gas residence time.The cooled gas then

4. The 50-psig saturated steam required i n the5. Char towers are provided

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SYNTHANE GASIFICATIONThe synthesis gas i s produced by f l ui di zed gasi f i cati on of Pittsburgh seam coala t 68 atmospheres. (4)the following steps:1. Coal preparation, which incl udes crushing, screening, si zi ng, and drying ofthe run-of-mine coal (not shown on figure 3).2. Coal pretreatment i n the top section of gasi f i cati on uni t to destroy cakingproperties.3. Free-fall carbonization plus steam-oxygen gasification of the pretreatedcoal in a fluidized bed.4. Entrained char removal in cyclone separators and tar removal by water scrub-bing. 5. The f i r s t hot-carbonate puri f i cation unit , which reduces the CO2 content to1 percent and removes essenti al l y al l the H2S and COS. Char towers are provided for

removal of residual sul f ur compounds.A steam-methane reformer uni t, which converts about 95 percent of the CH4to CO and Hp to decrease the amount of purge gas from the methanol synthesi s uni t inaddition to producing H2 for synthesis.A reverse shi f t conversion uni t, which reduces the H2:CO r at i o of the re-former gas product from 4.3: l to 2.3:l .by of f gas from the pur i f i cati on system.8. A second hot carbonate puri f i cati on un i t which selecti vel y reduces the C02content to 2.8 percent.water vapor, i s cooled and compressed to meet C02 requirements of the reverse shi f tconverters.9. The methanol synthesi s uni t which operates a t the same condi tions as theother case.The gasi f i ers are designed to operate at a pressure of 1,000 psia and at amaximum temperature of 1,800" F with coal throughput of 580 pounds per hour persquare foot o f cross-sectional area. The assumptions f or the methanol synthesi sare the same as those used i n the entrained gasi f i cati on system. The thermalefficiency of the plant is 41.6 percent, based on a gross heating value o f 13,400B tu per pound of coal and gross heating values of methanol and byproduct tar of10,259 B tu per pound and 130,000 B tu per gallon, respectively.

Figure 3 i s a flow diagram of the process and includes

6.

7. C02 requirement f or the reaction i s suppliedOff gas from the regenerator, namely COP saturated with

CAPITAL INVESTMEN7The total investment i s estimated to be $331.7 mil l ion f or the entrained gasi-f i cati on system, or $252.7 mil l i on lower than f or the Synthane gasi f i cati on system.Table 1 i s a capi tal requirement comparison of the two systems, and fi gure 4shows the distribution of capital requirement f or major processes. Detailed cost

summaries of the major processing units are not included, but the costs of theindividual units are l i sted. General f aci l i ti es include administrative buil dings,shops, warehouses, rai l road spurs, rol l i ng stock, roads, waste water treatment, andfences. The cost of steam and power di str i buti on, cool ing water towers, plant andinstrument ai r , f i r e protecti on, and sani tary water are included in plant uti l i ti es.OPERATING COST

Table 2 presents the estimated operating cost comparison for the entrained andSynthane gasification systems.days for downtime, two 10-day shutdowns for equipment inspection and maintenance,and 15 days f or unscheduled operational i nterrupti ons. With labor a t $6 per hour,payrol l overhead at 30 percent of payrol l , and depreciation a t 5 percent of thesubtotal for depreciation all owing credi t f or sul fur recovered a t $25 per t o n , andwi t h the cost of coal as a var i abl e, the following operating costs are derived:

A n assumed 90-percent operating factor allows 35

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\

cos t o fcoalper ton$111315

Per year, MM P er ga ll o n P er MMBtuE ntrai ned Synthane E ntrained Synthane E ntrai ne d Synthane$77.7 $116.6 $0.15 $0.23 $2.25 $3.4482.8 122.7 .16 .35 2.38 3.6387.8 128.9 .17 .26 2.50 3.81

cost ofcoalper ton

3.84 6.35 4.43 7.23 5.46 9.153.98 6.49 4.57 7.46 5.614.13 6.64 4.72 7.67 5.76 9.44

Methanol se l l in g pr ic eEntrained I Synthane I Entrained I Synthane- IE ntra ine d I Synthane12-pCt DCF I 15-pct DCF I 20-pc t DCF

The DCF computer program takes i n to account the c a pi ta l expen diture pr io r t os tartup so that the intere st during construction i s de leted f rom the c api ta l requi re -ment. P rovisions are made f o r recovery o f the working ca pi tal i n the 20th year.UNIT COST SUMMARY

The s e ll in g p ri c e used t o determine the hig h-c os t elements i n the process wasbased on a 15-percent DCF f o r a 20-year pr oj e c t l i f e , wi th coal a t $13 per ton. Abreakdown of the co s t elements f o r th e two systems i s shown i n ta b le 3.shows the s e ll in g p ri c e o f major processes f o r th e two systems. F igure 6

SUMMARY OF CO MPAR I S O N SAs shown i n tabl e 1, the to ta l investment fo r the entrained ga s ifi ca tio n systemi s $252.7 mil l i o n, o r 43 percent lower than f o r the Synthane system. About 60 per-

cent o f the d i fference i s i n synthesi s gas preparation, cons i s t ing o f the f l u id i z edga s if ic at io n system and the methane reforming u n i t fo r co nverting th e methane i n theproduct to synthesis gas.investment for the Synthane gas i f ica t ion u n i t i s i t s higher operat ing pressure; a lsoit req uire s more separa tion o f such impu ri tie s as ammonia, char, and ta r from thegas stream. The major p a r t o f th i s c ap ita l cos t di ffe re nc e comes from th e steam-methane reforming u n i t t o process approximately 35 percent (dry base) o f methane i nthe gas stream. T his high-temperature reforming reac tion i s endothermic and req uire sno t on ly high cap ital cos t but als o high-temperature steam to supply the heat requiredf o r the reaction. I n ad ditio n to these, the Synthane system require s ex tra processesover the entrained ga s if ic at io n system such as a second pu ri fi c a ti o n step and CO2compression. The higher ca pi tal cos t of the methanol-synthesis u n i t f o r the Synthanesystem, even though both systems have s im il a r feed gas composition and fl o w ra tes , i sdue t o the higher compression ra ti o of the feed gas,cost.

It i s apparent that the reason f o r t h i s h igh ca pi ta l

r e s u l t i n g i n a higher compressionDi fferences i n ca pi tal cos ts f o r these two systems are shown i n fi gu re 4.

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The operating co st for th e entrained ga s if ic ati on System i s about 33 percent lessInc rease s i n maintenance, overhead,han for the Synthane system as shown i n tab le 2.and ind i re ct and f i xed costs , which are d i re ct l y re la ted t o the capi ta l investment,represent the main diff ere nce .The average s e l l i n g p r i c e was based on thre e coa l co s ts ($11, $13, and $15) andthree DCF rates o f re tur n (12, 15, and 20 perce nt).pr ice f o r the entrained ga si f ic at io n i s 17 to 25 cents per gal lon o f product lowerthan f o r the S ynthane.gasification, o r $2.51 t o $3.68 per MMBtu.a 40-percent decrease.Over th i s range, the s e l l in g

This represents about

CONCLUSI ONResul ts of th is study c l ea rl y ind ica te the entrained ga si f ic at io n system i s more

economical than the Synthane f l u i d i z e d system t o produce methanol from coal. Thecommercia l avai lable Lurgi f ixed-bed ga si f ic at io n u n i t w i l l y i e l d s i m il a r r e s u l t sowing t o the formation o f methane i n the produc t as i n the flu id iz ed system. One o ftwo al tern ati ves would be a combination o f a high-Btu gas pl a nt with methanol as i t sbyproduct. T his would elimi na te the h igh co s t o f a methane-steam reforming un it,but it would have a lower methanol conversion yi e l d because the p a rt ia l pres sure o fthe hydrogen and carbon monoxide i s reduced by the h ighe r methane content i n the gasstream plus the f ac t th a t the methanol i s s ynthesiz ed on a "once through" basis with-out recir cul atio n. The other al ter na tive would be the separation o f methane from thegas stream by a cryogenic method, bu t th i s i s a lso considered a high-capi ta l process.Even though th e Synthane co al ga s if ic a ti o n system may not be the most su ita bl e processt o produce methanol fro m coal owing t o i t s hi gh methane content, i t i s comparable t oother g as if ic a tio n systems th a t produce high-Btu gas.

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REFERENCE1) Intra-Bureau R eport No. 77-12, "Methanol via E ntrained G as ifi ca tio n o f P ittsbu rghSeam Coal, 5,000-Ton-Per-Day P lant. " P rocess E val ua tion O ff ic e , U . S . Bureau o fMines, Morgantown, W . Va.

Carbonate P u r if i c a ti o n Computer Program," March 1968.

Series, No. 98, v. 66, 1970.

Seam Coal, 5,000-Ton-Per-Day P la nt ."Mines, Morgantown, W. Va., September 1976. '

2) Wellman, P . , and S . K a t e l l . U. S. Bureau o f Mines Info rmation C ir cu la r 8366, " H o t

3) Danner, G. A . Methanol Technology and Economics. Chem. Eng. P rog. Symposium

4) Intra -B urea u R eport No. 76-17, "Methanol vi a Synthane G as if ic a tio n o f Pi ttsburghProcess Evaluation Office, U.S. Bureau of

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TABLE 1. - C api tal requirements: Comparison o f entrained ga s ifi ca tio nsystem with Synthane qasification system

. .9,i91 ,40042,452,900

U n i tCoal preparation..........Gasi icati n. .............Dust removal ..............Pur i f i ca t i on No. 1........Methane reforming.. .......Waste heat recovery No. 1.CO P compression.. .........S hi ft convers ion. . ........Reverse s h i f t conversion..Waste heat recovery No. 2.Pur i f i ca t i on No. 2........Methanol synthesis.. ......Oxygen plant..............Sulfur recovery plant.. ...Waste water treatment.. ...F lue gas proces sing.......Steam and power plant.. ...P1 ant f a c i 1 t ies . . ........P l an t u t i l i t i e s ...........Total construct ion. . .I n i t i a l c a t a l y s trequirements ............

Tota l p lant cost(insurance and taxbases). ............construction ............

depreciat ion .......In teres t dur ing

Subtotal for

Working capital.. .........Total investment.....

10;355;40012,723,70045,595,000

Entrained I Svnthane

16,475,20023,614,500

259,759,300

2,504,700

8,161,200 45,833,000

29,068 I 10041,665,000

458,315,300

3,672,100

2.278.900 I 9.117.00024;731 ; ZOO 39; 728;40032,462,9002,169,100 3.599.0001,629,2007,852,200

63,096,60047,200,0001.100.000

23; 304; 5004,513,90010,488,10029,244,30086,159,50022,000,0001.130.000

262,264,000 461,987,400

39,339,600 69,298,100

30,160,400 53,128,600

100

Difference$-1,820,600-37,671,800-6.838.100

-23i304 500

-29 244 300-23,062,900+25,200,000-30.000

-1 2,592,900-18,050,500

-1 98,556,000

-1,167,400

-1 99,723,400

-29,958,500

-229,681,900-22,968,200

-252,650,100

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TABLE 2. . nnual operati nq cost: Comoari son ofent r ai ned qasi f i cati on wi t h Synthane qasi f i cat i onEnt r a i nedl asi f i cati onos t i t emDi r ect cost:

Synt hanegasi f i cat i on D f f erenceRaw mater i al s:Coal at $11 per t on ...Raw wat er .............Catal yst and chemcal s

Methane...............Subtotal ............

D rect l abor ............D rect l abo r s uper v i s i onSubtotal ............

Mai ntenance l abor .......Mai ntenance l aborsuper vi s i on............Mai nt enance mat er i aland con t rac t s..........Subtotal ............

Payrol l overhead........Oper a t i ng s uppl i es......Total di r ec t cost ..

I ndi rect cost .............F i xed cost:Taxes and i nsurance.....Depr ec i at i on ............

Tot al . bef orec r edi t ............Sul f ur credi t ...........Tar credi t ..............Ammoni a credi t ..........

af t er credi t ....per at i ng cost.

$33. 776. 4001. 375. 7003. 109. 700233. 4008.5.810. 900.684. 300.1.809. 500.go. 200

$27. 965. 500691. 4001. 300. 200143. ZOO30. 100. 3002.312. 600346. 9002.659. 5004.845. 000

969. 0007. 267. 50013. 081. 5002.542. 1002. 616. 300

50.999. 7007.342. 9005. 245. 30015.080. 200

78. 668. 100994. 100

77. 674. 000

38. 495. 200 .8.394. 9002. 733. 100 .420. 500410. 000 .63 1003. 143. 100 .483. 6008.550. 000 .3.705. 0001.710. 000 .741. 000

12. 825. 000 .5.557. 50023. 085. 000 .10.003. 5004. 020. 900 .1.478. 8004.617. 000 .2.000. 700

73. 361. 200 .22.361. 50012. 338. 000 .4.995. 1009. 239. 800 .3.994. 50026. 564. 300 .11.484. 100

121. 503. 300 .42.835. 200995. 900 +l . 800

1. 744. 400 +1.744.4002. 184. zoo +2. 184.zoo116. 578. 800 .38.904. 800

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TABLE 3. - Unit cost comparison

Tota l ............... 1 .314

Cost per gal lon o f productProcess un i t E ntra ined gas i f i cation lsynthane gas i f i ca t ionCoal preparation......... 1 $0.014 1 $0.016

.505

Gasi f icat ion .............Dust removal .............P ur i f i c at ion No. 1.......Methane reforming. .......Reverse s h i f t conversion.S hi ft conversion.. .......P u r i f i c a ti o n No . 2.......Methanol synthesis .......S ulfu r recovery.. ........Waste water treatment....Flue gas processing.. ....

C02 compression ..........

.156.003.036

.023

.070.001

.011

--

.170.015

.005

.052. lo3

.009.015

-

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