Design of a 160 MW OTEC Plantship for Production of Methanol

8/7/2019 Design of a 160 MW OTEC Plantship for Production of Methanol

1/5

DESIGN OF A 160 IlV OTEC PLANTSHIP FOR PRODUCTIONOF METHAXOLW. H. Avery, DirectorDennis Richards, Head, Technical CoordinationOcean Energy ProgramsJohns Hopkins University Applied Physics LaboratoryJohns Hopkins RoadLaurel, Maryland20707

AbstractThe use of OTEC plantships at their full potentialto produce synfuels and energy intensive products would

energy greatly exceeding present world demands. Me-thanol is aparticularly attractive OTEC product be-cause it can replace unleaded gasoline asa motor ve-hicle fuel and isa preferred feedstock for high efficien-cy fuel cells designedfar electric power generation.Preliminary analyses indicate that OTEC methanol wouldbe a more economical motor vehicle fuel than unleadedgasoline at present prices.

make the tropical oceans a resource which could supply

OTEC methanol is produced ina process which in-volves reaction of oxygen, producedby water electroly-sis onthe OTEC ship, with coal to form carbon monoxide,which is then catalytically combined with hydrogen,produced in the same electrolysis process, to formmethanol. Coal is transported to the plantship bybulk carrier and the methanol product is returned toshore by tanker.

A preliminary description is presented in thepaper of the process requirements, and projected out-put and costs ofa 160 MW (nominal) OTEC methanolplantship. The design is based on scale-up of the1980 APL design of a4 0 MW ammonia plantship, withsubstitution of a methanol plant for the ammoniaplant and readjustment of the ship system to accom-modate the larger process and equipment space re-quired.Three industrial organizations have participatedin the design study. Brown and Root Development, Inc.(BARDI) performed the initial shipboard methanol plantdesign study and performance analysis benefiting fromthe detailed engineering design and cost informationwhich BARDI had assembled for a barge mounted methanol-from-natural-gas plant, and drawingon design,cost andoperating information for the TVA ammonia-from-coalpilot plant, employing the Texaco gasifier, which wasdesigned and built by BARDI. Informationon a moltencarbonate gasifier developed by Rockwell International,and ship integration and methanol synthesis data pro-vided by Ebasco Services, Inc., are providing the

basis for a second iteration of the plantship designand costs.Initial APL study of the molten carbonate gasi-

fier process ona 160 MW plantship showed a significantincrease in production over the initial shipboardmethanol plant designstudy, to 1450 metric tonsldayof fuel grade methanol, anda "first-cut'' estimateddelivered cost atU.S. ports of $0.45 to$0.60 pergallon.

IntroductionOcean Thermal Energy Conversion (OTEC) isatechnology which uses the temperature difference be-tween surface and deep watersin the tropicaloceans to

produce electric power. OTEC plantships cruisinginthe tropics use the electric power generatedto operateon-board plants which produce synfuels or chemicalThe products are temporarily stored on-board untiltheyare picked up at approximately monthly intervals fdelivery toU.S. and world markets. In selectivelo-cations OTEC power may also be produced by near moored or bottom mounted plants, where the electricpower may be transmitted via underwater cable to shore utilities or other uses.

The solar energy absorbed daily in the surfacwaters of the tropical oceans is equivalent to thenergy that would be released by combustion of160billion bbls/day of oil. Thus a process for extractonly 0.05%of the solar energy input and converting to chemical energy in the form of fuel would mapresent world production of petroleum. OTEC offersapractical approach to this goal.

In this paper we discuss an OTEC process ielectrical energy is converted to chemical energy bthe electrolysis of water, with the hydrogen and gen then employed in reaction with coal to formthanol which isa storable efficient substitute forunleaded gasoline or other fuels.OTEC Methanol

The use of OTEC plantships for production of thanol has been the subject of several recent re2 * The current paper presents the results of ourinitial investigations, and preliminary studies con-

ducted in a joint effort by Ebasco Industries andRockwell International under subcontract to APL.A schematic of the OTEC methanol process is psented in Fig.1. Coal is transported bya commer-cial coal carrieron amonthly supply cycle to theOTEC plantship which cruises at about112 knot at

plantship the coal isgasified byreaction with:I selected equatorial ocean site. On board theokygen generated by water electrolysis. Steamisinjected into the gasifier along with the coal touse the heat generated to form additional CO plushydrogen . The g a s i f i e r p r o d u c t is t hen mi xedwith the hydrogen generated by water electrolysisand conducted to the catalytic converter wherereaction to form methancl occurs.

The design of the OTEC methanol plantship derfrom the preliminary design ofa 40 (net) OTEC-ammonia plantship completed in1980 under DOE sponsor-ship.4 This, together with cbnceptual commercialplant scale-up designs5, formed the basis forthe study by Brown6 Root Development,Inc. (BARDI)discussed in reference2, which defineda 160 MWOTEC-methanol plantship with output of1000 mt/d offuel grade methanol. In this design theAF'L powersystems concept is retained, with two80 MW OTECpower systems(4-20 MW net turbo-generators) each

746 CH1972-918310000-0746$1.00 0 1983 IEEE

Authorized licensed use limited to: University of Massachusetts Amherst. Downloaded on September 3, 2009 at 18:02 from IEEE Xplore. Restrictions apply.


2/5

I

L

16.8kg/sr CH30H 1.02 kg/s HzCatalytic- Water 160 MWe OTEC8.04kg/s O2 electrolysis 4 plantship- q = 0.9 electricpowert Pure 15 MWth*waterGas clean up distillationWater+IMolten

gasificationSteam -+ carbonate Melt * carbonaterecycle, -+ SulfurSulfur removed,4 ash separation1450 rntlday handling7Ash

Plantship

Methanol500,000 mt/yr -I Coal tpreparation ,Coal

Land1210 rnt/plantship/day

1370 mt/dayMethanol fuel60% q HHV 45% q LHVtcell electr ic power,engines th = thermal

tLHV = lower hearing value212 MW 183,000 hpHHV = higher heating value

A PR I L 1983Fig. 1 OTEC plantship methanol process flow.

with a 12.2m diameter cold water pipe fore andaft of the centrally locatedprocess plant. TheBARDI study was basedon information availableto B A R D I on the cost and performanceof full scalemethanol process equipnent and provided costs andlayout requirements based on commercially availableequipment. A sketch of the OTEC-methanol plantshipprepared by BARDI is shown is Fig.2 . It was evidentat the conclusion of the study hcwever, that majorimprovements could be madein process efficierxywith a gasifier of more recent design developedbyRockwell International which uses a bath of moltensodium carbonate as the coal reaction vessel. Useof this gasifier is projectedto give major improve-ments through better syngas composition, use ofpulverized coal instead of water slurry and reducedcomponent layout volume.A flok- sheet for the pro-cess which is self-explanatory is shown in Fig.3 .The essential features of the process demon-

stration size molten carbonate gasifier are shownin Fig.4. A vessel lined with insulation (fusedalumina) contains a bath of molten sodium carbonate,about 4.4m deep in the proposed design, into whichpulverized coal, steam and oxygen are injected belowthe surface of the melt. The bath is highly turbulentso that mixing and heat transfer are very rapid,chemical-equilibrium is attained, and minimum volumeis required for the process. The sulfur in the coalreacts with the carbonateto form sodium sulfide whichis retained in the melt along with the ash in the coal.The result is an exit gas with lowCog ( - 1 2 % volume

Fig. 2 OTEC 160 MW methanol plantship.of theCO), low sulfur(0.03% volume asH 2S ) andminimal particulates. Accordingly, the volume re-quirements for gas cleanup compared with thosequired in the initial study are greatly reducedthough salt regeneration processes are added.Anoverflow continuously bleeds some of the melt a quench tank where the soluble salts are dwhile the insoluble ash particles form a slThe ash is removed by clarification and filtand the salt solution undergoes regeneration

747


3/5

treatmentdisposal Sulfur to shore

Make upcarbonatefrom shoreregenerationdisposaland storageUnit 1200 Unit1400

Coal Coalfrom shoreUnit 900Unit 850MethanolAcid gasShiftGasCoalCoalhandling,+ +synthesis+removal+conversion+clean up+gasification-processing DistillationUnit 1000and storage Unit 800Unit 700Unit 600Unit 500 to 2 F I & CH30HOTECpower Electrolysis H2

systemUnit 100

Methanol+ storage andUnit 1100transferUnit 200

WaterPlantship treatment recoveryandUnit1500 and productionutilities

Fig. 3 OTEC/methanol plantship simplifiedflowchart - molten salt coal gasification.eheat burner port

nse aluminatable refractory

Thermowell

Green liquid slurryFig. 4 Rockwell International process demonstration unit.

the sulfur is separated as hydrogen sulfide gas.The H2S is converted to elemental sulfur in a Clausplant and the salt further processed for recycling.

Estimates of Methanol delivered costs via themolten salt coal gasification process are shown inTable 1. This estimate was based upon theOTECpower-platform costsas given in reference2,substituting cost estimates for the Rockwell gasifier

Table 1OTEC methanol cost estimate (1980s)

commercial 1s t plantship 160 MW, 1450 MT/D.(SM)

Plant investment 393Methanol plant 155Subtotal 548

Interest during construction* 74Total 003 contingency 62230% contingency 809

--

Annual cost (SM) 0%contingency 30% contingencyFixedcost** 33.2 49.6 43.2Operating cost 64.5Crew 80 @ $65,000 5.2 5.2 6.8Catalysts @ materials6.0 6.86.0 7.8Shipping CH30H @ $1 l/ mt 5.55.5 7.2 7.8Shipping coal @ $1l/rnt 4.64.6 6.0 7.26.0Coalcost @ $50/mt -20.6 20.6 26.8 26.8

Total annualcost75.191.5 97.8 119.1

x * ** * x * * x * * X * *

(1210 mt/d)- - -

Methanol production (gal/y) 166 millionMethanol cost *** 0.45($/gal a t US. por t )

($/gal a t U.S. port)

0.59

Methanol sales pr ice*** * 0.55 0.72

Equivalent unleadedgasoline price 0.73 0.96*A t 13% interest, 10% funds first year, 40% second year,50% thi rd year

9% nominal inflation,l2.7% nominal discount rate, 10% ITC""Based on DOE/EIA 0356/1, MARAD Tit leXI, 12 %% equity,"'"'30% levelized nominal return on equity** *9 % levelized nominal return on equity

process-capacity in place of the prior process. Theongoing work indicates that a substantially largerthruput can be attained at some increment in inment but reducing the delivered methanol cost.748

Authorized licensed use limited to: University of Massachusetts Amherst. Downloaded on September 3, 2009 at 18:02 from IEEE Xplore. Restrictions apply.


4/5

Process StudiesIn the present processstudy ao. operating eoneoff Guam has been assumed which has a high annualaverage L T of 24.1"C and which would have access toall Pacific Basin coalsources, although a L'tah(Sunnyside) reference coalis being used for analyses.The peak OTEC power generation of189.9" occurs in

August-October and it is proposed by Malcolm Jones6that this power level (to the electrolysis plant)be maintained continuously. Sufficient steam fromprocess waste heat is available for supplementalelectric power generatior. to balance out the lowerLT months (minimm O T E C power of165.8MW). An addi-tional small coal fired boiler and a steam turbinegenerator ratedat-35 Mw would permit maintenanceof production at levels near full methanol synthesisplant capacity with an OTEC20 MW (net) unit do mfor maintenance.

Run of mine coal and sodium carbonate make-upis transferred from the coal collier to the plantshipbunkers via conveyors over a tow-trailing mooring buoyconcept. (Methanol product and other liquids are off-loaded to receiving tankers via hard-pipe connectionson an icterleaved cycle.) Automatic coal handlingequipment processes the coal through a hammermill 2nddryer (to 1 / 4 " size and 16:; moisture) to storagehoppers. Coal and sodium carbonate are conveyed byweigh-belt feeders to surge and feed hoppers and thento a pressurized injection hopper system. Four gasi-fiers are provided, of which oneis a standby-spare,and operate at 2.034 MPa and9 8 2 O C . The coal-carbonate feed rate is controlled by rotary feedersand introduced with recycled product gas throughthree nozzles at the bottom of each gasifier vessel.Oxygen and steam mixture is introduced through alter-nately spaced nozzles. A heated nozzle controls themelt inventory by continuous overflow through a with-drawal chamber to a pressure equalized quench tankfrom which the molten carbonate-ash slurry is con-tinuously withdrawn for processing. The referencecoal and product gas composition is shown in Tables2 and 3.

Product gas heat is recovered and provides super-heated s t e m for all process needs including compressor

Table 2Sunnyside Utah reference coal composition

C 70.0 w t%H 4.90 9.7N 0.9S 1.0Moisture 7.0Ash 6.5

Table 3Medium-Btu gas compositionco 48.539 vol %HZ 35.709CH 4 2.280COZ 6.044H Z 0 6.994NZ 0.312Ar 0.091H2S 0.031

drives, oxygen heating, and supplemental power tion as noted earlier. A soot blower system rany solids carryover.A particulate scrubber furthecools and dehumidifies the gas for following and a low temperature control valve regulates gasifier pressure. The raw gas is compressed andpart of the gas undergoes a CO shift conversicess to provide additional hydrogen by the rCO + H 2 0 -+ CO2 + H z before the combined streams the acid gas removal system.The Rectisol columnremoves all sulfur compounds from entering gasin abottom section by scrubbing with CO2 loaded from an upper section where cold lean methanolabsorbes theCOz. The desired leaving gasCCI2 contentis controlled by bypass of sulfur free gas fbottom section. CO, CO2 andH 2 S are removed from twash methanolby additional processes, withH 2 S sentto the Claus-sulfur plant and CO2 utilized forgas requirements.

Compressed hydrogen from the electrolyzersystem is alded to the processed gas enterinthe methanol synthesis compressor, which withrecycled loop gas then enters an IC1 low premethanol synthesis column where the reactions

CO + 2 H 2C H 3 0 Bcog + H z 2 co f E 2 0

and co2 + 3 H 2 2 C H 3 0 H + H 2 0take place over a copper based catalyst.

Crude methanol from the synthesis reactorincluding approximately 15% H20 is condensed aflashed to remove dissolved gases, with a smafraction of the gas purged to maintain the level, following which the methanol (with sodihydroxide, XaOH, added for corrosion protection)is distilled to99% + fcel grade. Light ends(higher alcohols) purge gases can be utilizedas fuel and lower alcohols stored as product.

This very simplified description omits themany intermediate and auxiliary processes whichare however, well developed. Excepting the moltecarbonate gasifier and sodium carbonate regenewhich has been proven at a1 ton/hr process demonstrtion size, and the electrolyser systems for wrequired efficiencies have been demonstrated atthe 200-500KT? size (multi-megawatt electrolyzersare available at lesser efficiencies) all proceequipment has been proven in multiple installations world wide. At this time (August1983)the process study6 is near completion with a- layout and arrangement similar to that shownin Figure2, with equipment sizes and costs deteThe significant increase in both product and process rates indicate that a small increase platform length will be necessary over the edesign, but the overall economics indicate thadelivered methanol costs will be less than testimates in Table1. Design output is now1750mt/d of methanol from1360 mt/d coal supply.Carbonate make-up(5 2 mt/d) sulfur and other produash, and wastewater are all relatively minor quantity.Concluding Comments

The OTEC coal to methanol process requiresone half to one third the coal requiredin currentcoal conversion technologies, the% and o2 from749


5/5

water electrolysis eliminates the need to burncoal to provide the heat for the large hydrogenshift process required. Thus not only are gasifierand associated gas clean-up equipment sizes muchsmaller but the expensive oxygen separation plantis eliminated. Considering the ultimate combustionor chemical conversion of the methanol, the totalC02 discharged to the atmosphere per ton of methanolwill be similarly reduced to one half to one third,Several other important considerations follow forspecific methanol markets including: mine productionrates, capital, and operating costs are proportion-ately reduced; the lifetime of assigned coal reservescould be doubled or tripled; land requirementsincluding required boundary separation distancesfor the large gasification and synthesis plantsare eliminated, as are local and global gasificationplant emissions, and possible critical water supplies.Against these obvious benefits must be set therequired transportof coal from mine to OTEC plantshipincluding possible port development; the returnshipment (in greatly reduced quantities)of wasteproducts for treatment and disposal; and methanoland other product shipment to users, all of whichwill require dedicated transport/tankers withpurpose design handling equipment.

With methanol a preferred and proven substitutefor unleaded gasoline7'* (with minor additives), apreferred energy supply for high efficiency fuelcells , as well as a proven replacement for fueloilsin gas turbines and boilers, a potentially hugeliquid fuel market could be developedfor OTECmethanol based on comparable petroleum costprojections. Possible scenarios could includededicated coal supply and coal/methanol transportsystems servicing OTEC plantship fleets: e.g.Western U . S . or Alaskan coal to the Eastern Pacific,or Australian, Chinese or other coals to the WesternPacific or Eastern Indian Ocean;with methanoldelivered to markets suchas West CoastU.S. , Hawaii,Japan, Australia, etc.

9

OTEC plantships are capital intensive andunique construction facilities are required forhull construction, outfitting, and deployment.10While the gasification-synthesis plant land siteenvironmental-societal considerations will notpertain, the at-sea operational environmentalprotection requirements will be similar with theadditional constraintsof the ocean environmentand vessel manning-safety aspects. While our OTECnethanol plantship design studies basedon existingor developing technologies and equipmentshowthat OTEC methanol to be commercially attractive,several of the process requirementsas well as OTECpower system and plantship ocean engineeringaspects must be proven to the pointof privateinvestor satisfaction to obtain active commercialinterest. Multi-year research, development, andtetts to demonstrate the practicality of someaspects, fudged to be critical to investor confidencehave been proposed.

AcknowledgementThe support of theU.S. Department of Energyfor this workis gratefully acknowledged, particularlythe guidance and advice byWilliam E. Richards,Eugene Burcher and Peter Ritzcovan;and the essentialwork by Brownd Root Development Inc., Ebasco Services,Incorporated and Rockwell International Corporation.

References1.

2 .,

3.

4.

5.

6.

7.

8.

9.

10.

W. H. Avery, "Remarks for Planning Session forEstablishment of the Pacific InternationalCenter for High Technology Research,'' Honolulu,Hawaii, May 31, 1983.W. H. Avery and D. Richards,W. G. Niemeyerand J . D. Shoemaker, "OTEC Energy Via MethanolProduction," Presented at The 18th Inter-society Energy Conversion Engineering Conference,Orlando, FJA, Aug. 21-26, 1983.JHU/APL, 0QR/82-4, Quarterly Report, Ocean EnergySystems, Oct-Dec 1983, OTEC Methanol.George, J . F. and Richards, D., "Baseline Designsof Moored and Grazing40 MW OTEC Pilot Plants,"Vol. A, Detailed ReportJHU/ApL SR-BO-lA, andVol. B, Engineering DrawingsJHU/ApL SR-80-1B,June 1980.Richards, D., Francis,E. J., and Dugger, G.L .,"Conceptual Designs for Commercial OTEC-AmmoniaProduct Plantships," Presentedat 3rd MiamiInternational Conferenceon Alternative EnergySources, Miami Beach,FLAY Dec. 15-17, 1980.Ebasco Services Inc. and Rockwell InternationalCorp., "Coal to Methanol OTEC Plantship StudyUsing the Rockwell Molten Carbonate CoalGasification System," Draft Report July7, 1983.Personal Communication toW. H. Avery fromMerle Fisher, Bankof America, April 1982.A complete report is to be issued soon.Rischard, J, F. , "Emerging Energy andChemical Application of Methanol:Opportunities for Developing Countries,"The World Bank Report lSBN 0-8213-0018-0,April 1983, p, 47.Patal, P.S., Maru, H. C., andBaker, B. S.,Energy Research Corp., National Fuel CellSeminar, 11-14-82, Abstracts 1982,p. 88.Franc i s , E. J., Richards , D . , and Rogalski,W. W., "Building Ocean Thermal EnergyConversion Facilities and Plantships--Requirements for Unique ConstructionFacilities,'' Presented at 8th Ocean EnergyConference, Washington, D.C., June 1981.

750

Authorized licensed use limited to: University of Massachusetts Amherst Downloaded on September 3 2009 at 18:02 from IEEE Xplore Restrictions apply

Design of a 160 MW OTEC Plantship for Production of Methanol

Documents

Transcript of Design of a 160 MW OTEC Plantship for Production of Methanol