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HomeMy WebLinkAboutAn Alternative Approach to Liquid Hydrocarbon from Coal 1981COA 017 LIBRARY CO! "AN ALTERNATIVE APPROACH TO LIQUID HYDROCARBONS FROM COAL" PROPERTY OF: Alaska Power Authority 334 W. 5th Ave. Anchorage, Alaska 99501 COA 017 DATE ISSUED TO ee Se lees ee Ie HIGHSMITH 42-225 PRINTED INU.S.A. i 5205/A40 WGFV/MPA 3 March 1981 ea AN ALTERNATIVE APPROACH TO LIQUID HYDROCARBONS FROM COAL 1. INTRODUCTION With the decline of conventional oil and gas reserves in the foreseeable future there is considerable economic and political pressure to develop routes to liquid hydrocarbons from coal. The production of methanol by coal gasification with oxygen followed by water-gas shift to make the extra hydrogen needed for synthesis has many attractions. It does, however, suffer from the disadvantage that this conventional process route rejects almost half the carbon in the coal to the - atmosphere as carbon dioxide in producing the hydrogen requirements. This not only leads to environmental problems but depletes the coal stocks much more quickly than if all the carbon could be turned into methanol. However, if electric power is available in sufficient quantity from a non-fossil fuel source (to limit carbon dioxide emission) it can be used to electrolyse water to oxygen and hydrogen. The oxygen can then be used for the gasification and the hydrogen added to the carbon monoxide from the gasifier to form synthesis gas for methanol production. This reduces the coal requirement for a given methanol output to less than 50% of that required by the conventional route and carbon dioxide discharge to less than 5%. This is the MGFC process route. In parallel with the development of alternative routes to liquid fuels, there are numerous investigations into the production of electric power from renewable sources jie, wind, sun, wave, tide or hydro-electric schemes. However, although a number of these routes will in time reach practical implementation, the large-scale renewable energy source of the next ten years or so must remain hydro-electric power. It is submitted, that in certain areas of the world there are appropriate combinations of coal reserves and undeveloped hydro-electric potential to make it attractive to implement methanol production on the above basis, and that feasibility studies should be put in hand for such areas. Concurrently, the production of gasoline from methanol could also be examined. COMPARISON OF CONVENTIONAL AND ELECTROLYTIC ROUTES On the basis of studies by the Electric Power Research Institute in California (EPRI) to compare a number of gasifiers using a feed of Illinois No.6 coal, comparative material balances have been developed for the conventional and electrolytic routes to methanol and are shown on the accompanying block diagrams, Figures 1 and 2. It can be seen that although the gasifier produces some hydrogen there is a substantial deficit against-the requirement for methanol production. To make this up, the conventional route uses. the water-gas shift process for which additional carbon monoxide has to be produced. Steam is also needed in this process, and, assuming that this is generated by a coal-fired boiler, there is a requirement for 930 tons of coal per, hour compared with 403 tons per hour when using the electrolysis route, in both cases for the production of 600 tons per hour of methanol. The energy balances also favour the electrolysis approach as follows: Conventional Process 40 x 10° BTU/ton of product Electrolysis Route 339% 10° BTU/ton of product The EPRI reports contain capital costs for coal handling, gasification and gas. clean-up facilities. Using these as bases, and taking the expected costs of "solid polymer" commercial electrolysis units gives the fol’cwing figures: Conventional Process - Capital Cost, US $ 1630 x 10° Electrolytic Process - Capital Cost, US $ 1200 x 10° (including $550 x 10° estimated cost of electrolysers) Assuming production costs mostly made up of capital charges (say, 30%), coal costs (say, US $50 per ton) and electricity charges (4.5 cents per kWh) then the cost per ton of methanol would he.-approximately US, $134 using the conventional process and US $260 using electrolysis. Since the MGFC° process uses some 4000 kWh of electricity per ton of methanol produced, it is very sensitive to the electricity cost. As the cost of electricity approaches 1 cent per Kwh, the cost’ of producing methanol using electrolysis reduces to $134 per ton. A summary of the comparison of the conventional and electrolytic routes wimang, Frow coal is set ouk an the attached Lables ety ADVANTAGES AND DISADVANTAGES OF THE ELECTROLYTIC MGFC ROUTE Given that electrical power iS derived from a renewable source, which is central to the concept of the electrolytic route, the system has the following main advantages; = Overall efficiency is appreciably higher than that of many other coal to liquid processes. - Conversion of carbon to liquid product is very high - Pollution is reduced appreciably The main problem is short-term economics. Renewable energy systems for generating electrical power will produce it at a higher cost than that produced by conventional power stations. This is the case with hydro-power, on account of its higher capital costs: other systems will be more expensive stiil,probably for several decades. The ccst of power froma coal-fired power station has three contributory components: a) Capital Costs b) Fuel Costs c) Operating and Maintenance Costs whilst the cost of power from a renewable source is governed only by (a) and (c). It is probable that over the life of an installation to use power from a renewable resource, the cost of electricity will eventually fall to a level well below that of the conventional system, owiag to the ever increasing costs of fossil fuel, compared with the very low operating and maintenance costs for renewable Sources. Unfortunately, this does not mean that in developed areas the price of the electricity from a renewable source will fall below that of the conventional system ie, its value will be whatever the market is prepared to pay for it irrespective of its cost. Accordingly, near any urban area it is unlikely that the price of electricity will be sufficiently low to make the MGFC process route attractive. In remote areas, however, with an abundance of potential renewable power and coal, the economics, in the absence of a market for surplus power, are entirely different. The advantage of the MGFC route is that it provides remote areas with a means of despatching their energy to centres of population and industry, in an, easily transsortable,and directly useful form, by means of a resource - conserving and eavirenentally benevolent ACASS From the point of view of many Western Governments the proposal should be considered as a means of obtaining liquid fuels and chemical feedstocks from coal which maximises the liquid yield from a given amount of coal. This must be a very strong reason for encouraging its development as a long-term means of conserving the ever-decreasing supply of fossil fuels. In this case the short-term economics must be of secondary importance and the case can be substantiated on technical grounds. 7 aE TE —e me Figure 1: CONVENTIONAL PROCESS eeeeeeSeSeeeeeeS OXYGEN CO + H,O—>co, + H 696.5 507.7 346.4 79%8 363 H, ° 792.1 < 226, | —— COAL | GASIFIER | mse ACID GAS [syn | 930.4 oo, t/h 138, 3 CH,OH 6co teh 372t/h steam Y STEA} CO 1032.7 | BOILER CO, 53.9 ay 95% CH. 79,3 co 4 2 = ie 851.7 v Hy 38.7 . y Gasoline HS 301 s 250 t/h cos 24 29.6 3800 KWh/h N, 7.9 2, 000, 695 t/y (833, 35daase) O, 256.8 t/h 2A COAL 402. 7t/h STEAM 120t/h Ts: _#H,O 497.7 t/h VY ELECTROLYSER |¢ 2 ——__| _,#, 5d. QUENCH | ACID{ BiG. GAS | 442.4 lies. t/h - > | GASIFIER| a Qo Naphtha Tar Phenols Oils, ctc. 2500 MW Figure 2. ELECTROLYTIC PROCESS 1725 cells Vv Nine ° | y CO, 27.4 > CO 525 CH, 40,3 Cc, Dae | MeOH SYN v CH,OH 600t/h a &r> © Camparison of routes to Methanol fran Coal 600 tons of Methanol per hour in both cases ( 4 Conventional Processes shift plus methanol | Lurgi gasifier and CO | synthesis j Coal requirement. 930 including that for steam raising. tons per hour i Oxygen requirement fran oxygen plant. toms per hour 697 Water requirement — including that for steam ! boilers and for CO shift | (conventional route) or | a Sian route), ! Carbon dioxide j discharged to atmosphere | from the plant. i i i 1698 852 tons per hour i Energy requirement overall. 10® Btu per tm of . methanol | | | Y | Capital cost of coali-to- | | methanol plant - includin ! cost of oxygen nek _| ! (conventimal route) ! electrolysis plant “| (MGFC weave. US $ mi Hion| = 1630 Note - = above is based m™ the use of Illinois Inskitute 2 milli tons p.a.) MGFC Slagging Lurgi (British Gas Corporation) gasifier and water electrolysis plus methanol synthesis 403 None - the 186 tph requirement is provided by electrolysis,as also the 55 tph hydrogen. ' cheap power bought in___} i 618 27 33 1200 No. 6 coal as Sale for theie CMP 1 SCN \ CaGrss