Direct Liquefaction of Coal

A detailed set of engineering design estimates for direct liquefaction of coal has not been reported recently. Cost and performance estimates done here were based on 1993 U.S. DOE design estimates [22, 23]. These estimates were updated to 2007, but they are not considered as definitive or on as consistent a basis as the estimates used for indirect liquefaction. The liquid products of direct liquefaction are typically very aromatic and contain large fraction of sulfur-, nitrogen-, and oxygen-containing molecules. Costs associated with the production of clean transportation fuels that meet U.S. or developed-world fuel specifications have typically not been included in published cost estimates. Direct-liquefaction product quality has more typically been representative of heavy feed to a refinery rather than fuel products from it. For this work, the cost of upgrading all product streams was estimated so that only clean liquid transportation fuels were produced by the process. Total capital cost for a direct liquefaction plant producing 50,000 bpd of liquid transportation fuels, including complete upgrading to finished products specifications was estimated at $5.5 billion, or about $115,000 per stream-day-barrel. The best estimates suggest an overall thermal efficiency of about 60%, and a yield of about 2.6-3.0 bbl liquid liquid transport fuels per tonne of coal [24]. This compares with about 2.1 bbl of liquid transportation fuel per tonne of coal, and a thermal efficiency of 50% for indirect liquefaction using FT synthesis. Duddy [25] recently reported a capital cost of $115,000 per stream-day-barrel and 3.1 bbl of liquid transportation fuels for Axens' direct coal liquefaction process.

Direct liquefaction plant emissions are projected from 5 [25] to 8.5 [17] kg CO2/ gal of product. This would make direct liquefaction plant CO2 emissions less than that for the FT plant. The estimated cost of liquid transportation fuels produced is about $0.20/gal higher than for a comparable indirect CTL plant using FT synthesis. The LC GHG footprint, with CO2 venting, of a direct liquefaction plant is expected to be slightly better than that for a venting CTL-FT plant. The direct liquefaction plant with CCS will be disadvantaged relative to the indirect liquefaction plant because it will have more flue-gas CO2 that will have to be recovered, and that

5 It is important to note that although these conclusions are considered valid, there is much less engineering data on MTG and few design calculation relative to FT and more are needed.

is more costly than CO2 capture in indirect liquefaction. This could be improved through engineering modification to the plant design, but these changes will come at a cost and will not overcome the higher CO2eq avoided cost. To improve the quality of these numbers, more definition to direct liquefaction requires more and better engineering data and up-to-date estimates of capital and operating costs and process importance.

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