Many economic analyses of biomass gasification for low — and medium-energy gas, synthesis gas, and methanol production have been performed after biomass gasification developments started to increase in the 1970s. The basic approach to many of these analyses is illustrated here by focusing on the manufacture of methanol. For stand-alone methanol plants using biomass feedstocks, the se­quence of operations has generally consisted of gasification to a low — or medium — energy gas, steam reforming to essentially all hydrogen and carbon oxides, water gas shift to produce a gas with a molar ratio of hydrogen: carbon monoxide of 2:1, acid gas scrubbing to remove carbon dioxide, and methanol synthesis. The gas compositions that would ideally be obtained from each step, using Bailie’s indirectly heated steam-gasification process as the source of the synthesis gas, are shown in Table 9.12. Analysis of the cost of synthesis gas production alone, which was reported in the early 1980s for this process (Bailie, 1980,1981), re­sulted in a projected capital cost of $22,050/dry t ($20,000/dry ton) of biomass feedstock capacity per day, and a synthesis gas cost of $3.04 to $3.39/GJ ($3.21 to $3.57/MBtu) at a feedstock cost of $31.58/dry t ($28.64 dry ton), or $1.70/GJ ($1.79/MBtu). At that time, the posted prices of natural gas and methanol were $3.16/GJ ($3.00/MBtu) and $10.54/GJ ($10.00/MBtu), or $0.145/L ($0.56/gal). Average capital costs for the steam gasification of biomass in mid-1990 nominal dollars range from about $55,000 to $88,000/dry t ($50,000 to $80,000/dry ton)

of biomass feedstock capacity per day depending upon plant size and other fac­tors, so the impact of time on equipment costs is evident. The feedstock and operating costs are also higher.

A plethora of economic projections has appeared in North America on the production of synthesis gas and methanol from biomass since this early work. Governmental regulations regarding motor fuel compositions and the use of oxygenates are undoubtedly responsible in part for this renewed interest. The details of a comparative economic analysis that compared the capital, operating, and methanol production costs of Wright-Malta’s steam gasification process, Battelle’s steam-air gasification process, IGT’s steam-oxygen RENUGAS pro­cess, and Shell Oil’s coal gasification process as applied to the steam-oxygen gasification of biomass are summarized in Tables 9.13 and 9.14 (Larson and Katofsky, 1992).

“Larson and Katofsky (1992).

kThis process produces about 2 to 3 mol % C;+, but is not included in the analysis. CHHV of product gas/Sum of HHVs gasifier (and combustor in Battelle case).

According to this analysis, the capital, operating, and methanol production costs from a plant supplied with 1650 dry t/day of wood feedstock ranges from $204 to $338 million, $35.3 to $43.7 million/year, and $0.17 to $0.27/L, respectively. The feedstock cost was assumed to range from $38.19 to $41.88/dry t. At a 90% capacity factor, methanol production ranges from 293 to 417 million L/year depending on the process. Production is highest with the Wright-Malta process and lowest with the Battelle process because a substantial portion of the feedstock is used as fuel to the combustors for the latter process. A generally conservative approach was used for this economic assessment. All unit operations with the exception of biomass gasification were established, commercial technologies when the analysis was performed. The overall cost of methanol is more attractive for the two indirectly heated steam gasification processes (Wright-Malta and Battelle) compared to the methanol cost estimated for the directly heated gasification processes (IGT and Shell). The cost of the oxygen plant is a major contributor to product cost for the directly heated processes. Also, a few of the assumptions made by the analysts appear to disproportionately and adversely affect the cost of methanol from the Wright- Malta process, which when adjusted would provide still lower cost methanol. The utilities and purchased energy costs for this process seem to be excessive because only a small amount of purchased energy would be necessary, as already mentioned in the discussion of the reported autothermal nature of this process. In addition, the requirement for 17 gasification kilns operating in parallel to achieve a target plant capacity of 1650 t/day because of the kilns’ low throughput capacity contributed significantly to product cost for the Wright-Malta process. Nevertheless, this type of comparative analysis illus­trates the various facets of such economic assessments that should be examined and emphasizes where improvements might be made in the economics of each process.