Feasibility of a peat biogasification process

Abstract

A feasibility study was conducted to determine if biogasification may be an economical process for the conversion of peat into pipeline quality methane (SNG). United States' peat resources, in terms of energy content, are greater than the energy recoverable from uranium, shale oil, or the combined reserves of petroleum and natural gas. Experiments and costing of SNG by the biogasification of peat were based on a two-stage process. In the first (assumed to follow wet harvesting of peat) an alkaline oxidation pretreatment of peat was employed to produce soluble, low molecular weight acids, wood sugars, and other soluble organic fragments. Unreacted peat solids were separated (to be processed as a potential boiler fuel) while the recovered liquid, containing the soluble organic material, was anaerobically fermented to methane and carbon dioxide in the second stage of the process. In this study, up to 26% of the energy value in peat was converted to methane in the two-stage process; more than 50% of the material from the first stage was fermented to methane in the second. More work is needed to optimize the first stage. Preliminary cost estimates are: a 79.2 × 10³ GJ/day (75.0 billion BTU/day) plant, the total capital requirement is approximately $323 million (April 1978 costs). The annual operating cost is approximately $44 million. For a plant operating at a 90% stream factor, with peat delivered to the plant site as a 3% solids slurry at a cost of $0.0033/kg ($3/ton) dry peat, the average cost for SNG is estimated as $3.16/GJ ($3.34/million BTU). A significant advantage of biogasification appears to be that technical difficulties of dewatering, necessary for peat utilization in conventional gasification or direct combustion, are eliminated.