Comparison of Biomass to Bio-oils Reactor Systems: Direct Conversion vs. Companion Coal Gasification

It is well known that the United States’ dependence on crude-oil negatively affects its economy, safety, and environment. To alleviate these negative consequences, a more economical and environmentally-friendly source of fuel, such as biomass, should be explored. The conversion of biomass to bio-oils involves the pyrolysis of biomass at about 500°C, thus requiring a great deal of heat. This heat source could be the excess waste heat from a coal gasifier. As such, this report specifies the design of an industrial plant that produces bio-oils from biomass by using the waste heat from a coal gasifier. It is designed to produce 2.24×108 kg/yr of bio-oil that can be sold at $0.79/kg. This plant involves coal and biomass solids handling, a coal gasification reactor, a biomass pyrolysis reactor, and a series of separation units to remove waste products from the syngas and isolate the bio-oil. The syngas contains methane, hydrogen, and carbon monoxide and is sold as a by-product credit. The plant is expected to run on feeds of 1.5x1011 kg/yr of coal and 5.4 x108 kg/yr of raw biomass. The coal gasification reactor was sized based on the heating duty of steam at 273000 kJ/s and the biomass pyrolysis reactor was sized based on a heating duty of 7026 kJ/s. The plant’s operating factor (POF) is 0.9 at 7884 hrs/yr running 24 hrs/day and 328.5 days/yr. The total bare module equipment cost, including all pumps, heat exchangers, grinders, separators, absorber, and reactors is $93 million. The total capital investment of the plant is $173 million. The DCFRR and NRR are 12.59% and 20% respectively. Given that selling price of bio-oil ($0.79/kg) associated with this plant is about six times more expensive that the average cost of bio-oil ($0.13/kg), it is not recommended that a Class – 1 Estimate be conducted. Before a Class – 1 Estimate can be conducted, the unnecessary costs associated with this proposed plant must be addressed and reduced. Specific attention must be paid to the following two heat exchangers, E-127 and E-129. Additionally, attention should be given to discover a cheaper source of industrial, liquid oxygen