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Through the use of a metal catalyst, gasification of wet biomass can be accomplished with high levels of carbon conversion to gas at relatively low temperature (350 °C). In a pressurized-water environment (20 MPa), near-total conversion of the organic structure of biomass to gases has been achieved in the presence of a ruthenium metal catalyst. The process is essentially steam reforming, as there is no added oxidizer or reagent other than water. In addition, the gas produced is a medium heating value gas due to the synthesis of high levels of methane, as dictated by thermodynamic equilibrium. While good gas production was demonstrated, biomass trace components caused some processing difficulties in the fixed catalyst bed tubular reactor system used for the catalytic gasification process. Results are described for tests using both bench-scale and scaled-up reactor systems.

Abstract:  The application of pollution prevention concepts to chemical process design is often hampered by lack of sufficient information about potential design alternatives. The high cost of collecting this information can thus present act as a constraint on the thoroughness of the final design optimization. One approach to dealing with such data constraints is the application of design heuristics. Particularly when coupled with the use of robust optimization methods, heuristic approaches can provide useful insight and direction at all stages of the design effort. Pacific Northwest National Laboratory has been developing a heuristic-based tool for use in chemical process design. Known as the Process Heuristic Review of Environmental Design (PHRED) this design tool uses conventional backwards chaining expert systems techniques to identify and prioritize applicable design heuristics based on a minimal set of process data. The development philosophy and current status of the PHRED tool are discussed in this paper.

Bench-scale reactor tests are under way at Pacific Northwest Laboratory to develop a low temperature, catalytic gasification system. The system, licensed under the trade name Thermochemical Environmental Energy System (TEES®), is designed for to a wide variety of feedstocks ranging from dilute organics in water to waste sludges from food processing. The current research program is focused on the use of a continuous feed, tubular reactor. The catalyst is nickel metal on an inert support. Typical results show that feedstocks such as solutions of 2 percent para-cresol or 5 percent and 10 percent lactose in water or cheese whey can be processed to >99 percent reduction of chemical oxygen demand (COD) at a rate of up to 2 L/hr. The estimated residence time is less than 5 min at 360°C and 3000 psig, not including 1 to 2 min required in the preheating zone of the reactor. The liquid hourly space velocity has been varied from 1.8 to 2.9 L feedstock/L catalyst/hr depending on the feedstock. The product fuel gas contains 40 percent to 55 percent methane, 35 percent to 50 percent carbon dioxide, and 5 percent to 10 percent hydrogen with as much as 2 percent ethane, but less than 0.1 percent ethylene or carbon monoxide, and small amounts of higher hydrocarbons. The byproduct water stream carries residual organics amounting to less than 500 mg/L COD.