Low-temperature conversion of high-moisture biomass: Topical report, January 1984--January 1988

Abstract

Pacific Northwest Laboratory (PNL) is developing a low-temperature, catalytic process that converts high-moisture biomass feedstocks and other wet organic substances to useful gaseous and liquid fuels. The advantage of this • process is that it works without the need for drying or dewatering the feedstock. Conventional thermal gasification processes, which require temperatures above 750'C and air or oxygen for combustion to supply reaction heat, generally cannot utilize feedstocks with moisture contents above 50 wt%, as the conversion efficiency is greatly reduced as a result of the drying step. For this reason, anaerobic digestion or other bioconversion processes traditionally have been used for gasification of high-moisture feedstocks. However, these processes suffer from slow reaction rates and incomplete carbon conversion. • The PNL high-moisture gasification system, in which thermocatalytic conversion takes place in an aqueous environment, was designed to overcome the problems usually encountered with high-water-content feedstocks. The process uses a reduced nickel catalyst at temperatures as low as 3Sooc and pressures ranging from 2000 to 4000 psig-conditions favoring the formation of methane gas rather than hydrogen and carbon oxides. Tests have produced gases containing up to 55% methane. By comparison, gases produced by conventional thermal gasifiers typically contain only 5% to 15% methane. When compared with anaerobic digestion, the PNL-produced gases contain similar amounts of methane, but the reaction rate is 300 to 400 times faster. Furthermore, carbon conversion is nearly complete, whereas with anaerobic digestion it is only about 50% to 80%. Over 180 tests have been conducted to evaluate the effectiveness of the process on feedstocks defined as high-moisture biomass. These tests also included 11 experiments at liquefaction conditions to determine oil product compositions and yields. All experiments were conducted batchwise in a 1-L, bolted-closure, highpressure autoclave (reactor), with a magnetically coupled stirrer. The reactor and associated sample lines were made of stainless steel to minimize i i i corrosion. The entire system, except for certain valves and the instrumentation, was housed in a 0.25-in.-thick plate steel barricade. Many other safety features were built into the system, including remotely controlled monitoring and sampling procedures.

Low-temperature conversion of high-moisture biomass: Continuous reactor system results

“…Analysis of the effluent condensate has determined that the highest concentrations of unconverted organic constituents are the small organic acids followed by phenols and cyclopentenones. The latter two groups are similar to that reported earlier in high-pressure liquefaction experiments (Elliott, Sealock, and Butner 1988) feedstock a l s o showed no s i g n i f i c a n t change i n t h e major c a t a l y s t components.…”

Development of a catalytic system for gasification of wet biomass

“…and food processh-_g residues), which are not efficiently gasified in conventional, low-pressure thermal systems (Elliott and Sealock I985;Sealock et al 1988). Later s_dies appl;.ed the technology to the destruction of hazardous organic chemical wastes and organic chemical maeufacturing wastewaters (Baker and Sealock 1988) as well as biomass feedstocks ('Elliott et al 1991).…”

“…Batch reactor test results have demonstrated process applicability to a wide range of organic components (Sealock et al 1988;Baker and Sealock 1988;Elliott et al 1993b). Development of catalysts for this processing environment has also been an important factor in making this processing technology viable (Elliott et al I993a).…”

Bench-scale Reactor Tests Of Low-temperature, Catalytic Gasification Of Wet Industrial Wastes

“…The nickel effectively catalyzes the reaction of the organics with the water to produce a mixed product gas of methane, carbon dioxide, and a lesser amount of hydrogen. The proportions of the three gases are determined by the concentration of the organic in water and the amounts of carbon, hydrogen, and Oxygen in the organic material since the gas composition appears to be near equilibrium in the case of active catalysts [4]. In cases of less active catalysts, the hydrogen concentration is not driven to very low levels by catalysis of the methanation of carbon oxides with the hydrogen.…”

“…From this research evolved the concept of a pressurized, catalytic gasification system for wet biomass feedstocks to produce fuel gas [3]. Extensive batch reactor testing [4] and limited continuous reactor system (CRS) testing (51 were undertaken in the development of this system under sponsorship of the U. S. Department of Energy. A wide range of biomass feedstocks were tested and the importance of the nickel metal catalyst was identified.…”