Biomass Gasification and Syngas Cleaning

BEI’s thermochemical program conducts research into biomass gasification and syngas cleaning. Here is a listing of some of our more significant published papers in this area. Click on title to view article in a new window from the publication Website.

Steam/oxygen gasification system for the production of clean syngas from switchgrass

Karl M. Broer, Patrick J. Woolcock, Patrick A. Johnston, Robert C. Brown (2014), Fuel

A pilot-scale 25 kg/h fluidized bed, oxygen/steam blown gasifier and syngas cleaning system was developed to convert switchgrass into clean syngas. The system is rated for operation at gage pressures up to 1 bar. The reactor vessel incorporated a novel guard heating system to simulate near-adiabatic operation of large commercial-scale gasifiers, and was effective for gasification temperatures up to 900 °C. After removing particulate from the gas stream via cyclones, a warm-gas cleaning operation based on oil scrubbing was used to remove tars. Sulfur compounds were removed via solid-phase adsorption. Ammonia was removed by water scrubbing.

[ILLUSTRATION]Feed system and fluidized bed gasifier

The new feed system and fluidized bed gasifier at Iowa State University.

Baseline gasification tests with steam and oxygen were conducted at equivalence ratios (ER) between 0.21 and 0.38 using switchgrass as fuel. Measurements on the raw and cleaned syngas included permanent gas composition, C2 hydrocarbons, water, heavy and light tars, gasification residues (char and ash), hydrogen sulfide (H2S), carbonyl sulfide (COS), carbon disulfide (CS2), ammonia (NH3), and the first reported measurements of hydrogen cyanide (HCN) for oxygen/steam blown gasification. Heavy tars were removed with high efficiency by the method employed, although more difficult to remove light tars reduced overall tar removal efficiency to less than 80%. The sulfur scrubbing system demonstrated 99.9% removal efficiency, resulting in less than 200 ppb of H2S in the cleaned gas. The NH3 scrubbing system also accomplished greater than 99.9% removal efficiency, resulting in final NH3 concentrations of less than 1 ppm.

Hybrid Processing

DongWon Choi, Alan A. Dispirito, David C. Chipman, and Robert C. Brown, (2011). Hybrid processing (chapter 9), Thermochemical Processing of Biomass: Conversion into Fuels, Chemicals and Power, Wiley & Sons

An alternative approach available for the biorefinery is the thermochemical processing of biomass into uniform intermediate products that can be biochemically converted to fuels and other chemicals, called hybrid thermochemical/biological processing or simply hybrid processing. This emerging approach is not only applicable to lignocellulosic biomass utilization, but also applicable to virtually any carbonaceous material, such as biogases, organic waste products, agricultural waste material, and industrial and municipal wastes, enabling the utilization of a wide range of feedstocks for the production of biofuels and other bioproducts.

There are two distinct approaches to hybrid processing: (i) gasification of the carbonaceous waste material into a volatile gaseous mixture called synthesis gas or syngas, followed by fermentation; (ii) fast pyrolysis of the waste material into bio-oil, followed by hydrolysis and/or fermentation of the anhydrosugar found in bio-oil. In this chapter, microorganisms capable of utilizing syngas or bio-oil for their growth and their potential applications in syngas fermentation and bio-oil fermentation will be discussed.

Resolving inconsistencies in measurements of hydrogen cyanide in syngas

Karl M. Broer, Patrick A. Johnston, Alex Haag, Robert C. Brown (2015), Fuel[ILLUSTRATION]Reactor experimental setup

Reactor experimental setup consisted of: (1) variable rate feed system equipped with two augers, (2) plenum thermocouple probe and heated plenum packed with steel spheres, (3) fluidized bed comprised of silica sand and crushed limestone, (4) reactor body with three thermocouple probes, the middle for reactor temperature control, the other two for temperature monitoring, (5)  Watlow ceramic heaters encasing the reactor to maintain temperature, and (6) two gas cyclones.

Syngas from biomass and coal gasification contains ammonia (NH3) and hydrogen cyanide (HCN) that originate from fuel bound nitrogen (FBN). Despite being minor constituents of the syngas, they are of great interest. They represent NOX precursors when the syngas is burned for process heating or IGCC applications and catalyst poison if the syngas is to be converted to fuels or chemicals. Measuring NH3 and HCN via wet chemical methods can be challenging and laborious, which may account for the relative paucity of NH3 and HCN measurements reported in the literature. Three frequently cited studies report HCN yields that are insignificant regardless of operating conditions and biomass feedstock types. These studies have been cited by other authors as justification for not measuring HCN in studies of nitrogen evolution during gasification. Other authors have reported much higher yields of HCN, on the order of a few tens of percent. Tellingly, sample collection methods are distinctive for these two ranges of HCN measurements. The present study investigated the analytical methods underlying these results, and found the lower numbers to be the result of flawed sampling methodologies.

A techno-economic analysis of polyhydroxyalkanoate and hydrogen production from syngas fermentation

DongWon Choi, David C. Chipman, Scott C. Bents, Robert C. Brown (2010), Applied Biochemistry and Biotechnology

A techno-economic analysis was conducted to investigate the feasibility of a gasification-based hybrid biorefinery producing both hydrogen gas and polyhydroxyalkanoates (PHA), biodegradable polymer materials that can be an attractive substitute for conventional petrochemical plastics. The biorefinery considered used switchgrass as a feedstock and converted that raw material through thermochemical methods into syngas, a gaseous mixture composed mainly of hydrogen and carbon monoxide. The syngas was then fermented using Rhodospirillum rubrum, a purple non-sulfur bacterium, to produce PHA and to enrich hydrogen in the syngas. Total daily production of the biorefinery was assumed to be 12 Mg of PHA and 50 Mg of hydrogen gas. Grassroots capital for the biorefinery was estimated to be $55 million, with annual operating costs at $6.7 million. With a market value of $2.00/kg assumed for the hydrogen, the cost of producing PHA was determined to be $1.65/kg.

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