|Energy from Rice Straw 83
Project Leader and Principal UC Investigators
John R. Goss,Department of Agricultural Engineering, UC Davis
The objectives of the project, as modified from the original proposal, are to obtain performance data for the previously constructed fluidized bed gasifier converting rice straw to low-Btu gas; and to design, construct and test producer gas conditioning systems for engine and heated air operation. Another objective was to obtain performance and stack emission data for the combustion of producer gas when burned in a fire box that approximates steam boiler operations. The project is continuing to update reference listings for gasification and to prepare reports on completed work.
Extensive modifications have been made to the fluidized bed gas producer and fuel feed system, whose earlier performance was reported last year. Between January 21 and April 26, eight test runs were conducted with a mixture of chopped and cubed rice straw. Gas was satisfactorily produced and combusted during the runs for a total of 20 hours. Rice straw feed rates ranged from 485 to 940 pounds per hour. The hot gas contained from 60 to 65 percent of the energy in the fuel and the cold gas contained 40 to 46 percent of the fuel energy. The low gasification efficiencies are the result of the large amounts of char separated by the hot cyclones and the fly ash carried by the hot gas exiting the final cleaning cyclones.
A computer summary of the data analysis characterizes the process and the product to provide design information to commercialize the process. With support from other funds, satisfactory hot gas production was achieved with almond shell screenings, coarse hammer-milled wheat straw and alfalfa seed straw.
A producer gas conditioning system for engine operation was assembled and tested with gas generated in the fluidized bed from a mixture of cubed and chopped rice straw. The system contained a prototype hot gas filter and full-scale, cooler-condenser. The quality of the cool clean gas from this system was within the established range of temperature and solid particulate content for sustained engine operation. With contract support from other agencies, development has continued on a fluidized-bed gas producer-engine system for electric power generation using high ash crop residues. Performance testing of the system early in 1984 on the Davis campus will use six different crop residues, including rice straw.
The pollution constituents were determined from the stack effluent of a small horizontal furnace fueled with hot producer gas generated from a mixture of soft cubed and chopped rice straw by the fluidized-bed gas producer. This determination was made by the Engineering Evaluation Branch of the California Air Resources Board. The gaseous emissions of SO2, CO, hydrocarbons and NOx, were less than the allowable amounts for most installations. The particulate content was above the allowable amount but was attributed to a malfunctioning of the hot gas cyclones during the test. This was not discovered until after the test was made. A second determination of the furnace stack effluent will be made using producer gas generated from rice straw.
Several units using crop residues for power generation by direct combustion are in commercial use in California. Another unit is being developed in Arizona that will generate producer gas from cotton residues. The project, funded by the Rice Research Board, has proven the technical feasibility of generating producer gas from rice straw, and that this gas is acceptable for sustained engine operation. The economic feasibility of generating producer gas from rice straw is not promising at present costs and present availability of natural gas. However, the technology is now available and can be used when the economic climate becomes favorable.
The project has developed an up-to-date listing of 710 references for gasification. One Master of Science thesis was completed in 1983 and two technical papers were presented on the chemical composition, deformation and fusion temperatures of crop residue ash. This kind of information must be known to avoid fouling of the refractory sand bed of a fluidized bed gas producer.