Hydrogen Generator Gas For Vehicles And Engines Vol. 3&4 

These Volumes present an explanation of how biomass can be converted to a gas in a Downdraft Gasifier and details for designing, testing, operating, and manufacturing Gasifiers and Gasifier Systems, as well as knowledge that was put into practical use during World War II including detailed step-by-step procedures for constructing a Producer Gas Generator for fueling internal combustion engines. HYDROGEN GENERATOR GAS FOR VEHICLES AND ENGINES: Volumes 3 & 4 also gives extensive detail on biomass fuels, gas testing and cleanup in­strumentation, and safety considerations that will be extremely valuable to all those who work with Gasifiers at any scale.

The combustion of biomass in wood stoves and industrial boilers has increased dramatically in some areas, and forest, agricultural, and paper wastes are being used extensively for fuels by some industries. However, more extensive biomass use still waits for the application of improved conversion methods, such as gasification, that match biomass energy to processes currently requiring liquid and gaseous fuels. Examples of such processes include glass, lime, and brick manufacture; power generation; and transportation.

Biomass, like coal, is a solid fuel and thus is inherently less convenient to use than the gaseous or liquid fuels to which we have become accustomed. An overview of various processes now in use or under evaluation for converting biomass to more conventional energy forms such as gas or liquid fuels is provided in this book. It shows how sunlight is converted to biomass through either traditional, activities (e.g., agriculture and silviculture) or via new innovative techniques that have been developed such as energy plantations, coppicing, and algaeculture.

In one sense, biomass gasification is already a well proven technology. Approximately one million downdraft Gasifiers were used to operate cars, trucks, boats, trains, and electric generators in Europe during World War II, and the history of this ex­perience is outlined in this book. However, the war's end saw this emergency measure abandoned. Development of biomass gasification was disrupted in 1946 as the war ended. and inexpensive (150/gal) gasoline became readily available. The magnitude of damage inflicted on Gasifier technology by this disruption can be seen by the fact that it was difficult for even the "advanced" technology of the 1980s to achieve .on tests what was routine operation in the 1940s. The design, research, and manufacturing teams of that decade have all disbanded. We have from the past only that small fraction of knowledge that has been published, whereas the large bulk of firsthand experience in operation design has been lost and forgotten.

Gasification was rediscovered in an era of fuel shortages and higher oil prices, in its rebirth, however, the existing technology uncovered major problems in connection with effluent and gas cleanup and the fuel supply, which were less important during the emergency of World War II. Today, these problems must be solved if biomass gasification is to reemerge as a fuel source but with space-age advan­ces in materials and control systems available for use in today's process designs, a continuous development effort and lively open exchange should enable us to incorporate latter-day chemical and chemical engineering techniques to build clean, con­venient, and reliable systems.

Biomass is a renewable fuel, provided that consumption does not exceed annual production. The biomass feedstock is often a low-cost byproduct of agriculture or silviculture. As such, Biomass could easily supply at least 20% of U.S. energy needs on a renewable basis.

Ultimately though, the accelerated use of gasification technologies depends upon their ability to compete with fossil fuels, which in turn depends on unpredictable factors about resources, economics, and political conditions. At present, gasification and other energy processes are being developed slowly in the United States because of relatively plentiful supplies of low-cost gaseous and liquid fossil fuels. However, political changes and volatile conflicts in key oil production regions could rapidly and dramatically alter this situation, as witnessed during WWII, the OPEC oil crises of the seventies and in the aftermath of Hurricane Katrina eternally cheap oil cannot just be taken for granted.

Biomass can contain more than 50% moisture (wet basis) when it is cut; it is generally desirable to dry biomass containing more than 25% moisture (wet basis) before gasification. Drying often can be ac­complished using waste heat or solar energy. If the temperature of the drying air is too high, the outer sur­faces of the chunk will become dry and begin to pyrolyze before the heat can reach the center. For effi­cient drying, hot air, which if cooled to 60°-80°C would be moisture saturated, is preferred. The moisture slows feedstock drying (as well as slowing surface pyrolysis). Thus more air is required, improving the drying process (Thompson 1981). During operation of a gasifier and engine combination, 1-in. wood chips can be dried from 50% to 5% moisture content, with drying capacity to spare, using a 20-minute residence time with the hot engine exhaust, tempered with 90% recycle of dryer gases.

Commercial dryers are available in many forms and sizes, and it is beyond the scope of this handbook to recommend such equipment for commercial-scale operations. A simple batch dryer for drying small quan­tities in shown in Fig. 3-6 and a commercial dryer is shown in Fig. 3-7.

Biomass Pyrolysis Pyrolysis is the breaking down (lysis) of a material by heat (pyro). It is the first step in the combustion or gasification of biomass. When biomass is heated in the absence of air to about 350°C (pyrolysis), it forms char­coal (chemical symbol: C), gases (CO, CO2, H2, H20, CH4), and tar vapors (with an approximate atomic makeup of CH1200.5). The tar vapors are gases at the temperature of pyrolysis but condense to form a smoke composed of fine tar droplets as they cool. All the processes involved in pyrolysis, gasification, and combustion can be seen in the flaming match of Fig. 4-2. The flame provides heat for pyrolysis, and the resulting gases and vapors burn in the luminous flame in a process called flaming combustion. After the flame passes a given point, the char may or may not continue to burn (some matches are chemically treated to prevent the charcoal from smouldering). When the match is extinguished, the remaining wood continues to undergo residual pyrolysis, generating a visible smoke composed of the condensed tar droplets.