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BIOMASS GASIFICATION FOR AGRICULTURAL ENERGY SOURCES AND SOIL ENRICHMENT
Small-scale farmers are dependent on petro-industry products and inefficient biomass uses to warm greenhouses in winter and to fertilize crops. This use of fossil fuels contributes to air and ground water pollution. Greenhouses can be warmed, and soil can be enriched economically and without contributing to climate change. A gasification system that converts biomass into usable gas and biochar can produce fuel to warm greenhouses and provide an organic soil amendment at a low cost to the user.
Phase I of the Biomass Gasification Project gave birth to many success stories and demonstrated enormous potential for members of the local agricultural community and for students within the university.
Watauga County Cooperative Extension is willing to promote the technology and help set up educational workshops for local growers. One local business owner in particular, Bucky Black, President of Resource Wood Incorporated, is enthusiastic about the work the ASU P3 team has accomplished thus far and sees a CHPB gasification system as an ideal way to put his waste stream to use. He also plans to expand his business by collecting waste wood from the surrounding community and gasifying it to produce and sell electricity, creating jobs in the area in the process. The greenhouse testing facility was built on Mr. Black’s land and will be used by students and Mr. Black for many years.
Aspects of the project have been incorporated into three different ASU undergraduate courses (solar biomass dryer for Solar Thermal Technology, water purification with biochar filters for Water and Waste Water Technologies, and feasibility of gasification of construction waste for energy for Biofuels Technology) and two senior capstone projects.
Heat recovery for soil heating
The heat recovery system actually comprises several subsystems. One subsystem draws heat from the produced gas after it exits the gasifier, another one draws heat from the engine where the produced gas is combusted, and the third subsystem circulates the exhaust from the blower and the engine through the feedstock hopper to preheat and dry the biomass before it enters the gasification chamber. Excess heat is stored in a standard water heater. From the water heater, the heat is transferred to the soil in the flower beds via a network of water‐filled PEX tubes embedded in the soil.
The heat recovery system has been built and will be tested. There is strong evidence that the system will perform adequately. The following can be estimated:
- each pound of dry biomass that is gasified produces around 7,000 Btu of theoretical recoverable heat (Bliss and Black, 1977),
- the gasifier consumes about one pound of biomass per hour,
- the heat exchange system transfers 70% (low estimate) of the recoverable heat from the gas to the storage water, and
- the stored water and the soil start at 30°F (-1°C).
Following from the above estimates, the gasifier will need to operate for 3 to 4 hours for the heat recovery system to provide enough heat to raise the soil temperature to around 70°F (21°C), which is near the optimal soil temperature for minimizing germination time for most vegetables (University of Minnesota, 1999). At that point, the system will be able to easily maintain that temperature.
Greenhouse testing facility
The greenhouse is a semi-permanent structure with space for growing plants in soil beds and a separate housing for the gasification system and data-logging equipment. The housing is fireproof and well-ventilated, thus providing a perfect environment for conducting research in a safe manner. The greenhouse is structurally sound and can be reproduced inexpensively.
A working gasifier capable of processing multiple sizes, shapes, and types of feedstock was designed and built from scratch. The air intake nozzles and hearth are fully customizable so as to allow compatibility with a wide range of feedstock and engine sizes. The gasifier design and fabrication methods as well as the heat recovery system design will be shared with ALL Power Labs (