Grantee Research Project Results
Final Report: A Continuous-Operation Variable-Feedstock Biomass Gasifier Design Based on Indigenous Materials
EPA Grant Number: SU835130Title: A Continuous-Operation Variable-Feedstock Biomass Gasifier Design Based on Indigenous Materials
Investigators: Pohlman, Nicholas A. , Prokup, Christopher , Ryan, John , Barnes, Jonathan , Mackey, Michael , Musika, Rudolf
Institution: Northern Illinois University
EPA Project Officer: Hahn, Intaek
Phase: I
Project Period: August 15, 2011 through August 14, 2012
Project Amount: $14,935
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2011) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Sustainable and Healthy Communities , P3 Challenge Area - Air Quality , P3 Awards , Sustainable and Healthy Communities
Objective:
The objective of this research project is to confirm the thermal efficiency of a new design for a continuous-operation, natural-updraft pyrolytic biomass gasifier cookstove constructed from indigenous materials and fabrication methods available in developing nations. The cookstove will enable smallholder farmers to utilize their biomass waste materials – i.e. maize stover, water hyacinth, etc – as a fuel to cook their food and heat their homes. Additionally, the co-product biochar may be useful as a soil amendment to marginal lands.
The performance of an existing biomass cookstove was quantified directly through temperature and emissions measurements. The results of the scientific inquiry motivated conceptual improvements to certain features that should increase thermal efficiency. While the new design primarily emphasizes performance, it does attempt to work within the constraints of indigenous raw materials and limited fabrication methods of developing nations. Preliminary construction of a clay version of the cookstove concept was tested, but material failures limited the full-scale evaluation. A sheet metal version is under construction to confirm that the design features described in the next section do indeed optimize the delivery of heat for cooking and limited emissions of particulate matter and noxious gases.
The unique cookstove design uses pyrolysis reactions that are operationally flexible to allow multiple forms of biomass fuels. This benefit would allow the technology to be applied at any location thereby reducing the reliance on wood, which is becoming a more scarce and expensive commodity. Different material densities and chemical compositions of biomass will require adjustment to operational parameters that are explored in the new design. The pyrolysis reaction also yields biochar co-products, which are more useful than the leftover ash of open fire burning. The biochar is a critical component in the sustainable life cycle of the biomass system. The inert carbon embedded in the biochar is a direct method for carbon sequestration that also has the benefit of being an amendment to improve the fertility of marginal soils. Plant growth in different mixtures of biochar and top soil will indicate the appropriate concentration levels to improve agricultural yield both of harvested food as well as leaves, stalks, and roots that can supply the biomass for the cookstove.
Summary/Accomplishments (Outputs/Outcomes):
The temperature results indicate that multiple parameters affect the delivery of thermal energy by the combustion of biogases released during pyrolysis. First, the introduction of oxygen for combustion of biogases must be controllable and uniform to get the maximum concentration of heat energy. A band of uniformly spaced holes around the circumference of the cookstove allows the oxygen to mix more evenly with the hot biogas. The rotation of a ring with the same hole pattern allows operational adjustment of the air-gas mixture that may vary depending on different materials and/or ambient conditions. Second, the primary air from natural updraft must have some diffusion through a granular pile, either through raw biomass or biochar, to limit the oxygen in the pyrolysis chamber. If the primary air delivers too much oxygen, the pyrolysis breaks down into direct burning of the biomass fuel. The new design moves the position of the primary air intake to the bottom of the cookstove. This also creates the secondary benefit of working in parallel with the biochar evacuation from the cookstove. Finally, the quantity and type of biomass added to the system influences the continuous operation. Using an airlock and gravity fed inlet, more control of known quantities of biomass can be added. These three features are incorporated into the conceptual design that will be on display at the National Sustainable Design Expo.
Emissions tests indicate that most hydrocarbons released by the pyrolysis appear to burn in the cookstove combustion chamber. Additionally, no particulate matter is observed once pyrolysis is at steady state, which is a significant benefit to end users who may use the design in enclosed structures. The rate that the hot gases exit the cookstove depends on the area constraints between the combustion zone and the exit chimney. Sufficient air velocity is required to support the passive draft of the system, but this must be balanced with regard to longer residence times of the hot gases for increased heat transfer. Further testing is necessary to find the optimal conditions that exist among the multiple parameters of biomass fuels used, dimensions of the cookstove (which may vary widely depending on the fabrication method), and ambient conditions of the environment.
Lastly, the biochar was mixed with different quantities of top soil to examine germination of seeds. Concentrations from 5–10% of biochar indicate measurable improvement in the growth of lettuce seeds. Higher concentrations ultimately lead to toxicity in the soil that then becomes a detriment to plant growth performance. Longer term and repeated tests of the same soil mixtures must determine whether food yields of seed bearing plants achieve similar performance improvements.
Conclusions:
The results show that the pyrolysis technology can use natural flow of hot gases for cookstove purposes. The passive control methods are suitable for developing nations where access to resources may be limited. The design feature improvements should result in the greater delivery of thermal energy and quantity of biochar co-products produced from the continuous-operation, natural-updraft pyrolytic biomass gasifier cookstove.
Supplemental Keywords:
Biomass pyrolysis, Variable-feedstock gasifier, Cookstove and furnace, Biochar soil amendmentThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.