Grantee Research Project Results
Final Report: Biofueled Thermoelectric Cookstove
EPA Contract Number: EPD18004Title: Biofueled Thermoelectric Cookstove
Investigators: Leavitt, Frederick A
Small Business: Hi-Z Technology, Inc.
EPA Contact: Richards, April
Phase: II
Project Period: February 1, 2018 through January 31, 2020 (Extended to November 30, 2021)
Project Amount: $300,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2017) Recipients Lists
Research Category: SBIR - Integrated Cookstove-Heating-Electricity Generation for Small Homes , Small Business Innovation Research (SBIR)
Description:
Hi-Z Technology developed a clean burning bio-fueled thermoelectric cookstove designed to be used by families in remote locations with little or no access to electric power. The stove was fueled using available bio-matter such as wood, crop residue, other plant matter and animal dung. The stove generates electric power to charge cell phones and power LED lights.
The electrical power is generated by directing a portion of the heat produced by the burning fuel through a thermoelectric module. To maintain a temperature difference across the module a portion of the electrical power produced was used to power a fan that directed cooling air across a heat sink fixed to the cold side of the thermoelectric module.
To enhance combustion, some of the cooling air was directed into the combustion zone ensuring sufficient oxygen was present to allow complete combustion of the fuel. In this manner the efficiency of the combustion was maximized allowing for the use of less fuel and essentially eliminated all smoke, thereby reducing emissions.
It should be noted though, at the request of Hi-Z's commercialization partner, Greenway Appliances of India, whose stove was modified, and with the EPA's permission, Hi-Z initially, at the beginning of Phase II: 1) designed and fabricated a Power Ring, to sit on top of their stove but returned to the Phase I stove after Greenway decided they didn't like it, and 2) devote resources on making the stove "cleaner" (instead of just cheaper). Multinationals increasing want to buy carbon offsets to fund highly efficient, lower emission stoves.
Summary/Accomplishments (Outputs/Outcomes):
Hi-Z improved the stove to increase its efficiency and lower emissions by a) minimizing heat lost, b) maximizing combustion efficiency and c) maximizing heat transfer from the hot exhaust gases into the cooking vessel.
Heat lost from the combustion chamber was minimized as follows: Blow tubes were added to ensure the combustion air was fed into the combustion chamber to ensure good mixing while preventing the flame from impinging on the combustion wall surface, thereby keeping the combustion walls as cool as possible, insulation was packed around the combustion chamber to reduce conductive and convective heat loss out the combustion chamber wall, the pot supports were lowered to increase efficiency and a pot skirt was added.
Most of the work performed during this effort was spent determining the best way to introduce air into the combustion to maximize efficiency. This problem was compounded by the fact that the cooling fan was an axial fan. Axial fans can move a lot of air but they can't build much pressure. Ultimately the best combustion was obtained with the air introduced just above the fuel with the air directed downwards towards the fuel rather than upwards.
Maximizing heat transfer into the cooking vessel was accomplished in two ways. First, it was determined that the tip of the flame needed to remain inside the combustion chamber. If the flame tip was allowed to extend beyond the combustion chamber and imping onto the cooking vessel then soot would deposit onto the cooking vessel. Since soot consists of unburned carbon, the presence of soot represent lost energy which could have been used to heat the vessel. The buildup of soot also insulates the pot impeding the flow of heat into the vessel.
The second method used to improve heat transfer into the cooking vessel was the use of a "pot skirt". Without a pot skirt hot exhaust gases contact the bottom of the cooking vessel and then pass out beyond the perimeter of the vessel where the energy contained in the hot gases are lost. A pot skirt fits around the cooking vessel redirecting hot exhaust gases from below the vessel up the sides of the vessel greatly increasing the heat transfer area.
Conclusions:
This project demonstrates that with modifications to a cook stove already popular in the targeted market segment, an improved version can result in a stove that can achieve a higher cooking efficiency with lower emissions, as well as produce electrical power.
Greenway Appliances India is Hi-Z's commercialization partner.
Greenway was founded in 2011 and is a manufacturer of naturally drafted cookstoves. Greenway sells thousands of its clean burning stoves annually in India and other Asia Pacific countries, as well as in Africa and South America.
Because Greenway already has a successful product, they have well established market channels that can immediately put a new stove in front of the customer. Many entities have attempted to provide an improved cook stove for rural Indian families but most have failed due to a lack of understanding of the convoluted distribution system necessary to get a product into the local stores.
Greenway's existing stoves are also cleaner than traditional mud stoves, as they reduce smoke by ~70%, so each stove distributed and used by an end user does qualify for a carbon credit, which has resulted in even more stove sales for the company.
Over the last few years, Greenway has received carbon offset funding to distribute their clean burning stoves from: 1) an Indian non-profit entity for stoves in a remote area of India 2) a Korean multinational for stoves in Zambia, Africa, and just recently (contract pending), 3) up to several thousand stoves from a multinational to distribute stoves in India over a few years.
With Hi-Z's two prototypes, Greenway will be able to advertise that not only is their newest stove even cleaner than their existing ones, the other prototype also creates power!
It's likely however, that the clean burning thermoelectric cookstove will be funded primarily through the carbon market than to the end user directly, due to its higher cost. While Hi-Z was not able to substantially reduce its thermoelectric module cost, in the carbon offset market, however, the attractiveness of providing power to those without, should persuade the multinationals to fund the extra amount, as they are considering the full project cost and not the individual stove.
SBIR Phase I:
Biofueled Thermoelectric Cookstove | Final ReportThe 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.