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CCAT rocket stove
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This Improved Fuel Stove, or Rocket Stove, is the final project for Appropriate Technology class at Humboldt State University. The project goal is to construct a demonstration rocket stove for the Campus Center for Appropriate Technology on campus at Humboldt State University. The rocket stove will serve as an example of improved fuel stove technology and development; students and public touring the center will learn about the design, function and need for improved fuel stoves around the world. The rocket stove will also enable the residents of the center to cook with traditional biomass, reducing their dependence on petroleum based forms of energy. It is important to note that rocket stoves are designed for populations around the world who still depend on biomass for their cooking fuel. The use of rocket stoves in developed nations is not necessary. Developed nations using modern cooking methods are not faced with health and environmental issues related with traditional cooking methods. The improved fuel stove was designed, built and tested by Daniel Moyer and Tyler Jones.
Populations continue to increasingly rely on biomass for cooking fuel, thus hindering the next step toward modern cooking methods. Populations in developing nations want the same modern, self cleaning, convection, downdraft stove found in American suburbs. Many people argue that modern cooking methods are more appropriate. Modern cooking methods are efficient at fuel conversion and produce less atmospheric particulates, however the dependence on petroleum hinders the appropriateness of modern cooking methods.
Improved cook stoves are an attempt to address the negative environmental and social effects of the three rock fire. Improved Stoves increase efficiency of fuel consumption and reduce the amount of pollution released into indoor cooking environments. Improved fuel stoves designs are constructed with metal housing and insulating materials enclosing the fire. Improved fuel stoves improve heat transfer and fuel combustion, resulting in an efficient clean burning wood stove. In order to understand why improved fuel stoves are necessary, one must first look at the unhealthy and unsustainable traditional cooking methods.
Improved Cook Stove
A rocket stove is a type of improved biomass stove. Improved stoves reduce the demand for biomass fuel and improve living conditions for populations who currently use three rock fires. The main justifications for improved stoves are economical, social, and environmental. Stove programs can produce economic benefits. The stove saves time and money for the users. In urban areas, where people purchase biomass fuel, the payback time for the cost of a improved stove is short, thus providing extra cash from purchasing less fuel. "In rural areas, more efficient stove can reduce the time spent collecting fuel for cooking, freeing time for child care and income-producing activities."  Improved stoves can help moderate the environmental externalities of over harvesting trees.
Indoor Air Quality
Indoor air quality is the main driving factor in the decimation programs around the developing third world. Soot and ash produced when cooking with traditional three rock fires creates unhealthy amounts of indoor air particulates, resulting in respiratory and breathing issues. Improved indoor air quality and fuel efficiency have social and health benefits, especially for women and children. In order to reduce indoor air pollution, improved stoves must improve combustion of the wood fuel. Improving combustion reduces the amount of smoke and harmful emissions produced during the burning process. "A hotter fire burns up more combustible gases and produces less smoke" . The key to having efficient combustion is to burn wood at a high temperature. Several methods can be used to increases the temperature of the fire. Having good air draft into the fire is essential to increasing combustion temperature. Insulation around the fire can help the fire to burn hotter. "Lift the burning sticks up off the ground so that air can scrape under the sticks and through the charcoal" . The most important factor in improving combustion is metering the fuel. Metering the fuel allows only the burning portion of the wood to be heated. "Meter the sticks into the combustion chamber to make a hot, fierce, jumpy looking fire that does not make charcoal"  . Fully burned biomass fuel produces less smoke and harmful emissions reducing indoor air pollution.
Improved Fuel stoves can reduce the amount of wood fuel needed to cook. Improving the heat transfer efficiency of energy from the fire to the cooking vessel reduces the amount of energy wasted, thus reducing the amount of wood needed. In order to improve the fuel efficiency of rocket stoves you must improve the heat transfer from the fire to the cooking vessel. The crucial factor in improving stove efficiency is having the hot air and gas released from the fire contact the cooking vessel in the largest possible surface area. This is accomplished through the use of a pot skirt that creates a narrow channel forcing hot air and gas to rub along the bottom and sides of the cooking vessel. Increasing heat transfer can also be accomplished through the use of wide pots. "Using a wide pot creates more surface are to increase the transfer of heat"  . Increasing the speed of the hot gases that rub against the pot can improve heat transfer. Improved stoves are insulated and lifted off of the floor preventing childhood burns.
Improved stove programs face many political, social and economic obstacles that must be addressed if an improved stove program is going to succeed. One of the major obstacles to the success of improved stove programs in rural areas is the freely available biomass resources that lead people to continue to rely on biomass for cooking. Improved stove programs have failed in areas were fuel is not purchased or fuel is easy to collect. "Many stove programs have failed because the target group has no shortage of wood or do not perceive shortages and thus see no pressing reason to adopt improved stove" (Barnes 1994). Stove programs must be conducted in areas that have a need for improved stoves. "Programs must be targeted carefully to situations in which people pay high prices for fuel or walk long distances to collect fuel wood to other biomass materials" . Ease of use is a major concern where stoves require fuel wood to be cut into small pieces. Stove users that have neither the time nor the tools to cut the wood into small sizes, may result in the improved stove going unused. "No matter how efficient or cheap the stove, individual households have proved reluctant to adopt it if it is difficult to install and maintain or less convenient and lass adaptable to local preferences than its traditional counterpart" . The high price of the improved stoves can be a formidable barrier to their adoption. "Although in the long run improved fuel stoves save money, the initial cash outlay required may prevent poorer people from affording the stove" .
Ways to Succeed
Stove programs have a better chance of success in urban areas where people buy both the fuel and the stove. Programs in rural areas succeed where fuel wood has already been harvested and people are spending extended periods of time gathering fuel. Improved stoves that have a quick payback period generally are more likely to be adopted in poorer rural areas. "Programs have been most effective where households pay relatively high prices for wood fuels; in such cases, the improved stoves can pay for themselves in fuel savings very rapidly, even though they are usually more expensive to produce and buy than traditional stoves" . Targeting specific areas where cooking fuel is expensive can ensure improved stoves to be quickly adopted and purchased. The evaluation of improved stoves is an important in understanding how and why improvements and changes in design should be implemented.
The respect for indigenous culture is important in the improved stove design. Feedback and a two way interaction with local users should be designed in any improved stove program. "Stove dissemination programs are most effective when they allow for interaction and feedback between designers, producers, and users" . Stoves need to be adapted to each region around the world. The different styles of cooking in various countries dictate different stove designs. "Stoves should be modified or redesigned to meet regional requirements" . Improved stoves are most successful where local knowledge and customs are taken into account. "Households have been most receptive when the dissemination process takes full account of the capacities and the needs of local stove producers and consumers" . Stove programs do best in areas where people have an unequivocal need to save fuel and the improved stoves can be produced cheaply by local industries or artisans. "Improved stoves are most popular when they are easily and locally manufactured and have clear advantages in fuel economy, durability, ease of use, and cleanliness" . Populations utilizing improved stove realize the benefits and advantages to their health and local environment.
Materials used in the construction of the rocket stove main body are made from recycled metal barrels. An old lemon oil can was trimmed to the proper dimensions, becoming our pot skirt. The insulated combustion chamber is comprised of ceramic insulated bricks purchased at a local pottery supply store. The chamber is held together with eighteen gauge stainless steel metal plating fastened with 3/8 inch hardware. The hardware used to construct the rocket stove includes machine screws, nuts, washers and sheet metal screws; all hardware utilized was purchased from a local hardware store.
|Insulated ceramic bricks||$29.60|
|8 Quart Stock Pot||$19.99|
|Ceramic brick cement||$3.95|
|2 square feet Sheet Metal||$19.99|
|Misc. Nuts, Bolts and Fasteners||$20.00|
|8 Quart Stock Pot||$8.49|
|16 Gallon Drum||Free|
- The square combustion chamber was constructed out of insulative bricks. Bricks were cut and shaped using a hack saw. Heat resistant putty was used as sealant.
- A metal bracket supports a sheet metal case that holds the combustion chamber in place. The metal was cut out with tin snips and fastened with screws at the edges.
- Drill and tin snips are used to cut a square out of the barrel corresponding to the dimensions of the metal casing. The casing for the combustion chamber fits into the hole, protruding on both sides.
- The casing is firmly secured to a metal beam that stretches across the barrel. This beam is secured on both sides with L brackets.
- Vermiculite is poured into the barrel in order to insulate the combustion chamber. This insulation fills the space between the chamber and the barrel and is filled as high as the top of the chamber.
- At the top opening of the combustion chamber we constructed a metal shelf. This shelf is circular and perfectly fits inside of the barrel. It has a square cut in it corresponding to the top opening of the combustion chamber. This allows for gasses to pass through, but seals them off from the bottom half of the barrel. The shelf is secured firmly to the outside of the barrel with L brackets and screws.
- In the top half of the barrel, we constructed a skirt. This skirt surrounds the cooking pot, leaving a small gap on the bottom and the sides. The skirt was constructed out of a can. We used tin snips to cut a square opening in the bottom to channel the hot gasses. The top of the can was cut completely open with a Sawzall. The skirt is fastened to the shelf with screws and washers.
- The pot is inserted into an opening in the top of the barrel. Here we have cut out a circle with tin snips and then carefully bent the metal down at a right angle using square pliers and a mallet. This way the pot is extra sealed and the opening for it is not jagged or sharp.
- We cut a hole out of the upper side of the barrel and fastened a circular metal chimney over the hole using screws.
- To use our rocket stove, burn fuel inside the combustion chamber and set the pot inside the skirt.
- A well constructed rocket stove will allow for air to circulate. With this in mind, it is important to provide an even pathway for the air. The chimney, the combustion chamber and the skirt gap should all have the same cross-sectional area.
- Unless oxygen is being circulated, the fire will smother. When building the combustion chamber it is necessary to provide a shelf for the fuel. This way, fresh air will be pulled underneath the burning fuel.
- The chimney should be short, reaching just above the cookpot. This allows for hot gasses to flow more rapidly through the system.
- Heat will radiate from the combustion chamber. For improved efficiency, insulate around the chamber.
Testing is essential to rocket stove projects. Testing should happen throughout the entire life of a stove project. The evaluation of improved stoves helps determine if the model is marketable, whether production costs are as low as possible, and if improvements are needed. "Careful testing of stoves has resulted in a more accurate understanding of how to make a better stove. Without experimentation and testing, the development of a stove is based on conjecture"  . Technical advances in energy efficiency alone will not ensure success. Stove programs must be complemented by appropriate project design, implementation and proper institutional support. Without proper testing, stove programs will have unrealistic expectation of the efficiency of improved stoves. Stove programs can overestimate the efficiency of improved stoves when tested in a controlled lab setting. Improved stoves never do as well in real households. "The fuel savings that can be attained in a laboratory often have little relationship to savings possible under field conditions"  . Many stove programs in controlled lab settings achieved a 75% reduction in fuel consumption. After examination of early stove programs, fuel efficiency expectations of improved stoves have been substantially reduced. "Most people in the stove community now agree that a 50% decrease in fuel consumption should be considered a major achievement and that should be content with a savings of 25% or even less" . Laboratory settings can be valuable with designing and initial testing of improved stoves; testing in field conditions can ensure the final product is built and designed correctly. Producing a stove design that adheres and conforms to local culture is vital in ensuring a successful stove program.
Types of Testing
In testing our stove, we wanted to find out how long it would take to boil water and how much wood was being used. We also inspected the ashes to determine if the wood was fully combusted. Ultimately we did three types of tests.
- We boiled water from a cold start and from hot start. Hot start means that we started the test when there was already wood burning. The starting temperature for the water was sixty three degrees.
- We maintained a boil for 30 minutes. We did not start the clock until all of the wood that initially brought the water to a boil had burned out. This gave us more accurate results.
- It took 13 minutes and .36 pounds of wood to heat four liters of water 108 oF. This was done from a cold start (nothing burning initially). The starting temperature was 62oF and the final temperature was 170oF.
- From a hot start, it took 10 minutes and .56 pounds of wood to heat the same volume of water 149 oF. The starting temperature was 63 oF and the final temperature was 212 oF.
- From a hot start, it took 11 minutes and .72 pounds of wood to heat six liters of water 146 oF. The starting temperature was 64 oF and the final temperature was 210 oF.
- To keep six liters of water boiling for half of an hour it took .18 pounds of wood. The starting temperature was 212 oF and the final temperature was 210 oF.
The results of our testing demonstrated that the project was a success. The first thing that we noticed was that the air circulation is excellent. We never had a problem getting enough air into the fire or with having smoke back out of the combustion chamber. This makes starting a fire very easy. Also, we were happy to see that there were hardly any ashes left over. The wood burned hot and combusted completely. Although the top of the stove gets hot when the fire is burning fast, the vermiculite does a very good job of insulating the bottom part. The lower half of the stove never got too hot to touch and the very base never even got warm. Once a fire is going, it must be tended regularly. As well as adding new wood as the fire burns, it is important to constantly push burning pieces all the way into the chamber. Our stove is very efficient. To cook spaghetti in our stove would require roughly one pound of wood and would take only a few minutes longer than a regular stove. By using a lot of wood and creating a big flame, it is possible to boil water quickly. With less wood, the same amount of water can be boiled but it takes longer. It takes a lot of wood to heat water initially, but to keep it boiling requires very little wood. One pound of wood would keep six liters of water boiling for about two and a half hours. When our stove is burning, the pot and the skirt get a lot of soot. Periodically, it will be necessary to clean this soot out.
In building a rocket stove, we learned some important things. First, it would be possible to construct this type of stove using only recycled materials. The hardware would be the most difficult to find. It would also be possible to construct our rocket stove with out the use of power tools. We could have used a hammer and spike instead of a drill. We also could have used a hacksaw instead of a Sawzall. We only used this tool once, to cut the skirt out. As we anticipated, the top of the stove got hot. If our stove was placed inside of another barrel and insulated, it would be more user-friendly. Personally, I would rather deal with the hot surface than to put more work into the stove. In a situation where there were children using the stove, the hot metal could be dangerous. The one thing that our stove lacks is a shelf for extra long pieces of wood to rest on while they are combusting.
Populations around the world are going to continue to use biomass fuel for the indefinite future. The use of improved stoves can help control the external costs to both the environment and human society. "It seems inevitable that an increasing amount of biomass fuel will be bought and burned in purchased stoves" . Fuel savings may not be the driving factor in the adaptation of improved stoves. Improved stoves work because they make cooking quicker, safer, and cleaner. Improved stoves protect children from the dangers of burns from the open fire, reduce respiratory diseases, and burn clean and free of soot.
- Barnes, D.F., K. Openshaw., K.R. Smith., and R.V. Plas. What Makes People Cook with Improved Biomass Stoves? World Bank Technical Paper No. 242. Energy Series. Washington, D.C.: World Bank.
This publication from the World Bank gives a comparison of stove programs throughout the third world. The paper gives an overview of the general lessons from stove programs: consumer preferences, stove design, role of government and donor agencies and the role of subsidies. The paper presents the role of politics in improved stove programs; considerable information regarding the emergence of government based stove programs is included in the paper. Advantages of included the stove market and consumer preferences section. This topic was not specificity addressed in any other publication. The main disadvantage of this publication is the role to the publisher. The World Bank has provided this paper with good intentions that must be questioned.
- Bryden, Mark., Dean Still., Damon Ogle., and Nordica MacCarty. 2001. Designing Improved Wood Burning Heating Stoves. Creswell, OR: Aprovecho Research Center.
- Witt, Mark., Kristina Weyer., David Manning. 2006. Designing a Clean Burning, High Efficiency, Dung Burning Stove: Lessons in cooking with cow patties. Creswell, OR: Aprovecho Research Center.