Improved rice husk gas stove in the Philippines
Improved rice husk gas stove in the Philippines
Rice husks are the largest by-product of the rice milling industry in the world. They are often discarded, causing environmental pollution. Mr. Alexis Belonio T. of the Philippine Rice Research Institute has used rice husks as a fertilizer additive and as a biofuel for cooking. He has designed a gas stove that uses rice husks as fuel. With the increasing price of fuel, especially liquefied petroleum gas, rice husk gas stoves are an effective and environmentally friendly alternative. This stove is designed from an improved Vietnamese rice husk stove that is very popular in rural areas of the Mekong Delta (Figure 1).
In the Philippines, the price of a rice husk gas stove is about 45 USD/unit (954,000 VND/unit). One kilogram of rice husk cooks in one hour. Using this stove costs only 0.06 USD/hour (1,272 VND/hour) compared to a gas stove which costs up to 0.38 USD/hour (8,056 VND/hour). Therefore, the rice husk gas stove won the "Energy Globe" award in 2014 in the Philippines along with many other awards, because it has the potential to be widely popularized in rice-growing countries such as Sri Lanka, Vietnam, India and Cambodia...
Rice husk gas stove has the following advantages:
- Very promising to replace gas stoves in the cost-saving field, the stove produces a blue flame without smoke. One ton of rice husks will be converted into 23 11 kg gas cylinders (3.95 kg of rice husks produce 1 kg of gas).
- Reduce family expenses for cooking, rice husk price is cheaper than electricity, liquefied gas, firewood, coal
- Reduce environmental pollution caused by dumping rice husks into canals and burning them. In the Philippines, using rice husk gas stoves consumes 1,095 rice husks/year.
- Reduces CO2 emissions compared to traditional coal or firewood stoves. Reduces pressure on deforestation for timber exploitation, 1 ton of rice husk is equivalent to 847.45 kg of firewood or 510.20 kg of charcoal.
- Create more jobs through production and distribution of stoves and rice husks to homes.
1. Structure of rice husk gas stove
a. Chamber to burn rice husk to create gas
This is a chamber that holds rice husks and burns them in anaerobic conditions to convert them into gas. The chamber is a round tube with a diameter of 10 - 30 cm, 40-110 cm high depending on the rice husk storage capacity serving the number of people in the household. The chamber burns rice husks with 2 layers, the outer tube is made of galvanized iron No. 18, the inner round tube is made of stainless steel No. 20. The outer tube and the inner tube are 2 cm apart, in the middle is inserted non-flammable insulation material such as rice husk ash. At the bottom of the chamber there is a stainless steel mesh to both hold the rice husks and discharge the rice husk ash after cooking.
The outside of the gas husk chamber has a protective aluminum mesh layer to prevent scalding.
b. Rice husk ash chamber
The ash chamber is located below the combustion chamber. The chamber has a slot for easy removal of the husk. The chamber must be airtight to receive air from the fan blowing upwards.
c. Fan
A fan is attached to the furnace to blow air for the rice husk to gas conversion process. The axial fan is 3-inch diameter and is powered by electricity.
d. Burner
The burner converts gas from the combustion chamber into blue flame. The circular burner has 1 row of holes 3/8-in. in diameter. The second row of holes on the outside provides air for complete gas combustion without smoke.
Above the burner is a pot holder for cooking.
Figure 2: Detailed structure of rice husk gas stove components
2. Effectiveness
After filling the combustion chamber with rice husk, ignite the rice husk with a piece of paper. Under anaerobic combustion conditions, carbon monoxide (CO), hydrogen (H2), and methane (CH4) gases are produced. Other gases include carbon dioxide (CO2) and water vapor.
The layer of burnt rice husk in the chamber will move down at a speed of 1-2 cm/min depending on the amount of air supplied and consume 1.59 - 2.0 kg of rice husk/hour. Boiling 1 liter of water (from 29 oC to 100 oC) takes 8 - 9 minutes. Cooking a pot of rice for 4-6 people takes 9-12 minutes.
Figure 3: Operating principle of rice husk gas stove
Advantages of rice husk gas stove:
- The stove starts easily, ignite the stove with a piece of paper, when gas is generated, light the fire with a match;
- Almost no smoke during cooking. This is the biggest advantage compared to traditional rice husk stoves and wood stoves in the countryside;
- Fill the jar with 2 kg of rice husks to cook a pot of rice and 2 dishes for 4-6 people;
- Flame can be adjusted through fan speed;
- Ash after burning is a material used in soil improvement, as a growing medium for vegetable and flower varieties;
- Very safe, not flammable or explosive like liquefied gas cylinders
However, rice husk gas stoves also have disadvantages:
- Difficult to popularize in places where rice husk is not available. The stove is designed to burn rice husk, cannot use other materials;
- Rice husk is a bulky material, difficult to transport and store. In the Philippines, the government encourages factories to distribute rice husk to households through tax policies.
- Need electricity to run the fan, in areas without electricity can use 12 volt battery and transformer.
The current price of a 12 kg gas cylinder is 413,000 VND/cylinder, equivalent to 34,416 VND/kg, while the average price of 1 kg of rice husk is 500 VND/kg, producing 1 kg of rice husk gas costs only 2,000 VND/kg. On the design of the rice husk gas stove in the Philippines, mechanical factories are encouraged to produce in conjunction with rice milling factories to organize distribution to create products with added value.
According to Bannhanong