Improved chulas principles of combusation
- 1. COMBUSTION – IMPROVED CHULHAS J. JOHN GUNASEKAR Professor (Bio-Energy) Anbil Dharmalingam Agricultural College and Research Institute Trichy Lecture 7 ERG 211 RENEWABLE ENERGY AND GREEN TECHNOLOGY (1+1)
- 2. CONTENT Combustion Improved chulha Single pot – double pot – conventional chulha Biomass gas stove – constructional features – principles and applications
- 3. THERMOCHEMICAL CONVERSION TECHNOLOGY : COMBUSTION, GASIFICATION AND PYROLYSIS Combustion of Fuels Fuel - is a combustible substance burns in presence of air/oxygen and generates heat Can be utilized for domestic and Industrial purposes. Elements present in fuel: C,H,N,O,S Principally classified based on the reaction temperature availability of oxygen residence time type of product
- 4. COMBUSTION OF FUELS Combustion of organic materials generate heat, carbon dioxide and water and also produce carbonaceous residues, smoke and tar and obnoxious gases of carbonyl derivatives, unsaturated compounds and carbon monoxide.
- 5. COMBUSTION OF FUELS The selection of right type of fuel depends on various factors such as availability, storage, handling, pollution and cost of fuel at the utility point. The knowledge on the fuel properties helps in selecting the right fuel for the right purpose.
- 6. DIRECT COMBUSTION In combustion, the waste fuel is burnt in excess air in a controlled manner to produce heat. The combustion heat is used to produce steam in a boiler. The steam is expanded through a turbine connected to a generator, thereby producing electricity.
- 7. DIRECT COMBUSTION Flue gases from efficient combustion are mainly carbon dioxide and water vapour, with small amounts of other air emissions (obnoxious gases of carbonyl derivatives, NOx and carbon monoxide), depending on the nature of the biomass fuel. The flue gases are cleaned using flue gas scrubbers, bag filters and electrostatic precipitators, and if required, further chemical processing to reduce emission of oxides of nitrogen (NOx) and other pollutants.
- 9. PRINCIPLES OF COMBUSTION Combustion refers to the rapid oxidation of fuel accompanied by the production of heat or heat and light. Complete combustion of a fuel is possible only in the presence of an adequate supply of oxygen. Oxygen (O2) is one of the most common elements on earth making up 20.9% of atmospheric air. Rapid fuel oxidation results in large amounts of heat. Solid or liquid fuels must be changed to a gas before they will burn. Usually heat is required to change liquids or solids into gases.
- 10. PRINCIPLES OF COMBUSTION N2 reduces combustion efficiency by absorbing heat from the combustion of fuels and diluting the flue gases. Nitrogen also increases the volume of combustion by-products, which then have to travel through the heat exchanger and up the stack faster to allow the introduction of additional fuel-air mixture.
- 11. PRINCIPLES OF COMBUSTION This nitrogen also can combine with oxygen (particularly at high flame temperatures) to produce oxides of nitrogen (NOx), which are toxic pollutants. C, H and S in the fuel combine with O2 in the air to form CO2, water vapour and SO2, releasing 8,084 kcal, 28,922 kcal and 2,224 kcal of heat respectively.
- 12. PRINCIPLES OF COMBUSTION Under certain conditions, carbon may also combine with oxygen to form CO, which results in the release of a smaller quantity of heat (2,430 kcal/kg of carbon). Carbon burned to CO2 will produce more heat per unit of fuel than when CO or smoke is produced. Each kilogram of CO formed means a loss of 5654 kcal of heat (8084-2430). C + O2 → CO2 + 8084 kcal/kg of Carbon 2C + O2 → 2 CO + 2430 kcal/kg of Carbon 2H2 + O2 → 2H2O + 28,922 kcal/kg of Hydrogen S + O2 → SO2 + 2,224 kcal/kg of Sulphur
- 13. 3 T’S OF COMBUSTION 1) Temperature high enough to ignite and maintain ignition of the fuel, 2) Turbulence or intimate mixing of the fuel and oxygen, and 3) Time sufficient for complete combustion. Too much fuel with the available combustion air may result in unburned fuel and CO generation. A very specific amount of O2 is needed for perfect combustion and excess air is required for ensuring complete combustion.
- 14. CONDITIONS FOR EFFICIENT COMBUSTION Combustion Controls Combustion controls assist the burner in regulation of fuel supply, air supply, (fuel to air ratio), and removal of gases of combustion to achieve optimum boiler efficiency. Conditions for efficient combustion of any fuel in a furnace: A sufficient amount of air (higher than stoichiometric amount of air) must be supplied for completion of the combustion reactions. The fuel mass and the oxygen of the air must be in free and intimate contact.
- 15. CONDITIONS FOR EFFICIENT COMBUSTION Conditions for efficient combustion of any fuel in a furnace: While burning solid biomass and other solid fuels, the volatile combustion products leaving the fuel bed must be intimately mixed with the secondary air. The volatile combustion products leaving the fuel bed must not be allowed to cool below the ignition point until the reactions are complete.
- 16. STOICHIOMETRIC CALCULATION OF AIR REQUIREMENT The amount of air needed to burn one kg of fuel completely based on combustion equations. Kg of Air = 11.53 C + 34.34 (H2 – O2/8) + 4.29 S Kg of Fuel Where, C, H2, O2 and S are the fractions by weight of each chemical constituent of the fuel. Excess Air During combustion, insufficient amount of air causes a reduction in fuel efficiency, creates highly toxic carbon monoxide gas and produces soot. To ensure enough oxygen to completely react with the fuel, extra combustion air is usually supplied.
- 17. STOICHIOMETRIC CALCULATION OF AIR REQUIREMENT Excess Air This extra air, called “Excess Air,” is expressed as the percent air above the amount theoretically (Stoichiometric) needed for complete combustion. In real-world combustion, the excess air required for gaseous fuels is typically about 15%. % O2 measured % Excess Air = ------------------------------------ x 100 20.9 - % O2 measured
- 18. STOICHIOMETRIC CALCULATION OF AIR REQUIREMENT Combustion efficiency Combustion efficiency is a measure of how effectively energy from the fuel is converted into useful energy. Combustion efficiency is determined by subtracting the heat content of the exhaust gases, expressed as a % of the fuel’s heating value, from the total fuel-heat potential, or 100%. Stack heat losses % Combustion Efficiency = 100% - ----------------------- x 100 Fuel heating value
- 19. BIOMASS COMBUSTION Biomass combustion simply means burning organic material. For ages, humans have used this basic technology to create heat and, later, to generate power through steam. Direct combustion is the most common method for converting biomass to useful energy.
- 20. WOOD BURNING STOVES In India, 80 per cent of total population lives in villages. The major energy demand of rural population is for cooking which contributes to about 98 per cent of their total energy consumption. Wood, agricultural waste and biomass are used as fuel in rural kitchen. The cooking appliances which are commonly used in rural houses have very low thermal efficiency (10 to 15 per cent) and hence per capita energy consumption in rural areas is much higher than that in
- 22. CONVENTIONAL STOVES Conventional stoves waste a lot of energy and pose many pollution hazards. Most traditional stoves can utilize only 2 – 10 per cent of the energy generated by the fuel. Black smoke emission consists of particles of sizes up to 5, CO, CO2, oxides of nitrogen and sulphur, hydrocarbons, aldehydes, ketones etc. These pollutants are detrimental to environment and to the health of rural women. It causes headache, watery eyes, common cold and sneezing.
- 23. CONVENTIONAL STOVES Conventional stoves (chulha) take more time for cooking, more difficult to fire and consume more fuel. The growing gap between availability and demand for fire wood, poor thermal performance and pollution caused by traditional stoves forced the technologists to concentrate their attention on improving the thermal efficiencies of stoves. Change Those Stoves And Save Our
- 24. TNAU SINGLE POT CHULHA The single pot chulha has a double wall with a gap of 2.5 cm. It has a grate at the bottom of the combustion chamber. The ash can be collected below the grate. The outer wall has two rectangular secondary air openings on both sides at the lower portion. The inner wall has 1cm diameter holes which maintain a triangular pitch of approximately 3 cm.
- 25. TNAU SINGLE POT CHULHA Separate mounds are provided for holding bigger and smaller vessels. The secondary air enters through the rectangular opening in the outer wall, gets heated in the annular chamber and distributed through the holes in the combustion chamber. The preheated air helps in
- 26. TNAU SINGLE POT CHULHA TNAU Single Pot Stove 1. Outer wall 2. Inner wall 3. Mount 4. Air hole 5. Leg Salient features Height : 21 cm. Inner wall diameter : 18 cm. Outer wall diameter : 24 cm. Fuel inlet opening : 15.5 x 15 cm. Leg height : 5 cm. Efficiency : 24%
- 27. TNAU DOUBLE POT CHIMNEYLESS CHULHA This double pot portable chulha (Chimneyless) is made with two walls with an air gap of 2.5 cm. There are two secondary air inlets, one on the outer wall with rectangular shape (17 cm x 1 cm) near the combustion chamber and the other circular hole of diameter 5 cm at the bottom of the second pot. A cast iron grate is placed at the bottom of the combustion chamber.
- 28. TNAU DOUBLE POT CHIMNEYLESS CHULHA Salient features Overall dimension : 55 x 30 x 25 cm (L x B x H) Fuel inlet opening : 15.5 x 15 cm Air inlet : 17x1 cm Size and No. of legs : 5x5 cm 6nos Efficiency : 26% Figure 70 TNAU Double Pot Stove 1. First pot hole 2. Second pot hole 3. Tunnel 4. Outer wall 5. Fire box 6. Air hole
- 29. BIOMASS GAS STOVE The biomass gas stove has been developed for small scale thermal application in Agriculture and allied industries. This stoves widens the market for agro wastes, makes possible a higher efficiency and in some cases reduce the time and investment, all by comparison with combustion.
- 30. BIOMASS GAS STOVE The biomass gas stove is a natural convection type updraft gasifier consisting of a cylindrical body made of clay, sand and paddy husk with its top open and bottom closed. The diameters and height of the stove are 290mm and 630mm respectively. The dimensions can be changed depending on the applications.
- 31. BIOMASS GAS STOVE An iron grate to hold the biomass is fixed at 50 mm from the base of the reactor. The bottom is provided with an air opening cum ash removal door. At the top, provision is made to place vessel for cooking, boiling etc.
- 32. EFFICIENCY OF BIOMASS GAS STOVE The conventional wood burning stoves give a thermal efficiency of 12-15 percent and the temperature of the flame obtained by direct combustion of biomass in the stove is in the range of 400-500° C only, whereas in the biomass gas stove the efficiency is 25 per cent and the temperature of the flame obtained is in the range of 600-700° C. The saving in fuel and time over the conventional wood stoves are 10 per cent and 40 per cent respectively.
- 33. APPLICATIONS OF BIOMASS GAS STOVE The biomass gas stove can be used for thermal applications in farm households, tea shops, jaggery manufacturing, small scale paddy parboiling, arecanut boiling and other agro- industrial applications.
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