RU2122680C1 - Solid fuel combustion process - Google Patents

Abstract

FIELD: thermal engineering; combustion of solid fuels including vegetable wastes. SUBSTANCE: process involves feeding primary and secondary air streams to combustion zone as well as secondary air to inlet and outlet of combustion zone in proportion of (0.8-1.42):1.0; proportion of masses of primary and total air is 1;(3.0-68). In addition, heated air is fed to inlet of combustion zone; bin and conveyer are cooled down by some portion of secondary air. Vegetable wastes are burned in furnaces assembled with farm-purpose driers. EFFECT: improved reliability and completeness of fuel combustion, increased service life. 3 cl, 2 dwg, 3 tbl

Description

 The invention relates to a power system, and in particular to methods of burning solid fuel, and can be used for burning, for example, plant waste.

 The burning of plant waste pursues the following goals - obtaining a coolant, in particular, for grain dryers and their disposal.

 A known method of burning solid fuel / 1 / by feeding a stream of primary air mixture with an excess air coefficient α <1, burning it, mixing combustion products with a stream of secondary air mixture, afterburning the resulting air mixture with the addition of air, and the coefficient of excess air is maintained equal to α = 0.1 -0.4 in the first air mixture and α = 0.05-0.2 in the second. However, it is rather difficult to use it for burning plant wastes due to the specific properties of incineration facilities. Closest to the technical nature of the claimed method is the selected method as a prototype method / 2 / for burning solid fuel by supplying primary and secondary air flows to the combustion zone. Secondary air is supplied along the perimeter of the combustion zone and the ratio of the secondary air flow at the boundaries of the zone is maintained within 1.5 - 2.0: 1.0 with a total ratio of the mass of the primary and total air flow of 1: 1 - 1.5.

 The disadvantage of this method is that the furnaces for grain dryers, as a rule, are aggregated with air heaters, in which the flue gases heat the external air supplied to the drying of grain or seeds, and the exhaust gases are emitted through the chimney into the atmosphere. The temperature of the flue gases at the inlet to the air heater should not exceed 920 - 970K in the case of its manufacture from carbon steel and 1270 - 1340K in the case of manufacture from chrome or chromium-nickel steel / 2 /.

 The theoretical burning temperature of plant waste: sunflower husk, straw chopper, corn cobs is 1730 - 1970K (Table 1) according to experimental data confirmed by theoretical calculations.

 Given the coefficients of excess air in the prototype, the temperature of the flowing gases at the inlet to the air heater is unacceptably high. In some cases, a solid fuel firebox can be aggregated directly with agricultural product dryers without an air heater, i.e. a mixture of flue gases with air is used as a heat carrier, for example, for drying corn cobs. So in this case, the temperature of the coolant should not exceed 323 - 333K at the inlet to the dryer, i.e. requires even greater dilution of the flue gases with air than indicated in the prototype.

 We also note that for agricultural furnaces for burning plant waste, due to the economy and simplification of manufacture and operation, in particular, the use of cheap building materials (fireclay and refractory concrete), the temperature in the fuel combustion zone should not exceed 1550 - 1600K, but not should fall below 1170 - 1260K to maintain a stable combustion process (Table 2), i.e. the ratios of air flows in the combustion zone indicated in the prototype are not optimal.

 The essence of the invention lies in the fact that in accordance with the method of burning solid fuel by supplying primary and secondary air flows according to the invention to the combustion zone, secondary air is supplied to the beginning and end of the combustion zone in a ratio of 0.8 - 1.42: 1.0, moreover, the ratio of the masses of the primary and total air is 1: 3.0 - 68. In addition, heated air is supplied to the beginning of the combustion zone, and the bunker and the conveyor of the combustion zone are cooled by part of the secondary air.

 New is the supply to the beginning and end of the combustion zone of secondary air in a ratio of 0.8 - 1.42: 1.0 and the mass ratio of primary and total air is 1: 3.0 - 68, as well as the supply of heated air to the beginning of the combustion zone, and cooling of the hopper and the conveyor of the combustion zone with part of the secondary air.

 Thus, the claimed method meets the criteria of the invention of "novelty."

 The invention meets the criterion of "inventive step", because A result has been achieved that satisfies the existing need, namely: rational and efficient burning of plant waste in furnaces, aggregated with agricultural dryers with a high degree of completeness of fuel combustion, reliable and long-term operation.

 The invention is also industrially applicable, because can be used in agriculture for drying grain.

 Figure 1 shows a General view of the furnace for plant waste; figure 2 - collector of secondary air (section aa).

 The furnace consists of a diffuser 1 with partitions forming channels 2 with valves 3 for supplying primary air to individual combustion zones on the grate 4, an ash bin 5 with a conveying device 6 for removing ash (screw) from the furnace, a hot air collector 7 with valve 8, a collector 9 secondary air, rectangular tuyeres 10, junction box 11, valves 12 of this box, blowing fan 13, screwing strap 14, fuel pipe 15, secondary air pipe 16 with valve 17, lining of the furnace 18, combustion manifold 19, engine hstupenchatogo tubular air heater 20, the sedimentary chamber 21, the diffuser 22, the air heater 23 and the nozzle 27 with the valve 24, exhauster 25 and chimney 26.

 The principle of operation of the furnace is as follows. Fuel (plant waste) is fed to a nozzle 15 by a conveyor (not shown) and then it goes to the grate 4, where it is ignited and moved to ash hopper 5 by ash, unburned fuel residues and ash are removed from the furnace by conveyor 6. Primary air (for fuel combustion) enters the diffuser 1 and through channels 2 to the individual combustion zones on the grate 4. Depending on the type of fuel and its humidity, the air supply to each of the 3 combustion zones on the grate is regulated by valves 3.

 The lower channel in the diffuser does not communicate directly with the grate, it forms a cavity with a hopper 5 and an auger 6 of ash. Cooling these working bodies, the heated air through the hot air collector 7 enters the secondary air collector, where it mixes with the outside air and enters through the tuyeres 10 to the beginning of the fuel combustion zone. Air is also supplied to the secondary air manifold by the blower fan 13 through the junction box 11. Depending on the aerodynamic resistance of the material layer, the secondary air supply to the manifold 10 from the junction box 11 and the hot air collector is changed using valves 8 and 12. The secondary air supply to the end of the zone combustion to dilute the products of combustion of fuel is carried out through a pipe 16 provided with a valve 17. The diluted products of combustion through the combustion manifold 19 enter a two-stage first tubular air preheater 20, the flue gases are fed into the tube, and outside air is sucked into the air heater branch pipe 23 having a valve 24, the heated air is directed through valve 27 into the dryer. Exhaust flue gases are cleaned in the sedimentation chamber 21, sucked into the diffuser 22 and the exhaust fan 25 through the chimney are thrown out.

 The primary air is supplied through the three upper channels of the diffuser, depending on the fuel supply. The supply of secondary air (for combustion and afterburning of volatiles) is carried out at the beginning of the flame zone of fuel combustion (under the fuel layer), depending on the readings of the temperature sensor T1 and at the end of the zone of flame combustion of the volatiles, depending on the readings of the temperature sensor T2, located at the end of the zone of combustion of volatile .

 Knowing the actual temperature of fuel combustion T1, it is possible, with the goal of normal and trouble-free operation of the furnace, to calculate and implement the necessary supply of secondary air for afterburning and diluting volatiles to the beginning of the combustion zone (from the tuyere plane and above). Knowing the temperature T2, we can verify that the specified supply of secondary air to the beginning of the combustion zone is calculated correctly or correct it, as well as determine the necessary supply of secondary air to the end of the combustion zone for safe operation of the air heater, if any, or to supply the coolant to the dryer .

 Knowing the temperature of the mixture of flue gases with air at the outlet of the combustion manifold T3, one can control the ratio of the primary and total air flows.

 Examples of the implementation of the claimed method of burning solid fuel.

 The properties of plant waste as objects of combustion are shown in table 1. Table 2 shows the main parameters of the combustion process that are characteristic of the plant waste and equipment used.

 Table 3 shows specific examples and obtaining the ratio of the flows of primary, secondary and total air, as stated in the formula.

 The necessary calculations are performed according to the following formulas.

 The theoretical amount of air needed to completely burn 1 kg of fuel.

V ⁰ = 0.0889C ^p + 0.256H ^p - 0.033 (O ^p - S ^p ),
Where
C ^p , H ^p , O ^p , S ^p - respectively carbon, hydrogen and sulfur values are taken from / 4 /;
V ⁰ = 3.44 + 1.27 - 1.17 = 3.54 m ³ / kg.

Volume of combustion products
V _g = V _g + 1.016 (α-1) V ^o ≃ 5.4 m ³ / kg
Specific heat of combustion products / 3 /:
- enthalpy of outdoor air Hb ≈ 20 kJ / kg;
- chemical enthalpy H _x = Q _n / V _g = 2.53 MJ / kg;
- total enthalpy H _rev = 2.55 MJ / kg.

Air content in combustion products
V _L = (V _g -V ⁰ ) / V _g ≈ 19.5%
For the indicated values of U _about and V _i according to / 3 / theoretical combustion temperature t _g = 1900K.

где
B_т - подача топлива, кг/ч;
Q_н - низшая теплотворная способность топлива, кДж/кг;
L₀ - теоретическое количество воздуха, подаваемого на горение, м³/ч;
t₁ - температура горения, К;
t_в - температура воздуха, К;
t_т - температура теплоносителя, К;
C_т - теплоемкость теплоносителя, кДж/кг К;
C_в - теплоемкость воздуха, кДж/кг К.The calculation of the amount of air supplied to the dilution of the combustion products is carried out according to the formula / 3 /

Where
B _t - fuel supply, kg / h;
Q _n - net calorific value of fuel, kJ / kg;
L ₀ - theoretical amount of air supplied to the combustion, m ³ / h;
t ₁ - combustion temperature, K;
t _in - air temperature, K;
t _t - coolant temperature, K;
C _t - heat capacity of the coolant, kJ / kg K;
C _in - heat capacity of air, kJ / kg K.

 1. Copyright certificate 1322002, F 23 C 11/00, 1987.

 2. RF patent N 2034196, class. F 23 C 11/00, 1995.

 3. Reference thermal power enterprises of non-ferrous metallurgy. Edited by O.N. Bagrova and Z.L. Berlin.- M.: Metallurgy, 1982, p. 445.

 4. Ptitsyn S.D. Zernosushilki.- M.: Mashgiz, 1962, p. 177.

Claims (3)

 1. A method of burning solid fuel by supplying primary and secondary air flows to the combustion zone, characterized in that secondary air is supplied to the beginning and end of the combustion zone in a ratio of 0.8 - 1.42: 1.0, wherein the mass ratio of the primary and total air is 1: 3.0-68.  2. The method according to claim 1, characterized in that heated air is supplied to the beginning of the combustion zone.  3. The method according to claim 1, characterized in that the cooling of the hopper and the conveyor of the combustion zone is carried out with part of the secondary air.

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