RU2236643C1 - Method of and device for combustion of hard fuel, mainly, wood wastes - Google Patents

Abstract

FIELD: agricultural, timber and wood-working industries.

SUBSTANCE: proposed method of combustion of hard fuel-wood wastes comes to loading of fuel, drying, combustion and after-burning. Part of flue gases is used for drying, their consumption is brought to minimum. Consumption of flue gases is determined by formula Q_a=Q_d(1+τ_l/τd ^. n), where Q_a and Q_d are actual and designed consumption of flue gases taken for drying; τ_l, τ_d are duration of loading cycle and loaded fuel designed combustion cycle; n is number of connected flue gas sources. When loading the fuel, drying is not carried out. Device for combustion of hard fuel, namely wood waste contains at least two drying columns, at least two combustion chamber, after-burning drying columns, at least two combustion chambers, after-burning chamber heat exchanger and smoke sucker. Drying columns are connected to each other in lower part by gas lines to bypass flue gases, and are connected in upper part by gas lines with valves making it possible to regulate taking off of flue gases from combustion chamber for drying columns and are connected to smoke sucker through upper part of heat exchanger.

EFFECT: provision of more complete combustion of hard fuel and equalizing temperature of flue gases in time.

3 cl, 1 ex, 3 dwg

Description

The invention relates to a technology for burning fuel, mainly plant waste, and can be used in agriculture and the timber and wood processing industries in the production of heat, heated air and water.

Known methods of burning solid fuel by periodically loading it on the grate, drying, igniting and burning the volatiles, burning the coke residue and a device for its implementation, comprising a housing, a combustion chamber and a grate (Kostanyan K.A. et al., Fuel and its use, Moscow, publishing house of the People's Commissar of the RSFSR, 1938, p. 52-53).

This method is simple, but it is inefficient, characterized by low completeness of fuel combustion.

The closest analogue of the claimed method is a method of burning solid fuel, in which it is loaded, dried and afterburned volatile substances, and part of the flue gases is diverted for drying (SU 951001 A, F 23 B 1/04, 08/15/1982). The same source of information describes a device for burning solid fuel, containing drying shafts, combustion chambers, afterburner, heat exchanger and smoke exhaust.

The disadvantages of the known method and device are the insufficient completeness of fuel combustion and significant fluctuations in the temperature of the flue gases over time, due to a violation of the tightness of the drying chamber during loading and moisture fluctuations in the fuel supplied to gasification and combustion.

The objective of the invention is to increase the completeness of combustion of solid fuel and equalize the temperature of the flue gases in time.

The problem is solved due to the fact that in the method of burning solid fuel - vegetable waste, in which they are loaded, dried, burned and burned, and for drying, part of the flue gases is diverted, the flow rate of which is minimized, the flow rate of distracted flue gases is determined by the formula

Q _f = Q _p (1 + τ ₃ / τ _p · n),

where Q _f and Q _p - the actual and estimated costs of exhaust gases for drying; τ ₃ , τ _p - the duration of the cycles of loading and generation of loaded fuel; n is the number of connected flue gas sources, and when loading, drying is not carried out.

The problem is also solved due to the fact that the device for burning solid fuel - vegetable waste contains at least two drying shafts, at least two burning chambers, a afterburner, a heat exchanger and a smoke exhauster, and the drying shafts in the lower part of the ducts are connected to each other to a friend with the possibility of bypassing the flue gases, and in the upper part - gas ducts with valves that allow controlling the selection of flue gases from the combustion chambers to the drying shafts, are connected to the smoke exhauster through the upper part of the heat exchanger.

The invention is illustrated by drawings.

Figure 1 shows a diagram of a device with two drying shafts; figure 2 - technological scheme of aggregation of the device with bins BV - 40, in which the grain is dried.

The device includes drying shafts 1, 2; combustion chambers 3, 4; step grate 5, 6; overturning grate 7, 8; afterburner 9; heat exchanger 10; duct 11.12; air duct damper 13.14; chimney 15; fan 16; primary blast air network 17; secondary blast air network 18; boot means 19; heated air fan 20; active ventilation bunker (BV - 40) 21; noria 22; hopper screw 23; combustion chamber door 24; ash chamber door 25; valves 26, 27, 28, 29; the partition 30, 31; cover 32, 33; pipe 34, 35; air valve 36, 37; smoke exhaust 38; duct 39, 40.

During the implementation of the method, fuel is loaded into the drying shaft, dried, burned and afterburned volatiles, drying is carried out by diverting part of the flue gases in accordance with the formula Q _f = Q _p (1 + τ ₃ / τ _p · n), and when loading, the flue gases are dried do not serve.

The kindling material is placed on the grate 7 and the combustion chamber 3 is melted. Fuel is supplied to the drying shaft 1 by the loading means 19, while the valves 26 and 27 are closed. To fill the shaft 1, open the valves 26 and 27, form the position of the partition 30, the thickness of the fuel layer on the grates 5 and 7. Then replenish the shaft 1 with fuel and close the lid 32. The flue gases with suspended particles from the combustion chamber 3 enter the chamber 9, where they are burned, then the flue gases enter the heat exchanger 10 and the exhaust fan 38 through the chimney 15 is emitted into the atmosphere. In a similar way, fuel is loaded into chamber 2, melted, and grates 6 and 8 are filled.

The necessary temperature regime of fuel combustion is established by changing the primary blast supplied through the network 17, and the secondary blown through the network 18. Moreover, the temperature in chambers 3, 4 and 9 is maintained at about 1000 ... 1100є C, which is 50 ... 100є C lower slag grates and chamber walls. As the fuel burns out, its layer in the chamber 1 is lowered, focal residues are removed when the grate 7 is rotated, ash and slag are manually removed through the door 25.

The heat output of the device is summed up from the heat output of chambers 3 and 4, and during the subsequent loading of mine 1, the fuel level in it is lower than the level of valves 26 and 27. Upon receipt of the burning of wet fuel, it is dried by supplying part of the flue gases from the chamber 3 to the shaft 1, the selection of flue gases is regulated by changing the position of the valve 36, the pipe 34 is connected to the upper part of the heat exchanger 10, the duct 39. When replenishing the shaft 1 with fuel, the valves 26 are closed, 27, the shutter 13 on the duct 11 is opened and part of the flue gases is supplied to the fuel layer in the mine 2 through its ducts, thereby speeding up the process of drying the fuel in the mine 2. In a similar way, part of the flue gases is sent to the mine 1 when replenished and fuel shafts 2, wherein the alignment load cycles in mines is not tolerated. The heat capacity of the device is changed by the position of the valves 26 and 27 on the chamber 1 and the corresponding valves on the chamber 2.

Outside air is sucked into the heat exchanger 10 by the fan 20, heated and sent to the hopper (BV - 40) 19, which is aggregated with a device for burning solid fuel. The hopper 19 is loaded with wet grain using elevator 22. Heated at 10 ... 15є С air in an amount of 10 ... 12 thousand m ³ / h enters the inner pipe, penetrates the grain layer in the radial direction and dries it. Grain of conditioned humidity is unloaded using a screw 23 and elevator 22 and sent to the consumer.

Vegetable waste: chopped straw, sunflower husk, cobs, chopped stalks of corn and sunflower, as well as waste from the timber and wood processing industries, as a rule, have high humidity, reaching 20 ... 25% or more. Burning fuel with high humidity is ineffective, because the heat output of the device decreases, fuel losses with focal residues increase, so it must be dried before burning, which is provided for by the design of the device.

The permissible moisture content of plant waste coming to incineration, determined experimentally in the laboratory and during an economic audit, is: for sunflower husk - 17-18%, for chopping straw, corn cobs, chopped corn stalks, sunflower - 20-22%, for straw , grass briquettes - 18-20%, for sawdust and wood chips - 25-28%. At a humidity below the specified level, a stable combustion process is ensured, minimum losses with entrainment and focal residues, and the minimum amplitude of the temperature fluctuation of the flue gases in time.

Drying is carried out with a part of the flue gases leaving the upper part of chambers 3 and 4, having a temperature of no higher than 300 ° C, which simplifies the design of the drying shafts, prevents loss of fuel with volatile substances and, at the same time, allows to be limited to a relatively small part (no more than 25 %) flue gases. The selection of flue gases in the drying shaft is regulated by the position of the damper 36. The temperature of the gases leaving the heat exchanger 10, it is advisable to maintain at least 80 ... 100є C in order to avoid the formation of condensate.

It is obvious that the drying process is possible with the lid 32 closed, otherwise the flue gases may not enter the drying shaft, since a small vacuum must be maintained in the afterburner 9.

Consequently, continuous loading is excluded, and in case of cyclic loading, it is necessary to provide an increased supply of flue gases to the fresh fuel against the calculated one to exclude the entry of moist material into the combustion chamber, and the larger the mass of fuel being loaded, the longer the loading cycle and the majority of the flue gases should be distracted for drying, i.e. the actual consumption Of diverted flue gases for drying can be written

Q _f = Q _p (1 + τ ₃ / τ _p · n),

where τ ₃ is the duration of the load cycle; τ _p is the duration of the fuel generation cycle, i.e. time until the next boot; n is the number of sources from which flue gases are supplied; Q _p is the estimated supply of flue gases for drying, determined by the known mass, humidity and the upper limit of permissible humidity with which the fuel enters the combustion chamber.

Indeed, the smaller the value of τ ₃ and the greater n, the less it is necessary to apply Q _f for drying.

The proposed device contains two drying shafts, however, depending on the type of fuel, the afterburner can be aggregated with 3 or more drying shafts.

The connection of the drying shafts 1 and 2 by flues to the upper part of the heat exchanger 10 is due to the need for additional cooling of the flue gases. Cooling the flue gases from the afterburner 9 at the outlet of the heat exchanger below 180 ... 200 ⁰ C is not economically feasible, as this causes a significant increase in its heat exchange surface, dimensions and cost of the device. This is due to low coefficients of heat transfer from the flue gas heats the air (K = 30 ... 35 W / m ² · ^Je C). To a lower temperature (80 ... 100є C and below), you can cool the flue gases in the drying mines, in which the heat transfer coefficient, and most importantly the heat transfer surface is many times higher. Diluted flue gases with a temperature below 180 ... 200 ° C can be evacuated from the heat exchanger by fan units in a heat-resistant or conventional design, which are significantly cheaper than a smoke exhauster. The supply of flue gases to the lower part of the heat exchanger due to their low temperature potential is impractical, since it will reduce the efficiency of the heat exchanger.

Example 1. Burning husks of sunflowers with a moisture content of ~ 25%. Laboratory studies have established that a stable combustion regime with a regulated temperature and minimal fuel loss is possible at a moisture content of not more than 17%, i.e. drying is required at 8%.

We take the heat output (power) of the device to 250 kW, which is enough to dry the grain in the OBV-160 compartment, consisting of 4 BV-40 bins with a capacity of 40 tons of wheat each.

The calorific value of sunflower husk is 14.2 MJ / kg, the efficiency of the device is ~ 70%, it is equipped with two drying shafts, i.e. when drying, use n = 1 heat source, two combustion chambers, one afterburner, heat exchanger, fuel loading means. The total fuel supply will be ~ 100 kg / h, and the throughput of each drying shaft is 50 kg / h. The air supply for burning fuel to each combustion chamber with a specific theoretical supply of g ≈ 6 kg of air / kg of fuel and an excess air coefficient of τ _B = 1.3 will be ~ 390 m ³ / h, and part of the flue gases to be dried to dry the fuel is up to 17% Q _p ≈ 63 m ³ / h or ~ 16% of the total consumption of flue gases in each combustion chamber.

We take the dimensions of the drying shaft: diameter 0.6 m, height 0.6 m, then its capacity with a bulk fuel mass of ~ 300 kg / m ³ will be 50 kg, we also take the loading cycle duration τ ₃ = 10 min, and τ _p will be 60 min In this case

Q _f = Q _p (1 + τ ₃ / τ _p · n) = 63 · (1 + 10/1 · 60) = 73 m ³ / h.

According to the data obtained during laboratory tests and the above calculation, fuel losses with mechanical underburning and entrainment will not exceed 2 ... 3%, i.e. as when burning high-quality solid fuel, and the temperature change of the flue gases from the receipt of a fuel not equal in moisture content will not exceed 1 ... 2%, which is quite acceptable when preparing a coolant for grain dryers and active ventilation units (OBV-160).

Claims (2)

1. The method of burning solid fuel - plant waste, in which they are loaded, dried, burned and burned, and for drying, part of the flue gases is diverted, the flow rate of which is minimized, characterized in that the flow rate of the distracted flue gases is determined by the formula Q _f = Q _p (1 + τ ₃ / τ _p · n), where Q _f and Q _p - the actual and estimated costs of exhaust gases for drying; τ ₃ , τ _p - the duration of the cycles of loading and generation of loaded fuel; n is the number of connected flue gas sources, moreover, when loading, drying is not carried out. 2. A device for burning solid fuel - vegetable waste by the method according to claim 1, containing at least two drying shafts, at least two burning chambers, a afterburner, a heat exchanger and a smoke exhaust, and the drying shafts in the lower part are connected to each other by gas ducts the possibility of bypassing the flue gases, and in the upper part with flue gas ducts with valves allowing to regulate the selection of flue gases from the combustion chambers to the drying shafts, are connected to the smoke exhauster through the upper part of the heat exchanger.

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