SU1746143A1 - Method of automatic control of fuel/air ratio in multizone furnace - Google Patents

Description

the gas-air ratio in this zone deviates significantly from the stoichiometric one. So, if the specified air flow rate in the preceding zone is greater than this, the air flow rate in the burner of this zone decreases. When its value is less than 0.6, a blooming plume is formed, the heat exchange in the furnace deteriorates dramatically. In addition, the length of the combustion zone increases due to the afterburning of part of the fuel in the lean oxidizer-smoke from the preceding zones. The combustion process continues in the methodical zone, and in case of its insufficient length, in the smoke and hogs. The temperature of the leaving smoke rises, fuel consumption deteriorates.

If the specified air flow rate in the preceding zone is less than this, the ratio of the air and fuel consumption in the burners of this zone increases. When the air flow rate is greater than 1.6, vibrations and flames from the burner nozzles start, torches can be lost and extinguished, which requires an emergency stop of the furnace.

The aim of the invention is to improve the control accuracy, reduce the specific fuel consumption, prevent underburning and impair combustion stability.

The essence of the method is to regulate the supply of fuel and air to each zone of the furnace after the first in the working range of ratios while maintaining the required balance of fuel and air to the furnace. If the ratio of the air and fuel flow rates in each zone after the first from the stoichiometric ratio to the marginal air flow rate deviates from the adjacent air zone, the air to fuel ratio changes by redistributing the total air flow between this and the adjacent air zones. At the same time, the air supply is reduced to the zone with a large predetermined ratio of air and fuel consumption and increased to the zone with a smaller specified ratio,

Combustion of fuel in zones with an air flow rate not lower than the minimum allowable level prevents the formation of a blooming flare and deterioration of heat exchange conditions. The fuel entering the zones is burned within their limits, the degree of heat utilization of the leaving smoke in the methodical zone increases and underburning is eliminated, which contributes to fuel economy. Air supply to the burners in quantities not higher than the maximum allowable prevents emergency shutdowns of furnaces due to

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flare failures. The reduction in unplanned stoppage of furnaces in this connection also reduces fuel consumption.

The method is carried out as follows. Zonal regulation systems are set to given ratios

Dov air and fuel si, ..., a. g

The flow rates of gas and air in each zone are measured, and the ratios of the flow rates of air and fuel in each zone after the first in terms of the costs in this zone and the preceding zones are estimated.

When deviations of these ratios from the given values change the air supply to the zones until the deviations are eliminated.

At the same time, the ratio of the air and fuel consumption in the burners of each zone after the first aa aa ao is compared.

With a stoichiometric ratio and when deviating to the maximum air flow rate, the ratios of air and fuel consumption in the adjacent preceding zone are changed. When it rises under the conditions of a3 nI, the maximum allowable a; the premax increases the given ratio of air and fuel consumption in the adjacent preceding zone, increases the air flow into it and decreases by the same amount into this zone, stabilizing a

, before

(ZIM3KCWhen reducing the ratio of thermal powers of the preceding and given zones, the correction value of stn is gradually reduced to 0, maintaining further

Zn

set a and a s in zones. When reducing an to the minimum acceptable "before min K, the specified ratio in the adjacent preceding zone is reduced, the air flow to the preceding zone is reduced by the same amount and increased in this to ensure aV apreA min.

With a decrease in the thermal power of the preceding zone or an increase in it in a given ratio of air and fuel consumption in the preceding zone, it is reduced to sgnm, maintaining

significant relationship a la m

The drawing shows the block diagram of the device that implements the method.

The device includes zonal flow meters 1 (16, etc. by the number of heated zones) gas, adders 2 (17), unit 3 (18) gas-air, blocks 4 (19) multiplied and, air flow meters 5 (20), adders 6 (21), blocks 7 (22) of comparison, blocks 8 (23) of switching, regulators with amplifiers 9 (24), actuators 10 (25), executive bodies 11 (26) of air flow, setting devices 12 (27) limit ratio of gas-air per zone, blocks 13 (28) multiplication, blocks 14 (29) comparisons, threshold elements 15 (30)

Flow meters 1 (16 and so on) are connected to adder 2. Outputs of adder 2 and setpoint 3 are connected to block 4. Flow meters 5 (20, etc.) are connected to adder 6. Outputs of blocks 4 and 6 are connected to inputs unit 7, which is connected via the switching unit 8 to the input of the regulator 9. The output of the regulator 9 is connected via the actuator 10c to the executive unit 11. The setting unit 12 and the flow meter 1 are connected to the unit 13. The inputs of the unit 14 are connected to the outputs of the unit 13 and the flow meter 5, and its outputs are with the inputs of the threshold element 15 and the switching unit 23 of the preceding zone, One threshold element 15 is connected to block 23. The inputs of block 8 are connected to a threshold element and a block comparing the limiting and actual air flow to the subsequent zone. Flowmeters 1 and 5 are connected to the corresponding adders of the subsequent zones. Blocks 16-30 of the preceding zone, like other zones, are connected in the same way.

The device works as follows. The setting units 3 and 18 set the required ratios of gas and air flow rates in this and the adjacent preceding zones of the furnace, and the setting units 12 and 27 set the limit ratios. If the setting device 18 is set to "more than the setting device 3, then the setting device 12 sets the minimum allowable apredmin, and otherwise the maximum allowable compression equipment max. Similarly, adjust the setpoint 27.

The signals from the gas flow meters to this zone 1 and the preceding ones (16, etc.) enter the adder 2. The signals from the adder 2 and setpoint 3 are multiplied in block 4. The signals from the flow meters 5 (20, etc.) of air to this and the preceding zones are summed up in block 6, after which, in block 7, the signals from blocks 6 and 4 are compared. When the air flow rate in the burner of the adjacent subsequent zone is equal to a ni + i, the apredmax unit 7 is connected via switch unit 8 to controller input 9 , and the unit for comparison of the limit and actual air flow to the next zone is turned off from the regulator 9. From the signal from the block 7, the regulator 9 is activated and through the actuator 10 acts on the executive body 11 of the air flow until it reaches the correspondence between the required unit 3 and the actual flow

air in the given zone taking into account supply of gas and air to the previous zones. Blocks 16-30 of the base system in the adjacent preceding zone work in a similar way.

The product of the signals of the flow meter 1 and the setting device 12 comes from the output of the block 13 to the block 14, where it is compared with the signal of the flow meter 5. When the flow rate deviates

10 air to the limiting threshold element 15 acts on block 23, connecting block 14 to the input of controller 24 of the adjacent preceding zone and disconnecting from it block 22 of comparison,

5If the setting device. 12 set a premax

and the signal of sensor 5 exceeded the signal from block 13, through block 23 to controller 24, the signal from block 14 is supplied to increase the air supply. The controller 24 by means of the executive mechanism 25 opens the actuator 26 on the air duct of the adjacent preceding zone. The increase in air flow in it leads to an increase in the signal from the flow meter 20. Sig5 signal from block 6, the antiphase signal from block 4. increases, and from block 7 output, through block 8, a signal is received to reduce air flow to regulator 9. It is using mechanism 10 and the executive body 11 reduces air flow in this zone, which reduces the sensor at the input of the adder 6. The controller stops working when the balance of signals from blocks 4 and 6. The air flow to this zone decreases by 5 seconds by the same amount increases by the adjacent previous zone.

At the same time, the signal from the flow meter 5 at the input of the unit 14 is reduced. With the balance of signals from the blocks 5 and 13 at the input

0 of block 14 (when the air flow rate in this zone is equal to the maximum allowable), the controllers 24 and 9 stop changing the air flow into the zones. When the signal from block 13 exceeds the signal from the flow meter 5, the threshold element 15 is activated, block 23 disconnects block 14 from controller 24 and connects block 22 to it. Further regulation is performed as in the basic version.

0 When the air flow ratio 1 set in block 12 is set, the premin is changed to the reverse sign of the air flow correction c. the previous zone and the operation of the system is similar.

5 Tests were carried out on a ring furnace of a 18.2 m ring rolling line for heating billets made of carbon and alloyed steels up to 1150-1260 ° С. The furnace has four heated natural gas zones and a methodical numbering of the heated zones taken along the metal. The specified air flow rate, 0,, 2; aa, 8. The values of the maximum and minimum allowable air flow rate on the burners were preliminarily determined before the pre-max 0.6 and premax 1.65. The temperature regime was maintained according to the technological instruction. Thus, the production of tires and rings from blanks with a diameter of 520–530 mm and a height of 190–210 mm of medium carbon steel is provided by the rolling equipment of the line at a level of 60–30 pieces per hour depending on the complexity of the rolled section.

With a furnace capacity of 40 blanks per hour, the metal was heated to 1240–1260 ° C at a temperature in the I – IV zones of 1180.1240.1280, 1290 ° C and the fuel consumption in them was 350, 430, 320, 220 m3 / h. Taking into account the stoichiometric amount of air of 9.8 m3 / M3, the air flow was set in zone IV and II: 220 0.8 9, m3 / h and (220 + 320) 0.8 9.8-1725 2510 m3 / h. Then the required air flow to the second zone was determined: (2.0 + 320 + 430) 9.8 1.2-1725-2510 7170 m3 / h and the maximum allowable: 430 1.65 9, m3 / h Since the required air flow exceeded the maximum permissible, increased the ratio of air and gas consumption in zone III by increasing the air flow to it by 7170-6950 220 m / h and maintained air flow in zone III at the level of 2510 + 220 2730 m3 / h, and in zone II - 6950 m3 / h Then, the required air flow into the zone was determined: (350 + 430 + 320 + 220) 1.0 9.8-1725-2730-6959 1530 m3 / h and its limit value 350 0.6 9.8 2060 m3 / h.

Since the required air flow rate is less than the limit, the ratio of air flow to gas in the P zone was reduced, reducing the air supply to it by 1530-2060 -530 m3 / h and maintaining air flow in the I zone to 2060 m3 / h. At the air flow rate in zone II 6950-530 6420 m3 / h, the air flow rate for the flow in it was a z 1.5, which is lower than the maximum allowed. Therefore, the ratio of air and gas flow rates in zone III was reduced to the required a, 8 by reducing the air flow therefrom from 2730 to 2510 m3 / h, and in zone II, the air flow was set at 6640 m3 / h, which is less than the maximum permissible (6950 m3 / h ), and regulation was stopped at the coefficients of air flow (in terms of balance) a, 0; a 2 1.15; a, 8 and air flow rates for flow, 6; , "V aVo.8

The temperature of the escaping products of combustion in the smoke was 930–940 ° C, the formation of a blooming flare in the I zone and the burning of fuel in the methodical zone

was observed. In zone II, steady burning was ensured without vibrations and stall failure. The specific consumption of topdive was 111.9 kg / ton.

Comparative tests in combustion management according to a known method were carried out with the same distribution of gas consumption by zones (350, 430, 320, 220 m3 / h) and air flow rate (1.0; 1.2; 0.8; 0.8 ;). Air flow in the I-IV zone

1530, 7170, 2510, 1725 m3 / h were maintained.

At the same time, in the 1st zone, the air flow rate for the supply was 0.45, due to the formation of bloating plumes from the burners of the zone, overheated fuel was discharged through leakages of the I and methodological zones, traces of CO were found in the flue after the smoke. Periodic extinguishing of burners of zone II due to the large air flow rate for them (

“2P - 1.7 required operative intervention of the heaters. With the indicated fuel consumption by zones and

the productivity of 40 blanks per hour, their temperature at issue was 1220 - 1230 ° С, the difference in cross section - 40-50 ° С. Conditioned heating of the metal was achieved at fuel consumption for HV zones 470, 450,

210 m / h, respectively, and air flow rates of 2670, 7400, 2590, 1650 m3 / h. At the same time, no incomplete combustion products were found in smoke and hogs. There was an intense fuel burnout of about

until the middle of the methodical zone and period5

ical breakdown of torches from burners of zone II. The temperature of the combustion products in the smoke was 1070-1100 ° С. Specific fuel consumption of 123.8 kg y, t. / T.

5 The application of the method allows to increase the accuracy of regulation to reduce the specific fuel consumption by 10-11%, to prevent underburning of the fuel and to ensure its steady burning conditions.

Claims (1)

0 claims The method of automatic control of the fuel-air ratio in a multi-zone furnace, including measuring in each zone fuel and air consumption, determining the ratio of air and fuel consumption in each area after the first in terms of expenses in this area and the preceding areas, changing the air flow when this ratio deviates from a predetermined value, characterized in that, in order to increase the control accuracy, reduce the specific fuel consumption, prevent underburning and disturbance of combustion stability, with The ratio of air and fuel consumption is modified by redistributing the total air flow between this and the adjacent preceding zones, and the air supply is reduced to the zone with a large predetermined the ratio of air and fuel costs and increase to the zone with a lower preset ratio.  Dunn ((.-Ta) Zone In the subsequent, the Zone Sijnevu previous P (1-1) zone