SU1462067A1 - Method of controlling combustion process - Google Patents

Abstract

The invention relates to methods for controlling combustion processes by adjusting the air supply to the furnace and is intended for use in fuel combustion units when co-firing two or more species with a randomly varying ratio of fuel consumption of each type and with recirculation of flue gases to the combustion zone. The purpose of the invention is to increase the accuracy of control of the combustion process. During preliminary mixing of recirculating gases with air, the content of oxygen, carbon monoxide and the total content of carbon dioxide and sulfur are measured additionally in flue gases, and the content of oxygen in the mixture of recirculating gases and air is measured. Measurements are made either in pre-dried samples of the analyzed gases, or with an additional measurement of the water vapor content in the samples of gases. Based on the measurement results, the ratio of specific, terrestrial volumes of dry combustion products and air consumed for combustion, and the actual coefficient is calculated. flue gas recirculation. The optimal ratio is determined by the calculated ratio. proportionality between heat, the release in the furnace and the flow of primary air. For this ratio and the calculated coefficient. flue gas recirculation determines the optimal oxygen content in the flue gases. Optimal values proportionality and oxygen content are used as specified in the regulation and correction of the primary air flow rate. Using the previously constructed adjustment characteristic of the correction regulator, an additional effect was made on the regulator c. a decrease in the primary air flow rate, which made it possible to increase the efficiency of the boiler unit. Q & (L

Description

one

The invention relates to heat and power engineering, in particular to methods of controlling combustion processes by controlling the air supply to the furnace, and is intended for use in fuel-burning units when co-burning fuels of two or more types with an arbitrarily varying ratio of fuel consumption of each type and circulation.

flue neither.

of gases

to the mountain zone

The purpose of the invention is to increase the accuracy of the regulation of the combustion process,

In general, the method is carried out as follows.

The heat gap in the furnace is determined. The operation can be performed by one of the known methods, for example

M - experimentally established correction for other components (except CO) of chemical and mechanical underburning of fuel. The specified proportionality coefficient of heat-air ratio is determined as a linear function of the fuel characteristic V by the formula

heat of combustion by the amount of consumption and summation of the terms obtained for individual types of fuel. The content of carbon monoxide (CO) in flue gases is measured with the expression of measurement results relative to the volume of dry combustion products. Measured

oxygen and

(O, p) oxide

content

carbon (COp) and the total content of carbon dioxide and sulfur (CO, p) in the recirculated flue gases also with high pressure measurements relative to the volume of dry combustion products. The oxygen content is measured (.O., cm; in the mixture of recirculating flue gases with air at the entrance to the furnace; the measurement result is expressed relative to the volume of the mixture that does not contain water vapor. The ratio of the costs of all types of simultaneously combusted fuels at the time of measurement, the generalized value of the fuel characteristic, related to theoretical combustion with the stoichiometric ratio of the costs of combustible fuels and oxidizer, according to the formula

de

50

QHq- 20.9

the generalized fuel characteristic, in its physical sense, is the ratio of the specific theoretical volumes of dry combustion products and consumed for air combustion; invariant characteristics of the burned fuel mixture; volume content of acid-type in atmospheric air- VP 7

le, / a,

 A, - A ,.

(2)

where a is the proportionality coefficient, in the physical sense, representing the ratio of the average heat of combustion of the combusted fuel mixture to the specific theoretical volume of consumption,. blown on the burning of the air;

A and A, j - invariant characteristics of incinerated recycling

mixes.

Calculate the actual flue gas recirculation rate (g) using the formula.

g

(“Ir + 1) (20.9 - Og,

(3)

() (0g. Cm - Oi, p)

where uLf is the balance coefficient of the excess air in the combustion zone, taken from the design characteristics of the burners or the firebox as a whole.

Calculate the actual coefficient of excess air in the recirculated flue gas (s) by the formula.

Otp

(R)

20.9-0.2.0 SB

(four)

M

Calculate the value of the specified oxygen content in flue gases (0;

2, T

) According to the formula

20.9 + 0.4 CO + M

H -1- (Hr - 22..9l.f).

  20, + 0.4SOP + M

 one

  effective ratio

excess air in the controlled section of the flue behind the furnace, which is installed during testing of the fuel-burning unit according to the condition of ensuring maximum efficiency. Determine the required design value.

primary air flow rate (Vg)

formula

where Q - heat in the furnace.

The actual flow rate of the primary air is measured.

The position of the primary air flow regulator is changed to match the required calculated and actual flow rates (coarse adjustment operation) of the primary air. The actual oxygen content in the flue gases is measured and the difference between the measured and set oxygen content is calculated. In addition, the position of the regulator of the primary air flow rate is adjusted so that the obtained values of the indicated difference tend to zero (fine control operation).

The specified expression of measurement results relative to the volume of dry combustion products (in terms of the volume of gases remaining after the removal of water vapor from them) is explained as follows: the specific yield of dry combustion products for each type of combustible fuel is, as a rule, stable the specific yield of water vapor, and hence the total specific volume of combustion products, is often subject to significant fluctuations. Accordingly, the expression of the content of oxygen and other components by the volume of dry products Gorani less susceptible to fluctuation of m, which contributes to the achievement of the objects of the invention; In the majority of known industrial instruments and newly developed gas analyzers, by the principle of operation, the removal of water vapor from the analyzed gas and the expression of the analysis result is directly relative to

4620676

volume of drained gases. This is consistent with the requirements of optimizing the control of the combustion process in terms of the composition of the combustion products; gas analyzers, such as determinants of oxygen content in gases with sensors based on selective oxygen sensitivity of zirconium oxide,

10 shows the measurement result with respect to the natural volume of the gases being analyzed. The advantage of such gas analyzers is continuity of action, however, the condition

15 optimization of the control of the combustion process, they correspond with a strictly stable composition of the combusted fuel. The use of such gas analyzers to increase the efficiency of the combustion process during co-combustion of two or more types of fuels with a randomly varying ratio of fuel consumption of each type and with recycling of dm gases into the zone

25 according to the purpose of the invention, it is possible under the condition of additional measurement of the content of water vapor in the analyzed gas, which allows expressing the results by recalculation

30 measuring oxygen and

other components relative to the volume of dry combustion products.

The method in the manual combustion control mode was tested in

3g boiler installations of ferrous metallurgy enterprises. The content of oxygen and carbon monoxide in the furnace. gases, the content of oxygen, carbon monoxide and the total content of carbon dioxide and sulfur oxides in the recirculated flue gases, as well as the oxygen content in the mixture of recirculated flue gases with air, are measured by standard gas analyzers.

45 Example. In the furnace of an industrial boiler unit equipped with flue gas recirculation to the combustion zone, natural gas, blast furnace gas and fuel oil are burned together. Invariant characteristics of this fuel mixture are preliminarily determined as follows: y 2.25; (f 0.73; A, 625 kcal / m; A 300 kcal / m. The furnace of the boiler unit gg is equipped with a flat torch burner device, for which the air excess coefficient oi is equal to 0.05, the mechanical shortage of fuel M is equal to zero.

The coefficient of excess air in a controlled cross section of the flue behind the furnace is set to 0.12. The measured amount of heat in the furnace (minus the heat introduced by the recirculated gases) is Qr 71.410 kcal / h. Measurements are determined,%: C0 0.05; O, p "3.75; COP 0.03; R0, j, p 18.4; Oj 18.35. According to the formula (1), 1.292; according to formula (2), a. 1012 kcal / m; by the formula (3) calculated g 0,137; -by the formula (4)

ten

eight

until a zero value is reached, the deviation of the measured oxygen content in the flue gases from the set value of the oxygen content in the flue gases, characterized in that, in order to improve the control accuracy, the combustion process during the combustion of several types of fuel with an arbitrarily varying cost ratio recirculation of flue gases to the combustion zone, with preliminary mixing of recirculated gas with air, add jjjfcjj j I, 9 f 4.x ,, .--- V -, J f J ...- -1-1 - II

calculated oi-p 0,2823; According to the formula (5), 0 1.58% is calculated in flue gases; by the formula (6) is defined V, "71350. The measured actual flow rate of primary air (adjusted to normal conditions) is 71500. The impact on the regulating flow of the primary air is reduced to 71350, after which the actual firing is measured.

the carbon monoxide content, the oxygen and carbon monoxide contents and the total carbon dioxide and sulfur dioxide contents are measured in the rediscineating flue gases, the oxygen content in the mixture of recirculating gases and air is measured dried samples of the analyzed gases

oxygen in the flue gases 0, j, which is 25 or with an additional measurement of the water vapor content in the samples, is gortoy is 1.61%, and the difference Oe is calculated, t is O Gg%.

Using the previously constructed adjustment characteristic of the adjustment regulator, an additional effect is made on the regulator with a decrease in the primary air flow rate in such a way that the difference reaches zero, which allows: to increase the efficiency of the boiler unit by 0.15%.

formula of invention

The method of controlling the combustion process by adjusting the flow rate of the primary air is proportional to the heat gap in the furnace with a given coefficient of proportionality and the correction of the flow rate of the primary air

thirty

35

40

45

In accordance with the measurement results, the ratio of the specific theoretical volumes of dry combustion products and expendables to air combustion and the actual flue gas recirculation coefficient are calculated. The optimal proportionality coefficient between the heat generation in the furnace and the primary air consumption is determined from the calculated ratio this ratio and the calculated actual flue gas recirculation coefficient determine the optimal oxygen content in the flue gases and optimal values of the proportionality coefficient and oxygen content are used as given in the regulation and correction of the primary air flow rate.

0

eight

until a zero value is reached, the deviation of the measured oxygen content in the flue gases from the set value of the oxygen content in the flue gases, characterized in that, in order to improve the control accuracy, the combustion process during the combustion of several types of fuel with an arbitrarily varying ratio of their flow rates and recirculation - by flue gases in the combustion zone, with preliminary mixing of recirculating gases with air, add J f J ...- -1-1 - II

5, the content of carbon monoxide is measured in flue gases in the flue gases, the content of oxygen, carbon monoxide and the total content of carbon dioxide and sulfur in the flue gases are measured, and the mixture of recirculated gases with air is measured the oxygen content, the aforementioned measurements are made or in preliminary dried samples of the gases being analyzed.

. water vapor retention in samples

five

0

five

call, based on the measurement results, calculates the ratio of the specific theoretical volumes of dry combustion products and the expenditure on air combustion and the actual recirculation rate of flue gases, determines the optimal value of the proportionality coefficient between the heat release in the furnace and the primary air flow, using this calculated ratio the ratio and the calculated actual flue gas recirculation coefficient determine the optimal oxygen content in the flue gases and The optimal values of the proportionality coefficient and the oxygen content are used as given in the regulation and correction of the primary air flow rate.

Claims (1)

The key point of the invention is to control the process of controlling the flow rate by facilitating the paths of wine air in proportion to the heat in the furnace with a given coefficient of proportionality and correction of the primary air flow rate until the deviation of the measured oxygen content in the flue gases from the specified value of the oxygen content in the flue gas is reached gas, characterized in that, in order to improve the accuracy of control, the combustion process when burning several types of fuel with randomly varying with the use of their costs and with the recirculation of the flue gases to the combustion zone, when the recirculating gases are mixed with air beforehand, the content of carbon monoxide is additionally measured in the flue gases, the content of oxygen, carbon monoxide and the total content of carbon dioxide and sulfur are measured in the recirculated flue gases in a mixture of recirculated gases the oxygen content is measured with air, the above measurements are carried out either in previously dried samples of the analyzed gases, or with an additional measurement of co. .containing water vapor in gas samples, the ratio of the specific theoretical volumes of dry combustion products and the air consumed for combustion and the actual flue gas recirculation coefficient are calculated from the measurements, the optimal value of the proportionality coefficient between the heat release in the furnace and the primary air flow rate is determined from the calculated ratio this ratio and the calculated actual flue gas recirculation coefficient determine the optimal oxygen content in flue gases, the aforementioned optimal values of the coefficient of proportionality and oxygen content are used as specified in the regulation and correction of the flow rate of primary air.