SU1698582A1 - Method for adjusting process of combustion - Google Patents

Description

by oxygen analysis and chemical underburning analyzers. The task of extreme control of the fuel combustion process here is solved with the help of a stabilizing regulator acting on the fuel-air ratio on a hydrogen pulse in flue gases. The disadvantage of this method is the incomplete use of the possibilities of not only economic, but also environmental optimization of the combustion process, for example, due to the neglect of toxic nitrogen oxides.

There is also known a method of burning fuel to reduce the content of nitrogen oxides in combustion products, based on reducing the concentration of nitrogen oxides in flue gases by changing the air supply by signals from the fuel consumption sensor and supplying water or water vapor between the fuel and oxidant streams. Here, water or water vapor more evenly enters the combustion zone with the intensive formation of nitrogen oxides, which reduces the required amount of water and more radically suppresses the formation of nitrogen oxides.

The disadvantage of this method is low profitability and insufficient efficiency of suppression of nitrogen oxides, i.e. failure to ensure the environmental-economic optimum in the regulation of the process of fuel combustion due to the fact that here improvement of one indicator is achieved due to the deterioration of the other and there is no complex effect of various methods of suppressing nitrogen oxides on the mode of fuel combustion,

The aim of the invention is to increase the fuel economy and environmental friendliness by reducing nitrogen oxides in combustion products released into the atmosphere.

The goal is achieved by the fact that in a known method of controlling the process of burning liquid and gaseous fuels, based on reducing the concentration of nitrogen oxides in flue gases by changing the air supply by signals from the fuel consumption sensor and supplying moisture (water, water vapor or water together). In the combustion zone according to the invention, the air-fuel ratio and the increment of nitrogen oxides are measured before the moisture is supplied to the combustion zone to obtain the ratio of the increment of nitrogen oxides to the increment of hydrogen in the products burning, equal to zero, register the value of the concentration of hydrogen achieved in this case and begin to supply moisture to the combustion zone, control its consumption to achieve the minimum concentration of nitrogen oxides and hydrogen and in flue gases and then stabilize the consumption of moisture.

In addition, the air-fuel ratio is reduced to the achievement of hydrogen concentrations in the flue gases, which was recorded prior to the commencement of the assortment of moisture into the combustion zone at a ratio of nitrogen oxides increments to hydrogen increments equal to zero.

0 The proposed method has a new compared to the known operation.

Figure 1 shows the dependence of the magnitude of chemical underburning of the fuel on the coefficient of excess air with

5 different combustion modes; figure 2 - the dependence of the concentration of nitrogen oxides N0% in the flue gases from the concentration of hydrogen (H2) in the flue gases during the combustion of fuel oil and natural gas; Fig. 3 shows a diagram of the device that implements the proposed method for regulating the process of burning fuel; Fig. 4 shows the dependence of the reduction of nitrogen oxides in flue gases when regulating the combustion process of the top 5 according to the proposed method.

FIG. 1 shows the experimental dependence of the magnitude of chemical underburning on the coefficient of excess air when burning fuel oil in the steam boiler TGMP-314, Here

0 curve 1 corresponds to the initial combustion mode of the fuel with steam atomization of fuel oil in steam-mechanical injectors, and curve 2 corresponds to the combustion of fuel with local dosed input of water into the combustion zone. Of

5 of FIG. 1, it can be seen that the second combustion mode has a smaller value of the critical excess air coefficient compared to the first mode. But to realize this advantage, i.e. with the same

With 0 values of the excess air coefficient, it is impossible to achieve lower heat losses due to chemical incomplete combustion of fuel, it is not possible to use known methods to control the combustion process.

5 As a result of studies of the combustion processes of liquid and gaseous fuels, it has been established that, in the area of micronediurn, there is a pronounced extremum of nitrogen dependence on hydrogen (Fig. 2). The area of effective reduction of nitrogen oxides in flue gases is in the range of hydrogen concentrations from 0.015 to 0.04% by volume, at which the magnitude of chemical fuel underburning is negligibly small and almost completely compensated by a decrease in heat loss with exhaust gases compared to the zero chemical mode. underburning fuel. Thus, by reducing the excess air to a value of D NOX / A H2 0, the concentration of nitrogen oxides in the flue gases significantly decreases (here ANOx and D At the concentration increment). However, a further decrease in the excess air ratio is inefficient, as there is an increase in the hydrogen concentration and, accordingly, an unacceptable increase in chemical underfuel, and also an increase and then an ineffective decrease in nitrogen oxides, therefore, the optimization of the top burning process is first carried out by decreasing the coefficient of excess air putta Emission rate: 9 - its minimum, the value of increasing the concentration of hydrogen in the flue gases to the ratio ANOx / AN2 0, the corresponding concentration hydrogen up to 0.04 vol.%. Here the region of effective reduction of excess air ends by reducing the flow rate of blast air, as the efficiency of the combustion process decreases sharply due to chemical incomplete combustion of fuel and the effect of reducing nitrogen oxides becomes even less. compared with the previous mode. Only at a higher value of hydrogen in the flue gases (respectively, and smaller excess air ratios) does the concentration of nitrogen oxides become lower, but a decrease in their magnitude is not equivalent to a deterioration in the fuel combustion process and is not economically feasible. The surge in the concentration of nitrogen oxides in the combustion products of the fuel is explained by the mutual influence on the level of the concentration of nitrogen oxides in the zone of their active generation, both the maximum temperature of the mixture and the concentration of oxygen.

A decrease in the air excess factor, due to a decrease in the flow rate of air supplied to the burners during the organization of the combustion process with extremely low air excess, on the one hand leads to a decrease in oxygen concentrations in the zones of active generation of nitrogen oxides, and on the other hand, to an increase in temperatures in the local zones of the torch with decreasing a to 0.95. The multidirectionality of the effect of these two factors leads to such an unusual, at first glance, result of an increase in the concentration of nitrogen oxides in the combustion products of fuel with a monotonic increase in hydrogen. Therefore, with the achievement of ANOx / AN2 0 in the range of concentrations of hydrogen in flue gases from 0.015 to 0.04% by volume in order to more deeply reduce the concentration of nitrogen oxides in the zone

Combustion with the intensive generation of nitrogen oxides feeds moisture (water, water vapor or together) and simultaneously controls the concentration of hydrogen and nitrogen oxides. The total amount of moisture supplied to the combustion zone is in the range of the known method, but, unlike it, here the inclusion of the supply of moisture and the increase in its consumption is carried out stepwise by gradually increasing its consumption, itpw current / 4 control of water and nitrogen oxides the minimum concentration of hydrogen in the flue gases and a deeper suppression of nitrogen oxides (f T.4). The signal for a tremendous increase in the supply of moisture to the burning zone is a surge of increase in concentration of both nitrogen oxides due to acholding of the plume and freezing of nitrogen oxides and hydrogen due to the process of preparing the fuel for combustion and the actual burning process. moisture burning depends on the type of flue-burner devices of temperature limitations and operating conditions of the steam KSTLOR and is currently carried out by operating personnel on a regime map 8 by controlling the control valve. Without automatic control of the burning process by the proposed method, the proposed method in practice cannot achieve environmental and technical-economic advantages, since only the proposed method achieves selective suspension of the supply of moisture to the combustion zone in accordance with the above listed conditions for the simultaneous control of hydrogen and nitrogen oxides during discrete including injection of water or steam into the combustion zone. Moreover, since the resolving level for monitoring various changes in hydrogen is 0.001% by volume, for reliable determination of the optimum point of the process, i.e. minimum NOX and H2 with a discrete fixed amount of injected moisture, the deviation of hydrogen from the controlled is allowed 0.002% vol. Usually, when using the Optima-Chromium system for this purpose, the exposure time after water injection before measuring the hydrogen concentration is more than two, no less than ten minutes, which corresponds to the typical time for stabilization of the fuel combustion process when a disturbance is applied to the boiler process.

The minimum concentration of hydrogen in the flue gases and the fixation of this value with

stopping the increase in moisture consumption, as significant, is carried out at the moment of increasing hydrogen (chemical underburning of fuel) at the current value of its concentration of 0.005-0.01 vol.% (figure 4). Here, as stated above, an increase in the amount of injected moisture results disruption of the combustion process, causing a spike in the growth of concentrations of both hydrogen and carbon monoxide, and is unacceptable under the terms of fuel combustion efficiency and equipment reliability. In the intermediate modes of moisture injection into the combustion zone from the beginning of its implementation to the establishment of the optimal value, a decrease in the concentrations of hydrogen and of nitrogen oxides is observed in the combustion products of the fuel.

An even deeper suppression of the formation of nitrogen oxides can be achieved further with a constant fixed injection of moisture into the combustion zone by a subsequent decrease in the air excess factor until the hydrogen concentrations in the flue gases that occurred before the injection of moisture into the combustion zone are reached. Here, the realization of an additional effect from the improvement of the conditions of mixing the fuel with the oxidizing agent due to the introduction of moisture into the combustion zone and the additional turbulization of the flame is achieved, thereby reducing the critical coefficient of excess air. The possibility of implementing the method of controlling the process of burning fuel is explained by the scheme shown in FIG. Here, fuel consumption sensors 1 and air 2 are included in the fuel and air supply path. Changes in fuel, air and water or steam injection are carried out, respectively, by regulators 3, 4 and 5 and by actuators 6 and 7, affecting regulators of changes in fuel consumption 8, water 9 and air 10. Measuring instrument 11 for oxide emissions Nitrogen and hydrogen concentrations in the flue gases of the steam boiler 12 with a hydrogen generator 13 transmit signals to the IMOx / A 14 A transmitter, the output of which is connected to the limiter 15 as specified by hydrogen. The scheme is equipped with a meter 16 concentration of nitrogen oxides in the atmosphere.

The device works as follows.

Using the meter 11 emissions of nitrogen oxides, hydrogen in flue gases, for example, the system Optima-Chrom, on a working boiler 12 is established mode with extremely low excess air on the hydrogen content in flue gas

gases 0,005% vol. Further suppression of nitrogen oxides is performed by changing the hydrogen target with a corresponding change in the corrective effect.

air supply, an increase in the hydrogen reference and a decrease in the air supply are made by the air regulator 4 until ANOx / AH2 0 is reached. After this, the ANOX / H2 calculation device 14 turns on the restrictor 15 and no further change in the hydrogen reference is made. If necessary, a deeper suppression of nitrogen oxides in emissions scheme And in the controller 5 injection allows the passage of a signal from the gauge 16 nitrogen oxides in the atmosphere to the opening of water injection 9, after which there is a decrease in the hydrogen content in the flue gases of the steam boiler 12. The task of hydrogen remaining before

The injection-activated mode, which was previously introduced into the Optima-Chrom corrector, brings the latter back to working condition and generates a correction device in the direction of further reducing the excess air coefficient before the limiting value of hydrogen is established in the flue gases. In the absence of the need for deep suppression of nitrogen oxides, water injection is turned off, and this increases

hydrogen in flue gases and Optima-Chrom, changing the corrective action, automatically sets the new value of the excess air coefficient, outputting the system to a predetermined content

hydrogen, but not more than that, where ANOx / AH2 0 Control system, including elements 14, 15, 5 and 13, is implemented using a K-1-20 microcontroller (MS 2702 Electronics)

Example The concentrations of nitrogen oxides (N0), hydrogen (Na), carbon monoxide (CO), oxygen (Oz) were measured on the TGMP-314 steam boiler of a 300 MW power unit. Experimental data of experimental measurements of these values when burning fuel oil without moisture injection with various The concentrations of hydrogen in the flue gases with a decrease in the coefficients of excess air are given in 1–4 experiments of the table, and for injections of moisture are given in experiments 5 and 6.

The results of experimental verification of the method shown in the table. presented graphically in figure 4.

From the analysis of experimental data, it follows that the inclusion of moisture injection at the time A NOx / A N2 0 leads to further suppression of nitrogen oxides, and the subsequent correction of the fuel combustion mode by hydrogen (returning its value to the initial value corresponding to the mode before the start of moisture injection) additional reduction of nitrogen oxides (experiment 6), when burning fuel with extremely low excess air relative to the final initial operating mode (experiment 3). Combustion of fuel without moisture injection with a decrease in the excess air ratio leads to a more gentle decrease in nitrogen oxide concentrations and its absolute value with an accompanying sharp increase in heat loss with chemical incomplete combustion of fuel (experiment 4) compared with the recommended option (experiments 5 and 6).

Thus, the proposed method for controlling the combustion process of liquid and gaseous fuels as compared with the known provides for improved efficiency due to more rational combustion of the fuel, leading to an increase in the prevented damage to the environment. Significant differences of the method are both in its organization and in providing precision measurements and in determining specific concentrations of hydrogen in flue gases, the signals of which control the injection of moisture into the combustion zone and the coefficients of excess air, which ensure the optimization of the process of fuel combustion by ecological, and in economic terms.

Compared with the known method, which is adopted for the best development in regulating the combustion process according to environmental characteristics, regulating the combustion process of the fuel according to the proposed method leads to a reduction in emissions of toxic nitrogen oxides with flue gases from only one steam boiler of a 800 MW power unit by 0.311 t / h When the unit cost of the prevented damage to the environment

from nitrogen oxides 100 rubles per ton and the number of operating hours of the power unit 6500 h / year, prevented environmental damage from emissions of nitrogen oxides from one steam boiler is equal to 202176 rubles. per year and for a power plant with six power units exceeds 1 million rubles. in year.

Claims (2)

1. A method for controlling the combustion process of liquid and gaseous fuels by measuring the concentration of nitrogen oxides in flue gases, changing the supply of blast air to establish a predetermined excess air ratio and supplying moisture to the combustion zone, characterized by that, in order to increase the efficiency of combustion and reduce the concentration of nitrogen oxides in the flue gases, the concentration of hydrogen in the flue gases is additionally measured, before applying moisture by changing air flow reduce the coefficient of excess air to the dependence of the concentration of nitrogen oxides on the hydrogen concentration of the minimum value, then serves moisture and increase consumption moisture until the beginning of the increase in at least one of the measured concentrations of gases, nitric oxide or hydrogen and stabilize the consumption of moisture at the achieved level. 2. A method according to claim 1, characterized in that, after stabilization of the moisture consumption, by changing the air flow, the excess air ratio is reduced to achieve a hydrogen concentration in the flue gases equal to its value before the moisture supply. d, 99 0.99 1.00t, 0i 1 o) fuel oil, nafotoo row TPMfl-M. four 0 0,0iwЩ00tff SJnpueedwt / 10} (napsfou ke ate 6KZ-2M 0 0,01Ц050,10 FIG. 2 JU Figz. ff, ff