RU2145401C1 - Method of burning liquid and gaseous fuels - Google Patents

Abstract

FIELD: heat-power engineering; boiler units or other fuel-consuming units where liquid and gaseous fuels are burnt together or separately. SUBSTANCE: burning of fuel is effected by means of four-orifice burners and automatic control system of fuel combustion; recirculation gases are fed in two flows at rated relationship. One recirculation flow is fed to root zone of flame core and other flow is fed to peripheral area of combustion zone. EFFECT: reduced effluents of nitric oxides with combustion products; enhanced efficiency of recirculation; reduced expenses for reduction of emissions of nitric oxides. 2 dwg

Description

 The invention relates to a power system, directly to boiler units or other fuel-using installations in which liquid and gaseous fuels are burned together or separately.

 Known methods of burning liquid and gaseous fuels with the introduction of recirculating flue gases into the air path of the burner devices - analogue / 1, pp. 246-248 /. Recirculation of flue gases through the burner allows you to reduce the heat load of the screens and redistribute the heat perception of the heating surfaces of the boilers, as well as reduce the yield of nitrogen oxides. However, to reduce the yield of nitrogen oxides with this method of fuel combustion, recirculation gases must be supplied in significant volumes, which can lead to a violation of the stabilization of the fuel combustion processes with the appearance of soot and carbon monoxide, and thereby to a decrease in the boiler efficiency and a decrease in the reliability of its operation.

 Reducing the yield of nitrogen oxides is also achieved by using the method of burning fuel with the introduction of recirculation gases into the air ducts to the burners - analogue / 1. p. 248 /. In addition to the above drawback, this method also has a disadvantage associated with the gas supply of the boiler room through leaks in air ducts due to increased resistance of the air path due to an increase in the volume of the gas-air mixture.

 A known method of simultaneous combustion of liquid and gaseous fuels when feeding them into the combustion chamber using a vortex burner. Air is supplied by the central and peripheral annular flows, and recirculation gases are supplied between the air flows at a speed of 1.08-1.5 times the average speed of the central air flow, liquid fuel is sprayed into the central stream by a nozzle located along the axis of the burner into the gaseous fuel fed from the annular collector into the peripheral air flow / 2 /.

This method has the following disadvantages:
- excessive cooling by gases of recirculation of the peripheral zone of the plume to achieve the required temperature under the conditions of suppression of nitrogen oxides in the combustion core, which leads to combustion instability;
- significant volumes of recirculation gases are required, which entails an increase in energy costs for own needs;
- increased losses with flue gases.

 A known method of burning fuel in a gas-oil burner, presented in (3) is a prototype. According to this invention, cold air is supplied through the central channel, and recirculating gases through the peripheral channels. Between the channels for supplying recirculation gases, a channel for supplying hot air is arranged. Burner design according to A.S. N 700746 and the method of its operation described in (3) provide adjustment of the combustion mode over a wide range. The effectiveness of this method of burning fuel in terms of reducing emissions of nitrogen oxides is relatively low. This is due to the simultaneous occurrence of two multidirectional processes: cold air helps to cool part of the torch region in which nitrogen oxides are formed, which allows their yield to be slightly reduced; on the other hand, due to the increase in the proportion of the oxidizing agent in the combustion core to the maximum, the formation of nitrogen oxides is intensified.

 The main disadvantage of the above method of burning fuel is to intensify the process of formation of nitrogen oxides by supplying cold air to the combustion zone. Recirculation gases are supplied only to the peripheral zone of the flare, where the formation of nitrogen is almost complete. Therefore, the effect of recirculation gases with such a supply on the formation of nitrogen oxides is significantly weakened.

 This invention is aimed at eliminating the disadvantages inherent in analogues and prototype.

 The objective of the invention is to reduce the yield of nitrogen oxides during joint or separate combustion of liquid and gaseous fuels. For this, it is necessary that the recirculation gases enter the flare’s highest temperature zone.

 The problem is solved in that the recirculation gases are divided into two streams. One of them, constituting from 20% to 35% of the total volume of recirculation gases, is fed swirled or straight through to the root zone of the core of the fuel flame through an additional channel, and the second stream of recirculation gases is fed between the annular and peripheral air flows.

 The accepted fraction of the supply of recirculation gases to the radical zone of the torch of their total consumption to the burner is also confirmed experimentally when conducting studies on a boiler with a head sample of a four-channel gas-oil burner. With a decrease in the recycle fraction of less than 20%, the efficiency of suppressing the generation of nitrogen oxides is significantly reduced. When the proportion of recirculation is more than 35%, the reliability of the burner device decreases due to the separation of the torch from the embrasure of the burner associated with significant ballasting of the root zone of the torch by the products of fuel combustion.

 An essential distinguishing feature of the present invention is the division of recirculation gases into two streams in the above ratio and the supply of one of the streams to the root zone of the core of the fuel flame through a special central rather than peripheral channel.

The effectiveness of regulating the characteristics of the gas-oil plume in terms of temperature and oxygen concentration in the combustion zone depends on the method of introducing recirculation gases into the burner device or the place of entry into the combustion chamber. It is known that the fuel torch exiting the burner consists of several zones having different temperature levels and oxygen concentrations. Nitrogen oxides are most intensively formed in the combustion core, which has a higher temperature and oxidizer concentration than the rest of the flare zone. Recirculation gases are introduced into the combustion chamber to solve several problems, namely:
- reduction in the formation of nitrogen oxides;
- redistribution of heat flows between radiation and convective heating surfaces of the boiler;
- maintaining the required temperature of steam overheating;
- reduction of skidding of heating surfaces and their corrosion damage (for liquid fuels).

 By dividing the recirculation gases into two streams, their total volume can be reduced, since the introduction of a part of the recirculation gases into the flare core allows its temperature to be more effectively reduced, while providing a lower yield of nitrogen oxides and at the same time solving the above problems.

 Recycling of part of the products of fuel combustion in the root zone of the combustion core due to the introduction of "cold" flue gases and thereby reducing the concentration of the oxidizing agent due to dilution by the cooled combustion products makes it possible to achieve a significant decrease in the temperature of the flame core.

 According to the data of / 1, pp. 38-39 / and other literature, the effect on the course of combustion processes by lowering the excess air and temperature in the torch core can significantly reduce the concentration of nitrogen oxides in flue gases. To achieve this effect, it is enough to introduce no more than 20-35% of the total volume of recirculation gases into the core of the fuel plume burning. Since the combustion core occupies no more than 1/3 of the volume in the zone of the burning fuel flame, the volume of recirculated gases supplied directly to the combustion core should not exceed 1/3 of their total volume. The rest of the recirculation gases is supplied to the peripheral zones of the flame to cool them and provide conditions for two-stage combustion of fuel due to the layered separation of air flows. In the combustion zone, conditions are provided for the occurrence of nitrogen reduction reactions.

 The proposed method of burning fuel can be implemented using a burner device, schematically shown in FIG. 1.

 The gas-oil burner contains a housing with central (1) and peripheral (2) channels for supplying primary and secondary air, respectively, an axial channel (9) with a fuel oil nozzle (4) installed in it, an annular channel (5) for supplying natural gas with its release through the nozzles (6), an additional axial channel (7) for supplying recirculation gases to the combustion core and a channel (8) for supplying recirculation gases to the peripheral zones of the fuel flame. In contrast to the known designs of burner devices for implementing the proposed method of burning fuel, the burner device has an additional channel (7) for supplying recirculation gases between the axial channel (9) for installing a fuel oil nozzle (4) and a primary air channel (3).

 To implement the method in the general case of variable loads of the boiler unit, apply an automatic control circuit that can withstand a given amount and ratio of recirculation gas flows supplied through the burner in the operating range of the boiler loads. In the particular case - with a constant load of the boiler over a long period of operation, the method of burning fuel can be implemented with the automatic control circuit switched off with the control of the output of nitrogen oxides in flue gases.

 A schematic diagram of a system for automatically controlling a fuel combustion process is shown in FIG. 2. The system contains air flow sensors 1 and fuel 2 and 3, automatic gas analyzers 4 and 5 for determining, respectively, the content of nitrogen oxides and carbon monoxide in flue gases, taken respectively from the convection shaft and furnace of the boiler unit 6. The system includes a signal converter 8, the input of which is communicated with gas analyzers 4 and 5, and the output - with a computing device 9, the input of which receives a signal from the setpoint of the quantity and ratio of recirculation gases 10. The output of the computing device 9 is communicated with the input m of the regulator 11, to the output of which the signals of the sensors 1, 2, 3 are received. Recirculation gases through the recirculation smoke exhauster line 13 go through the regulating organs of the sliders 15 and 16 to the corresponding channels of the burner 7. The regulator 11 is in communication with the guide apparatus 14 of the blower fan and the regulating organs of the shutters 15 and 16.

 The proposed method of burning fuel is as follows. For the current load of the boiler, the corresponding operation mode of the burner device with a minimum output of nitrogen oxides in the fuel combustion products (according to sensor 4 of Fig. 2) and in the absence of chemical underburning (according to sensor 5 of Fig. 2) is established. The fuel-air ratio is established (by sensors 1, 2, 3 of Fig. 2). In this case, the quantity and ratio of the supplied recirculation gases to the axial channel 7 of the burner (Fig. 1) and the peripheral channel 8 (Fig. 1) is set by the adjuster 10 (Fig. 2) with the supply of a signal from it to the computing device 9, the output of which is communicated with the controller eleven.

 When the boiler load changes or when the nitrogen oxide emissions exceed the specified operating value from the settings 4 and 5, signals are sent to the converter 8, the output of which is connected to the computing device 9, which is connected to the set ratio of the quantity and ratio of recirculation gases 10. After the computing device 9, the signal to the regulator 11, the input of which is connected with the adjuster of the air flow rate 1 and fuel 2, 3. The regulator 11 sends signals to the regulating bodies of the gate valves 15, 16 to change the ratio of recirculation gases AI, supplied respectively to the axial 7 and peripheral 8 channels of the burner (Fig. 1), as well as to change the total amount of recirculation gases, to the regulator of the gate 17 of the recirculation smoke exhauster 13. The regulator 11 acts on the guiding devices 14 of the blower fan, changing the flow rate air, and maintains the required fuel-air ratio.

 Recirculation gases flowing through the axial and peripheral channels act respectively on the combustion core and the peripheral zone of the flame, thereby reducing the temperature of the flame, providing a predetermined excess of air and creating conditions for reducing the formation of nitrogen oxides. Subsequently, when the load and the mode of fuel combustion are changed, the sequence of operations for implementing the proposed method of fuel combustion is repeated in the manner described above.

 Automatic control allows to achieve maximum suppression of nitrogen oxides, without leading to excessive ballasting of the ignition zone and the initial stage of combustion and, accordingly, without impairing the stability of combustion and without increasing emissions of soot particles in a wide range of boiler loads.

 The technical and economic efficiency of the proposed method of burning fuel consists primarily in reducing emissions of nitrogen oxides with a reduced consumption of recycle gases and, accordingly, the cost of their supply. Evaluation of the effectiveness of the proposed method showed that the use of the proposed method of burning fuel can reduce emissions of nitrogen oxides by 60-70% or more compared with the technical solution shown in the prototype, as well as 20-30% to reduce the cost of supplying recirculation gases through the burner device .

Sources of information taken into account during the examination
1. Akhmedov R. V. Fundamentals of regulation of furnace processes. M .: Energy, 1977, p. 245-248.

 2. A.S. USSR N 1151761. Tsirulnikov L. M., Nurmukhamedov M. N., Abramov A. A. et al. Method for burning fuel, B. I. 1986, N 15.

 3. A.S. USSR N 700746. Akhmedov D.M., Abramov A.A., Zborschenko A.T. Gas oil burner.

Claims (1)

 The method of burning liquid and gaseous fuels by feeding them into the combustion chamber through the corresponding channels of the vortex burner, blast air - circular, central and peripheral flows, and recirculation gases - between air flows, characterized in that one of the two flows of recirculation gases, constituting from 20 up to 35% of their total volume, is fed twisted or straight through to the root zone of the core of the fuel flame between the axial channel of the fuel oil nozzle and the primary air channel, and this flow is regulated automatically Eski content of nitrogen oxides for convective boiler shaft, with correction largest chemical unburned carbon and the relationship "fuel-air" in the furnace boiler influence on regulators guide apparatus exhauster recirculation vanes and the two streams of gas recirculation.

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