and the boiler unit.

Present invention relates to field of heat power engineering in particular to methods of conducting the process of fuel combustion and may be used in boiler units for burning different types of fuel.

Is known method of operation of a boiler unit which may be used for burning slagging brown coal by utilizing the heat from the flue gases to heat cold air, subsequent mixing of cooled gas with cold air and supplying the resulting mixture for fuel combustion. At the same time, according to the applicants, to increase the efficiency by reducing slagging of heating surfaces by burning of slagging brown coal and to reduce costs for their own needs for mixing with cold air is taken 20 - 35% of the total amount of cooled flue gases [1].

It is also known a boiler for various fuels combustion, containing a furnace with burner devices and a convective gas duct, connected to a flue duct through of exhauster and equipped with an air preheater which is connected to outlet and an inlet pipes of the cold air respectively with burner device through a combustion air ventilator with an air duct. The last through a bypass pipe with the valve united with a flue duct that by an additional recirculation pipeline is connected to the burner device. On the flue duct between sites connect to it the bypass pipe and supplementary recirculation pipe is installed a gate valve [2].

However, both the known inventions have number of drawbacks. In particular, at the known method operation of the boiler unit disadvantage is that the in using cold air for fuel combustion in terms of reducing the cost of their own needs operation of the boiler unit not taken into consideration, the excess part of the cold air which can reach 60% of the theoretically necessary part of the cold air for the combustion of slagging brown coal. Excess part of the cold air increases the mass of cooled gases emitted to the atmosphere, which reduces the efficiency of fuel combustion and increases costs for own needs of the boiler unit and adversely affects the environment.

It is known that for the complete combustion of any fuel is used in real conditions cold air comprising the theoretically necessary part of the cold air containing oxygen which is involved in a chemical reaction of fuel combustion, and the excess part of the cold air containing oxygen that is not participate in the chemical reaction of combustion fuel. In modern burner device the ratio of excess part of the cold air for the combustion solid fuel is taken as equal 1,2 - 1,6, and the combustion of liquid and gaseous fuels 1,05 - 1,15 [3, p. 43], [6, p.2]. In the above ratios integers part numbers represent theoretically necessary parts of the cold air oxygen which is involved in a chemical reaction of fuel combustion, and tenths and hundredths of these number represent excess portions of the cold air containing oxygen that no participate chemical reaction in the fuel combustion. It is known [3, p. 106 - 109], that when is done the complete combustion of various fuels, the amount excess part of the cold air increases with a decrease volume of combustion of fuel caused by the need to reduce heat generation of the boiler unit.

Thus, for powdered of brown coal the excess part of the cold air might be from 20% to 60% of the theoretically required amount of the cold air, which indicates the significant loss of heat, and consequently to reduce the effectiveness of fuel burning. Therefore, the use of for mixing 20 - 35% from total quantity of the cooled gases [3, p. 43, 109] leads only to some saving of heat but a large part of the heat is still emitted with the cooled gases corresponding to excess part of the cold air used in the combustion process that reduces the efficiency of the boiler unit and increases its costs for own needs.

The disadvantages of the known boiler include: inability to controlling supply of the cold air to the combustion of fuel depending on decrease in the amount of combusted fuel if necessary, decrease generation of heat energy and the use of a recirculation pipeline are leading to bad mixing of the cooled gases with the cold air because the beginning of mixing process takes place only in the burner.

This results in an uneven concentration of the oxygen in an air - gas mixture and incomplete fuel combustion which reduces efficiency of operation and increases costs for own needs of the boiler unit.

The task of the present invention is to eliminate these disadvantages increasing environmental and economic efficiency of fuel combustion by reducing emission into the atmosphere of the cooled gases with harmful impact on the environment.

Posed problem is solved by the fact that proposed method of operation of the boiler unit by recovering heat from the flue gases by substituting of the excess part of the cold air, containing oxygen that is not participate in chemical reaction of fuel combustion with an equal part by mass of the cooled gases which allows to maintain in the flue gases content of oxygen less than 1% in the absence of carbon monoxide, by controlling supply of the cold air and the cooled gases to obtain a mixture of depending on the kind, properties, and / or the amount of combusted fuel in according to the load of the boiler unit. Then, the specified part of the cooled gas is mixed with the cold air, utilizing the heat of the flue gases and the resulting of the mixture is fed to fuel combustion. Posed problem is solved by the fact that the proposed boiler unit for implementing the claimed method containing the furnace with burners and the convective gas duct is connected thru the exhauster via the flue duct with the stack. In the convective gas duct is installed an economizer and the air preheater that connected via the combustion air ventilator and the duct supply of the cold air and the duct supply the warm mixture of cold air and the cooled gases which is connected to the burner of the boiler unit. The flue duct connected to the cold air duct by bypass pipe. On the cold air duct is installed throttle valve with an actuator and on the bypass duct is installed valve with an actuator. At the beginning of the convective gas duct is installed a sensor of sampling flue gases which is connected to a gas analyzer that defines content of oxygen and the carbon monoxide in the flue gases. The gas analyzer is connected to an electronic control unit of the actuators of the throttle valve and of the valve of the boiler unit.

All of the above improvements of the boiler unit allow implement the proposed method thereof reducing heat consumption for own needs of the boiler unit and increase the economic and environmental efficiency its works.

Substitution of excess part of the cold air containing oxygen that is not involved in the chemical reaction of fuel combustion on the cooled gases reduces heat loss with the leaving cooled gases and reduces emissions of gases harmful impact on the environment.

Excess part of the cold air, participating in the fuel combustion process is the necessary supplement to the missing part of the theoretically necessary part the cold air to create appropriate speed and turbulent conditions of flow oxygen from the burners for providing the full and effective process fuel combustion.

It is known, that factor of excess part of the cold air depends on the type, properties and amount of combusted fuel [3, p. 106 - 109]. Thus if need to reduce the production of thermal energy on typical boiler unit the amount of required fuel and the theoretically necessary part of the cold air are reduced and the excess part of the cold air is increased to maintain appropriate speed and turbulent conditions of expiration of oxygen from the burner.

If not increase the supply excess part of cold air, then on a specified exhaust velocity occurs «breakthrough of flame» in the burner which leads to an emergency situation and an excessive increase excess part of the air leads to another an emergency situation «breakaway of flame» from the burner [4, p. 310 - 311].

For the burners that are designed for two types of fuel (gas - fuel oil) which allow the regulation of the fuel combustion process, necessary to control the excess of the cold air for trouble-free operation of the burners. The oxygen contained in the excess part of cold air that does not participate in the chemical reaction of fuel combustion in zone of high temperatures 1200 - 1300 °C from the complete fuel combustion in the furnace is oxidized nitrogen are forming gases, emitted into the atmosphere, which are harmful to the environment, and the excess part of air gives rise to the excess part of cooled gases that contributes to the loss of thermal energy and increase emissions of flue gases also making harmful impact on the environment.

If you reduce the excess part of the cold air for complete combustion of the fuel under real conditions, in the furnace gases will be created carbon monoxide, which is also harmful emissions and indicates a lack of oxygen in the fuel combustion zone as unburned fuel and its loss.

It is known that the chemical composition of the air includes 79% nitrogen and 21% oxygen, i.e. for create of appropriate speed and turbulent conditions for the flow of the oxygen from the burner is taking part 79 % nitrogen and 21% oxygen. However, the presence of oxygen as a chemical element is not required to create these conditions and leads to a loss of useful thermal energy and create the harmful emissions. While nitrogen has the primary function of providing the high-speed and turbulent conditions for complete combustion of fuel, as a neutral gas that is not harmful to the environment. Therefore, to create the appropriate physical conditions for complete combustion of the fuel instead of excess cold air, must be used nitrogen which is part of the cooled gases and is contained more 70% of them.

Using a part of the cooled gases instead of the excess part cold air will create the appropriate speed and turbulent conditions expiration of oxygen burner that helps to reduce heat losses and to reduce emissions of gases harmful impact on the environment.

The possibility of automatic control the supply of cold air and cooled gases by means of actuators and valves throttle based on the samples flue gases taken at the beginning of convective gas duct and based of it analysis is performed by gas analyzer allows to maintain the oxygen content of the flue gases is less than 1% in the absence of carbon monoxide on all standard boiler units operating under different permissible loads and using different types of fuel, stipulated technical conditions of burners.

The technical result is to increase the utilization efficiency of the cooled gases by substitution of excess part of the cold air containing oxygen that is not involved in the chemical reaction of fuel combustion on the cooled gases, leading to a decrease in mass emitted into the atmosphere cooled gases. This reduces the heat loss and increases economic efficiency and reduces mass of gases emissions, harmful impacts on the environment, of the boiler unit.

The invention is explained hereinafter in more detail based on the illustrated example of embodiment.

On the drawing schematically shows a furnace with convective gas duct well as a schematic diagram of air ducts and flue ducts of the boiler unit.

The boiler unit contains the furnace 1 with the burners 2, the convective gas duct 3 connected through the exhauster 4 and the flue duct 5 to the stack 6. In the convective gas duct 3 is placed the economizer 7 and the air preheater 8. The duct 9 of cold air with installed the regulating throttle valve 10 is connected with bypass pipe 11, on which is mounted the regulating gate valve 12. Throttle valve 10 and gate valve 12 are equipped by actuators. The bypass pipe 11 is connected with the flue duct 5. Cold air duct 9 is also connected to the air preheater 8 through the combustion air ventilator 13 by duct 14 mixture cold air and cooled gas. Air preheater 8 is connected to the burners 2 through duct 15 of heated mixture air and gases.

In the convective gas duct 3 is installed a sensor 16 of sampling of the flue gases that is connected to the gas analyzer 17 determining the content of oxygen and carbon monoxide in the furnace gases. The gas analyzer 17 is connected to the electronic control unit 18, which is associated with the actuators of the regulators throttle valve 10 and gate valve 12, and operates in the automatic mode.

The boiler unit operates as follows.

Held preparation boiler unit for operation, by unit checking the elements of protection, of locks and alarm boiler unit. Run the exhauster 4 and the combustion air ventilator 13 for ventilation flow paths of flue gases, and cold air. It is fulfilled control of fuel pipelines by pressure testing. Organize control of the upper and lower water level in the drum, and at operating the exhauster and the combustion air ventilator are created the required vacuum in the furnace 1. Held the control on the absence of outside air suction into the furnace in accordance with current instructions and supply fuel to the burner 2 for kindling of the boiler unit [5, p.43].

After feeding at the burner, for example, of natural gas, in them there is a mixing of cold air with fuel and ignition of fuel flaring is carried out in the furnace of the boiler unit

1. Furnace gases enter in the convective gas duct 3, in which they give away the thermal energy to the economizer 7 and the air preheater 8 to the temperature cooled gases and, due to the pressure created by the exhauster 4, are removed through the flue duct 5 in the stack 6. After completion of phase kindling of the boiler unit fulfill it connection to heating network. To quit the boiler unit on nominal mode of operations, increased cold air delivery through a duct 9, by opening the control throttle valve 10 in accordance with the regime map for supplying theoretically necessary amount of cold air, containing the oxygen required for complete combustion of the fuel, respective nominal operation condition of the boiler unit. The cold air is then passed into the air duct 14, in which also is supplied and part of the cooled gases thru the bypass pipe 11 using the controlled gate valve 12 in content of carbon monoxide and oxygen in furnace gases. The content of oxygen and of carbon monoxide in the furnace gas is determined by the sampling sensor 16 and the gas analyzer 17. In this case the cooled gases involved in the combustion process is carried function of excess part of the cold air creating the required speed and turbulent conditions the flux of oxygen from the burners 2.

Supply of theoretically necessary part of the cold air thru the air duct 9 and part of cooled gases on equally by mass parts of the excess cold air thru the bypass pipe 11 in the common for them the air duct 14, represents process of substituting the excess part of the cold air by part the cooled flue gases equal mass. Begins the process of mixing and heat recovery heat of the cooled gases by direct action with the cold air in the air duct 14, by which the resulting mixture is supplied to the combustion air ventilator 13, where the mixing process is intensified. Further the air-gas mixture is supplied to the air preheater 8 in which it is heated by waste heat from the furnace gases by means of regenerative heat transfer and stirring is continued. By the duct 15, heated air-gas mixture supplied to the burners 2 in turbulent regime to create a uniform oxygen concentration. Increase in the oxygen supply to the burner 2 allows them to increase the flow of fuel, which is flaring performed in the furnace 1 of the boiler unit. From the furnace 1 the furnace gases enter in the convective gas duct 3, at the beginning which is performed sampling of the furnace gas by the sensor 16. The samples of the furnace gases are supplied to the gas analyzer 17 for determining of the percentage of oxygen and carbon monoxide in it. The results obtained are converted by the gas analyzer 17 into electrical impulses and transmitted to the electronic control unit 18 of the actuators of the regulating throttle 10 and of the regulating valve 12.

At the appearance in the furnace gases of carbon monoxide supply of the cold air is increased by opening the throttle valve 10 on the air duct 9, and reducing the supply of cooled gases, closing the gate valve 12 on the bypass pipe 11 of cooled gases. In the absence of carbon monoxide in the furnace gases and oxygen content in them more than 1%, cold air is decreased, by closing the throttle valve 10 on the air duct 9 , and is increased the supply of the cooled gases, opening the gate valve 12 on the bypass pipe 11 of the cooled gases. Ratio of cold air and cooled gases is not constant and depends on the type, properties and amount of combusted fuel, therefore extremely important to control and regulate the supply of the cold air in the transition of the boiler unit to another type of fuel or changing the mode of operation of the boiler unit, when is required less fuel for burning it. The cool air contains oxygen which is oxidizer for fuel and nitrogen. In the zone of active fuel combustion, the oxygen and nitrogen gases are formed gases of nitrogen oxides which are emitted into the atmosphere, and which harmful of the environment. [6, p. 4]. Increase of overall performance the boiler unit is carried out by a significant reduction of masses excess part the cold air used for complete combustion, by substitution on equal mass part of the cooled gases. The process of substitution is controlled and regulated to maintain the in the furnace gases oxygen content less than 1 % and the absence of carbon monoxide.

The economic and the ecological efficiency of the present invention are illustrated by the following example.

The following is an example of specific performance of the proposed method of operation of the boiler unit, in applied to the excess part of the cold air supplied with the theoretically necessary part of cold air into the burners 2 and which are emitted into the atmosphere together with the cooled gases.

The calculations of the excess part of the cold air, due to suction it along the body of boiler unit, is beyond the frame of this calculation.

The proposed method of operation of the boiler unit is designed for the current model of the boiler unit, located on TPS - 1 of Chisinau, Republic of Moldova, corresponding to applicable regulatory requirements [5].

Data for calculating the economic and environmental efficiency of the proposed method of operation of the boiler unit:

- Rated load of the boiler unit, is 25.0 MW;

- Coefficient of performance of the boiler unit, is 82.0%;

- Type of fuel: natural gas with a higher calorific value is 40.144 MJ/m ³ ;

- Number of operating hours, is 3648 h/year;

- Average annual temperature of cold air, is + 9.4 °C;

- Enthalpy of cold air, is 24.9 id/kg;

- Specific weight of the cold air, is 1.25 kg/m ³ ;

- Temperature of cooled gases, which are thrown into atmosphere, is + 150 °C; Enthalpy of cold air and cooled gases refer to 1 m ³ of natural gas used for burning of fuel at the boiler unit. [3, p. 45]. - Enthalpy of cooled gases at temperature + 150 °C, is 2559.0 kJ/m ;

- Enthalpy of air at temperature + 150 °C, is 2165.0 kJ/m ³ ;

Assume a theoretical and the actual amount of cold air required for complete combustion of the fuel and of combustion products [3, p. 326 - 327]:

- Excess air ratio in the furnace end, is Or = 1.05;

- The theoretically necessary volume of cold air, is V ^° _B = 9.01 m ³ /m ³ ;

- Excess volume of cold air, is AV _B = 0.451 m ³ /m ³ ;

- The theoretical volume of cooled gases, is V ^° _r = 10.22 m ³ /m ³ ;

- Excess volume of water vapor, is AV^o ^ 0.005m ³ /m ³ ;

- Content of the total share of triatomic gases in cooled gases, is 0.266. Specific volume quantity of excess cold air for 1 m of the natural gas, is:

0.456 m ³ /m ³ (0.451 + 0.005);

The excess cold air for 1 m ³ of the natural gas, is: 0.57 kg/m (0.455x1.25);

Determine the annual loss of natural gas for heating of the excess part of the cold air up to the temperature of cooled gases, and annual volume of triatomic gases, which are emissions to the atmosphere:

a) The total amount of natural gas that is burned per hour / year at nominal capacity of25.0 MW boiler unit, is 2734.0 / 9973632 m ³ h/year : [25.0 x 3600 / (0.82 x 40.144)] / [( 2734.0 x 3648)];

b) The specific heat loss of boiler unit for heating the excess parts of cooled gas per 1 m ³ of natural gas is: 970.9 kJ; (2165.0 x 0.455 - 24.9 x 1.25 x 0.455);

c) Sentries heat loss through the use of excess cold air of the boiler unit, is: 2654.4 MJ/h (970.9 x 2734.0 / 1000);

d) Sentries natural gas losses due to the use of excess cold air of boiler unit, is: 66.1 m ³ /h (2654.4 / 40.144);

e) The annual loss of natural gas, is: 241132.0 m ³ /year (66.1 x 3648);

f) The annual quantity of triatomic gases that been formed as a result of heating of the excess cold air by burning the natural gas, which are emissions to the atmosphere and are making the harmful effect on the environment, is: 819.0 t/year (10.22 x 0.266 x 1.25 x 241132) /1000;

On the proposed method of operation of the boiler unit is taken substitution of the excess part of the cold air on equal mass part of cooled gases at maintenance in the furnace gas the oxygen content of 0.5% and the absence of carbon monoxide in it. This part of the cooled gases is 0.51 kg per 1 m of natural gas (0.57 x 0.9). Thus, the remaining part of the excess cold air, containing oxygen that is not involved in the chemical reaction of the fuel combustion and came all together with the theoretically necessary part of the cold air, is 0.06 kg/m ³ (0.57 - 0.51).

Additional data for the calculation of economic and environmental efficiency of the proposed method of operation of the boiler unit, taking into account the substitution part of the excess part of the cold air on equal mass part of the cooled gases:

- Excess air ratio in the furnace end, is = 1.005;

- The theoretically necessary volume of cold air, is V ^° _B = 9.01 m ³ /m ³ ;

- Excess volume of cold air, is AV _B = 0.0451 m ³ /m ³ ;

- The theoretical volume of cooled gases, is V ^° _r = 10.22 m ³ /m ³ ;

- Excess volume of water vapor, is AV _h2o = 0.005m ³ /m ³ ;

- Content of the total share of triatomic gases in cooled gases, is 0.266. Determine the annual loss of natural gas for heating the excess part of the cold air up to the temperature of cooled gases and annual volume of triatomic gases, which are emissions to the atmosphere taking into account of substitution of cold air by equal weight part of the cooled gases:

a) The specific heat loss of boiler unit for heating the excess parts of cooled gas per 1 m ³ of natural gas is: 96.0 kJ (2165.0 x 0.045 - 24.9 x 1.25 x 0.045);

b) Sentries heat loss through the use of excess cold air of the boiler unit, is 262.5 MJ/h (96.0 x 2734.0 / 1000);

c) Sentries natural gas losses due to the use of excess cold air of boiler unit, is:

6.54 m ³ /h (262.5 / 40.144);

d) The annual loss of natural gas, is: 23858 m ³ /year (6.54 x 3648);

e) The annual quantity of emissions triatomic gases that been formed as a result of heating of the excess cold air by burning the natural gas harmful for the ambient is: 81.0 t/yr (10.22 x 0.266 x 1.25 x 23858)/ 1000;

Economic effect of the present invention for a typical boiler unit capacity of 25 MW, consisting in reducing the amount of combustion of natural gas, which is: 23858.0 m ³ /yr.

Environmental effect is to reduce emissions of triatomic gases harmful impact on the environment, which is 81.0 t/yr.

Thus, the invention, compared with the existing types of boiler units, allows:

- Substantially reduce the fuel consumption for heating the excess part of the cold air on the value of the thermal energy contained in the cooled gases that uses for substituting;

- Reduce emissions of triatomic gases in the atmosphere, that have a harmful impact on the environment on the mass amount of cooled gas substituting for the excess cold air;

- May be used on all existing and under construction standard boiler units with minor design changes to flue and air ducts.

Bibliographic data:

1. USSR Inventor's Certificate 846924 from 06.03.1979 (the prototype).

2. USSR Inventor's Certificate 987287 from 23.09.1981 (the prototype).

3. Zah R. G. Boiler units, edition the Energy, the Moscow, 1968, p. 43, 45-46, 103-106, 326, 327.

4. Ionin A. A. Gas supply, edition the Stroyizdat, the Moscow, 1975, p. 310 - 311.

5. «Rules of technical operation of power stations and networks in the Russian Federation)) the Order the Ministry of Energy RF, June 19, 2003 N°223. Registered by the Ministry of Justice RF June 20, 2003 M>4799 _p . 43

6. «Monitored chemical underburning is an effective method reduce nitrogen oxide emission)), dts. P. V. Rosliacov, cts I.L. Ionkin, cts L.E. Egorova, the Moscow Power Engineering Institute (the technical University), 2009, p. 4, 6. http ://www. combienergy. ru/ nts 15. html

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