RU2829657C1 - Method of preparing coal dust at thermal power plant using gas piston drive of mill - Google Patents

Abstract

FIELD: various technological processes.

SUBSTANCE: invention relates to systems for preparation of coal dust at thermal power plants (TPP) for its combustion in furnaces of boilers and can be used in electric power industry and other industries during grinding of raw materials, fuel and materials. Method consists in the fact that coal 10, drying agent and ventilation gas are supplied to mill 2, coal is ground in mill 2, and dust-gas mixture from mill 2 is sent successively to separator 3 for screening of coarse off-grade dust and its return back to mill 2. Finished dust is supplied to dust supply system 4 and further to burners 5 of boiler 6. As a drive of the mill, a gas piston engine (GPE) is used. At that, natural gas is supplied to GPE 11, and exhaust gas flow from GPE 13 is directed to heat exchanger 12, after it the whole exhaust gas flow 13 or its part is directed for mixing with hot air to control temperature and consumption of drying agent of coal and to provide ventilation of the mill. Water is supplied to heat exchanger 12, where it is heated and discharged. Water heated in heat exchanger is removed for heat supply and/or hot water supply to consumers. Heated water from the GPE elements cooling system is discharged into heat exchanger 12. Heat exchanger 12 is built in GPE unit or external heat exchanger is used. Heat exchanger-economizer is used.

EFFECT: method provides energy saving due to reduced use of electric energy for own needs of thermal power plants.

6 cl, 2 dwg

Description

The invention relates to systems for preparing coal dust at thermal power plants (TPP) for its combustion in boiler furnaces and can be used in the electric power and other industries for grinding raw materials, fuel, and materials.

In the generally accepted classification of pulverization systems for thermal power plants burning solid fuel, the individual (for one boiler) systems occupy a preferential place, the fundamental technology of which is as follows. From the bunker of raw crushed coal, it is fed into a descending shaft, where the drying agent is also directed. The main component of the drying agent is hot air taken from the main flow after the air heater of the boiler, and the optimal drying parameters in temperature and flow rate are maintained by mixing either cold air or exhaust flue gases of the boiler with the hot air. Coal with the drying agent enters the mill, from where the dust rises to the separator due to ventilation by the same agent; In it, large, substandard dust is sifted out and sent back to the mill, and the finished, fine dust is sent to the burners by direct injection after mixing with primary air (or in systems with an intermediate bin, it is first deposited by a cyclone in the finished dust bin, and from there, mixed with primary air, it is sent to the burners). The drive of the rotary mechanisms of the mills is traditionally carried out by a synchronous electric motor.

A method for preparing pulverized fuel at a thermal power plant is known (patent RU2788060 C1 IPC F23G5/027 20006/01, published on 16.01.2023, bulletin No. 2), which consists of crushing solid fuel, separating the resulting crushed pulverized fuel and hot air, and feeding the pulverized fuel for combustion in the furnace of a steam boiler with the formation of exhaust flue gases, with pyrolysis of pre-sorted and crushed solid household waste in a gasification tank, the supply of exhaust gases, the formation of generator gas and solid coke residue as a result, the generator gas is fed to the burner devices of the steam boiler and used as a backlight fuel, and the solid coke residue with solid fuel is crushed in a ball drum mill with the supply of hot air for drying, the resulting pulverized combustible mixture with air is fed into the cyclone, separated, the air is released into the atmosphere, and the dust-like combustible mixture is fed into an intermediate bunker, after which the dust-like combustible mixture is sent to the burner devices of the steam boiler for combustion. The scheme also includes a device for traditional dust preparation at the thermal power plant.

The disadvantage of this technical solution on the scale of the entire dust system is the low energy efficiency of the mill's electric drive, since electricity for it is supplied from the thermal power plant's own needs, where it is generated with an efficiency of 35-38%.

A known method of dust preparation at a thermal power plant with a hammer mill (patent RU2487759, IPC B02C 13/04, published 20.07.2013, bulletin No. 20), which comprises a sieve with a clamping frame and a holder, a motor, a stator frame, a rotating device, a rotor spindle, and hammer cutters. The motor is mounted on the stator frame and is connected to the mill rotating device by means of a clutch. The rotating device, sieve and sieve holder together form a grinding chamber. The rotor spindle of the rotating device is connected to the clutch. Hammers with a plurality of cutters are mounted on the rotating device. A large spacer sleeve having inner and outer edges is mounted on the rotor spindle between adjacent frame plates. Both sides of the inner edge and both sides of the outer edge are firmly fixed on the respective adjacent frame plates of the hammers, wherein the inner edge of the spacer sleeve is located on the rotor spindle, and the outer edge is at a distance from the inner side of the mounted hammer cutter, which is from 1 to approximately 60 mm from the trajectory of the hammer cutter.

The disadvantage of this technical solution on the scale of the entire dust system is the low energy efficiency of the mill's electric drive, since electricity for it is supplied from the thermal power plant's own needs, where it is generated with an efficiency of 35-38%.

A ball mill is known (patent RU193347U1, IPC B02C 17/04, B02C 17/06, B02C 17/10, published on 24.10.2019, bulletin No. 30), containing loading and unloading devices, grinding balls, a shaft on which a hollow drum is mounted, disks are placed on the shaft, dividing the drum into sections, while their diameter is increased from the loading device to the unloading device, in the end surface of the drum in the first section there is an annular window for loading the material, and in the last section of the drum there are openings for unloading the finished product, according to the utility model, the hollow drum is made of two parts of variable diameter: the first of a smaller diameter - for preliminary grinding, the second with a diameter 1.4-1.5 larger than the diameter of the first part - for fine grinding, and the diameter of the grinding balls of the second part in 1.4-1.5 larger than the diameter of the balls of the first part, on the inner cylindrical part of the drum of larger diameter, hooks are installed, and their working surface is made at an angle of 30-45° to the radius of the drum, to regulate the distance between the disks on the shaft, spacers are installed between them.

Another disadvantage of this technical solution on the scale of the entire dust system is the low energy efficiency of the mill's electric drive.

A known installation for preparing pulverized fuel (patent RU 197671U1, IPC F23K 1/00, B02C 17/00, published 21.05.2020, bulletin No. 15) consists of a raw coal bin and a finished dust bin, a mill, a separator, dampers, a cyclone, a mill fan, and a finished dust pipeline. In the installation, coal is fed into a ball drum mill, hot (primary) air is supplied, which is necessary for drying the fuel and transporting it, from a hot air box under some pressure, as well as under the action of a vacuum created in the mill by a fan. In the mill, the fuel is crushed and dried, which is sent to the separator, where it is divided into two streams. The finished fine dust is sent to the cyclone, and the coarse (undermilled) dust is returned to the inlet neck of the mill. The cyclone precipitates the finished dust, which is transferred to the dust bunker, where it is accumulated. From the dust bunker, the dust feeders feed the finished dust in the required quantity into the finished dust pipeline and send it through the burners into the boiler furnace for further combustion. The smallest particles that do not settle in the cyclone are transferred to the mill fan, from which they are distributed among the burners.

Another disadvantage of this technical solution on the scale of the entire dust system is the low energy efficiency of the mill's electric drive.

The closest in technical essence to the proposed invention is the method of pulverization (described in patent RU 94313U1, IPC F23K 1/00, published 20.05.2010, bulletin No. 14), according to which the feeder directs coal from the bunker to the mill simultaneously with hot flue gases supplied from the gas intake window of the boiler furnace through the gas intake shaft to the mill. Raw coal in the mill is dried, crushed and transferred through the dust pipeline to the burner device, into which hot air is simultaneously supplied. The fuel in the burner device is mixed with air, where it is ignited and burned in the boiler furnace. The temperature of the gases coming from the furnace to the additional air heater and the mill is adjusted by supplying cold flue gases from the recirculation smoke exhauster.

The disadvantage of this technical solution is the high energy losses associated with the presence of an electric drive for the operation of the mill, which at the thermal power plant consumes electricity from the thermal power plant’s own needs, where it is usually generated with an efficiency of 35-38% (with 62-65% of unavoidable energy losses).

The technical objective of the proposed method for preparing coal dust is to ensure energy conservation in the dust preparation system of a thermal power plant by using a gas piston engine (GPE) as a mill drive and maximum utilization of the energy of the GPE exhaust gases and the heated water of the GPE elements cooling system.

The technical result consists in reducing the use of electricity for the thermal power plant’s own needs and energy conservation.

This is achieved by a method for preparing coal dust at a power plant, in which coal, a drying agent and ventilation gas are fed into a mill, coal is ground in the mill, the dust-gas mixture from the mill is sent sequentially to a separator for screening out large substandard dust and returning it back to the mill, and the finished dust is sent to the dust supply system and then to the boiler burners, according to the invention, a gas-turbine power unit is used as a mill drive, natural gas is fed to the gas-turbine power unit, and the exhaust gas flow from the gas-turbine power unit is sent to a heat exchanger, after which the entire exhaust gas flow or part of it is sent for mixing with hot air to regulate the temperature and flow rate of the coal drying agent and to provide ventilation of the mill, while water is fed to the heat exchanger, where it is heated and removed.

The additionally heated water in the heat exchanger is diverted for heating and/or hot water supply to consumers.

Also, heated water from the cooling system of the gas turbine elements is diverted to the heat exchanger.

The heat exchanger is also built into the gas pressure unit.

In addition, a remote heat exchanger is used.

A heat exchanger-economizer is also used.

The essence of the invention is explained by drawings, where Fig. 1 shows a block diagram of a technological complex implementing a method for preparing coal dust, and the following designations are adopted:

1 - GPD (without equipment for generating electricity), installed as a mill drive;

2 - mill (hammer, ball drum or medium-speed roller);

3 - dust separator;

4 - dust supply system to the boiler (direct injection or with an intermediate dust bin);

5 - burners;

6 - boiler;

7 - bunker for raw crushed coal;

8 - main drying agent (only hot air from the main air heater);

9 - descending shaft for drying raw crushed coal;

10 - supply of coal, drying agent and ventilation gas to the mill;

11 - supply of natural gas to the gas pump;

12 - built-in or remote heat exchanger;

13 - exhaust gases of the gas turbine engine;

14 and 15 - use of exhaust gases after heat exchanger 12, namely:

14 - supply of exhaust gases to the main coal drying agent to regulate drying parameters;

15 - the flow of emissions of the remaining exhaust gases into the atmosphere through its own pipe or their discharge into the boiler exhaust gas box leading to the TPP chimney;

16 - water supply pipeline to the heat exchanger;

17 - pipeline for removing heated water from the heat exchanger for the purpose of heat supply and/or hot water supply to consumers;

18 - water supply to the gas turbine engine for cooling the gas turbine engine elements;

19 - removal of water heated during cooling of the gas turbine elements to the inlet of the heat exchanger.

Fig. 2 shows the diagram of the distribution of energy supplied to the gas turbine engine with natural gas. The following designations are used in it:

20 - energy of natural gas entering the gas turbine engine = 100%;

21 - useful energy ≈ 85%;

22 - mechanical energy transmitted to the mill rotor (to the drive of the ball mill drum) ≈ 42%;

23 - utilized thermal energy of exhaust gases ≈ 23%;

24 - utilized thermal energy of water cooling the elements of the gas turbine engine (this is the engine cooling water jacket, oil circuit cooler) ≈15%;

25 - total energy losses ≈15%, including:

26 - thermal energy losses in the gas turbine itself ≈ 5%;

27 - losses of thermal energy with exhaust gases of the gas turbine engine emitted into the atmosphere ≈ 10%.

The method for preparing coal dust at a power plant according to the invention is carried out as follows. A GPD1 is used as a mill drive. The output shaft of the GPD 1 is directly connected to the rotor shaft of a hammer or roller mill 2 (in the case of a ball drum mill - to the drum drive). The power of the GPD 1 is the same as in the case of an electric motor. An electronic control system ensures an optimal rotation speed of the rotor of the mill 2. The installation with the GPD 1 does not contain equipment for generating electricity. Natural gas 11 is fed into the GPD 1. Coal, drying agent and ventilation gas are fed 10 to the mill 2 through a descending shaft 9; coal is ground in the mill 2; the dust and gas mixture from the mill 2 is directed sequentially to the separator 3 for screening out large, substandard dust and returning it back to the mill 2, and the finished dust is directed to the dust supply system 4 to the boiler 6 and then to the burners 5 of the boiler 6. The entire flow of exhaust gases 13 with an initial temperature of 400-600 °C from the gas-exhaust unit 1 is directed to the heat exchanger 12, for example, an economizer built into the gas-exhaust unit block or located separately ("remote"); water is fed to the heat exchanger 12 via pipeline 16 for heating it; heated water is discharged via pipeline 17 for heating and/or hot water supply to consumers. In the cooling system of the GPE elements 1, the cooling water supplied to the GPE 1 through the inlet 18 is heated and is discharged through the outlet 19 to the inlet of the heat exchanger 12, mixing with the flow 16. The cooled exhaust gases 13 after the heat exchanger 12 are used in the following way (in Fig. 1 they are shown by dotted arrows). The entire flow of exhaust gases 13 or part of the flow of exhaust gases 13 is directed through the exhaust gas inlet 14 for mixing with hot air 8 to regulate the temperature and flow rate of the coal drying agent and to ensure ventilation of the mill 2; the remainder of the exhaust gases 13 by the emission flow 15 can be emitted into the atmosphere through its exhaust pipe or directed into a common box with the boiler exhaust gases leading to the TPP chimney.

This method provides positive side effects: replacing the long flue gas duct for mixing the thermal power plant flue gases into the drying agent with a short flue gas duct of exhaust gases after the heat exchanger located next to the mill; mixing into the coal dust preparation tract of a virtually inert gas with an oxygen content of about 1%, which will increase the fire safety of the entire dust preparation system in comparison with the method of drying coal with hot air only.

In order to ensure the requirements for gas supply to industrial facilities, natural gas is supplied to GPD 1 within the pulverization department of the thermal power plant using the "pipe in pipe" option, and to reduce noise levels in production areas - by covering GPD 1 with a noise-proof casing. The operating conditions and parameters of GPD 1, its dimensions, motor service life before major and medium repairs, consumables and other information about GPD are provided by manufacturers within the technical specifications for GPD, taking into account the exclusion of unnecessary in this case electric power generating equipment contained in a mini-CHP with GPD, and, as an option, the placement of a built-in heat exchanger in the GPD block.

Energy saving as a result of using the present invention is ensured as follows. When using an electric drive for a mill, electric power for it is supplied from the TPP's own needs, and it is generated at a coal-burning TPP with an efficiency of 35-38%. This is a well-known fact, following from the theory of energy distribution in a steam turbine cycle of a TPP (Rankine cycle), and has been repeatedly confirmed. As shown by tests of a gas turbine engine when using it as a source of only mechanical energy (i.e. without equipment generating electric power), the efficiency of converting fuel energy into mechanical energy is approximately 42%; in addition, most of the heat of the gas turbine exhaust gases (about 23%) and the heat of the water heated during cooling of the gas turbine elements (about 15%) are used usefully. Losses in the gas turbine engine itself are about 5%; another 10% is lost with the emission of exhaust gases into the atmosphere with a temperature of 130-150°C.

As a result, energy losses for a traditional electric drive are 65-68%, while for the proposed method with a gas-turbine engine - about 15% (i.e. more than 4 times more than when using an electric drive). The fuel efficiency coefficient in the gas-turbine engine variant can reach 85%.

The use of the invention makes it possible to ensure energy conservation in the dust preparation system at the thermal power plant by using a gas-turbine drive as a mill drive and maximum utilization of the energy of the gas-turbine exhaust gases and the heated water of its cooling system and to reduce the use of electricity for the thermal power plant's own needs.

Claims (6)

1. A method for preparing coal dust at a thermal power plant (TPP), in which coal, a drying agent and ventilation gas are fed into a mill, the coal is ground in the mill, the dust and gas mixture from the mill is sent sequentially to a separator for screening out large substandard dust and returning it back to the mill, and the finished dust is sent to a dust supply system and then to the boiler burners, characterized in that a gas piston engine (GPE) is used as a mill drive, natural gas is fed to the GPE, and the exhaust gas flow from the GPE is sent to a heat exchanger, after which the entire exhaust gas flow or part of it is sent for mixing with hot air to regulate the temperature and flow rate of the coal drying agent and to provide ventilation of the mill, while water is fed to the heat exchanger, where it is heated and removed. 2. A method for preparing coal dust at a power plant according to paragraph 1, characterized in that the water heated in the heat exchanger is diverted for heat supply and/or hot water supply to consumers. 3. A method for preparing coal dust at a power plant according to paragraph 1, characterized in that heated water from the cooling system of the gas-turbine engine elements is discharged into a heat exchanger. 4. A method for preparing coal dust at a power plant according to paragraph 1, characterized in that the heat exchanger is built into the gas pressure unit. 5. A method for preparing coal dust at a power plant according to paragraph 1, characterized in that a remote heat exchanger is used. 6. A method for preparing coal dust at a power plant according to paragraph 1, characterized in that a heat exchanger-economizer is used.