Research and development in the field of design of coal-fired boilers

The article introduces two research and development works of Joint Stock Union "Emalians" (Russian Federation) in the field of designing coal-fired boiler for large capacity units (330 MW and 660 MW). Briefly describe the main structure, technical and ecological characteristics of boilers.

Boiler PP-1000-24.5-565KT

The Taganrog boiler factory under the Emalians Joint Stock Union is designing the PP-1000-24.5-565 KT boiler, with a steam capacity of 1,000 t / h to operate in the component of the unit with a capacity of 330 MW. .

The boiler (Figure 1) is designed to burn D-grade coal of the Kuznetsk coal mine. Boiler type direct flow, supercritical steam pressure, single steam re-drying (one time) and solid slag discharge. Boiler guarantees to operate and start with sliding parameters.

The boiler is arranged in a shape including a prismatic combustion chamber, the cold funnel in the lower part, the horizontal smoke path, the turning chamber, moving to the downward convection tunnel. In the horizontal smoke section, the heating surfaces of categories 1 and 2 superheater and including the water heater are arranged.

The blinds of the combustion chamber and including the barrier surfaces of the horizontal and downward flue lines in the form of panels from the smooth vertical pipes welded into a closed wall block (not allowing smoke to escape) by strips flat steel between two pipes.

The air is dried in three-compartment heat-recovery type air dryers. Turbine warmers can be set, thereby reducing the exhaust smoke temperature.
Thanks to the turbine heater arrangement, the total boiler efficiency can be increased from 92.5 ‰ to 94.

To ensure that it meets the stringent ecological standards of the Russian Federation, the boiler design applies the following measures:

- The combustion chamber is designed with a square cross section. Nozzles and all fuel and air inlets entering the combustion chamber are arranged in a tangential manner.

- Three layers of horizontal slot-type direct injection nozzles are arranged in the corners of the combustion chamber.

- Arrange the NOx reduction layer to N2 by supplying 16 - 20 ‰ of fine powder coal (R90 = 7 ‰) above the upper nozzle layer with excess air coefficient α ≤ 0.35.

- Arrange periodic burning by supplying air level 2 through the nozzles on the side walls of the combustion chamber into the area of the nozzle floors from the outside of the eddy current in the combustion chamber.

- Arranging to bring level 3 air into the top of the reduction equipment in quantity 20

- 23% to exhaust the combustible substances of the fuel brought from the reduction zone.

The main nozzles on each of the 3 floors are structured in the form of a uniform nozzle block. Each injector block (Fig. 2) has two fuel inputs from different mills and two starter injectors. The nozzles of each injector block have the ability to rotate in the vertical plane, so that the height of the torch position in the combustion chamber can be adjusted. To rotate the nozzles, each unit is fitted with an additional electric actuator.

The NOx elimination nozzles are positioned higher than the main nozzles, each with its own powder coal path in the center of the device. The recirculating cold air is introduced through the outer tube of the deoxygenated nozzle to reduce the oxygen concentration in the reduction zone and to cool the deoxygenated nozzles when the mill is shut down.

For better mixing, the inlet of a mixture of coal-air, recirculating gas, and level 3 air entering the combustion chamber is performed in a reverse vortex direction compared to the main nozzles.

The aforementioned combustion scheme allows for reduction of NOx emissions to 350 mg / m3, while maintaining operational reliability of heating surfaces in the combustion chamber and at the outlet from the combustion chamber and unrestricted boiler loads on the curing condition of heated surfaces.

In addition to the above measures, in order to perfect the ecological characteristics, the boiler structure has applied the most modern design solutions to improve economic - technical indicators and optimize the criteria. in terms of volume - the size of the boiler.

Boiler PP-2050-25-570KT

In 2007, LHCP "Emalians" researched and developed the PP-2050-25-570KT boiler design, boiler capacity of 2050 t / h, unit 660 MW with supercritical parameters, burning coal at Ekibastusk mine. (almost like coal mines Hon Gai, Cam Pha), using madut as a starter fuel.

Tower boilers, boiler chamber height of nearly 55 m (depending on bevel conveyor height), roofing with lightweight panels. The important advantage of the tower kiln is that the smoke flow is more evenly distributed compared to the Π and T-shaped boilers. This facilitates reduction of abrasion on the heating surfaces. In addition, in this type of boiler the aerodynamic drag is minimal due to uniform smoke flow and the smoke diversion is performed on the length side of the convection tunnel. Reducing the resistance of the smoke glands, allowing to reduce the energy consumption for smoke extraction.

Another advantage of this type of furnace is a more compact layout, thereby reducing equipment costs by reducing the length of the tube and the shield surface. The curtain walls of the boiler are divided into the lower radiation part, the upper radiation part and the screens of the upstream convection smoke. After the combustion chamber in the smoke line going up, overheating and convection tubes are arranged, including the water heater.

Class 1 and 2 superheated steam temperatures are high, so high quality heat resistant steels should be used.

The rectangular combustion chamber of the boiler is designed with high thermal stress cross-section (over 5 MW / m2) and low emission vortex-type nozzles arranged in opposite directions, ensuring coal burning with High ash, stable low volatile and high efficiency.

The rectangular combustion chamber (28 x 12 m) is equipped with 32 vortex-type powder coal nozzles, arranged on two floors, in opposite directions on the front and rear walls of the combustion chamber. On the main nozzles (on the 3rd floor) put 8 coupling nozzles of the NOx removal layer. Fine-grained coal is fed into those nozzles for an amount of 15 of total fuel consumption. On the reducing floor, put 10 level 3 wind nozzles.

The NOx elimination nozzles and nozzles are directed downwards at an angle of 10 ° to the horizontal plane, with a tangent component, each creating two eddy currents.
Powder coal processing system closed type, blowing directly. Fuel is dried by hot air. Coal is crushed in 8 shaft type mill, the average speed of rotation MVS - 265 type.

Air drying is performed using tubular air dryers. The turbine heat exchanger heater is placed inside the air dryer to reduce the exhaust smoke temperature. The heat exchanger water part is connected to the short-cut section of the low-pressure heater.

In summary, the PP-1000-24.5-565KT boilers for the 330 MW unit and PP-2050-25-570KT for the 660 MW unit all meet the stringent environmental standards of Russia and the EU, The boiler is equipped with complete electrostatic dusts, ensuring the concentration of dust discharged into the atmosphere at 30 mg / m3, wet limestone SOx reduction equipment to achieve SOx concentrations lower than 200 mg / m3 ( standard level is 400 mg / m3).

Due to the high pressure and vapor temperature parameters, the heating surfaces are designed with high temperature resistant steels (austenitic steels). Boiler operates with a steam temperature of 600 / 620oC, is equipped with modern auxiliary equipment, so that the efficiency of the unit reaches 44 - 46.