The development of the boiler pot and furnace two aspects:
In the first half of the 18th century, steam turbines used in coal mines in the United Kingdom, including the original Watt steam engine, had a steam pressure equal to atmospheric pressure. The second half of the 18th century switched to steam above atmospheric pressure. The 19th century, the commonly used steam pressure increased to about 0.8 MPa. In line with this, the earliest steam boiler is a large-diameter cylindrical water-filled vertical shell, and later switched to horizontal shell, fired in the brick furnace below the shell.
As the boiler is bigger and bigger, in order to increase the heating area, a fire barrel is installed in the shell, a fire is burned at the front of the fire barrel, the smoke comes out from behind the fire barrel, and is discharged to the chimney through the brickwork flue and heats the exterior of the shell, Known as the fire tube boiler. Initially only installed a fire tube, known as the single-fire boiler or Cornell boiler, and later added to two fire extinguishers, known as double-fire boiler or Lan Kaixiang boiler.
Around 1830, a fire-tube boiler appeared after mastering the production and expansion of high-quality steel pipes. Some tubes are housed in the shell and form the main heating surface of the boiler through which fire (flue gas) flows. Install as many tubes below the water line of the pan as horizontal external tempering tube boilers. It's metal consumption is low, but requires a lot of masonry.
Mid-19th century, appeared in the water boiler. Boiler heating surface is the water outside the shell, replacing the shell itself and the shell fire tube, fire tube. Boiler heating area and steam pressure increase is no longer limited by the shell diameter, is conducive to improving boiler evaporation and steam pressure. This boiler in the cylindrical shell was renamed the drum, or drum. The original water pipe boiler only straight pipe, straight pipe boiler pressure and capacity are limited.
Turbines began to develop in the early twentieth century, requiring the deployment of boilers with high capacity and steam parameters. Straight water pipe boiler can not meet the requirements. With the development of manufacturing technology and water treatment technology, there have been bent water tube boilers. The beginning is the use of multi-drum style. With the application of water wall, superheater and economizer, and the improvement of steam and water separation components inside the drum, the number of drums gradually decreases, which not only saves the metal but also improves the pressure, temperature, capacity and efficiency of the boiler .
Auxiliary circulation boiler, also known as forced circulation boiler, which is based on the natural circulation boiler developed. Circulation pumps are installed in the downcomer system to enhance the water circulation on the heated surfaces. There is no boiler drum in the DC boiler. The feedwater is fed into the economizer by the feedwater pump. The heated surface is evaporated by the water wall and the superheater to turn overheated steam to the steam turbine. The flow resistance of all the parts is overcome by the feed pump.
After World War II, both types of boilers saw a rapid development as generating units at the time required high temperature, high pressure and large capacity. The purpose of the development of these two boilers is to reduce or eliminate the use of drums, small diameter tubes can be used as the heating surface, the heating surface can be relatively freely arranged. As automation and water treatment technologies advance, they are maturing. The DC boiler is the only boiler that can be used at supercritical pressure. The largest single capacity in the 1970s was 27 MPa with a 1,300 MW generator set. Later developed by the auxiliary circulation boiler and the combination of the DC boiler complex cycle boiler.
In the development of the boiler, the type of fuel has a great influence on the hearth and combustion equipment. Therefore, not only the development of various types of furnace to adapt to different fuel combustion characteristics, but also improve the combustion efficiency to save energy. In addition, technological improvements in furnaces and combustion equipment also require minimization of pollutants (sulfur oxides and nitrogen oxides) in boiler fumes,
The early shell boiler with a fixed grate, multi-burning with high-quality coal and firewood, coal and slag are used by hand. After the emergence of straight-tube boiler mechanized grate began to be used, including chain grate has been widely used. Grate under the wind never sub-paragraph "system warehouse wind" into a section of the supply air.
Early furnace low, low combustion efficiency. Later, people realized the function of the furnace volume and structure in combustion, made the furnace high, and used furnace arch and secondary air, so as to improve the combustion efficiency.
When the generator set power exceeds 6 MWh, the grates of these layers are too large in size and complicated in structure to be easily arranged. Therefore, in the 1920s, the use of chamber burners and chamber burners to burn pulverized coal and oil was started. Pulverized coal pulverized coal pulverized with a burner into the furnace combustion, the capacity of the generator set is no longer subject to combustion equipment restrictions. Since the beginning of World War II, almost all power plant boilers use chamber burners.
Early manufacture of pulverized coal fired with a U-shaped flame. The pulverized coal flowing from the burner first descends in the furnace and then turns up again. Later appeared the front wall of the cyclone burner layout, the flame in the hearth to form L-shaped torch. As the boiler capacity increases, the number of cyclone burners also begins to increase, either on the two side walls or on the front and back walls. Around 1930 there was a direct current burner arranged in the corners of the furnace and mostly in the form of a tangential combustion.
After the Second World War, oil was cheap and many countries started to adopt oil-fired boilers widely. The degree of automation of oil-fired boilers is easy to improve. After oil price increases in the 1970s, many countries have redirected their use of coal resources. At this time, the capacity of power plant boilers is also getting larger and larger. It requires that the combustion equipment not only can burn completely but also has stable fire, reliable operation and low load performance, and must also reduce the pollutants in exhaust smoke.