In addition, since 1950s, preheaters for preheating air have been used in industrial furnaces in China. The main forms are tubular, cylindrical radial and cast iron block heat exchangers, but the heat exchange efficiency is low. In 1980s, domestic heat exchangers, such as jet type, jet radiation type and composite table type, were developed one after another, which mainly solved the problem of medium and low temperature waste heat recovery. The recovery of flue gas waste heat below 100 degrees has achieved remarkable results, and the heat exchange efficiency has been improved. However, at high temperature, it is still limited by the material of heat exchanger, with short service life, heavy maintenance workload or high solid cost, which affects its popularization and use.
At the beginning of the 20th century, China developed a ceramic heat exchanger. Its production process is basically the same as that of kiln furniture, and thermal conductivity and oxidation resistance are the main application properties of the material. Its principle is to place the ceramic heat exchanger near the outlet of the flue with high temperature, without adding cold air and high temperature protection. When the kiln temperature is 1250- 1450℃, the flue outlet temperature should be 1000- 1300℃, and the waste heat recovered by ceramic heat exchanger can reach 450-750℃.
Ceramic heat exchanger has been well developed under the limitation of metal heat exchanger, because it solves the problems of corrosion resistance and high temperature resistance and becomes the best heat exchanger for recovering high temperature waste heat. After years of production practice, it shows that the effect of ceramic heat exchanger is good. Its main advantages are good thermal conductivity, high high temperature strength, good oxidation resistance and thermal shock resistance. Long service life, small maintenance, reliable and stable performance and simple operation. It is the best device to recover the waste heat of high temperature flue gas at present. At present, ceramic heat exchangers can be used in main hot kilns in metallurgy, nonferrous metals, refractories, chemicals, building materials and other industries.
Other ways of flue gas waste heat recovery:
1. Waste heat recovery device (gas-water)
Heat pipe waste heat recovery device is a special equipment for coal-fired, oil-fired and gas-fired boilers, which is installed at the smoke outlet of the boiler to recover the waste heat of flue gas to heat domestic water or make up water for the boiler. Its structure is as shown in the figure: the lower part is a flue, the upper part is a water tank, and there is a partition in the middle. The top is provided with a safety valve, a pressure gauge and a thermometer interface, and the water tank is provided with a water inlet and a sewage outlet. When working, the flue gas flows through the flue of the heat pipe waste heat regenerator to scour the lower end of the heat pipe, which absorbs heat and conducts heat to the upper end, and the upper end of the heat pipe emits heat to heat water. In order to prevent ash blockage and corrosion, the outlet flue gas temperature of waste heat recovery device is generally controlled above the dew point, that is, the flue gas temperature of oil-fired and coal-fired boilers is ≮ 130℃, and the flue gas temperature of gas-fired boilers is ≮ 100℃, saving fuel by 4- 18%.
2. Waste heat recovery device (gas-gas)
Heat pipe waste heat recovery device is a special equipment for oil, coal and gas boilers. Installed in the flue or flue of boiler to recover the waste heat of flue gas and heat the air. Hot air can be used as combustion-supporting and drying material for boilers. Its structure is as shown in the figure: the pipeline is surrounded by boxes, and the middle partition separates the channels on both sides. The heat pipe is a full fin pipe, and a single heat pipe can be replaced. When working, high-temperature flue gas flows upward from the left channel to wash the heat pipe, at this time, the heat pipe absorbs heat, and the heat release temperature of flue gas drops. The heat absorbed by the heat pipe leads to the right end, and the cold air washes down the heat pipe from the right channel. At this time, the heat pipe releases heat and the air absorption temperature rises. The flue gas temperature at the outlet of the waste heat recovery device shall not be lower than the dew point.
3, waste heat ammonia absorption refrigeration
The absorption refrigeration unit that uses ammonia as refrigerant and water as absorbent to realize solution circulation is the ammonia absorption refrigeration unit. Because ammonia is used as refrigerant, the refrigeration temperature is between -30 degrees and 5 degrees, and the application range is very wide. Waste heat recovery refrigeration can be used as air conditioning or industrial cold source. After nearly 10 years of research, Taishan Group has made some achievements in this respect.