Usually, when using the dryer equipment, the heat source is first considered, generally improving the efficiency and saving energy, and using the local material to complete the drying process. Next, I will introduce two common environmentally friendly reuse heating systems.
Steam is a clean, safe and inexpensive source of heat. If steam of 0.4 to 0.8 MPa is available, the drying medium (air, nitrogen, etc.) can be heated to 150-160° by a heat exchanger. With steam as the heat source, indirect heat exchange is often used, and various forms of heat exchangers are used as heating equipment. The heat exchanger is generally formed in the form of a slab tube and a U-tube. In order to prevent corrosion and increase heat transfer efficiency, steel products are generally galvanized.
The heat transfer coefficient of the above heat exchanger is generally 80 to 250 KJ / (m 2 · h · ° C), which mainly varies with the mass flow rate of the heated air, and the relatively economical air mass flow rate is 4 to 10 kg / (m 2 / s). This heating method is more economical and reasonable when using waste steam from power plants and enterprises.
It should be noted that this heat exchanger must also be equipped with a good automatic drainage system, and the displacement of the steam trap should exceed 3 to 4 times the amount of condensation water in the heat exchanger. In addition, the heat exchanger should be used to drain the remaining water when it is not in use, so as not to burst and rupture the tube in the cold weather.
2. The flue gas
Flue gases are generally produced by the combustion of solid or liquid fuels, most of which contain a certain amount of dust and carbon black. Except in a few cases, they are generally utilized in indirect heating. According to different flue gas temperatures, the drying medium can be heated to 250-450 ° C through a high temperature heat exchanger, up to 600 ° C.
The heat exchangers are available in a variety of tubes, plates, sleeves, slabs and monoliths. Their heat transfer coefficients are generally 40-100 KJ/(m2·h·°C). The gas velocity in the heat pipe of the heat exchanger is generally 6-15 m/s.
The heat utilization of the flue gas depends mainly on the temperature of the exhaust gas, the insulation of the equipment and piping, the fuel loss and the type of heat exchanger used. In order to improve heat utilization, part of the exhaust gas is returned to the combustion chamber.
In short, it should be considered comprehensively based on production scale, investment size, operating costs, flue gas temperature and source.
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