1. Application of heat pipe heat exchanger in industrial boiler
The operating efficiency of industrial boilers in China is generally low, usually 8~10% lower than the design efficiency. The main reason is that the exhaust gas temperature is high, the excess air coefficient is too large, the ash content is too high, and there is another type of small industrial boiler. It refers to a small boiler with a capacity of 2t/h or less. There is no heating surface at the tail, and the exhaust gas temperature is higher, which can be 250 °C. Therefore, the use of heat pipe heat exchanger to recover flue gas waste heat, reduce the flue gas temperature to improve boiler efficiency, has a good prospect.
1. Matching of heat pipe heat exchanger and conventional heat exchanger
In addition to small industrial boilers without tail heating surfaces, most small industrial boilers have cast iron economizers at the tail, and large industrial boilers with steel economizers and steel pipe air preheaters at the end. Heat pipe heat exchangers can be matched to conventional heat exchangers in their application, each with its own characteristics. For example, cast iron economizer has a wide range of applications, and its advantages are: durable, pressure-bearing (feed pump can be installed at the economizer inlet), and the price is low; the disadvantages are: large weight, large size, easy to block ash, and complicated structure (by Rib tube and cast iron elbow are connected). The heat pipe economizer has good low temperature corrosion resistance. Under the same flue gas temperature condition, the wall temperature is high, the structure is compact, the volume is small, the weight is light, and the flue gas side resistance can be designed to be small; the disadvantage is that the price is high. Usually the water side is atmospheric. Cast iron economizer and heat pipe economizer have their own advantages and disadvantages. If it is a boiler without economizer, we advocate the installation of heat pipe economizer; if it is a boiler with cast iron economizer, we advocate the installation of heat pipe The heat exchanger (air preheater or economizer) is matched with the existing cast iron economizer without dismantling the iron economizer. The specific application form is determined according to the actual situation. In particular, we have an air preheater behind the iron economizer, which is suitable for retrofitting small industrial boilers with iron economizers.
For industrial boilers above 4t/h, the tail pipe has been equipped with steel pipe economizer and steel pipe air preheater. If the exhaust gas temperature is greater than 180 °C, a heat pipe heat exchanger can be installed behind it.
2, heat pipe heat exchanger features
Gas-gas-type heat pipe heat exchanger, ie heat pipe air preheater, is applied in industrial boilers. It can arrange ribs on both sides of hot and cold fluids. It has excellent thermal performance and compact structure, which can best reflect the advantages of heat pipe heat exchanger. . Gas-water heat pipe heat exchanger, ie heat pipe economizer, is used in industrial boilers. Its main advantage is its low temperature corrosion resistance because it has a higher thermal resistance on the water side than cast iron or pipe economizer. Its thermal resistance on the gas side is smaller than the latter two, so under the same conditions, the wall temperature is higher, it is not easy to corrode and block the ash; however, the iron economizer is easy to corrode and block the ash.
3. Application of heat pipe water heater
The heat pipe water boiler has a unique structure, compact volume, and small heat exchange capacity, for example, 9.36×104 KJ/h (2×104 Kcal/h), which is required for drinking water for employees of factories below 2000 people. It can also be designed in the form of boiling water-hot water. When the water is supplied, the cold water enters automatically, and the boiling water automatically flows out. When it is not needed for boiling water, it is switched to another outlet, that is, hot water is supplied.
Since the heat exchanger of the heat pipe water heater has a small amount of heat exchange, it is generally combined with various types of economizers or various types of air preheaters.
4, various combination devices
In industrial boilers, combined heat recovery is often used in combination, as described above. The most common way we promote in the promotion is to simultaneously heat the air and water. It has obvious advantages: the use of hot air rib combustion has great benefits for improving ignition and combustion. The hot air temperature does not have to be too high, more than 50 ° C. Visible effects; in addition, hot water into the boiler or hot water supply activities is also urgently required by the factory. A good solution in the application of a combined heat exchanger is that substantially half of the heat pipes are used to heat the air, and the other half are used to heat the hot water. The combination of gas-gas and gas-water is connected in parallel and in series.
Second, the application of heat pipe heat exchanger in industrial furnace (smelting furnace)
Industrial kiln (smelting furnace) is a large energy consumer, and the variety of kiln is very numerous. The domestic average level of thermal efficiency of the furnace is half of the foreign advanced level. The total annual consumption of standard coal is more than 100 million tons, which has great energy saving potential. The exhaust gas temperature is higher, often exceeds 300 ° C, and some reach 500 ~ 600 ° C or even higher. As a waste heat recovery scheme, more air preheaters (of course, waste heat boilers can also be used), for flue gas temperature At medium and low temperature residual heat below 400 °C, the air preheater is mainly used, and the heat pipe heat exchanger can be used here. China's Ministry of Machinery Industry standard "mechanical industry energy-saving design technical regulations" mentioned: when the industrial furnace kiln exhaust temperature is below 400 °C, heat pipe heat exchangers should be used.
A large part of the industrial furnaces and kiln are not equipped with induced draft fans, which require low heat-resistance equipment. At the same time, due to the narrow position, the equipment is required to be compact, and it is especially suitable for the application of heat pipe air preheaters. We apply the following layouts:
(1) Kiln + heat pipe air preheater
(2) Kiln + heat pipe water heater + heat pipe air preheater (for high exhaust gas temperature)
(3) Kiln + jet or aluminized tube air preheater + heat pipe air preheater (for higher preheated air temperature)
(4) Kiln + various types of air preheater + heat pipe water heater or heat pipe water heater and water heater composite device
(5) Kiln + heat pipe waste heat boiler
(6) Kiln + other heat exchanger + heat pipe waste heat boiler
(7) Kiln + heat pipe waste heat boiler + other heat exchanger
1. Air preheater or waste heat boiler
The definition of the heat pipe heat exchanger should be considered from the following aspects:
1 According to the needs of enterprises, if industrial furnaces need combustion support, air preheaters should be used as much as possible. When the process requires steam, use a waste heat boiler.
2 According to the possibility of waste heat recovery, the waste heat boiler is only possible in industrial furnaces with a exhaust gas temperature greater than 300 °C.
3 Reliability, if carbon steel-water heat pipe is used, the maximum working temperature of the working fluid in the pipe is 300 °C to ensure safety; the lowest wall outside the heat pipe is larger than the acid dew point to avoid corrosion. / These restrictions also have a direct impact on the choice of heat exchanger type.
4 Economical, type selection When there are multiple options, economic comparison is required. (1), (2), (3), (4), (5), (6), (7) are selected according to the specific circumstances.
2. Gas-gas and gas-water combined heat pipe heat exchanger
Since the exhaust temperature of industrial kilns is often high, sometimes exceeding 400 ° C, it can reach 500 ~ 600 ° C, or even higher. As a gas-gas heat pipe heat exchanger, the maximum allowable flue gas inlet temperature is only 350~400 °C under normal conditions. At this time, the gas-water and gas-gas combined heat pipe heat exchanger is a good one. The scheme is to apply a gas-water heat exchanger in a region where the flue gas temperature is higher than 350 to 400 ° C, and a gas-gas heat pipe heat exchanger in a region where the flue gas temperature is low. The above divided temperature is based on the application of carbon steel water heat pipe, and the maximum allowable temperature of the working medium is 300 ° C, which belongs to the above form (2).
3. Matching of heat pipe heat exchanger
Industrial kilns sometimes require hot air to support combustion at temperatures of 300 to 400 ° C or higher. When the hot air temperature exceeds 250 °C, only the heat pipe air preheater will make the maximum working temperature of the carbon steel water heat pipe exceed 300 °C, so the air is heated from the inlet temperature to 250 °C, and the heat pipe air preheater is used. A conventional air heater is used when the temperature rises to a higher value at 250 ° C, which is a reasonable arrangement, as in the above form (3). Conventional air preheaters are available in aluminized steel tubes or jets because they are well matched to the heat pipe air preheater.
4. Different types of heat pipe waste heat boilers of heat pipe waste heat boilers can be divided into two types:
Single-tube type and header type, the former is suitable for small-capacity waste heat boilers, and the heat pipe discharge section is directly inserted into the steam drum. The maximum capacity we have developed is 2t/h (evaporation); the latter is suitable for large-capacity waste heat boilers. The heat pipe exothermic section is inserted into the vertical large-diameter pipe. These large-diameter pipes are led out from the header and passed to the steam drum. The capacity we have developed is 1-10t/h (evaporation). The structure of the two forms of steam side is different.
Due to the limitation of the maximum working temperature of the carbon steel-water heat pipe working medium of 300 °C, the steam working pressure of the waste heat boiler will not exceed 1 MPa, and the inlet temperature of the flue gas should not be too high, such as 450~500 °C is the highest value. When the temperature of the flue gas inlet is high, the above form (6) can be used.
5. Gas-water heat pipe heat exchanger in industrial furnace
In industrial kilns, due to the needs of life or the needs of production processes, it is sometimes necessary to apply the above forms (4). In many cases, it is a composite device for heat pipe water heaters and water heaters, which has considerable application prospects, especially in township enterprises. .
Third, the conclusion
Heat pipe heat exchangers can play an irreplaceable role in industrial boilers and industrial furnaces. This equipment can be widely used in the technical transformation of existing boilers and furnaces, as well as in new boilers and furnaces.
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