It is summarized that most of the drying requires heat source heating, and its energy consumption accounts for more than one-third of the total production cost. The hot air furnace and its heat exchange equipment are commonly used in China's dry heat source, and the heat exchange equipment has various forms, but development New high-efficiency and low-energy equipment to gradually update old equipment is a top priority. The heat exchange equipment composed of heat pipes as heat transfer elements is more unique and is being applied to various industries more and more widely. This paper mainly introduces the development of heat pipe technology and a series of characteristics of heat exchange equipment.
Among the many heat transfer elements, the heat pipe is one of the well-known heat transfer elements of the zui, which can transfer a large amount of heat through a small cross-sectional area thereof without any external power. International research and application of heat pipe technology began in the 1960s. Since the 1970s, China has carried out research on heat transfer performance of heat pipes and application research of heat pipes in electronic component cooling and spacecraft. In the early 1980s, China's heat pipe research and development focused on energy conservation and rational use of energy. Since 1976, the heat pipe research group of Nanjing Institute of Chemical Technology has started the application and development of heat pipe technology in industrial waste heat recovery, mainly researching heat pipe heat exchange equipment. In April 1980, the gas-gas heat pipe heat exchanger developed by Nanjing Institute of Chemical Technology and Nanjing Refinery was officially put into operation in Nanjing Refinery; at the end of 1981, China* Taiwan carbon steel-water heat pipe waste heat boiler It was successfully developed by Nanjing Institute of Chemical Technology and put into operation in Jiangsu Rudong Fertilizer Plant. The formal operation of the above two heat pipe heat exchange equipments has greatly promoted the design and calculation of heat pipe heat exchangers and the heat transfer performance, internal resistance, steel-water compatibility, liquid filling, design, waste heat recovery applications, etc. It solves some technical problems in the application of cheap carbon steel-water two-phase closed thermosyphon in waste heat recovery. After 1983, the energy-saving effect of the heat pipe heat exchanger industrial application gradually received the attention of the society, and the application of the heat pipe heat exchanger entered the industrialization promotion stage. In September 1983, approved by the Jiangsu Provincial Government, Nanjing Thermal Energy Technology Development Center was established with the support of Nanjing Institute of Chemical Technology. This is a scientific research and production complex. The main task is to undertake various engineering application projects and bring heat pipe technology to the market. In August 1993, Jiangsu Shenguo Heat Pipe Group Co., Ltd. was established on the basis of the Nanjing Heat Pipe Technology Development Center approved by the Jiangsu Provincial Government Reform Commission. In 2004, it was converted into Nanjing Shengnuo Heat Pipe Co., Ltd.
As the technology of carbon steel-water heat pipe is becoming more and more mature, the heat exchange capacity of the heat exchanger is getting bigger and bigger. In 1986, the large-scale separated heat pipe heat exchanger was put into operation in the 1300m3 blast furnace hot air furnace of Meishan Iron and Steel Plant, and the heat recovery reached 3000kW. The investment was recovered during the year; the integrated heat pipe air preheater used for the waste heat recovery of the large chemical fertilizer section in 1988 was successfully developed by Hubei Fertilizer Plant and Nanjing Institute of Chemical Technology. The heat recovery amounted to 11163kW (9.6 million kcal/hour). The heat pipe steam generator of the 75m2 sintering machine of the second sintering plant of Maanshan Iron and Steel Co., Ltd. was also successfully developed, and the heat recovery was 3176kW, which set a precedent for the domestic waste heat recovery of metallurgical industry. Because carbon steel-water gravity heat pipe has simple structure, low price, convenient manufacture and easy application in industry, the development and research of industrial application of heat pipe technology has been rapidly developed. We have developed heat pipe gas-gas heat exchangers. , heat pipe waste heat boiler, high temperature heat pipe steam generator, high and medium temperature heat pipe hot air stove and other heat pipe products. With the continuous improvement of science and technology, the field of heat pipe research and application is also expanding. At present, heat pipe and heat pipe heat exchangers have been widely used in high-efficiency heat and mass transfer equipment in petroleum, chemical, power, metallurgy, building materials, light industry, transportation and other fields, as well as electronic device chip cooling, notebook computer CPU cooling and circuit control board. Wait for the cooling.
At present, in addition to micro-heat pipes have been mass-produced and mass-produced, whether it is heat pipe heat exchange equipment in industrial processes or heat pipe heat exchangers for waste heat recovery, each equipment is different in scale, size and use of various equipments. All can be designed and manufactured according to the existing process conditions and site conditions.
2 heat pipe working principle and classification
2.1 Working principle of gravity heat pipe Gravity heat pipe - two-phase closed thermosiphon, as shown in Figure 1, the heat pipe consists of a closed casing and working fluid. One end of the heat pipe is an evaporation section (also called: heated section, heating section), and the other end is a condensation section (also called: cooling section, heat release section).
The heat pipe absorbs heat from the high temperature fluid outside the pipe, passes through the heat pipe wall to the working medium in the pipe, and the working fluid absorbs heat, boils and evaporates, and turns into steam. The steam rises to the heat release section under the pressure difference, and is outside the pipe. The cryogenic fluid cools, the steam condenses and releases latent heat of condensation to the outside, the low temperature fluid gains heat, and the condensate returns to the heated side by gravity. Therefore, the work of the gravity heat pipe has a certain directionality, and the evaporation section must be placed below the condensation section. Through the continuous evaporation and condensation of the working fluid in the pipe, the high temperature fluid heat is transferred to the low temperature fluid to heat the low temperature fluid. The heat transfer area can be expanded by welding the spiral fins at a high frequency on the heating section of the heat pipe and the outer surface of the condensation section.
Since the inside of the heat pipe is generally pumped into a certain vacuum, the working fluid is extremely easy to boil and evaporate, and the heat pipe starts very quickly, so it has a high thermal conductivity. Compared to metals such as silver, copper, and aluminum, heat pipes per unit weight can transfer several orders of magnitude more heat.
2.2 Classification of heat pipes The structure and types of heat pipes are numerous, widely used, and the classification methods are various. Commonly used classification methods are:
2.2.1 According to the working temperature inside the heat pipe, the low temperature heat pipe (-273~0 °C), the normal temperature heat pipe (0~250 °C), the medium temperature heat pipe (250~450 °C), the high temperature heat pipe (450~1000 °C), etc.
2.2.2 According to the combination of shell and working fluid, carbon steel-water heat pipe, copper-water heat pipe, aluminum-acetone heat pipe, carbon steel-naphthalene heat pipe, stainless steel-sodium heat pipe, etc.
2.2.2 According to the structure, the ordinary heat pipe, the separate heat pipe, the capillary pump circuit heat pipe, the micro heat pipe, the flat heat pipe, the radial heat pipe and the like are divided.
3 Common structure and characteristics of heat pipe heat exchangers Heat exchangers consisting of heat pipes as heat transfer elements are called heat pipe heat exchangers. Heat pipe heat exchangers are available in various forms, such as gas-gas, gas-vapor (liquid), Separate type, etc., there are heat pipe type air preheater, heat pipe type steam generator, heat pipe economizer, cooler and the like.
3.1 integral heat pipe heat exchanger
3.1.1 Gas-Gas Heat Pipe Heat Exchanger The heat exchanger has a rectangular outer casing, and the inside is composed of a plurality of single heat pipes. The arrangement of the heat pipes may be arranged in a triangular arrangement in a staggered manner, or may be arranged in a square shape as shown in the figure. 2 is shown. In the center of the interior of the rectangular casing is a tube sheet (middle orifice plate) which divides the casing into two parts, forming a passage for hot fluid and cold fluid. When the cold and hot fluids flow through the respective channels at the same time, the heat pipe transfers the heat of the hot fluid to the cold fluid, achieving heat exchange between the two fluids, reducing the temperature of the hot fluid to a discharge temperature or process requirement, and the cold fluid The temperature rises to meet the needs of the process. In the heat exchanger, the number of heat pipes depends on the amount of heat exchange. In order to make the equipment compact, the fins are wound on the heat pipes, so that the number of heat pipes required can be greatly reduced. Therefore, the heat pipe heat exchanger can improve the heat exchange efficiency and reduce the space occupied by the equipment. Compared with the conventional tube-type gas-gas heat exchanger, the volume and weight of the heat pipe heat exchanger are smaller than those of the tubular type when the same gas amount is processed, and the gas flow resistance drop is relatively small.
3.1.2 gas-liquid heat pipe heat exchanger gas-liquid heat pipe heat exchanger is a heat exchanger for heat exchange between gas and liquid. Since the heat transfer coefficient of the gas side is much smaller than that of the liquid side, In the heat exchange process, the main heat resistance is on the gas side, so the heat pipe on the gas side can be wound with fins, while the heat pipe on the liquid side generally does not need to be finned, and can be designed in the form of a sleeve or directly inserted into the water tank. Figure 3 shows. The unique feature is that when the wall of the gas side heat pipe is damaged, the water on the water side does not leak into the gas side, which increases the reliability of the equipment.
3.1.3 Gas-Vapor Heat Pipe Heat Exchanger Gas-vapor heat pipe heat exchanger is usually called heat pipe type steam generator, also called heat pipe type waste heat boiler. The structure is basically the same as gas-liquid type, but the cold water inlet is connected to the feed water. Steam is generated. Similarly, the heat pipe condensation section can be designed as a sleeve type, connected to the drum by the ascending and descending tubes, or directly inserted into the drum. The evaporator and the steam drum form a natural circulation of water vapor under a certain position difference, and no external power is required. Its structure is shown in Figure 4. At present, the steam pressure generated by the heat pipe type steam generator can reach 2.5 MPa, and the temperature of the incoming flue gas can be as high as 1000 °C. The heat pipe steam generator Zui is characterized by compact structure, small size, safety and reliability. The damage of the heat pipe components does not affect the circulation of the steam system, and there is no need to stop for maintenance.
3.2 Separate heat pipe heat exchanger The heating section and the condensation section of the heat pipe are respectively used in two independent tanks, each of which is provided with a plurality of independent heat pipes welded by the finned tubes and the upper and lower headers. Tube bundle. As shown in Figure 5. The tube bundles corresponding to the heating section and the condensation section are connected by a steam riser and a condensate downcomer to form separate closed systems. Here, the heating section is separated from the condensation section, and they are coupled by a steam riser and a condensate downcomer to form a further structural form having a heat transfer effect of the heat pipe. When a certain degree of vacuum is formed inside the tube bundle, when the hot fluid passes through the heating section, the working medium in the heating section tube bundle absorbs heat and then vaporizes, and the generated steam is collected in the upper header box of the upper portion of the heated section, and is transported to the cold through the steam riser tube. The tube in the condensation section of the fluid passes through the cold fluid outside the tube, and the latent heat of condensation condensed by the steam condenses the cold fluid outside the tube, and the liquid condensed by the vapor collects in the lower header of the lower part of the condensation section. Under the action, the condensate descending tube is returned to the heating section tube bundle to continue to evaporate. This cycle is repeated to complete the transfer of heat from the heating section to the condensation section. Its uniqueness is:
(a) The heat pipe heating section and the condensation section can be arranged separately according to the site conditions, which can realize long-distance heat transfer, which brings greater flexibility to the process design, and also increases the size of the device and comprehensive utilization of heat energy. The optimization of the thermal energy utilization system has created favorable conditions;
(b) The circulation of the working medium relies on the difference of the condensate and gravity, no external power is required, no mechanical operating parts, which increases the reliability of the equipment and greatly reduces the operating expenses;
(c) The heat pipe heating section tank and the condensing section tank are independent of each other, and it is easy to separate and seal the fluid.
(d) The heating section and the exothermic section tube bundle can select different structural parameters and materials according to the performance of cold and hot fluids and process requirements, so that the dew point corrosion and ash accumulation of the equipment can be effectively solved;
(e) According to the process requirements, the fluid can be mixed in a smooth and countercurrent flow to adapt to a wide temperature range;
(f) The system heat exchange element consists of a plurality of heat pipe bundles, each of which is independent of each other. Therefore, one or even several pieces of damage or failure will not affect the safe operation of the entire system.
3.3 Structural Features Compared with conventional heat exchange equipment, heat pipes have the following characteristics:
(1) The heat pipe heat exchange equipment is safer and more reliable than the conventional heat exchange equipment, and can be continuously operated for a long time. Conventional heat exchange equipment is generally a wall-to-wall heat exchange, and cold and hot fluids flow on both sides of the wall respectively. If there is leakage in the pipe wall or the wall, the production loss will be caused. The heat exchange device composed of the heat pipe is the secondary wall heat exchange, that is, the hot fluid can pass through the evaporation section of the heat pipe and the wall of the condensation section to transfer the cold fluid, and the heat pipe is generally impossible to destroy at the same time in the evaporation section and the condensation section, so Greatly enhance the reliability of equipment operation;
(2) The heat transfer efficiency is high, and the cold and hot sides of the heat pipe can be wound with fins as needed to increase the heat transfer area;
(3) effectively avoiding the flow of cold and hot fluids, each of the heat pipes is a relatively independent closed unit, the cold and hot fluids flow outside the pipe, and the cold and hot fluids are completely separated by the intermediate sealing structure;
(4) Effectively prevent dew point corrosion. By adjusting the number of heat pipes or adjusting the heat transfer area ratio of the hot and cold sides of the heat pipe, the heat pipe wall temperature is raised above the dew point temperature. This method of changing the heat flux density can make the heat pipe smaller. The heating area inputs heat, and the heat is outputted with a larger cooling area. Conversely, the heat can be input in a larger area, and the heat is outputted in a smaller cooling area, so that the heat flow on the heat transfer area of ​​the unit heating and cooling occurs. Variety. As shown in Fig. 6, the figure (a) shows that the length of the evaporation section of the heat pipe is larger than the length of the condensation section, and the fins are wound. It is obvious that the heat transfer area of ​​the evaporation section is larger than the heat transfer area of ​​the condensation section. When the heat transfer amount Q is constant, the evaporation section is The heat flux density is much smaller than the heat flux density of the condensation section, and the opposite is shown in Figure (b), so as to control and regulate the heat pipe wall temperature;
(5) Effectively prevent ash accumulation, the heat exchanger can be designed with variable cross-section to ensure that the fluid flows through the heat pipe heat exchanger and achieve the purpose of self-cleaning;
(6) There is no rotating part, no additional power consumption, no need to change components frequently, even if some components are damaged, it will not affect normal production;
(7) The damage of a single heat pipe does not affect other heat pipes, and the impact on the overall heat transfer effect can be ignored.
4 Application fields of heat pipe technology
4.1 Chemical and petrochemical
4.1.1 Application of heat pipe technology in the synthetic ammonia industry The synthetic ammonia industry plays an important role in the chemical industry and is also a major energy consumer. The synthesis of ammonia from the beginning of gas production until the synthesis of ammonia is accompanied by a hot process, rational use and control of ammonia production and release The heat can not only save energy consumption in production, reduce cost, but also increase CO conversion rate and ammonia synthesis rate. In the industrial production of synthetic ammonia, heat pipe technology can not only recover low-temperature waste heat preheating combustion air or generate low-pressure steam as raw material steam, but also recover high-temperature waste heat to produce medium-pressure steam as a supplement to raw material steam, and can control fixed-bed catalytic reactor. The chemical reaction temperature makes it a good reaction to the zoi, thereby increasing the CO conversion rate and the ammonia synthesis rate. China's small chemical fertilizer plants spread over more than 1,700 counties across the country. Steam is one of the raw materials for small fertilizer production. It has always been supplied by boiler houses. On the other hand, small fertilizer production has a large amount of waste heat. Recycling the waste heat from the small fertilizer plant to turn it into steam can not only meet the needs of its own process production, but also have extra external supply. The waste heat recovery of small fertilizer production is quite difficult. The process gas contains a large amount of dust and CO, CO2, CH4, H2 and other gases, and has low temperature corrosion, so it is difficult to achieve general purpose equipment recovery. Practice has proved that the use of the characteristics of the heat pipe itself through the correct design, can complete the waste heat recovery task under such harsh conditions, the following is a small fertilizer waste heat recovery process: Figure 7 is the process of blowing gas combustion gas waste heat recovery system The device recovers the heat of combustion of the blow air, and the blown air discharged from the gas furnace contains CO and H2 flammable gas, and the combustion air is burned in the combustion furnace, and the high temperature flue gas of about 900 ° C is produced and passed through the high temperature heat pipe steam generator. Enter the secondary heat pipe air preheater at 400 °C, heat the air from the first stage heat pipe air preheater, and heat the air from 140 °C to 320 °C to the combustion chamber as the combustion air for the blow air. The flue gas temperature of the secondary heat pipe air preheater enters the heat pipe economizer at about 280 ° C, and the deoxidized water is heated to 130 ° C and sent to the steam drum. At this time, the flue gas temperature drops to about 140 ° C and then enters the first stage heat pipe air. Preheater, preheating air at 25 °C normal temperature to 130 °C into the secondary heat pipe air preheater, after the zui flue gas temperature drops to about 120 °C into the chimney, this process can produce 1.6~2.5MPa medium pressure steam , used directly for transformation or other sections. The energy is gradually recovered and the waste heat is fully utilized.
4.1.2 Application of heat pipe technology in the sulfuric acid industry There is a large amount of high-grade waste heat generated in the sulfuric acid production process. It is estimated that when pyrite is used as raw material for melting in a boiling furnace, the remaining heat can be recovered by the waste heat boiler to obtain 4.0MPa (gauge pressure). 400 °C superheated steam l.0 ~ l.2 tons / ton of sulfuric acid, a plant with an annual output of 100,000 tons of sulfuric acid can produce about 24.4 million kWh of electricity per year, except for a part of the plant, there can be a lot of excess electricity lose. If the recovered electricity cost is calculated in the cost accounting of sulfuric acid production, the production cost of sulfuric acid will be reduced by 15-20%. The residual heat of the sulfuric acid plant comes from the following parts: 1 the heat of removal of the boiling bed; 2 the cooling heat of the high temperature SO2 furnace gas; 3 the heat of the red hot slag discharge; 4 the cooling heat of the SO3 gas. Among them, 12 parts are the main heat of Zui. Although most of the sulfuric acid plants in China have recycled these two parts of heat, most of the latter two parts of the heat are not used. Heat pipe technology provides convenience and possibilities for the recovery and utilization of these heat. Figure 8 is a system flow for recovering SO3 waste heat by a heat pipe steam generator. The temperature of the SO3 gas from the converter is about 310 °C, and is cooled to about 150 °C through the heating section of the heat pipe steam generator, and enters the SO3 absorption tower, an annual output of 12 The 10,000 tons of sulfuric acid plant can recover more than 1,000 tons of steam and save the electricity consumption of one blower.
Because the conditions for the production of sulfuric acid are quite harsh, factors such as high temperature, high dust content, and strong corrosivity often cause damage to the equipment, causing losses in the entire production stoppage. The damage of individual pipe fittings of heat pipe equipment does not affect the overall equipment efficiency, so there is no need to stop maintenance, so heat pipe technology has a broad development prospect in sulfuric acid production. In the process of pyrite sulphuric acid, sulphuric acid and smelting flue gas, the series of heat pipe steam generators, heat pipe economizers and superheaters have been developed in the sulphuric acid industry.
4.1.3 Application of heat pipe technology in petrochemicals In the petrochemical production, various types of heating furnaces are widely used, and it is of great significance to improve the thermal efficiency of the heating furnace. The residual heat of the exhaust gas of the heating furnace is recovered, and the combustion air of the heating furnace is preheated to improve the thermal efficiency of the heating furnace. The exhaust temperature of the heating furnace is generally around 260~350 °C. The temperature of the flue gas is reduced to 160 °C through the heat pipe heat exchanger, which can increase the combustion air from normal temperature to above 120 °C, and the efficiency of the heating furnace can be increased by 6%~8. %. The heat pipe heat exchanger is particularly suitable for its compact size, low pressure drop, flexible layout and control of dew point corrosion. At the same time, the heat pipe cracking furnace, the heat pipe oxidation reactor, the cyclohexanol dehydrogenation reactor, the catalytic cracking regeneration heat extractor and the like have been successively developed, and remarkable effects have been obtained.
4.2 Application of heat pipe technology in building materials and textile industry Kaolin spray drying heat pipe type high temperature hot air furnace: The key to high temperature and high concentration spray drying is to have hot air with higher temperature. It is hoped that the temperature of hot air can reach above 500 °C. The whiteness of the kaolin of dry matter is strict, so it is required to avoid the contaminants mixed into the powder during the drying process. The high-temperature heat pipe heat exchanger (also called: coal-fired hot-blast stove) which uses the flue gas as the heat source is very suitable for this process. Claim. The coal combustion outlet temperature reaches above 900 °C, the high-temperature flue gas flows through the heating section of the heat pipe heat exchanger, and the normal temperature air enters the condensation section of the heat exchanger through the blower, and is in a countercurrent arrangement form, and the air is heated up to 500 by heat exchange. Discharge above °C, enter the spray tower as dry hot air, and the flue gas temperature is reduced to below 200 °C. In the heat exchanger, different heat pipes are used in different temperature sections to meet the different requirements of temperature, heat transfer and material strength, and a combined heat pipe heat exchanger is formed, as shown in FIG.
Secondly, heat pipe heat exchangers have been applied in the waste heat utilization of glass kiln, cement kiln, ceramic kiln, tunnel kiln, etc. and waste heat recovery of sizing machine in textile industry.
4.3 Application of heat pipe technology in metallurgical industry The metallurgical industry is a large energy consumer. Every year, a large amount of heat is discharged into the atmosphere, which wastes resources and pollutes the environment. The rational use of waste heat recovery is a heavy task of the metallurgical industry. Heat pipe technology has broad application prospects in the metallurgical industry. The current successful domestic application is reflected in the following two aspects, namely the waste heat recovery of the blast furnace hot blast stove and the waste heat recovery of the sintering machine.
(a) blast furnace hot blast stove waste heat recovery iron blast furnace hot blast stove is a regenerative furnace type, the temperature of the flue gas discharged during the heat storage process can sometimes be as high as 400 ° C, use this part of flue gas to heat the combustion required for combustion Air can not only save fuel, but more importantly, it can increase the temperature of the top of the regenerator, so that the hot air temperature in the ironmaking furnace can be increased, and the hot air temperature can increase the coking ratio of the ironmaking. In general, For every 100 °C increase in hot air above 1000 °C, the coke consumed per ton of iron can save 15 kg.
China's * blast furnace hot blast stove heat pipe air preheater was officially put into use in Maanshan * ironworks in 1982. After use, the effect is remarkable, the fuel gas consumption is reduced by 4%, and the hot air temperature of the furnace is increased after using the heat pipe air preheater. As a result, the coke consumption per ton of iron is reduced by 10 kg, and the entire investment can be recovered in that year. . The main parameters of the device are shown in Table 1.
After nearly 10 years of development, by the 1990s, this technology has been perfected. At present, many large steel companies in China have adopted this technology. The large heat exchange capacity of Zui has reached 20,000 kW, due to its large capacity and many double Preheating (while preheating the air and gas), as a result of the use of a separate heat pipe air preheater. Figure 10 shows the process and parameters of the waste heat recovery of a blast furnace hot blast stove of a steel company. The flue gas (250 ° C) discharged from the hot blast stove is lowered to 145 ° C through the heating section of the separate heat pipe heat exchanger, and is discharged into the atmosphere by the chimney. The cooling section of the split heat pipe heat exchanger consists of two parts, one part heating the combustion air and the other part heating the fuel gas. This double preheating system allows the fuel gas and the combustion air to be heated to 130 ° C or more and burn into the furnace. Increased combustion efficiency. The operation shows that the hot air temperature of the furnace is 42.4 °C higher than that before the adoption of this technology, which saves 6.36 kg of coke consumption per ton of iron. In June 1993, the blast furnace produced 184,787 tons of iron, saving a total of 1,175 tons of coke. Approximately RMB 430,000/month, while gas consumption has also decreased, saving 8648.3 kg/month by calorific value, or about RMB 102,000/month.
(b) Waste heat recovery of the sintering machine The metallurgical sintering process consumes a relatively high energy consumption, accounting for 10% to 12% of the total energy consumption of steel and metallurgy. According to the thermal equilibrium measurement of some sintering plants in the metallurgical industry, the total energy consumption of the general sintering plant is 250. ~ 300GJ / t, sintering thermal efficiency is only about 50%, and the residual heat is very large. How to rationally and effectively develop and utilize the residual heat of sinter has been a topic of concern for sintering workers at home and abroad. After more than ten years of continuous research and development, the waste heat recovered from the sintering machine of 24 ~ 360m2 can produce steam of 0.5 ~ 1.6MPa 3 ~ 20T / hr, the steam generated can be directly used for mixing, so that the feed temperature is greatly Increase, thereby increasing the yield by 4% to 5% and reducing the power consumption per ton by 0.5 kWh. After measuring and calculating a 75m2 sintering machine, the economic effect of recovering this residual heat can reach 700,000 yuan/year. Under normal circumstances, equipment investment can be recovered in eight months, and the total investment recovery of the system is no more than 14 months.
4.4 Application of heat pipe technology in power engineering Figure 11 is a flow chart and design parameters of a 130T/hr power station boiler application heat pipe air preheater. Under normal circumstances, the cost of the heat pipe air preheater of the power station boiler can be Ll ~ Recycling within 1.2 years, the heat pipe should be operated safely for five years. The utility model has the advantages that the wall temperature can be maintained above the dew point temperature by design, the low temperature condensation can be prevented, the low temperature corrosion caused by the condensation can be avoided, and the adhesion of the ash under the action of the acid dew can be avoided. Since the separator on the flue gas side and the air side has a good sealing structure, the amount of air leakage into the flue gas is also reduced (below 2%). These advantages make the application of heat pipe air preheaters in power station boilers very attractive.
4.5 Application of heat pipe technology in environmentally friendly flue gas desulfurization process The desulfurization method currently widely used at home and abroad is wet limestone-gypsum flue gas desulfurization technology, and more than 90% of domestic and international thermal power plant desulfurization technologies adopt this method. In the selection, the economical, efficient and reliable flue gas heat exchange device is the key link in the desulfurization process. The unpurified high-temperature flue gas is used to heat the desulfurized net flue gas through the heat exchanger, so that the net flue gas is from 40 ° C. Heat up to 80 ° C or more to increase the lift of the flue gas, as shown in Figure 12. The desulfurization heat exchanger can not only recover the heat of the high-temperature flue gas, save energy, but also ensure the normal operation of the desulfurization tower, reduce the water consumption, and at the same time improve the desulfurization efficiency of the desulfurization tower and reduce the secondary pollution to the atmosphere.
4.6 Application of Heat Pipes on Stabilized Frozen Soil Subgrade In the permafrost regions of the Qinghai-Tibet Railway, how to avoid the subgrade sinking and frost heaving of the roadbed has led to the research of engineering topics for the stability of the heat pipe. The former Soviet Union used low-temperature heat pipes in the foundations of highway subgrades and reservoirs. Canada also used heat pipes to rectify the frozen soil diseases of railway roadbeds to prevent the deformation of the roadbed. China has carried out experiments on the culverts of the Qinghai-Tibet Highway and the foundation of the northeast power transmission and transformation equipment. The low temperature heat pipe independently developed by our group company has been successfully used for the solidification of the Qinghai-Tibet Railway frozen soil roadbed. At the same time, the application and promotion of technologies such as the stability of roads, bridges and pipelines in cold regions and the melting of snow in road areas are being carried out.
4.7 Other applications The heat dissipation of heat pipe technology in electrical and electronic engineering, such as heat dissipation of electronic components in a sealed enclosure, heat dissipation of CPU, cooling of high-power electronic components, etc.;
Applications in space flight technology, solar energy applications, nuclear power engineering, etc.;
The application of the heat pipe in the air conditioning fresh air heat exchange can use the discharged turbid air to preheat (or pre-cool) the incoming fresh air to achieve effective power saving.
5 Heat pipe heat exchanger design and selection The design of heat pipe heat exchanger mainly includes two parts, the heat calculation of heat exchanger and the limit check of heat pipe. The main task of the design calculation is to obtain the total heat transfer coefficient, and then determine the total heat transfer area based on the average temperature difference and heat load to determine the number of heat pipes. The design is similar to conventional heat exchanger design, but should also be considered in the design:
(1) Choosing an appropriate standard head-on wind speed, if the wind speed is too high, the pressure drop will be too large and the power consumption will increase. If the wind speed is too low, the heat transfer coefficient of the outer membrane will be reduced, and the heat transfer capacity of the heat pipe will not be fully exerted;
(2) Select the appropriate heat pipe parameters, according to the design conditions, select the appropriate parameters for different types of heat exchangers used in different occasions, and choose a larger spacing for corrosive gases with higher dust content. The finned tube with a larger pitch of the fins wrapped around the heat pipe, a thicker fin and a lower fin height, and a denser fin spacing can be selected for a cleaner gas;
(3) Pay attention to the verification of the original parameters and the verification of the calculation formula. The design of heat pipe heat exchangers should pay special attention to the original parameters. Most of the waste heat recovery equipment is designed as an additional equipment in the already operated system. Therefore, the impact on the related equipment in the system is strict, and the original parameters of the site need to be precise. Determination, and select the appropriate structure according to the site conditions and system requirements;
(4) For important projects and lack of experience, some important design parameter formulas should be tested and verified as necessary;
(5) According to the different working temperature, the heat pipe can be divided into high, medium and low temperature heat pipes. As the heat pipe heat exchanger, the working temperature of each heat pipe is different along the air flow direction, so the heat pipe is internally temperature-dependent. Different use of different working fluids;
(6) After the selection of the working fluid of the heat pipe, the heat pipe material is selected according to the compatibility of the working medium and the pipe and the economy.
6 Conclusion With the successful development of heat pipe technology products and the large-scale promotion and application, the enterprises have obtained huge economic and social benefits. At the same time, the development and application of heat pipe technology also requires engineering and technical personnel from various industries to work together with us to open up new application areas.
references
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[4] Wang Lei. Manufacture of gravity heat pipe heat exchanger. Soda industry, 2002, 1:9~4
[5] Wang Minjie, Ning Yiqing. Heat pipe waste heat boiler recovery H device - flue gas waste heat research. Boiler pressure vessel safety technology.
Among the many heat transfer elements, the heat pipe is one of the well-known heat transfer elements of the zui, which can transfer a large amount of heat through a small cross-sectional area thereof without any external power. International research and application of heat pipe technology began in the 1960s. Since the 1970s, China has carried out research on heat transfer performance of heat pipes and application research of heat pipes in electronic component cooling and spacecraft. In the early 1980s, China's heat pipe research and development focused on energy conservation and rational use of energy. Since 1976, the heat pipe research group of Nanjing Institute of Chemical Technology has started the application and development of heat pipe technology in industrial waste heat recovery, mainly researching heat pipe heat exchange equipment. In April 1980, the gas-gas heat pipe heat exchanger developed by Nanjing Institute of Chemical Technology and Nanjing Refinery was officially put into operation in Nanjing Refinery; at the end of 1981, China* Taiwan carbon steel-water heat pipe waste heat boiler It was successfully developed by Nanjing Institute of Chemical Technology and put into operation in Jiangsu Rudong Fertilizer Plant. The formal operation of the above two heat pipe heat exchange equipments has greatly promoted the design and calculation of heat pipe heat exchangers and the heat transfer performance, internal resistance, steel-water compatibility, liquid filling, design, waste heat recovery applications, etc. It solves some technical problems in the application of cheap carbon steel-water two-phase closed thermosyphon in waste heat recovery. After 1983, the energy-saving effect of the heat pipe heat exchanger industrial application gradually received the attention of the society, and the application of the heat pipe heat exchanger entered the industrialization promotion stage. In September 1983, approved by the Jiangsu Provincial Government, Nanjing Thermal Energy Technology Development Center was established with the support of Nanjing Institute of Chemical Technology. This is a scientific research and production complex. The main task is to undertake various engineering application projects and bring heat pipe technology to the market. In August 1993, Jiangsu Shenguo Heat Pipe Group Co., Ltd. was established on the basis of the Nanjing Heat Pipe Technology Development Center approved by the Jiangsu Provincial Government Reform Commission. In 2004, it was converted into Nanjing Shengnuo Heat Pipe Co., Ltd.
As the technology of carbon steel-water heat pipe is becoming more and more mature, the heat exchange capacity of the heat exchanger is getting bigger and bigger. In 1986, the large-scale separated heat pipe heat exchanger was put into operation in the 1300m3 blast furnace hot air furnace of Meishan Iron and Steel Plant, and the heat recovery reached 3000kW. The investment was recovered during the year; the integrated heat pipe air preheater used for the waste heat recovery of the large chemical fertilizer section in 1988 was successfully developed by Hubei Fertilizer Plant and Nanjing Institute of Chemical Technology. The heat recovery amounted to 11163kW (9.6 million kcal/hour). The heat pipe steam generator of the 75m2 sintering machine of the second sintering plant of Maanshan Iron and Steel Co., Ltd. was also successfully developed, and the heat recovery was 3176kW, which set a precedent for the domestic waste heat recovery of metallurgical industry. Because carbon steel-water gravity heat pipe has simple structure, low price, convenient manufacture and easy application in industry, the development and research of industrial application of heat pipe technology has been rapidly developed. We have developed heat pipe gas-gas heat exchangers. , heat pipe waste heat boiler, high temperature heat pipe steam generator, high and medium temperature heat pipe hot air stove and other heat pipe products. With the continuous improvement of science and technology, the field of heat pipe research and application is also expanding. At present, heat pipe and heat pipe heat exchangers have been widely used in high-efficiency heat and mass transfer equipment in petroleum, chemical, power, metallurgy, building materials, light industry, transportation and other fields, as well as electronic device chip cooling, notebook computer CPU cooling and circuit control board. Wait for the cooling.
At present, in addition to micro-heat pipes have been mass-produced and mass-produced, whether it is heat pipe heat exchange equipment in industrial processes or heat pipe heat exchangers for waste heat recovery, each equipment is different in scale, size and use of various equipments. All can be designed and manufactured according to the existing process conditions and site conditions.
2 heat pipe working principle and classification
2.1 Working principle of gravity heat pipe Gravity heat pipe - two-phase closed thermosiphon, as shown in Figure 1, the heat pipe consists of a closed casing and working fluid. One end of the heat pipe is an evaporation section (also called: heated section, heating section), and the other end is a condensation section (also called: cooling section, heat release section).
The heat pipe absorbs heat from the high temperature fluid outside the pipe, passes through the heat pipe wall to the working medium in the pipe, and the working fluid absorbs heat, boils and evaporates, and turns into steam. The steam rises to the heat release section under the pressure difference, and is outside the pipe. The cryogenic fluid cools, the steam condenses and releases latent heat of condensation to the outside, the low temperature fluid gains heat, and the condensate returns to the heated side by gravity. Therefore, the work of the gravity heat pipe has a certain directionality, and the evaporation section must be placed below the condensation section. Through the continuous evaporation and condensation of the working fluid in the pipe, the high temperature fluid heat is transferred to the low temperature fluid to heat the low temperature fluid. The heat transfer area can be expanded by welding the spiral fins at a high frequency on the heating section of the heat pipe and the outer surface of the condensation section.
Since the inside of the heat pipe is generally pumped into a certain vacuum, the working fluid is extremely easy to boil and evaporate, and the heat pipe starts very quickly, so it has a high thermal conductivity. Compared to metals such as silver, copper, and aluminum, heat pipes per unit weight can transfer several orders of magnitude more heat.
2.2 Classification of heat pipes The structure and types of heat pipes are numerous, widely used, and the classification methods are various. Commonly used classification methods are:
2.2.1 According to the working temperature inside the heat pipe, the low temperature heat pipe (-273~0 °C), the normal temperature heat pipe (0~250 °C), the medium temperature heat pipe (250~450 °C), the high temperature heat pipe (450~1000 °C), etc.
2.2.2 According to the combination of shell and working fluid, carbon steel-water heat pipe, copper-water heat pipe, aluminum-acetone heat pipe, carbon steel-naphthalene heat pipe, stainless steel-sodium heat pipe, etc.
2.2.2 According to the structure, the ordinary heat pipe, the separate heat pipe, the capillary pump circuit heat pipe, the micro heat pipe, the flat heat pipe, the radial heat pipe and the like are divided.
3 Common structure and characteristics of heat pipe heat exchangers Heat exchangers consisting of heat pipes as heat transfer elements are called heat pipe heat exchangers. Heat pipe heat exchangers are available in various forms, such as gas-gas, gas-vapor (liquid), Separate type, etc., there are heat pipe type air preheater, heat pipe type steam generator, heat pipe economizer, cooler and the like.
3.1 integral heat pipe heat exchanger
3.1.1 Gas-Gas Heat Pipe Heat Exchanger The heat exchanger has a rectangular outer casing, and the inside is composed of a plurality of single heat pipes. The arrangement of the heat pipes may be arranged in a triangular arrangement in a staggered manner, or may be arranged in a square shape as shown in the figure. 2 is shown. In the center of the interior of the rectangular casing is a tube sheet (middle orifice plate) which divides the casing into two parts, forming a passage for hot fluid and cold fluid. When the cold and hot fluids flow through the respective channels at the same time, the heat pipe transfers the heat of the hot fluid to the cold fluid, achieving heat exchange between the two fluids, reducing the temperature of the hot fluid to a discharge temperature or process requirement, and the cold fluid The temperature rises to meet the needs of the process. In the heat exchanger, the number of heat pipes depends on the amount of heat exchange. In order to make the equipment compact, the fins are wound on the heat pipes, so that the number of heat pipes required can be greatly reduced. Therefore, the heat pipe heat exchanger can improve the heat exchange efficiency and reduce the space occupied by the equipment. Compared with the conventional tube-type gas-gas heat exchanger, the volume and weight of the heat pipe heat exchanger are smaller than those of the tubular type when the same gas amount is processed, and the gas flow resistance drop is relatively small.
3.1.2 gas-liquid heat pipe heat exchanger gas-liquid heat pipe heat exchanger is a heat exchanger for heat exchange between gas and liquid. Since the heat transfer coefficient of the gas side is much smaller than that of the liquid side, In the heat exchange process, the main heat resistance is on the gas side, so the heat pipe on the gas side can be wound with fins, while the heat pipe on the liquid side generally does not need to be finned, and can be designed in the form of a sleeve or directly inserted into the water tank. Figure 3 shows. The unique feature is that when the wall of the gas side heat pipe is damaged, the water on the water side does not leak into the gas side, which increases the reliability of the equipment.
3.1.3 Gas-Vapor Heat Pipe Heat Exchanger Gas-vapor heat pipe heat exchanger is usually called heat pipe type steam generator, also called heat pipe type waste heat boiler. The structure is basically the same as gas-liquid type, but the cold water inlet is connected to the feed water. Steam is generated. Similarly, the heat pipe condensation section can be designed as a sleeve type, connected to the drum by the ascending and descending tubes, or directly inserted into the drum. The evaporator and the steam drum form a natural circulation of water vapor under a certain position difference, and no external power is required. Its structure is shown in Figure 4. At present, the steam pressure generated by the heat pipe type steam generator can reach 2.5 MPa, and the temperature of the incoming flue gas can be as high as 1000 °C. The heat pipe steam generator Zui is characterized by compact structure, small size, safety and reliability. The damage of the heat pipe components does not affect the circulation of the steam system, and there is no need to stop for maintenance.
3.2 Separate heat pipe heat exchanger The heating section and the condensation section of the heat pipe are respectively used in two independent tanks, each of which is provided with a plurality of independent heat pipes welded by the finned tubes and the upper and lower headers. Tube bundle. As shown in Figure 5. The tube bundles corresponding to the heating section and the condensation section are connected by a steam riser and a condensate downcomer to form separate closed systems. Here, the heating section is separated from the condensation section, and they are coupled by a steam riser and a condensate downcomer to form a further structural form having a heat transfer effect of the heat pipe. When a certain degree of vacuum is formed inside the tube bundle, when the hot fluid passes through the heating section, the working medium in the heating section tube bundle absorbs heat and then vaporizes, and the generated steam is collected in the upper header box of the upper portion of the heated section, and is transported to the cold through the steam riser tube. The tube in the condensation section of the fluid passes through the cold fluid outside the tube, and the latent heat of condensation condensed by the steam condenses the cold fluid outside the tube, and the liquid condensed by the vapor collects in the lower header of the lower part of the condensation section. Under the action, the condensate descending tube is returned to the heating section tube bundle to continue to evaporate. This cycle is repeated to complete the transfer of heat from the heating section to the condensation section. Its uniqueness is:
(a) The heat pipe heating section and the condensation section can be arranged separately according to the site conditions, which can realize long-distance heat transfer, which brings greater flexibility to the process design, and also increases the size of the device and comprehensive utilization of heat energy. The optimization of the thermal energy utilization system has created favorable conditions;
(b) The circulation of the working medium relies on the difference of the condensate and gravity, no external power is required, no mechanical operating parts, which increases the reliability of the equipment and greatly reduces the operating expenses;
(c) The heat pipe heating section tank and the condensing section tank are independent of each other, and it is easy to separate and seal the fluid.
(d) The heating section and the exothermic section tube bundle can select different structural parameters and materials according to the performance of cold and hot fluids and process requirements, so that the dew point corrosion and ash accumulation of the equipment can be effectively solved;
(e) According to the process requirements, the fluid can be mixed in a smooth and countercurrent flow to adapt to a wide temperature range;
(f) The system heat exchange element consists of a plurality of heat pipe bundles, each of which is independent of each other. Therefore, one or even several pieces of damage or failure will not affect the safe operation of the entire system.
3.3 Structural Features Compared with conventional heat exchange equipment, heat pipes have the following characteristics:
(1) The heat pipe heat exchange equipment is safer and more reliable than the conventional heat exchange equipment, and can be continuously operated for a long time. Conventional heat exchange equipment is generally a wall-to-wall heat exchange, and cold and hot fluids flow on both sides of the wall respectively. If there is leakage in the pipe wall or the wall, the production loss will be caused. The heat exchange device composed of the heat pipe is the secondary wall heat exchange, that is, the hot fluid can pass through the evaporation section of the heat pipe and the wall of the condensation section to transfer the cold fluid, and the heat pipe is generally impossible to destroy at the same time in the evaporation section and the condensation section, so Greatly enhance the reliability of equipment operation;
(2) The heat transfer efficiency is high, and the cold and hot sides of the heat pipe can be wound with fins as needed to increase the heat transfer area;
(3) effectively avoiding the flow of cold and hot fluids, each of the heat pipes is a relatively independent closed unit, the cold and hot fluids flow outside the pipe, and the cold and hot fluids are completely separated by the intermediate sealing structure;
(4) Effectively prevent dew point corrosion. By adjusting the number of heat pipes or adjusting the heat transfer area ratio of the hot and cold sides of the heat pipe, the heat pipe wall temperature is raised above the dew point temperature. This method of changing the heat flux density can make the heat pipe smaller. The heating area inputs heat, and the heat is outputted with a larger cooling area. Conversely, the heat can be input in a larger area, and the heat is outputted in a smaller cooling area, so that the heat flow on the heat transfer area of ​​the unit heating and cooling occurs. Variety. As shown in Fig. 6, the figure (a) shows that the length of the evaporation section of the heat pipe is larger than the length of the condensation section, and the fins are wound. It is obvious that the heat transfer area of ​​the evaporation section is larger than the heat transfer area of ​​the condensation section. When the heat transfer amount Q is constant, the evaporation section is The heat flux density is much smaller than the heat flux density of the condensation section, and the opposite is shown in Figure (b), so as to control and regulate the heat pipe wall temperature;
(5) Effectively prevent ash accumulation, the heat exchanger can be designed with variable cross-section to ensure that the fluid flows through the heat pipe heat exchanger and achieve the purpose of self-cleaning;
(6) There is no rotating part, no additional power consumption, no need to change components frequently, even if some components are damaged, it will not affect normal production;
(7) The damage of a single heat pipe does not affect other heat pipes, and the impact on the overall heat transfer effect can be ignored.
4 Application fields of heat pipe technology
4.1 Chemical and petrochemical
4.1.1 Application of heat pipe technology in the synthetic ammonia industry The synthetic ammonia industry plays an important role in the chemical industry and is also a major energy consumer. The synthesis of ammonia from the beginning of gas production until the synthesis of ammonia is accompanied by a hot process, rational use and control of ammonia production and release The heat can not only save energy consumption in production, reduce cost, but also increase CO conversion rate and ammonia synthesis rate. In the industrial production of synthetic ammonia, heat pipe technology can not only recover low-temperature waste heat preheating combustion air or generate low-pressure steam as raw material steam, but also recover high-temperature waste heat to produce medium-pressure steam as a supplement to raw material steam, and can control fixed-bed catalytic reactor. The chemical reaction temperature makes it a good reaction to the zoi, thereby increasing the CO conversion rate and the ammonia synthesis rate. China's small chemical fertilizer plants spread over more than 1,700 counties across the country. Steam is one of the raw materials for small fertilizer production. It has always been supplied by boiler houses. On the other hand, small fertilizer production has a large amount of waste heat. Recycling the waste heat from the small fertilizer plant to turn it into steam can not only meet the needs of its own process production, but also have extra external supply. The waste heat recovery of small fertilizer production is quite difficult. The process gas contains a large amount of dust and CO, CO2, CH4, H2 and other gases, and has low temperature corrosion, so it is difficult to achieve general purpose equipment recovery. Practice has proved that the use of the characteristics of the heat pipe itself through the correct design, can complete the waste heat recovery task under such harsh conditions, the following is a small fertilizer waste heat recovery process: Figure 7 is the process of blowing gas combustion gas waste heat recovery system The device recovers the heat of combustion of the blow air, and the blown air discharged from the gas furnace contains CO and H2 flammable gas, and the combustion air is burned in the combustion furnace, and the high temperature flue gas of about 900 ° C is produced and passed through the high temperature heat pipe steam generator. Enter the secondary heat pipe air preheater at 400 °C, heat the air from the first stage heat pipe air preheater, and heat the air from 140 °C to 320 °C to the combustion chamber as the combustion air for the blow air. The flue gas temperature of the secondary heat pipe air preheater enters the heat pipe economizer at about 280 ° C, and the deoxidized water is heated to 130 ° C and sent to the steam drum. At this time, the flue gas temperature drops to about 140 ° C and then enters the first stage heat pipe air. Preheater, preheating air at 25 °C normal temperature to 130 °C into the secondary heat pipe air preheater, after the zui flue gas temperature drops to about 120 °C into the chimney, this process can produce 1.6~2.5MPa medium pressure steam , used directly for transformation or other sections. The energy is gradually recovered and the waste heat is fully utilized.
4.1.2 Application of heat pipe technology in the sulfuric acid industry There is a large amount of high-grade waste heat generated in the sulfuric acid production process. It is estimated that when pyrite is used as raw material for melting in a boiling furnace, the remaining heat can be recovered by the waste heat boiler to obtain 4.0MPa (gauge pressure). 400 °C superheated steam l.0 ~ l.2 tons / ton of sulfuric acid, a plant with an annual output of 100,000 tons of sulfuric acid can produce about 24.4 million kWh of electricity per year, except for a part of the plant, there can be a lot of excess electricity lose. If the recovered electricity cost is calculated in the cost accounting of sulfuric acid production, the production cost of sulfuric acid will be reduced by 15-20%. The residual heat of the sulfuric acid plant comes from the following parts: 1 the heat of removal of the boiling bed; 2 the cooling heat of the high temperature SO2 furnace gas; 3 the heat of the red hot slag discharge; 4 the cooling heat of the SO3 gas. Among them, 12 parts are the main heat of Zui. Although most of the sulfuric acid plants in China have recycled these two parts of heat, most of the latter two parts of the heat are not used. Heat pipe technology provides convenience and possibilities for the recovery and utilization of these heat. Figure 8 is a system flow for recovering SO3 waste heat by a heat pipe steam generator. The temperature of the SO3 gas from the converter is about 310 °C, and is cooled to about 150 °C through the heating section of the heat pipe steam generator, and enters the SO3 absorption tower, an annual output of 12 The 10,000 tons of sulfuric acid plant can recover more than 1,000 tons of steam and save the electricity consumption of one blower.
Because the conditions for the production of sulfuric acid are quite harsh, factors such as high temperature, high dust content, and strong corrosivity often cause damage to the equipment, causing losses in the entire production stoppage. The damage of individual pipe fittings of heat pipe equipment does not affect the overall equipment efficiency, so there is no need to stop maintenance, so heat pipe technology has a broad development prospect in sulfuric acid production. In the process of pyrite sulphuric acid, sulphuric acid and smelting flue gas, the series of heat pipe steam generators, heat pipe economizers and superheaters have been developed in the sulphuric acid industry.
4.1.3 Application of heat pipe technology in petrochemicals In the petrochemical production, various types of heating furnaces are widely used, and it is of great significance to improve the thermal efficiency of the heating furnace. The residual heat of the exhaust gas of the heating furnace is recovered, and the combustion air of the heating furnace is preheated to improve the thermal efficiency of the heating furnace. The exhaust temperature of the heating furnace is generally around 260~350 °C. The temperature of the flue gas is reduced to 160 °C through the heat pipe heat exchanger, which can increase the combustion air from normal temperature to above 120 °C, and the efficiency of the heating furnace can be increased by 6%~8. %. The heat pipe heat exchanger is particularly suitable for its compact size, low pressure drop, flexible layout and control of dew point corrosion. At the same time, the heat pipe cracking furnace, the heat pipe oxidation reactor, the cyclohexanol dehydrogenation reactor, the catalytic cracking regeneration heat extractor and the like have been successively developed, and remarkable effects have been obtained.
4.2 Application of heat pipe technology in building materials and textile industry Kaolin spray drying heat pipe type high temperature hot air furnace: The key to high temperature and high concentration spray drying is to have hot air with higher temperature. It is hoped that the temperature of hot air can reach above 500 °C. The whiteness of the kaolin of dry matter is strict, so it is required to avoid the contaminants mixed into the powder during the drying process. The high-temperature heat pipe heat exchanger (also called: coal-fired hot-blast stove) which uses the flue gas as the heat source is very suitable for this process. Claim. The coal combustion outlet temperature reaches above 900 °C, the high-temperature flue gas flows through the heating section of the heat pipe heat exchanger, and the normal temperature air enters the condensation section of the heat exchanger through the blower, and is in a countercurrent arrangement form, and the air is heated up to 500 by heat exchange. Discharge above °C, enter the spray tower as dry hot air, and the flue gas temperature is reduced to below 200 °C. In the heat exchanger, different heat pipes are used in different temperature sections to meet the different requirements of temperature, heat transfer and material strength, and a combined heat pipe heat exchanger is formed, as shown in FIG.
Secondly, heat pipe heat exchangers have been applied in the waste heat utilization of glass kiln, cement kiln, ceramic kiln, tunnel kiln, etc. and waste heat recovery of sizing machine in textile industry.
4.3 Application of heat pipe technology in metallurgical industry The metallurgical industry is a large energy consumer. Every year, a large amount of heat is discharged into the atmosphere, which wastes resources and pollutes the environment. The rational use of waste heat recovery is a heavy task of the metallurgical industry. Heat pipe technology has broad application prospects in the metallurgical industry. The current successful domestic application is reflected in the following two aspects, namely the waste heat recovery of the blast furnace hot blast stove and the waste heat recovery of the sintering machine.
(a) blast furnace hot blast stove waste heat recovery iron blast furnace hot blast stove is a regenerative furnace type, the temperature of the flue gas discharged during the heat storage process can sometimes be as high as 400 ° C, use this part of flue gas to heat the combustion required for combustion Air can not only save fuel, but more importantly, it can increase the temperature of the top of the regenerator, so that the hot air temperature in the ironmaking furnace can be increased, and the hot air temperature can increase the coking ratio of the ironmaking. In general, For every 100 °C increase in hot air above 1000 °C, the coke consumed per ton of iron can save 15 kg.
China's * blast furnace hot blast stove heat pipe air preheater was officially put into use in Maanshan * ironworks in 1982. After use, the effect is remarkable, the fuel gas consumption is reduced by 4%, and the hot air temperature of the furnace is increased after using the heat pipe air preheater. As a result, the coke consumption per ton of iron is reduced by 10 kg, and the entire investment can be recovered in that year. . The main parameters of the device are shown in Table 1.
After nearly 10 years of development, by the 1990s, this technology has been perfected. At present, many large steel companies in China have adopted this technology. The large heat exchange capacity of Zui has reached 20,000 kW, due to its large capacity and many double Preheating (while preheating the air and gas), as a result of the use of a separate heat pipe air preheater. Figure 10 shows the process and parameters of the waste heat recovery of a blast furnace hot blast stove of a steel company. The flue gas (250 ° C) discharged from the hot blast stove is lowered to 145 ° C through the heating section of the separate heat pipe heat exchanger, and is discharged into the atmosphere by the chimney. The cooling section of the split heat pipe heat exchanger consists of two parts, one part heating the combustion air and the other part heating the fuel gas. This double preheating system allows the fuel gas and the combustion air to be heated to 130 ° C or more and burn into the furnace. Increased combustion efficiency. The operation shows that the hot air temperature of the furnace is 42.4 °C higher than that before the adoption of this technology, which saves 6.36 kg of coke consumption per ton of iron. In June 1993, the blast furnace produced 184,787 tons of iron, saving a total of 1,175 tons of coke. Approximately RMB 430,000/month, while gas consumption has also decreased, saving 8648.3 kg/month by calorific value, or about RMB 102,000/month.
(b) Waste heat recovery of the sintering machine The metallurgical sintering process consumes a relatively high energy consumption, accounting for 10% to 12% of the total energy consumption of steel and metallurgy. According to the thermal equilibrium measurement of some sintering plants in the metallurgical industry, the total energy consumption of the general sintering plant is 250. ~ 300GJ / t, sintering thermal efficiency is only about 50%, and the residual heat is very large. How to rationally and effectively develop and utilize the residual heat of sinter has been a topic of concern for sintering workers at home and abroad. After more than ten years of continuous research and development, the waste heat recovered from the sintering machine of 24 ~ 360m2 can produce steam of 0.5 ~ 1.6MPa 3 ~ 20T / hr, the steam generated can be directly used for mixing, so that the feed temperature is greatly Increase, thereby increasing the yield by 4% to 5% and reducing the power consumption per ton by 0.5 kWh. After measuring and calculating a 75m2 sintering machine, the economic effect of recovering this residual heat can reach 700,000 yuan/year. Under normal circumstances, equipment investment can be recovered in eight months, and the total investment recovery of the system is no more than 14 months.
4.4 Application of heat pipe technology in power engineering Figure 11 is a flow chart and design parameters of a 130T/hr power station boiler application heat pipe air preheater. Under normal circumstances, the cost of the heat pipe air preheater of the power station boiler can be Ll ~ Recycling within 1.2 years, the heat pipe should be operated safely for five years. The utility model has the advantages that the wall temperature can be maintained above the dew point temperature by design, the low temperature condensation can be prevented, the low temperature corrosion caused by the condensation can be avoided, and the adhesion of the ash under the action of the acid dew can be avoided. Since the separator on the flue gas side and the air side has a good sealing structure, the amount of air leakage into the flue gas is also reduced (below 2%). These advantages make the application of heat pipe air preheaters in power station boilers very attractive.
4.5 Application of heat pipe technology in environmentally friendly flue gas desulfurization process The desulfurization method currently widely used at home and abroad is wet limestone-gypsum flue gas desulfurization technology, and more than 90% of domestic and international thermal power plant desulfurization technologies adopt this method. In the selection, the economical, efficient and reliable flue gas heat exchange device is the key link in the desulfurization process. The unpurified high-temperature flue gas is used to heat the desulfurized net flue gas through the heat exchanger, so that the net flue gas is from 40 ° C. Heat up to 80 ° C or more to increase the lift of the flue gas, as shown in Figure 12. The desulfurization heat exchanger can not only recover the heat of the high-temperature flue gas, save energy, but also ensure the normal operation of the desulfurization tower, reduce the water consumption, and at the same time improve the desulfurization efficiency of the desulfurization tower and reduce the secondary pollution to the atmosphere.
4.6 Application of Heat Pipes on Stabilized Frozen Soil Subgrade In the permafrost regions of the Qinghai-Tibet Railway, how to avoid the subgrade sinking and frost heaving of the roadbed has led to the research of engineering topics for the stability of the heat pipe. The former Soviet Union used low-temperature heat pipes in the foundations of highway subgrades and reservoirs. Canada also used heat pipes to rectify the frozen soil diseases of railway roadbeds to prevent the deformation of the roadbed. China has carried out experiments on the culverts of the Qinghai-Tibet Highway and the foundation of the northeast power transmission and transformation equipment. The low temperature heat pipe independently developed by our group company has been successfully used for the solidification of the Qinghai-Tibet Railway frozen soil roadbed. At the same time, the application and promotion of technologies such as the stability of roads, bridges and pipelines in cold regions and the melting of snow in road areas are being carried out.
4.7 Other applications The heat dissipation of heat pipe technology in electrical and electronic engineering, such as heat dissipation of electronic components in a sealed enclosure, heat dissipation of CPU, cooling of high-power electronic components, etc.;
Applications in space flight technology, solar energy applications, nuclear power engineering, etc.;
The application of the heat pipe in the air conditioning fresh air heat exchange can use the discharged turbid air to preheat (or pre-cool) the incoming fresh air to achieve effective power saving.
5 Heat pipe heat exchanger design and selection The design of heat pipe heat exchanger mainly includes two parts, the heat calculation of heat exchanger and the limit check of heat pipe. The main task of the design calculation is to obtain the total heat transfer coefficient, and then determine the total heat transfer area based on the average temperature difference and heat load to determine the number of heat pipes. The design is similar to conventional heat exchanger design, but should also be considered in the design:
(1) Choosing an appropriate standard head-on wind speed, if the wind speed is too high, the pressure drop will be too large and the power consumption will increase. If the wind speed is too low, the heat transfer coefficient of the outer membrane will be reduced, and the heat transfer capacity of the heat pipe will not be fully exerted;
(2) Select the appropriate heat pipe parameters, according to the design conditions, select the appropriate parameters for different types of heat exchangers used in different occasions, and choose a larger spacing for corrosive gases with higher dust content. The finned tube with a larger pitch of the fins wrapped around the heat pipe, a thicker fin and a lower fin height, and a denser fin spacing can be selected for a cleaner gas;
(3) Pay attention to the verification of the original parameters and the verification of the calculation formula. The design of heat pipe heat exchangers should pay special attention to the original parameters. Most of the waste heat recovery equipment is designed as an additional equipment in the already operated system. Therefore, the impact on the related equipment in the system is strict, and the original parameters of the site need to be precise. Determination, and select the appropriate structure according to the site conditions and system requirements;
(4) For important projects and lack of experience, some important design parameter formulas should be tested and verified as necessary;
(5) According to the different working temperature, the heat pipe can be divided into high, medium and low temperature heat pipes. As the heat pipe heat exchanger, the working temperature of each heat pipe is different along the air flow direction, so the heat pipe is internally temperature-dependent. Different use of different working fluids;
(6) After the selection of the working fluid of the heat pipe, the heat pipe material is selected according to the compatibility of the working medium and the pipe and the economy.
6 Conclusion With the successful development of heat pipe technology products and the large-scale promotion and application, the enterprises have obtained huge economic and social benefits. At the same time, the development and application of heat pipe technology also requires engineering and technical personnel from various industries to work together with us to open up new application areas.
references
[1] Zhuang Jun, Zhang Hong. Heat pipe technology and its engineering application, * edition. Beijing: Chemical Industry Press, 2000
[2] Tu Chuanjing et al. Gravity heat pipe heat exchanger and its application in waste heat utilization. Hangzhou: Zhejiang University Press, 1989
[3] Wang Lei. Heat pipe heat exchanger and its application in waste heat recovery. Soda industry, 2000, 5:34~36
[4] Wang Lei. Manufacture of gravity heat pipe heat exchanger. Soda industry, 2002, 1:9~4
[5] Wang Minjie, Ning Yiqing. Heat pipe waste heat boiler recovery H device - flue gas waste heat research. Boiler pressure vessel safety technology.
Reishi Mushroom
Reishi Mushroom, also known as Ganoderma or Lingzhi, is a polypore mushroom that grows on wood in dark and moist environment. It usually consist of a rounded and soft mushroom cap and a long stem. The Ganoderma genus includes about 80 species. Among them, Ganoderma Lucidum, or red Reishi, is the most studied and used species.
Ganoderma and its extensive use has been
documented in many traditional Chinese medical literature for more than a
thousand years due to the health benefits it has. In ancient China, because
wild Ganoderma was very difficult to find, it was only served to the emperors. Therefore,
it was also called [The Magic Herb". Nowadays, thanks to the development of
modern cultivation and processing techniques, Ganoderma has become more available
and more affordable to people. Many scientific researches have also been done
on the potential health benefits of Reishi Mushroom.
Studies have shown that Reishi Mushroom has multiple health benefits. It is effective in enhancing overall immunity, protecting the liver, and improving sleep quality. The main two active compounds are called Ganoderma polysaccharides and triterpenes. Ganoderma polysaccharides can activate human`s immune system, increasing the activity and number of immune cells. Triterpenes, on the other hand, can fight directly against pathogens and abnormal cells such as tumor cells. Therefore, Reishi Mushrooms is also good for assisting cancer treatment.
Most people may think that wild Reishi Mushrooms are better than cultivated ones while in fact that is not the case. Since Reishi Mushrooms are a type of fungi, they acquire their food by absorbing dissolved molecules. Therefore, they are very likely to absorb pollutants into their tissues, including heavy metals such as mercury. That is also why many countries use mushrooms to clean up waterways and soil. However, since it is impossible to control and screen the source of every mushroom we collect, wild Reishi Mushrooms are very likely to have contaminants inside. Also, Reishi Mushrooms use their spores to spread and reproduce. As it reaches maturation phase, the spores will shoot out from tiny tubes underneath the cap. The spore powder is also where most of the nutrients of Reishi Mushroom are stored. In the wild, we cannot keep monitoring every growth stage of Reishi Mushroom, so most of the time the Reishi Mushrooms we collect do not have much spores left, which means they have much less nutritious value. Besides, there are other factors that may affect the quality of Reishi Mushrooms such as sunlight, humidity, parasites etc. GANOHERB on the other hand, has been focusing on growing Reishi Mushroom for 29 years. It has multiple self-built Ganoderma farms and therefore is able to control and monitor every step that may affect the quality of Reishi Mushroom, delivering the Reishi Mushroom with highest quality and safety. We strictly controls every single step of the cultivation process to ensure each step is ideal for the growth of Reishi Mushroom. GanoHerb has acquired 4 organic certifications from the EU, the US, Japan, and China. Our goal is to let the world share the traditional Chinese treasure.
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Ganoherb International Inc , http://www.ganoherb.com