First, the current status of domestic steam traps Steam traps are used in steam heating equipment and steam pipes, steam can automatically exclude the equipment and piping condensate, air and other non-condensable gases, and to prevent steam leakage Automatic valve. Steam is widely used in industrial production and living facilities, and it is produced in the process of heating, drying, keeping warm, sterilizing, steaming, concentrating, exchanging heat, heating and air-conditioning in steam pipeline system or using steam Of the condensate water need to be excluded by the steam trap, and does not allow steam leakage. The performance of steam traps is crucial for the normal operation of the steam system, the improvement of the thermal efficiency of steam turbines and the rational use of energy. Especially in the first reduction of energy such as coal, oil and natural gas, governments all over the world regard energy conservation and new energy development as important national policies. Steam traps, on the other hand, play a key role in the energy savings of steam-using systems. According to the statistics of relevant departments in our country, at present there are about 4.324 million steam traps in the country and about 80% of the products fail to meet the current national standard of less than 3%. The leak rate is mostly about 10% A steam trap will waste 4.44 tons of standard coal, the national use of traps that are less than the current national standard will have to waste 14,323,300 tons of standard coal, equivalent to 1,826,203 yuan, which is a considerable figure, This shows that the role of energy-saving steam trap big, and its importance in the development of the national economy can not wait and see. With the further intensification of foreign energy crisis and the rapid development of modern industrial technology, the demand for full utilization of heat energy is increasing day by day. The research on steam traps has been widely carried out abroad. Foreign steam traps manufacturers to adapt to the needs of the modern industry, research and development work more in-depth, rapid development of production. This article will be combined with good company's steam trap product line introduces various types of steam traps and their applications. Second, the working principle of a variety of steam traps When the steam condensing, it will release the energy of the vaporization (latent heat) and the formation of condensate. Condensate contains only the energy contained in the water at the saturation temperature (sensible heat). However, to ensure maximum heat transfer efficiency in the steam system, the condensate must be vented out of the system. In addition, some non-condensable gases and air from the boiler and air from the piping must be vented from the steam system when the steam system is started At the same time must retain useful steam, these functions are by an automatic device - steam traps to complete. Spirax Sarco, a UK market leader in steam traps, has been manufacturing and selling steam traps since 1910 and is an energy-efficient company specializing in providing knowledge, services and products to steam users. The company's product range is complete and widely used in steam systems where steam traps are the most important product line of the company, such as the CS49H Thermodynamic Steam Trap which has long been a reliable trap The incarnation of its various types of trap leakage rate is far below the current national standard of 3%. Steam traps are available in a variety of different hydrophobic modes, some in response to changes in sensing density (such as mechanical), others in response to changes in temperature and some in static pressure through the hot condensate itself And dynamic pressure changes and sensor switch. Traps currently in the world, according to the working principle of division, there are three main categories 1, mechanical steam traps: the use of condensate and steam density difference between the operation. The first major category of mechanical traps is the float trap, the current leading international product for the link float trap, the working principle shown in Figure 1. In addition to the drainage trap steam trap function, requires good air discharge performance, all good Branch Float Steam Traps are equipped with a thermostat air device TV, as standard. Some steam traps, in addition to air-venting units, also feature a steam-lock release, which is mainly used in situations where steam blockage of condensate can not reach steam traps, known as steam locks, such as the use of a siphon to remove condensate (rotary drum equipment ) Or a long pipe in front of the trap. Float steam traps drain condensate immediately after the condensate has been generated, allowing rapid drainage of large volumes of condensate as pressure and load change, which is most suitable for heat transfer when used with other types of traps with the same caliber High demand, the device does not allow a variety of water heat exchanger equipment and equipment with automatic temperature control the best choice. At the same time this type of trap outlet is always immersed in the condensate water, with a real sense of drainage gas barrier function. Good Branch can provide various types of float steam traps to meet the needs of a variety of process technology. (1) At the start-up phase, the thermo-static evacuation device (TV) exhausts air, otherwise the accumulation of air in the trap will cause air lock. (2). When the condensate reaches the trap, the float rises, the valve opens and the hot condensate closes the vent valve. Condensate is discharged at a saturated temperature. (3). When all the condensed water is discharged, the steam enters the steam trap. At this point float drops, the valve closed. The spool is always below the water level to prevent direct steam leakage. Another main form of mechanical traps inverted bucket traps, the working process shown in Figure 2. Inverted bucket traps can be used in high pressure applications. If you do not rule out the air in the inverted bucket will hinder the normal operation of the trap, and inverted bucket traps exhaust very slow, so for a large number of occasions, the need for a separate air thermostatic air vent valve, otherwise it will cause the device Water, affect the heat transfer efficiency. Therefore, it is usually advisable to install a separate vent valve to ensure prompt and efficient start-up of the equipment. Many inverted bucket traps require a check valve to prevent loss of water seal (flashover) in the event of sudden pressure changes or overheating. Water seal is one of the keys to ensure that the inverted bucket traps avoid leakage of steam. The inverted bucket trap also discharges condensate at the saturated steam temperature. All mechanical steam traps have some condensation inside the body after the trap has been shut down, so that traps may be compromised by freezing and require thermal insulation if installed in a cold outdoor environment. (1) Condensate reaches the trap and forms a water seal inside. The weight of the inverted bucket itself opens the valve and the condensate drains along the inverted bucket. (2) steam into the bucket, resulting in buoyancy Bucket rise, the valve closed. (3) The steam in the inverted bucket is continuously cooled and overflows from the exhaust holes, and the condensed water enters the inverted bucket at the same time, the valve is opened again, and the entire working cycle continues. (4) The exhaust hole in the inverted bucket constantly discharges the air to the top of the trap. Due to the small vent hole and the slow exhaust, it is often necessary to install a separate exhaust valve. 2, Thermostatic steam traps Thermostatic steam traps work according to the temperature difference between steam and supercooled condensate or air / steam mixture. It can be used to allow the presence of subcooling station condensate water, can make use of the sensible heat in condensate water. This trap has a liquid-filled, stainless-steel sealed capsule whose liquid-filled evaporation temperature is below the saturated steam temperature. Select a different fill liquid, condensate discharge temperature is different, generally lower than the steam saturation temperature of 5-10 degrees. Pressure balance trap can be automatically adjusted according to pressure changes, the drainage temperature is kept with the saturation temperature curve changes. At the same time the trap is normally open in cold, exhaust air performance. (1). When starting, the capsule is cold, the valve is fully open, cold air and condensate are drained by the trap. (2). When the condensate temperature is close to the steam saturation temperature, the filling liquid evaporates, the pressure generated on the diaphragm, to overcome the pressure, before the steam into the trap to push the spool close to the valve seat, close the valve. (3) Condensed water is cooled down to or below the set temperature of the steam saturation temperature, the pressure in the sealed bladder drops, the valve opens again, and the condensate is discharged. Bimetallic steam traps work on the well-known bimetallic thermal sensing properties. The working process shown in Figure 4. Bimetal working curve near the steam saturation curve, bimetal traps generally below the steam saturation temperature of 25-30 degrees condensate discharge to make full use of the condensate in the sensible heat. Bimetal traps are easily affected by the size of the backpressure. Increasing the backpressure reduces the discharge temperature and increases the amount of water accumulated in the equipment. (1) During the start-up phase, the valve is open and condensate and air are rapidly discharged. (2). The hot condensate passes through the trap and the bimetal is heated to expand, pushing the spool close to the seat. The valve closes when condensate discharge temperature is close to the steam temperature. (3). Condensate cooling, bimetal shrink, the valve opens again, and discharge of condensate. Continuous work cycle. Thermostable steam traps have the following advantages: small size, light weight, and large condensate displacement at the same time, fully open in cold state, good air discharging performance, outdoor installation without being damaged by freezing, water hammer, corrosion . Ideal for hot and non-critical steam equipment. The disadvantage of the thermostatic steam trap is that condensing water is discharged below the steam saturation temperature and therefore can not be used for heating equipment that requires the immediate discharge of condensate. To avoid accumulation of heat in the heat exchange equipment, a 1 -2 m cooling pipe. Bimetallic traps respond to temperature changes relatively slowly. 3, Thermodynamic Steam Trap (Disc steam traps) Thermodynamic steam traps (also known as disc traps in the country) are widely used at home and abroad due to their compact structure, simple principle and reliable operation. , Even to the extent of being abused. Thermodynamic steam trap works as shown below. It is based on the low pressure condensate and high-speed flash steam dynamic pressure difference between the work of the whole process is only a moving parts? Stainless steel disc, which has good clamping force and can prevent the return of condensate back to the equipment to ensure that the equipment Maximum working efficiency. (1). When starting, the inlet pressure acts on the lower part of the disc, ejecting the disc, and the air and colder condensate drain immediately. (2). When only hot condensate below the steam temperature flows through the trap, the pressure drop produces flash steam. High-speed flash steam creates a low pressure zone under the disc, bringing the disc closer to the seat. (3) At the same time, the flash vapor collected at the top of the disc also presses the disc against the inner and outer rings of the seat. (4) Due to the heat dissipation from the top cover, the flash vapor above the disc condenses, the pressure drops, the disc rises again and drains the condensate. Work cycle is repeated. Due to the principle of the thermodynamic steam trap requires that the pressure into the trap is not less than a certain value, while the back pressure of the trap generally can not be higher than 50% of the inlet pressure (the back pressure of the outlet of the thermoelectric steam trap Up to 80%), otherwise the trap will not work properly. In addition, the thermodynamic trap is intermittent. Therefore, thermodynamic traps generally can not be used for applications that use heat exchangers with high heating efficiency and temperature control equipment. Thermodynamic traps are generally used in the condensate drainage of constant pressure systems, such as steam main pipe, mixing hot pipe, pressing machine and other applications. Thermal power trap in the closing process, there is a strong impact between the valve core and valve seat, valve core and valve seat if the material is not properly selected, processing unreasonable, it is likely to cause valve core and seat wear, greatly reduced Trap life. Good company thermodynamic traps spool and valve seat with special materials and undergo a rigorous heat treatment, at the same time has a unique three-hole condensate outlet to ensure the smooth operation of the disc in the closure process to avoid uneven wear and tear , Improve service life. In general, thermodynamic traps are small, lightweight, operate automatically at their working pressure range and are unregulated and can be used in high pressure and overheating systems, protected from water hammering and freezing, and can be installed in any orientation, with only one Has a moving parts, long service life, easy maintenance, can be widely used in the condensing water discharge. Thermodynamic trap is determined to be used in the case of too low inlet pressure or high back pressure, exhaust air performance is poor, but the use of disc with a gas barrier can effectively exclude the air. Third, steam traps selection As various types of steam traps have different advantages and disadvantages and different conditions, so many years of various types of steam traps long-term coexistence, used in a variety of steam system equipment There is no universal trap. From a working point of view, a float steam trap can be used in almost every application, but in fact it is not so. A thermodynamic steam trap is usually installed on a smaller installation space, Cold Drainage In order to take full advantage of the application of sensible heat in condensate water, the float trap is not suitable. The simple technique of steam traps allows users to try a trap to meet all the requirements, such as float-type traps, but the application requirements and equipment performance mean that a trap can not meet all applications, Otherwise it will affect the efficiency of the entire system. Therefore, to ensure proper selection of steam traps, the following factors should be considered: • Applications • Maximum load • Equipment type • System pressure • Minimum load • Material • Back pressure • Safety factor • Connection method • Steam temperature • With temperature control • Condensate recovery · Pressure differential · Lifting height after steam trap · Whether to install emptying device In addition to the above factors, we should also consider other factors, such as the ambient temperature will be below zero? Frozen trap will cause some damage, especially brass or cast iron traps. Is there any serious vibration affecting the steam trap in the system? How much air will be in the system during start-up / operation? There are two options available to facilitate the selection, but the first option is always the first option (second choice in brackets). Steam Trap Selection Chart 4, the installation of steam traps After selecting the right trap type and caliber, the correct installation to ensure the most effective work trap. The steam trap is only one of the important parts of the steam trap. The correct installation of the steam trap can affect the overall operation. Steam trap installation should follow the following principles: ◠All traps have a small discharge port, such as the pipeline of impurities, welding slag into the trap, it is easy to cause blockage, resulting in trap leakage or Damage, so the need to install a Y-shaped trap upstream of the trap. ◠For systems that are not directly vented to the atmosphere, Spiratec detection devices should be installed upstream of the trap to facilitate monitoring and timely detection of trap failure or equipment flooding. In some cases, a mirror was installed downstream of the trap to replace the Spiratec detector. Such as the installation of the mirror should be installed from the spray-type traps (such as thermodynamic traps) at least one meter downstream. ◠When there is back pressure in the drain pipe, install a check valve downstream of the trap to prevent the inlet pressure of the trap from decreasing or the steam space in the shutdown. ◠It is not advisable to bypass by bypassing forgetting to close will result in steam leaks or trap failures and increased condensate piping pressure, affecting the operation of other traps. ◠The trap should be installed at a position lower than the outlet of the steam-consuming equipment. There should be a drop pipe of about 150mm between the inlet of the steam trap and the outlet of the equipment. ◠Ensure proper installation direction of traps, especially for mechanical traps with vertical lifting mechanism (such as float-type and inverted bucket traps). Improper installation may lead to trap wear and tear, steam leakage and steam leakage . ◠Although thermodynamic steam traps can work in any installation orientation, they can be installed in horizontal pipes for maximum service life. ◠To save money, some users use a trap to drain condensate from multiple devices, which is called group hydrophobic. However, in fact, due to the different working conditions of each equipment, it will lead to the phenomenon of water accumulation in the system. Therefore, the group should avoid hydrophobic. ◠For temperature-controlled heat exchange equipment, the condensate drain pipe should be avoided to increase upward because the pressure inside the heat exchanger decreases when the system load is reduced and it is not enough to discharge the condensate water, thus causing the equipment to generate water, Water hammer and other phenomena. • Traps should be located as close as possible to the outlet of the drain to prevent steam locks. When the pipe between the condensate outlet and the steam trap is full of steam, the condensate will not reach the trap, resulting in gas locks and equipment accumulating water, affecting work efficiency. ◠If the thermostatic steam trap is used in steam space where water is not allowed, install a cooling section upstream of the steam trap, usually about 2 meters. ◠inverted bucket traps used in superheated steam or system pressure fluctuations in the system, the check valve should be installed at the import to avoid losing water seal and leakage of steam. ◠In some applications, inverted bucket traps should be installed with a separate drain valve to ensure efficient operation of the equipment because the inability to quickly remove air will result in longer warm-up time and equipment water. ◠If the bimetal trap is installed in a system with back pressure, the change of backpressure will affect the condensing water discharge temperature. Increasing the backpressure will reduce the temperature of discharge and increase the possibility of water accumulation in the equipment. ◠Mechanical traps installed in outdoor low temperature environment should be added to the insulation. V. Steam Trap Monitoring The following causes may cause traps to fail: ◠Steam traps, as with all mechanical mechanisms, are also inevitably subject to wear and tear and fail to function properly. ◠Poor boiler water treatment, high boiler water TDS values ​​can cause boiler water entrainment to enter the steam system, reducing or plugging the trap drain, keeping in mind that a 15mm trap has a drain hole typically around 3mm . ◠Pipeline impurities, system water hammer or corrosion can cause fatal damage to the trap. ◠In addition, if the trap selection, improper installation also makes the trap does not work properly. Steam traps fail to leak steam or fail to drain. Leak steam trap can cause energy waste, can not guarantee a stable pressure and temperature, increase the pressure of condensate pipes affect the performance of other equipment, equipment, such as erosion. The trap plug will lead to water equipment, resulting in temperature control is not correct, damage to product quality, reduce heat output, water hammer damage to equipment. In order to maintain the normal operation of steam traps, routine maintenance is indispensable. For example, regular maintenance and replacement of internal parts can not replace steam traps. However, maintenance efficiency can be improved by effective detection methods. Here are some commonly used methods of detection: • Spray water on a steam trap • Observe trap discharge into the atmosphere • Use a sight glass • Use a temperature gauge • Use an ultrasonic detector • Use a conductivity detector Due to space limitations , This article does not start a detailed discussion of the above method. Steam traps are small components compared to the entire steam system, but the proper functioning of steam traps plays an important role in the energy consumption of the steam system. Often, in a system retrofit, traps account for 7% -10% of the cost, while they contribute more than 40% to the overall system's energy savings. In order to improve the efficiency of the system, for different applications and conditions, engineers should choose a reliable and suitable type of steam traps, and should be properly installed, pay attention to routine maintenance and regular testing.
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