6 Development trends
7 Corrosion problems
8 routine maintenance
9 other applications
10 Operation
Introduction editor
The waste heat boiler, as the name implies, refers to a boiler that uses various waste gases, waste materials or waste heat in waste liquids and heat generated by combustion of combustible materials to heat the water to a certain temperature. The oil-fired boiler, gas-fired boiler and coal-fired boiler with smoke box and flue waste heat recovery and utilization are also called waste heat boilers. The waste heat boiler can produce hot water or steam through waste heat recovery to be supplied to other sections.
Working principle editing
Fuel, gas, and coal are burned to produce high-temperature flue gas to release heat. The high-temperature flue gas enters the furnace first, then enters the waste heat recovery device of the front smoke box, then enters the pyrotechnic tube, and finally enters the waste heat recovery device in the rear smoke box flue, high temperature. The flue gas becomes low-temperature flue gas and is discharged into the atmosphere through the chimney. This type of boiler is very energy efficient because the waste heat boiler greatly increases the utilization of heat released by fuel combustion.
Category editing
Waste heat boilers are classified into fuel waste heat boilers, gas waste heat boilers, coal-fired waste heat boilers and external heat recovery boilers according to fuel. According to the use, it is divided into waste heat hot water boiler, waste heat steam boiler, waste heat organic heat carrier boiler and so on.
Feature editing
The high-temperature flue gas released from coal-fired combustion is sent to the inlet of the waste heat boiler through the flue, and then flows through the heat exchanger, the evaporator and the economizer, and finally discharged into the atmosphere through the chimney. The exhaust gas temperature is generally 150-180 ° C, and the flue gas The heat released by the temperature from the high temperature to the exhaust gas temperature is used to turn the water into steam. The boiler feed water first enters the economizer, and the water absorbs heat in the economizer to rise to a saturation temperature slightly lower than the steam drum pressure to enter the drum. After the water entering the drum is mixed with the saturated water in the drum, the steam is absorbed along the down pipe below the drum to absorb the heat. Usually only a part of the water turns into steam, so the steam and water mixture flows in the evaporator. . The steam-water mixture leaves the evaporator and enters the upper drum. The water is separated by the steam-water separation equipment. The water falls into the water space of the drum and enters the down pipe to continue to absorb the heat. The steam enters the superheater from the upper part of the drum, and absorbs heat to make the saturated steam become superheated steam. . According to the three stages of the steam production process, three heating surfaces, namely the economizer, the evaporator and the superheater, if only superheated steam is not required, only saturated steam is required, and the superheater may not be installed. When there is reheat steam, a reheater can be added.
Core component editing
Drum introduction
A pot holder for pickling, thermal measurement, water level gauge, water supply, dosing, continuous sewage discharge, emergency water discharge, safety valve, air valve, etc., and a manhole device are provided on the drum. The drum is equipped with two spring safety valves; two water level gauges are made of quartz tube type two-color water level gauge, which is safe and reliable, easy to observe and correct. A casing type pipe socket is adopted in the inlet pipe hole of the drum and other pipe holes where a large temperature difference may occur, thereby preventing cracks due to thermal fatigue in the vicinity of the pipe hole. The inner device of the drum is provided with a separating device for separating steam and water, and a connecting pipe for boiler water supply and dosing. The drum is equipped with two supports, one for the fixed support and one for the movable support.
Activity hood
The water distribution tank is composed of a water distribution box and a connecting pipe; the boiler feed water is taken out from the drum and led to the water supply box by the down pipe. In order to make the temperature of each part of the header not deviate, the water supply distribution box and the lower header are used for water inlet. Multiple discrete downcomers are introduced.
The collecting header is composed of a water collecting box and a connecting pipe. In order to make the temperature of each part of the header not deviate, the steam-water mixture is introduced into the water collecting box by a plurality of connecting pipes, and then introduced into the drum by the rising pipe.
The movable hood pipe group is composed of an upper collecting box, a lower collecting box and a pipe group, and 180 φ45×5 seamless steel pipes are connected between the upper and lower collecting boxes, and the lower hood is welded by flat steel between the pipes.
Due to the process, the movable hood often needs to move up and down, and there is a gap between the movable hood and the mouth of the furnace. In order to prevent the high-temperature smoke from leaking out, a water sealing groove is formed in the upper part of the movable hood, and the water seal is used. Sealing, in order to prevent slag from splashing into the sealing groove, a slag blocking plate is arranged at the end of the sealing groove, and in order to facilitate cleaning of the debris in the water tank, a cleaning hand hole is also opened on the water sealing groove.
Flue
It consists of a distribution header, a lower header, a tube set, and an upper header.
Waste heat boiler
The boiler feed water is led out from the drum into the distribution header. In order to prevent the temperature of each part of the header from deviating, the water in the distribution header and the lower header is introduced by the dispersion descending tube. After the water enters the lower header, it is dispersed into 132 φ42×4. The seamless steel tube and the 6mm thick flat steel have a circular flue heating surface of φ2400mm, and then a steam-water mixture is introduced into the upper header, which is introduced into the drum by the riser.
In order to avoid the flame zone, the lower part of the bundle is a U-bend, and the angle between the flue of the furnace section and the horizontal is 55 degrees.
In order to prevent deformation of the flue, a reinforcing ring is provided at an appropriate position on the flue.
The box and pipe materials are all 20 (GB3087-1999).
The flue pipe sections of the inclined section, the second section of the flue, the last section of the flue, and the last section of the flue are composed of a distribution header, a lower header, a tube set and an upper header.
The boiler feed water is taken out from the drum into the distribution header. In order to prevent the temperature of each part of the header from being biased, the water in the distribution header and the lower header is introduced by the dispersion descending tube. After the water enters the lower header, it is dispersed into 132 φ42×4. The seamless steel tube and the 6mm thick flat steel have a circular circle flue heating surface of φ2636mm, and then a soda-water mixture is introduced into the upper header, which is introduced into the drum by the riser.
In order to prevent deformation of the flue, a reinforcing ring is provided at an appropriate position on the flue. In order to facilitate maintenance, there are also manholes in the flue. The box and pipe materials are all 20 (GB3087-1999).
Oxygen muzzle
An oxygen muzzle is arranged on the flue of the furnace mouth section, and the oxygen muzzle port is composed of a tube bundle and a top and bottom header box. Due to the high temperature here, in order to prevent structural deformation at the inlet, a detachable water-cooling sleeve structure is adopted, and the oxygen lance inlet is adopted. In order to prevent the external spray of smoke, an oxygen muzzle nitrogen sealing device (including nitrogen plugging) is also provided.
Cutting tube
A cutting pipe is arranged on the flue of the furnace mouth section, and the unloading pipe is composed of a pipe bundle, an upper and lower header, and a wear plate. ZG series needle tube waste heat recovery device is a special high-efficiency energy-saving product specially designed for flue gas waste heat recovery. The needle-shaped tube is used to strengthen the heating element to expand the heating surface, and the heating surface of the water pipe smoke side can be greatly increased, and the smoke airflow forms a strong turbulent flow through the surface of the needle tube, thereby improving the heat transfer efficiency and reducing the accumulation of soot. The waste heat recovery device has the advantages of structural introduction, high thermal efficiency, long operating life, safety and reliability, long operating life, safety and reliability, and convenient maintenance.
Development trend editor
In recent years, with the sharp increase in various energy prices, people's choice of boilers began to focus on its operating costs. In reality, enterprise production cannot be separated from steam boilers, heating or bathing in hotels, hotels, communities, bathing centers. Without the hot water boiler, the fuel cost of the boiler is a very large expenditure. In order to avoid the objective phenomenon of “can afford the boiler and can't afford the boilerâ€, the savvy boiler manufacturer has carried out a series of energy-saving renovations on the boiler. The main content of the reform is the waste heat recovery of the boiler. Customers of waste heat boilers are very recognized for their equipment.
In fact, energy conservation is one of the key factors for a country's sustainable development. If we still adhere to the traditional way of using energy and cannot effectively recycle resources, it will aggravate the entire resource environment of society and cause energy. Rapid depletion. According to reliable data, China's industrial energy consumption accounts for the largest share of total costs, while the effective use rate of energy is only about 30%. The cost is much higher than that of developed countries in Europe. Therefore, considering the economic benefits, the promotion of energy-saving equipment is A major move that is imperative. The shortage of energy is a serious test that the whole world is facing now. In such a large background, it is one aspect to seek development and develop new energy. More importantly, it is necessary to save energy. At present, the design and development of domestic waste heat energy-saving boilers have gradually matured. With the development of society, people will increasingly find that energy-saving equipment is an inevitable trend. The signboard of energy-saving boilers is not only a heavy weight of business promotion, but also a major contribution to society and the environment.
Corrosion problem editor
The common waste heat boiler adopts the heat exchange of the flue pipe, and the minimum wall surface temperature of the metal heating surface is approximately in a multiple relationship with the hot fluid discharge temperature. Regarding the pipe heat exchanger, if the temperature of the wall surface of the metal heating surface is not less than 150 ° C, the exhaust gas temperature is usually not lower than 300 ° C, otherwise it will inevitably cause low temperature condensation corrosion.
Considering the extremely low temperature operating conditions of the equipment, with a safety factor of 1.5 times, the exhaust heat of the waste heat boiler is not lower than 450 ° C. At this time, the waste heat boiler can recover about 0.5 tons of heat, and the recovery efficiency is still very low. In addition, at this time, the temperature is only the calibration temperature. When the operating condition must be stopped due to the operation demand, there is no way to directly stop the wall temperature adjustment control.
When the temperature of the metal wall surface of the heating surface of the waste heat boiler is lower than the condensation point of sulfuric acid vapor, liquid sulfuric acid is formed on the outer surface. Corrosion caused by condensation on the heated surface of the tail of each heat exchange device has been frequent for a long time. As a result, in the design of the waste heat boiler, it is necessary to improve the exhaust gas temperature or use the non-metal materials with extremely poor heat transfer to alleviate the occurrence of condensation and corrosion, but still does not basically deal with the problem. Nonetheless, waste heat recovery equipment often corrodes until one or two years of operation until perforation.
Gravity heat pipe waste heat boiler was once introduced, although the characteristics of its isothermal heat transfer can be used to reduce the exhaust gas temperature at a certain level, but the lowest wall temperature of the tail heating surface will still be lower than the acid dew point temperature, and it can not prevent the corrosion caused by condensation. Moreover, the heat pipe generally has a state in which the non-condensable gas is generated and accumulated, and the gradual aging, the gravity action causes the thickness of the heat transfer liquid film to be uneven, and the heat transfer is unstable.
The appearance of the composite phase-change annular heat pipe heat exchange technology has changed this situation. It adopted the principle of heat pipe, proposed the concept of phase change section, and initiated the new concept of wall temperature as the most fundamental design parameter of heat exchanger. From the basic treatment of low temperature corrosion problems. The phase change section deals with the problem of low temperature corrosion, so that the final exhaust temperature is infinitely close to the dew point without corrosion, and the purpose of energy saving is completed. After adjusting the boiling point temperature of the phase change section, the closed-loop control can be completed on the lowest wall temperature surface of the heating surface, and the wall temperature constant and the height adjustment effect are easily completed.
Since the heat pipe is vacuumed, the fluid resistance is extremely small, and the inner and outer layers of the annular heat pipe are only 10 mm apart, so the heat transfer speed is extremely fast, and a large amount of heat energy is transmitted through the small cross-sectional area at a long interval without requiring any additional power. Due to the common structure of the annular heat pipe, it has been widely used in the fields of thermoelectric industry, chemical industry and petrochemical industry, power engineering, textile industry, glass industry and electrical and electronic engineering.
The annular heat pipe is a double-walled dog structure, which is divided into an inner pipe and an outer pipe. The annular heat pipe has the following advantages: the heat absorption section is inside the heat release section and can receive higher pressure. The shortest interval between the suction and heat release sections minimizes the temperature of the medium vapor. Under the same working conditions, the service life is several times that of the ordinary gravity heat pipe. It can be placed at an angle of inclination, which brings maximum convenience to product design. The suction and heat release sections are parallel, and the heat transfer speed is several times higher than that of the conventional gravity heat pipe. The starting temperature can be set arbitrarily. When the exhausting temperature is lower than the dew point temperature, the system does not absorb heat, preventing the temperature of the smoke from falling below the dew point and causing corrosion. Therefore, the final exhaust gas temperature can be infinitely close to the dew point, and the waste heat recovery efficiency is greatly improved.
Daily maintenance editor
1. Observe the water level with the water level meter and timely repair the damaged water level table.
2. The pressure gauge is damaged and the dial is not clear and replaced in time.
3. Valves that run, run, drip or leak can be repaired or replaced in time;
4. The insulation layer and the reinforced inner liner are intact.
5. Each shift should regularly check the flexibility and working conditions of the transmission device, and timely lubrication should be carried out to ensure its normal operation;
6, check and repair the fan, water supply pipe valve, feed pump, etc.;
7. Check all the connecting pipe flanges and other parts of the boiler system must be tight and airtight;
8. If the induced draft fan is subjected to severe vibration, it should be stopped for inspection. Generally, the internal impeller wears and should be replaced.
9. No water can be accumulated on the ground at the bottom of the boiler header and the heated pipe to prevent moisture from corroding the base;
10. Regularly check the shaft end seal of the three-way flapper valve, the operation of the spindle and the electric device, and eliminate the fault in time;
11. Always check whether the boiler steam pressure, water level, superheated steam output and temperature are normal;
12. Check all base anchor bolts for looseness. Must be secured, otherwise it will cause vibration;
13: The water level gauge must be flushed once per shift;
14. Safety valve manual steam release or water discharge experiment at least once a week, automatic steam release or water discharge experiment at least once every three months;
15. The pressure gauge is flushed once a week during normal operation, and the trap is checked at least once every six months; and the working pressure red line is marked on the dial, and the seal is sealed after calibration;
16, high and low water level alarm, low water level interlocking device, overpressure, over temperature alarm, overpressure interlocking device, at least one alarm interlock test every month;
17. Equipment maintenance and safety accessories test verification, detailed records should be made, boiler operation management personnel should check regularly. [1]
Other application editing
Through research, we have learned that the industry in which waste heat utilization is widespread is extensive, and progress in various fields of thermal energy utilization is progressing. Because of the different fields, the methods are different. From the research, not only the new understanding of waste heat utilization, but also many new waste heat utilization methods have been discovered.
For example, there are three main methods for utilizing engine waste heat, namely thermoelectric power generation, exhaust gas turbine power generation, and fluorocarbon turbine power generation. Temperature difference power generation mainly uses thermoelectric power generation materials for power generation. However, since the energy conversion rate of thermoelectric materials is low, it is necessary to develop a thermoelectric exchange material with a high conversion rate. Exhaust gas turbine power generation is to use the exhaust gas to drive the turbine to drive the generator to generate electricity. This power generation method has certain influence on the performance of the engine and needs further research.
China's first 12 MW manganese ferrosilicon alloy ore furnace flue gas generator was operated at Sinosteel Guangxi Ferroalloy Co., Ltd. on 2009.9.21. The equipment mainly uses the energy of waste heat in the flue gas to generate electricity. The waste heat utilization of the power plant is mainly the heat pump technology, and the heat pump is a machine that transports the heat energy of the low temperature to the high temperature position. In principle, the heat pump and the refrigerator are the same, the difference is the purpose of use. Although the use of heat pump technology will reduce the temperature of circulating cooling water, it is not easy to meet the national emission standards. Therefore, the main problem of heat pump technology using the waste heat of power plants is the water temperature problem.
For example, the use of waste heat in air conditioners, because the air conditioner is installed indoors, the use of waste heat of air conditioners is closely related to family life. Conventional air conditioners generally discharge the heat absorbed in the room through the outdoor unit, which not only generates a lot of greenhouse gases, but also wastes a lot of heat. The following is a detailed description of a method for processing hot water using central air conditioning waste heat. The steps are as follows:
I Install a water trap in the high temperature zone of the central air conditioning condenser. The water trap accommodates 50%-100% of the condensation pipe in the high temperature zone and forms a separate closed heat exchange zone;
II. The output end of the water trap is connected to the input end of the hot water tank, and the output end of the hot water tank is connected to the input end of the water trap, so that the water in the hot water tank enters the high temperature area of ​​the condenser and is discharged by the condenser through the inlet of the water trap. After heating, the water outlet is returned to the hot water tank to form circulating water heat.
Operational editing
It is well known that a boiler that utilizes the sensible heat of various exhaust gases and waste heat after waste incineration as a heat source is called a waste heat boiler, which is also called a waste heat boiler.
Therefore, the state advocates vigorously developing waste heat utilization, energy conservation and emission reduction, and plays a positive role in protecting energy and improving the quality of human living environment. In the design of waste heat boiler, how to divide the temperature section reasonably is the basis for rationally arranging the heating surface of the waste heat boiler and maximizing the utilization of waste heat. Under the condition of the inlet flue temperature of the waste heat boiler, there are two requirements for the exhaust gas temperature. One is to limit the exhaust gas temperature, and the exhaust gas temperature is within a reasonable range; the other is to limit the exhaust gas temperature. Require the maximum use of waste heat.
In either case, for medium and low temperature waste heat utilization, the narrow point temperature difference directly affects the evaporation of the waste heat boiler and the arrangement of the heated surface. The narrow point temperature difference, also called the node temperature difference, is the minimum temperature difference between the evaporator outlet flue gas and the heated saturated water vapor during heat exchange. With the change of the temperature difference of the narrow point, the relative heat exchange area of ​​the waste heat boiler, the relative evaporation amount, and the relative exhaust gas temperature also change.
When the narrow point temperature difference is reduced, the exhaust heat temperature of the waste heat boiler will decrease, the flue gas waste heat recovery will increase, and the steam output will also increase, which corresponds to the high heat recovery efficiency of the waste heat boiler, but the average heat transfer temperature difference will decrease. Small, it will increase the heat exchange area of ​​the waste heat boiler, and the manufacturing cost will increase. Therefore, when selecting the narrow point temperature difference, attention should be paid to the rationality of economic and technical comparison. Since the exhaust gas temperature is limited by various conditions such as heat transfer, environment, and user, in the calculation process of boiler evaporation amount, there are two methods for calculating the evaporation amount, that is, calculating the evaporation amount according to the exhaust gas temperature and calculating the evaporation amount according to the narrow point.
Calculating the evaporation amount according to the narrow point is to select the minimum narrow point temperature difference under economic conditions, and the evaporation amount obtained is the maximum evaporation amount under the economic condition of the boiler, thereby obtaining that the exhaust gas temperature is the lowest exhaust gas temperature under economic conditions. Therefore, using the narrow point to calculate boiler evaporation and exhaust temperature is relatively reliable, more accurate, and most economical. When the narrow point temperature difference is reduced, the investment cost of the boiler will increase a lot due to the larger increase of the heat exchange area of ​​the waste heat boiler; but when the narrow point temperature difference is larger than the design point value, the total investment cost and unit heat recovery The reduction in costs has to be moderated.
From the perspective of the investment cost and the best utilization efficiency of waste heat, there must be a question of how to choose the narrow temperature difference of the waste heat boiler reasonably. The narrow point temperature difference is the heat exchange area and evaporation amount of the waste heat boiler. [2] The importance of the exhaust gas temperature in accordance with. To this end, we must first consider the narrow point temperature difference when designing the waste heat boiler, and determine the reasonable narrow point temperature difference, which is the premise to ensure the economic and technical rationality. At present, the general range of the narrow point temperature difference is 10-20 ° C, and the minimum is 7 °C.
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