[China Glass Network] Features of heat pipe preheating boilers and their applications in the related glass industry. The operation of the waste heat boiler in the daily work process and related precautions.
The reuse of exhaust gas produced after burning heavy oil (or other fuel) in glass furnaces, and the so-called secondary utilization in glass, the cement industry has basically begun to use. The use of waste heat can reduce the cost of the enterprise, and the company is willing to invest and improve the utilization of waste heat.
At present, the utilization of kiln costs is generally a waste heat steam boiler or a waste heat power generation boiler. Here we only talk about the application of waste heat steam boilers. In the waste heat utilization, the boiler can be simply described as a direct heat exchange type and an indirect heat exchange type boiler according to different heat exchange modes. The direct heat exchange type is similar to the smoke tube type boiler according to the structure. The direct heat exchange type is generally small capacity, low parameters, low water quality requirements, simple structure and low heat exchange efficiency. The indirect heat exchange type refers to a heat pipe type boiler, which is generally applied at a relatively low temperature and in a corrosion resistant environment, and has a large heat exchange efficiency and a low failure rate.
The basic principle of heat pipes is:
The working principle of the heat pipe is briefly described as follows: the heat pipe absorbs heat from the flue gas, transfers heat to the water in the steam drum through the medium in the heat pipe, and heats the water to vaporize.
The heat exchange of the heat pipe is two-wall heat exchange, and the cold and hot sides are separated by a partition, and the sealing between the heat pipe and the separator is good; the cold and hot gases flow outside the heat pipe, and the heat transfer efficiency is high. The thermal design can ensure that the wall temperature of the heat pipe is accurately higher than the dew point temperature of the flue gas, avoiding the dew point corrosion, and at the same time making the dust in the flue gas not easily accumulate on the pipe wall and the fins, thereby ensuring long-term stable operation of the equipment. Because of indirect heat transfer, even one or two heat pipes (damage or aging) do not affect their use. The heat pipe has a large thermal conductivity and has the property of transmitting a large heat flow at a small temperature difference. The use of a heat pipe waste heat boiler for low temperature waste heat utilization under low temperature flue gas conditions is a feature that fully utilizes the heat pipe, and recovers more heat in the case of a small temperature difference.
According to the working temperature inside the heat pipe: low temperature heat pipe, normal temperature heat pipe, medium temperature heat pipe, high temperature heat pipe, etc., according to the combination of shell and working fluid: copper-water heat pipe, carbon steel-water heat pipe, aluminum-acetone heat pipe, carbon steel - Naphthalene heat pipe, stainless steel - sodium heat pipe, etc. The carbon steel-water heat pipe used in the kiln flue gas is simple in structure and relatively cheap in cost, and meets the requirements of corrosive gas in the exhaust gas of the kiln. And less resistance, reduce system power, and save on operating costs.
Among the exhaust gases generated by the kiln, a large amount of fluoride and SO3 contained in the flue gas are corroded and damaged to the equipment. Although the concentration of SO2 in flue gas is much larger than SO3, the effect on dew point temperature is much smaller than that of SO3. SO3 is almost completely dissolved in water vapor near the dew point temperature, but SO2 is rarely dissolved in flue gas. water vapor. Considering its dew point corrosion, its advantages in heat pipe boilers are obvious in flue gas waste heat boilers, and its application is gradually expanding.
Due to the process or kiln structure, the exhaust temperature is generally 320--450 ° C, the exhaust temperature can be reduced to 180--220 ° C, the boiler can be based on customer specific requirements, such as steam usage, use temperature , the export temperature is required to be no less than a few degrees, and it can be adapted to local conditions.
In the process of using waste heat boilers, it is generally necessary to pay attention to several aspects:
(1) Low temperature corrosion. In the waste heat boiler backup furnace, if the boiler is not suitable for a long time, consider opening the inlet or outlet of the boiler to make the flue gas enter the boiler body to keep the heat pipe at a certain temperature to prevent low temperature corrosion.
(2) The effect of scaling. If the boiler is used for a long time or has been deactivated, the drum or the heat pipe will be rusted or scaled. In this case, it is generally necessary to find a professional company to clean it. In order to avoid such a situation, the boiler must not be stopped for too long. , uninterrupted, high frequency and some use.
(3) The boiler is fouled or corroded due to improper treatment of softened water. In the use of waste heat boilers, it is strictly in accordance with industrial boiler water quality standards. Its feed water (low pressure boiler) requirements: turbidity FTU ≤ 2.0, hardness ≤ 0.030mmol / L, 8.0 ≤ PH ≤ 9.5, dissolved oxygen ≤ 0.1mg / L, oil ≤ 2.0mg / L, total iron ≤ 0.3mg / L. Unqualified water supply directly affects its efficiency, safety and longevity.
(4) Continuous blowdown during boiler use. There is a sewage valve at the bottom of the drum of the waste heat boiler, and the opening degree of the valve should be maintained during the use thereof. The opening degree can be adjusted according to the level of the steam pressure, the amount of steam used, etc., but during the operation. To open this continuous blowdown, because the water in the boiler is at a high concentration here at the bottom of the drum, it is mainly salt and sundries (produced in the water, or the cleaning is not completely filtered). It is necessary to continuously discharge the higher concentration portion of the drum water to reduce the risk of the boiler structure.
(5) During the use of the boiler, the cleaning of the boiler is also important. Generally, the boiler needs to be cleaned after about 10 days of operation. The basis of the cleaning can be based on the number of days of boiler use, the resistance of the boiler inlet and outlet reaches the set value, and the boiler induced draft fan The size of the vibration, the change in the gas production of the boiler, etc. In the cleaning of boilers, small boilers are usually purged with steam or compressed air, washed with water, and large boilers are generally cleaned by ultrasonic or gas explosion. After cleaning the small boiler, keep a certain temperature on the outer wall of the heat pipe to prevent accelerated corrosion.
Pay attention to the following aspects in daily boiler inspection:
1) The three major safety accessories (thermometer, pressure gauge, safety valve) of the boiler are indispensable. If there is any fault, it should be dealt with in time. It is not allowed to take the disease. The pressure gauge and safety valve should be inspected regularly.
2) Selection of boiler feed water pump, generally available horizontal (vertical) single-stage (multi-stage) centrifugal pump. When selecting the model, mechanical seal should be considered. Filler seal is easy to leak, maintenance is frequent, water leakage is difficult to handle, and operating cost increase. The water supply method can consider frequency conversion, reduce the impact on the boiler operation, and also have a certain protection effect on the water pump. The arrangement and consideration of the spare pump should be spared, switchable, and directly operated on site.
3) The selection of check valves for boiler feed water is more important in the selection of check valves in steam boilers. The arrangement of check valves is generally horizontal. The choice of check valves is considered to be tight. It should not be used for a long time. malfunction.
4) The arrangement of the pressure sensor in the inlet and outlet sections of the boiler body, the installation position, if the installation is not suitable, the measurement is not allowed to be said, and it is easy to block.
5) The filter used for boiler water inlet, the choice of softened water device and deaerator, have a great impact on boiler water quality.
6) The steam outlet pipe arrangement of the drum and the sub-cylinder steam trap. The selection and arrangement of the pipe trap are also important for the normal operation of the steam.
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