Operating condition

As we all know, the boiler that uses the sensible heat of various exhaust gases and the waste heat after waste incineration as the heat source is called a waste heat boiler, also known as a waste heat boiler.

Therefore, the state advocates vigorously developing waste heat utilization, energy saving and emission reduction, which play a positive role in protecting energy and improving the quality of human living environment. In the design of a waste heat boiler, how to reasonably divide the temperature zone is the basis for rationally arranging the heating surface of the waste heat boiler and maximizing the use of waste heat. Given the inlet flue gas 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 required to be within a reasonable range; the other is to not limit the exhaust gas temperature. The maximum use of waste heat is required.

In either case, for the utilization of medium and low temperature waste heat, the narrow temperature difference directly affects the evaporation capacity of the waste heat boiler and the layout of the heating surface. The narrow point temperature difference is also called the nodal temperature difference, which is the minimum temperature difference between the flue gas at the outlet of the evaporator and the heated saturated water vapor during the heat exchange process. With the change of the narrow point temperature difference, the relative total heat exchange area of the waste heat boiler, the relative evaporation capacity, and the relative exhaust gas temperature also change.

When the narrow point temperature difference decreases, the exhaust gas temperature of the waste heat boiler will decrease, the flue gas waste heat recovery will increase, and the steam output will increase accordingly, which corresponds to a high waste heat boiler thermal efficiency, but the average heat transfer temperature difference will decrease accordingly. Smaller, it will increase the heat exchange area of the waste heat boiler and increase the manufacturing cost. Therefore, when choosing a narrow temperature difference, attention should be paid to the rationality of economic and technological comparison. Because the exhaust gas temperature is restricted by various conditions such as heat transfer, environment, users, etc., in the calculation process of boiler evaporation capacity, there are two methods for calculating evaporation capacity, namely calculating the evaporation capacity according to the exhaust gas temperature and calculating the evaporation capacity according to the narrow point.

Calculating the evaporation capacity according to the narrow point is to select the smallest narrow point temperature difference under economic conditions, and the obtained evaporation capacity is the maximum evaporation capacity under the economic conditions of the boiler, and the exhaust gas temperature is the lowest exhaust gas temperature under economic conditions. Therefore, it is more reliable, more accurate and the most economical to use the narrow point to calculate the boiler evaporation and exhaust gas temperature. When the narrow point temperature difference decreases, the heat exchange area of the waste heat boiler increases greatly, and the boiler investment cost will increase a lot; 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 investment costs and the best waste heat utilization efficiency, there must be a problem of how to reasonably select the narrow point temperature difference of the waste heat boiler. The narrow point temperature difference is an important basis for determining the heat exchange area, evaporation capacity and exhaust temperature of the waste heat boiler. For this reason, when designing a waste heat boiler, we must first consider the narrow point temperature difference, and determining a reasonable narrow point temperature difference is a prerequisite to ensure that the economy and technology are more reasonable. At present, the general range of the narrow point temperature difference is 10-20 ℃, and the minimum can reach 7 ℃.