A newcomer is asking questions regarding boiler superheaters and spray water temperature reducers
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On the drawings of our company, the steam generated by the boiler passes through a low-temperature superheater, then a water spray desuperheater, and subsequently through a high-temperature superheater. Question 1: What is the function of each of these two superheaters? Question 2: What is the purpose of using a spray water cooler in between? I earnestly ask the experts to share their insights
This is how I think about this issue; please judge whether it is correct: 1. It is estimated that the temperature difference between the two is quite large. If a superheater is used, the excessive temperature difference could cause damage to the equipment, so a stepwise heating method is adopted. 2. Spraying water in between is done to ensure that the steam has a certain level of humidity, meeting the requirements for its use at the rear.
The temperature with a spray-type temperature reducer added in the middle is used to prevent the steam from overheating, right? We haven’t used one like that here
The two-stage superheaters are designed to fully absorb the heat from the flue gas, preventing the heat from high-temperature flue gas from moving backward or being wasted; water injection in between is used to control the temperature of the main steam at the boiler outlet. If the primary superheater is able to sufficiently absorb the temperature of the flue gases and the main steam temperature is satisfactory, it should also be possible to do without multiple superheaters and water spray cooling.
To reduce investment costs, the two superheaters can be combined into one unit. The material used for this unit must be the same as that used for high-temperature superheaters, which is costly; by using a lower-grade material, costs can be saved.
1. Purpose of designing a two-stage superheater: Both flue gas and steam require heat exchange balance calculations. There are various operating conditions regarding the flow rate of flue gas; scenarios such as 50%, 100%, 110% etc., are assumed. In the condition of maximum flow rate, more heat is released due to the temperature drop of the flue gas. If only one stage of superheater were used, there would be a risk of the superheated steam exceeding its specified temperature. Therefore, a two-stage superheater is employed. The steam exiting the first stage of superheater has its temperature reduced through water spray cooling, and then it is heated by the second stage of superheater, so that the superheated steam reaches the required temperature and pressure before entering the steam distribution network. 2. Spray water desuperheater: It serves only a regulating function; it adjusts the amount of water entering based on different operating conditions, thereby ensuring that the steam in the superheated pipes does not exceed its allowable temperature. As a result, the wall temperature of these superheated pipes does not go above the temperature limit specified for the material used in their construction, providing protection for the pipes. If the pipe wall temperature exceeds the limit, the superheater equipment is completely destroyed.
1. Superheated steam, 2. Prevent the steam temperature from becoming too high.