What are the two main factors that affect steam temperature changes?

To adjust the temperature of the steam generator, we first need to understand the factors and trends that affect the change of steam temperature, grasp the influencing factors of steam temperature, and correctly guide us to effectively adjust the steam temperature so that the steam temperature can be controlled within the ideal range. Generally speaking, the factors that affect the change of steam temperature can be divided into two parts, namely the influence of the flue gas side and the steam side on the change of steam temperature.

1. Influencing factors on the flue gas side:

1) The influence of combustion intensity. When the load remains unchanged, if the combustion is strengthened (the air volume and coal volume increase), the main steam pressure will rise, and the main steam temperature and reheat steam temperature will increase due to the increase in smoke temperature and flue gas volume; otherwise, they will decrease, and the steam pressure will increase. The amplitude of temperature change is related to the amplitude of combustion change.

2) The influence of the position of the flame center (combustion center). When the furnace flame center moves upward, the furnace outlet smoke temperature increases. Since the superheater and reheater are arranged in the upper part of the furnace, the radiant heat absorbed increases, causing the main and reheat steam temperatures to increase. Reflected in the actual operation, when the coal mill switches to the middle and upper layer coal mill operation, the main reheat steam temperature rises. In addition, when the water seal at the bottom of the steam generator is lost, the negative pressure in the furnace will suck cold air from the bottom of the furnace, raising the center of the flame, which will cause the main reheat steam temperature to rise significantly. In severe cases, the steam temperature will The superheater wall temperature exceeds the limit in all aspects.

3) The influence of air volume. The air volume directly affects the flue gas volume, which means it has a greater impact on the convection type superheater and reheater. In our steam generator design, the steam temperature characteristics of the superheater are generally convection type, and the steam temperature characteristics of the reheater are also different. It is a convection type, so as the air volume increases, the steam temperature increases, and as the air volume decreases, the steam temperature decreases.

2. Influence on the steam side:

1) The influence of saturated steam humidity on steam temperature. The greater the saturated steam humidity, the more water content, and the lower the steam temperature. Saturated steam humidity is related to the quality of soda water, the water level of the steam drum and the amount of evaporation. When the quality of the boiler water is poor and the salt content increases, it is easy to cause the co-evaporation of steam and water, causing steam to be entrained; when the water level in the steam drum remains too high, the separation space of the cyclone separator inside the drum is reduced, and the separation effect of steam and water is reduced, which is likely to cause steam entrainment. Water; when the boiler evaporation suddenly increases or is overloaded, the steam flow rate increases and the steam’s ability to carry water droplets increases, which will cause the diameter and number of water droplets carried by the saturated steam to greatly increase. The above situations will cause a sudden drop in steam temperature, which in serious cases will threaten the safe operation of the steam turbine. Therefore, try to avoid it during operation.

2) Influence of main steam pressure. As the pressure increases, the saturation temperature increases, and the heat required to change water into steam increases. When the amount of fuel remains unchanged, the evaporation volume of the boiler decreases instantaneously, that is, the amount of steam passing through the superheater decreases, and the superheater The temperature of the saturated steam at the inlet rises, causing the steam temperature to rise. On the contrary, the pressure decreases and the steam temperature decreases. However, it should be noted that the impact of pressure changes on temperature is a temporary process. As the pressure decreases, the fuel volume and air volume will increase. Therefore, the steam temperature will eventually rise, even to a large extent (depending on the increase in fuel volume). degree). When understanding this article, keep in mind “Beware of extinguishing fires when the pressure is high (the amount of fuel will be reduced a lot, causing combustion to worsen), and beware of overheating when the pressure is low.”

3) The influence of feed water temperature. As the feed water temperature increases, the amount of fuel required to produce the same amount of steam decreases, the amount of flue gas decreases and the flow rate decreases, and the furnace outlet flue temperature decreases. Overall, the heat absorption ratio of the radiant superheater increases, and the heat absorption ratio of the convective superheater decreases. According to the characteristics of our biased convective superheater and pure convective reheater, the main and reheat steam temperatures decrease, and the desuperheating water volume decreases. On the contrary, the decrease in feed water temperature will cause the main and reheat steam temperatures to increase. In actual operation, it is especially obvious when performing high-speed decoupling and input operations. Pay more attention and make timely adjustments.