Solutions to insufficient superheat of steam produced by the boiler

This issue needs to be considered comprehensively: Starting with the steam side: 1. Determine whether the saturated steam produced contains a significant amount of water; check the liquid level control and steam-water separation equipment； 2. Is the gas production too high? Whether it is operating at reduced pressure, and whether the area of the steam generation section is too large. 3. Is the water spray heater leaking? Considering the flue gas side as well: 1. Is the flue gas temperature insufficient? Increase the temperature ； 2. Is the flue gas volume insufficient? Increase the excess air coefficient, sacrificing thermal efficiency in order to boost the flue gas volume. 3. Is the boiler operating at too low a load? Increase the load to above 60% of the design load. 4. Check for scaling and ash accumulation in the overheating section, and enhance soot blowing. Other reasons: 1. Whether the area of the overheating section is inadequately designed; redesign and recalculate. The superheating section involves convective heat transfer, so it should be analyzed based on the characteristics of convective heat transfer. If there are any mistakes, please criticize.

I’d like to share my own opinion as well: The analysis on the second floor is quite comprehensive. I believe that industrially designed boilers with mature design principles generally do not suffer from issues such as insufficient flue gas temperature or inadequate heat exchange area in the superheating section. The issues raised by the poster mainly relate to operation control and equipment problems. Operation control: Severe water carryover in steam, too low load, excessive steam generation (i.e., high steam flow rate and short residence time in the superheating section). Equipment issues: Leakage or malfunction of the spray water temperature reduction valve, ash accumulation in the superheater, low efficiency of the steam-water separation equipment, etc

The isolation valves before and after the spray cooling water were both closed, so there shouldn’t be any leakage. I tried to keep the oxygen content in the flue gas at 6-9%, but it didn’t work; the temperature only increased by a few degrees. Our furnace temperature is much lower than the designed value. Our SAIC container (also known as a cooking pot) is equipped with a cyclone separator for separating soda from steam, so steam should not carry water. Our auxiliary boiler also produces less steam than designed.

The steam separation equipment can also fail, and even if the valves are closed tightly, leaks may still occur. I’m not sure what the water level control in the drum is, nor what the boiler load is

Based on the above answers, I would like to add my own insights on the key points: First, there may be problems with the cyclone separator inside the boiler drum. Here, we have a newly installed 130 t/h coal-fired boiler that was built just a few thousand years ago. During the trial operation phase, the temperature of the superheated steam was extremely low, and it was also impossible to monitor the liquid level in the drum. The cause was found to be the fact that the sealing plate of the cyclone separator had not been fully welded to the inner wall of the drum; moreover, the water side outlet pipe of the level gauge did not extend from the sealing plate of the cyclone separator into the drum, which led to false readings of the liquid level and the presence of water in the steam. As a result, the temperature of the superheated steam remained low, and ultimately the boiler suffered tube failure. Sigh~~ ； Secondly, if the furnace temperature is low and deviates from the design specifications, it is recommended to add a secondary combustion zone inside the furnace in order to increase the temperature at the furnace outlet. Of course, the amount and height of this addition need to be determined through careful consultation with the design team.

Adjust the burner position to increase the furnace exit temperature

We keep the level of the drum liquid at 50%, and the designed gas production rate is 55 T/H. During the maintenance work, we added some refractory bricks inside the furnace; as a result, the furnace temperature increased slightly, but it still does not reach the designed level. Our burners are imported, and increasing the superheat by about 20 degrees still does not enable the temperature to reach the design value. Is there any other way?

By how much does the furnace temperature need to increase now? What was the designed temperature? If there are heating surfaces at the bottom of the furnace, dig them out and take a look...

Firstly, I think the liquid level in your drum should be controlled at 50%, which is a bit high; this makes it easy for liquid to be carried over. The level we usually control is around 40%； Second, it’s best for you to check whether the demister screen in the steam drum is in good condition and if there are any damages ； Third, check whether there are any problems with the cyclone separator inside the steam drum; poor separation can also lead to liquid carryover. Fourth, inspect the tubes of the superheater to see if there is rust, dust, or other debris blocking the spaces between the fins, which could impair heat transfer. Fifth, it is possible to increase the pressure in the steam drum slightly, thereby raising the evaporation temperature; after that, the pressure can be reduced again, so that the steam temperature exceeds the saturation temperature at that pressure. Additionally, I believe it is necessary to reduce the oxygen content in the flue gas, as this will raise its temperature and thus help to increase the superheating temperature