Recently due to black smoke problem our mill was compelled to operate at 60~70% loading. Our boiler is installed with superheater. I am concerned and have doubts if there will be any undesirable consequences to the Superheater? Will the Superheater gets overheated and bend? Will it affect the Steam and Power Balance of the mill?
Members’ comments and supports would be highly appreciated.
Mr CS Tan has excellently outlined what one should be looking out for in the operation of the Superheater in Boilers to prevent overheating and distortion of superheater tubes.
I will add to that by sharing an experience of a friend who was operating a mill in Johore several years ago.
The mill had bought, installed and commissioned a boiler equipped with superheaters.. After less than 2 years in operation, the superheater tubes failed. The boiler manufacturer attributed the failure of the superheater to wrong operating procedure, namely:
1. Superheater drain valves not opened during steam built-up during boiler start up operation.
2. Again superhaeater drain valves not opened after boiler shutdown.
The boiler manufacturer decided to install an automatic drain valve for the superheater tube bank to prevent steam starvation during start up and shutdown.
Again, after less than 2 years of replacing the damage superheater tubes and installing automatic drain valves, the superheater tubes failed again. The problem was finally resolved by reducing the number of tubes in the superheater tube bank. This effectively increased the flow of steam in the remaining tubes of the superheater and prevented overheating of the tubes.
Lessons for Mill Engineers:
1. Inspect your superheater tubes for signs of overheating (distortion) during inspection.
2. Check your superheated steam temperature and the degree of superheat.
3. Do not run your boiler at very low throughput for long period.
4. If you need to invest in a bigger boiler for future requirement, inform your boiler supplier so that the superheater can be sized for your current capacity requirement instead of the rated capacity of the boiler.
5. Refer to the SOPs by Mr. CS Tan.
Superheater operating at 70 % loading Let me share the followings which most of us are quite aware of, 1) unlike downcomer and generating tubes which used wate