Which of the following is NOT a maintenance method of a boiler?
Chemical lay-up is NOT a maintenance method of a boiler.
A steam boiler layup is a maintenance procedure that helps to prevent corrosion within the boiler on both the waterside and fireside when you plan to take the boiler out of service for an extended period of time.
The main goal of laying up a boiler is to increase its lifespan. When a boiler isn't being used to provide heat, it should be turned off.
A secondary purpose of laying up a boiler is an opportunity for cost savings and to inspect its condition while it is shut down. This is useful for determining the water treatment requirements on the waterside and the combustion efficiency on the fireside.
Boiler lay-up can be classified into various categories based on the methods used as follow:
(1) Dry lay-up:
Dry lay-up is recommended for boilers that will be out of service for 1 month or more. The boiler is drained, dried, and stored in a dry environment here.
This includes placing desiccant trays in the boiler drums, such as silica gel, to maintain a constant low humidity environment. The boiler is then shut down to prevent oxygen from entering.
If the boiler is to be stored open, the boiler and superheater must be thoroughly dried and a positive dry airflow from the bottom to the top must be maintained throughout the storage period.
(2) Wet lay-up:
This method is most suitable for short-term lay-up or where the boiler may have to be operated quickly. However, this method should not be used for a long period of time under sub-zero temperatures.
The wet method requires precautions to prevent water from freezing in the boiler or in its components.
For boilers that must be kept in an emergency standby mode, wet lay-up is recommended. Filling the boiler, feedwater heaters, and deaerators with demineralized water, treating it with a chemical oxygen scavenger, and adjusting the pH between 10 and 11 are all part of this procedure.
Boilers should not be stored in the wet lay-up mode for more than 6 months in general. The dry lay-up procedure provides better corrosion protection for periods longer than 6 months.
(3) Short-term lay-up:
?You should perform the short-term layup if you plan to shut down your boiler for 5–10 days. A short-term lay-up is a wet lay-up that involves filling the boiler with concentrated, chemically treated boiler water, preferably with a pH of 12.4 or higher (or as close as possible).