Boiler Shutdown and Washout Procedure
Proper shutdown, cool-down, and washout of a boiler prior to inspection or removal from service is very important. Boiler water dissolved solids, sludge, and mud must be gradually diluted and removed as the boiler cools; otherwise, they can bake onto hot boiler surfaces giving the appearance of scale and often being just as hard to remove. A full year of successful water treatment can be marred by an improper shutdown.
Some operators alternate operation of boilers, for example between a #1 and #2 boiler, without following recommended take-down procedures. Each time a stand-by boiler is started up and taken off-line, some settled sludge could bake onto the heat transfer area when the temperature cools and the internal water circulation is low.
Unless the deposits are examined carefully at inspection time, it may be assumed incorrectly that the deposits noted are scale formed during operation. In order to judge effectiveness of the treatment program as well as to eliminate unnecessary boiler cleaning, proper care must be taken in removing the boiler from service.
For a period of 3 – 7 days prior to shutdown, manual (bottom) blow should be increased. A general rule is to at least double the daily blowdown schedule.
If the boiler is using a polymer treatment, the feed rate should be doubled 3 – 7 days prior to shutdown.
The lower normal recommended conductivity range should be the now desired target point. For example, if normal conductivity range is 2,000 – 3,500 umhos, the 2,000 point is the target to get the solids level down to.
IMPORTANT! Make sure other treatment readings remain in the recommended range, especially sulfite. Running the sulfite level a little higher than normal would even be recommended.
On day of shutdown, lower the boiler pressure and cool the boiler at the rate recommended by the boiler manufacturer.
Follow the boiler manufacturer’s procedures in shutting down the boiler. Pay particular attention that the water level remains at normal operating levels.
When the boiler and furnace temperatures are under 110 degrees F, the boiler may be drained.
AS SOON AS THE BOILER IS DRAINED, open the manhole and handholes and flush the boiler with a high-pressure water hose. If this is not done quickly, while any mud is still in a soft and fluid condition, the residual heat in the boiler may dry and bake the mud, making subsequent removal more difficult.
NEVER LEAVE A BOILER FILLED WITH WATER WITHOUT TAKING PROPER MEASURES TO PREVENT CORROSION AND PITTING.
Generally, a boiler stored wet should have over 200 ppm of sulfite, a ph over 10.5, and an initial dose of polymer and/or phosphate treatment.