Removal from Service and Cooling the Boiler
How many times have you had what you thought were perfect results in a customer’s boiler all year, only to open it and find scale, debris, or leaks. Of course the chemical supplier gets blamed for the poor conditions found when the boiler is opened. Let us say right here that you should always have your customer follow the boiler manufacturers recommendations for removal from service, but the following are some tips that will help your customer and you.
Following the proper procedure for removal of a boiler from service is important for many reasons, however, two major reasons that should always be kept in mind are: 1. cooling the boiler too rapidly or unevenly can cause extreme expansion and contraction of the boiler metal and/or refractory. These types of stresses can cause leaks to develop at rolled tube ends. 2. Following the proper procedure is to prevent the settling and “baking on” of boiler sludge as the boiler is cooled. Sludge deposited because of improper cooling and draining a boiler increases maintenance costs and leads to erroneous interpretation of boiler system treatment program results.
Normal boiler water sludge and other suspended matter in an operating boiler are kept in suspension by sludge conditioners and by the circulation of water in the boiler. When the boiler is no longer fired, the circulation of water slows or ceases altogether and the boiler water solids tend to settle and adhere to internal heat transfer surfaces. Therefore, 48-72 hours before removing a boiler from service, it is necessary to properly condition the solids so that rapid settling and erroneous deposit patterns are avoided.
Notification-Make sure your customer notifies you that the boiler is being removed from service and indicates the probable date when the boiler will be open for inspection. (Plan on taking pictures for you and the customer to put in files. If it is a competitively held boiler account take pictures to show how it is getting worse or to compare with what a good boiler should look like that has been properly treated)
Additional Blowdown-The amount of continuous blowdown should be increased by approximately 15% and frequency of bottom blowdown should be doubled, at a minimum.
Increase the Hydroxide Alkalinity-The hydroxide alkalinity, OH or O should be increased to the maximum recommended limit for each particular boiler. Use Amsolv BW-8150 to bring up the alkalinity. Higher alkalinity levels ensure fluid sludge and help soften any existing deposits due to system control excesses.
Double the Dosage of Amsolv BW-5320 Sludge Conditioner-The normal dosage of Amsolv BW-5320 should be doubled to increase the fluidity of the boiler water solids, especially during the periods of low water circulation when the boiler is no longer being fired. If not currently using BW-5320 as part of your regular boiler program, use approximately 1 ˝ pints per 500 gal. of water in the boiler. This dosage is equal to 400 ppm of BW-5320 and should be maintained while doing the heavy blowdown.
Increase the Oxygen Scavenger Level-Maintain twice the normal residual of sulfite utilizing AmGuard 7800, AmGuard 7815, or AmGuard 7825 throughout the period of time when the boiler is being removed from service.
COOLING THE BOILER
After the boiler has been properly “set up” for a minimum of 48 hours, it can then be made ready for internal inspection. Follow as closely as possible the following procedures to prevent structural damage and to avoid unnecessary cleaning of the waterside.
- Blowdown Heavily-Immediately after the boiler is taken off line and while it is still under pressure, blowdown heavily from the continuous blowdown line and from all the bottom blowdown lines.
- Replace the Blowdown Water-Hot; deaerated feed water should be used to replace the water blown down. Do not introduce cold makeup water at this time.
- Repeat Blowdown Process-Repeat the blowdown process cited above several times while the boiler is cooling.
- Open the steam Vent Valve-To avoid creating a vacuum, open the steam vent valve.
Open the Drain Valves-Slowly drain the entire boiler by opening the drain valves. Boilers that have been operated with high hardness feed water and/or high boilerwater suspended solids should be refilled to normal operating level with deaerated feed water, then again drained before being opened for inspection.
PROCEDURE AFTER COOLING AND DRAINING THE BOILER
- Immediately remove manhole and/or handhole covers necessary for access and inspection.
- Complete a quick inspection as soon as possible, before any sludge deposits have had time to dry.
- Immediately wash the boiler waterside surfaces using a high pressure water hose.
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