5. Turn the pointer of the solu-bridge upper dial until the dark segment of the tube reaches its widest opening.
6. Calculate the result in ppm by multiplying the dial reading either by 0.9 or by a factor recommended by local instructions. For example, when the dial reading is 4,000 micromhos and the factor used is 0.9, then 4,000 x 0.9 = 3,600 ppm.
7. Record the results of the test in ppm.
Q22. Scale deposited on metal surfaces of' boilers consists largely of what scale-forming element?
Q23. What are the two broad types or methods of chemical treatment of boiler water?
Q24. Results of a phosphate test would need to be between what lower and higher ppm to be at an acceptable level?
Q25. In a causticity test without tannin, when the mixture turns pink, what does this mean?
Q26. A sample of boiler water for a sodium sulfite test should be cooled to what temperature before conducting the test?
Lesson Objective: Describe met hods and procedures involved in fireside and waterside cleaning.
Boiler heat transfer surfaces must be kept clean to provide for safe and economical boiler operation. In this section we will describe the methods and procedures involved in fireside and waterside cleaning.
Excessive fireside deposits of soot, scale, and slag cause the following conditions: reduced boiler efficiency, corrosion failure of tubes and parts, reduced heat transfer rates and boiler capacity, blocking of gas passages with high draft loss and excessive fan power consumption, and fire hazards.
Methods for cleaning boiler tiresides include wire brush and scraper cleaning, hot-water washing. wet-steam lancing, and sweating.
When too much soot is deposited and the passages become plugged, hand lancing, scraping, and brushing are generally used. Special tools required for reaching between the lanes of tubes may be made from flat bars, sheet metal strips cut with a saw-toothed edge, rods, and similar equipment. Some boilers have different sizes of tubes, so you need various sizes of brushes and scrapers to clean the boiler tubes. The brushes or scrapers are fastened to a long handle, usually a piece of pipe, inserted and pushed through the tubes.
This method of cleaning is often used to clean superheaters, economizers, and other sections of the steam generator that are difficult or impossible to reach by brushing or scraping. The water may be applied with hand lances and/or boiler soot blowers. Dry out the boiler setting immediately after water washing to reduce damage to the refractory and other parts of the setting.
Safety is always paramount; therefore, always be cautious when washing boiler firesides. Some precautions you should observe are as follows:
Wet the boiler refractory and insulation as little as possible. Install canvas shields or gutters where possible to reduce wetting of refractories.
Protect electrical equipment from water damage.
Provide all necessary instructions and protective equipment for workers.
Provide a compressed air lance to loosen scale after water washing.
Provide adequate equipment to heat and pump the hot water. The water should be heated and maintained at a temperature close to about 150°F, because water exceeding this temperature cannot be handled safely and efficiently. However, because cold water does not clean satisfactorily, you have to maintain the water temperature as close as 150 degrees as possible. A water pressure of 200 to 250 psig should be provided at the cleaning lances or soot blowers. The water jets must penetrate the tube banks and strike with enough force to break up the slag accumulations.
Start the water washing at the top of the unit and work down.
The unit must be dried out immediately after washing.
The wet-steam lancing method is similar to the hot-water method except that wet steam is used instead ofContinue Reading