hot water. The steam should be wet and at a pressure of 70 to 150 psig. The unit must be dried out immediately after lancing is completed.
Fireside slag can be removed from the convection superheaters by forming a sweat on the outside of the tubes. Cold water is circulated through the tubes. and moisture from the air condenses on the tubes to produce sweat. The hard slag is changed into mud by the sweat, and the mud can be blown off by an air or a steam lance. A large tank filled with water and ice can be used as the cold-water source. Steam can be blown into the area around the tubes during the cold-water circulating period to provide adequate moisture in the air.
The procedures for cleaning boiler tiresides are as follows:
1. Remove the boiler from service and allow it to cool. Make sure the boiler is cool enough for a person to enter. Someone must be standing by whenever a person is in the boiler. DO NOT force-cool the boiler.
2. Disconnect the fuel line openings. Secure all valves, and chain. lock. and tag all fuel lines to the burner and install pipe caps.
3. Disconnect the electrical wiring. Secure and tag the electrical power to the boiler. Disconnect the burner conduit and wiring. Mark and tag all electrical wiring to ensure proper reinstallation.
4. Open the boiler access doors by loosening all nuts and dogs and swing the door open. Be careful not to damage the refractory door lining.
5. Remove the burner from the boiler openings. Follow the manufacturer's instructions for specified burners. Wrap this equipment with plastic, rags. or other suitable protective coverings. Remember. soot and loose carbon particles must be kept out of the moving parts of the burner because they can cause the burner to malfunction.
6. Provide all spaces with free-air circulation by opening doors and windows, or provide fresh air by mechanical means. An assistant should be stationed outside the opening and be ready at all times to lend a hand or to be of service in case of a mishap.
7. Cover the floor area around the tube ends with drop cloths to catch soot. Position a vacuum cleaner hose at the end of the tube being cleaned. Keep soot from contacting wet areas because soot and water form carbonic acid.
8. Remove tube baffles where possible and pass a hand lance or rotating power cleaner brush through each tube slowly and carefully so no damage occurs to personnel or equipment.
9. Inspect tube surfaces for satisfactory condition before continuing on to the nest tube. Use a drop cord or flashlight for viewing through the entire length of a tube. Wire brush all tube baffles either by hand or use of power tools.
10. Apply a light coat of mineral oil to all cleaned surfaces. To do this, fix an oil soaked rag to the end of a brush or rod long enough to extend through the tubes and thoroughly swab each surface, including baffles. Mineral oil is the only lubricant that prevents rusting and also burns off freely without leaving a carbon deposit.
11. Clean all flat surfaces by brushing with the hand or power tools. Make sure that powered equipment is grounded.
12. Use an industrial vacuum cleaner to remove loose soot.
Any waterside deposit interferes with heat transfer and thus causes overheating of the boiler metal. Where waterside deposit exists, the metal tube cannot transfer the heat as rapidly as it receives it. What happens? The metal becomes overheated so that it becomes plastic and blows out, under boiler pressure, into a bubble or blister.
The term waterside deposits include sludge. oil, scale. corrosion deposits. and high-temperature oxide. Except for oil. these deposits are not usually soluble enough to be removed by washing or boiling out the boiler.
The term waterside corrosion is used to include both localized pitting and general corrosion. Most, if not all, is probably electrochemical. There are always some slight variations (both chemical and physical) in the surface of boiler metal. These variations in the metal surface cause slight differences in the electric potential between one area of a tube and another area. Some areas are ANODES (positive terminals).
Iron from the boiler tube tends to go into solution more rapidly in the anode areas than at other points on the boiler tube. This electrolytic action cannot be completely prevented in any boiler. However, it can be reduced by maintaining the boiler water at the proper alkalinity andContinue Reading