How to clean the boiler with trisodium phosphate?

 If the boiler is not cleaned for a long time, a large amount of scale will be generated. The harm of scale on the boiler is not only an impact on the thermal conductivity. In severe cases, the superheater of the heated surface may burst or overheat. Natural water is an aqueous solution of electrolyte, which is prone to electrochemical corrosion in contact with metals. It is known that sodium hexametaphosphate is used for water softening when using a boiler. So how to clean the boiler with trisodium phosphate?

Boiler cleaning method:

1. Flush

Condenser---Before flushing the water supply system, the condenser, hot well, deaerator, and water supply tank should be manually cleaned with 2% trisodium phosphate (Na31PO4.12H20) solution, and then rinsed with ordinary water system.

It is best to use demineralized water for the formal flushing of the system. The cycle power for flushing is provided by the condensate pump, and the condenser hot well is used as a water storage container. In order to prevent suspended matter from damaging the condensate pump, a filter should be installed at the inlet of the pump. Flushing should start from the condenser well and gradually pass through the condensate and feed water system to the boiler population. The flushing of each part should be carried out until the waste water becomes clear. Generally, water samples are collected at some discharge ports to confirm the end of flushing. For all circuits with bifurcations (such as drain outlets, vents, instrument connectors, etc.), or circuits with parallel paths (such as bypass pipelines), the isolation of these branches and branch lines should be considered during the operation to ensure the system Wash thoroughly. It is recommended to prepare a checklist before starting the cleaning operation, indicating the operation sequence of each branch and bypass pipeline, and the corresponding valve status.

2. Alkaline washing

Condenser---The alkaline cleaning of the water supply system uses a solution containing 2000ppm trisodium phosphate (2000ppm Na3P04 or 1000ppm disodium phosphate (Na2PO4) and compatible wetting agent. Alkaline chemicals are usually in dry powder form, so before use They need to be mixed into a concentrated solution form, and then injected into the circulation system. After the alkali is completed, it is necessary to replace the cleaning solution with condensed water or demineralized water and flush the system.

Condenser---The water supply system usually needs only one alkaline wash during its operating life. For feedwater heaters, usually only the pipe side of the alkali is needed. If petroleum-based preservatives have been used on the shell and pipe side of the feedwater heater and cannot be removed with hot condensate, the system should be alkali washed in two stages.

At the beginning of alkaline washing, the condenser---the water supply system should be kept full of demineralized water. The alkaline washing cycle is usually formed by a chemical cleaning pump, and the alkaline washing solution is injected at the chemical cleaning header and continuously circulated for at least 24 hours at a temperature of 200F. A higher flow rate is generally used for alkaline washing, because the high flow rate has a better effect on the removal of insoluble particles at the pipe elbow. The deaerator is generally cleaned in this system, but it can also be bypassed. The same is true during alkaline washing. Pumps and other equipment that may be damaged by the alkaline solution or abraded by the suspended solids should be bypassed or the internals removed.

When the cleaning is completed, replace the fluid in the system with demineralized water to discharge the waste alkaline solution. The water side and the shell side of the feedwater heater should be rinsed separately.

At the beginning of the pickling operation, the condenser---the water supply system should be kept full of demineralized water. Then use a chemical cleaning pump to establish a cycle corresponding to the full load flow of the equipment, including low-pressure heaters, deaerators, and high-pressure heaters, and the feedwater pump should be bypassed. After the acid washing cycle is established and the fluid in the system reaches 200F, a mixed solution of glycolic acid, formic acid and ammonium dichloride inhibitor is injected into the system. To ensure uniform concentration, the acid solution should be injected at a constant rate, that is, the injection time is equal to the time required for a complete cycle through the system. After the pickling is completed, the system can be filled with demineralized water to drain the waste pickling solution and flush the system. After pickling, the system should be filled with condensed water containing 40ppm ammonia and 500ppm hydrazine to passivate the system. During the passivation operation, the PH value should be maintained at 9. O or greater, hydrazine concentration above 200ppm. Note that if some parts of the water heater are made of stainless steel, the solution prepared by the above method cannot be used for pickling.