The aim of the chemical feed system is to minimize the corrosion of all materials within the steam/water cycle, to minimize deposition of corrosion product or other impurities within the cycle and to ensure the plant integrity over the plant life.
The chemical reagent should be specified under which the boiler shall be operated and provided details of dosing, sampling, monitoring and blow down arrangements that will maintain the chemistry within defined parameters. The chemical reagent and the equipment supplied to maintain it within specification should be compatible with the source and type of condensate coolant and the anticipated all staffing levels at the plant.
The chemical reagent should be specified for the following but not limited to: the condensate, feed water, boiler water, and cooling tower indicating target values for impurities and acceptable operating ranges for each specified parameters.
The chemical feed system shall also specify the maximum impurity concentration in the superheated steam to be produced together with evidence of its compatibility with the steam turbine. The proposal chemical reagent will be assessed no against international standards.
The system shall identify the source and composition of water used for spray attemperation of superheater. The system supply a schedule including P&ID for the steam water cycle indicating the positions of the dosing and sampling points and the chemicals to be dosed and the parameters to be continually measured at each point.
Especially boiler water dosing system shall be designed to maintain the steam/water cycle chemistry (scale control) under all normal operating conditions including condenser peaks and also for wet off load storage of the boilers.
The chemical feed system shall provide dosing equipment including the following items:
- Chemical storage and daily tanks
- Mixing and dilution tanks
- Dosing pump
- Pipe work and double insulation valves
- Drain and wash down for spillage
For volatile chemicals such as ammonia or hydrazine are included there shall be suitable traps, scrubbers or absorbers fitted to minimize the emission of harmful vapors.
The chemical feed system shall also provide remote control of the dosing pumps including closed loop control from on-line cycle chemistry monitors. Chemical Reagent and Regeneration supply, storage and transfer. The equipment for the storage and handling of chemicals and regenerations shall be designed such that;
- The manual handling of chemicals during unloading and transfer to storage shall he kept to a minimum.
- Solid chemicals shall be delivered and stored in dry, covered conditions and silos shall have moisture traps fitted.
- Liquid chemicals shall be stored in tanks constructed from or lined with corrosion resistant material.
- Tanks shall be insulated and heated as necessary to maintain the chemicals in a liquid state.
- Each tank shall have a separate bund to retain the whole tank volume in the event of spillage or leakage.
- Tank or silo tilling connections shall be separated from each other within an individual locked enclosure and clearly marked with the chemical type.
- Chemicals releasing volatile or harmful vapors shall have suitable traps and scrubbers fitter to the tank vents.
- Automatic safety showers shall be installed adjacent to chemical unloading facilities and within the water treatment plant.
- Transfer of liquid chemicals from bulk storage to the regeneration system shall provide the minimum risk of spillage and leakage. Vacuum transfer shall be provided.
- Transfer of regenerates from measuring / dilution tanks to service vessels shall provide minimum risk of leakage and spillage. Transfer by water ejector shall be provided.
The bulk chemicals are to be used for other water treatment plant application, if required they shall meet the minimum purity standards for the more generous duly. The purity standards shall also take into account local environmental discharge legislation with respect to heavy metals.