8.5　Start-up System of Once-Through Boilers

8.5.1　The type selection and equipment configuration of start-up system of once-through boilers shall comply with the following requirements:

1　The built-in separator system should be adopted for once-through boiler start up system.For units that are not started up frequently,start-up system in form of atmospheric flash tank or start-up system equipped with circulating pump should be adopted；for units that are started up and stopped frequently,start-up system equipped with circulating pump should be adopted.

2　For air-cooled units,start-up system equipped with circulating pump should be selected.

3　The capacity of start-up system for once-through boilers shall match the minimum once-through circulation load.

4　The number of built-in startup separators should not be less than two.

8.5.2　The recovery and discharge system of condensate generated during start-up of once-through boilers shall be designed in accordance with the following requirements:

1　When the separators recover a portion of high pressure drain water generated during start-up to the deaerator water tank,necessary provisions shall be made to ensure the safe operation of deaerator and feedwater tank.

2　The water storage tank at the downstream of atmospheric flash tank shall have a capacity sufficient to receive the cleaning water during start-up,overflow resulting from vapor-water swelling,drain water of boiler proper and blow-down water after boiler shutdown.The start-up drain system of each boiler shall be provided with two drain pumps,which should be sized at 2×100%capacity for boiler start-up system equipped with atmospheric flash tanks,and at 2×50%or 2×75%capacity for boiler start-up system equipped with circulating pump.The capacity of each pump should match with the discharge water amount provided by the boiler manufacturer and no margin may be taken into account.However,the total capacity of the pump shall satisfy the requirement that no overflow occurs for storage tank located at atmospheric flash tank downstream during vapor-water swelling.

3　When the boiler is equipped with start-up atmospheric flash tank,independent drain flash tank may not be required.