9.5　Boiler Auxiliary System and Associated Equipment

9.5.1　The blowdown system and device of boilers shall comply with the following requirements:

1　Two to four boilers should share one blowdown flash system.

2　Boilers should be provided with one stage continuous blowdown flash system.The drum boiler of high pressure thermal power plant may adopt two-stage continuous blowdown flash system considering the utilization of the flashed steam.A bypass system shall be provided to allow switching from continuous blowdown system to periodic blowdown flash tank.

3　The capacity of periodic blowdown flash tank shall be determined considering the need for emergency drain of boiler.

9.5.2　The noises generated as a result of steam discharge to atmosphere of boilers shall comply with the environmental protection regulations.The piping for steam discharge to atmosphere during startup of boiler shall be equipped with silencers.Silencers shall be installed on the vent pipe of drum safety valve and superheater safety valve with the minimum popping pressure.

9.5.3　Measures shall be taken to prevent the low temperature corrosion and ash clogging of air preheater.To prevent these problems，air heating system should be provided according to actual conditions.Hot air recirculating system，steam air heater or other air heating systems may be selected through techno-economic comparison.If the coal quality is favorable，the ambient temperature is relatively high，or the cold end of air preheater is made of corrosion resistant materials such that air preheaters can really be immune from corrosion and ash clogging，the heating system may be eliminated.For regenerative trisector air preheaters，if the primary air is heated first，the air heating system may not be provided at the primary air side，but rather only provided at the secondary air side.

1　The steam air heater system shall comply with the following requirements:

1）The location of steam air heaters shall be determined through techno-economic comparison.In severe cold regions，steam air heater should be located at the inlet of fans.

2）The steam air heater shall be in such a structure and arrangement that permit resistance to be reduced.For steam air heaters with low annual utilization hours，they may be of movable structures.

3）The ambient temperature used for steam air heater selection should be taken as the outdoor air temperature employed for heating calculation in winter for heating regions or the average temperature of the coldest months in winter for non-heating regions.Appropriate heating area margin should be reserved.

2　Hot air recirculation system should be employed for tubular air preheater，low-sulfur and low-ash coal or in areas with relatively high ambient temperature.If hot air recirculation system is used for regenerative air preheaters，it shall be necessary to take into account the requirement on anti-abrasion of fans and air ducts.The hot air recirculation rate should not be excessive.The hot air extraction point shall be arranged at places where the ash content is low.