Study On Improving Chemical Defoaming Efficiency Of Nuclear Power Plant Siting In Coastal Area

At present,in the operation process of the coastal nuclear power plants in China and abroad,the water flow will violently roll and aerate in the siphon well,which leads to a large amount of bubbles formed.The bubbles rise to the surface and gather to form yellowish foams,which is not easy to collapse and is continuously pushed to the open sea.In order to eliminate the environmental pollution caused by yellow foams,chemical defoaming method which has a high efficiency is usually adopted.A certain amount of defoaming agent is added to the water system to achieve the purpose of eliminating foams.The recirculating cooling water system of trial nuclear power plant is directly connected to the sea,and the expenditure of antifoaming agent is huge.The expenditure of defoaming agent in a unit is up to 5.0 million RMB per year which is far more than other plants.Study on foaming mechanism and influencing factors of defoaming in nuclear power plant and analysis of differences,We can put forward defoaming efficiency improvement program and reduce the amount of defoamer.This work was performed from two aspects:(1)The causes of foam in nuclear power plants is analyzed and the structure of circulating water system was modified.With the observation of the drainage condition in the nuclear power plant,it was found that the flow channel in the siphon well is not full in the low tide level,which leads to the cooling water badly aerated to form a large amount of foam.Through local sink arrangement of condenser and submerged discharge design,aeration can be reduced,which effectively reduces foam formation.This scheme is economical for new nuclear power plants.(2)The influencing factors of antifoaming agent dosage was analyzed,a new defoaming solution was proposed for controlling the key influencing factors.A temporary defoaming system was built to study the effects of unit operating state,hydrology and water quality,and the kinds of defoaming agent on the amount of defoaming agent.Through the analysis of the dosage of defoaming agent,it is concluded that the dosage of defoaming agent is mainly related to unit operation,tidal level,chlorophyll and defoamer type.Bulab4498 and 9216-02V were selected,which was found to have the best defoaming effect.Combined with chlorophyll,tidal level and unit condition,a set of defoaming scheme design can be used to effectively reduce the defoaming cost.Based on this study,an automatic defoaming system was built in the nuclear power plant and the defoaming scheme was implemented to effectively solve the foam problem.The mensal dosage of one unit is reduced from 12,100 kg to 4,450 kg,and the defoaming efficiency was significantly improved.The nuclear power plant selects the best defoaming agent through defoaming test,and combines the concentration of defoamer with the tidal level,water quality and circulating water pump to establish a defoaming scheme,which can improve the defoaming efficiency.Through local sink arrangement of condenser and submerged discharge design in new nuclear power plant,it is expected that the nuclear power plant drain is foamless.