Circuit feedwater heater

The secondary circuit comprises the steam generators, turbine, condenser, condensate pumps, deaerator, feedwater pump, feedwater heaters, bypass line, connecting pipes and control valves. 

Fleat exchanger or condenser test tube Condensers, feedwater heaters, and other heat exchangers installed within the circuit Accumulation of scale and corrosion pertinent to plant-specific conditions... 

In the turbine circuit, when there was no feedwater heater, the temperature difference was sizable between the inlet and outlet of the steam generator (SG), leading to severe thermal expansion of the structural material. The steam at the turbine inlet is superheated to 633.15 K and 8 MPa steam is extracted from the high pressure turbine (HPT) at 0.345 MPa with a quality of 0.855. A moisture separator is installed between the HPT and the low pressure turbine (LPT) to minimize erosion of the LPT blades. 

The pre-boiler cycle consisting of feedwater heaters, feed pumps and feed lines are liable to corrode by the condensate return. The main contributors to corrosion are carbon dioxide and oxygen. Corrosion must, therefore, be minimized. This is done by feedwater control, which reduces the ingress of harmful impurities and gases to the boiler water circuit and also to the steam. The best way to prevent corrosion is by controlling the pH, which should be maintained in the range of 8.5-9.2. 

At some stage the deterioration of performance becomes so great that the heater should be taken out of service in order to either (i) replace it with a new heater, or (ii) re-tube the heater, which generally involves more down-time than replacement. Case C portrays the situation when heater 5 is out of service, causing greater upset to the feedwater circuit than Case B. Notably, the temperature of the feedwater to the boiler is lower. 

Lin (1983) also reported on a detailed investigation of the distribution of iodine volatilized from the reactor water in BWR water—steam circuits with forward-pumped heater drains. In this plant design, only the main condensate is directed to the condensate polishing system, whereas the different drains from the turbine are fed directly back to the feedwater tank. Under such plant conditions, about 75% of the iodine carried by the main steam flow is precipitated together with the condensate in the moisture separator downstream from the high-pressure part of... 

The steam turbine plant has a simplified heating circuit with feedwater heating in the deaerator. To enhance thermal efficiency, the heat circuit provides for 0.3 MPa steam extraction from the turbine to supply the heating-system water heater. The steam pressure in a take-off is selected to secure the heating-system water heat up of 120°C. 

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