Closed feedwater heaters

Since our purpose is limited to introducing essergetic functional analysis, only simplified models will be considered. Let us first restrict our attention to closed feedwater heaters for which... 

Noncontact heat exchangers, which transfer heat between fluids through a conductive barrier (Figure 23.9), are used in a wide variety of applications, including nuclear steam generators, condensers, and closed feedwater heaters. 

Feedwater heater A steam-to-water heat exchanger that heats the boiler feedwater, generally with steam extracted from a steam turbine. In a closed feedwater heater the two fluids are separated by the use of shell and tube construction. In an open feedwater heater the fluids are mixed. A feedwater heater that separates entrained gases from the feed-water by vigorous agitation with steam. 

Feedwater heaters of various types, sizes, and shapes have been employed since the earliest days of boiler plant design. Their primary purpose is to increase the thermodynamic gains of the steam cycle and reduce problems of thermal shock in the boiler. Typically, they may be classified as HP or LP, open or closed FW heaters. Some types of open FW heaters additionally provide FW mechanical dearation. 

Transients - coolant temperature decrease Caused by (1) steam extraction line to heater is closed, or (2) feedwater is bypassed around heater. SBWR is designed such that no single operator error of equipment failure shall cause a loss of more than 55.6 C feedwater heating. 

A less common type of fuel-gas trip to a heater is a low-pressure trip. A pressure transducer generates a milliamp output from a boiler feedwater pump. Should this milliamp output fall below a certain level, the instrument air signal to the fuel-gas regulator actuator will be shut off. These fuel-gas valves are air-to-open, meaning that loss of instrument air flow causes the valve to close. 

Oxygen, even in very small amounts, may cause serious corrosion in feedwater lines, stage heaters, economizers, boiler metal, steam operated equipment and condensable piping. It must, therefore, be removed from the closed system. The solubility of oxygen varies with both pressure... 

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