From Power Plant Water Chemistry: A Practical Guide


The preboiler system of a typical utility steam generating unit (Fig. 2-1) includes a steam surface condenser, several closed tube-in-shell feedwater heaters, a deaerating feedwater heater, and sometimes an economizer. For industrial systems, feedwater heaters, with the exception of the deaerator, are often omitted unless the steam drives a turbine. The preboiler circuit condenses the turbine exhaust steam and prepares the condensate for return to the boiler. The condensation process significantly improves the efficiency of a unit, as is outlined in greater detail in Supplement 2-1 at the end of this chapter.

Preboiler/Boiler/Afterboiler Schematic

Figure 2-1

The potential for contaminant introduction to a steam generating plant is greatest in the preboiler system, especially at the condenser or via condensate return from an industrial process. This makes chemistry control and monitoring of condensate and feedwater extremely important.

Condensate/Feedwater System Construction Materials

A variety of materials have been used for feedwater heater and condenser tubes. The most common include 90 10 and 70 30 copper nickel, 304 stainless steel, carbon steel, Admiralty metal (70% copper and 29% to 30% zinc depending on whether 1% arsenic or tin has been added for increased corrosion resistance), and Monel (70% nickel, 30% copper). In previous years, copper alloys were widely selected due to the excellent heat transfer properties of these materials. Recently; as copper corrosion and its effects on downstream components have become better recognized, the use of copper alloys has declined. Stainless steel is becoming favored for feedwater heater tubes; and stainless steel, titanium, or...

Products & Services
Deaerators are used to remove dissolved, corrosive gases from boiler feed water. They heat incoming makeup water for injection into the boiler, and return the condensate to a temperature which minimizes the solubility of these gases.
Economizers are mechanical devices that are designed to reduce energy consumption, or to perform other useful, energy-related functions (such as preheating fluids).
Condensate Polishers
Condensate polishers use ionic exchange to remove mineral contaminants that can limit performance and reduce system life in boilers, heat exchangers, HVAC cooling towers, steam turbines, nuclear power plants, and industrial processes.
Condensers are devices which accept a vapor stream and convert it to a liquid using heat transfer and/or compression.They are used in steam turbines for power plants, in cooling units for in-process fluids, and in air conditioning systems for buildings and automobiles.
Evaporators are systems consisting of a heat exchanger or bath, valves, manifolds and temperature controls for conversion of a product (e.g., liquefied gas) from a liquid to a gaseous state.

Topics of Interest

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