T E X T

The economizer is a feed-water heater in which flue gases are used as a heating medium. It is used to increase the temperature of feed water before it enters the boiler, by absorbing heat from the flue gases leaving the boiler.

The economizer is interposed between the boiler and stack. The economizer increases boiler efficiency, it lowers the temperature of the exhaust gases and heats up the incoming feed water as it passes through the economizer on its way to the steam drum.

A typical economizer consists of two or more solid-forged mild steel headers, to which series of tubes are connected. The tubes are rolled into the headers. When headers are not employed, return bends, usually connected by flange joints to the straight run of tubing, are used. The steel tubes range from 1 to 2 in. in diameter.

The economizer consists of a number of multi-loop tube elements enabling the feed water to make several passes across the gas stream as it passes through the economizer. The water temperature within the economizer should not be allowed to exceed a temperature 30°C below the corresponding evaporation temperature. It is thus important to maintain minimum temperature values under all steaming conditions. If the normal feed temperature entering the economizer is about 140°C, there is an allowable margin of some 15-20°C, but the feed temperature should never be allowed to fall below the 115°C limit under steaming conditions.

Economizers are parallel or counterflow – parallel when the gases and water flow in the same direction; counterflow when they flow in opposite directions. The counterflow is considered to be more effective, resulting in a greater heat transfer.

Air vents must be provided for the release of air when filling the economizer, or when raising steam. Drain valves fitted to the lower headers enable the economizer to be emptied of water when required.

Efficient soot blowing arrangements must be provided to keep the heat exchange surfaces free from soot. This is important not only in the interests of efficiency, but also to reduce the possibility of an uptake fire starting in sooty deposits.

Suitable access and the necessary fitting and drains should be provided for the water washing of the uptake heat exchangers when the boiler is shut down.

NOTES:

As a heating medium – в качестве греющей среды

The flue gases leaving the boiler – газы, покидающие котел

Being placed in the uptakes – причем он (экономайзер) размещен в дымоходе

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