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Construction of economizer

In constructions of continuous and of return bends, the bends are usually made of forged steel and are carefully machined to receive the tube ends. Gaskets which are, necessary where the tube ends bear against the female joint of the return bend, may be of some soft material such as cranite. In order to keep the gas passage restricted to the straight, section of the tubes and to give support to the tubes, it is customary to use tube sheets of cast iron. The outside casing is then made of removable steel-plate panels which are insulated, it thus being necessary to remove the whole side to obtain access to a certain tube. When there is a reversal of gas passage, soot hoppers are commonly placed below the economizer to collect any soot carry- over from the boiler, the soot being piped to the ashpit.

Economizer when used in combination with air heaters are practically always set nearest to the boiler flue-gas exit. Although most economizers do not heat the feed-water to a point where it vaporizes, a number of steaming economizers have been built and operate successfully. In these, the individual parallel-tube elements run separately to the top rear drum of the boiler and are rolled directly into the drum. Relief connections between the drum and the economizer are not provided. In addition to a gain in over-all boiler efficiency of 10 to 12 per cent, depending upon the drop in gas temperature, an economizer will provide nearly as much additional generating capacity. Maintenance, it is claimed, will amount to as little as 1/2 to 1 per cent per year.