Tuesday, October 4, 2016

Wetback vs. Dryback Firetube Boiler

firetube boiler
Victory Energy firetube boiler, Frontier series, will
be available in a dryback version
Differing boiler designs will provide their own array of positive attributes with regard to boiler efficiency, intended use, maintenance burden, and other factors. One distinguishing feature of firetube boilers is whether they are "wetback" or "dryback" design.

Not surprisingly, the difference between these two designs can be found at the "back" of the boiler, the end opposite where the fuel and air are introduced and ignited. The "wet" and "dry" designation indicates whether the firetubes, as they extend to the rear end of the boiler, discharge the hot gases into a reversing chamber surrounded by boiler water (wet) or partially isolated from it (dry).

A dryback boiler has a rear wall lined with refractory. The rear wall forms one side of the reversing chamber on a multi-pass boiler. While the refractory is certainly a point of long term maintenance, its presence as a heat sink has been noted to assist in maintaining setpoint pressure during a boiler off cycle. This tends to lengthen the off cycle of the boiler and provide some benefit. The dryback design will also have appropriately sized access doors or panels on the rear of the boiler to provide for maintenance, thus a space requirement particular to this design.

A wetback (thankfully, also called a water-back) boiler will generally have a reversing chamber constructed of steel that is contained within the confines of the boiler pressure vessel. There will be water between the reversing chamber and the boiler rear wall. Generally, the service access required at the rear of the boiler is less than for a dryback.

Victory Energy manufactures both wetback and dryback boilers in a number of configurations to meet a wide range of needs. Their extreme duty series, designated Frontier, has traditionally been a wetback boiler, but manufacturing of dryback versions is planned. The dryback product range will extend from 50HP to 2500HP and cover applications in the industrial and commercial spaces.