Drums

Introduction

The recent development in boiler fields involves, critical pressure boilers or once through boilers in which drum is not necessary. But other than critical pressure boilers, it involves two regimes of liquid and vapour phase where separation of steam from liquid surface takes place in steam drum. The number of drums required for a boiler depends on evaporator requirement, boiler pressures, stability, manufacture experience on the type of configuration. Widely single drum boiler and bidrum boiler are in use and in certain cases three or four drum design also available but they are outdated now. For higher capacity and high pressure boilers are economical with single drum boilers and for industrial process steam application where bidrum boilers works out to be economical. In practice it was found a that drum cost around 10% of the boiler pressure part cost.

Optimal Configuration Of Drums

In world wide practice drums are designed in cylindrical shape with two dished end with or without hole at its end  or cylindrical shell with tube sheet at its end or cylindrical shell with water box but the uniqueness of the drum is cylindrical shape.

For square when compared to circular drums it calls for 1.414 times greater thickness in turn weight of the drum number fo welds for making a square is more where as a single fusion weld will do for circular drums. Square chamber has t be placed in diagonal position for the lift of steam and therefore opening has to made in the bends, which is very stress prone area. Practically speaking square section are inferior in strength compare to circular section. According to IBR regulation square and header. The main advantage of square header is at one side opening for tubes can be made and other opposite side opening for mechanical  cleaning can be made for straight inclined tubes. For this purpose some manufacturer prefer square header, where inclined tubes are used.

Stubs And Attachments In The Steam Frum/Shell

According to the IBR regulation 281, there are certain minimum requisite fo mounting fitting and auxiliaries to be provided in pressure vessels for the safety of the sytem. Ibr regulation says that every boiler to be provided at least with the following

• two safety valves
• two means of indication water level gauge
• a steam pressure gauge
• a steam stop valve
• a feed check valve
• one feed apparatus when the heating surface exceeds 200 sqft and two independent feed apparatus each such apparatus shall have a capacity of not less than the minimum continuous rating of the boiler
• a blow down cock or valve
• a fusible pug when boiler has internal furnace
• an attachment for inspector pressure gauge
• a man hole where the size and construction feasible