As for as pressure you have essentially two types: the subcritical and supercritical. According to water and steam circulation you have the once through type and the natural circulation arrangement.
The once through circulation principle is used on all supercritical units although this type of boiler does need recirculation at low loads to avoid overheating the water-wall tubes.
Most subcritical boilers work with the natural circulation principle. Natural circulation is based on a balance between the heated water coming from the steam drum and turning gradually into steam as it flows downwards in the down comer pipe or tubes into the water drum ( if the boiler is fitted with one ) or into the ring header, in the case of radiant units. From here, the water-steam mixture rises, due to its lower density, up the water wall tubes into the steam drum.
As for heat distribution boilers can be classified as radiant and radiant-convective. In radiant boilers all of the evaporation is done in the furnace water-walls from where the steam goes first to the steam drum where the water-steam mixture is separated by the steam separators and flows to the superheater panels.
In radiant-convective arrangements, the heat to evaporate is provided by both a radiant furnace and a convective tube bank.
All supercritical units are fully radiant. Subcritical boilers can be radiant or convective. Generally speaking utility boilers working above 100 bar and around 220 bar (critical) are radiant. Most of industrial boilers working all the way to 100 b and slightly above are of the radiant-convective type.
As far as construction goes, boilers can be classified as package, modular and field-erected. A package boiler is completely shop assembled and shipped to the site where it is laid on a foundation and connected to the steam, water and fuel lines.
A modular boiler is made up of modules ( the furnace is broken down into front wall and side-wall tubes and the boiler bank can be fully shop assembled ), taken to the site and quickly assembled on its foundation.
Can anyone please explain how radiant convective boiler works???
ReplyDeleteThanks in advance
The energy in the boiler may be extracted as radiant or convective & conduction. The furnace or radiant section of boiler is an open area accommodating the flames. The walls of the furnace section are lined with finned tubes called membrane panels, which are designed to absorb the radiant heat from the flame.
ReplyDeleteThe convection section is designed to absorb the heat from hot gases by conduction and convection method.