Importance of draught in boiler operation and performance.
In the boiler operation we normally have three types of draught fans. they are 1. forced draught fan. 2. induced draught fan and 3. secondary air fan.
The functions of these fans are primarily to maintain sufficient Furnace draught in order to make the combustion of the fuel in grate such that the release of heat is maximum for steam generation.
more often we experience problems in combustion of fuel such as black smoke emissions through chimney, unburnt fuel in the ash, fouling of tubes ( water tubes and superheater tubes) etc, because of improper functioning of draught fans . we now look into this fans functioning.
1. F.D. Fan(forced draught fan). The function of this fan is to supply sufficient amount of primary air (oxygen) to burn the fuel in furnace, also should be able to supply certain amont of excess air for complete combustion. The design of F.D fan is such that sufficient amount of air to be supplied with sufficient pressure ( draught). if proper care was not taken in volume and pressure requirements then it would create more problems. Most of the time boiler manufacturers provide fans with best design options thereby it will perform well when experiences worst conditions. more over boiler may use multi fuels sometimes for which this fans may not sufficient to supply required air. Therefore carefull consideration will be given in selection when we place order for boiler. most of the times the end user are forced to change the fan to higher capacity after experience more difficulties while operating. Therefore one must consider the F.D fan size for worst fuel and operating conditions likely used so that it can takes care of best fuel and operating conditions. as a thump rule a 10% more in pressure and 25% more in capacity is ideal for the selection.
2. I.D.Fan.(induced draught fan). The primary function of this fan to suck the hot combustion gases from boiler furnace through no of heat exchangers such as furnace tubes, super heater tubes, boiler bank tubes, economiser tubes, air preheater tubes, M.D.C, ESP etc keeping sufficient draught in respective zones. modern boiler employes balanced draught design thereby keeping negative draught of -2mm to -5mmwc. Any under capacity fan will result back firing, fouling of tubes more unburnts black smoke emissions which drastically effect boiler operation and performance. therefore care must be taken before order of boiler as explained in F.D.fan case. most common problems are fan become unbalanced, more vibrations, bearing failures, erosion of fan blades, and ducts etc.
3. S.A.fans (secondary air fan). In normal conditions the problems within S.A fans are neglible. it function is to burn volatiles and carbon left after primary combustion.
for more information one easily approach me by mail or phone given below.
K GOPALAN.
Kgopalan1956@gmail.com
9420663740/9208956202.
