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As steam is generated from evaporation of water, remaining water in boiler becomes more and more concentrated. This must be drained away during blow down.
The challenge is to control draining to minimum.
Recovering Waste Heat from Blow down
Since it is necessary to blow down to control total dissolved solids in boiler water, methods can be adopted to recover some of heat back from drained hot water.
Blow down tanks, heat exchanger tubes and pumping arrangements can be fabricated to recover back some of heat back into boiler.
Stopping Dynamic Operation
Whenever a boiler starts or stops, a few minutes are spent running forced draft fan for purging combustion chamber of unburnt gases. This is a necessary step for safe operation of a boiler.
During this time heat from boiler water in shell or tubes will be lost to purging air.
To avoid this type of losses, it is better to maintain a steady firing condition in boilers.
Reducing Boiler Pressure
By reducing boiler pressure, some of heat losses through leakages or transmission may be reduced slightly. However there can be problems with boiler with reduced pressure. The boiler circulation may be upset and steam lines may have insufficient capacity and flow to transport low pressure steam.
Operating at Peak Efficiency
When operating two or more boilers, improved efficiency can sometimes be obtained by unequal sharing of load so that combined load operates at peak efficiency.
Preheating Combustion Air
Any heat loss from skin of boiler to boiler room can be utilized back for combustion. By preheating intake air combustion in furnace becomes more efficient.
Switching from Steam to Air Atomization
For burners with steam atomization, switching to air atomization will naturally result in less steam consumption overall and better boiler efficiencies. This is only applicable for heavy fuel oil burners.
Switching to Lower Cost Fuel
When comparing natural gas and fuel oil, if cost is same or more per BTU delivered, switch over to fuel oil.
The reason for this is that in combustion process, hydrogen combines with oxygen to form water. The latent heat of vaporization is lost when water vapor leaves boiler stack.
Fuels like natural gas with higher hydrogen to carbon ratio will lose this heat more than those with lower hydrogen-carbon ratio like fuel oil.
However one must also recognize that there will be increased maintenance, operating costs and greater need for more excess air in order to achieve complete combustion for fuel oil. In addition, soot deposits and incomplete combustion might also affect overall costs.
Some of ways mentioned above may not be feasible at all for your plant. Each of them may result in only a few percentage points of boiler efficiency improvement. However, if carried out carefully and with proper tools and instruments, they do add up to huge savings.
Many years of working experience in Marine, Facilities, Construction has given the author material for writing e-books and articles related to engineering, and management. Subscribe to facworld ezine More information at Marine Engineer and M & E Engineer