Higher moisture in the fuel leads to unbalanced draft in the furnace or combustion chamber. Which ultimately results into poor mixture of air & fuel, higher moisture fuel demands more excess air. So optimization of fuel moisture will help to reduction in LOI.
2-Maintaining balanced draft in furnace:
Unbalanced draft is nothing but more FD air/less ID draft or less FD air /More ID Draft.
More FD & less ID causes back fire & improper mixing of air & fuel.
More ID & less FD causes escape of fuel particles from furnace without proper combustion
3-Maintaining 3Ts of combustion:
3Ts of combustions are: Temperature, Time & Turbulence
Temperature: For proper combustion temperature of the furnace must be sufficient enough to burn the fuel completely.
Time: There must be sufficient time for combustion
Turbulence: There should be proper turbulence in furnace for proper mixing of air & fuel
4-Increasing the secondary air quantity & pressure:
This will help to increase the residence time of fuel in furnace resulting into complete combustion
5-Maintaining the required excess air:
Lesser excess air than required will lead to incomplete combustion that is conversion of carbon into carbon monoxide instead of carbon di-oxide. So sufficient air is required to achieve complete combustion.
6-Using correct or designed GCV of a fuel:
Lesser GCV fuel requires more air for combustion, even may not achieve the designed parameters of Boilers like flow, pressure & temperature.
7-Ultimate & Proximate analysis of fuel:
In order to achieve proper combustion, we must know the contents of fuel properly. Need to operate the Boilers at designed parameters of fuel. For example if FC of the fuel increases, then need to increase air & combustion time and need to reduce turbulence.
So it is very important to know the fuel contents.
8-Operating the Boilers at stable loads:
Stable loaded Boilers will not lead into much LOI, as air & fuel mixture is constant & will not vary frequently. LOI cannot be reduced in variable load boilers.
9-Operating the Boiler at little positive draught:
Operation of Boiler at positive draught will help for complete combustion. If boiler is operated at more negative draught, then there will be more chances of escaping of unburnt fuel particles from the furnace & causing secondary combustion at super heaters & other convective zones.
10-Reusing unburnt or cinder:
Generally unburnt/cinder from Boiler Bank & economiser zones are re-injected into furnace by using “Cinder re-injection” system. This will help in re-burning of cinder & reduction in LOI