Import ance of Air Distr ibution b etw een Burners - F ront Wall F iri ng written by: Dr V T Sathyanathan • edited by: Lamar Stonecypher • updated: 3/17/2010 Coal, oil and gas burners performance will depend upon making oxygen available for hydrocarbons being burned at the right quantity at th burner design sensitive to air flow distribution. In the case of any burner system, the total air is divided into primary air, secondary, and tertiary air. Each of this air plays a very vital role in gives the initial ignition oxygen, the secondary air allows the higher hydrocarbon or char to burn, and the tertiary ensures the delayed com introduced by designers to reduce NO x level. While this distribution of total air will be normally 30% primary, 55 to 60% secondary, and abo burners are designed to ensure the intended ratio by actual design of the resistance introduced in each section for the required flow area. register pressure or windbox pressure depending upon wall firing or tangential firing. Airf low eq ual izati on i n m ul ti bu rn ers – Coal f ir ed b oiler There are three important factors to be kept in mind when airflow equalization is done among burners. The primary air has to be kept at the minimum required level with designed excess air level The secondary and tertiary air combined together enter the individual burner, and this needs to be equal between all burners The proportioning of secondary and tertiary air is done within the burner and also needs to be equal in all burners but the setting can the variation in burners due to manufacturing tolerances. All burner and boiler designers provide air equalizing dampers at inlet of each burner. This damper or shroud is used to vary the resistance so as to achieve equal flow of air at all loads. Many burner manufactures nowadays prefer to factory-set the secondary air swirl position an preferred setting is 30 degree open for creating a moderate swirl. This keeps the flame long and reduces the flame temperature. The seco normally kept full open. The damper or the shroud provided in the burner is all first set to full open to create the required furnace to windbo manufactures of burner- provide individual air flow measurement in each burner. This can be used to set equal air flow between burners. In practice to keep the static pressure equal in all burners after the shroud or damper provided for flow equalization. After setting equal airflow when the burner is lighted up the flame colour, flame temperature, the overall CO level and NO xlevels are check 60%, 80% and 100%) for proper performance. In case required a minor adjustment can be done after identifying which burner need to be Airf low eq ual izati on i n m ul ti bu rn ers – Oi l / Gas fire d bo il er Oil and Gas fired boilers are more sensitive to air flow equalization between burners for few reasons. These burners are designed for much lower excess air levels The primary, secondary and tertiary airs are all proportioned inside the burner unlike coal burner. Any minor deviation in proportioning can increase the CO level very high. It can also cause lot of soot formation which has its own effe The procedure for equalizing air flow between all burners is the same as coal fired boiler. Abo ut th e Au thor Dr V T Sathyanathan is a boiler consultant with 35 years of experience in various areas of high pressure boiler trouble shooting. He holds boilers. Related Reading Tuning of Front Wall Coal Burners in Large Capacity Boilers- A well tuned burner gives the optimum performance of the boiler. This requir fuel flow and the swirl level which ensures air fuel mixing. Reading a Coal Flame in Tangential Firing Boilers - In a tangential coal fired boiler, the furnace act as a single burner and so it is required t quality of the flame. It is necessary to start from the control room of the boiler, then go to the mill, furnace, bottom ash and fly ash areas an Combustion Tuning in High Ash Pulverized Coal Fired Boilers having Direct Tangential Firing System - Combustion tuning in boilers will le more so in high ash coal fired boilers. In high ash coal fired boilers having direct tangential firing systems, proper combustion will ensure m thus an optimal furnace outlet temperature
