Combustion air for firing systems

Combustion air is generally consisting of primary air (for atomisation of liquid fuels), secondary air for combustion and tertiary air for ensuring completion of combustion of any remaining oil droplets/fiiel particles and for protecting furnace refractory lining. These are controlled by suitable control dampers in the air lines. 

Preheated air can be obtained by heat recovery from exit gases. It can increase furnace temperature, can reduce fuel consumption (by minimising loss of unbumt fuel droplets), and will be found useful for completing the combustion. Excessive air can decrease furnace temperature, or the flame can get extinguished. 

Since liquid fuels and natural gas have better atomisation and stable flame characteristics, they need only a small amount of excess air for proper combustion. The volume of flue gases generated is therefore less as compared to the volume of flue gases produced when solid fuels are used. 

Larger volumes of flue gases carry away more amount of usable heat in case of solid fuels. Hence, excess air volume shall be controlled by monitoring CO2 and 

Too less an amount of air can cause explosive mixture inside fiimace or deposits of unbumt fuel particles on downstream equipments. 

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Chemical Regeneration. In most MHD system designs the gas exiting the toppiag cycle exhausts either iato a radiant boiler and is used to raise steam, or it exhausts iato a direct-fired air heater and is used to preheat the primary combustion air. An alternative use of the exhaust gas is for chemical regeneration, ia which the exhaust gases are used to process the fuel from its as-received form iato a more beaeftcial oae. Chemical regeaeratioa has beea proposed for use with aatural gas and oil as well as with coal (14) (see Gas, natural Petroleum). 

Ptilverizers The pulverizer is the heart of any solid-fuel suspension-firing system. Air is used to dry the coal, transport it through the pulverizer, classify it, and transport it to the burner, where the transport air provides part of the air for combustion. The pulverizers themselves... 

Biomass has some advantageous chemical properties for use in current energy conversion systems. Compared to other carbon-based fuels, it has low ash content and high reactivity. Biomass combustion is a series of chemical reactions by which carbon is oxidized to carbon dioxide, and hydrogen is oxidized to water. Oxygen deficiency leads to incomplete combustion and the formation of many products of incomplete combustion. Excess air cools the system. The air requirements depend on the chemical and physical characteristics of the fuel. The combustion of the biomass relates to the fuel bum rate, the combustion products, the required excess air for complete combustion, and the fire temperatures. 

Finally, the mass flux of conversion gas is primarily controlled by the volume flux of primary air and conversion concepf, whereas for a gas-fired system the mass flux of gas fuel into the combustion chamber is limited by the gas fuel fan capacity and the burner design. 

Firing occurs only on one level, so the number of burners in relation to the number of tubes is smaller than in side-fired systems. This simplifies distribution piping for fuel gas and preheated combustion air, which is nowadays standard in all efficient plants. 

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