Hi Abstract! Hi FANS AND BLOWERS FOR COMBUSTION PROCESS.

Hi Abstract! Hi FANS AND BLOWERS FOR COMBUSTION PROCESS.

Hi INTRODUCTION

The burning of gas, oil, coal, or other combustible material requires air. When the end result of the burning is to be an efficient combustion process, in compliance with Federal and State Clean Air Act requirements, the volume of supply air must be reliably controlled. Insufficient air volume will result in wasted fuel and excessive particulate along with potentially explosive gases in the exhaust system. Too much air increases the amount of heat carried up the stack by the excess draft. Either extreme increases the cost and difficulty of controlling exhaust emissions.

Hi NATURAL AND MECHANICAL DRAFT

Air can be supplied to the combustion process by natural or mechanical draft. Natural draft simply refers to the use of a chimney or stack to induce an upward flow of air. The stack effect pulls air into the combustion chamber. The amount of airflow depends on the stack’s height and diameter, the prevailing wind velocity, and the resistance of the burner mechanism or fuel bed itself. The demand for air-cleaning apparatus on combustion systems, particularly oil and coal, has increased the overall system resistance to such an extent that natural draft alone is seldom sufficient. Mechanical draft refers to the use of fans or blowers to create airflow through the combustion area. When mechanical draft is incorporated, the chimney or stack is used primarily to direct the exhaust gases up and away where they will not be a nuisance. Because wind velocity and direction are less important, the combustion process can be much more carefully controlled. Mechanical draft is accomplished in one of two ways: when air is blown or forced into the combustion chamber it is known as forced draft; & when the air is drawn through the combustion chamber it is called induced draft. When both forced and induced draft are used, the system is termed a balanced-draft system. Generally, the fans or blowers used for induced-draft applications are larger and more expensive than those used for similar forced-draft applications. The combustion process itself

creates gases and elevated temperatures that expand the exhaust airstream, requiring fans with greater volumetric capacity than would be required on the supply side of the combustion process to supply clean, ambient air. Also, the hot exhaust serves to lower the density of the airstream, so density corrections must be applied to the fan static pressure (SP) to overcome the actual system resistance. The fact that the exhaust or flue gases are hot often requires induced-draft fans to be of a construction suitable for higher temperatures. 

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