Simulation of Combustion Control by tweaking Air- Fuel Ratio

Abstract

Combustion is the most critical process in Gas Fired Boilers. Air-Fuel Ratio is the key factor in enabling a stoichiometric (complete) combustion.  In this paper we have improvised the combustion process by continuously adjusting the Air – Fuel Ratio by altering the quantity of inlet air with respective to the Oxygen Content in the Boiler Stack. The optimum Air- Fuel Ratio for Natural gas is identified as 9.53m3 Air to 1m3 Fuel. In most scenarios, a liquid and gas fuel burner achieves this desired balance by operating at 105% to 120% of the optimal theoretical air.  This results in an excess oxygen level of 3%. In the combustion zone, it is difficult to measure excess air. In the stack, however, it can be easily measured using Oxygen analysers.  When operating with 5%-20% excess air, it would correspond to a 1% to 3% oxygen measurement in the stack. We force the value of an Oxygen Analyser for this purpose which will adjust the Air Ratio with respect to the Oxygen content in the Stack. Simulation of this project is done using SIEMENS TIA software and resulted efficient adjustment of Air- Fuel Ratio with respect to the given Oxygen content in stack.