GFM 700 for optimization of a burner control system

Improved control oxygen/gas ratio, lower emission of NOx & CO, decreased energy consumption

Waste gases from plants are used as a fuel gas for furnaces. The composition of fuel gas is however dependent on the production of waste gases, which can have a fast changing composition. The furnace is controlled by a flowmeter in the air supply line and a flowmeter in the fuel gas line. A lambda-sensor located in the exhaust measures the air to fuel/gas ratio. The customer was not happy with the exisiting configuration as the system gave a slow response time on changes in gas compositions, and was not accurate. Due to the lower accuracy normally a lambda-value (oxygen /gas ratio) of 1:20 was established causing a relatively high concentration of NOx in the exhaust gases and a low energy efficiency due to a high air surplus.

In the fuel gas line a KROHNE ultrasonic gas flowmeter has been installed. A GFM 700 is not only able to measure the gas flow rate, but in combination with a flow computer can also accurately measure the gas molecular weight. The optimal required air supply for a specific gas mixture is calculated as a function of the molecular weight of a gas. The lambda-sensor in the exhaust has been removed. For safety reasons the customer required a fully redundant system whereby two GFM 700’s are placed in line.

As a result the customer was, all within environmental regulations, able to:

	improve the oxygen / gas ratio (lambda)from 1:20 to 1:10;
	respond faster on changing gas compositions (within 1 second)
	decrease the concentration of NOx,
	decrease the emission of CO
	decrease the energy consumption (up to 10%)

For more information please contact KROHNE
e-mail: helpdesk@krohne-altometer.nl

Key Words: Flow, gas flow, ultrasonic, non-ultra, burner control system

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