Premix Burner Control System and Method

Abstract

A fan modulated premix burner control system includes a regulating control valve for regulating the pressure of gas fed to a premix chamber. The pressure of the gas is based on the pressure of air also fed into the chamber to produce a constant air / fuel ratio. The system also includes an air restrictor for reducing the pressure of the air to permit operation of the burner at low fan speeds.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]This application claims the benefit of provisional patent application No. 61 / 026,041, filed Feb. 4, 2008, which is hereby incorporated by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates generally to gas burners. More specifically, the present invention relates to a control system for premix gas burners and a method for maintaining flow of an air / fuel mixture to the premix gas burner.[0004]2. Description of the Related Art[0005]Premix gas burners operate by mixing gaseous fuel and air prior to produce an air / fuel mixture. The air / fuel mixture then enters the burner and is ignited and burned. A fan is often used to induce mixing of the air and fuel.[0006]However, typical methods of controlling the air / fuel mixture limit minimum firing rates of the burner due to their inability to maintain the desired air / fuel mixtures at very low fan pressures. That is, the controls are not sensitive en...

AI Technical Summary

Benefits of technology

[0008]The present invention discloses a method of maintaining flow of an air / fuel mixture to a burner. The burner is fed from a premix chamber enclosing a variable speed fan. The premix chamber also defines an air inlet, a fuel inlet, and an outlet in fluidic communication with the burner. The method includes the step of regulating a flow of gaseous fuel though the fuel inlet with a regulating control valve to maintain a specified pressure. The gaseous fuel and air are drawn into the premix chamber by operation of the fan. Mixture of the gaseous fuel and the air in the premix chamber are affected by operation of the fan to produce an air / fuel mixture. The air / fuel mixture is forced to the outlet by operation of the fan. The method continues with the step of lowering an inlet air pressure of air drawn through the air inlet by reducing the area of an air duct ahead of the air inlet to decrease the flow rate of the air / fuel mixture.

[0009]The present invention also discloses a premix burner control system. The system includes a housing defining a gas inlet for receiving a gaseous fuel, an air inlet for receiving air, and at least one outlet for connection to a burner. A fan is disposed in the housing for drawing the gaseous fuel and the air into the housing, affecting mixture of the gaseous fuel and the air to produce an air / fuel mixture, and forcing the air / fuel mixture to the outlet. A motor is operatively connected to the fan for turning the fan. A variable speed drive is operatively connected to the motor for turning the fan at a plurality of speeds to control a flow rate of the air / fuel mixture into the outlet. A regulating control valve in fluid communication with the gas inlet regulates the flow and pressure of the gaseous fuel. A restrictor device is in fluid communication with the air inlet for controlling an air inlet pressure of air drawing through the air inlet and into the housing. The restrictor device is operable to lower the air inlet pressure of the air drawn through said air inlet by reducing the area of an air duct ahead of said air inlet to decrease the flow rate of the air / fuel mixture.

[0010]By lowering the inlet air pressure ahead of the air inlet with the restrictor device, a constant air / fuel ratio can be obtained even at very low fan speeds. As such, the control system and method of the present invention permits operation of the burner at a wider range of fan speeds, thus improving efficiency and economy of the burner.

Problems solved by technology

However, typical methods of controlling the air / fuel mixture limit minimum firing rates of the burner due to their inability to maintain the desired air / fuel mixtures at very low fan pressures.

That is, the controls are not sensitive enough to react to minute changes in pressure that occur at reduced flow rates.

Eventually, the firing rate, i.e., the rate at which the air / fuel mixture is burned, is limited with these typical control systems.

For example, the fan motor may actually stall or the air pressure changes may be so minute that the control valve is no longer able to adequately sense the changes and react accordingly.

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