Metering combustion control

The present invention relates generally to combustion control for use in fired equipment and deals more particularly with a metering combustion control for fired equipment.

Combustion control strategies applied to fired equipment, both commercial and industrial, generally are one of three general category types or some subtle variation to one or the other of them. The control strategies as known to a person skilled in the art are: 1) single point positioning control also known as jackshaft positioning; 2) parallel positioning control; and 3) metered cross-limited control.

Each of these are fuel/air ratio combustion control strategies wherein a firing rate demand signal generated as a result of an attempt to maintain a selected “process variable” (PV) equal to a desired “set-point” (SP) is simultaneously directed to a fuel flow regulating element and a combustion air flow regulating element.

The currently known and implemented combustion control strategies are not entirely satisfactory. To applicant\'s knowledge, none of the known combustion control strategies meet Underwood Laboratories (UL) approval as a parameter based combustion control instrument capable of carrying out a metering fuel/air ratio combustion control strategy.

The currently known and implemented metered cross-limited combustion control strategies are not entirely satisfactory. Current implementations utilize two, or more, PID (Proportional-Integral-Derivative) control logic blocks, one for fuel and one for air. Cross-limiting logic must be applied to coordinate the two independent proportional integral derivative logics. This combination requires considerable skill to tune and calibrate, and results in a slow firing rate demand response time.

Accordingly what is needed is a parameter based combustion control instrument capable of choosing via parameter selection a selected one of a single point positioning control strategy, a parallel positioning control strategy and a metering fuel/air ratio combustion control strategy.

In accordance with a broad aspect of some embodiments of the invention, combustion is controlled in a fired equipment by metering both the fuel flow rate and the combustion air flow rate in a desired ratio corresponding to a master firing rate demand, and by trimming the master firing rate demand directed to the combustion air regulating element in response to an error based correction adjustment determined from the respective values of the fuel flow meter and combustion air flow meter input signals to drive the ratio between the fuel flow rate and the combustion air flow rate toward the desired ratio for controlling the combustion in accordance with the master firing rate demand

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a function schematic representation of an example of a parallel positioning combustion control system.

FIG. 2 is a functional schematic representation of an example of a parallel positioning combustion control system with oxygen trim.

FIG. 3 is a functional schematic representation of an example of a full metering combustion control system with fuel flow and combustion air flow cross limiting.

FIG. 4 is a functional schematic representation of an example of a metering combustion control system with oxygen trim according to some embodiments of the present invention.

FIG. 5 shows a flowchart of the basic steps of the method according to some embodiments of the invention.

FIG. 6 shows a combustion controller enabled device according to some embodiments of the invention for providing combustion control in a fired equipment.

FIG. 7 is a functional block diagram of an example of a signal processor for carrying out the invention.

FIG. 8 is a functional block diagram of an example of a combustion controller for carrying out the steps of the method according to some embodiments of the invention.

FIG. 9 shows a combustion controller chipset according to some embodiments of the invention for providing combustion control in a fired equipment.

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