US 4,576,570 A · Automatic combustion control apparatus and method

Abstract

A method and apparatus for controlling the combustion of multiple fuels, especially fuels having diverse combustion air requirements. A heating rate demand signal indicative of the heating rate desired is generated and is compared with a fuel based fuel heating rate signal. The larger of the two signals is selected to be an air demand signal that serves as set point for a combustion air controller. The flow rates of each of the fuels being burned is monitored and the resulting signals are scaled and summed to produce the heating rate signal. The fuel signals are also scaled by factors reflecting the combustion air requirements of the fuels. The signals are summed and combined with the fuel heating rate signal to produce a feedforward signal which in turn is combined with a signal reflecting the measured combustion air flow to produce an equivalent air heating rate signal. This latter signal is communicated to the combustion air controller and if different than the air demand signal causes an adjustment of the combustion air controller. The equivalent air signal is also compared with the heat demand signal and the lower of these two signals is communicated to a fuel heating demand subsystem which controls the metering of the fuels. An 0.sub.2 set point generator modifies the feedforward signal should a deviation occur between the 0.sub.2 set point and the measured 0.sub.2 content of flue gas exhausted by the combustion process.

Claims19

Dependent claims

For a combustion process using multiple fuels having diverse combustion air requirements, a method for controlling the fuel-to-air ratio, comprising the steps of:

(a) generating a heating rate demand signal indicative of the amount of heating required;
(b) measuring the current fuel flow rate for each fuel being burned and generating a fuel heating rate signal indicative of the heating capacity of said fuels;
(c) generating individual fuel demand signals in a fuel heating rate demand development subsystem;
(d) adjusting the flow of individual fuels in response to their individual demand signal;
(e) generating an air requirement signal for measured fuel flows and their air requirements;
(f) generating a feedforward signal related to said air requirement signal;
(g) comparing said heating rate demand signal with said fuel heating rate signal and communicating the higher of said signals to a combustion air flow controller;
(h) adjusting said air controller in response to said communicated signal;
(i) measuring the actual air flow;
(j) generating an equivalent air heating rate signal which is a function of the measured air flow and said feedforward signal;
and,
(k) comparing said equivalent air heating rate signal with said heating rate demand signal and communicating the lower of said signals to said fuel heating rate demand development subsystem.

9 more elements

Apparatus for controlling the combustion of multiple fuels having diverse excess air requirements, comprising:

(a) means for generating a heating rate demand signal;
(b) sensors for monitoring the flow rates of fuels being burned;
(c) scaling means for converting signals received from said sensors to signals representing the heating value per unit time of each of said fuels;
(d) first summing means for summing said signals to arrive at a gross fuel heating rate signal;
(e) other scaling means for converting said sensed signals to signals representing the theoretical air required per unit time for each of said fuels;
(f) other summing means for summing said signals;
(g) means for generating a feedforward signal as a function of the fuel mixture being burned and the heating values of said fuels;
(h) multiplying means for combining said feedforward signal with a signal representing the measured combustion air flow to produce an equivalent air heating rate signal;
(i) a low select comparator for comparing said heating rate signal with said equivalent air heating rate signal, said low select comparator operative to selectively communicate the lower of heating rate demand and equivalent to a fuel demand development subsystem;
(j) a high select comparator for generating an air demand signal for communication to a combustion air controller, said high select comparator operative to select the higher of said heating rate demand signal and said gross heating rate signal;
and
(k) continuously recalibrated cross-limiting means for limiting the fuel flow rates to the available combustion air and for assuring sufficient combustion air for the measured fuel flows.

9 more elements

For a combustion process using multiple fuels having diverse combustion air requirements, a method for controlling the fuel-to-air ratio, comprising the steps of:

(a) generating a heating rate demand signal indicative of the amount of heating required;
(b) measuring the current fuel flow rate for all fuels being burned and generating a fuel heating rate signal indicative of the heating capacity of said fuels;
(c) comparing said heating rate demand signal with said fuel heating rate signal and communicating the higher of said signals to a combustion air flow controller;
(d) adjusting said air controller in response to said communicated signal;
(e) measuring the actual air flow;
(f) generating a third signal which is a function of the measured air flow and the continuously calculated fuel-to-air ratio signal;
(g) comparing said third signal with said heating rate demand signal and communicating the lower of said signals to a fuel heating rate demand development subsystem;
(h) generation of individual fuel demand signals in the fuel heating rate demand development subsystem;
(i) adjusting the flow of individual fuels in response to their individual demand signals.
(j) generating a theoretical air requirement (fuel mix) factor from measured fuel flows and their theoretical air requirements;
(k) generating a total air requirement factor from measured fuel flows, theoretical air requirements, and excess air requirements which may be calculated as a function of load and/or fuel mixture;
(l) generating a feedforward signal as a total air requirement factor for continuously adjusting the fuel-to-air ratio;
(m) generating a feedforward signal as a theoretical air requirement factor for continuously adjusting the fuel-to-air ratio;
(n) correcting the feedforward fuel-to-air ratio signal by feedback control from flue gas O.sub.2 measurements;
(o) generating an O.sub.2 set point as a function of load and fuel mixture from the theoretical air requirement and the total air requirement factors for precise coordination with the feedforward adjustment, provided as a total air requirement factor;
(p) generating the O.sub.2 set point as a function of fuel mixture and load from the load signal and the theoretical air requirement factor;
(q) continuously calibrated cross-limiting signals for valid cross-limit functions at all instants of time.

14 more elements

Dependencies are inferred from the claim text.

Automatic combustion control apparatus and method

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Automatic combustion control apparatus and method

Life of this patent

Abstract

Claims19