# US 7,607,913 B2 · CO controller for a boiler

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- Number: US 7,607,913 B2
- Document ID: US7607913B2
- Status: Granted
- Kind: B2
- Application number: 11/546,523
- Filed: 2006-10-10
- Published: 2007-05-17
- Granted: 2009-10-27
- Earliest claimed: 2005-10-27
- Assignees: OSIsoft, Inc.
- Inventors: Charles H. Wells
- Web page: https://patentgrep.com/patent/US7607913B2

## CPC

- F23N 1/022: {using electronic means}
- F23N 5/006: {the detector being sensitive to oxygen}
- F23N 5/003: {using detectors sensitive to combustion gas properties (F23N5/02, F23N5/18 - F23N5/26 take precedence)}
- F23N 2221/10: Analysing fuel properties, e.g. density, calorific
- F23N 2223/14: Differentiation
- F23N: REGULATING OR CONTROLLING COMBUSTION (control devices specially adapted for combustion apparatus in which combustion takes place in a fluidised bed of fuel or other particles F23C10/28; condition responsive controls for regulating combustion in domestic stoves with open fires for solid fuel F24B1/187)

## Abstract

A CO controller is used in a boiler (e.g. those that are used in power generation), which has a theoretical maximum thermal efficiency when the combustion is exactly stoichiometric. The objective is to control excess oxygen (XSO2) so that the CO will be continually on the “knee” of the CO vs. XSO2 curve.

## Claims

### Claim 1

A method of controlling excess oxygen in a combustion process in a boiler, the method comprising:
(a) having data comprising carbon monoxide concentration and excess oxygen measurements;
(b) fitting a curve for said carbon monoxide concentration measurements versus said excess oxygen measurements, wherein said fitting relies on one or more fit parameters, and wherein the values of said one or more fit parameters are found by said fitting;
(c) determining an excess oxygen setpoint for said combustion process of said boiler based on said one or more fit parameters; and
(d) adjusting said excess oxygen setpoint for said combustion process of said boiler to said determined excess oxygen setpoint, wherein said combustion process uses carbon based fuel.

### Claim 2 (depends on 1)

The method of claim 1, wherein said excess oxygen and carbon monoxide concentration measurements are fitted in a moving window data store.

### Claim 3 (depends on 2)

The method of claim 2 further comprising calculating a sensitivity to said one or more fit parameters of said fitted curve based on the moving window data store.

### Claim 4 (depends on 2)

The method of claim 2, where the moving window data store records data for a time range between 5 and 60 minutes.

### Claim 5 (depends on 1)

The method of claim 1, wherein the carbon based fuel is from a group consisting of coal, natural gas, oil, hog fuel, grass, and animal waste.

### Claim 6 (depends on 1)

The method of claim 1, wherein a first derivative of said fitted curve is used to determine to said excess oxygen setpoint.

### Claim 7 (depends on 6)

The method of claim 6, wherein said derivative is computed analytically.

### Claim 8 (depends on 6)

The method of claim 6, wherein said derivative is computed numerically.

### Claim 9 (depends on 6)

The method of claim 6, wherein said excess oxygen setpoint is determined based on an operator-selected target slope and said one or more fit parameters.

### Claim 10 (depends on 1)

The method of claim 1, wherein said fitting said curve is accomplished in real time.

### Claim 11 (depends on 1)

The method of claim 1, wherein said fitted curve is a power law curve of the form y=αxβ, wherein y is the carbon monoxide concentration, wherein x is the excess oxygen, and wherein α and β are said fit parameters.

### Claim 12 (depends on 11)

The method of claim 11, further comprising calculating a derivative of said power law curve, wherein said excess oxygen setpoint is determined based on α, β, and an operator-selected target slope.

### Claim 13 (depends on 12)

The method of claim 12, wherein γ is said operator-selected target slope, and wherein said determined excess oxygen setpoint is equal to (αβ/γ)1/(1−β).

### Claim 14 (depends on 11)

The method of claim 11, further comprising calculating a sensitivity of said excess oxygen setpoint to said fit parameters of said power law curve.

### Claim 15 (depends on 14)

The method of claim 14, wherein said sensitivity of said excess oxygen setpoint is equal to:
[(α/β)1/(1−β)+{1/(1−β)}(αβ/γ)β/(1−β)]δβ+[β/γ]1/(1−β)δα.

### Claim 16 (depends on 1)

The method of claim 1, further comprising plotting said carbon monoxide measurements versus said excess oxygen measurements.

### Claim 17 (depends on 16)

The method of claim 16, further comprising plotting said fitted curve on said plot of said carbon monoxide measurements versus said excess oxygen measurements.