# US 5,044,287 A · Method of controlling combustion in a fluidized bed furnace

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- Number: US 5,044,287 A
- Document ID: US5044287A
- Status: Granted
- Kind: A
- Application number: 07/537,627
- Filed: 1990-06-13
- Granted: 1991-09-03
- Earliest claimed: 1989-06-16
- Assignees: Ebara Corporation
- Inventors: Masaaki Furukawa; Hiroshi Yoshida; Takeyuki Naito; Keiichi Sato
- Web page: https://patentgrep.com/patent/US5044287A

## CPC

- F23G 5/30: having a fluidised bed
- F23C 9/003: {for pulverulent fuel (for fluidized bed F23C10/02)}
- F23G 5/002: {characterised by their grates (F23G5/05 takes precedence)}
- F23G 5/14: including secondary combustion
- F23N 1/022: {using electronic means}
- F23N 5/006: {the detector being sensitive to oxygen}
- F23G 2203/10: Stoker grate furnace
- F23G 2207/101: for temperature
- F23G 2207/103: for oxygen
- F23L 2900/07003: Controlling the inert gas supply
- F23N 5/18: using detectors sensitive to rate of flow of air or fuel
- F23N 2221/12: Recycling exhaust gases
- F23N 2225/06: for determining flow
- F23N 2225/16: burner temperature
- F23N 2233/06: at the air intake
- F23N 2235/06: at the air intake
- F23N 2237/16: secondary air
- F23N 2237/18: fluidized bed burners
- F23N 2241/18: Incinerating apparatus
- F23G: CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23C: METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN {A CARRIER GAS OR} AIR (burners F23D)
- 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)
- F23L: SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ({air-supply arrangements for fluent fuels F23C;} firebridges with means for feeding air or steam F23M3/04; baffles or shields with air supply passages F23M9/04); VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS {(dampers and throat restrictors for open fire-places F24; air inlet valves for open fire fronts F24)}; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES

## Abstract

A method for controlling combustion in a furnace into which combustible material, e.g., urban refuse, industrial waste, and a controlled quantity of combustion air are fed. The furnace includes a mixing/stirring region where unburnt gas and secondary combustion air are mixed and stirred. A part of exhaust gas derived from the furnace is blown into the mixing/stirring region depending on variation in the quantity of the secondary combustion air, and a flow rate of mixture gas consists of the exhaust gas and the secondary combustion air to be fed into the mixing/stirring region is maintained within a predetermined region so that effective combustion takes place.

## Claims

### Claim 1

In a method of controlling combustion in a fluidized bed type furnace having a combustion chamber, the lower portion of the combustion chamber being a mixing/stirring region in which unburnt gas and secondary combustion air are mixed and stirred together, said furnace being supplied with a quantity of combustible material varying per unit time and a quantity of combustion air which is controlled in response to the quantity of the combustible material, the improvement wherein a flow rate of mixture gas comprising secondary combustion air and exhaust gas to be fed into the mixing/stirring region is maintained within a predetermined range by blowing a part of exhaust gas into the mixing/stirring region depending on variation in said quantity of combustion air.

### Claim 2 (depends on 1)

The method as claimed in claim 1, wherein when a part of exhaust gas is also blown into the upper portion of the combustion chamber, and when a quantity of exhaust gas to be blown into the mixing/stirring region increases or decreases, the flow rate of exhaust gas to be blown into the upper portion of the combustion chamber is decreased or increased in opposition to the quantity of said increase or decrease of the blown exhaust gas so that a flow rate of the circulating exhaust gas to be introduced into the furnace is maintained within a predetermined range.

### Claim 3 (depends on 2)

The method as claimed in claim 2, wherein a temperature at the upper furnace region is normally monitored and the flow rate of exhaust gas to be blown into the upper portion of the combustion chamber is correctly controlled in response to said upper furnace temperature so that said upper furnace temperature is maintained within a range of from 750.degree. C. to 950.degree. C.

### Claim 4 (depends on 1, 2, 3)

The method as claimed in any one of claims 1 to 3, wherein the mixing/stirring region is formed by a throttle section of the combustion chamber.

### Claim 5 (depends on 1, 2, 3)

The method as claimed in any one of claims 1 to 3, wherein the part of exhaust gas to be fed to the mixing/stirring region is mixed with secondary air to be blown into a throttle section of the combustion chamber in the horizontal direction or in the slantwise downward direction.

### Claim 6 (depends on 1, 2, 3)

The method as claimed in any one of claims 1 to 3, wherein the part of the exhaust gas to be fed to the mixing/stirring region is mixed with secondary combustion air to be blown into a throttle section of the combustion chamber in the horizontal direction or in the slantwise downward direction thereby to create a swirling flow in the throttle section.