Firetube boiler heater system

• US 4,519,770 A
• Filed: 04/21/1983
• Issued: 05/28/1985
• Est. Priority Date: 06/30/1980
• Status: Expired due to Term

• Current Assignee: Alzeta Corp.
• Original Assignee: Alzeta Corp.
• Inventors: Kendall, Robert M., Krill, Wayne V., Kesselring, John P.
• Primary Examiner(s): Focarino, Margaret A.
• Application Number:
  US06/487,068
• Time in Patent Office: 768 Days
• Field of Search: 431/7, 431/170, 431/326, 431/328, 431/329, 431/350, 126/91 A, 126/92 AC, 126/92 C, 122/161, 122/4 D, 122/167, 122/169, 239/145
• US Class Current: 431/7
• CPC Class Codes: F23D 14/18 using catalysis for flameless combustion

Abstract

The burner system is adapted for retrofit into the combustion chambers of firetube boilers. The burner is comprised of a hollow shell molded from a porous ceramic fiber matrix. Fuel and air reactants flow outwardly through the fiber matrix shell and are combusted along a shallow reaction zone on the outer surface. Heat is transferred primarily by radiation to the walls of the combustion chamber at temperatures which result in relatively low NO_x emissions and high combustion efficiencies as compared to boiler systems with conventional burners.

Claims

1. A burner for use in a heater having a combustion chamber with firetube walls, the burner including the comination of a burner shell comprised of a matrix of ceramic fibers having interstitial spaces between the fibers providing a flowpath for an air-fuel mixture with combustion of the mixture occurring in a reaction zone along a shallow outer layer of the shell whereby heat transfers primarily by radiation from the reaction zone outwardly to the firetube walls of the combustion chamber, mounting means for supporting the burner shell and for mounting the shell in the heater wherein said burner shell is separable and detachable from the combustion chamber, and with the reaction zone spaced from and in direct line of radiant view with the firetube walls of the combustion chamber, and means for directing a flow of the air-fuel mixture into the shell and outwardly through the fiber matrix.

2. A burner as in claim 1 in which the fibers of the matrix are comprised of substantial portions of alumina and silica.

3. A burner as in claim 2 in which the matrix includes a refractory metal compound.

4. A burner as in claim 3 in which the refractory metal compound is aluminum.

5. A burner as in claim 1 in which strands of a catalytic metal are interspersed through the matrix.

6. A burner as in claim 1 in which the matrix is comprised of at least two layers with one layer on the upstream side of the direction of flow and a second layer on the downstream side of the direction of flow with the layer on the upstream side formed of a composition which is less catalytically active than the layer on the downstream side for minimizing flashback of combustion through the shell.

7. A burner as in claim 1 which includes a centerbody mounted within and radially spaced from the inner surface of the shell to form a flow annulus therebetween, and means forming apertures through the centerbody for directing the flow of mixture into the annulus for maintaining a high velocity flow of the mixture into the shell.

8. A firetube heater system of apparatus comprising the combination of a combustion chamber having firetube wall surfaces, a burner shell mounted within the chamber and separate and detachable therefrom, said shell being radially spaced from and in direct line of radiant view with the firetube wall surfaces, said burner shell comprising at least one layer of ceramic fiber matrix with interstitial spaces between the fibers providing a flowpath for an air-fuel mixture with combustion of the mixture occurring in a shallow reaction zone along the outer surface of the shell with heat transferring primarily by radiation from the reaction zone outwardly to the firetube wall surfaces, and means for directing a flow of the air-fuel mixture into the shell and outwardly through the fiber matrix.

9. A heater system as in claim 8 which includes mounting means for the burner shell in the combustion chamber as a replacement for a conventional burner therein.

10. A method for combusting an air-fuel mixture for heating the firetube wall surfaces in a heater having a combustion chamber with firetube walls, and a burner shell separate and detachable from the firetube walls, comprising the steps of directing a flow of the mixture through interstitial spaces in a matrix of ceramic fibers, forming the burner shell, combusting the mixture at a shallow reaction zone on a side of the matrix downstream of the flow, and radiating heat from the reaction zone directly to the firetube wall surfaces at a rate which maintains the temperature of the matrix in the zone below the adiabatic flame temperature of the mixture and also below the use temperature of the fibers.

11. A method as in claim 10 in which heat conduction from the reaction zone through the matrix in a direction upstream of the flow is at a rate which maintains the temperature of the upstream side of the matrix below the ignition temperature of the mixture for preventing flashback into the upstream flow of gases.