GB2196102A - Multiport gas burner - Google Patents

Abstract

A multiport type natural gas burner comprises a number of elongate ports, a common mixture manifold at one end of each port to supply a mixture of air and gas to the ports and a combustion tunnel at the other end of the ports to surround the flames issuing from the ports. The burner is designed to obey the following equations:- <IMAGE> where G is the maximum gas flow rate in m<3>/sec, N is the number of parts, D, L, and V are burner dimensions, R is the air/gas ratio, F is the turndown factor, and A and B are constants. <IMAGE>

Description

SPECIFICATION Premix natural gas burner The present invention relates to a premix natural gas burner of the multiport type.

Multiport-type natural gas burners are well known and comprise a number of elongate ports, a common mixture manifold at one end of each port to supply a mixture of air and gas to the ports and a combustion tunnel at the other end of the ports to surround the flames issuing from the ports.

The ports may be arranged as a parallel array and may be formed by a number of tubes or as bores extending through a block.

The manifold may be supplied with the airgas mixture by a standard air blast injector.

The length of the combustion tunnel is not critical but will not generally be less than 0. 1 m. The inner surfaces of the tunnel may be parallel, or may converge towards the tunnel exit thus increasing the exit velocity of the combustion products.

The tubes/blocks and the combustion tunnel may be constructed using refractory concrete or other materials such as ceramic fibre which are capable of withstanding high temperatures.

The manifold section will generally be constructed of a metal such as mild steel.

A pilot flame or other manual or automatic means of ignition and flame detection apparatus may also be provided.

Burners of the above described type are generally attractive because of the inherent simplicity of their design but their sound output may be high especially when the thermal input rate of the burner exceeds 100KW.

The conventional methods of reducing noise levels in this kind of burner lead to problems of flame instability including flame "light-back" (also called "flash-back") and "self-oscillation" which is a form of combustion-driven oscillation.

It is an object of the present invention to provide a multiport type natural gas burner in which, for any given maximum gas flow rate at which the burners to operate, the sound power output is lower than the conventional burners of this type while the problems of flame instability are alleviated.

According to the present invention therefore we provide a multiport type natural gas burner of the type defined in which if' the maximum gas flow rate (m3/sec) at which the burner is to operate is G, then: AN15D4 G > . (1) (L+0.85D)o.5vo.5(1 +R) and BFND2.14 G > . (2) (1+R) Where N is the number of ports, D is the diameter of the ports (m), L is the length of each port (m) V is the volume of the manifold (m3) R is the air/gas ratio on a volume flow basis F is the turndown factor (i.e. the maximum/minimum desired gas flow rate) and A and B are constants.

For natural gas A=1.8132x 102, and B=1.344 Preferably the port diameter D lies in the range 0.001 to 0.010m, suitably within the range 0.003 to 0.010m and desirably is 0.006m.

Preferably the port length L lies in the range 0.005 to 0.05m and suitably within the range 0.01 to 0.2m.

The manifold volume desirably lies within the range 0.001 to 0.06m3.

The gas input rate may be equal to or exceed 100KW.

The sound power output is preferably less than 0.1 watts, suitably less than 0.01 watts, conveniently less than 0.001 watts and desirably less than 0.0001 watts.

Embodiments of the invention will now be particularly described with reference to the accompanying drawings in which Figure 1 is front elevation of a typical premix natural gas fired multiport burner, and Figure 2 is a section along lines ll-ll of Fig.

1.

Referring to the drawings, the burner comprises a manifold 1 for receiving a mixture of natural gas and air via a supply pipe 2, a refractory burner block 3 through which there extends an array of elongate ports 4 for receiving the air/gas mixture from the manifold 1 and a refractory combustion tunnel 5 forming a central combustion chamber 6 for combustion of the gas/air mixture supplied to the chamber 6 by way of the ports 4.

The manifold 1 comprises a steel casing 7 to the front of which is bolted the burner block 3 by several nut and bolt assemblies 8, the bolts 9 extending through the block 3 and into the tunnel 5 to secure that member to the block 3.

In use, the gas/air mixture supplied to the manifold 1 is distributed from the manifold 1 to the ports 4. The mixture emerging from the ports 4 into the chamber 6 is ignited by a pilot burner (not shown) or an equivalent ignition device and is combusted within the chamber 6.

The various features and operation of the burner will be readily apparent to those skilled in the art and further description is deemed to be superfluous.

We have discovered that if a multiport type gas burner which is to operate at a given maximum gas flow rate is designed to obey the two equations given earliers, the resultant burner will operate at a sound power output which is lower than that obtainable from a conventional multiport type gas burner operating at the same given maximum gas flow rate.

Furthermore such a burner will be free of the flame instability problems encountered when attempting to reduce noise levels by conventional methods.

As an example a burner was built in accordance with the equations (1) and (2) wherein N=240, D=0.006m, L=0.100m and V=0.014m. The burner was fired with a stoichiometric mixture of natural gas and air at an input rate of 190KW. The turndown factor was 9.

The sound power output was measured as 85dB(A-weighted) re. 1 x 10-12) watts). A conventional burner for use in the same application as the above example and fired at the same gas and air rates had a sound power output of 101 dB(A).

We have found that the (un-weighted) sound power output can be estimated from the equation below.

W=C G255 (1+R)3.61 N-1.55 D-2.52 where W is the sound power output of the burner in watts and C is a constant and the remaining symbols are as given above previously.

For natural gas C=5.156x10-3.

Claims (13)

1. A multiport type natural gas burner of the type defined in which if the maximum gas flow rate (m3/sec) at which the burner is to operate is G, then AN'.5D4 G > (L+0.85D)0.5V0.5(1 +R) and BOND2 '4 G (1+R) where N is the number of ports, D is the diameter of the ports (m), L is the length of each port (m), V is the volume of the manifold (m3) R is the air/gas ratio on a volume flow basis, F is the turndown factor (i.e. the maxi mum/minimum desired gas flow rate), and A and B are constants.

2. A burner as claimd in claim 1 in which each port diameter is in the range 0.0001 to 0.010m.

3. A burner as claimed in claim 2 in which each port diameter lies in the range 0.003 to 0.010.

4. A burner as claimed in claim 3 in which the port diameter is 0.006m.

5. A burner as claimed in any of the preceding claims in which the port length is in the range 0.005 to 0.5m.

6. A burner as claimed in claim 5 in which the port length is in the range 0.01 to 0.2m.

7. A burner as claimed in any of the preceding claims in which the manifold volume is in the range 0.001 to 0.06m3.

8. A burner as claimed in any of the preceding claims in which the sound power output is less than 0.1 watts.

9. A burner as claimed in claim 8 in which the sound power output is less than 0.01 watts.

10. A burner as claimed in claim 9 in which the sound power output is less than 0.001 watts.

11. A burner as claimed in claim 10 in which the sound power output is less than 0.0001 watts.

12. A multiport burner substantially as hereinbefore described with reference to the drawing.

13. A multiport burner substantially as hereinbefore described with reference to the example.