GB2178839A - Combuster - Google Patents

Abstract

A combustor suitable for disposing of lean fuel gas mixtures, e.g. solvent-laden exhaust streams, has a combustion chamber 2, a heat exchanger 1 comprising a matrix of elongate tubes 6 for supplying lean fuel gas to the combustion chamber and a burner 9 located within the combustion chamber. The burner is adapted to mix fuel gas and the lean fuel gas which enters at inlet 4 and issues from the elongate tube outlets. The heat exchanger is in an heat exchange relationship with flue gas emerging from the outlet and the combustion chamber and passing above plate 11. The passage of the flue gases from the combustion chamber over the external surfaces of the tubes of the heat exchanger enables the pre-heating of the lean fuel gas mixture prior to its entry into the combustion chamber. <IMAGE>

Description

SPECIFICATION Combustor The present invention relates to combustors and more particularly relatesto combustors forthe com- bustion of lean combustible gas.

Current emphasis on the need for energy conservation and anti-pollution measures requirescombus- tiontechnologyforburning low grade fuels and fuel/ air mixtures which under standard operating condi tionsmaynoteven normallybeflammable.

Lean fuel/air streams may be burned by recuperating heat from the exhaust gases and transferring itto the incoming fuel/air stream. The present invention relatesto a recuperative combustorwhich is suitable for the incineration of lean fuel/air streams, in particularfor solvent laden plant exhaust streams from paper, film and fabric coaters, tape manufacturers, paint shops etc which are normallyvented to atmosphere.

The hot flue gas from the recuperative combustor may be used for heating solvent drying ovens, for space heating and for other purposes.

Thus according to the present invention there is provided a combustorsuitablefordisposing ofa lean combustiblegas,thecombustorcomprising acombustion chamber, a heat exchanger comprising a matrix of elongatetubes forsupplying lean fuel gas to the combustion chamber, a burner located within the combustion chamber, the burner being adapted to mix fuel gas and the lean combustible gas issuing from at least some of the elongate tube outlets, the heat exchanger being in an heat exchange relationship with flue gas emerging from the outlet of the combustion chamber.

The passage of the flue gases from the combustion chamber overthe external surfaces of the elongate tubes ofthe heat exchanger enables the pre-heating ofthe lean fuel gas mixture priorto its entry into the combustion chamber.

Preferably the lean combustible gas is afuel/oxygen containing gas mixture. The term 'gas' is also intendedto includevapour. The burner is intendedto consume fuel/oxygen containing gas mixtures having compositions below the normal lean or lower limit offlammability at room temperature and atmospheric pressure.

Preferably the burner comprises a housing having a perforated outlet plate at least one hole of the plate being connected to a fuel line, the outlet ofthefuel line protruding beyond the plane ofthe plate and having exit holes in its periphery adapted to spread fuel gas over at least some of the holes.

The burner is suitably attached to the outlet face of the heat exchanger, for example by bolting, so thatat least some of the outlets of the heat exchanger can passthe gas mixture into the housing ofthe burner, the gas mixture being subsequently burned.

The lean combustible gas may be a lean fuel gas stream and may be a solvent laden air stream. The fuel gas supplied by the burnerfuel line may be a hydrocarbon gas such as natural gas, methane or propane. Other suitable fuel gases may be produced by the evaporation of volatile liquids.

The invention also includes a method of disposing of a lean combustible gas, the method comprising the steps of (a) passing the lean combustible gas into the inlet of the combustor as hereinbefore described, (b) passing fuel into the burner adapted to mix the fuel gas and the lean combustible gas mixture, and (c) igniting the offuel gas and lean combustible gas mixture.

The invention will now be described by way of example only and with reference to Figures 1 to 3 of the accompanying drawings.

Figure lisa perspective view of the combustor with a portion cut away to illustrate the combustion chamber and burner.

Figure2 shows a vertical section through the burner and Figure3 shows an end view of the burner.

The combustor comprises a heat exchanger sec- tion 1 and a combustion chambersection 2 adjacent to the heat exchanger section.

The heat exchanger comprises a rectangular matrix of elongate tubes 3, the interior of each tube com municatingwith an inlet manifold 4. Thetubesare supported byafixedtubesheetatthe inlet end and by a floating tubesheet at their outlet end. The heat exchanger is surrounded by a housing 5, the top and bottom faces ofthe housing being spaced apartfrom the heat exchanger so as to provide an outlet passageway 6 for exhaust gases. There is an internal baffle 7 located midway along the heat exchangerto deflect the exhaust gases in appropriate cross-flow over the outside surfaces of the tubes 3.

The combustion chamber section is linked to the heat exchanger section in front of the floating tubesheet 8 and may be separated for inspection etc.

A burner 9 is fitted to the floating tubesheet 8 and has an associated ignition system 10.Adividing plate 11 (which may be attached to floating tubesheet 8) may be usedto ensurethat none ofthe combustion cham ber volume is bypassed prior to the exit of the gases to theshell side of the heat exchanger 1 . The end wall has a refractory cement lining 12to prevent the burnerflame impinging directly onto the combustion chamber wall.

The burner is shown is more detail in Figures 2 and 3. The burner comprises a stainless steel plate cube 20 and has open opposite faces. The cube is bolted to the floating tubesheet 21 at one of the open faces and collects the outlet flow from a fraction of the tubes 22.

A burner plate 23 having a regular array of holes 24 is attached to the other open face. Afuel gas feed pipe 25 passes into the burner cube 20 and turns through 900to protrudethroughthecentreholeoftheburner plate 23. The end ofthefeed pipe is blanked offsothat fuel gas passes through four evenly spaced outlet holes 26 around the periphery of the pipe 25. The outlet holes 26 are located adjacent to the burner plate 23 so thatfuel gas is directed over the outer surface ofthe burner plate (ie perpendiculartothe axis of the holes of the burner plate).

A high energy spark igniter 10 is located close to the burner. The igniter may be retracted after ignition of the burner. Aflame detector 13 is also located in the combustionchamber2.Theinteriorofthecombus tion chamber may be viewed with a sight glass (not shown). The heat exchanger section 1 and combus tion chamber section 2 are lagged with a suitable insulating material 14 such as thick ceramic fibre blanketsurroundedwithaluminiumcladding.The exhaust gases exit from the combustor at the outlet 15.

During use, the control and start up of the combus tor is bymeansof a burner management controller (not shown). Initiallythe air is supplied to the inlet4 and fuel is supplied to the burner 9 which is then lit by the igniter 10. Various safety features form part of the control operation such as provisionforfuel switch off ifthe flame is not ignited.

When the burner has raised the temperature ofthe combustion chamber to the desired value, the air supply is replaced byasolventladen airstream (lean combustible gas) which is supplied to the inlet 4. The burner 9 maythen be operated on a reduced fuel feed or be switched off completely, the action of the burner being governed by the controllerfor example based on the combustion chamber gas exittemperature. At complete fuel shut off, the solvent laden air stream is still passed from the inlet to the combustion chamber, the solvent being burned by recuperation of heat from the exhaust gases.

In an alternative embodiment of the invention, the flue gases exitfrom the combustion chamber through an annularoutletformed between a cylin drical baffle and the housing of the combustion chamber. This arrangement reduces temperature dif ferences between the elongate tubes and tends to prevent distortion of the outlet face of the heat ex changer.

Claims (12)

1. A combustor comprising a combustion cham ber, a heat exchanger comprising a matrix of elon gate tubes forsupplying a lean combustible gas to the combustion chamber, a burner located within the combustion chamber, the burner being adapted to mixfuel gas andthe lean combustible gas issuing from at least some of the elongate tube outlets, the heat exchanger being in an heat exchange relation ship with flue gas emerging from the outlet ofthe combustion chamber.

2. Acombustoraccording to claim 1 inwhichthe burner comprises a housing having a perforated out let plate at least one hole of the plate being connected to a fuel line.

3. A combustor according to claim 2 in which the outlet ofthe fuel line protrudes beyond the plane of the outlet plate and has exit holes in its periphery adapted to spread fuel gas over at least some of the holes.

4. Acombustoraccording to any of claims 1 to 3 having an igniter and/orflame detector in the housing.

5. A combustor according to any of claims 1 to 4 in which the housing is lined with a refractory material.

6. A combustor according to any ofthe preceding claims in which the flue gas outlet from the combus tion chamber is an annulararrangement.

7. A combustor as hereinbefore described and with reference to the accompanying drawings.

8. A method of disposing of a lean combustible gas comprising the steps of (a) passing the lean combustible gas into the inlet of a combustor according to any of claims 1 to 7, (b) passing fuel gas into the burner adapted to mix the fuel gas and the lean combustible gas, and (c) igniting the mixture of fuel gas and lean combustible gas.

9. A method according to claim 8 in which the lean combustible gas is a lean fuel/air mixture.

10. A method according to claim 9 in which the lean combustible gas is a solvent laden air stream.

11. A method according to any of claims 8 to 10 in which the fuel gas is a hydrocarbon gas.

12. A method of disposing of a lean combustible gas as hereinbefore described and with reference to the accompanying drawings.