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Copy of
a Presentation on DRAX
Contents
DRAX Torches
Effectiveness of a gas flame
Example temperature differences
VHRR "Volumetric Heat Release Rate"
Improving flame by pre-heating gas and air
Pre-heating produces cracking
Catalysis and sooting
Laboratory test burners
Burner performance
Technical Development needed for production electric torch
Applications of the DRAX burner
Typical users of the DRAX ultra-hot burner
DRAX Torches Limited
Private London-registered company - winner of competitive UK
Government DTI
Smart grant
 | R&D programme successfully completed |
| strong patent filing |
| patent fully owned and controlled by company |
| gas-preheated burners successfully demonstrated |
| electric-preheated burners successfully demonstrated |
| burners now ready for detailed design for mass-production |
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Effectiveness of a gas flame
‘Effectiveness’ of a gas flame depends on heat transfer from flame to work-piece.
Heat transfer depends upon
| temperatures of flame and work-piece |
| other factors, principally :
 | turbulence within flame |
| ‘intensity’ of flame* |
|
* measured as "volumetric heat release rate"
At very high flame temperatures (oxy-acetylene), flame temperature is the
dominant factor. At lower gas flame temperatures,
the other factors are more significant.
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Example temperature differences
You cannot heat a work-piece to the temperature of the gas in a flame:
| Flame temperatures (in C ) |
Work- piece temperatures (in C ) |
| methane / air 1950 |
glass 900 – 1000 |
| propane / air 1990 |
brass / bronze 950 – 1050 |
| acetylene / air 2265 |
copper 1087 |
| methane / oxygen 2780 |
steel 1450 - 1540 |
| propane / oxygen 2820 |
pure iron 1540 |
| acetylene / oxygen 3070 |
quartz 1610 |
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VHRR "Volumetric Heat Release Rate"
VHRR = rate of heat production divided by the volume of the flame.
At a given temperature, the higher the VHRR the greater the heat transfer
Principal elements contributing to VHRR:
| flame surface area per unit volume of flame brush |
| heat release rate per unit of flame surface area * |
* calculated as VHRR = {heat of reaction per unit mass of fuel} X {fuel concentration in the un-burnt mixture} X {laminar flame speed}
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Improving flame by pre-heating gas and air
Pre-heat Input Air
| Well-known techniques and effects |
Pre-heat Fuel Gas
| Unusual : not normally done
(except to improve flow/atomisation of heavy oil) |
|
flow rates are 25x lower than air |
|
therefore apparently a useless thing to do, but ... |
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Pre-heating produces cracking
| fuel cracks into faster reacting molecules and radicals |
| products of cracking have higher heats of combustion |
| result: an increase in the effective flame speed |
 shorter turbulent flame brush
increased VHRR
Also
increased flow rate possible (no flame
lift-off)
increased turbulence
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Catalysis and sooting
Catalysis has the following effects:
| cracking at lower temperatures |
| amplifies effectiveness of fuel preheat |
Which resulting in:
| increase flame speed |
| increase heat of combustion |
But also causes sooting:
| by-product of cracking |
| forms on surface blockage |
Sooting can be stopped by:
| catalytic cracking |
| air bleed |
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Laboratory test burners
| Gas preheat burners have a capacity up to more than 20kW, supplied with propane and
compressed air, high turbulence flame. |
| Electric pre-heat burners have capacity up to typically 10kW, supplied with propane and
mains power (low pressure air), medium turbulence flame. |
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Burner performance
Results achieved with test burners
| dramatic flame shortening with preheat (30cm to 3cm) |
| flame 500oC hotter than a standard ‘Bunsen’ burner |
| large volumetric heat release rate (100 MW/m3 ) |
| work-piece temperatures up to 1800 C (Platinum can be melted) |
| iron and steel heated to white heat, where they can be easily worked,
iron and steel also melted after 30-60 seconds in flame |
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Technical Development needed for production electric torch
| flame optimisation |
| life-time study and failure mode analysis |
| electric ignition |
| design for safety (e.g.. minimise hot surfaces) |
| design cost-effectiveness |
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Applications of the DRAX burner
| speeding up processes normally carried out with propane/air burners :
with a flame 500 C hotter than a standard propane flame, the DRAX torch
will heat a work-piece much faster |
| allowing more rapid thermal input to work-piece with less heat damage to
surrounding components |
| brazing of high thermal conductivity alloys (e.g.. copper) |
| brazing with strong high temperature alloys |
| brazing with minimum heat to surrounding parts |
| preheating of parts prior to electric arc/MIG/MAG/TIG welding |
| releasing seized nuts/bolts |
| blacksmith work (working of iron/steel parts with hand tools) |
| rough cutting of steel/removal of old rusted parts eg. automotive
exhaust |
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Typical users of the DRAX ultra-hot burner
| users of small oxy-propane burners |
| users of small acetylene burners |
| workshops with electric arc/MIG/MAG/TIG welding sets |
| automotive repair workshops |
| cycle repair/assembly workshops |
| pipework fabricators/plumbers using brazed joints |
| blacksmiths/horseshoe farriers (to replace forges) |
| home hobby workshops |
There will be major ‘Third World’ manufacturing/licensing opportunities
: enquiries have been received from dozens of non-industrial countries, and
there is a government ‘acetylene replacement/reduction’ programme in some
countries.
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