WO2002079700A1

WO2002079700A1 - Gas fired heating device and a method of generating a flow of hot gas

Info

Publication number: WO2002079700A1
Application number: PCT/DK2001/000212
Authority: WO
Inventors: Carl-Johan SÄRKINEN
Original assignee: Icopal A/S
Priority date: 2001-03-29
Filing date: 2001-03-29
Publication date: 2002-10-10

Abstract

A gas fired heating device (1) comprises a heating gun (2) with a combustion chamber (3), an igniter (4), a trigger (5), and a sequence control means (5, 9, 10, 13), operatively associated with the trigger. By way of the sequence control means, activation of the trigger initiates gas supply and firing of the igniter prior to the air supply having reached full operational flow. Thus ignition takes place in a gas-rich atmosphere while regular combustion takes place in a more lean atmosphere. This facilitates ignition and ensures fast and efficient combustion during operation.

Description

Gas Fired Heating Device and a Method of Generating a Flow of Hot Gas

The present invention relates to gas fired heating devices and to methods of generating a flow of hot gas. The invention more particularly relates to mobile or portable heating devices for a variety of uses such as roofing installations, welding of roof coverings and other applications where an amount of flameless heat may be needed.

On construction sites the demand for heating for many purposes is frequently met by propane fired torches. Said devices are capable of yielding a high heat power output but they may be hazardous in use and may be the cause of fires. Therefore the provision of flameless heating devices is a safety priority.

US patent 5,649,824 discloses a portable heating unit provided with a double wall barrier associated with a gas nozzle, a blower and an igniter. The fan provides air for the combustion as well as air for cooling the outer barrel walls. As small diverter tube is provided inside the housing for facilitating ignition, which is difficult in the main air gas stream. The unit is adapted for being fed with pressurized gas.

US patent 5,155,925 provides an LPG powered hair dryer which includes an LPG bottle, a fan, a battery and a thermal sensor. When gas discharge comes to a stop, the fan motor is made to stay on until the unit has cooled. Ignition takes place inside a burner interior to the main body of the dryer.

The invention in a first aspect provides a gas fired heating device according to claim 1. The invention solves the problem of igniting the gas flow very effectively. As will be familiar to those having operating experience with gas fired equipment ignition is generally not possible in the full flow of gas and air mixture. Reducing the flow, however, usually presents difficulties in achieving a proper ratio of the constituents in the mixture. Generally a low flow rate of gas is required. Also the gas air mixture should be richer in gas. Once combustion has commenced, the flow must be increased to the operating value and the mixture ratio should be lean in gas in order to ensure a complete combustion.

The device according to the invention provides ignition of the combustion and increasing the supply of gas and air to the normal flow by simple timing steps. Thus once the trigger is activated, gas is fed into the combustion chamber where it creates along with air present in the chamber a mixture rich in gas. This gas is ignited and feeding of air for combustion is then provided.

The device according to the invention does not need to rely on structural measures such as dedicated ignition chambers etc. as taught in the prior art and therefore allows for a simpler and more compact design of the combustion chamber.

According to a preferred embodiment, the trigger is associated with a switch for opening the gas interrupting valve. Thus there is no need to bother about adjusting the flow of gas, it is a simple on-off control.

According to a preferred embodiment, the trigger comprises a piezoelectric pulse generator. This generator operates by way of storing in a spring energy provided during initial stages of compressing the trigger and subsequently releasing the energy from the spring to create an electric impulse during a final stage of compression. Thus, the operator's manipulation of the trigger by the physical motion delays the electric impulse. Manipulation of the trigger will thus initially activate the gas interrupting valve and then at a later stage of compression release the piezoelectric generator. The operator can control the motion and is therefore able to intentionally control the delay from activation of the gas feeding and the ignition. This provides to the operator a simple way of controlling the ignition timing against the gas feeding which will ramp up the gas ratio starting from nothing. Thus by a few trials the operator may tune the timing appropriately for the particular settings and ambient circumstances.

According to a preferred embodiment, the air supply comprises a fan adapted to respond to activation of the air control means by slowly ramping up the supply of air. Thus the air feed will be small initially and will then climb to the full operative flow rate.

The fan may be connected to the combustion chamber through an air hose serving to add a delay in the entry of air into the combustion chamber.

The sequence control means may comprise an electronic delay unit for delaying the activation of air supply, e.g. according to a timer setting on the electronic delay unit .

According to a preferred embodiment, the air supply is adapted to feed air to the combustion chamber at a reduced rate during intervals without combustion of gas.

This reduced air feeding serves to cool the combustion chamber and serves to displace any gas from the combustion chamber in intermissions between active combustion.

The gas supply may comprise a container of combustible gas, a gas adjusting valve and a gas hose. The gas adjusting valve provides an option for setting the gas flow as required.

The gas hose may be arranged inside the air hose. This effectively protects the gas hose and simplifies manipulation and handling of the heating gun.

The combustion chamber may comprise a shroud for protection. This protects the operator and any surrounding matter against being charred or burned. The heating gun may preferably be adapted for diverting a part of the air flow to cool the shroud as well as the combuston chamber barrel.

According to a preferred embodiment, the gas interrupting valve, the air supply, the air control means and an electric power unit are accommodated in a utility carriage to which the heating gun is connected by a cord with the connections for gas, air and electric control. Arranging the gas interrupting valve in the utility carriage ensures that gas pressure is relieved from the gas hose for the heating gun in intervals without combustion for added safety.

The invention in a second aspect provides a gas fired heating device as recited in claim 13.

In this device the air supply is adapted to feed air for cooling at a reduced rate during intervals without combustion of gas. This cools the heating gun and scavenges the combustion chamber for any residual gas.

In a preferred embodiment, the air supply may comprise means for switching off the reduced rate air feeding contingent on an appropriate control, e.g. the expiry of a timer since suspending the combustion of gas or the temperature having dropped to a suitably low value.

The invention in a third aspect provides a method as recited in claim 15.

This method facilitates the practical applications of generating flow of hot gases by way of providing more efficient ignition inside the combustion chamber. Also the provision subsequent to ignition of a lean mixture of air and gas provides for fast and complete combustion so as to prevent escape of gas and prevent the formation of extensive flames.

Preferred embodiments appear from the appended claims

Further objects and advantages and features of the invention appear from the appended description of preferred embodiments given with reference to the drawings wherein

Fig. 1 shows a schematic drawing of the components in the device according to the invention, and

Fig. 2 illustrates a cross section in a heating gun according to the invention.

All figures are schematic and not necessarily to scale and show only items essential to the understanding of the invention, whereas other items have been deleted for the sake of clarity. Throughout the figures the same references are used for identical or similar items.

Reference is first made to Fig. 1 which shows a schematic outlay of the components in the system. Thus Fig. 1 shows a heating device 1 generally comprising heating gun 2, cord 26, utility carriage 24 and gas bottle 15. The gas bottle 15 is fitted with a gas adjusting valve 16 from which gas is communicated to gas interrupting valve 6 and from there to gas hose 17. The gas interrupting valve 6 is a normally closed valve which is opened by an electric signal provided from the electronic control unit 13. The gas adjusting valve and the electronic control unit are fitted in the utility carriage 24.

The utility carriage 24 also accommodates a fan 7 adapted for feeding air from the ambient surroundings into air hose 12. The air hose 12 comprises a flexible hose of an inside diameter of 32 mm. The gas hose 17 is also a flexible hose of a sturdy structure according to the prevailing safety standards and with an inner diameter of about 3 mm. Inside the utility carriage 24, the gas hose is routed into the interior of the air hose so as to lie generally encapsulated and protected inside the air hose. Inside the utility carriage also an electric control cable 18 from the electronic control unit is routed into the interior of the air hose so as to lie also encapsulated and protected inside the air hose.

The electronic control unit 13 comprises a power unit 14 and a means for detecting the signal from the electric control cable 18 and for outputting suitable control signals together with any necessary electric power for gas interupting valve 6 and fan 7. Thus, the utility carriage 24 to the right in Fig. 1 is connected by a single cord 26 which accommodates conduits for air and gas as well as for electric signals.

The cord 26 connects to heating gun 2 which is a unit adapted for hand held manipulation.

In another embodiment, the gas interrupting valve comprises a normally closed valve which is opened pneumatically by a pressure increment in a pneumatic control conduit (not illustrated) .

Reference is now made to Fig. 2 for a description of the heating gun 2. Fig. 2 illustrates a cross section of the heating gun 2 in order to facilitate explaining and understanding the inside structure of the heating gun. Heating gun 2 to the left connects to the cord 26 with the conduits for gas, air and for electric signalling. Gas is fed into gas pipe 22 which opens into mixing plenum 21. Air from the cord feeds into air plenum 8 from where part of the air passes through vents 20 into the mixing plenum 21 and another part of the air passes through vents 20 into the shroud cooling chamber 25 which is an annular chamber defined between the heating gun barrel 28 and the shroud 19.

From the mixing chamber, a mixture of air and gas passes through flameholder passages 23 into combustion chamber 3 where the combustion takes place. The hot gases are discharged through the muzzle 29 to the right in Fig. 2. The combustion chamber 3 in its upper portion also comprises spark plug 4.

The heating gun 2 also comprises a trigger lever 5 illustrated in the upper portion of Fig. 2. The trigger lever is spring loaded by means not particularly shown in such way as to be conveniently operable by hand. The trigger lever 5 is associated with an electric trigger switch 9 and with a piezoelectric pulse generator 10. The trigger switch 9 connects to the electric control cable 18 and thereby provides a means for electrically sensing the operation of the lever by the electronic control unit 13 (shown in Fig. 1) .

The piezoelelectric pulse generator 10 comprises a piezoelectric unit together with a spring loaded hammer and a release mechanism. The piezoelectric pulse generator by the effect of pressing the trigger lever compresses a spring so as to store energy. Towards the end of the compression motion, the hammer is suddenly relased and strikes by the action of the spring a piezoelectric unit whereby a high voltage electric pulse is generated. The high voltage electric pulse is transferred by the lead wire 11 to the spark plug 4 where an electric discharge is generated. The electric spark ignites the mixture of gas and air in the combustion chamber.

Following this description of the structure, a brief explanation of the operation shall be presented. The gas bottle stores liquid pressurized gas which is a mixture of various combustible gas constituents, mainly propane. The gas adjustment valve is set for stepping down the pressure to a predetermined value such as 0.2 bar. Other values may also be selected depending on the requirement for heat output. For instance a gas discharge presssure of 0.5 bars or of 1 bar may also be used in case a higher heat power output is required.

The fan is an electric fan driven by an electric motor. A suitable motor may be a 36 W electric motor adapted for

24 V DC in order that it may be powered by a suitable power supply comprising e.g. a 24 V battery. The power supply 14 is part of the electronic control unit 13. The power supply is provided with a control (not illustrated) adapted for permitting tuning of the power output in order to make the fan develope a rate of air supply that matches the prevailing rate of gas supply as will be evident to those skilled in the art.

Inside the heating gun, the vents and the flameholder passages generally only provide a minor throttling on the flow. Thus the flameholder passages should generally only serve to create a velocity of the mixing flow sufficient to prevent any flashback into the mixing plenum. Presuming a burning velocity of the mixture of about 0.5 m/s, a suitable velocity of the flow of mixture in the flameholder passages is 1.5 m/s.

The flow of air during normal operation must be sufficient to ensure complete combustion of the gas. With liquid pressurized gas (LPG) complete combustion of the gas according to the stoichiometric composition requires a volume of air of 25 times the volume of gas. The flow of air during normal operation must be at least equal to that value and may be higher. The upper limit to the rate of air supply is dictated by considerations regarding combustion stability to a level of about 50 times the flow of gas. Thus, in case of e.g. a burner being fed with 0.1 m³ of gas per hour the rate of air supply should be in the range from 2.5 m³ per hour up to 5 m³/h which will be set by tuning of the control.

The moment the trigger is released, this change of state is detected by the trigger switch 9 and from there by the electronic control unit 13. The electronic control unit 13 by immediately stopping the flow of gas by suitable signal to the gas interrupting valve and switching the fan from operating at full rated power down to operating at a preselected reduced level of power. This reduced level of power or idle level may e.g. be 5% of the full rated power. The combustion in the combustion chamber immediately turns off and a reduced flow of air is maintained inside the combustion chamber as well as inside the shroud cooling chamber 25. The flow of air promptly scavenges any residual gases and maintains a cooling effect so as to cool down the structure of the heating gun.

In one preferred embodiment, the heating gun comprises a thermal sensor 27 also connected by the electric control cable 18, the electronic control unit 13 and adapted for sensing the tempeature inside the heating gun at a point close to the combustion chamber. The thermal sensor senses the moment when the temperature has dropped to a suitable low value in order that the electronic control unit may then stop the fan completely.

In another embodiment, the electronic control unit comprises an electronic timer adapted for switching off power to the fan completely following the lapse of a predetermined interval of time selected so as to ensure suitable cooling of the heating gun.

The cooling of the heating gun protects the heating gun components and prevents any hazards to the operator or to the surroundings due to high outside temperatures of the heating gun.

In order to switch on again the heat output, the operator simply compresses the lever. In this state, the fan may be running at the reduced level or it may be stopped altogether. Compression of the lever first activates the trigger switch 9 causing the electronic control unit to open the gas interrupting valve 6 so as to very quickly feed gas into the combustion chamber. The electronic control unit 13 also switches the fan to full power operation. The fan, however, comprising a rotary propeller device responds fairly slowly and therefore gradually ramps up the feeding of air.

In respect of the embodiment with a pneumatically operated gas interrupting valve, the valve control conduit may be connected to the air hose and adapted to respond to the pressure inside the air hose. Preferably, the pneumatic valve is adapted for responding progressively to the pressure in the air hose and tuned to remain closed as long as the fan is running at the reduced power level and to promptly open as soon as the fan has gained some momentum over and above that level.

Continued compression of the trigger lever compresses the piezoelectric unit and, at a point close to fully compressing the lever, causes the unit to fire the spark in the spark plug. Given the slow response of the fan together with the delay line effect of the air hose and given the prompt response of the gas interrupting valve with the immediate pressurized feeding of gas, however, the gas/air mixture in the combustion chamber will at normal operation of the trigger generally be rich in gas and low in air flow at the instant the spark fires. This enhances ignition of the gas/air mixture inside the combustion chamber. The air supply is gradually ramped up and therefore intensifies the combustion, gradually taking combustion up to the normal point of operation where the quantity of air is sufficient to provide in the combustion chamber a mixture of gas and air which is lean in gas . The delay in the fan may be so significant that ignition may fail due to lack of air. If that is the case, however, the operator may keep the lever depressed in order to allow the fan to accelerate somewhat and may then release the trigger and promptly reactivate it before the fan has come to a stop, thereby causing ignition to take place at intermediate values of air flow.

By a few trials the operator will gain the experience about exactly how to ignite the unit most effectively at the prevailing conditions.

In the preferred embodiment, the gas interrupting valve 6 is a valve which is normally closed and which is opened by feeding of electric power. This is a safety precaution as the gas will not be fed out from the gas interrupting valve unless all connections are fully operational. In intervals without combustion there is no pressurized gas inside the cord from the utility carriage.

In another preferred embodiment, the electronic control unit may comprise a fan timer adapted for delaying the switching on of full fan power relative to the switching on of the gas supply. In this embodiment, the electronic control is adapted for checking whether the fan is already running and for immediately switching on the fan at the low level if necessary. This extends the time interval upon activating the lever in which a rich gas is available for ignition. Although specific embodiments have been described above it is emphasized that the invention may be exercised in several ways and that the explanation given above exclusively serves to clarify the invention and not to limit the scope of protection conferred, which is exclusively defined by the appended claims.

Claims

1. A gas fired heating device comprising

-a heating gun with a combustion chamber, an igniter and a trigger,

-a gas supply with a gas interrupting valve,

-an air supply with an air control means, and

-a sequence control means operatively associated with the trigger, with the gas interrupting valve and with the air control means in order to respond to activation of the trigger by opening the gas interrupting valve, after the expiry of a first time delay activating the igniter, and after the expiry of a second time delay activating the air control means to launch feeding of air into the combustion chamber.

2. The heating device according to claim 1, wherein the trigger comprises a spring loaded button operatively associated with a switch for opening the gas interrupting valve.

3. The heating device according to claim 1, wherein the trigger is associated with a piezoelectric electric pulse generator, driven by energy stored in a spring during initial stages of compressing the trigger and effective to create an electric impulse upon releasing the stored energy during a final stage of compressing the trigger in order to implement the first time delay.

4. The heating device according to claim 1, wherein the air supply comprises a fan adapted to respond to activation of the air control means by slowly ramping up the supply of air so as to implement tήe second time delay.

5. The heating device according to claim 4, wherein the air supply comprises an air hose adapted to delay the feeding of air to the combustion chamber.

6. The heating device according to claim 1, wherein the sequence control means comprises an electronic timer for delaying the activation of the air supply means.

7. The heating device according to claim 1, wherein the air supply is adapted to feed air to the combustion chamber at a reduced rate during intervals without combustion of gas.

8. The heating device according to claim 1, wherein the gas supply comprises a container of combustible gas, a gas-adjusting valve, and a gas hose.

9. The heating device according to claim 1, wherein the gas hose is arranged inside the air hose.

10. The heating device according to claim 1, wherein the combustion chamber comprises a shroud for protection.

11. The heating device according to claim 10, wherein the heating gun is adapted for diverting part of the air flow to cool the shroud and the combustion chamber barrel.

12. The heating device according to claim 1, comprising a utility carriage housing the gas interrupting valve, the air supply, the air control means and an electric power unit, and connected to the heating gun by a cord accommodating a hose for gas, a hose for air and an electric control cable.

13. A gas fired heating device comprising -a heating gun with a combustion chamber, an igniter and a trigger,

-a gas supply with a gas interrupting valve, -an air supply with an air control means, and -a control means operatively associated with the trigger, with the gas interrupting valve and with the air control means in order to respond to activation of the trigger by opening the gas interrupting valve, activating the igniter, and activating the air control means to launch supply of air for the combustion,

-wherein the air supply is adapted to feed air for cooling at a reduced rate during intervals without combustion of gas.

14. The gas fired heating device according to claim 13, wherein the air supply comprises means for switching off the feeding of air for cooling contingent on the temperature having dropped below a predetermined threshold value or on the elapse of a predetermined interval of time since suspending the combustion of gas.

15. A method of generating a flow of hot gas, comprising -feeding into a combustion chamber a flow og combustible gas, -igniting inside the combustion chamber a mixture of gas and air rich in gas,

-subsequent to ignition feeding into the combustion chamber a flow of air for combustion in order to establish a lean mixture of air and gas, and -ejecting from the combustion chamber a flow of hot gases .

16. The method according to claim 15, comprising feeding a flow of air for cooling of the combustion chamber exterior during intervals of combustion and feeding during idle intervals a reduced flow of air for cooling.