EP0531072A1

EP0531072A1 - Improvements in or relating to flame safeguard devices

Info

Publication number: EP0531072A1
Application number: EP92307883A
Authority: EP
Inventors: Roger M. c/o British Ceramic Service Forrester
Original assignee: BRITISH CERAMIC SERVICE Co Ltd
Current assignee: BRITISH CERAMIC SERVICE Co Ltd
Priority date: 1991-09-03
Filing date: 1992-08-28
Publication date: 1993-03-10
Also published as: GB9118790D0

Abstract

A burner assembly (10) suitable for a kiln comprises a pilot burner (14) and a main burner (12). The burner assembly also comprise means (22,25) for controlling a supply of fuel to the pilot burner and to the main burner. A first flame sensor (20) is provided for the pilot burner, and a second flame sensor (32) is provided for the main burner. The control means is adapted to be selectively connected to the first flame sensor on the second flame sensor.

Description

The present invention concerns improvements in or relating to flame safeguard devices, especially such devices when used in kilns
Flame safeguard devices have long been employed, these devices ensuring that fuel, for example gas, is supplied to a burner only when the burner flame is ignited or when an ignition cycle is in operation, for example, a spark plug is being actuated.
There are many proprietory control devices which combine automatic fuel shut-off, ignition, timer and flame detection functions. Such devices come in many forms but will be referred to herein, in general terms, as "flame safeguard controllers". A controller of this nature may be so designed that when it is actuated to ignite a burner it initiates an ignition cycle, for example, it causes a spark plug to spark. A timer then operates for a predetermined time during which the controller checks that a good spark is being generated. At the end of the time, the controller opens a solenoid valve thereby allowing air/fuel mixture to the burner, the mixture being ignited by the spark which continues to spark until a probe in the burner senses the existence of a flame and after a further predetermined time when the flame stability is ensured the controller stops the ignition cycle. The probe then continues to monitor the flame and if it detects flame failure the controller closes off the fuel supply to the burner.
In modified burners, ignition may be achieved by a constantly ignited pilot but such systems are disadvantageous in that in certain conditions the pilot may be extinguished and in others the pilot may fail to immediately ignite the flame of the main burner. Clearly either of these situations could give rise to serious consequences.
It is an object of the present invention to obviate or mitigate these and other disadvantages.
According to one aspect of the this invention there is provided a burner assembly comprising a pilot burner and a main burner control means for controlling a supply of fuel to the pilot burner and to the main burner, characterised by a first flame sensor for the pilot burner and a second flame sensor for the main burner, the control means being adapted to be selectively connected to the first flame sensor or the second flame sensor.
Preferably the assembly also includes changeover means connected between said control means and said first and second flame sensors to effect said selective connection of the control means to the first or second flame sensor.
The control means may comprise first means for controlling the supply of fuel to the pilot burner second means for controlling the supply of fuel to the main burner and a flame safeguard controller associated with said first and second control means and connectible to said first and second sensors.
According to another aspect of the present invention, there is provided a burner assembly including a pilot burner and a main burner, first means for controlling the supply of fuel to the pilot burner, second means for controlling the supply of fuel to the main burner, a first flame sensor for the pilot burner, a second flame sensor for the main burner, a flame safeguard controller connectible with said first and second valves and with said first and second probes and changeover means to selectively connect the controller with the first probe or the second probe dependent upon the position of the second control means.
Preferably said changeover means comprises a relay arrangement adapted to switch the connection of the controller with the first sensor to the second sensor on a transmission of a signal being passed to the second control means to open the fuel supply to the main burner.
Preferably means are provided to cause the main burner to operate constantly, intermittently in response to temperature control means or in a pulsed manner.
According to another aspect of the invention there is provided a method of operating a burner assembly comprising igniting a first flame in a pilot burner, sensing the first flame with the use of first flame sensor connected to control means supply fuel to a main burner to ignite a second flame in the main burner disconnecting the control means from the first flame sensor and connecting said control means to a second flame sencor to sense said second flame.
Preferably said pilot burner is ignited by transmitting a signal from said control means to a spark plug to generate a spark in said pilot burner and thereafter supplying fuel to said pilot burner from a pilot burner fuel line.
Said spark plug may be caused to spark by said control means for a predetermined period of time.
Said fuel may be supplied to said pilot burner by opening of a valve on said pilot burner fuel line by said control means after said predetermined period of time to ignite said first flame.
The sparking of the spark plug may be maintained for a further predetermined period while said flame at said pilot burner is being sensed.
Preferably said sparking is stopped after said predetermined period of time and the sensing of the first flame at the pilot burner is maintained.
The connection between the control means and the first sensor may be changed over to a connection between the control means and the second sensor by changeover means substantially simultaneously with said step of supplying fuel to the main burner.
Preferably the fuel supply to the main burner is shut off after another predetermined period of time, and said connection between the control means and the second sensor may be changed substantially simultaneously therewith to said connection between the control means and the first sensor.
An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawing which shows diagrammatically a burner assembly for a kiln and same of its associated control equipment.
A burner assembly 10 for a kiln is intended to operate in a pulsed fashion, that is it is ignited for a relatively short period of time, for example a few seconds, and the extinguished for a further short period of time, which again may be a few seconds or parts of seconds. Burner assemblies operated in this fashion are desirable in that they can lead to ease of installation in the kiln and flexibility in operation and control. Temperature control within the kiln is determined by, for example, varying the duration of pulses either during a burner or cycle or during a burner shut-down cycle or both.
It will be self evident that in a burner which is ignited and extinguished with this frequency it is essential that there is a secure flame safeguard control which ensures that fuel is not supplied to the burner if there is nothing present to ensure ignition of the fuel.
The burner assembly 10 shown in Fig. 1 has a main burner 12 and a pilot burner 14 so situated within the assembly that the pilot will ignite any fuel/air mixture in the main burner.
The pilot 14 is supplied by a first gas line 16 which has a first solenoid operated control valve 18 incorporated therein. A combined ignitor of the sparking plug type and flame detecting probe 20 is provided in the pilot 14.
There is provided also a flame safeguard controller 22, the construction and operation of which does not form part of the present invention and consequently will not be described in detail in this specification. The first control valve 18 is connected to the controller by a lead 19 and the combined ignitor and first probe 20 is connected thereto by a lead 21 which inccorporates an ignitor transformer 23. The controller 22, on receipt of a signal to light the burner 10 causes the spark plug of the ignitor 20 to spark for a period of time which is determined by the controller and during this time controller ensures that a satisfactory spark is being generated. At the end of the predetermined time the controller causes the first solenoid valve 18 to open thereby allowing a gas/air mixture to pass to the pilot, the air being supplied by a pipe 24 and the mixture being ignited by the spark plug which continued to spark while the probe with which it is combined confirms that a constant flame has been established in the pilot 14. The controller then shuts off the supply to the spark plug 20 but the probe remains in operation sensing the presence of a flame in the pilot 14 so that if the pilot flame fails the fuel supply can be cut off by closing the first solenoid operated valve 18.
A further pulse generating assembly 25, which again does not form part of the present invention and consequently will not be described in detail, can then determine that the main burner 12 should be ignited and provided that the controller 22 is sensing that the pilot 14 remains ignited a second solenoid valve 26 in a gas supply line 28 can be opened by a signal passed from the controller through lead combination to supply fuel to the main burner 12, air being supplied through pipe 30. This mixture is ignited by the pilot flame. The main burner is provided with an independent flame sensing probe 32 which is conected to the controller by a lead 33.
The leads 21, 33 to the pilot and main burner probes 20,32 connect to a relay arrangement 40 connected by a lead 42 to the flame safeguard controller 22. The signal passed through the lead 27 via relay 43 to cause the opening of the second valve 26 simultaneously actuates the relay arrangement 40 to change the connection of the flame safeguard controller 22 with the pilot probe 20 to the second main burner probe 32, the first valve 18 remaining in its opened condition at all times so that the pilot remains constantly ignited. A predetermined time cycle of the controller 22 then commences during which time a signal is generated by the probe 32 to show that the main burner flame has been established. Operation is then maintained but if a flame is not detected in the main burner the controller 22 closes the second valve 26.
When the pulsing apparatus 25 indicates that the main burner should be extinguished a signal is generated to close the second valve 26 then causing the relay 40 to switch over such that the pilot probe 20 is again connected to the safeguard controller 22.
The apparatus described with reference to the drawings thus provides a burner assembly which can be safely operated on a pulsed cycle as the single flame safeguard controller 22 ensures that excess quantities of unburned fuel cannot be emitted from the burner assembly. The burner assembly has a constant flame 14 at the pilot burner and pulsed operation of the main burner is achieved in any desired fashion by the pulse generator 25. In a modification the pulse generator can be substituted by a thermostatic arrangement which controls the fuel supply to the main burner. It will be realised that a separate flame safeguard controller could have been provided for the supply to the main burner. This would have considerably reduced the efficiency of the pulse firing cycle of the main burner, bearing in mind that the controller has a built in delay at every flame ignition cycle and as this delay can be greater than the duration of the pulse required or, more especially, the shut-off period,-the controller would not be suitable for this application.
Additionally, the unique use of the changeover relay assembly 40 means that a standard flame safeguard controller can be used in a pulse firing situation and the single flame safeguard control assembly can be utilised to monitor not only the condition of the pilot but also the main burner.
Various modifications can be made without departing from the scope of the invention, for example, the arrangement of burners can be different from that shown in the drawings the circuitry between the valve sensor, ignitor etc. and the controller may be varied in any appropriate manner.
Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

A burner assembly (10) comprising a pilot burner (14) and a main burner (12), control means (22,25) for controlling a supply of fuel to the pilot burner (14) and to the main burner (12), characterised by a first flame sensor (20) for the pilot burner and a second flame sensor (32) for the main burner (12), the control means (22,25) being adapted to be selectively connected to the first flame sensor (20) or the second flame sensor (32).
A burner assembly according to Claim 1, characterised by changeover means (40) connected between said control means (22,25) and said first and second flame sensors (20,32) to effect said selective connection of the control means (22,25) to the first or second flame sensor (20,32).
A burner assembly according to Claim 1 or 2, characterised in that said control means (22) comprises first means for controlling the supply of fuel to the pilot burner (14), second means (25) for controlling the supply of fuel to the main burner (12) and a flame safeguard controller (22) associated with said first and second control means and connectible to said first and second sensors.
A burner assembly including a pilot burner and a main burner (12), first means (22) for controlling the supply of fuel to the pilot burner, and second means (25) for controlling the supply of fuel to the main burner, characterised by a first flame sensor (20) for the pilot burner, a second flame sensor (32) for the main burner (12), a flame safeguard controller (22) and associated with said first and second control means and connectible to said first and second sensors, and changeover means (40) to selectively connect the controller with the first sensor (20) or the second sensor (25) dependent upon the position of the second control means.
A burner assembly according to any preceding Claim, characterised in that said changeover means comprises a relay arrangement (40) adapted to switch the connection of the controller (20) with the first sensor (20) to the second sensor (32) on a transmission of a signal being passed to the second control means (25) to open the fuel supply to the main burner (12).
A burner assembly according to any preceding Claim, characterised in that means are provided to cause the main burner (12) to operate constantly, intermittently in response to temperature control means or in a pulsed manner.
A method of operating a burner assembly comprising igniting a first flame in a pilot burner (14), sensing the first flame with the use of first flame sensor (20) connected to control means (22,25), supplying fuel to a main burner (12) to ignite a second flame in the main burner (12), disconnecting the control means (22,25) from the first flame sensor (20) and connecting said control means to a second flame sensor (32) to sense said second flame.
A method according to Claim 7, wherein said pilot burner (14) is ignited by transmitting a signal from said control means (22,25) to a spark plug to generate a spark in said pilot burner (14), and thereafter supplying fuel to said pilot burner (14) from a pilot burner fuel line.
A method according to Claim 8, wherein said spark plug is caused to spark by said control means (22,25) for a predetermined period of time.
A method according to Claim 9, wherein said fuel is supplied to said pilot burner (14) by the opening of a valve (18) on said pilot burner fuel line by said control means (22,25) after said predetermined period of time to ignite said first flame.
A method according to Claim 10, comprising maintaining said sparking of the spark plug for a further predetermined period while said flame at said pilot burner (14) is being sensed.
A method according to Claim 11, wherein said sparking is stopped after said predetermined period of time and the sensing of the first flame at the pilot burner (14) is maintained.
A method according to any preceding claim comprising changing over said connection between the control means (22,25) and the first sensor (20) to a connection between the control means (22,25) and the second sensor (32) by changeover means (40) substantially simultaneously with said step of supplying fuel to the main burner.
A method according to any preceding claim, comprising shutting of the fuel supply to the main burner (12) after another predetermined period of time and substantially simultaneously changing said connection between the control means (22,25) and the second sensor (32) to said connection between the control means and the first sensor.