Ignition system in industrial convenor oven

Hi All, This is my first post here,and I would try my best to state as much clearly I can. It will be great if someone in here can give some inputs regarding the ignition system and automation used in food industry.
We are discussing about upgrading our industrial baking ovens, which are of conveyor type. The conveyor oven contains dies on it which rotates on the big gas stove.
The main reason of upgrading our system is for two reason , one is safety and the other is heat control system. The safety reason is very important, as the operators who ignites daily the oven ,does it by manually by throwing fired paper on the opened LPG gas. Sometimes, the operators doesn't open air valve much and by the time they realise it , they feel burst fire.
There are total seven such big ovens and few of them had the ignition system which was like pilot valves opens first and then the main valve. This system used to give lot of starting problem and at last our people have bypassed this ignition system.
If you need any more information, I'll try to provide as much I can. My main concern here is the safety of the operators, and I would like to let you know these oven operators are great and they practically know how much to open up valves to let LPG flow for the required baking of the wafers and other stuff. Since, our oven temp sensors are not accurate and the pressure gages are broken much. Please let me know what are the best valves and the sensors and controls to used.

Some details of oven :
Fuel : LPG
Temp control : manually adjust the fuel valve
Temp range : 230- 270 C
Pressure of Inlet LPG: 2kg

Fireye and Honeywell are my first thoughts.

See link

http://www.industrialcontrolsonline...aign=branded&gclid=CMbZ24zch68CFckJRQodMn9WAw

I take it new ovens are not an option.

Sounds like a near rebuild / overhaul of each oven is needed.

Honeywell and or Fyereye are my first thoughts also.

You may wish to consider another option that may or may not be good for you. The oven on my boat stove (LPG) has a pilot light that must be lit at all times to allow the main flame valve to turn on. From you description this alone would be an improvement.

Here in USA this project would have more inspectors than workers. Find out who they are and get a good idea of what they want. Find out what codes are acceptible to them. Get copies of the lates codes from them if you can.

I would get a good combustion controls guy in there. You will maybe also have to control stack gas temperature (you should anyway to ensure efficiency and to ensure stack gas temp is high enough to prevent condensation.

IF you are supplying gas from the headspace in LPG tank and you have no evaporator then you can use the tank as a source of "cold" and use it to help refrigerate if needed or air conditioning.

Gages valves etc etc should be rated for LPG and working pressure. Get gages with liquid damping.

Temperature monitoring and controls - with this many ovens I think it would be worthwhile to spend a little money to enable self checking and calibration of RTD based temperature measurement. Thermocouple is another option.

Each oven should have a gas shut off valve to allow service work. In addition I would considr putting in a master valve near an outside exit so that if something goes wrong you can leave shut off all gas and get outside. Fire department may want one also on building exterior.

Dan Bentler

I used to work on the control systems of brick kilns (tunnel kilns), similar to your conveyor oven, only larger and hotter.
While gas ignition was initiated by a PLC, the safety part of it was via a special mechanical burner relay.
Unfortunately, I can't remember the brands for any of this equipment, but the types of equipment needed were:
- Cutoff valve for the gas, this was for a whole bank of burners.
- Gas control valve for each burner
- Ignition circuit, the burners had in built spark plugs for ignition
- Valve for controlling air flow
- Flame detectors, these detected that ignition had occurred
- Gas safety relay, this was a mechanical relay that connected to the gas valve cut off, triggered the ignition circuit and took the flame detectors as an input. This relay had an inbuilt timing circuit to handle the startup sequence.
- PLC with thermocuoples handled the gas and air flow, along with controlling the temperature.

If we lost flame at any time, the gas safety relay would drop out and cut off that burner.

Some safety reated PLCs, Pilz especially, are rated for burner control and can replace the mechanical burner control relays. We did not use them because all our equipment had to be cirtified by the Australian Gas Association (I think I got the name right), and the Pilz safety PLC had not been cirtified at that point.

Sorry I can't give you a list of equipment or diagrams, but hopefully you will be able to research this.
Maybe start with Pilz and look up burner control.

Thanks everyone for the inputs, Ill discuss these suggestions with maintenance head and keep you update of the rebuilding of the ignition system in the oven.