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Whether there should be a non return valve in gas fired, gas turbine to avoid back fire, whether it happens.
This question caused me to think a little harder than normal.
Combustion requires the fuel and air (oxygen) to be in a particular range. In a natural gas pipeline/supply, there is no air (should be no air) and so it's "safe" from the risk of ignition--until it's allowed to mix with air and be exposed to an ignition source, and then it's, well, explosive.
So, if I understand your question correctly you are concerned about the possibility of flame making it's way back through the fuel nozzle and into the gas fuel supply piping and causing an explosion and/or fire.
That would be very difficult in my opinion. First, in a combustion turbine there is a LOT of air (oxygen), actually there is as much as three to five times the amount of air required for combustion of the fuel! Only a portion of the air flowing through a gas turbine is used for combustion; the rest is used for cooling and dilution of the hot combustion gases before they enter the first stage turbine nozzle. So, if the fuel pressure/flow were to decrease to a point where the pressure was less than the pressure in the combustor (which would need to occur for an ignition source (hot combustion gases) to make it's way into the fuel nozzle/fuel supply piping) the flame in the combustor would be "blown out", extinguished.
And, even if hot combustion gases made their way back into the fuel nozzle/fuel supply piping there would likely not be sufficient air/oxygen for combustion to occur.
GE-design heavy duty gas turbines use check valves (non-return valves) in the liquid fuel line primarily as part of the pressure atomization equipment. The check valves have a "cracking" pressure of approximately 100 psig (or thereabouts; sometimes to 50 psig valves are used in series), which means that the supply pressure has to be greater than 100 psig before there will be flow through the valve in the forward direction. At 100 psig and higher as the fuel passes through the tip of the liquid fuel nozzle it is "swirled" to help with atomization of the liquid fuel particles. At pressures less than 100 psig, the atomization is very poor and there will be incomplete combustion.
But, the same is true for liquid fuel: the fuel and air (oxygen) have to be in the right proportions for combustion to occur. Even if hot gases made their way back into the fuel supply piping, unless there was sufficient air (oxygen) for combustion or ignition it probably wouldn't occur. (Now, with distillate, that mightn't be the case, but again, air (oxygen) would be required.)
In an automobile, this is what happens when "flooding" occurs. Excessive fuel for the amount of air present in the cylinder ("combustor") prevents ignition even in the presence of a spark.
I hope this helps. I spent a good deal of time ruminating on this, and possible reasons why you might be asking the question and some parallel "examples" and I came up with the same reasoning each time.
I also looked up the definition of backfire in an internal combustion engine. And it refers to an explosion (uncontrolled combustion) of fuel in the exhaust of the engine instead of in the engine. Though I have seen poorly timed internal combustion engines "backfire" through the carburetor, that's due to abnormal ignition timing in a reciprocating engine (and I've only seen or heard of that on four-stroke engines).
Combustion requires the fuel and air (oxygen) to be in a particular range. In a natural gas pipeline/supply, there is no air (should be no air) and so it's "safe" from the risk of ignition--until it's allowed to mix with air and be exposed to an ignition source, and then it's, well, explosive.
So, if I understand your question correctly you are concerned about the possibility of flame making it's way back through the fuel nozzle and into the gas fuel supply piping and causing an explosion and/or fire.
That would be very difficult in my opinion. First, in a combustion turbine there is a LOT of air (oxygen), actually there is as much as three to five times the amount of air required for combustion of the fuel! Only a portion of the air flowing through a gas turbine is used for combustion; the rest is used for cooling and dilution of the hot combustion gases before they enter the first stage turbine nozzle. So, if the fuel pressure/flow were to decrease to a point where the pressure was less than the pressure in the combustor (which would need to occur for an ignition source (hot combustion gases) to make it's way into the fuel nozzle/fuel supply piping) the flame in the combustor would be "blown out", extinguished.
And, even if hot combustion gases made their way back into the fuel nozzle/fuel supply piping there would likely not be sufficient air/oxygen for combustion to occur.
GE-design heavy duty gas turbines use check valves (non-return valves) in the liquid fuel line primarily as part of the pressure atomization equipment. The check valves have a "cracking" pressure of approximately 100 psig (or thereabouts; sometimes to 50 psig valves are used in series), which means that the supply pressure has to be greater than 100 psig before there will be flow through the valve in the forward direction. At 100 psig and higher as the fuel passes through the tip of the liquid fuel nozzle it is "swirled" to help with atomization of the liquid fuel particles. At pressures less than 100 psig, the atomization is very poor and there will be incomplete combustion.
But, the same is true for liquid fuel: the fuel and air (oxygen) have to be in the right proportions for combustion to occur. Even if hot gases made their way back into the fuel supply piping, unless there was sufficient air (oxygen) for combustion or ignition it probably wouldn't occur. (Now, with distillate, that mightn't be the case, but again, air (oxygen) would be required.)
In an automobile, this is what happens when "flooding" occurs. Excessive fuel for the amount of air present in the cylinder ("combustor") prevents ignition even in the presence of a spark.
I hope this helps. I spent a good deal of time ruminating on this, and possible reasons why you might be asking the question and some parallel "examples" and I came up with the same reasoning each time.
I also looked up the definition of backfire in an internal combustion engine. And it refers to an explosion (uncontrolled combustion) of fuel in the exhaust of the engine instead of in the engine. Though I have seen poorly timed internal combustion engines "backfire" through the carburetor, that's due to abnormal ignition timing in a reciprocating engine (and I've only seen or heard of that on four-stroke engines).
