Please assist me on this. what are the effect of condensate on gas turbine operation, in the aspect of megawatt skyrocketing from lower value of MW to outrageous value which lead the unit to trip on high exhaust temp. Frame 6b gas turbine. with MARK 6 control system.

what could cause the unit to be affected by condensate.

 

@Akin,

It's presumed to be natural gas condensates you are referring to. Please confirm.

It's been said that a single quart (less than 1 liter) of natural gas liquids (condensate) will cause a 10 MW bump on a GE-design Frame 5 heavy duty gas turbine-generator. So, it would probably be a little higher for a Frame 6B (since it will generally burn more fuel, that is, increased fuel flow-rate).

What could be the sources of natural gas condensate or liquids? For most GE-design heavy duty gas turbines the OEM recommends the natural gas have at least 50 deg F of superheat in order to prevent condensates from forming as the gas flows through the gas control valves and through the gas fuel nozzle passages in the combustors. Every pressure drop will result in a temperature drop, so if the natural gas's dewpoint temperature is very close to the actual natural gas temperature of the incoming fuel then it's a pretty sure bet that natural gas condensates will form. Often if natural gas condenses as it flow through the gas control valves it will form a small pool in the piping between the gas control valves and the bottom of the gas fuel manifold(s) in the turbine compartment. When the pool gets large enough to be displaced by the flow-rate of the natural gas fuel it will be blown into the fuel nozzles and into the the combustors, usually, the lowest combustors but not always just the lowest combustors. And that's when the "fun" begins--the temperature of the combustion gases rises significantly which causes the work extracted by the turbine section to spike (often significantly--particularly when the machine is running at or near Base Load) and also results in excessive exhaust temperatures as sensed by the exhaust thermocouples.

Natural gas liquids can be moved along in a natural gas supply pipeline by the flow-rate of the gas as it enters the turbine and similar things can happen, usually with similar results. HOWEVER, many different liquids have been found in natural gas supply pipelines, including gasoline, diesel fuel, and natural gas compressor fluids and/or hydraulic fluids. Many natural gas suppliers these days are negligent when it comes to supplying clean, dry natural gas to their customers (and that includes removing or reducing silica which can plate on the gas control valve internals and cause increased wear/erosion of gas control valve internals).

Another possible source of natural gas liquids would be from a non-working or full so-called "knock-out" drum (basically a cyclone separator) which is designed to remove most all entrained liquids (gasoline; diesel fuel; natural gas compressor lubricating oil; natural gas compressor seal oil; hydraulic oil; water; etc.) but isn't working or isn't draining or being drained properly. The liquids can "spill over" into the natural gas flow and cause unwanted problems such as you are describing. (Not all installations use knock-out drums/separators but many do and if the gas is known to have entrained liquids or low dew-point temperatures then the installation and proper use of a knock-out drum/separator is highly recommended and prudent. But it must be checked and observed to be working properly, and properly maintained and kept in operation. (I once visited a site which was having LOTS of exhaust over-temperature trips and was told the knock-out drum was working properly. When we opened the drain we filled a 5-gallon bucket with liquids. And when the separator was opened it was found the internals had been removed (nobody knew when...) and never replaced (and couldn't be found).)

Again, presuming you are referring to natural gas condensates or liquids the above should answer most, if not all, of your questions (even the ones you didn't ask).

 

@Akin,

It's presumed to be natural gas condensates you are referring to. Please confirm.

It's been said that a single quart (less than 1 liter) of natural gas liquids (condensate) will cause a 10 MW bump on a GE-design Frame 5 heavy duty gas turbine-generator. So, it would probably be a little higher for a Frame 6B (since it will generally burn more fuel, that is, increased fuel flow-rate).

What could be the sources of natural gas condensate or liquids? For most GE-design heavy duty gas turbines the OEM recommends the natural gas have at least 50 deg F of superheat in order to prevent condensates from forming as the gas flows through the gas control valves and through the gas fuel nozzle passages in the combustors. Every pressure drop will result in a temperature drop, so if the natural gas's dewpoint temperature is very close to the actual natural gas temperature of the incoming fuel then it's a pretty sure bet that natural gas condensates will form. Often if natural gas condenses as it flow through the gas control valves it will form a small pool in the piping between the gas control valves and the bottom of the gas fuel manifold(s) in the turbine compartment. When the pool gets large enough to be displaced by the flow-rate of the natural gas fuel it will be blown into the fuel nozzles and into the the combustors, usually, the lowest combustors but not always just the lowest combustors. And that's when the "fun" begins--the temperature of the combustion gases rises significantly which causes the work extracted by the turbine section to spike (often significantly--particularly when the machine is running at or near Base Load) and also results in excessive exhaust temperatures as sensed by the exhaust thermocouples.

Natural gas liquids can be moved along in a natural gas supply pipeline by the flow-rate of the gas as it enters the turbine and similar things can happen, usually with similar results. HOWEVER, many different liquids have been found in natural gas supply pipelines, including gasoline, diesel fuel, and natural gas compressor fluids and/or hydraulic fluids. Many natural gas suppliers these days are negligent when it comes to supplying clean, dry natural gas to their customers (and that includes removing or reducing silica which can plate on the gas control valve internals and cause increased wear/erosion of gas control valve internals).

Another possible source of natural gas liquids would be from a non-working or full so-called "knock-out" drum (basically a cyclone separator) which is designed to remove most all entrained liquids (gasoline; diesel fuel; natural gas compressor lubricating oil; natural gas compressor seal oil; hydraulic oil; water; etc.) but isn't working or isn't draining or being drained properly. The liquids can "spill over" into the natural gas flow and cause unwanted problems such as you are describing. (Not all installations use knock-out drums/separators but many do and if the gas is known to have entrained liquids or low dew-point temperatures then the installation and proper use of a knock-out drum/separator is highly recommended and prudent. But it must be checked and observed to be working properly, and properly maintained and kept in operation. (I once visited a site which was having LOTS of exhaust over-temperature trips and was told the knock-out drum was working properly. When we opened the drain we filled a 5-gallon bucket with liquids. And when the separator was opened it was found the internals had been removed (nobody knew when...) and never replaced (and couldn't be found).)

Again, presuming you are referring to natural gas condensates or liquids the above should answer most, if not all, of your questions (even the ones you didn't ask).

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