jhamil1
Mechanical
- Oct 28, 2008
- 18
All,
Thank you in advanced for the help/advise. I have a situation where the fuel gas used by the compressor units is coming from either the discharge side (1008 psi @ 98-120degF) or the suction side (700 psi @ 58-68 degF) of the pipeline. Typically the fuel gas is ran from the discharge side in winter and suction side during the summer. The fuel gas is typically supplied to the engines @ 40 to 60 psi. Thus, the gas must be cut down using fuel regulators. The first cut regulators cut the pressure down to 210 psi, then it goes into a coalescer. From the coalescer, it goes to a second cut regulator that knocks the pressure down to 60 psi. The problem is that the first cut regulator is failing due to what the operators call "sludge". Click the following link for a schematic of the current situation.
The question I was asked to solve, "Can we move the first cut regulators after the coalescer, so it will 'filter' the gas and keep the regulator from failing?" I am new to the industry and have a lot to learn, but I am trying to dig deeper instead of relying on word of mouth. That being said, I have a few questions.
This is already processed gas coming up the pipeline from the operators. Below is the gas analysis of the gas entering this station in mol percent.
CO2 - 1.595
N2 - 0.556
C1 - 94.264
C2 - 2.840
C3 - 0.469
iC4 - 0.071
nC4 - 0.096
iC5 - 0.032
nC5 - 0.024
C6+ - 0.053
First I began reading relevant information in the GPSA engineering data book on dehydration. My first response to the problem is that the first cut regulator pressure drop is to large, dropping the temperature below the water and hydrocarbon dew point causing hydrate formation in the fuel regulator. I read the methods on how to find the water content and hydrate condition using the Katz method for an estimation. I then downloaded the GCAP software and plotted the phase diagram for the natural gas components and plotted the dew point curves for the hydrocarbons and water; compared this value to the GPSA estimates. BUT, this model assumes this is production gas NOT processed gas.
1.) Is this a correct assumption?
If it is, this is where my dilemma begins.
2.) Since this is processed gas, wouldn't the dew point curve of both water and hydrocarbons shift towards the phase diagram of the gas composition (i.e. to the left)?
I have also found a requirement for natural gas specifications in the salable gas stream from the GPSA data book. It states the water content is a maximum of 4-7 lb/MMscf and the hydrocarbon dew point to 15 degF and 800 psig. If this is the correct assumption, the regulator would never drop liquids from the gas. Thus, leading to the question "what is clogging up the regulators?" I do have some other ideas as to why but I would like to address this topic first.
---Addition Information---
Prior to entering the station, the gas travels through a scrubber.
---Other Questions---
3.) Does a coalescer remove the heavy hydrocarbons or only water from the gas or both?
4.) Is the term scrubber accurate or is it a slug catcher. If scrubber is the correct term, what function does it perform?
Again, I know there is a lot of questions, if you could answer them by numbering the answer with the question it would be appreciated. That way we can all keep track of responses.
Thank you in advanced for the help/advise. I have a situation where the fuel gas used by the compressor units is coming from either the discharge side (1008 psi @ 98-120degF) or the suction side (700 psi @ 58-68 degF) of the pipeline. Typically the fuel gas is ran from the discharge side in winter and suction side during the summer. The fuel gas is typically supplied to the engines @ 40 to 60 psi. Thus, the gas must be cut down using fuel regulators. The first cut regulators cut the pressure down to 210 psi, then it goes into a coalescer. From the coalescer, it goes to a second cut regulator that knocks the pressure down to 60 psi. The problem is that the first cut regulator is failing due to what the operators call "sludge". Click the following link for a schematic of the current situation.
The question I was asked to solve, "Can we move the first cut regulators after the coalescer, so it will 'filter' the gas and keep the regulator from failing?" I am new to the industry and have a lot to learn, but I am trying to dig deeper instead of relying on word of mouth. That being said, I have a few questions.
This is already processed gas coming up the pipeline from the operators. Below is the gas analysis of the gas entering this station in mol percent.
CO2 - 1.595
N2 - 0.556
C1 - 94.264
C2 - 2.840
C3 - 0.469
iC4 - 0.071
nC4 - 0.096
iC5 - 0.032
nC5 - 0.024
C6+ - 0.053
First I began reading relevant information in the GPSA engineering data book on dehydration. My first response to the problem is that the first cut regulator pressure drop is to large, dropping the temperature below the water and hydrocarbon dew point causing hydrate formation in the fuel regulator. I read the methods on how to find the water content and hydrate condition using the Katz method for an estimation. I then downloaded the GCAP software and plotted the phase diagram for the natural gas components and plotted the dew point curves for the hydrocarbons and water; compared this value to the GPSA estimates. BUT, this model assumes this is production gas NOT processed gas.
1.) Is this a correct assumption?
If it is, this is where my dilemma begins.
2.) Since this is processed gas, wouldn't the dew point curve of both water and hydrocarbons shift towards the phase diagram of the gas composition (i.e. to the left)?
I have also found a requirement for natural gas specifications in the salable gas stream from the GPSA data book. It states the water content is a maximum of 4-7 lb/MMscf and the hydrocarbon dew point to 15 degF and 800 psig. If this is the correct assumption, the regulator would never drop liquids from the gas. Thus, leading to the question "what is clogging up the regulators?" I do have some other ideas as to why but I would like to address this topic first.
---Addition Information---
Prior to entering the station, the gas travels through a scrubber.
---Other Questions---
3.) Does a coalescer remove the heavy hydrocarbons or only water from the gas or both?
4.) Is the term scrubber accurate or is it a slug catcher. If scrubber is the correct term, what function does it perform?
Again, I know there is a lot of questions, if you could answer them by numbering the answer with the question it would be appreciated. That way we can all keep track of responses.