Hi, I'm Mark with Kimray, where we help energy producers solve their biggest control challenges.
Today, we're going to follow the pipes on a gas dehydration system.
This is the inlet to the gathering station from several different well.s
After going through the main line, slug catcher, and manifold the gas is run through compressors.
Once the gas has been compressed, it flows from the compressor discharge into the contactor tower.
Located at the base of the contactor tower, there's a 3-valve manifold which includes the gas inlet valve,
bypass valve, and gas outlet valve.
On startup, all three valves are open.
This allows gas to bypass the tower but also allows gas from the pipeline to pressurize the tower.
After the entire startup procedure has been completed the bypass valve will be slowly closed,
forcing all the gas from the compressors into the bottom of the contactor tower.
Inside the tower are trays, approximately 18" apart, as indicated on the outside by the cleanouts.
Those enclosures can be removed to clean debris off of the trays.
Three things are required to calculate the size of a glycol pump: temperature, pressure and flow rate.
The gas temperature needed for this calculation is located at the
contactor tower. On this tower, the gas temperature is currently 82 degrees.
Next, we'll look at the pressure gauge which is showing that we're operating at 760-pounds.
Flow rate can be supplied by the producer or we can find a sales point and look at the meter.
At the base of the contactor tower is a liquid level controller, dump valve and sight glass.
These components help eliminate any free water, condensate, or other contaminants from coming into
contact with the triethylene glycol or TEG in the tower.
This tower has a scrubber built into it but some locations may have a
standalone separator before it reaches the contactor tower.
Once the gas has been dehydrated within the tower,
the gas leaves the tower and flows to the meter run to be measured and sent off-site for further processing.
Before starting a dehydration unit, we should look at the level of glycol shown in the sight glass on the reboiler.
After we've made sure that the reboiler is full of glycol then we would light the burner.
The reboiler looks like a single vessel, but is actually two pieces – the reboiler and the surge tank.
Inside the reboiler is a baffle that will ensure the glycol level will always cover the fire tube.
The regenerated glycol flows over the baffle and into the surge tank.
Other control devices associated with the reboiler are a high temperature shutdown thermostat and a
thermostat that controls the main burner both are set to the appropriate settings
Inside the burner assembly, or flame arrestor, is a standing pilot and a main burner.
After the burner is lit, the TEG in the reboiler will begin to warm up to
approximately 375 degrees before we start circulating glycol.
The gas from the contactor tower also comes into this boiler skid to provide instrument gas
for the thermostat and the control valves as well as provides the drive to
make the pump operate and allow the triethylene glycol to circulate.
To recap, the bypass valve is open to allow gas to go around the contactor tower.
The outlet of the tower is open so there's equalize pressure throughout the tower.
The burner has been lit and the reboiler is up to temperature. So now it's time to
start circulating the glycol.
This is the outlet of the surge tank which is part of this reboiler.
TEG comes out of the surge tank at 375 degrees and as seen here, has burned the paint off the piping.
The glycol at this point is called "lean" or dry glycol.
It exits the surge tank and moves through the considerable amount of piping related to heat exchangers.
The Y Strainer is a simple, but important device that blocks rust or particles that may have come from the
reboiler before going into the pump.
The "lean" glycol flows to the suction of the pump through the Y strainer.
This port is referred to as the suction block.
The glycol travels through the internal workings of the pump, ending up at the discharge block of the pump.
This is the proper sound of a 450 energy exchange pump stroking.
It sounds cushion; there's no metal-to-metal sound.
This particular glycol pump is set at the lower end of its stroke rate,
probably below the recommended stall rate; however, the customer's system is
clean and good enough to allow the pump to stroke and maintain the dew point
required for the pipeline. The producer also has a unique setup where there is a
210 pump that runs during the summer months when there is less gas flowing
and the smaller pump can handle the flow.
After the lean glycol has moved through the pump it passes through this check valve which is installed to
help reduce wear and tear on the pump.
This check valve can stick and be restricted by rust,
so it's a good place to troubleshoot from time to time.
"Lean" glycol continues down this pipe underground to the contactor tower.
The natural cooling that the earth provides acts as a heat exchange and cools the
glycol down even more before it enters the tower.
The lean glycol Inlet to the tower goes up a gas-to-glycol heat exchanger.
It then enters the top of the tower and drops a glycol down through a series of trays.
As gas is coming up through the bottom of the tower, the glycol is flowing down from the top of the tower.
The gas flows up through bubble caps which forces it to contact the downward flowing glycol.
The gas gives up water and becomes drier as it passes up through each succeeding tray
to meet pipeline criteria as it leaves the top of the tower.
Water vapor in the gas is absorbed by the TEG and the lean glycol then becomes saturated with water
becoming a "rich" or wet glycol where it leaves the bottom of the tower and back
to the reboiler to be regenerated.
After the wet glycol leaves the tower it
passes through a filter canister before entering the glycol pump.
This filter is critical to reducing wear in the pump and to help avoid the plugging of heat exchangers
and must be regularly cleaned or replaced.
As it enters the pump, this "rich" glycol travels through the internal workings and helps move the pistons back and forth.
The rich glycol comes out of the pump and at
this location experiences a pressure drop from 750-pounds operating pressure to atmosphere.
It travels through this pipe and starts to be used in the glycol-to-glycol heat exchange system.
This exchange system works because the
pressure drop creates a temperature drop. That temperature drop then acts as a cooling agent.
As cool glycol is going through the pipe, the warm, dry
glycol is coming out of the surge tank on the outside of the pipe.
The wet and dry never come into direct contact with each other.
The cooling effect caused by
the movement of the two temperatures of glycol, cool the glycol down as it goes through the system.
The rich glycol comes out of the other end of the
exchanger and into the flash separator.
The three-phase flash separator
separates the rich glycol from contaminants which could include
lubrication oil, free water, and condensate.
Those contaminated liquids exit and our move to a storage tank.
The glycol comes out of this system and into the inlet of the still column.
The still column is a packed column which allows
the rich glycol to drop down through it. That glycol, rich in water, hits the 375º glycol in the reboiler.
Water, which boils at 212º, flashes off as steam.
The steam goes back through the still column but the glycol is trapped
and drops back down into the reboiler. The glycol then goes to the reboiler and
starts its journey over again, multiple times a day.
Typically the glycol will last 18 to 24 months before it needs to be changed.
The steam from a steel column enters a BTEX elimination system used to capture and recycle BTEX and V.O.C.s.
The contaminated steam is condensed back to
a liquid, collected and transferred to storage, while the residual V.O.C. vapors
are sent to the burner to be incinerated.
Want to learn more about oilfield equipment?
Keep watching the rest of our videos in Kimray's Oil & Gas 101 series.