Diaphragm metering pump skids for glycol injection in gas dehydration
- Glycol Injection Package
Process description of glycol injection and advantages of diaphragm metering pumps:
Glycol is used for gas dehydration mostly. There are cases, especially when the moisture rate is low, when
- methanol is injected to reduce the freezing point of the water downhole (hydrate formation)
- during transportation – in Germany in wintertime when consumption increases or peaks
- when there is a supply shortage and gas stored in underground caverns is fed into the distribution system
During the underground storage the gas will absorb moisture from the surrounding salt dome and requires treatment. Methanol can be burned together with the gas and usually does not require secondary treatment and removal like glycol.
Faster dehydration and higher gas flows:
When the gas flows are higher and the moisture content is elevated glycol (different kinds - EG, TEG, MEG) is used which absorbs the moisture in the gas and allows trouble free compression and further transportation of the gas. There are different processes from simple injection to so called high speed trays (GESIP® process) which provide faster dehydration and allow higher gas flows.
The glycol is separated from the gas taking the moisture along and its pH-value is measured - the moisture absorbed naturally contains other contaminations such as H2S, sulfur and solids which make the water acidic and extremly corrosive.
The problem is solved by injecting caustic soda to neutralize the water; then the glycol is heated to around 120° C causing the water content to evaporate. Then the glycol is ready to be reused and injected into the incoming gas again. In addition to glycol injection any big dehydration package always requires one or more chemical injection packages for neutralization.
As glycols are not as dangerous as many other chemicals pumped in the different injection processes of the oil and gas industry plunger pumps are used in some installations. Glycol is slightly harmful to water only and non-explosive.
Process advantages by using diaphragm metering pumps:
However, over the years, many plunger pump installations have caused severe problems, especially when the stand-by pump installed was switched on because the main pump needed service or broke down. Offshore the humidity is high, salt-spray is present day and night. The surface of the plunger will collect humidity, minor glycol leakages worsen the problem because salt crystals stick to it. On many occasions the plunger surface was pitted by electrolytic corrosion already when the stand-by pump was started. This caused instant plunger packing problems as the pitted plunger damaged the packing and ‒ since the main pump was down in the first place – the operation had to be stopped to avoid compressor damage. The costs and production losses caused by this don't need further explanation!
So, for a seemingly less dangerous and basically uncomplicated application spending a little bit more money for a zero leakage, hermetically tight diaphragm pump where all moving parts operate immersed in protecting and lubricating hydraulic oil will pay back big time in actual operation. Another major advantage – repacking a plunger pump properly requires lots of special knowledge to make sure that the packing rings are installed and rotated correctly and the stuffing box is not too much tensioned which means excessive wear, not to mention the requirement for scheduled retightening.
Anybody capable of exchanging a car wheel and handling a torque wrench is also perfectly able to replace a damaged diaphragm – frequently after 20.000 h and more of continuous service. Looking at the total cost of ownership (TCO) often makes a decision easy and money saving – LEWA offers the equipment required to assist you in this by low down times, fast and low cost maintenance and, very efficient pumps with little friction losses and reduced energy consumption. Save, in a long future and make LEWA your partner from engineering to preventive maintenance. Adding a LEWA condition monitoring system (LEWA CMS) to your high quality pump and package will make a good thing even better!
