One of the most difficult and important applications for many off-shore installations is the injection of methanol or ethanol at high pressure.
In addition to being toxic these fluids also are non-lubricating and flammable so the elimination of glands and complete freedom from leakage and monitored containment afforded by diaphragm pumps combined with their inherent safety and environmental consideration is of critical advantage to the user.
Before start-up or during operation, the injection is a must to prevent hydrates and icing. Stopping the injection would result in an expensive and extremely undesirable production stop.
The market offers a selection of proven sandwich diaphragm metering-and process diaphragm pumps for this application. The designs offered are in use since more than 30 years, some installations (1000bar/14.500psig) (North Sea, West Africa, Golf of Mexico; South America) since more than 10 years.
PTFE diaphragms are very notch-insensitive and can easily cope with solids and rust particles and & ethanol because of their transportation in non-stainless steel tanks.
One of the biggest fears of off-shore operators is that the stand-by pump is being switched-on and does not perform. In the harsh and corrosive off-shore environment this is a frequent problem for packed plunger pumps where the ambient conditions can lead to pitting of the metallic plunger by high humidity and salt spray. Modern diaphragm pumps are designed to avoid this problem as the plunger operates in an oil bath, also properly designed diaphragm pumps are able to withstand high suction pressures. Dry start-up and operation will, contrary to packed plunger pumps, not damage a diaphragm pump.
Long service life of PTFE (20000h) and stainless steel diaphragms (10000h) are the basis for continuous, uninterrupted, low cost operation.
State of the art manufacturers offer condition monitoring systems – evaluating several pump operating conditions. Early recognition of even developing problems makes a scheduled shut-down possible saving even more time and money.
The more recent applications in the field of H2S and CO2 re-injection require the largest diaphragm pumps available to date.

LEWA GmbH is based in Leonberg, Germany. www.lewa.com