Worldwide more and more oil and natural gas is being extracted under conditions that are becoming increasingly extreme: for example, on the high seas or in the frozen polar sea. All plants and systems involved in their extraction must therefore be specially designed for adverse on-site conditions. This also applies to odorizing systems that add odorants to LPG (liquefied petroleum gas), which consists of virtually odorless butane and propane. An international group that transships LPG at a loading terminal in Beira, Mozambique, wanted a suitable system for this purpose. The system needed to be usable both at sea and at the terminal itself.
"After receiving the special order to supply an odorizing system for operation on land and at sea, we first had to consider the different factors that are relevant for such an application," said Walter Richter, Head of Sales Odorization & Gas Distribution at Germany-based LEWA GmbH. "The main focus was resistance to seawater, the option to transport the system easily, and current-free system operation." Since the system would also be used on board a ship, it first had to be integrated into a stainless steel cabinet to protect it from splash water and waves hitting the deck. To increase its corrosion resistance, it was also coated with offshore paint. Since the plant needed to be protected against salt water even when its doors are open, the integrated pump and drip pan were also coated with this paint.
PKH compressed air pump also works without current
"Due to the fact that there is no electrical power available at the installation site on the ship's deck, we had to work out a system without current-dependent components," explained Richter. "This was mainly reflected in the choice of pump and the type of metering." The PKH compressed air pump, a purely pneumatic unit which is designed for the gas flow of 500 m3 per hour at 30 bar required on site, was installed. The odorant added to the LPG as it flows through is metered via a mechanically pre-set throttle valve with a fixed dosing rate, so that no electronic control is necessary.
The common additive ethyl mercaptan is used for odorization in this system. "In the case of LPG, this chemical compound is preferable to the alternative THT (tetrahydrothiophene), as the latter mixes inadequately with the liquid gas," Richter added. The odorant tank has a capacity of 200 liters. An additional lifting device can lift it out of the cabinet for filling.
Lifting cage enables change of operating location
Due to the customer's requirement for using the system both at sea and alternately in a terminal on land, a lifting cage was also installed around the odorizing system. It enormously facilitates system transport, since neither dismantling nor cumbersome packaging is required for movement by crane. "All in all, the system can be used flexibly and is independent. At the same time, it is protected against adverse influences such as seawater. In addition, the plant was certified in accordance with the current international ASME standard," Richter said in summary. The odorizing system is to be installed by the middle of this year.