Safe Conveyance of Sour Crude Oil Despite Demanding Process Conditions
Sour crude oil contains a high amount of impure sulfur. To convert sour crude oil into valuable and refined fuel the impurities occurring as elemental sulfur in solution and as hydrogen sulfide gas need to be removed. Due to the presence of hydrogen sulfide, sour crude oil is toxic, hazardous and extremely corrosive which makes its transportation to the preparation system challenging.
Critical applications of conveying mixtures of acidic hydrocarbon/water to the washing system have always been a challenge for any pump manufacturer. This was also the case in one recent project Lewa handled in the Emirate of Abu Dhabi. Lewa have designed and supplied 16 pumps to a major construction company in Abu Dhabi specifically designed to handle this critical application.
On the project Lewa was asked to provide a solution to pump liquid hydrocarbons from the flare knock-out drum or the blow-down drum respectively and convey the acidic hydrocarbon/water mixture back into the oil line to the washing system. Since the differences in these processes are only minor, it was possible to supply 16 mechanically identical pumps of the Lewa Ecoflow series, driven by 55 kW electric motors, measuring 2.7 x 1.9 m, 1.9 m high, and weighing 4200 kg
To ensure high reliability in operating the system, despite the project s difficult conditions, the customer defined a series of strict selection criteria. The critical fluid characteristics that had been taken into consideration while designing the pumps are: high content of sulfur of about five percent, high chlorine content, high temperatures and highly humid conditions under which even stainless steel corrodes. Since the medium conveyed is very volatile and extremely hazardous, Lewa selected hermetically tight diaphragm pump heads made of superduplex stainless steel. The diaphragm itself, due to the eroding effect of the particles in the corrosive liquid, is made of wear-resistant PTFE.
Special suction valves ensure a low NPSHr value
While designing the pumps, it was also necessary to take into consideration that the mixing ratio of water to hydrocarbons in the liquid phase varies significantly and that the pressure can vary between 20 and 45 bar. "So we designed the pumps to handle a flow rate between 0.5 and about 15 m³/h of the acidic mixture," says Sriram Iyer, who works for Lewa in Dubai. To ensure that the pumps work reliably despite the changing flow rate, the net positive suction head of the system (NPSHa) also had to be kept higher than that required at the pump suction (NPSHr). When pure hydrocarbons are conveyed on hot summer days, their vapor pressure rises and the risk of cavitation increases. Various options were analyzed with the customer to tackle this issue. Lewa offered integrated special suction valves to keep the suction pressure requirements low and satisfy all process conditions.
According to the customer, since commissioning, the installed Lewa pumps have been running smoothly and with high reliability – fulfilling the expectation of the maintenance and operating personnel. The on-call time agreement that permits uninterrupted work at the plant even when one of the pumps needs maintenance is also working seamlessly.
Picture: In all, 16 mechanically identical Ecoflow pumps were delivered by Lewa to the customer. There, they work under difficult process conditions to convey a highly volatile mixture of hydrocarbons and hydrogen sulfide conveying water back into the oil line to the washing system.. (Image: Lewa GmbH)
Source: LEWA GmbH