Introduction
Whilst OPEC Ltd. has been involved in the development of a range of oil spill clean up equipment for emergency oil spill response, the company has also been developing an extensive range of products to deal with the minor spillage of oils and floating chemicals, as well as setting up permanent installations.
The evolvement of permanent installations has been born out of necessity, on the basis of "prevention is better than cure". The company's activities have been wide spread in terms of types of locations and varying deployment specifications of the wide range of equipment that is now available. There are addendums to this case history which clearly illustrate the types of installations and locations that are now in operation world wide.
The Refinery
In 1979, we were invited to put forward a proposal for a specification of oil recovery equipment which would successfully clear the surface oil from an API separator on a U.K. coastal refinery. To prove the capabilities an initial demonstration was carried out on one of the refinery lagoons, as a result of which a mobile unit very similar to the inland pollution control response unit was purchased.
The refinery in question were experiencing great difficulties with the oil removal devices that were installed at that time. These mechanical devices were dependent upon the use of electric motor driven cable systems, which pulled an adjustable scraper with a rubberised flexible base, which pushed the surface oil along to a slit tube which was manually adjusted to cope with the varying levels of effluent in the API separator tanks. The oil and water which were pushed into the tube were then transfer pumped into the 10,000 tonne oil storage tank.
There were sets of 4 and 5 API separators, totalling 28. Each API separator measured approximately 7m wide, 21m long and 3.5m deep, construction was all steel with girder support all above ground.
The refinery maintenance section were finding it increasingly difficult to maintain the scraper equipment in good working order, due to various wear and tear factors, and they decided to investigate alternative methods to remove the surface oil.
The Trial
OPEC Ltd. was invited, together with a number of other suppliers of alternative mechanical surface oil removal devices, to carry out a 2 week trial during which time product assessment and evaluation would take place by the maintenance division and project engineers. Two items of equipment which were proposed for this trial were withdrawn before the trial took place, due to the fact that the manufacturers concerned could not supply the equipment with suitable EXD Class IIB gases, explosion proof motors. OPEC volunteered to select the API separator which received the material pumped ashore from tanker slops. The tests lasted 2 weeks, at which time the only API separator totally free of surface oil was the one on which the Series 552 was deployed.
Installation and Operation
After further assessments an initial order for 5 Series 552 units was agreed and the installation took place over 2 days.
Where possible the company took advantage of the items of equipment in situ, in order to keep the capital cost of installation to a minimum. It was agreed that the surface skimming devices should be removed, but the slit tubes and the pumps connected to these were left in place. The machines were sited on top of the extension to the safety walkways, through which a small rectangular hole was cut and a deflector plate held by brackets was fixed beneath each machine so that collected oil being squeezed from the rope mop would drain through the open base of the machine and be deflected by the deflector plate into the slit tube and then transfer pumped into the oil storage tank.
Figure 1 shows the general view of the multi-machine installation and figures 2 and 3 give a more detailed view of the equipment location.
Fig 1 General layout of the mop on an API Separator
Fig 2 Close-up of mop material holding back the oil
With the benefit of experience gained during the initial 2 week trial, the equipment installation was made so that the Series 552 recovery system would operate with maximum efficiency, see figure 4. Each machine is installed with the rope mop deployment shown with an unusual flow pattern on the oily water surface. Figure 4 shows the direction of the inflow of effluent and the amount of resonance time can be assessed by the sheer size of this settlement tank. As the arrow indicates, the outgoing rope mop falls on to the oil water surface and travels to the floating pulley fixed top centre of the diagram. It then travels back to the floating pulley placed in the corner top left of the illustration and then moves almost across the whole width of the separator, to the floating pulley placed at the bottom left hand corner of the separator and then travels to the floating pulley bottom centre of the tank, before it then flows back up into the oil mop drive unit.
Figure 2 shows a slight variation to that in Figure 4, in that the incoming rope mop travels around the floating pulley which is slightly further away, in order to reduce the angle of the incoming mop into the machine.
4 Specified drawings for E-Series on an API separator
The OPEC mop has an affinity to oil and does not absorb water.
Figure 3 shows a close up of the rope material holding back the surface oil lying on the API separator, acting as a sorbent boom whilst not in operation.
After the initial installation of 5 machines a further 23 machines were supplied for operation as illustrated.
The equipment shown in these photographs have been refurbished since the initial operation, which took place between 1979 and 1980. At one time, the equipment was operating 24 hours per day, 7 days per week.
Financial Consideration
The total equipment installation, including capital cost and cost of labour to set up the equipment, came to an amount considerably lower than the ANNUAL MAINTENANCE COST to the systems (mechanical scraper) that was previously in use.
Conclusion
The Series 552 system complete with flameproof motor drive, Standard 30 metre length of rope mop and floating pulleys (or guide rollers as preferred), prove to be a simple but cost effective oil recovery system.
- An effective oil removal system which picks up very little free water.
- A system which requires no manual attendance or supervision.
- No manual adjustments required to cope with constant oil water level variance in each API separator to ensure oil is skimmed from the surface.
- Very low annual maintenance costs by comparison to any other system.
The E-Series is an up graded system based on the Series 552.
