with that residence time, the solids did not settle, and the hydrocarbons did not fully separate from the sour water. As the unit operated, hydrocarbons and solids were pumped with the sour water from the tanks to the feed/effluent heat exchanger and eventually to the stripper column. The heat exchanger fouled with coked hydrocarbons and solid particulates sticking to its surface, reducing heat transfer efficiency and necessitating cleaning. To perform the cleaning, the system had to be shut down, drained, purged, and cleaned before reassembly. The cleaning process typically takes about a week, incurring significant operating expense for the refiner. As a result, the refinery staff were keen to find a solution. It was suggested that they remove the solids and separate the hydrocarbon liquid phase from the water. With a simple, cost-effective contaminant removal system, provided on a rental basis, they could evaluate this approach to solving their exchanger fouling problem. If successful, they could then consider installing a permanent system in the future. Torsep contamination removal system The system includes the Envision emulsion separator for liquid-liquid coalescing, where the oil phase is separated from the bulk sour water phase. Upstream of the emulsion separator is an Endur Tetra separator for the removal of solid particulates. The first stage removes solid particulates and protects the downstream emulsion separator from rapid plugging. The two separators are described in more detail in the following sections. Endur Tetra solid separator The operating cost of fluid quality management is highly dependent on the choice of element and vessel size. The vessel needs to be large enough and contain sufficient filter elements to allow for a reasonable time between filter changeouts. However, the larger the vessel, the higher the capital cost. Therefore, the Capex of the vessel must be weighed against the Opex of filter changeouts. In this opportunity, an available rental unit was utilised, and the vessel size resulted in an expected changeout frequency of one to two weeks. This was sufficient to keep Opex low.
For solid particulate control, a suitable media configuration was applied to capture and retain the particulate contaminants in the inlet liquid flow with a defined level of efficiency. The media is a locked-pore configuration of cross-linked fibres, which prevents particulate release under higher differential pressure conditions. In the Endur Tetra separator, *1 liquid enters the vessel through the inlet nozzle at the top, it is diverted by the inlet baffle, and passes through the solid particulate filter elements from outside to in. The particulate is retained by the media, and the clean liquid passes through the media into the riser, down the centre riser support, through the tube sheet, and into the outlet chamber, exiting through the outlet nozzle. Some of the features of the separator and the filter elements include: u Preferred flow configuration : The separator elements flow from outside to in. This flow configuration maximises dirt capture within a given vessel size, thereby allowing the lowest overall Opex for a given Capex. v Optimised element configuration : The element maximises contamination holding capacity while also maximising packing density within a housing. w Ergonomic : The elements are approximately 40in long and come with an ergonomic handle that allows easy removal and installation. x Coreless element configuration : The Tetra element features a coreless design, making it lighter and providing a less strenuous changeout process. The coreless design will also have reduced disposal volume. Envision emulsion separator The Envision separator *1 is a single-stage, liquid emulsion separation system. The separator elements can capture and coalesce small, discontinuous phase droplets from a continuous phase, which may be aqueous or hydrocarbon in nature. In this case, the refiner needed to remove hydrocarbons from the sour water. The liquid enters the vessel through the inlet nozzle located at the centre of the vessel head on one side. It travels through the tube sheet, down the riser, and through the separator element from inside to out. As the liquid passes through the media of the separator element, small, single-micron droplets of the hydrocarbon phase
Refining India
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