Slop system

Four skimming connections with trycocks are normally provided at the outlet end of the drum, at the normal liquid level, and at 150 mm, 450 mm, and 500 mm below the normal level. Liquid hydrocarbon skimmed from these connections can be pumped to a suitable slop system. A coimection to the suction of a blowdown drum pumpout pump, if available, is adequate for this purpose. 

Gasoline is being diverted to the refinery slop system through an open start-up connection. 

The furnace operators drain their knock-out drums to the refinery slop system. The amine mixes with large quantities of water in the slop system. 

The water in the slop system is drawn off to the refinery effluent treating plant where the operators note a tremendous increase in the nitrogen level in their effluent. 

This chapter covers the design of facilities to handle equipment drainage and contaminated aqueous effluents that are sent for appropriate disposal blowdown drum systems to receive closed safety valve discharges, emergency vapor blowdowns, etc. and facilities for process stream diversion and slop storage. Also covered are criteria for selecting the appropriate method of disposal. Design of flares is covered in a subsequent chapter. 

The first vessel in the blowdown system is therefore an acid-hydrocarbon separator. This drum is provided with a pump to transfer disengaged acid to the spent acid tank. Disengaged liquid hydrocarbon is preferably pumped back to the process, or to slop storage or a regular non-condensible lowdown drum. The vented vapor stream from the acid-hydrocarbon separator is bubbled through a layer of caustic soda solution in a neutralizing drum and is then routed to the flare header. To avoid corrosion in the special acid blowdown system, no releases which may contain water or alkaline solutions are routed into it. 

The pumping unit consisted of a submersible pump installed in a 10,000-gal reservoir tank, which also served as a holding tank (Figure 12.16). Fluids pumped from the wells were all returned to the tank for separation. All the oil and some water produced overflowed from the tank into another oil-water separator and then into the slop oil treatment system of the refinery. Clarified water from the bottom of the tank was recycled by the submersible pump through the eductor units to continue operations. 

A chemical process operator taped down the acknowledge button on the instrument cabinet to slop an incessant alarm after a level alarm switch had slipped. The alarm switch slipped down its support into a sump and alarmed every few minutes as the sump pump cycled on and off, The acknowledge button, common to a number of alarms, deactivated the whole system. A critical high-temperatme alarm was not. sounded because of this modification. The operator failed to see the alarm light, and the situation eventually led to a hirge toxic vapor release. [1]... 

In general, the in-plant control methods employed by the industry (sour-water stripping, spent-caustic neutralization and oxidation, slop oil recovery, etc.) will determine the final effluent characteristics and the level of pretreatment required for discharge to the municipal collection system. The following specific in-plant practices are frequently employed ... 

The water content in surface slops is lowest with oil drums and highest with pump-induced water circulation systems. Nevertheless, some dynamic skimmers such as the autostables can draw off a thin enough water layer to be fairly rich in oil. 

Vacuum distillate. This stream was directed to the refinery s recovered oil system (i.e., slop) and eventually reprocessed at the delayed coker. 

The RCMs and the equivolatility curves of this chemical system ean be seen in Figure 13.1, where the numbers in the equivolatility emwes denote the relative volatility of acetone versus methanol in the presence of water. The RCM indicates that any mixture of acetone and methanol, even premixed with water, will produce the acetone-methanol azeotrope at the top of the column. However, by continuously adding water (a heavy entrai-ner) into the column, it can be seen from the equivolatility curves that the acetone is becoming more and more volatile than the methanol in the extractive section. Acetone and methanol can then be separated in the extractive section if the number of trays in this section is sufficient. Acetone will go toward the top of the column while methanol will be carried with the water toward the column bottom. In the rectifying section, owing to the lack of methanol in this section, only the separation of acetone and water is performed. Pure acetone will preferably go to the top of the batch extractive distillation column. After the draw-off of the acetone product and a slop-cut period, where the acetone in the column is completely depleted, the methanol product can be collected at the top of the column. The heavy entrainer (water) can be collected at the column bottom. 

Luyben W. L., Multicomponent batch distillation. 1 Ternary systems with slop recycle, Ind. Engng. Chem. Res., 27, 642-647 (1988). 

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