Slop storage

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. 

Provide settling facilities to separate hydrocarbon liquid from the flare seal water effluent, and appropriate means of disposal, e.g., to slop storage. 

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. 

Slop storage - Slop storage facilities are of three basic types according to the materials handled ... 

Materials accumulated in slop storage are normally routed to rerunning facilities or blended into appropriate tankage for disposal. 

If pressure slop storage is required to handle slop materials in the light ends range, it must comply with the following ... 

As an alternative to special pressure slop storage, the necessary holdup may be provided in a non-condensible blowdown drum. 

Light and heavy atmospheric slop storage are normally both necessary in the average refineiy. Sizing depends on the refinery complexity, volume and number of finished and intermediate products, and available means of disposal or reruiming. 

Generation of combustible vapors is a hazard not only for the storage of pure flammable liquids but also for the storage of any sludge or mixture where a combustible component is present or can be produced by reaction. Sludge (slop tanks) and mixture (e.g., oil/water) tanks may be particularly vulnerable because they are sometimes open to the air explosive atmospheres may form inside and outside the tank. Facilities may not always recognize the hazard. In addition, even tanks appearing to be empty may pose a hazard if they still contain combustible vapors. 

Figure 5.24 Slop oil recovery process (A) Slop oil. (B) Preheated slop oil. (C) Solids. (D) Clean oil. (E) Waster water. (F) Steam. (G) Condensate. (1) Oil lagoon with puming station. (2) Storage tank. (3) Preconditioning tank. (4) Spiral heat exchanger. (5) Preconditioning (mixing) tank for flocculants. (6) Three-phase centrifuge. (7) Storage tank. (8) Plate heat exchanger. (9) Disc separator. (10) Screw conveyor.

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