Processing facilities drainage

It is common practice to equip a drainage system or sump with a pump to return the collected inventory to storage or process facilities. Alternatively, for certain toxic materials, the spill is sometimes altered chemically to a nonhazardous substance by draining the spillage to a basin filled with a neutralizing slurry where the reaction forms an insoluble sludge. For acids, in particular, soda ash, limestone, or weak caustic solutions may be used. The reacted product becomes a solid that is neutral and can be disposed of accordingly. 

There are several drainage mechanisms employed at process facilities—surface runoff or grading, spiU containment (diking), gravity sewers (oily water, special, sanitary), and pressurized sewer mains and lift station collection sumps. 

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 purpose of the facilities described in this chapter is to provide for safe handling of various drainage materials and emergency streams, so that they may be safely routed to the sewer, tankage, flare, or other appropriate destination. Drainage systems specified herein ensure that flammable or toxic materials may be disposed of without hazard of fire or injury when equipment is taken out of service. Also described are systems to handle process water drawoffs, cooling water, and other aqueous effluent streams which may be contaminated with hydrocarbons, and which could otherwise create hazardous conditions if they were discharged directly to the sewer. 

Solids should be removed from process liquors and vessels should be designed so that deposition of solids does not occur, e.g. by avoiding sharp corners and stagnant areas by providing facilities for complete drainage of the process liquor. 

Payer80 states that the UNSAT-H model was developed to assess the water dynamics of arid sites and, in particular, estimate recharge fluxes for scenarios pertinent to waste disposal facilities. It addresses soil-water infiltration, redistribution, evaporation, plant transpiration, deep drainage, and soil heat flow as one-dimensional processes. The UNSAT-H model simulates water flow using the Richards equation, water vapor diffusion using Fick s law, and sensible heat flow using the Fourier equation. 

Drainage areas can be defined by the process fire area, which has been established by the spacing, segregation and arrangement provisions for the facility. Open drainage channels should be used where they will not interfere with the use of the area, i.e., crane access, maintenance activities, etc. They should be designed to minimize erosion, and if excessive velocities are encountered they should be paved. No more than 5 m/s (15 ft/s) velocity should be allowed in paved surface runoff channels or troughs. 

Wastewaters may be collected in separate drainage systems (for process, sanitary, and storm water) althongh industrial and stormwater systems may in some cases be combined. In addition, ballast water from bulk crude tankers may be pnmped to receiving facilities at the refinery site prior to removal of floating oil in an interceptor and treatment as for other wastewater streams. 

Within practical limits of plant and individual unit layout, the high point of grade should passthrough process buildings and areas, large equipment pads and centerlines of roadways and pipeways so that drainage will be away from these facilities and equipment. 

The sulfuric acid plant has boiler blowdown and cooling tower blowdown waste streams, which are uncontaminated. However, accidental spills of acid can and do occur, and when they do, the spills contaminate the blowdown streams. Therefore, neutralization facilities should be supplied for the blowdown waste streams (Table 15), which involves the installation of a reliable pH or conductivity continuous-monitoring unit on the plant effluent stream. The second part of the system is a retaining area through which non-contaminated effluent normally flows. The detection and alarm system, when activated, causes a plant shutdown that allows location of the failure and initiation of necessary repairs. Such a system, therefore, provides the continuous protection of natural drainage waters, as well as the means to correct a process disruption. 

Any liquid, gaseous or aerosolic waste discharged in the environment. Generally, it is a complex mixture. For example, wastewaters include mine water effluent, mill process effluent, tailings impoundment area effluent, treatment pond or treatment facility effluent, seepage and surface drainage. Volume 1(9,10,14), Volume 2(2,5). 

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