Sour-water treating

C. Sour water treating is found in natural gas processing, refining, and the substitute fuel processes. Cmmpounds present normally include a few to all those listed in A. 3. above. In addition, the water pH is normally controlled with caustic soda or other salt. In the past, processing has been near ambient temperatures and pressures. Future operations may, however, be at elevated temperatures and pressures. 

Various patents (22—24) have been issued claiming the use of tetrakis(hydroxymethyl)phosphonium sulfate in, for example, water treating, pharmaceuticals (qv), and in the oil industry where this compound shows exceptional activity toward the sulfate-reducing bacteria that are a primary cause of hydrogen sulfide formation and consequent problems associated with souring and corrosion (25). 

Chevron s WWT (wastewater treatment) process treats refinery sour water for reuse, producing ammonia and hydrogen sulfide [7783-06-04] as by-products (100). Degassed sour water is fed to the first of two strippers. Here hydrogen sulfide is stripped overhead while water and ammonia flow out the column bottoms. The bottoms from the first stripper is fed to the second stripper which produces ammonia as the overhead product. The gaseous ammonia is next treated for hydrogen sulfide and water removal, compressed, and further purified. Ammonia recovery options include anhydrous Hquid ammonia, aqueous Hquid ammonia, and ammonia vapor for incineration. There are more than 20 reported units in operation, the aimual production of ammonia from this process is about 200,000 t. 

Steam strip spent doctor solution to hydrocarbon recovery before air regeneration replace treating unit with other, less objectionable units (Merox) Use sour water oxidizers and gas incineration ... 

Certain refinery wastewater streams are treated separately, prior to the wastewater treatment plant, to remove contaminants that would not easily be treated after mixing with other wastewater. One such waste stream is the sour water drained from distillation reflux drums. Sour water contains dissolved hydrogen sulfide and other organic sulfur compounds and ammonia which are stripped in a tower with gas or steam before being discharged to the wastewater treatment plant. 

Chevron WWT [Waste water treatment] An integrated process for treating sour water from oil refineries, particularly for removing ammonia, hydrogen sulfide, and carbon dioxide. Only physical processes are used—volatilization and condensation under various conditions. Developed by Chevron Research Company and used in 14 plants worldwide in 1985. Martinez, D., in Chemical Waste Handling and Treatment, Muller, K. R., Ed., Springer-Verlag, Berlin, 1986, 180. 

B. Sour gas treating involves the removal of the acid gas components CO2 and H2S from natural gas. Most ways of doing this involve water solutions. Treating is normally at near ambient temperatures and at pressures to 7100 kPa (70 Atm). The treating of high acid gas content natural gas is becoming more important as the value of natural gas increases. 

Hydrotreating generates sour wastewater from fractionators used for product separation. Like most separation processes in a refinery, the process water used in fractionators often comes in direct contact with oil and thus can be highly contaminated. It also contains hydrogen sulfide and ammonia and must be treated along with other refinery sour waters. In hydrotreating, sour wastewater from fractionators is produced at the rate of about I.O gallon per barrel of feed. 

Isomerization processes produce sour water and caustic wastewater. The ether manufacturing process utilizes a water wash to extract methanol or ethanol from the reactor effluent stream. After the alcohol is separated, this water is recycled back to the system and is not released. In those cases where chloride catalyst activation agents are added, a caustic wash is used to neutralize any entrained hydrogen chloride. This process generates a caustic wash water that must be treated before being released. This process also produces a calcium chloride neutralization sludge that must be disposed of off-site. 

The first step in good pretreatment practice is the segregation of major wastewater streams. This frequently simplifies waste treating problems as well as reducing treatment facility costs. Treatment at the source is also helpful in recovering byproducts that otherwise would not be economically recovered from combined wastes downstream [35]. Four major pretreatment processes that are applicable to individual process effluents or groups of effluents within a refinery are sour water stripping, spent caustics treatment, ballast water separation, and slop oil recovery. These are discussed below. 

The purpose of sour water pretreatment is to remove sulfides (H2S, ammonium sulfide, and polysulfides) before the waste enters the sewer. The sour water can be treated by stripping with steam or flue gas, air oxidation to convert sulfides to thiosulfates, or vaporization and incineration. 

Most of the filtrate is recycled as wash water. However the overall system generates a net water surplus, which must be treated before final discharge. First the surplus water passes through a Sour Water Stripper to remove dissolved gases that are then incinerated. The water is then treated in a biotreatment facility180. 

Employing a reusable solvent for ammonia recovery could suppress the treatment of a large amount of wastewater. For an ROI of two years the investment in treating the sour water would be of 490 x 8400 x 2 = 8.23 M. ... 

A portion of the condensed gasoline is pumped back to the tower as reflux. The sour water collected in the overhead drum is sent to battery limits for treating. 

For convenience, the discussion of materials for these various processes is divided into five chapters. Crude units and utilities are discussed in this chapter. FCCs, fluid cokers, delayed cokers, sour water strippers, and sulfur plants are covered in Chapter Two. Desulfurizers, reformers, hydrocrackers, and flue gas are discussed in Chapter Three. Hydrogen plants, methanol plants, ammonia plants, and gas treating are discussed in Chapter Four. Underground piping, pipelines, production equipment, and tankage associated with the refinery industry are covered in Chapter Five. Discussed throughout these chapters are many common environments and equipment (e.g., sour or foul water, distillation, etc.) that appear in the various types of refinery process plants. 

Table 51 gives an example of the efficiency of the flotation operation. Flotation also treats about 180 m -h of the effluent from sour water biological purification. 

As shown, elemental sulfur is produced by the reversible reaction between SO2 and H2S. COS and CS2 appear in small amounts, but even traces of these compounds are hard to remove in tail-gas treating units. Ammonia comes in with the sour-water stripper off-gas. In the Claus process, it is thermally decomposed into nitrogen and water. 

Process Water Desalter water Excess sour water Water drawn from oil-storage tanks Accumulator draws Treating plant waste Barometric condeners... 

Fluoridation of potable water suppHes for the prevention of dental caries is one of the principal uses for sodium fluoride (see Water, municipal WATER treatment). Use rate for this appHcation is on the order of 0.7 to 1.0 mg/L of water as fluoride or 1.5 to 2.2 mg/L as NaF (2). NaF is also appHed topically to teeth as a 2% solution (see Dentifrices). Other uses are as a flux for deoxidiziag (degassiag) rimmed steel (qv), and ia the resmelting of aluminum. NaF is also used ia the manufacture of vitreous enamels, ia pickling stainless steel, ia wood preservation compounds, caseia glues, ia the manufacture of coated papers, ia heat-treating salts, and as a component of laundry sours. 

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