Tanks, reaction

Automated controls for flocciJating reagents can use a feedforward mode based on feed turbidity and feed volumetric rate, or a feed-back mode incorporating a streaming current detector on the flocculated feed. Attempts to control coagulant addition on the basis of overflow turbidity generally have been less successful. Control for pH has been accomplished by feed-forward modes on the feed pH and by feed-back modes on the basis of clarifier feedwell or external reaction tank pH. Control loops based on measurement of feedwell pH are useful for control in apphcations in which flocculated sohds are internaUy recirculated within the clarifier feedwell. 

The treated water contains sufficient concentration of surface film-forming agents if cold water spends about 12 min and warm water at least 20 min in the tank [19]. Sudden temperature variations over 10°C must be prevented because the active form of Al(OH)3 is sensitive to them [20]. If mixing with cold water or subsequent warming cannot be avoided, a short-term electrolytic aftertreatment must be provided in a small reaction tank. The development of undisturbed protective films in the tubing assumes continuous water flow with forced circulation by pumps [20]. 

A higher content of AI2O3 and SiOj is critical for the composition of the protective films in the tubing, assuming the water contains silicates or silicic acid. The protective films have a maximum thickness of 1.5 mm and cannot grow further. The corrosion process can be stopped even in copper pipe networks with type I pitting [21] by providing a reaction tank with impressed current aluminum anodes. 

High levels of silica in the raw water supply can lead to serious risks of deposition in boilers, especially if cycles of concentration (COC) also are high. The incoming silica can be reduced by adsorption on magnesium hydroxide [Mg(OH)2] precipitate during lime-softening processes, or by the addition of magnesium hydroxide in a reaction tank, followed by filtration. 

Prait, N.H. Trans. Inst. Chem. Eng. 25 (1947), 163. The heat transfer in a reaction tank cooled hy means of a coil... 

Method Cyanide is destroyed by reaction with sodium hypochlorite under alkaline conditions. System component Reaction tanks, a reagent storage and feed system, mixers, sensors, and controls two identical reaction tanks sized as the above-ground cylindrical tank with a retention time of 4 h. Chemical storage consists of covered concrete tanks to store 60 d supply of sodium hypochlorite and 90 d supply of sodium hydroxide. 

In Sweden where demand exists for huge hypochlorite tanks, a new lining technique has been developed. The technique is applied to large reaction tanks, manufactured with capacities of 100-150 m3. The lining utilises titanium alloy. 

A number of processes can be considered double alkah processes, but most developmental work has emphasized sodium-based systems, which use lime for regeneration. This system pretreats the flue gas in a prescrubber to cool and humidify the gas and to reduce fly ash and chlorides. The gas passes through an absorption tower where SO2 is removed into a scrubbing solution, which is subsequently regenerated with lime or hmestone in a reaction tank. 

Rubber dampens by transforming kinetic energy into static energy. This basic rubber property is utilized in protection against explosion and impact and effectively reduces or eliminates noise, vibration and water hammer in pipelines and reaction tanks with agitators. 

Ethyl Acetate. The production of ethyl acetate by continuous esterification is an excellent example of the use of azeotropic principles to obtain a high yield of ester (2). The acetic acid, concentrated sulfuric acid, and an excess of 95% ethyl alcohol are mixed in reaction tanks provided with agitators. After esterification equilibrium is reached in the mixture, it is pumped into a receiving tank and through a preheater into the upper section of a bubblecap plate column (Fig. 5). The temperature at the top of this column is maintained at ca 80°C and its vapor (alcohol with the ester formed and ca 10% water) is passed to a condenser. The first recovery column is operated with a top temperature of 70°C, producing a ternary azeotrope of 83% ester, 9% alcohol, and 8% water. The ternary mixture is fed to a static mixer where water is added in order to form two layers and allowed to separate in a decanter. The upper layer contains ca 93% ethyl acetate, 5% water, and 2% alcohol, and is sent to a second recovery or ester-drying column. The overhead from this column is 95—100% ethyl acetate which is sent to a cooler and then to a storage tank. This process also applies to methyl butyrate. 

Hydrogenation is conducted in hardening plants (Fig. 34.24). The converter is a pressurized reaction tank, equipped with a highspeed mixer and assisting baffles, means for... 

A typical Fenton s treatment installation requires facilities for storing and dosing chemicals (hydrogen peroxide, ferrous catalyst, acid and alkali for pH adjustment), a reaction tank, a settlement tank or centrifugal pump for solids removal and a UV-VIS lamp if photo-Fenton s is to be employed. The use of Fenton s and photo-Fenton s systems are likely to grow in use over the next decade as environmental legislation becomes more widespread, and as the systems become more efficient. 

The control of sulfite scaling requires that a minimum amount of free hydroxide ion be recirculated to the scrubber therefore, fresh additive (lime or slaked lime) is added in the reaction tank external to the scrubber where calcium sulfite is formed (Reaction 4). An amount of calcium sulfite equivalent to the SO2 removed (or the fresh Ca(OH)2 added) is conveyed from the system to a pond or vacuum filter, and the remainder is recycled to continue the removal process. 

Heterogeneous crystallization is minimized by providing seed crystals for homogeneous crystallization (crystallization on the seed crystals) and by designing the reaction tanks so that the liquor leaving them is close to saturation and not highly supersaturated. This requires the knowledge of precipitation kinetics of calcium sulfate and sulfite. 

The Air Quality Control Systems (AQCS) using lime/limestone wet scrubbing have three basic types of chemical process equipment (1) scrubbers, (2) reaction tanks, and (3) solid-liquid separators, in addition to several auxiliary pieces of equipment such as pumps, demisters, and reheaters. The SO2 in the flue gas is transferred into the liquid in the scrubber, the sulfur in the liquid is converted to solid calcium sulfite, and calcium sulfate in the reaction tanks and solid calcium sulfite and sulfate are separated from the liquid and disposed from the solid-liquid separators such as clarifiers, vacuum filters, and ponds. 

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