Effluent hold tank

Handling. Adipic acid is non-toxic, non-hygroscopic, and usually comes in powder form. It is easy to handle and no hazards are encountered in the usual applications other than possible dust explosions, which are typical of any organic dust. At Shawnee, it is routinely dry-fed directly to the effluent hold tank, although it has been added to the fresh limestone slurry makeup tank in some instances. 

Buffer Reaction Mechanism. The mechanism by which adipic acid buffers the pH is simple. It reacts with lime or limestone in the effluent hold tank to form calcium adipate. In the absorber, calcium adipate reacts with absorbed S02(H2S03) to form CaS03 and simultaneously regenerates adipic acid (the buffer reaction). The regenerated adipic acid is returned to the effluent hold tank for further reaction with lime or limestone. With a sufficiently high concentration of calcium adipate in solution, usually on the order of 10 m-moles/liter to react with the absorbed S02, the overall reaction rate is no longer controlled by the dissolution rate of limestone or calcium sulfite. 

Forced oxidation is achieved by air sparging of the slurry in an oxidation tank, either on the bleed stream to the solids dewatering system or on the recirculated slurry within the scrubber slurry loop. For a one-scrubber-loop forced oxidation system, the slurry effluent from all scrubbers in the system (e.g., the venturi scrubber and spray tower at Shawnee constitute a two-scrubber system, and the spray tower alone or TCA, a one-scrubber system) are sent to a single effluent hold tank, which is the oxidation tank. For a two-loop forced oxidation system, there are two scrubbers in series (e.g., venturi and spray tower at Shawnee) with effluent from each scrubber going to a separate tank the effluent hold tank for the upstream scrubber (with respect to gas flow) is the oxidation tank. For either one-loop or two-loop forced oxidation systems, the oxidation tank may be followed by a second tank, in series, to provide further limestone dissolution and gypsum desupersaturation time prior to recycle to the scrubber. 

Limestone Long-Term Tests with Two Scrubber Loops and Forced Oxidation. The venturi/spray tower system was modified for two-scrubber-loop operation with forced oxidation as shown in Figure 2. Two tanks were used in the oxidation loop (venturi loop) air was injected to the first of these tanks through a simple 3-inch diameter pipe below the agitator. Adipic acid was dry-fed to the spray tower effluent hold tank. This was accomplished by manually adding one-pound increments hourly to maintain specified concentration, usually totaling only a few pounds per hour. A small screw feeder would serve the purpose in a full-scale plant. 

The run was controlled at a nominal limestone stoichiometric ratio of 1.2 and 1,500 ppm adipic acid concentration in the slurry liquor. Slurry solids concentration was controlled at 15 percent. The flue gas flow rate was varied between 20,000 and 30,000 acfm (8.4 to 12.5 ft/sec superficial gas velocity) as the boiler load fluctuated between 100 and 150 MW. The slurry recirculation rate was fixed at 1,200 gpm (L/G = 50 to 75 gal/Mcf). The effluent hold tank residence time was only 4.1 minutes. 

Table 5 lists the test results of such a lime run, Run 951-2E, using within-scrubber-loop forced oxidation with 1,330 ppm adipic acid. The system configuration used for this run was the same as that shown in Figure 3, except that the oxidizing air was injected into the effluent hold tank (oxidation tank). A single... 

Onstream hours Fly ash loading Adipic acid concentration, ppm (controlled) Scrubber gas velocity, ft/sec Liquid-to-gas ratio, gal/Mcf Slurry solids concentration, wt % (controlled) Scrubber inlet pH (controlled) Oxidation tank level, ft Oxidation tank residence time, min Effluent hold tank residence time, min Average percent SO2 removal Average inlet SO2 concentration, ppm SO2 make-per-pass, m-moles/liter Percent oxidation of sulfite to sulfate Air stoichiometry, atoms oxygen/mole SO2 absorbed Oxidation tank pH Percent limestone utilization Scrubber inlet liquor gypsum saturation, % Filter cake solids content, wt % 1,688 High 1,300 1,700 5.4- 9.4 85 150 15 5.0- 5.1 18 2.8 8.3 93.4 2,660 4.0- 8.9 99.8 1.4- 2.4 4.9 92.6 93 86... 

To oxidize this bleed stream, it is necessary only to install an oxidation tank and the associated agitator and compressed air system anywhere between the effluent hold tank and the solids dewatering area. Thus, the bleed stream oxidation scheme is particularly well suited for retrofit when modifications of the existing scrubber system for within-scrubber-loop forced oxidation are not possible due to physical constraints. 

Table 7 gives the results of a typical bleed stream oxidation test, Run 915-1C, which was conducted with adipic acid-enhanced limestone on the venturi/spray tower system. The effluent slurries from the venturi and the spray tower were discharged into a common effluent hold tank. The scrubber bleed stream was pumped from the effluent hold tank to an oxidation tank into which air was injected through a 3-inch diameter pipe. The final system bleed was withdrawn from the oxidation tank and sent to the solids dewatering system. 

Percent sulfite oxidation in effluent hold tank 54... 

For runs without forced oxidation, a single effluent tank 20 ft in diameter with 8.5-ft tank level was used. For runs with forced oxidation, two tanks in series were used with an oxidation tank preceding the effluent hold tank. The oxidation tank was 8 ft in diameter with an 18-ft tank level. 

Electric power needed to operate ancillary scrubber equipment such as effluent hold-tank mixers, saturation spray pumps, and thickener rake (7 percent). 

Effluent holding tank Holding tank transfer pumps x 2... 

The water authority may limit the quantity of final treated effluent, and monitoring of the final out-fall may have to be considered in conjunction with a holding tank. 

A plant discharges an aqueous effluent at a volumetric flow rate F. Periodically, the effluent is contaminated by an unstable noxious waste, which is known to decompose at a rate proportional to its concentration. The effluent must be diverted to a holding tank, of volume V, prior to final discharge, as in Fig. 1.17 (Bird et al. 1960). 

A hold tank is installed in an aqueous effluent-treatment process to smooth out fluctuations in concentration in the effluent stream. The effluent feed to the tank normally contains no more than 100 ppm of acetone. The maximum allowable concentration of acetone in the effluent discharge is set at 200 ppm. The surge tank working capacity is 500 m3 and it can be considered to be perfectly mixed. The effluent flow is 45,000 kg/h. If the acetone concentration in the feed suddenly rises to 1000 ppm, due to a spill in the process plant, and stays at that level for half an hour, will the limit of 200 ppm in the effluent discharge be exceeded ... 

In Step 7, after the energetics hydrolysate from the continuously stirred tank hydrolysis operation has been pumped into a holding tank, acid is added to precipitate aluminum, and the hydrolysate is filtered through an automatic filter press to remove precipitated aluminum compounds. The liquid effluent goes to the dunnage hydropulper (Step 9). The filter cake from the press is sent to an electrically heated screw conveyor (Step 15) for 5X treatment. 

A 10,000 gallon holding tank receives an aqueous byproduct effluent stream from a continuous chemical process. The tank is well mixed and drains into a river. The tank receives 2400 gallons/day of a certain byproduct that decomposes in the tank with a rate coefficient of 0.2... 

For another nearby site, an estimate was prepared to determine the cost of using PIMS technology in three 1000-gal holding tanks. Each unit would hold approximately 4000 of apatite. Other factors included in the estimate are 13,000 for effluent monitoring, 12,000 for tank costs, 14,000 for emplacement costs, for a total cost of 43,000 (D17996I, p. 8). 

The Neutralization Module accepts the ton container contents from the TCC module and destroys the agent batchwise through hydrolysis with water followed by caustic addition. The Neutralization Module consists of three units, each located inside a Containment Level A toxic cubicle. There are two HD Reactors and one TCC Effluent Tank in each of the three neutralization units. In each neutralization unit, drained agent held in the Agent Holding Tank is processed in batch neutralization reactions. The rinse and spray water from the TCC Module and spent decontamination solution are stored in the TCC Effluent Tank and process in separate batch reactions. In the neutralization reaction HD reacts with water to yield the principal hydrolysis products of thiodiglycol and hydrochloric acid. After the hydrolysis is complete and sample analysis results confirm the destruction of HD, 18 percent sodium hydroxide is added to the reactor to raise pH in order to increase the hydrolysate biodegradability. The hydrolysate is then pumped to the Hydrolysate Tank in the VOC Treatment Module. 

The feed rate is manually set as required for either pH or reactant stoichiometry control. Soda ash is added to the fourth reactor as sodium makeup. Reactor effluent slurry flows by gravity to the thickener centerwell. Clarified liquor overflows from the thickener to the forward feed hold tank from which it is pumped to the tray tower. A horizontal belt filter is used for further dewatering of the thickener underflow solids. 

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