Scrubber liquor

Nowadays economy and ecology render the reuse of the sulfite solution increasingly important. Normally the scrubber liquor is recovered as dilution water directly in the neutralization of sulfonation plant or in the slurry preparation unit of synthetic detergent plants. In some special cases, when the presence of sulfites is incompatible with the slurry composition, it is possible to install as optional a sulfite oxidation unit. This oxidation takes place with atmospheric air. 

Dissolved Concentrations of Calcium and SO2 Species. The equilibrium dissolved concentrations of total calcium and SO2 (sulfite plus bisulfite) species are important because comparison of these equilibrium concentrations with actual measured values determines the degree of gypsum saturation, and hence the potential for gypsum scale formation in the scrubber. As a first approximation, the fraction gypsum saturation of a scrubber liquor, having specified pH and specified concentrations of magnesium and chloride, is proportional to the measured calcium concentration, and inversely proportional to the measured S02 concentration. 

Quench elbow and primary scrubber. Here, the gases are scrubbed in a packed tower scrubber for particulates and acid gases, using a scrubber solution with a pH of 7.0 to 8.5. The recirculating scrubber liquor is cooled and, in turn, cools the hot gas from 1,000°F to approximately 60°F. 

In the phosphoric acid plant, the contributing sources of effluent are the cooling tower bleedoff and the scrubber liquor solution that contains concentrations ranging for phosphate from 160 to 200 mg/L and for fluoride from 225 to 7000 mg/L. 

CooKna tower bleed scrubber liquor NPK effluents... 

An application in power production, particularly in coal-fired power plants, is the analysis of flue gas scrubbers which remove excess SO2 following coal combustion. Tests run by SAMBESRL at the EPA s Research Triangle Park facility (8,9) have demonstrated the effectiveness of IC in determining sulfite and sulfate in flue gas desulfurization systems. Table III gives results of direct IC analysis of scrubber liquors compared with turbidimetric and titration methods. 

NATIONAL (cont.) cleaning or etching scrubber liquor 12.43 6.19 ... 

Figure 3 shows percent SO2 remaining in the scrubbed gas as a function of alkali/acid gas stoichiometric ratio at steady-state. The numbers beside each point are chloride concentration in the scrubber liquor. From an examination of this figure, it does not appear that chloride concentration has any significant effect on SO2 removal in the range studied. 

Solids Precipitation. Although chloride concentration in the scrubber liquor has little effect on removal efficiency, it has a significant effect on the operation of the column. Chloride concentrations greater than about 6.6 percent (see Table III), lead to some deposit of salts in the scrubber column. Nevertheless, it appears that if chloride level is maintained below about... 

Table III. Chloride Concentration of Scrubber Liquor in Various Runs ...

Run No. Cake Moisture, percent Average Chloride Concentration in Scrubber Liquor, percent Scrubber Feed Scrubber Discharge Comments... 

Most of the scrubber liquor is cooled (105°F) and recycled in the raw state. Part of the cooled liquor is filtered to remove accumulated ash particles and flows through the pH meter, conductivity meter, and then the cooling spray. Another portion (without cooling) is filtered and flows to the regenerator at a controlled rate. As shown, sodium hydroxide solution also flows to the regenerator at a controlled rate. The mixture of solutions is heated to about 220°F, and chemical reaction releases the ammonia and steam these products return to the system under the force created by their vapor pressures. 

The ammonium salt products crystallized from the concentrated spent scrubber liquors may be used as valuable constituents of fertilizers. Or they may be first reduced to ammonia and hydrogen sulfide with natural gas, followed by conversion of the hydrogen sulfide to sulfur by a Claus-type sequence [39]. In this French-designed modification, the ammonia is recycled to the scrubbing circuit. 

The metals content of an aqueous waste stream can be substantially decreased by complexation or adsorption methods and the recovered metal used to offset a part of the treatment costs [82]. Unexpended hypochlorite can also be neutralized by contacting this stream, in the correct proportions, with spent scrubber liquor from sulfur dioxide emission control systems (Eq. 5.35). 

Emission problems in a causticization operation arise chiefly in the area of dust control of the exit gases from the lime kiln since the water circuit is virtually self-contained. Effective containment is obtained by the use of scrubbers, which achieve some 99% mass removal efficiency from the exhaust gases. Spent scrubber liquor may be returned to the causticization circuit for recycle. Using spent scrubber liquor, either for the slaking of lime or to prepare fresh sodium carbonate solutions for causticization, avoids creating a water emission problem from this aqueous waste stream. It also improves the raw material balance of the process. 

During operation, the TDU s operating parameters are measured and recorded to ensure correct operation and to prevent accidental releases of contaminants. While there are several possible parameters to monitor, the following are recommended where applicable treated soil exit temperature, vacuum in the TDU, pressure drop in the APC, waste feed rate, afterburner temperature, off-gas exit temperature from the TDU, stack gas velocity and temperature, and the flow rate and pH of acid-gas scrubber liquor. ... 

Representative results are shown in Table VIII for T = 50°C pH = 5.0. The manganese concentration was varied from 0.1 to 1.0 ppm, values which are representative of those found in scrubber liquors (12). The concentration of manganese is the total value, l.e., the sum of that contributed by the calcium sulfite and that added to the solution. These results were also fit to an expression of the form of equation (2) with the maximum likelihood estimates being ... 

The sulfite oxidation rate in hold tanks of antipollution scrubbers is central to flue gas desulfurization technology. The accurate description of the rate of disappearance of sulfite slurry particles (from the scrubber liquor) bears upon both process selection and economics. This article will describe a mathematical model for a semi-batch, stirred tank reactor in which S(IV) anions, sulfite and bisulfite, are reacted with dissolved oxygen gas at saturation. Experimental work to secure several physical parameters and to verify the... 

Nine forced oxidation runs were performed with manganese, manganese plus iron, Springfield limestone, or Springfield limestone plus fly ash. The common factor involved in all these runs was the presence of manganese ions in the scrubber liquor. The presence of manganese caused a significant reduction in the adipic... 

Bleed stream oxidation of unenhanced lime or limestone slurry is usually not feasible because the pH rise caused by the residual alkali in the oxidation tank makes it difficult to redissolve the solid calcium sulfite. With adipic acid-enhanced limestone scrubbing, however, this constraint is removed because of the low operating pH and low residual alkali in the bleed slurry. Thus, the oxidation tank can be maintained at a low pH for good sulfite oxidation, while achieving high SO2 removal efficiency with a sufficiently high concentration of adipic acid in the scrubber liquor. 

Limestone Utilization. Two types of limestone were used for regenerating the spent scrubber liquor Fredonia limestone from Kentucky, ground to 96.A wt. % through 325 mesh, with a Ca content of 93.6 wt. % as CaCO and Mg content of A.2 wt. % as MgCO and Sylacauga limestone from Alabama, ground to 97.7 wt. % through 325 mesh, with a Ca content of 95.7 wt. %, and Mg of 1.3 wt. %. 

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