Hydrogen peroxide scrubber

After evaluation of the three processes, the final decision was made based on practical considerations. The calcine scrubber, being offered under license by Mesco in Japan, placed the onus of realization of the project within CPM. Since CPM is not set-up to carry out this type of project, timikey alternatives were preferred. Then, comparing the hydrogen peroxide and sodium hydroxide options, the possibility of the participation of the hydrogen peroxide bidder in other projects was the deciding factor. A partnership of this nature would decrease mobilization and other costs, and would simplify the a inistration of the project. The hydrogen peroxide scrubber is scheduled to come on-line in early November 2000. 

It was found that the concentration of total oxidants measured in the off-gas from the hypo unit varied with process conditions. Precise analysis of the off-gas showed that under certain conditions chlorine dioxide is formed in the reaction step where the hypochlorite concentration is approximately 160-180 g l-1. In the sections below formation of chlorine dioxide in the hypochlorite unit is discussed with regard to process conditions and peak load of the feed stream. In essence, the emission of chlorine dioxide can be reduced to nearly zero by using a scrubber in which the chlorine dioxide reacts with hydrogen peroxide. 

The second option involves the use of a CIO2 scrubber. This is a technique presently used in the paper and pulp industry. In the scrubber, the chlorine dioxide reacts with another chemical, such as a sulphite, DMSO, white spirit or an alkaline hydrogen peroxide solution. The hydrogen peroxide solution is most suited to the process described in this chapter as there are no waste streams. The reaction of chlorine dioxide with the alkaline hydrogen peroxide solution is rapid [10]. The reaction equation is as follows ... 

Dasgupta, P. K., S. Dong, H. Hwang, H.-C. Yang, and Z. Genfa, Continuous Liquid-Phase Fluorometry Coupled to a Diffusion Scrubber for the Real-Time Determination of Atmospheric Formaldehyde, Hydrogen Peroxide, and Sulfur Dioxide, Atmos. Environ., 22, 949-964 (1988). 

The device was a chemical scrubber in which chemicals were added to the water passing counter-current to the air flow to react with the pollutants. Typical oxidizing agents used included hypochlorites, peroxides, and permanganates. Caustic, hydrogen peroxide, and bleach were all used at different times. The OCSD was interested in exploring conversion of the scrubbers to biofilters in order to reduce the operating costs and the costs of chemicals. 

Tail gas emissions are controlled by improving the S02 conversion efficiency and by scrubbing the tail gas. In a double absorption process plant, a five-bed converter has 0.3 percent unconverted S02, as compared with 0.5 percent for a four-bed converter. A Lurgi Peracidox scrubber may be used to remove up to 90 percent of the residual S02 in the tail gas from a double absorption plant. Hydrogen peroxide or electrolytically produced peroxymonosulfuric acid is used to convert the S02 to H2S04 in the Lurgi scrubber. 

An alternate approach to catalytic scrubbing is the injection of ozone, chlorine, or hydrogen peroxide into the flue gas upstream of the scrubber. Ozone is the more powerful oxidizing agent, with chlorine just behind. Hydrogen peroxide is not always practical because of the long reaction times required. 

Li, J. and Dasgupta, P. K., Measurement of atmospheric hydrogen peroxide and hydroxymethyl hydroperoxide with a diffusion scrubber and light emitting diode-liquid core waveguide-based fluorometry. Anal. Chem., 72, 5338-5347, 2000. 

Trichloroethylene is mixed with an excess of combustible solvent and burned in a chemical incinerator equipped with an afterburner and scrubber. It may be destroyed in aqueous waste streams or groundwater by UV peroxidation, involving treatment with hydrogen peroxide in the presence of UV light (Yost 1989 Sundstrom et al. 1990). Oku and Kimura (1990) have reported reductive dechlorination using sodium naphthalenide in tetrahydrofuran at 0°C for 10 minutes. Chlorine is removed as sodium chloride to the extent of 97-100%. 

Hydrogen peroxide technology has a high initial capital cost because of the need to have two scrubber vessels. The operating costs, initially high because of the cost of the reagent, may drop in the future as a result of either of the following events ... 

Hydrogen peroxide Air Hematin-p-cresol Spectrofluorimetry >10ngm Diffusion scrubber. 

Hence, it is usual to employ mildly acidic conditions to destroy sulphides in solution in order to minimise the amount of H2O2 required. In the gas phase, hydrogen sulphide can be removed by scrubbing the gas stream with a hydrogen peroxide solution. Here, alkaline conditions are more effective owing to better absorption of H2S and avoidance of sulphur precipitation in the scrubber. 

The HCl-free gas is treated in a sulfur dioxide scrubber where SO2 is absorbed and continuously oxidized to sulfuric acid. Complete oxidation is assured by recycling a portion of the absorbent through an electrolytic cell that generates hydrogen peroxide in-situ. The hydrogen peroxide quickly oxidizes absorbed sulfur dioxide. 

Hydrogen peroxide solutions produce a 50% H2SO4 solution that is usually blended with the acid plant s concentrated acid. They are commonly used as start-up scrubbers since the reagent cost is high (typically on the order of US 600-1000/tonne of 50% H2O2-H2O peroxide solution). Some peroxide scrubbers are used continuously at American sulfur burning acid plants (Brown, 2011). 

SO2 and HCl are the most frequent pollutants in the combustion flue gas. To take them out, the flue gas is rapidly cooled to 80 °C by injection of cold water and subsequently washed with alkaline water in two packed scrubbing towers in series (each tower 6 m high). Caustic soda solution is used to keep the pH in the scrubbers at a constant level. The SO2 and HCl are both neutralized in this way and the sodium sulfite from SO2 is oxidized in a reaction tank with hydrogen peroxide (H2O2). Resulting are sodium sulfate and sodium chloride. Both are non-toxic, but they cause a salt load on the municipal sewage system. 

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