Sulfur dioxide removed with

One of the primary reasons that the spray dryer-scrubber is able to achieve excellent sulfur dioxide removal with such low liquid-to-gas ratios is the small size of the droplets produced by the high speed centrifugal atomizer. This type of atomizer also has an easily controlled turndown capability which is a desirable feature that has been demonstrated in the pilot tests. As gas flow decreases, the amount of sodium carbonate solution can be decreased in direct proportion without interfering with sulfur dioxide removal efliciency. The atomizer actually produces finer droplets at the lower liquid flow rates. This appears to compensate for any gas-liquid mixing problems that could impair performance. 

Ennis. C. E., 1977, Sulfur Dioxide Removal with Ammonia A Fresh Perspective, Second Pacific Chemical Engineering Congress (PACHEC 1977), Denver, CO. 

It is generally unacceptable to emit sulfur dioxide, thus the scmbber effluent must be treated for sulfur dioxide removal. If the plant aheady possesses faciUties for the production of sulfuric acid, this rather concentrated sulfur dioxide stream can be easily fed into the wet gas cleaning circuit and disposed of in the sulfuric acid plant. The quantity is so small that it does not put any additional burden on the sulfuric acid plant. Because no tellurium is carried over with the selenium dioxide during roasting, it is possible to produce a selenium product which can be purified to commercial grade (99.5-99.7%). 

Regenerable absorption processes have also been developed. In these processes, the solvent releases the sulfur dioxide in a regenerator and then is reused in the absorber. The WelLman-Lord process is typical of a regenerable process. Figure 11 illustrates the process flow scheme. Sulfur dioxide removal efficiency is from 95—98%. The gas is prescmbbed with water, then contacts a sodium sulfite solution in an absorber. The sulfur dioxide is absorbed into solution by the following reaction ... 

Liade AG offers the Clintox process for sulfur dioxide removal. This process uses a physical solvent to absorb the sulfur dioxide. A concentrated sulfur dioxide stream is produced by regeneration. The Clintox process can be iategrated with the Claus process by recovering sulfur dioxide from the iaciaerated tail gases and recycling the sulfur dioxide to the front of the Claus unit. 

While the use of low-sulfur fuels is one mechanism to reduce sulfur dioxide emission, alternatively most approaches focus on scrubbing or ridding the emissions in smoke stacks of sulfur dioxide gas. A number of different types of scrubbers, i.e., sulfur dioxide removal systems, are available for industry. One system sprays the flue gas into a liquid solution of sodium hydroxide. The hydroxide combines with SO2 and O2 to form the corresponding sulfate which can be removed from the aqueous solution ... 

Scrubbing Efficiency. The effect of the stoichiometric ratio of total alkali fed to the scrubber [Ca(0H)2 plus NaOH] to total acid gas (SO2 plus HC1) is shown in Figure 2. The theoretical limit for reaction of the alkali with the acid gases is indicated in the figure. (Actually, some removal of HC1 can be expected with no alkali present.) Sulfur dioxide removal efficiencies were found to exceed 99 percent when alkali/acid stoichiometric ratios were greater than about 1.9. HC1 removal efficiencies generally exceed SO2 removal efficiencies at any given alkali/ acid stoichiometric ratio. 

Fabric filters are the preferred collection equipment as additional sulfur dioxide removal takes place in the baghouse Cl,2) Typically, under conditions such that 80% of total inlet SO2 is removed, 60 to 70% of the removal takes place in the spray dryer with 10 to 20% additional removal taking place in the bag filters... 

The combustion of sulfur-rich char is accompanied by the production of an undesirable reaction product, viz., sulfur dioxide. However, most of the sulfur dioxide should be removed from the combustion gases before they leave the combustor. This may be accomplished by the introduction into the combustor of suitable additives which can absorb sulfur dioxide. Limestone is such an additive. The limestone reacts with sulfur dioxide in the presence of oxygen to form calcium sulfate, which is a solid product and can be easily removed from the reactor. In this work, a model is proposed for the prediction of sulfur dioxide removal from the combustion gases, based on knowledge of gas-solid reactions taking place on a single pellet. 

The Shell flue gas desulfurization (SFGD) process described in 1971 [4] removes sulfur oxides from flue gas in a PPR using a regenerable solid adsorbent (acceptor) containing finely dispersed copper oxide. At a temperature of about 400°C, sulfur dioxide reacts with copper oxide to form copper sulfate according to the reaction. 

A third emission reduction choice is to remain with the existing front end process, which continues to produce a sulfur dioxide-containing waste gas stream, and move to some system which can effectively remove the sulfur dioxide from this waste gas before it is discharged. Many methods are available, each with features which may make one more attractive than the others for the specific sulfur dioxide removal requirements (Table 3.8). Some of the selection factors to be considered are the waste gas volumes and sulfur dioxide concentrations which have to be treated and the degree of sulfur dioxide removal required. It should be remembered that the trend is toward a continued decrease in allowable discharges. The type of sulfur dioxide capture product which is produced by the process and the overall cost are also factors. Any by-product credit which may be available to offset process costs could also influence the decision. Finally, the type of treated gas discharge required for the operation (i.e., warm or ambient temperature, moist or dry, etc.), also has to be taken into account. Chemical details of the processes of Table 3.8 are outlined below. 

In the double-catalysis plant a major portion of the sulfur trioxide is removed from the gas in an intermediate absorption tower after the second stage of conversion. The balance of the gas, which is returned to the converter for the final two stages of conversion, is a very weak sulfur dioxide gas with a high oxygen-to-sulfur dioxide ratio. The equilibrium conditions for this gas leaving the converter are very close to 100% conversion of the total sulfur dioxide entering the converter. In steady state operation, which is not possible with copper converter gas, over 99.8% conversion of sulfur dioxide to sulfur trioxide is expected in double-catalysis plants. 

C) but did not return to the initial value (Section A) within 40 min. The addition of 15% water vapor (Section D) further decreased the sulfur dioxide removal efficiency. Curve b in Figure 2 depicts the analyses of carbon dioxide when the bauxite catalyst was subjected to the water treatment. The mirror image resemblance of curves b and a in Figure 2 suggests that the reaction stoichiometry is closely represented by Equation 1 and that the poisoning effect of water is essentially caused by its competition for chemisorption on the alumina Lewis acid sites with the sulfur precursor of the intermediate (9) reductant carbonyl sulfide. 

Double-Bed Catalysts. Because the temperature of the colder section in the nonisothermal catalyst bed could not be readily controlled, an apparatus was constructed that contained two separate furnaces, each containing 20 g of Surinam red mud. The temperature of the first bed was varied to determine the optimum operating conditions with an inlet gas of 0.57% sulfur dioxide, 0.89% carbon monoxide, and 3% water vapor in helium. The exhaust gas analyses from the first furnace are shown in Figure 6. These results indicate that the hydrogen sulfide and sulfur dioxide removal efficiency increases with temperature up to about 400 °C. Beyond this temperature there is little improvement. 

As a direct result of this pilot effort, a wetted film packing was found which exhibits excellent sulfur dioxide absorption with an exceptionally low pressure drop. This packing has outstanding mass transfer characteristics and high specific surface area. The packing developed by Munters Corp. is a key element in the limestone-based sulfur dioxide removal system. 

Research-Cottrell realized that the industrial and utility markets required different types of sulfur dioxide removal equipment. Therefore, it contracted with Ab Bahco Ventilation of Sweden to market their sulfur dioxide removal technology in the U.S. and Canada. Bahco technology is particularly applicable to industrial boiler and process applications (7, 8, 9). The first U.S. Bahco installation will handle seven stoker-type boilers at the Rickenbacker Air Force Base in Columbus, Ohio. 

Feeding solutions from the absorber system and the regeneration system through surge tanks enables the entire recovery process to operate smoothly and reliably despite frequent gas flow and concentration fluctuations. In addition, the surge tanks allow the regeneration section to be shut down for up to 3 days without interfering with the sulfur dioxide removal in the absorption section. This is possible because the absorber is the only part of the system that contacts the flue gas and removes the sulfur dioxide. 

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