Sulfur dioxide feeding

Excess sulfur dioxide feed to a chlorine dioxide reactor, leading to excessive exothermic reaction, combined witli failure of the cooling system... 

Are low-pressure alarms and automatic shutoff valves provided on chlorine/sulfur dioxide feed lines ... 

Excess sulfur dioxide feed to a chlorine dioxide reactor, leading to excessive c.xothennic reaction, combined witli failure of the cooling system Backflow of process reactants to a sulfur dioxide feed tank, resulting in the formation of corrosive sulfurous acid or explosive reactions witli incompatible materials... 

Backflow of process reactants to a sulfur dioxide feed tank, resulting in... 

Design criteria The required contact time = 1-5 min sulfur dioxide feed rate = 1.1 lb per lb of residual chlorine sodium sulfite feed rate = 0.57 lb per lb of chlorine sodium bisulfite feed rate = 0.68 lb per lb of chlorine sodium thiosulfate feed rate = 1.43 lb per lb of chlorine. 

Provision of the sulfur dioxide feed gas for a contact plant is usually obtained by sulfur combustion, but there are many other potential sources. Pyrite, FeS2, is burned (Eq. 9.27) and other sulfidic minerals are roasted (Eqs. 9.28 and 9.29), the latter primarily for their metal values rather than for the sulfur dioxide. 

Based on the results of this program, a new primary reactor has been designed and installed at El Paso. This reactor produces 10 tons of sulfur/day when using pure sulfur dioxide feed and 7.8 tons/day on 12% sulfur dioxide feed gas. 

Operation was resumed at El Paso on October 28, 1973, using a 12% sulfur dioxide feed gas. Only minor operational difficulties have been encountered to date with this feed. However, curtailed natural gas use forced shutdown of the plant on several occasions. The future availability of natural gas for industrial use could limit application of the ASARCO sulfur dioxide reduction process. It is probable that a suitable reducing gas can be generated using other fossil fuels, although this alternative has yet to be proved. 

Many large smelting operations that produce veiy high concentrations of sulfur dioxide feed the gas stream directly into a sulfuric acid plant The design and operation of acid plants of this type ate not discussed in this text, as they are considered to represent a separation and chemical manufacturing operation, not a gas purification process. On the other hand, the removal of sulfiu dioxide from dilute smelter oif-gas streams and the recovery of unconverted sulfur dioxide finm the acid plant tail gas constitutes gas purification problems and are reviewed in this chapter. 

This is an exothermic, reversible, homogeneous reaction taking place in a single liquid phase. The liquid butadiene feed contains 0.5 percent normal butane as an impurity. The sulfur dioxide is essentially pure. The mole ratio of sulfur dioxide to butadiene must be kept above 1 to prevent unwanted polymerization reactions. A value of 1.2 is assumed. The temperature in the process must be kept above 65°C to prevent crystallization of the butadiene sulfone but below lOO C to prevent its decomposition. The product must contain less than 0.5 wt% butadiene and less thM 0.3 wt% sulfur dioxide. 

Ma.nufa.cture. The preparation of sulfuryl chloride is carried out by feeding dry sulfur dioxide and chlorine into a water-cooled glass-lined steel vessel containing a catalyst, eg, activated charcoal. Alternatively, chlorine is passed into Hquefted sulfur dioxide at ca 0°C in the presence of a dissolved catalyst, eg, camphor, a terpene hydrocarbon, an ether, or an ester. The sulfuryl chloride is purified by distillation the commercial product is typically 99 wt % pure, as measured by ASTM distillation method D850. 

Other components in the feed gas may react with and degrade the amine solution. Many of these latter reactions can be reversed by appHcation of heat, as in a reclaimer. Some reaction products cannot be reclaimed, however. Thus to keep the concentration of these materials at an acceptable level, the solution must be purged and fresh amine added periodically. The principal sources of degradation products are the reactions with carbon dioxide, carbonyl sulfide, and carbon disulfide. In refineries, sour gas streams from vacuum distillation or from fluidized catalytic cracking (FCC) units can contain oxygen or sulfur dioxide which form heat-stable salts with the amine solution (see Fluidization Petroleum). 

The Claus process converts hydrogen sulfide to elemental sulfur via a two-step reaction. The first step involves controUed combustion of the feed gas to convert approximately one-third of the hydrogen sulfide to sulfur dioxide (eq. 9) and noncatalytic reaction of unbumed hydrogen sulfide with sulfur dioxide (eq. 10). In the second step, the Claus reaction, the hydrogen sulfide and sulfur dioxide react over a catalyst to produce sulfur and water (eq. 10). The principal reactions are as foUow ... 

The amount of combustion ait is tightly controlled to maximize sulfur recovery, ie, maintaining the appropriate reaction stoichiometry of 2 1 hydrogen sulfide to sulfur dioxide throughout downstream reactors. Typically, sulfur recoveries of up to 97% can be achieved (7). The recovery is heavily dependent on the concentration of hydrogen sulfide and contaminants, especially ammonia and heavy hydrocarbons, ia the feed to the Claus unit. 

A derivative of the Claus process is the Recycle Selectox process, developed by Parsons and Unocal and Hcensed through UOP. Once-Thm Selectox is suitable for very lean acid gas streams (1—5 mol % hydrogen sulfide), which cannot be effectively processed in a Claus unit. As shown in Figure 9, the process is similar to a standard Claus plant, except that the thermal combustor and waste heat boiler have been replaced with a catalytic reactor. The Selectox catalyst promotes the selective oxidation of hydrogen sulfide to sulfur dioxide, ie, hydrocarbons in the feed are not oxidized. These plants typically employ two Claus catalytic stages downstream of the Selectox reactor, to achieve an overall sulfur recovery of 90—95%. 

In two processes under development as of 1997, the sulfur dioxide stream reacts with reduciag gas over a proprietary catalyst to form elemental sulfur. Both processes have achieved a sulfur recovery of 96% ia a single reactor. Multiple reactor systems are expected to achieve 99+% recovery of the feed sulfur. The direct sulfur recovery process (DSRP), under development at Research Triangle Institute, operates at high temperature and pressure. A similar process being developed at Lawrence Berkeley Laboratory is expected to operate near atmospheric pressure. 

Scmbbers for removing sulfur dioxide from smelter off-gases have been under development for many years. They are widely used in Japan. The calcium sulfate (gypsum) obtained from this process is suitable feed for waUboard production (see Calcium compound, calcium sulfate Sulfur removal and recovery). 

Inadequate water removal from hydrocarbon feeds in a sulfur dioxide... 

Liquid solvents are used to extract either desirable or undesirable compounds from a liquid mixture. Solvent extraction processes use a liquid solvent that has a high solvolytic power for certain compounds in the feed mixture. For example, ethylene glycol has a greater affinity for aromatic hydrocarbons and extracts them preferentially from a reformate mixture (a liquid paraffinic and aromatic product from catalytic reforming). The raffinate, which is mainly paraffins, is freed from traces of ethylene glycol by distillation. Other solvents that could be used for this purpose are liquid sulfur dioxide and sulfolane (tetramethylene sulfone). 

This process includes two main sections the burner section with a reaction chamber that does not have a catalyst, and a Claus reactor section. In the burner section, part of the feed containing hydrogen sulfide and some hydrocarbons is burned with a limited amount of air. The two main reactions that occur in this section are the complete oxidation of part of the hydrogen sulfide (feed) to sulfur dioxide and water and the partial oxidation of another part of the hydrogen sulfide to sulfur. The two reactions are exothermic ... 

Figure 5. NO conversion on Cu/Ti02 catalysts prepared according different procedures. The feed is the standard one containing 20 ppm of sulfur dioxide.

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