Sulfuric Acid Plant Operation

Sulfuric acid plants are designed with optimized catalyst volumes and bed inlet temperatures to give a reasonable approach to equilibrium in each bed to achieve the maximum possible conversion of sulfur dioxide to sulfur trioxide. As shown by the examples in Table 2.8, this results in a significantly smaller volume in bed 1 than the remaining beds. The total catalyst volume used normally corresponds to a loading of 180-220 liters of catalyst per tonne of sulfuric acid produced per day although many plants use more, depending on conditions and the source of the sulfur dioxide. Lower volumes of catalyst are normally used in double-absorption units. 

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In the contact section of the plant, the saturated gas is first dried by contact with 93% acid and then the sulfur dioxide in the gas is oxidized to sulfur trioxide. The sulfur trioxide is absorbed in 98% acid where it combines with the free water present to produce additional sulfuric acid. Figure 3 is a typical flow diagram of a double-catalysis sulfuric acid plant operating with sulfur dioxide gas from copper converters. 

A typical sulfuric acid plant operating on sulfur as the main raw material consists... 

Conventional contact process sulfuric acid plants operate with four adiabatic catalyst beds, or passes. Heat of reaction is removed after each bed by heat exchange to generate steam or by quenching with cold air. 

A continuous bleed is taken from the reactor to remove high boilers. Values contained in this bleed are recovered in the bleed stripper and the distillate from this operation is recycled to the esterification reactor. The bleed stripper residue is a mixture of high boiling organic material and sulfuric acid, which is recovered for recycle in a waste sulfuric acid plant. 

Owing to the cycHc nature of the TBRC operation, waste heat recovery from the off-gases is not practical and the SO2 content of the gas varies with the converter cycle. In order to supply a relatively uniform flow and strength SO2 gas to a sulfuric acid plant, a system has been installed at RonnskAr whereby the SO2 from fluctuating smelter gases is partially absorbed in water. During smelter gas intermption, SO2 is stripped with air and the concentrated gas deflvered to the acid plant. 

Pan and cascade burners are generally more limited ia flexibiHty and are useful only where low sulfur dioxide concentrations are desired. Gases from sulfur burners also contain small amounts of sulfur trioxide, hence the moisture content of the air used can be important ia achieving a corrosion-free operation. Continuous operation at temperatures above the condensation poiat of the product gases is advisable where exposure to steel (qv) surfaces is iavolved. Pressure atomiziag-spray burners, which are particularly suitable when high capacities are needed, are offered by the designers of sulfuric acid plants. 

Liquid SO is usually produced by distilling SO vapor from oleum and condensing it. This operation is normally carried out at a sulfuric acid plant where the stripped oleum can be readily refortified or reused. EHminating all traces of sulfuric acid from the SO vapor stream is important to minimize polymerization of the Hquid condensate. When this is done, it is frequently possible to utilize unstabilized Hquid SO if precautions are taken to prevent it from freezing before use. At some plants, gaseous 100% SO is utilized directly instead of producing Hquid. 

The uppermost hearth serves to dry the damp ore in the hot (ca 500°C) gases exiting the top of the toaster. These gases may contain up to 15% of the total cmde oxide and up to 6% sulfur dioxide, high enough to be fed to a sulfuric acid plant. In some pyrometaHurgical operations, desulfurization is continued in a sintering step. 

TABLE 14-21 Operating Characteristics of Various Types of Fiber Mist Eliminators as Used on Sulfuric Acid Plants ... 

Centaur A process for reducing sulfur dioxide emissions from sulfuric acid plants. An activated caibon with both absorptive and catalytic properties is used. The technology uses fixed beds of Centaur carbon to oxidize sulfur dioxide to sulfuric acid in the pores of the carbon. The sulfuric acid is recovered as dilute sulfuric acid, which is used a make-up water in the sulfuric acid production process. Developed by Calgon Carbon Corporation in the 1990s. Calgon Carbon and Monsanto Enviro-Chem operated a Centaur pilot plant at an existing sulfuric acid facility in 1996. 

Cominco [Consolidated Mining Smelting Company] A process for absorbing sulfur dioxide from smelting operations. The sulfur dioxide is absorbed in an aqueous solution of ammonium sulfite regeneration is by acidification with sulfuric acid. The ammonium sulfate byproduct is sold. Operated at the Cominco smelter at Trail, Canada, and at other smelters and sulfuric acid plants in the United States. Licensed by the Olin Mathieson Corporation. The name has been applied also to a lead extraction process. 

Peracidox A process for removing sulfur dioxide from the tail gases from sulfuric acid plants by absorption in peroxomonosulfuric acid (Caro s acid). The peroxomonosulfuric acid is generated on-site by the electrolytic oxidation of sulfuric acid. Developed by Lurgi and Sud-Chemie and first operated in 1972. 

Smelter Acid. If acid is produced involuntarily, as in a smelter operation, it is possible to estimate the cost of acid production in the same manner as that for an elemental sulfur acid plant. To the smelter, however, acid output is simply a mandated concomitant of the process required to produce the metal. Depending on the location of the smelter, the sources of demand, the size of the market, and competition from other producers, the acid sale price may or may not be sufficiently high even to yield a positive net-back, much less a desired rate of return on investment for the acid portion of the operation. This situation does not necessarily lead to closure. Positive or negative, the effect should be registered only in the overall profitability of the entire smelter operation. 

The lead-chamber process is more economical than the contact process, but it produces a more dilute and less pure product. Thus, the chamber process can compete only in the market that can use a relatively impure and dilute acid. Although chamber-acid plants now in use will undoubtedly be operated for many years to come, it seems probable that all sulfuric acid plants constructed in the future will employ the contact process or some still more efficient process. 

Sulfur burning acid plants operate steadily almost all the time. The main significance of this is that temperature is constant at every point in the plant s catalyst beds. It means that none of the gas s heat is being used to heat catalyst. 

The book begins with a 9 chapter description of sulfuric acid manufacture. These chapters introduce the reader to industrial acidmaking and give reasons for each process step. They also present considerable industrial acid plant operating data. We thank our industrial colleagues profusely for so graciously providing this information. 

Estimate by the turnover-ratio method the fixed-capital investment required for a proposed sulfuric acid plant (battery limit) which has a capacity of 140,000 tons of 100 percent sulfuric acid per year (contact-catalytic process) using the data from Table 19 for 1990 with sulfuric acid cost at 72 per ton. The plant may be considered as operating full time. Repeat using the cost-capacity-exponent method with data from Table 19. 

Independent chemical companies own and operate most of the sulfuric acid plants. Plant capacities are generally in the range of 500-1500 tons fresh sulfuric acid/day. However, a number of acid plants are installed within, or immediately adjacent to, the petroleum refinery area most of these acid... 

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