Refinery sulfur production

Carbonyl sulfide occurs as a by-product ia the manufacture of carbon disulfide and is an impurity ia some natural gases, ia many manufactured fuel gases and refinery gases, and ia combustion products of sulfur-containing fuels (25). It tends to be concentrated ia the propane fraction ia gas fractionation an amine sweetening process is needed to remove it. 

Refinery Sulfur Production. By PAD district, approximate annual refinery sulfur production in 1978, assuming a 330 day operating year, was 310,000 LT in district I 524,000 LT in district II 993,000 LT in district III5 59,000 LT in district IV and... 

Table I presents a refinery sulfur recovery capacity forecast made by the National Petroleum Council (NPC). The top portion of the table represents the initial conditions based on current crude input and refinery product slates the bottom indicates additional capacity required for each of three, non-additive, scenarios. As the NPC study shows that sulfur production, as a percent of capacity, in 1982 is expected to be 60% in district I, 54% in district II, 71% in district III, 72% in district IV, and 49% in district V...

Historical data were obtained on U.S. refinery operations and the production of sulfur from U.S. refineries from 1971-1977. A two-parameter model was developed correlating past levels of sulfur recovery with the quality and rate of crude processed and the qualities and amounts of end products. An overall correlation coefficient of 0.91 was obtained. 

Figure 1. Refinery sulfur model past and projected trend of key variables and resultant refinery sulfur production in the U.S., selected cases.

Sulfttr Content. The amount of sulfur in crude is important in terms of handling the crude within the refinery and the undesirable effects of sulfur in finished products. High-sulfur crudes require special materials of construction for refinery equipment because of their corrosiveness. Certain refinery processes require desulfurization of sour charge stocks prior to use as a feedstock, not only because of their corrosiveness, but also because of the effect of sulfur-bearing compounds on expensive catalysts, From the standpoint of the consumer, sulfurous gasoline has an unforgettably offensive odor unless specially sweetened and it may corrode the fuel system and engine parts, as well as pollute the atmosphere after it has been burned,... 

Sulfur is naturally present in many crude oils and petroleum fractions, most commonly as organic sulfides and heterocyclic compounds. Residual fuel oils are variable products whose sulfur contents depend not only on their crude oil sources but also on the extent of the refinery processing received by the fuel oil blending components. Sulfur, present in these fuel oils in varying amounts up to 4 or 5% w/w, is an undesirable constituent, and many refining steps aim to reduce the sulfur content to improve stability and reduce environmentally harmful emissions. 

Sulfur produced by microorganisms in H2S removal plants such as described in the previous section, can be handled in a number of ways. Dried sulfur solids can be used in sulfuric acid production (99% sulfur purity needed) or the formed sulfur sludge can be directed to a smelter where it is converted into high purity sulfur (>99.9%). Unfortunately, currently more sulfur is produced worldwide than is needed as pure chemical and therefore sulfur is also stored in landfill (95-98% sulfur purity needed). Although solid sulfur is considered as a non-hazardous refinery waste, landfill is an undesirable option, partly because acidification by oxidation has to be prevented. 

Depending on the sulfur content in the crude oil, both types of crude oil refineries can have the plants for catalytic waste gas cleaning with the production of sulfur in their technological structure. If more sulfur is produced than the refinery can sell to the chemical industry, it is often reasonable to install plants for sulfuric acid production inside the refinery. 

The sorbent used in the Irvad process is Alcoa Selexsorb (CD grade), which is tailored for polar compounds. The process is essentially a TSA process. Adsorption is performed in a countercurrent moving bed with a slurry of fine-sized alumina. Desorption is performed with hydrogen at various temperatures up to 520 °F. Hydrogen is used for its high thermal conductivity and heat capacity, as well as its ready availability in the refineries. Gasoline products with sulfur as low as 0.5 ppmw were claimed (Irvine, 1998). 

At oil and gas production sites, sulfur dioxide (SO2) and sulfur trioxide (SO3) are produced by the burning of sulfur-containing fuels. In oil refineries, SOx are produced by the combustion of sulfur-containing fuels, including the coke that is burned off of catalysts in FCC regenerators. SOx irritate the respiratory tracts of people and other animals. When adsorbed to particulate matter, SOx are especially bad. While gaseous SOx molecules are trapped by mucous in the upper respiratory tract, inhaled particulates can penetrate deep into lungs. 

The 1989 world production of sulfur in all forms is given in Table 14.1 by region and for major producing countries. Recovered sulfur accounted for 63 percent of brimstone production in 1989. Most of the recovered sulfur was derived from sour gas wells in Canada, the Soviet Union, and the United States. U.S. oil refineries recovered nearly 4 million tons of sulfur from the hydrotreating of sour crudes. Canadian tar-sands comprise the major source of other recovered sulfur production. Frasch and open pit mines in... 

The world production of sulfuric acid (1989) is presented in Table 14.4. Nearly two-thirds of the world s new sulfuric acid production derives from brimstone burning. The balance of new acid production comes largely from pyrite combustion and nonferrous ore smelting. Recycled spent sulfuric acid is a significant fraction of acid production only in the United States and Oceania, primarily Australia. In the United States 52 percent of the spent acid comes from petroleum refineries, 38 percent from plastic and synthetic materials producers, and the balance from a wide variety of sources. 

Crude oil is recovered from the reservoir mixed with a variety of substances gases, water, and dirt (minerals) (4). Thus, refining actually commences with the production of fluids from the weU or reservoir and is followed by pretreatment operations that are appHed to the cmde oil either at the refinery or prior to transportation. Pipeline operators, for iastance, are iasistent upon the quahty of the fluids put iato the pipelines therefore, any cmde oil to be shipped by pipeline or, for that matter, by any other form of transportation must meet rigid specifications ia regard to water and salt content. In some iastances, sulfur content, nitrogen content, and viscosity may also be specified. 

Sulfur, another inorganic petrochemical, is obtained by the oxidation of hydrogen sulfide 2H2S + O2 — 2H2 0 + 2S. Hydrogen sulfide is a constituent of natural gas and also of the majority of refinery gas streams, especially those off-gases from hydrodesulfurization processes. A majority of the sulfur is converted to sulfuric acid for the manufacture of fertilizers and other chemicals. Other uses for sulfur include the production of carbon disulfide, refined sulfur, and pulp and paper industry chemicals. 

Economic Aspects. Most hydrogen sulfide is made and used captively or sold by pipeline at prices which are highly variable, depending on locahty. Production ia the United States exceeds 1.1 X 10 t/yr-It has been estimated that 2.4 x 10 t/yr of sulfur are recovered from H2S-containing refinery streams and 1.8 x 10 t/yr of sulfur are recovered from H S-containing natural gas (120). 

Spent Sulfuric Field. Spent sulfuric acid recovered from petrochemical and refinery processes can be fed to a high temperature furnace at 870—1260°C, where it is transformed kito sulfur dioxide, water, and other gaseous products. After suitable scmbbkig and drykig, the gases are passed to a conventional contact sulfuric acid plant (263). 

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). 

Citric acid is used to chelate vanadium catalyst in a process for removing hydrogen sulfide from natural and refinery gas and forming elemental sulfur, a valuable product (133). 

Petroleum products are obtained from crude oil. In the process of getting the crude oil from the ground to the refinery, many possibilities for emission of hydrocarbon and reduced sulfur gaseous emissions occur. In many cases, these operations take place in relatively remote regions and affect only those employed by the industry, so that little or no control is attempted. 

A modem petroleum refinery is a complex system of chemical and physical operations. The cmde oil is first separated by distillahon into fractions such as gasoline, kerosene, and fuel oil. Some of the distillate fractions are converted to more valuable products by cracking, polymerization, or reforming. The products are treated to remove undesirable components, such as sulfur, and then blended to meet the final product specifications. A detailed analysis of the entire petroleum production process, including emissions and controls, is obviously well beyond the scope of this text. 

Fluid catalytic cracking units present formidable emission control problems. Contaminants are present in both reactor product gas and regenerator flue gas. The reactor product contains hydrogen sulfide, ammonia, and cyanides, plus combined sulfur and nitrogen in the liquid products. Hydrogen sulfide, ammonia and cyanides are handled as part of the overall refinery waste water cleanup. The combined sulfur and nitrogen may be removed by hydrotreating. 

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