Edward J. Swain
Bechtel Corp.
Houston
Current supply-demand patterns for U.S. sulfur will continue through this decade. About half of it will be used to produce phosphatic fertilizers and the other half in approximately 30 chemically oriented industries.
Those are the results of a study of U.S. sulfur production conducted recently by Bechtel Corp.'s process technology group, Houston.
Primary sources for the data are the U.S. Department of Energy (DOE), U.S. Department of Interior's Bureau of Mines (BOM), and Oil & Gas Journal.
SOURCES
Sulfur is produced or recovered from four sources: Frasch, pyrites, hydrocarbon operations, and other forms.
Most sulfur production prior to the mid-1950s was of a discretionary nature, produced either by Frasch mining (elemental sulfur) or as sulfuric acid from pyrites.
In the mid-1950s, the production of nondiscretionary recovered sulfur from hydrocarbon operations-natural-gas treating facilities and petroleum refineries-entered the scene as a source of elemental sulfur.
U.S. Bureau of Mines'data for sulfur production between 1985 and 1989 show about an 8.5% increase in total sulfur production in all forms.
For 1985, total world production was 53.7 million metric tons; for the U.S., 11.6 million metric tons. For 1989, total world production was 58.3 million metric tons; the U.S. produced 11.6 million metric tons.
The worldwide increase in sulfur production resulted from nondiscretionary recovered sulfur from hydrocarbon operations in countries outside the U.S. The U.S. in 1985-1989 averaged about 20% of total worldwide production. This value of U.S. sulfur production will be maintained for the 1990s.
The historical U.S. production and recovery of elemental sulfur, 1980-1989, is shown in Fig. 1.
FRASCH MINING
The production of elemental sulfur from Frasch mines has become a swing source of sulfur to meet U.S. demand over the past decade. This role of being a swing source will continue in the 1990S.
Frasch sulfur mines are located only in Louisiana and Texas.
In 1989, Texas mines were operated by Pennzoil Sulphur Co. and Texas Gulf (Elf-Aquitane). In Louisiana, mines were operated by Freeport Sulfur Co.
Pennzoil is the leading producer of Frasch sulfur in the U.S. at its mine near Culberson, Tex.
The facilities at Culberson have a design production capacity of 2.50 million metric tons per year (mt/y).
During 1989, 1988, and 1987, the facilities were operated at approximately 79%, 65%, and 60% of design capacity, respectively.
Proved reserves at the end of 1989 at Culberson were reported to be about 29.67 million metric tons. At 1989's production rate, this gives the mine about 14.8 years of remaining life.
During the summer of 1988, Pennzoil obtained three federal leases for offshore Louisiana Gulf Coast. As of yet, no reported finds of sulfur have been made.
Freeport Sulfur Co. is the second major producer of Frasch sulfur in the U.S. at its three mines at Garden Island Bay, La., Grande Isle, La., and Caminada, La.
Proved reserves at the end of 1989 at the three producing mines are reported to be about 6.2 million metric tons. At 1989's production rate, this gives the mines about 4.1 years of remaining life.
During summer 1988, Freeport and a consortium of firms purchased 11 leases from the U.S. offshore the Louisiana Gulf Coast. Main Pass Block 299 has been explored and has an estimated reserve of 67 million metric tons of sulfur. Production from Block 299 is expected to start in April 1992.
Texas Gulf has been a minor Frasch sulfur producer from its mine at Boling, Tex. Texas Gulf closed that mine in 1988 and is not expected to open it unless sulfur supplies are short and sulfur prices increase dramatically.
HYDROCARBON OPERATIONS
Production of recovered elemental sulfur from naturalgas processing plants and petroleum refineries reached an all-time high in 1989.
RECOVERED SULFUR-NATURAL GAS
Sour, wet, acid gases are treated at natural-gas plants that prepare the raw gases for sale as a rich methane gas stream and NGL products.
In sour natural gas, the sulfur occurs as free hydrogen sulfide. Desulfurization of sour natural gases yields a concentrated hydrogen sulfide gas (acid gas) stream. The hydrogen sulfide then is converted to elemental sulfur, usually by the Claus process.
The process has been well developed with three converter stages that obtain up to 98% recovery of the sulfur in the rich feed stream. To meet sulfur-emission environmental standards, the gas stream leaving the Claus unit enters a tail-gas treating unit in which total sulfur recovery for the system approaches 99.8%.
U.S. total gas withdrawals have been dropping gradually from a peak of 66 bcfd in 1971 to 57.53 bcfd in 1989. They increased during 198589, up from 53.52 in 1985.
About 75% of the gas produced during 1989 was nonassociated; the other 26% was associated.
This ratio changed only slightly over the 1985-89 period.
Although the quantity of gas withdrawal has been falling historically, the raw gases are becoming leaner (that is, containing fewer heavy hydrocarbon components), but the hydrogen sulfide content is increasing.
Production of recovered elemental sulfur during 1989 as nondiscretionary by-product from natural-gas plants was from 64 plants (23 companies) in operation as of Jan. 1, 1990 (OGJ, July 10, 1990, p. 82).
By source, about 64% of the recovered sulfur from natural gas during 1989 was produced by four companies at 23 plants, including Amoco Production Co., Chevron U.S.A. Inc., Exxon Co. U.S.A., and Shell Western E&P Co.
The recovered sulfur produced from natural-gas plants grouped by PAD districts during 1985-1989 is listed in Table 1.
All six states in PAD district No. 3 (Alabama, Arkansas, Louisiana, Mississippi, New Mexico, and Texas) produce natural gas that represents about 71 % of the total U.S. marketed gas production. Therefore, that district is expected to be a leader in recovering elemental sulfur from natural gas.
The 57% increase (1989 vs. 1985) in recovered elemental sulfur in the combined No. 4 and No. 5 PAD districts is due to several natural-gas plants recently installed to treat raw gases produced in the Overthrust Belt region of Wyoming.
Although 761 natural-gas plants were operating as of Jan. 1, 1990, only 64 plant sites had sulfur recovery units (SRUs), according to the BOM.
PAD No. 3 contains 49 of these SRUs with 7,281 metric tons/day capacity; PAD No. 4, 8 with 3,432 metric tons/day capacity; and PAD No. 2, 5 with 340. SRU plants and capacities in the other two PADs are negligible.
These 64 SRUs have an estimated design capacity of 11,311 metric tons/day and recovered some 6,951 metric tons/day of sulfur.
The 64 SRUs had an estimated operating utilization rate of about 61%. Excess capacity is installed to provide operability of the total treating complex in meeting environmental standards.
RECOVERED SULFUR-REFINERIES
Sour gases produced at petroleum refineries now are being treated before entering the refinery fuel system. Recovered sulfur from U.S. refineries by PAD districts is shown in Table 2.
The increasing quantities of sour gases being produced in refineries result from the following causes:
- Processing medium-high sulfur and medium-heavy gravity crude oils vs. low sulfur-light gravity crude oils
- Hydrotreating virgin-cracked naphtha and light virgin-cracked distillates
- Thermal processing and catalytic cracking of vacuum gas oils and reduced crude oils
- Hydrodesulfurization and hydrocracking of atmospheric, vacuum gas oils, and reduced crude oils.
The sour gases produced are treated to meet the air quality standards of sulfuremission levels of the refinery process heaters-boilers flue gases.
Sulfur recovered by U.S. petroleum refineries has increased 72% in the last 10 years, according to DOE, even though crude runs reported by the DOE dipped about 1.8 million b/cd from the 1980s.
In 1989, crude runs were just about up to the 1980 crude runs (Table 3).
The elemental sulfur recovered from refineries, expressed as metric tons of sulfur/1,000 bbl of crude-oil input, has increased 73% over the last 1 0 years as well (Fig. 2).
Production of recovered elemental sulfur, a nondiscretionary by-product from crude-oil refineries, originated from 104 plants (52 companies) in operation as of Jan. 1, 1990, as reported by DOE and Oil & Gas Journal surveys.
H2S-rich gas streams from the Conoco and Exxon refineries at Billings, Mont., are pipelined over the fence to Montana Sulfur & Chemical Co. where sulfur is recovered in an SRU.
By source, about 59% of the recovered sulfur from refineries during 1989 was produced by seven companies at 33 refineries, including Amoco Oil Co., Chevron U. S. A. Inc., Exxon Co. U.S.A., Mobil Oil Corp., Shell Oil Co., Star Enterprise, and Unocal Corp.
The recovered sulfur produced from refineries grouped by PAD districts 1985-1989 appears in Table 2.
As refineries located in PAD district No. 3 represent about 45% of the total U.S. refinery operating capacity, it is reasonable to expect that the district will be the leader in recovered elemental sulfur from refinery gases.
The 1989 recovered quantity-10,654 metric tons/calendar day of sulfur from U.S. petroleum refining operations-represents about 55.8% of the sulfur contained in the crude oil processed.
During 1989, the sulfur-recovery factors within the PAD districts were estimated to be as follows: PAD No. 142.9%; PAD No. 2-44.0%; PAD No. 3-66.7%; and combined PAD Nos. 4 and 5-51.0%.
These recovery factors are based on the quality of crude oil charged to U.S. refineries (Table 4).
The 5-year history of crude-oil quality presented in Table 4 indicates an approximate decrease of 0.10 API/year and an increase of 0.04 wt % in sulfur content of crude oil being processed in U.S. refineries.
If this trend continues, coupled with additional downstream processing units installed to upgrade the bottom-of-the-barrel fraction into transportation fuels, the resulting percentage of recovered sulfur should increase to about 61% of the contained sulfur in crude oil by 1995.
Table 5 summarizes the number of U.S. petroleum refineries, their crude-oil distillation capacities, and their sulfur-recovery capacities as of Jan. 1, 1990, by PAD districts.
Although only 105 refineries (53% of all U.S. refineries) have sulfur-recovery plants, these represent 83% of the total available crude-oil distillation capacity. These 105 refineries mostly have medium-to-large, crude-oil distillation capacities and complex downstream facilities.
Most recent U.S. refinery projects include new SRUs or are expanding their existing SRUS.
The recovery of elemental sulfur from petroleum refineries should continue to be a growing source in the near and long term to meet U.S. sulfur demands.
The 104 SRUs processing H2S-rich gas from petroleum refineries have an estimated design capacity of 19,212 metric tons/day, and they recovered some 10,654 metric tons/day of sulfur during 1989.
The 104 SRUs had an estimated operating utilization of about 55%.
Excess capacity is installed to provide operability of the total refinery complex in meeting environmental standards.
PRICING
Sulfur-shipment values are reported by the Bureau of Mines both as Frasch and recovered sources.
The largest sulfur end use is for sulfuric acid production. In turn, the largest end use of sulfuric acid is for phosphatic fertilizer production. Therefore, the pricing Of sulfur normally follows the demand pricing of U.S. phosphatic fertilizers.
The average value, F.O.B. plant, for shipment of recovered elemental sulfur varies widely by geographic region (Table 6). Low values are common in the Rocky Mountain states (PAD No. 4) and on the West Coast (PAD No. 5).
Somewhat higher values are common in the Midcontinent eastern states (PAD No. 1), and the southern states (PAD No. 3) are near the values for Frasch sulfur.
The reported average sales values of elemental sulfur were slightly higher by only 1.2% throughout the U.S. during 1989 vs. 1988. The prices were not as high, however, as they were during 1981-1982.
In 1989, prices for Frasch sulfur were only 3.3% higher than 1988 prices, whereas 1989 prices for recovered sulfur rose only 2.2% over 1988 prices. The lower U.S. fertilizer markets and continuing increase in recovered sulfur from the natural-gas treating facilities in Wyoming are still distorting the average value calculated for all recovered elemental sulfur shipments in 1989.
Although the average value of recovered sulfur, F.O.B. plant, is not large, the revenue should help defray the capital investment and operating cost of installing an SRU in a petroleum refinery to meet air-quality standards or in a natural-gas plant to meet product quality.
IMPORTS, EXPORTS
During 1989, about $210 million worth of imported sulfur entered the U.S. marketplace. Imported sulfur mainly comes from Canada and Mexico .
Canadian sulfur is mainly from natural-gas plants in Alberta and British Columbia as well as the many sulfur stock piles in Alberta. The stock piles were established some 15 years ago and reached a peak of about 21 million tons in late 1978.
Withdrawal of sulfur from these piles to serve the U.S. and worldwide markets was less than 4 million tons as of mid-1990.
At least 1 million tons of this sulfur is not readily recoverable because it has sunk into the ground.
Sulfur imported from Canada is at a freight-cost disadvantage over sulfur imports from Mexico.
During 1989, approximately $107 million worth of exported sulfur left the U.S.
Sulfur is usually exported from Gulf Coast ports and has been shipped to Brazil, Belgium/Luxembourg, and Mexico in recent years. increased sulfur exports from Middle East countries such as Saudi Arabia are making inroads in Western Europe and North Africa markets.
U.S. sulfur exports should gradually decrease in the near future.
Copyright 1991 Oil & Gas Journal. All Rights Reserved.
