Sulfur recovery in U.S. refineries is at an all-time high

Edward J. Swain
Consultant Houston

Sulfur is produced through three main routes: Frasch mining, recovery from pyrites, and recovery from crude oil and natural gas. Sulfur recovery from U.S. refineries reached an all-time high in 1995: 13,753 metric tons/calendar day (mt/cd).

Frasch mining has lost its place as the primary source of elemental sulfur. During the past decade, Frasch has become a swing source of sulfur, and will continue to be so for the foreseeable future.

Current demand patterns for sulfur are expected to continue through the next decade. About half of world sulfur production will be used to produce phosphatic fertilizers. The other half will be used in some 30 chemically oriented industries.

The data reported in this article were collected by the U.S. Bureau of Mines/U.S. Geological Survey, unless otherwise noted.

Sulfur from natural gas

Fig. 1 [18817 bytes] shows U.S. sulfur production for the 10-year period ending in 1995. Recovery from petroleum operations accounted for 70% of sulfur production in 1995, compared to 59% in 1986.

To meet U.S. environmental standards for sulfur emissions, 99.8% of the hydrogen sulfide in natural gas must be removed. Processors typically use the Claus process and tail gas treating to achieve these recovery levels.

Oil & Gas Journal reports 623 natural gas treating plants in the U.S., and 64 associated sulfur recovery units at the beginning of 1996 (OGJ, July 1, 1996, pp. 65, 110). Table 1 [10717 bytes] shows the distribution of these facilities by Petroleum Administration for Defense District (PADD). (For a map of PADDs, see OGJ, Jan. 13, 1997, p. 46.)

Table 2 [11437 bytes] shows the U.S. Bureau of Mines/U.S. Geological Survey data for sulfur recovered from natural gas plants between 1991 and 1995.

The six states in PADD 3 (Alabama, Arkansas, Louisiana, Mississippi, New Mexico, and Texas) are responsible for about 70.5% of total U.S. natural gas production. But PADD 3 is responsible for only 50.5% of sulfur production from natural gas (Table 2).

PADD 4 (the Rocky Mountain Region) produced almost 45% of the sulfur recovered from U.S. gas processing plants in 1995. This is because there are several large gas plants treating the raw gases produced in the Overthrust Belt in Wyoming, and these gases contain high concentrations of hydrogen sulfide.

Sulfur from refineries

Sulfur is recovered during refining operations to reduce sulfur concentrations in refined products and fuel gases. Low concentrations of sulfur in fuel gases are necessary to meet emissions standards for process heaters, boilers, and flue gases.

U.S. refineries are producing greater quantities of sour gases because they are:

• Processing medium-to-high sulfur, medium-to-low gravity crude oils
• Hydrotreating virgin and cracked naphthas and light distillates
• Thermally processing and catalytically cracking vacuum gas oils and reduced crudes
• Hydrodesulfurizing and hydrocracking atmospheric distillates, vacuum gas oils, and reduced crudes

Table 3 [11695 bytes] shows sulfur recovered at U.S. refineries, by PADD. Refineries in PADD 3 (the Gulf Coast) represent about 45% of U.S. distillation capacity. In 1995, these plants produced about 57% of the sulfur recovered at U.S. refineries.

Sulfur recovered by U.S. refineries has increased 41% in the last 10 years, although crude runs have increased only about 10%.Table 4 [17552 bytes] shows the 10-year history of crude runs and sulfur recovery from U.S. refineries. The sulfur recovery rate, expressed as metric tons/1,000 bbl crude input, has increased 28% over the period.

As of Jan. 1, 1996, of the 166 refineries operating in the U.S., 110 had sulfur recovery facilities. But, although 66% of operating plants produced sulfur, they accounted for 89% of U.S. crude distillation capacity. These refineries are mostly medium-to-large plants with complex downstream facilities.

The six refining companies that recovered the most sulfur in 1994 were:

• Exxon Co. U.S.A., 1,463 mt/cd
• Amoco Oil Co., 1,056 mt/cd
• Chevron U.S.A. Inc., 1,005 mt/cd
• Star Enterprise, 894 mt/cd
• Mobil Oil Corp., 826 mt/cd
• Koch Refining Inc., 628 mt/cd.

Given reported sulfur unit expansions and additions, refineries should continue to be a growing source of elemental sulfur to meet U.S. demand.

The quantity of sulfur recovered at U.S. refineries during 1995 represents 61.6% of the sulfur in the crude oil feeds. PADD 3 refiners had the greatest recovery rate (73.2%) while PADD 1, the East Coast, had the lowest (34.4%).

It should be noted that refineries that operate sulfur recovery units maintain an excess of capacity to provide flexibility in meeting environmental standards. Recently, sulfur plant utilization at U.S. refineries has averaged about 58%.

Based on expected changes in environmental legislation, sulfur recovery from crude oil charged to U.S. refineries should increase to about 63% by 2000.

A major portion of the unrecovered sulfur winds up in the bottom-of-the-barrel fractions: asphalt, road oils, petroleum coke, and residual fuel oils. Given demand patterns and the complexity of the U.S. refining industry, these products constitute a small proportion of refinery output.

One of the driving forces for increased sulfur recovery at refineries in the coming years is the declining quality of the U.S. crude slate. Over the last 10 years, the API gravity of U.S. crude runs has decreased an average of 0.12°/year (OGJ, Jan. 13, 1997, p. 46). During the same period, sulfur content has increased by an average 0.21 wt %/year.

During the last 5 years, however, these trends have slowed. In the first half of the 1990s, gravity declined 0.06°/year and sulfur, only 0.002 wt %/year.

If the 10-year trend continues, coupled with additional downstream processing units installed to upgrade the bottom of the barrel to light, clean-burning transportation fuels, an additional 152,000 metric tons (mt) of sulfur will be recovered between now and 2000.

Sulfur prices

Sulfur shipment values are reported by the U.S. Bureau of Mines/U.S. Geological Survey for both Frasch and recovered sources (Table 5 [12453 bytes]).

The largest end use of elemental sulfur is sulfuric acid production, and the largest end use of sulfuric acid is phosphatic fertilizer production. As a result, the price of sulfur normally is determined by the demand for and price of phosphatic fertilizers.

Globally, the phosphatic fertilizer industry was weak in 1993 and 1994. Coupled with increased sulfur recovery, this caused drastic price decreases. Prices recovered somewhat in 1995, but it is doubtful that U.S. sulfur prices will reach $75/mt over the next 5 years.

In the U.S., sulfur prices vary widely by geographic region. During 1995, average prices for PADD 1 shipments were $53.64/mt, while in PADD 4, they were only $13.43/mt. Prices at the lower end of this scale (which are common in PADDs 4 and 5) do not help defray the costs of operating a sulfur recovery unit in a refinery or gas processing plant.

Imports, exports

About 2.2 million mt of elemental sulfur were imported into the U.S. during 1995. Canada and Mexico are the two major sources.

Canada is the world's largest exporter of sulfur; nearly 90% of its production is exported. Sulfur recovery from natural gas processing represents 78% of Canada's total sulfur production. In 1995, that amounted to about 9 million mt. The remaining 22% of Canada's sulfur production came from refineries.

The majority of Canada's sulfur is recovered in Alberta and British Columbia and exported out of the Port of Vancouver. The average 1995 export price for Canadian sulfur was $38.92/mt.

Sulfur production in Mexico also comes solely from petroleum sources. In 1995, the price of sulfur from Mexico averaged $57.56/mt.

U.S. sulfur is exported to countries in Western Europe, South America, Africa, and the Far East. Export prices have declined in the past 5 years because of decreasing global sulfur demand and increasing competition from other sulfur-producing countries. These countries include Canada, the former Soviet Union, Poland, and Saudi Arabia.

It is doubtful that the U.S. sulfur export market will reach 1 million mt in the coming year.

The Author