SULFUR RECOVERY PEACHES ALL-TIME HIGH IN 1991

Recovery of elemental sulfur from natural gas R processing plants and petroleum refineries in the U.S. reached a record high in 1991. The production of elemental sulfur from Frasch mines has taken the role of a swing source of sulfur to meet U.S. demand over the past decade. This role should continue into the next decade.

These were the conclusions of a report issued by Edward Swain, process planning engineer for Bechtel Corp., Houston. This article updates a previous sulfur production report by Swain by adding 1990 and 1991 data (see OGJ, Mar. 25, 1991, p. 45).

SULFUR SOURCES

Sulfur is a key raw material for the worldwide chemical and fertilizer industries. The current demand patterns for sulfur are expected to continue through the next decade with about half of it being used to produce phosphatic fertilizers and the other half used in some 30 chemically oriented industries.

Sulfur is produced or recovered from four sources:

Frasch
Pyrites
Hydrocarbon operations
Other forms. Table 1 shows historical U.S. production data by Frasch mining, natural gas plant recovery, and petroleum refinery recovery.

FRASCH

Frasch sulfur has been loosing its place as a primary source of elemental sulfur in the U.S. All operating U.S. Frasch mines are in Louisiana and Texas.

At 1991 production rates, Pennzoil Sulfur Co.'s Culberson, Tex., mine has about 15.8 years of remaining life. freeport Sulfur Co.'s three producing Louisiana mines have only 3.7 years of life at 1991 rates. Freeport, however, has added about 39.1 million metric tons, or about 43.8 years, to the company's sulfur reserves.

Texas Gulf (Elf Aquitaine) is a minor Frasch sulfur producer with a mine at Boling, Tex.

NATURAL GAS

Sulfur occurs in sour natural gas as free hydrogen sulfide. Desulfurization of sour natural gases yields a concentrated hydrogen sulfide gas (acid gas) stream. The hydrogen sulfide is then converted to elemental sulfur, usually by the Claus process. The Claus process has three converter stages that recover as much as 98% of the sulfur from the feed stream. The gas stream leaving the Claus unit enters a tail gas treating unit, where total recovery for the system approaches 99.8%.

U.S. Petroleum Administration for Defense District (PADD) No. 3 (map) produces about 71% of the total U.S. marketed gas production. It is therefore expected that PADD 3 will continue to lead the U.S. in recovering elemental sulfur from natural gas.

PETROLEUM REFINERIES

Sour gases produced at petroleum refineries are treated before entering the refinery fuel system. This treatment is necessary to meet air quality standards for sulfur emission levels of flue gases from refinery process heaters and boilers.

Because refineries in PADD 3 represent about 45% of total U.S. crude distillation capacity, they have been, and will continue to be, the leader in elemental sulfur recovery from refinery gases. Sulfur recovered from U.S. petroleum refineries has increased about 74% in the last 10 years, even though crude runs have grown only 13%. The sulfur content of the U.S. crude slate has increased over the same period, contributing to the rise in sulfur recovery (Table 2).

Elemental sulfur recovered from refineries, expressed as metric tons/1,000 bbl crude input, has increased about 53% over the period, as well.

SULFUR PRICES

The largest sulfur end use is for sulfuric acid production. The largest end use of sulfuric acid, in turn, is for phosphatic fertilizer production. The pricing of sulfur, therefore, normally follows the demand and pricing of phosphatic fertilizers.

As both the U.S. and worldwide phosphatic fertilizer industries have been weak and there has been an increase in nondiscretionary quantities of sulfur, worldwide sulfur prices have decreased over the past several years (Table 3). It is doubtful, according to Swain, that near-term U.S. sulfur prices will reach $100/ton over the next 5 years. The average value, fob plant, for shipment of recovered elemental sulfur varies widely by geographic region, as illustrated by Table 4. Low values are common in PADD 4 and PADD 5 states.

Somewhat higher values had been typical in PADD 1,

PADD 2, and PADD 3 states. Sulfur prices in 1991, however, in these three regions approached a common price of $71/metric ton.

These low prices fall far short of defraying the cost of operating a sulfur recovery unit in a U.S. refinery to meet air quality standards, or in a natural gas plant to meet product quality specifications. Swain does not, however, foresee any reversal of this trend in the near term.