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Clinsulf-SDP reaches up to 99.85% sulphur recovery

Summary

The first commercial scale Clinsulf™-SDP plant started up at Nynäs Refinery in Sweden in December 1995. Since then it has been operating at sulphur recovery rates well above its design rate of 99.1% and there have been no unplanned outages. P. M Heisel and J. Kunkel of Linde AG and Ulf Nillson and P. Eriksson of Nynäs AB report on operating experiences to date.

Abstract

Sulphur recovery plants throughout the world face tightening ­environmental regulations. The well known modified Claus process is under continuous optimization to reach higher sulphur recovery rates. Nevertheless, in many cases tail gas treatment processes have to be added downstream. To date, three groups of tail gas clean-up processes have ­established some market share: direct oxidation processes which catalytically oxidize H2S to elemental sulphur1, subdewpoint (SDP) processes which extend the Claus reaction at low temperatures in a number of additional catalytic beds and hydrogen sulfide (or SO2) recycle processes 2, 3 for higher sulphur recoveries of up to 99.99%.

All of these processes add a clean-up process to the Claus process which makes the whole system more complicated and thus prone to more maintenance, higher cost and more downtime. The Clinsulf ™ process developed by Linde AG of Germany takes a new approach as it integrates the catalytic Claus and a subdewpoint tail gas treatment to give a high performance two-stage process which can achieve a sulphur recovery rate of up to 99.8%.

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FSC redefines itself

Summary

In early August 1998, a psychological debate was underway between Freeport Sulphur Company (FSC) and US phosphate producers to determine prices in the final quarter, and more importantly to establish whether FSC could still exercise a decisive leadership role in depressed sulphur markets. Jason Stevens tracks developments within FSC.

Abstract

FSC (recently divorced from former majority owners, Freeport-McMo­Ran Resource Partners) had earlier pushed for a $5/lt increase in sulphur prices on the back of terminating operations at its Culberson Country Mine, which effectively took 600,000 lt/y of sulphur out of domestic markets.

FSC claimed the closure was a­­ ­direct result of excessive Canadian dumping of sulphur on US markets.

It is estimated that about 1,4 million tonnes of Canadian sulphur entered the United States in 1997.

FSC declared it would meet near-term commitments by liquefying solid inventories held at its Port Sulphur Terminal, and from production at its sole remaining mine, Main Pass 299, located offshore, Louisiana in the Gulf of Mexico.

FSC’s push for higher prices was met with immediate resistance from phosphate producer’s who claimed markets were fundamentally in balance.

FSC took further steps to enhance its position by buying up available spot tonnage and benefiting from recovered producers willingness to hold off on making any deals until it had settled its contracts.

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Marsulex: hungry for growth

Summary

The recent IT Holdings, Inc ("Intertrade") and BCT Chem­trade acquisitions from ­­Trelle­borg by Marsulex confirms its growing presence on the North American landscape as it follows a high-growth strategy. Report by Jason Stevens.

Abstract

The key piece in the Intertrade acquisition, manufacturing com­plex in Copperhill, Tennessee, will allow Marsulex to effectively match involuntary supply services with steady market demand, by raising its sulphuric acid capacity by over 700,000 t/y.

Marsulex told Sulphur that this extra swing capacity unlocks a greater flexibility to respond to customer needs in the industrial and fertilizer markets, which currently consume nearly all of its acid volumes.

The Copperhill complex consists of a sulphuric acid and liquid sulphur dioxide manufacturing facility, as well as a plant that uses proprietary technology to produce sulphonated organics – value-added chemicals used in the manufacture of detergents, resins, and pharmaceuticals.

Marsulex is currently assessing the possibility of producing new products at the complex which also converts excess energy generated by the sulphur burner into electricity – some of which is then utilized by the Tennessee Valley Authority.

The Intertrade acquisition also gives Marsulex a stronger foothold along the United States western sea­board, through its subsidiary, Sulex Inc, which operates two sulphur pril­ling facilities at Long Beach, California and Anacortes, Washington State.

The Chemtrade acquisition gives Marsulex a truly international dimension, allowing it to build on existing long-term relationships with smelter and oil refineries, primarily in northern Europe, for the removal of sulphur and sulphuric acid.

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Meeting acid quality ­requirements

Summary

In order to meet product acid quality requirements the ­sulphuric acid produced as a byproduct of metallurgical and smelting operations must be treated to remove the mercury content, typically to less than 0.5 ppm. Lisa Connock ­reports on the most popular techniques used to achieve these levels as well as a new technique which removes the mercury from the product acid rather than ­metallurgical gas entering the acid plant.

Abstract

Many sulphide ores contain varying amounts of mercury which is volatilzed during metallurgical roasting and smelting operations. The mercury occurs in the sulphur dioxide gas partly as elemental mercury and partly in a chemically bound form. In a normal wet gas cleaning system, where metallurgical process gases are purified and cooled before passing through wet electrostatic precipitators, the elemental mercury vapours present in the process gases are only separated to a relatively small extent. Therefore, mercury easily enters the following stages where it is absorbed by sulphuric acid and results in a contaminated product which does not meet product acid quality requirements.

Acid containing less than 1 ppm is a standard requirement, while less than 0.5 ppm is mandatory for sulphuric acid designated for food processing or animal feed production and fertilizer manufacture. In fact, low mercury acid (e.g. containing 0.1 ppm Hg) often attracts a premium over typical merchant grade product containing up to 0.5 ppm mercury.

The most popular gas purification techniques for mercury removal are the Boliden Norzink process (34 plants worldwide) and the Thiosul­phate pro­cess (4 plants worldwide). Both of these processes treat the smelter gas before it enters the sulphuric acid plant.

A further option is to remove the mercury from the product acid using the relatively new Molecular Recog­nition Technology developed by IBC Advanced Technologies, which uses specially designed ligands to remove the mercury.

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Solving problems with bolt-on jackets

Summary

Bolt-on systems have evolved over the past 25 years and are used throughout the molten sulphur processing and sulphur transport industry. H. Gaines of Controls Southeast, Inc. and P. C. Wielatz of PME Enterprises, Inc. compare bolt-on systems with the traditional fabricated weld-on systems and discuss what to look for in the design, fabrication and installation of a bolt-on system.

Abstract

Thermal maintenance of molten sulphur is a difficult problem frequently faced by engineers in the sulphur industry. In a refinery, maintaining a tem­perature window of 280-310°F (138-154°C) is critical (Fig. 1). Below 280°F, hydrogen sulphide can be emitted if vapour space exists, creating a potentially hazardous situation. Above 320°F (160°C) the viscosity of molten sulphur rises exponentially. Tempera­ture main­ten­ance problems can shut down an entire unit or bring a marine terminal’s discharge operations to a standstill. When cross- contamination occurs, the results are usually even more devastating.

These problems are all too well known, as are the traditional solutions. The sulphur processing and transport industry has tried several methods of maintaining process temperatures over the years. Gut lines have been installed in transfer and transport piping with some success. However, the risk of cross-contamination associated with gut tracing has led to alternative means of thermal maintenance being sought. Tube tracing schemes of many varieties have been installed on molten sulphur core piping, pumps, valves and other components, but with very limited success. A track record of freeze-ups has indicated that tube tracing provides inadequate thermal maintenance for sulphur handling. “Blistered pipe” has been generally effective but is quite expensive because it is difficult to manufacture and install.

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Smelter acid ascendent in merchant markets

Summary

Falling copper prices have caused recent cutbacks in SX-EW leaching by copper producers in the southwestern United States, increasing availability of sulphuric acid from smelters for sale in the North American merchant market. Jason Stevens reports.

Abstract

Mr Bruce D. Farmer, President and Chief Executive Officer of Kennecott Utah Copper Corpo­ration told Sulphur that this availability has been offset only slightly by recent raw material shortages at several southwestern smelters.

The merger between Union Pa­cific and Southern Pacific railroads in 1997 continues to produce poor rail service, negatively affecting western smelters – and other bulk chemical shippers – by increasing transit times to customers and requiring larger tank car fleets to ship the same tonnage. The persistence of serious operational problems in the Houston-New Orleans corridor required Federal intervention. As these problems were resolved, rail congestion moved westward to Los Angeles.

“Strong industrial activity in the United States has absorbed much of the unexpected surplus of smelter acid. However, as occurred last spring, when smelter producers get out of balance, sulphuric acid tonnage moves into the Florida phosphate market at negative netbacks,” said Mr Farmer.

Kennecott produced 857,000 short tonnes (st) of sulphuric acid in 1997. With the plant now operating at design capacity, Kennecott expects to exceed the 1 million st mark by the end of 1998.

Falling copper prices have prompt­ed a more cautious approach by some companies favouring the leaching process previously mentioned in Sulphur no 245.

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Equipment advances for sulphur recovery units

Summary

Sulphur reports on some new technical and equipment innovations for sulphur recovery units, including an alternative to sulphur seal legs, an SO2 injection system to increase the capacity of Claus units by more than 100%, a novel cooled wall thermal reactor and a new sulphur degassing system

Abstract

The quest to provide sulphur recovery units that are more reliable, recover more sulphur, are safer and easier to operate, and reduce capital and operating costs, continues to generate a great deal of interest worldwide and has led to many technical and mechanical improvements to standard proven technologies and the introduction of new technical and equipment innovations.

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