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Cross-border flows

Summary

Investment in base metals resources and transport infrastructure is opening up a complex array of possibilities for regional sulphuric acid supply in southern Africa. Chris Cunningham reports.

Abstract

In 1999, when Sulphur reviewed sulphuric acid markets in southern Africa, specifically markets in the Copperbelt of Zambia and the Demo­cratic Republic of Congo (Sulphur No 262), trade was staying fairly strictly within borders.

Zambia was in the throes of painful privatisation of a severely run-down copper industry. This, combined with logistical problems and high product price, meant that rail shipments of acid from South Africa were curtailed. In any event, a successfully run sulphur burning plant in the Copperbelt was meeting much of the requirements of the area’s copper leach operations.

For its part, South Africa continued as an important producer of smel­ter acid through its base and precious metals industries, and as a major im­porter of sea-borne brimstone. Namibia had only one major user of acid, which could supply its own needs by burning domestically produced pyrites.

Since then, a series of events has started to give the question of acid balance a more regional feel. The eventual completion of Zambian copper’s sell-off and the start of large-scale investment programmes in the country, ambitious plans for the development of infrastructure in Namibia, the emergence of major projects in base metals production in south western Africa, even a significant mishap in an acid plant, all have contributed to a fresh and complex round of options that should start to give shape to the acid market over the next few years.

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Dry ice blasting removes sulphurcrete

Summary

A new simple method for the cleaning of sulphur condensers in Claus sulphur recovery units has been developed and implemented. Michael Heisel and Alex Buinger of Linde Gas AG presents a dry ice blasting technique, which can successfully remove the troublesome sulphurcrete that builds up in condenser tubes. Advantages of the new technique include reduced downtime, quicker start-up and no wastes.

Abstract

Sulphurcrete consists of elemental sulphur, salts formed from sulphur plus CO2, SO2, NH3 and dust from abrasion of Claus catalysts. The hardness of this material matches that of granite.1 Over time sulphurcrete builds up and plugs the tubes of sulphur condensers. Traces of sulphuric acid are formed under the sulphurcrete layer leading to corrosion. For these reasons sulphurcrete has to be removed. The majority of Claus plant operators will be fully aware how difficult a task that is.

Sulphur recovery plants have the important task of converting toxic hydrogen sulphide to harmless elemental sulphur. It is important that the sulphur recovery plants have a very high on-stream factor and any downtime required for cleaning sulphur condensers must be as short as possible. However, due to its extreme hardness, extreme measures are needed for its removal e.g. drilling. That in turn causes substantial mechanical stress on the equipment being cleaned, often leading to damage of the equipment. Removal of sulphurcrete by washing is not an option as it is insoluble in most common solvents, especially those that are easy to handle, such as water.

Although this problem is common to many of the roughly one thousand Claus plants world-wide there was no satisfactory solution available until recently when a surprisingly simple method for the removal of sulphurcrete was introduced using dry ice blasting.

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Too much too soon?

Summary

India has kept up the pace of construction and upgrade in its downstream oil industry. Now it faces over-supply and the need for further investment to meet new environmental ­standards for fuels. Chris Cunningham reports.

Abstract

Since 1996 India’s refiners have transformed the shape of the nation’s supply-demand pattern for automotive fuels. Culminating in a rush of major refinery openings in 1998/9, the industry’s efforts have meant the replacement of a massive bill for low-sulphur diesel with the more manageable costs of crude imports. Apart from the effects on the balance of its fuel bill, India has raised its production of value-added refinery products and is fast becoming a significant producer of refinery sulphur, another commodity which accounts for a hefty red mark on its balance of payments.

On the down side, the refinery programme could be seen as an in­stance of mistiming. Its logic was driven by the government’s demand for domestic oil companies to supply the fuel – low sulphur diesel – to drive its plans for the modernisation of Indian agriculture. However, last year demand for fuel fell whilst the refineries demonstrated that they could convert crude at high levels of efficiency, to the point of major surplus.

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Liquid redox enhances Claus process

Summary

Claus units can easily achieve sulphur recovery efficiencies exceeding 99.9+% by employing a liquid redox system such as LO-CAT as a tail gas treating unit. The significantly lower capital cost of this combination compared to conventional amine-based tail gas units offsets its higher operating costs. Further benefits include reduced sensitivity of the Claus unit to changes in feed gas composition and flow rate and excellent turndown capability. Gary J. Nagl of USFilter Gas Technology Products discusses the merits of this process combination.

Abstract

Throughout the years, the Claus process has undergone a continuous evolution in attempts to increase the sulphur recovery efficiency of the process. In the 1930s, a thermal stage was added to the two catalytic stages, which increased the recovery efficiency from 95% to approximately 97%. In the 1970s, the SCOT process was introduced which added hydrogenation/hydrolysis plus amine separation to treat the tail gas from the Claus process. In 1988, Super­Claus was introduced, which added a selective oxidation reactor to the end of the Claus process, increasing the efficiency to approximately 99%. And just recently, EuroClaus1 was introduced, which replaced the second Claus reactor in the Super­Claus process with a selective hydrogenation catalyst increasing the efficiency to 99.5%.

It is obvious that the trend is to achieve higher and higher sulphur recovery efficiencies. It is anticipated that in the near future Claus units installed in developed nations will required sulphur recovery efficiencies of 99.5% or better. Coupling a Claus unit and a liquid redox process, such as the LO-CAT® either directly or indirectly in combination with a hydro­genation/hydrolysis reactor, how­ever, can reliably achieve 99.9+% sulphur recovery.

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Meeting targets

Summary

Refinery options to meet low sulphur gasoline targets are steadily growing. New technologies have been developed and some of them are already in commercial operation. Lisa Connock rounds up some of the recent developments in post treating FCC naphtha to meet future specifications for low sulphur gasoline.

Abstract

Regulations governing the properties of transportation fuels are evolving rapidly as governments in many parts of the world introduce new legislation to reduce undesirable emissions from internal combustion engines. These regulations address a number of fuel properties, including oxygen content, vapour pressure, benzene, overall aromatics content, boiling range, olefin content and sulphur levels. While significant refinery investments have been required to meet each of the required properties to date, reducing sulphur to target levels is likely to represent the highest cost element to refiners over the next decade.

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