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Publication > Issue > Articles

Claus unit reliability

Summary

David C Parnell and Timothy R Armstrong, TPA, Inc, discuss the influence of equipment and controls in the operation of today's sulphur recovery units.

Abstract

The most influential variable affecting the unit performance for modified Claus sulphur recovery units (SRU), is the feedstock. This is especially true for Claus units operating in refineries, wherein the SRU is often fed a second gas stream (from a sour water stripper), as well as the acid gas from an amine unit.

Both the feed gas quality (composition) and rate significantly affect the sulphur recovery unit performance, including both reliability and overall efficiency (percentage of the sulphur recovered.) Unfortunately, the control and/or regulation of these important gas feed variables is frequently not within the jurisdiction of the Claus plant operating staff.

However, there are some items in both the design and operation of the SRUs that can improve the unit reliability as well as the overall sulphur recovery percentage. These reliability options in the sulphur plant involve both equipment and control schemes, including automatic shutdown functions. The principal equip­ment items involved in the improved reliability are the air blowers, the feed gas knock­out drums, thermal reactor (combustion chamber), burner(s), waste heat boiler, sulphur condensers, catalytic reactors, the catalytic reactor feed heaters (reheaters), liquid sulphur seals and incinerator(s). Materials of construction, including refractory, are also very important relative to the overall unit reliability.

The critical controls for unit reliability centre around the air (oxygen) feed rate as a function of the sour gas feed rate, and the automatic shutdown devices. Additional important controls involve the catalytic reactor feed temperature, water flow to the boiler and sulphur condensers, and steam pressure controls.

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Sultran embraces ­information systems technology

Summary

Sultran's computer-driven network system developed to better manage its sulphur logistics system is a critical component in ensuring future success for the company and its customers. Jason Stevens spoke to outgoing CEO, Kevin Doyle, about the merits of the system and its role in the changing landscape of Canadian sulphur logistics.

Abstract

Since Sultran’s inception in 1976, the electronic network of software systems and supporting hardware has progressed at an unrelenting pace.

According to Kevin Doyle, outgoing CEO of Sultran, the computer-based network which is used to better manage the entire logistics process through a series of computer programs, has become at least as important to Sultran’s customers as the physical movement of the goods.

While customers require the sulphur to move efficiently and expeditiously, they also need very current and accurate information on inventories, location and movement through the system, ships’ positions and a host of other data.

“Railroad reporting systems would report to us where our 2000 or so railcars were throughout the system as of 12 hours ago. However, today that is not good enough. We really don’t care where they were 12 hours ago – we need to know where they are now and when and where they are going to be at a specific point in the future,” said Mr Doyle, in an interview with Sulphur magazine recently.

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New materials put acid in its place

Summary

Sulphur takes a look at some of today's popular materials for application in the production and handling of sulphuric acid.

Abstract

The development and application of specialised materials for a ­variety of sulphuric acid concentrations continues. The search for materials possessing the highest corrosion resistance under the most challenging conditions, whilst still maintaining manufacturability, mechanical strength, etc, remains the common objective.

The reducing and oxidising properties of sulphuric acid greatly affect the selection of a material for sulphuric acid service. At lower concentrations (around 65%), and temperatures up to 66ºC (151ºF), the acid is reducing and better handled by materials resistant to reducing conditions. Similarly, at higher concentrations, the acid is oxidising and materials resistant to oxidising media are essential.

The manufacture of sulphuric acid via conventional contact pro-cesses typically involves acid concentrations ranging from 93-99% at temperatures up to around 130ºC (265ºF), with plant sizes ranging from less than 100 t/d to well over 3,500 t/d.

Sulphur dioxide is dried using 93-98% sulphuric acid, converted to sulphur trioxide, and then to sulphuric acid in a packed tower, normally in contact with 98% sulphuric acid.

Therefore, requirements of a structural material for handling hot, concentrated sulphuric acid include:

  • corrosion- and erosion-resistance under the nominal operating conditions of acid concentration, temperature and flow rate;
  • the ability to resist short-term ­excursions from these conditions;
  • corrosion-resistance against con­taminated coolants, such as brackish water or seawater;
  • ease of fabrication and welding;
  • good mechanical properties, met­al­lurgical stability, and availability.

 

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Oil Sands projects gather pace

Summary

While sulphur recovered annually from the processing of Alberta's vast Oil Sands is to date only some 10% of the 7.3 million tonne total (mainly from sour gas processing), recent announcements may change this picture. Report by Jason Stevens.

Abstract

During the last 18 months no fewer than seven majors (Shell, Syncrude, Suncor, Imperial, Esso, Mobil and Gulf Canada) have announced new Oil Sands projects in excess of $13 billion, which could eventually result in 1-2 million extra tonnes of sulphur coming onto an already saturated market by the turn of the century.

Alberta gas plants dominate sulphur recovered from gas – supplying 6.4 million tonnes – while British Columbia’s contribution is much lower at just under a million tonnes.

Inventory statistics provided by Alberta, reveal stocks of 9.7 million for the period January to September. This is 1 million tonnes higher than the same period for 1996 which showed about 8.7 million tonnes.

In 1996 sulphur producers found markets for 6.1 million tonnes, or 82% of the total – 7.3 million tonnes – produced.

In the 1997 the industry faced stronger than expected demand for sulphur which resulted in increased exports for the fourth straight year. At the close of 1997 Canada exported offshore between 5.6 million and 5.8 million tonnes, registering an increase of about 10% over 1996. About 1.5 million tonnes was shipped to the United States.

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Prediction of sulphur markets, the weather, global warming and other issues

Summary

Peter Clark, Director of Research, Alberta Sulphur Research Ltd, gives his ­personal views on the value of predictions – not only in respect to the difficulty in predicting sulphur market fluctuations, but also in ­predicting that complex, highly emotive area, the climate, which was the recent focus of the Kyoto sessions in Japan.

Abstract

Nearly every year I attend conferences and hear predictions of future sulphur production and markets. This year in Vienna, Mr Kitto gave an eloquent assessment of past predictions and presented some thoughts on factors likely to influence future markets. He concluded that most of the predictions made in the last 10 years were inaccurate, that they had failed to see even major factors affecting the market and even suggested that the more accurate predictions contained an element of luck. In fact, I would have been very surprised if the predications had been accurate.

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