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The sulphate process - here to stay

Summary

Tioxide is a leading world producer of titanium dioxide, with factories employing both the sulphate and chloride process routes. In the following article, Tioxide provides a perspective on the future prospects for sulphate titanium dioxide plants and for sulphate technology.

Abstract

M uch has been written about the respective merits of the sulphate and chloride process routes in titanium dioxide production, particularly concerning the environmental impact. The debate has tended to be coloured by the views of producer who are competitive in only one of the two technologies. Tioxide produces around 80% of its output by the sulphate process and the remainder via the chloride route. We vi w the two processes a being complementary rather than in competition and both proc sses will continue to play key roles in th d velopm nt of the company's future.

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Destination Plant City

Summary

The 5th annual meeting of the Phosphate Maintenance Roundtable takes place on 21-22 MarchJ 1996J at the Plant CitYJ FloridaJ Convention Center. Jim Chandler of IMCAgricoJ Uncle SamJ LouisianaJRoundtable chairmanJand I<.evin Bryan ofPCS Phosphate Co. J A uroraJNorth CarolinaJprogramme chairmanJ have organised another outstanding programme of interest to plant and operating personnel.

Abstract

The Phosphate Maintenance Roundtable is an annual event attended mostly by plant people with a maintenance background. Processes covered at the meeting include thos for sulphuric and phosphoric acid and fertilizer granulation, as well as for related faciliti s. The objective of the Roundtable is to promote communication between plants and companies for improved equipment reliability, safety performance, and environmental excellence. This is accomplished by the active participation of all delegates. Indeed, the delegates themselves are the presenters and act as facilitators on subjects of interest to plant personnel - both from maintenanc and operations. Interaction among participants is actively encouraged and time for open discussions and questions is built into the schedule.

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Accepting the challenge

Summary

Much of the world's 35 million tla of elemental sulphur production must move long distances from the point ofproduction to the point of consumption. Road, rail, ship, barge and pipeline transportation is involved in hauls from a few hundred to thousands of kilometres. Moreover, these transportation and handling challenges must be met within industrial infrastructures that vary widely in their sophistication. The form of the sulphur product also must be such as to be readily accommodated within all of these systems. In the following article, Jim Hyne * reviews the many and varied aspects of the challenge of handling and transporting elemental sulphur in both its liquid and solid forms.

Abstract

The factors that drive the technology associated with handling and transporting elemental sulphur are minimisation of environmental impact, maintenance of high product quality and, of course, cost. In recent years the environmental factor has become increasingly important as fugitive emission regulations and sat ty considerations have been tightened, especially in the developed industrial regions of the world.

Product quality and purity specification have also been a continuing force determining and improving handling and transportation techniques. More sophisticated and efficient equipment for sulphuric acid manufacture has resulted in increased sensitivity to impurities in the feed elemental sulphur. Contaminants such as hydrogen sulphide, moisture, chloride, among others, are of importance and can also have a detrimental effect on both the environment and the handling equipment involved in the transportation of the sulphur.

Cost becomes a critical factor when netbacks to the producer approach or are less than the cost of transportation and handling.

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RAR process finds new uses

Summary

At the recent Sulphur 95 conference in Abu Dhabi) last October) S. Villa of KTI presented a new process scheme which utilizes KTI's RAR process for tail gas treating) acid gas enrichment and purification simultaneously.

Abstract

KTI's RAR (Reduction Absorption Recycle) process is a regenerative liquid absorption-desorption process for removing hydrogen sulphide from gas streams. The gas desorbed during regeneration of the laden wash solution has a considerably higher concentration than the original gas. RAR was developed originally as a Claus tail gas treatment process, producing a regenerated gas stream sufficiently concentrated in hydrogen sulphide to be recycled back to the Claus unit.

Th basis of the process is well known, since the principles do not differ from other similar processes used for the same duty. However, by judicious choice of the most appropriate high-selectivity solvent, it can be applied to other, more complex, hydrogen sulphidecontaining gas streams which are either too dilute or too contaminated for direct processing through normal Claus units.

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Aluminizing stands the test of time

Summary

Following a review of the latest literature and recent discussions with sulphuric acid plant owners) Kim Wynns* and George Bayer** reaffirm the benefits of aluminizing 304H to combat high-temperature sulphidation and polythionic stress corrosion cracking.

Abstract

Aluminized austenitic stainless steel is still the material of choice by many design ers for combating high-temperature sulphidation seen in sulphuric acid plants as well as in gas processing and refineries. In the last decade, bare 304H emerged as the front runner in sulphuric acid plant design when the price of stainless steels dropped and the higher design temperatures became a factor. Recent discussions with sulphuric acid plant owners who changed from the carbon steel design to the stainless steel design indicate that, for the most part, they are pleased with the choice. Unfortunately, as sulphuric acid plants and sulphur recovery units have matured over the years, and as rates and yields have been driven higher and higher, pressure on the operating regime has resulted in higher than expected sulphidation corrosion, flaking of the protective oxide film, and increased fouling of the catalyst.

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A better understanding of LRSR processes

Summary

Liquid redox sulphur recovery processes involve complex chemical processes. Understanding their basic chemistry is crucial to ensure reliable and economical operation. Lisa Connock reports on the current status of liquid redox processes and the process improvements that have been made as a result of recent R&D.

Abstract

Liquid redox sulphur recovery (LRSR) processes remove hydrogen sulphide (H2S) from gas streams and convert the hydrogen sulphide into solid elemental sulphur. LRSR units are frequently used on gas streams where the sulphur throughput is small (less than 20 tid for ironbased liquid redox processes, up to 50 tid for the Stretford process), high-efficiency hydrogen sulphide removal (99.9+%) is required or gas flow/composition fluctuations preclude the use of other sulphur recovery processes.

Figure 1 hows a simple schematic of a LRSR system. Sour gas contacts LRSR solution in an absorber, the LRSR solution absorbs the hydrogen sulphide and converts it into elemental sulphur, and sweet gas exits the system. The solution carrying the sulphur particles flows to d wnstream equipment which regenerates the solution and separates the sulphur from the solution.

LRSR processes usually use a chemical agent (usually a metal) in the aqueous solution to catalyse the oxidation of hydrogen sulphide to elemental sulphur. The most common catalysts are vanadium and iron. The well established Stretford process (licensor: British Gas) utilizes a vanadium catalyst, whereas the SulFerox process (licensor: The Dow Chemical Company/Shell Oil Company) and the ARI Lo-Cat /Lo-Cat II process (licensor: Wheelabrator Clean Air Systems) are the two most prevalent iron-based liquid redox processes.

Detailed descriptions of these processes have been presented in previous issues of Sulphur1-S and will not therefore be included in this article. In this article, we focus on the recent developments to LRSR processes which have been brought about by a gr ater undertanding of the basic chemistry invo v . In the past, liquid redox sulphur recovery processes have had a reputation for being prone to frequent shutdowns caused by sulphur plugging and foaming problems. The high cost and high consumption of chemicals has also been an area of great concern. A greater understanding of the redox chemistry has led to many improvements. Research and development work continues to further optimize · these processes.

Some of the issues which drive the chemical evolution of these processes and the changes which have resulted were emphasized at the Gas Research Institute (GRI) 7th Sulphur Recovery Conference, held in Austin Texas in September 1995.

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