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Sulphur management in refineries

Summary

Refiners face a sulphur 'squeeze' – having to take in more sulphur in the form of sourer crudes while achieving lower sulphur levels in products and emitting less SO2.

Abstract

Refiners face significant challenges over the next few years. Diminishing availability of sweet crudes means many refiners are increasingly required to process sour crudes containing higher levels of sulphur. Yet at the same time, refiners are hamstrung both by emissions legislation on sulphur oxides and product specifications on ultra-low sulphur fuels. As a result sulphur management within refineries is more important than ever.

There is no single applicable solution to this conundrum, as every refinery has a different configuration. However, while previous sulphur management solutions have typically been employed on a case by case basis in order to meet specific and individual challenges with a particular section of plant, refiners are increasingly having to look at the entire sulphur flow through the refinery in order to achieve synergies and lower emissions.

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Sulphur in Soils, Crops and Fertilizers

Summary

Mark Evans reviews the latest publication by Dr HLS Tandon, covering sulphur in agriculture, with an emphasis on the situation in India.

Abstract

The issue of a widening sulphur nutrient deficit continues to exercise the minds of agricultural experts around the world, and the continuing depletion of reserves of sulphur in soils threatens to limit further advances in agricultural productivity. India faces particularly acute problems in this respect. This has prompted the renowned agronomist Dr. HLS Tandon to seek practical ways of replenishing India’s soil sulphur reserves. His new book, Sulphur in Soils, Crops and Fertilisers, promises to lay the foundations for the wider and more knowledgeable use of this vital nutrient.

Sulphur in Soils, Crops and Fertilisers – from Research to Practical Application is the fifth book that Dr. HLS Tandon has authored on the subject of sulphur in agriculture and the 48th practical reference book that the Fertilizer Development and Consultation Organisation (FDCO) has published on plant nutrients, fertilizers and integrated plant nutrient management. It continues FDCO’s quest to provide technically sound and easily understood synopses on plant nutrient sulphur for practical use by all stakeholders.

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ASRL review: Liquid sulphur degassing and Claus tail gas treatment

Summary

P.D. Clark, Technical Manager, Alberta Sulphur Research Ltd and Professor of Chemistry, University of Calgary and M.A. Shields, N.I. Dowling, R. Sui and M. Huang, Alberta Sulphur Research Ltd.

Abstract

Degassing of liquid sulphur produced by the Claus process is important because it reduces the hazard due to H2S release from the liquid in storage and transportation systems. New research in our laboratories using solid catalysts based on alumina or silica has shown that the solid acts first to decompose H2SX and the sparge gas, then drives the released gas from the liquid, so displacing the H2SX equilibrium (Fig. 1). This process is usually referred to as the "Amoco" degassing process, which seems only to have been implemented using air as the sparge gas. To our knowledge, Amoco did not discuss the most important facet of degassing with alumina, namely, the decomposition of H2SX by basic sites on the catalyst surface. This mechanistic information turns out to be very important as it suggests that sparge gases other than air can be used, a feature which leads to possible new developments in sulphur recovery. The story relayed in this article is a classic example of the utility of basic research where a few experiments with an initial specific goal opened the door to things that could not have been predicted a priori. Well, at least not by us!

Mechanism of solid catalyst degassing

As is appreciated by all undergraduate students from their first course in catalysis, a catalyst works by speeding up a reaction and in any system where both products and reactants are observed in equilibrium, the catalyst simply speeds up attainment of that equilibrium, catalysing both the forward and reverse reactions. Thus, the catalyst depicted in Fig. 1 is just as capable of forming H2SX as it is of decomposing it. Hence the sparge gas is a vital component in a degassing technology as it displaces the system towards a degassed state by removing H2S liberated from the sulphur. Fortunately, mass transfer of H2S from the gas phase back to the liquid is a limited process which, in theory, suggests that Claus tail gas could be used as the sparge gas even though it contains some H2S. Such an adaptation may be a significant advance in liquid sulphur degassing, as the air degassing results in formation of water and SO2, which complicates compression of the sparge off-gases into the plant. Typically, the contaminated air off-gas is compressed back into the main burner air supply, but plugging with sulphur and corrosion is a common occurrence in these systems. The advantage of using Claus tail gas is that it can be piped back into the Claus plant upstream of the tail gas unit so all H2S liberated by degassing is then treated before it reaches the incinerator.

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Nickel leaching project update

Summary

Nickel leaching projects have run into a variety of technical and financial problems, but are still being driven forward by continuing high nickel prices and a shortage of sulphate ores.

Abstract

Nickel, in increasing demand for the production of stainless steel, is found in two major types of ores; sulphides and laterites. Most nickel production has historically been based on smelting of the higher grade sulphide ores, producing sulphuric acid as a by-product. However, with demand for nickel continuing to increase dramatically and availability of sulphide ores limited, there has been a move towards greater exploitation of laterite ores, which are by their nature more easily accessible and closer to the surface.

However, the concentration of nickel in laterites is often quite low – as little as 1%, so large volumes of rock must be mined – often via an open cast or strip mining method – and then treated in order to extract the nickel using sulphuric acid. There are two main methods of doing this; high pressure acid leaching (HPAL) and heap leaching.

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The market for diammonium phosphate

Summary

Diammonium phosphate accounts for 40% of phosphate fertilizer demand worldwide, and its rapid expansion has had a significant impact on the sulphur market.

Abstract

DAP has become the phosphate fertilizer of choice, having a very high nutrient content of 64%; 18% of it nitrogen and 46% phosphate. This makes it one of the most concentrated and efficient fertilizers to ship around the world. Its use has been growing steadily over the past two decades, and DAP now represents over 40% of the world phosphate market.

Feedstocks

All phosphates ultimately derive from phosphate rock. There are essentially two main types of phosphate rock; igneous and sedimentary phosphates – the latter more widely spread and representing about 80% of global production, the former mainly exploited in South Africa and Russia. While the P2O5 content of sedimentary phosphates is generally falling as the higher grade strata become mined out, the grade of igneous phosphates is still relatively high. The average grade of sedimentary phosphates was 33.7% P2O5 in 1976, but had dropped to 29.7% 30 years later, and in parts of central Florida has fallen to 28.5%. Igneous concentrates, conversely, range from 34-40% P2O5 or even higher, and average 37-38% P2O5 content. Associated with the higher phosphate content is a corresponding lower level of impurities, including calcium oxide, meaning that lower volumes of sulphuric acid are required to treat igneous phosphates, and less phosphogypsum is generated. The volcanic process of formation also helps to ‘boil off’ many heavy metal impurities like cadmium, arsenic, lead and mercury which can cause issues in phosphate fertilizer manufacture.

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Superior pumps and valves for acid applications

Summary

November 2011 marks the 120th anniversary of Lewis Pumps. Established in 1891 with its first vertical acid pump manufactured in 1914, Lewis Pumps continues to grow its product lines in markets throughout the world. Customers in over 120 countries rely on Lewis products to keep their plants running smoothly. With a complete line of sulphuric acid pumps and valves, sulphur pumps, and specialty items, Lewis Pumps continues to evolve to meet the needs of customers. Ken Black of Weir Minerals – Lewis Pumps highlights key milestones and developments and reports on current and future plans.

Abstract

To meet the requirements for larger equipment operating at higher temperatures, Lewis Pumps relies on an expanding selection of large vertical acid pumps composed of proprietary Lewmet® material. Concentrated sulphuric acid at temperatures encountered in the contact process is highly corrosive. With trends toward higher acid stream temperatures to maximise energy recovered from the process, Lewis’ Lewmet® alloy provides maximum resistance to corrosion, erosion, abrasion, and galling.

he sulphuric acid industry has been a particular focus of Lewis Pumps over many decades. Offering a range of vertical acid pumps in sizes from 2" (50 mm) to 18" (450 mm), Lewis Pumps has been able to satisfy the changing demands of the sulphuric acid market. Recent developments within the industry have seen an increase in the size of acid plants, with larger plants requiring larger pumps. Operating temperatures have also been on the rise, and plants that previously ran at 175-195°F (80-90°C) are now reaching temperatures of 200-250°F (95-120°C). These changes have required special attention from engineers and metallurgists at Lewis Pumps.

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Sulphur removal from high CO2 streams

Summary

There has been recent emphasis on the reduction of CO2 emissions and the recovery of CO2 for use. In order to recover CO2 as a product, or to inject it under a nonhazardous classification, producers should thoroughly research the maximum acceptable contaminant levels. In the case of sulphur based compounds, treatment can be challenging. This article* provides an overview of the treatment options to remove sulphur from streams with greater than 90 mol-% CO2. The optimum technology for a given project differs based on a variety of factors including the owner's risk tolerance (for newer processes), facility location, product treating specifications, feed rate and composition, and the values of products and utilities.

Abstract

Capturing CO2 and utilising it for enhanced oil recovery (EOR) has increased in popularity as it offers a means to create a valuable product out of this waste gas. Other possible uses for CO2 include welding, water treatment, medicine, and the food industry. If no product use is available, CO2 can also be injected for disposal. One of the challenges in the re-use or disposal of CO2 from processing facilities is ensuring that any contaminants that could adversely impact the well formation or end user are removed.

One category of problematic contaminants is sulphur-based compounds. The required level of removal is dependent on the final CO2 disposition, and in the case of EOR or sequestration, is often unclear.

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Reliable scrubbing of sulphur tank vents

Summary

Several technologies are used for sulphur tank vents to remove sulphur contaminants. H2S scavengers provide economic H2S removal at concentrations of 500 ppm or less in the gas stream. Scrubbing technology reduces operating costs at higher concentrations, but both scavengers and packed tower scrubbers suffer from pluggage caused by the entrained elemental sulphur particulates. S. Meyer and A. Trapet of MECS describe how the DynaWave technology offers a solution which reduces operating costs and maintenance issues.

Abstract

Storage of molten sulphur in tanks or pits is a typical means of stocking sulphur for use in a variety of applications. In some cases, these tanks use air to purge the liquid sulphur to strip out H2S, or SO2. In other cases, air is used to "sweep" the vapour space above the liquid sulphur to remove accumulated H2S and SO2 gases plus Sulphur vapour. In both cases, the air must be removed from the vapour space and vented. Since this air will contain varying levels of H2S, SO2, and sulphur vapour, the vent air must first be scrubbed to remove the sulphur contaminates before it can be released to the atmosphere.

The most prevalent issue affecting sulphur tank or pit applications is the formation of elemental sulphur in the gas stream. Vaporous sulphur will condense into elemental sulphur when the gas temperature falls below the sulphur dewpoint. Elemental sulphur is sticky and will quickly plug ducting if the ductwork is not steam traced.

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BAYQIK® field report

Summary

With 2½ years of successful operation to date, the BAYQIK® process has demonstrated its capability in the treatment of high grade SO2 process gas under the robust and challenging environment and process conditions of a nonferrous metallurgical production plant. T, Weber, M. Kürten, B. Erkes and K. Stemmer of Bayer Technology Services GmbH report on the first years of operating experience. Throughout this time, the process has shown excellent performance and allows smooth and safe operation. Former SO2 stack emission fluctuations have been eliminated with the installation of the BAYQIK® unit, and with the steady state operation of the conventional double absorption plant the overall plant reliability has been increased significantly. During a scheduled shutdown of the lead production plant the BAYQIK® unit underwent a detailed inspection, which showed no corrosion or critical fouling of the tube converter and indictated an expected catalyst lifetime of 7-8 years.

Abstract

In 2006, Bayer Technology Services (BTS) started to develop a new process for the treatment of high grade SO2 gases – BAYQIK®. Less than three years later, Europe’s largest lead producer started up the world’s first BAYQIK® plant in a lead smelting plant in Stolberg, Germany. Due to a capacity enhancement of about 30% in the lead smelting process, without increasing the total process gas volume flow, the concentration of SO2 rose from about 12 to 18 vol-%.

After mechanical completion the BAYQIK

® unit was connected to the existing plant within a five days shutdown. Since start up in April 2009 the unit has been on-stream for more than 19,000 hours of successful operation at SO2 inlet concentrations of up to 21 vol-% and volume flow rates ranging from zero to 17,000 m³/h.

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