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Publication > Issue > Articles

The seven deadly sins of sour water stripping

Summary

Sour water systems should be designed to minimise operating problems, maximise on-line factor and optimise the quality of the feed gas to the sulphur recovery unit. D. Engel, P. le Grange, M. Sheilan and B. Spooner of Sulphur Experts describe the process of sour water stripping and focus on the most common mistakes (the seven deadly sins) made in operating and designing these units.

Abstract

Sour water stripping is the first step in the treatment of ‘process’ wastewater in many industrial operations, particularly in refineries. Water streams from a number of process units throughout a refinery complex are typically sent to the sour water stripper (SWS), which is designed to remove hydrogen sulphide (H2S) and ammonia (NH3) from the process water. There are several variations in the designs of sour water strippers, all playing upon the same theme of using heat to break the bonded ions in the NH4SH salt contaminant in the wastewater. This liberates gaseous ammonia and hydrogen sulphide in a produced sour water acid gas (SWAG). In some designs the NH3 and H2S are separated in separate columns and sent to individual destinations, but in the majority of SWS applications the effluent acid gas from a sour water stripper overhead is processed in a sulphur plant. Keywords: sour water stripping, SWS, stripper column, acid gas temperature, flash vessel, hydrocarbons, metallurgy

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Improved heat recovery in sulphuric acid plants

Summary

Sulphuric acid plants are significant producers of energy. In this article Chemetics discusses the main methods of heat recovery for the secondary heat of the sulphuric acid plant, Outotec provides case studies on the application of state-of-the-art solutions for more efficient heat recovery from old sulphuric acid plants and NORAM highlights some of the options available to maximise energy recovery.

Abstract

Today, sulphuric acid plants are commonly used as a local source of steam, and therefore energy, within a metallurgical or fertilizer complex. Control and management of the heat produced from a sulphuric acid plant is critical to the profitability and operability of the site. Energy sources from a sulphuric acid plant can be summarised as follows: 1. Combustion of sulphur inside furnace to produce SO2: S + O2 → SO2 (ΔH = -295 kJ/mol) 2. Oxidation of SO2 to SO3 inside catalytic converter: SO2 + ½O2 → SO2 (ΔH = -99 kJ/mol) 3. Absorption of SO3 into sulphuric acid: SO3 + H2O → H2SO4 (ΔH = -138 kJ/mol) 4. Absorption of moisture in ambient air inside drying tower: H2O(g) → H2O(l) (ΔH = -141 kJ/mol) Keywords: energy recovery, ALPHA System, hot water recovery, Chemetics, Outotec, NORAM, HEROS

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Improved WSA plant layout for smelter applications

Summary

M. Thellefsen, M. Møllerhøj and E. Eriksson of Haldor Topsoe describe a new WSA layout for smelter applications featuring an improved heat exchange layout, which replaces the molten salt system with a combination of gas/gas heat exchangers and a high pressure steam system. The new layout significantly improves process control and plant operation, especially for fluctuating flows and SO2 concentrations.

Abstract

Due to the nature of the metallic ore and smelter unit operations, smelter off gases fluctuate in both flow rate and SO2 concentration and the downstream sulphuric acid plant must be able to operate smoothly under these challenging conditions, maintaining low SO2 emissions and keeping the operation of the plant within the design limits. Keywords: molten salt system, SO2 conversion, WSA, layout, WSA condenser, heat exchange, Topsoe

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Iran and the Gulf

Summary

The easing of sanctions on Iran offers the chance for the increasing volumes of sulphur from the South Pars project to find a wider market.

Abstract

In January, the UN International Atomic Energy Agency (IAEA) confirmed that Tehran had fulfilled its obligations under an agreement to limit its nuclear enrichment programme. This was the trigger for the progressive easing of international sanctions against the country which have steadily ramped up from 2006 as concerns over the country’s nuclear ambitions have grown. The UN had mandated an arms embargo and asset freeze, and had added travel bans on individuals and sanctions on the provision of financial services. The US and EU, as well as some other states, had also imposed further sanctions on oil sales and oil equipment, and the US in particular had not only mandated sanctions on all companies doing business with Iran, it had also caused some difficulties by trying to extend those to companies outside the US that dealt with Iran that had US subsidiaries or operations. Keywords: OIL, OPEC, PARS, SOUR, REFINERY, ASSALUYEH, KHANGIRAN, TABRIZ

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Morocco's phosphate boom

Summary

Morocco is in the middle of a $16 billion investment programme which will see the country double its phosphate rock and triple its processed phosphate output, with a corresponding increase in sulphur consumption.

Abstract

The segment of sulphuric acid demand represented by phosphates is around 55%, most of that – around 90% – for fertilizer use, the remainder being consumed in various industrial uses, mostly in the food and animal feed industries as well as detergents, cleaners, metal finishing, toothpaste and many others. As the largest segment of demand, sulphuric acid and by extension sulphur demand continue to be driven mainly by the phosphate fertilizer market. And in the world of phosphate, while China is the largest producer, Morocco holds by far the world’s largest phosphate reserves – at around 50 billion tonnes P2O5, the country claims around 75% of all of the world’s phosphates, according to the IFDC’s re-rating of world phosphate reserves in 2010. Keywords: OCP, SLURRY, CONCENTRATE, BOUCRAA, JORF LASFAR, MESKALA, SAFI, DAP, MAP, PHOSPHORIC, PHOSACID, GABON

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