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Sulphur in Southern Africa

Summary

Higher volumes of recovered sulphur from refining will not offset the increasing demand for sulphur and sulphuric acid for southern Africa's metal and mining industries.

Abstract

Sub-Saharan Africa remains – with the exception of the Republic of South Africa - the world’s most underdeveloped region. It has tremendous mineral wealth, but has suffered from political problems that have constrained development for decades. However, since the turn of the millennium China’s voracious demand for raw materials has led to both a boom in inward investment into Africa by Chinese companies, and high commodity prices more generally around the world which have also led traditional mining companies into developing capacity in the region more rapidly, in particular in the copper belt of central southern Africa. Uranium demand is also on a high, with Namibia a beneficiary, and Madagascar is set to become a major nickel producer. These industries are leading to major increases both in smelter acid production and sulphuric acid demand for leaching. Regional demand for acid is also considerable for phosphates production in Senegal and South Africa. Brimstone sulphur production, however, has lagged far behind demand, with only South Africa’s refineries and synthetic fuel production accounting for any significant slice of demand.

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Sulphur World Symposium 2012

Summary

The Sulphur Institute (TSI) held its 2012 Sulphur World Symposium at the Hilton Hotel, Antwerp, Belgium, from April 22nd – 25th.

Abstract

The historic Belgian port of Antwerp was the gathering point for the sulphur industry in April, at the Sulphur Institute’s annual Sulphur World Symposium. And in spite of its long history, the port is also still one of the major centres of the sulphur and sulphuric acid trade in northwest Europe, and the symposium found time to take in a visit to the solvadis sulphuric acid terminal at Duval and the 1,000 t/d Lanxess sulphuric acid plant at Lillo Caprolactam. Setting the scene The conference began with two papers that took in the ever-changing world economy and the oil and gas industry that produces most of the world’s sulphur. Todd Overdonk of ExxonMobil gave an interesting and credible attempt to look at how the global energy outlook might have changed by 2040. The global population of course continues to rise, but that rise is levelling off. In OECD countries the age profile is also changing towards a more elderly population, and this is also true of China, leading to a levelling off of economic output. Conversely, working age populations are rising rapidly in India and Africa. In the OECD energy efficiency will moderate energy demand going forward, while the developing world will see economic output rise by 250% to 2040 and energy demand by 50%. While this represents a global increase in energy demand of 0.9% per year, per unit GDP this is in fact a contraction of -1.9% per year due to increasingly efficient use of energy. Todd predicted that by 2040 90% of transportation fuels would still be oil-based (today it is 95%), with a continuing shift to diesel worldwide, and new demand driven by the marine, aviation and commercial transportation (trucks) sectors. Fuel demand for personal vehicles will be relatively flat, with growth in car ownership ameliorated by a continuing shift to hybrids, and major gains in fuel use efficiency. Electricity will supply 40% of residential and commercial demand by 2040, supplanting biomass in the developing world, while industrial energy demand will grow by 30% to 2040 as Chinese demand tapers off, but with strong growth from India and Africa. Overall, by 2040 electricity demand will be 80% higher, with large increases in nuclear (up 85%) wind (up 500%) and solar (up 900%, albeit from a low base), but the main increase will be in gas demand, especially from unconventional sources. Global CO2 emissions will probably peak in 2030 and begin a slow fall. Again efficiency gains will contribute to this. Overall oil demand will grow by 0.7% per year, gas by 1.6%, coal by -0.2% and nuclear by 2.2%. This look to the future was followed by a focus on the here and now, as Valérie Plagnol of Credit Suisse looked at the global financial situation, with special emphasis on the ongoing crisis in the euro area. Markets seemed to be calmer she said (at time of speaking!) with the appetite for risk increasing and inter-bank pressures easing, and ECB bond purchases have stabilised the euro. But while eurozone debt is sustainable overall, individual countries still have issues, especially Greece, Italy and Portugal. The core scenario for Europe was, she said, of gradual crisis containment, but fiscal stabilisation and other structural adjustments would lead to a long period of slow growth. Greek debt remained unsustainable and large discrepancies remain among euro area states. Unemployment may reach unbearable levels – in Spain it is already over 20%. In the US, consumers still remain on the sidelines with confidence still shaky, but corporations have large hoards of cash and have the capacity to lead growth, while in emerging economies debts are low and the margin for manoeuvre remains high. China is shifting to a consumption led economy as investment levels are now unsustainable, and rising wages will mean a loss of competitiveness.

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Sulphuric acid alkylation

Summary

Increasingly stringent environmental regulations are leading to a boost in demand for alkylation capacity, and safety concerns about the hydrofluoric acid route are also leading to a slight preference for the sulphuric acid process, boosting acid demand in refineries in the US and worldwide.

Abstract

The use of alkylate as a blending component is not a new technology. Alkylation was first commercialised as far back as 1938, and became a staple way of producing high octane aviation fuel during World War II. While in the 1950s refiners’ interest to the use of alkylate as a blending component in automotive motor fuel, installed capacity remained relatively flat due to the comparative cost of other blending components. However, its use began to pick up in the 1970s and 1980s as tetra-ethyl lead (TEL) was phased out as a gasoline component, and it was given another boost in the 1990s as the Clean Air Act amendment began to impose more stringent restrictions upon gasoline blend components. Lower olefin, aromatic, sulphur, Reid vapour pressure (RVP) and drivability index (DI) specifications for finished gasoline blends became driving forces for increased alkylate demand, primarily in the US, and the phase-out of methyl t-butyl ether (MTBE) in the US in the late 1990s has further increased the demand for alkylation capacity. Finally, in the US, the increasing use of ethanol as a gasoline component has led to greatly increased demand for alkylate as a balancing component. It is reckoned that in California the proportion of alkylate used in gasoline has risen from 17% (when MTBE was permitted) to 23% now that up to 10% gasoline is blended. The alkylation reaction combines isobutane with light olefins (primarily C4s but also some C3) in the presence of a strong acid catalyst. The resulting highly branched, paraffinic product is a low vapour pressure, high octane (90-94 RON) blending component. Although alkylation can take place at high temperatures without a catalyst, the only processes of commercial importance today operate at low to moderate temperatures using either sulphuric or hydrofluoric (HF) acid catalysts. The light olefins and most or all of the isobutane come from the refinery fluid catalytic cracking (FCC) unit, hence alkylation units are found only in refineries having FCC units. As the US has a preponderance of FCC capacity this has also helped with the relative concentration of alkylation capacity in the US.

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Wet gas sulphuric acid technology developments

Summary

The recovery of sulphur in off-gases in the form of sulphuric acid can provide an effective response to stricter environmental regulations and increasing operating costs in a wide range of industries such as oil refining, coking, coal gasification, viscose and smelting. In this article we report on the latest developments to Topsøe's WSA process and recent applications for MECS's SULFOX technology.

Abstract

The recovery of sulphur in off-gases in the form of sulphuric acid can provide an effective response to stricter environmental regulations and increasing operating costs in a wide range of industries such as oil refining, coking, coal gasification, viscose and smelting. In this article we report on the latest developments to Topsøe’s WSA process and recent applications for MECS’s SULFOX technology.

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Adapting to changing requirements

Summary

Sulphur recovery units (SRU) in the oil and gas industries are generally designed according to certain criteria such as sulphur recovery efficiency, capacity, acid gas feed compositions and tail gas treating requirements, to meet the regulations and operating conditions known at the time of design. Often, the regulations or operating conditions change over time which results in a need to revamp the SRU. This article discusses different types of revamps based on recent case studies.

Abstract

There are many different scenarios that may require the revamp of an existing sulphur plant. Typical reasons for an SRU revamp could include one or more of the following1: l The sulphur plant feed compositions have changed due to a change of feedstock at the facility. l The sulphur plant is designed for amine acid gas only and the design has to be modified to process an ammonia acid gas stream. l As a result of changes in environmental regulations, the pit vent needs to be recycled back to the front end of the SRU and/or from the sulphur storage tank and truck/rail loading rack. These vent streams can all be collected and recycled to the reaction furnace via a blower. l As a result of modification in other parts of the facility, such as adding a flue gas desulphurisation unit to collect the sulphur compounds, a new stream containing SO2 is generated and it has to be routed to the sulphur plant. l Adding a new tail gas unit to the existing SRU, the recycle stream from the TGU needs to be treated in the SRU. l As a result of facility expansion, the capacity of the SRU needs to be increased by a small percentage such as 20% or significantly, up to 100% to double the capacity using oxygen enrichment options. l Where the feed composition to the sulphur plant has changed to a leaner acid gas, modification may be required to maintain a stable flame in the reaction furnace using techniques such as fuel gas firing, oxygen enrichment, adding acid gas enrichment or changing the catalyst to Ti for better hydrolysis of COS/CS2. l In some cases like gasification applications such as syngas, using 100% oxygen enrichment to achieve stable combustion temperature is required. For a coal to chemicals application where in order to properly process several lean streams, some streams are routed to the tail gas unit and an additional hydrolysis reactor is added in the tail gas unit. (RATE has developed a special scheme). l New feed compositions may contain new impurities such as BTEX or others that polishing unit may be required upstream of SRU such as carbon filter, or changes in the SRU operation such as fuel gas firing, oxygen enrichment or the acid gas enrichment. l The design capacity of the SRU significantly reduced where the current equipment cannot maintain a stable operation due to high turn down and equipment has to be modified. l As a result of changes in the environmental regulation, the amine solvent in the tail gas has to be changed to a more efficient solvent. l As a result of changes in environmental regulations, a caustic scrubber has to be added after the incinerator to absorb the SO2. l To reduce the natural gas consumption, reduce CO2 emission, simplify operation changing the RGG/inline burner in the TGU to indirect steam heater and to use low temperature hydrogenation catalyst in the TGU reactor. l Old sulphur plants used to be designed with fired heaters using natural gas or acid gas firing. In order to improve the sulphur recovery, reliability and operability in many the sulphur plants fired heaters are changed to steam heaters. l In some old amine units the amine acid gas from the regeneration column is not adequately cooled so the acid gas saturated with water at 82°C was routed to the SRU. To prevent entering excess water from entering the SRU burner / reaction furnace RATE installed a cooler to cool the acid gas to 43-49°C to remove the water in the amine acid gas knockout drum prior entering the SRU burner and furnace. l Adding sulphur degassing to the existing facility: new regulations require that liquid sulphur has to be degassed to 10-30 ppmw of H2S before solidifying or transporting as liquid. Degassing can be carried out inside or outside of the pit. In pit degassing requires 12 to 24 hours residence time depending on the selected technology. If the degassing is outside of the pit, normally 30 minutes residence time is required. The degassed sulphur can be stored in a second compartment of the sulphur pit or in an above ground storage tank. In most cases existing sulphur pits do not have an adequate residence time for internal degassing. In these cases external degassing is selected unless the owner decides to increase the size of the pit and use internal degassing.

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Safe and trouble-free SRU start-ups

Summary

The start-up of Claus sulphur recovery units can be wrought with many problems such as burner and/or refractory damage, production of carbon (soot), catalyst deactivation, major equipment damage, or internal explosions resulting in plant destruction and safety risks to personnel. B. Gene Goar of Goar Sulfur Services & Assistance provides guidelines and procedures for the safe and trouble-free start-up of Claus sulphur plants

Abstract

Initial Claus SRU start-up Once the construction and installation of an SRU has been completed, many tasks have to be completed before the unit can be used to process acid gas feed, containing a high percentage of H2S. Proper cleaning and pressure testing of the equipment and piping, refractory dry-out and curing, catalyst loading and blowing, and check-out of the instrumentation and controls (including the ESD system) must be completed with a high degree of diligence and care. Once the refractory installation in the reaction furnace is completed, a careful dry-out and curing procedure must be performed. This is done by firing the main burner with fuel gas (methane preferably). (Note: Never, never use refinery fuel gas for this purpose, because its composition is much too variable.) A proper dry-out procedure is normally furnished by the refractory vendor; and, it should be followed very closely. During this initial (very first) firing procedure, excess air can be used to moderate and control the flame temperature in the furnace, using levels of 60-200% excess air (1,371-816°C) or as needed, to control the temperature to match the profile dictated by the dry-out and curing procedure. This is permitted because the process equipment and/or the catalyst beds have not been exposed to H2S or sulphur yet. Before any firing of the main burner (or any burner), the furnace (or chamber) must be properly purged with nitrogen to remove any possible combustibles, which entails using five volume sweeps of nitrogen in a five minute period, or the time required to get five volume sweeps. Then the igniter/pilot may be lit, and once a flame is confirmed by a flame scanner, the initial fuel gas firing may begin.

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