BC Insight - Nitrogen+Syngas, Sulphur, Fertilizer International
Login
BCInsight Ltd
China Works
Black Prince Road
London, SE1 7SJ
United Kingdom
Tel: +44 (0)20 7793 2567
Fax: +44 (0)20 7793 2577

Publication > Issue > Articles

Acid gas enrichment flow sheet selection

Summary

Ralph H. Weiland of Optimized Gas Treating, Inc. and Tofik K. Khanmamedov of TKK Company analyse how HIGHSULF™ can produce a Claus plant feed stock of excellent quality even from sour gas streams that would otherwise present disposal problems. HIGHSULF™ is also examined as a means of producing a high quality Claus feed directly from a raw gas such as sulphur plant tail gas. Analysis is carried out by the ProTreat™ amine simulator using the mass transfer rate approach.

Abstract

Sour gases containing only small concentrations of H2S, such as those associated with the Burgess shale of North Texas, can present unique challenges because the acid gas produced in the treating plant is sub-quality for Claus sulphur plant feed and cannot be vented or incinerated. Even in plants with a moderate CO2:H2S ratio of say 4:1, if complete acid gas removal is necessary (LNG for example), using a single contactor will produce an acid gas stream containing only 20% H2S. This is too dilute for a conventional Claus plant (Fig. 1). Sulphur plants are most efficient when operated with a feed containing 55% or more H2S. The balance of the SRU feed is CO2 and water, possibly with small amounts of hydrocarbons or other components. Lower concentrations of H2S result in greater sulphur plant complexity, larger equipment, and higher cost. Streams having less than 32% or so H2S are near the lower limit for a straight-through Claus process. Such streams cry out for enrichment. HIGHSULF™ (a trademark of TKK Company) is a general, patented, process strategy1-8 that can be applied incrementally in amine treating plants to increase the H2S concentration in the off-gas from the regenerator and produce an increasingly high quality Claus sulphur plant feed. HIGHSULF technology recognises that the higher the H2S content of the gas being treated in an amine unit, the greater will be the H2S concentration in the off-gas from its regenerator. HIGHSULF processing actually takes steps to increase the H2S content of the feed gas to the amine plant itself. As a result, the family of HIGHSULF processes produces a more concentrated product stream, as discussed by Khanmamedov1-8. One such application is upgrading the acid gas from the main amine plant regenerator to higher H2S content by processing the regenerator off-gas in another, smaller amine plant. This is termed acid gas enrichment (AGE). It is almost always the case that this secondary treating or AGE unit can very profitably apply HIGHSULF technology. Within the overall HIGHSULF strategy, there are numerous flow sheet configurations that can be applied to AGE. This article examines several possible processing schemes applied to the enrichment of a very low (8%) H2S-content gas and to a marginally treatable gas (34% H2S). The role of selectivity AGE depends critically on process selectivity for preferential absorption of H2S and rejection of CO2. Attaining the maximum selectivity for H2S over CO2 is achieved by using the right solvent under the right process conditions in the right equipment. The perfect process in AGE would remove all the H2S and none of the CO2, thereby feeding the Claus plant with pure, wet H2S. Detailed discussions of selectivity have been presented in many places3,4,9,13,14 so only a brief review is given here. The equilibrium solubilities of H2S and CO2 in selective solvents such as methyldiethanolamine (MDEA) do not differ radically from each other (chemical solvents do not have great inherent thermodynamic selectivity). The differences in absorption rates (the selectivity) are really determined by reaction kinetics and the hydraulic and mass transfer characteristics of the contacting equipment (as expressed by the relative magnitudes of gas- and liquid-side mass transfer coefficients). The mass transfer characteristics of the contacting equipment is a factor that has been largely overlooked by many practitioners, possibly because of poor understanding of separation equipment from the standpoint of its inherent mass transfer rates and what affects them. The effect of reaction kinetics has likewise been misinterpreted and misapplied by others to what remain equilibrium models nonetheless. MDEA is the most commonly used amine in selective treating. It reacts with H2S and CO2 at chemical rates that are at opposite ends of the spectrum. H2S absorption is accompanied by an instantaneous proton transfer reaction associated with H2S dissociation and amine protonation. On the other hand, MDEA is non-reactive with CO2, and CO2 reacts only very slowly with water to form bicarbonate ion (amine carbamate is not formed). Thus, from a reaction kinetic standpoint, MDEA is highly selective for H2S. As devices for carrying out mass transfer, trays and packing (both random and structured) behave quite differently hydraulically and in terms of inter-phase contact. The most obvious reason for this difference is that trays usually have a continuous liquid phase and dispersed gas phase. The opposite is always true of packing with liquid film flows that are relatively quiescent compared to the highly agitated state of the liquid flowing across trays. Vapour flows are quite turbulent for both trays and packing. Consequently, it is only to be expected that these types of equipment would have different mass transfer characteristics. These differences are decisive in selectivity because the mass-transfer resistance to H2S absorption is primarily in the gas phase, while for CO2 it is in the liquid phase. Thus selectivity can be completely controlled by proscribing the relative resistances to mass transfer offered by the two phases through the judicious selection of tower internals and reaction kinetics. Phase resistances are functions of the type (trays, random packing, structured packing) and mechanical details (tray passes, weir heights, packing brand, size, crimp angle, etc.) of the contacting equipment itself as well as the way it is operated hydraulically (flow rates and phase properties that depend on temperature and pressure) and how reaction kinetics affects mass transfer in the liquid. AGE processes are completely dependent on relative rates of mass transfer. Only a true heat- and mass-transfer-rate based model, such as ProTreat™ (a trademark of Optimized Gas Treating, Inc.), deals directly with the mass transfer characteristics of equipment, and correctly applies chemical reaction kinetics to the calculations, thus providing a realistic chance of reliably predicting performance in a specific piece of equipment. Reliable simulations cannot be done unless the simulation tool itself is cognizant of the mass transfer behaviour of the internals, and the engineer doing the calculations also keeps in mind the hydraulic regime in which the column is operating, e.g., spray versus froth regimes for trays as discussed by Weiland16. To summarise, selectivity is a function of the reaction rate of CO2 with the amine. Because CO2 does not react with tertiary and sterically-hindered amines, these are the only amine-based solvents that make any sense in highly selective treating applications. Commercially, this makes them the only contenders in AGE, with MDEA (sometimes assisted by partial neutralisation) and the hindered amines as the only realistic candidates. Because the hindered amines currently in commercial use are all members of the FLEXSORB® family and are proprietary to ExxonMobil Corporation, the remainder of this article focuses on generic MDEA. Two applications of HIGHSULF™ are considered: upgrading a marginally processable Claus feed (34% H2S) to super-high quality, and enriching a very low quality (8% H2S) acid gas to quite acceptable quality. The purpose is to point out the advantages and disadvantages of several HIGHSULF schemes relative to each other and relative to a completely conventional AGE process flow sheet. AGE flow sheets The most common (and least effective) processing scheme for AGE is the conventional flow sheet shown in Fig. 2. The low quality acid gas (H2S, CO2 and trace other components) is contacted with selective solvent in the low pressure AGE absorber. This is intended to recover most of the H2S and reject as much of the CO2 as possible. The shortcoming of this scheme is that the acid gas feed itself is fixed by upstream processing, whereas, if it could be made to contain more H2S, the gas to the SRU would automatically be of higher quality. The flow sheet shown in Fig. 3 is the simplest implementation of the patented HIGHSULF process that permits controlling the effective composition of the AGE unit feed gas. Depending on the extent to which the HIGHSULF technology is applied, the combined feed to the AGE absorber can be made fairly rich in H2S, allowing an even richer SRU feed to be produced. An alternative scheme is shown in Fig. 410,11, where the raw acid gas enters the AGE absorber at an intermediate tray so that the bottom section of the absorber removes the bulk of the recycle H2S before it joins the low quality acid gas feed. Mak et al.9 proposed another set of processing schemes constructed around the notion of using two absorbers, as shown in Fig. 5. However, in this approach, a separate column is used in an attempt to enrich the already rich SRU feed (AGE No. 1 in Fig. 5). The weak acid gas is enriched in yet another separate operation (AGE No. 2). Thus no advantage is taken of the richer acid gas that could be fed to AGE No. 2 by admixing with a slipstream of SRU feed. Enriching moderate H2S acid gas streams The 25 MMscfd acid gas from a main amine treating unit contains 34% H2S, 64% CO2 and 1% each of methane and ethane and is at 15 psig (1 bar) and 120°F (49°C). This is at the lower operability end of a straight-through sulphur plant and can be enriched considerably by treating with MDEA. The solvent used is 3,500 gpm (795 m3/h) of 45 wt-% MDEA at 120°F. All absorbers contain 20 conventional valve trays and are sized for 70% flood. Regenerators contain 30 trays with 120°F condensers. Reboiler conditions are 15 psig and 275 MMBtu/hr duty. The main constraint on all operating schemes is that gas to incineration cannot exceed 75 ppmv H2S. This is a somewhat arbitrary stipulation but it ensures that comparisons are done under the same requirements. Conventional amine unit The conventional scheme (Fig. 2) sets the comparison standard. Under the stated conditions, the ProTreat amine simulation package predicts that enrichment to 62% H2S (wet basis) is possible, while sending only 40 ppmv H2S to incineration. At 20 trays, the absorber appears to have more trays than required. This means the H2S leak is controlled principally by amine lean loading, which is a direct function of reboiler duty but, more importantly, the extra trays are removing CO2 and diluting the SRU feed gas. When run with ten trays in the AGE absorber, simulation indicates 73% H2S in the SRU feed and 69 ppmv H2S in the gas to incineration. HIGHSULF with combined feeds HIGHSULF technology endeavours to produce a better quality SRU feed by using part of the SRU feed itself to enhance the H2S content of the plant’s acid gas feed. In its simplest implementation, recycle gas is combined with raw feed. ProTreat simulation predicts that the quality of the SRU feed is a function of the extent of application of the HIGHSULF strategy. Figure 6 shows how the degree of enrichment and the H2S leak to the stack vary with increasing levels of application of HIGHSULF. As HIGHSULF is applied beyond 65%, the H2S leak to the stack suddenly escalates because the AGE absorber becomes overloaded and H2S breaks through into the incinerator gas. However, by the time this happens, the wet SRU feed has reached nearly 82% H2S. The best a conventional AGE unit could do under identical conditions of flow and energy usage was 72% H2S. Obviously there is a limit to how vigorously HIGHSULF can be applied before the operation collapses. However, it is remarkable that when the optimal extent of HIGHSULF™ is applied, the SRU feed quality can be increased so much, for zero operating cost, that the dry gas now contains 87% H2S and only 13% CO2. HIGHSULF with separate gas feeds The recycled gas is quite a bit higher in H2S content than the original acid gas stream so the next logical step might be to send the recycle gas to the bottom of the AGE absorber and introduce the acid gas itself part way up the column. In this way the higher CO2 content of the acid gas has less opportunity to be absorbed into the solvent and reduce its H2S holding capacity. This kind of scheme corresponds to Fig. 4. Preliminary ProTreat simulations showed that introducing the acid gas below tray 14 from the top in a 20-tray column was almost optimal from the standpoint of keeping the incinerator gas safely below the 75 ppmv maximum allowed. The simlated results plotted in Fig. 7 correspond to acid gas feed below tray 14. There is scarcely any improvement of the two feeds case over the common-feed setup. In this case, therefore, the addition of a second gas-feed nozzle and the associated complication of the special tray arrangement at the mid-tower feed point are not worth the trouble. From a process performance standpoint, the two flow sheets are equivalent, and both produce an extraordinarily high quality Claus plant feed. Using two AGE absorbers When two AGE absorbers are used, there is the question of how to split the common solvent flow from the regenerator between them. In the present case, this was done on the basis of equal ratio of solvent flow to H2S flow in the entering gas streams. Figure 8 shows the effect of various extents of regenerator acid gas recycled to AGE Absorber No. 1 in Fig. 5. It is immediately evident that this flow sheeting scheme gives inferior processing to HIGHSULF. The reason is that reliance for improved performance has been placed entirely on the recycle gas AGE unit. The acid gas AGE unit is still feeding on the original gas, not a gas whose H2S content has been in any way enhanced, as it is in HIGHSULF. Therefore, no advantage is being taken of the effect of SRU gas recycle on performance of the acid gas AGE unit. The acid gas AGE unit goes sour because of H2S breakthrough at only abut 51% SRU gas recycle, and at that point, the plant itself is producing only about 75% H2S in the SRU feed gas. This is still an improvement over conventional AGE, but falls well short of HIGHSULF processing.  Enriching low H2S acid gas streams

Add to basket


A review of research programmes underway at ASRL

Summary

As part of its activities ASRL conducts a programme of basic research on sulphur chemistry and technology related to current and future interests of its member companies. The overall objective of these investigations is to augment the business activities of ASRL member companies providing information to aid short and long term developments in the fields of natural gas production, oil refining, sulphur production, sulphur handling and use.

Abstract

Each January, the ASRL Technical Advisory Committee, a body of experts drawn from the ASRL member companies, meets to review progress in ongoing projects and discuss potential new areas of research. The objective of the TAC is to design a programme which addresses both short and long term needs for the members, a very considerable challenge given the rapid pace of events in today’s energy industry. The main features of the 2010-2011 research programs are shown in the accompanying figures. with some selected topics being discussed in the following sections.
Sulphur recovery efficiency, handling and safety
The world needs energy more cheaply, with fewer emissions, particularly CO2 and SO2, and wants it in a manner which is safe for both the public and the people working in the industry. Sulphur recovery, an integral component of many energy developments, is no exception, with now extraordinarily stringent limits applied to Claus plant operations in refineries and gas processing facilities in many parts of the world. Tail gas treatment and liquid sulphur handling have been areas of investigation at ASRL for some time, with particular interest in design of a TGT process which can achieve 99.9 %+ recovery with high thermal efficiency and, of course, at low cost.

Add to basket


Safe sulphur handling

Summary

Sulphur is considered to be a hazardous commodity, not only because it is prone to explode and cause fires, but also because of the negative impact on the environment in the event of dust emissions and spillage through careless handling. As a hazardous commodity, sulphur handling comes with ever-stricter requirements for minimising pollution and calls for operators to secure ship loading and unloading operations by eliminating spillage and minimising dust emissions. To meet these requirements, state-of-the-art environmentally-friendly equipment is often required.

Abstract

Cargotec’s Anders Svensson says “There are three main issues when unloading sulphur: a high explosion risk, extreme corrosion, and stringent regulations for environmental protection. Accommodating these issues requires state-of-the-art environmentally-friendly equipment, which was the trigger for Cargotec looking at different solutions and developing a range of unloaders that can offer economical, clean and safe sulphur-unloading operations”.
The risk of explosions and fires are amongst the largest hazards when handling sulphur and they also involve the most serious consequences. To ensure safe sulphur handling, Cargotec has developed a system, known as the ‘4S’ (Siwertell Sulphur Safety System), which is designed to minimise the risk of explosions and detect fires.

Add to basket


Improved checkerwall design

Summary

The checkerwall can be used as a static mixer to improve SRU process performance. E.L. Collins, N. Teator and J.J. Bolebruch of Blasch Precision Ceramics report that by using vectoring devices to mix gas flow in the reaction furnace downstream of the wall, a new design of checkerwall has been developed that can greatly increase efficiency by improving mixing with minimal increase of pressure drop.

Abstract

Basic checkerwall
A little more than a decade ago, as Blasch Precision Ceramics began to steadily grow their hex head ferrule business, they began to field requests from some of their SRU-operating customers to develop a checkerwall that would be easy to install, mechanically stable under all conditions, allow for design with varying degrees of open area, and could incorporate the use of an integral manway, if desired (Fig. 1). At that time, concerns were strictly mechanical, and there were no requests for mixing or flow management. The goal for many operators was to put in a checkerwall that would survive a campaign intact.

Add to basket


Improved catalyst and performance testing

Summary

In response to the industry need for more efficient sulphur recovery, BASF has developed and commercialised a new titania-based catalyst for enhanced conversion of COS and CS2. Crucial to the development was the design and construction of a test unit capable of judging catalyst performance at high conversions that mimic commercial conditions. A. Maglio and R. McCaffrey of BASF Corporation discuss these latest developments.

Abstract

The Claus process is the environmental workhorse of the refining and sour natural gas industries, allowing conversion of H2S into elemental sulphur and minimising emissions. The process begins with partial oxidation of H2S, followed by reaction of the newly created SO2 with residual H2S over an alumina or titania catalyst in a series of catalytic converters. The H2S feed is usually contaminated with substantial quantities of hydrocarbons, CO2 and, in some cases, NH3. These impurities lead to a complex series of reactions in the hot, anoxic region of the furnace which limits the total sulphur recovery of the plant. Environmental regulations typically require overall conversion of at least 99%.

Add to basket


Oil sands project update

Summary

In spite of the global recession and environmental concerns from some quarters, the prospects remain good for higher oil production from heavy and sulphur-laden bituminous oil sands.

Abstract

A couple of years ago, with commodity prices rising high, the oil sands of Venezuela and Canada looked like a good bed for oil extraction companies looking to source new supplies for an energy-hungry world. The situation has changed dramatically since then, with a recession causing a slump in global oil demand and a sharp drop in prices, increasing environmental questions being asked in Canada, and political difficulties in Venezuela driving away investors.
Nevertheless, output from oil sands production is running at 1.5 million bbl/d in Canada – almost half of production – and heavy oil and oil sands production in Venezuela is at more than 500,000 bbl/d. And as new projects come onstream over the next decade, both countries hope to be producing at least 3 million bbl/d each by 2020.

Add to basket


Sulphur from oil sands

Summary

With local opposition going as far as an attempted boycott of gasoline produced from Alberta oil sands, Dr J.B.Hyne of Hyjay R & D Ltd, Calgary, Alberta, provides a personal perspective on the future of oil sand sulphur.

Abstract

The question of how much sulphur will be realistically and profitably produced from oil sand sources in the foreseeable future is primarily one of how much, how easily and how acceptably the production process can be carried out. Whether or not the sulphur marketer and end user are interested in some of these questions is hardly relevant, since without oil sands production there will be no primary material from which to recover the sulphur of interest.
So readers of Sulphur will just have to suffer the indignity of keeping up with the world energy supply question going forward if they are interested in knowing what the supply of sulphur from the oil sands source is going to be. The link is there; its significance is clear. And its impact, coupled with the ever-present companion question of new uses for the yellow element and its compounds, will be a major determining factor in the sulphur market of the future. That is what we attempt to address here, very conscious of the uncertainties and the differences of opinion that complicate the issue.

Add to basket


Acid production with nearly zero emissions

Summary

Refinement of the BAYQIK® sulphuric acid process, characterised by the conversion of SO2 rich gases, has resulted in a new production process for sulphuric acid based on the reaction of pure sulphur with pure oxygen. M. Kürten, T. Weber, B. Erkes, and K. Stemmer of Bayer Technolgy Services present the new SULFO2BAY® process.

Abstract

The combustion of elemental sulphur and the roasting of sulphidic ores with air yield gases containing various concentrations of SO2. Whereas the combustion of elemental sulphur yields an SO2 concentration of 10-12% by volume and an oxygen concentration of 9-11 vol-%, the roasting of sulphidic ores yield significantly higher SO2 concentrations as a function of the sulphide content of the raw material. During the technical refinement of the production process for these non-ferrous metals, the incremental replacement of air with enriched oxygen has proven to be advantageous due to the autothermal production process thus achieved. Over the course of capacity increases within the roasting process, this trend has led to SO2 concentrations in the offgas of up to 30 vol-% today. Further processing of this offgas with high SO2 values requires the addition of air in the downstream plant sections to avoid exceeding the current technical limitation of approx. 13 vol-% SO2 prior to the first reaction stage for the conversion of SO2 to SO3. Higher SO2 values lead to thermal overload and thus damage to the vanadium catalyst. To avoid dilution of the offgas through the addition of air and the larger plants that this necessitates, Bayer Technology Services (BTS) developed an isothermally controlled method in 2006. The so-called BAYQIK® process1 offers a number of advantages:

Add to basket


Sulphuric acid plant modelling

Summary

Technology is fundamental to the profitable design and operation of environmentally friendly phosphate and sulphuric acid plants and processes. In this study, Chai Bhat and Ven Pinjala, AspenTech examine how modeling technology can help in debottlenecking existing plants, achieving high product purity, increasing energy recovery, and automate process analysis to optimise plant operations.

Abstract

aspenONE Engineering enables engineers to model the sulphuric acid and phosphoric acid processes in one integrated environment. It has been successfully utilised by plant owners/operators, engineering and construction companies, and technology providers to improve yields, increase plant efficiency and quality, and reduce capital and operating costs.
Operation of a sulphuric acid facility can be challenging because of the high cost of maintenance of sulphuric acid plants, stringent requirements on SO2 emissions, importance of energy efficiency, and accurate equipment sizing and rating. aspenONE Engineering has been successfully used by many companies to design every sub-process of the sulphuric and phosphoric acid plant in one integrated environment.

Add to basket


Sulphuric acid towers under discussion

Summary

The topic of this year's Sulphuric Acid Workshop at the 34th Annual Clearwater Convention was the design, operation and maintenance of sulphuric acid towers. Mark Evans reports

Abstract

The Central Florida Section of the American Institute of Chemical Engineers (AIChE) held its 34th Annual Clearwater Convention at the Sheraton Sand Key Resort on 11-12 June. The conference began with the 13th Annual Sulphuric Acid Workshop, which attracted an auditorium full of keen participants under the expert chairmanship of Rick Davies and Jim Dougherty.
The topic this year was the Design, Operation and Maintenance of Sulphuric Acid Towers.
Six presentations by industry experts formed the basis of the discussions and debates.
Orlando Perez of Aker Solutions opened the session by discussing Acid Brick Lining – Understanding the Art. He explained that the best choice of materials cannot make up for poor design, while vice versa the best design will be let down by a poor choice of materials. However, a well-designed brick lining can have a working life of more than 30 years. Any failure quickly becomes evident, however. Orlando Perez proceeded to discuss the key facets of successful operations, beginning with the choice of lining for the tower. Acid brick provides the first line of defence, he noted, offering thermal and mechanical protection to the membranes. The mortar bonds the brick together and provides a uniform bed joint, while the membrane protects the steel substrate.

Add to basket


The merits of titania

Summary

Recent studies provide a greater insight into how to use titanium dioxide catalyst in sulphur recovery facilities to best effect. The higher cost of titania compared to alumina catalysts can in many cases be justified due to the wide range of benefits offered by titania catalysts.

Abstract

Claus reactors in sulphur recovery units can be loaded with either alumina or titania based catalysts to reach equilibrium of the Claus reaction:
H2S + SO2  3S + H2O
However, because titania catalyst is more expensive than alumina, operators of sulphur recovery facilities are sometimes reluctant to pay the price to use a titania product in the converter(s). The conventional wisdom is: “We’ll just run the first converter hotter to get COS and CS2 hydrolysis and make up for the lost Claus conversion in the downstream reactors”.

Add to basket


Sulphur transport: to pipe or not to pipe?

Summary

The decision of Adnoc earlier this year to decide to take sulphur from its new Shah sour gas production site to the coast by rail rather than by pipeline has thrown into sharp relief the decisions facing sulphur producers over long-distance transport of sulphur.

Abstract

The Abu Dhabi National Oil Company (Adnoc) Shah sour gas development project deep in the Arabian desert is one of the largest sour gas projects in the world, processing 500 million cubic feet per day of gas. With a cost of $10 billion, the project has had a long gestation period and suffered the departure of one of the principals – ConocoPhillips – in April this year. It will also be treating gas with a very high H2S content (23%) and consequently producing extremely large volumes of sulphur deep in the desert; of the order of 10,000 t/d. Adnoc wishes to sell the sulphur from the project and so needs to move it from the gas processing plant to a terminal at Habshan on the coast – a distance of around 135km. But how to move the sulphur was a question which has rumbled on for some time; the original development plan called for building what would have been the world’s longest liquid sulphur pipeline. However, in June the final decision was made to instead form the sulphur at the gas plant and move it in rail shipments instead.

Add to basket


Stop quenching those sulphur vapour lines

Summary

In sulphur recovery units the treated tail gas, tail gas bypass and sweep air lines are normally routed to the incinerator. T.C. Willingham of Controls Southeast, Inc. explores several of the common pipe routings that result in corrosive conditions that can lead to line failures. Specific problems associated with these common pipe routings, as reported from the field, are examined. Several recommendations and industry best practices for preventing or minimising similar line failures are provided.

Abstract

In refineries and natural gas plants, the sulphur recovery unit (SRU) and the tail gas treating unit (TGTU) are essential to the processing of oil and gas. The SRU removes much of the hydrogen sulphide in the sour gas stream to produce a tail gas that is routed to the TGTU for further processing. The TGTU removes the balance of the hydrogen sulphide and other sulphur compounds to produce a “treated tail gas” that is routed to the incinerator. For TGTUs featuring SCOT technology, temperatures of the treated tail gas range from 40-55°C. While the treated tail gas temperature is well below the freezing point of sulphur (120°C), there is ordinarily no danger of sulphur plugging or corrosion in the line since the sulphur compounds have been removed from the gas stream. In addition to treated tail gas, the tail gas bypass and sweep air lines are also routed to the incinerator. The tail gas bypass line allows tail gas to be routed directly to the incinerator in the event of a TGTU upset. This line is normally not flowing due to a diverter valve which routes tail gas to the TGTU instead of directly to the incinerator through the bypass line. The sweep air line continuously removes sulphur vapours from the vapour space of sulphur pits and tanks and, therefore, must be kept above 120°C to prevent plugging and corrosion.

Add to basket


The Sulphur Doctor

Summary

Problem No. 3 Poorly designed, constructed or operated waste heat boiler of the SRU This is the third in a series of short articles on the subject of "common problems" with Claus Sulphur Recovery Units (SRUs). In this issue, B. Gene Goar of Goar Sulphur Services & Assistance discusses the waste heat boiler, based on his wide and varied experience in the design, operation, trouble-shooting and remedial problemsolving of Claus SRUs.

Abstract

As mentioned in the last article of this series, the reaction furnace and
waste heat boiler are analogous to the “heart and lungs” of the human body. The lungs of the body receive oxygen (air), process it, and remove the CO2 produced. Likewise, the waste heat boiler receives the hot process gases from the reaction furnace, cools them to a reasonable temperature, and removes the resultant heat by producing steam. When H2S (acid gas) is processed in a SRU, two products are obtained: elemental sulphur and a significant amount of energy in the form of heat
(~6.0-6.7 MMBtu/long ton of sulphur). It is just as important for the waste heat boiler to remove this heat (energy) from the SRU process gases as it is for the lungs to remove CO2 from the human body. Once the hot gases enter the waste heat boiler at 2,000-2,500°F (1,093-1,371°C), the boiler typically cools the gases down to 550- 640°F (288-338°C). The outlet temperature is normally designed to be somewhat above the sulphur dewpoint of the gases.

Add to basket