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ASRL Review - New technologies for sulphur recovery at the 1-10 tonne/day scale

Summary

In this edition of the ASRL Review, we discuss new technologies for recovery of sulphur at low tonnages, namely in the 1 - 10 t/d range. It seems that people are not entirely happy with existing technologies and would welcome a simpler process. Obviously, low tonnage sulphur recovery is not a simple matter but the increasing environmental concern over flaring of low volume, sometimes slightly sour, gas is an important issue for the industry. In this article, we describe some of the recent work in our laboratories aimed at low tonnage recovery and analyse why this topic presents such a formidable technical challenge.

Abstract

Typically, the modified Claus process has been applied for sulphur recovery in applications manufacturing 10-4,000 t/d of sulphur, although there are some examples beyond either end of this range. Sulphur capture at <1 t/d is usually accomplished using once through chemical scavengers such as solvent-based triazine formulations, iron-based adsorbents, zinc oxide and porous carbon, but, usually, the solid adsorbents are only applied for very low levels of H2S. Sulphur recovery requirements of 1-10 t/d are typically handled using aqueous iron chelate technology but it has been an aim of the sour gas industry to develop alternative sulphur recovery methods for this scale of operation. An overview of sulphur recovery technologies, including some of the ‘new-directions’ work at ASRL is given in Figure 1.

 

As in most sectors of industry, increased environmental awareness is driving sulphur recovery to higher levels particularly with respect to direct use of low H2S-content sour off-gases for steam and small-scale power production. Much of this type of gas is found in locales not directly connected to pipeline gathering systems but the gas would be of value for steam and power production if the sulphur emissions could be controlled. One important example in Alberta is the sour off-gas produced from steam stimulated recovery of heavy oil and bitumen where the sour hydrocarbon mixture would be used to generate steam.

Over the last three years, research programs at ASRL have focused on new approaches to small-scale sulphur recovery for both high pressure sour gas and low pressure acid gas. The anticipated process temperatures for 1-10 t/d applications (>250°C) would require that reactor systems work at sub-dewpoint conditions for high pressure applications but gas phase processing can be envisaged for low pressure acid gas if the correct strategy is adopted. In the following sections we describe the results of research that could be used to underpin small-scale sulphur systems for both low and high pressure applications.

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Sulphur in central Asia

Summary

With large-scale production of sulphur expected from sour oil and gas processing in central Asia, storage of sulphur may be an increasing issue for producers.

Abstract

The three oil and gas-rich states of Turkmenistan, Uzbekistan and Kazakhstan sprawl across a huge area of central Asia (see Figure 1). While all three nations have large hydrocarbon reserves, the lack of domestic demand and relative geographical isolation make for logistical difficulties for exports to major end-use markets. A lack of pipeline infrastructure, and difficulties in attracting finance and technical assistance, arising from domestic political concerns, hamper the development of these resour­ces. Oil production from Turkmenistan and Uzbekistan has declined since 2004 due to lack of new investment and technical capacity to bring new oilfields online.

Nevertheless, Kazakhstan is a major oil producer, and Turkmenistan a major gas exporter, and the most recent political shift in the region, caused by the death of Turkmen presiden Saparmurat Niyazov (also referred to as Turkmenbashi) and the election of Gurbanguly Berdymukhammedov in early 2007 have led to renewed interest by investors, and hopes for a more stable financial and political environment.

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An alternative to double absorption

Summary

In recent years, regulatory pressure to reduce SO2 emissions from sulphuric acid plants coupled with the increased value of energy has enhanced the desirability of the AE&C single absorption–scrubbing process. Leonard J. Friedman of Acid Engineering & Consulting, Inc. reviews the modern AE&C designed single absorption–scrubbing process, highlighting its advantages compared to double absorption, and reviews several recent projects where the process has been installed in sulphur burning and spent acid regeneration sulphuric acid plants.

Abstract

Since 1971 when the US Environmental Protection Agency (EPA) established new source performance standards (NSPS) for sulphur burning and spent acid regeneration sulphuric acid plants at four pounds per ton of sulphur dioxide per ton of acid produced (equivalent to 99.7% conversion efficiency and about 400-450 ppm SO2), the double absorption process has been the chosen route for the production of sulphuric acid. Essentially all new sulphuric acid plants (sulphur burning or regeneration) constructed in the last 35 years are double absorption units.

Recently EPA has determined an emission level of 1.0 to 1.25 lb/t (99.9% conversion efficiency and about 100-120 ppm SO2) to be achievable, and has been using its enforcement division and permit process to convince acid producers to meet this lower emission level, although NSPS re­mains at 4 lb/t. Europe has also moved to the 1.0–1.25 lb/t emission requirement. Two possible process modifications in the double absorption plant are required to meet this reduced emission requirement: either de-rate the production capacity of the plant by about 15% by operating at reduced SO2 and higher O2 concentration to the converter; or add a fifth catalyst bed, increase catalyst loading to about 230-250 l/t (40% or more increase), and use a partial first bed and full fourth and fifth catalyst beds of expensive low ignition catalyst – in most cases requiring a new converter for existing plants and increased capital and operating costs for new plants.

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Meeting changing requirements

Summary

The selection of a Claus tail gas treating process to comply with more stringent emissions regulations is determined by several factors, including costs, location and feed gas composition. Different situations require different solutions. In this article we feature recent case studies illustrating some of the options available.

Abstract

With the sulphur content of crude oil and natural gas on the increase and tightening sulphur content in fuels, refiners and gas processors are pushed for additional sulphur recovery capacity. At the same time, environmental regulatory agencies of many countries continue to promulgate more stringent standards for sulphur emissions from oil, gas and chemical processing facilities. It is necessary to develop and implement reliable and cost effective technologies to cope with the changing requirements. In response to this trend, several new technologies are now emerging to comply with the most stringent ­regulations.

Typical sulphur recovery efficiencies for Claus plants are 90-96% for a two- stage, and 95-98% for a three- stage plant. Most countries require sulphur recovery efficiency in the range of 98.5% to 99.9+%. Therefore the sulphur constituents in the Claus tail gas need to be reduced further.

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All at sea?

Summary

Transport and storage of elemental sulphur, both solid and molten, is an extremely specialised business, due to inherent dangers and environmental issues. Various codes of safe practice apply, especially with regard to offshore shipments. However, some confusion remains as to whether sulphur should be categorised as a hazardous cargo. At present, if shipped in bulk, sulphur does indeed fall into that category. But if it is formed into a shape, it does not.

Abstract

Sulphur suppliers around the world warrant strict purity specifications to their customers and take vigorous measures to ensure that these standards are met. They are particularly concerned about avoiding any risk of contamination. Sulphur is easily contaminated by loose scale and rust and residues of previous cargoes. Maple Shipping Ltd., for example, advises vessel owners of the following criteria which must be met if a cargo inspection certificate is to be issued:

All receiving holds must be in a “grain clean” condition

  • All residues of previous cargoes must be completely removed (including residues from the undersides of hatch covers)
  • All loose rust and scale are to be removed from all metal surfaces in the holds (including undersides of hatch covers)
  • All receiving holds are to be washed down with fresh water.

The possible hazards arising from sulphur cargoes concern:

  • Corrosion
  • Gas emissions
  • Flammability

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Sultran's fresh milestones

Summary

This year marks the 31st anniversary of Sultran Ltd. The company has provided three decades of service as the logistical management company for the Canadian sulphur industry, and it has created a pace-setting integrated and reliable transportation and terminal system that has ensured the competitiveness of Western Canadian sulphur in international markets.

Abstract

As sulphur prices skyrocket in today’s booming commodity markets, it is remarkable to recall that the product was once so poorly valued. Matters were not helped by the low priority that had been given to devising effective logistical and handling systems to ensure that the product reached the customer in a timely and economical way. An escalation in the demand for sulphur during the 1970s (especially from the North American phosphate fertilizer industry) triggered a fundamental reappraisal of how the product was transported and handled from source to final customer, thus paving the way for the establishment of Sultran Ltd.

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New sulphuric acid producing plant

Summary

From sulphur burning to smelter gas capture, Sulphur's annual survey covers recent and planned construction projects for sulphuric acid production.

Abstract

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