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Publication > Issue > Articles

Physical solvents for gasification

Summary

W. Patrick Hegarty, Process Consultant and B. Gene Goar of Goar Sulfur Services & Assistance provide insight into physical solvents such as Rectisol and Selexol in gasification applications.

Abstract

The growth of gasification projects worldwide is creating renewed interest in physical solvent acid gas removal processes. Physical solvent processes are attractive for gasification applications at high pressures featuring selective absorption of H2S from CO2 rich gases, followed by bulk CO2 absorption and rejection. Many papers have been written on these processes but they typically present only general information. The purpose of this article is to provide some insight into these processes that are not widely known or appreciated.

The commercially proven physical solvent processes include:

  • Rectisol, which uses a refrigerated methanol solvent, is licensed by Linde and Lurgi.
  • Selexol, which uses a refrigerated mixture of the dimethyl ethers of polyethylene glycol, is available from Dow, Clarient and Coastal Chemical. Process design is offered by UOP and Uhde.
  • Fluor Solvent, which uses propylene carbonate solvent, is offered by Fluor.
  • Purisol, which uses n-methyl pyrrolidone solvent, is offered by Lurgi.

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The development of large-scale, single train ammonia plants

Summary

Venkat Pattabathula of Incitec Pivot Ltd and Jim Richardson of Süd-Chemie discuss some of the innovations which have shaped the past fifty years of the ammonia industry.

Abstract

In 1983, on the occasion of the 75th anniversary of the foundation of the American Institute of Chemical Engineers (AIChE), a blue ribbon panel of distinguished chemical engineers picked what they believed to be the world’s 10 greatest chemical engineering achievements. Embracing such feats as wonder drugs, synthetic fibers, atomic energy, and synthetic rubber, the citation also included “the breakthrough which permitted the production of large quantities of ammonia in compact, single unit plants”.

Recognizing the importance of this accomplishment in the challenge to feed humanity, it further stated: “The basic process for synthesizing ammonia was developed early in the 20th century, but what was needed was an inexpensive way to produce it in tremendous quantities. How well the chemical engineer succeeded is shown by the fact that as recently as 60 years ago, the annual production of synthesized ammonia was just over 300,000 tons. Thanks to chemical engineering breakthroughs, a single ammonia plant can today, produce [this amount] with ease and annual production is measured in millions of tons”.

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Not as easy as it looks

Summary

The bulk solids cooler offers several advantages over rotary drum or fluid bed coolers. Although the basics of the technology are simple, many details need to be considered to ensure reliable operation. Neville Jordison of Solex Thermal Science discusses how to get the details right.

Abstract

The concept of a bulk solids cooler for fertilizer products was introduced to the industry over 20 years ago. Since then more than 60 coolers of this type have been installed in fertilizer plants around the world cooling virtually every type of granular and prill fertilizer – urea, ammonium nitrate, NPK’s, MAP, DAP etc. The basis of the technology is the gravity flow of product moving through a bank of welded heat exchanger plates, cooled with water. The advantages of the technology compared to the rotary drum or fluid bed coolers are virtually no dust emissions, low power consumption, compact design (a major consideration in retrofit projects) and a simpler overall system with little ancillary equipment, such as fans and scrubbers. These advantages quickly established the bulk solids type cooler as the preferred choice of cooler in many fertilizer plants.

The heart of the equipment is the bank of exchanger plates. The product to be cooled flows slowly between the plates. Cooling water flows through the plates in counter flow and the product is cooled by conduction. Mass flow of the product is achieved by means of a discharge feeder mounted as an integral part of the exchanger below the plate bank. The discharge feeder also regulates the flow of product through the exchanger to keep it full at all times. A 3D view of a bulk solids cooler is shown in Fig. 1.

The basics of the technology are very simple; however, there are a lot of details that need to be considered to ensure reliable operation.

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When in Rome...

Summary

The Nitrogen+Syngas Conference and Exhibition 2009 was held at the Sharaton Roma Hotel from February 22nd-25th 2009.

Abstract

Opening the conference for the final time, John French of British Sulphur surveyed the dramatic and unexpected swings that global markets had taken over the past year. However, he remained cautiously optimistic that there would be a recovery at least in the syngasbased chemicals sectors, during the second half of 2009, and maintained that the nitrogen business remains vital for the provision of the world’s food and that the industry will survive the current challenges and will thrive once more.

This being the 100th anniversary of the demonstration of the Haber-Bosch process, the next item of business was a paper given by Federico Zardi of Casale Group, followed by the Ammonia Pioneers Awards, presented by Nitrogen+Syngas magazine (see boxed text, page XX).

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Adapting to a changing economy

Summary

The newer generation of ammonia, methanol and hydrogen plants are designed for more severe conditions than previous generations and the demand for catalyst activity has therefore increased. In addition, new feedstocks for syngas production need new purification technologies to protect the downstream catalytic processes. Catalyst and absorbent suppliers are responding to these changing demands by constantly improving their range of purification products.

Abstract

The importance of hydrocarbon purification is often overlooked in the synthesis gas generation plant, but poor performance, incorrect product selection or improper catalyst and absorbent change out policies can lead to significant operational issues in the downstream catalytic unit operations. In a large-scale syngas plant the cost associated with ongoing poor purification performance can amount to as much as three or four times the cost of maintaining the purification section per year.

There are a large variety of poisons that can be found in the various feed gases (natural gas, refinery off gases, LPG and naphtha) to a syngas plant, see Table 1.

Olefins in the hydrocarbon feed can also be considered a poison due to their tendency to form carbon if allowed to pass downstream to the steam reforming section. The level should be limited to 1-2 mol- % depending on the precise process conditions and reforming catalyst.

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Hydrogen in refining

Summary

Over the next few years, new environmental regulations and changing feedstocks and product slate will require considerable new investment in hydrogen capacity at refineries worldwide.

Abstract

If the ammonia and methanol industries are discounted, demand for hydrogen is currently dominated by the refining industry. In the US alone, hydrogen production capacity at refineries stood at 3.1 billion cubic ft/day in 2008. While hydrogen capacity has grown in the US at a rapid rate, around 7-10% per year, things have moved even faster in western Europe. Hydrogen consumption at European refineries tripled between 2002 and 2008. However, over the coming few years, refineries worldwide are set to dramatically increase their demand for hydrogen.

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Trucks and urea: a growing market for nitrogen producers

Summary

Selective catalytic reduction systems, using a urea solution to generate ammonia, has already become a significant source of urea demand in Europe. Alister Wallace from Integer Research looks at how the market has developed in Europe, and the prospects for North America and the rest of the world.

Abstract

Selective catalytic reduction (SCR) is a novel solution to an extremely damaging problem – the emission of nitrogen oxides (NOx) and particulate matter (PM) from heavy-duty diesel vehicles. These two pollutants place a heavy burden on the public health services of industrial and urban areas, especially in areas where heavy-duty diesel vehicles are prevalent. The corner stone of this technology is the production and distribution of a 32.5% urea solution known as AdBlue in Europe and Diesel Exhaust Fluid (DEF) in the US.

SCR technology has been embraced by European commercial vehicle manufacturers, and allowed them to meet the European Commission’s Euro IV and V legislation in early 2006. It has been used since the 1970s to reduce NOx emissions from coal-fired power plants. However, SCR is not the only technology capable of doing the job, and exhaust gas recirculation (EGR) combined with a diesel particulate filter (DPF) presents manufacturers with another option, albeit one that comes with a 3-5% penalty to fuel economy.

Integer has been involved with the AdBlue market and working with European stakeholders for over three years producing reports and organising industry conferences in Europe, Asia and the US. This article draws heavily from this experience, and from our research for our forthcoming North American DEF market study.

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