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North America's syngas boom

Summary

With shale gas production in the US continuing to increase, the past five years have seen a complete reversal of fortune for North America's gas-based chemical industries.

Abstract

After a turbulent couple of decades, the US and by extension Canadian gas-based chemical industries are enjoying something of an ‘Indian summer’, buoyed by a combination of low gas prices, written down capacity and proximity to large end-use markets. But it is still startling to reflect upon how different the picture was just a few years ago. Gas prices had been steadily increasing, following a dip in the years following deregulation in the 1980s and early 90s, and by 2007-8 had climbed to the highest seen. As gas demand continued to increase for power production, there was serious talk of moving back to coal-based ammonia production, and new plants based on refinery petroleum coke feedstock. Large amounts of LNG capacity were built around the Atlantic basin with the aim of exporting it into a US market that would be up to 140 bcm per year, and the LNG market has been depressed for several years as a result of the non-emergence of this capacity.

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Improving your urea plant

Summary

Now operating under the umbrella of Maire Tecnimont, Stamicarbon held their 12th urea technology symposium in Brussels from May 7th – 10th this year, with plenty of ideas on ways to get the most out of operators' urea plants.

Abstract

The first morning’s papers took an overview of the industry as well as the company and its technologies. On a strategic level, Stephen Zwart described urea as “a great way to monetise natural gas”. Urea demand for fertilizer use continues to increase, and urea prices are maintaining historical highs due to continuing world food demand. As a solid with a nitrogen content of 46%, it is the most efficient way of transporting nitrogen around the world, and if sited near to end use markets or in a cheap gas location with good port access, there can be considerable competitive advantage for producers. Stamicarbon are attempting to contribute to low cost of ownership and operation via their technological offerings. This moved the symposium neatly onto Joey Dobree’s presentation, which looked at achieving economies of scale via Stamicarbon’s plants, at urea capacities up to 6,000 t/d. The concept for such a large plant, which Stamicarbon describe as their ‘MEGA’ technology, takes a typical Urea2000plus plant and adds a medium pressure (ca 20 bar) recirculation section, reducing the load on the HP stripper and pool condenser and allowing for greater scale-up. This can also be used as a revamp option. However, Stamicarbon also believe that the Urea2000plus technology can itself be designed as a single line 6,000 t/d plant for a grassroots option, as can the new Avancore concept. Avancore, launched at this symposium back in 2008, is now Stamicarbon’s flagship technology offering. Avancore takes the proven Urea2000plus concept with pool condenser and a downstream adiabatic urea reactor but lowers the height profile of the plant by putting the pool condenser at the top while maintaining a gravity-driven operation to the stripper for ease of operation and maintenance. For smaller (<2,300 t/d) plants the downstream urea reactor can be dispensed with. All-Safurex construction also removes the need for oxygen passivation, and the HP/LP scrubbers are replaced by a medium pressure scrubber, again simplifying the process. Bart Gevers described the first license for the technology, at the new Tierra del Fuego Energy y Quimica SA plant in southern Chile. This is a 2,700 t/d urea melt plant which differs from the originally proposed Avancore layout by sending the overhead vapour from the reactor not to an MP scrubber but rather an MP carbamate condenser, itself used as part of an adiabatic flash upstream low pressure recirculation system. Finally, Hans van den Tillaart looked at the Stamicarbon low energy urea melt plant concept. By direct heat integration between the HP pool condenser and the MP rectifying heater and between the MP condenser and the first stage evaporator heater, the steam consumption can be lowered considerably. For a urea melt plant with downstream prilling tower, turbine extraction steam consumption can be lowered from 868 kg/t product to 558 kg/t product.

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Environmentally conscious

Summary

A look at Yara's new Urea7 plant at Sluiskil, producing both improved plant yields and helping lower vehicle emissions.

Abstract

There is a growing demand worldwide for nitrogenous fertilisers to be produced with an ever-lower impact on the environment. Yara has seen a significant improvement in urea production thanks to the new Urea7 plant that ThyssenKrupp Uhde has just completed at Sluiskil in the Netherlands. Some of this urea will be sold in solution form as AdBlue®, and so the plant will also make an important contribution towards reducing emissions from vehicle exhausts. The low-emission plant has a production capacity of 3,500 t/d of urea, making it the largest in Europe and one of the largest plants of its kind in the world. Today the fight against world hunger and the desire for a clean environment are two of the most pressing social objectives. The growing global population, the demand for food that this brings with it, and the need for environmentally-friendly biofuels are creating a continuous increase in the global demand for nitrogenous fertilisers. With a high nitrogen content of over 46% urea is one of the world’s most important nitrogenous fertilises, and this was a major factor in Yara Sluiskil BV, part of the Norwegian chemical group Yara International and the world’s largest producer of urea, deciding to expand capacity at its plant in the Dutch province of Zeeland, which also houses production lines for ammonia, CO2, nitric acid and nitrate granulation facilities. In 2008 ThyssenKrupp Uhde was commissioned to act as the lump-sum turnkey contractor on the design and construction of the Urea7 plant for environmentally friendly production of urea solution. The project covered the engineering, the supply of all equipment, construction and assembly, and the subsequent commissioning of the plant, and required extensive technological expertise and experience in this area. “It was important for Yara to bring on board an experienced contractor which could boast a proven technology and a winning project execution concept”, said Dr Richard Saure, head of sales for ammonia and urea plants at ThyssenKrupp Uhde. The international company, with its head office in Dortmund, has been designing and building fertiliser plants around the world for over 80 years; it has also been working successfully with Yara for many of those years. Even in the few years since 1994 ThyssenKrupp Uhde has constructed 18 new urea plants worldwide with an annual capacity of 10 million tonnes.

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Metal dusting: an update

Summary

A review of some recent developments in the understanding of metal dusting corrosion.

Abstract

Metal dusting is a severe carburisation (carbon addition) corrosion attack on steel and similar metal surfaces that takes place in a carbon super-saturated atmosphere. It is most commonly encountered in high temperature reforming processes such as syngas production, and as might be expected it is particularly apparent in plants working at lower steam: carbon ratios, such as methanol and gas to liquids (GTL) production. At high temperatures (typically 400-800C), carbon monoxide tends to dissociate at metal surfaces to form carbon, which draws metal ions, particularly iron, nickel and cobalt, from the metal structure, to be carried away in the gaseous flow. The consequences can be very severe, from pitting to deep attack and eventual catastrophic failure. A recent literature survey summarises published work to date on the phenomenon1. Three mechanisms for metal dusting attack have been proposed; one by Grabke and co-workers, where the solid C forms iron carbides (eg Fe3C) at the surface and grain boundaries, forming a site for graphite to grow which destabilises the neighbouring carbide, and releasing Fe particles which catalyse further C nucleation. Albertson proposed that the carbides are oxidised at the interface with graphite, forming a porous layer allowing further C penetration. Lastly, Zeng and Natesan described a carbon crystallisation catalysed by Ni with metal dusting driven by accumulation of C in the Ni matrix and the free energy difference between good and poor crysallinites. The literature shows that metal dusting can be reduced by ‘poisoning’ the surface using S or P adsorption, alloys with high Ni content or quantities of Sn or Cu, the addition of carbide formers such as Mo, W or Nb, or protective oxide formation with alumina, silica or chromia, and related mechanical and chemical surface treatments such as scale formation.

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Ammonia plant performance and economics

Summary

Significant efforts have been continuously put into developing optimised production technology for ammonia plants with the objective to improve overall energy efficiency and feedstock utilisation. Major efforts have also been focused on developing state-of-the-art catalysts for large scale plants that benefit from economy of scale.

Abstract

Since the Haber-Bosch process was first developed in the 1920s, the ammonia industry has achieved a huge improvement in ammonia manufacture. The most significant progress came about in the 1960s with the advent of steam methane reforming (SMR) and the single stream ammonia plant. Without this development the world would be a very different place today. Since the 1960s all process licensors and operators have strived to make the process as efficient as possible; overall, a plant built today uses some 30% less energy per tonne of ammonia produced than one constructed 40 years ago. This means that energy efficiencies for ammonia plants in operation today vary widely due to asset age, energy costs and utility constraints. Most plants operate well above the practical minimum energy consumption with the best operating around 28 GJ/tonne and an average efficiency of 37 GJ/tonne (Fig. 1)1. If all plants worldwide were to achieve the efficiency of the best plants, energy consumption could fall by 25%.

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Improving plant performance

Summary

A variety of tools and techniques are available to analyse, monitor and improve the manufacturing performance of ammonia and urea plants. Monitoring the steam reformer is extremely important in an ammonia plant. Johnson Matthey Catalysts and Quest Integrity Group report on the powerful techniques they offer for steam reformers. For urea plants, IPCOS and Stamicarbon have joined forces to provide a single solution that combines the benefits of both advanced process control and non-linear optimisation of urea plants.

Abstract

Monitoring steam reformers Many customers consider the steam reformer (reformer) to be the most complex and expensive part of their ammonia, methanol or hydrogen plant. Monitoring the plant during both normal and unfamiliar operations is therefore extremely important. In extreme cases, getting it wrong can lead to complete reformer tube failure. Whilst these cases tend to be the result of deviation from procedure, operation under normal conditions can also be far from optimum, having an impact on plant efficiency and reliability. Any time and money spent on monitoring a reformer is therefore a worthwhile investment; a well operated reformer is key to ensuring that a synthesis gas plant remains efficient, produces the maximum potential product and operates reliably with minimal downtime. Furthermore, optimised reformer operation reduces emissions per unit of product and is potentially safer. Day-to-day monitoring and operation of steam reformers relies upon the expertise of experienced plant operators; however, their resources are often limited. When challenges occur, external experts can provide specialised services and assist operators by looking at the plant from an entirely new perspective. Reformers suffer from a range of potential issues which can all lead to limitations on achievable production rates, reformer/ plant efficiency and can lead to significant down time to determine the root cause and affect repairs.

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Complete reformer failure… could it happen to you?

Summary

This is a case study based on the actual experiences of an operator of a large modern top-fired reformer. They suffered from significant tube failures during a plant start-up, resulting in losses running to US$ millions in terms of lost profits and downtime.

Abstract

This is a case study based on the actual experiences of an operator of a large modern top-fired reformer. They suffered from significant tube failures during a plant start-up, resulting in losses running to US$ millions in terms of lost profits and downtime. This catastrophic failure was caused by over firing during start-up and was the result of a number of coincident factors. At the time of the incident, the site had steam shortages and this led to pressure to conserve of steam. In addition to this, the plant was under pressure to avoid a shutdown if at all possible due to low product stocks. The burners on their reformer usually received fuel from two different sources and these were mixed. One of the sources was of low calorific value, and the other a much higher calorific value. At the time of incident, the plant was unexpectedly receiving all of its fuel from the high calorific value source.

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Plant Manager+ Problem No. 13 3-Way valves in urea melt lines

Summary

In nearly all urea plants, urea and water is separated in an evaporation or concentration section at vacuum pressures. The urea melt can have a concentration of 99.6 wt-% when the urea melt is sent to a prilling tower or a Sandvik Process Rotoformer or a somewhat lower concentration when a granulation technology is applied. It is obvious that it is important to control the temperature of the urea melt just above the crystallisation temperature in order to maintain it in liquid condition. On the other hand, when the temperature is too high several negative side reactions in the urea melt occur, resulting in higher biuret contents in the final product and higher ammonia and urea dust emissions from the finishing section. Therefore, urea melt lines are typically jacketed pipes and the pressure of the steam in the jacket is controlled by the required urea melt temperature. Urea melt pumps and 3-way valves (at the suction and discharge side of the urea melt pumps and just upstream of the prilling bucket) function in a challenging environment: handling a process liquid close to its crystallisation temperature while at the same time proper sealing is vital. The picture shows the sealing challenges of a traditional urea melt pump. Fortunately, successful innovations are available that provide a reliable solution.

Abstract

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