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By no means a foregone conclusion

Summary

The balance between carbon dioxide removal technologies may have shifted a bit in recent years, but all the options are still open.

Abstract

Regardless of the process used, in its raw state ammonia synthesis gas generated from a carbon-containing fossil fuel contains carbon oxides (chiefly carbon mon­oxide) as well as hydrogen. The carbon oxides are not only unwanted ballast as far as the ammonia synthesis reaction is concerned: they are highly deleterious to ammonia synthesis catalyst, even in only trace amounts. So it has always been of prime importance to eliminate them as far as possible before the gas is admitted to the synthesis loop.

Carbon monoxide is virtually insoluble in water and common non-aqueous solvents and is surprisingly non-reactive chemically, although it is extremely toxic by inhalation. So it is quite difficult to devise an efficient and safe, yet economical, regenerative method for separating it in bulk from synthesis gas. In comparison, carbon dioxide is a much more favourable candidate.

Even in the earliest days of commercial ammonia production, therefore, it was standard practice to convert the carbon monoxide as far as possible to carbon dioxide before separation by a process originally known as the “water gas shift reaction” – a reference to the so-called “water gas” mixture obtained by passing steam over heated coke – but nowadays referred to simply as shift conversion. It has the incidental benefit of increasing the amount of hydrogen in the synthesis gas as well.

CO + H2O = CO2 + H2

With the catalysts and technology of the time (roughly equivalent to the high-temperature shift section of a modern ammonia plant) the reaction, which is an equilibrium (reversible) reaction, was not complete; but it did convert the bulk of the carbon mon­oxide to carbon dioxide. In those less energy-conscious days the synthesis gas – which was initially generated at near atmospheric pressure – was com­pressed to a high pressure, allowing fairly efficient removal of the carbon dioxide by water-washing alone. The few percent of carbon monoxide and residual carbon dioxide were taken out under high pressure in a so-called copper liquor wash process, using an ammoniacal solution of copper chloride, from which the carbon monoxide could be recovered by depressurizing the laden solution.

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Hydrogen great promise for syngas derivative

Summary

Although synthesis gas is used for both ammonia and methanol production, the third side of the triangle that of hydrogen production is sometimes overlooked. However, with the market for hydrogen steadily increasing, it is sure to become more important in future. In this article Nitrogen & Methanol reviews hydrogen production techniques and the evolving market for hydrogen.

Abstract

The global demand for hydrogen is currently around 550 billion Nm3 per annum (50m t/a). Around two thirds of this is used for bulk chemical production. Ammo­nia and methanol represent about 40% of that, and processing and refining of gasoline the other 60%. Of the rest, there are various uses, from fat and oil processing, other chemical production, along with more specialised applications like pharmaceuticals, metals, semiconductors etc.

At present, there are three main methods of producing hydrogen on a commercial scale. Electrolysis is one possibility, although it is not usually economic to do so from fossil fuel-based energy sources, and consequently this is confined to hydroelectric applications at present, apart from some from chlor-alkali electrolysis. Secondly, it can be taken as a by-product from other chemical processes, such as ammonia, methanol, ethylene or ethylene oxide plants, but in particularly from petrochemical refinery off-gases. About 65-75% of hydrogen in the US and Europe is currently estimated to come from this route.

However, an increasingly common route is from oxidation of fossil fuels. Either partial oxidation using gasification of coal or heavy residues, or by steam reforming of natural gas. For any application requiring more than 1,000 Nm3/ hour, steam reforming is the preferred option, and consequently this represents an estimated 50% of global hydrogen production. As refineries become subject to more stringent environmental regulations, in particular relating to emissions of NOx and SOx, so demand for deliberately produced hydrogen has increased. Other considerations are also driving the hydrogen market – as oil reservoirs become depleted, so lower quality crude is increasingly finding its way into refineries, necessitating greater use of hydrogen treating and removal of sulphur. Also, increased for more cracked, short carbon chain products and fewer aromatics is also leading to more use of hydrogen in refineries.

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The European perspective

Summary

The European Union's Integrated Pollution Prevention and Control (IPPC) initiative enshrines a non-adversarial approach to pollution control

Abstract

The molecular species involved in nitrogen fertilizer manufacture (even the products themselves) are simple inorganic materials and for the most part fall into the category of materials that occur naturally in the environment, though only in very low concentrations. The products involved are ammonia, urea, nitric acid, ammonium nitrate and ammonium nitrate derivatives, in particular calcium ammonium nitrate. Ammonia is the starting point for the production of all the others, and nitric acid is mostly used in the production of ammonium nitrate, although, like ammonia, it has other industrial uses.

Essentially, the main materials of concern are as follows:

Into water: Ammonia, ammonium nitrate, urea.

Into air: Nitrogen oxides, sulphur dioxide, ammonia, urea dust, ammonium nitrate/CAN dust and fume.

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Casale symposium 2001

Summary

The Casale Group of companies held a three-day symposium in its home town of Lugano, Switzerland, from May 21st-23rd this year. Nitrogen & Methanol eavesdropped on proceedings.

Abstract

Around 130 delegates found themselves in the beautiful surroundings of the Italian lakes for Casale’s 2001 symposium this year. Although primarily for customers to discuss their experience with Casale technology, several technical papers were also presented. Convening on Monday May 21st, welcoming addresses were made by Gianrico Corti, ­president of the Lugano Municipal Board, and by Casale’s Dr Umberto Zardi, and the first day of the conference was chaired by the familiar face of Dr Max Appl.

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Old plants for new

Summary

In future editions we shall present various points of view on the merits and possible demerits of dismantling used nitrogen plants and moving them to other locations. This opening article surveys some of the factors that deserve consideration.

Abstract

The idea of purchasing existing production facilities and relocating them at a site enjoying better feedstock prices and/or ­market logistics is not new.

Cannibalizing an old plant for spare parts is the commonest way of utilizing used equipment. In the fertilizer sector it is also fairly common practice to move a whole major component, such as a storage tank or a granulation unit.

Constructing a new production complex from items moved from one or more existing sites is less ­frequent because the economic advantages of such a relocation are not always clear-cut. In this introductory article, we examine some of the issues which arise in plant relocations of one kind or another. In the coming months we will be presenting a number of case studies of relocations which will look at the practicalities of moving “second hand” plants.

A number of circumstances are currently combining to increase interest in the use of existing plant and equipment. They may be summarized as follows.

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