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Liquid Nitrogen Wash is a process mainly used for the production of ammonia synthesis gas within fertilizer production plants. It is usually the last purification step in the ammonia production process sequence upstream of the actual ammonia production. [1]
The purpose of the final purification step upstream of the actual ammonia production is to remove all components that are poisonous for the sensitive ammonia synthesis catalyst. [2] This can be done with the following concepts:
The liquid nitrogen wash has two principle functions: [1]
The carbon monoxide must be removed completely from the synthesis gas (i.e. syngas) since it is poisonous for the sensitive ammonia synthesis catalyst. [4] The components argon and methane are inert gases within the ammonia synthesis loop, but would enrich there and call for a purge gas system with synthesis gas losses or additional expenditures for a purge gas separation unit. The main sources for the supply of feed gases are partial oxidation processes.
Since the synthesis gas exiting the partial oxidation process consists mainly of carbon monoxide and hydrogen, usually a sulfur tolerant CO shift (i.e. water-gas shift reaction) is installed in order to convert as much carbon monoxide into hydrogen as possible.
Shifting carbon monoxide and water into hydrogen also produces carbon dioxide, usually this is removed in an acid gas scrubbing process together with other sour gases as e.g. hydrogen sulfide (e.g. in a Rectisol Wash Unit). [1]
The liquid nitrogen wash consists of
The name liquid nitrogen wash is a little misleading, since no liquid nitrogen is supplied from outside to be used for scrubbing, but gaseous high pressure nitrogen, supplied by the Air separation Unit that usually also provides the oxygen for the upstream Partial Oxidation. [7]
This gaseous high pressure nitrogen is partially liquefied in the process and is used as washing agent. In a so-called nitrogen wash column, the impurities carbon monoxide, argon and methane are washed out of the synthesis gas by means of this liquid nitrogen. These impurities are dissolved together with a small part of hydrogen and leave the column as the bottom stream.
The purified gas leaves the column at the top. The now purified synthesis gas is warmed up and is mixed with the required amount of gaseous high pressure nitrogen in order to achieve the hydrogen to nitrogen ratio of 3 to 1, and can then be routed to the ammonia synthesis. [5]
At operating pressures higher than about 50 bar(a), the refrigeration demand of the liquid nitrogen wash is covered by the Joule–Thomson effect, [4] and no additional external refrigeration, e.g. by vaporization of liquid nitrogen is required.
The liquid nitrogen wash is especially favorable when combined with the Rectisol Wash Unit. The combination and advantageous interconnections between a Rectisol Wash Unit and a liquid nitrogen wash lead to smaller equipment and better operability.
The gas coming from the Rectisol Wash Unit can be sent to the Liquid Nitrogen Wash at low temperature (directly from the methanol absorber without being warmed up). [5] Since part of the purified gas is reheated in the Rectisol Wash Unit, small fluctuations in flow and temperatures can easily be compensated leading to best operability.
To improve the hydrogen recovery, an integrated hydrogen recycle from the liquid nitrogen wash to the Rectisol Wash Unit can be installed, which uses the already existing recycle compressor of the Rectisol Wash Unit to recycle the hydrogen-rich flash gas from the liquid nitrogen wash back into the feed gas of the Rectisol Wash Unit. This leads to extremely high hydrogen recovery rates without any further equipment.
The Haber process, also called the Haber–Bosch process, is the main industrial procedure for the production of ammonia. It converts atmospheric nitrogen (N2) to ammonia (NH3) by a reaction with hydrogen (H2) using a finely divided iron metal catalyst:
Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principally used for producing ammonia or methanol. Syngas is combustible and can be used as a fuel. Historically, it has been used as a replacement for gasoline, when gasoline supply has been limited; for example, wood gas was used to power cars in Europe during WWII.
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Steam reforming or steam methane reforming (SMR) is a method for producing syngas (hydrogen and carbon monoxide) by reaction of hydrocarbons with water. Commonly natural gas is the feedstock. The main purpose of this technology is hydrogen production. The reaction is represented by this equilibrium:
The Sabatier reaction or Sabatier process produces methane and water from a reaction of hydrogen with carbon dioxide at elevated temperatures and pressures in the presence of a nickel catalyst. It was discovered by the French chemists Paul Sabatier and Jean-Baptiste Senderens in 1897. Optionally, ruthenium on alumina makes a more efficient catalyst. It is described by the following exothermic reaction:
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Pressure swing adsorption (PSA) is a technique used to separate some gas species from a mixture of gases under pressure according to the species' molecular characteristics and affinity for an adsorbent material. It operates at near-ambient temperature and significantly differs from the cryogenic distillation commonly used to separate gases. Selective adsorbent materials are used as trapping material, preferentially adsorbing the target gas species at high pressure. The process then swings to low pressure to desorb the adsorbed gas.
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Industrial gases are the gaseous materials that are manufactured for use in industry. The principal gases provided are nitrogen, oxygen, carbon dioxide, argon, hydrogen, helium and acetylene, although many other gases and mixtures are also available in gas cylinders. The industry producing these gases is also known as industrial gas, which is seen as also encompassing the supply of equipment and technology to produce and use the gases. Their production is a part of the wider chemical Industry.
Kipp's apparatus, also called a Kipp generator, is an apparatus designed for preparation of small volumes of gases. It was invented around 1844 by the Dutch pharmacist Petrus Jacobus Kipp and widely used in chemical laboratories and for demonstrations in schools into the second half of the 20th century.
Ammonia production takes place worldwide, mostly in large-scale manufacturing plants that produce 183 million metric tonnes of ammonia (2021) annually. Leading producers are China (31.9%), Russia (8.7%), India (7.5%), and the United States (7.1%). 80% or more of ammonia is used as fertilizer. Ammonia is also used for the production of plastics, fibres, explosives, nitric acid, and intermediates for dyes and pharmaceuticals. The industry contributes 1% to 2% of global CO
2. Between 18–20 Mt of the gas is transported globally each year.
A methane reformer is a device based on steam reforming, autothermal reforming or partial oxidation and is a type of chemical synthesis which can produce pure hydrogen gas from methane using a catalyst. There are multiple types of reformers in development but the most common in industry are autothermal reforming (ATR) and steam methane reforming (SMR). Most methods work by exposing methane to a catalyst at high temperature and pressure.
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Syngas fermentation, also known as synthesis gas fermentation, is a microbial process. In this process, a mixture of hydrogen, carbon monoxide, and carbon dioxide, known as syngas, is used as carbon and energy sources, and then converted into fuel and chemicals by microorganisms.
The Glossary of fuel cell terms lists the definitions of many terms used within the fuel cell industry. The terms in this fuel cell glossary may be used by fuel cell industry associations, in education material and fuel cell codes and standards to name but a few.
An air separation plant separates atmospheric air into its primary components, typically nitrogen and oxygen, and sometimes also argon and other rare inert gases.
A cryogenic gas plant is an industrial facility that creates molecular oxygen, molecular nitrogen, argon, krypton, helium, and xenon at relatively high purity. As air is made up of nitrogen, the most common gas in the atmosphere, at 78%, with oxygen at 19%, and argon at 1%, with trace gasses making up the rest, cryogenic gas plants separate air inside a distillation column at cryogenic temperatures to produce high purity gasses such as argon, nitrogen, oxygen, and many more with 1 ppm or less impurities. The process is based on the general theory of the Hampson-Linde cycle of air separation, which was invented by Carl von Linde in 1895.
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