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Products from Coal

12th November 2012

Coal gasification is an established technology which, in combination with sour shift, acid gas removal and syngas purification, can be readily used to generate syngas for the production of methanol, SNG, ammonia and a range of other products

Products from Coal
In many regions the conversion of coal to SNG is now seen as more attractive than traditional alternatives, such as the import of LNG

Johnson Matthey Catalysts (JM Catalysts) and Davy Process Technology offer technology and catalysts for a range of products from coal, including sour shift and syngas purification, methanol, di methyl ether (DME), ammonia, substitute natural gas (SNG), Fischer Tropsch (FT) and Oxo alcohols (Oxo).

Synthesis gas can be generated using several different types of coal gasification technology. Regardless of the upstream technology, Johnson Matthey is able to adapt its downstream process design to efficiently condition the gas by adjusting the ratio of hydrogen to carbon monoxide. This is done using the water shift reaction.  In addition to adjustment of the hydrogen to carbon monoxide balance, Johnson Matthey is able to supply purification materials to polish the raw gas, and both technology and catalysts for further conversion to products such as methanol and SNG. 

Using coal to produce synthesis gas suitable for subsequent conversion to methanol, SNG or other products is generally done using an entrained flow gasifier in which oxygen is used to partially combust the coal.  This generates a raw synthesis gas rich in carbon monoxide.  The gasification temperature is such that the non-combustible parts of the coal form a slag that can be separated from the produced gas.  The high temperature also ensures that there is a low methane content in the raw gas and this helps improve the efficiency of downstream methanol synthesis.

The raw gas from the gasifier has a large excess of carbon oxides and it is convenient to remove this in the form of carbon dioxide and, at the same time, remove other undesirable components, such as H2S.  Most of the carbon dioxide will be removed in an acid gas removal system, which is normally a liquid wash system.  This means that to achieve efficient production of methanol or SNG a stoichiometric gas with low levels of carbon dioxide should be generated.  Such a stoichiometric gas typically has an “R” ratio of approximately 2 for methanol or 3 for SNG where R = (H2 – CO2) / (CO + CO2).  This can be accomplished using the water gas shift reaction followed by an acid gas removal system:

CO   +   H2O   ↔   CO2  +  H2

The extent of the above reaction is determined by the thermodynamic equilibrium with greater conversion achieved at lower temperatures and with higher steam addition.  At commercial conditions the equilibrium is such that the hydrogen to CO ratio would be significantly greater than 3 and so it is convenient to use a single reaction stage with a bypass for methanol or SNG.

SNG Technology from Johnson Matthey Catalysts/Davy Process Technology

Global energy markets are changing.  In many regions there is strong demand for energy security using natural resources.  China is increasingly considering the conversion of coal to flexible and cleaner burning Substitute Natural Gas (SNG).  In many regions the conversion of coal to SNG is now seen as more attractive than traditional alternatives, such as the import of LNG.

The development of a large coal-to-SNG project involves several stages of chemical processing and employment of significant capital equipment – so for a successful implementation of an SNG project reliability is a key consideration.  The capability of JM Catalysts and Davy provides a proven and unrivalled technology package for the SNG industry.  Combined skills and capabilities in the SNG markets are characterised by:

• Experience
CRG methanation catalysts have been proven in commercial operation for more than 25 years.  JM Catalysts is the market leader in the supply of catalysts into SNG plants.
• Efficiency
Careful choice of process configuration and heat integration leads to maximum value of recovered heat
• Reliability
Attention to key pieces of mechanical design ensures maximum overall plant reliability

This combination of catalyst and technological expertise makes JM Catalysts and Davy the world's leading supplier of SNG technology.  This expertise has led to our technology being selected for six large SNG plants in China, including one located in Inner Mongolia, supplying the domestic gas needs for Beijing and another in the West China to feed gas into the strategic west – east gas pipeline.

The CRG methanation process and catalysts from Davy and JM Catalysts provide a low risk way of converting synthesis gas to high value SNG.  This SNG process uses technology originally developed during the1960s and 70s to produce Towns Gas and SNG for distribution in the domestic network in the UK.  The technology was adopted widely throughout the UK, Japan and the USA as well as a number of other applications worldwide.

The CRG SNG process normally consists of a two stage bulk methanation step with heat recovery between the reaction stages, raising superheated steam.  The temperature rise across the methanation reactors is controlled by recycling gas from the outlet of the second reactor and mixing it with the fresh feed to the first reactor.  The final gas quality can be adjusted by adding single or multiple trim methanation steps with heat recovery until the heating value of the gas reaches the desired value.

Today, CRG technology from JM Catalysts/ Davy offers a proven, reliable and efficient way of making SNG from a coal feedstock.

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