Licensed Processes

Substitute Natural Gas (SNG)

Select each section header below to expand, or click here to expand/collapse all sections
Introduction

Substitute natural gas (SNG) is a synthetic fuel gas designed to contain high levels of methane (CH4) and therefore act as a natural gas substitute. JM Davy is the world’s leading supplier of SNG technology, with our licensed plants providing more than half of global SNG production.

Our process is a clean and efficient way to upgrade the energy stored in solid hydrocarbons, such as coal and petroleum coke, to a useful and easily transportable form. The final SNG product is also high in quality, being suitable for injection into gas distribution networks or, alternatively, conversion to LNG.

A key step in SNG production is methanation, which converts synthesis gas (syngas, predominantly CO, CO2 and H2) into methane.

Johnson Matthey and JM Davy have over 100 years’ experience in methanation research. Our methanation technology combines JM Davy’s design with CRGTM catalysts from Johnson Matthey which have been specially developed for methanation. CRG is the world’s most widely used and proven catalyst family for this application, with over 30 years of operating service for syngas to SNG.

This Davy process is based on extensive practical experience and has been consistently proven in commercial operation. We have developed a range of options tailored to suit the various plant feedstocks and needs of our diverse clients.

Coal or petcoke feed are converted to syngas through commercially available gasification technology. The syngas then undergoes sour shift, carbon dioxide removal and sulphur removal in preparation for methanation.

The JM Davy methanation technology then produces SNG from the syngas feed, with the process design optimised and tailored to specific product and client requirements.

Process Flowsheet

Roll over the orange squares to see more information

Tap diagram to view larger
Key Reactions

Two main reactions take place in the methanation step of the SNG process, with CRG catalysts from Johnson Matthey specially developed to promote both reactions. This delivers a superior quality product without the need for multiple catalysts.

The reverse of the vapour-phase shift reaction converts carbon dioxide to carbon monoxide:

SNG_big_equation1

The vapour-phase methanation reaction converts carbon monoxide and hydrogen to the final SNG product:

SNG_big_equation2

Process Description

This vapour-phase process employs a number of simple catalysed steps to convert coal or petcoke derived syngas feed to high-methane content SNG.

The key conversion takes place in the methanation step, a Davy technology which utilises CRG catalysts from Johnson Matthey.

Process feedstock

The process feedstock is syngas (CO, CO2 and H2) derived from coal or petcoke gasification. The syngas contains a high proportion of CO and will also be contaminated with sulphur impurities.

Sour shift

This step consumes excess CO to produce more H2 which is required for downstream methanation.

Johnson Matthey offers a market-leading sour shift catalyst which is highly tolerant of sulphur impurities. Additionally, Johnson Matthey can supply proprietary reactor internals to significantly improve pressure drop performance of the sour shift unit.

Acid gas removal

Commercially available technology for acid gas removal is used to reduce the CO2 and sulphur content of the syngas.

Methanation

The Davy methanation system comprises three steps which achieve the required product quality while maximising catalyst life:

SNG_small_flowsheet

Firstly, the syngas feed is ultrapurified using Johnson Matthey PURASPEC catalysts. This removes sulphur impurities down to extremely low levels to protect the catalyst used in the subsequent methanation step.

The key methanation conversion proceeds by two equilibrium reactions which form methane from CO, CO2 and H2. The overall conversion is highly exothermic:

CO shift:

SNG_small_equation1

Methanation:

SNG_small_equation2

The majority of the conversion takes place in the bulk methanation step which, due to the high concentration of reactants, produces a large amount of heat and takes place at high temperature.

The trim methanation step, which takes place at lower temperatures to encourage the methanation equilibrium, is used to convert residual unreacted CO, CO2 and H2 into product.

The resulting dry substitute natural gas (SNG) is high-purity and suitable for use within gas distribution networks.

SNG_small_flowsheet - processoption_coal

In the non-stoichiometric flow sheet, the syngas does not pass through a sour shift system. Instead, following sulphur removal, it proceeds directly to the methanation step, where the CRG catalyst facilitates both the shift and methanation reactions. CO2 is then removed from the product gas instead of the feed, which means that a very low CO2 content can be achieved.

As the methanation step in this flow sheet performs all of the shift duty, the catalyst volume is larger than that used in an equivalent capacity stoichiometric route. However, the overall flow sheet is smaller resulting in a reduced plot size and lower net capital expenditure.

Catalysts

Johnson Matthey catalysts are the driving force behind the Davy SNG process. In particular, the families of PURASPEC® and KATALCO® CRG catalysts have been developed specifically for SNG applications, demonstrating outstanding performance and reliability for a range of feedstocks and temperatures.

PURASPEC® and KATALCO® are registered trade marks of Johnson Matthey Plc.


Johnson Matthey’s PURASPEC range of catalysts is ideally suited to purifying the syngas feed for an SNG plant. This range of catalysts is designed to remove sulphur down to the extremely low levels which are required by the methanation catalyst. The exact choice of catalyst depends on the composition of sulphur compounds in the syngas.


Part of Johnson Matthey’s KATALCO range, CRG catalysts have been developed in conjunction with JM Davy’s methanation technology. Advantages of the CRG catalysts include:

A unique formulation

  • Enables CRG to catalyse the methanation and shift reactions simultaneously.

Excellent stability at high temperatures

  • Makes CRG ideal for the bulk methanation step.

High activity at low temperatures

  • Makes CRG the obvious choice for the trim methanation step.

Availability in a range of shapes and sizes

  • Provides the optimum combination of low pressure drop and high active area.

Structural strength

  • Enables CRG to withstand transient start-up and upset conditions without damage.

Excellent poison retention

  • Underpins long catalyst life and durability.

Being supplied pre-reduced and stabilised

  • Avoids expensive start-up equipment
    and enables a rapid plant start-up.
The JM Davy Advantage

This proven Davy SNG process centres on our methanation core technology, which offers many advantages, both in terms of process technology and catalysis:

+Long-term proven process:

  • CRG catalyst from Johnson Matthey has been used in SNG plant operation for over 30 years.
  • JM Davy has many years’ experience in high temperature equipment design and specification.

+Efficient design:

  • Heat recovery maximised.
  • Compressor power minimised.
  • Methanation stages minimised.
  • Both shift and methanation reactions proceed with a single, pre-reduced and highly active catalyst.
  • No additional steam is required during operation.

+Low equipment costs:

  • Our methanator design uses no proprietary equipment.

+Design flexibility:

  • JM Davy will adjust process design and heat recovery to meet client-specific requirements.
Core Technologies

Explore the methanation technology that underpins JM Davy’s SNG process:

The offgas from a coke oven, termed coke oven gas (COG), is often used as fuel. However, JM Davy’s SNG process can add greater value to COG by upgrading it to SNG or, more typically, LNG.

The GOG feed is generally high in hydrogen and requires no sour shift. Sulphur removal is required prior to methanation. Conversion of the resulting SNG to LNG, if required, employs a final liquefaction step.

Process Flowsheet

Roll over the orange squares to see more information

Tap diagram to view larger
Key Reactions

Two main reactions take place in the methanation step of the SNG process, with CRG catalysts from Johnson Matthey specially developed to promote both reactions. This delivers a superior quality product without the need for multiple catalysts.

The reverse of the vapour-phase shift reaction converts carbon dioxide to carbon monoxide:

SNG_big_equation1

The vapour-phase methanation reaction converts carbon monoxide and hydrogen to the final SNG product:

SNG_big_equation2

Process Description

This vapour-phase process employs a number of simple catalysed steps to convert purified coke oven gas to high-quality SNG suitable for liquefaction.

Process feedstock

The process feed is coke oven offgas which typically contains high levels of H2, with CH4, CO, CO2 and some hydrocarbons also present.

COG Purification

Due to the nature of the coal feed to the coke oven, the resulting offgas usually contains relatively high levels of sulphur and possibly other impurities.

Purification – with a focus on desulphurisation – is required prior to the methanation step primarily to protect the methanation catalyst from sulphur poisoning.

Methanation

The offgas from a coke oven unit is of variable composition due to changes in the make-up of the coal feed.

JM Davy’s methanation unit is designed to accommodate these changes while always meeting the required product specification.

The system comprises three steps:

SNG_small_flowsheet

The COG feed is first ultrapurified using Johnson Matthey PURASPEC catalysts. This further reduces sulphur impurities down to extremely low levels, again to protect the methanation catalyst from sulphur poisoning.

The key methanation conversion proceeds by two equilibrium reactions which form methane from CO, CO2 and H2. The overall conversion is highly exothermic:

CO shift:

SNG_small_equation1

Methanation:

SNG_small_equation2

The majority of the conversion takes place in the bulk methanation step which, due to the high concentration of reactants, produces a large amount of heat and takes place at high temperature.

The trim methanation step, which takes place at lower temperatures to encourage the methanation equilibrium, is used to convert residual unreacted CO, CO2 and H2 into product.

The resulting substitute natural gas (SNG) typically contains less than 50ppm CO and CO2 and is therefore suitable for liquefaction to LNG product.

Liquefaction

Depending on the composition of the feed gas, some CO, CO2, N2 and H2 may remain in the SNG product.

CO and CO2 will tend to form solids in the liquefaction plant and need to be removed to less than 50ppm. Whenever possible, JM Davy will design the methanation plant to achieve less than 50ppm CO and CO2 in order to avoid a separate removal step. Any remaining H2 and N2 must also be removed as these will not condense during liquefaction.

The liquefaction process involves dehydration of the gas followed by refrigeration to condense the methane product.

Catalysts

Johnson Matthey catalysts are the driving force behind the Davy SNG process. In particular, the families of PURASPEC® and KATALCO® CRG catalysts have been developed specifically for SNG applications, demonstrating outstanding performance and reliability for a range of feedstocks and temperatures.

PURASPEC® and KATALCO® are registered trade marks of Johnson Matthey Plc.


Johnson Matthey’s PURASPEC range of catalysts is ideally suited to purifying the syngas feed for an SNG plant. This range of catalysts is designed to remove sulphur down to the extremely low levels which are required by the methanation catalyst. The exact choice of catalyst depends on the composition of sulphur compounds in the syngas.


Part of Johnson Matthey’s KATALCO range, CRG catalysts have been developed in conjunction with JM Davy’s methanation technology. Advantages of the CRG catalysts include:

A unique formulation

  • Enables CRG to catalyse the methanation and shift reactions simultaneously.

Excellent stability at high temperatures

  • Makes CRG ideal for the bulk methanation step.

High activity at low temperatures

  • Makes CRG the obvious choice for the trim methanation step.

Availability in a range of shapes and sizes

  • Provides the optimum combination of low pressure drop and high active area.

Structural strength

  • Enables CRG to withstand transient start-up and upset conditions without damage.

Excellent poison retention

  • Underpins long catalyst life and durability.

Being supplied pre-reduced and stabilised

  • Avoids expensive start-up equipment
    and enables a rapid plant start-up.
The JM Davy Advantage

This proven Davy SNG process centres on our methanation core technology, which offers many advantages, both in terms of process technology and catalysis:

+Long-term proven process:

  • CRG catalyst from Johnson Matthey has been used in SNG plant operation for over 30 years.
  • JM Davy has many years’ experience in high temperature equipment design and specification.

+Efficient design:

  • Heat recovery maximised.
  • Compressor power minimised.
  • Methanation stages minimised.
  • Both shift and methanation reactions proceed with a single, pre-reduced and highly active catalyst.
  • No additional steam is required during operation.

+Low equipment costs:

  • Our methanator design uses no proprietary equipment.

+Design flexibility:

  • The Davy SNG process has the flexibility to handle variations in feed gas composition from a coke oven.
  • JM Davy will adjust process design and heat recovery to meet client-specific requirements.
Core Technologies

Explore the methanation technology that underpins JM Davy’s SNG process:


Core Technologies

Explore the methanation technology that underpins JM Davy’s SNG process: