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Maximising biomethane production efficiency using advanced automation technology


Rosella Mimmi

Biomethane presents a great new opportunity for Europe in terms of a low cost, eco-friendly form of energy and the market for this product is growing rapidly, says Rosella Mimmi at Emerson Automation Solutions, but there are challenges being faced in this sector in order to conform to strict regulations.

Biomethane presents a great new opportunity for Europe in terms of a low cost, eco-friendly form of energy and the market for this product is growing rapidly. New regulations within many European countries, not only enable biomethane to be added to the natural gas networks, but incentives are available to increase the amount of biomethane added to the grid. However, there are a number of challenges facing operators wanting to inject biomethane into the grid. They must comply with very stringent regulations and standards, deliver continued reliable, efficient and safe operations, and ensure there is lifecycle support for all plant assets. Advanced automation technology is enabling operators biomethane injection to meet these challenges and take advantage of a thriving new market.

What is biomethane?

Biomethane is a mix of gases produced from both biological (upgrading of biogas) and thermochemical processes. Biomethane is gaining a lot of attention, especially in Europe due to the increasing focus and desire for renewable energy. Critically, as a renewable gas it can make a significant contribution in meeting the European Union’s renewable energy targets. As a result, biomethane production is showing the highest level of growth of any gas market in the world.

Because biogas has a low thermal efficiency and a chemical composition not compliant with fuel gases used by transmission and distribution infrastructures, it has a restricted range of uses. It cannot be added to the gas network and sold on the open market, so in general it is used by the producer to produce heat and electricity for its own use. The upgrading process used to convert biogas into biomethane produces a fuel with compatible characteristics and the same benefits as natural gas. The new regulatory framework permits biomethane to be added to the natural gas network and in addition, most European countries have created incentives to increase the amount of biomethane injected into the grid.

After the upgrading treatment has been completed, biomethane has a quality and characteristics compatible with natural gas that contains more than 95% methane. Before injection into the grid can proceed the necessary stages of compression, odorisation and often propane injection must be performed. Here advanced automation becomes a critical part of the process.

Gas Analysis

Before these steps take place, the gas quality must be tested to ensure compliance with pipeline and safety standards. Only if the gas quality meets these standards can it be injected to the grid.

Gas chromatographs are used to perform this task and can be considered the heart of the analytical testing section. Together with the ancillary systems, the gas chromatograph analyses the gas and ensures the suitability of the gas in accordance to the end user’s requirements. It is essential therefore that the gas chromatograph has the necessary metrology approvals required to support consumer billing.

The analytical module of a biomethane plant and specifically the gas chromatograph can present some challenges for the operator. In general, injection stations are pre-fabricated modules, which means in order to transport them easily to the site, there is a restriction on size. 

Furthermore, because there is a need to produce very accurate and consistent analysis of the gas quality delivered to the customer, this can create a complex system that may increase operational and lifecycle costs. The system must also be very reliable.

The latest automation solutions address these challenges, with compact gas chromatographs now available to overcome the limited space available. Low utility and sample flow rates keep operational costs to a minimum and enhance the reliability of the system.

Should technical support be required, this can now be provided remotely, eliminating the need for costly site visits by engineers. Moreover, intuitive software and a unique ‘Maintainable Module’ simplify their operation, whilst maintaining highly accurate compositional data reporting with low measurement uncertainty.

Once the quality of the gas has been established, its value is converted into a signal that controls a three-way valve installed downstream. Depending on the value, the gas will either be directed back for additional processing or forwarded to a pressure reduction and metering station. This is very similar to a standard natural gas station, with gas filtered and then measured using a custody transfer flow meter and flow computer. Pressure regulators are used to reduce and stabilise the injection pressure to the required `final destination’ value. It is very important to select the correct regulator type and necessary overpressure protection to ensure safe operations.

Odorisation

Another important part of the process is odorant injection. As with natural gas, biomethane cannot be added to the distribution grid without the appropriate odorisation. Odorant injection systems vary in type from very simple and manually operated units (i.e. absorption type) to more complex and fully automated units. The fully automated systems control the concentration ratio using a microprocessor-based device that will monitor the liquid injected and automatically adjust the rate to maintain a constant odorant ratio.

Ensuring compliance with Health and Safety Executive and industry regulations are two of the challenges associated with odorant injection. Another challenge is trying to reduce operating costs. National energy authorities take odorisation into consideration when performing quality of service evaluations and conclude that poor odorisation can have a significant impact on operational costs. Traditional technologies such as absorption and pump systems produce several issues including uneven odorant distribution, unplanned downtime and a subsequent increase in the time maintenance engineers must spend visiting units that are often located remotely.

New solutions that use solenoid injection valves provide a great solution in terms of ease of use, reduced maintenance and the possibility of both remote access and control. The accuracy granted by solenoid injectors can be maintained over the entire flow range of the system, approaching infinite turn down. Automatic calibration during normal operation makes adjustments for any changes in mechanical components and also detects failures that can be flagged up by alarms. The system can also be configured to use redundant injectors and/or an emergency backup or bypass absorption system. The control system stores both real time and historical data. This can be viewed locally or remotely on a laptop using configuration software, or remotely using a SCADA system.

Integrated systems

It is critical that the gas chromatograph, flow meter, pressure regulators, odorant injection system and control system work together seamlessly to guarantee the quality of the gas produced and that the plant meets the other operating challenges discussed. 

Because of the breadth of components and technology required to monitor and control a plant of this type, this can present a challenge when designing and implementing a solution. Measurement accuracy and subsequent gas quality can be impacted should the complete solution not be installed, calibrated and connected correctly. It can also be difficult to assign responsibility should there be a malfunction. To help overcome this problem a vendor able to provide support for all the main devices can help to maximise operational performance of the plant and provide lifecycle care to ensure continued efficient production. 

Biomethane presents a great new opportunity for Europe in terms of a low cost, eco-friendly form of energy and the market for this product is growing rapidly.  To make this opportunity as trouble-free as possible, the vendor should be able to advise on the requirements to meet the latest standards and regulations.

 

FURTHER INFORMATION

Emerson Automation Solutions, http://www.emerson.com/en-us/automation-solutions
 

ABOUT THE AUTHOR

Rossella Mimmi is Demand Creation Manager at Emerson Automation Solutions.

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