Kevin Fernandes, Process Analytics Sales Engineer for Endress+Hauser Ltd, discusses applications for Raman spectroscopy in carbon capture and hydrogen analysis.
As the world looks to cut greenhouse gas emissions, carbon capture and the production of low-carbon hydrogen have critical roles to play. Carbon capture permanently removes CO2 produced by industrial processes or burning fossil fuels from the atmosphere and stores it underground. Increased use of hydrogen as a fuel, on the other hand, prevents carbon emissions at the outset because hydrogen emits only water when burned or used in a fuel cell, although the production process can release carbon.
Carbon capture requires careful monitoring for process control and optimisation as well as reducing total costs of ownership and safety risks. Chemical absorption based on amine solvents is considered to be the most mature technology and commercially feasible method for carbon capture. Key to optimising this process is solvent management, including CO2 loading and amine strength, and Raman technology from Endress+Hauser offers a fast and robust solution.
Raman spectroscopy utilises laser radiation to produce light in the visible or near-infrared wavelength regions to excite the vibrational modes of different gases in a sample. The resulting scattered radiation changes colour based on the type of chemicals in the gas. A Raman analyser measures these scattered colours to determine the components in the gas and the intensity of each colour to determine component concentrations.
What started out as a single laser-generated colour now becomes its own rainbow since different gases in the sample produce specific wavelength spikes indicating their presence, and the relative intensity indicates relative concentration. The analyser looks for these specific spikes to create a chemical profile of the gas.
Amine-based carbon capture uses a solvent to remove CO2 from flue gas. A chemical reaction strips out the CO2 and allows the solvent to be reused. However, prolonged operation of the capture process causes solvent degradation and creates byproducts such as heat stable salts, thus reducing the capture efficiency.
From lab to process
The Raman spectroscopic models for solvent-based carbon capture were first developed in the laboratory before being evaluated in trials at two pilot-scale plants of different sizes. Two Raman probes with immersion optics were plugged into amine streams, and in situ measurements were used for obtaining on-line concentration profiles in different process conditions. Further, the capability of Raman instruments for monitoring solvent degradation compounds was identified during an additional trial. The methods proved reliable for chemical analysis in a range of CO2 capture solvents and mixtures in different concentrations.
Process optimisation
Raman technology has numerous benefits for carbon capture. The first is replacing time-consuming off-line analysis such as titration (more than two hours for sample preparation and measurement) with in-line monitoring, which gives measurement results in less than one minute without human interference. As well as reliably predicting the total CO2 and amine concentrations in changing process conditions, Raman monitors the variation of solvent quality and degradation, thus minimising solvent loss, and the performance of the absorber, desorber and other equipment. All this minimises downtime for the carbon capture plant and enables plant operators to optimise their processes.
Utilising hydrogen
Hydrogen can be produced from natural gas or even coal with virtually no greenhouse gas emissions by trapping the resultant CO2 underground. Even more environmentally friendly is so-called green hydrogen generated by electrolysis, where excess electricity can be channelled into an on-site installation that breaks water into its components, hydrogen and oxygen. This produces no carbon emissions but is an expensive process.
Blending green hydrogen with natural gas is a way to generate heat and power with lower emissions than using natural gas alone. These blends can be used for on-site consumption or sent out into the existing gas grid. Every incremental amount of hydrogen injected into a natural gas fuel system or pipeline abates a quantity of methane, and therefore COâ‚‚.
Hydrogen is highly combustible, and blending hydrogen with natural gas poses an increased risk of explosion. Hydrogen also has a volumetric heating value approximately one-third that of methane due to its low density, which means limits have to be imposed by gas producers and pipeline companies on the permissible volume to avoid reducing the overall heat value too much. Users such as gas turbine operators are particularly concerned about this since diluting heat value has a direct effect on a turbine’s horsepower output. With maximum blending amounts influenced by these performance and safety concerns, being able to accurately measure how much hydrogen has been mixed into the stream is vital.
Real-time measurement
Endress+Hauser’s Raman Rxn5 analyser delivers real-time, reliable composition analysis of rapidly changing gas turbine fuels blended with hydrogen by taking simultaneous readings from up to four probes located in different parts of the process stream. Together, the Raman analyser system provides calculations of the Wobbe index – a reference used to compare the energy output of different gas blends. The Wobbe index is critical when using alternative fuel sources like hydrogen which has a lower Btu per volume than natural gas. Reliable, nearly instantaneous feedback about the integrity of the gas blend helps to prevent too much hydrogen being added, which could damage the combustion system. In addition to hydrogen content, a Raman analyser can also handle many of the commonly measured natural gas components. As the probe is located remotely from the analyser, there is no need for the operator to handle a sample, enhancing safety.
With the potential for four-channel availability and fibreoptic lengths up to 150 metres, a Raman analyser can also monitor hydrogen composition over a long length of pipeline after being injected. This data can be used to monitor the mixing quality or to corroborate predictive models of how hydrogen will behave in the gas grid at scale. This is especially useful for gas utilities looking to meet renewable gas portfolio standards in their distribution networks, without compromising safety or quality for their customers and other stakeholders.
The entire injection process can be automated and packaged as a single skid, sized to reflect the incoming hydrogen supply. Built around a Raman analyser, the skid’s automation and instrumentation system determines the maximum injection flow to offload the greatest amount of hydrogen, or to optimise the mix to match the requirements of a gas turbine or other combustion process.
When combining Raman spectroscopy with a comprehensive control strategy, companies can maximise the use of carbon capture and hydrogen without compromising safety or efficiency, ultimately reducing overall carbon emissions for a sustainable future.
For further information, please contact:
Kevin Fernandes
Process Analytics Sales Engineer
Endress+Hauser Ltd.
Floats Road
Manchester
M23 9NF
Tel. +44 161 286 5000
info.uk@endress.com
www.uk.endress.com
Endress+Hauser UK
- +44 161 286 5000
- info@uk.endress.com
- https://www.uk.endress.com
- Floats Road Manchester M23 9NF GB
About us
A strong partner worldwide
Endress+Hauser is a global leader in measurement instrumentation, services and solutions for industrial process engineering. We provide process solutions for flow, level, pressure, analytics, temperature, recording and digital communications, optimising processes in terms of economic efficiency, safety and environmental impact. Our customers come from various industries, including chemical, food & beverage, life sciences, power & energy, primaries & metal, oil & gas and water & wastewater.
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- Net sales of 2.4 billion euros – a strong partner
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