Carbon capture from combined heat and power plants

While carbon capture continues building new possibilities for a sustainable future, the combination of carbon capture technology with combined heat and power plants generates yet another symbiosis in the quest for a circular, no-waste, no-emissions model.

Around 230 Mt of captured CO2 are used each year, mainly in applications related to the fertilizer industry, according to the IEA. A figure that speaks of two movements: the challenges of implementing carbon capture, and the continued efforts to advance the technologies enabling it, supporting the transition to a low-carbon economy.

A particular model is currently being praised for its potential. That is the integration of carbon capture in combined cycle power plants with district heating systems and heat pumps. The result: an integrated, circular ecosystem that can enable a truly revolutionary approach to sustainable energy production.

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What is carbon capture in combined heat and power plants

As defined by the Encyclopaedia Britannica, carbon capture is “the process of recovering carbon dioxide from the fossil-fuel emissions produced by industrial facilities and power plants”, with the aim of minimizing the release of CO2 and mitigating pollution.

Carbon capture typically addresses large point sources, and has been incorporated in sectors which have presented more difficulties in mitigating their emissions. As such, its adaptation to CHP plants is a natural move that presents a viable option for both new and retrofitting projects, all while allowing the plant to operate (that is, to simultaneously generate electricity and useful thermal energy). 

The basic working principle behind carbon capture in combined heat and power plants is as follows: the plant operates normally, so that the fuel is burned in the plant to generate electricity and waste heat is used for heating purposes; however, CO₂ capture technologies are integrated into the flue gas treatment system; after CO₂ is captured, it is compressed and transported via pipelines to permanent storage sites.

Available technologies for carbon capture and challenges

An overview of the main current technologies available for carbon capture (beyond their applications in CHP plants), offers visibility on the different models that are being implemented:

Direct Air Capture (DAC) 

These technologies are able to capture CO₂ directly from the ambient air (as opposed to capturing it from point sources like power plants or industrial facilities). Consequently, the DAC approach is not typically applied to CHP plants.

The most expensive technology to date to perform carbon capture, it is also less efficient than other methods mentioned in this list. This is because atmospheric CO₂ is significantly more dilute than in other sources (such as, for instance, flue gas produced by CHP plants), resulting in more energy spent in the process and increased overall costs.

IEA figures count 27 DAC plants commissioned worldwide, with plans for 130 more facilities. As the organization mentions, this number “would nearly reach the level required in 2030 under the Net Zero Emissions by 2050 (NZE) Scenario, or around 65 MtCO2/year.”

Point source capture

This method for carbon capture focuses on concentrated sources like power plants, combined heat and power plants and several other kinds of industrial facilities. That is, locations where emissions are concentrated in one location.

Methods within this approach include pre-combustion, post-combustion, and oxy-fuel combustion. Post-combustion capture is the most common option for CHP plants, offering additional benefits, as it can be retrofitted to existing CHP plants, and doesn’t interfere with the primary electricity and heat generation processes within the plant.

Other innovative techniques

Membrane separation, cryogenic separation, and adsorption-based capture are all being explored as additional avenues for CO₂ removal, as well as chemical looping and calcium looping.

The BECCS approach has been particularly praised for carbon capture in combined heat and power plants,

Standing for Bioenergy with Carbon Capture and Storage, it is a carbon capture technology that combines bioenergy production with the capture and permanent storage of CO₂ emissions.

Described as a negative emissions technology, the method removes more CO₂ from the atmosphere than it emits, and offers two options (heat-driven and electricity-driven), both of which are based on absorbing CO₂ from flue gasses.

Before carbon capture can live up to its potential, a series of challenges need to be solved. In fact, the IEA is quick to remind that ‘CO2 use does not necessarily lead to emissions reduction’, and that factors such as the source of the CO2 or the type of energy used for the conversion process must be taken into account, among others.

Additionally, there’s a challenge that applies specifically to carbon capture in combined heat and power plants: the additional energy required for the process might reduce overall plant efficiency if the right measures are not taken into account. 

This is precisely why optimizing energy use and integrating waste heat recovery will remain essential elements of any successful carbon capture system. And this is where heat pumps and district heating networks come in.

carbon captured

The role of industrial heat pumps to push efficiency in carbon capture to the next level

Reusing captured heat for district heating systems presents a new model for efficiency and circularity made possible by the use of heat pumps integrated with carbon capture technologies.

Simply put, heat pumps allow for the recovery of residual heat released by carbon capture systems. Thanks to their capacity to upgrade and elevate the temperature of captured waste heat, it could then be employed for district heating generation, all while ensuring top efficiencies.

A similar model has been presented in Beiron, J., Normann, F., Johnsson, F. (2023), ‘Carbon capture from combined heat and power plants  - Impact on the supply and cost of electricity and district heating in cities (International Journal of Greenhouse Gas Control, 129).

Heat pumps have also been suggested for enhancing efficiency in carbon capture technologies. In this case, heat pumps transfer and employ waste heat from industrial processes to power carbon capture processes. Looking at the specifics, evaporators in heat pumps are in charge of absorbing industrial waste heat but, for example, in a DAC process, are also coupled with the adsorption tower and condenser in the DAC. This way, a closed circuit is generated, allowing the heat pump condenser to release heat to the district heating network and/or to the desorption tower. A model paraphrased from the paper by Xiaoxue Kou et al., (2024), published under a CC BY 4.0 license.

It’s important to note that all models’ effectiveness greatly depends on careful design that takes into account factors such as temperature gradients and the energy source powering the heat pumps, among other aspects.

Designed correctly, a synergistic approach to energy generation emerges, where CHP plants, carbon capture technologies and heat pumps all work together as part of an ecosystem that minimizes energy waste and CO₂ emissions. A model that effectively shifts the traditional understanding of emissions from being considered as waste to being valuable resources for heating applications.  

In other words, rather than allowing waste heat and CO₂ emissions to dissipate into the environment, these are understood as resources to be harnessed, repurposed, and used. 

At ARANER, we’re at the forefront of the state-of-the-art thermal engineering innovations that are shaping the energy landscape of the future. As such, we’re key allies for companies looking to innovate and take energy efficiency in carbon capture to the next level. 

Through our detailed, personalized look at each project, we’re able to provide the best solution to complex thermal engineering developments, even when faced with challenging conditions. As such, our district heating line and industrial heat pumps are ready to contribute to develop the carbon capture technologies of the future.

Looking to optimize carbon capture processes and develop truly circular models via the integration with district heating? At ARANER, we can help you. Get in touch with us and speak to our team to learn how.

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