Author: Keshav Goela      Posted on: 17-12-21

As the world looks to decarbonise and achieve the coveted “net-zero” planetary goal, biogas is once again in the spotlight. While biogas has its merits, one of the major drawbacks is that it is accompanied inevitably with CO2 generation - a gas that is mistakenly treated as waste.

Recycling the CO2 generated as a byproduct of biogas production is an excellent way to avoid CO2 wastes. But not many consider it viable or they are not aware of the possibilities. As it is not a “core” business related to biogas; biogas plant owners are unaware of the profit center this byproduct could become.

Another reason why biogas plant owners do not actively implement CO2 recycling solutions is due to ineffective solutions. An expert is needed and this is where GAS LAB comes into the picture. We are pioneers in CO2 solutions for biogas treatment. As technical agnostics, we excel at the following techniques: Scrubbing (water/solvent), PSA, and our proprietary flagship technology for Amines upgrading & separation. It is to be said that we take great care to avoid the methane “slip” that may be treated as irrelevant by some designers, forgetting it is a major contaminant, far worse than CO2 itself.

Apart from experience accumulated over 60 years of operation, GAS LAB is one of the few experts in the field investing in R&D to implement innovative technical solutions that complement the economic success of your biomethane project. The biogas upgrading with our carbon capture experience will certainly deliver the best fit solution for customers. In fact, we frequently surprise our customers with options initially discarded because they were assumed as “too expensive” due to past experience with other suppliers. Allow us to elaborate on our solutions for biogas plants:

Water Scrubbing is a simple technique that is compact and easy to operate. However, the controls require constant attention and we excel at it. The separation process is based on the significantly higher Henry’s Law solubility of CO2 in water when compared with methane. To improve efficiency, the process is designed at medium to high pressures.The biggest benefit of this system is that it requires little chemical consumables, just water.

This technique delivers available biomethane to about 90-95%, but when correctly controlled you can even reach 97%, hence a “slip” of just 1 % of biomethane is a good figure. Water scrubbing is cost effective in small and medium size projects. Scrubbing also reduces the available carbon dioxide. Therefore, optimization of the project including CO2 applications leaves fewer options. But because such projects are usually in a rural surrounding, adding the gas to irrigation water (pH adjustment) can be favoured and therefore boost the profit of the overall project.

Organic Scrubbing is an alternative to water scrubbing. Although the yield is similar to water scrubbing, it is not a very popular technique as it replaces water with organic solvents. The trick is that the solvents can dissolve CO2 about 10x more than water does. This allows the customer to reduce the size of the equipment noticeably. However, the marginal gains and the issues involved with solvents hasn´t favored this technology: Corrosion is an issue, and the process is very temperature sensitive. And CO2 recuperation is made quite complicated.

PSA (Pressure Swing Adsorption) is one of our specialties. It is gaining more and more popularity since 2009, and for good reasons. The term adsorption refers to the chemical process where a media carries another chemical without reacting with it under specific conditions of temperature and pressure, to be discharged when these are modified. Heating and/or cooling are therefore inherent to the process.

The PSA technique separates CO2 effectively through a non-continuous process: Biogas is compressed and then expanded. Therefore, it is customary that several PSA columns operate alternatively in a plant. The yield is efficient at around 99%. Also, energy consumption is not high because added heat is not required, but, similar to the Amines process, it needs a sulphur removal process. It is to be noted that using our technology correctly, the life span of membranes can be significantly increased.

The supplier of PSA systems has to be experienced in balancing the chemical process and flow variations. The GAS LAB engineering team with its widespread experience handles the challenge of feed stream variation with outstanding results. There is also a delicate balance of gas recycling (retentate) because the process is pressure and temperature sensitive. If poorly performed the slip may rise easily to 4-5%. If correctly designed and operated, it should stand under 1%.

A feature of the PSA membranes is its outstanding performance separating nitrogen, which is a contaminant in the biomethane. This rejected nitrogen is mixed with the CO2 and is easily extracted when the CO2 is liquified due to its different physical properties.

The PSA technique is well suited to mid-sized plants, and a perfect candidate for CO2 recovery projects. You can aim at the possibility of a CO2 liquefaction system, to obtain food grade quality product for further use on site or resale. Landfill emissions treatment for example is the perfect candidate for PSA technology.

Amines Upgrading is the star process at GAS LAB and we are proud to state that we excel in this technology. Its aim is to adsorb the CO2 recycling the amines and discharge it later for compression. It is done chemically and heat is required in the process. Its energy costs per cubic meter is higher, but overall cost operations are lower when used in large systems, optimized by leading control technology. Purity of methane and CO2 is very good, and the best fit option if CO2 liquefaction is on the menu.

It is a pH sensitive process. Initial investment is high, and process balance is crucial, therefore optimal controls and exhaustive evaluation of the process are critical to obtain the optimal performance: Up to 99.8% efficiency of separation.

Since 2006 amines systems are more and more appreciated, especially with biogas pioneers, in the Northern European countries. Projects are becoming larger every day, proof of the economic success of biogas plants. Emission wise, the next step is inevitably appreciating the CO2 as a source of income, not just an unwanted byproduct. It is simply a question of time and understanding the benefits of technologies companies such as GAS LAB have to offer.

Carbon capture upgrading in existing plants can be implemented as an add-on to increase revenues. Though small plants may not prove feasible for liquefaction, there are several options where recycling can be done with great direct benefits. Water treatment or irrigation are the favoured candidates. Actually, the integration of carbon capture in an existing “small” biogas project may still bring good profit if well executed, possibly through direct recycling in water treatment.

The net zero goal through carbon capture is worrying all the planet and we have to adapt to paradigm changes. If you want to review your biogas project or your actual biogas plant, it will be our pleasure to guide you towards the best fit solution, and it will not be an “off the shelf” system. Biogas and standard customization: The right choice and our motto.