CO2, energy transition and champagne!

Before raising a glass to 2022, let’s have a look at Carbon Dioxide, CO₂ – that is possibly the last thing you will do in 2021 without paying further attention to it…

Energy transition and CO₂

In an earlier blog, we talked about some energy carriers playing the main role in the energy transition, hydrogen, and ammonia. Strongly linked to that is also CO₂, which possibly is not so obvious.

Since energy production from sustainable sources such as sun, wind, and water cannot fulfil today’s needs, hydrocarbons and coal will be used for energy production for a while, including their CO₂ emissions.

To produce hydrogen, mainly hydrocarbons and coal are used today. This is often called ‘grey’ hydrogen since the production proceeds are accompanied by the release of CO₂. On the contrary, hydrogen from a fully CO₂ neutral production is called ‘green’ hydrogen, produced by electrolysis from renewable sources.

‘Grey’ hydrogen becomes ‘blue’ hydrogen when the CO₂ emissions are captured and stored underground. This Carbon Capture and Storage (CCS) technique can reduce CO₂ emissions in other industries, such as power plants and during cement production. Therefore, directly captured CO₂ will form a ‘waste’ product during the early stages of the energy transition.

After capturing, the CO₂ has to be compressed and/or cooled and transported safely to (underground) storage, like old oil and gas wells. The transport mainly will take place by pipelines.

Safety aspects of CO₂

Pressurised pipelines always form a potential risk, but are also filled with CO₂? 

In principle, CO₂ is not toxic. It is widely used, from sparkling water to fire extinguishers. The use of fire extinguishers is a good example to explain the properties of CO₂: CO₂ is not flammable and displaces the air containing oxygen from the fire, which extinguishes the fire. Therefore, a potential hazard is an oxygen displacing capability due to the presence of CO₂, which can already take place at moderate release volumes.

Another property of CO₂ is its specific weight which is 1.5 times that of air. This results in an accumulation of CO₂ close to the ground. Depressions might be filled with CO₂, and without dominant external wind, CO₂ ‘flows like water’. The density gradient (heavy CO₂ below air) leads to a significant reduction of mixing and entrainment of air. Therefore, it takes a long time to vent depression once it is filled. Inhaled by human beings or animals, this might result in a loss of consciousness or death due to asphyxiation by hypoxia. From concentrations of 15% (per volume) or more life-threatening situations might arise depending on the exposure time.

Although not toxic, CO₂ is indeed considered to have harmful effects.

Storage conditions and phase change

Depending on the application, CO₂ is stored under refrigerated, semi-refrigerated and/or pressurized conditions. Common bulk storage conditions in insulated tanks are -30^oC and 20 bar pressure. Typical pipeline storage conditions are approximately 100 bar and ambient temperature.

At low temperatures and ambient pressure, CO₂ is in a solid state; at increased temperatures, it undergoes a phase transition from solid to a gaseous state by sublimation (at -78.5^oC). Above 31^oC and a pressure of 73.8 bar, CO₂ is in a supercritical state; the density is comparable to a liquid state and the viscosity to a gaseous state. In the intermediate pressure range (5.1-73.8 bar), the phase transition occurs from solid via liquid to the gaseous state with increasing temperature.

Therefore, hazardous releases might include CO₂ as flashing liquid, solid particles (rainout; sometimes called ‘snow’) and gas depending on the storage conditions.

Incidents involving CO₂

Different accidents due to an unintended release of CO₂ have taken place in the past.

In 2008, in Mönchengladbach (Germany), 15 tons of CO₂ were accidentally released from a fire extinguishing installation. By a coincidental failure of the doors, the CO₂ was released to the outside. Due to still air conditions, the CO₂ could displace the air for a long time; the fire truck’s engine stalled on their arrival due to the lack of oxygen. 107 people were injured, 17 were hospitalized. In the still air conditions, the CO₂ was diluted by a helicopter hovering above the gas cloud entraining air.

At Lake Nyos in Cameroon, a magma chamber continuously leaked CO₂ into the lake until, in 1986, a huge amount of CO₂ (estimation: 1.6 million tons) were released from the lake due to a landslide or volcanic eruption. The CO₂ cloud travelled by gravity more than 20km down the valley, killing more than 1700 people and 3000 livestock; thousands of people were injured.

Potential risks

Large amounts might be released if CO₂ is released from pressurized pipelines or CCS installations. The volume between two shut-in valves will be released during a pipeline leakage or rupture. Therefore, the distance between the shut-in valves has to be designed such that the potentially released amount of CO₂ does not form a risk to the built environment.

As could be seen from the Mönchengladbach incident, with only 15 tons of CO₂ released, effect distances are already in the order of a few hundred meters. It can be much more at catastrophic ruptures of pipelines, including strong heavy gas dispersion behaviour at moderate wind speed and stable wind conditions. Risks also depend on the state (pure gas or pressurized liquefied situation) and outflow direction (vertical or horizontal): pure cryogenic CO₂ jets are also used for special effects. Due to strong turbulent mixing and vertical orientation, they quickly dilute and don’t reach ground level.

Champagne

Returning to the end of 2021 and Champagne: approximately 7.5 grams of CO₂ is dissolved in a bottle of Champagne. This would release approximately 5 litre of gaseous CO₂, which is comparable to the CO₂ emitted by a human breath within 15 minutes which does not form any safety issue.

The risk during unbottling is probably much more of an issue with a cork propelled by the 6 bar internal pressure of the Champagne bottle. But this would be another story. If you really want to be safe, we suggest the safety invention below.

Enjoy your sparkling Champagne on New Year’s Eve, and Happy and Safe New Year 2022!