+ Ship-based Carbon Capture and Storage, how does it work?

Click here for a quick introduction into the workings of a post combustion carbon capture plant, in this case a coal fired power plant, but the basic operation is the same.

For Ship Based Carbon Capture systems we need the following ingredients.

• Absorption: A tall absorption column connected directly to the exhaust pipe of the engine. The exhaust (flue)-gases enter the bottom of the column, where they are cleaned with a shower of an amine (like for instance ammonia, but other solvents are possible too), solved in water. This shower captures the CO2 from the gas, at the top of this column, clean exhaust gas enters the atmosphere.
• Desorption: The CO₂-rich solvent now on its turn needs to be cleaned. This happens in the desorption phase. The amine is heated, which release the CO₂ in gas form out of the amine. The clean solvent then goes back to the shower, making this a closed loop.
• Cooling & Compression: The CO₂ in gas form is then cooled and compressed, in order for the product to be stored most efficiently. This leads us to the next ingredient.
• Space: this requirement introduces two essential constraints: height and storage space.
  1. The absorption column is a gravity-based system. For the solvent to capture as much of the CO₂ as possible, the hot exhaust gas which enters the bottom of the column into the ‘shower’ must have a minimum contact time with the solvent. To maximize the capture rate, a minimum height is required. For example, a 3MW ship engine would require a 14m high absorption column (van den Akker 2017).
  2. Storage space. The capture plant on board produces a steady flow of liquid CO₂. As a rule of thumb: every m³ of LNG produces around 0.9-1 m³ of LCO₂. (of course, this depends on the exhaust gas flow rate and varies with engine settings. See also the question on: where do we leave the CO₂. One last note: LCO₂ weighs 2.5 times more than LNG… The influence of this weight on the stability of the vessel must not be overlooked!

+ How much does it cost?

Not cheap unfortunately, at least not anno 2020.

Science bases their cost estimations on land based applications of carbon capture, and on the installation of comparable systems on board of ships (like scrubbers for instance) to determine retrofit costs. Generally, costs are expressed in a form like [€/tonCO₂ captured]. Such a metric allows to guestimate the costs for your vessel size, i.e. amount (tons) of CO₂ you expect to capture. However, never believe someone who tells you they know how much it will cost you exactly, accurate to the penny. There are simply too many factors in play and the technology is too new.

Most of the time you will see cost ranges. The low limit (i.e. cheaper option) will probably indicate that the parameter is based on a large ship, where economies of scale definitely play a role. The upper limit will apply to the smallest vessel studied. Which factors are included in this metric? In literatur, this includes, but is not limited to: CAPEX (function of size, storage pressure, type of solvent used, size of storage), OPEX, retrofit costs (don’t forget loss of operational time/income).

Due to the complexity of the cost determination, we decided to dedicate a separate page on this topic, see here

+ Where do we leave the CO2?

If we want to know the net amount of CO₂ we can avoid, we have to take into account the full supply chain. The entire scope of the Ship Based Carbon Capture problem starts at the engine (compare the amount of CO₂ captured to the do-nothing business as usual case), and ends at the end-of-life solution of the CO₂. In between we have efficiency of the capture process (capture rate) and Transportation.

The last phase, the end-of-life, can consist of two general paths. Storage and Utilization.

Permanent geological storage: This solution is often times considered beneficial, because we take the carbon fully out of the 'system'. How? By pumping the CO₂ into empty oil- or gasfields. It is estimated that the total worldwide storage capacity of this type can be as much as 27.200 Gigatons. If your vessel would produce 50000tons of CO₂ annually, this would use up 0.000001% of the total capacity.

Utilization: This solution basically means that the CO₂ will be somehow used for another application. Common examples of this are: foods & beverage industry (sparkly water), horticulture (plant growth stimulation in greenhouses) etc. There are ups and downs to the utilization option. On a positive note: we look at the CO₂ not as a waste product, but as something with value, i.e. we can make money with the carbon, which is in favor of our business case. The downside of utilization is in the fact that for many of the solutions offered, the carbon will eventually still end up in the atmosphere. We can argue that by using our CO₂, there is a lower demand for the CO₂-feedstock originally used in these applications. This can become a very complex puzzle, and requires a full life cycle analysis of this utilization option. To use the horticulture as an example: currently greenhouses are often equipped with gas-engines who provide power, heat and CO₂. If we take out this engine, we prevent the use of fossil fuel (natural gas in this case). If the power and heat are generated with green electricity, we have a win-win solution.

What do you think is the best solution? Which is more sustainable in the long term?

+ For which vessels does it work?

What do you mean “which vessels”? In theory, couldn’t it work for all vessels?

Yes, but with a few caveats.

Cost: Carbon capture appears to be most cost effective for LNG vessels. Why? The first estimates of ship based carbon capture cost are around 150-450€/ton CO₂ , which is super expensive. The most expensive and energy consuming components in any Capture installation are: Cooling and Compressing. LNG is stored at –162 Degrees Celcius. Heat from the environment leaking into the storage tanks makes for a constant boil off at the tanks’ walls. This gas needs to be vented, but is still wicked cold. Why not use this cold to extract heat from the gaseous CO₂ at the end of the capture phase? The colder this gas can be, the less compression is needed to liquefy it, I.e. simultaneously save on expensive compression stages. Therefore, the research into ship based carbon capture took the direction of their focus more on LNG vessels rather than Diesel vessels.

Size: What about the size of the vessel? As mentioned in ‘how does it work’, the capture installation is rather high. The relative amount of space the installation takes up, with respect to the total size of the ship will become less significant if the size of the mothership will increase. This means that the relative cost of capture is lower for the largest vessels.

New/old: Depending on the type of vessel you have, and the amount of spare space you have on board to put storage tanks, retrofitting an existing vessel is definitely possible. For new vessels, the capture system can be incorporated in the design, where the CO₂ storage can for instance be neatly and safely incorporated in the hull design, leading to a minimal loss of cargo space, and minimal impact on the stability of the ship (you could design a smart ballasting system which will keep the center of buoyancy perfectly fixed during the trip, while the light LNG is burned and the heavy CO₂ is stored.

For existing vessels you'll need to find a storage solution on a place that's safe and not impairing operation. External tanks can be a good solution here. Now that we're on the topic: here's an out of the box idea for you: if you have a container ship or space on your ship to store TEU containers, why not put the CO₂ in there? Specifically interesting further down the supply chain. Once in port, you can put these containers directly on a truck/train to be further transported.

+ Who can build this for me?

Heerema is working together with a consortium led by TNO called DERISCO2.

Bouman will be providing the CCS plant. more information will follow!