In the last week of November, ShipInsight reported on an innovative idea for a carbon capture and storage system installed onboard ships. In the Decarbonice project NYK, Sovcomflot, Knutsen OAS and Ardmore, ship builders, including DSME and the mining company Vale, have teamed up with Denmark based Maritime Development Center (MDC).
We at ShipInsight thought this an interesting concept even though it could, if adopted, result in another piece of equipment that would achieve environmental goals but do little for the economy of the ship.
Shipping has absorbed many of them in recent years – Ballast treatment systems, SCR systems EGR systems and scrubbers to name but a few so maybe one more wouldn’t be impossible. In fact if shipping becomes subject to a carbon levy as some are advocating, then technology of this type may be self-financing in the long run even after power to run it and loss freight revenues are taken into account.
The initial report from MDC carried little information on the project beyond a cartoon showing the principles. So we asked Henrik Madsen of MDC to clarify some of our questions on the concept.
SI: How long does the condensing and cryogenic process take?
HM: The process is basically a continuous process, where dry ice is produced continuously and within a very short period is formed to suitably shaped blocks and sent travelling towards storage within the seabed sediments.
SI: It is conventional wisdom that burning one tonne of oil fuel produces about 3 - 3.25 tonnes of CO2. So if a ship is burning 20 tonnes of fuel each day it will be producing at least 60 tonnes of CO2. You cannot indefinitely add over 40 tonnes of weight to the ship each day without consequences for safety and stability. How will you handle it?
HM: Each dry ice block will weigh a few tons. As you state, a ship burning 20 tons of fuel per day will produce some 60 tons of CO2 per day. This means that we will produce and dispatch 1-2 dry ice blocks per hour.
SI: What volume does the captured CO2 equate to? This information would be needed for calculating storage capacity on board.
HM: The need for storage will be limited to the dry ice produced for a few blocks.
SI: Will the volume decrease as the dry ice sinks?
HM: Dry ice has a density of 1.6t/m3. Since this is relatively much higher than for sea water, the descent in the water will pick up speed to some 15-25 m/s. With this speed we are ensured that the dry ice will penetrate deep into the soft sea bed sediments, where it will be permanently stored.
SI: Will the dry ice not sublime and revert instantly to gas?
HM: As you correctly point out, dry ice will sublime when it is in air at ambient temperature. Dry ice can, however, not exist in gas form at a pressure above 50 atm., corresponding to 500 meter water depth. We have calculated the loss to about 1% during the minute is takes for the dry ice to reach 500 meter water depth. We also have different options in terms of various forms of cladding, which can eliminate any sublimation. The scientists we have consulted also point to the fact that a CO2 hydrate will be formed immediately on the surface of the dry ice block, which will also significantly reduce any sublimation.
SI: At what depth of water is it safe to drop dry ice into the sea? Near land, are we not likely to create a man-made disaster such as Lake Nyos in the 1960s?
HM: As you understand our solution is not intended for operations in less than 500 meter water depth. This is also why we present it as a deep sea shipping solution. It thus complements the many solutions for short sea shipping being proposed.
Of course every answer to a question can prompt others but since the idea is at an early stage we thought that it might be better to address those questions as the project progresses and developments are made.
Some of the questions we will pose in due course are:
- What form of handling will be needed to jettison blocks of the size and weight envisaged?
- Although the oceans are vast, some trade lanes are heavily used, will the accumulation of dry ice blocks mean that instead of burying themselves in sediment they actually begin to pile up and create ridges and mountains on the seabed?
We are sure that ShipInsight readers could think of others.