Bulgarian scientists with technology reducing Black Sea hydrogen sulfide content

Few of the fans of the lovely Black Sea coastline are aware that the sea keeps a special secret. And it is that life in its waters is limited to just the upper layer of about 150 m. The depths that open under it exhibit high concentrations of hydrogen sulfide where only microorganisms adapted to the lack of oxygen can thrive. The harmful gas, the byproduct of decay, has been accumulated for centuries.
Can we work to remove the hydrogen sulfide content of the Black Sea or at least reduce its concentrations? Scientists have been for quite some time mulling this question on the look out for solutions. All the more so that the otherwise harmful gas is rich in hydrogen that has been increasingly considered as an alternative fuel option with a future.

The job is quite some challenge, explains Prof. Venko Beshkov, Director of the Institute of Chemical Engineering at the Bulgarian Academy of Sciences who coordinates the international project for the extraction of hydrogen sulfide from seawaters to use it for power generation. Scientists from Romania and Georgia are also involved in the project. It has received financing under the 7th framework programme for science research in the EU.
The hydrogen sulfide quantity in the Black Sea waters is such that it is practically an inexhaustible source of energy. It is assumed that its total quantity is close to 4.6 billion tons, the equivalent of about 9 billion MW of energy. During combustion hydrogen transforms into water and is back to the Earth’s cycle and besides, this takes place without any harmful emissions. Under laboratory conditions the breakdown of hydrogen sulfide is much easier than the breakdown of water. And it is also true that both substances resulting from the breakdown – hydrogen and sulfur – can be utilized. However seen in an economic perspective, the problem looks hard to resolve, because the hydrogen sulfide quantities in the Black Sea are so vast that their removal would only be impossible unless a method is found to make up for the huge expenses.
Where do problems stem from? Unlike the Black Sea coastline in Turkey and Georgia that tends to be very steep, and the big depths are relatively close to the shore, the Bulgarian and Romanian shores are slanting and full of life. The great depths where hydrogen sulfide is found are far from the coast. This is quite good for tourists but provides a major economic puzzle for researchers. The possible power generation from hydrogen should take place on a special platform in deep waters and the extracted hydrogen should be transported at 30 to 40 km from the shore. So, scientists have opted for unconventional solutions. More from Prof. Beshkov:
“I had the idea of using hydrogen sulfide not for the direct extraction of hydrogen through electrolysis as anybody would expect, but rather the direct use of hydrogen sulfide for energy. At the next stage this energy could be used to carry out electrolysis from seawater for obtaining hydrogen.”
The question is how energy can be generated from hydrogen sulfide. Prof. Beshkov says that a technology has been developed for the purpose.
“This is done with a device known as a combustible cell”, the scientist explains. “The device is a container for the fuel, in this case, hydrogen sulfide and the oxidizer. The chemical reaction results in the generation of electric energy that can be used for the decomposition of water. The method looks luring but it is not ideal either.”
What are the method’s drawbacks?
We have already mentioned one of them – the big depths where hydrogen sulfide concentration is higher, are too far from the Bulgarian shores. For this reason the experimental station shall most probably be installed on board the ship owned by the Bulgarian Academy of Sciences Institute of Oceanology in the City of Varna which is involved in the project too. Its scientists will locate the most suitable point of the sea for the experiment. For this purpose they are going to study the hydrogen sulfide distribution in the Bulgarian section of the Black Sea as well as the precise chemical composition of deep seawater.
The other problem is with the storage and transportation of the hydrogen obtained into the sea that has to reach the coastline. Pipelines won’t do as hydrogen is very aggressive chemically on the one hand, and pipeline facilities tend to be very expensive. Fortunately, there are new technologies focused on gas storage.
“We have concentrated our efforts on capturing and storage of hydrogen in substances able to keep it safely, and then release it when only lightly heated,” Prof. Beshkov says. “We plan to store hydrogen in alloys from light metals that can be placed in containers under pressure that will be used for transportation to the shore.”
Now in the three years to come, researchers have to find out whether this theoretical construction will be able to work out at sea and whether it will be valid in economic terms.
“Well, we do have Plan B”, explains Prof. Beshkov. “And it has to do with using the energy made from hydrogen sulfide instead of looking for ways to store and transport hydrogen. Our Romanian partner said that hydrogen sulfide could be used to provide energy for their oil rigs.”
As to fixing the key problem, i.e. the cleansing of the Black Sea from the hydrogen sulfide, Prof. Venko Beshkov is not a great optimist:
“We have been trying to rescue the sea from the accumulation of more and more hydrogen sulfide. However, for the time being, our scale of work is insignificant compared to this enormous resource and challenge”.

Translated by Daniela Konstantinova

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Bulgarian scientists with technology reducing Black Sea hydrogen sulfide content

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