In Norway, which has plenty of natural gas in the North Sea, they have to export the gas, change it into electricity or even burn it for no use whatsoever and this is due to the difference in terrain, explains senior consultant Peter Brøndum from Grontmij, who has participated in developing a solution to the Norwegian dilemma.
»The best way of transporting natural gas is through large pipe lines. The gas is under high pressure and can therefore easily be moved directly to the places where it is needed. In Denmark and other flat countries, it is relatively simple to establish a piping system for distribution of the gas. But in a country that consists of large mountains and deep fjords such as Norway, this is an almost impossible task,« explains Peter Brøndum.
Turning gas into liquid
Without piping systems, you have to turn the gas into liquid, making it possible to transport and store it in containers. Natural gas in liquid form takes up 600 times less space than as gas, and therefore, liquid natural gas can be stored in containers of a manageable size. But it is no simple matter to turn the gas into liquid. This requires cooling to extreme freezing temperatures.
When natural gas is transported at sea, it is in liquid form. The gas is held at the temperature of below minus 155 C, but at such a low temperature, there is a lot of evaporation. And to prevent the pressure from rising in the tank, a large amount of the evaporated gas has to be let out. Obviously, it would be possible to burn the gas and thereby make use of it, but since a ship only sails with natural gas half the time, the ship would have to have two alternative fuel systems. Therefore, it is a poor idea to sail with natural gas with regard to energy and the environment.
3,600 tons of CO2 saved per trip
This is where the Danish-Norwegian project comes in. On the basis of patents from the Norwegian energy development institute SINTEF, Grontmij and I.M. Skaugen have developed a compact and effective cooling system that condensates the evaporated gas, making it liquid again, which means that it can be pumped back into the tank. Even though energy is consumed re-cooling the gas, it results in an enormous plus in the energy as well as the CO2 accounts:
»Natural gas mainly consists of methane, which is a much worse greenhouse gas than CO2. On a long trip with one of the Norwegian coasters, you risk evaporation of up to three percent of the cargo. This actually corresponds to 180 tons of natural gas or pollution corresponding to 3,600 tons CO2, as methane is more than 20 times worse than pure CO2. Add to this that a lot of energy that could have been used more sensibly disappears into the thin air,« emphasises Peter Brøndum.
Mini-LNG system
The first of the newly developed condensation systems has just been mounted on one of the gas coasters that I.M. Skaugen is having built in China. Five further ships are on their way, but the perspectives of the system, which is called Mini-LNG, where the last letters stand for Liquid Natural Gas, go far beyond this:
»The method can be developed further, making it possible to use it on the large ocean-going gas tankers, and then we are dealing with very large amounts of methane that is not emitted into the atmosphere. But the perspectives on land are even larger. Precisely evaporation is one of the major problems making it very difficult to store natural gas. You have to burn it right away and turn it into electricity, for example. But you cannot save electricity either, and if it is not needed right away, it goes to waste. Therefore, we are now going to develop the method further, making it possible to use it on larger ships as well as on land,« reveals Peter Brøndum.
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