LNG: how we work with the coolest truck fuel

LNG, from Liquefied Natural Gas, is natural gas but in a liquid state. Under normal conditions, natural gas is colourless, odourless and lighter than air. LNG, however, looks like a bluish clear liquid with a low viscosity. And it has roughly 600 times less volume than in gaseous form. Conveniently, it is neither toxic nor corrosive.

From gas to liquid

The gas is liquefied by cooling it to a temperature below -82.7 °C and increasing the pressure at the same time. However, for practical reasons it is preferable to have natural gas liquid at normal atmospheric pressure. To do this, though, it needs to be cooled down to -162 °C. And why is this better? Because the thermal insulation of the tanks is lighter than a high-pressure vessel would weigh.

What do we need to be careful of? As we said, it has a very low temperature which can cause frostbite. And, of course, its fumes are flammable. After all, it's still natural gas.

Our white spires

You probably won't miss one or sometimes two large tanks at an LNG station. The first and larger one serves as an LNG storage tank. It is a large volume vessel with very good thermal insulation. It has two shells. Sort of like a thermos. In order to insulate it as well as possible, there is a vacuum between the inner and outer shell. For the record, our "vacuum thermos" is estimated to last at least 15 years. After that, we can do a vacuum check, paint repair, valve replacement, etc. and extend the life to another 15 years.

But even as a thermos can't hold ice forever, the storage tank also gets slightly warm over time. Especially when refueling vehicles. As the LNG heats up, it evaporates and the pressure builds up in the tank, which is undesirable. Therefore, the vapours are cooled again and condensed or removed from the tank. We choose the first option most often. Liquid nitrogen is used for cooling, which is stored in a smaller container nearby - the second white tower. Nitrogen is ideal because it does not react naturally with anything and is neither flammable nor toxic. After all, the air around us is 78% nitrogen. In one case, in Jažlovice on D1, we use a different technology. We use a compressor to extract the vapours into separate pressure tanks and offer them as fuel for CNG vehicles.

And why aren't LNG tanks buried underground like in fuel stations? LNG behaves a little differently than diesel or gasoline. You need to create hydrostatic pressure for the pump, which is best with a vertical vessel. Also for this reason, horizontal containers on mobile fillers have to be put on a pedestal. Above ground tanks are also safer in the event of a leak, where LNG can spill into the surrounding area and evaporate more quickly. The legs of the tank can withstand this. In the underground variant we would have the technology drenched in liquid gas and an explosive mixture would more easily form below the surface.

Where LNG comes from

LNG for our stations comes from European terminals, to which it is transported by sea on special LNG tankers, mainly from the USA and Qatar. Qatar and the USA are among the largest exporters of LNG, together with Australia.

The extracted natural gas is transported by pipeline to the port, where it is converted into LNG in a liquefaction plant and loaded onto tankers. At the port of destination, the LNG is transferred to a tank truck and transported to a filling station. There is also a cleaner option, which we also offer. This is bioLNG, i.e. liquefied biomethane produced by the decomposition of organic waste.

How often do we fill our tanks? In Nýřany on the D5, where we have the largest consumption and the smallest tank, we usually have a delivery twice a week. At the newest stationary station in Hradec Králové, which customers are still getting used to, a delivery once a month is enough for now. We usually refill nitrogen once every week or two. Again, it depends on the station's usage.

Where LNG serves you

The most appropriate use of LNG at present is as a truck fuel. Manufacturers offer both gasoline and diesel engines. The gasoline type works on the same principle as a conventional gasoline engine, but burns only LNG. It is used, for example, by Iveco and SCANIA trucks. The second type is called a dual combustion diesel engine. This type of engine burns 95% LNG and 5% diesel, which acts as a carrier for the ignition mixture. It can be found in VOLVO trucks.

Conventional gasoline and diesel engines have a limited energy density of the air-fuel mixture because liquid fuels are not as easily mixed in the cylinder. On the other hand, in an LNG engine, the mixing of fuel and air is more efficient because the gases are usually well mixed even in a very short time. Since LNG boils at around -160 °C (rapidly turning to gas), a small amount of LNG can be converted from the tank to a high-pressure gaseous form using minimal energy. A suitably designed high power engine can thus produce a higher energy density air-fuel mixture.

As a result, LNG engines have 70% lower nitrogen oxide emissions and produce 20% less CO₂ than diesel engines. The aforementioned BioLNG even has up to 95% lower CO₂ emissions compared to a diesel engine when looking at the "well-to-wheels" calculation, which takes into account the entire life cycle of the fuel.

See how we built the filling station in Hradec Králové: