Frequently asked about LNG

LNG is Liquified Natural Gas that can be transported by LNG ships or trucks. LNG is used as a fuel in industrial production, heavy road transport and maritime transport, among others.

At normal atmospheric pressure, natural gas remains in liquid form if its temperature does not exceed -163°C. This is why well-insulated containers are needed for its storage and transport.

In liquefaction, the density of natural gas increases so that it is almost 600 times the normal density. This enables the cost-effective transport of natural gas outside gas networks. Vaporised LNG can also be fed into a gas pipeline. One tonne of LNG corresponds to about 1,400 cubic metres of gaseous natural gas.

Stored LNG warms up due to a heat leak, and some of the liquid consequently turns into a gas called boil-off gas (BoG). This gas must be removed from the tanks in order to control the pressure and temperature. The formation of boil-off gas is affected by factors such as the insulation of the tank, outside temperature and the volume of LNG stored.

Boil-off gas can be utilised in the process in the same manner as normal natural gas, or it can be re-liquefied, for example by means of nitrogen, back into the tank. When the LNG storage cycle is kept continuous, hardly any boil-off gas is generated. In industrial customer tanks, the tanks should be replenished sufficiently often to prevent the temperature of LNG from rising too high. When filling a tank, the boil-off gas is taken into account by using a sufficient space reservation. Together with the customer, Rohe can analyse the most suitable solution for each situation.

The construction of a customer tank for LNG requires permits issued by various authorities. The permitting practice varies to some extent from one municipality to another, and the necessary permits must be determined in connection with the design of the customer tank.

An application for a building permit or operating permit must be submitted to the local authority in charge of supervision of construction.

A building permit is required if the amount of gas stored is at least 5 tonnes. The building permit is issued by Tukes, the Finnish Safety and Chemicals Agency. During the permit processing stage, Tukes requests an opinion from the rescue authority and the Centre for Economic Development, Transport and the Environment.

The specific features of the facility should be discussed with the local rescue authority as early as the design stage.

The facility may only be commissioned after Tukes has given an operating permit following a commissioning inspection carried out by Tukes. An approved inspection body carries out the necessary technical inspections during the construction phase. The operator must make sure that the inspections are carried out. If the amount of gas to be stored is more than 0.2 tonnes but less than 5 tonnes, the facility must be notified to Tukes.

Rohe carries out the studies required by the permitting process and safety as part of its total service!

Natural gas is a combustible gas, and in uncontrolled conditions it can form explosive concentrations. To prevent and control this, the operator must carry out an explosion hazard assessment of the equipment before putting the equipment into operation. The assessment must take into account the scale and circumstances of the equipment. The Finnish Natural Gas Decree (551/2009) provides details for the zone classification of certain facilities.

When an explosion hazard is assessed at a facility, the operator must draw up an explosion protection document. It must be ready during the commissioning phase, but a preliminary explosion protection document must be included in the building permit application.

The basic idea in the assessment of risk of explosion is that potential leakage situations are assessed in advance, preparations are made for them by means of planned technical solutions, and procedures for potential exceptional situations are prepared in advance. The assessment should be as practical as possible.

In all cases, an assessment of the consequences of a gas or LNG emission must be carried out. This can be done on the basis of standard SFS-EN 13645. Validated simulation software, for example, can be used to support the assessment of the consequences.

More detailed information and operating guidelines related to LNG customer tanks can be found in a publication of the Finnish Gas Association: https://www.kaasuyhdistys.fi/julkaisut/lng-asiakassailiot/

Rohe carries out the studies required by the permitting process and safety as part of its total service!

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