Information of interest
Natural gas value chain
Natura Gas Value Chain
NATURAL GAS TRAVELS A LONG WAY FROM THE GAS FIELD TO THE FINAL CONSUMERS.
The natural gas chain is a set of stages through which gas passes, from being found in the field until it reaches the final consumer.
The chain will consist of different stages depending on whether the natural gas is transported in gaseous or liquid form.
The following describes each of the links that constitute the natural gas value chain.
A gas field is the underground accumulation of this hydrocarbon. Hydrocarbons saturate the pores and fissures of the rocks that house them. This can be defined as a porous and permeable geological formation which accumulates liquid hydrocarbons and / or natural gas in a structure or trap, sealed by an impermeable layer or formation, which prevents its migration to the surface and its loss into the atmosphere.
Once extracted from the field, the natural gas must be processed and treated for transportation and later marketing (safety and quality standards must be met at the facilities and delivery points).
In order to transport natural gas in its liquid state (LNG), components must be eliminated that may interfere with the gas cooling process, while for pipeline transport, corrosive compounds must be removed that could damage the pipeline. To achieve these goals the water content is reduced and the acid gases (hydrogen sulphide and carbon dioxide), as well as nitrogen and mercury, are removed.
Once the gas is treated it can be transported in the gaseous phase through pipelines, or in the liquid phase in LNG carriers.
In the gaseous phase, the gas chain is simplified as liquefaction, shipping and regasification are unnecessary.
Natural gas liquefaction
Once the natural gas has been treated, it is liquefied for transportation by sea, making use of the fact that the liquid phase occupies a volume about six hundred times smaller than the gaseous phase.
The liquefaction process involves huge investment and consumes a lot of energy, so that, in general, this method is chosen only when the distance to the point of consumption is too large for "economic" transportation by an overland pipeline. It is estimated that for distances greater than 2,500 kilometres it becomes economically profitable to do so in the form of LNG.
The LNG production process is based on cooling the natural gas to a temperature of approximately -160 ° C, at which point it becomes liquid at atmospheric pressure.
As described above, before liquefaction, the natural gas must undergo a series of processes, upon extraction at the gas field, to remove any heavy hydrocarbons and pollutants that remain after treatment.
The gas fed into the liquefaction plant typically arrives at ambient temperature, which is usually that of the pipeline at the point of entry into the plant, and at a pressure depending on the conditions of the gas network.
An additional advantage of LNG is that the points of consumption are not linked to particular sources of gas, which facilitates the diversification of provision, increasing the security of supply and competitiveness in the marketing phase.
The transportation of LNG to the regasification plants in carrier ships is highly specialized, in their design, the materials and the fact that the liquefied gas must be kept under cryogenic conditions at all times during transport.
As no cargo containment system is 100 percent effective, there is a natural and inevitable evaporation of some of the transported LNG. This amount, technically termed "boil-off”, depends on the containment system of the carrier, the quantity transported and the outside temperature.
The storage tanks used on the vessels may be one of two types (membrane tanks or self-supporting, independent spherical tanks) and the propulsion of the vessels is achieved with Dual Fuel Diesel Electric (DFDE) engines that use the 'boil-off' as well as fuel oil.
The LNG carriers have load capacities that can vary between 25,000 m3 and 270,000 m3, with the most common volumes today being between 140,000 m3 and 170,000 m3.
Once the carrier docks in the regasification terminal, LNG is unloaded, stored and regasified. The unloading is made with the carrier’s unloading arms, with the LNG pumped directly into cryogenic storage tanks.
For injection into the transport network, LNG is converted back to its gaseous state by the mere physical process of increasing its temperature (a vaporization process using heat exchange with sea water).
LNG can also be loaded directly into tanker lorries for road transport to satellite regasification plants. These plants feed the distribution networks that the transport network does not reach. The LNG can also be delivered directly to those industrial installations that have a sufficient volume of consumption to merit their own regasification facilities.
From the high pressure pipelines, natural gas reaches the point of consumption through distribution networks (a set of gas pipes of smaller diameter and design pressure).
The regulation and metering stations (RMS), located in the nodes that connect the transport and distribution networks adapt the gas flow pressure to that required for use by the end users.
The pressure at which the gas is supplied depends on the type of customer, ranging from pressures of less than 0.05 bar for domestic consumers up to pressures above 40 bar in deliveries to electricity generating plants and large industrial consumers.