FOR DOMESTIC, COMMERCIAL AND INDUSTRIAL UTILIZATION & TRANSPORTATION
Liquefied natural gas (further referred to as LNG) has been used as a cost effective, low emission and reliable energy source for many decades in different parts of the world. First commercial applications for covering of peaks in natural gas demand were built in the USA in the 1940s. The trade in LNG began in 1964, when the first LNG cargos were delivered from Algeria to France and Great Britain. In these days there are already 19 countries exporting LNG and 30 countries, where this energy carrier will be exported to . With its 27 million tonnes of LNG consumption in 2014 the European Union is the third-largest utilizer of LNG after Japan and South Korea . But until recently, LNG as energy carrier remained for Germany insignificant, despite its first position in the natural gas demand among the EU-28.
Figure 1 - The natural gases used in Germany .
The gas supply situation in Germany is determined mostly by domestic gas production as well as by imports from abroad. Russia, Norway and the Netherlands are the main natural gas import countries. A relatively small remaining quantity of natural gas comes both from Denmark and in form of bio methane conditioned to the H-gas quality.
Figure 2 – Wobbe number range defined by DVGW Code of Practice G 260:2013. Reference temperatures being 25 °C and 0 °C for energetic and volumetric quantities respectively .
Compared to the natural gases imported from Russia and Norway the natural gases produced in Germany and imported from the Netherlands are low calorific (L-gas). Together they cover about one third of the German natural gas consumption per annum (see Figure 1).
Against this background, the cessation of the natural gas production in the Groningen gas field, the main German natural gas import source from the Netherlands, is expected by 2030 . According to the German transmission network operators, the natural gas fields in Germany are being depleted as well, so one cannot rely on the long term production of the local natural gas.
Germany’s ambitious climate targets, the efforts to secure the own energy supply in the future and the understanding of the necessity of the energy supply diversification move alternative and still new energy sources such as LNG to the forefront.
Table 1 – The average compositions of LNG (chosen as being representative among compositions reported by the receiving terminals in Rotterdam, Zeebrugge and Swinoujscie; calculated at -160 °C) .
Technical requirements for the use of gaseous LNG in the German gas networks
The estimation of the prospects of the network-connected utilization of gaseous LNG (further referred to as NG) requires the overview and understanding of the technical criteria which are needed to make the use of this energy carrier possible.
NG can be injected into the natural gas network as a basic gas or added to the natural gas as a part of the gas mixture. In both these cases, the Wobbe number (here and further in the text is meant its upper value Ws) has to match. This guarantees the principle of the natural gas interchangeability in the public natural gas supply, as defined by the code of practice of the German Technical and Scientific Association for Gas and Water (further referred to as DVGW) DVGW Code of Practice G 260:2013 “Gas composition”.
Table 2 – Quality parameters of LNG being delivered or to be delivered to the receiving terminals in Rotterdam and Swinoujscie. Reference temperatures being 25 °C and 0 °C for energetic and volumetric quantities respectively [7, 8, 9].
With respect to the Wobbe number, all fuel gases being used in German public gas networks are classified into two groups: low calorific, L-gases, and high calorific, H gases, with a low Wobbe index and a high one respectively (see Figure 2). The summarized range of the Wobbe number is shown in Figure 2 with the nominal value 44.6 MJ/m3 for L-gases and 54.0 MJ/m3 for H-gases .
Based on the chemical compositions of the LNGs, the gas quality parameters of them can be calculated. The results are presented in Table 2.
Thus one can see, that the determined Wobbe numbers of the NGs delivered or to be delivered to the receiving terminals in Rotterdam and Swinoujscie fit the value range set for the H-gases, but do not match the range set for L-gases (see Table 2 and Figure 2), which means that these NGs can be used for substitution of H-gases
in the gas networks without any treatment of them. Contrary to that, the injection of NGs as basic gases into the public natural L-gas network needs their ballasting with low calorific or even non-flammable gases. Hence, bearing in mind the upcoming L-gas supply bottleneck, the substitution of L-gas by NGs will incur additional costs.
Table 3 – The German natural gas sources’ Wobbe numbers and GCV. Reference temperatures being 25 °C and 0 °C for energetic and volumetric quantities respectively .
In case of the injection of NG into the natural gas network for the purpose of its use as a part of gas mixture with natural gas, Gross Calorific Value (further referred to as GCV) of the both gases has to be taken into consideration. This requirement can be explained by the fact that the Germany’s gas billing system is based on energy consumption while consumed natural gas volumes are not taken into account. That is why gas distribution system operators are obliged to avoid deviations of GCV in their networks of more than ±2 % over the billing cycle . The common way to achieve this is gas blending. In case of the admixture of NGs with the relatively high GCVs (see Table 2 and 3) to the natural gas stream, NGs must be ballasted.
In case of ballasting of NGs with air the content of oxygen must not rise beyond the permitted limit set at 3 mol% for distribution networks and 0.001 mol% set for transportation networks . This risk occurs only in cases of air injection to each NG
till the achievement of L-gas quality (see Table 4). The calculation results presented in Table 4 show the content of ballasting gas needed to the matching the GCV requirements by NGs to be injected into the natural gas network. All the presented gas compositions also meet criteria for Wobbe number. Instead of using of nitrogen, the air admixture causes the 3 mol% limit excess of oxygen in some NGs treated, which are shown in Table 4 in bold italics.
Table 4 - Ballasting of the NGs to meet the GCV requirements. Reference temperatures being 25 °C and 0 °C for energetic and volumetric quantities respectively [7, 8, 9]. * NG from Trinidad and Tobago has to be treated by blending with propane instead of nitrogen. This can be explained by its lower GCV than Norwegian pipeline gas one’s. ** It should be mentioned, that a gap between Wobbe number’s nominal value of the NG from Trinidad and Tobago and natural gas from the Netherlands is too wide, so there is no technical possibility results from the calculation to inject the NG into the natural gas stream.
According to the current DIN standard for the calculation of the compression factor of gases, the maximum permitted value for nitrogen is equal 50 mol%  that is much more than the calculated values in each of the gas mixtures (see Table 4).
All the determined gas mixtures of NGs and nitrogen or air feature the relative density range 0.59 to 0.69 which matches the requirements set in the DVGW Code of Practice “Gas composition” at 0.55 to 0.75.
Apart from the Wobbe number and GCV, one of the parameters of NG, which has to be matched, is the methane number. Due to gas engines’ fuel requirements set out
in DIN 51624:2008 “Automotive fuels – Compressed natural gas – requirements and test methods” every fuel gas going to be used as an engine fuel has to have a methane number over 70 in order to protect internal combustion engines from knocking . Table 2 presents the calculated values of methane numbers for some NGs. All of the determined values are in the limits of 75 to 89.
Table 5 – Methane content of NGs ballasted till the matching of qualities of natural gas transported and distributed in networks.
Furthermore, a methane content of at least 80 mol% is mandatory . Table 5 shows, that not each NG of the determined above ballasted does comply with the mentioned requirement. These are presented in bold italics. This means these ballasted NGs have to be excluded from automotive usage. All the technical requirements on the NG quality mentioned above are summarized in an overview and shown in Table 6.
Table 6 – Overview of the technical requirements on the fuel gases for the networkconnected use in Germany.
Conclusions and outlook
A good impulse to the establishment of the German LNG market might be given by the use of LNG as a solution for the upcoming L-gas supply bottleneck as well as for diversification of Land H-gas sources.
The technical requirements for the ballasting of the LNGs to be delivered to Germany from the terminals in the Netherlands, Belgium and Poland from the Algeria / Arzew, Nigeria, Norway, Qatar, Trinidad and Tobago can be matched for the benefit of the German gas consumer. The financial efforts of the LNG conversion itself remain to be estimated. However the ballasting of gaseous LNGs with pure nitrogen instead of air is required in some cases, e. g. for the injection of NG into the natural gas flow. Therefore the implementation of appropriate technical measures is important.
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Gas Importers, Paris, 2013.
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Part 2: Calculation using molar-composition analysis”, Deutsches Institut für Normung, Berlin, 2010.
Alexey Mozgovoy, Project Manager at the Gas- und Wärme-Institut Essen e.V.,
Frank Burmeister, Dr. Rolf Albus / Gas- und Wärme-Institut Essen e.V., GermanyProject Manager at the Gasund Wärme-Institut Essen e.V.
ALEXEY MOZGOVOY Alexey Mozgovoy is a Scientist and Project Manager for LNG Supply in the Fuel and Appliance Technology Division at the Gas- und Waerme-Institut Essen e.V., Germany. He is responsible for LNG research and development activities of the Institute and manages projects in smallscale liquefaction and distribution. Alexey Mozgovoy has spent more than 15 years studying natural gas network construction, operation and fuel gas sources in Germany and in Russia. Alexey Mozgovoy is an author of many papers on the topic of LNG application as a fuel gas for industry, transportation and network-connected gas supply published in renowned technical and scientific journals. He is a member of the German Technical and Scientific Association for Gas and Water’s (DVGW) and works actively on national regulations on fuel gases and appliances distributing them.