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Discussion on the construction of LNG refueling station and LNG gasification station

Time:2016-08-30

LNG加气站与LNG气化站合建的探讨
2016-08-30

     At the beginning of the operation of the single LNG refueling station, as there are fewer vehicles, the big amount of the BOG will cause great loss. In the standard of GB50156-2012 (Design and Construction standard of the vehicle fueling station> firstly indicates that the LNG refueling station can be constructed together with the LNG gasification station, which can save the land space, and transmit the BOG to the pipelines of the LNG regasification station. It can save the natural gas and reduce the environmental pollution. 
 
   The technical process is in diagram 1. There are four modules: 1. LNG truck offloading module; 2. LNG regasification module; 3. LNG transferring module; 4. LNG refueling module. In order to save time and consider the different pressures of the tanks for regasification station and refueling station, the submerged pump is used to transfer the liquid. For module 3, there are two types of design: type 1, with module 3, i.e. with a small LNG tank less than 30 m3 transferring LNG; type 2, without module 3, i.e. LNG is directly filled for the vehicle.
     The semi-trailer can also fill LNG into the small tank. However, for this type, the LNG refueling station is independent with the LNG regasification station which is not the scope of discussion here.  

       The model 1 of combination is applicable to the modification project and there must be some distance between the LNG refueling station and the LNG regasification station. It will increase the land covered and the cost because it adds one submerged pump and a small LNG tank. The model 2 of combination is applicable for a new project. Compared with model 1, the land will be less and cost will be lower. Please be noted that the tank volume shall be less than 60 m3 according to GB50156-2012, so in the combination model, the tank volume shall be less than 60 m3.


   The general arrangement of the LNG refueling station and LNG regasification station shall be adaptable to the local conditions and it is better to have easy access to roads. If the storage area is near the LNG refueling area, the refueling speed can be improved because of the shorten pipelines. According to the technical process, for model 1 and model 2, the main difference is in module 3. 
 
       2.1、Classification of refueling station
     During the design of the combination of LNG refueling station and LNG regasification station, it has to be clearly confirmed the classification of the LNG refueling station in order to control the fire prevention distance. In Model 1, the storage tank areas of LNG refueling station and LNG regasification station are relatively independent, and the feed gas of the refueling station comes from the small LNG storage tank which can be in accordance with the tank volume to confirm the classification of the LNG refueling station. In Model 2, because the LNG refueling station and the LNG regasification station share the same tank, while according to GB50156-2012,there is no need to confirm the classification. In this model, the LNG regasification station also has the function of LNG filling, so it is suggest not to classify the station. So the distance between the LNG dispenser and the LNG tank shall be in accordance with the table 4.0.9 of the standard of GB50156-2012, i.e. the safety distance shall not be less than 25 meters.

     2.2、Fire prevention distance of the storage tank
       During the design, the fire prevention distance of the LNG regasification station shall be in accordance with the standard of GB50028-2006. In GB50156-2012(edition 2014), it has clearly stated that the construction of the LNG refueling station and the LNG regasification station shall be in accordance with this standard, but also with the relevant rules of the national standard of GB50028-2006<Design Specification of Town gas). So, in the combination mode 1, it has to be clearly stated the fire distance between the two storing areas by referring to the below three basis: 1. In the consideration of the independence of the two storing areas which can be referred to the GB50028-200 <Town gas design specification> table 9.2.4 and the fire distance can be considered based on the two liquid storage tank. 2. Since in the standard of GB50156-2012 (edition 2014) has clearly stated that the LNG refueling station can be constructed in the combination of the LNG regasification station, so the fire distance can be considered as it is inside the station. While in the table 9.2.5 of the GB50028-2006, it only states the fire distance between the storage tank of the LNG regasification station and the natural gas storage tank and the liquefied petrol gas full pressure storage tank. So it is can be referred as the liquefied petrol gas full pressure storage tank. 3. According to the notes in the table 9.2.5 of the standard of GB50028-2006, it states the fire distance as per the GB50016-2014<Structure design fire prevention specification> (table 4.2.2). Through the comparison, under the same conditions, in basis 1, the fire distance is the longest; in basis 2, the fire distance is the second; in basis 3, the fire distance is the shortest. So it is suggested to follow basis 1 to define the fire distance between the two storing areas. 
 
       2.3、The length of the main technical pipeline


     The reasonable arrangement of the technical pipeline related to the operational efficiency of the technical system. No matter the LNG refueling station or the LNG regasification station, the technical pipelines are made up of the cryogenic liquid phase pipe and gas phase pipes. The technical pipelines shall be the shortest under the condition that the arrangement is in accordance with the general arrangement requirements to reduce the loss of the flow pressure and to reduce the heat which can produce BOG. In the technical system of the combined station, the length of the inlet technical pipe of the submerged pump will affect the operation of the pump as it will affect the pre-cooling duration of the system. So in the general arrangement, it is very important to control the length of the technical pipe of the submerged pump inlet.
      Set the length of the technical pipeline between the storage tank of the LNG regasification station and the submerged pump 1 as L1; the length of the technical pipe between the submerged pump 1 and the small LNG storage tank as L2; the length of the technical pipe between the small LNG storage tank and the submerged pump 2 as L3; the length of the technical pipe between the submerged pump 2 and the LNG dispenser as L4. According to the design of the LNG refueling station and the operational experience, the length of the technical pipe between the LNG storage tank and the submerged pump shall not be over 3 m, i.e. neither L1 nor L3 shall be over 3 m. L2 is decided by the actual distance between the two storing areas and the two storing areas shall be as close as possible. L2 has little impact on the LNG refueling process but has much impact on the BOG evaporation. Although BOG can return to the pipeline but economically speaking, L2 shall not be over 160 m and L4 shall not be over 30 m. It can be seen that in the combination mode 1, the total length of the technical pipe of the LNG refueling station and the LNG regasification station has something to do with the actual distance between the two storing areas, and the total length of the main technical pipes (sum of the L1, L2, L3, L4) shall not be over 196 m. In the combination mode 2, the total length of the LNG refueling station and the LNG regasification (sum of L3 and L4) shall not be over 33 m.


 
       3、Construction area


       According to the standard of GB50137-2011 <Construction land standard of the urban land classification and the plan>, the land used for the refueling station belongs to the commercial service facility land of the urban construction; the land used for the LNG regasification belongs to the fuel gas land of the urban construction land which is the public facility land. So the combination construction of the LNG refueling station and the LNG regasification station has the problem of the difference of the lands.


Although the LNG refueling station is similar to the oil filling station, the combination of LNG refueling station and the LNG regasification station includes offloading, storage, pressure regulating, gas filling and the other complicated process which are the production process. So the combined station is different from the oil filling station. Meanwhile, LNG refueling station is a kind of the energy infrastructure construction project. So during the construction, the constructor shall communicate well with the local government to well deal with the land used for the combination construction.


The construction of LNG refueling station can improve the living environment of the city and realize the goal of energy-saving and pollution exhaustion. Currently, the construction of LNG refueling station is widely promoted nationwide, however, there are still some cities with lower speed. There are many reasons for that but the most important reason is it is difficult to get approved to use the land. So it is suggested that the government shall support the enterprises to acquire the land to promote the fast development of the LNG vehicle industry.


       4、Conclusion and suggestion

The construction of LNG refueling station depends on the land. From the point of land saving and natural gas energy, it is suggested to combine the construction of LNG refueling station and the LNG regasification station but the modes of the combined construction shall be decided based on the demand.

If there is no clear specification, in the combination mode 1, it is suggested to consider the safety distance as if it is outside the station. The total length of the technical pipes of the LNG refueling station and the LNG regasification station shall be not over 196 m. In the combination mode 2, it is suggested not to classify the LNG refueling station and the safety distance between the LNG dispenser and the LNG storage tank shall not be less than 25 m. The total length of the technical pipe of the LNG refueling station and the LNG regasification station shall not be over 33 m.

 Because of the difference of the land to be used by the LNG refueling station and the LNG regasification station, it is suggested that the government shall well deal with the land used for the combination station. It is suggested the government shall come up with relevant promoting rules to help with the fast development of the LNG vehicle industry. 

 

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