Converting the LNG-Peakshaver to be fit for processing LH2

Abstract

To reach the goals of the European Green Deal (CO2 emission reduction of 55% by 2030 and climate neutral by 2050), North-Western Europe has to import sustainable energy as locally produced renewable energy will not be sufficient to meet the total demand. This will be realised by importing green hydrogen from areas with a surplus of renewable energy. If those areas are in another continent, the hydrogen is expected to be imported by vessel and received and stored in a hydrogen import terminal. Since Gasunie has an LNG plant in the Port of Rotterdam that becomes available within a few years, they want to investigate the possibilities to retrofit this plant into a hydrogen import terminal.

This research has investigated if the current LNG-Peakshaver can be retrofitted to an LH2 import terminal. This import terminal will receive, store and process LH2 to be delivered to the hydrogen Backbone (future hydrogen grid in the Netherlands owned by Gasunie). The imported LH2 will be received from maritime vessels at conditions just above ambient pressure and below its boiling point (-253˚C). It will be stored in the retrofitted LNG storage tanks, and depending on the hydrogen demands of the grid, LH2 will be processed (regasified) to the requirements of the grid (5˚C and 50 bar). This send-out process is very similar to LNG and requires pumps, BOG compressors and evaporators as process equipment.

The differences in physical and chemical properties have been analysed to determine if retrofitting LNG process equipment into LH2 application is feasible. The three main property differences that most affect the processes at the terminal are 1. the lower temperature (-253˚C instead of -162˚C), 2. the lower density and 3. the lower latent heat of vaporization of LH2 as compared to LNG. In view of these differences, it has been established that the reuse of the current LNG equipment is not possible. Even the pipes cannot be reused, as the LH2 pipes must be vacuum insulated to prevent liquid oxygen formation at the outside of these pipes.

Enhanced research has been carried out into the required process equipment. For the LH2 pumps, cavitation and the low pressure-head of the centrifugal pump are a problem. To overcome these, a special inducer is used, and three HP pumps in series to reach the desired pressure of 50 bar. Regarding the hydrogen BOG compressors, a vertical labyrinth (reciprocating) type is considered. However, manufacturers cannot yet design compressors that operate at temperatures as low as -250˚C. For the evaporator, a Super-ORV design with seawater as the heat source is considered the best option to evaporate the LH2. This design is an enhanced ORV that improves the heat transfer, which is desirable considering the lower temperatures of LH2.

Retrofitting the LNG tank is essential since it is the most expensive part of the plant. The current inner tank material and insulation are not capable of handling LH2. Therefore, two solutions have been explored to retrofit the storage tank. The more expensive solution -resulting in a lower BOR- is implementing a new vacuum insulated storage tank inside the existing concrete construction. The other option is to attach membrane insulation panels at the inside of the current storage tank.

Simulations have been performed to analyse the desired terminal configuration with regard to energy efficiency. The differences in configuration depend on the tank's insulation method, BOG processing, and cold exergy utilization. From these results, it is concluded that a compressor that can handle temperatures as low as -250˚C is essential for an LH2 terminal as it dramatically improves energy efficiency. Considering the terminal configuration, it is concluded that a membrane insulated tank combined with a recondenser to process the BOG flow is the desired solution if the terminal has baseload send-out. However, when a low minimum flow is required, a vacuum insulated tank in combination with “cold” BOG compressors is the best solution. Both configurations have an energy efficiency loss for baseload send-out of 0,13% of the HHV. To determine the feasibility of the terminal configuration, a further cost-efficiency evaluation is essential, next to this energy efficiency analysis.

The overall conclusion is that for the storage tank, the most expensive part of the plant, potential solutions to retrofit it exists. Especially the membrane insulation method is very promising and deserves more in-depth research. However, reusing the LNG process equipment is not possible. The equipment for the LH2 process is not yet commercially available except for the LH2 pumps. Further research is recommended because an LH2 import terminal has many advantages over other hydrogen import terminals, namely a relatively simple and flexible send-out process that requires little energy input.