CO2 transportation research: Liquefaction of gas mixtures and recovering liquefaction cost (Flexible Funding 2020)

Prof. Kumar Patchigolla at Cranfield University was awarded funding in the UKCCSRC’s Flexible Funding 2020 call to look at the “CO₂ transportation research: Liquefaction of gas mixtures and recovering liquefaction cost”.

Increase in CO₂ emissions has led to global warming driving humanity to adopt Carbon Capture Utilisation and Storage (CCUS) processes more extensively. In this research project, work is carried out to lower the cost of CCUS deployment, in particularly for the marine sector by using a cold energy utilisation technology. Captured CO₂ is liquified and transported in a ship container at optimal conditions of -28.5°C and 15 bar. After the ship container has unloaded the liquid CO₂, the empty container tends to warm up due to heat transfer from ambient temperature. A Cold Thermal Energy Storage (CTES) unit is designed to utilise the cold energy of liquefied CO₂ to precool the ship container before loading, saving operational cost.

Fig. 1. Schematic of the (a) cold thermal energy storage 3D design and (b) cold energy utilisation technology

The designed CTES system consisted of heat exchanger, control centre, inlet and outlet valves as shown in the Fig. 1a. Heat exchanger thermodynamic calculations were done for the required flow of cold energy using liquefied CO₂. The material of the ship container was identified, and a process flowchart was created accordingly using Aspen HYSYS providing the flow rate of the liquefied CO₂ into the CTES system. It is concluded that the CTES unit of volume 15m³ utilising phase change material (PCM) can store 309 kWh of cold energy required to cool down a typical 11,500m³ ship container. Commercial PCM E-26 were chosen as the material costing £1.95/Kg and Carbon steel grade A517 was selected for manufacturing storage tank costing £0.97/kg. The cost estimates were excluding the packaging and transport costs. It has also been estimated that a typical ship taking around 200 trips per year, saving 309 kWh of energy per trip and with current UK electricity cost of 1 MWh being £1000, the overall cost saving by the proposed CTES system is £200,000 per year. This concept has the potential to its return within several years of implementation.

Additional research has been secured to explore its potential implementation with Oman shipping company.

Furthermore, as part of this project, we were able to arrange a site visit to Uniper Grian Power Plant in Kent, UK, where they are having significant long-term regasification capacity at the Grain LNG terminal, to convert LNG back to natural gas. We would like to extend our thanks to Uniper colleagues for their support in showing our future “Heat Engineers” around the power plant.

Fig.2. Uniper power plant site visit for Prof. Patchigolla’s group along with MSc Advanced Heat Engineering students at Cranfield University