Carbon Capture in the Refining Process (First Grant Scheme)

In the refinery, CO2 comes from two different sources – firstly by fuel combustion in the CHP boiler (around 35% of total CO2 emission), and process heater/furnace (around 45%), and secondly from the H2 plant (around 20%). The fuel combustion in the boiler/heater/furnace is identified as major source of CO2 emission in the refining process accounting for around 80% of total CO2 emission. However, the CO2 sources by fuel combustion are widely distributed throughout the complex and their flue gas has relatively low CO2 mole fraction (4-15%). Therefore, deploying and operating carbon capture units to these sources result in significant capital investment and running cost as well as operational difficulty. Unlike the CO2 emissions by fuel combustion, the CO2 emissions from the H2 plant are characterised by a single source having highly concentrated CO2 (50-60%), which implies that it would be more efficient to capture CO2 from the H2 plant than from the other sources.

The proposed research aims to develop a Vacuum Swing Adsorption(VSA) process to capture CO2 from a H2 plant in the refining process. For post-combustion capture, the amine process is, to date, closest to commercialisation and ready to be deployed, but a cyclic adsorption process can be more energy-efficient than the amine process in this particular case due to a high CO2 fraction in the feed. Moreover, it should be emphasised that the CO2 VSA unit supplementary to an existing H2 PSA process has operational flexibility, as it can be operated in various modes, including capture-mode, non-capture mode or controlled-load capture mode.

The research will focus on finding an optimal configuration for the CO2 VSA process based on a commercial adsorbent. The target is to achieve 90+% CO2 recovery with 95+% purity from the H2 PSA off-gas. A lab-scale multi-column VSA rig will be constructed to demonstrate that the target can be achieved by a well-designed cyclic adsorption process. The design and optimisation of the VSA process will be facilitated by a proper simulation work in parallel with operation of the rig. An overall process design of an example H2 plant integrated with the VSA process will be implemented for the purpose of optimising its steam network.