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.

The UK has a clear target to reduce its CO2 emission by 80% by 2050. The largest CO2 source in industry has been identified as stemming from the power-generation sector, accounting for about 32% of total CO2 emissions in the UK. CO2 emissions from refineries are also important - they account for more than 3% of total emissions, which amounts to around 15 MtCO2 per annum. Given the imminent UK targets for the reduction of CO2 emissions, it has become a necessity to endeavour to reduce CO2 emissions from all types of industry, including cement works, refineries, petrochemical plants, steel industries, as well as power stations. The technology to be developed will contribute to the UK government achieving its target for CO2 emission cut.

Refineries will be able to cut their CO2 emission by more than 20% from the current level by revamping their H2 plant using the technology to be developed in this project. Furthermore, the properties of crude oil are becoming heavier and sourer and the environmental regulation on sulphur content in fuel oil is becoming tighter all over the world. This is leading to an increase in demand for H2 for desulphurisation and heavy oil cracking in refineries. Therefore, the share of CO2 emission by H2 production out of the total CO2 emission in refineries is likely to increase gradually and a novel carbon capture process should be devised to reduce the carbon emission from H2 plants. Unlike the Gemini and sorption-enhanced reaction processes, disruption to the existing H2 plant operations can be minimised by the propored CO2 VSA process during its retrofit. Furthermore, it is expected that the refiners will be able to operate the H2 plant in various modes: capture mode, non-capture mode, or controlled-load mode at any time because the CO2 VSA is basically a capture process supplementary to the existing plant.

Even though the development of the CO2 VSA process is targeted at a H2 plant in the refinery, it can also be adapted to post-combustion carbon capture at a coal/gas-fired power plant or a cement process. The energy consumption for a VSA process at a power plant would be larger than that for a H2 plant due to the difference of CO2 concentration in the feed. Additionally, the process configurations for a power plant would be more complicated for the same reason. Nonetheless, it is expected that its economic feasibility can be significantly improved in the near future, considering that several emerging materials, such as MOFs, have already been reported to have greater CO2 capacities (almost twice as much) than those of commercial adsorbents.

Consumers will be able to use less carbon-intensive petroleum products, such as automobile fuels. In the long term, consumers can benefit an alleviated climate change on their daily life as this technology will prevent a significant amount of greenhouse gas from being emitted to the atmosphere when it is applied to all the industries including power and cement plants.