May 24, 2018
The International Energy Agency (IEA) considers carbon capture and storage (CCS) to be an important climate mitigation technology in its Blue Map strategy for reducing carbon dioxide emissions. CCS is needed to successfully transition to a low-carbon economy and achieve the Paris ‘below 2 degree’ international climate change target.
Nickel-containing Type 304L (UNS S30403) is a contributor to the success of CCS operations where there are concerns about corrosion from wet liquid carbon dioxide in the process streams. Carbon dioxide dissolved in water forms carbonic acid, a weak acid that can attack carbon steels under certain process conditions. However, Type 304L is typically resistant to such conditions.
Keeping CO2 out of the atmosphere
Type 304L played a key role in Shell’s Carbon Capture and Storage Quest project, launched in 2015 with the goal to capture and store up to one million tonnes of carbon dioxide per year from the expanded Scotford Upgrader at Fort Saskatchewan, Alberta. The facility was built on behalf of the Athabasca Oil Sands Project (AOSP) joint venture owners (current partners include Shell, Chevron, and Canadian Natural Resources), with support from the Canadian and Alberta Governments. Funding was part of the province’s commitment to reduce emissions from large-scale industrial sites, which account for up to 70% of emissions in Alberta.
The carbon dioxide is captured from the Scotford steam methane reformer units, which produce hydrogen for upgrading bitumen to lighter oil products. Captured carbon dioxide is transported 65 kilometres from the facility via underground pipeline to several wells at a permanent underground storage site. The nominal design life of the plant is 25 years.
Reaching targets ahead of time
Since commercial operation start up almost three years ago, it reached the milestone of capturing over two million tonnes of CO2 ahead of schedule.
Quest is the first application of this technology at an oil sands upgrader. From a global perspective, it is comparable to the emissions of approximately 250,000 motor vehicles per year.
Shell Canada stresses that a key component to this success has been the integration of the newer project with the existing process units. This facilitated the “fine-tuning” and optimisation of the operation, resulting in 99% plant reliability (unplanned downtime of less than 1%) during the first year.
Based on Shell Canada’s operating and engineering experience, austenitic stainless steel is used in the capture and compression sections of the process, as well as for the injection tubing at the wells.
How it works
The capture facility is interconnected to various process gas streams in the three Hydrogen Manufacturing Units (HMUs) where hydrogen is produced for the conversion of AOSP bitumen to crude oil. The carbon dioxide is removed by contacting the gas stream of methane, carbon dioxide, carbon monoxide, and hydrogen with an amine solution.
The carbon dioxide is separated from the amine in a regeneration process that produces 95% carbon dioxide at a pressure slightly above atmospheric pressure. The carbon dioxide stream is then compressed to a supercritical state and dehydrated by a multi-stage compressor and transported via pipeline for off-site deposition.
The CO2 enters the pipeline at roughly 40 °C and 10 MPa pressure. This is also sometimes known as a dense-phase state. It is injected into the wells at a slightly lower temperature in a liquid state.
A big step forward for CCS
The successful design, construction, and operation of this Alberta plant represents a significant stride forward using this technology. The Global CCS Institute’s data shows that there are “currently 21 large-scale CCS facilities in operation or under construction globally; these facilities can remove 37 million tonnes per annum of CO2 that otherwise could have entered the atmosphere. This is the equivalent to taking almost eight million passenger vehicles off our roads.”