Written by Paul Tait from the University of Edinburgh.
Introduction and acknowledgements
Firstly, I’d like to say a big thanks to UKCCSRC for providing me with such a fantastic opportunity through its ECR International Exchange Fund. My 4-week placement at the University of Texas at Austin was hugely beneficial to my research and understanding of mass-transfer processes, and provided me with a clear picture of what I needed to do upon my return.
I should also thank Professor Gary T. Rochelle and his P.A. Maeve Cooney, for inviting me to Austin and making the necessary arrangements for my stay.
Finally, I’d like to thank all the members of the Rochelle group I met during my stay for being so welcoming, in particular Lynn Li, who introduced me to the wetted-wall column and did such a great job of looking after me. Thanks!
Week 1: 20/05/13 – 25/05/13
Arriving late on the evening of the 20th, the majority of the first week of my stay was spent making transportation arrangements, getting sorted out with access cards and keys for the chemical engineering building & lab at UT Austin, and attending the carbon management program’s bi-annual review of research meeting on the 22nd and 23rd of May.
On the morning of the 21st I attended a meeting with Prof Gary Rochelle, who heads the group. The plan for the duration of my stay was discussed, along with some general discussion about the facilities available at UT Austin. I provided him with information about the nature of my PhD project and my own academic background as a chemistry graduate, which led to the suggestion that I spend the majority of my time working with Lynn Li, a 4th year PhD student who carries out experimental work on solvent development using the wetted-wall column. It was decided that I should also spend some time, if possible, with Chao Wang, another 4th year who is involved with the characterisation of structured and random packings for use in CCS applications. However, this would depend on whether or not he would be carrying out experiments within the next 3 weeks, as the pilot facility at Pickle Research Center is often used by sponsors of the carbon management program for commercial testing.
Having attended the majority of the bi-annual review of research meeting (I missed 2 presentations on the 23rd due to an important teleconference with my industrial supervisor), it appears that there is a strong focus on solvent development and characterisation, as opposed to the approach at Edinburgh University which tends to look at the integration of CCS with the power plant and the grid. As a former chemist I found the work on the identification and testing of new solvent degradation inhibitors particularly interesting. These solvents are degraded artificially by thermal cycling in pressurized cylinders, but once the ACTTROM unit is up and running at Peterhead power station it may be advantageous for researchers at UT Austin to also send samples to the UK for degradation by exposure to real flue gas.
On Friday, to celebrate Tarun Madan’s graduation and the end of the review of research meeting, the group went out to sing karaoke! This was more of an Asian style of karaoke than you find in British pubs: Each group hires a room for a set time, brings their own drinks (conveniently, there was a liquor store next door with all kinds of weird, wonderful and not-so-wonderful Korean alcohol) and you get to put on as many songs as you want up on a giant widescreen TV & projector. Even though I’m terrible at singing it was a great way to get to know the people I would be working with, and a really fun experience!
For those of you wondering what a wetted-wall column is, here's a photo...
Week 2: 27/05/13 – 31/05/13
On Monday I began work with Lynn Li on the wetted-wall column. The plan was to observe her experiments and carry out a few under her supervision for the duration of this week, before processing the data obtained and attempting some experiments on my own the following week.
On Tuesday afternoon I had another meeting with Prof. Rochelle, who will unfortunately be away from the beginning of next week until the end of my stay. We discussed several things relating to column design, the most important being the annulus size. I realised that the annulus in my current design is much too large, which is a potentially fatal flaw as this will decrease the value of kg, making any absorption experiment mainly gas-film controlled when it is the liquid properties we are actually interested in. I also managed to clear up a few things with him about my understanding of column characterization and mass transfer.
I continued work with Lynn on the WWC throughout the week, observing experiments on Tuesday and beginning to work with the apparatus myself through the following days. While solvents were being prepared I began to work my way through the book “Gas-Liquid Reactions” by Danckwerts and Sharma, which really helped me understand mass-transfer theory as applied to the reaction between amine and CO2, especially since I was never short of someone to ask for help if I didn’t understand something fully.
On Friday I obtained data on my own for a piperazine/diglycolamine blend at a loading of 0.3mol CO2/mol solvent. I also had a final, informal meeting with Professor Rochelle who will be at the TCCS-7 conference next week before going on holiday the week after. He reiterated something he had mentioned previously: that the main purpose of the Carbon Management Programme at Austin is to train young people to be capable engineers, which I felt, was an excellent first priority to have. He also suggested that I attend GHGT-12 which will be held at Austin next year if I am able to, and gave me a stack of GHGT-12 bookmarks to advertise it to my workmates in Edinburgh!
Over the weekend I went to a Memorial Day barbecue and pool party at Lynn’s apartment complex. I asked Paul Nielsen, another student who drove me there, if it was common to have a pool in your apartment complex in Austin. “Not really”, he said. “I mean I have one too, but…” it’s a different world. There were a few dead ants in the pool but I’m sure I’ve swam in much worse before, for example, the sea at Portobello beach.
Week 3: 03/06/13 – 07/06/13
The plan for this week was to analyse the data obtained from the wetted-wall column experiments, starting on Monday afternoon. The overall mass transfer coefficient (KG) and hence the liquid side mass transfer coefficient (kg’) was determined using an excel spreadsheet which a previous graduate student had designed. Lynn was kind enough to provide me with a copy which I could study and understand fully in my own time. The next part of the analysis involved confirming the CO2 loading of the amine solutions analysed. This was done by injection into phosphoric acid solution and analysing the gas liberated using an IR spectrometer. With over 30 samples to be injected a minimum of 3x each, followed by calculations to determine the loading, this took up the majority of the rest of the week.
Since I was under 25 and thus unable to hire a car without paying through the nose for it, I had picked up a bike in my first week as a means of transport with which to explore the cyclist-friendly parts of Austin. At the barbecue the previous weekend, I had met two guys who frequently take part in Austin Social Bike Ride which happens every Thursday night, so that was my first social event for the week. There must have been 100 people there, some of the bikes covered in neon lights, some with speakers strapped to them, even one guy pulling his two dogs in a trailer behind him and a double-decker bike consisting of one frame welded to the top of another! It was a really fun way to see parts of the city I might otherwise not have, and ended back at a bar downtown. I enjoyed it so much I went back the following Thursday.
I also explored the Austin greenbelt by bike at the weekend. Being the start of summer, it was a bit rockier than I expected…this is a dried-out riverbed I cycled through. The photo in the right is the Texas State Capitol building.
After finishing up the analysis over the Monday and Tuesday of this week, I visited the pilot plant at Pickle research center. It was similar in scale to the UKCCSRC pilot plant at PACT, except they only use synthetic flue gas whereas we will have the option of using real flue gas from the gas turbine.
The facilities include:
An 18-inch wide by 20ft tall (2x10ft beds) absorber column for solvent and packing experiments
A 6-inch diameter plastic column for air/water experiments
A stripper column with reboiler
A 2-stage flash stripper. This was used to investigate whether flash stripping is more energetically favourable than using a stripper/reboiler in a previous project.
Unfortunately, the plant wasn’t operating while I was there as most of the operators were on holiday. I was shown around by Micah Perry who runs solvent analysis at the plant. He mentioned that the response of the plant to step-changes is very slow, since they have a very large solvent inventory compared to the holdup in the column, and it can take around 4 hours to start up. This seems very long considering the 100tCO2/day pilot plant at Ferrybridge usually achieves steady operation within 45-90min.
Micah also raised some points about the viability of using piperazine-based solvents on an industrial scale, citing several occasions in which the heat during the summer in Austin had caused the plant to lose more water to atmosphere than expected, causing the piperazine to precipitate out of solution. As well as increasing the startup time required the next day, this has the potential to cause serious damage to the plant if left unnoticed. I found this interesting, as I observed similar problems due to extreme cold during the commissioning of the pilot plant at PACT in which the water inside the system froze and blew out a large number of gaskets. This drives home the fact that certain solvent systems may be suitable for certain climates, but completely unsuitable for others.
Friday night was my send-off, and I was taken out for proper Mexican food from a proper Mexican food truck, followed by a few drinks in one of Austin’s many beer gardens. A few of us decided to go out downtown after that, forgetting that my final weekend coincided with the Republic of Texas Bike Rally, purportedly the largest rally in Texas and one of the biggest in the whole USA. We found East 6th Street all but abandoned by the locals, and after a while drinking next to a selection of increasingly giant, increasingly intoxicated bikers sporting t-shirts which proclaimed things like “OBAMACARE = DEATH AND TAXES”, we departed for a less leathery part of town for the rest of the night.
On Saturday evening, while out a walk to reflect on my time there, I encountered the much more agreeable Austin Naked Bicycle Ride and gave them a big cheer as they sped past. As a picture of them would definitely be unsuitable for the UKCCSRC website, here’s one I took a bit earlier of the sunset over the Colorado river.
Overall, my visit to UT Austin has been hugely beneficial to my understanding of mass transfer theory and for my wetted-wall column design. The visit will have a direct impact on the design of my apparatus and hence, the functionality of the carbon capture lab at Edinburgh University which will support the ACTTROM and GAS-FACTS projects. I was also able to explain the purpose of the ACTTROM unit to Professor Rochelle, which he thought was “quite a nice idea” if my memory serves me correctly. Although not hugely relevant to my own research, the work being carried out on solvent degradation inhibitors was very interesting and it was great to see this and other research being presented at the biannual review of research meeting. Although it was a shame that the pilot capture plant at Pickle Research Center was not in operation at the time, it was still interesting to visit and raised some questions in my mind about the viability of different solvent systems in different climates. It also made me realise that having a large solvent reservoir does not lend itself well to flexible operation.
On a personal level, I had a fantastic time in Austin and the graduate students in Professor Rochelle’s group could not have been more welcoming. I made some good friends during my time there and I really hope I have the opportunity to collaborate with them, or return to Austin in the future!