ES 杂志第 29 期清洁空气
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Our latest podcast looks at a variety of carbon capture and storage processes available to industry, and the challenges facing operators using them. Listen now to find out how Servomex provides optimum solutions
Carbon capture podcast transcript
MH: Welcome, once again, everybody to another Servomex podcast, today on the subject of CCUS, which is carbon capture, utilization and/or storage. This is a very, very hot topic around the world at the moment. And I’m once again joined by Maria Mokosh, our application development engineer in EMEA. Hi, Maria.
MM: Hi, Matt. Good morning.
MH: CCUS, as I said, is a very hot topic around the world at the moment, very closely linked with emissions, with decarbonization, and climate change, more importantly. Back in 2015, the Paris Agreement was signed by a large number of nations. And this agreement was put in place to agree to not allow global temperatures to rise beyond another 1.5 degrees Celsius. That implemented a carbon budget, so an amount of CO2 or a volume of CO2 that could be emitted over the next few years before that temperature increase was seen. Countries were committed to become net zero by 2050.
If countries were to meet that goal of 2050, the current agreement among the science community is that we would actually use up our carbon budget about a decade too soon. That’s the current thinking. At the start of 2020, there was about 440 billion tons of carbon left in that budget, so we’ve gone nearly two years beyond that already. And even if we used up that budget by 2040, there was still only a 50-50 chance, according to the data, of actually not achieving the temperature increase. So 2030 is the is the current proposed target for being carbon net zero.
And since then, a lot of countries have put in their own pledges, in addition to the Paris agreement, to try and meet that target, the UK being one, for example. Servomex, as a company, with our sister companies and our parent company Spectris Group, have put in our own roadmap to achieve carbon net zero by 2030, and to work with our suppliers and customers to ensure that our value chain is carbon net zero by 2040.
This ties in very nicely with our Clean Air initiative and our Clean Air Solutions, of which there’s a two-part podcast you can go onto our website to listen to, that we we’ve recorded previously. And what Servomex wish to do is work with our customers to take collective action via our Clean Air Solutions to enable gas clean-up and emissions phase solutions. You’ll remember, those of you who have listened to the podcast, we spoke about a three-phase approach, combustion control, gas clean-up, and emissions, and really carbon capture spans the last two of those phases.
Carbon capture, utilization, and storage, quite simply, as the name suggests, is the attempt to capture carbon, typically as it as it leaves the process – or catch CO2 specifically, as it leaves the process – to stop it being emitted into the atmosphere to stop it contributing to the global warming effect. By the end of 2020, there were approximately 20 plants in operation around the world, and another 40 in development. The current global capacity for carbon capture is considered to be around 40 million tonnes per year, something in that area. But if all those projects were to proceed, the capacity is believed to increase to around 130 million tonnes a year.
Most of these projects are in the US and Europe, those two regions are very much leading the way when it comes to carbon capture. And just a few notable projects, which are considered demonstration projects. What that means is these are projects that aren’t running at full capacity at the moment, they’re just trying to prove that different types of technology for carbon capture work because there’s, as we’ll discuss later, there’s lots of different ways of doing this.
So, the first one to mention is the Tomakomai project, which is in Japan. This is capturing, year on year – it’s been running for a few years now – but year on year, about 100,000 tonnes a year, but achieved 300,000 in its last year. This has now stopped and what they’ve done is they’ve stored the CO2 underground, and they’re closely monitoring that CO2 storage at the moment, just to check everything is stable, and there’s no risks or problems involved with storing CO2.
There’s a project in the UK called Drax, or called the BECCS project, which has a capacity of a tonne of CO2 a day, which is very, very significant. It’s not running at that capacity yet, but that’s a very big number, currently, in CCS terms. And this has been put in place to target a proposed zero-carbon Humber CCUS hub, which will mean storing captured CO2 in the North Sea and will be aiming for around 17 million tons of CO2 per year.
And then there’s the Northern Lights project, which is the first cross-border project that’s being developed in Europe, specifically in Norway, but it will cater for the wider European market. This is a partnership between Equinor, Shell, and Total, and aims to capture 800,000 tonnes a year by 2024 and will store the CO2 off Norway’s west coast.
What we’re going to talk about today are four main areas of carbon capture technology. The first is pre-combustion capture, the second post-combustion capture, the third oxyfuel combustion, and then a fourth, which is capturing CO2 that’s already in the air, already in the atmosphere, so extracting it from the air. The industries that Servomex traditionally work with would be included in the first three of those types, but we will touch on the fourth type for balance. So, Maria, I’m hoping you can give me a little intro into these four different types of technology – shall we start with pre-capture?
MM: Yes, indeed, there are these three main industrial ways to capture it: pre-combustion, oxyfuel, and post-combustion, and then there is this little bit apart, which is direct capture from air.
Okay, so let’s start with pre-combustion. Pre-combustion carbon capture, as the name indicates, removes CO2before combustion of fuel. Coal, oil, or natural gas is heated in pure oxygen, resulting in a mix of carbon monoxide and hydrogen. The syngas, mainly carbon monoxide and hydrogen, plus some CO2, produced from the gasification process, undergoes a catalytic gas shift process, with water vapor converting most of the carbon monoxide into additional carbon dioxide and hydrogen. So far, this part of the process, also known as steam reforming, has been used for decades to produce hydrogen from coal and natural gas.
The next step, namely the capture of CO2, combined with the necessary purification of hydrogen, has been added to the established process. The gases are fed into the bottom of reactor. In the reactor the gases will naturally begin to rise. A solvent amine, again, has been established here, is poured into the top. The amine binds the CO2 and falls to the bottom of the reactor. Hydrogen continues rising up and out of the reactor.
The next step is to heat the amine CO2 makes, to release CO2. It rises to the top where it can be collected, compressed, and moved into a reservoir, and the amine drops to the bottom for reuse. Same as for post-combustion carbon capture, desulfurization added before the CO2 absorber will improve the efficiency and reduce solvent degradation.
Further, the monitoring of CO2 purity, hydrogen purity, and a purity such as carbon monoxide, hydrogen sulfide, and water vapor, makes sense in the product streams for CO2 and hydrogen. Hydrogen, together with a non-shifted carbon monoxide, can act as a feed for gas turbine or fuel cell for producing electricity. The resulting emissions, vented to atmosphere, will contain mainly oxygen, nitrogen, and water vapor, and reduced concentrations of CO2 and NOx. They should be monitored, for example, by traditional infrared, UV and paramagnetic technologies. For safety, ambient oxygen and carbon dioxide leakage should be monitored at the CO2 storage site.
The advantage of pre-combustion carbon capture is that part of the process is already in use, for example, for SMR – steam methane reforming – and coal gasification. The disadvantage is that, although the pre-combustion carbon capture process is lower in cost, it is not a retrofit for older power plants. As with post-combustion, pre-combustion carbon capture can prevent 80 to 90% of power plants emission from entering the atmosphere. So that’s a pretty good goal.
MH: That was pre-combustion Maria, so what about post-combustion capture?
MM: In post-combustion carbon capture, CO2 is removed from flue gas which the burning of fossil fuels produces. The CO2 content can vary depending on the fuel used. Widely proven has been the chemical absorption process, using amines to separate CO2. However, other options such as membrane absorption are in the process of being rolled out, large scale, so we expect to see more variants in the coming years.
In a typical reaction, CO2 is bound to an absorbent, for example, amine, at lower temperatures, then at higher temperature CO2 is released again producing a CO2 stream of up to 90% purity and leaving the absorbent free again to be recycled and reused for CO2 capture. The produced pure CO2 product has to be compressed and fed to a storage reservoir and the remaining flue gas is vented to atmosphere. The flue gas at this point mostly contains nitrogen, argon, and oxygen, especially if NOx and SO2 scrubbers are included before the absorber. In addition to traditional infrared, UV, and Paramagnetic technologies, which are used to measure the flue gas content from power plants, the same measurement techniques can be used to control emissions after the CO2capture process.
Some components which are typically included in flue gas can be problematic for amines. SO2 and NO2 can be irreversibly absorbed, thus reducing the solvent efficiency. Others, such as H2S and water vapor, can be absorbed concurrently with CO2, which will affect the product purity and cause equipment corrosion. Thus, to improve the efficiency and reduce solvent degradation, these components should be removed by pre-filtration or scrubbing.
For process control, it should be recommended to measure the input and remaining impurities and the purity of the CO2 product. At the storage side, ambient oxygen and CO2 leakage need to be monitored for safety reasons, due to CO2 being an asphyxiant. The disadvantage of this process is that it requires a lot of energy, depending on the solvent used. Other separation mediums and separation techniques, such as membrane technology and more modular techniques,are currently being tested large scale – further optimization is expected in the next years. The advantage already is that post-combustion carbon capture can be added to existing power plants and industrial processes.
MH: Okay, thanks Maria, for those explanations. So oxyfuel combustion, quite simply, is the combustion of a fuel with pure oxygen or near-pure oxygen, as opposed to the more traditional combustion air that’s used. In order to get the pure oxygen, what they typically do is use some kind of air separation unit, or something very similar to air separation, cryogenic technology, to denitrify the air, so remove the nitrogen, which makes up the bulk of air that we breathe, and then leaving oxygen and the other trace components, use that to fire and oxidize the fuel.
This brings a number of challenges. For one, there’s a much higher safety concern when combusting with pure oxygen. Pure oxygen is much more reactive than the oxygen in there. So it’s enriched, it makes reactions typically more lively, and increases flame temperature quite dramatically, which can actually affect the way that a fuel combusts. This is currently used, typically, on gaseous fuels, it’s been challenging to use this on solid fuels. One of the reasons as to why it’s been challenging with solid fuels is there’s a concern over how the flame temperature will actually affect the valency of the some of the heavy metals that are in fuels such as coal. So, basically, the valency of a material is how readily it will combine with other materials. If you change the valency of a heavy metal, you risk forming other types of emissions that may have different environmental impacts to the CO2 that we’re trying to remove, so it’s being piloted, but it’s much more common to find this in gaseous combustion, natural gas for example, and syngas.
So, the reason that oxyfuel combustion is perhaps desirable in terms of carbon capture is because you take the nitrogen away from the reaction, which means you no longer produce NOx, which is it an emission in itself, which is quite heavily regulated around the world. If you remove the potential to form NOx, what you do is produce a gas stream that is relatively CO2 rich, and the other gases that you form, from other contaminants and hydrocarbons, can be removed using traditional clean-up technologies. For example, sulfur, which will oxidize to form SO2 can be removed using flue gas desulfurization technologies which have been used for decades. And what that leaves you with is a relatively pure stream of CO2, which you can then capture, using post-capture technologies. And then you can sequester it, you can store it somewhere you can transport it away, and it involves very little clean-up.
One of the measurement challenges of oxyfuel is the fact that you now have a much higher level of excess oxygen post-combustion. So in a typical combustion reaction using air, you would expect to perhaps have less than 10%, perhaps less than 5%, excess oxygen left over, but when you’re burning or oxidizing with pure oxygen, you’re going to have a lot more; you’re going to have potentially enriched oxygen levels, so greater than 21%, depending on on your level of process control, which means typical and traditional measurement technologies like Zirconia, which are used in in-situ Zirconia combustion analyzers and Servomex’s FluegasExact 2700, become unusable because the way Zirconia technology works, it’s only suitable to measure up to 21% oxygen, which is the level of oxygen that the Zirconia cell is being exposed to on its reference side so it can’t measure more than that.
Servomex do have a way of utilizing the FluegasExact 2700 in this application. We have specially designed software, which will actually allow a Zirconia even being referenced to air to monitor up to 50% oxygen. So, we do have a solution for oxyfuel combustion processes.
Oxyfuel combustion isn’t a new thing; it’s been used in the glass and metal industries for a long time, glass especially, because the very high flame temperatures are needed. Whereas they’re not needed in combustion of fossil fuels for power generation. What they actually need to do is recycle some of the flue gas that’s produced, in order to bring the temperature of the main combustion chamber down, because we just don’t need the very high flame temperatures that can be up in the 1500 Celsius or above. But that is useful in in the glass industry.
Because of the high temperatures, there’s other considerations for plant operators, such as flame temperatures and how the other materials in the process can withstand much higher temperatures. Hence this this recertification of flue gas, which has become common practice.
Oxyfuel combustion can certainly be retrofitted in a way to existing processes with some level of modifications to burners and even turbines further downstream. But it makes it quite an appealing technology to consider when it comes to pairing that with a post-combustion type CO2 capture.
Aside from the combustion control measurement I’ve mentioned, which is possible in oxyfuel combustion with the FluegasExact 2700 in its modified state, with the software that I mentioned earlier, the Laser 3 Plus can make the measurement as long as the excess oxygen level doesn’t exceed 21%, so it depends on the level of control over the process. And obviously, process to process, that can change.
There’s some other measurements to be made. The O2 stream, that has been cryogenically separated, is often measured for quality purposes. That can be monitored with Paramagnetic technology, either in the form of an OxyExact 2200, which is capable of measuring enriched oxygen, even in a hazardous area if zoning is an issue… If not, the MultiExact 4100, which is our 19-inch rack-mount unit, fitted with Paramagnetic, can also monitor up to 100% oxygen in a safe area.
And then we have, of course, the traditional emissions monitoring system, so a 4900 Multigas in our case, monitoring CO, NOx, SO2 and oxygen, but also CO2 now – so, much higher levels, of course, of CO2. So we’re looking at using traditional NDIR technology. Then we have the carbon capture measurements, so the CO2 purity, of course, using the SpectraExact 2500 Infrared analyzer, we then have some of the measurements Maria has already mentioned. Further downstream or in the value chain, we have the pipeline and the CO2 storage. So again, looking for the CO2 levels and other contaminants that could cause sweet or sour corrosion in storage and pipelines. And then the storage itself, where we’re looking for oxygen, or can look for oxygen, for safety purposes.
So, Maria, we’ve covered the three industry-level carbon capture technologies. We mentioned a fourth one, right at the beginning, which is this direct air capture plant. Can you tell us a little bit more about that technology?
MM: Well, the CO2 capture from ambient air is quite an interesting, and quite an ambitious, technology. The fourth option to capture CO2 is the CO2 capture from ambient air, which is obviously quite ambitious. Currently, the world’s largest plan to suck CO2 out of ambient air is running in Iceland. It’s a project called Orca. At the Orca project, a concentrated carbon dioxide stream is mixed with water, and injected at a depth of about 1000 meters into basalt rock. At this depth, CO2 behaves more like a liquid than a gas; it seeps into the spaces in porous rock and, long-term, the expectation is that it would turn into limestone.
MH: And there’s another one of these plants that’s planned to open in 2024, which is called DAC1, so Direct Air Capture One. And that’s very similar to the method you just described, pulling CO2 from the air, and then ultimately transporting it via a pipeline and storing it under the Permian Basin.
MM: Yeah, there are supporters, which says that these carbon capture and storage technologies will become a major tool in the fight against climate change. However, critics obviously mention that the technology is still very expensive, and it might take decades to operate at large scale. So we are best to prevent creation of CO2in the first place.
MH: That’s a very good point, Maria, very good point. And the emissions targets that I mentioned right at the start, driven by that 2015 Paris Agreement and subsequent agreements between individual countries, it’s been made clear that those targets will not be met by reduction alone – although that, of course, is one of the best strategies, to not produce the CO2 in the first place. But obviously, that’s not realistic; industrial processes will always be there producing fuels, and products, and power that the world needs. So that’s really driven the development of these four carbon capture technologies that we’ve been talking about today, because if we assume some of those emissions will always be emitted, we of course, then can deal with them in other ways, such as capturing them.
MM: Carbon Capture and Storage, as the name indicates, requires some type of storage site for the captured CO2. So, after CO is captured, the next step is transporting it to a storage site. The current method of transporting CO2 is through a pipeline or by vessel. Carbon dioxide pipelines do exist, for example, for enhancing oil production. Pipelines can transport CO2 in three states: gaseous, liquid and solid. Solid CO2 is commonly known as dry ice, and not very cost-effective to transport via pipeline. Commonly, pipelines transport CO2 in its gaseous state. A compressor pushes the gas through the pipeline – sometimes an intermittent compressor is used to keep the gas moving.
The transported CO2 must be free of hydrogen sulfide, and dry, otherwise sweet and sour corrosion of the pipeline can occur. Accidents with CO2 pipelines have so far been rare, probably due to the low number of existing pipelines. However, because CO2 is an asphyxiant which you cannot see or smell, there have been recommendations to add an odor to the gas to help detect any leaks. CO2 detectors and ambient oxygen measurements, as a safety measure, especially where people work and live, are strongly recommended.
Ships or tanker trucks transport CO2 as liquid. Liquid CO2 requires low pressure and constant low temperature, so cargo tanks need to be both pressurized and refrigerated. Same as for pipelines, because CO2 in high concentration is causing asphyxiation, CO2 detectors and ambient oxygen measurement should be recommended for safety reasons.
Regarding storage, there are two places which have been identified so far: underground and underwater. Underground storage, also called geological sequestration, is already in use by the oil and gas industries to squeeze out any extra oil and gas from depleted reservoirs with the help of CO2. Oil and gas reservoirs are well suited to store CO2, as they consist of layers of porous rock formations with overlying rocks that form a seal and keep the gas contained.
Geological sequestration involves injecting CO2 into underground rock formations. At a depth of about 1000 meters, CO2 behaves more like a liquid than a gas. It seeps into the porous rocks, which means that a great amount of CO2 can be stored in a relatively small area. Especially when combined with water, CO2 can essentially form limestone over the next years.
Apart from the fact that we are just moving our CO2 problem from the point where it is created to storage, there are also environmental concerns. What happens if the carbon dioxide leaks out underground? We can’t really answer this question today, because the process is new, and we don’t know the long-term effects. However, most experts support that measurement of CO2 leakage around CO2 storage sites, and underground, are required for monitoring of any CO2 movement, and for safety.
CO2 usage would obviously be the best solution if we could use up all the CO2 which we are creating and separating. Unfortunately, right now, the creation of CO2 due to our industrial processes is way higher than what we’re actually using. The CO2 demand is supposed to increase over the next couple of decades. Right now, most of it is used in fertilizer production. And the next highest usage is in beverages, for fizzy drinks basically. So projections are that the global demand is going to increase, especially for areas where CO2-derived products are used, for example, carbon-based fuels such as methanol production, also some chemicals such as plastics polymers. There’s also been some recent development in using CO2 in the creation of building materials, such as CO2-cured concrete, and also CO2 for enhancing the yields of biological processes.
The second option for storing CO2 is underwater. Technically, it is possible, if you could safely release CO2 at about 3500 meters below water surface, because then CO2 will compress into a slushy material and fall to the ocean floor. However, the method is very theoretical, has not been tested yet, because of concerns for the safety of marine life and the possibilities that CO2 could resurface. We have seen that in an accident in the 1980s in Cameroon, where emissions of CO2 from a lake which was above a volcano killed nearly 2000 people and a lot of animals, they died from asphyxiation. That’s one of the reasons why underwater storage is considered unsafe.
The second reason is that CO2 can be, even though it has sank to the ocean floor, it still can be soaked in water, and thus increasing the water acidity and affecting any marine life which reuses carbon carbonate, such as shells and corals. So that’s another point not to use underwater storage.
MH: Thank you everybody for listening and tuning into this podcast on CCS and CCU. Thank you very much, Maria, for your inputs today.
MM: Thank you for the invitation.
MH: Please do remember to visit servomex.com to find out more about CCS and CCU – go to the resources section and you’ll find other podcasts, videos, application notes and product brochures. Thank you again and we’ll see you next time.
SangWon Park, IP＆E业务部总监
Keith Warren, 产品经理
Rhys Jenkins, 光谱分析仪IP＆E产品经理
Huiyu Guan, 中国IP＆E业务发展经理
Stephen Firth, 全球业务发展经理
Karen Gargallo, 应用与开发主管