Technology and environmental protection: An overview of several latest carbon dioxide capture technologies

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http://www.chinaenvironment.com　　2009-3-18　　China Environmental Protection Network　　　　Can technology restore our clear skies and white clouds? 　　Do carbon capture technologies work? 　　In recent years, some climate scientists, particularly figures like James Hansen from NASA, have said that 385 parts per million is too high; what we need is not only to slow down the increase in carbon dioxide levels but also to address the damage that has already been caused as soon as possible. This task is like searching for 385 invisible, colorless needles in a pile made up of 1 million straws. How many chances do we have to find them and take them away? 　　Many scientists and engineers believe it is almost zero. They say it is completely impossible to eliminate carbon dioxide from the air, as it would require too much energy. But this has not stopped a few researchers from trying. They argue that capturing carbon dioxide from the air is not only theoretically feasible but will soon also become a practical tool to combat global warming. In short, they believe that failing to find a way to remove carbon dioxide from the atmosphere is something we cannot afford; it represents a crucial last line of defense for humanity. If Hansen is right, and we can’t go back to the way things were, then no amount of solar power generation or higher energy efficiency will be able to save us. We need to remove carbon dioxide directly from the atmosphere, and fast. 　　Capturing carbon dioxide is not difficult. In fact, in the near future, it may become possible for us to compress the large amounts of carbon dioxide emitted by power plants and factory chimneys and bury them deep underground. In 2005, a special committee of the **Intergovernmental Panel on Climate Change (IPCC)** concluded that this carbon capture and storage (CCS) strategy is likely to play an important role in addressing climate change. The entire CCS industry, strongly supported by governments **and energy companies, has sprung up like mushrooms after rain, turning this vision into reality. 　　However, once carbon dioxide leaks into the open air, capturing it becomes more complicated. The carbon dioxide concentration in the atmosphere is about one percent of that in flue gases. The IPCC concludes that, considering the energy required, it is not cost-effective to capture carbon dioxide directly from the air. 　　Klaus Lackner from Columbia University in the United States held a different opinion. He is also a member of the IPCC; as a particle physicist, he has been working for many years to advance technologies for capturing carbon dioxide from the air. He established the theoretical value of the minimum energy required to remove carbon dioxide from the air, and believed that the figures provided by the IPCC were incorrect. He said that capturing carbon dioxide from the air does indeed require more energy than capturing it from flue gases, but the difference is not significant. 　　This calculation convinced Rackner that an air filter was a practical solution, but he was unable to persuade his colleagues at the IPCC. For this reason, he realized that he had to make one by himself. 　　Lakna indeed did the same. In mid-2008, he and his colleague Alan Light created a filter made of plastic to capture carbon dioxide from the air, and they obtained a patent for it. This device can collect dozens of kilograms of carbon dioxide per day from the air passing through the vertical plastic sheets. Lakna said that if given two years along with $20 million in venture capital – which is not easy to obtain at the moment – he could build a model capable of removing 1 ton of carbon dioxide per day, enough to fill a standard container. Lakner believes that such devices will soon attract the interest of companies that are forced to purchase carbon emission quotas; millions of such devices will eventually be deployed to remove carbon dioxide from the atmosphere, which will help save us from global warming. 　　Of course, Lacna is not the only one working on carbon capture technology. Research teams from the University of Calgary in Canada and the Swiss Federal Institute of Technology have also developed carbon capture devices on a laboratory scale. 　　Freeing itself from the constraints of pipes If people are paying increasing attention to technologies for capturing carbon from the air, it is entirely because of the tremendous potential advantages they offer. On the one hand, air filters can capture carbon dioxide from anywhere, regardless of scale, including cars, airplanes, and heating systems. These devices generate more than one-third of the world’s carbon dioxide emissions, but it is impractical to capture them entirely in exhaust pipes or flues. More importantly, the carbon dioxide emitted mixes quickly with the air, so the carbon dioxide concentration is almost the same everywhere; thus, an air filter can be placed directly at the location that needs to be isolated. In contrast, carbon dioxide capture from power plants often requires hundreds of kilometers of pipelines. As David Case of the University of Calgary said, air carbon capture technology is separate from other energy economies. 　　Three years ago, Case and his student Josua Storallov created their first carbon capture prototype, using the \"spray tower\" technology for removing sulfur dioxide from the dust emitted by coal-fired power plants. Like sulfur dioxide, carbon dioxide is also an acidic gas that can be absorbed by an alkaline solution of sodium hydroxide. 　　Case’s prototype device was a thick cardboard cylinder 4 meters tall, lined with polyvinyl chloride. The air to be treated is blown in from the top, where it is sprayed with a sodium hydroxide solution; the sodium hydroxide reacts with carbon dioxide in the air to form sodium carbonate droplets. 　　This full-flow filter can also be installed in an aircraft hangar, where air is blown in from one end by a fan and passes through a thin mist of sodium hydroxide sprayed from nozzles in the ceiling. The channels on the floor will collect the sodium carbonate solution. 　　Although this system can function, it consumes a tremendous amount of energy. At the end of this process, sodium carbonate needs to be converted back into sodium hydroxide. Although sodium hydroxide is not expensive, it isn’t cheap enough to be discarded after being used just once. This requires a furnace heated to 900°C. Case believes he can reduce the energy required by half, cutting the overall cost of capturing and storing carbon dioxide to around $100 per ton. Although this is much higher than the fines that polluters pay under the EU’s emission control plans, once countries take climate change seriously, those fines might be far higher than they are at present. 　　Case admitted that air filters can never be the most economical solution to the problem of global climate change, but he believes we may still have to use them anyway. 　　While Case was busy refining his existing technology, other researchers were also seeking more innovative approaches. Eldo Steinfield, who specializes in solar technology at the Swiss Federal Institute of Technology in Zurich (ETH), showed great interest in air filters after visiting Lachner’s research institute. He said, “We have decided to use solar technology to achieve this.” ” 　　Making smart use of sunlight to remove carbon – The concept of ETH is an improved energy generation technology known as concentrated solar power, which is primarily used in desert areas around the world. Such power plants include solar tracking mirrors, which focus sunlight to generate steam to drive the generators. Steinfield explained, “We remove the boiler and then place a solar reactor there, so that we can remove carbon dioxide from the air.” ” 　　Steinfield’s reactor is a transparent tube filled with calcium oxide particles. In the desktop version, the tubes are only a few centimeters tall, and arc lamps are used in place of natural light. When the tube is heated to 400°C, air mixed with a small amount of steam is pumped in and passes through these particles from bottom to top. Under such temperature conditions, calcium oxide reacts with carbon dioxide to form calcium carbonate. Steinfield said, “When the air leaves, there’s no carbon dioxide left there.” We can reduce the carbon dioxide content of 385 parts per million to almost zero. ” 　　In less than 15 minutes, most of the particles were converted into calcium carbonate. At this point, Steinfield closed the inlet valve, increased the luminosity, and raised the temperature in the reactor to 800°C. This allows carbon dioxide to be separated as a pure gas stream and sent for isolation, in order to convert calcium carbonate into calcium oxide. The researchers have run their reactor through 5 cycles of absorption and release, with no decline in performance. Steinfield believes that his device can be scaled up to remove large amounts of carbon dioxide from the atmosphere, but he is not yet aware of the cost per ton of carbon dioxide removed. 　　Using sunlight to remove carbon dioxide from the air is clearly an advantage over Case’s furnace. However, Lakner believes that if you intend to fill the desert with solar concentrators, this could be more environmentally meaningful than simply converting sunlight into electricity. 　　Lakna’s strategy is to reduce the energy consumption required to remove carbon dioxide from the air. He and his colleagues tried various different designs, but the core of these designs was ion exchange resin, a polymer that can be impregnated with sodium hydroxide. Sodium ions are tightly bound to the polymer, but hydroxide ions are loose and can be easily replaced by carbon dioxide; when carbon dioxide combines with sodium, it forms sodium bicarbonate. Lakna said that the device in Calgary is also based on basically the same chemical principles, but because the surface area of the resin sheets is much larger, the reaction occurs much more quickly. 　　This resin has a second major advantage: it deforms when wet, which reduces its affinity for carbon dioxide. Lakna said, “In this way, we just need to add some water to accelerate the absorption of carbon dioxide.” ” 　　The air filters at the University of Calgary and the Swiss Federal Institute of Technology require a temperature of 900°C to regenerate their carbon dioxide-absorbing materials, but Lakhna’s design can achieve this at 40°C. Lakna is processing a very small amount of energy, but he has not yet conducted a detailed analysis of the cost per ton of carbon dioxide processed. 　　But he believes that this technology will be cheap enough to be suitable for commercial use. Fruit and vegetable growers often use large amounts of carbon dioxide in greenhouses to enrich the air, incurring an additional cost of $300 per ton of product produced. Lakna believes that connecting its air filter directly to the greenhouse can significantly reduce production costs. 　　Micro greenhouse: Lakna’s demonstration unit is actually a micro greenhouse about 1 meter long. One end is fitted with a plastic tube filled with ion exchange resin, which can absorb carbon dioxide from the air. When most of the sodium hydroxide resin is converted to sodium bicarbonate, Lachner empties the tube and inserts it into the humid air inside the greenhouse, allowing carbon dioxide to be released rapidly into the greenhouse. The device can produce about 1 kilogram of carbon dioxide per day, which is converted into the biomass of tomato plants in the greenhouse. 　　Oil and gas companies also often purchase carbon dioxide in tons to flush oil from abandoned oil fields. Lakna estimates that when the filter captures 1 ton of carbon dioxide per day, that will be the moment when his filter becomes a success in the oil and gas as well as gardening markets. But the reality he must face now is waiting for venture capital to fund the development of a prototype device that can produce 1 ton of carbon dioxide per day. Due to a lack of investment, a small company that was preparing to commercialize its results finally closed down recently. 　　Using air capture technology to address climate change faces huge economic challenges. Only when a reasonable price is set for carbon investment can this technology take off. If such a scenario becomes a reality, it could open up a new market with enormous potential: synthesizing fuel from thin air. Case said that mixing the captured carbon dioxide with hydrogen can produce fuel. Fuel produced by capturing carbon dioxide from the air does not result in net emissions, as the carbon dioxide it releases comes from the air itself. 　　Of course, hope still remains. If we can switch on a large scale to solar, wind, and nuclear energy in a timely manner, it is not too late to avoid the climate crisis. However, if this cannot be done, the air filter might serve as a lifeline in a last resort. However, this will also be a difficult task. At current emission levels, we will need filter systems with a capacity of 20 million tons per day to absorb the carbon dioxide emitted by the transportation sector. 　　385 parts per million: This is the current level of carbon dioxide in our atmosphere. Although this represents only an increase of 1/1,000,000 compared to before humans started messing things up, the polar ice caps are beginning to melt, climate patterns are changing, and plants and animals are migrating toward the poles in search of suitable habitats. How to deal with carbon dioxide in the atmosphere has become an important issue of global concern. News source: Science and Technology Daily