气候解决方案:利用二氧化碳发电
Climate Solution: Use Carbon Dioxide to Generate Electricity
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2019-08-12 22:30
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火星译客

Sending atmospheric CO2 into underground methane hydrates could clean the air and create revenue

 将大气中的CO2送入地下甲烷水合物中可以净化空气并创造收益。

Climate Solution: Use Carbon Dioxide to Generate Electricity

The world is quickly realizing it may need to actively pull carbon dioxide out of the atmosphere to stave off the ill effects of climate change. Scientists and engineers have proposed various techniques, but most would be extremely expensive—without generating any revenue. No one wants to foot the bill.

世界各国正快速地意识到,我们可能需要积极主动地将二氧化碳抽离大气以削弱气候变化带来的不利影响。科学家和工程师们已经提出了各式各样的技术方案,但是大部分都太昂贵——不能产生任何收益。无人愿意为此买单。                                                            

One method explored in the past decade might now be a step closer to becoming practical, as a result of a new computer simulation study. The process would involve pumping airborne CO2 down into methane hydrates—large deposits of icy water and methane right under the seafloor, beneath water 500 to 1,000 meters deep—where the gas would be permanently stored, or sequestered. The incoming CO2 would push out the methane, which would be piped to the surface and burned to generate electricity, to power the sequestration operation or to bring in revenue to pay for it.

一项新的计算机模拟研究结果表明,过去十年里探索出的一种方案现在可能更接近实用。方案实施的过程中需要将空气中的CO2用泵打入甲烷水合物中,甲烷水合物是海底500-1000米的大量冰水和甲烷形成的沉积物,这些气体将会被永久储存或隔离在这里。被输送进来的CO2会将甲烷排出,排出的甲烷可被输送到地表,进行燃烧产生电能来支持固碳操作或者产生利润来支付固碳成本。                                                           

Many methane hydrate deposits exist along the Gulf of Mexico shore and other coastlines. Large power plants and industrial facilities that emit CO2 also line the Gulf Coast, so one option would be to capture the gas directly from nearby smokestacks, keeping it out of the atmosphere to begin with. And the plants and industries themselves could provide a ready market for the electricity generated.

大量甲烷水合物存在于墨西哥湾沿岸和其他海岸线上。排放CO2的大型发电厂和工业设备也坐落于墨西哥海湾区,因此有一种方案是直接从附近的烟囱捕获CO2,保证CO2一开始就无法进入大气。并且这些发电厂和工厂本身就可以为发出的电能提供一个现有的市场。                                                                                

A methane hydrate is a deposit of frozen, latticelike water molecules. The loose network has many empty, molecular-size pores, or “cages,” that can trap methane molecules rising through cracks in the rock below. The computer simulation shows that pushing out the methane with CO2 is greatly enhanced if a high concentration of nitrogen is also injected, and that the gas swap is a two-step process. (Nitrogen is readily available anywhere, because it makes up 78 percent of the earth’s atmosphere.) In one step the nitrogen enters the cages; this destabilizes the trapped methane, which escapes the cages. In a separate step, the nitrogen helps CO2 crystallize in the emptied cages. The disturbed system “tries to reach a new equilibrium; the balance goes to more CO2 and less methane,” says Kris Darnell, who led the study, published June 27 in the journal Water Resources Research. Darnell recently joined the petroleum engineering software company Novi Labs as a data scientist, after receiving his Ph.D. in geoscience from the University of Texas, where the study was done.

甲烷水合物是由冰冻的笼状水分子沉积形成。这种宽松的网络结构存在着很多分子大小的空隙,或者称之为“笼子”,它可以捕获从岩石裂缝中上升的甲烷分子。计算机模拟结果表明,如果同时注入高浓度氮气,那么CO2对甲烷的驱替作用将大大增强,气体交换是一个两步过程。(氮气随处可获取,因为氮气占据地球大气层的百分之七十八。)第一步,氮气进入网络结构的“笼子”,这将破坏“笼子”对甲烷分子的束缚,甲烷分子得以逃逸。在另一步中,氮气促进CO2在清空的“笼子”里进行结晶。研究负责人克里斯·达内尔表示,这个被扰动的系统“试图达到一个新的平衡;这个平衡中CO2更多,甲烷更少,”这项研究于6月27日发表于《水资源研究》期刊。达内尔在进行这项研究的德克萨斯大学获得地球科学博士学位之后,以一名数据科学家的身份加入了石油工程软件公司诺维实验室。

A group of labs, universities and companies had tested the technique in a limited feasibility trial in 2012 on Alaska’s North Slope, where methane hydrates form in sandstone under deep permafrost. They sent CO2 and nitrogen down a pipe into the hydrate. Some CO2 ended up being stored, and some methane was released up the same pipe. That is as far as the experiment was intended to go. “It’s good that Kris [Darnell] could make headway” from that experience, says Ray Boswell at the U.S. Department of Energy’s National Energy Technology Laboratory, who was one of the Alaska experiment leaders but was not involved in the new study. The new simulation also showed that the swap of CO2 for methane is likely to be much more extensive—and to happen quicker—if CO2 enters at one end of a hydrate deposit and methane is collected at a distant end.

2012年,一些实验室、大学和公司在阿拉斯加的北坡开展了一种有限可行性试验对该技术进行测试,在那里,甲烷水合物形成于深层冻土下的砂岩内。他们把CO2和氮气通过管道输送到水合物中。部分CO2最终被储存,部分甲烷被释放到同一条管道中。这就是实验的目的所在。美国国家能源技术部门的博斯维尔·雷表示,“克里斯·达内尔能从这项实验中取得进展是件好事”,博斯维尔·雷曾经是阿拉斯加实验的领导者一直,但他并未参与这次的新研究。这项新研究也表明,如果CO2在一个水合物沉积物的一端进入并且在另一端收集甲烷,那么CO2对甲烷的置换将会更加广泛和高效。

The technique is somewhat similar in concept to one investigated in the early 2010s by Steven Bryant and others at the University of Texas. In addition to numerous methane hydrate deposits, the Gulf Coast has large pools of hot, salty brine in sedimentary rock under the coastline. In this system, pumps would send CO2 down into one end of a deposit, which would force brine into a pipe that is placed at the other end and leads back to the surface. There the hot brine would flow through a heat exchanger, where heat could be extracted and used for industrial processes or to generate electricity. The upwelling brine also contains some methane that could be siphoned off and burned. The CO2 dissolves into the underground brine, becomes dense and sinks further belowground, where it theoretically remains.

这项技术在概念上与21世纪十年代初德克萨斯大学的史蒂文·布莱恩特等人研究的一项技术有所相似。除了大量的甲烷水合物之外,墨西哥湾的海岸线沉积岩下还存在着大量的热盐海水。在这个环境系统里,泵将CO2输送至沉积物的一端,这将会迫使盐水进入沉积物另一端的管道并回到表面。在流动过程中热盐水将会通过一个热交换器,热量被收集并用于工业生产或发电。这些上涌的盐水也包含了一些甲烷,可以将其抽取并燃烧利用。二氧化碳溶解在地下的盐水中,变得浓稠并继续沉到地下更深处,理论上它仍然存在。

Either system faces big practical challenges. One is creating a concentrated flow of CO2; the gas makes up only .04 percent of air, and roughly 10 percent of the smokestack emission from a typical power plant or industrial facility. If an efficient methane hydrate or brine system requires an input that is 90 percent CO2, for example, concentrating the gas will require an enormous amount of energy—making the process very expensive. “But if you only need a 50 percent concentration, that could be more attractive,” says Bryant, who is now a professor of chemical and petroleum engineering at the University of Calgary. “You have to reduce the [CO2] capture cost.”

两种系统都面临着巨大的实际挑战。其一是产生了CO2的集中流动;这种气体只占大气的0.04%并且大约占传统发电厂和工业设备烟囱排放的10%。例如,如果一个高效的甲烷水合物或者盐水系统需要输入浓度为90%的CO2,那么浓缩气体的过程就需要大量的能源——这将导致这个工艺过程非常昂贵。卡尔加里大学的化学和石油工程学教授布莱恩特说道:“但是如果你只需要将CO2浓缩至50%,那这会变得很有吸引力,你必须降低CO2的捕获成本”

Another major challenge for the methane hydrate approach is how to collect the freed methane, which could simply seep out of the deposit through numerous cracks and in all directions. “What kind of well [and pipe] structure would you use to grab it?” Bryant asks.

甲烷水合物方案的另一个大的挑战是,如何收集逸散的甲烷,它们可以轻易地通过大量的裂缝从沉积物中向各个方向逃逸。布莱恩特问道:“你将会使用哪种井槽(和管道)结构去捕捉它?”

Given these realities, there is little economic incentive today to use methane hydrates for sequestering CO2. But as concentrations rise in the atmosphere and the planet warms further, systems that could capture the gas and also provide energy or revenue to run the process might become more viable than techniques that simply pull CO2 from the air and lock it away, offering nothing in return.

鉴于以上事实,目前用甲烷水合物来封存CO2的经济动机微乎其微。但是随着大气中CO2浓度的升高和地球进一步变暖,能够捕获CO2并且提供能源或者收益来运行这些过程的系统将会比直接收集大气中的CO2进行封存且不产生任何回报的技术更加具备可行性。

ABOUT THE AUTHOR(S)

关于作者

Mark Fischetti

马克·菲斯凯蒂

Mark Fischetti is a senior editor at Scientific American,. He covers all aspects of sustainability.

马克·菲斯凯蒂是《科学美国人》的一名高级编辑。他涉猎了可持续发展的所有方面。

Credit: Nick Higgins

图片来源:尼克·希斯金

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