工作温度1000℃！沙特拟制造全球首台光热发电粒子吸热器

2018-02-07    轉載自: http://www.cspplaza.com/article-11414-1.html

目前，沙特国王大学（KSU）机械工程学教授Hany Al-Ansary正联合美国桑迪亚国家实验室（Sandia National Laboratories）在该国利雅得附近开展塔式光热发电粒子吸热器（PHR）的技术研究工作。

　　据了解，上述研究属于新型太阳能热发电技术，其工作温度可达到1000°C左右，几乎是目前熔盐塔式光热发电系统工作温度（565°C）的两倍，有望在提高系统工作效率的同时降低光热发电成本。

　　冷热罐均可安装在集热塔内部

　　与塔式熔盐光热电站中的储罐布置方式不同，采用粒子吸热器的光热电站的热罐和冷罐可以与换热器一起安装在集热塔的内部，这样可以减少泵的使用，从而降低相关成本。

　　在一座采用粒子吸热器的装机20MW的塔式光热电站中，集热塔高150米，直径约30米，储罐可垂直安装于集热塔内部，冷罐的位置大约在集热塔中部，在此情况下，只需将吸热颗粒从塔身中间泵到顶部对其进行加热。

　　同时，桑迪亚国家实验室研究小组展开了一项创新测试，他们通过设置一种人字形障碍物，减缓了沙粒的下降速率。如果没有障碍物的话，即使只有1米高的落差，沙子的下降速度也会增至5m/S或6m/S。

　　在集热过程中，受阻的粒子流在吸热器的各个集热面都会维持密集的“粒子帘”状态，并吸收太阳辐射。

　图：粒子吸热器技术原理（来源：SUNSHOT）

　　Al-Ansary团队的研究人员发现，由于人字形障碍物的设置，在实验室状态下，粒子温度达到了约1000°C，而且没有出现沙粒结块现象，甚至在小试装置中也达到了700°C以上的温度。

图：设置人字形障碍物减缓粒子下降速率（来源：桑迪亚国家实验室）

　　沙子或为最佳粒子选择

　　配置储热系统的塔式光热电站顺应未来低碳发展的需要，并能实现24小时发电。粒子吸热器技术有可能降低塔式光热发电的成本，因为它可以将现有565°C的熔盐工质运行温度提高近一倍。

　　高温意味着高效。粒子吸热器能够与高效率的超临界二氧化碳和吸气式布雷顿动力循环相匹配，使太阳能在高温热化学过程中取代化石燃料，比如满足在800°C的温度下分解水以提取氢气或在1300℃下的喷气燃料中制造碳中性太阳能燃料。

　　目前，研究人员已经研究了多种类型的粒子，而在此过程中，沙子的低成本优势得以显现。当系统输出功率为5MW时，这种粒子吸热器将需要2000吨沙子进行循环工作。

　　Al-Ansary指出：“我们对沙子工质十分感兴趣，因为无论用量多大，你都无需考虑其成本问题。”一定程度上来说，一些材料，特别是工程粒子可能在初始投资中占据相当的比重。“当你需要数千吨工程粒子时，你可能需要投入较高的资金。”

　　沙特电力公司助力粒子吸热器技术走向商业化

　　一直以来，有很多清洁能源领域的创新性研究在实验室研究获得成功后，由于缺乏商业化试验而导致相关技术最终“流产”。然而粒子吸热器研究小组非常幸运，他们得到了沙特电力公司的支持，并可以积极开展相关工作。

　　目前，沙特电力公司正在资助和协助研究小组利用红砂作为吸热介质开展研究工作，并致力于推动该项目于2018年进入商业化测试阶段，这对该技术的推广至关重要。

　　与熔盐储热类似，沙子每天损失的能量不到其储存能量的1％，但是其温度几乎可以达到熔盐工质的两倍。Al-Ansary表示，这是其对粒子吸热器感兴趣的主要原因，同时他本人拥有15项专利，相关研究成果还在一些行业期刊上获得发布。

　　“熔盐工作温度限制在565°C左右。”他说，“但是，采用不同种类的粒子作为吸热介质，可以获得更高的温度，甚至高达1000°C。我们小组采用不同的围护结构设计，使用简单的砌筑材料和隔热性能良好的箱体，能够实现每天的热损失降低到1％以下。”

　　全球首台商业化粒子吸热器拟于2018年年中开始制造

　　据了解，沙特电力公司将制造世界上第一台商业化粒子吸热器，并计划在1月和2月完成最后的原型测试后，于2018年年中付诸实施。

　　“沙特电力公司表示，他们正在准备下一个阶段，大概输出功率约5MW，并希望能成功发电以出售电力。”他说。

　　“一旦我们完成了对KSU小型100kW电力设施的测试，且测试结果得到确认，沙特电力公司便可以开展他们的工作了。”

　　“事实上，沙特电力公司的部分工程师每天会和我们一起开展研究工作，并进行一定程度地调整。在我们的共同努力下，我们可以确保粒子吸热器的设计是成熟的。当我们进入第三阶段的工作时，其将完全实现商业化。”

　　另外，桑迪亚国家实验室建设的光热发电系统镜场面积更大，这对早期测试起着非常重要的作用。虽然位于利雅得的测试设备较小，但是其可以作为完整的发电系统（含换热器和燃气轮机系统）进行全流程演示。

　　缺乏电力的沙特偏远地区市场潜力巨大

　　事实上，除利雅得外，沙特阿拉伯的部分缺乏电力的偏远地区太阳能资源也十分丰富（DNI值约为2600kwh/㎡/y），适宜开发光热电站。

　　Al-Ansary说：“沙特国家电网事业部对这个想法十分感兴趣，因为我国许多偏远地区都缺乏电力，这些地区至多建设装机5MW或者10MW的燃气电站。“他们告诉我，这些地区大约需要1GW的装机量，因此他们可以建造约200座大小的电站。”

　　与熔盐塔式光热发电系统不同，燃气电站利用热压缩空气进行发电，目前装机5MW的燃气电站已实现商业化应用。这种涡轮机已通过欧盟直接燃气加热接收器的测试。这种经过验证的设计与光热发电的粒子吸热器的设计概念相契合，只需在设计上进行些许更改。

　　正如Al-Ansary所述，这项研究从实验室规模到走向商业化是一个不寻常的过程，需要冷静与信心。尽管创新的清洁技术对于创造一个宜居的环境至关重要，但是要实现轻松的跨越绝非易事。“但是，幸运的是，我们获得了支持。”Al-Ansary补充道。

Particle Receivers to Get First Commercial Trial – in Saudi Arabia

Posted on  January 18, 2018  Author   Susan Kraemer

轉載自:    http://www.solarpaces.org/particle-receiver-first-commercial-trial-2018

A new solar technology is twice as efficient, cutting the cost of solar thermal energy, by raising operating temperatures to 1,000°C, almost twice the 565°C molten salt temperature in current concentrated solar power (CSP) tower plants.

For most innovative research in clean energy, the dreaded “Valley of Death” after lab scale success is the sad place where great innovations go to die for lack of commercial trials.

But that will not be the case for particle heating receiver (PHR) technology that was first conceptualized at Sandia National Laboratories and is now being researched worldwide.

PHR is cutting edge technology for tower CSP, a form of solar that converts the sun’s heat to power. CSP with thermal energy storage is an important key to powering a carbon-constrained future, because its thermal storage enables solar generation at any time of day or night.

There is an unobstructed path from lab to commercialization for Hany Al-Ansary, Professor in Mechanical Engineering at King Saud University (KSU) and international collaborators investigating one alternative approach using a red sand abundantly available near Riyadh in Saudi Arabia.

The KSU approach relies on the sand flowing through a cavity receiver in the tower, while other promising approaches use different particles in free fall or in an enclosed receiver.

Saudi Arabia will be first to commercialize particle receiver technology

The Saudi Electricity Company is funding and assisting with the research into using the red sand approach for heat absorption in PHRs, and intends to enter the planning phase of a commercial trial in 2018. This sort of commercial support and trial is essential to developing technologies.

Like molten salts, sand loses less than 1% of its stored energy daily, but it can achieve a temperature almost twice as high. This is the main reason for the interest in particle receivers, according to Al-Ansary, who holds 15 patents and has published in peer-reviewed journals.

“Molten salt is limited to around 565°C,” he said. “but depending on which type of particles, you can get much higher temperatures, up to 1,000°C. Our group worked on different containment structure designs, and with simple masonry materials and a well-insulated tank, we reduced heat loss to under 1% per day, similar to molten salt.”

What is the advantage of particle receivers?

Tower CSP with thermal energy storage is an important key to powering a carbon-constrained future, because its thermal storage enables solar generation at any time.

Particle receiver technology has the potential to reduce the cost of tower CSP, because it can nearly double today’s power tower temperatures, which top out in molten salt technology at 565°C.

High temperatures increase efficiency, making particle receivers a good fit with high efficiency supercritical CO2 and air-breathing Brayton power cycles, and enable solar to replace fossil fuels in high-temperature thermochemical processes like splitting water to extract hydrogen at 800°C or make carbon-neutral solar fuels like jet fuels at 1,300°C.

Researchers have investigated many materials for the particles. The advantage of sand is cost. At 5 MW, this particle receiver design would cycle more than 2000 tons of sand through its system.

“We’re excited about sand because it doesn’t matter how much you need, the cost is almost nothing,” he pointed out. At scale, some materials, particularly engineered particles, could become a considerable fraction of initial costs. “When you are talking about thousands of tons of an engineered material, that can become prohibitive at some point.”

Al-Ansary presented the paper on the results of the red sand tests in particle receiver tower CSP at the 23rd SolarPACES Conference in Chile.

How the particle receiver works

At a 20 MW-electrical scale, the receiver aperture would be about 10 meters wide by 10 meters tall and sand would be fed from the hopper to fall in a curtain a few cm thick through a 10 to 15 meter wide slot, exposing the sand particles to the heat of 1000 suns of intensely focused sunlight from a solar field of mirrors reflecting sunlight into the receiver aperture.

Unlike the energy storage tanks in molten salt CSP, the hot and cold storage tanks could be stacked right inside the receiver tower along with the heat exchanger, so there is much less pumping of storage material, reducing parasitic costs.

For a 20 MW plant, the tower would be about 150 meters tall and about 30 meters in diameter with the storage tanks stacked vertically inside. The discharge point of the cold tank would be about half way up the tower, “so we only need to lift the particles from the middle to the top to heat them.”

The sand particles never fall fast, thanks to chevron-shaped obstacles that slow their descent, an innovation previously tested at Sandia in the US by the international research group. Without the obstacles, sand accelerates to 5 or 6 meters per second, even in just a 1 meter drop height.

The obstructed flow maintains a dense curtain of particles everywhere in the receiver, so that all the concentrated radiation is absorbed by the falling particles.

With particles slowed by the chevrons, Al-Ansary’s group got results of about 1,000°C in the lab without the sand agglomerating, and even out in the field, attained temperatures above 700°C.”