Only 400 degrees is needed to produce "net zero emission" green energy!

Produced by: Science Popularization China

Authors: Chen Jintao (Beijing University of Aeronautics and Astronautics), Chen Lin, Hao Yong, Liu Mingkai, Wang Bin, Guo Ke (Institute of Engineering Thermophysics, Chinese Academy of Sciences)

Producer: China Science Expo

Due to its advantages of zero carbon, greenness and high energy density, hydrogen energy will definitely play an important role in the future energy structure. It is of great significance for the adjustment of energy structure, low-carbon development of industry and the realization of "dual carbon" goals.

【用】The inextricable bond between the Beijing Winter Olympics and hydrogen energy

Hydrogen energy can be used in many areas.

Take the 2022 Beijing Winter Olympics as an example. All carbon emissions generated by this Winter Olympics have been neutralized, and it is called the "greenest" Winter Olympics. Behind the "greenest" are a lot of "technology and hard work", especially in the use of hydrogen energy.

First of all, unlike previous Olympic Games that used liquefied natural gas or propane as torch fuel, the Beijing Winter Olympics torch "Flying" is ignited by hydrogen, **using the world's first high-pressure hydrogen storage torch, **which has successively solved many technical problems such as hydrogen flame visibility, adaptability to complex surfaces, large-scale decompression, safe use of hydrogen, and hydrogen fuel storage, achieving zero carbon emissions for the torch in the history of the Winter Olympics for the first time.

Beijing Winter Olympics lighting ceremony scene

(Photo source: CCTV official website)

In fact, both Olympic Games held in Beijing have an inseparable relationship with hydrogen, and the contribution of hydrogen energy to environmental protection is not limited to the torch.

During the 2008 Beijing Summer Olympics, my country's first hydrogen refueling station was built in Beijing, achieving a breakthrough from "0 to 1" for hydrogen fuel cell vehicles. During the 2022 Winter Olympics, a total of 816 hydrogen fuel cell vehicles will be put into use, becoming the main means of transportation, achieving a breakthrough from "1 to 100" for hydrogen fuel cell vehicles, greatly reducing pollution emissions.

Hydrogen buses running in the Winter Olympics area

(Photo source: CCTV official website)

After years of in-depth research, people have gone from being afraid of hydrogen to having high hopes for it today. Hydrogen energy has already occupied an irreplaceable place in the process of energy structure transformation. The Beijing Winter Olympics has provided a world-class showcase for hydrogen energy, allowing the use of hydrogen energy not only in the air and on the ground, but also in the hearts of the general public.

[Breaking] Traditional hydrogen production process: carbon emissions follow you everywhere

If we want to use hydrogen energy safely and conveniently, the first thing we need to solve is the problem of hydrogen production.

Hydrogen is a secondary energy source that cannot be obtained directly from nature and needs to be prepared by other means. As can be seen from Table 1, the traditional methods of hydrogen production mainly include: hydrogen production from fossil energy, industrial by-product hydrogen, electrolysis of water and other methods. At present, the two main methods of hydrogen production are industrial natural gas reforming and coal gasification.

Table 1 Current status of hydrogen production structure in the world and China

(Data source: Reference [1])

Industrial natural gas reforming is the most widely used hydrogen production method in the world, accounting for more than 62% of the total hydrogen production. The main advantages of natural gas reforming are that natural gas is an abundant energy source and the main energy source with the lowest carbon content. The cost of mining is very low. After long-term development, it has formed a complete and mature technology, which is easy to expand the production scale.

But this method is not environmentally friendly. Natural gas reforming involves a series of chemical reactions that convert methane into hydrogen, a process that emits large amounts of carbon dioxide, exacerbating climate change issues.

At the same time, the process has a high reaction temperature (800-1000 degrees Celsius) , and the industry generally uses the method of burning part of the methane to supply the reaction heat, which directly leads to high energy consumption and high carbon dioxide emissions per kilogram of hydrogen produced, and leads to a decrease in the amount of hydrogen that can be produced per cubic meter of natural gas. Every kilogram of hydrogen produced emits 8-11 kilograms of carbon dioxide into the atmosphere.

Schematic diagram of hydrogen production-storage-transportation industry chain

(Photo source: veer photo gallery)

Another major way to produce hydrogen is coal gasification. my country's current energy utilization structure is still dominated by coal, and coal resources are relatively sufficient and the cost is relatively low, so coal gasification is widely used in my country.

However, the process of coal gasification hydrogen production is complicated, and compared with industrial natural gas reforming hydrogen production, it consumes more energy and has higher carbon emissions. Coal gasification hydrogen production technology emits 20-25 kg of carbon dioxide per kilogram of hydrogen. In addition, coal gasification is more likely to produce other pollutants such as sulfur dioxide and nitrogen oxides, which can easily cause air pollution. Therefore, the comprehensive economic and environmental benefits of coal gasification hydrogen production are not as good as natural gas reforming hydrogen production.

However, it must be said that both of the above two traditional hydrogen production technologies are accompanied by greenhouse gas emissions to varying degrees. In the context of "dual carbon", directly using traditional hydrogen production technology to carry out large-scale production of hydrogen energy will lead to an irreconcilable contradiction between hydrogen energy and carbon emissions, which seriously restricts the efficient production and widespread use of hydrogen energy.

However, if we can capture all the carbon dioxide produced in the process of converting carbon-containing energy into hydrogen energy, and seal it or convert it for use, we can significantly reduce or even avoid carbon emissions, and make hydrogen produced from carbon-containing energy into truly "sustainable" and "green" hydrogen energy. Can we do this? The answer from Chinese scientists is: Yes.

Hydrogen Energy

(Photo source: veer)

[Stand] Breakthrough in the principle of natural gas hydrogen production with "net zero emissions"

The Distributed Energy Supply and Renewable Energy Laboratory of the Institute of Engineering Thermophysics, Chinese Academy of Sciences , proposed for the first time a new principle of sequential separation of multiple products and a new method of methane steam reforming driven by sequential separation, achieving a breakthrough in the principle of "net zero emission" natural gas hydrogen production under mild conditions of 400 degrees Celsius.

With this new technology, theoretically 4 cubic meters of hydrogen can be produced from every cubic meter of natural gas. The actual test result is about 3.85 cubic meters, which is more than 50% higher than the unit hydrogen production of industrial natural gas reforming (2.5 cubic meters). The elimination of combustion and the reduction of energy consumption for product separation have reduced the energy consumption corresponding to the production of each kilogram of hydrogen by 20-40%.

At present, the prototype developed by the team has achieved a methane conversion rate of >99%, a hydrogen and carbon dioxide yield and selectivity of >99% under mild conditions of 400 degrees Celsius and normal pressure, thereby directly obtaining high-purity hydrogen and carbon dioxide. It has also completed a reliability verification of up to 3 weeks and 6,000 cycles, preliminarily demonstrating the broad prospects for the transformation and application of this technology.

At the same time, in this new technology, all carbon elements in natural gas are directly captured in the form of high-purity carbon dioxide through orderly separation of multiple products, avoiding direct emission of carbon dioxide into the atmosphere. The technology can produce high amounts of hydrogen and achieve "net zero emissions" at the same time, realizing the dream of "having your cake and eating it too".

【Science】Sequential separation + gradual collection + high-purity capture = net zero emissions

So, how did the researchers achieve this breakthrough in the principle of hydrogen production?

First, by separating the target products hydrogen and carbon dioxide in sequence, natural gas is consumed and converted to produce more hydrogen and carbon dioxide through reactions. In this process, the consumption ratio of natural gas increases step by step with the completion of each hydrogen production and decarbonization step until it is finally 100% converted.

Secondly, the hydrogen and carbon dioxide produced in each intermediate separation step are collected to obtain high-purity hydrogen and high-purity carbon dioxide products respectively, and the optimal conversion effect of natural gas raw materials into hydrogen and carbon dioxide products is achieved. At the same time, the sequential separation of the two products can produce the most favorable pressure conditions for separation, thereby minimizing the energy consumption of the separated products.

Schematic diagram of the experimental platform

(Image source: Reference [2])

Unlike traditional hydrogen production technology, this new principle does not deliberately pursue the one-time conversion of natural gas into hydrogen, so it does not require a very high reaction temperature. However, by changing to a gradual hydrogen production route and optimizing the corresponding process, it can achieve the same 100% conversion effect of natural gas as traditional hydrogen production.

Stability of gas production and H2/CO2 ratio over 6000 cycles

(Image source: Reference [2])

The biggest contribution of this technology to emission reduction is that while achieving direct capture of high-purity carbon dioxide and reducing carbon dioxide emissions, it also transforms carbon dioxide from a difficult-to-treat waste gas into a resource with multiple potential uses.

For example, it can be injected into oil wells to increase crude oil recovery, or directly injected into the ground for storage; it can be used as a chemical raw material, as well as for food processing and preservation, medical purposes, firefighting, etc. Facing the future energy structure dominated by renewable energy, another important conversion pathway for carbon dioxide is to convert it into high-value-added chemicals (such as formic acid, methanol, etc.) through green electricity (such as photovoltaics), and further manufacture a wide range of industrial products.

This new technology has two significant advantages: high-purity carbon capture and complementarity with renewable energy. It will help promote the accelerated penetration of renewable energy in the fields of energy, chemical industry, etc.

[Hope] "Net zero emissions" will show its strength!

The main significance of this "net zero emission" hydrogen production technology under mild conditions is that, under the background of the "dual carbon goals" and the major national demand for vigorously developing renewable energy, it changes the traditional extensive energy use and hydrogen production model and develops sustainable hydrogen production technology suitable for the characteristics of my country's energy structure.

The new principle of orderly separation of hydrogen and carbon dioxide products has enabled this new technology to achieve breakthroughs in many aspects, such as reducing hydrogen production temperature and energy consumption, integrating hydrogen production and decarbonization, and miniaturizing equipment, providing a new perspective for examining the entire chain of hydrogen energy technology.

Schematic diagram of distributed clean energy multi-energy complementary energy system (self-made)

(Image source: self-made by the author)

This technology is expected to promote the transformation of hydrogen production ideas from the current centralized, large-scale to distributed, small-scale, and object-oriented, which is of great significance to the large-scale development of low-carbon, sustainable hydrogen energy technology.

First of all, the new technology can significantly reduce the high carbon dioxide emissions associated with hydrogen production based on carbon-containing energy, reduce energy consumption, and improve energy utilization efficiency, making hydrogen energy based on carbon-containing energy sustainable.

Secondly, in response to the challenges currently encountered in all links of the entire chain of hydrogen energy technology, this technology uses natural gas as a carrier to better solve the problems of "production", "storage" and "transportation" of hydrogen energy, thereby significantly reducing the storage and transportation costs and safety risks of hydrogen energy, and accelerating the development, application and popularization of hydrogen energy.

Thirdly, the idea of ​​distributed hydrogen production based on natural gas can make full use of the existing gas pipeline site infrastructure and significantly reduce investment costs.

Finally, distributed hydrogen production coincides with the distributed characteristics of low-carbon energy such as solar energy and industrial waste heat. The combination of the two can not only further enhance the sustainability of hydrogen energy, but also enhance the absorption capacity of renewable energy by leveraging the advantages of carbon-containing energy.

Conclusion

Reducing carbon emissions is the common goal of fossil energy technology and renewable energy technology. To achieve this goal, we need to start from the reality of the energy structure, start from both "saving" and "increasing", and develop efficient and low-carbon fossil energy utilization technology, stable and low-cost renewable energy technology.

Therefore, on the basis of clean and efficient use of fossil energy (coal, natural gas, etc.), we must further leverage this advantage of our dominant position to accelerate the development of renewable energy such as solar energy, while achieving the decarbonization of fossil energy technology, thereby achieving a win-win situation for both while assisting energy transformation.

The "dual carbon" strategy is by no means a one-sided fight in a certain field or industry, but requires joint action from all sectors of society to jointly seek green and sustainable development solutions. In this process, scientists are responsible for opening up new ideas and finding new breakthroughs. The road ahead is long but also bright, and we will reach our destination if we keep going.

References:

1. Liu Shangze, Yu Qing, Guan Jian. Current status and prospects of hydrogen energy utilization and industrial development[J]. Energy and Energy Conservation, 2022, No.206(11):18-21.DOI:10.16643/j.cnki.14-1360/td.2022.11.038.

2. Yunyi Ling, Hongsheng Wang, Mingkai Liu, et al. Sequential separation-driven solar methane reforming for H2derivation under mild conditions[J]. Energy Environ. Sci., 2022, 15, 1861. DOI: 10.1039/d1ee03870b.