Shulou(Shulou.com)11/24 Report--

Hao Jiahao

College of Future Technology, University of Chinese Academy of Sciences

Training unit: Institute of physical and Chemical Technology, Chinese Academy of Sciences

As we all know, carbon dioxide is not only the main emission of global industry, but also a typical greenhouse gas. From this point of view, it can be said to be a proper waste.

As we all know, we can be said to be in the forefront of the world in controlling carbon emissions, focusing on a responsible big country. From this point of view, this carbon dioxide is harmful to us rather than good, ah, it is really the case. Is it?

Don't worry, we have cool techs, turn the waste of carbon dioxide into a magic weapon of energy storage, make a large carbon dioxide "portable battery", and let it also contribute to the realization of the "double carbon goal".

Let's first understand the concept of energy storage.

The concept of energy storage, that is, energy storage, refers to the process of converting one form of energy into another form of energy through a medium or equipment, and then releasing it when needed. Energy storage is divided into cold storage, heat storage and electricity storage. Portable battery is a kind of electricity storage.

The idea of storing electricity did not come out of thin air. As far away as ancient Greece, it has been known that amber fragments can produce electricity to attract light particles after friction. However, the electricity generated by friction is very easy to disappear. Marsenbrock, from the University of Leiden in the Netherlands, invented the "Leiden bottle" in 1746 because he saw that the electricity collected easily disappeared from the air, trying to find a way to preserve it. This is the first device to store electricity.

Leiden bottle | Photo Source: Wikipedia technology is always evolving over time. Nowadays, we have a variety of ways to store electricity, such as electrochemical energy storage, pumped energy storage, compressed air energy storage, carbon dioxide energy storage and so on.

Why store energy? At present, much of the electricity we use comes from coal-fired power generation. Burning coal for power generation produces a lot of carbon dioxide, which is a greenhouse gas and is not friendly to our environment. Therefore, we think of using renewable energy such as wind and solar energy to achieve energy transformation and reduce carbon dioxide emissions from the source.

According to data released by the National Energy Administration on July 31, the installed capacity of renewable energy in China reached 1.322 billion kilowatts by the end of June, historically surpassing coal power and accounting for about 48.8 percent of the country's total installed capacity. Data show that at present, the total installed capacity of power generation in the country has reached 2.71 billion kilowatts, an increase of 10.8 percent over the same period last year. Among them, hydropower installed 418 million kilowatts, wind power installed 389 million kilowatts, photovoltaic power generation installed 470 million kilowatts, biomass power generation installed 43 million kilowatts. Relevant institutions predict that by 2050, renewable energy is expected to account for 78.0% of China's energy system.

However, wind energy and solar energy have significant unfavorable factors such as intermittence, volatility and uncertainty, and the electricity generated is unstable, which is difficult to match with the different electricity consumption of users during the day and night. Moreover, the electricity consumption of users varies not only during the day and night, but also in different seasons.

According to the investigation, the peak period of power demand is in winter and summer every year, the characteristics of "usually abundant, cutting-edge tension" and "overall abundance and local tension" of power supply and demand in our country are becoming more and more obvious. The just-concluded peak summer, the rising national temperature and the continuous release of air conditioning cooling load; the coming peak winter, the heating demand brought about by the temperature drop, all bring great challenges to energy consumption.

At this time, the energy storage system plays the role of "cutting peaks and filling valleys" for the power grid. It is like a large portable battery, which is stored when it uses less electricity but generates more electricity, and is released when it uses more electricity but does not generate enough electricity. If we put a portable battery in every link of power generation, transmission, distribution and electricity consumption, we can match the power generation with the electricity consumption of users, which can not only meet our electricity demand, but also reduce the waste of excess power.

What is the carbon dioxide "portable battery" technology? We mentioned pumped energy storage, compressed air energy storage and carbon dioxide energy storage, all of which are large-scale and long-term energy storage technologies that can be used for peak regulation. But different ways of energy storage also have their own advantages and disadvantages. Pumped storage is a kind of energy storage technology that converts electric energy into water potential energy. Its installed proportion is large and its application is relatively mature. However, there are some objective problems, such as high requirements for geographical environment, long construction period, large initial investment, destruction of ecological environment and so on.

Pumped Storage | Photo Source: Tongshan County people's Government compressed air energy storage and carbon dioxide energy storage are a kind of compressed gas energy storage technology.

Compressed air energy storage tank | Photo source: China National Energy Reserve

Carbon dioxide energy storage system | Photo Source: Beijing Bouridingneng Power Technology Co., Ltd. in terms of physical properties, the critical point of carbon dioxide (7.39 MPa and 31.4 ℃) is easier to liquefy than air (3.77 MPa and-140.5 ℃), and carbon dioxide is non-toxic, non-flammable and safety grade A1. And supercritical carbon dioxide (SCO) has excellent thermodynamic properties: low viscosity, high density and good thermal conductivity. In the same state and pressure, the storage density of CO is higher than that of air, and the liquid storage is the highest, so the carbon dioxide energy storage system has higher energy storage potential.

Carbon dioxide three-phase diagram and density change diagram carbon dioxide energy storage is a promising new large-scale long-term energy storage technology, which has the characteristics of high electricity-to-electricity conversion efficiency, high energy storage density, long life and low cost. it can meet the huge market demand of renewable energy, such as large-scale power consumption, power grid peak cutting and valley filling, thermal power energy storage and peak regulation, and has good economic and social benefits.

As shown in the figure, the carbon dioxide energy storage system is mainly composed of carbon dioxide high and low pressure storage tanks, compressors, turbines (steam turbines), cold storage heat exchangers and thermal storage subsystems. Its working principle can be divided into two processes: energy storage stage and energy release stage.

Basic schematic diagram of carbon dioxide energy storage system | Photo Source: during energy storage by the Institute of physical and Chemical Technology of the Chinese Academy of Sciences, the low-pressure gaseous carbon dioxide in the low-pressure storage tank is compressed by a compressor to a supercritical state. at the same time, the compression heat is absorbed into the intercooler and the heat is stored in the heat storage tank through the heat storage medium. finally, the carbon dioxide is liquefied and stored in the high-pressure storage tank by normal temperature water.

Basic schematic diagram of carbon dioxide energy storage system | Picture Source: when the Institute of physical and Chemical Technology of the Chinese Academy of Sciences releases energy, the carbon dioxide in the high-pressure storage tank is heated and gasified by the heater, and then enters the turbine to drive the turbine impeller to generate electricity. At the same time, the cold capacity of the low-temperature heat storage medium at the outlet of the heater is stored in the cold storage tank, and the carbon dioxide at the outlet of the last-stage turbine is returned to the low-pressure storage tank.

By inputting industrial trough electricity or wind power, the system stores carbon dioxide internal energy, pressure energy and thermal energy of heat storage working fluid, and releases carbon dioxide to drive turbine power generation at the peak of power consumption. in order to achieve renewable energy grid and grid energy storage peak regulation, at the same time, the system operation with heat load can also achieve regional heating, relying on the regional distributed energy system to achieve efficient multi-energy co-supply.

What scenarios can carbon dioxide energy storage be applied to? First of all, on the power generation side, the carbon dioxide energy storage system can act as portable battery of wind, light and other new energy plants and portable battery of coal-fired power plants.

Carbon dioxide energy storage technology is also very useful on the power grid side. we often see on the news that all kinds of large-scale power outages have caused huge economic losses to a large number of households or operating factories. if the distribution station of the power grid is equipped with carbon dioxide "portable battery", then we can use the electricity stored by carbon dioxide to give priority to power supply to some key areas and recover a lot of economic losses.

Similarly, we can also use carbon dioxide energy storage technology on the user side, such as some power-intensive industrial parks and offshore platform microgrids and so on.

Carbon dioxide energy storage in the future carbon dioxide energy storage is a new long-term large-scale energy storage technology, and it is in a critical period of technical demonstration and promotion. There is a trillion-level energy storage market behind it, which will produce huge economic benefits if it is popularized on a large scale.

At present, Energy Dome Company of Italy completed a pilot project of "carbon dioxide battery" of 4MW h in June 2022; in August 2023, the scientific research team of Institute of Physics and Chemistry of the Chinese Academy of Sciences also built the first demonstration and verification project of 100 kilowatt carbon dioxide energy storage in Langfang City, Hebei Province. In addition to demonstration projects, there are also larger, 100-megawatt projects in the pipeline. What is the concept of a 100 megawatt carbon dioxide energy storage system? For example, a carbon dioxide energy storage system of 100MW / 400MW ·h (100MW refers to its generating power, and 400MW ·h refers to its generating capacity). The capacity of 400MW ·h means that the system can generate 400000 kilowatt-hours of electricity. According to the monthly electricity consumption of 350 kilowatt-hours per household, the system can supply nearly a thousand users with one charge and discharge for a month. However, it takes only a few hours for the system to complete a charge and a discharge.

Countries that have added carbon-neutral carbon reduction targets to legislation (part of the table) | Image Source: at present, countries around the world have set dual-carbon targets in line with their national conditions, and China is no exception. From the perspective of advanced technology, carbon dioxide energy storage is a new technology that can support "carbon peak and carbon neutralization", which can ensure the grid connection and power grid security of high proportion of renewable energy, and accelerate the transformation of energy structure. at the same time, it can also produce good economic and ecological benefits. In addition to reducing carbon dioxide emissions from the source, carbon dioxide energy storage can also be combined with carbon capture technology. A large amount of carbon dioxide is stored in the process of compressed carbon dioxide energy storage. Storing this carbon dioxide as "portable battery" can reduce carbon dioxide in the atmosphere, thus alleviating Greenhouse Effect and maintaining the ecological environment.

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop). Author: Hao Jiahao

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.