Coal, with the highest carbon content, is the main raw material to produce human carbon necessities via coal gasification to chemicals technology. How- ever, huge CO2 emission from the water-gas shift unit included in the coal- based chemicals process to increase the H/C ratio of syngas has caused great concern. Thus, a hybrid energy system that integrates renewable hydrogen from nuclear/renewable energy with coal to produce fuel and chemicals has been proposed. The applicability of hybrid energy systems in coal-rich countries, especially China and the United States, is analyzed as well as the carbon emission reduction potential and economic feasibility. The hybrid energy system is feasible in most coal-intensive countries and will lead to significant carbon emission reduction potential in the coming 5–15 years. Moreover, with the sharp decline in power cost from renewable/nuclear energy and the carbon tax introduction, the hybrid system shows potential to become economically competitive.
Context & Scale
Although renewable power generation has become the most promising alternative of fossil fuel power generation given its advantage to reduce carbon emission, fossil fuel remains essential for providing the necessary ‘‘carbon’’ for human life. The coal gasification to chemicals process is one of the major carbon necessities to supply technologies but emits copious CO2 due to the adjustment of the H/C ratio of syngas through the water-gas shift unit. It is clear that clean hydrogen supply is the key to CO2 emission reduction in coal chemical industries. Hence, a hybrid energy system has been proposed as an effective and reasonable solution to integrate nuclear/renewable energy with coal for low-carbon fuel and chemicals production. In terms of resources endowment, geographical distribution, and industry development, we found that the hybrid system is applicable in coal-rich countries and will lead to more than 1,200 Mt CO2 emission reduction potential, which is equivalent to 90% of the CO2 emission of Japan in 2014. Moreover, the feasibility of carbon-neutral cycle via CO2 capture and conversion system to produce fuel and chemicals with zero carbon emission is analyzed. From the economic point of view, power generation cost from nuclear/renewable energy and the carbon trading policy are essential for the economic superiority of hybrid energy systems. We believe that the decarbonization approach to fossil fuel utilization will be achieved with the development of key low-carbon technologies.
Context & Scale
Although renewable power generation has become the most promising alternative of fossil fuel power generation given its advantage to reduce carbon emission, fossil fuel remains essential for providing the necessary ‘‘carbon’’ for human life. The coal gasification to chemicals process is one of the major carbon necessities to supply technologies but emits copious CO2 due to the adjustment of the H/C ratio of syngas through the water-gas shift unit. It is clear that clean hydrogen supply is the key to CO2 emission reduction in coal chemical industries. Hence, a hybrid energy system has been proposed as an effective and reasonable solution to integrate nuclear/renewable energy with coal for low-carbon fuel and chemicals production. In terms of resources endowment, geographical distribution, and industry development, we found that the hybrid system is applicable in coal-rich countries and will lead to more than 1,200 Mt CO2 emission reduction potential, which is equivalent to 90% of the CO2 emission of Japan in 2014. Moreover, the feasibility of carbon-neutral cycle via CO2 capture and conversion system to produce fuel and chemicals with zero carbon emission is analyzed. From the economic point of view, power generation cost from nuclear/renewable energy and the carbon trading policy are essential for the economic superiority of hybrid energy systems. We believe that the decarbonization approach to fossil fuel utilization will be achieved with the development of key low-carbon technologies.
Introduction
Coal is a critical enabler in the modern world, providing 40% of the world’s electricity, and is an essential raw material for 70% of the world’s steel production and 90% of cement production. The conventional coal utilization pattern, however, causes a large amount of CO2 emission due to its high carbon content. According to the International Energy Agency (IEA), 70% of CO2 emission comes from fossil fuel combustion, in which coal occupies more than 40%. In view of the CO2 uptake capacity of natural world (~3 billion tons per year), CO2 emission needs to be reduced by 60%–70%, ca. 5–7 billion tons carbon per year, to maintain the balance of our ecosystem.1 It is urgent for coal, the principal CO2 emission contributor, to undergo low-carbon transformation.
The Paris agreements since 2015 have propelled governments to make domestic climate-change plans. Consequently, renewable energy will become a major source of power generation by 2030 accounting for 33% of global overall power generation by that time. Electricity from coal-fired power plants will continue to decline, and the proportion of renewable electricity is estimated to reach 35%–50% in most coal-rich countries. China, as the world’s largest coal consumer and CO2 emitter, accounting for more than 50% of the global coal consumption and 27% of global CO2 emission, has announced national strategies to raise the proportion of electricity generated by non-fossil fuel to 31% in 2020 and 50% in 2030. Although renewable power generation has already become the most promising alternative to fossil fuel power generation given its effectiveness in reducing carbon emission, fossil fuel remains essential for providing the necessary ‘‘carbon’’ for human life. Thus, it is necessary to transform most utilization of coal, a fossil fuel with the highest carbon content, from burning to producing necessities as raw material.
According to BP World Energy Statistics, the worldwide proved energy reserve is 1,405.4 billion tons coal equivalent (tce) at the end of 2015, whereof coal accounts for more than 55%. Major energy-consuming and -producing countries e.g., China, the United States (US), Russia, Australia, and India, have abundant proven coal re- serves that can provide 639.74 billion tce, accounting for 78.6% of the total global coal reserves (Figure 1). A low-carbon solution of coal utilization therefore needs to be developed due to the notably abundant coal reserves and an indispensable ‘‘carbon’’ provider for human development.
Since the 1950s, the main pattern of coal utilization as raw material is coal to chemicals via gasification, and this has already carved out a share of the chemicals market. According to the Gasification and Syngas Technologies Council (GSTC) Worldwide Syngas Database, chemical production shared 45% of coal gasification products in 2008, and from 2008 to 2010, 22% of new gasifier additions were intended for chemical production. However, the principal issue of current coal chemical projects is the resultant tremendous CO2 emission as shown in Figure 2A.2–6 Carbon emission of coal-based chemical industries mainly includes indirect CO2 emission from heat/ electricity supply and direct CO2 emission from the coal chemical conversion process, e.g., water-gas shift reaction.7–9 Notably, carbon emission of coal to carbide or coking process is 80% lower than for other processes since they only involve indirect carbon emission from the heat/electricity supply.10,11 Other coal chemical industries shown in Figure 2A always include the water-gas shift unit to increase the H/C ratio of the syngas that comes from the coal gasification unit by consuming a part of C. During this process, more than 50% of the carbon turns into CO212 and is emitted into the atmosphere.
It is clear that either clean power or hydrogen supply is the key to CO2 emission reduction in the coal chemical industries. Thus, it will be an effective and reasonable solution to integrate nuclear/renewable energy with coal for low-carbon fuel and chemicals production, i.e., hybrid energy systems (see Figure 2B). Nuclear/renewable energy can supply heat and electricity 13,14 for low-/high-temperature water electrolysis 15,16 processes to produce clean hydrogen, after which the hydrogen will be mixed with the syngas from the coal gasification unit to adjust the H/C ratio for downstream chemicals synthesis processes (Fischer-Tropsch synthesis,17 methanol to olefin,18,19 methanation process,20,21 etc.). In this case, the water-gas shift unit can be eliminated and the CO2 emission significantly reduced.
Herein, the hybrid energy system is proposed as a way to mitigate the carbon emission in coal-based chemical industries. Possibilities of hybrid energy systems replacing conventional coal conversion systems are analyzed in terms of countries’ resources, geographical distribution, and coal chemical industry development. Moreover, the carbon reduction potential and the economic feasibility of fuel/chemical productions via hybrid energy systems are estimated.
Hybrid Energy System for Coal to Chemicals
China Scenario
Feasibility Analysis from Geographical and Industrial Perspective. As a major part of China’s industrial sector, the output value of the coal-based chemical industry is around 132.2 billion US dollars ($), accounting for 3.7% of the gross industrial output value in 2014. Meanwhile, the related CO2 emission is about 495 million tons, occupying 7.2% of the total industrial carbon emission.22 Based on the incomplete statistics from the China Gasification Database released by the US Department of Energy (DOE), the main existing and developmental coal chemical plants and projects are shown in
Figure 1. Proven Energy Reserves Structure in 2015
The equivalent heat values of coal, oil, and natural gas are 0.714 tce/ton, 1.429 tce/ton, and 1.33 tce/1,000 m3. Coal accounts for more than 55% of the worldwide proved energy reserves, and coal resources in major energy-consuming and -producing countries account for 78.6% of the total global coal reserve.
Figure 4A. Excluding coal to carbide and coking processes, the remaining CO2 emission from the coal-based chemical industry is about 264 million tons. However, the emission intensity (8.57 tons CO2 per $1,000 of GDP) is 4.5 times the average industrial emission intensity (1.89 tons CO2 per $1,000 of GDP), and is far above the average domestic carbon emission intensity (0.94 tons CO2 per $1,000 of GDP).
Based on China’s development plan of coal-based chemical industry and the fore- cast of the industrial end products demand,23–26 the coal-based chemical industry is going to boom in the next 15 years. By 2020, the production capacity of coal- based synthetic natural gas (SNG), oil, olefin, ethylene glycol, and methanol will reach 30 billion Nm3/year, 20 million tons/year, 15 million tons/year, 5 million tons/year,23 and 80 million tons/year, respectively. With the full production capacity, the related carbon emission may increase to 0.89 billion tons by 2020 and 1.7 billion tons by 2030, and the carbon emission intensity may reach 8.95 kg CO2/$ in 2030. Researchers have predicted that the CO2 emission will keep increasing at an annual rate of 3% and the total emission will exceed 11.5 billion tons in the absence of government intervention in 2020, and may even exceed 15 billion tons in 2030.27 Accordingly, the Chinese government has set up a target to control the greenhouse gas emissions, whereby the domestic CO2 emission intensity will be reduced by 40%–45% in 2020 and 60%–65% in 2030 based on the GDP in 2005, and the emission peak should be reached in 2030. Along with the urgent demand for carbon reduction, a low-carbon strategy is vital for the sustainable development of the coal- based chemical industry.
(A) The carbon emission per unit production of major coal chemical industries.
(B) Low-carbon technology roadmap for fuel/chemical production in coal-based chemical industry.
From both geographical and sector perspectives, we assessed the viability of replacing a conventional coal system with a hybrid energy system. As shown in Figure 3A, the emission source is mainly located in the northwestern part of China, the middle- eastern area of China, and the eastern coast, which in total account for 65% of total CO2 emission. Not surprisingly, the distribution of CO2 emission is in line with the geographical distribution of energy resources, as illustrated in Figure 3B. China has abundant and widely distributed energy resources:28–32 the northwestern area and yellow river basin are rich in coal, natural gas, and solar and wind energy;28–30 the northeastern and mid-southern area has abundant biomass 32 and coal; although the eastern coastal area is deficient in fossil resource, offshore wind energy is mainly distributed here and most of the nuclear power projects under the government’s plans will be constructed in this area. The complementary distributions of fossil resource, nuclear energy, and renewable energy provide superior conditions for the implementation of a hybrid energy system.
The geographical distribution of coal-based chemical industry sectors coincides with the distribution of CO2 emission, as illustrated in Figure 3C. For instance, coal to ammonia and coal to methanol productions are mainly distributed, and thus contribute to 69.7% of CO2 emission, in the northern part of China (Inner Mongolia, Shanxi, Hebei), the northwestern area (Shaanxi, Xinjiang), the middle-eastern district (Anhui, Henan, Hu- bei), and the eastern coast (Shandong, Jiangsu).33 Moreover, more coal plants are under construction or planned in these regions, which may exceed 80% of the total production capacity, and thus will face a great challenge for CO2 mitigation. Owing to the abundant non-fossil resources in these areas, the integration of nuclear/renewable energy with fos- sil energy provides an efficient solution, i.e., both low-carbon strategy and sustainable economic development with constrained carbon emission, which will have profound implications for reduced carbon emission from China’s coal-based chemical industry.
Taking into consideration the energy resource distribution and energy consumption patterns, four large-scale low-carbon integrated systems are proposed in China (see Figure 3D): (1) integration of solar energy, wind energy, and natural gas with coal in the northwestern part, (2) integration of biomass with coal in the east-central area, (3) integration of natural gas, wind, and biomass with coal in the northern area, and (4) integration of nuclear energy, wind energy, and coal along the eastern coast.
Carbon Reduction Potential of Hybrid Energy System. Based on the geographical distribution of energy resources and coal-based chemical industry planning in China, a comparison of CO2 emission between the conventional coal system and hybrid system is conducted by assuming the utilization rate of the hybrid system at 40% in 2020 and 80% in 2030 (Figure 4B). This indicates that CO2 emission of the hybrid system is 647 Mt with emission intensity per GDP of 6.43 kg CO2/$ in 2020, which is 24% less than that in the conventional system. In 2030, the reduction capacity of CO2 emission from hybrid systems is equivalent to 90% of the Japanese CO2 emission (1,345 Mt) in 2014 and 33% of the European CO2 emission (3,696 Mt) in 2014, respectively, and the emission intensity is 2.67 kg CO2/$, which is 70% less than that in the conventional system of the same year. Both carbon emission and emission intensity in 2030 will reach 22% and 57% less than that in 2020.
Potential of Carbon Reduction for Coal Chemical Industry Worldwide
According to the World Gasification Database released by the DOE, there are numerous coal chemical plants existing or under construction in coal-rich countries (excluding China), such as the US, India, South Africa, Indonesia, and Australia (Figure 4C), and the major coal gasification projects include coal-based synthesis ammonia, oil, and SNG. Thus, there is huge potential to develop low-carbon hybrid energy systems in these countries. Feasibility analysis from a geographical and industrial perspective is conducted, taking the US as an example.
According to the US Energy Information Administration (EIA) data, coal resources in the US are mainly distributed in Appalachia in the east, the midwest, and west, which account for 22.6%, 28.1%, and 49.3% of the already explored reserves, respectively. The nuclear plants in the US are distributed in the eastern coastal area and central eastern area; the solar power plants are widely distributed in the eastern coastal and southwestern areas. According to the US wind resources investigation data published by the National Renewable Energy Laboratory (NREL) and the American Wind Energy Association (AWEA), the wind resources of the US are mainly distributed in the midwest and the Pacific, and Atlantic coastal areas. Biomass resources are mainly distributed in the northwestern and midwest areas. The geographical compatibility of coal resources and low-carbon clean energy make it possible for the implementation of a hybrid energy system. In fact the major clean energy labs in the US all have made techno- economic evaluations of the production of chemicals from hybrid energy systems.34,35 Thus, the following implementation of the hybrid energy system can be considered:
(1) coal-nuclear or coal-solar integration for the production of fuels/chemicals in the eastern area; (2) a coal-wind or coal-nuclear system for the production of fuels/chemicals in the midwestern plain area, and coal/biomass-wind system for the production of fuels/chemicals in northern midwestern area; (3) coal-biomass or biomass gasification for the production of fuels/chemicals in the northwestern area, and solar-biomass system for the production of fuels/chemicals in the southwestern area.
From the global perspective, 29% of the present synthesis ammonia is produced by using coal and petrol coke; coal-based methanol accounts for only 2% without considering the situation in China. In the global coal to oil planning, more than 20 million tons of coal to oil projects are under planning/construction, while Sasol’s synthesis oil scale is around 160,000 barrels per day.36 India, Indonesia, and Australia are also considering the coal to oil projects. According to the forecast made by IHS, there will be a 6% increase of global methanol demand on a yearly basis, while the increase for synthesis ammonia is around 2%. Table 1 shows the expected scale of major fuel chemicals production in 2020 and 2030.23 With full pro- duction capacity, the percentage of coal-based synthesis ammonia and methanol stay the same. The hybrid energy technology replacement rate is assumed to approach 40% and 80% in 2020 and 2030, respectively.
A comparison is made in Figure 4D regarding the carbon emission reduction potential of the coal to chemicals industry by using a hybrid energy system under the scenario in China and then globally. There is a more than 900 million tons CO2 emission reduction by using a hybrid energy system for global coal to chemicals in 2020, with China’s contribution to carbon emission reduction at 23%. In 2030, with the in- crease in global demand for fuel and chemicals, the total global carbon emission reduction will reach 1.5 billion tons with China’s contribution up to 80%. The major reason for this lies in the fact that China’s coal to gasification, coal to olefin, and coal to ethylene glycol will enter the rapid development period according to the planning of the National Development and Reform Commission (NDRC).
Economic Feasibility Analysis of Hybrid Energy Systems
The process flowchart of a comprehensive hybrid system for various fuel/chemical productions is presented in Figure 5A. In this system, nuclear/wind/solar-assisted water electrolysis is applied to produce hydrogen 16,37–39 in order to adjust the H/C ratio of syngas, hence to eliminate the water-gas shift process and to constrain the carbon emission. Besides this, biomass can be gasified to produce fuel and chemicals.40,41 and the amount of CO2 absorbed during the biomass growth is almost equivalent to the amount of CO2 produced during the combustion process. Thus it is possible to achieve zero carbon emission in a biomass-based system. The economic feasibility of the hybrid energy system, based on the energy resource prices, is presented in Table 2. All of the analyzed projects are assumed to be located in China. The fluctuation of coal price is in accord with the average coal price level in the last ten years in China, while the renewable electricity price is based on the cur- rent situation and forecast scenarios in the future 5–15 years.
Nuclear-Coal Integration System
A comparison is made in Figure 5B between a nuclear-assisted hybrid system and a conventional coal-based system 12 in terms of system economic performance. Referring to the current coal price ($111/ton) and nuclear power generation price ($41.7/MWh), the fuel/chemical costs via hybrid energy systems are 4%–38% higher than those of conventional coal-based systems, but will approach the present coal-based chemical production cost when the nuclear electricity price falls to $31.7/MWh. In most of the hybrid energy systems, hydrogen cost accounts for more than 60% of the total fuel/chemicals production cost. For instance, the proportion of renewable hydrogen cost is up to 83% in the nuclear-assisted ammonia production system due to its high demand for hydrogen. However, renewable hydrogen cost accounts for just 32% in a nuclear integrated coal to ethylene glycol system due to the long and complex process consuming large amounts of utilities (power and steam).
Wind/Solar-Coal Integration System
Renewable hydrogen cost is also the key component of a wind/solar integrated coal to chemicals system. The current hydrogen production cost from renewable energy (wind/ solar) assisted water electrolysis technology 15,38,39,46 is still 1.8–2.8 times the cost of a coal-based hydrogen production process but will further decline to $0.69/Nm3 and $1.6/Nm3, respectively, if considering the lowest wind and solar electricity price level (see Table 2). Referring to the present wind ($70/MWh) and solar ($100/MWh) electricity price, ammonia cost via the hybrid energy system is 2.4 and 3.4 times the cost of conventional coal-based system due to its high hydrogen demand (e.g., renewable hydrogen cost accounts for 88% and 92% of total ammonia cost). Therefore, the more hydrogen is required per unit product, the higher its production cost is compared with the conventional coal-based chemical production system. Even if adopting the lowest price of wind power and solar power, most chemical production costs in the hybrid energy system are still higher than those in the coal-based system (Figure 5C) except the wind integrated coal to ethylene glycol system, where the production cost is slightly (~7%) lower than in the coal-based system.
In terms of economic feasibility, based on the price fluctuation of fuel chemicals in the last 2 years and minimum acceptable rate of return (12%), the current wind/solar energy to ethylene glycol system can achieve relatively better economic performance due to its high added value. For the wind/solar energy to olefin system to achieve economic feasibility, the price of wind power needs to be lower than $50/MWh while that of solar power needs to be lower than $38/MWh, which is over 24% less than the lowest assumed solar power price level in our study. For the wind/solar energy to traditional bulk chemicals (methanol/synthetic ammonia/SNG) system, it is difficult to achieve economic feasibility because of their low added values.
Renewable energy power generation technology has been developing by leaps and bounds in recent years, and accordingly the wind/solar power generation costs have fallen sharply. Therefore, the wind/solar energy integrated coal to high value-added chemicals system is still promising.
Biomass-Coal Integration System
In the major food-producing areas, which are rich in straw and other biomass re- sources, utilization of biomass energy is an effective way to relieve the pressures of shortage of conventional energy resources and serious environment pollution. High value-added fuel and chemicals production via a biomass gasification process is similar to the process of coal gasification.47–49 Based on $31.7/ton of biomass raw material, the cost of ethylene glycol and methanol production is equivalent to the cost of a coal-based system, and the cost of biomass-based synthetic ammonia/ oil/SNG/olefin is 5%–10% lower that of the coal-based system (see Figure 5D).
To conclude, the current cost of hybrid systems to produce fuel/chemicals is more expensive than the conventional coal-based systems from an economic point of view. However, a break-even point will appear for some areas, depending on the market price of products. Taking into consideration cheap nuclear electricity price in the long run along with the introduction of a carbon tax, the hybrid system shows the potential to become economically competitive. For the wind/solar energy integration system, it is economically feasible to produce high value-added chemicals (olefin, ethylene glycol) rather than traditional bulk chemicals. With the falling prices of renewable energy due to the rapid development of renewable energy generation technology, the integration system will have a bright future. The economic performance of biofuel and biochemicals appears competitive with the conventional system given the low biomass price.
Carbon Tax Impact on the Economic Competitiveness of Hybrid Energy System
As one of the most cost-effective tools of emission reduction, carbon tax has attracted considerable attention from international organizations and governments. Most of the Nordic countries began to levy a carbon tax or related energy tax in the 1990s, and Australia began to levy a carbon tax of $23/ton CO2e on major domestic polluters in 2012. In 2013, China launched its ‘‘pilot emission trading scheme’’
in seven provinces and cities, and the carbon trading price fluctuates between $2 and $20 per ton CO2e.50 According to the State and Trends of Carbon Pricing Report released by the World Bank, the carbon prices in most nations or regions are still generally low, ranging from $5/ton CO2e to $15/ton CO2e. Only in some Nordic countries where carbon taxes are implemented do carbon prices can reach more than $50/ton CO2e.51 However, the researchers believe that the carbon tax that complies with the Paris agreement’s temperature targets should reach a level of $40–80/ton in 2020 and $50–100/ton in 2030.51 Based on the above literature, the carbon price is set between $5 and $50/ton CO2e in this paper. Taking the methanol production system as an example, to achieve the same production cost as that of the traditional coal to methanol system based on coal price of $79.4/ton, the nuclear power and wind power price in the hybrid system need to range between $23.4–$47.1/MWh and $17.5–$35.1/MWh, respectively, and the solar power price needs to be lower than 23.3$/MWh. Therefore, based on the electricity price assumption in Table 2, when the carbon tax is higher than $26.2/ton CO2e, the nuclear energy integrated coal to methanol system will become competitive; when the carbon tax is higher than $11.4/ton CO2e, the wind energy integrated coal to methanol system will become competitive. Due to the high price of solar photovoltaic power generation, the solar energy integrated coal to methanol system is at a competitive disadvantage in the short term.
Carbon-Neutral Cycle via CO2 Capture and Conversion System
In the process of using fossil resources for fuel and chemicals production, it is essential to minimize the occurrence of the reaction C / CO2 via a hybrid energy system. On the other hand, capture and transformation of CO2 into useful chemicals or fuels will be another major opportunity to achieve a carbon-neutral cycle. The utilization of CO2 as a feedstock to produce methanol,52,53 gasoline,54,55 and other chemicals has attracted wide attention. Sandia National Laboratories (SNL) has developed the direct solar thermolysis of H2O/CO2 reactor and analyzed the feasibility of liquid hydrocarbon fuel and chemicals production through such technology.35 Moreover, extensive studies on the process design, techno-economic analysis, and life cycle assessment 56,57 of renewable energy integrated CO2 conversion to chemicals systems have been put forward. This indicates that by implementing a renewable hydrogen and CO2 hydrogenation process for methanol, the life cycle greenhouse gas emissions alone can be reduced by 86% compared with using conventional petroleum-based fuels.56 In our previous work, we analyzed energy efficiency and economic feasibility of nuclear- or solar-assisted CO2 hydrogenation for a methanol production system.58 The overall energy efficiency of the carbon-neutral process is 21.9%–73% lower than that of the conventional coal to methanol system, but the production cost is 92%–134% higher given the $35/ton CO2 capture cost.58,59 Thus, the CO2 and renewable hydrogen con- version to produce a fuel and chemicals system is promising due to its carbon-neutral characteristic. However, there are also many challenges in this field, such as the development of low-temperature and high-efficiency CO2 hydrogenation processes,52,53 and the application of high-performance, low-cost, and environment-friendly CO2 capture technologies.60,61 Furthermore, a huge concern is the lower economic competitiveness due to its more expensive renewable hydrogen consumption relative to the conventional CO hydrogenation process.
Summary and Outlook
Coal utilization, in particular coal to chemicals, urgently needs low-carbon strategies due to their high carbon footprint. Here the hybrid energy system was proposed to meet the huge demand for coal chemical products while at the same time meeting the CO2 emission constraints. Geographically, such integrated systems are feasible as the renewable and nuclear energy resources fit well in most coal-rich countries, especially China and the US. Meanwhile, it will also be economically practical as the rapid development of renewable energy technologies will greatly reduce the cost of their power generation. As a result, the hybrid strategy will lead to a great reduction in carbon emission. In 2030, with the increasing global demand for fuel and chemicals, the total global carbon emission reduction will reach 1.5 billion tons with China’s contribution up to 80%. Hopefully this will herald the decarbonization approach to fossil fuel utilization with the development of related low-carbon technologies. However, there are still problems to be addressed in the hybrid energy system, such as the safety of the nuclear power plants and proper disposal of nuclear waste, the intermittent problems of wind/solar power generation, and the long-term stable supply of biomass.
SUPPLEMENTAL INFORMATION
Supplemental Information includes Supplemental Experimental Procedures, four figures, and eight tables and can be found with this article online at https://doi. org/10.1016/j.joule.2018.02.015.
ACKNOWLEDGMENTS
This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA02000000), the Youth Innovation Promotion Association of Chinese Academy of Sciences and the Key Technical Personnel of Chinese Academy of Sciences, and the Ministry of Science and Technology of China (grant 2016YFA0602603). The work was also supported by the Sail Plan Project (17YF1428600) funded by Shanghai Science and Technology Committee, and the Frontier Scientific Research Project, funded by Shell under contract no. PT19253.
AUTHOR CONTRIBUTIONS
Q.C. examined literature, wrote the main section of the manuscript, and provided supporting data on the carbon emission reduction and economic feasibility of hybrid energy systems. M.L. made language modification and suggestions on the manuscript structure. Y.G. and X.Y. made language modification. Z.T. proposed the specified research routes of the article. Y.S. conceived the original idea and supervised all writing. M.J. put forward the preliminary idea of the article. All authors discussed and contributed to preparing the manuscript.
Source: Qianqian Chen, Min Lv, Yu Gu, Xiyi Yang, Zhiyong Tang, Yuhan Sun,1 and Mianheng Jiang
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