Subsequently, the central government continuously accelerated the establishment of the "1+N" policy system and successively issued the "Opinions on Fully, Accurately, and Comprehensively Implementing the New Development Concept and Doing a Good Job in Carbon Peak and Carbon Neutrality" and the "2030 Carbon Peak Action Plan", setting a timetable and roadmap for China to achieve the goals of "carbon peak and carbon neutrality". The China Urban Rail Transit Association also released the "Action Plan for Green Urban Rail Transit Development in China" in August 2022, fully implementing the national "dual carbon" goal, coordinating the dual carbon action and green urban rail development of the urban rail industry, with green transformation as the main line, clean energy as the direction, energy conservation and carbon reduction as the focus, intelligent empowerment, innovation driven, and carrying out six major green urban rail actions to achieve carbon peak and carbon neutrality goals, and build a green urban rail.
1. Current situation of green development of urban rail transit
1.1 Current Development Status of Urban Rail Transit
As of the end of 2022, a total of 55 cities in China (excluding Hong Kong, Macao, and Taiwan) have opened urban rail transit operating lines, totaling 308 lines with a total length of 10287.45km. The cumulative passenger volume completed throughout the year is 19.302 billion, with a total passenger turnover of 158.437 billion kilometers. Urban rail transit passenger volume accounts for 45.82% of the total public transportation passenger volume. In the future, cities with super large network scales will mainly focus on local optimization of the network, and cities with initial network scales will show a rapid expansion trend of the network scale as the number of lines continues to increase.
1.2 Energy consumption and carbon emissions status of urban rail transit
The energy consumption of urban rail transit is mainly based on electricity consumption. In the total carbon emissions of rail transit, indirect emissions generated by purchased electricity account for 90%, and electricity consumption is the main factor of carbon emissions. In general, the energy consumption of train traction accounts for about 53% of the total energy consumption, and the energy consumption of power and lighting accounts for about 47% of the total energy consumption; The energy consumption of station ventilation, air conditioning, lighting, escalators and other systems accounts for 70% to 80% of the energy consumption of station equipment systems; Traction and environmental control are key research directions for energy conservation and carbon reduction.
In 2022, the total energy consumption of urban rail transit in China was 22.792 billion kW · h, of which the traction energy consumption was 11.315 billion kW · h. With the continuous increase of newly put into operation lines, the overall energy consumption index continues to grow, and the total carbon emissions show a continuous growth trend. In 2022, the average total electricity consumption per vehicle kilometer of urban rail transit will be 3.72 kW · h, a year-on-year decrease of 0.48%. The average total electricity consumption per person kilometer of each city will be 0.144 kW · h, a year-on-year increase of 34.02%. The greater the passenger intensity of urban rail transit, the more conducive it is to reducing the average energy consumption per person kilometer and carbon emissions. Increasing the proportion of rail transit passenger travel to achieve green and low-carbon travel is also an important aspect.
1.3 Application status of energy-saving and carbon reduction technologies in urban rail transit
At present, urban rail transit has taken many effective measures in terms of technological energy conservation and intelligent empowerment, in order to increase the proportion of passenger travel, reduce energy consumption, and improve transportation and operation efficiency, achieving good results in energy conservation and emission reduction.
1.3.1 Technical energy-saving measures
By adopting energy-saving technologies and optimizing design schemes to achieve technological energy conservation, it mainly includes: optimizing the curve radius through route selection, optimizing the energy-saving slope of the route, optimizing the position of the interval pump room, and reasonably determining the train composition to achieve energy-saving operation of the route; Realize vehicle energy conservation through VVVF AC variable frequency transformation, lightweight design of vehicles, intelligent air conditioning and lighting of trains, automatic control of trains, etc; By reasonably setting the voltage levels and power supply zones of the AC/DC network, selecting energy-saving amorphous alloy transformers, setting up traction and follow-up stations, applying regenerative braking and energy storage technology, using high conductivity steel aluminum composite rails, adopting energy-saving LED lamps, and using photovoltaic power generation in the field, the power supply system can achieve energy conservation; By reasonably determining the ventilation and air conditioning system standard, adopting fan frequency conversion control, group control and wind and water energy-saving control, and applying magnetic levitation direct expansion air conditioning units, energy-saving of the ventilation and air conditioning system can be achieved; Implementing energy management and energy conservation through the establishment of network and line energy management systems; Realize energy-saving operation mode through timetable control of station lighting, ventilation and other mechanical and electrical equipment; By reasonably controlling the scale of civil engineering and determining the system capacity, the design scheme can be optimized for energy conservation.
1.3.2 Wisdom Empowerment
The "Steel Requirements for the Development of Smart Urban Rail Transit in China" released in March 2020 proposed the construction of a smart passenger service system, an intelligent transportation organization system, an intelligent energy system system, an intelligent train operation system, an intelligent operation and maintenance safety system, an urban rail cloud and big data platform, and other related modules, all of which have clear requirements for empowering urban rail transit with intelligence.
Empowering the proportion of passenger travel through technologies such as real name registration for boarding, contactless payment, integrated ticket inspection, smart stations, and smart trains in the smart passenger service system; The networked operation and intelligent scheduling of the intelligent transportation organization system can achieve refined transportation organization and optimized resource allocation, empowering the improvement of transportation efficiency; The construction of intelligent energy system system includes power quality optimization control, regenerative braking and new energy, permanent magnet traction and bidirectional converter, and intelligent energy system empowerment to improve energy efficiency of the energy system; The fully automatic operation and interconnectivity of the intelligent train operation system empower efficient passenger services and train operations; The construction of a multi-disciplinary intelligent operation and maintenance security system empowers the improvement of networked operation and maintenance efficiency; The urban rail cloud and big data platform serve as the digital foundation for smart urban rail, with unified deployment and support of business systems, achieving resource intensification and energy conservation of weak current systems, and empowering the overall smart urban rail system.
2 Green Development Paths for Urban Rail Transit
Based on the goal of green and low-carbon development of urban rail transit, urban rail transit enterprises should combine their own advantages with national supporting policies, practice the concept of green and low-carbon development, establish enterprise green and low-carbon development institutions, formulate a framework for green urban rail construction work, coordinate planning and adapt to local conditions, and implement dual carbon development at three levels of "line network, line, and station section" according to the network concept. Energy saving and consumption reduction measures and passenger flow attraction measures should be implemented from the planning and design source, adhere to the principle of energy conservation and resource priority, adhere to the orientation of green, low-carbon, and energy-saving effects, promote innovation and upgrading of green construction and green equipment, optimize energy structure, optimize system operation mode and process flow, innovate operation mode and maintenance mode, rely on smart empowerment of intelligent energy management, and integrate green and intelligence. Building a green and low-carbon plan The green development system throughout the entire lifecycle, including green low-carbon design, green low-carbon construction, green low-carbon operation, and green low-carbon maintenance, is shown in Figure 1.
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2.1 Green and low-carbon planning
Based on planning and passenger flow assessment of existing operating lines, scientifically and reasonably carry out network planning and construction planning, coordinate and integrate multi-level networks in urban (suburban) areas, and improve network coverage. The concept of integrating the four networks (mainline railway network, intercity railway network, urban/suburban railway network, and urban rail transit network) and station city integration is used to promote the planning and construction of the railway network, strengthen the connection between stations and surrounding businesses such as commercial, road, and pipe gallery, reshape the integrated urban spatial layout, and enhance the passenger rail transit travel experience. With the concept of resource sharing, we will strengthen the optimization and sharing of network resources, create conditions for the interconnection and intercommunication of resources and equipment facilities such as vehicles, signals, power supply, vehicle maintenance, and passenger services. Decompose and implement the dual carbon goals in network planning, existing line renovation planning, energy planning, energy conservation and environmental protection planning, and carry out special demonstrations on dual carbon and green rail transit.
2.2 Green and low-carbon design
Building a green engineering design system, the design documents for new and renovated projects should determine green design goals and implementation paths, clarify green design schemes, and specify energy-saving and carbon reducing green measures during the construction and operation periods, such as reasonable control of civil engineering scale, green construction technology and methods, reasonable line laying methods, energy-saving slopes, wiring schemes, equipment system capacity, and green equipment configuration schemes. Implement the standards for green urban rail construction, meet the requirements for energy intensity, carbon emission intensity, increase in travel proportion, creation of green buildings, and utilization of green energy, and improve the level of energy conservation and carbon reduction in urban rail.
2.3 Green and low-carbon construction
2.3.1 Green and low-carbon construction
Prioritize the use of construction materials such as cement and steel that have obtained green labels, and promote the electrification of construction machinery and clean energy consumption. Strengthen the integrated design of prefabricated construction, and coordinate the production, construction, installation, decoration, and other aspects of prefabricated construction for components. Promote refined construction management, adopt lean construction organization methods, and coordinate the management of construction related elements and links. Promote the informatization of construction management, achieve energy consumption monitoring of high energy consuming engineering machinery and equipment, and group control management of similar equipment; Promote the innovative application of new technologies such as 5G, Internet of Things, artificial intelligence, and building robots in the construction field, and promote the integration of green construction and new generation information technology. In the process of green construction, fully utilize the national dual carbon financial policy tools, strive for support from national green finance policies such as green bonds and green loans, use market-oriented energy-saving and emission reduction mechanisms, promote contract energy management models in new line construction and existing operation line upgrading, and mobilize social capital to participate in energy-saving transformation and operation maintenance.
2.3.2 Green and low-carbon equipment
(1) Vehicle technical equipment. The research and application of vehicle technology equipment mainly focus on green upgrades in hydrogen energy vehicles, vehicle permanent magnet synchronous traction technology, silicon carbide converter technology, lightweight vehicle structure design, green procurement of lightweight trains, LED lighting and intelligent lighting, air conditioning frequency conversion and temperature intelligent control, and the integration of software, hardware, and network of onboard equipment systems.
(2) Power supply technology equipment. The research and application of power supply technology equipment mainly focus on green upgrades in areas such as bidirectional converter and networked collaborative control of traction power supply systems, dedicated rail reflux technology, energy storage technologies such as supercapacitors/flywheels/lithium batteries, amorphous alloy energy-saving transformers, DC3000V traction power supply technology, natural ester transformers, clean air insulated GIS, and environmentally friendly gas insulated switchgear.
(3) Mechanical and electrical technology equipment. The R&D and application of electromechanical technology and equipment are mainly green upgrading from DC lighting system, LED lamp application, intelligent lighting control technology, photoconductive lighting technology, energy Internet technology, magnetic suspension direct expansion air conditioning unit, wind and water linkage energy-saving control system, etc.
(4) Weak current technology equipment. The research and application of weak current technology equipment mainly focus on green upgrades in virtual grouping technology, intelligent train dispatching system, construction of line network cloud platform and big data platform, ATO energy-saving operation, efficient IT equipment application, acceleration of natural cooling source/near end cooling/liquid cooling and other cooling energy-saving technology applications, flattening/cloud network integration/cloud edge collaborative system architecture optimization, etc.
2.3.3 Green energy substitution
(1) Photovoltaic power generation technology. Develop a photovoltaic energy development plan based on the network and line conditions, fully utilize the protected areas along the elevated lines, the roofs of above ground station buildings, the roofs and facades of vehicle bases that have not been developed, and other site resources that can install photovoltaic power generation facilities, and develop and apply photovoltaic power generation systems. Promote the synchronous design of photovoltaic power generation and building integration, and build a "photovoltaic storage direct flexible" system that integrates photovoltaic power generation, energy storage, DC distribution, and flexible electricity use.
(2) Alternative technologies for fossil fuels. According to the adaptability of heat pump technology in the area where the vehicle base is located, various types of ground, gas, and water source heat pump systems should be promoted and applied according to local conditions, and clean heating should be achieved by combining the heating network, electric energy, solar energy, and geothermal energy near the rail transit. Increase the use of green electricity and continuously increase the proportion of green electricity used in rail transit.
2.4 Green and low-carbon operation
(1) Green operation management mechanism. Urban rail transit enterprises should formulate energy-saving and carbon reduction goals and plans in conjunction with their development plans, establish a green and low-carbon management framework of "line network level line level station section level", decompose energy-saving and carbon reduction management goals at different levels, establish an assessment system and reward and punishment system, and continuously promote them on a regular basis.
(2) Green operation management mode. Based on network and passenger flow analysis, relying on intelligent train dispatching system to achieve precise matching of networked transportation capacity and volume; Adopting technologies such as multi route operation and flexible grouping to reduce empty train operation; Optimize the energy-saving control and time-sharing zoning control of the electromechanical equipment system to achieve energy-saving operation of the equipment system.
(3) Green operation management platform. Based on the cloud data integration base of the line network urban rail cloud platform and big data platform, an intelligent energy management platform that matches the "line network line station section" management architecture is constructed around the goal of "comprehensive energy perception and energy-saving data-driven". At the network level, emphasis is placed on intelligent energy management decision-making and evaluation, at the line level on comprehensive energy dispatch management, and at the station level, emphasis is placed on energy system interconnection and mutual assistance, coordinated and interactive regulation of source, network, load, and storage. Through intelligent empowerment of energy management, green and intelligent integration, intelligent energy management capabilities such as energy consumption measurement and carbon emission monitoring are enhanced. The overall architecture is shown in Figure 2.
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2.5 Green and low-carbon maintenance
Establish maintenance regulations for major equipment such as vehicles, optimize energy-saving and carbon reduction management mechanisms, build a comprehensive operation and maintenance management platform for the power grid, monitor equipment status, diagnose faults, manage health, and support maintenance decisions based on the operation status and online monitoring data of professional equipment such as vehicles, power supply, communication, and electromechanical systems. Apply a networked operation and production organization model, reasonably formulate maintenance systems for vehicles and equipment systems, optimize production processes, promote large-scale and specialized maintenance, improve the utilization efficiency of operation equipment and facilities, reduce maintenance energy consumption, and achieve low-carbon maintenance.
3 Conclusion
At present, although urban rail transit has achieved certain results in green and low-carbon development, China's urban rail transit is in a rapid development stage, and the demand for urban rail transit will continue to grow for a considerable period of time in the future. The industry is under enormous pressure to reduce carbon emissions, and urban rail transit enterprises are still in the initial stage of green transformation in planning and design, green construction, green low-carbon technology application, operation mode, and maintenance system. The green evaluation and green standard system have not yet been established, and the support of national green and low-carbon policies is still insufficient. On the basis of analyzing the current situation and advantages of urban rail transit development in China, this article proposes the goal of green and low-carbon development of urban rail transit and the specific path that runs through the entire life cycle of planning, design, construction, operation, and maintenance, providing reference and inspiration for accelerating the green and low-carbon transformation of urban rail transit. In specific implementation, the relationship between passenger service quality and energy conservation and carbon reduction should also be handled well, as well as the relationship between the application of green and low-carbon new technologies and energy conservation and carbon reduction, regional environmental differences, project progress, and project investment, to ensure the efficient promotion of the "carbon peak" and "carbon neutrality" work of rail transit.
