◎Reporter Zhang Ye
On the one hand, a large amount of urban sewage and waste water need to be purified and treated, and on the other hand, the air-conditioning units of high-rise buildings consume a lot of energy for cooling and heating.
In the southern new town of Nanjing City, Jiangsu Province, two energy centers are under construction, but they are linked together. After the sewage has been treated up to the standard, it will continue to use the "waste heat" to provide cooling and heating for the building.
The reporter learned from the recent signing ceremony for the cooperation of renewable energy centralized energy supply in the southern new city that this is the first renewable water centralized energy supply project planned and constructed in Nanjing. heating and cooling.
How sewage recycling can turn waste into treasure
"Reclaimed water", also known as reclaimed water, refers to urban domestic sewage, industrial waste water, etc. that have been properly treated to meet certain water quality indicators, can meet certain use requirements, and can be used instead of tap water and surface natural water for non-drinking purposes. Beneficial use water.
In the past, most of these reclaimed water after harmless treatment were used for sanitation cleaning, garden watering, landscape replenishment, fire water and industrial water.
In fact, the potential of the reclaimed water after spending a lot of effort to purify it is far more than that.
"Reclaimed water has a big characteristic, that it is cold in summer and hot in winter." Yi Ming, energy conservation manager of Yuanda Energy Utilization Management Co., Ltd., told the Science and Technology Daily reporter that taking Nanjing as an example, the reclaimed water is 4-5 degrees Celsius lower than municipal tap water in summer, and in winter, Its average temperature can reach 11-12 degrees Celsius, which is also much higher than tap water exposed to cold air.
According to reports, the reclaimed water centralized energy supply project will build 2 energy centers.
In the energy center, magnetic levitation chillers are used in summer, and regenerated water is given priority for cooling. When cooling is insufficient, cooling towers are used to further dissipate the regenerated water.
Zhou Ming said that through this "water air conditioner", water that was once "stained" can be transformed into high-quality "green energy".
Compared with the traditional distributed energy supply, the use of recycled water for energy supply can save 70% of the air-conditioning power distribution and 80% of the air-conditioning room area.
Since the gas boiler for heating and the cooling tower scattered on the roof of the building are eliminated, the building quality and the environment of the new urban area are greatly improved, and the user cost is saved.
The reclaimed water from the energy center can also be used to replenish water in urban rivers, irrigate greenery and flush roads, saving 22 million tons of water every year.
At the same time, compared with conventional energy supply methods, the use of recycled water for energy supply can save 12,000 tons of standard coal and reduce carbon dioxide emissions by 29,500 tons per year.
At the same time, the reclaimed water centralized energy supply project also uses a high-efficiency magnetic levitation centrifugal chiller and a dual-mode heating unit. The magnetic levitation technology eliminates the need for lubricating oil for the entire air-conditioning system, saving 40% energy compared to traditional air-conditioning.
After the reclaimed water centralized energy supply project is fully put into production, it will cover 2.4 million square meters of public buildings.
Challenges remain in scaling up utilization
Reclaimed water heating technology was put into use in Europe as early as the 1970s.
In recent years, several pilot projects have been built in Xi'an, Shenyang, Changsha, Changzhou and other places in my country. However, compared with a large number of sewage treatment facilities and vast demand for cooling and heating, the current scale of reclaimed water heating facilities is still small.
The "14th Five-Year Plan" and the outline of the long-term goals for 2035 proposed to implement the national water-saving action, establish a rigid constraint system for water resources, strengthen agricultural water-saving and efficiency, industrial water-saving and emission reduction, and urban water-saving and loss reduction, and encourage the use of recycled water.
In recent years, while strengthening sewage treatment and improving sewage treatment standards in various places, they are also accelerating the utilization of reclaimed water and expanding its use and consumption.
So how long does it take for reclaimed water to go from water source to energy?
According to expert analysis, reclaimed water is used as the main energy source for reclaimed water cooling and heating, and municipal electricity is used as an auxiliary. The cost after operation is lower, but the initial investment is higher than that of general heating projects, especially the price of core equipment such as water source heat pumps is higher.
Therefore, relevant energy companies call on the state to attach importance to this green and low-carbon technology and provide policy support for the utilization of renewable water energy.
Compared with the traditional technology, the reclaimed water cooling and heating technology has many advantages, but it also has certain limitations.
Since this technology requires reclaimed water as the water source, long-distance water transfer not only increases the construction cost, but also lowers the water temperature and reduces the effective utilization of thermal energy.
Therefore, the energy center should be built next to the sewage treatment plant.
Therefore, experts suggest that the construction of sewage treatment plants should focus on miniaturization and decentralization, which will be more conducive to the promotion and popularization of this technology.
However, this also puts forward higher requirements for the overall planning of urban construction.
"To achieve carbon peaking and carbon neutrality goals, the full use of renewable energy is a key point, including the use of some new energy sources, as well as the use of sewage sources and river water sources, so that it is possible to achieve low carbon or even zero in local areas. Leading by carbon.” Chen Zhenqian, a professor at the School of Energy and Environment of Southeast University, believes that the development of low-carbon technologies such as centralized energy supply with recycled water has positive demonstration significance.