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• The influences of the geometric parameters of the reactor on the SCPP-HPCR are investigated. • A formula is proposed to calculate the CO 2 emissions reduction of the system. • The optimal operating conditions of the SCPP-HPCR is analyzed. • 2.38 kg of CH 4 is degraded and 375.52 kg of CO 2 is reduced through the system one day. The increase of 1.09 °C in global temperature resulted in significant catastrophes because of the extreme climate. The climate change rate can be slowed down by reducing the levels of CH 4 and CO 2 in the atmosphere. The solar chimney power plant integrated with a honeycomb photocatalytic reactor (SCPP-HPCR) uses the photocatalytic technology to remove atmospheric CH 4. In addition, CO 2 emissions can be reduced from coal fired power plant due to the generating capacity of the system. In this paper, the influence of the geometric parameters of the reactor and turbine on the overall performance of the SCPP-HPCR is studied by numerical simulation. The obtained results showed that the flow resistance inside the system was mostly caused by the HPCR at low turbine speed, and primarily by the turbine at high turbine speed. Reducing the pore diameter of the reactor could improve the photocatalytic performance of the SCPP-HPCR more than increasing the turbine speed. The SCPP-HPCR having a pore diameter of 3 mm, porosity of 0.85, and constant turbine speed of 180 rpm, built in Qianyanzhou, China, could remove 2.38 kg of CH 4 and reduce 375.52 kg of CO 2 in one day. [ABSTRACT FROM AUTHOR]

• The concept of the SC in buildings coupling PCRs for atmosphere CH 4 removal was quantitively verified. • The effects of CH 4 degradation and indoor ventilation by the system were analyzed. • The photocatalytic efficiency, purification rate, and fresh air rate were analyzed. • The new system could degrade 57.27 μg/s of atmospheric CH 4 under optimal conditions. The techniques for the removal of methane from the atmosphere are highly challenging due to its stable chemical properties, dispersed sources, and low concentrations. This paper proposes a practical small-scale solar chimney (SC) in buildings with photocatalytic reactors (PCRs) for atmospheric methane removal. Two comprehensive numerical models on photocatalytic reaction and indoor ventilation are developed. The numerical simulation considers the performance of methane removal and indoor air ventilation of the proposed system, as well as its specific crucial parameters such as the type of PCRs, solar radiation, and flow channel width. The obtained results show that the SC with honeycomb photocatalytic reactor (HPCR) is more able to remove atmospheric methane than SC with plate photocatalytic reactor (PPCR) under the premise of meeting the ventilation standards. In addition, there is a maximum methane purification rate of 57.27 μg/s under the condition that the air gap width is 0.3 m, the length of the HPCR is 1.5 m, and the porosity is 0.85. It is then proved that the SC in buildings with PCRs can allow small-scale, zero-energy consumption, continuable, and decentralized low-concentration atmospheric methane removal while improving the indoor ventilation. [ABSTRACT FROM AUTHOR]

• The numerical simulation is used to validate the effectiveness of atmospheric methane removal by SCPP-PCR. • The performance and influencing factors of photocatalytic oxidation of methane by the SCPP-PCR were analyzed. • The photocatalytic efficiency and purification rate were introduced to evaluate the effect of SCPP-PCR on methane removal. • The optimum dimension of photocatalytic reactor with pore diameters of 2–4 mm was determined. Methane (CH 4) is the second largest contributor to global warming among all greenhouses gases. A solar chimney power plant integrated with a photocatalytic reactor (SCPP-PCR) is a promising large-scale method for removing CH 4 from the atmosphere. This study used computational fluid dynamics (CFD) to investigate the performance and factors influencing photocatalytic oxidation of methane by the SCPP-PCR system. The geometry of a SCPP is the same as the prototype of the SCPP built in Manzanares (Spain). The PCR is designed based on a honeycomb monolith photoreactor. The numerical results revealed that the SCPP-PCR system can degraded 21,312 g methane per day with the actual solar radiation data when the channel diameter of the honeycomb PCR was 4 mm and channel length was 8 m. Although increasing the length or decreasing the channel diameter of the PCR would improve photocatalytic efficiency, the rate of airflow of the system would be reduced. The maximum methane purification rate of the SCPP-PCR system was determined. [ABSTRACT FROM AUTHOR]

During their rapid economic development and industrialization, megacities in the developing nations with high populations (especially in the east and south Asia) are plagued by severe air pollution problems (e.g., heavy haze), which impose a threat not only to public health but also to the sustainable development of society and the economy. To relieve the burden of air pollution for the general public, this article reviewed several geoengineering measures based on solar chimneys, which have the large-scale elimination ability on pollutants in the air, particularly for particulate matter. These geoengineering measures include driving the polluted air penetrate the planetary boundary layer into the troposphere to avoid the dramatic growth of concentrations of particulate matter, spraying water on the top of the solar chimney into the air to scavenge pollution, and intercepting fine particles in the air driven by the solar energy with large filters. Compared with traditional methods (e.g., giant spray trucks), those solar chimney geoengineering measures have the following advantages: 1) they can be operated 24 h a day, thus keeping the pollution removal function stable and continuous; 2) they are environment-friendly and can generate clean electricity to compensate for energy consumption; 3) they are also robust and operational with very low maintenance for a long period. Given the advantages of the solar chimney geoengineering measures and the economic and human health losses caused by air pollution, those geoengineering approaches deserve to be studied further and implemented in those countries that are suffering from heavy air pollution problems. [ABSTRACT FROM AUTHOR]

The acceleration of urbanization process, which triggered a series of environmental issues, has become increasingly prominent. Air pollution, especially atmospheric fine particulate matter (PM 2.5 ), is one of the most severe pollutions affecting the human health and living standard. In this article, a novel solar chimney with an inverted U-type cooling tower and a water spraying system (SCIUCTWSS) was proposed to mitigate the urban air pollution. In this system, an inverted U-type cooling tower was used to take place of the traditional chimney erected in the center of the collector; a water spraying system was installed at the turning point of the inverted U-type cooling tower to enhance the driving force; a filtration screen is placed near the entrance of the collector to filter out PM 2.5 and large particulate matter from the airflow. The clean air out of the system’s outlet can immediately improve the air quality in the spectrum of human activity. A mathematical model to describe the fluid flow, heat transfer of the system was further developed. Influence of injected water from the water spraying system on the pressure, velocity, temperature, and air density distributions were analyzed. The numerical simulation results indicated that water injection is efficient that can strengthen the natural convection and has a positive influence on the heat transfer process within the system. This proposed SCIUCTWSS in this article is able to process atmospheric air at a volume flow rate of 810 m 3 /s, corresponding to the volume of 69,984,000 m 3 of air to be cleaned in one day. However, in view of the economic and human comfort, the amount of injected water should be taken into comprehensive consideration. [ABSTRACT FROM AUTHOR]