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Bimodal Reaction Sequences Occurring through the Active Intermediates
Published in Robert Bakhtchadjian, Bimodal Oxidation: Coupling of Heterogeneous and Homogeneous Reactions, 2019
A bridging area between chain-radical reactions and heterogeneous catalysis became the class of reactions known as catalytic combustion.71–74 These reactions are the best examples of heterogeneous–homogeneous processes.71–73 Catalytic combustion is mainly flameless oxidation of fuel by dioxygen or air in the presence of the heterogeneous catalyst. In the 1960s, it was appeared as an alternate way of combustion, permitting to replace the conventional (homogeneous) combustion of fuel, usually, accompanied by the release of heat and light in the form of flames, and posed many environmental problems. Catalytic combustion occurs at remarkably lower temperatures than conventional combustion, without producing significant quantities of NOX, CO, and soot. Conditionally, it may be divided into low- (<300°C), medium- (300–900°C), and high-temperature (>900°C) processes. Presently, catalytic combustion has a very wide application in heat production, as well as in control of pollution. Note only one of the wide applications of catalytic combustion processes, the so-called three-way catalysts are used to reduce pollutants (NOx, CO, hydrocarbons) in the exhaust gases of internal combustion engines. The mechanism of catalytic combustion has been investigated in many systems,68,71–74 some of which will be covered in Chapter 3.
Combustion Emission
Published in Achintya Mukhopadhyay, Swarnendu Sen, Fundamentals of Combustion Engineering, 2019
Achintya Mukhopadhyay, Swarnendu Sen
New concepts for combustion technology have been introduced to the gas turbine industry to reduce NOx. This includes lean premixed (LPM) combustion (or lean–premixed pre-vaporised [LPP] combustion when liquid fuels are employed), rich-burn quick-quench lean-burn (RQL) combustion, catalytic combustion and selective catalytic reduction (SCR) [10,11]. Among these, the RQL techniques are hampered by soot formation and incomplete mixing between fuel-rich combustion products and air. Catalytic combustion suffers from challenges associated with cost, safety and durability. In SCR, a chemical is added to the exhaust gas to convert harmful NOx to compounds with less pollutants, but the major drawbacks are size and cost. Lean-premixed combustion appears to be the most promising technology recently because it offers a practical solution to reducing the emissions of nitrogen oxides (NOx) and it is simple to implement in practical combustors. In LPM combustion, the temperature of the flame is significantly reduced due to excess air present in the combustion zone which consequently eliminates production of thermal NOx. In addition, the lean operating condition elevates low maintenance requirements because the lower combustor exhaust temperature increases the lifetime of the turbine blades and other mechanical components [12].
Emissions Control Measures
Published in Neil Petchers, Combined Heating, Cooling & Power Handbook: Technologies & Applications, 2020
Catalytic combustion is combustion occurring close to a solid surface that has a special catalyst coating. The catalyst accelerates the rate of a chemical reaction and can itself be recovered unchanged at the end of the reaction. As a result, reactions occur faster and with lower energy requirement. Catalytic combustion can be effective in reducing NOX emissions, as well as emissions of CO and unburned hydrocarbons, by allowing combustion to occur at lower temperatures. However, at present, this control option has limited applicability due to catalyst degradation at temperatures above 1,830°F (1,000°C).
Impacts of Nano-Sized Co3O4 on Ignition and Oxidation Performance of N-Decane and N-Decane/1,2,4-Trimethylbenzene Mixtures
Published in Combustion Science and Technology, 2022
Fanggang Zhang, Yilun Liang, Juan Wang
Liquid hydrocarbon fuels are widely used in various engines as they have high energy density and are easy to store and transport. However, there are also many problems in the application of liquid fuels. A key issue is the poor ignition and oxidation performance of long-chain hydrocarbons because injection and droplet vaporization of these fuels are technically challenging (Kyritsis et al. 2004). To address this problem, new combustion technologies are urgently needed. Till now, extensive research has shown that catalysts are useful in enhancing combustion performance and optimizing combustion process (Devener et al. 2009; E et al. 2018; Fisher et al. 2017; Kumar, Babu, and Kumar 2019; Mei et al. 2016; Okumura et al. 2003; Shimizu et al. 2010; Van Devener and Anderson 2006; Wang et al. 2009; Wickham et al. 2006). Catalysts can decrease ignition temperature and shorten ignition delay (Shimizu et al. 2010; Williams and Schmidt 2006), and the addition of nano-scale catalyst has been proved to dramatically increase the burning rate of nitromethane (McCown and Petersen 2014). Transition metal oxide catalysts are one of the most extensively used groups of catalysts and have been demonstrated to play a critical role in catalytic combustion (Hu, Peng, and Li 2008; Liotta et al. 2013; Paredes et al. 2009; Rodrigues, Filipa Ribeiro, and Fernandes 2018; Setiawan et al. 2015; Solsona et al. 2008). Compared with noble metal catalysts, transition metal oxide catalysts have advantages of low cost and good thermal stability in high temperature, and thus have more opportunities to be applied to catalytic reactions widely.
Comparison of separated and combined photodegradation and biofiltration technology for the treatment of volatile organic compounds: A critical review
Published in Critical Reviews in Environmental Science and Technology, 2022
Meng-Fei Han, Xu-Rui Hu, Yong-Chao Wang, Zhen Tong, Can Wang, Zhuo-Wei Cheng, Ke Feng, Miao-Miao Qu, Jian-Meng Chen, Ji-Guang Deng, Hsing-Cheng Hsi
Condensation is a simple recovery technology, which is mainly suitable for high concentration VOCs. To obtain high recovery efficiency, the system generally requires high pressures or low temperatures, revealing high energy consumption. Adsorption is utilizing porous adsorbent to capture VOCs from the exhaust gas. This method is mainly used for the treatment of a single component with higher economic values. Absorption is using low-volatility or nonvolatile solvents to absorb VOCs. The absorption performance mainly depends on the structural characteristics of the absorbent. Combustion is an efficient control technology to remove VOCs at a temperature of 800-1200 °C but presents some disadvantages including the generation of harmful by-products, high investment costs, and operating safety issues. Catalytic combustion can reduce the operating cost of combustion, generally operating at a relatively lower temperature by the addition of special catalysts. But the catalyst can be poisoned, resulting in high maintenance costs. Advanced oxidation is characterized by the generation of free radicals with strong oxidizing power. The macromolecular VOCs can be oxidized to small molecular substances by the electrical, light or chemical oxidation energy. Biodegradation is a method using microorganisms to convert organic matter to H2O, CO2 and biomass. This method has been widely used in the removal of VOCs due to low energy consumption and easy maintenance.
Cordierite-supported metal oxide for non-methane hydrocarbon oxidation in cooking oil fumes
Published in Environmental Technology, 2019
Yonghai Huang, Honghong Yi, Xiaolong Tang, Shunzheng Zhao, Fengyu Gao, Jiangen Wang, Zhongyu Yang
Many techniques were used to control the VOCs emission such as adsorption, absorption, thermal oxidation and catalytic combustion [12,13]. Among all the methods, catalytic combustion has been recognized as the best way to remove VOCs because of low power consumption, avoiding the formation of NOx and high efficiency. Noble metal and transition metal oxides are widely used catalysts in the method of catalytic combustion. Although noble metal catalysts have a high catalytic activity, its availability is limited by high cost and poor stability [14,15]. Compared with the noble metal catalysts, transition metal oxides catalysts such as Mn, Co, Cu and Fe are mainly used in the method of catalytic combustion on account of cost-effective, high stability and satisfactory catalytic activity in certain cases [16–18]. Some people used catalytic combustion to remove COFs but they didn’t measure the VOCs in COFs. Wang et al. [4,6] reported catalytic oxidation of COFs over a series of Pt catalysts and good performance was shown in this case. But they only considering the particulate matters from COFs and did not pay attention to the purification of VOCs from COFs. Yang et al. [19] used an OIL Infrared Oil Meter to measure oil concentration for calculating the activity of the catalyst. Although they also used GC-MS to characterize COFs, this method could not effectively measure the removal efficiency of VOCs in COFs.