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The environment
Published in Tom Denton, Alternative Fuel Vehicles, 2018
Euro 6 imposed a significant reduction in NOx emissions from diesel engines (67% reduction compared with Euro 5) and established similar standards for petrol and diesel. Exhaust gas recirculation (EGR) reduces the amount of nitrogen available to be oxidised to NOx during combustion but further exhaust after treatment may be required in addition to the diesel particulate filters (DPFs) required to meet Euro 5. To comply with Euro 6, diesel cars may also be fitted with: ► A NOx absorber (also known as a lean NOx trap), which stores NOx and reduces it to nitrogen by catalytic action.► Selective catalytic reduction (SCR) using an additive (diesel exhaust fluid (DEF) or AdBlue) containing urea, which is injected into the exhaust to convert NOx into nitrogen and water. ► The use of Cerium,8 a fluid injected into the fuel tank each time the vehicle is refuelled which assists the DPF regeneration by nanoparticle catalytic action lowering the regeneration temperature.
Heat Recovery Steam Generator (HRSG)
Published in S. Can Gülen, Gas Turbine Combined Cycle Power Plants, 2019
The casing houses the HP, IP and LP heat transfer sections. In addition, it also contains the selective catalytic reduction (SCR) system, which is included to reduce the nitrogen oxide (NOx) emissions in the gas turbine exhaust gas. The standard SCR design includes an aqueous ammonia (NH3) evaporation and injection system. The catalyst modules are field-installed into the structural steel reactor housing which is typically placed in between the HP evaporator tube banks (for temperature requirements). Typically, an oxidizing catalyst system is also included in the SCR package to reduce carbon monoxide (CO) and non-methane, non-ethane, unburned hydrocarbons (VOC1) to the emission guarantees specified in the contract.
Gas Turbine Exhaust Treatment
Published in Tony Giampaolo, Gas Turbine Handbook Second Edition, 2002
Selective catalytic reduction (SCR) is a process in which NOx is removed from the exhaust gas stream by the injection of ammonia (NH3) into the stream and the subsequent chemical reaction in the presence of a catalyst. For a given gas condition (temperature, gas composition, etc.) the performance of the SCR is a function of the catalyst type and geometry, the residence time of the gas in the reactor, and the amount of ammonia injected upstream of the reactor. Selection of the catalyst is specific to the temperature in which it is expected to operate. The ammonia utilized in the process may be either anhydrous or aqueous. The injection systems differ slightly depending on the type of ammonia injected. The basic chemical reactions11 are:
High-temperature determination of ammonia by tunable diode laser absorption spectroscopy (TDLAS)
Published in Instrumentation Science & Technology, 2023
H. Cui, J. Li, F. Wang, G. Lv, W. Wang, J. Fan
Environmental issues associated with pollutants generated by coal-fired power plants have garnered considerable attention.[1] Nitrogen oxides (NOx) generated during coal combustion are key pollutants and are significant contributors to acid rain and photochemical smog.[2] The United States Environmental Protection Agency (EPA) regulates NOx emissions under the authority of the Clean Air Act (CAA). These regulations were formulated to promote the development of post-combustion NOx reduction technologies, such as selective catalytic reduction (SCR)[3,4] that uses ammonia (NH3) as the reducing agent. To obtain the best denitration, the quantity of injected NH3 must be proportional to the quantity of NOx.[5] However, excessive NH3 may result in degradation in operation in coal-fired power plants.[6,7] Therefore, real-time and accurate determination of NH3 is crucial for operational optimization.
The effect of fusel oil as a reductant over the multi-metallic catalyst for selective catalytic reduction of NOx in diesel exhaust at low-temperature conditions
Published in Petroleum Science and Technology, 2023
Şilen U. H. Sümer, Sinan Keiyinci, Ali Keskin, Himmet Özarslan, Zeycan Keskin
One of the most promising technology to decrease the harmful effect of NOx emissions is selective catalytic reduction (SCR) systems which have good efficiency, practicality, and stability (Dhas et al. 2019). Since the operation in SCR systems is in the exhaust part, it does not adversely affect the engine, fuel consumption, and operating conditions. Therefore, SCR systems can be considered as the most appropriate option for industrial sources, power plants, and heavy vehicles where a high volume of diesel engines are used such as trucks, buses, and heavy-duty machines (Huang et al. 2019).
Modeling of NO mass transfer characteristics absorbed in sodium persulfate solution with a bubble reactor
Published in Journal of Environmental Science and Health, Part A, 2023
Jing Liu, Chang Li, Xiaoyang Zhang, Hao Zhang, Jiyun Tang, Yong Dong
Commercial marine transportation is among the most energy-efficient and cost-effective ways to move goods and people around the world.[1] Nevertheless, the exhaust pollution caused by marine diesel engine emissions is becoming increasingly serious.[2,3] The International Maritime Organization (IMO) has revised < MARPOL 73/78> Annex VI to impose more stringent requirements on the control of NOx emissions from diesel exhaust of ships. NOx emissions from ships with low-speed diesel engines as the power source not exceeding 3.4 g·(kWh)−1, and NOx emissions from ships with high-speed diesel engines as the power source not exceeding 2.0 g·(kWh)−1.[4] In order to conform to the strict regulations, some technologies have been successfully applied to ships to control emissions,[5] such as selective catalytic reduction (SCR), which has the advantages of high efficiency, low by-products, and mature technology. However, some problems exist in SCR when it is applied for NO removal,[6–10] especially when it is adopted combined with exhaust gas cleaning systems (EGCS) for SO2 removal, such as the mutual restriction of their operation principles. If EGCS is applied to absorb SO2 before SCR, the exhaust gas temperature will not be sufficiently high to allow SCR to work. If SCR is used before EGCS, the existence of SO2 results in the passivation of SCR catalysts, which weakens the SCR function and causes ammonia leakage.[11] Wet scrubbers are considered as a promising technique to solve the problem[12] and the effective absorption of 90% insoluble NO in NOx is crucial for wet scrubbing methods to remove NOx when it is adopted for ships.