Application and Development of Selective Catalytic Reduction Technology for Marine Low-Speed Diesel Engine: Trade-Off among High Sulfur Fuel, High Thermal Efficiency, and Low Pollution Emission

Abstract

In recent years, the International Maritime Organization (IMO), Europe, and the United States and other countries have set up different emission control areas (ECA) for ship exhaust pollutants to enforce more stringent pollutant emission regulations. In order to meet the current IMO Tier III emission regulations, an after-treatment device must be installed in the exhaust system of the ship power plant to reduce the ship NOx emissions. At present, selective catalytic reduction technology (SCR) is one of the main technical routes to resolve excess NOx emissions of marine diesel engines, and is the only NOx emission reduction technology recognized by the IMO that can be used for various ship engines. Compared with the conventional low-pressure SCR system, the high-pressure SCR system can be applied to low-speed marine diesel engines that burn inferior fuels, but its working conditions are relatively harsh, and it can be susceptible to operational problems such as sulfuric acid corrosion, salt blockage, and switching delay during the actual ship tests and ship applications. Therefore, it is necessary to improve the design method and matching strategy of the high-pressure SCR system to achieve a more efficient and reliable operation. This article summarizes the technical characteristics and application problems of marine diesel engine SCR systems in detail, tracks the development trend of the catalytic reaction mechanism, engine tuning, and control strategy under high sulfur exhaust gas conditions. Results showed that low temperature is an important reason for the formation of ammonium nitrate, ammonium sulfate, and other deposits. Additionally, the formed deposits will directly affect the working performance of the SCR systems. The development of SCR technology for marine low-speed engines should be the compromise solution under the requirements of high sulfur fuel, high thermal efficiency, and low pollution emissions. Under the dual restrictions of high sulfur fuel and low exhaust temperature, the low-speed diesel engine SCR systems will inevitably sacrifice part of the engine economy to obtain higher denitrification efficiency and operational reliability.

Mitigation of Ship Emissions: Overview of Recent Trends

“…Although the urea-SCR system is a challenge for diesel engines, due to its size and design limitations, it is nonetheless among the reliable solutions approved by the IMO, because of its versatility, with respect to a variety of ships using sundry fuels . In these systems, the urea solution is atomized to mix well with the exhaust gases, thus promoting the conversion of urea to ammonia via reactions – NH 2 −CO −NH 2 · x normalH 2 normalO → NH 2 −CO −NH 2 + x normalH 2 normalO NH 2 −CO −NH 2 → NH 3 + NHCO NHCO + normalH 2 normalO → NH 3 + CO 2 NH 2 −CO −NH 2 + normalH 2 normalO → 2 NH 3 + CO 2 The ammonia-laden exhaust gas is then introduced into a monolithic reactor where NO X reduction is carried out in the presence of a vanadium catalyst impregnating the monolithic ceramic support via reactions –. ,, …”

“…In these systems, the urea solution is atomized to mix well with the exhaust gases, thus promoting the conversion of urea to ammonia via reactions – NH 2 −CO −NH 2 · x normalH 2 normalO → NH 2 −CO −NH 2 + x normalH 2 normalO NH 2 −CO −NH 2 → NH 3 + NHCO NHCO + normalH 2 normalO → NH 3 + CO 2 NH 2 −CO −NH 2 + normalH 2 normalO → 2 NH 3 + CO 2 The ammonia-laden exhaust gas is then introduced into a monolithic reactor where NO X reduction is carried out in the presence of a vanadium catalyst impregnating the monolithic ceramic support via reactions –. ,, 4 NH 3 + 4 NO + normalO …”

“…41 In recent decades, selective catalytic NO X reduction using molten/dissolved urea (referred to as urea-SCR) as a source of ammonia has been used in systems with operating temperatures between 250 and 450 °C. 42 Although the urea-SCR system is a challenge for diesel engines, due to its size and design limitations, 43 it is nonetheless among the reliable solutions approved by the IMO, because of its versatility, with respect to a variety of ships using sundry fuels. 44 In these systems, the urea solution is atomized to mix well with the exhaust gases, thus promoting the conversion of urea to ammonia via reactions 16−19.…”

Effect of Ultrasound Irradiation on the Properties and Sulfur Contents of Blended Very Low-Sulfur Fuel Oil (VLSFO)

“…The demand for VLSFO is expected to continue over the long term, as the adoption possibility of future regulations governing scrubber wash-water cannot be ruled out. Moreover, using VLSFO may also be beneficial in improving the efficiency of selective catalytic reduction [6], the only method of NO X emission reduction recognized by the IMO, as denitrification catalysts can be easily contaminated by SO 2 [7] and suffer from operational problems, such as sulfuric acid corrosion [8].…”

Modeling, simulation and control of hybrid power systems for vessels.

“…An exhaust gas recirculation (EGR) or a selective catalytic reduction (SCR) system, for example, could be used to deal with the NO x emission increase. However, it must be noted that the after-treatment system can have an impact on the engine operation, and involve implementation and operational costs with consumables [86].…”