Total Marine Diesel Emission Control Technology Using Nonthermal Plasma Hybrid Process
The regulations governing marine diesel engine NOx emission in the International Maritime Organization (IMO) emission standards have become more stringent. Because it is difficult to fulfill these requirements by means of combustion improvement alone, effective aftertreatment technology is needed to achieve efficient NOx reduction. Here, we propose an effective PM and NOx simultaneous reduction aftertreatment system that employs a nonthermal plasma (NTP) hybrid process. Compared with selective catalytic reduction (SCR), the proposed technology offers the advantage of treatment at a low temperature of less than 150°C, without the use of urea solution and harmful heavy-metal catalysts. First, laboratory-scale experiments are performed with a stationary diesel generator (YDG200VS-6E, YANMAR Co., Ltd., Japan) (specifications: single cylinder; rotating speed, 3600 rpm; and maximum output power, 2.0 kW). Marine diesel oil (MDO, sulfur = 0.067 mass%) is used as a fuel. The system mainly consists of a marine diesel engine, an adsorption chamber containing adsorbent pellets that can adsorb/desorb NOx in an exhaust gas by controlling their temperature, an NTP reactor, and a diesel particulate filter (DPF). Whole exhaust gas flows to the system at 300 NL/min. The aftertreatment comprises (a) adsorption, (b) desorption, and (c) cooling processes. In the adsorption process, an exhaust gas first passes through a DPF, where particulate matter is removed. Subsequently, the gas is cooled by an air-cooling radiator and then passes through an adsorption chamber where NOx is removed by adsorption. The mass flow rate of these gases is measured at the exit of the chamber by a NOx analyzer. The clean gas then flows out of the system. In the desorption process, the exhaust gas first passes through a heat exchanger integrated into the adsorption chamber, where it heats the adsorbent pellets to induce thermal desorption of NOx. Simultaneously, N2 gas is supplied to the pellets at 10 NL/min. Then, NOx is eluted. The NOx + N2 gas is subsequently reduced to N2 using the NTP reactor. The NOx concentration is measured after the confluence of the exhaust gas and the reduced gas. In the cooling process, the remaining NOx in the pellets is desorbed by introducing air into the adsorption chamber at 50 NL/min with the help of the residual heat. The desorbed NOx is recirculated into the intake of the engine to enhance total NOx reduction. Based on the measured NOx concentrations and the power consumptions for NTP generation, adsorbed NOx in the adsorption process, and desorbed NOx and treated NOx in the desorption and cooling processes are found. Considering these obtained values, the energy efficiencies upon NOx removal are calculated and the performance of the system is evaluated. The time-dependent NOx emission from the aftertreatment system is shown in Fig. 1. The white circles indicate the mass flow rates of untreated NOx, and the black circles indicate those of the treated NOx. The shaded areas indicate the masses of NOx treated in processes (a)-(c). A series of processes (a)-(c) are repeated. As a result, a NOx removal of 437 g/kWh is achieved with significant energy efficiency. Next, based on the above laboratoryscale experiments, we developed the system into a pilot-scale aftertreatment. Pilot-scale experiments are performed for the first time with a marine diesel engine (6DK-20, Daihatsu Diesel MFG, Co., Ltd., Japan) (specifications: six cylinders, rotating speed, 900 rpm; maximum output power, 1,100 kW; mass flow rate of exhaust gas, 6,815 Nm3 /h; and load, 100%). The system consists of a scale-up adsorption chamber, 48 surface-discharge-type NTP reactors, DPFs, and coolers. DPF regeneration using plasma-induced O3 is performed in parallel. An exhaust gas with a mass flow rate of 800 Nm3 /h is among the total emissions flowing to the system. The aftertreatment comprises (a) adsorption and (b) desorption processes. These processes are repeated alternatively. N2 gas at 200 L/min is introduced into the adsorption chamber in the desorption process. Pilot-scale experiments are performed under a number of different conditions of process duration and under an amount of power applied to the NTP reactors. The performance of the system was evaluated in the same manner as the laboratoryscale experiments. The results showed that this system has high energy efficiency in the NOx removal of 161 g/kWh. Application of the recorded energy efficiency to the requirement of the IMO emission standards from Tier II to III corresponds to 4.3% of the engine output power. This loss of only 4.3% of output power indicates high performance and fulfills the most recent IMO emission standards for 2016 using present-day technology.
Masaaki Okubo Takuya Kuwahara Keiichiro Yoshida Masashi Kawai Kenichi Hanamoto Kazutoshi Sato Tomoyuki Kuroki
Osaka Prefecture University,Japan Daihatsu Diesel MFG.Co.,Ltd.,Japan
国际会议
上海
英文
1-14
2013-05-13（万方平台首次上网日期，不代表论文的发表时间）