Article pubs.acs.org/IECR
Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX-XXX
Experiment and Prediction Studies of Marine Exhaust Gas SO2 and Particle Removal Based on NaOH Solution with a U‑Type Scrubber Jinxi Zhou,† Song Zhou,† and Yuanqing Zhu*,† †
College of Power and Energy Engineering, Harbin Engineering University, Harbin 150001, P.R. China ABSTRACT: Marine diesel engines produce exhaust gas including a lot of SOx and particulate matter (PM), and laws have been promulgated to regulate ship exhaust emissions. This paper proposes a U-type exhaust gas cleaning (EGC) system that is capable of removing SO2 and particulate matter (PM) simultaneously. The purpose of this study was to find the relationships between removing efficiency and parameters of EGC system, then get the optimal structural and operational parameters. The experimental results show that the SO 2 absorption rate in the scrubber was mainly influenced by liquid−gas ratio, pH value, and temperature in the range of experimental operating conditions. With the system stable running, when the liquid−gas ratio and temperature were determined, the pH value must be in a fixed range of 6.5−7.5. The further research was also carried on for the EGC system applicable to ships. On the basis of SO2 removal efficiency, the prediction and experimental validation of particulate matter (PM) were studied. When comparing the results of prediction and experiment, the data show good agreement. PM removal efficiency was related to liquid−gas ratio, droplet size, and height of chamber. The height of spray chamber was the key structure factor, and the droplet size was the operational parameter affecting PM removing efficiency. The increasing of liquid−gas ratio both could lead to an increase in the SO2 and PM removal efficiencies. Thus, according to this study, the usage of EGC system can removed SO2 and PM at same time, and it can satisfy future ships emissions regulations. The theoretical analysis and experimental results of scrubber can be extended to apply in marine exhaust gas after-treatment technologies.
1. INTRODUCTION Marine diesel engines with sulfur-containing heavy fuel oils (HFO) are the main serious pollutant sources destroying the public health and environment.1−7 The pollutants mainly include SOx, NOx, and particulate matter (PM).8−10 Sulfur is chemically bound to marine fuel oils. It originates in the crude oil and is largely found in the HFO. In the combustion process of engines, sulfur reacts with oxygen in the air and forms SOx. PM emissions is largely dependent on the fuels types, loads, and combustion conditions of engines and some references assumed that fuel sulfur content (FSC) could significantly affect the PM emissions.11−13 In addition to above pollutants emissions, a high amount of polycyclic aromatic hydrocarbons (PAHs), other metals, and nonmetallic elements are emitted, which stick to the particles.14−16 Laws have been promulgated to regulate ship exhaust emissions of NOx and sulfur. Sulfur and NOx emission controlled areas have also been set.17,18 For particulate matter emission regulations of ships, it has not been clearly defined all over the world. However, the PM emissions from marine diesel engines and their perniciousness for human health have also deserved urgent attention. Usually, the methods of controlling PM emissions are synchronized with sulfur emissions. To solve the PM and sulfur emissions problems of ships, using low-sulfur fuel oil or installed EGC systems were suggested according to © XXXX American Chemical Society
their generation mechanism. However, the price of low-sulfur fuel oil is far higher than HFO and the output cannot meet the usage requirements for ships. Considering the cost, the EGC system would be a better selection which would be more likely accepted by ship owners.19 The EGC system not only can remove almost all of SOx but capture part of primary PM and reduce secondary PM (nucleation mode) formed from SO2. Because of the unresolved wastewater treatment problems, selective catalytic reduction (SCR) technology has been the only NOx reduction method.20,21 In this study, the relationships between removing efficiency of SO2 and PM and parameters of EGC system were investigated. The results of prediction and experiment were compared on the basis of desulfurization efficiency in scrubber. In addition, the main concerns were the optimal experimental conditions and structure parameters for the removal efficiencies of PM and SO2, including temperature, pH, liquid−gas ratio, droplet size, and height of spray chamber. The optimal factors for SO2 reduction and PM reduction were achieved, and removal modeling and mechanism were also deduced. Received: Revised: Accepted: Published: A
June 11, 2017 September 30, 2017 October 12, 2017 October 12, 2017 DOI: 10.1021/acs.iecr.7b02397 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
2. EXPERIMENTAL SECTION 2.1. Experimental Engine and Fuel. The study engine was a four-stroke diesel engine, and the parameters are presented in Table 1.
spray chamber were mainly used to decrease temperature and remove PM from exhaust gas. For the study engine, the exhaust gas flow rates were 80−270 N m3/h and the concentrations of SO2 were 500−1000 ppm. The droplet size was around 2000 μm. NaOH was fed to keep pH value and ensure the desulfurization efficiency. The operation mode of the EGC system was a closed-loop cycle, and the schematic diagram of EGC system is presented in Figure 1.
Table 1. Parameters of Diesel Engine engine parameters
values
type rating power (kW) rating RPM (r/min) no. of cylinders cylinder bore (mm)
K4100ZD 41.2 1500 4 100
However, the EGC system was applied in a marine diesel engine with HFO and some measures must be done. Thiophene was added into the diesel oil to adjust the fuel sulfur content (FSC), and the diesel oil properties are shown in Table 2. The temperature of exhaust gas was changed by heat Table 2. Selected Fuels Properties product property
values
density at 15 °C (g/cm3) net calorific value (MJ/kg) viscosity at 50 °C (mm2/s) ash %(m/m) carbon (wt %) hydrogen (wt %) nitrogen (wt %) sulfur (wt %) oxygen (wt %) vanadium (mg/kg) nickel (mg/kg)
834 42.5 3.03
