Exhaust Gases Cleaning Technology for Vessels

Abstract

The present investigation aims to propose results of development of an effective system for the purification of exhaust gases that are emitted to the environment by ship power plant from sulfur oxides (SOx) and solid particles. Numerical simulation of a combined scrubber with vortex plate based on the developed theoretical approach was performed. Mathematical model of aerohydrodynamic and heat-mass transfer processes contains five interconnected modeling blocks. There was investigated the influence of the scrubber’s geometric characteristics onto the quality of its work. As a result, for the elements of vortex plate the rational design parameters were determined (the angle of blades installation for the swirls =60-90, the ratio between internal and outer radius of the swirls R1/R2=0,6-0,7). The interaction of gas aerosol with water foam was studied during numerical simulation. It was done with consideration of hydrodynamic regime on the surface of a vortex plate. As a result, for the scrubber rational design and operating parameters were formulated (inlet flow velocity V=18-25 m/s, the height of foam layer H=70-150 mm, inlet dust concentration 40-50 g/cub.m of the gas to be cleaned, cross-sectional area of the purification unit up to 2 sq.m). Computer-based solid-body scrubber model was created during numerical simulation. CFD modeling of the main hydrodynamic processes based on this model was carried out. It was done for all developed structural solutions for scrubber elements. The main results obtained during CFD modeling of the scrubber operation make it possible to analyze the technology of its use and to achieve a reduction in energy costs while maintaining the quality of gas cleaning. The developed theoretical model of a scrubber gives an ability to simulate the flow of a gas-dust stream considering all changes that were done in the geometry of the scrubber. The very model can also be used to optimize the scrubber’s design depending on the type of production and parameters of the gas to be contaminated. During research works there was formulated a conclusion about the necessity to take into consideration the uneven distribution of the field of velocity when modeling the process of gas purification and cooling inside a scrubber. In order to determine the efficiency of heat transfer process inside the scrubber, heat transfer coefficients were found out. They were compared with characteristics of a traditional scrubber’s model based on a perforated plate. Calculation data have shown an excess of the heat transfer coefficient of the vortex plate by 5-7%. It was stated also that the value of the heat transfer coefficient depends on average velocity and moisture content of the gas to be supplied. The rational design and operational parameters of the scrubber obtained on the models made it possible to develop a pilot industrial model of the scrubber and method of engineering calculation. During experimental studies of the scrubber, new scientific results were obtained. They allow one to establish the technological range of irrigation density values, at which the maximum efficiency of trapping solid particles and sulfur oxides (SOx) is ensured. Experiments were carried out that reveal the relationship between the angle of blades installation of the swirl and the height of the installation of the baffle plate onto the efficiency of foaming and total resistance of the vortex plate.