Hot gas is mostly generated by the combustion and has large thermal energy but usually contains particulate matter at a high concentration. Hence it has to be removed before introducing it to a gas turbine at high temperatures to utilize its thermal energy. Cleaning technology at high temperature has been studied closely in relation to the development of combined power generation technology such as Integrated Gasification Combined Cycle and Pressurized Fluidized Bed Combustion Combined Cycle power generation. Different from the ordinary conventional dust collection technology, not only the particle collection but also the interaction between gas and filter surface have to be considered in its development since physical and chemical properties of dust change at elevated temperature and pressure. In other words, basic understanding of these properties of dust and filter materials and their interaction are essential for the development of hot gas cleaning technology. In this paper, recent developments in the field of hot gas cleaning has been reviewed.
Coal is an important energy resource for meeting the future demand for electricity since coal reserves are much greater than those of other fossil fuels. However, carbon dioxide emission during coal combustion is greater than that of other fossil fuel because of the higher carbon content. Development of a high efficiency power generation system is essential in order to reduce the carbon dioxide emission from coal for power generation. As a high efficiency coal utilized power generation system, the Pressurized Fluidized Bed Combustion Combined Cycle System (PFBC) and the Integrated Coal Gasification Combined Cycle System (IGCC) have been developed. In these systems, a high temperature dust collection technology is applied for the protection of gas turbines from erosion. It is important to develop an optimal collection method depending on the particle property because the properties of particulates generated at high temperature and pressure are different from those generated by the conventional pulverized coal combustion. In this study, the characteristics of particulate matters from pressurized coal combustion for high efficiency power generation systems are investigated through experiments with a pressurized drop tube furnace as well as by numerical simulation employing a percolation model. It is found that the particulate matters generated from the combustion at high pressure and temperature contains less unburned carbon with a higher fraction of agglomerated spherical particles.
The cohesion of ash particles at high temperature creates problems in power generation plants such as blocking high temperature filters, choking plant lines, and corroding heat transfer surfaces and/or gas turbines. These problems affect the stable operation of various high-efficiency power-generation plants fueled by burning coal, biomass, and/or waste. In this review paper the reported troubles caused by ash adhesive properties at high temperatures are introduced in the first part, then the methods to determine the fundamental properties of ash particles at high temperature conditions are presented, and finally the concept to control the ash adhesion is discussed.
On the gas cleaning technology using ceramic filters at high temperatures, we are confronted to many difficulties such as cracking of filter, rapid increase in filter pressure drop and insufficient filter cleaning. Many researches have been conducted to find the optimum operating condition of filter at low pressure drop in order to prolong the filter life. This paper reviews the experimental and numerical simulation works on the dust collection and the detachment process of dust layer on rigid ceramic filter surface. The dust layer formed on the ceramic filter has a dense structure in the initial stage of filtration being porous with a decrease in filtration velocity and an increase in temperature. The change in filter pressure drop during cleaning operation can be predicted by CFD. The cleaning efficiency increases with the porosity of dust layer and it is strongly influenced by the adhesive and cohesive forces of dusts at high temperatures. Therefore, the porosity of dust layer is a crucial factor in maintaining a high cleaning efficiency. The main difficulty in conducting experimental works in this field arises from the difficulty in finding appropriate experimental conditions which sufficiently mimic the actual utility plant.
Hot gas cleaning technology has become a subject of world attention in terms of improved plant efficiency and lower flue gas emission from power plant. The application of Ceramic Tube Filter (CTF) to Pressurized Fluidized Bed Combustion (PFBC) combined cycle would be very promising as a clean coal technology. 71MWe PFBC combined cycle power plant by J-Power/EPDC in Wakamatsu was operated for approximately 11,500h and achieved extremely low dust emission (<0.2 mg/m3N) using a hot gas cleaning system combining cyclones and full scale Ceramic Tube Filter (CTF). The gas turbine installed downstream of the CTF was protected from the severe erosion with fly ash. CTF is one of the key technologies in hot gas cleaning domain. In this paper, the major concerns of CTF such as the seal mechanism, the pressure drop performance and the optimization in reverse cleaning conditions are reviewed for the commercial use of CTF.
Energy source is dependent on oil and natural gas in the world. However, the cost of such sources will increase in near future. In order to make provisions for this, the development of high efficiency power generation technology with coal and its steady operation are required. In the present paper, the history of development and demonstration test of dry gas clean-up technology for coal gasification power system is introduced. The dry gas clean-up technology has been evolved from a granular packed-bed dust collector (dry moving-bed dust removal system) to a dry moving-bed gas clean-up equipment which can simultaneously remove both sulfur and dust.
A discrete-trapezoidal sectional model is presented in order to simulate the time evolution of aerosol by condensation as well as by coagulation. The model calculates both number and volume concentrations of particles in the sectional regimes for testing the conservation of aerosol properties approximating the particle size distribution in an individual section with a linear function. The validity of the model was tested by the following two example calculations: the comparison of numerical result with the analytical result, and the numerical diffusion problem with coagulational and condensational growths. The test calculation with condensational growth showed that the seed particles in the sectional regime scavenged the condensational monomers in the discrete regime. The number of seed particles was conserved by the discrete-trapezoidal sectional model with a spacing factor of 2.460, whereas it was not conserved by the discrete-sectional model even with a spacing factor of 1.120.
Pollinosis, especially by cedar pollen, is discussed in the present paper. According to a recent report, the prevalence of cedar pollinosis patients was 16.2% in Japan. The main reason of increasing the cedar pollinosis patients in Japan is the postwar planting policy. In the present report, we review the mechanisms of pathogenesis, methods for clinical examination and treatments of pollinosis by cedar pollen.