| Fine particulate matter such as PM2.5 which derived from coal-fired power plants and other industries has a tremendous negative impact on the environment and human health. Using membrane filter to collect PM2.5 and other fine particles is an efficient method. However cake resistance in bag filter is too high which consumes high energy cost and hinders the development of bag filter. Cake resistance is usually determined by cake structure. Among other parameters influencing cake structure, porosity is the most important parameter which is closely associated with interparticle forces and particle properties. Humidity is one of the main external effective factors for adjusting the interparticle forces because liquid bridge may form between the gap of fine particles under moist environment which would enhance adhesion force between particles. During a traditional coal pretreatment process, coal was usually treated by coal washing before entering into the boiler and flue gas was generated from desulfurization and denitration process. These procedures would bring a certain amount of water into the flue gas. Thus it is of great importance to investigate the effect of humidity on the forces between dust particles in bag filter to energy saving purpose.In addition, the porosity is also related to particle properties. Particle size is the most basic parameters describing aerosol particles and dust particle size is rarely consistent. Therefore, evaluating the effect of particle size on performance of dust removal under different humidity porosity is also very important.This study investigated the effect of humidity on interparticle forces when relative humidity low 100% and air reached saturated. Using PTFE membrane as filter media, the effect of humidity on filter cake stacked behavior, cake resistance and mass loading was investigated. On the basis of these, the effect of particle size on performance of dust collecting under different humidity was also studied.Particle collapsed angle under different humidity showed that:(1) when the relative humidity was lower than 100%, force between the particles increased linearly; when the relative humidity reached 100%, adhesion between particles grew rapidly. When air reached saturation, as temperatures continued to rise, absolute humidity and the water vapour partial pressure increased as the temperature increased, particles collapsed angle linearly grew, compared with the unsaturated air particle interactions, adhesion between particles grew faster. (2) PTFE membrane under high humidity showed high cleaning performance which makes it possible to apply it to the bag filter at a high humidity. When the humidity changed from 0.0028g/g dry gas (dust concentration is 19.62g/m3)to 0.0414g/g dry gas (dust concentration is 30.91g/m3), filtration time changed from 609s to 5634s.Filtration experimental results indicated that:(1) Under fixed filter material and gas components, filter cake pressure drop ΔPc can be seen as a function of dust concentration c, surface filtration velocity Vs, porosity ε,filtration time t and particle diameter dp. Where c and t is the independent variable, and all humidity, Vs, dp are found to have a big influence on ε. (2) With increasing the humidity, adhesion force between particles increased, and micro-structure of filter cake was more lax, leading to a much lower cake resistance and higher mass loading, this would effectively extend the filtration cycle, reducing backwashing frequency. (3) With decreasing the particle size, filtration resistance increased, indicating that the dedust performance for smaller particles was more sensitive to the environment humidity. |
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