The mechanical integrity of ceramic filter elements is a key issue for hot gas cleanup systems. To meet the demands of advanced power systems, the filter components sustain thermal stresses of normal operations (pulse cleaning), of start-up and shut-down, and of process upsets such as excessive ash accumulation without catastrophic failure. They must also survive various mechanical loads associated with handling and assembly, normal operation, and process upsets. For near-term filter systems, the elements must also survive operating temperature of 1650°F for three years. Objectives of the testing conducted were as follows: (1) measure basic physical, mechanical and thermal properties of candle filter materials and relate these properties to in-service performance, (2) perform post-exposure testing of candle-filter materials after service at Tidd and Karhula and compare post-exposure results to as-manufactured results to evaluate property degradation, (3) based on measured properties and in-service performance, develop an understanding of material requirements for candle-filter materials and help establish property goals, and (4) establish a test protocol for evaluation of candle filter materials.
The objectives of this program have been: (1) the post-test evaluation of candle filters, (2) to measure the material properties of current filter materials, destructively and non-destructively, and to relate these properties and behaviors to in-service performance, (3) to develop an understanding of the material requirements for hot gas filter elements, (4) to develop material property goals for filter materials, and (5) to establish test matrices and a protocol to evaluate candidate filter materials.
Abstract: Clay based ceramic materials have been used in various parts of the world as a medium to purify and store water at points of use. United Nations and several other non governmental agencies are distributing these sustainable clay ceramic filters with embedded organic or carbonaceous materials to areas with scarcity of potable water. For example, rural areas in developing low income economies, disaster relief operation during flooding and many more on the list. Several studies have taken place on these clay ceramic filters. There is a large amount of literature documented on the flow behavior through these clay ceramic filters, field studies on microbial removal effectiveness, structural damage of filters while in use and during transport, people/societies satisfaction and health impact of using these ceramic filters. Here gravity operated frustum shaped clay ceramic filter have been manufactured using distinct volume ratios of clay and sawdust (organic material). This study has been done in order to individually assess the material parameter influencing flow, leaching and strength of these clay composite filters. Reduction in flow is seen with time and filtration events imposing the need for scrubbing/cleaning of these filters. Similarly with fractional changes in embedded organic / carbonaceous material, there is a change in micro-structural and mechanical properties. Micro-structural, flow and mechanical characteristics change geo-spatially due to non availability of similar raw material constituents at different locations around the globe. Functional challenges such as water contaminants, material composition are not the same everywhere. In this situation it is a must to investigate the stochastic effects on micro-structural, filtration flow/percolation and mechanical properties of these ceramic clay materials. The cumulative flow has been modeled using a multi-parameter stochastic multiplicative model with time and volume fraction of the organic raw material used in the initial manufacture of the filter. The asymptotic regimes of cumulative discharge have been mathematically simulated using a predictor transformation for each of the different types of samples discussed. Material studies also confirmed a linear relationship between porosity and volumetric content of organic material used in the manufacture of these clay ceramics. Mechanical properties of materials depend on the micro-structural features, compositional ratios as well as loading rates which they bear. Tensile fracture toughness development is found to follow a multiplicative behavior with respect to predictor variables like amount of organic material used for manufacturing, micro-structural porosity and applied force. Plastic flow during manufacture is found to influence mechanical properties in clay ceramics. The alkalinity of the filtrate and its changes with time and material has been studied. Stochastic multivariate regression analysis on the principles of non equilibrium processes with respect to flow taking place through the filters has been used to provide extension to regression hypothesis proposed by Onasager for aqueous solution and porous flow mechanics. It was found that transport processes were dependent on each other but they also varied with time without losing their interdependence. It is to be noted that microbial transport though these micro-nano porous ceramic filters are negligible. These filters showed similar microbial removal as confirmed by different authors earlier. This phenomenon may help in reduction of health problems due to drinking water. So in order to test these filters in an economically low income society setting, these filters were introduced in Eweje Village, Ogun State, Nigeria. A nine month survey was conducted with an objective to find the independent variables which may influence health in areas where these filter are being utilized. It was found that time of filter usage, traditional medicinal knowledge/medical facility access and money were the top influencers of health in Eweje Village, Ogun State, Nigeria.
Approximately four million years of human history has passed. We have been using materials to make a variety of tools. The first materials used were naturally occurring materials such as animal bones, stones, wood etc.; and some of these familiar materials are porous. Porous materials are so familiar that they are sometimes forgotten or ignored. The taste experience of ice cream is created not only by adjusting ingre dients, but also by including air as an ingredient, i.e. pores that give the smooth texture of ice cream. This book is designed to describe and explain about pores, the synthesis of materials with pores (porous materials), and applications of porous materi als. This book is intended for engineers and scientists of different disciplines and specialities, and is expected to be useful in the design and synthesis of porous materials for existing as well as potential new applications. Let us rediscover pores. K. Ishizaki, S. Komameni and M. Nanko January 1998 1 Introduction 1.1 WHAT ARE POROUS MATERIALS? Porous materials are dermed as solids containing pores. Figure 1.1 shows different porous materials. Generally speaking, porous materials have a porosity of 0.2-0.95. The porosity means the fraction of pore volume to the total volume. Porous materials have been used in various applications from daily necessities, such as purifying drinking water by activated carbon or porous ceramics, to uses in modern industries, for example removing dusts from high purity process gases for semiconductor production.
The objective of this study is to evaluate changes in structure and mechanical properties of ceramic filter materials under simulated corrosive process conditions. Due to an analysis of the mechanisms of degradation firstly an optimization of materials shall be enabled and secondly a material selection for specific applications shall be relieved. This publication describes the investigations made on many ceramic support materials based on oxides and carbides. Both commercially available and newly developed support materials have been evaluated for specific applications in hot gas cleaning.
Field testing in several of the Westinghouse Advanced Particulate Filtration (APF) systems has indicated that the oxide-based materials are more susceptible to thermal shock which results from system transients (i.e., combustion of char or reducing gases; system startup/turbine transients). The current clay bonded silicon carbide filter materials have a higher thermal shock resistance, but appear to be more susceptible to high temperature creep, as well as to changes that occur within the binder phase(s). Strength has frequently been used to assess what effects advanced coal fired process systems have on the stability and projected life of the various porous ceramic filter materials (Tables 1 and 2). Based on the numerous phase changes that occur, and the influence of pulse cleaning on the thermal fatigue characteristics of both the alumina/mullite and clay bonded silicon carbide filter materials, alternate material properties as thermal conductivity, thermal coefficient of expansion, elastic modulus, fracture toughness, and emissivity as a function of thermal/chemical aging are now being considered as critical factors for projecting filter durability and operating life. Table 3 provides a summary of the as-manufactured material properties for the alumina/mullite and clay bonded silicon carbide filter materials which have been used in the Westinghouses̀ APF systems. Effort is currently being directed to determine how these properties change during thermal aging of the filters in various subpilot and pilot plant systems.
