Studies on Dehumidification Potential of Clay with Additives and Impregnated With CaCl2 Composite Desiccants

Abstract

The present work features the preparation and estimation of properties, dehumidification performance assessment and utilization of clay based composite desiccants. Transported clay suitable for pot making is used as desiccant carrier. Composite desiccant is formulated such that transported clay is heat treated (burnt clay) and impregnated with CaCl2. To improve the performance of desiccant carrier, composite desiccants were synthesized using two additives namely saw dust and horse dung. Transported clay are moulded to near spherical shape and are subjected to shadow drying and later dried at higher temperature in a furnace. The heat treatment at 500°C reveals higher weight reduction and porosity. Heat treated desiccants are then characterized by scanning electron microscopy (SEM), Brunauer Emmet Teller (BET) and X-ray diffraction (XRD) techniques. The BET test reveals that clay samples subjected to 500°C posses higher pore volume and clay-horse dung particles exhibit higher surface area. Heat treated desiccants namely clay, clay with 20% saw dust and clay with 20% horse dung are impregnated with CaCl2 solution of 50% concentration by soaking method. The SEM image and elements analysis indicated that the composite desiccant has porous surface and uniform distribution of CaCl2 due to heating at 500°C. XRD pattern indicates the porous nature of burnt clay-additives composite desiccant. The decrease in height of diffraction peaks with CaCl2 impregnation reveals the presence of CaCl2. The variation of thermo - physical properties like thermal diffusivity, specific heat, density and thermal conductivity of burnt clay with and without impregnation of CaCl2 and the effect of additives, namely, saw dust and horse dung at various percentages is investigated. Rapid transient measurement technique is used for the measurement of thermal diffusivity. Specific heat is determined by energy balance. The addition of saw dust and horse dung is seen to increase the specific heat of clay additives with CaCl2 impregnated desiccants. The packed bed performance under the influence of inlet air humidity ratio, and temperature is presented experimentally. The heat of adsorption during the process is low and the bed operates at constant temperature, one dimensional PGC mass transfer model is adopted from conservation principle. The experimental results for reduction in moisture content are compared with theoretical results.iv Adsorption - desorption experiments for moisture removal and addition from atmospheric air are conducted in vertical column in static and fluidized states. The desiccant beds are subjected to an initially set value of process air velocity, relative humidity, temperature and mass of bed. Moisture removal capacity, moisture addition capacity and heat content are the parameter indices adopted to measure the heat and mass transfer characteristics of vertical packed and fluidized bed comprising clay - additives - CaCl2 composite desiccants. On comparing packed and fluidized beds, fluidization improves dehumidification performance and results in higher desorption rates. The results of the experimental study reveals that higher adsorption rates increases the water content of desiccant particles and found to enhance the cooling effectiveness coupled with dehumidification. Irrespective of the clay composite desiccant beds, higher enthalpy of process air exiting the composite desiccant beds is associated with higher adsorptivity. A forced circulation laboratory model desiccant drying system operating in open loop was constructed and arranged. The green pea drying process is divided into two processes involving dehumidification by desiccant bed and grain drying by dehumidified process air. Moisture removal from the process air takes place by vertical packed composite desiccant bed. The grains were dried for process time of one hour. The experimental study reveals average heat content of air entering the dryer is 1.46, 2.46 and 2.38 kJ for burnt clay - CaCl2, burnt clay - horse dung - CaCl2 and burnt clay - sawdust - CaCl2 beds of mass 700 g. The drying is quite sharp during initial process time of 500 s and from then onwards drying of green peas proceeds at constant rate. Finally the potential and perspective of fabricated desiccants in dehumidification and thermal enhancement is being outlined. The key contributions of the present research work highlights the development of low cost composite desiccants using naturally available materials like clay, horse dung and saw dust. These desiccants have potential application in agriculture, HVAC industry, and water extraction from atmospheric air.