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Principles of unit operations
01 Jan 1960-
TL;DR: In this article, the authors present an approach to unit operations in chemical engineering, including the following: Mass Transfer, Heat Transfer, Evaporation and Crystallization, Humidification, and Drying.
Abstract: Unit Operations in Chemical Engineering. STAGE OPERATIONS. Mass Transfer Operations. Phase Relations. Equilibrium Stage Calculations. Countercurrent Multistage Operations. Countercurrent Multistage Operations with Reflux. Simplified Calculation Methods. Multicomponent State Operations. MOLECULAR AND TURBULENT TRANSPORT. Molecular Transport Mechanism. Differential Mass, Heat, and Momentum Balances. Equations of Change. Turbulent-Transport Mechanism. Fundamentals of Transfer Mechanisms. Interphase Transfer. APPLICATIONS TO EQUIPMENT DESIGN. Heat Transfer. Mass Transfer. Simultaneous Heat and Mass Transfer--Humidification. Simultaneous Heat and Mass Transfer--Drying. Simultaneous Heat and Mass Transfer--Evaporation and Crystallization. The Energy Balance in Flow Systems. Fluid Motive Devices. Particulate Solids. Flow and Separation through Fluid Mechanics.
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TL;DR: In this article, a review of the separation technologies used for animal slurry treatment and the physical and chemical processes involved in separation is presented, and a simple separation efficiency expression can be used to assess the efficiency of slurry separation.
Abstract: Animal slurry contains plant nutrients that are essential for crop production. However, intensive livestock production may lead to a surplus of plant nutrients on farms and, as a consequence, discharge or emission to the environment. In order to ensure that the slurry applied to fields matches the nutrient requirements of the crops, techniques have been developed to reduce the nutrient content of slurry by means of separation. This review discusses the separation technologies used for animal slurry treatment and the physical and chemical processes involved in separation. These processes need to be understood before efficient, reliable and cheap separation technologies that take into account the actual properties of slurry and the likely end-use of the separation products can be developed. A simple separation efficiency expression can be used to assess the efficiency of slurry separation. It is indeed important to measure the amount and composition of the slurry before treatment, the dry-matter-rich fraction and the liquid fraction. The separation efficiency of mechanical separators for the removal of dry matter and phosphorus (P) is ranked as follows: centrifugation > sedimentation > non-pressurized filtration > pressurized filtration. In general, the separation of total N and NH + follows the same pattern, but the separation efficiency is lower than for dry matter and P. Treatment with a flocculant before separation improves separation efficiency significantly. Of the polyacrylamide polymers tested, high-molecular-weight, linear cationic polymers with a medium charge density (20-40 mol%) were found to be the most efficient flocculants. The best mechanical separation techniques for flocculated slurry are screens or filter belts. The separation efficiency of polyacrylamide-treated slurry can be improved by adding a multivalent ion to coagulate particles and for precipitation of phosphorus. Aluminium sulfate (Al2(SO4)3 )o r ferric chloride (FeCl 3) seem to be very efficient for improving the mechanical separators. Alternatively, the mineral struvite (MgNH4PO4) may be formed by changing the slurry characteristics, such as by the addition of magnesium (Mg) or by increasing the pH to 9. The struvite crystals are removed during solid-liquid separation. The products of the solid-liquid separation may be further treated by evaporation, membrane filtration or ammonia stripping in order to obtain the desired end-products; however, low-maintenance and/or cost-efficient operation of these post-treatments has not yet been demonstrated. The separation should be developed as a whole-system approach, paying attention to parameters such as the value of end-products, environmental consequences and economy.
342 citations
TL;DR: Avnir et al. as discussed by the authors analyzed and reinterpreted previously published experimental data, revealed the following surface-fractal dimensions, all falling in the expected range 2.0 to 3.0.
310 citations
TL;DR: In this article, a full factorial design was used to analyze the effects of pH, stirring rate and contact time in adsorption capacity of food dyes acid blue 9 and food yellow 3 onto chitosan.
195 citations
07 Jan 2011
TL;DR: In this paper, a review of the separation technologies used for animal slurry treatment and the physical and chemical processes involved in separation is presented, and a simple separation efficiency expression can be used to assess the efficiency of slurry separation.
Abstract: Animal slurry contains plant nutrients that are essential for crop production. However, intensive livestock production may lead to a surplus of plant nutrients on farms and, as a consequence, discharge or emission to the environment. In order to ensure that the slurry applied to fields matches the nutrient requirements of the crops, techniques have been developed to reduce the nutrient content of slurry by means of separation. This review discusses the separation technologies used for animal slurry treatment and the physical and chemical processes involved in separation. These processes need to be understood before efficient, reliable and cheap separation technologies that take into account the actual properties of slurry and the likely end-use of the separation products can be developed. A simple separation efficiency expression can be used to assess the efficiency of slurry separation. It is indeed important to measure the amount and composition of the slurry before treatment, the dry-matter-rich fraction and the liquid fraction. The separation efficiency of mechanical separators for the removal of dry matter and phosphorus (P) is ranked as follows: centrifugation > sedimentation > non-pressurized filtration > pressurized filtration. In general, the separation of total N and NH4 + follows the same pattern, but the separation efficiency is lower than for dry matter and P. Treatment with a flocculant before separation improves separation efficiency significantly. Of the polyacrylamide polymers tested, high-molecular-weight, linear cationic polymers with a medium charge density (20–40 mol%) were found to be the most efficient flocculants. The best mechanical separation techniques for flocculated slurry are screens or filter belts. The separation efficiency of polyacrylamide-treated slurry can be improved by adding a multivalent ion to coagulate particles and for precipitation of phosphorus. Aluminium sulfate (Al2(SO4)3) or ferric chloride (FeCl3) seem to be very efficient for improving the mechanical separators. Alternatively, the mineral struvite (MgNH4PO4) may be formed by changing the slurry characteristics, such as by the addition of magnesium (Mg) or by increasing the pH to 9. The struvite crystals are removed during solid–liquid separation. The products of the solid–liquid separation may be further treated by evaporation, membrane filtration or ammonia stripping in order to obtain the desired end-products; however, low-maintenance and/or cost-efficient operation of these post-treatments has not yet been demonstrated. The separation should be developed as a whole-system approach, paying attention to parameters such as the value of end-products, environmental consequences and economy.
166 citations
TL;DR: In this paper, the authors measured apparent mass diffusivities during osmotic processing of model fruit (apple) and vegetable (potato) tissues and found that temperature had the largest positive effect on moisture and soluble solids diffusivity.
145 citations