Crystallization
is an important part of many chemical industries.
Efforts are being invested to improve the performance of the crystallization
process by designing novel crystallizers. An important aspect in the
development of new crystallizers is the ability to describe the behavior
of such units in terms of rigorous dynamic mathematical models and
solving the resulting models efficiently. The current bottleneck in
modeling crystallization systems is the complexities associated with
the crystal birth, growth, and death processes using population balance
equations. In this article, various crystal birth, death, and growth
models are introduced and reviewed. Population balance models as well
as solution methods (e.g., analytical, moment methods, discretization
(classes/sectional) methods and Monte Carlo methods) are also reviewed,
and new advances in solution methods are described. Population balance
equations are used in other fields, and developments from other fields
that can be extended to crystal population balance equations are included
in this review.
This review aims at the treatment of the entire landfill, including the waste mass and the harmful emissions: leachate and landfill gas. Different landfill treatments (aerobic, anaerobic and semi-aerobic bioreactor landfills, dry-tomb landfills), leachate treatments (anaerobic and aerobic treatments, anammox, adsorption, chemical oxidation, coagulation/flocculation and membrane processes) and landfill gas treatments (flaring, adsorption, absorption, permeation and cryogenic treatments) are reviewed. Available information and the gaps present in current knowledge is summarized. The most significant areas to expand are landfill waste treatments, which in recent years has begun to grow but there is an opportunity for much more. Another area to explore is the treatment of landfill gas, a very large field to which not much effort has been put forth. This review is to compare different treatment methods and give direction to future research.
The development of a portable oxygen concentrator is of prime significance for patients with respiratory problems. This paper presents a portable concentrator prototype design using the pressure/vacuum swing adsorption (PVSA) cycle with a deep evacuation step (−0.82 barg) instead of desorption with purge flow to simplify the oxygen production process. The output of the oxygen concentrator is a ~90 vol % enriched oxygen stream in a continuous adsorption and desorption cycle (cycle time ~90 s). The size of the adsorption column is 3 cm in diameter and 20 cm in length. A Li+ exchanged 13X nanosize zeolite is used as the adsorbent to selectively adsorb nitrogen from air. A dynamic model of the pressure and vacuum swing adsorption units was developed to study the pressurization and depressurization process inside the microporous area of nanosized zeolites. The describing equations were solved using COMSOL Multiphysics Chemical Engineering module. The output flow rate and oxygen concentration results from the simulation model were compared with the experimental data. Velocity and concentration profiles were obtained to study the adsorption process and optimize the operational parameters.
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