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The Editor feels honored to have been asked to undertake the important and challenging endeavor of developing the Encyclopedia of Chemical Processing that will cater to the needs of the rapidly changing world of the 21st century. The Editor is humbled to follow the impeccable work of the previous editor, Professor John J.
McKetta, who led the development of the Encyclopedia of Chemical Processing and Design, a total of 69 volumes, which has become one of the most authoritative reference sources for scientists, engineers, and practitioners for several decades. I would like to express my most sincere thanks and appreciation to the authors for their excellent professionalism and dedicated work. Needless to say, an encyclopedia of this nature would never exist if the expert authors had not devoted their valuable time to preparing the authoritative entries on their assigned topics.
I wish to thank all my colleagues and friends as well as the editorial board members for all their suggestions, comments, assistance, volunteerism, and patience. In particular, I appreciate the encouragements, guidance, and assistance provided by Mr. Russell Dekker, Dr. Chai-sung Lee, Dr. Angus, Dr. Liu, Dr. Speight, Dr. Robert Dye, Dr. Sunil Kesavan, Dr. John Zabasajja, Dr. Abhay Sardesai, Dr. Hirotsugu Yasuda, Dr. Retzloff, Dr. Patricia Roberts, Dr. Kelly Clark, Dr.
Encyclopedia Biomaterials Biomedical Engineering
Jeffrey Yen, Dr. Peter Pujado, and Dr. Stephen J. I also would like to thank Mr. Jonathan E. Wenzel, Ms.
Leah A. Leavitt, Dr. Cutright, Dr. Bryan Lanterman, Dr. Qingsong Yu, and Dr. Patricia A. Darcy for providing various assistance while editing. I am also deeply indebted to the former and current employees of the Publisher for their dedicated work toward successful completion of the project, to name a few, Ms. Alison Cohen, Ms.
Oona Schmid, Ms. Marisa Hoheb, Ms. Maria Kelley, Ms.
Meaghan Johnson, and Ms. Joanne Jay. The contributions of those mentioned made this Encyclopedia possible. Sunggyu Lee Editor. Absorption Equipment A Karl B. Absorption can be used to recover valuable gaseous components such as hydrocarbons or to remove unwanted gaseous components such as hydrogen sulfide from a stream. A valuable solute can be separated from the absorbing liquid and recovered in a pure, concentrated form by distillation or stripping desorption.
The absorbing liquid is then used in a closed circuit and is continuously regenerated and recycled. Examples of regeneration alternatives to distillation or stripping are removal through precipitation and settling; chemical destruction through neutralization, oxidation, or reduction; hydrolysis; solvent extraction; and liquid adsorption. Absorption is one of the main methods of separation used in the chemical processing industry.
Accompanied by chemical reaction between the absorbed component and a reagent in the absorbing fluid, absorption can become a very effective means of separation. Absorption can also be used to remove an air pollutant like an acid gas from stream. Then, the system could be a simple absorption in which the absorbing liquid is used in a single pass and then disposed of while containing the absorbed pollutant. Operations of Absorption Towers In the past it was the custom to call absorbers operating as cleanup towers to remove undesirable gaseous effluents by the name of scrubber.
At that time most of the effluent gases being removed were acid gases being scrubbed with water. The designation of scrubber to scrub the discharge gas and clean it seemed rather natural. Today the same kind of operation is carried out, but with more stringent regulations imposed by the local air pollution control agency. The name scrubber is now applied to those operations in which particulate matter is removed but the scrubbing operation may also include the simultaneous removal of gaseous pollutants. All rights reserved. In this chapter the term absorber will refer to the removal of gaseous contaminants.
General Considerations Filters, heat exchangers, dryers, bubble cap columns, cyclones, etc.
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However, units of special design for one-of-a-kind operations such as packed or plate towers are quite often designed and built under the supervision of plant engineers. Thus, there is a large variety of this type of equipment, none of it essentially standard. However, in both cases the flow is continuous. In the ideal equilibrium stage model, two phases are contacted, well mixed, come to equilibrium, and then are separated with no carryover.
Encyclopedia Of Chemical Processing (5 volume set) - mydepceitio.tk
Real processes are evaluated by expressing efficiency as a percentage of the change that would occur in the ideal stages. Any liquid carryover is removed by mechanical means. In the continuous absorber the two immiscible phases are in continuous and tumultuous contact within a vessel that is usually a tall column. A large surface is made available by packing the column with ceramic or metal materials. The packing provides more surface area and a greater degree of turbulence to promote mass transfer. The penalty for using packing is in the increased pressure loss in moving the fluids through the column, which causes an increased demand for energy.
In the usual countercurrent flow column, the lighter phase enters the bottom and passes upward. Transfer of material takes place by molecular and eddy diffusion processes across the interface between the immiscible phases. Contact may be also cocurrent or cross-flow. Columns for the removal of 1. Absorption can take place in a countercurrent, cocurrent, or cross-flow device.
Vertical countercurrent towers are either built with a metal, plastic, or ceramic packing or constructed as plate towers with various types of plates. This chapter will discuss the solvents used to carry out absorption and the various types of absorption equipment. The gas solubility should be high in the absorbing solvent.
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The gas leaving an absorber is usually saturated with the solvent; therefore, the solvent should have a low vapor pressure. A lower viscosity solvent is advantageous to promote more rapid absorption rates and improve flooding characteristics.
The solvent should not be corrosive to the materials of construction of the absorber. It should be nontoxic and nonflammable. Depending on the region where the absorber is to be constructed, the solvent should have a low freezing point. Nonaqueous Systems At first glance, an organic liquid appears to be the preferred solvent for absorbing hydrocarbon and organic vapors from a gas stream because of improved solubility and miscibility.
The lower heat of vaporization of organic liquids results in energy conservation when solvent regeneration must occur by stripping.
Many heavy oils such as No. Care must be exercised in picking a solvent that will have sufficiently low vapor pressure so that the solvent itself will not become a source of volatile organic pollution. Obviously, the treated gas will be saturated with the absorbing solvent. An absorberstripper system for recovery of benzene vapors has been described by Crocker. Although water is the most common liquid used for absorbing acidic gases, amines monoethanol-, diethanol-, and triethanolamine; methyldiethanolamine; and dimethylaniline have been used for absorbing SO2 and H2S from hydrocarbon gas streams.
Such absorbents are generally limited to solid particulate free systems because solids can produce difficult to handle. Furthermore, because of absorbent cost, absorbent regeneration must be practiced in almost all cases. Aqueous Systems Absorption is one of the most frequently used methods for removal of water-soluble gases.
Acidic gases such as HCl, HF, and SiF4 can be absorbed in water efficiently and readily, especially if the last contact is made with water that has been made alkaline. Less soluble acidic gases such as SO2, C12, and H2S can be absorbed more readily in a dilute caustic solution. Lime is a cheaper and more plentiful alkali, but its use directly in the absorber may lead to plugging or coating problems if the calcium salts produced have only limited solubility.
A technique often used is the two-step flue gas desulfurization process, where the absorbing solution containing NaOH is used inside the absorption tower, and then the tower effluent is treated with lime externally, precipitating the absorbed component as a slightly soluble calcium salt. The precipitate may be removed by thickening and the regenerated sodium alkali solution is recycled to the absorber.