Showing papers in "Chemical Engineering in 1998"

Homing in on the best size reduction method

Abstract: Old-time textbooks called the unit operation crushing and grinding, but it has acquired a better name, size reduction. As long as materials enter a process in big pieces, but must be treated in smaller pieces, there will be a need for rugged mechanical equipment to do the job. The designer, faced with the task of buying the best machine, finds plenty of equipment descriptions, but really needs a guide that accelerates homing in on the most appropriate type. This article is intended to be that guide. We were able to categorize the machines into nine types. For a first pass, an engineer works with two parameters: output particle size and Mohs hardness. This narrows the choice of equipment to one, two, or three categories. Finally, applying special requirements of a particular industry segment will reduce the choice to a single category. Now, the task becomes selecting the best vendor among those offering similar equipment. This article is organized so as to introduce the first-pass process, and then to follow on with a description of machines in each category. This spotlights many special requirements that may dictate putting two types of machines in series, or adding a classifier.

How to specify pressure-swing adsorption units

Abstract: This article provides information on how PSA works, and on how to select and specify the equipment for such a system.

Abating halogenated VOCs

Abstract: In this article, we summarize the advantages and limitations of ten major technologies (condensation; adsorption by carbon; pressure- and temperature-swing adsorption; membrane separations; a combination of rotor concentration plus adsorption; conventional thermal oxidation; flameless thermal oxidation; catalytic oxydation; rotor concentration plus oxidation; biotrickling filtration) for dealing with halogenated VOCs (HVOC). We also present the results of a recent DuPont study that assesses not only their technical but also their economic feasibilities. The findings are summarized in a selection map that shows the best end-of-pipe treatment for any given combination of flowrate and HVOC concentration. As already noted, this is useful not only for selecting an end-of-pipe option but also for benchmarking possible pollution-prevention strategies.

Corporate espionage : No longer a hidden threat

Abstract: In the U.S. alone, theft of formulas, process information, blueprints, business plans and customer lists is causing losses of $250 billion/yr. The best defense? Good training programs, clearcut procedures and strict employment contracts.

Improving boilers and furnaces

Abstract: The guidelines for burning fuels are detailed in a table. Even with good controls, one must have some excess air for safety purposes. CO will increase drastically along with smoke when air is deficient, i.e., excess fuel. State-of-the-art monitoring and controls are commercially available in the US. Use these instruments to measure several components (CO, NO{sub x}, CO{sub 2}, SO{sub 2}). The authors recommends the following procedures for better performance: train workers in both safety and fuel-saving operations; always control the air-to-fuel ratio so that a slight excess of air is present; install a CO-monitoring controller, especially when using natural gas; industrial analyzers cost around $50,000, portable analyzers cost under $1,000. Get both. Payback for both should be less than 12 months, depending on the burner capacity and the quality of training. These procedures will save fuel. They may save on insurance rates. In fact, they may save your life.

Extractive distillation : Separating close-boiling-point components

Abstract: This article focuses on the selection of cosolvents for various hydrocarbons separations using extractive distillation.

Mix or match: Choose the best mixers every time

Abstract: This article describes the basic types of mixers, and summarizes their advantages and disadvantages. It focuses on general design considerations, intended functions, capacity ranges, strengths and weakness, and typical applications for the various types.

New molecules get on the fast track

Abstract: Combinatorial chemistry and computer-based molecular simulation are teaming to yield performance-based compounds.

Optimizing dryer performance : Through better control

Abstract: This two-part article will highlight a number of traditional and advanced control systems for both batch and continuous dryers in systems involving air drying with water as the solvent. This part (1) will review the fundamentals of the drying process, and discuss some basic dryer designs and control parameters. Part 2 will focus on more-advanced control startegies

Optimizing dryer performance through better control. Part 1

Abstract: Drying is among the most difficult processes, as evidenced by the wide assortment of dryer types available. Enhanced process control can improve both product quality and the energy efficiency of the drying process. This two-part article will highlight a number of traditional and advanced control systems for both batch and continuous dryers in systems involving air drying with water as the solvent. Part 1 reviews the fundamentals of the drying process, and discusses some basic dryer designs and control parameters. Part 2, to appear in March, focuses on more-advanced control strategies.

Pilot plants confirm process validity

Abstract: This article discusses the type of equipment used, the parameters studied, and the data collected to proceed with confidence to commercial scale-up.

Safe, efficient handling of acids

Abstract: Acids are among the most widely used chemicals in the chemical process industries (CPI). They serve as reactants, solvents and catalysts in such diverse industries as chemicals and pharmaceuticals manufacture, petroleum refining and minerals processing. Their corrosive nature strongly influences the design of process equipment and piping systems, and dictates various storage and handling procedures. This article provides such information applicable to inorganic acids in general, plus guidelines relevant for sulfuric acid, in particular. And this article offers insight into the proper selection and handling of hose for acid service.

Put the breaks on wastewater emulsions

Abstract: Emulsions in wastewater pose a vexing problem for facilities attempting to recycle water and stay in compliance with permissible discharge limits. But the challenges are no less formidable for routine maintenance. The removal of emulsions, a major constituent of which are fats, oils and greases (FOGs), is necessary to prevent them from depositing on pipes and fouling filtration media. Some of the havoc caused by emulsions can be avoided if emulsions are broken and removed from wastewater streams. Successful emulsion breaking requires a basic understanding of emulsions, their chemical composition, and the technologies required to remove them from water. The paper discusses emulsion basics and emulsion breaking, including counteracting emulsions, testing procedures, physical separation methods, removal strategies, bentonite-based powders, and post-polishing.

Life cycle costs for chemical process pumps

Abstract: Though construction and startup costs are always a concern, proper investment in equipment and installation will save money down the line This is particularly important for heavily used items, such as centrifugal pumps, one of the workhouses of the chemical process industries (CPI) By properly sizing and installing a centrifugal pump, the life and efficiency of the pump can be increased At the same time, maintenance costs can be reduced When considering a new pump, there are several areas that require attention The first is the baseplate design The impeller is another area of concern The seal chamber, the third area of importance, must be designed for proper heat dissipation and lubrication of seal faces Lastly, the power end must be considered Optimum bearing life, effective oil cooling and minimum shaft deflection are all vital The paper discusses installation costs, operating cost, maintenance cost, seal environment, and extended bearing life

Calculate ΔP of a fixed-bed filter

Abstract: This article presents a pair of graphs for estimating the pressure drop in a fixed-bed granular filter based on well-known correlation proposed by Ergun. It allows to calculate the pressure drop in a porous medium composed of particles of a given diameter and porosity. Only a few equations are needed.

Toxics and combustibles: Designing gas-detection systems

Abstract: When a plant decides to install a gas-detection system, several questions come to mind: How many detectors are needed and where should they go? Simple questions--but unfortunately ones without a simple answer. However, there are some general considerations that plant personnel can use to rough out a gas-monitoring installation. Any evaluation process should include the following five steps. Each is discussed: (1) Understand the application; (2) Identify potential danger points; (3) Establish design goals; (4) Determine gas characteristics; and (5) Profile the plant and potential release scenarios.

Designing and troubleshooting plate heat exchangers

Abstract: Since they were introduced in the 1930s, plate heat exchangers (PHE) have improved considerably, becoming both cost-effective and versatile. PHE models offer an economical alternative to the more-traditional shell-and-tube models, in a more compact size. However, to allow PHEs to achieve top efficiency and to minimize maintenance costs and downtime, design engineers must carefully consider operating conditions and potential maintenance requirements. Process engineers, in turn, must be aware of simple, but critical, troubleshooting techniques. This article will outline both specification and operating tips. The paper discusses plate depth and patterns, materials selection, gasket material, temperature and gasket life, glued or gluefree gaskets, opening the PHE, replacing the gaskets, plate inspection, closing the PHE, corrosion and erosion.

CPI drive refractory advances

Abstract: Although the steel industry consumes the lion's share of refractory material, the push for improving product quality and performance comes from the chemical process industries (CPI), modest consumers of refractories. Progress in adapting better materials in the CPI is slow, partly due to concerns over the costs of unscheduled outages triggered by premature failures. However, as more operators learn that improved materials are available, these will replace the older refractories in short order. We think that substitutions that waited three years for approval could now occur in six months. This article emphasizes the customer's role in achieving the best possible installed quality and suggests that the time to commercialize new products could be dramatically reduced.