Archives :: Technical & Practical

Displaying 341 - 360 of 533 stories.
February 1, 2009
Eye injuries of all types occur at a rate of more than 2,000 per day in the U.S., and half of those occur in the workplace. In 2006, the U.S. Bureau of Labor Statistics (BLS) reported over 52,000 workplace injuries to the eyes and face, and approximately 70% of those were eye injuries [1]. The need to protect the face and eyes in the workplace is clear. FIGURE 1.  Safety glasses help shield eyes from...
February 1, 2009
Global warming is of major concern today. There is increasing pressure on industry to reduce both energy usage and the associated CO2 emissions. An important and profitable action that industry can take is to recover more process energy and thus improve the efficient use of that energy. This not only reduces the cost of primary energy supply and lowers CO2 emissions, but also provides benefits in terms of...
February 1, 2009
The use of gasketed plate-and-frame heat exchangers has gained tremendous acceptance in the chemical process industries (CPI) over the past 20 years due to their high heat-transfer coefficients, compactness and low cost. However, it is important for the engineer who is selecting this type of heat exchanger to be aware of critical areas in design or selection so that possible operating or maintenance...
January 13, 2009
I would like to draw your attention to a few points on the November 2008 article, Pressure Relief System Design (pp. 40–45): 1. Pressure drop and pressure loss: The inlet pressure “drop” that the author refers to under Relief system piping is non-recoverable pressure loss, and does not include a “drop” in pressure due to elevation increase. It should be labeled as a pressure...
January 1, 2009
As an energy resource, global coal reserves represent 2,000 billion barrels of oil equivalent. In 2007, global oil reserves were about 1,300 billion barrels of oil. World wide, oil demand will grow 40 to 50% by 2030. But coal offers an opportunity to diversify worldwide liquid-fuel supplies and coal utilization to produce fuels that can extend the lifetime of world oil reserves. This is a strategic...
January 1, 2009
Here, we present criteria needed for the intelligent, effective specification of trays for a distillation or stripping column. Among the key parameters and accessories during specification are column diameter, tray spacing, number of trays, number of passes, type of downcomers, weir heights, provision of downcomer backups, tray pressure drops, design of bottom seal pan, column bottom arrangement, and...
January 1, 2009
Here, a design approach for continuous stirred-tank reactors is outlined for both reversible and irreversible second-order reactions Multiple CSTRs (continuous stirred-tank reactors) are advantageous in situations where the reaction is slow; two immiscible liquids are present and require higher agitation rates; or viscous liquids are present that require high agitation rates. Unlike in plug-flow reactors...
January 1, 2009
Ceramic filters are well suited for high-temperature processes that are subject to strict emissions limits, including those for dioxins About Incineration Incineration processes are being widely used more and more to deal with the disposal of waste materials. In many countries, land filling of waste materials is not practical or desirable due to a lack of appropriate sites. Incineration has the benefit of...
January 1, 2009
In today’s fast track schedules for constructing new capital facilities, the process of designing, delivering and erecting piping often falls in the project’s critical path. This is particularly true for facilities constructed in emerging economies, where the facility generally resides in a remote location, posing significant logistical challenges. Squarely positioned in the center of the...
January 1, 2009
Frequently, in chemical processing equipment it is possible to place the shaft support bearings in the chemical that is being processed. In some cases, this precludes the use of oil- or grease-lubricated bearings because the operating conditions are not conducive to the use of such materials. For example, bearings that are lubricated with oil or grease can be problematic when submerged in liquids such as...
December 1, 2008
In a fired thermal fluid heater, a thermal fluid is heated by the metal surfaces of a fired heater or fluegas heat-recovery exchanger. Generally, the heat input rate is controlled to achieve some desired bulk-fluid temperature exiting the heater. However, in being heated to the outlet setpoint, the fluid film in contact with the heating surface is always exposed to a higher temperature than the bulk fluid...
December 1, 2008
Organic-based thermal fluids provide relatively trouble-free service for significant periods of time. However, there comes a time when any fluid (either aromatic- or aliphatic-based) needs to be replaced. Since aromatic-based fluids generally cost more and are complicated to dispose of, they receive far more attention than aliphatic-based fluids when the time comes for replacement. Aliphatic-based fluids...
December 1, 2008
Lubricant contamination in gearbox bearing housings can substantially reduce gear life. In critical applications, dual-face, magnetic bearing-protector seals will keep contamination out (Figure 1). Dual-face, magnetic bearing protectors are preferred in many difficult applications, such as wet cooling tower gearboxes, while advanced rotating labyrinth seals are more universally applicable. Both users and...
December 1, 2008
Engineers often need to fit experimental data to an empirical relationship for extrapolation or modeling without resorting to a full mathematical treatment based on physical principles or theory. The most widely used platform in science for doing this is MS Excel, and while its "off-the-shelf" Trendline tool is useful, it is limited to only 4 or 5 simple functions. Excel’s Solver add-in, on...
December 1, 2008
The thermal conductivity of hydrocarbons is an essential parameter that needs to be known when designing heat transfer equipment. Presented here is a simple-to-use correlation that was developed for predicting thermal conductivities of liquid paraffin hydrocarbons, petroleum fractions and atmospheric natural hydrocarbon gases as a function of temperature and molecular weight or relative density. Results...
November 1, 2008
Process modeling has progressed from the "molecule accounting" of steady-state flowsheeting packages to become a central platform for capturing and deploying chemical process industries’ (CPI) intellectual property (IP). Systematic modeling has moved center stage to help companies differentiate themselves from their competitors while also providing a set of tools with which it is possible...
November 1, 2008
  Pressure relief systems are vital in the chemical process industries (CPI) for handling a wide variety of situations. They are used to prevent pressurization above a system’s design pressure; for venting during an unusual or emergency situation; and for normal depressurization during a shutdown, as examples. In some cases, such as when non-combustible gases including steam, air and nitrogen...
November 1, 2008
Management is a process of managing risk; maintenance management is a process of managing risk for operational reliability. Since it is hard to manage what cannot be measured, effective maintenance management demands good data on machine health — a comprehensive condition monitoring program, carried out by skilled and determined personnel, using appropriate tools and technology. Condition-based...
November 1, 2008
A very common heat exchanger in the chemical process industries (CPI) is the vertical thermosiphon reboiler (VTR; Figure 1). Due to size and fluid-flow restrictions, however, its heat transfer rate is often quite low. The subcooled region formed at the thermosiphon’s tube-bundle base usually causes reduction in the tubes’ average heat-transfer coefficient. Improvements in performance can be...
October 15, 2008
Pumps Centrifugal pumps with cast or forged steel casings are typically appropriate for systems with large flowrates Positive displacement pumps frequently can handle smaller flowrates of less than 100 gal/min Sealless pumps (canned motor or magnetic drive) avoid the installation of mechanical seals A typical centrifugal pump can be expected to deliver operational head of about: where g is gravitational...
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