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November 1, 2012
Preventing dust explosions is not rocket science, and still these disasters occur. This article is written to help prevent these accidents. It describes how and why these explosions happen and what can be done to avoid them. Why they occur Dust explosions occur when three conditions are present simultaneously. The first is that there is a dust cloud of a combustible material (the fuel). The second...
September 1, 2012
Contact agitated dryers are used for drying wet powders, slurries, filter cakes, and applications where off-gases during the drying cycle must be contained. If the applications are also heat-sensitive, such as specialty chemicals, polymers, food products and pharmaceuticals, contact drying must take place at low heating temperatures, at residence times in tune with the tolerance of the product, and...
August 1, 2012
There is a temptation that steam design engineers find difficult to resist — to put condensate from high-pressure (HP) steam mains directly into the low-pressure (LP), pumped condensate-return (CR) mains. After all, the CR main is so convenient — it is generally laid right next to the outgoing steam main in the same tunnel, trench or racks as the CR main returning to the steam plant. And, the...
August 1, 2012
The earliest application of the fundamental concepts of fluidization dates back to 16th century when a German scientist (Georgius Agricola) described a process to upgrade ores. However, it was not until the 1930s, with the development of the Winkler coal-gasification process, that commercial use of fluidized beds on an industrial scale was recognized. The need for gasoline during the World War II...
June 1, 2012
Throughout the chemical process industries (CPI), the need to drain a tank or process vessel arises. In batch-type plants, it is a regular occurrence and is one factor that affects the total cycle time per batch and ultimately the entire production capacity of the plant itself. Figure 1. In a vertical cylindrical, flat-bottom tank, liquid is flowing into the outlet nozzle (point 1) located at x...
April 1, 2012
In the chemical process industries (CPI) it is often necessary to verify material specification at various points in the process. In that effort, it is usually impossible — or at the very least impractical — to measure the whole production. Instead, small samples must be extracted from a parent population. Such is the case in particle size characterization of bulk solids, process streams and...
February 1, 2012
Various misconceptions arise when it comes to the thermal design of cooling towers. Sometimes related parameters, such as range, approach, effectiveness, liquid-to-gas ratio ( L/G), wet-bulb temperature, cooling water temperature, relative humidity, number of transfer units (NTU) and other terms create a confusion for the designer in effectively sizing, selecting and evaluating a particular cooling tower...
October 1, 2011
Equilibrium stage simulations are the nearly universal process design tool for mass transfer columns that contact vapor and liquid in countercurrent flow. Whether the service is absorption, stripping, distillation, fractionation, quench or evaporation, equilibrium stage models make mass and heat balances easy. They quickly estimate stream conditions and physical properties. They are easily altered, so a...
September 1, 2011
Dilute-phase conveying systems generally use centrifugal fans and positive displacement blowers for supplying conveying air to the conveying system. However, for some conveying systems, compressed air from a central compressor station is also used. The two important criteria required for pneumatic conveying are air flow and air delivery pressure. Different air movers have different characteristics in the...
September 1, 2011
This article presents equations that allow the user to calculate liquid volume as a function of liquid depth, in both vertically and horizontally oriented tanks with dished heads. The equations accommodate all tank heads that can be described by two radii of curvature (torispherical heads). Examples include: ASME flanged & dished (F&D) heads, ASME 80/10 F&D heads, ASME 80/6 F&D heads...
May 1, 2011
Many operations involving ideal gases are readily calculated using a basic knowledge of thermodynamics. Non-ideal gas behavior, however, can deviate significantly from that of ideal gases, and in some cases, large errors can be introduced in process calculations if a gas is improperly assumed to behave ideally. The pressure, volume and temperature ( PVT) relationship of a gas defines its behavior and is...
May 1, 2011
Due to their simplicity of construction, lack of moving parts, ability to operate at a wide range of temperatures and pressures, low capital and operating cost, cyclones have been the workhorse for gas-solid separation in a wide variety of industries. If properly designed and installed, cyclones can be used to control particulate emissions as low as 5 microns in size, and sometimes to smaller sizes in...
April 1, 2011
Manufacturers of specialty chemicals are routinely required to reduce costs and increase the production of their high-value products. Specifically, competitive pressures from the developing world, increases in raw material costs and volatility in energy costs are putting significant pressure on manufacturers to minimize processing costs and maximize product yields. The economic impact of optimization...
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