Typical Locations in Process Systems


Typical Locations in Process Systems  [c.175]

Typical Locations in Process Systems  [c.175]

Typical products are suppHed as white powders having particle diameters ranging in size from a few micrometers to a few millimeters, depending on the grade. Gel powders can be mixed dry with the soil or partially hydrated and then sprayed onto the sod. Some manufacturers also seU Hquid forms. The gels resist aerobic biodegradation and persist in sod for several years even under wet conditions. Decomposition occurs in several months under exposure to sunlight. The particles hydrate when in contact with water, absorbing from 40 (seawater) to 500 (distilled water) times their weight of water and swelling proportionately. EuU absorption requires a few hours. The pH of absorbed water is neutral. Hydration and swelling are reversible. Plant root systems create a sufficient pressure gradient to extract more than 90% of the water held by the polymer. The polymers, which may be used in combinations with mulches (62) or other treatments designed to slow evaporation, improve water retention and location in porous sods and help to protect plants where rainfall is marginal. The gels are considered nonhazardous and are compatible with many fertilizers, although polymer dose rates may have to be increased.  [c.229]

Industrial Power. The original use for terrestrial solar modules was in industrial apphcations. These systems employ an array of modules typically between a few hundred watts and a few kilowatts to charge storage batteries, which are then used to power the load. Usually the batteries contain enough reserve to deUver power for up to a week in the case of bad weather. Industrial systems are located in areas where no power grid exists, and where the alternative forms of remote power generation, such as diesel generator sets or thermoelectric generators, are either impractical or economically unfeasible. Desirable module attributes are high efficiency to reduce the size and therefore the cost of the site and mounting stmcture, and high rehabiUty (34). In general, the cost of the solar array is a minor percentage of the entire project cost, thus the market size is relatively inelastic to module price.  [c.474]

Pipes and Pipelines. Samples may be withdrawn both from closed pipe cross sections and from the outfall of open pipes. The simplest system for the former consists of an in-pipe sampling probe as shown in Figure 11 (18). In the chemical industry, many pipe samples are taken from organic Hquids, which may be toxic, highly reactive, and flammable. The amount of sample taken should be minimised in order to reduce worker exposure and sample disposal problems. Adequate ventilation must be provided because the vapors from many Hquids are more dangerous than the Hquids. Splash guards are necessary when sampling corrosive and toxic Hquids. For these appHcations in-line samplers are preferred. These trap and isolate a predeterrnined, precise volume of Hquid from the line and deHver it to a closed container. Samplers can be installed on either side of the suction or discharge side of pumps. Typical devices include sampling plugs, multiport valves, and pneumatic samplers (19). The sampling plug is usually inserted in a bypass line as shown in Figure 12. The plug has both sample and vent connections. When open, the Hquid pumped through the bypass line passes through the plug and can be returned to the line. When closed, a small constant volume of Hquid is trapped in the plug and, on rotation of the tap, is drained into the sample bottle while the tap is simultaneously vented (19). If exposure to air can cause a problem in the process, the valve can be vented with nitrogen and then closed before the Hquid in the bypass line is returned to the process. Mainstream sampling is usually performed with a sharp-edged probe facing directly into the flow at some preset point. In pressurized systems, sampling sites can rarely be statistically designed with regard to location and once installed are difficult to relocate. Care has to be taken when discharging plug samplers using pressurized systems in order to prevent the Hquid venting through the valve connections (19). Sometimes a safety valve is inserted in the bypass to prevent blockage of the pump discharge.  [c.303]

The blended materials, now called furnish, move from the blenders to the formers. A typical mill will have 3—4 formers, one for each surface (top and bottom layers) and one or two for core (middle layer). A mat-carrying plate or caul will pass under the former. This caul will be preweighed and the weight entered on the forming line computer. The caul may be a sheet of steel or aluminum, a wire screen, or a plastic sheet and will generally be the size of the hot-press. On some of the newer systems, the mat-forming and transport system maybe a continuous wire screen. The speed of the caul system is such that enough mats may be formed in the time required to press a load of boards, the objective being to maintain the formers in a constant and uniform state of operation. As the caul enters the first former, a layer of fine surface particles is spread uniformly on the caul. The layer will be 20—25% of the panel weight and, depending on the type of former used, may be distributed in such a way that there is a gradation of finer particles on the bottom surface, ranging to coarser particles at the top of this layer. A desirable characteristic of particleboards is a smooth surface, and finer particles on each surface help to achieve this goal. A moisture sensor is often located between the first and second formers.  [c.392]

The technologies used to combust wastes depend on the form and location of components to be burned. Typically soHd wastes ate burned, alone or in combination, and both with and without supplementary fossil fuels. SoHd wastes can be burned in mass-bum or pile-burning systems such as hearth furnaces, spreader—stokers, ashing and slagging rotary kilns, or fluidized beds. The choice of combustion technology depends on the degree of waste preparation which is practical the availabihty of existing combustion systems, eg, a spreader—stoker for hog fuel utilization, adapted to the cofiring of hog fuel and WTS and the type of energy recovery contemplated. Energy recovery from the soHd wastes can be accompHshed in the form of medium or high pressure steam, eg, 4.5—8.6 MPa (44—85 atm) (672—783 K), suitable for cogeneration or condensing power generation purposes low pressure steam, eg, 314—1030 kPa (3.1—10.2 atm), saturated, suitable for process purposes or the direct production of process heat in the form of heated air or hot combustion products. Energy recovery from gaseous wastes can be accompHshed through electricity generation from gas-fired boilers, combustion turbines, or internal combustion engines. Alternatively, these gaseous fuels can be used to generate process heat in conventional fashion.  [c.52]

Before a pump selection can be made, the duty conditions must be specified. These include type of fluid, density or specific gravity, temperature, viscosity, flow, inlet and oudet pressures, and presence of soHds or corrosive/erosive material in the Hquid. For a typical process installation, an accurate estimate of the pumping system is required, starting with the source of the Hquid (tank, vessel, pipeline, basin, etc) through the plaimed system layout to the terminal point (see Pipelines Piping systems). Piping sizes must be deterrnined, based on suitable flowing velocities for the fluid or for the fluid mixture in the case of slurries. Pressure drops through the entire piping system must be estimated, including all valves, fittings, process equipment such as heat exchangers, heaters, and boilers, and any losses through orifices or control valves. Difference in pressures between the suction and discharge location, together with changes in elevation between these two, completes the various elements of the system and makes it possible to estimate or design a complete pumping system.  [c.288]

Acid gases (CO2 and H2S) are removed after the third or fourth compression stage. This is an optimum location since the gas volume has been reduced significantly in the previous stages and the acid gases have not contaminated any final products. When the sulfur content of the feed is low as for naphtha feeds, scmbbing with a dilute caustic soda solution is economical. Typically 4 to 12% free caustic solution is used. Relatively weak solutions are preferred to avoid the precipitation of sodium salts and to minimize the formation of sodium complexes and "yellow oil." The pyrolysis gas leaving the scmbber contains less than 1 ppm of acid gases, and is further treated by a water wash to remove any hydroxide carryover. A detailed analysis has been given (63). Plants designed to process high sulfur content feeds, eg, higher than 500 ppm, often contain a regenerative acid gas removal system upstream of the caustic scmbber. These systems may employ monoethanolamine, diethanolamine, or alkazid as solvents with a standard absorber—desorber design.  [c.440]

Rapid Expansion from Supercritical Solutions. Rapid expansion from supercritical solutions (RESS) across an orifice or nozzle is used commercially to precipitate soflds. In this technique a solute, eg, dmg, polymer, or crystalline compound, is dissolved in a near-critical or supercritical fluid. The homogeneous solution is depressurized rapidly by spraying the solution through a nozzle or orifice, which may be heated to prevent freezing owing to Joule-Thompson cooling. Modeling indicates that high (>10 ) supersaturations are attainable. Nucleation rates are on the order of j (cm -s) ) and density reduction time scales are as small as 10 seconds (109—111). By controlling upstream and downstream temperatures and pressures the desired precipitated morphology may be attained. Thus, particles, spheres, films, or fibers can be formed, depending on the material. RESS has been appHed to inorganics and ceramics (qv) such as siUca (Si02) and polycarbosilane (1), organics and pharmaceuticals (qv) (85,86), polymers (112), and two-solute systems (87). Polymer blend formation using RESS has been examined (113). Poly(ethyl methacrylate) and poly(methyl methacrylate) were precipitated into a homogeneous mixture from chlorodifluoromethane. Phase behavior measurements coupled with fluid dynamic modeling of the RESS process reveal that the location for the occurrence of phase separation with respect to the nozzle is a primary factor in determining whether particles or fibers are formed. An influential variable that can govern the transition between fibers and particles is the length-to-nozzle-diameter ratio, E/Z9, where a small ratio typically results in particles (111,112).  [c.228]

Design of a groundwater monitoring program minimally includes consideration of materials, location, indicator parameters, and timing. Material selection is important for both the well casing and well screen. Materials of constmction must be inert to the fluid being tested and to the ambient soil. The material must not release any type of chemical that could be interpreted, as present in the groundwater. Typical inert materials include Teflon, polypropylene, PVC, and stainless steel (3,8,9). Material durabiUty is also an issue, especially because many monitoring systems must be utili2ed for 50 years or more. The screens should also be evaluated regarding the potential for clogging, either via the porous media or biological activity.  [c.404]

X-Ray and y-Ray Tests. Radiographic imaging tests (1—6,28) are widely used to examine interior regions of metal castings, fusion weldments, composite stmctures and brazed honeycomb mechanisms, and many other metallic and nonmetaUic components. Radiographic energy, in the form of photons, maybe excited using either an x-ray tube or a radioisotope, such as iridium-192 [14694-69-0] or cobalt-60 [10198 0-0] Co. Higher energy levels penetrate greater thickness of the same material. X-ray energies in the 8—160 kV range penetrate up to 76 mm of light alloys and 6 mm of steel. Radioisotopes such as iridium-192 are used for thinner steel pipe walls or lower density metals. Cobalt-60 is used for steel thickness in the range of 25 to 190 mm. Penetrating radiation, introduced at intensity Iq on the side of the part facing the source or tube, is recorded by film, real-time imaging systems, or by detection gauges on the opposite side (Fig. 6). Anomalies in the path are imaged on the recorded plane, provided that the alignment and exposure are correct. Maximum detection sensitivity occurs for radiography when the significant dimension of the anomaly is oriented parallel to the x-ray beam. Radiographic tests are made on pipeline welds, pressure vessels, nuclear fuel rods, and other critical materials and components that may contain three-dimensional voids, inclusions, gaps, or cracks aligned so that portions are parallel to the radiation beam. Because penetrating radiation tests measure the mass of material per unit area in the beam path, these can respond to changes in thickness or material density, and to inclusions of density different from that of the material in which the inclusions are embedded. The typical film radiographic test sensitivity used in industrial inspection can detect thickness or density differences equal to about 2% of material thickness. For the most critical nuclear and aerospace appHcations, however, specifications may call for demonstration of better contrast sensitivity in such penetrating radiation tests. When cracks foUow irregular paths, some parts of which are aligned with the path of the radiation beam for 2% or more of the total beam path length in the test material, it is possible to visualize the cracks with great clarity if the cracks effectively reduce the thickness of material through which the probing beams must pass. However, x-ray and y-ray film imaging tests are insensitive to cracks, disbonds, and laminar discontinuities that He in planes perpendicular to the radiation beams or to defects representing Httle change in thickness. In extmsions and hot forgings, many discontinuities, which may originally have been three-dimensional voids or discontinuities, are flattened and gready elongated in the deformation process. These discontinuities are usually parallel to the surface of the product and penetrating radiation tests rarely detect such laminar flaws. In fusion-welded pipe and tubing, however, often both the longitudinal welds made in the mill and the circumferential or girth welds made during tubing erection or during the laying of pipelines in the field provide ideal subjects for radiography inspections. In large-diameter pipelines, x-ray or y-ray sources are often propeHed into the open end of the pipeline on crawlers having detectors of girth weld locations for distances of several kilometers. The isotope source traveling on the pipe centerline emits radiation circumferentially, producing an interpretable weld image and a permanent record for further reference.  [c.129]

A process plant typically consists of a charging system, a reactor system, and an outlet or product system. AH reactants must be introduced in the correct order and the reaction must be weU understood. Provision should be made for controlling instabiHty or excessive pressure or temperature. Highly viscous materials, or those in which soHds are present, may cause fouling, poor agitation, and local overheating, with possible decomposition. Some ha2ardous reactions must be blanketed with an inert gas for safety and quaHty control. In any reaction system, reHef devices should be instaHed with weU-designed vent systems. For extremely ha2ardous processes, it may be necessary to provide emergency dumping, dilution, or other emergency controls. Withdrawal or removal of products from closed-system operations can be ha2ardous. Such locations should be monitored with suitable sensing and alarm devices.  [c.97]

Wetting, which is the establishment of molecular contact at the Van der Waals level, can occur in a time-dependent fashion at the interface. This is usually treated in terms of the spreading coefficient F,j = Fj — Fj — Fij, which is used to estimate the wettability of phase i spreading on phase j, with component surface tensions FJ, Fj and interfacial surface energy, Fjj. When F,j is positive, spreading occurs and good molecular contact is achieved between the surfaces. The dynamics of wetting and de-wetting has received considerable attention from Brochard et al and an excellent molecular understanding is developing for many polymer systems. For our purposes, we provide a brief phenomenological description of wetting to illustrate potential problems in evaluating the time-dependence of welding. Fig. 2 shows a schematic region of the plane of contact of a polymer interface [13]. Due to surface roughness, etc., good contact and wetting are not achieved instantaneously at all locations. Typically, wetted pools are nucleated at random locations at the interface and propagate radially until coalescence and complete wetting are obtained. This problem can be treated phenomenologically as a two-dimensional nucleation and growth process such that the fractional wetted area, 0(/), is given as [13]  [c.357]


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