Solids Handling Systems

Screw conveyors, consisting of a screw mounted in a trough, are widely used. They can move particles of any size up to a few inches, in any straight direction, for distances up to 

300 ft horizontally and up to 30 ft vertically, and at temperatures up to 900 F. Screw conveyors can be fitted with special screws for sticky materials, can be sealed to keep in dust and keep out moisture, and can be jacketed for cooling and heating. The screw, which ranges from 6 to 20 in. in diameter, typically rotates at from 25 to 100 rpm. Volumetric flow capacities, when the trough is 30% full and the screw is rotating at 50 rpm, range from 75 ft /hr for a 6-in.-diameter screw to 3,000 ft /hr for a 20-in. diameter screw. 

Vibratory conveyors are limited to straight distances, usually horizontal, up to 100 ft, but are not suited for fine particles less than 100 mesh in size. Solids must be free flowing, but temperatures up to 250°F can be handled. Widths range from 1 to 36 in. with pan heights to at least 5 in. Experiments are usually necessary to properly size a vibratory conveyor. For an 18-in.-wide conveyor with a 5-in. pan height and a 20-ft length, a typical mass flow capacity is 70,000 Ib/hr or 700 ft /hr for solid particles having a bulk density of 100 Ib/ft.  

Rakes of phthalic anhydride with a bulk density of 30 Ib/fF are to be conveyed a horizontal distance of 40 ft from a bin to a packaging facility at the rate of 1,200 ff/hr. Size and cost a bin and conveying system as of a CE index of 394. 

Assume a bin storage time of 8 hr. Therefore, the bulk solids volume is 8(1,200) = 9,600 ft Assume an outage (gas space above the bulk solids) of 20%. Thus, the bin volume above the hopper = 9,600/ (1 - 0.20) = 12,000 ft Neglecting the volume of the hopper below the bin and assuming a cylindrical bin with a height equal to 150% of the diameter, the hopper dimensions are 22 ft in diameter by 33 ft high. From Table 16.32, the purchase cost of the bin in carbon steel is 450(12,000)° = 34,000. Because flakes may tend to mat and interlock, consideration should be given to the addition of a vibrator to the hopper. 

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For certain types of stochastic or random-variable problems, the sequence of events may be of particular importance. Statistical information about expected values or moments obtained from plant experimental data alone may not be sufficient to describe the process completely. In these cases, computet simulations with known statistical iaputs may be the only satisfactory way of providing the necessary information. These problems ate more likely to arise with discrete manufactuting systems or solids-handling systems rather than the continuous fluid-flow systems usually encountered ia chemical engineering studies. However, there ate numerous situations for such stochastic events or data ia process iadustries (7—10). 

Solids handling systems Bins Volume, ft 10-100,000 ft Cp = 450 5 Carbon steel at atmospheric pressure... 

One physical property of significant importance in many coal-processing schemes is particle size. For any given process, there usually exists an optimum particle size range that is desired for the feed material. This desired size range may be a function of the conversion technique employed (i.e., moving bed, fixed bed, fluidized bed, etc.), or it may be determined by the solids handling systems used (i.e., dry lock, hopper, slurry, etc.). Some current coal conversion processes require feed to be pulverized to less than -200 mesh while other processes can handle feed up to 1/4 in. (6 mm). 

Roberts, A. W. 1988. Modern Concepts in the Design and Engineering of Bulk Solids Handling Systems. Newcastle, Australia The University of Newcastle Research Associates (TUNRA). 

This chapter provides a brief outline of the development of understanding of pressures that develop in silos and their consequences for the safety of the silo structure. More structural failures occur in silos than in any other engineered structural form, considering the numbers of each, and these failures occur in all countries and all industries. Structural design considerations for silos are therefore a key aspect of bulk solids handling systems. 

G. D. Dumbaugh, "A Comparative Review of Vibratory Drives for Bulk SoHds Handling Systems," Proceedings of the 10th Powder andBulk Solids Conference, Chicago, May 1985, pp. 425—470. 

The weighing and proportioning of liquids and solids has also benefited from this technical revolution. Sensing devices and special-purpose computers give a level of precision and speed not possible in the era of elec tromechanical devices. The net result is that packaging and material handling systems now have the sophistication of chemical processes. 

Personnel Hazards The following case history illustrates how vacuum can be harmful and dangerous to personnel. A plant superintendent was checkiug an open nozzle on a glass-lined reactor on which there was a vacuum pump pulling vacuum, when suddenly his arm was sucked into the nozzle, up to his shoulder. He could not remove his arm until help arrived to release the vacuum on the vessel. He was injured painfully, though not seriously. The injury could have been veiy serious if help had not been nearby. Personnel hazards can also result from vacuum conveyor systems for solids handling. 

Fluidized-bed adsorbers have several disadvantages. The continuous handling and transport of solids is expensive from an equipment standpoint fluidized-bed systems must be large to be economical. Solids handling also presents a potential for mechanical problems. Careful control is required to keep the adsorbent fluidized, while minimizing adsorbent loss with the gas-phase attrition of the adsorbent can be high, requiring substantial makeup. 

Brown, N. P. and Heywood, N. I. (eds) Slurry Handling. Design of Solid-Liquid Systems (Elsevier. Amsterdam, 1991). 

Dust explosions usually occur in two stages a primary explosion which disturbs deposited dust followed by the second, severe, explosion of the dust thrown into the atmosphere. Any finely divided combustible solid is a potential explosion hazard. Particular care must be taken in the design of dryers, conveyors, cyclones, and storage hoppers for polymers and other combustible products or intermediates. The extensive literature on the hazard and control of dust explosions should be consulted before designing powder handling systems Field (1982), Cross and Farrer (1982), Barton (2001), and Eckhoff (2003). 

After the flushing and visual checking is finished, the equipment is tested under simulated conditions. Again, safe fluids such as air, water, and steam are used wherever possible. Sometimes inexpensive compounds with similar boiling points to the process chemicals are used to check distillation or other separative steps. For solids-handling equipment sometimes salt, the actual raw material, or product purchased for this test may be used. The purpose of these tests is to see whether every piece of equipment performs properly before more expensive and possibly more hazardous process compounds are charged to the system. It also gives the... 

CH4 emitted from manure depends primarily on (i) the management system such as solid disposal system, liquid disposal systems, e.g., ponds, lagoons, and tanks, which can emit up to 80% of manure-based CH4 emissions, while solid manure emits little or no CH4. (ii) Environmental conditions are also important. The higher the temperature and moisture, the more CH4 produced, (iii) CH4 emissions also depend on the quantity of the manure produced, which depends on the number of animals housed, the amount of feed the consumed, and the digestibility of the feed, (iv) Manure characteristics depend on the animal type, feed quality, and rumen microbes present in the rumen and digestive tracks. Manure handled in liquid form tends to release more amount of CH4 when compared to solid or manures thrown into the pasture, which do not decompose anaerobically. High temperatures with neutral pH and high moisture content enhance CH4 production [45],... 

Destoop, T., Mathematical of Dense Phase Conveying Systems - A Revolutionary Move Towards Smart System Control, Woe. of1994 Bulk Solids Handling Conf, Rosemont, IL (1994)... 

Anon, Dynamics of Gas/Solids Systems, Pneumatic Handling ofBulkMat., Part A Fundamentals, Bulk Solids Handling Unit, Thames Polytechnic, London (1983)... 

Salts of a substrate having an acid or an amine functionality are prepared by dissolving the substrate and the counter-base (or acid) separately in appropriate solvents, mixing the two solutions in equimolar ratios, and removing the solvents under vacuum to afford a solid. This method has two distinct advantages First, the composition of the substrate remains the same during various crystallization attempts, and second, this portion of the work can be automated with the use of liquid handling systems. 

A butoxylcarbonylation reaction was conducted in a liquid-liquid biphasic system under process conditions, but the removal of the product was conducted in a liquid-solid biphasic system at a lower temperature (84). lodobenzene or 4-bromoacetophenone reacted with CO at a pressure of 1-8 atm in the presence of a palladium-benzothiazole complex catalyst in the ionic liquid [TBA]Br (m.p. = 110°C) in the presence of Et3N base. The catalyst/ionic liquid system was recycled by extractive removal of the butyl ester product with diethyl ether. The solid residue, containing the catalyst, [TBA]Br, and Et3N.HBr, remained effective in subsequent carbonylation tests. After each cycle, the yields were still close to the initial value. A slight decrease in yield was attributed to a loss of catalyst during handling. 

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