Gravity feed

Since acrylic polymerizations liberate considerable heat, violent or mnaway reactions are avoided by gradual addition of the reactants to the kettie. Usually the monomers are added by a gravity feed from weighing or measuring tanks situated close to the kettie. The rate of monomer addition is adjusted to permit removal of heat with full flow of water in the condenser and a partial flow in the cooling jacket. Flow in the jacket can be increased to control the polymerization in cases of erroneous feed rates or other unexpected circumstances. A supply of inhibitor is kept on hand to stop the polymerization if the cooling becomes inadequate. 

In determining the proper size and number of cyclones required for a given application, two main objectives must be considered. The first is the classification or separation that is required, and the second is the volume of feed slurry to be handled. In the case of hydroclones, before determining whether these objectives can be achieved, it is necessary to establish a base condition as follows Feed liquid - water at 20 C. Feed solids - spherical particles of 2.65 specific gravity Feed concentration - less than 1 % solids by volume Pressure drop - 69 kPa (10 psi) Cyclone geometry - "standard cyclone" as described above. 

These distributors are fabricated of pipe lengths tied to a central distribution header (usually) %vith orifice holes drilled in the bottom of the various pipe laterals off the header. This style of distributor can be fed by pressure or gravity for clean fluids. The gravity feed is considered better for critical distillation application when uniformity of the flow of the drip points (or flow points) through out the cross-section of the tower is extremely important, and is excellent for low flow requirements such as below 10 gpm/ft2 [131]. 

Water distribution must give uniform water flow over the tower packing. Many towers use a gravity feed system discharging the water through troughs and ceramic, metal... 

Figure 3-14. Catalyst metals content versus catalyst addition rate for 22°API Gravity Feed. (Source Katalystics Regional Technology Seminar, New Orleans, Louisiana, December 15, 1998.)...

We first note the very large differences in column performance for the two methods. Effective plates per second represents the speed characteristics of a column (e.g., the number of plates that can be generated in a given time interval) (13). As can be seen, HPLC is 100 to 1000 times faster than classTcal LC. (We shall discuss the differences between PLB and PB in the next section.) This improved performance arises mainly from the use of significantly smaller particle sizes in HPLC. Moreover, in classical LC, the mobile phase is delivered to the column by gravity feed, hence, the very low mobile phase velocities. In HPLC, it is desireable to improve performance... 

Sometimes storage tanks are located on a hill, in order to allow the gravity feeding of tank cars. Care must be taken uder these circumstances to see that any slopover cannot flow into the processing, utilities, or service areas in case of a tank fire.3,4... 

Some pieces of equipment will be elevated to simplify the plant operations. An example of this is the gravity feed of reactors from elevated tanks. This eliminates the need for some materials-handling equipment. 

Gravity feed is to be used for charging additives to the reactor, for discharging the reactor to the hold tanks, and for feeding the dryer. 

A simphstic view of a FIA analytical system is outfined in Fig. 2.19. The liquid flow can be obtained in a number of ways, most commonly by using a peristaltic pump. In addition, gravity-feed systems, overpressure systems on liquid vessels and simple and double piston pumps normally associated with HPLC systems, are often used. The interrelation of the pumping system and the bore size of the transport tubing to a great extent modify the theoretical considerations involved and the operation of the FIA regime. In common with CFA, the minimization of dead volumes—in detector cells and between T pieces for example—is particularly important. Injections of the sample into... 

Custom-built, gravity feed sample input rack, equipped with a narrow-beam infra-red (IR) source/detector pair. 

The transfer of material from mixing tanks or holding tanks to processing equipment or to a filling line, whether by pumping or by gravity-feed, is... 

Among the formulation variables that control extrudability of a product, several studies (25,26,33-35) point to the fluid or moisture content of the wet feed material being more critical than others. The force or torque of extrusion and power consumption are often inversely proportional to moisture content of the extrudate as seen from Figures 11 and 12 (26,36-38), while the particle size of pellets increases linearly with water content when extruded with gravity feed basket and roll extruders (33). Using instrumented gravity feed and radial screw extruders, a three- to fourfold decrease in the force has been noted, with a 10% increase in water content of feed material (37). 

Figure 12 Influence of the amount of water on the extrusion forces (gravity feed extruder) and power consumption (twin screw extruder) on extrusion of MCC. , gravity feed extruder (N) , twin screw extruder (W). Source From Ref. 37.

A gravity feed extruder with L/D = 2 recorded (28) higher forces, compared to power generated from a twin-screw extruder with L/D = 0.9, upon extrusion of mixtures of MCC with either lactose or DCP. The extrudate from the basket extruder was denser with a smoother surface than that from the screw extruder. Similarly, material extruded through a screen with L/D = 4 in a basket extruder was denser than that with L/D = 2 (37). However, a smaller L/D ratio is preferred in an axial extruder. An improper L/D ratio could result in a loosely bound extrudate with large surface defects (37), resulting in a formulation less amenable to pelletization, as seen from Figure 14. Since the mean diameter of the pellet often approximates the diameter of the die used in extrusion, choice of the latter is also dictated by desired pellet size. 

Baert L, Remon JP, Knight P, Newton JM. A comparison between the extrusion forces and sphere quality of a gravity feed extruder and a ram extruder. Int J Pharm 1992 86 187-192. 

It is the authors experience that with a formulation compressed without a forced feeder in R D, the scale-up in a different country, but by gravity feed and without a forced feeder, was perfect. In a second country, however, all production presses operated with forced feeders, and the target tablet hardness was not achieved. It was possible to conclude that press speed was not the cause of the problem but it was much later (and based on laboratory experiments) that it was possible to conclude that the lubricant was ovennixed on the tablet press, resulting in a softer tablet. Fortunately, the drug was very soluble and no dissolution problem resulted, but slower dissolution could be a problem with a drug of low solubility. 

The continuous-stream flow-injection system (Figure 2) consisted of a gravity-feed electrolyte reservoir, a sample injection valve (Rheodyne, Model 50) fitted with a 30 /xL-sample loop, and a flow-through electrochemical detector cell. The channel diameter of the Teflon tubing for the stream was 0.8 mm. The tubing length from injector to detector was 10 cm. 

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