Continuous weigh

The main features in which the Radford process differs from the batch operation are in thermal dehydration and compounding. Water-wet nitrocellulose on a continuous vacuum belt filter is vacuum-dried followed by hot air transfusion (80°C) to reduce the moisture to less than 2%. After cooling, alcohol is sprayed on the nitrocellulose to a concentration of 15—20%. The alcohol-wet nitrocellulose is then transferred from a surge feeder to a compounder by a continuous weigh-belt along with the other ingredients of the composition, which are also weighed and added automatically. 

Automatic weighing has largely replaced manual weighing in the chemical-process industries because of the advent of larger-capacity processes and the need to economize on labor. Also, the dependability of weighing equipment has increased markedly, and investment cost has decreasea. Both batch and continuous weighing are used. 

Continuous Weighing This procedure involves a device that is sensitive both to the total amount of material flowing and to changes... 

To model the amidation and cyclization reactions, an internal standard was weighed into the feed, and the feed placed on a balance for continuous weighing during the reaction. The HPLC system was calibrated using units of mol/kg, so that density effects could be neglected. A series of experiments... 

Continuous web dryers, 9 119-120 Continuous weighing, 26 248 Continuum hypothesis, of flow phenomena, 11 735-736... 

The number of influences in a thermobalance, which is a continuously weighing balance , is relatively large. To a great extent these are dependent on the construction of the balance. Normal macro balances are not affected by small vibrations if they are properly installed, regardless of whether this is on an upper or lower floor. Important for good reproducibility are good thermostated housing reproducible gas flow conditions... 

This experiment is typical of many that are conducted using classical adsorption techniques, such as the measurement of isotherms and control of evacuation temperature and pressure. There is a high probability that such a treatment will increase the number of OH groups on the surface, but there is no direct evidence of this. An improvement could be made if the sample were continuously weighed during the cycle in a vacuum microbalance (160), but even this would not be entirely free from ambiguity. 

TG-FT-IR, Pyrolysis analyses were performed on the preliquefaction solids using thermogravimetric (TG) analysis with on-line analysis of the evolved products (including an infrared spectrum of the condensables) by FT-IR. The TG-FTIR method has been described previously (23-25). The Bomem TG/plus instrument was employed. A sample is continuously weighed while it is heated. A flow of helium sweeps the products into a multi-pass cell for FT-IR analysis. Quantitative analysis of up to 20 gas species is performed on line. Quantitation of the tar species is performed by comparison with the balance reading. 

Except for continuous weighing, control of the flow of solids is less precise than that of fluids. Several devices used for control of feed rates are shown schematically in Figure 3.7. They all employ variable speed drives and are individually calibrated to relate speed and flow rate. Ordinarily these devices are in effect manually set, but if the solid material is being fed to a reactor, some property of the mixture could be used for feed back control. The continuous belt weigher is capable ordinarily of 1% accuracy and even 0.1% when necessary. For processes such as neutralizations with lime, addition of the solid to process in slurry form is acceptable. The slurry is prepared as a batch of definite concentration and charged with a pump under flow control, often with a diaphragm pump whose stroke can be put under feedback control. For some applications it is adequate or necessary to feed weighed amounts of solids to a process on a timed basis. 

Figure 3.7. Solids feeders with variable speed drives, (a) Rotary vane (star) feeder with variable speed drive, (b) Horizontal screw feeder, (c) Belt feeder taking material from a bin with an adjustable underflow weir, (d) Rotary plate feeder Rate of discharge is controlled by the rotation speed, height of the collar, and the position of the plow, (e) Continuously weighing feeder with variable speed belt conveyor.

FEEDER (Gravimetric). Frequently in the form of belt scales, the function of a gravimetric feeder is lo continuously weigh material as... 

The feed tank is mounted on the ceiling using chains and a weighing cell. Continuous weighing of the feed vessel stands for an exact mass balance not influenced by pulsation of the feed pump, volumetric or viscosity effects. To ensure that the connected feed pipes do not block with solidifying liquid they are equipped with an explosionproof electric heating wire which holds an adjustable temperature. 

Palik torsion balance Kiflfer continuous weighing chain link balance... 

In the TGA test, a small sample, approximately 2 to 10 mg. is placed in an apparatus that continuously weighs it while it is being heated. The heating rate is held as constant as possible, usually at around 10°C per minute. 

In thermogravimetry (TG or TGA) the change in sample mass is determined as a function of temperature and/or time. The instrument is a thermobalance that permits the continuous weighing of a sample as a function of time. The sample holder and a reference holder are bounded to each side of a microbalance. The sample holder is in a furnace, without direct contact with the sample, the temperature of which is controlled by a temperature programer. The balance part is maintained at a constant temperature. The instrument is able to record the mass loss or gain of the sample as a function of temperature and time [m = /( )]. Most instruments also record the DTG curve, which is the rate of the mass change dm/dt = f(T). 

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