Operational Parameters

The key operational parameters for DTA (or DSC), as given by Sarasohn (84), are shown in Table 5.7. If a large sample size is chosen, lower heating rates are required. This in turn decreases the AT sensitivity and peak resolution. Small samples are perhaps the most convenient to use, especially with 

Large Useful for detecting low-level transitions. Useful for nonhomogeneous 

Small Good resolution of curve peaks. Peaks are sharp, transition temperatures 

Can react with sample. Dynamic preferred over static. 

The key operational parameters for packed columns are the same as those seen in tray columns — there are three gas and liquid loads and the pressure drop along the column. Together these three factors not only affect column performance but are the determining factors in the choice of packing size, packing type, and column diameter. They also have practical limits to their range, a feature we saw before in the case of tray columns. 

Presstire drop in column packed with 3.5 cm Pall rings. 

Both gas and liquid loads are expressed as superficial velocities (i.e., volumetric flow rates divided by column cross section, Vq = QgMc = Ql/ c)-Pressure drop is usually reported in units of millimeter H2O per meter packing or, in the case of distillation, per theoretical plate. 

The factors forcing us to set limits on the range of loads are, at the high end, the onset of flooding, and at the low end, channeling and incomplete wetting. 

Flooding can be caused by both excessive gas and liquid flow rates. When gas loads exceed a certain limit, the pressure drop becomes so large that gravity flow can no longer proceed. The liquid piles up on top of the packing and is in part blown out of the tower. Excessive liquid loads lead to a similar situation. 

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The preceding definitions of economic potential and total annual cost can be simplified if it is accepted that they will be used to compare the relative merits of difierent structural options in the flowsheet and difierent settings of the operating parameters. Thus items which will be common to the options being compared can be neglected. 

The ultrasonic controls section, shown in Figure 7, provides the means for the user to set the operating parameters for the inspection. The majority of the controls are direct equivalents of those found on a conventional ultrasonic flaw detecfor some additional controls are provided to give access to the special features of the CamuS system. The Controls area is sub-divided into three parts. 

However, it is expected that this situation will change, since a number of novel "non-invasive NDT techniques are now becoming available. With some of these techniques, the time required for a shutdown can be reduced. Other techniques make it possible to perform inspections whilst the installation is in full service. It is obvious that the availability of such techniques could support the knowledge already available on operational parameters and degradation mechanisms, in order to base shutdown intervals on actual plant condition. 

In plant maintenance, the availability of quantitative and non-invasive screening NDT methods will reduce the time needed for shutdowns and increase the intervals between them. Modem NDT methods will become just as important a tool for Risk Based Inspection approaches and maintenance planning as operational parameters and degradation mechanisms already are. 

Scanning method. The sequence of control over operating parameters of a mass spectrometer that results in a spectrum of masses, velocities, momenta, or energies. 

Control Devices. Control devices have advanced from manual control to sophisticated computet-assisted operation. Radiation pyrometers in conjunction with thermocouples monitor furnace temperatures at several locations (see Temperature measurement). Batch tilting is usually automatically controlled. Combustion air and fuel are metered and controlled for optimum efficiency. For regeneration-type units, furnace reversal also operates on a timed program. Data acquisition and digital display of operating parameters are part of a supervisory control system. The grouping of display information at the control center is typical of modem furnaces. 

Other important operating parameters include plasticizer changes, gas type and pressure, gap length between spinneret and quench bath, line speed, and rope tension. All variables must be carefully controlled to obtain a hoUow fiber of desired characteristics. 

Operating parameters of this German plant, on the basis of one cubic meter of raw gas, iaclude 0.139 m O2, 0.9 kg briquettes, 1.15 kg steam, 1.10 kg feed water, 0.016 kWh, and 1.30 kg gas Hquor produced. Gasifier output is 1850 m /h and gas yield is 1465 m /t dry, ash-free coal. The coal briquettes have a 19% moisture content, 7.8% ash content (dry basis), and ash melting poiat of 1270°C. Thermal efficiency of the gas production process is about 60%, limited by the quaHty and ash melting characteristics of the coal. Overall efficiency from raw coal to finished products is less than 50%. 

The resulting overall energy balance for the plant at nominal load conditions is shown in Table 3. The primary combustor operates at 760 kPa (7.5 atm) pressure the equivalence ratio is 0.9 the heat loss is about 3.5%. The channel operates in the subsonic mode, in a peak magnetic field of 6 T. AH critical electrical and gas dynamic operating parameters of the channel are within prescribed constraints the magnetic field and electrical loading are tailored to limit the maximum axial electrical field to 2 kV/m, the transverse current density to 0.9 A/cm , and the Hall parameter to 4. The diffuser pressure recovery factor is 0.6. 

Operational Constraints and Problems. Synthetic ammonia manufacture is a mature technology and all fundamental technical problems have been solved. However, extensive know-how in the constmction and operation of the faciUties is required. Although apparendy simple in concept, these facihties are complex in practice. Some of the myriad operational parameters, such as feedstock source or quaUty, change frequendy and the plant operator has to adjust accordingly. Most modem facihties rely on computers to monitor and optimize performance on a continual basis. This situation can produce problems where industrial expertise is lacking. 

Operating parameters include temperature, pressure, oxygen concentration, and residence time. Materials of constmction include stainless steel, nickel, and titanium alloys (the latter for extremely corrosive wastes containing heavy metals). Vented gases from the process may require scmbbing or other emission controls. 

Volatile acids, reported as acetic acid, are the most important operational parameter. In a weU-operating digestion process, the value should be <1 g/L (3.8 g/gal). A value >6 g/L (23 g/gal) indicates malfunctioning optimum pH is 6.8—7.2, and a pH <6.8 indicates excessive volatile acid production. Formerly, lime was added to the digester contents if the pH showed an undesirable drop. However, the reduction in pH indicated a change in organism that could not be remedied with lime (2). 

Table 6. Operating Parameters for Electrowinning of Chromium from Chrome Alum...

Table 8. Chemical Composition and Operating Parameters for Chromium Electroplating Baths...

Table 2. Typical Operating Parameters for Immobilized Glucose Isomerase and Penicillin V Acylase...

En2yme techniques are primarily developed for commercial reasons, and so information about immobilisation and process conditions is usually Limited. A commercially available immobilised penicillin V acylase is made by glutaraldehyde cross-linking of a cell homogenate. It can be used ia batch stirred tank or recycled packed-bed reactors with typical operating parameters as iadicated ia Table 2 (38). Further development may lead to the creation of acylases and processes that can also be used for attaching side chains by ensymatic synthesis. 

The discrete logic must have access to operational parameters such as controller modes. That is, the discrete logic must be able to switch a controller to manual, auto, or cascade. Furthermore, the discrete logic must be able to force the controller output to a specified value. 

The following types of devices are commonly applied to measure the various operational parameters of thickeners and clarifiers. They have been used in conjunction with automatic valves and variable-speed pumps to achieve automatic operation as well as to simply provide local or remote indications. 

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