Types of Operation

The mode of operation, whieh ean be bateh, fed-bateh, or eon-tinuous, should be eonsidered during the preliminary stages of large-seale design. Bateh operation often involves simplieity in maintenanee of aseptie eonditions and minimizes operating losses due to eontami-nation or equipment failure. 

In eontrast, fed-bateh type involves feeding the reaetor with fresh nutrients or earbohydrates or both during fermentation when low glueose eoneentrations (10-50 mg/L) are required to maintain the produetivity of mieroorganism. 

The mode of operation, which can be batch, fed-batch, or continuous, should be considered during the preliminary stages of large-scale design. Batch operation often involves simplicity in maintenance of aseptic conditions and minimizes operating losses due to contamination or equipment failure. 

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Recirculating systems can make aquaculture feasible in locations where conditions would otherwise not be conducive to successful operations. Such systems can also be used to reduce transportation costs by making it possible to grow animals near markets. In areas where there are concerns about pollution or the use of exotic species, closed systems provide an alternative approach to more extensive types of operations. 

Difficulties of Moving-Bed Operation. The use of a moving bed iatroduces the problem of mechanical erosion of the adsorbent. Obtaining uniform flow of both soHd and Hquid ia beds of large diameter is also difficult. The performance of this type of operation can be gready impaired by nonuniform flow of either phase. 

In advancing-front or layer melt crystallizations, mother Hquor flows over a cooled surface on which material is crystallized. The advancing front of crystals grows in the direction from the cooled surface into the mother Hquor. A variety of techniques can be used to take advantage of this type of Operation. 

Definite Integral The concept and derivation of the definite integral are completely different from those for the indefinite integral. These are by definition different types of operations. However, the formal operation J as it turns out treats the integrand in the same way for both. 

Vessels for high-temperature serviee may be beyond the temperature hmits of the stress tables in the ASME Codes. Sec tion TII, Division 1, makes provision for construction of pressure vessels up to 650°C (1200°F) for carbon and low-alloy steel and up to 815°C (1500°F) for stainless steels (300 series). If a vessel is required for temperatures above these values and above 103 kPa (15 Ibf/in"), it would be necessaiy, in a code state, to get permission from the state authorities to build it as a special project. Above 815°C (1500°F), even the 300 series stainless steels are weak, and creep rates increase rapidly. If the metal which resists the pressure operates at these temperatures, the vessel pressure and size will be limited. The vessel must also be expendable because its life will be short. Long exposure to high temperature may cause the metal to deteriorate and become brittle. Sometimes, however, economics favor this type of operation. 

Gravity vessels are suitable for low-, medium-, and high-temperature operation in the last case, the housing will be lined completely with refrac tory brick. Dust-recoveiy equipment is minimized in this type of operation since the bed actually performs as a dust col-lec tor itself, and dust in the bed will not, in a successful application, exist in large quantities. 

In case A the solvents are immiscible, so the rate of feed solvent alone in the feed stream F is the same as the rate of feed solvent alone in the raffinate stream R. In like manner, the rate of extraction solvent alone is the same in the stream entering S as in the extract stream leaving E (Fig. 15-12). The ratio of extraction-solvent to feed-solvent flow rates is therefore S /F = E /R. A material balance can be written around the feed end of the extrac tor down to any stage n (see Fig. 15-12) and then rearranged to a McCabe-Thiele type of operating line with a slope of F /S [Eq. (15-11)]. 

FIG. 22-84 General stages in downstream processing for protein production indicating representative types of operations used at each stage. 

Although the continuous-countercurrent type of operation has found limited application in the removal of gaseous pollutants from process streams (Tor example, the removal of carbon dioxide and sulfur compounds such as hydrogen sulfide and carbonyl sulfide), by far the most common type of operation presently in use is the fixed-bed adsorber. The relatively high cost of continuously transporting solid particles as required in steady-state operations makes fixed-bed adsorption an attractive, economical alternative. If intermittent or batch operation is practical, a simple one-bed system, cycling alternately between the adsorption and regeneration phases, 1 suffice. 

Installation of a shut-off valve in the expander exhaust line prevents baekflow during expander isolation (Figure 6-37). Although the need for this valve may not be immediately obvious, it ean be very bene-fieial if the expander is operated for an extended period in the windmilling mode. Often this type of operation is not antieipated during the initial evaluation of valve requirements, but beeomes neeessary at some later date. For example, it is useful when it is deemed prudent... 

A eompany will typieally eategorize its suppliers aeeording to their type of operation, for example ... 

There are many types of failures assoeiated with a gas turbine, sinee these units are very eomplex in their overall makeup. The failures in the hot seetion far outnumber the problems in the eompressor due to the high temperatures assoeiated with the hot seetion. Hot-seetion failures are usually eonneeted to problems assoeiated with fuels. Turbine failures ean be very eostly, the average eost runs about 500,000 for units between 10 and 50 MW and about 700,000 for units above 50 MW. These average failures result in downtime of between 12 and 16 weeks. The type of operation the unit experienees is a major faetor in the problem. The unit has a more trouble-free operation if it is a baseload unit. 

Many eonsumer applianees must plaee themselves in the standby mode when the user has walked away from the produet. This type of operation is ealled green eertified. This eertifieation dietates that the produet must use less than 5 watts of power while in the standby mode. The switehing power supply alone would have quieseent operating eurrent greater than 5 watts, so a very low power switehing power supply, with mueh lower quieseent eurrents, ean be used to power only that portion of the produet needed to reaetivate the produet upon demand. 

In insulator analysis an electron gun is also necessary to compensate for the positive ion current at the sample surface. Two types of operation are typical. 

Both types of tapes have found broad applicability throughout the industry. Some of the major uses for single-coated tapes include packaging, masking, electrical, office and medical related applications. Double-coated tapes are quite commonly used in assembly type of operations. 

These simplified schematles provide an overall view of the types of operations, equipment and eonfigurations typieally employed in adsorption operations. Additional diseussions on these systems ean be found among the referenees cited in Seetion (B) of the suggested readings at the end of this ehapter. 

Electrodialysis can be applied to the continuous-flow type of operation needed in industry. Multi-membrane stacks can be built by alternately spacing anionic- and cationic-selective membranes. Among the technical problems associated with the electrodialysis process, concentration polarization is perhaps the most serious (discussed later). Other problems in practical applications include membrane scaling by inorganics in feed solutions as well as membrane fouling by organics. 

Hazardous waste operations often include tasks and activities that are conducted on a periodic basis, are of very short duration, are transient in nature, or otherwise pose little hazard. Developing a brief HASP template (e.g., fill in the blank ), a permit, or a checklist system that includes essential HAZWOPER-type information may suffice for these types of operations. 

Wlien a different type of operation is initiated or [OSHA Referenee. 120(h)(3)(iii)]... 

In judging the adequacy of provisions you will need to apply the relevant standards, legislation, codes of practice, and other agreed measures for the type of operation, application, and business. These activities are quality assurance activities and may be subdivided into design assurance, procurement assurance, manufacturing assurance, etc. Auditing, planning, analysis, inspection, and test are some of the techniques that may be used. 

Customer" Expectations. Keep in mind that the output of your PSM systems design must address the needs of a range of "customers," including senior management, facility and other operating personnel, and the PSM team itself. As you approach designing the PSM system, you may want to revisit their expectations. Systems will also have to reflect issues such as plant size, location, type of operation, and types and quantities of materials used. 

Business and production cycles. Certain types of operations and facilities have predictable production cycles for example, some facilities may have scheduled annual turnarounds or a seasonal production peak. You are likely to get better cooperation and results if you re able to schedule the installation during moderate periods rather than at peak times. 

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