Shutdown time

Advantages (a) High organic concentrations can be treated. (b) Modest space requirements. (c) Short start-up and shutdown times. 

These shutdown times are moderate 2.4Ffor5 = 0.1 and 3F for 5 = 0.05. Equation (14.2) governs the outlet concentration during the shutdown interval. For this shutdown strategy, it becomes... 

First of all, before we compare flow reactors, let us mention the batch reactor briefly. The batch reactor has the advantage of small instrumentation cost and flexibility of operation (may be shut down easily and quickly). It has the disadvantage of high labor and handling cost, often considerable shutdown time to empty, clean out, and refill, and poorer quality control of the product. Hence we may generalize to state that the batch reactor is well suited to produce small amounts of material and to produce many different products from one piece of equipment. On the other hand, for the chemical treatment of materials in large amounts the continuous process is nearly always found to be more economical. 

Regarding reactor sizes, a comparison of Eqs. 5.4 and 5.19 for a given duty and for s = 0 shows that an element of fluid reacts for the same length of time in the batch and in the plug flow reactor. Thus, the same volume of these reactors is needed to do a given job. Of course, on a long-term production basis we must correct the size requirement estimate to account for the shutdown time between batches. Still, it is easy to relate the performance capabilities of the batch reactor with the plug flow reactor. 

An optimum processing time of 180 min is required for a complete cycle of 100 kGy dose. A shutdown time of at least 8 h was necessary after every 100 kGy addition to allow sufficient diffusion of oxygen in the PTFE powder. The total time for the whole process from 20 to 500 kGy was approximately 50 h, including the 8 h shutdown intervals after every 100 kGy addition. To achieve 500 kGy, the doses were added to the PTFE powder in 100 kGy steps. These treatment parameters were chosen in order to avoid excess temperature rise, which might favor deactivation of the radical formation, as well as to control agglomerate size and chemical structure via absorbed dose. Further information on the electron accelerator (ELV-2) facility can be found in [11]. 

For most reactions, the rate decreases as the reaction proceeds (important exceptions being a number of biological reactions which are autocatalytic). For a reaction with no volume change, the rate is represented by the slope of the curve of X (moles converted per unit volume) versus time (Fig. 1.10), which decreases steadily with increasing time. The maximum reaction rate occurs at zero time, and, if our sole concern were to obtain maximum output from the reactor and the shutdown time were zero, it appears that the best course would be to discharge the reactor after only a short reaction time tr, and refill with fresh reactants. It would then be necessary, of course, to separate a large amount of reactant from a small amount of product. However, if the shut-down time is appreciable and has a value ts then as we have seen in the example on ethyl acetate above, the average production rate per unit volume is ... 

Absorption of a component of a gas stream into a liquid is a common practice in the chemical industry to affect cleanup of vent gases, conduct chemical reactions, purify products, or to recover products from process streams. The enhanced mass transfer capability of RPBs provides the opportunity to perform absorption processes in smaller equipment, to lower inventories, to shorten startup and shutdown times, and to lower pressure drop (48). Figure 8 provides a visual comparison of the size of a conventional absorber tower next to three RPBs that handle the equivalent gas and liquid flows (9). 

High labor and handling costs as well as the start-up and shutdown times required to fill and empty the reactor are important drawbacks in a batch operation. Continuous flow systems are nearly always more cost-effective than batch reactors, especially when large volumes are to be treated, i.e., the main application of this reactor configuration is wastewater treatment. The removal of phenolic compounds from waters has been performed using SBP and HRP in continuous stirred tank reactor (CSTR) [49, 75, 76, 81, 83, 84],... 

Thus, for conditions of minimum annual cost and a production of 1 million kg/year, not all the available operating and shutdown time would be used. 

Total annual cost = operating and shutdown costs/cycle X cycles/year + annual fixed costs Annual production = (production/cycle) (cycles/year) operating + shutdown time used/year... 

Consolidating the investigation process can still ensure that the facilities are operating with the highest margin of safety, while at the same time ensuring that procedures are in place that will minimize plant shutdown time following chemical events or other safety infractions. 

A further complication arises from the age of the weapons as well as their varied history— leakers" and "gelled agents require changes in standard" operations, for example. The shutdowns and restarts resulting from these feed stock variations can be planned for and shutdown times can be minimized. 

This expression allows 30 min for shutdown time per charge and takes into account that the conversion is 50%. Thus... 

Plasma arc pyrolysis Involves passing an — Short start-up and shutdown times, electric current through a low-pressure increasing safety,... 

The parameter fp is the total number of fissions after irradiation time T per initial fissile atom, calculated by techniques described in Chap. 3. Equation (2.94) applies for operating times < 1.2614 X 10 s (4 years), shutdown times <10 s, and <3.0. A more detailed technique for calculating fission-product decay-heat power from an arbitrary time-dependent fission power, including contributions from the fission of U, U, and Pu, is given in the ANS Standard [A2]. 

The transient poisoning ratio, which is the ratio of the neutron absorption in Xe to fission absorption if the reactor is to be started up again after shutdown time t, is obtained from Eq. (2.122) ... 

The main purpose of the first series of runs was to determine the effectiveness of the pulse system for scale reduction, and determination of the shutdown time. This run lasted for 1560 hours and the average reduction of salinity for 13 weeks was 1762 p.p.m. The production rate of the pilot plant was 5200 gallons per day. Almost no adherent scale deposited on the membrane. However, part of the soft sludge was held back by the expanded plastic spacer material and caused a slow increase of voltage. When the over-all voltage reached 125% of the mean operating value, reversed polarity was applied for 1 or 2 hours. This procedure was adopted in addition to the short cycle pulse system. 

On the basis of the above decisions, a summary of the operations and production schedule is presented below. (Start-up and shutdown time are neglected in the calculations.)... 

Some manufacturers (140, 213) market quick-opening types of manways, in which a latch replaces bolting as a means of keeping the manway in place. These offer advantages of reducing shutdown time and labor (140), but little has been published about their field performance. 

In large-diameter columns, when shutdown time is critical, and if manhole location permits, two tray installation crews are often used simultaneously inside the column. This practice suffers from the hazards of falling objects and/or poor ventilation and should be avoided whenever possible. If it has to be used, precautions are required for minimizing the risks. 

Maintenance shutdown time is usually much longer and is inconvenient because the machine must be disassembled into many separate components. A modular concept is not possible in the design of these heavy industrial machines. 

Only the coohmt has to be circulate, and the same tope free from fission fragments. A schedule of replace-circulation cools the reaction and absorption zones. No 65 ment can readily be worked out to keep the reactor gas is evolved from the reaction zone and poisoning fac- operating with minimum shutdown times, in accordance tors, due to retention of fission product neutron absorb- with the power output and resultant use rate of the ers in the reaction zone, do not become critical because plutonium. 

Turbomolecular pumps have replaced the previously used diffusion pumps because they do not use oil, thereby preventing contamination, and have short start-up and shutdown times. Modem turbomolecular pumps often run for several years before mechanical failure occurs from wear on the bearings. 

About two events turned out to be caused by a critical organizational or management problem such as a violation of the prescribed shutdown time of a system or not informing the operating team of an important system operation setpoint which has been found during a trial operation. 

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