Frequent starts

Frequently a piece of equipment is used in different processes during its lifecycle. This could result in process conditions that exceed the safe operating limits of the equipment. Equipment inspection may provide a poor prediction of the equipment s useful life and reliability, due to the change of material handled or change in process chemistry over the life of equipment. Batch operations are also characterized by frequent start-up and shut-down of equipment. This can lead to accelerated equipment aging and may lead to equipment failure. This chapter presents issues and concerns related to the safe design, operation, and maintenance of various pieces of equipment in batch reaction systems, and provides potential solutions. 

Erequent start/stop Minimize frequent start/stop by proper sizing of of equipment may equipment (e.g. pump capacity) lead to equipment, Implement mechanical integrity program failure. Develop procedure to investigate causes for frequent reset of control Minimize frequent start/stop of equipment ... 

Basic process control system (BPCS) loops are needed to control operating parameters like reactor temperature and pressure. This involves monitoring and manipulation of process variables. The batch process, however, is discontinuous. This adds a new dimension to batch control because of frequent start-ups and shutdowns. During these transient states, control-tuning parameters such as controller gain may have to be adjusted for optimum dynamic response. 

I. The reaction between the ethereal solution of butyl bromide and the magnesium frequently starts without any assistance, but the presence of a trace of iodine is of no disadvantage and renders more certain the beginning of the reaction. 

To meet the load demand for more frequent starts and reversals, as for cranes and other hoisting applications. f) To achieve the required speed variation through variation in rotor circuit impedance. 

During start-up since only the outer cage is in the circuit with a very high current, the motor is heated up quickly by every start and may not be suitable for frequent starts and reversals. 

Note For such duties, the starting heat is kept as low as possible by suitable rotor design to eliminate the effect of frequent starts and stops. The margin for starting heat and braking heat should be taken into account if these are considerable. The manufacturer is a better guide for suggestions here. 

They have in-built safety features to prevent excessive frequent starting, by means of thermostats and low-level electrolyte monitors... 

More importantly, such alloys also possess a very low temperature coefficient of electrical resistance (of the order of 220 idQ.IQ.rC, typical), which causes only a marginal change in its resistance value with variation in temperature. They can therefore ensure a near-consistent predefined performance of the motor for which the resistance grid is designed, even after frequent starts and stops. They are also capable of absorbing shocks and vibrations during stringent service conditions and are therefore suitable for heavy-duty drives, such as steel mill applications. 

Their moment of inertia is kept low to restrict their times of acceleration and deceleration (equation (2.. t)) to facilitate frequent starts and stops,... 

Frequent starts and stops may also cause this because of excessive heat. 

Frequent starts It is not a fault condition, but rapid heating of motor s stator and rotor due to frequent starts will be no less severe than a fault condition, hence considered in this category. 

Metal parts are also joined by a range of fasteners rivets, bolts, or tabs. In using them, the stress concentration at the fastener or its hole must be allowed for fracture frequently starts at a fastening point. 

Both top and bottom halves of the journal bearings should be inspected for misalignment wear as well as excessive in-line wear, which can occur in turbines with frequent starts. An indication of the condition of the thrust-bearings can be made by removing a small section of the turbine shaft, usually on the governor end, and axially moving or bumping the shaft. The amount of axial shaft movement will indicate the thrust clearance and, if it is found to be 0.012-0.015 inches, it can be considered normal. 

The moment of inertia of a driven load is very important in the proper selection of a motor for those situations in which the motor accelerates a heavy load or makes frequents starts. Moment of inertia is WR as Ib-fti. This is the product of the weight of an object and the square of the radius of gyration (i.e., WR = Wk, where W = weight in lb, and k is the radius of gyration in ft where R = radius of a disk, and k = R/(2). Other details exist for calculating the radius of gyration of other shaped objects. ... 

Wound-rotor motors are suitable for constant-speed applications that require frequent starting or reversing under load or where starting duty is severe and exceptionally high starting torque is required. 

Freeze thermostat (low water temperature limit) Single-phase protection (preventing attempts to start with loss of one phase of a three-phase electrical supply) Time out (preventing too-frequent starting and motor burn). 

If a plant has been shut down long enough for all pressures to equalize and is then restarted, the suction pressure will pull down below normal until the liquid refrigerant has begun to circulate. Under such circumstances the low-pressure switch may operate. This is a normal occurrence, but may require the addition of a delay timer to prevent frequent starting of the compressor motor. 

Most patients have a mixture of non-in-flamed and inflamed lesions. Inflamed lesions can be superficial or deep, and arise from non-inflamed lesions. The superficial lesions are usually papules and pustules (5 mm or less in diameter), and the deep lesions are large pustules and nodules. Papules are small, raised, red spots, while pustules are predominantly yellow (Figs. 11.3,11.4). Pustules frequently start as solid lesions, like papules, which soon liquefy. Usually, the roof of the pustule bursts, allowing the pus to escape. The pustule represents a par-... 

Overviews of batch process design are available within the literature [35, 36] however, it is useful to summarize the main features when considering the arguments for B2C. A batch process is one where the individual steps of the manufacturing cycle are carried out in discrete intervals, resulting in frequent start-up and shutdown of the unit operahons involved. Thus, a scheme that requires... 

A frequent starting point for such calculations are the values of Volta potentials, between electrodes and electrolytes (which can be measured by the same methods as Volta potentials between metals). According to Eq. (9.7),... 

Proportional plus rate controllers are useful with processes which are frequently started up and shut down because it is not susceptible to reset windup. 

Since the early work dealing with Zeise s salt, many complexes have been prepared with the formula [PtL(C2H4)X2], where L = quinoline, pyridine, or ammonia and X=C1 , Br , I, or N()2. Similar compounds have been prepared that contain other alkenes than C2H4. Many of the complexes containing dienes, trienes, and tetraenes as ligands also contain carbonyl ligands. In fact, metal carbonyls are frequently starting complexes from which alkene complexes are obtained by substitution reactions. 

Darbepoetin alfa has a longer half-life than epoetin alfa and prolonged biologic activity. Doses are administered less frequently, starting at once a week when administered IV or SC. 

In the introduction we pointed out that calculations in chemistry and physics frequently start from an ideal model and proceed to improvements. This procedure is clear in the following two cases. 

This reaction, shown in Scheme 7.164, has been used frequently starting from... 

Until now we have studiously avoided defining what constitutes an explosion or go result in an impact test, except mentioning that go s are judged on the basis of sound, flash, gas volume etc. What physical events produce these observed manifestations Based primarily on the studies of Bowden (Ref 2) it is clear that in an impact test explosion frequently starts as a relatively mild deflagration which can propagate as slowly as lOm/sec, which turns into a much more violent deflagration, (lOO-lOOOm/sec), in the confined (by striker anvil) explosive. For many insensitive explo-... 

Analysis of DNA or RNA frequently starts with the size separation of extracted nucleic acids by electrophoresis on agarose or... 

The state of the hydrocarbon chains in mesophases and micelles is reflected in the Krafft phenomena. In aqueous solutions of surfactants the Krafft point is defined as the temperature at which the solubility reaches the critical micelle concentration when the temperature is increased further, the solubility rises rapidly since the monomers form micelles (Figure 5) (10). Lipids that do not form micelles frequently start to swell by the uptake of water at a well-defined temperature they are transformed into a mesomorphous state (Figure 6) (11) The relation between these two Krafft phenomena is explained to some extent by the... 

---