Abnormal operation

Abnormal conditions as described in this section should result in automatic corrective actions. 

Functions important to the safe operation of the facility should have redundant components. For incinerators burning alpha bearing wastes a secondary enclosure shall be provided as protection against failure of the safety components. 

Temperature transients may be caused by a high proportion of material with a high heat value in the waste. To avoid such temperature transients, the operating procedures should ensure that waste materials with high heat values are segregated and fed into the incinerator in smaller proportions together with waste with a low heat value. 

Normal operation is defined as plant operation within specified operational limits and conditions. Examples include starting up and shutting down the plant, normal power operation, shutdown, maintenance, testing and refuelhng. 

There are more serious abnormal operating conditions when the operators face a malfunction or fault in one of the normal core cooling systems 

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Nimmo, I. 1995. Adequately Address Abnormal Operations. Chemical Engineering Progress, 91(9), 36-45. 

These applications have considerably more stringent performance requirements than any other application. Circulating water pumps, boiler feed pumps, forced-draught (FD) and induced-draught (ID) fans, pulverizers (ball mills) and condensate pumps are components in a thermal power station that may require extra safety in a standard motor to make it able to fulfil these requirements and withstand abnormal service conditions and system disturbances. Abnormal operating conditions may be one or more of the following ... 

Protection against overloading This can be achieved by an overcurrent relay. The basic requirement of this relay is its selectivity and ability to discriminate between normal and abnormal operating conditions. Three types of such relays are in use thermal, electromagnetic and static. Thermal relays are employed for motors of up to medium size and electromagnetic and static relays for large LT and all HT motors, as discussed in Section 12.5. 

Most often, the bearing or the lubricant is blamed for the failure. This is like blaming the fuse for an electrical failure. The failure is most likely a result of some abnormal operating condition, or lack of proper maintenance. In short, something causes the bearing to fail prematurely. 

Idling and minor stoppages—due to the abnormal operation of sensors or other proteetive deviees. 

Cleaning also prevents failures due to abnormal operating modes. Fouling of the rotor blades on turbines can cause thrust-bearing failures. Deposits on... 

Topies should embraee a knowledge of the hazards and preeautions, ineluding the use and maintenanee of proteetive deviees ineluding personal proteetion, under both normal and abnormal operating eonditions ineluding emergeneies. 

Materials of construction should be chosen so the equipment will withstand the low est temperature that can be reached during abnormal operation. In the past, materials have been used that will withstand normal operating temperatures but that may become brittle at lower temperatures reached during plant upsets or abnormal operation, for example, when the pressure in a vessel containing liquefied petroleum gas is reduced and the vessel is cooled by evaporation of the liquid (see Section 10.5.2). Some spectacular failures have resulted [12] (see Section 9.2.1 g). 

Centralized Reliability Data Organization Input Guide Nuclear 1800 Component failure events causing abnormal operation engineering data for 20,000 components found in liquid metal reactors (e.g., LMRs). Gives generic data lor 45 equipment items (valves, pumps, etc.) Liquid metal reactor sites and test facility systems and components 62. 

A variety of electromechanical relays was used for the detection of abnormal operating conditions (e.g., overload, short-circuit, etc.), leading to the isolation of the faulty components. In the second half of the twentieth century electromechanical relays were progressively replaced by electronic controls that arc capable of faster response and higher reliability. 

The foundations of any turbogenerator installation play a significant part in the safe operation of the machine. Industrial turbines will normally operate at above synchronous speed and will drive an alternator via a reduction gearbox. Any vibration or out of balance occurring under both normal or abnormal operation must be accommodated by the foundations, and their design should therefore best be undertaken by a specialist organization. The layout... 

The acceptable operating envelope for centrifugal compressors is very limited. Therefore, care should be taken to minimize any variation in suction supply, back-pressure caused by changes in demand, and frequency of unloading. The operating guidelines provided in the compressor vendor s O M manual should be followed to prevent abnormal operating behavior or premature wear or failure of the system. 

Two types of ultrasonic systems are available that can be used for predictive maintenance structural and airborne. Both provide fast, accurate diagnosis of abnormal operation and leaks. Airborne ultrasonic detectors can be used in either a scanning or contact mode. As scanners, they are most often used to detect gas pressure leaks. Because these instruments are sensitive only to ultrasound, they are not limited to specific gases as are most other gas leak detectors. In addition, they are often used to locate various forms of vacuum leaks. 

Abnormal operating conditions or neglecting necessary maintenance precautions cause most bearing failures. Bearings may experience premature and/or catastrophic failure on machines that are operated heavily loaded. 

For a normal machine, this assumption is valid after the rotating element has achieved equilibrium. When the forces associated with rotation are in balance, the rotating element will center the shaft within the bearing. However, several problems directly affect this self-centering operation. First, the machine-train must be at designed operating speed and load to achieve equilibrium. Second, any imbalance or abnormal operation limits the machine-train s ability to center itself within the bearing. 

The detection of abnormal operation can only occur if normal operation is monitored. Since refrigeration is a thermal cycle, the obvious readings to be taken will be temperature and the related refrigerant pressure. 

Distinguish normal from abnormal operating conditions (Bastl and Fenkel, 1980 Long and Kanazava, 1980). 

Topics should embrace a knowledge of the hazards and precautions, including the use and maintenance of protective devices including personal protection, under hoth normal and abnormal operating conditions including emergencies. 

Figure 36 shows the performance of the interpretation system during a period of 30 hours. To detect an abnormal operation, the Mahalanobis... 

The conditions that may arise during abnormal operation, such as at start-up and shutdown, must be considered, in addition to normal, steady state, operation. 

Hydrogenation catalyst, Acid, Fuel Riesthuis, P. et al., J. Loss Prev. Process Ind., 1997, 10(10), 67 In the presence of precious metal hydrogenation catalyst, hydroxylamine salts may disproportionate and form dinitrogen monoxide. Such a mixture is present in a process whereby the hydroxyamine is formed by hydrogenation of nitrate. An explosion in the degassing line, after a period of abnormal operation, was attributed to nitrous oxide build-up. Fuel, in the form of hydrogen and methane diluent, was already present. 

Neuropathic and functional pain is often described in terms of chronic pain. Neuropathic pain (e.g., postherpetic neuralgia, diabetic neuropathy) is a result of nerve damage, but functional pain (e.g., fibromyalgia, irritable bowel syndrome, tension-type headache) refers to abnormal operation of the nervous system. Pain circuits may rewire themselves and produce spontaneous nerve stimulation. 

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