Systems unwanted operation

If the motor drives plant of high inertia (e.g. fans) the time during which the large current is drawn may be extended. Such a current flowing for an extended period may cause the unwanted operation of overload or over-current protection relays within the supply system. 

In any vacuum system the operator must ensure that any unwanted lines are isolated and all vacuum points are shut off when not in use. Vacuum is easily lost by relatively small leaks which, of course, are not readily apparent as the leaks are into the pipe or vessel. If the required vacuum is not attained, it is best to first locate the fault by the following procedure Isolate the vacuum pump or ejector and check that the gauge adjacent to the pump or ejector is performing correctly. If this is satisfactory, close all valves in the system and then open up each section in turn working away from the vacuum source. This will reveal the faulty section or sections and will reduce the area of search for leaks. Alternatively, the system may be pressurized and checked for leaks with soapy water as previously described. 

A contaminant is universally defined as a foreign or unwanted substance that can have harmful effects on a system s operation, life, or reliability. Solid and fluid contaminants are classified into three major categories organics, inorganics, and particulates of organics and inorganics. 

The safety assessment therefore needs to consider the implication of unwanted operation (for instance via the functional hazard assessment as a specific functional failure mode applied to specific flight phases). The usual design practice (to ensure high system integrity) is to design parallel multiplex systems. However, when it is important to avoid unwanted operation, items may be put in series to avoid unwanted operation (Lloyd and TVe, p. 47) as demonstrated for the angle-of-attack (A of A) sensors in Fig. 6.4. 

Erom 1955—1975, the Ziegler-Natta catalyst (91), which is titanium trichloride used in combination with diethylaluminum chloride, was the catalyst system for propylene polymerization. However, its low activity, which is less than 1000 g polymer/g catalyst in most cases, and low selectivity (ca 90% to isotactic polymer) required polypropylene manufacturers to purify the reactor product by washing out spent catalyst residues and removing unwanted atactic polymer by solvent extraction. These operations added significantly to the cost of pre-1980 polypropylene. 

The basic approach is to direct the system to the safest operating level relative to people or the environment when any emergency condition is detected, including power loss. An important concept of process control safety is to have adequate redundancy to reduce unwanted shutdowns and maintain an adequate level of certainty that a safe state will result if a real emergency does occur. As far as possible, instruments should be of the fail-safe type. 

A type of waterside maintenance chemical treatment. Any of a very wide range of chemicals that prevent or reduce tendencies of deposition, fouling, scaling, corrosion, or other unwanted phenomena to occur in a water system. Typically for smaller boiler plants, individual inhibitors are blended together to produce various multifunctional formulations specific for particular water chemistry and/or operating conditions. Larger boiler plants tend to use individual active component inhibitors. 

The selectivity for various rotational speeds should be determined with stirrers of small and large Ds/D,-, while maintaining the other design and operating variables constant (see Table 5.4-26). Plots of yields of unwanted products S versus N, x99, and PA r should then be made for both stirrers to determine the independent parameter which best correlates the data for both stirrer systems. 

Chemical treatment is what the name implies-the addition of a foreign substance to effect the removal of unwanted substances. This includes such operations as neutralization, coagulation, ion exchange, and electrodialysis. These, along with the advanced physical systems, have been referred to at times as tertiary treatment or advanced treatment processes. 

Attrition of particulate materials occurs wherever solids are handled and processed. In contrast to the term comminution, which describes the intentional particle degradation, the term attrition condenses all phenomena of unwanted particle degradation which may lead to a lot of different problems. The present chapter focuses on two particular process types where attrition is of special relevance, namely fluidized beds and pneumatic conveying lines. The problems caused by attrition can be divided into two broad categories. On the one hand, there is the generation of fines. In the case of fluidized bed catalytic reactors, this will lead to a loss of valuable catalyst material. Moreover, attrition may cause dust problems like explosion hazards or additional burden on the filtration systems. On the other hand, attrition causes changes in physical properties of the material such as particle size distribution or surface area. This can result in a reduction of product quality or in difficulties with operation of the plant. 

A measure is preventive if it prevents the occurrence of a runaway, a decomposition, or a hazardous secondary reaction. The system conditions remain close to operating conditions. Excessive increases in temperatures and/or pressures are avoided. Preventive measures include feed rate control systems, interlocks to prevent the reaction from starting unless sufficient diluent is present or the cooling system is working, and tests for the presence of catalysts or unwanted impurities. Preventive measures are always to be preferred over protective or mitigating (defensive) measures. 

An Emergency Shutdown (ESD) system is a method to rapidly cease the operation of the process and isolate it from incoming or going connections or flows to reduce the likelihood of an unwanted event from occurring, continuing, or escalating. The aim of an ESD system is to protect personnel, afford protection to the facility, and prevention of an environmental impact from a process event. 

In the case of batch operation, damages by the so-called contamination - that is, the entry of unwanted organisms into the systems, with resultant spoilage of the products - is limited to the particular batch that was contaminated. 

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