Start-up/shut-down

Explosibility and Fire Control. As in the case of many other reactive chemicals, the fire and explosion hazards of ethylene oxide are system-dependent. Each system should be evaluated for its particular hazards including start-up, shut-down, and failure modes. Storage of more than a threshold quantity of 5000 lb (- 2300 kg) of the material makes ethylene oxide subject to the provisions of OSHA 29 CER 1910 for "Highly Hazardous Chemicals." Table 15 summarizes relevant fire and explosion data for ethylene oxide, which are at standard temperature and pressure (STP) conditions except where otherwise noted. 

System integration involves numerous miscellaneous development activities, such as control software to address system start-up, shut-down and transient operation, and thermal sub-systems to accomplish heat recovei y, heat rejection and water recoveiy within the constraints of weight, size, capital and operating costs, reliability, and so on. Depending on the application, there will be additional key issues automotive applications, for example, demand robustness to vibrations, impact, and cold temperatures, since if the water freezes it will halt fuel cell operation. 

Although continuous stirred-tank reactors (Fig. 3.12) normally operate at steady-state conditions, a derivation of the full dynamic equation for the system, is necessary to cover the instances of plant start up, shut down and the application of reactor control. 

Other than an important and far-reaching guide word, but consequently more vague in its application. It covers all conceivable situations other than that intended such as, start-up, shut-down, maintenance, catalyst regeneration and charging, failure of plant services. 

Analysis and modelling of the dynamic behaviour of the catalyst is useful to closely describe the performance during start up, shut down and load variation of stationary applications, and of critical relevance for SCR-NH3 of mobile diesel engine emissions. Use of dynamic models for exhaust transients has not been extensively reported in the literature for the design of improved catalysts, although it is a very valuable method. On the contrary, as will be discussed later, use of this tool to derive mechanistic implications is much less convincing. 

When the specified production capacities are low, processes based on batch reactors will usually have lower capital investment requirements than processes calling for continuous operation, so batch reactors are often preferred for new and untried processes during the initial stages of development. As production requirements increase in response to market demands, it may become more economic to shift to continuous processing but, even in these cases, there are many industrial situations where batch operation is preferable. This is particularly true when the operating expenses associated with the reactor are a minor fraction of total product cost. At low production capacities, construction and instrumentation requirements for batch reactors are usually cheaper than for continuous process equipment. Moreover, it is generally easier to start up, shut down, and control a batch reactor than a comparable capacity continuous flow reactor. 

The choice of the tubular geometry is related to its main advantages in terms of quick start-up, mechanical resistance, and possibility of realizing sealless stacks. The reduced size drastically reduces thermal shocks and the related mechanical stress, due to quick load changes and start-up/shut-down. 

Other Start-up Shut down Relief system Power/service failure Corrosion/erosion Materials of construction T oxicity/asphyxia Maintenance (provision of isolation, etc.) Double valves (trapped liquids) Valve access Provision for testing instruments, trips, alarms Fire Static electricity Noise Thermal radiation Ionising radiation Sampling Spares Anything else ... 

Intermediate products Equipment Instrumentation Plant layout Start-up Shut down... 

All batch and semibatch processes are transient, as are continuous processes being started up, shut down, or in transition from one operating state to another. The accumulation terms in balance equations for transient systems are not zero (as they are for steady-state systems) but rather are derivatives of system variables with respect to time, and balance equations are consequently differential rather than algebraic. 

For upset conditions, indicate autoretrigeration, liquid water, wet sour service, carry-over of crack-inducing agents or corrodents, etc. Consider start-ups, shut-downs, regeneration, presulfiding, loss of flow, etc. 

Optimize fuel cell hybrid vehicle system, considering a variety of energy storage options and system operating characteristics, including fuel cell idling and start-up/shut-down... 

Achieve fully automatic operation during normal, start-up, shut-down and stand-by modes ... 

Mechanical deactivation is due to strong stresses of packed catalysts beds during start ups, shut-downs and catalyst regeneration. 

In certain situations the plant operator may wish to override the automatic mode and adjust the controller output manually. In this case there is no feedback loop. This manual mode of operation is very useful during a plant start-up, shut-down, or emergency situation. Testing of a process to obtain a mathematical model is also sometimes carried out in the manual mode. Commercial controllers have a manual/automatic switch for transferring from the automatic mode to the manual mode or vice versa. Bumpless transfers that do not upset the process can be achieved with commercial controllers. 

Signals to the Plant Protection and Instrumentation System (PPIS) and the NSSS Control Subsystem (NCS) are supplied by neutron detectors. During power operation, the neutron flux levels are monitored by detectors located in wells between the reactor vessel and the concrete cavity wall. These detectors are distributed symmetrically around the reactor vessel at about the core midplane. During low power operation, starting up, shutting down, and while shut down, the neutron flux levels are monitored by source-range detectors, located in selected side reflector elements near the bottom of the active core. 

What are the effects of changes of state of the media in case of deviations from nominal operating conditions (e.g. state of aggregation, viscosity, interfacial tension) Are the plant and its parts designed properly as to process conditions, structural strength and materials for the cases normal operation, start-up, shut-down and emergency shut-down ... 

Work is being planned to determine if the CPF in PWR vessels is acceptably low when small surface flaws (approximately 4-6 mm - 0.16-0.24 in - in depth) are postulated at the vessel inner surface and normal reactor start-up, shut-down and system leak testing occur along the allowable P-T boundaries defined by reguiatory requirements, the ASME evaluation procedures, and procedural and hardware constraints. 

Table 775Recent research in start-up/shut-down procedures for PEFCs... 

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