Shutdown

In this accident, the steam was isolated from the reactor containing the unfinished batch and the agitator was switched ofiF. The steam used to heat the reactor was the exhaust from a steam turbine at 190 C but which rose to about 300°C when the plant was shutdown. The reactor walls below the liquid level fell to the same temperature as the liquid, around 160°C. The reactor walls above the liquid level remained hotter because of the high-temperature steam at shutdown (but now isolated). Heat then passed by conduction and radiation from the walls to the top layer of the stagnant liquid, which became hot enough for a runaway reaction to start (see Fig. 9.3). Once started in the upper layer, the reaction then propagated throughout the reactor. If the steam had been cooler, say, 180 C, the runaway could not have occurred. ... 

Process operations. The third source of process waste we can classify under the general category of process operations. Operations such as start-up and shutdown of continuous processes, product changeover, equipment cleaning for maintenance, tank filling, etc. all produce waste. 

Sources of waste in process operations a. Start-up I shutdown in continuous processes... 

In continuous processes, all those sources of process waste associated with start-up and shutdown also apply to product changeover in multiproduct plants. 

Minimize the number of shutdowns by designing for high availability. Install more reliable equipment or standby equipment. 

Design continuous processes for flexible operation, e.g., high turndown rate rather than shutdown. 

Knowing where waste is going is the key to reducing it. When reducing waste from process operations, a steady-state mass balance is not usually comprehensive enough. A balance that takes into account start-up, shutdown, and product changeovers is required. 

Designing for a minimum number of shutdowns and product changeover s. 

In recent years much more attention has been given to pipeline isolation, after instances in which the contents of export pipelines fed platform fires, adding significantly to damage and loss of life. Many export and in field pipelines are now fitted with emergency shutdown valves (ESDV) close to the production platform, to isolate the pipeline in the event of an emergency. 

Thermal power plant components operated at high temperatures (>500°C) and pressures, such as superheater headers, steamline sections and Y-junctions, deserve great attention for both operation safety and plant availability concerns. In particular, during plant operation transients -startups, shutdowns or load transients - the above components may undergo high rates of temperature / pressure variations and, consequently, non-negligible time-dependent stresses which, in turn, may locally destabilize existing cracks and cause the release of acoustic emission. 

Main steamline section and weld of the same Unit 4 f600 MW3 as above the weld connects 2 steamline sections of different materials (stainless steel and low-alloy steel) through a transition material section, ahead of the Y-piece where branching of the turbine inlet lines takes place (255 mm internal diameter, 44.5 mm thickness). Ultrasonic inspection pointed out potential integrity problems in the weld. The requirement was again that AE could support safe operation of the weld until the next incoming planned maintenance shutdown. 

The results of over 1 year of continuous, on-line acoustic emission (AE) structural surveillance of high temperature / high pressure steam headers, gained on 2 M-scale 600MW supercritical multifuel ENEL power units in normal operation, are presented in the paper. The influence of background noise, the correlation between plant operating conditions (steady load, load variations, startup / shutdown transients) and AE activity and the diagnostic evaluation of recorded AE events are also discussed. 

Make maintenance planning more flexible, by providing, wherever possible, viable alternatives to unplanned shutdowns and to immediate component replace or repair actions. Increased flexibility of maintenance planning, by conditionally running under surveillance components with potential or incipient stmctural integrity problems, means improved plant availability, reduced energy replacement and maintenance costs. 

Steam headers and steamline sections may undergo high rates of temperature / pressure variations during plant operation transients - startups, shutdowns or load transients - and are... 

This header has undergone repair after through-thickness cracking of an assembly weld after 108.000 hours of service, it is presently in operation and periodically submitted to ultrasonic inspection during planned maintenance shutdown. Continuous on-line AE monitoring of the integrity of critical welds is expected to contribute supporting continued and safe operation of the header until its replacement, platmed to take place in 1999. 

Different plant operating conditions (steady load, load variations, startups / shutdowns) have been encountered during the monitoring period. Electrical load, steam pressure and steam temperature values vs time have been acquired and stored during the entire period. At the same time, the RMS values of the acoustical background noise were have been continuously checked and stored, thus providing a quick check of proper instrumentation condition and a correlation between variations of plant parameters and the acoustical behaviour of the components. 

Localized AE sources appear during load variations, startups or shutdowns, but their positions are uniformly spread over the length of the two bodies of the header this can be seen from the histogram of the localized AE events for the front body (fig.S) and for the rear body (fig.9). 

Radiographic inspection is considered as a legal alternative for pressure testing of petrochemical installations. It has the major advantage that it does not require shutdown of the installation. Other NDT techniques such as ultra-sound or eddy-current may be used alternatively or complementary. 

The system has been in full use during the shutdown periods of 1996 and 97 in the nuclear industry in Sweden. Performed tests have produced excellent results under sometimes difficult conditions... 

In addition, NDT plays an important part in industrial maintenance. During plant shutdowns for instance, many thousands of ultrasonic wall thickness measurements are taken on piping, vessels, furnace tubes etc. All these thickness readings have to go into extensive data bases, and this process is, thanks to modem computers and data loggers, ever more automated. 

In maintenance practice, we base our decisions on NDT that is performed during shutdowns. A significant amount of money could be saved if we would have NDT methods that minimise the time required for that shutdown, or, a step further, avoid it by performing inspections onstream. 

Maintenance schemes and standards require defined intervals between shutdowns for invasive inspections. During a shutdown, the installation is opened and inspected. This is usually the... 

However, it is expected that this situation will change, since a number of novel "non-invasive NDT techniques are now becoming available. With some of these techniques, the time required for a shutdown can be reduced. Other techniques make it possible to perform inspections whilst the installation is in full service. It is obvious that the availability of such techniques could support the knowledge already available on operational parameters and degradation mechanisms, in order to base shutdown intervals on actual plant condition. 

In plant maintenance, the availability of quantitative and non-invasive screening NDT methods will reduce the time needed for shutdowns and increase the intervals between them. Modem NDT methods will become just as important a tool for Risk Based Inspection approaches and maintenance planning as operational parameters and degradation mechanisms already are. 

The RCCA s (32 to 52 assemblies in the core), regulate the neutron flux in the reactor, and are used for emergency shutdown of the reactor activity. In normal working conditions, the RCCA s are suspended above the fuel elements. 

Conversion of acetaldehyde is typically more than 90% and the selectivity to acetic acid is higher than 95%. Stainless steel must be used in constmcting the plant. This is an estabHshed process and most of the engineering is weU-understood. The problems that exist are related to more extensively automating control of the system, notably at start-up and shutdown, although even these matters have been largely solved. This route is the most rehable of acetic acid processes. 

The modified Reppe process was installed by Rohm and Haas at thek Houston plant in 1948 and later expanded to a capacity of about 182 X 10 kg/yr. Rohm and Haas started up a propylene oxidation plant at the Houston site in late 1976. The combination of attractive economics and improved product purity from the propylene route led to a shutdown of the acetylene-based route within a year. 

An extraction plant should operate at steady state in accordance with the flow-sheet design for the process. However, fluctuation in feed streams can cause changes in product quaUty unless a sophisticated system of feed-forward control is used (103). Upsets of operation caused by flooding in the column always force shutdowns. Therefore, interface control could be of utmost importance. The plant design should be based on (/) process control (qv) decisions made by trained technical personnel, (2) off-line analysis or limited on-line automatic analysis, and (J) control panels equipped with manual and automatic control for motor speed, flow, interface level, pressure, temperature, etc. 

As the economic value of coproducts has decreased, it has become more difficult to provide capital for environmental controls on air emissions and wastewater streams such as toxic phenoHc effluents from chemical recovery operations. Some former coke and manufactured gas sites may require remediation to clean up contaminated soil and groundwater. These difficulties will force the shutdown of some operations and discourage recovery of coproducts in future installations. 

Advantages of the pitot method of measurement are low pressure loss and easy installation. In some cases, installations in existing lines are made without process shutdown by hot tapping the line (7). 

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