Time events

Time events can be handled very efficiently by stopping and reinitializing the integration routine at the corresponding time point. No localization of the switching point is necessary. 

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Figure 4.11 A Gantt or time-event chart of the batch process.

The reactor now becomes batch, requiring the reaction to be completed before the separation can take place. Figure 4.14 shows the time-event chart for a repeated batch cycle. Note in Fig. 4.14 that there is a small overlap between the process steps. This is to allow for the fact that emptying of one step and filling of the following step occur at the same time. 

Clearly, the time chart shown in Fig. 4.14 indicates that individual items of equipment have a poor utilization i.e., they are in use for only a small fraction of the batch cycle time. To improve the equipment utilization, overlap batches as shown in the time-event chart in Fig. 4.15. Here, more than one batch, at difierent processing stages, resides in the process at any given time. Clearly, it is not possible to recycle directly from the separators to the reactor, since the reactor is fed at a time different from that at which the separation is carried out. A storage tank is needed to hold the recycle material. This material is then used to provide part of the feed for the next batch. The final flowsheet for batch operation is shown in Fig. 4.16. Equipment utilization might be improved further by various methods which are considered in Chap. 8 when economic tradeoffs are discussed. 

Fl9 4.14 Time-event chart for a repeated batch cycle for Example 4.5. 

Figure 8.8 Time-event chart for Example 4.4 with two reactors in parallel.

Batch processes can be synthesized by first synthesizing a continuous process and then converting it to batch operation. A Gantt (time-event) diagram can be used to identify the scope for improved equipment utilization and the need for intermediate storage. 

Development of laser technology over the last decade or so has permitted spectroscopy to probe short-time events. Instead of having to resort to the study of reactants and products and their energetics and shuctures, one is now able to follow reactants as they travel toward products. Fast pulsed lasers provide snapshots of entire molecular processes [5] demanding similar capabilities of the theory. Thus, explicitly time-dependent methods become suitable theoretical tools. 

However, in the case of a root cause analysis system, a much more comprehensive evaluation of the structure of the accident is required. This is necessary to unravel the often complex chain of events and contributing causes that led to the accident occurring. A number of techniques are available to describe complex accidents. Some of these, such as STEP (Sequential Timed Event Plotting) involve the use of charting methods to track the ways in which process and human events combine to give rise to accidents. CCPS (1992d) describes many of these techniques. A case study involving a hydrocarbon leak is used to illustrate the STEP technique in Chapter 7 of this book. The STEP method and related techniques will be described in Section 6.8.3. 

Sequentially Timed Events Plotting Procedure (STEP)... 

The first case study describes the application of the sequentially timed event plotting (STEP) technique to the incident investigation of a hydrocarbon leak accident. Following the analysis of the event sequence using STEP, the critical event causes are then analyzed using the root cause tree. 

This case study concerns the events leading up to the hydrocarbon explosion which was the starting point for the Piper Alpha offshore disaster. It describes the investigation of the incident using the sequentially timed events plotting (STEP) technique. Based on the STEP work sheet developed, the critical events involved in the incident are identified and analyzed in order to identify their root causes. 

In order to accurately describe the actual sequence of events that make up the accident techniques such as STEP (sequential timed event plotting—see Chapter 6 and the case study in Chapter 7) can be used by the investigator. 

All data recorded in the data base have been acquired from plant records. Statistical reductions of data for generation of reports or specific end use are available. Data are currently collected from four operating plants (eight units). Time clocks have been installed on components, to record actual exposure time. Event data are available on a broad variety of safety and commercial grade components including pumps, valves, transformers, diesels, filters, tanks (vessels), and heat exchangers. 

Part of the concern about global climate change stems from the human tendency to seek meaniiig in events that may or may not be more than simply a random event. A particularly cold winter, a particularly hot summer, an especially rainy season, or an especially severe drought will all send people off on a search for the greater meaning of the phenomenon. Is it a pattern, or a one-time event Must we build a dike, or has the danger passed Since the summer of... 

Machine-trains or process systems that have specific timing events (e.g., a pneumatic or hydraulic cylinder)... 

Dynamic simulation with discrete-time events and constraints. In an effort to go beyond the integer (logical) states of process variables and include quantitative descriptions of temporal profiles of process variables one must develop robust numerical algorithms for the simulation of dynamic systems in the presence of discrete-time events. Research in this area is presently in full bloom and the results would significantly expand the capabilities of the approaches, discussed in this chapter. 

Design modifications for the accommodation of feasible operating procedures. Section V introduced some early ideas on how the ideas of planning operating procedures could be used to identify modifications to a process flowsheet, which are necessary to render feasible operating procedures. More work is needed in this direction. Clearly, any advances in dynamic simulation with discrete-time events would have beneficial effects on this problem. 

From a theoretical point of vie v, the blinking kinetics of these CdTe QDs can be quantified by analysis of the on- and off- time probability densities, P(ton) and respectively. Figure 9.8 displays the luminescence intermittency statistics for CdTe QDs in trehalose environment. The distribution of off times involved in the blinking is almost linear on this scale, indicating that the lengths of off times events are distributed according to an inverse po ver-la v of the type, P tos) = Pof where Pq is... 

Giobai time interval Global time points Unit-specific time event Time slots Precedence-based... 

The time events are synchronized by one autosampler, and the diverting valve of the MS is used to select column effluent to monitor. Figure 4.12 shows an electronic diagram for this scheme. 

Hardware requirements — The system controller responsible for synchronizing the events is defined as LC System 1. It requires at least two time event outputs to trigger the injection of LC System 2 and start MS data collection. If MS fails, the injection of LC System 1 should be inhibited. Autosampler with ready-in, alarm-in, and stop inputs indicate capability to be stopped remotely. The autosampler of LC System 2 must be able to prepare a sample before the run from LC System 1 is finished and hold the sample in the injector loop until an injection signal is received. A manual injection input devices indicates that the autosampler can perform the required function. 

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