Multiple train flow

Knowledge of the flow patterns for RO systems is fundamental to the understanding of how an RO system functions. Arrays, passes, recycle, and multiple trains are terms used to describe an RO system that are discussed in this chapter. 

Multiple trains or "skids" placed in parallel are used when larger flow rates need to be treated. For example, an 800-gpm RO might require 1 skid, if the vendor has that size skid in their inventory. Alternatively, one could use two 400-gpm RO skids to make up the 800 gpm production rate. 

Another form of redundancy is the excess capacity often built into plants with more than one processing line. If two sets of drying towers are used, for example, the capacity of each may be more than 50% of the plant design capacity. The primary justification for multiple trains usually is to enhance turndown capability or to allow continued operation even when one train must be shut down. The same approach may be taken with the cooling section. Given the sizes of chlorine gas headers, valves would be expensive and probably ineffective as shutoff devices. Many plants therefore use U- or J-shaped traps in the piping. These can be filled with water or acid to stop the gas flow and to isolate equipment for maintenance. 

Backup supplies are always useful when a utility is lost Spare equipment or multiple-train equipment may be used in order to keep the utility on line even if one part of the system shuts down. An alternative or supplement is to provide backup from a different utility system. The number of different air systems found in a plant provides an opportunity to do this. Moreover, nitrogen can be used to back up some of the air systems. All these tie-ins require careful review during hazard analyses. Usually, the backup supply is activated when the primary supply loses a certain amount of line pressure. If this is done by means of a single pressure regulator and the pressure is also low on the backup system, the flow may be opposite to that intended. It is essential to keep nitrogen out of an air supply to a confined, inhabited space (e.g., the instrument air supply to a control room), and it is essential to keep air out of nitrogen when it is used as an inert gas. 

One of the most common errors in laying out a control structure for a plant with multiple units in series is the use of PI level controllers. If P controllers are used, the process flows rise or fall slowly down the train of units with no overshoot of flow rates. Liquid levels rise if flows increase and fall if flows decrease. Levels are not maintained at setpoints. See Fig. 7.14. 

The program used for training, the flow diagram for which is given by Jurs et al. follows an error-correction procedure to arrive at acceptable values for the components of V. Initially aU the Fj components have -f 1 (or — 1) as their value. An initial dot product is then formed with the first mass spectrum in the training set. If the value of the dot product is outside the dead zone on the correct side, the response to the question, for example whether oxygen is present in the empirical formula, is deemed to be correct, and the next spectrum is processed. Whenever a spectrum is wrongly classified, a correction is made to F a ft multiple of the vector S is added to the old vector F in order to form a new vector F . 

To sum up, a rail transportation model for multiple products shipped by trains between chemical production sites can be formulated as a multi-layer, multi-commodity time-space expanded network flow model. In other words, an operational multi-chemical rail transportation problem is provided (in short MC-RTP). 

To evaluate the performance of a simulation run, the flow and stock matrices are returned by the model. These matrices can be used to calculate a desired number of performance measures (e.g. the number of dispatched trains, average stock levels, etc.). These depend on the purpose of the study. It has to be noted that each simulation run is a stochastic experiment. Hence, multiple replications are necessary to evaluate the performance of a certain SC configuration properly. 

When very large flows are to be treated, die adsorber vessel size may be 0 large that it is not practical and ship them. It then becomes advantageous to design the adsorbers in multiple parallel trains. The feed... 

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