Automatically generated streams

The plausible way of solution of this problem is the combination of balancing with other chemical engineering calculations (simulation). So-called automatically generated streams are calculated as certain functions (e.g., fractions) of so-called reference streams. IBS generates such standard streams (flow rates) automatically when the reference stream is entered. This complementing of direct measurements is the only way of making balancing viable in older plants with insufficient instrumentation. 

The automatically generated stream is an unmeasured flow whose value is derived as a function of another, measured stream (so-called reference stream). As soon as data of the reference stream are entered, the program creates automatically generated stream. From this moment, the automatically generated (estimated) streams are viewed as if they were measured (usually with greater measurement errors than the other streams). 

The multiple-stream heat exchanger unit, often called LNG, is used to simulate heat transfer between multiple hot or cold streams (Fig. 3.11-left). Typical applications are the simulation of compact heat exchangers as the plate-type heat exchanger used extensively in gas processing. The simulation of this unit includes the automatic generation of multiple interconnected heaters, as illustrated in Fig. 3.11-right. 

An electric arc is automatically generated between the workpiece and a non-consumable tungsten electrode at the joint line. The parent metal is melted and the weld created with or without the addition of a filler rod. Temperatures at the arc can reach 12 000 °C. The weld area is shielded with a stable stream of inert gas, usually argon, to prevent oxidation and contamination (see 7.1 F). 

A simple electrochemical flow-through cell with powder carbon as cathodic material was used and optimized. The influence of the generation current, concentration of the catholyte, carrier stream, flow rate of the sample and interferences by other metals on the generation of hydrogen arsenide were studied. This system requires only a small sample volume and is very easily automatized. The electrochemical HG technique combined with AAS is a well-established method for achieving the required high sensitivity and low detection limits. 

Reference to Table 4.1 indicates that olefins can be determined by the electrochemical generation in situ of halogens. Bromine is effective for both olefins and sulfur compounds and is the basis for an automatic coulometric titrator for continuous analysis of petroleum streams.17 The basic principle of this instrument is a potentiometric sensing system that monitors bromine concentration in a continuously introduced sample stream. The bromine in the solution reacts with the sample components and causes a decrease in the concentration of bromine. When this decrease is sensed by the potentiometric detection electrodes, the electrolysis current producing bromine adjusts itself to maintain the bromine concentration. Because the sample is introduced at a constant rate, the electrolysis current becomes directly proportional to the concentration of the sample component. Thus, the instrument records the electrolysis current as concentration of sample component and provides a continuous monitor for olefins or sulfur in petroleum streams. 

Automatic and automated instruments can be differentiated as follows automatic instruments tend to perform specific operations at given points in a process or analysis to save time or effort, e.g. robotics, while automated instruments tend to control some part of a process without human intervention and do this by means of a feedback mechanism from sensors. For example, an automatic conductivity detector might continuously monitor the conductivity of a process stream, generating some alarm if the conductivity goes outside a preset limit. An automated detection system could transmit the measured conductivity values to a control unit that, by utilising a feedback mechanism, adjusts relevant process parameters, e.g. temperature or cycle time, to maintain the conductivity of the stream within the preset limits. 

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