Dynamic fractionation systems continuous-flow

Figure 12.1. Schematic representation of continuous-flow systems for dynamic fractionation (rt) rotating coiled column (RCC) (h) stirred flow-through cell, [(h) From Shiowatana et al., 2001b.]...

In order for a process to be controllable by machine, it must represented by a mathematical model. Ideally, each element of a dynamic process, for example, a reflux drum or an individual tray of a fractionator, is represented by differential equations based on material and energy balances, transfer rates, stage efficiencies, phase equilibrium relations, etc., as well as the parameters of sensing devices, control valves, and control instruments. The process as a whole then is equivalent to a system of ordinary and partial differential equations involving certain independent and dependent variables. When the values of the independent variables are specified or measured, corresponding values of the others are found by computation, and the information is transmitted to the control instruments. For example, if the temperature, composition, and flow rate of the feed to a fractionator are perturbed, the computer will determine the other flows and the heat balance required to maintain constant overhead purity. Economic factors also can be incorporated in process models then the computer can be made to optimize the operation continually. 

Soil extractions under the best of circumstances provide information on net or residual available phenolic acids but there is no reliable way, at present, to determine when or where these compounds function as active inhibitors, and Many inhibitory effects of phenolic acids are rapidly reversed once phenolic acids are eliminated (e.g., leaching, microbial activity, root uptake) from the root environment. Sustained inhibition requires that phenolic acids at the right concentration and physicochemical state, and under the right environmental conditions be continuously present and in contact with a large fraction of the root system. Unfortunately available/active phenolic acids in soils are dynamic, ever changing. Realistic data on flows into and out of various phenolic acid pools in the soil are notoriously difficult to get by soil extractions, since each extraction represents a point in time and, if for example, input equals output, then net flow between two extraction times will appear to be zero. In fact, considerable flows may be occurring between sources and sinks within the soil that are just not detectable by way of soil extractions. 

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