Sometimes, it may be required to meet a certain flow specification at the outlet, or scale up or scale down an existing outlet flow. Depending on the specified outlet flow, one may need to either mix the process stream with another stream (if the outlet flow is higher than the process flow) or split the process stream into two streams (if the outlet flow is lower than the process flow). In previous releases, one would have to use either a Custom Mixing or Custom Splitting procedure depending on whether mixing or splitting was needed. Also, one might need to switch from a Custom Mixing procedure to a Custom Splitting procedure if the outlet flow specification had to be scaled down, or switch from a Custom Splitting procedure to a Custom Mixing procedure if the outlet stream specification had to be scaled up. This model allows the user to express such process design constraints directly, without the tedious task of replacing an existing Custom Mixing procedure by a Custom Splitting procedure and vice versa.
The flow specification of the main outlet stream may be either set by a downstream process or set by the user. In the latter case, the user may specify either the mass flow or the volume flow of the main outlet stream. If the volume flow of the main outlet stream is set, an iterative solution algorithm is employed in order to determine its mass flow. In this case, the user specifies the maximum number of iterations and the relative error. The maximum number of iterations corresponds to the maximum number of times that this algorithm can be repeated till it reaches convergence. The relative error is defined in terms of the specified (V) and calculated (V*) main outlet stream volume flows as |1- V*/V|. The solution is considered to have reached convergence if the calculated relative error is less than or equal to the specified value.
The add-in stream composition may be either set to match the process-in stream composition or set by the user. In the former case, the program will automatically set the composition of the add-in stream to be the same as that of the process-in stream as soon as you run the M&E balances. By default, the add-in stream composition is set to match the process-in stream composition.
If the mass flow rate of the main outlet stream is greater than that of the process stream, then this operation will adjust the flow of the adjustable add-in stream in order to meet the flow specification of the main outlet stream and it will set the flow of the adjustable outlet stream to zero. If the mass flow of the main outlet stream is lower than that of the process stream, then this operation will set the flow of the adjustable add-in stream to zero, and it will split the process a stream into the main outlet stream and the adjustable outlet stream in a way that the split percentage meets the flow specification of the main outlet stream.
The operating throughput is defined the total mass flow rate of the two inlet streams. The operating throughput per unit is calculated by dividing the operating throughput by the number of equipment units that are operated in parallel.
If the equipment size option is in Design Mode and the operating throughput exceeds the maximum throughput, then, the program assumes multiple, identical units operating in parallel with an operating throughput of less than the maximum. If the equipment size option is in Rating Mode and the operating throughput exceeds the rated throughput of the step (which is equal to the rated throughput of each unit times the number of units), a warning message is displayed advising the user to increase the number of units or reduce the operating throughput.
The interface of this operation has the following tabs:
● Oper. Cond’s, see Flow Adjusting: Oper. Conds Tab
● Utilities, see Throughput Operations: Utilities Tab
● Labor, etc, see Operations Dialog: Labor etc. Tab
● Description, see Operations Dialog: Description Tab
● Batch Sheet, see Operations Dialog: Batch Sheet Tab
● Scheduling, see Operations Dialog: Scheduling Tab