Flow intermediate streams

In constraint (3.4) we convert the mass flow rate to volumetric flow rate by dividing it by the specific gravity SG( r( tr of each crude type cr CR and intermediate stream cir CB. This is done as some quality attributes blend only by volume in the products blending pools. 

Constraint (3.9) sets an upper bound on intermediate streams flow rates between the different refineries. The integer variable y pipeR fi represents the decision of exchanging intermediate products between the refineries and takes on the value of one if the commodity is transferred from plant i I to plant i C I or zero otherwise,... 

If the HEN has more than the minimum number of exchangers (say nv more than the minimum) and nT variable target temperatures, then nv + nT of the intermediate stream temperatures and heater loads can be chosen as control variables. Stream split fractions are always available as control variables. These variables are adjusted to try to make the HEN feasible for the assumed, fixed values of the uncertain supply temperatures and flow rates. The HEN is feasible if and only if s 0. 

In a minimum unit HEN the intermediate stream temperatures and heater loads, and thus the breakpoint locations, are uniquely determined by the energy balance and energy recovery constraints. Thus for given supply temperatures and flow rates, the Arm violations (and surpluses) and load violations (and surpluses) in each exchanger k are also uniquely determined. 

Shown in Figure 4.2 is a simple refinery flow-sheet. There are many refineries in the world configured in this manner. These are often referred to as simple refineries. In many of these refineries, the crude oil column has greater capacity to the downstream processing units and the refinery sells the excess intermediate streams such as naphtha on the oil market. 

Ideal Recycle Reactor All reactor modes can sometimes be advantageously operated with recycling part of the product or intermediate streams. Heated or cooled recycle streams serve to moderate undesirable temperature gradients, and they can be processed for changes in composition such as separating products to remove equilibrium limitations, before being returned. Say the recycle flow rate in... 

Referring to Figure 2, by considering solute mass balances over n, (n — 1),. .. 2, 1 units in turn and eliminating intermediate solute mass fractions and flow rates, the amount of solute associated with the leached sohd may be calculated in terms of the composition of the sohd and solvent streams fed to the system. The resulting equation is (2)... 

The two portions of the feed stream recombine and flow into the high pressure separator where the Hquid is separated from the vapor and is fed into an intermediate section of the demethanizer with Hquid level control. The decrease in pressure across the level-control valve causes some of the Hquid to flash which results in a decrease in the stream temperature. The pressure of the vapor stream is decreased by the way of a turboexpander to recover... 

Flow-sheet models are used at all stages in the life cycle of a process plant during process development, for process design and retrofits, and for plant operations. Input to the model consists of information normally contained in the process flow sheet. Output from the model is a complete representation of the performance of the plant, including the composition, flow, and properties of all intermediate and product streams and the performance of the process units. 

As w as mentioned earlier, extra rows are provided as can be seen in Figure 1. This gives extra flexibility needed for process design case studies. Often, the set of case studies initially envisioned by the engineer or manager are not sufficient to answer all questions. The extra rows allow intermediate recycles or intermediate flows from or additions to the plant that might not have been envisioned initially. Another value of the intermediate rows is to provide component values at intermediate points in the process. The breakeven value of a proposed purchase stream from another plant would be one use of intermediate component values. 

---