Target compositions

NRA as in RBS or ERDA, and possible modification of the target composition as a result of irradiation must be considered. Nuclear reaction cross-sections are also usually not available in analytical form for direct evaluation of measured data. Concentrations are, therefore, often obtained by comparison of the measured data with results from standard samples of known concentration. 

Typically, waste streams are either disposed of or forwarded to process sinks (equipment) for lecycle/reuse. In case of hnal discharge, the taiget composition of the undesirable species in each waste stream corresponds to the environmental regulations. On the other hand, if the intercepted waste stream is to be recycled to a process sink, its target composition should satisfy the constraints imposed by the process sink. 

The target composition of the undesirable species in each MSA is assigned by the designer based on the specific circumstances of the application. The nature of such circumstances may be physical (e.g., maximum solubility of the pollutant in the MSA), technical (e.g., to avoid excessive corrosion, viscosity or fouling), environmental (e.g., to comply with environmental regulations), safety (e.g., to stay away from flammability limits), or economic (e.g., to optimize the cost of subsequent regeneration of the MSA). 

Next, a global representation of all process lean streams is developed as a lean composite stream. First, we establish Ns/> lean composition scales (one for each process MSA) that are in one-to-one coirespondence with the rich scale according to the method outlined in Section 3.5. Next, the mass of pollutant that can be gained by each process MSA is plotted vei us the composition scale of that MSA. Hence, each i xx ess MSA is represented as an arrow extending between supply and target compositions (see Fig. 3.5 for a two-MSA example). Ihe vertical distance between the arrow head and tail is given by... 

Stream Description Upper bound on flowrate kg mol/s Supply composition of benzene (mole fraction) x [ Target composition of benzene (mole fraction) x j... 

Upper bound Supply composition Target composition... 

Stream Description Flowrale Gj, kg/s Supply composition >1 Target composition... 

Stream Description Upper bound on flowrate L. kg/s Supply composition. Target composition. 

Cost estimation and screening external MSAs To determine which external MSA should be used to remove this load, it is necessary to determine the supply and target compositions as well as unit cost data for each MSA. Towards this end, one ought to consider the various processes undergone by each MSA. For instance, activated carbon, S3, has an equilibrium relation (adsorption isotherm) for adsorbing phenol that is linear up to a lean-phase mass fraction of 0.11, after which activated carbon is quickly saturated and the adsorption isotherm levels off. Hence, JC3 is taken as 0.11. It is also necessary to check the thermodynamic feasibility of this composition. Equation (3.5a) can be used to calculate the corresponding... 

Stream Upper bound on flowrate L kg/s Supply composition (ppmw) xj Target composition (ppmw) x - n,j ppmw Cj /kg MSA... 

Flowrate Supply composition Target composition Stream Description G,, kg/s (mass fraction) y (mass fraction) yl... 

The CID is a useful tool for insuring diermodynamic feasibility of mass exchange. On this dia am, N,p + 1 corresponding composition scales are generated. First, a composition scale, y, for the waste streams is established. Then, Eq, (3.5) is employed to create Nsp corresponding composition scales for the process MSAs. On the CID, each process stream is represented as a vertical arrow whose tail corresponds to its supply composition while its head represents its target composition. Next, horizontal lines are drawn at the heads and tails of the arrows. These horizontal lines define a series of composition intervals. The number of intervals... 

Stream Description Upper bound on flowrate (kg/s) Supply composition Target composition Equilibrium distributicHi coefficient mj = y/xj Cost Cj (Vkgof recirculation MSA)... 

There are two primary sources for aqueous pollution in this process—the condensate streams R] (1,000 kg/hr) and R2 (69,300 kg/hr). Both streams have the same supply composition, which corresponds to the solubility of benzene in water which is 1770 ppm (1.77 X10 kg bcnzcne/kg water). Consequently, they may be combined as a single stream. The target composition is 57 ppb as dictated by the VOC environmental regulations called NPDES (National Pollutant Discharge Elimination System). 

Scream Description Supply composition x j (ppmw) Target composition x j (ppmw) mj ej ppmw /kg MSA 4 /kgCE removed... 

Stream Description Supply composition X j (ppmw) Target composition X j (ppmw) Mj ppmw Cj S/kgMSA q VkgCE removed... 

Given a number Nr of waste (rich) streams and a number Ns of lean streams (physical and reactive MSAs), it is desired to synthesize a cost-effective network of physical and/or reactive mass exchangers which can preferentially transfer a certain undesirable species. A, from the waste streams to the MSAs whereby it may be reacted into other species. Given also are the flowrate of each waste stream, G/, its supply (inlet) composition, yf, and target (outlet) composition, yj, where i = 1,2,..., Nr. In addition, the supply and target compositions, Xj and x j, are given for each MSA, where j = 1,2, Ns. TTie flowrate of any lean stream, Ly, is unknown but is bounded by a given maximum available flowrate of that stream, i.e.. 

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