Bound water flow’ rate

Finally, we can solve the equations listed in Table 3.2.2 simultaneously using POLYMATH [19] or some other suitable mathematical software. The solution procedure used in POLYMATH is the bounded Newton-Raphson method described by Shacham and Shacham [20]. Table 3.2.5 lists the stream properties, which include the solution to the equations and specified temperatures and pressures at each line. The difference in the water flow rates into and out of the cooling tower is the water evaporated. Thus, to cool 164,700 Ibmol/h (74,700 kg mol/h) water requires evaporating 5,200 Ibmol/h (2,360 kg mol/h) of water. The evaporated water, along with water lost because of leaks, blowdown, and drift are a cost of operation. 

The loss below the CH step is due to decomposition of C-S-H and the hydrated aluminate phases. Although the TG curves of pure AFm phases are markedly stepped in this region (Fig. 6.2), those of cement pastes normally show only slight indications of steps. Weak peaks can, however, sometimes be seen on DTG curves. The absence of steps is probably due to a combination of low crystallinity, the presence of other phases and the presence of AFm phases of different compositions in mixture or solid solution or both. For typical experimental conditions with a 50 mg sample, heating rate of 10 deg C min and Nj flow rate of 15 ml min , the volatiles retained at about 150°C, after correction for COj, correspond to the non-evaporable water, and those retained at about 100"C to the bound or 11% RH water, but this last temperature, in particular, is very dependent on experimental conditions (T5). 

In all of these alternatives, the design team selects acceptable temperature levels and flow rates of the recirculating fluids. These are usually limited by the rates of reaction, and especially the need to avoid thermal runaway or catalyst deterioration, as well as the materials (rf construction and the temperature levels of the available cold process streams and utilities, such as cooling water. It is common to assign temperatures on the basis of these factors earily in process synthesis. However, as optimization strategies are perfected, temperature levels are varied within bounds. See Chapters 10 and 18 for discussions of the use of optimization in process synthesis and optimization of process flowsheets, as well as Example 6.3 to see how constrained optimization is applied to design an ammonia cold-shot converter. 

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