Process Calculations

Fiber engineers are notorious users of non-SI units feet or yards instead of meters, minutes or hours instead of seconds, grams instead of kilograms, and denier or dtex instead of tex. Nevertheless, most process calculations are quite simple, without difficult conversions being necessary. 

A few examples for a polyester spin-draw winding process will show this, and hopefully give an impression of how melt-spinning machines are designed. 

The process concerns the production of an industrial yam with a titer of 1670 dtex f 325. We assume that spinning holes are used with a diameter of 500 pm and an L/D ratio of 1.5 there are 325 holes per spinning plate. There are eight spinning bundles per extmder. The spinning speed is 800 m min and the spun yarn is immediately drawn five times on the same machine (an integrated process) and then wound with a speed of 4000 m min h 

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To verify the modelling of the data eolleetion process, calculations of SAT 4, in the entrance window of the XRII was compared to measurements of RNR p oj in stored data as function of tube potential. The images object was a steel cylinder 5-mm) with a glass rod 1-mm) as defect. X-ray spectra were filtered with 0.6-mm copper. Tube current and exposure time were varied so that the signal beside the object. So, was kept constant for all tube potentials. Figure 8 shows measured and simulated SNR oproj, where both point out 100 kV as the tube potential that gives a maximum. Due to overestimation of the noise in calculations the maximum in the simulated values are normalised to the maximum in the measured values. Once the model was verified it was used to calculate optimal choice of filter materials and tube potentials, see figure 9. 

Process calculations for traditional unit-operations equipment can be divided into two types design and performance. Sometimes the performance calculation is caHed a simulation (see Simulation and process design). The design calculation is used to roughly size or specify the equipment. EoUowing the... 

Process simulators stop generally at the process specifications for the equipment. For the detailed mechanical design of the equipment, such as heat exchangers and distillation columns, stand-alone programs are often used. They make process calculations, size the equipment, calculate thermal and mechanical stresses, design mechanical support of the parts of the equipment, design inlet and outlet nozzles, etc. 

However, any average drop size is fictitious, and none is completely satisfactory. For example, there is no way in which the high surface and transfer coefficients in small drops can be made avail le to the larger drops. Hence, a process calculation based on a given droplet size describes only what happens to that size and gives at best an approximation to the total mass. 

Process calculations, where material balances are performed, normally produce flow values in terms of a weight flow. The flow is generally stated as pounds per hour. Equation 2.10 can be used either with a singlecomponent gas or with a mixture. 

The preceding chapters offered some general guidance on the sizing of the various types of compressors. Before the start of the specification, the equipment should be sized, at least in a preliminary manner. Actually, part of this may be integrated into the process calculation. However, after the process calculations are complete, a review of the equipment best suited to perform the task at hand should be made. 

The problems experienced in drying process calculations can be divided into two categories the boundary layer factors outside the material and humidity conditions, and the heat transfer problem inside the material. The latter are more difficult to solve mathematically, due mostly to the moving liquid by capillary flow. Capillary flow tends to balance the moisture differences inside the material during the drying process. The mathematical discussion of capillary flow requires consideration of the linear momentum equation for water and requires knowledge of the water pressure, its dependency on moisture content and temperature, and the flow resistance force between water and the material. Due to the complex nature of this, it is not considered here. 

For each unit process, a reference flow may be defined, and the inputs and outputs to the unit process calculated in relation to the reference flow. For instance, the reference flow for mining of iron ore is the mass of iron ore mined per year, and the emissions to the air may be expressed as kg dust per metric ton of ore. 

Convert the free air rates to the proper product in the tanks using the corrections outlined in a previous paragraph. Keep in mind that the manufacturer s rating tables are in free air however, the actual process calculations provide flows in terms of the actual liquids at actual temperatures and pressures. It is important that the manufacturer be given the actual fluid conditions to ensure proper capacity rating. 

Shell-side fluid properties. From previous process calculations, the following properties were determined for the dry gas stream ... 

As Mollier charts are available for only a few pure components and practically no mixtures, this calculation method is very limited. For example, it cannot be used for most process calculations because these gases are usually mixtures. Some of the charts available for mixtures are the H-S charts presented by Brown for natural gases of gravities from 0.6 to 1.0. ... 

Stoichiometry in Reactive Systems. The use of molar units is preferred in chemical process calculations since the stoichiometry of a chemical reaction is always interpreted in terms of the number of molecules or number of moles. A stoichiometric equation is a balanced representation that indicates the relative proportions in which the reactants and products partake in a given reaction. For example, the following stoichiometric equation represents the combustion of propane in oxygen ... 

From such curves, taking A = 1, the values of D for different temperatures can easily be derived and an energy of activation for the process calculated. This has been found to be of the order of 239-247 kJ/mol. Increasing the carbon content of the steel progressively reduces both the rate of diffusion and the energy of activation . 

SAQ 8.7 The product value at 100% capadty will now be (total cost of production + 7 to 15% ROD, ie 16.04 to 1654 + 1.12 to 2.48. So the minimum product value will be 17.16 per kg of L-phenylalanine and the maximum product value 19.02 per kg of L-phenylalanine. It is rattier difficult to say whether this fictitious process would survive or could compete. Actual data are absolutely necessary. On the other hand this exercise gives us a better understanding of process economics and can also be used to compare a fermentative process for the production of amino adds with, for example, a chemo-enzymatic process. Calculate the return on investment over a 15 year period for an amino add fermentation, based on the following data and assumptions. Production capadty = 500 tonnes per annum Selling price of product = 50 kg Cost price of product = 24.5 kg 1 Capital = 40 million Taxes = 50%. Assumptions Cost of dealer discount, distribution and freight = 20% total sales Startup costs = 10% of capital Working capital = 25% of net sales Administration plus R and D costs = 12.5% of net sales. 

For a first-order process, calculate the rate constant, elapsed time, and amount remaining from the half-life (Example 13.6 and Self-Test 13.9). 

A white precipitate forms when 2.00 X 10 mL of 0.200 M potassium phosphate solution is mixed with 3.00 X 10 mL of 0.250 M calcium chloride solution. Write the net ionic equation that describes this process. Calculate the mass of the precipitate that forms, and identify the ions remaining in solution. 

The possibility of predicting solid state reactivity from calculated thermochemical data was first addressed with ketodiesters 65a-e, which were substituted with methyl groups to vary the extent of the RSE in the radicals 65-BRl - 65-BR3 involved along the photodecarbonylation pathway (Scheme 7.19). " All ketones reacted in solution to give complex product mixtures from radical combination (66a-e) and disproportionation processes. Calculations revealed RSEs of 8.9 kcal/mol, 15.1 kcal/mol, and 19.8 kcal/mol for radicals 65-BRl (primary enol radical), 65-BR2 (secondary enol radical), and 65-BR3 (tertiary enol radical), respectively. In the... 

Once the standard error of estimate of the mean forecasted response has been estimated, i.e., the uncertainty in the total production rate, one can compute the probability level, a, for which the minimum total production rate is below some pre-determined value based on a previously conducted economic analysis. Such calculations can be performed as part of the post-processing calculations. 

In the production of ammonia from hydrogen and nitrogen the conversion, based on either raw material, is limited to 15 per cent. The ammonia produced is condensed from the reactor (converter) product stream and the unreacted material recycled. If the feed contains 0.2 per cent argon (from the nitrogen separation process), calculate the purge rate required to hold the argon in the recycle stream below 5.0 per cent. Percentages are by volume. 

The groups incorporating the liquid and vapour flow-rates and the equilibrium constants have a general significance in separation process calculations. 

A batch process consists of the four steps given in Table 14.7. For repeated batch cycles of the same process, calculate the cycle time for ... 

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