Overall residence time

The F(t) curve for overall residence times for both cases. 

The common assumed emission rate is 1000 kg/h or 1 tonne/h. To achieve an amount equivalent to the 100 tonnes in the Level I calculation requires an overall residence time of 100 hours. Again, the concentrations and amounts mi and Em, or M can be deduced, as well as the reaction and advection rates. These rates obviously total to give the input rate E. Of particular interest are the relative rates of these loss processes, and the overall persistence or residence time, which is calculated as... 

Overall residence time 1.977E+01 1.407E+02 8.675E+01 6.274E+01... 

The first row describes the condition if 1000 kg/h is emitted into the air. The result is similar to the Level II calculation with 19700 kg in air, 57 kg in water, 24 kg in soil and only 0.2 kg in sediment. It can be concluded that benzene discharged to the atmosphere has very little potential to enter other media. The rates of transfer from air to water and air to soil are both only about 0.4 kg/h. Even if the transfer coefficients were increased by a factor of 10, the rates would remain negligible. The reason for this is the value of the mass transfer coefficients which control this transport process. The overall residence time is 19.8 hours, similar to Level II. 

In this multimedia discharge scenario the overall residence time is 59 hours, which can be viewed as 60% of the air residence time of 19.7 h, 30% of the water residence time of 140 h and 10% of the overall soil residence time of 53 h. The overall amount in the environment of 59,000 kg is thus largely controlled by the discharges to water, which account for (0.3 x 133863) or 40,000 kg. 

The Level II calculations at pH 5.1 include the reaction half-lives of 550 h in air, 550 h in water, 1700 h in soil and 5500 h in sediment. No reaction is included for suspended sediment or fish. The steady-state input of 1000 kg/h results in an overall fugacity of 3.43 x 1(H Pa, which is about 24 times the Level I value. The concentrations and amounts in each medium are thus about 24 times the Level I values. The relative mass distribution is identical to Level I. The primary loss mechanism is reaction in soil, which accounts for 936 kg/h, or 94% of the input. Most of the remainder is lost by reaction and advection in water. The air and sediment loss processes are unimportant largely because so little of the PCP is present in these media. The overall residence time is 2373 h thus, there is an inventory of PCP in the system of 2373 x 1000 or 2,373,000 kg. 

The third row shows the fate if PCP is discharged to soil. The amount in soil is 245100 kg, with only 7.43 kg in air. The overall residence time is 2452 hours, which is largely controlled by the reaction rate in soil. The rate of reaction in soil is 999 kg/h and there is no advection thus, the other loss mechanism is transfer to air (T31) at a rate of 0.11 kg/h, with a relatively minor 0.8 kg/h to water by run-off. The soil concentration of 0.136 g/m3 is controlled almost entirely by the rate at which the PCP reacts. 

The net result is that PCP behaves entirely differently when discharged to the three media. If discharged to air, it advects rapidly and reacts with a residence time of 632 h or about 26.3 days, with substantial transport to soil or water. If discharged to water, it reacts and evaporates to air with a residence time of 1153 h or 48 days. If discharged to soil, it mostly reacts with an overall residence time of about 2452 h or 102 days. 

Overall residence time 2.074E+03 4.588E+02 2.393E+03 1.894E+03... 

The reaction, A = 8, takes place in two CSTR stages at different temperatures and residence times. Find a relation for the minimum overall residence time at a specified overall conversion. 

Figure 16.7. Material balancing of continuous stirred tank crystallizers (CSTC). (a) The single stage CSTC. (b) Multistage battery with overall residence time t = (lIQ) Si Ki-...

The principles of additivity of residence times and additivity of variances can be extended to several reaction vessels in series (Fig. 2.19). Thus, for vessels A, B and C, if tA, 1b, tc are the residence times and a, a, passing through each of the vessels in turn, then the overall residence time will be tA + 7 -1- tc and the overall increase in the variance of a pulse will be a -(- + dispersion number for the vessel must... 

In the impinging stream contactor shown in Fig. 3.1 the particles pass through the four sub-spaccs in series described above, and the overall residence time distribution... 

This is the model for the overall residence time distribution of the particles in the impinging stream contactor under consideration. The model contains several parameters related to equipment structure and operating conditions, i.e. the mean residence times in the four sub-spaces, 7ac, 7im, 7fai and cs. Among the four parameters, the mean residence time in the impingement zone, t m, and that in the collision-slipping region, fcs, are symmetrical parameters, which have the same influence on the overall residence time distribution. It can be seen from Eq. (3.27) or... 

It is noted that the right-hand side of Eq. (10.20) is just the series expansion of an exponential function. Therefore the overall residence time distribution probability density function in the SCISR is obtained to be... 

The influence of channels, i.e. flow-guiding internal structures, also accounts for the overall residence time distribution in the square. This will be demonstrated by the observation of particles emitted at the structure inlet. The path of such an... 

The residence time of such a well is again best visible at the exit. The parabolic profile this time is much wider than for the structured case. The maximum relative deviation amounts to 233%, which is 6.5 times larger than for the structured well. This is important because it demonstrates that micro structures are indeed a means to obtain a narrow overall residence time distribution. The error introduced by manufacturing tolerances (estimated 5 pm absolute tolerance in a 320 pm wide channel) is 1.6% in width, a value which does not influence this evaluation. 

In order to facilitate control of the specified temperatures, the annealing schedule can be adjusted so that lower cooling rates are applied at the beginning h = 2/3 hy, rate hy in the second stage and h = 2/iy in the last. The overall residence time in the annealing range remains unchanged. 

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