Circulation flow system, measurement

Circulation flow system, measurement of reaction rate, 28 175-178 Clausius-Clapeyron equation, 38 171 Clay see also specific types color tests, 27 101 compensation behavior, 26 304-307 minerals, ship-in-bottle synthesis, metal clusters, 38 368-379 organic syntheses on, 38 264-279 active sites on montmorillonite for aldol reaction, 38 268-269 aldol condensation of enolsilanes with aldehydes and acetals, 38 265-273 Al-Mont acid strength, 38 270-271, 273 comparison of catalysis between Al-Mont and trifluorometfaanesulfonic acid, 38 269-270... 

In most of the investigations described below the reaction rates were measured by the circulation flow method proposed in 1950 (4). This method offers a possibility of realizing a steady-state heterogeneous catalystic reaction without any concentration and temperature gradients i.e., it belongs to the group of methods which were called nongradient (5). The scheme of the circulation flow system is shown in Fig. 1. 

At integrating (305) for the conditions of a flow system (93, 98), it proved to be convenient to introduce a constant k proportional to k. The value of k was also calculated from data obtained in circulation flow systems (4, 96, 99-103). If the volume of ammonia reduced to 0°C and 1 atm, formed in unit volume of catalyst bed per hour, is accepted as a measure of reaction rate, then k = (4/3)3 1 m)k (101). The constancy of k at different times of contact of the gas mixture with the catalyst and different N2/H2 ratios in the gas mixture can serve as a criterion of applicability of (305). Such constancy was obtained for an iron catalyst of a commercial type promoted with A1203 and K20 at m = 0.5 (93) from our own measurements at atmospheric pressure in a flow system and literature data on ammonia synthesis at elevated pressures up to 100 atm. A more thorough test of applicability of (305) to the reaction on a commercial catalyst at high pressures was done by means of circulation flow method (99), it confirmed (305) with m = 0.5 for pressures up to 300 atm. Similar results were obtained in a large number of investigations by different authors in the USSR and abroad. These authors, however, have obtained for some promoted iron catalysts m values differing from 0.5. Thus, Nielsen et al. (104) have found that m 0.7. 

Equation (359) with m = 0.5 was obtained empirically by M. G. Slin ko from experiments with a nickel catalyst. Starting from this result the general equation (359) was obtained theoretically for reaction (356) with exponent m not necessarily equal to 0.5, but of some value between 0 and 1, depending on the nature of the catalyst. In this form (359) was confirmed for all studied catalysts obtained values of m did not depend much on temperature. The theoretical K values (133) were employed in the calculations after they were checked experimentally. The values of m and absolute (i.e., calculated for unit area) k+ values for the same catalyst obtained in flow and circulation flow systems coincided within the accuracy of kinetic measurements. The table below gives approximated m values for some catalysts. 

Six temperature probes can be place inside each reactor and 13 probes can be places inside the column. There are also 4 scales (0-50 kg, 0-100 kg) with accuracy of 0.01 kg for measuring inlet and outlet flow rates. At the moment circulation flows are measured with rotameters. All measurements are connected to the Mitsubishi MELSEC logic and monitoring software to view and save the data. For safety reasons there are also locking system in automation and a separate alarm system. 

FIG. 2. Natural Circulation system behaviour FIG. 3. Natural circulation flow map measured in ten experiments performed in six achieved from the envelope of measured PWR simulators. curves in PWR simulator. 

The testing system (Fig. 1) was a 1.2 volume pressure apparatus made of metaplex (1). The har support covered with the membrane (2) of an effective surface area of 49.2 cm was fixed in the lower part of the apparatus. To maintain the dye concentration on the level required, continuous circulation of the permeate between the feeding tank (5) and the apparatus was applied. The solution was mixed with a magnetic stirrer (3) which prevents excess concentration of dye on the membrane surface. Pressure was generated by feeding the apparatus with an inert gas (nitrogen) from a cylinder (8). Samples for flow rate measurements and determinations of dye concentration in the permeate were taken through a stub pipe (4). 

To remove heat from the system, water firom the bottom of the column is circulated through a cooling water exchanger to the spray nozzles. The circulating water flow is measured and transmitted to the main control center. Low flow activates an alarm. 

In order to keep the graphite temperature from exceeding the chosen limits a separate cooling system has been provided. Flow, pressure and temperature of the circulating coolant are measured and controlled by reliable Instrumentation. 

The reactor is designed for a near-zero reactivity bum-up swing such that the safety rod system is vested with minimal positive reactivity at Beginning of Life (BOL) full power. A safety rod scram system provides a first line of defence for reactivity initiators. Moreover, passive reactivity feedbacks and passive self adjustment of natural circulation flow could maintain reactor power to flow ratio in a safe operating range even with failure to scram this safe passive response applies for all out-of-reactor vessel initiated events, i.e., for any and all events communicated to the reactor through the flibe intermediate loop. Periodic in situ measurements would be made to confirm the operability of these passive feedbacks. 

Moore and Arnold (1996) married the delayed coincidence system of Giffin et at. (1963) with a gas flow system described by Rama et al. (1987) for the measurement of Ra and Ra in seawater. In this procedure Ra is quantitatively extracted from a known volume of seawater onto a column of Mn-fibre. The meeisurement is based on the observation that Rn produced by Ra decay is quantitatively ejected from the Mn-fibre (Butts et al., 1988 Rama et al., 1987). The partially dried Mn-fibre is placed in an air circulation system and helium is circulated over the Mn-fibre and through a scintillation cell where alpha particles from the decay of Rn and daughters are recorded. Fig. 13-6 is a schematic diagramme of the gas flow system. 

Werther J, Rudnick C. Modeling the fluid mechanics of a circulating fluidized bed based on a local flow structure analysis. In Werther J, Markl H, eds. In-situ Measuring Techniques and Dynamic Modeling of Multiphase Flow Systems SFB 238 Progress Report 1994—1996, Verlag des SFB 238, Hamburg, 1996. 

The heat generation in the system was determined by the shaft speed and the torque measurements. Determination of the heat generation from the rise in fluid temperature and the fluid circulation flow rate gave only about 70% of the power loss, owing to the additional heat transfer into the body of the housing. 

Another scheme which makes duty control difficult is that often installed on high viscosity fuel oil systems. To prevent pipework blockages, such fuel needs to be kept above a minimum temperature. Should its flow drop, heat losses from the pipework can result in the temperature falling below this minimum. To ensure a flow is maintained, even if a heater is shutdown, fuel is circulated around the site via a heated storage tank. The pipework passes alongside every heater and each burner on the heater can have its own take-off. Since it is not practical to measure the flow to an individual burner, flow meters are installed on the supply to and return from the heater. Fuel consumption is then determined by the difference between these measurements. However, because consumption is small compared to the circulating flow, the calculation is very prone to measurement error. For example if the supply flow is 100 %, measured to 2 %, and the return flow is 95 %, also measured to 2 %, then the calculated consumption could vary by a factor of nine, i.e. from 1 % to 9 %. Such a measurement cannot be used as a DV. 

The arrangement that is chosen is largely based on intuition. The parameters in the model are the relative volumes of the CSTR s and PFR s that ms e up the model (minus one), and the circulation flow rates, divided by the reactor feed. The parameters are estimated by fitting of RTD-measurements. Then the conversion of a given chemical reaction in the simulated reactor is calculated. Since all elements are ideal reactors, the calculation methods of Chapter 3 may be applied, and so the entire reactor system can be described by relatively simple calculations. The calculated conversion is compared to the measured conversion, and when there are deviations, the model is adjusted. By trial and error one may arrive at a model that describes the real reactor satisfactorily. 

The total 166 sets of experimental data are identified. The test results illustrate that short disturbances of wind speed, power and valve opening have no significant impact on natural circulation flow, implying that the system seems to tolerate these disturbances. A correlation of two-phase, natural circulation flow rate is derived from constitutive equations by use of lumped system parameters were obtained. The empirical coefficients m and n were obtained by non-linear regression of 83 test data. Compared with 166 sets of the measured data, the deviation of 98.8% of the data points is within 15%. 

The primary control variables at a fixed feed rate, as in the operation pictured in Figure 8, are the cycle time, which is measured by the time required for one complete rotation of the rotary valve (this rotation is the analog of adsorbent circulation rate in an actual moving-bed system), and the Hquid flow rate in Zones 2, 3, and 4. When these control variables are specified, all other net rates to and from the bed and the sequence of rates required at the Hquid... 

After the SO converter has stabilized, the 6—7% SO gas stream can be further diluted with dry air, I, to provide the SO reaction gas at a prescribed concentration, ca 4 vol % for LAB sulfonation and ca 2.5% for alcohol ethoxylate sulfation. The molten sulfur is accurately measured and controlled by mass flow meters. The organic feedstock is also accurately controlled by mass flow meters and a variable speed-driven gear pump. The high velocity SO reaction gas and organic feedstock are introduced into the top of the sulfonation reactor,, in cocurrent downward flow where the reaction product and gas are separated in a cyclone separator, K, then pumped to a cooler, L, and circulated back into a quench cooling reservoir at the base of the reactor, unique to Chemithon concentric reactor systems. The gas stream from the cyclone separator, M, is sent to an electrostatic precipitator (ESP), N, which removes entrained acidic organics, and then sent to the packed tower, H, where SO2 and any SO traces are adsorbed in a dilute NaOH solution and finally vented, O. Even a 99% conversion of SO2 to SO contributes ca 500 ppm SO2 to the effluent gas. 

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