Reactor medium temperature

Hot spot develops in reaction medium. Temperature excursion outside the safe operating envelope, possibly resulting in a runaway reaction or decomposition. Potential mechanical failure of reactor wall. 

In our design considerations we have extrapolated the global rate expression for CO oxidation outside the conditions for which it was derived, and this extrapolation leads to erronous results. Experimental results on oxidation of CO in a flow reactor at varying pressure are shown in Fig. 13.3. The results clearly show that in the medium temperature range around 1000 K, an increased pressure acts to lower, not increase, the rate of CO oxidation. To secure adequate oxidation of CO, we would probably need to increase the postflame residence time in a high-pressure reactor compared to an atmospheric pressure reactor. 

Steam Superheater This unit superheats saturated steam from 250°C (and 4000kPa) to 380°C. The product steam is of medium pressure and suitable quality for in-house application and also for export. The superheater cools the reaction gases from the reactor exit temperature of 645°C to 595°C. Design pressure on the shell side is approximately 5000 kPa. The steam superheater is constructed from mild steel. 

As stated above, if a reactor is operated with a cooling medium temperature close to the critical cooling medium temperature, a small variation of the coolant... 

The Villermaux criterion and the Da/Si criterion are dynamic stability criteria, meaning that with a cooling medium temperature above the limit level, 20 resp. 30 °C, the reactor will be operated in the instable region and present the phenomenon of parametric sensitivity. If instead of B12, B is used, both criteria lead to the same result. This should not be surprising since they derive from the same heat balance considerations, that is, the heat release rate of the reaction increases faster with temperature than the heat removal does. 

For a sensitivity greater than 1, the reactor is difficult to control the change of the cooling medium temperature is amplified by the reactor. A sensitivity below 1 indicates a fairly controllable reactor. Nevertheless, in practice, a sensitivity up to 2 can be tolerated, provided a safety margin is in place. 

Figu re 6.11 Reactor temperature (°C) as a function of time (h) for the substitution reaction example in the isoperibolic batch reactor for different cooling medium temperatures indicated as parameter. 

A reliable control of the reaction course can be obtained by isothermal operation. Nevertheless, to maintain a constant reaction medium temperature, the heat exchange system must be able to remove even the maximum heat release rate of the reaction. Strictly isothermal behavior is difficult to achieve due to the thermal inertia of the reactor. However, in actual practice, the reaction temperature (Tr) can be controlled within 2°C, by using a cascade temperature controller (see Section 9.2.3). Isothermal conditions may also be achieved by using reflux cooling (see Section 9.2.3.3), provided the boiling point of the reaction mass does not change with composition. 

Additionally the semi-batch reactor with constant cooling medium temperature, also in cases where a stationary temperature can be achieved, shows a high sensitivity to its control parameters, that is, initial temperature and coolant temperature. This means that even for small changes in these temperatures, the behavior of the reactor may suddenly change from a stable situation into a runaway course. 

Figu re 7.9 Semi-batch reactor with the example slow reaction and constant cooling medium temperature at 50, 70, 90, 103, and 104°C. The feed time is 6 hours initial and cooling medium temperatures are equal. 

The polytropic mode this is a combination of different types of control. As an example, the polytropic mode can be used to reduce the initial heat release rate by starting the feed and the reaction, at a lower temperature. The heat of reaction can then be used to heat up the reactor to the desired temperature. During the heating period, different strategies of temperature control can be applied adiabatic heating until a certain temperature level is reached, constant cooling medium temperature (isoperibolic control), or ramped to the desired reaction temperature in the reactor temperature controlled mode. Almost after the... 

Figure 8.9 Temperature (solid line) and conversion (dashed line) profiles in a tubular reactor for two cooling medium temperatures 293 K and 300 K, the second leading to a hot spot.

The analysis of the incident showed that this reactor was equipped with an indirect heating-cooling system with oil circulation and computerized temperature control. In this plant, to obtain a nervous temperature control, the control algorithm of the cascade controller (see Section 9.2.4.3) was adjusted to have an on-off behaviour, by calculating the set temperature of the jacket proportional to the squared difference between the actual and set values of the reaction medium temperature as... 

Figure 3.58 shows the window when Constant temperature is selected on the Heat Transfer page tab. We specify a Medium temperature of 400 K. With the reactor at 430 K, this gives a 30 K differential driving force. 

It is important to remember that a deadtime or several lags must be inserted in most control loops in order to mn a relay-feedback test. To have an ultimate gain, the process must have a phase angle that drops below —180°. Many of the models in Aspen Dynamics have only a first-order transfer function between the controller variable and the manipulated variable. In the CSTR temperature controller example, the controlled variable is reactor temperature and the manipulated variable is medium temperature. The phase angle of a first-order process goes to only —90°, so there is no ultimate gain. The relay-feedback test will fail without the deadtime element inserted in the loop. 

The pH was maintained at 5.0 by the addition of 2 M NaOH (Micro DCU-300 B. Braun Biotech). The fermentation temperature was 30°C and the stirrer speed was 500 rpm (MCU-200 B. Braun Biotech). Cell mass was produced in an initial batch phase using a glucose concentration of 64 g/L. The concentrations of mineral salts, trace metals, vitamins, and Ergosterol/ Tween-80 were the same as in the fed-batch experiments. When the glucose in the batch medium was completely consumed, 1.9 L of dilute-acid hydrolysate was pumped into the reactor at maximum pump speed, by using a peristaltic pump (Ul-M Alitea AB). The ratio between batch volume and the final volume (i.e., after all the hydrolysate had been added) was similar to the ratio in the PDU fed-batch experiments, approx 1 4. The reactor medium was sparged with nitrogen (600 mL/min). The C02 content in the exhaust gas was measured with a gas analyzer (TanDem Adaptive Biosystems, Luton, UK). 

In the intermediate term, nuclear-heated steam reforming of natural gas could be utilised, using medium-temperature reactors, in spite of some carbon dioxide emissions, because of its advantages in economic competitiveness and in technical feasibility. Also, high-temperature reactors could be used to carry out high-temperature steam electrolysis, with higher conversion efficiency and fewer materials problems. 

Chemical reactors are the most important features of a chemical process. A reactor is a piece of equipment in which the feedstock is converted to the desired product. Various factors are considered in selecting chemical reactors for specific tasks. In addition to economic costs, the chemical engineer is required to choose the right reactor that will give the highest yields and purity, minimize pollution, and maximize profit. Generally, reactors are chosen that will meet the requirements imposed by the reaction mechanisms, rate expressions, and the required production capacity. Other pertinent parameters that must be determined to choose the correct type of reactor are reaction heat, reaction rate constant, heat transfer coefficient, and reactor size. Reaction conditions must also be determined including temperature of the heat transfer medium, temperature of the inlet reaction mixture, inlet composition, and instantaneous temperature of the reaction mixture. 

The Medium Temperature Shift conversion normally takes place in an isothermal system, but it may also be accomplished in an adiabatic reactor with an exit temperature around 300°C. A copper-zinc catalyst is used for this... 

This set of equations describes the behaviour of multiple, first order reactions in a tubular reactor using the relative conversion to desired product Xp and to undesired product Xx, the dimensionless temperature T and the dimensionless reactor length Z. The is characterized by the ratio of the reaction heats H in addition to kR, TR, y and p. The operating and design are determined by PC, the dimensionless cooling medium temperature Da, the dimensionless residence time in the reactor U, the dimensionless cooling capacity per unit of reactor volume and ATacp the dimensionless adiabatic temperature rise for the desired reaction, which, of course, depends on the initial concentration of the reactant A. 

Choose a value of Dac/Dam Ln in agreement with the investment costs of the reactor and determine from Table I a minumum value for the cooling medium temperature. 

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