Stirred tank heating

Figure 1.21. Continuous stirred tank heated by internal steam coil.

Regenass, W. (1997) The development od Stirred-Tank Heat Flow Calorimetry as a Tool for Process Optimization and Proces safety. Chimia, 51,189-200. 

Several control techniques have been developed to compensate for large dead-times in processes and have recently been reviewed by Gopalratnam, et al. (4). Among the most effective of these techniques and the one which appears to be most readily applicable to continuous emulsion polymerization is the analytical predictor method of dead-time compensation (DTC) originally proposed by Moore ( 5). The analytical predictor has been demonstrated by Doss and Moore (6) for a stirred tank heating system and by Meyer, et al. (7) for distillation column control in the only experimental applications presently in the literature. Implementation of the analytical predictor method to monomer conversion control in a train of continuous emulsion polymerization reactors is the subject of this paper. 

In a stirred tank heat is to be introduced through the vessel wtM. If the entire vessel jacket is heated, the test apparatus must be operated with a smaller temperature difference. By segmentation of the double jacket a temperature representative for the industrial plant can be attained in the test apparatus. 

Exercise Stirred Tank Heated with Condensing Steam... 

Stirred-Tank Heating Process Constant Holdup... 

Consider the stirred-tank heating system shown in Fig. 2.3. The liquid inlet stream consists of a single component with a mass flow rate Wf and an inlet temperature Ti, The tank contents are agitated and heated using an electrical heater that provides a heating rate, Q, A dynamic model will be developed based on the following assumptions ... 

Figure 2.3 Stirred-tank heating process with constant holdup, V.

Finally, substitution of (2-31) and (2-35) into (2-10) gives the desired dynamic model of the stirred-tank heating system ... 

The energy balance for the current stirred-tank heating system can be derived from Eq. 2-10 in analogy with the derivation of Eq. 2-36. We again assume that C/int = H for the liquid in the tank. Thus, for constant p ... 

Consider the stirred-tank heating system of Section 2.4.1 with constant holdup and a steam heating coil. We assume that the thermal capacitance of the hquid condensate is negligible compared to the thermal capacitances of the tank liquid and the wall of the heating coil. This assumption is reasonable when a steam trap is used to remove the condensate from the coil as it is produced. As a result of this assumption, the dynamic model consists of energy balances on the liquid and the heating coil wall ... 

This model of the liquid storage system exhibits dynamic behavior similar to that of the stirred-tank heating system of Eq. 2-36. 

A completely enclosed stirred-tank heating process is used to heat an incoming stream whose flow rate varies. 

Functions that exhibit time delay play an important role in process modeling and control. Time delays commonly occur as a result of the transport time required for a fluid to flow through piping. Consider the stirred-tank heating system example presented in Chapter 2. Suppose one thermocouple is located at the outflow point of the stirred tank, and a second thermocouple is immersed in the fluid a short distance (L= 10 m) downstream. The heating system is off initially, and at time zero it is turned on. If there is no fluid mixing in the pipe (the fluid is in plug flow) and if no heat losses occur from the pipe, the shapes of the two temperature responses should be identical. However, the second sensor response will be translated in time that is, it will exhibit a time delay. If the fluid velocity is 1 m/s, the time delay ( o = L/v) is 10 s. If we denote /( ) as the transient temperature response at the first sensor and fd(t) as the temperature response at the second sensor. Fig. 3.3 shows how they are related. The function/ = 0 for t < to. Therefore,/ and/are related by... 

The stirred-tank heating process descr erates at steady state with an inlet te and a heater input of 1920 Btu/min. 200 Ib/min, the liquid has constant denJ and specific heat (0.32 Btu/lb °F), and 1 constant at 1.60 ft. Then the inlet ternl to 90 °F, and the heater input is change Calculate the output temperature respc]... 

The contents of the stirred-tank heating system shown in Figure E4.10 are heated at a constant rate of Q(Btu/h) using a gas-fired heater. The fiow rate w(lb/h) and volume y(ft ) are constant, but the heat loss to the surroundings Q/ (Btu/h) varies with the wind velocity v (ft/s) according to the expressions... 

A stirred-tank heating system described by Eq. 4-37 is used to preheat a reactant containing a suspended solid catalyst at a constant flow rate of 1000 kg/h. The volume in the tank is 2 m, and the density and specific heat of the suspended mixture are, respectively, 900 kg/m and 1 cal/g °C. The process initially is operating with inlet and outlet temperatures of 100 and 130 °C. The following questions concerning process operations are posed ... 

Having considered PID controllers in Chapter 8, we now consider the other components of the feedback control loop. As an illustrative example, consider the stirred-tank heating system in Fig. 9.1. A thermocouple measures the liquid temperature and converts it to a millivolt-level electrical signal. This signal is then amplified to a voltage level and transmitted to the electronic controller. The feedback controller performs the control calculations and sends the calculated value as an output signal to the final control element, an electrical heater that adjusts the rate of heat transfer to the liquid. This example illustrates the three important functions of a feedback control loop (1) measurement of the controlled variable (CV), (2) adjustment of the manipulated variable (MV), and (3) signal transmission between components. 

Figure 9.1 Schematic diagram for a stirred-tank heating control system.

A physical variable is measured by a sensor which produces a physical response (e.g., electrical or mechanical) that is related to the value of the process variable. For example, in the stirred-tank heating system in Fig. 9.1, the thermocouple generates a millivolt electrical signal that increases as the temperature of the liquid increases. However, for this temperature measurement to be used in the control calculations, the millivolt-level signal must be converted to an appropriate voltage or current signal in a standard input range for the controller (see Section 9.1.1). This conversion is done by a transmitter. 

A stirred-tank heating system is shown in Fig. E13.9. Briefly critique these two control strategies. 

A feedforward-only control system is to be designed for the stirred-tank heating system shown in Fig. E15.il. Exit temperature T will be controlled by adjusting coolant flow rate, qc. The chief disturbance variable is the inlet temperature Ti which can be measured on-line. Design a feedforward-only control system based on a dynamic model of this process and the following assumptions ... 

Consider the stirred-tank heating system shown in Fig. E16.5. It is desired to control temperature T2 by adjusting the heating rate Q (Btu/h) via voltage signal V to the SCR. It has been suggested that measurements of T and Tq, as well as of T2, could provide improved control of T2. 

Consider the stirred-tank heating system of Fig. 6.14 and assume that the manipulated inputs are and w. Suggest a reasonable pairing for a multiloop control scheme and justify your answer. 

A stirred-tank heat exchanger with a bypass stream is shown in Fig. E18.17 with the available control valves. The possible manipulated variables are mass flow rate W2, valve stem positions Xc and and /, the fraction of mass flow rate wi that bypasses the tank before being added to the exit stream. Using the information given here, do the following ... 

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