Continuous heat balance

Batch with Constant Reflux Ratio, 48 Batch with Variable Reflux Rate Rectification, 50 Example 8-14 Batch Distillation, Constant Reflux Following the Procedure of Block, 51 Example 8-15 Vapor Boil-up Rate for Fixed Trays, 53 Example 8-16 Binary Batch Differential Distillation, 54 Example 8-17 Multicomponent Batch Distillation, 55 Steam Distillation, 57 Example 8-18 Multicomponent Steam Flash, 59 Example 8-18 Continuous Steam Flash Separation Process — Separation of Non-Volatile Component from Organics, 61 Example 8-20 Open Steam Stripping of Heavy Absorber Rich Oil of Light Hydrocarbon Content, 62 Distillation with Heat Balance,... 

A cat cracker continually adjusts itself to stay in heat balance. This means that the reactor and regenerator heat flows must be equal (Figure 5-4). Simply stated, the unit produces and bums enough coke to provide energy to ... 

There is one significant difference between batch and continuous-flow stirred tanks. The heat balance for a CSTR depends on the inlet temperature, and Tin can be adjusted to achieve a desired steady state. As discussed in Section 5.3.1, this can eliminate scaleup problems. 

This result is perfectly general for a constant-volume reactor. It continues to apply when p, Cp, and H are expressed in mass units, as is normally the case for liquid systems. The current example has a high level of inerts so that the molar density shows little variation. The approximate heat balance... 

Liquid is fed continuously to a stirred tank, which is heated by internal steam coils (Fig. 1.21). The tank operates at constant volume conditions. The system is therefore modelled by means of a dynamic heat balance equation, combined with an expression for the rate of heat transfer from the coils to the tank liquid. 

Liquid flows continuously into an initially empty tank, containing a full-depth heating coil. As the tank fills, an increasing proportion of the coil is covered by liquid. Once the tank is full, the liquid starts to overflow, but heating is maintained. A total mass balance is required to model the changing liquid volume and this is combined with a dynamic heat balance equation. 

The Contalab, initially supplied by Contraves, was purchased by Mettler-Toledo, which is now placing less emphasis on this design than on the RC1. Some comments here are appropriate, however, since it is another type of bench-scale calorimeter, and units continue to be used. Its measuring system is based on the heat balance principle, in which a heat balance is applied over the cooling/heating medium. For this purpose, both the flow rate of the coolant and its inlet and outlet temperatures must be known accurately. Figure 3.12 is a schematic plan of the Contalab. 

In order for a process to be controllable by machine, it must represented by a mathematical model. Ideally, each element of a dynamic process, for example, a reflux drum or an individual tray of a fractionator, is represented by differential equations based on material and energy balances, transfer rates, stage efficiencies, phase equilibrium relations, etc., as well as the parameters of sensing devices, control valves, and control instruments. The process as a whole then is equivalent to a system of ordinary and partial differential equations involving certain independent and dependent variables. When the values of the independent variables are specified or measured, corresponding values of the others are found by computation, and the information is transmitted to the control instruments. For example, if the temperature, composition, and flow rate of the feed to a fractionator are perturbed, the computer will determine the other flows and the heat balance required to maintain constant overhead purity. Economic factors also can be incorporated in process models then the computer can be made to optimize the operation continually. 

This is an overall heat balance of a continuous reactor more detailed heat balances are introduced in Chapter 8. 

If the deviation was an uncontrolled temperature increase, the temperature increase will continue and accelerate the reaction until the accumulated reactant has been converted. Therefore, it is important to know quantitatively the degree of reactant accumulation during the reaction course, as it predicts the degree of conversion, which may occur after interruption of the feed. This can be done by chemical analysis or by using a heat balance, for example from an experiment in a reaction calorimeter [4]. Since the accumulation is the result of a balance between the amount of reactant B introduced by the feed and the amount converted by the reaction, a simple difference between these two terms calculates the accumulation [5, 6]. 

The inlet jacket temperature Tji0 is adapted continuously to the heat-balance requirements by injecting a thermal agent (steam for heating period, chilled water for cooling period). This operation is realized by means of a controller whose... 

Whenever there is sufficient conductivity present in a dielectric to produce appreciable Joule heating in an applied field, the possibility of thermal runaway exists, for the accompanying rise in temperature will increase the conductivity still further. In alternating fields there may be additional heat generated through one or more relaxation processes, as described in Chapter 3, and this will hasten the onset of any thermal runaway condition. Whether thermal breakdown will eventually develop in this way or not will also depend on the rate at which heat is conducted away to the surroundings. The heat balance equation is expressed by the following continuity equation ... 

If more than one species is involved or if there are several input or output streams instead of just one of each, the procedure given in Section 8.1 should be followed choose reference states for each species, prepare and fill in a table of amounts and specific internal energies (closed system) or species flow rates and specific enthalpies (open system), and substitute the calculated values into the energy balance equation. The next example illustrates the procedure for a continuous heating process. 

Loss of catalyst from the unit is measured by changes in inventory in the vessels and by the additions of make-up catalyst. Accuracy of the measurement from day to day is not high, but reliable data are accumulated over a period of time. An instrument has been developed for continuous recording of catalyst loss from the stack, which consists of an optical device (light source and thermopile) to measure concentration of solids, and a flowmeter to measure the flue-gas rate (268). The two devices are coupled by a mechanism which automatically multiplies catalyst concentration by the gas-flow rate. Catalyst carry-over from the regenerator of a unit equipped with a Cottrell precipitator has been measured by heat balance in the catalyst-return line from the Cottrell to the regenerator (34). 

A sample is continuously heated at a constant rate (e.g. 10 C min ) while two changes are recorded (1) the temperature difference between an inert compound and the sample with a thermocouple (differential thermo analysis DTA) and (2) the weight loss measured with a balance (thermogravimetry TGA) (Mackenzie, 1957 Smykatz-Kloss, 1974). With DTA, information is obtained about endothermic and exothermic phase transformations (see Fig. 1-2), whereas with TGA adsorbed water and structural OH can be measured. 

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