Stirred tank with heating jacket

Applying the equation for conservation of thermal energy to the system, we have 

Rate of Accumulation of Rate of Thermal Rate of — Thermal - - Rate of Generation of  

Thermal Energy Energy In Energy Out Thermal Energy  

The temperature in the jacket can be determined from the steam tables knowing the pressure in the jacket, P. Since the mechanism for heat transfer in the steam jacket is condensation, saturated steam properties can be used and 

Note that the energy balance is solved for the variable y — V (T2 — T ) since it is the variable inside the derivative. This leads to ease in the use of the numerical integration routines for computer solution. 

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Figure 10.10 Exemplary data for heat transfer coefficients and stirrer power for a high-viscosity process medium in a batch stirred tank with heating jackets [5]...

Figure 3.13 Information—Flow Diagram for Stirred Tank with Heating Jacket.

The stirred tank with a jacket for heating or cooling (also called autoclave or digester) is the workhorse of the pharmaceutical, fine-chemicals, mineral and paper industries. It is used as a reactor, mixer, decanter, heater and cooler. The bubble and slurry-bubble columns too are akin to the STR. It is used as a batch reactor or semi- or fed-batch reactor for those reactions requiring a large residence time, as the tubular reactor would be too long and unwieldy. The STR is bulky, and the yield and selectivity could be low. 

FIGURE 9 Sectional view of a stirred-tank reactor/heat exchanger with both an external jacket and internal heat transfer coils. 

This section is concerned with the UA xtiT — Text) term in the energy balance for a stirred tank. The usual and simplest case is heat transfer from a jacket. Then A xt refers to the inside surface area of the tank that is jacketed on the outside and in contact with the fluid on the inside. The temperature difference, T - Text, is between the bulk fluid in the tank and the heat transfer medium in the jacket. The overall heat transfer coefficient includes the usual contributions from wall resistance and jacket-side coefficient, but the inside coefficient is normally limiting. A correlation applicable to turbine, paddle, and propeller agitators is... 

Consider a continuous-stirred-tank reactor (CSTR) with cooling jacket where a first order exothermic reaction takes place. It is required to derive a model relating the extent of the reaction with the flowrate of the heat... 

Figure 3.2. Model representation of a stirred-tank reactor with heat transfer to or from the jacket.

CONTINUOUS STIRRED TANK REACTOR REVERSIBLE REACTION AND JACKET COOLING HEAT AND TEMPERATURE EFFECTS WITH CP = F(T)... 

The standard esterification reactor is a stirred tank reactor. Due to the required latent heat for the evaporation of EG and water, heating coils are installed in addition to the heating jacket. In some cases, an external heat exchanger, together with a recirculation pump, is necessary to ensure sufficient heat transfer. During esterification, the melt viscosity is low to moderate (ca. 20 to 800mPas) and no special stirrer design is required. 

Sulfonation of p-nitrotoluene (PNT) is performed in a cascade of Continuous Stirred Tank Reactors (CSTR). The process is started by placing a quantity of converted mass in the first stage of the cascade, a 400-liter reactor, and heating to 85 °C with jacket steam (150°C). PNT melt and Oleum are then dosed in simultaneously (exothermal reaction). When 110°C is reached, cooling is switched on automatically. On the day of the accident, a rapid increase in pressure took place at 102 °C. The lid of the reactor burst open and the reaction mass, which was decomposing, flowed out like lava, causing considerable damage. 

A 2.5 m3 stainless steel stirred tank reactor is to be used for a reaction with a batch volume of 2 m3 performed at 65 °C. The heat transfer coefficient of the reaction mass is determined in a reaction calorimeter by the Wilson plot as y = 1600Wnr2KA The reactor is equipped with an anchor stirrer operated at 45 rpm. Water, used as a coolant, enters the jacket at 13 °C. With a contents volume of 2 m3, the heat exchange area is 4.6 m2. The internal diameter of the reactor is 1.6 m. The stirrer diameter is 1.53 m. A cooling experiment was carried out in the temperature range around 70 °C, with the vessel containing 2000 kg water. The results are represented in Figure 9.16. 

A liquid is stored in a 10m3 tank (cylinder with vertical axis, diameter 2m). The lower part of the tank is equipped with a jacket (height 1 m). At the storage temperature of 30 °C, the liquid shows a heat release rate of 15mWkg 1. The tank is stirred with a propeller type agitator. 

Starch is dispersed in the paper mill in large stainless steel tanks by injection of steam or by heat transfer from a steam-heated jacket. The tanks are stirred and equipped with baffles to prevent formation of a single vortex at the agitator shaft. A minimum heating time of 20 minutes at 95°C is normally required. Steam injection dilutes the starch paste by condensate, which must be considered for concentration control. Pastes that are prone to retrogradation are held at a temperature above 91°C or quickly cooled to 66°C to prevent amylose formation. Attention to storage temperature and water balance is an essential requirement for the effective use of starch in a paper mill. 

FIG. 19-1 Stirred tank reactors with heat transfer, (a) Jacket. (b) Internal coils. (c) Internal tubes, (d) External heat exchanger, (e) External reflux condensor. (f) Fired heater. (Wolas, Reaction Kinetics for Chemical Engineers, McGraw-Hill,... 

Examples of stirred tank reactors with heat transfer are shown in Fig. 19-1. If the heat of reaction is not significant, an adiabatic reactor may be used. For modest heat addition (removal), a jacketed stirred tank is adequate (Fig. 19-la). As the heat exchange requirements... 

Stirred tank reactors are provided with a jacket or immersion coil for heating or cooling the reaction medium. The temperature of the medium inside the tank is generally uniform. The rate of heat transfer depends on the heat transfer area, the difference in the temperature between the reaction medium and heating or cooling fluid and heat transfer coefficient. 

The flow of heat across the heat-transfer surface is linear with both temperatures, leaving the primary loop with a constant gain. Using the coolant exit temperature as the secondary controlled variable as shown in Fig. 8-55 places the jacket ( mamics in the secondary loop, thereby reducing the period of the primary loop. This is dynamically advanti reous for a stirred-tank reactor because of the slow response of its large heat capacity. However, a plug flow reactor cooled by an external heat exchanger lacks this heat capacity and requires the faster response of the coolant inlet temperature loop. 

Chapter 7, Reactor Design, discusses continuous and batch stirred-tank reactors and die packed-bed catalytic reactor, which are frequently used. Heat exchangers for stirred-tank reactors described are the simple jacket, simple jacket with a spiral baffle, simple jacket with agitation nozzles, partial pipe-coil jacket, dimple jacket, and the internal pipe coil. The amount of heat removed or added determines what jacket is selected. Other topics discussed are jacket pressure drop and mechanical considerations. Chapter 7 also describes methods for removing or adding heat in packed-bed catalytic reactors. Also considered are flow distribution methods to approach plug flow in packed beds. 

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