Batch reactors runaway

Scale-up of Stirred-Tank Batch Reactors-Runaway Reactions... 

Manufacturing industries in which batch reactor runaway incidents have been reported during the period 1962-1987... 

Adequate heat removal facilities are generally important when controlling the progress of exothermic chemical reactions. Common causes of thermal runaway in reactors or storage tanks are shown in Figure 7.4. A runaway reaction is most likely to occur if all the reactants are initially mixed together with any catalyst in a batch reactor where heat is supplied to start the reaction. 

Thermal runaway reactions are the results of chemical reactions in batch or semi-batch reactors. A thermal runaway commences when the heat generated by a chemical reaction exceeds the heat that can be removed to the surroundings as shown in Figure 12-5. The surplus heat increases the temperature of the reaction mass, which causes the reaction rate to increase, and subsequently accelerates the rate of heat production. Thermal runaway occurs as follows as the temperature rises, the rate of heat loss to the surroundings increases approximately linearly with temperature. However, the rate of reaction, and thus the... 

Some batch reactions have the potential for very high energy levels. If all the reactants (and sometimes catalysts) are put into a kettle before the reaction is initiated, some exothermic reactions may result in a runaway. The use of continuous or semi-batch reactors to limit the energy present and to reduce the risk of a runaway should be considered. The term semi-batch refers to a system where one reactant and, if necessary, a catalyst is initially charged to a batch reactor. A second reactant is subsequently fed to the reactor under conditions such that an upset in reacting conditions can be detected and the flow of the reactant stopped, thus limiting the total amount of potential energy in the reactor. 

Velo, E., C. M. Bosch, and F. Recasens (1996). Thermal Safety of Batch Reactors and Storage Tanks. Development and Validation of Runaway Boundaries. Ind. Eng. Chem. Res. 35, 1288-99. 

Finally, the oxidation reaction has to been run under strict conditions of temperature, which are impossible to be operated in a batch reactor. Indeed, utility stream in the Shimtec reactor was heated to 47 °C, which first initiates the reaction, accelerates its kinetics, and then controls the temperature when the heat of the reaction is too important. In a batch reactor, working with such UF temperature is impossible because of security constraints. It would certainly lead to a reaction runaway. We now consider this question in the next section. 

Runaway criteria developed for plug-flow tubular reactors, which are mathematically isomorphic with batch reactors with a constant coolant temperature, are also included in the tables. They can be considered conservative criteria for batch reactors, which can be operated safer due to manipulation of the coolant temperature. Balakotaiah et al. (1995) showed that in practice safe and runaway regions overlap for the three types of reactors for homogeneous reactions (1) batch reactor (BR), and, equivalently, plug-flow reactor (PFR), (2) CSTR, and (3) continuously operated bubble column reactor (BCR). 

One purpose of the hold tanks is to a buffer between the batch reactors and the continuous processing units that follow. Initially it woull appear that 2 hold tanks should be specified-one for each train. Each of these would be fed by 4 reactors. In case of a power failure it would be necessary to discharge those reactors that could have runaway reactions into the hold tanks immediately. At most, 4 reactors should be at this state. If properly sequenced this is 2 for each hold tank. Since a hold tank may be expected to contain at least 1 and possibly 2 reactor loads plus wash water, the system should be designed to hold 4 reactor loads plus an equivalent amount of wash water. 

At pressures above 6000 bar, free radical polymerisation sometimes proceeded explosively [ 1 ]. The parameters were determined in a batch reactor for thermal runaway polymerisation of acrylonitrile initiated by azoisobutyronitrile, dibenzoyl peroxide or di-/er/-butyl peroxide [2],... 

Biesenberg, J. S. etal., J. Polym. Eng. Sci., 1976,16, 101-116 Polymerisation of methyl methacrylate initiated by oxygen or peroxides proceeds with a steady increase in velocity during a variable induction period, at the end of which a violent 90°C exotherm occurs. This was attributed to an increase in chain branching, and not to a decrease in heat transfer arising from the increasing viscosity [ 1 ]. The parameters were determined in a batch reactor for thermal runaway polymerisation of methyl methacrylate, initiated by azoisobutyronitrile, dibenzoyl peroxide or di-ferf-butyl peroxide [2],... 

Sebastian, D. H. et al., Polym. Eng. Sci., 1976, 16, 117-123 The conditions were determined for runaway/non-runaway polymerisation of styrene in an oil-heated batch reactor at 3 bar, using dibenzoyl peroxide as initiator at 3 concentrations. Results are presented diagrammatically. 

In heat removal line (2), the heat production line and the heat removal line have only one point of intersection (S3). Here, a critical situation exists. In practice, S3 is not a stable point for operation because a small temperature increase will lead to a runaway reaction. The point S3 is of interest, however, for the calculation of the maximum AT that can be used for safe cooling of a batch reactor. At S3, the reaction temperature T and the AT are at maximum values and the slopes of the two curves are equal. Equation (3-9) and Equation (3-10) are true and valid at point S3. Substituting the value of UAS(T — Tm)max... 

Comenges, J. M. Z. (1991). "Fundamentals on Runaway Reactions Prevention and Protection Measures." Safety of Chemical Batch Reactors and Storage Tanks, ed. A. Benuzzi, and J. M. Zaldivar, 19-47. Dordrecht, The Netherlands Kluwer Academic... 

The parameters were determined in a batch reactor for thermal runaway polymerisation of styrene, initiated by azoisibutyronitrile, dibenzoyl peroxide or di-ferf-butyl peroxide. 

This criterion allows distinguishing two states in a batch reactor, no-runaway and runaway. For the semi-batch reactor, there are four different states, no-igni-tion, runaway, marginal ignition, and QFS. 

Runaway behaviour and parametric sensitivity of a batch reactor an experimental study. 

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. 

Emergency measures, such as pressure relief or containment, must be taken to mitigate the consequences of a runaway that can no longer be avoided. Nevertheless, by far a better measure is to redesign the process to reduce the MTSR to a level below Tm4. This may be achieved, for example, by using a semi-batch reactor instead of a batch reactor and ensuring that the feed rate is properly limited and... 

Zaldivar, J.M. (1991) Fundamentals on runaways reactions prevention and protection measures, in Safety of Chemical Batch Reactors and Storage Tanks, Benuzzi, A. and Zaldivar, J.M. (eds.) ESCS, EEC, EAEC, Brussels, 19 17. 

---