Stability of reactors

STABILITY OF REACTOR WITH SUSTAINED DISTURBANCES Constant KC=0, TSET=530, A=0, W=1... 

If Q,. and are plotted versus the reaction temperature, T, the results are illustrated in Figure 9.6.2. A solution of Equation (9.6.6) occurs when 2,. equals Qg, and this can happen as shown in Figure 9.6.3. Notice that for cases (I) and (III) a single solution exists. However, for case (II) three steady-states are possible. An important question of concern with case (II) is v. hether all three steady-states are stable. This is easy to rationalize as follows. At steady-state 1, if T is increased then Qr > Qg so the reactor will return to point 1. Additionally, if T is decreased, Qg > Qr so the reactor will also return to point 1 in this case. Thus, steady-state 1 is stable since small perturbations from this position cause the reactor to return to the steady-state. Likewise steady-state 3 is a stable steady-state. However, for steady-state 2, if T is increased, Qg > Qr and the reactor will move to position 3. If T is decreased below that of point 2, Q,- > Qg and the reactor will move to point 1. Therefore, steady-state 2 is unstable. It is important to determine the stability of reactor operation since perturbations from steady-state always occur in a real system. Finally, what determines whether the reactor achieves steady-state 1 or 3 is the start-up of the reactor. 

Procedure. Methods for collecting and analyzing the gas and liquid samples taken with the probes allow continuous samples to be withdrawn simultaneously at all four points within the catalyst bed. The bed ranged from 25 to 200 cc. in volume. Since the total flow rate of the probe samples is only a few percent of the total exit stream flow rate, the stability of reactor operation is not impaired, and the flow rate in the bed does not vary appreciably. A Chronofrac gas chromatograph (Precision Scientific Co.) was installed for analyzing probe and product gas samples. 

Recently, the fluidized bed membrane reactor (FBMR) has also been examined from the scale-up and practical points of view. Key factors affecting the performance of a commercial FBMR were analysed and compared to corresponding factors in the PBMR. Challenges to the commercial viability of the FBMR were identified. A very important design parameter was determined to be the distribution of membrane area between the dense bed and the dilute phase. Key areas for commercial viability were mechanical stability of reactor internals, the durability of the membrane material, and the effect of gas withdrawal on fluidization. Thermal uniformity was identified as an advantageous property of the FBMR. 

Discussions relating to the stability of reactors for finite variations are given by Welton in his report to the symposium, and by Ergen and Weinberg [16], Lipkin and Thieberger [17], and Chernick [18]. A general reference on the topics of this and the next section is the book by Schultz [19]. 

The purified isobutylene is then blended with a recycled methyl chloride stream containing a low level of isobutylene ( 5%). Finally, the comonomer, iso-prene or p-methylstyrene, is added. In this blending process, control of the ratio of comonomer to isobutylene is very important. This is because it has a significant impact on the composition of the polymer produced, the conversion of monomer, and the stability of reactor operation. For these reasons, a combination of both an analyzer and a mass balance control can be used to maintain the composition of the feed blend. The feed blend contains 20-40 wt% of isobutylene and 0.4-1.4 wt% of isoprene or 1-2 wt% of p-methylst5Tene, depending on the grade of butyl rubber to be produced the remainder is methyl chloride. 

Given a fuel temperature coefficient of -2 x lO AK/K/°C and the INSERTION of a control rod 5 inches with an average worth of 0.1% AK/K/inch. After stabilization of reactor power what will be the new fuel temperature (Assume no other reactivity changes.)... 

Figure 2 UV stability of reactor blend polypropylene copolymer plaques. (Delta L refers to the change in the L components of the LAB color space co-ordinates. KLY = 1 kcal/cm 4.18cal = 1J).

Accidents happening in polymerization reactors are practically always due to a lack of control of the course of reaction caused by a disturbance of the heat balance, which results in a temperature increase leading to loss of control of the reactor and a runaway reaction. In this section a systematic procedure based on a failure scenario with six key questions, allowing assessment of the criticality of a process, is presented. Since the heat balance is at the center of our concerns in matters of thermal control of reactors, the different terms of the heat balance will be examined. Finally, aspects of the dynamic stability of reactors and of the thermal stability of reaction masses are analyzed. 

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