Reactor temperature quench

Even if the reactor temperature is controlled within acceptable limits, the reactor effluent may need to be cooled rapidly, or quenched, to stop the reaction quickly to prevent excessive byproduct formation. This quench can be accomplished by indirect heat transfer using conventional heat transfer equipment or by direct heat transfer by mixing with another fluid. A commonly encountered situation is... 

As an example, the battery-limits capital cost can be estimated for the production of 10,000 t/yr of ethylene (qv) from ethanol (11). Seven processing blocks, ie, vaporizer, reactor, water quench, compressor, dryer, distillation, and energy recovery, can be identified. The highest temperature is 350°C (reactor), and the highest pressure is about 1.7 MPa (17 atm) (compressor, two towers). If a materials-pressure factor, + of 1.03 is assumed, then for N = 7 0 = 0.87 1/0 = 1 64 and f =0 K = 6.3. This gives the 1981 cost as 4.4 X 10 . The 1991 battery-Hmits investment can be obtained, by updating with the CE Plant Cost Index, as 5.3 x 10 . ... 

This is a more advanced partial combustion process. The feed is first preheated and then combusted in the reactor with a limited amount of air. The hot gases containing carbon particles from the reactor are quenched with a water spray and then further cooled by heat exchange with the air used for the partial combustion. The type of black produced depends on the feed type and the furnace temperature. The average particle diameter of the blacks from the oil furnace process ranges between 200-500 A, while it ranges between 400-700 A from the gas furnace process. Figure 4-4 shows the oil furnace black process. 

For extremely exothermic reactions, emergency quench systems are sometimes used to protect against a runaway reaction. If the reactor temperature exceeds a predetermined maximum safe temperature, the reactor contents are rapidly... 

Because of high reactor temperatures, the hydrocarbon volatiles vaporize immediately, and are vented from the reactor to a quench tower (Item 3), where they are sprayed with cooled, recycled, heavy oil, and the larger molecules (molecules containing eight carbon atoms (C8) or more) are condensed. The condensate leaves from the bottom of the quench tower and is collected in the heavy oil receiver (Item 4). Compounds that are not condensed (i.e., light oil, C3-C7) in the quench tower enter a non-contact condenser that uses cold water The light oils, C3 to C7, are condensed and collected in the light oil receiver (Item 6). 

There are several other aspects about CSTRs with exothermic reactions that should be mentioned at this point. The first involves the temperature of the feed. The colder the feed, the less heat must be transferred from the reactor. So control would be expected to be improved. However, as we will see in Chapter 3, a cold feed can produce some interesting dynamics for instance, an increase in feed flowrate initially decreases reactor temperature because of the sensible-heat effect. But as the reactant concentration in the reactor increases, the temperature eventually increases. A reactor temperature runaway can result if the cold feed quenches the reaction and reactant concentration builds to a very high level before the reaction lights off. ... 

If the reactions had higher activation energies and were more sensitive to temperature, the reaction rates could become so small with the low reactor temperatures that the process could quench (with nothing reacting and all temperatures dropping to the feed temperature). 

To conduct a reaction, the substrate and DAST were introduced into the reactor from separate inlets and mixed within a T-mixer, reacted, and quenched with a solution of saturated aqueous NaHC03. Using this approach, the authors identified dichloromethane (DCM) as the best solvent, employing a reactor temperature of 70 °C, coupled with 1.0 equiv. of DAST for the deoxyfluorination of alcohols and 2.0 equiv. when using substrates containing a carbonyl moiety. Under the aforementioned conditions, the effect of reactant residence time (8-32 min) was evaluated and the authors quickly identified 16 min as being the optimum residence time. As Table 6.2 illustrates, using this approach an array of fluorinated materials were synthesized in moderate to excellent yield. 

Step 3. The reaction is exothermal. After process/process energy saving for feed preheating, the excess energy is rejected to the cooling water. Because the only reason of the furnace is to ensure constant inlet reactor temperature the first control loop is inlet reactor temperature/fliel inflow. To prevent the thermal decomposition of the product, a second loop keeps constant outlet reactor temperature by manipulating the quench stream. 

TC2 outlet reactor temperature with quench flow,... 

The Beckmann rearrangement in superheated and SCH2O was performed at temperatures of 250-400 °C at fixed densities of 0.35 and 0.50 g/mL. The experiments were conducted using a batch reactor system. The reactor vessel was made from a piece of SUS 316 tubing, providing an internal volume of 10 cm A predetermined amount of reactant solution (cyclohexanone-oxime of 0.44 mmol and water of 0.20 or 0.28 mol) was loaded into the reactor in N2 atmosphere. The reactor vessel was immersed and vigorously shaken in a fluidized molten salt bath. The heating time to raise the reactor temperature from 20 °C to 400 °C was within 30 s and the temperature was controlled within 2°C. After a preselected reaction time of 3 min, the reactor was removed from the bath, and then quenched in a water bath. 

Figure 3.14 Temperatures in a three-stage adiabatic reactor with quench cooiing.

The molten PET or PBT products leaving the melt polymerization reactor are quenched, pelletized, and then crystallized by exposing the solid amorphous pellets to temperatures slightly under their (120-140 °C and 30-50 °C, respectively) in crystallization silos. Normally, PBT crystallization rate is so high that the crystallization step can be avoided by controlled quenching of the melt polymerization product [65, 67, 68]. 

Fig. 3.6. Temperature profiles in methanol reactors. Left) WatCT cooled tubular reactor right) quench reactor (saw tooth profile)...

Fig. 4-100 shows the plots of 75 % versus residence time and Fig. 4-101 the plot of AG400 and 7 800 versus residence time, each at two different temperatures. Depending on the reaction conditions, T5 % varies from 90 °C up to 220 °C. The evaporation start temperature is strongly influenced by the reaction temperature, as Fig. 4-100 clearly shows. Heating up to the reaction temperature influences the results a difference in the reactor temperature of 20 °C (435 °C and 455 °C) results in a decrease of the evaporation start temperature by 65 °C. The value at zero residence time is taken on quenching after the... 

The temperature profile of the reactor is also influenced by catalyst deactivation. During operation, the loss of catalyst activity is coimterbalanced by periodically increasing reactor temperature, which progressively displaces the temperature profile upward. The cycle is terminated when the upper temperature level reaches the metallurgical limit of the construction material of the reactor. If axial temperature is not properly distributed, early shutdown is likely to happen, especially when the deactivation process is too fast as in residue HDT. Therefore, in such cases it is desirable to have the lowest possible bed delta-Ts in order to delay the time to reach the maximum allowable limit. This implies more catalyst beds and consequently a larger reactor vessel with additional quench zone hardware. 

In both cases the pyrolysis gasoline/gas oil feed enters at the top of the first reactor. A recycle stream of hydrotreated gas oil is injected with the feed. The recycle streams serve as a reactant diluent, a heat sink to aid in reactor temperature control and as a solvent for polymer removal. Multiple catalyst beds are employed in the reactors to aid in temperature control. Quench oil is injected between the beds for reaction heat control. The first stage is operated at temperatures in the range of 107-177 C and at hydrogen partial pressures of the order of 48-68 atmospheres. 

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