Reactor wall temperature

Adiabatic Reactors. Like isothermal reactors, adiabatic reactors with a flat velocity profile will have no radial gradients in temperature or composition. There are axial gradients, and the axial dispersion model, including its extension to temperature in Section 9.4, can account for axial mixing. As a practical matter, it is difficult to build a small adiabatic reactor. Wall temperatures must be controlled to simulate the adiabatic temperature profile in the reactor, and guard heaters may be needed at the inlet and outlet to avoid losses by radiation. Even so, it is hkely that uncertainties in the temperature profile will mask the relatively small effects of axial dispersion. 

This criterion resembles much those for the temperature gradients on a particle level. The first term again represents the dimensionless activation energy yw, based on the reactor wall temperature Tw. The second term represents the ratio of the heat production rate and the heat conduction rate in radial direction. The last term accounts for the relative contributions of the radial conductivity and the heat transfer at the reactor wall. The latter contains the particle to bed radius ratio and the Biot number for heat transport at the wall, defined as ... 

This model formulation assumes that the reactor wall temperature on the coolant side is the same as the temperature of the reactor contents. The rate of reaction is modeled as... 

Govindarao10 also postulated generalized nonisothermal (constant reactor wall temperature) models for batch as well as cocurrent- and countercurrent-flow three-phase gas-liquid-solid systems carrying out a first-order reaction. 

All experiments were carried out in a simple flow system. A schematic diagram of the apparatus is shown in Figure 1. The quartz reactor (10 mm i.d.) was heated in a three-zone electric furnace which gave a flat ( 2°C) temperature profile over about 45 cm. Reactor temperatures were measured by a thermocouple which could be moved in a sheath attached to the outside of the reactor. Initially, the sheath was placed inside the reactor, but the inside temperatures agreed so closely with the reactor wall temperatures that the inner thermocouple was removed to minimize catalytic effects. 

Combustion experiments were performed in a continues packed bed reactor. The reactor consisted of a stainless steel cylinder of 400 mm length and 9 mm internal diameter. Two grams of catalyst, crushed and sieved to 250-355 pm, were placed in the middle part of the reactor, whilst the upper and lower parts were filled with glass balls (1mm). The reactor was placed inside an electric furnace, temperature being controlled by a PID controller (Honeywell) connected to a thermocouple placed inside the reactor, which monitored the reaction temperature. The system was provided with 5 additional thermocouples that measured the reactor wall temperature at different positions. 

Consider the CSTR illustrated in Figure 9.6.1. The reactor is accomplishing an exothermic reaction and therefore must transfer heat to a cooling fluid in order to remain at temperature T. Assume that the heat transfer is sufficiently high to maintain the reactor wall temperature at T,.. Therefore,... 

The pyrolysis unit consisted of an insulated 316 stainless steel preheater tube (1.3 cm i.d. X 50 cm length) which extended 1 in. into a 316 stainless steel fixed bed tubular reactor (2.5 cm i.d. x 46 cm length), which was heated by a cylindrical block heater. Two type J (iron-constantan) thermocouple probes were used to both monitor the internal catalyst bed temperature and maintain a consistent reactor wall temperature in combination with a temperature controller, A syringe pump, condenser, vacuum adapter, receiving flask, nitrogen cylinder, and gas collection system were connected as shown in Fig uTe 2. The reactor midsection was packed with 40 g of activated alumina, which was held in place by a circular stainless steel screen. The preheater and reactor were operated at 180-190 and 450 C, respectively. The entire process remained at normal atmospheric pressure throughout the mn. 

Sawdust and seneer shorts are especially suitable raw materials for catal> tic pyrolysis. In the present study the sawdust was treated with an appropriate amount of an EORA tar aqueous solution in a paddle mixer, the mixture was kept in a closed vessel for 48 hours and the catalyst-soaked wet sawdust (the moisture content 45 to 50% on the wet basis) was pyrolysed in a pilot-scale thermoreactor equiped with a two paddle rotating surer at a consumt reactor wall temperature of 550 to 6(K) C. The charcoal yield calculated as fixed carbon was increased from IS to 32.5% when the EORA tar concentration in the catalysed sawdust was 17% on the o,d wood basis. The bulk density of the charcoal was also increased from 188 to 220 g/1. The duration of the... 

During the first experiment with Avicel PH102 cellulose the reactor wall temperature gradually rose to 850°C (after 150 seconds of biomass flow) in a solar flux of 1000 w/cm. ... 

Another example of the use of equilibrium considerations in discussing reactions in discharges is by Ruppel, et al, for the reaction of CO and steam in an ozonizer at atmospheric pressure (17). In a flow system, as the space velocity is decreased, the percent conversion of CO tends toward the thermodynamic limit for this reaction, as determined by the external reactor wall temperature. 

Although the runs with natural gas presented above were made with a reactor wall temperature of 735° C., the mols of formaldehyde produced do not exceed the mols of ethane introduced with the natural gas. Thus the yields of formaldehyde obtained were 4.1 mols in the four pass and 5.67 mols in the recycle systems per thousand liters of gas, whereas 7.4 mols of ethane were introduced per thousand liters of natural gas (calcu-... 

Figure 2. Effect of reactor wall temperature, inorganic base, and reactor pressure on hydrogen yield...

FDP hydrogasification behavior at these relatively low temperatures. This is difficult to do in the present 3-inch id FDP reactor because the coal quickly heats to the reactor wall temperature and, if the wall temperature is below 725°-800°C, the coal adheres to the reactor walls and eventually plugs the reactor. However, the coal that did not contact the walls passed through the reactor and was collected, and its conversion and caking properties were determined. Results of these lower reactor wall-temperature experiments are shown in Figures 3 and 4. The effects of temperature on both the volatile matter and the carbon conversion of the FDP reactor char are shown at the reduced wall temperatures. 

Figure 4. Effect of estimated particle temperature on carbon conversion and volatile matter-reactor wall temperature...

This study illustrates the complex interaction between reactor kinetics temperature and the deactivation of the catalyst. An important finding, for the assumed mode of operation, is that service life can t be indefinitely extended by simply adding catalyst. Service life is found to be dependent on the reactor wall temperature. This indicates the importance of heat transfer and more generally the mode of operation in determining service life. 

In the previous discussion of the one-dimensional nonisothermal simulation results it has been shown that for certain operating conditions the ethane conversion can be increased considerably in a PBMR compared to conventional fixed-bed reactors. The price, which had to be paid, was the higher local heat generation and insufficient heat removal. The problem is more pronounced in the large-scale apparatus. For illustration, the temperature profile in the PBMR calculated with the extended version of the a -model is depicted in Fig. 5.22. Accounting for the thermal resistance of the shell side and of the membrane, a temperature maximum of more than 20 K above the inlet and outer reactor wall temperature is predicted. For the sake of completeness it has to be noted that the thermal resistance of the shell side was calculated for an annulus filled with inert particles. This constructional modification is, compared to a reactor with an empty annulus, necessary, otherwise the reaction is becoming uncontrollable. Because of... 

Figure 37.3 shows the variations of non-dimensimial droplet diameter squared in the shrinkage period as a function of distance from the reactor inlet for various reactor wall temperatures, for given <1q, Nq, Q, RHq, and Cq. At reactor wall temperature of 200°C, in order for the shrinkage period (period during which no solute is precipitated yet) to terminate, the droplets need to travel 500 mm from the reactor inlet, whereas for the case of the reactor waU temp)erature of 1,000 C, this length is reduced to 50 mm. It is observed that the variation of droplet diameter squared with x (and therefore t) is not linear. In fact, it seems that the rate of droplet size reduction ( evaporation rate) increases with distance from the reactor inlet. 

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