Reactor furnace temperature

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. 

Hot-Wall Reactors. A hot-wall reactor is essentially an isothermal furnace, which is often heated by resistance elements. The parts to be coated are loaded in the reactor, the temperature is raised to the desired level, and the reaction gases are introduced. Figure 5.6 shows such a furnace which is used for the coating of cutting tools with TiC, TiN, and Ti(CN). These materials can be deposited alternatively under precisely controlled conditions. Such reactors are often large and the coating of hundreds of parts in one operation is possible (see Ch. 18). 

The reactor is an 8-mm i.d. quartz tube located in a tube furnace. The quartz tube is packed with 20 by 30 mesh catalyst particles. The catalyst bed is positioned in the tube using quartz wool above and below the bed, with quartz chips filling the remainder of the reactor. The furnace temperature is controlled by a thermocouple inserted into the reactor tube and positioned about 3 mm above the catalyst bed. This allows operation at constant feed temperature into the reactor. 

Adiabatic with Intermediate Heat Transfer. Many tubular reactor systems use a series of adiabatic reactors with heating or cooling between the reactor vessels. For example, naphtha reforming has endothermic reactions of removing hydrogen from saturated cyclical naphthene hydrocarbons to form aromatics. The process has multiple adiabatic reactors with fired furnaces between the reactors to heat the material back up to the required reactor inlet temperature. 

The energy requirement of the furnace is zero for this adiabatic reactor case since the reactor exit stream at maximum temperature can provide enough heat. The design of the FEHE and the amount of bypassing are determined by the reactor inlet temperature T-m. A temperature difference of 25 K is assumed for the hot end of the FEHE. The hot reactor effluent enters the hot side of the FEHE at the high-temperature limit of 500 K, so the cold-side exit stream is 475 K. If the specified reactor inlet temperature is less than 475 K, bypassing is used. A fairly low overall heat transfer coefficient of... 

All of these systems have some common control loops. The system pressure is controlled by manipulating the fresh feed of A (F0A). The concentration controller with ratio control is used to control reactor inlet gas composition by manipulating the fresh feed of B (F0B). Bypassing (Fhy) around the FEHE is used to control gas mixture temperature Tmix. Reactor inlet temperature (Tin or T ) is controlled by manipulating the furnace heat input QF. The setpoints of these two temperature controllers are the same, and the controller output signals are split-ranged so that bypassing and furnace heat input cannot occur simultaneously. 

When reactor inlet temperature is decreased 10 K, production rate is decreased by only 4% and the exit temperature increases by 1.6 K. Note that the furnace heat input goes to zero at about 4 min, and the inlet temperature is maintained by using bypass flow around the FEHE. 

In Chapters 5 and 6, high-temperature exothermic tubular reactor systems were considered. All of these systems used feed-effluent heat exchangers (FEHE) to preheat the feed to the desired reactor inlet temperature by recovering heat from the hot reactor exit stream. Some of the systems also used a trim furnace to add additional heat if needed. 

Figure 7.2 shows the design alternative in which a furnace is installed between the FEHE and the reactor. Furnace inlet temperature is controlled by manipulating the... 

In the FS2 flowsheet with the furnace, the reactor inlet temperature Tin is controlled by manipulating furnace heat input Qp. 

Figure 7.10b demonstrates that changes in the setpoint of the reactor inlet temperature controller are handled smoothly. When reactor inlet temperature is increased, for a constant recycle flowrate, there are increases in production rate, bypass flowrate, reactor exit temperature, and furnace heat input. 

Figures 7.13 and 7.14 give results using the FS2 flowsheet with the furnace for this hot-reaction case. Figure 7.13 shows that a 10% decrease in recycle flowrate can be handled, but a 20% decrease produces a reactor mnaway. This occurs despite the fact that the reactor inlet temperature increases only slightly ( 0.5 K) during the transient. Figure 7.14 gives results for changes in the setpoint of the reactor inlet temperature controller. Rather surprisingly, inlet temperature can be increased by 2 K without a runaway. This is unexpected since the isolated reactor (Fig. 7.12) showed a runaway with a +2 K change in Tm. The difference may be due to the effect of pressure. In the isolated reactor simulation, pressure is held constant at 50 bar. In the simulation of the whole process, pressure drops as reactor temperature increases due to the increased consumption of reactants. Since the reaction rate depends on the square of the total pressure (P2), the decrease in pressure lowers the reaction rates. However, a 3 K increase cannot be handled.

The performance of this control structure, which does not use the furnace, is shown in Figure 7.31. At 0.1 hours, the feed composition is changed from 5 to 7.5 mol% chlorine. The reactor outlet temperature climbs because of the increase in reaction heat generation. The hotter gas entering the FEHE raises the temperature of exit stream, which raises the temperature of the mixture. The temperature controller increases the bypass flow to hold the reactor inlet temperature at 400 K. 

Figure 7.35 gives results for the same scenario of feed composition disturbance used previously. When feed chlorine composition is increased, both the furnace heat input and the bypass flow respond. The furnace heat input QP drops to zero for about 0.7 h. When the composition of chlorine in the feed is decreased, the bypass flow goes to zero, but the furnace heat input increases and holds the reactor inlet temperature Tin at... 

K. The reactor outlet temperature drops to 450 K instead of the 438 K that occurs without the furnace. Thus the chances of a reactor quench are reduced. 

Figure 13. Corrosion behavior of reduction reactor materials samples in anhydrous environment (O), Hastelloy C276 Cartech CB3 (V), Incoloy 825 (A), Inconel 625 (O), SS 310 and (0), SS 18-18-2. Furnace temperature, 482°C (900°F) anhydrous S03 12 cc/min argon 128 cc/min. Erratic erosion rate behavior of SS 310 and Cartech 20CB3 is caused by the spalling of the corrosion product. Negative values indicate weight gain per unit area.

Figure 14. Corrosion behavior of reduction reactor materials samples ( 7), Inconel 625 (O), silicon (Q), silicon nitride (%), alonized Inconel 62 (M silicon carbide and ( f), Inconel 657. Furnace temperature, 482°C S03, 25 see/min steam, 58 see/min argon, 78 see/min.

Weckhuysen and coworkers (Nijhuis et al., 2003) described equipment suitable for parallel Raman and UV-vis spectroscopic measurements. Openings on the opposite sides of a furnace allowed acquisition of Raman and UV-vis spectra through optical grade windows in a tubular quartz reactor. UV-vis spectra were recorded at 823 K. Gas-phase analysis was achieved with mass spectrometry and gas chromatography. A more advanced version of the design (Nijhuis et al., 2004) accommodates four optical fiber probes, placed at 10-mm vertical spacing along the tubular reactor. The temperature that the fibers can withstand is 973 K the reported spectra characterize samples at 823 K. 

Another concern we have is the propagation of disturbances. Consider, for example, an increase in the quenched reactor effluent temperature, Ti (Fig. 5.17). We can use Eqs. (5.4) and (5.5) to estimate the effect that this temperature increase has on the streams around the preheater upstream of the furnace. If the bypass flow is small under normal operating conditions, we can assume that (mCP)g (rhCp)c ... 

Just as we approached reactor control in Chap. 4, we will start by exploring the open-loop effects of thermal feedback. Consider Fig. 5.19, which shows an adiabatic plug-flow reactor with an FEHE system. We have also included two manipulated variables that wall later turn out to be useful to control the reactor. One of these manipulated variables is the heat load to the furnace and the other is the bypass around the preheater. It is clear that the reactor feed temperature is affected by the bypass valve position and the furnace heat load but also by the reactor exit temperature through the heat exchanger. This creates the possibility for multiple steady states. We can visualize the different... 

The next step in the analysis is to seek another functional relationship between the reactor exit temperature and the reactor feed temperature resulting from the heat exchange, bypass, and influence of the furnace. Once we find the second relation we can superimpose it on top of the reactor temperature rise expression shown in Fig. 5.20. Intersections between the two curves constitute open-loop, steady-state solutions to the combined reactor-FEHE system. 

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