Feed-effluent heat exchanger

NO -laden fumes are preheated by effluent from the catalyst vessel in the feed/effluent heat exchanger and then heated by a gas- or oil-fired heater to over 600° F. A controlled quantity of ammonia is injected into the gas stream before it is passed through a metal oxide, zeolite, or promoted zeolite catalyst bed. The NO is reduced to nitrogen and water in the presence or ammonia in accordance with the following exothermic reactions ... 

Consider the simplified flow diagram of a reactor system shown in Fig. 20. In this example, we have included the possibility of several input streams, a product recycle loop, and a feed-effluent heat exchanger so as to again represent a very general reactor system. The possible control variables or disturbances to the process are the flow rates of the input gases, the recycle... 

Fig. 20. Packed bed reactor system including feed-effluent heat exchanger.

The process centers on a fixed-bed downflow reactor that allows catalyst replacement without causing any interruption in the operation of the unit (Figure 9-28). Feedstock is introduced to the process via a filter (backwash, automatic) after which hydrogen and recycle gas are added to the feedstock stream which is then heated to reactor temperature by means of feed-effluent heat exchangers whereupon the feed stream passes down through the reactor in trickle flow. Sulfur removal is excellent (Table 9-18), and substantial reductions in the vanadium content and asphaltenes content are also noted. In addition, a marked increase occurs in the API gravity, and the viscosity is reduced considerably. 

Feed/effluent heat exchangers are used in many industrial processes to warm up the fluid before the reactor and to cool it down after treatment at high temperature. The conventional design of such heat exchangers is based on shell-and-tube units. But to increase the thermal effectiveness of the heat exchangers, the required heat length becomes very important, and high pressure drop will occur. 

Figure 5.1 PFR with feed effluent heat exchanger (FEHE).

The feed-effluent heat exchanger is assumed to be single-pass, countercurrent shell-and-tube design. Three partial differential equations are used for the temperatures of gas on tube side, gas on shell side, and the tube metal Eqs. (6.11), (6.12), and (6.13), respectively. The overall heat transfer coefficients on both tube and shell sides, U, and U are constant and are equal to 0.284 kJ s-1 m-2 K-1. Equal heat transfer area per volume is assumed for the shell and tube sides (A,/V, = As/Vs) and is 157 m2/m3, based... 

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 7.1 shows a typical chemical process in which a feed-effluent heat exchanger is coupled with an adiabatic exothermic reactor. The heat of reaction produces a reactor... 

This chapter has two alternative structures for feed preheating. Both use a feed effluent heat exchanger, but one also uses a furnace. Steady-state economics favor use of only a heat exchanger. Dynamic controllability favors the use of both a heat exchanger and a furnace. 

FIGURE 1 Typical temperature profiles for several process heat exchanger applications (a) product cooler (b) feed heater with condensing stream (c) multicomponent feed heater with vaporization and superheating (d) pure-component product condenser (e) multicomponent product condenser (f) typical feed-effluent heat exchanger. 

Processes with feed-effluent heat exchange... 

Figure 6.5 Energy flows in a process with a feed-effluent heat exchanger.

We considered two scenarios that are typical for the operation of reactors with feed-effluent heat exchange. The first set of simuiations traced the response of the ciosed-ioop system to a 10% increase in the production rate, imposed at t = 1 h by increasing the feed flow rate. Subsequently, we analyzed the response of the same situation, but with the added complexity of an unmeasured 10 K increase in the feed temperature occurring at t = 1 h. In both cases, the setpoint of the reactor temperature controller Tjqset was increased by 2 K at t = 1 h in order to maintain reactor conversion at the higher production rate. 

Listing C.l. Symbolic derivation of reduced-order model of the slow dynamics, and of the input-output linearizing temperature controller for the reactor-feed effluent heat exchanger system in Section 6.6... 

Figure 4.11 present the complete flowsheet together with the control structure. The reaction takes place in an adiabatic tubular reactor. To avoid fouling, the temperature of the reactor-outlet stream is reduced by quenching. A feed-effluent heat exchanger (FEHE) recovers part of the reaction heat. For control purposes, a furnace is included in the loop. The heat-integrated reaction system is stabilized... 

Figure 7.10 Simplified PFD of the EDC cracking/VCM separation section with heat-integration scheme (after Lurgi Company). (1) EDC preheater, (2) Feed effluent heat exchanger (FEHE), (3) EDC quencher condenser,...

Figure 9.13 Alkylation reactor with external cooling and feed-effluent heat exchanger.

An energy balance around the feed-effluent heat exchanger,... 

Following C02 removal, residual carbon oxides are converted to methane in the methanator (8). Methanator effluent is cooled, and water is separated (9) before the raw gas is dried (10). Dried synthesis gas flows to the cryogenic purifier (11), where it is cooled by feed/effluent heat exchange and fed to a rectifier. The syngas is purified in the rectifier... 

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