Fresh feed

In describing reactor performance, selectivity is usually a more meaningful parameter than reactor yield. Reactor yield is based on the reactant fed to the reactor rather than on that which is consumed. Clearly, part of the reactant fed might be material that has been recycled rather than fresh feed. Because of this, reactor yield takes no account of the ability to separate and recycle unconverted raw materials. Reactor yield is only a meaningful parameter when it is not possible for one reason or another to recycle unconverted raw material to the reactor inlet. By constrast, the yield of the overall process is an extremely important parameter when describing the performance of the overall plant, as will be discussed later. 

Forward-feed operation is shown in Fig. 3.12a. The fresh feed is added to the first stage and fiows to the next stage in the same direction as the vapor flow. The boiling temperature decreases from stage to stage, and this arrangement is thus used when the... 

Parallel-feed operation is illustrated in Fig. 3.12c. Fresh feed is added to each stage, and product is withdrawn from each stage. The vapor from each stage is still used to heat the next stage. This arrangement is used mainly when the feed is almost saturated, particularly when solid crystals are the product. 

Cold shot or hot shot. Injection of cold fresh feed for exothermic reactions or preheated feed for endothermic reactions to inter-... 

Zone 2. The primary function of this zone is to remove B from the pores of the soHd. When the soHd arrives at the fresh feed point, the pores contain the... 

The water—carbon slurry formed in the quench vessel is separated from the gas stream and flows to the carbon recovery system needed for environmental reasons and for better thermal efficiency. The recovered carbon is recycled to the reactor dispersed in the feedstock. If the fresh feed does not have too high an ash content, 100% of the carbon formed can be recycled to extinction. 

The cracked products leave as overhead materials, and coke deposits form on the inner surface of the dmm. To provide continuous operation, two dmms are used while one dmm is on-stream, the one off-stream is being cleaned, steamed, water-cooled, and decoked in the same time interval. The temperature in the coke dmm is in the range of 415—450°C with pressures in the range of 103—621 kPa (15—90 psi). Overhead products go to the fractionator, where naphtha and heating oil fractions are recovered. The nonvolatile material is combined with preheated fresh feed and returned to the furnace. The coke dmm is usually on stream for about 24 hours before becoming filled with porous coke, after which the coke is removed hydraulically. 

Tubular Reactors. The tubular reactor is exceUent for obtaining data for fast thermal or catalytic reactions, especiaHy for gaseous feeds. With sufficient volume or catalyst, high conversions, as would take place in a large-scale unit, are obtained conversion represents the integral value of reaction over the length of the tube. Short tubes or pancake-shaped beds are used as differential reactors to obtain instantaneous reaction rates, which can be computed directly because composition changes can be treated as differential amounts. Initial reaction rates are obtained with a fresh feed. Reaction rates at... 

In the case of the nozzle disk centrifuge, the flow of the soHds phase through the discharge nozzles may be so restricted that an excessive layer can accumulate inside the bowl sheU. When this layer reaches the zone utilized by the fresh feed stream entering the disk stack, reentrainment of the sedimented soHds by the fresh feed may lead to poor sedimentation performance. 

Fig. 13. Flowsheet of medium pressure synthesis, fixed-bed reactor (Lurgi-Ruhrchemie-Sasol) having process conditions for SASOL I of an alkaline, precipitated-iron catalyst, reduction degree 20—25% having a catalyst charge of 32—36 t, at 220—255°C and 2.48 MPa (360 psig) at a fresh feed rate of...

The recovered product melt can be put through the cycle again to increase purity, or fresh feed can be introduced to the cycle. 

Say the recycle flow rate in a PFR is V and the fresh feed rate is Vq, with the ratio R = V /Vq. With a fresh feed concentration of Cq and a produc t of Co the composite feed concentration is... 

Accordingly, the change in concentration (or in temperature) across the reactor can be made as small as desired by upping the recycle ratio. Eventually, the reac tor can become a differential unit with substantially constant temperature, while substantial differences will concurrently arise between the fresh feed inlet and the produc t withdrawal outlet. Such an operation is useful for obtaining experimental data for analysis of rate equations. 

Part of the effluent from a PER is returned to the inlet. The recycle ratio is R, fresh feed rate is Fq... 

The simplest case of combining T E and LLE is the separation of a binaiy heterogeneous azeotropic mixture. One example is the dehydration of 1-butanol, a self-entraining system, in which butanol (117.7°C) and water form a minimum-boiling heterogeneous azeotrope (93.0°C). As shown in Fig. 13-69, the fresh feed may be added... 

Although the figures given are for a step-by-step process, it is obvious that the same techniques will apply to a continuous system if the fresh feed containing KCl and NaCl is added at an appropriate part of the cycle, such as between steps G and 7 for the case of dilute feed solutions. 

Closed-Circuit Milling In closed-circuit miUing the taiUngs from a classifier are mixed with fresh feed and recycled to the miU. Calculations can be based on a material balance and an expUcit sohi-... 

FIG. 23-3 Temperature and composition profiles, a) Oxidation of SOp with intercooling and two cold shots, (h) Phosgene from GO and Gfi, activated carbon in 2-in tubes, water cooled, (c) Gumene from benzene and propylene, phosphoric acid on < uartz, with four quench zones, 260°G. (d) Mild thermal cracking of a heavy oil in a tubular furnace, hack pressure of 250 psig and sever heat fluxes, Btu/(fr-h), T in °F. (e) Vertical ammonia svi,ithesizer at 300 atm, with five cold shots and an internal exchanger. (/) Vertical methanol svi,ithesizer at 300 atm, Gr O -ZnO catalyst, with six cold shots totaling 10 to 20 percent of the fresh feed. To convert psi to kPa, multiply by 6.895 atm to kPa, multiply by 101.3. 

An inerease in ambient air temperature will deerease the available energy for the generator. This assumes that the fresh feed and eoke burn remains eonstant. The expander horsepower does not ehange, but the air blower horsepower inereases with inereased air temperature, eausing the exeess energy to deerease. Steam and water may need to be added to the flue gas flow at various points in the system to eontrol afterburning. In Figure 4-64, the solid eurves are for a normal flow of steam. The dotted eurves are for inereases in the steam rate by 3.05 times, 4.85 times, and 6.05 times the normal flowrate. 

Step 2. System calculations over the entire range of possible operating conditions are required. The range must cover from the air blower minimum flow point to the expander bypass point for all reasonable variations in the applicable parameters of COj/CO ratio, fresh feed rate, flue gas temperature, ambient air temperature, and so forth. 

In most applieations, the reaetion oeeurs between a dissolved gas and a liquid-phase reaetant in the presenee of a solid eatalyst. In some eases, the liquid is an inert medium and the reaetion takes plaee between the dissolved gases at the solid surfaee. These reaetors have many diverse applieations in eatalytie proeesses and are used extensively in the ehemieal industry. Triekle-bed reaetors have been developed by the petroleum industry for hydrodesulfurization, hydroeraeking, and hydrotreating of various petroleum fraetions of relatively high boiling point. Under reaetion eonditions, the hydroearbon feed is frequently a vapor-liquid mixture that reaets at liquid hourly spaee veloeities (LHSV in volume of fresh feed, as liquid/volume of bed, hr) in the... 

In a single eontinuous flow stirred tank reaetor, a portion of the fresh feed eould exit immediately in the produet stream as soon as the reaetants enter the reaetor. To reduee this bypassing effeet, a numher of stirred tanks in series is frequently used. This reduees the prohahility that a reaetant moleeule entering the reaetor will immediately find its way to the exiting produet stream. The exit stream from the first stirred tank serves as the feed to the seeond, the exit stream from the seeond reaetor serves as the feed to the third, and so on. For eonstant density, the exit eoneentration or eonversion ean he solved hy eonseeutively applying Equation 5-158 to eaeh reaetor. The following derived equations are for a series of tliree stii+ed tanks (Figure 5-23) with eonstant volume Vr. 

A chemical reactor, being started, was filled with the reaction mixture from another reactor which was alic.uly on line. The panel operator increased the flow of fresh feed while watching an eye level temperature recorder He intended to start cooling water flow to the reactor when the temperature began to rise, but did not because the tempe.r.j, ure recorder was faulty, thus a runaway reaction. 

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