Makeup Hydrogen

The quality of the hydrogen-rich gas from the hydrogen plant is an important variable to the performance of Hydrocrackers since it can affect the hydrogen partial pressure and recycle gas/feed ratio and thereby influence the catalyst stability (deactivation rate). The following guidelines should be used in operating the hydrogen plant to produce acceptable feed gas to a Hydrocracker. 

---

Heat exchangers are employed to cool the reactor effluent and the desulfurized liquid product is separated from the recycle gas at a pressure somewhat lower than that of the reactor section. Hydrogen sulfide and any light hydrocarbon gases are removed from the recycle gas which is then mixed with fresh (makeup) hydrogen, compressed, and mixed with further hydrocarbon feedstock. 

Description Fresh C7-C8+ (to Cn) feed is mixed with recycle hydrogen, makeup hydrogen and C7+ aromatics from the recycle tower. The mixture is heated by exchange (1) with reactor effluent and by a furnace (2) that also generates high-pressure steam for better heat recovery. 

Description The TAC9 process consists of a fixed-bed reactor and product separation section. The feed is combined with hydrogen-rich recycle gas, preheated in a combined feed exchanger (1) and heated in a fired heater (2). The hot feed vapor goes to a reactor (3). The reactor effluent is cooled in a combined feed exchanger and sent to a product separator (4). Hydrogen-rich gas is taken off the top of the separator, mixed with makeup hydrogen gas, and recycled back to the reactor. Liquid from the bottom of the separator is sent to a stripper column (5). The stripper overhead gas is exported to the fuel gas system. The overhead liquid may be sent to a debutanizer column or a stabilizer. The stabilized product is sent to the product fractionation section of the UOP aromatics complex. 

The reactor effluent is cooled, it flows to the separator, where the hydrogen-rich vapor phase is separated from the liquid stream. A small portion of the vapor phase is purged to control purity of the recycle hydrogen. The recycle hydrogen is then compressed, mixed with makeup hydrogen and returned to the reactor. 

The gas-product mixture exits the first reactor. Is cooled and fed to a second reactor to complete the Isomerization reaction at chemical equilibrium. The product mixture from the second reactor is cooled and fed to a gas separator, where the mixture Is separated from the excess hydrogen gas. Excess hydrogen Is combined with makeup hydrogen and fed through the recycle dryers for blending with feed. There is no hydrocarbon feed drying step required. 

Reactor effluent is cooled by heat exchange, and liquid products are separated from the recycle gas. Hydrogen-rich gas from the separator (2) is recycled back to the reactor together with makeup hydrogen. Liquid product is stripped of remaining light gas in the stabilizer (3) and sent to product fractionation. Unconverted toluene is recycled to extinction. 

It takes into account the on-stream factors that can cause unscheduled shutdowns. It is an important project consideration, particularly if the process is a primary source of makeup hydrogen to a hydro processor or other mainstream refinery processes. 

Revamp of a toluene hydrodealkylation process. This prob-lan considers some waste-minimization concepts. Our operating toluene hydrodealkylation unit, shown in Figure 5.13, involves the hydrogenation of toluene to benzene and methane. An equi-lihium side reaction produces a small quantity of biphenyl. To be more competitive, and eliminate waste, the process needs to be studied for a possible revamp. The customer for our small production of biphenyl has informed us that it will not renew its contract with us, and we have no other prospective buyer for biphenyl. Also, a membrane separator company believes that if we install their equipment, we can reduce our makeup hydrogen requirement. Make preliminary process design calculations with a simulator to compare the two alternatives below, and advise me of the technical feasibility of the second alternative and whether we should consider such a revamp further. For your studies, you will have to perform mainly material balance calculations. You will not make detailed distillation calculations, and liquid pumps need not be modeled. For the second alternative, calculate the required area in square feet of the membrane unit and determine if it is reasonable. 

Hydrogen Under New Management Makeup Hydrogen Recycle Hydrogen... 

The feed to a butane (C4) isomerization unit should contain maximum amounts of n-butane and only small amounts of isobutane, pentanes, and heavier material. The feed is dried, combined with dry makeup hydrogen, and charged to the reactor section at 230 to 340° F (110 to 170°C) and 200 to 300 psig (1480 to 2170 kPa). H2 is not consumed by isomerization reactions, but it suppresses polymerization of the olefin intermediates that are formed during the reaction. A small amount of organic chloride promoter, which is added to maintain catalyst activity, converts completely to HCl in the reactors. 

Makeup and Recycle Hydrogen. Compressors for makeup hydrogen are reciprocating machines, most of which are driven by eleetrie motors. Recycle gas compressors are can be reeiproeating or centrifugal the latter are often driven by steam. In naphtha hydrotreaters, the high-pressure off-gas can be purer than the makeup gas, beeause (a) conversion is nil, and (b) liquids in the makeup gas are absorbed by the naphtha. In most other units, the makeup gas is purer than the recycle gas. 

---