Resid Hydrocracker Reactor

The resid hydrocracking reactions are conducted in an ebullated or fluidized bed reactor to overcome the problems associated with a fixed

NI-MO ON ALUMINA BASE EXTRUDATES 0.963 mm x 3.93 mm 45 105

Table 3-8 Resid Hydrocracking Spent Catalyst Composition

COMPONENT

UNITS

WT%

NICKEL

Wt%

2.1

MOLYBDENUM

Wt%

3.73

COBALT

Wt%

0.006

CARBON

Wt%

12.18

SULFUR

Wt%

11.9

VANADIUM

Wt%

7.1

bed (see Figure 3-12). A liquid phase passes upward through a bed of catalyst at a velocity sufficient to maintain the catalyst particles in continuous random motion. This liquid velocity is achieved by circulating a liquid recycling stream by means of an ebullating pump external to the reactor.

An ebullating bed system offers the following advantages over the conventional fixed-bed system:

(1) CRACKING AND HYDROGENATION

(1) CRACKING AND HYDROGENATION

(2) HYDRODESULFURISATION AND DENITRIFICATION

(2) HYDRODESULFURISATION AND DENITRIFICATION

Hydrocracking
Figure 3-11. Resid hydrocracking reactions.

CATALYST ADDITION

LEVEL DETECTORS■

GAS/LIQUID

PRODUCT TO *

SEPARATORS <£33

CATALYST

MAKEUP H2 AND FEED OIL

CATALYST ADDITION

GAS/LIQUID

PRODUCT TO *

SEPARATORS <£33

CATALYST

MAKEUP H2 AND FEED OIL

Hydrocracker Reactor

MAX LIQ. LEVEL

EXPANDED LEVEL

SETTLED CATALYST LEVEL

DISTRIBUTOR GRID PLATE

EBBULATIOM PUMP

Figure 3-12. Resid hydrocracker reactor.

MAX LIQ. LEVEL

EXPANDED LEVEL

SETTLED CATALYST LEVEL

DISTRIBUTOR GRID PLATE

EBBULATIOM PUMP

Figure 3-12. Resid hydrocracker reactor.

1. Isothermal reactor conditions. The mixed conditions of this reactor provide excellent temperature control of the highly exothermic reactions without the need for any quench system. Undesirable temperature sensitive reactions are controlled.

2. Constant pressure drop. Since the catalyst is in a state of constant random motion, there is no tendency for pressure drop to build up as a result of foreign material accumulation.

3. Catalyst addition and withdrawal. The catalyst can be added or withdrawn from an ebullating bed on either a continuously or intermittent basis. This feature permits operation at an equilibrium activity level, thereby avoiding change in yield and product quality with time encountered in fixed-bed reactors due to aging of the catalyst.

Within the reactor, the feed enters the lower head of the reactor through a sparger to provide adequate distribution of the reactant stream. The ebullating stream is distributed through the lower portion of the reactor by an individual sparger. These spargers effect a primary distribution of the feed stream across the reactor cross-sectional area. The feed then passes through a specially designed distributor plate, which further ensures uniform distribution as the vapor and liquid flow upward through the catalyst bed.

The oil and hydrogen dissolved in liquid phase under relatively high hydrogen partial pressure react with each other when brought in intimate contact with active catalyst above the distribution plate. The primary reactions taking place are hydrocracking, hydrogenation, hydrodesulfur-ization, and denitrification. In addition, the organometallic compounds in the feed are broken down under high temperature and high hydrogen partial pressure and are, in part, adsorbed on the catalyst, the remainder passing through the catalyst bed, ultimately ending up in fuel oil. The metal buildup on the catalyst would result in complete deactivation of the catalyst. Therefore, the activity level of the catalyst is maintained by addition of fresh catalyst and withdrawal of spent catalyst in a programmed manner.

The temperature and the catalyst activity level control the conversion level. The other variables such as hydrogen partial pressure, circulating gas rate, reactor space velocity, and ebullating rate are unchanged in an operating unit.

The reactor average temperature is varied by the amount of preheating performed on the total oil and gas streams that pass through separate fired heaters. Normally, the oil heater outlet is maintained at a moderate temperature to minimize skin cracking of the oil, and the adjustment of the reactor temperature is done primarily by increasing the preheating of the hydrogen feed gas to the maximum temperature possible within the heater design limitation.

The ebullating oil flow is controlled by varying the speed of the ebullating pump. Within the reactor, the ebullating liquid is drawn into a conical collecting pan, located several feet above the catalyst bed interface to ensure catalyst-free liquid circulation down the internal stand pipe and into external ebullating pump. The ebullating liquid is distributed through the reactor bottom by its individual sparger.

The height of the fluidized bed of the catalyst in the reactor is related to the gas flow rate, the liquid flow rate, and the physical properties of the fluid, which in turn are affected by the operating temperature and pressure, conversion, size, density, and shape of the catalyst particles. All these parameters are maintained within the constraints imposed by these correlations.

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  • marie
    How to pump resid in a refinery?
    7 years ago
  • mantissa
    What is lhd in a resid hydrocracker in a refinery?
    6 years ago
  • Katy
    Is a hydrocracker fixed bed?
    5 years ago

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