Cracker zone

Fixed beds are the main interest of this Section. Usually it is adequate to assume that the fluid and solid are at the same temperature at a point. There are cyclic processes, however, where the solid is first heated with flue gases or by burning off carbon before contacting the reacting fluid for a time. A moving bed of heated pebbles (Phillips pebble heater) has been used for the production of olefins from butane and for the fixation of atmospheric nitrogen. A fluidized sand cracker for the production of olefins functions similaiiy, with burning in a separate zone. 

The Middle East should exploit every ton of stranded gas available. The heavy investments in crackers (primarily ethane) and downstream products (mostly polymers) already under way will bring the region close to this level. Iran s NPC is building the two largest crackers in the world in the Pars Special Economic Energy Zone, one of which is a naphtha cracker that will also produce 900,000 t/year of propylene. SABIC, meanwhile, is planning the start-up of its 1.3 mmt/year cracker by 2009 in Yanbu, Saudi Arabia and a joint venture between Chevron... 

Downstream of the reaction zone, the lower static pressure permits the reactor content to boil and applies the thermosyphon effect for circulation. EDC vapor leaves the horizontal vessel and either enters the reboiler of a column (e.g., reboiler of high-boil-heads and/or vacuum column) or a heat exchanger, which condenses the EDC vapor. The reaction heat is transferred to the column indirectly. A fraction of the condensed EDC is fed back to the reactor and the rest is directly sent to the EDC cracker without further distillation. 

To provide an example. Fig. Z16 shows a sin libed isometric view of a cell of a steam cracker with vertical tubes in the radiation zone and horizontal tubes in the convection zone. It also shows the positions of the adewaU burners, quench boilers, steam drum, and the injection device of the heavy cut which performs the supplementary direct quench. 

Moving bed gas adsorbers also have been proposed and used, patterned after moving bed gas oil crackers. In the Hypersorber of Figure 15.28, flows of gas and solids are countercurrent in a single vessel. After saturation, the solid is stripped with steam and removed at the bottom of the tower, and gas is lifted to cooling and adsorption zones. The control mechanism for solids flow and typical performance for ethylene recovery from cracked gases also are shown with the figure. Partly because of attrition losses and the advent of competitive processes for ethylene recovery, the Hyper-... 

A screw conveyor feeds through a cooled downpipe the electrically heated quartz-reactor which has a diameter of 5 cm and a fluidizing zone of up to 8 cm. The fluidizing gas is about 500 1/h of either nitrogen or circulated cracker gas. A cyclone separates solids from the hot pyrolysis gas stream an electrostatic precipitator and a system of intensive coolers and hydrocyclones condense the liquid portions of the cracked products, The non-condensable pyrolysis-gases are measured. 

Coke formation will always be a potential problem in any high temperature process involving hydrocarbons. Coke and tars formed during reaction can deposit on reactor surfaces or in quench heat exchangers, and several effects have been observed in a steam cracker tube (4, 9 ). As the reaction proceeds the tube will accumulate coke towards the reactor exit, while the inlet zone remains relatively coke free, as a result of the induction time associated with the formation of tars and coke (J ). Gas phase reactants may adsorb and react on this bare metal, and the components of the gas phase in the reactor should and do reflect this interaction (4, 9, JO). Since carbon formation depends on the nature of the gas phase species, these interactions should also influence coke formation towards the exit of the ractor. Again, this is found to be the case (4, 9 - 11). 

For most of applications, it is required to purity BPA from the mentioned byproducts before its further processing. Therefore, the BPA production line consists of a condensation reactor and the units responsible for the BPA purification. Among them, there is usually a unit for crystallization of the BPA-phenol adduct and stripping tower, where the adduct is cracked and phenol is recovered (as it was described earlier). There are also a recrystallization unit, a cracker for the o,p-isomers of BPA and a wastewater treatment facility. Additionally, there may be an isomerization unit, where the mother liquor is contacted with an acidic or amine-based ion-exchange resin as the isomerization catalyst under the conditions effective to convert the BPA byproducts to BPA. Next, the effluent from the isomerization zone can be contacted with a solid particle guard bed, composed of alumina, titanium oxide, silica, zirconium oxide, tin oxide, charcoal or silicon carbide [55]. This guard... 

Scheme 6.6.1 Examples of radical reactions taking place in the hot reaction zone of the steam cracker.

We consider in the following a world-scale steam cracker plant with a production capacity of 125th ethene (Figure 6.6.8). The plant runs on light-run naphtha that is heated in the convection zone of the crack oven to 600 °C. The naphtha is mixed with water vapor (4.5 MPa, 257.5°C) to realize a steam-to-naphtha ratio of 0.45. This mixture is introduced to the main crack oven, which is an 80m tubular reactor at 850°C. The residence time of the feedstock in this hot section of the crack oven is 0.5 s. Following the crack oven, the product mixture is quenched to 200°C. In a first distillation column light components (C1-C5) are separated from the heavier pyrolysis products (Cs+). 

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