Download Hdd Regenerator Crackeado [PORTABLE]
Fran Bottella
Heated feed is mixed with a heated catalyst and injected into a reactor, where the catalyst freely mixes with the feed as a fluid. As the feed is cracked, coke deposits on the catalyst, causing it to gradually deactivate. Cracked product is drawn off at the top of the reactor and is sent to a fractionator. Deactivated catalyst is drawn off the bottom of the reactor and is sent to a regenerator, where the coke is burned off by injecting heat and air. The cleaned (regenerated) catalyst is then sent back to the reactor, and the cycle repeats.
The catalyst moves around the reactor and regenerator circuits in seconds at very high velocities, so many internal surfaces on the catalyst circuit have to be protected against erosion by having ceramic coatings. The heat generated in the regenerator from burning the coke off the catalyst provides the majority of the heat required for the separation reactions taking place in the reactor, and the unit has to be heat-balanced between the reactor and regenerator. Coke burned off the catalyst in the regenerator creates a mix of carbon monoxide and carbon dioxide plus some SOx. This gas stream is passed through a CO boiler and recovery gas compressor to recover some energy, then cleaned of catalyst fines and evacuated to the atmosphere, so the FCC is a major emitter of CO2 from refineries.
In the conventional FCC process, the preheated high-boiling petroleum feedstock consisting of long-chain hydrocarbon molecules is mixed with cycle oil from the bottom of the distillation column and injected into the bottom of riser reactor where it is vaporized and cracked into smaller molecules by contacting with the hot regenerated catalyst from the regenerator. All of the cracking reactions take place in approximately 3 s. The coked catalyst and oil vapor are separated through a set of two-stage cyclones, then the coked catalyst is sent to the regenerator after stripping, and the oil vapor is piped to the fractionator.
Basically, there are two different configurations for an FCC unit: the "stacked" type where the reactor and the catalyst regenerator are contained in a single vessel with the reactor above the catalyst regenerator and the "side-by-side" type where the reactor and catalyst regenerator are in two separate vessels. These are the major FCC designers and licensors:[1][3][4][6]
The schematic flow diagram of a typical modern FCC unit in Figure 1 below is based upon one of the above configurations. The preheated high-boiling petroleum feedstock (at about 315 to 430 C) consisting of long-chain hydrocarbon molecules is combined with recycle slurry oil from the bottom of the distillation column and injected into the catalyst riser where it is vaporized and cracked into smaller molecules of vapor by contact and mixing with the very hot powdered catalyst from the regenerator. All of the cracking reactions take place in the catalyst riser. The hydrocarbon vapors "fluidize" the powdered catalyst and the mixture of hydrocarbon vapors and catalyst flows upward to enter the reactor at a temperature of about 535 C and a pressure of about 1.72 barg.
The reactor is in fact merely a vessel in which the cracked product vapors are: (a) separated from the so-called spent catalyst by flowing through a set of two-stage cyclones within the reactor and (b) the spent catalyst flows downward through a steam stripping section to remove any hydrocarbon vapors before the spent catalyst returns to the catalyst regenerator. The flow of spent catalyst to the regenerator is regulated by a slide valve in the spent catalyst line.
Since the cracking reactions produce some carbonaceous material (referred to as coke) that deposits on the catalyst and very quickly reduces the catalyst reactivity, the catalyst is regenerated by burning off the deposited coke with air blown into the regenerator. The regenerator operates at a temperature of about 715 C and a pressure of about 2.41 barg. The combustion of the coke is exothermic and it produces a large amount of heat that is partially absorbed by the regenerated catalyst and provides the heat required for the vaporization of the feedstock and the endothermic cracking reactions that take place in the catalyst riser. For that reason, FCC units are often referred to as being heat balanced.
The hot catalyst (at about 715 C) leaving the regenerator flows into a catalyst withdrawal well where any entrained combustion flue gases are allowed to escape and flow back into the upper part to the regenerator. The flow of regenerated catalyst to the feedstock injection point below the catalyst riser is regulated by a slide valve in the regenerated catalyst line. The hot flue gas exits the regenerator after passing through multiple sets of two-stage cyclones that remove entrained catalyst from the flue gas,
The amount of catalyst circulating between the regenerator and the reactor amounts to about 5 kg per kg of feedstock which is equivalent to about 4.66 kg per litre of feedstock.[1][7] Thus, an FCC unit processing 12,000,000 litres/day (75,000 barrels/day) will circulate about 55,900 metric tons per day of catalyst.
Depending on the choice of FCC design, the combustion in the regenerator of the coke on the spent catalyst may or may not be complete combustion to carbon dioxide (CO2). The combustion air flow is controlled so as to provide the desired ratio of carbon monoxide (CO) to carbon dioxide for each specific FCC design.[1] [4]
In the design shown in Figure 1, the coke has only been partially combusted to CO2. The combustion flue gas (containing CO and CO2) at 715 C and at a pressure of 2.41 barg is routed through a secondary catalyst separator containing swirl tubes designed to remove 70 to 90 percent of the catalyst fines in the flue gas leaving the regenerator.[8] This is required to prevent erosion damage to the blades in the turbo-expander that the flue gas is next routed through.
The expansion of flue gas through a turbo-expander provides sufficient power to drive the regenerator's combustion air compressor. The electrical motor-generator can consume or produce electrical power. If the expansion of the flue gas does not provide enough power to drive the air compressor, the electric motor-generator provides the needed additional power. If the flue gas expansion provides more power than needed to drive the air compressor, than the electric motor-generator converts the excess power into electric power and exports it to the refinery's electrical system.[3]
The steam turbine in the flue gas processing system (shown in the above diagram) is used to drive the regenerator's combustion air compressor during start-ups of the FCC unit until there is sufficient combustion flue gas to take over that task.
Fluid catalytic cracking is a chemical process that utilizes a catalyst and heat to break long-chain hydrocarbons into smaller-chain hydrocarbons. Typical products include gasoline, distillate, butane, and propane fuels. The catalyst is a sand-like solid material that is fluidized by the hot liquid and vapor fed into the FCCU. The catalyst can flow between the reactor and regenerator vessels in the FCCU due to this fluidity.
This Refining petroleum is a complex process that generates a diverse slate of fuel and chemical products, ranging from heating oil to gasoline [1]. The process involves cracking, separating, treating, restructuring and blending hydrocarbon molecules to generate petroleum products. A refinery is a chemical plant containing various units that carries out variety of operations involved in processing crude oil. The primary aim is to process the undesirable components of raw crude oil and upgrade them into more valuable products. Gasoline, jet fuel and diesel are among the most valuable products. Originally, thermal operations were used to crack heavy oil, but the discovery of catalyst that gives a higher yield of gasoline with a higher octane number quickly brought about the use of catalytic cracking units. Today, the most commonly used catalytic cracking unit is the Fluid Catalytic Cracker (FCC) [2]. The procedure consists of a catalyst section in which the catalyst can be manipulated [3] and a fractionating section that operate together as an integrated processing unit. Another aspect of research that uses similar procedure is still in current study for example the work of [4] have adopted the catalytic unit in kinetic studies. Also the unit is so efficient that they process biofuels too [5]. The catalyst section contains the reactor and regenerator, which, with the standpipe and riser, are said to be the catalyst circulation unit. The primary aim of the fluid catalytic cracking unit is to crack low-valued heavy gas oils into a lighter more valuable hydrocarbon using a moving bed catalytic converter. Fresh feed gas oil preheated in the heater is injected into the riser reactor through the inlet zone, leading to high turbulence and concentration gradients which partly crack the high molecular weight feed into low molecular weight products. The required heat for this endothermic cracking reaction is provided by hot catalyst. During this reaction, there is deposition of coke (carbon) on the catalyst (Zeolite) which reduces the catalyst activity [6]. The separation of the entrained catalyst from the product gas takes place in the cyclones at the top of the reactor (so as to minimize secondary reactions) and returned to the stripping section of the reactor where steam is injected to strip off the entrained hydrocarbons from the catalyst [7]. The fundamental purposes of the catalyst include selectivity of the reactions, transport of necessary heat to the cracking reactions, and absorption of the coke produced during conversion. This is removed from the catalyst via regeneration; a process of combustion, caused by introducing air into suitable equipment and under suitable conditions [8]. The catalyst is repeatedly circulated in the reactor as connected to the regeneration. In the regenerator controlling the temperature of the regenerator is necessary [9].
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