BRPI0504321B1 - Process and apparatus for maximizing fcc average distillates - Google Patents

Description

DETAILED MAXIMIZATION PROCESS AND APPARAT

FCC AVERAGES

FIELD OF THE INVENTION The present invention belongs to the field of fluid catalytic cracking (FCC) processes, in the absence of added hydrogen, of mixed hydrocarbon charges of different origins aiming at maximizing the fraction of medium distillates, more specifically, the invention is directed to a catalyst cracking process with double rising reactor that enables the achievement of a medium distillate of low aromaticity. Further, the invention is directed to the production of high octane cracked naphtha, and to the production of petrochemical inputs such as propene and ethylene in greater proportions than those obtained in conventional low conversion FCC processes.

BACKGROUND OF THE INVENTION Fluid catalytic cracking (FCC) is effected by contacting hydrocarbons in a tubular or riser reaction zone with a catalyst made of particulate particulate material. The loads most commonly subjected to the FCC process are, in general, those oil refinery streams from vacuum tower side sections called vacuum heavy diesel (GOPDD), or heavier than the previous one, from the tower bottom. atmospheric waste (RAT), or mixtures thereof.

These streams, typically in the range of 8 ° to 28 ° API, must undergo a chemical process such as the catalytic cracking process that fundamentally alters their composition into lighter, higher value hydrocarbon streams. economic.

During the cracking reaction, substantial proportions of coke, byproduct of the reaction, are deposited on the catalyst. Coke is a high molecular weight material consisting of hydrocarbons that typically contain from 4% to 9% by weight of hydrogen in its composition. The coke-coated catalyst, commonly referred to as “spent catalyst”, is sent to a regenerating vessel. In the regeneration zone, in a regenerating vessel kept at a high temperature, the coke deposited on the catalyst surface and pores is burned. Coke elimination through combustion allows for recovery of catalyst activity and releases sufficient heat to meet the thermal needs of catalytic cracking reactions. Fluidization of the catalyst particles by gas streams allows the transport of catalyst between the reaction zone and the regeneration zone and vice versa. The catalyst, in addition to fulfilling its essential function of catalyzing chemical reactions, is also the means of heat transport from the regenerator to the reaction zone. The technique contains many descriptions of hydrocarbon cracking processes in a fluidized catalyst stream, with catalyst transport between the reaction zone and the regeneration zone, and coke burning in the regenerator.

Despite the long existence of FCC processes, techniques are continually sought to improve the process by increasing the production of higher value-added derivatives such as gasoline and LPG. In general, it can be said that the main purpose of FCC processes is to maximize the production of these higher value derivatives. Maximization of these derivatives is achieved basically in two ways. One is the increase in the so-called “conversion”, which corresponds to the reduction in the production of heavy products such as clarified oil and light recycle oil. Another is the reduction of coke and fuel gas yields, that is, the lower “selectivity” to these products. Lower production of gas and coke, increasing process selectivity for LPG and gasoline, has the additional beneficial consequences of using smaller air blowers and wet gas compressors, large and energy-intensive machines in general. limiting capacity of UFCC. In addition, it is economically interesting to promote the increase of higher value added products.

An important aspect to consider is the possible interest or need to increase LPG production as needed by the refiner. It is well known to specialists that an important aspect of the process is the initial contact of the catalyst with the load, which has a decisive influence on process conversion and selectivity in generating noble products. In the FCC process, the preheated hydrocarbon charge is injected near the base of a riser or conversion zone, where it comes in contact with the regenerated catalyst stream from which it receives sufficient heat to vaporize it and supply it. endothermic reactions that predominate in the process.

After the riser, which is an elongated vertical pipe whose dimensions in industrial units are about 0.5m to 2.0m in diameter, by 25m to 40m in height, where chemical reactions occur, the spent catalyst, with coke deposited on its surface and pores, it is separated from the reaction products and sent to the regenerator to burn the coke in order to have the activity restored and generate the heat that, transferred by the catalyst to the riser, will be used by the process.

The conditions at the point of introduction of the load in the riser are determinant as to the products that form in the reaction. In this region occurs the initial mixing of the charge with the regenerated catalyst, heating of the charge to the boiling point of its components and the vaporization of most of these components. The total residence time of the hydrocarbons in the riser is about 1 to 4 seconds.

In order to process catalytic cracking reactions, the vaporization of the charge in the mixing region with the catalyst must occur rapidly, so that the vaporized hydrocarbon molecules can come into contact with the catalyst particles - whose size is about 60 microns - permeating through the catalyst micropores, and reacting at the acid sites. Failure to achieve this rapid vaporization results in thermal cracking of the liquid charge fractions. Thermal cracking is known to favor the formation of by-products such as coke and fuel gas, especially in cracking of residual fillers. Coke poisons acidic sites and can even clog the pores of the catalyst. Therefore, thermal cracking at the riser base undesirably competes with catalytic cracking, which is the objective of the process. Optimizing load conversion usually requires maximum removal of catalyst coke in the regenerator. Coke combustion may be achieved in either partial combustion or full combustion.

In partial combustion, the gases produced by the combustion of coke mainly consist of CO2, CO and H20 and the coke content in the regenerated catalyst is in the range of 0.1% to 0.3% by weight. In total combustion, performed in the presence of a greater excess of oxygen, practically all the CO produced in the reaction is converted to CO2. The oxidation reaction of CO to CO2 is strongly exothermic, causing full combustion to occur with large heat release, resulting in very high regeneration temperatures. However, total combustion produces catalysts containing less than 0.1% and preferably less than 0.05% by weight of coke, in this respect being more advantageous than partial combustion compensating for a lower catalyst / oil ratio, besides avoiding the use of a costly boiler for subsequent combustion of CO. The increase in spent catalyst coke results in an increase in regenerator combustion coke per unit mass of circulated catalyst. Heat is removed from the regenerator in conventional FCC units in the flue gas and mainly in the regenerated hot catalyst stream. An increase in coke content over spent catalyst increases the temperature of the regenerated catalyst and the temperature difference between the regenerator and the reactor.

Therefore a reduction in the flow rate of regenerated catalyst to the reactor, usually called catalyst circulation rate, is required in order to meet the thermal demand of the reactor and to maintain the same reaction temperature. However, the lower catalyst circulation rate required by the larger temperature difference between the regenerator and the reactor results in a reduction in the catalyst / oil ratio, reducing conversion but also coke deposition on the catalyst as opposed to movement. initial increase in coke content.

Thus, the circulation of catalyst from regenerator to reactor is defined by the thermal demand of the riser and the temperature established in the regenerator, as a function of coke production. As the riser-generated coke is affected by the catalyst circulation itself, it can be concluded that the catalytic cracking process works in a thermal equilibrium regime and, for the reasons mentioned, the operation at very high regeneration temperature is undesirable.

As a rule, with modern FCC catalysts, the temperatures of the regenerator, and hence of the regenerated catalyst, are kept below 760 ° C, preferably below 732 ° C, as the loss of activity would be very severe above this value. . A desirable operating range is 685 ° C to 710 ° C. The lower value is mainly dictated by the need to ensure proper coke combustion.

With the processing of increasingly heavy loads, there is a tendency to increase coke production and full combustion operation requires the installation of catalyst coolers to keep the regenerator temperature within acceptable limits. Catalyst coolers generally remove heat from a catalyst stream from the regenerator, returning to this vessel a substantially cooled catalyst stream. Several works in the patent literature propose the injection of an auxiliary stream such as water or other petroleum fractions at a point above the injection point of the main load to be cracked in order to promote an increase of the mixing temperature in the injection region. to increase the vaporized percentage of residual loads without changing the riser output temperature.

This approach is described in US Patent 4,818,372, which teaches a temperature controlled FCC apparatus including an up or down reactor, a device for introducing the hydrocarbon charge under pressure and in contact with a regenerated cracking catalyst, and by at least one device for injecting an auxiliary fluid downstream of the reactor zone where the charge and the catalyst come into contact, whereby a higher temperature is to be achieved in the charge-catalyst mixing region. This patent uses an inert external fluid whose main effect is cooling the injection region of this fluid, with temperature control and increased catalyst circulation.

As taught in US Patent 4,818,372, the segregated injection of an external current at an upper riser point is performed to control its temperature profile so as to maintain the initial riser portion at a relatively lower temperature. high without changing the riser top temperature (reaction temperature or TRX). Such control may also be accomplished by a heavy naphtha recycle as taught in US Patent 5,087,349.

To this same end, US Patent 5,389,232 teaches a heavy naphtha recycle at higher riser points. And US Patent 4,764,268 suggests injecting an LCO current into the top of the riser to minimize naphtha over-cracking reactions.

A similar alternative taught in US Patent 5,954,942 is for increased conversion by quenching or rapid cooling with an auxiliary steam stream in the upper riser region. Publication WO 93/22400 mentions the possibility of injecting a cracking product such as LCO over the riser in order to cool the riser and thereby promote increased catalyst circulation and enable improved performance of ZSM-5 based additives.

In view of the increasing demand for high quality middle distillates to the detriment of the gasoline market which is the main product of a conventional FCC, changes in the operation mode of the FCC unit have been discussed in order to increase the production of LCO Several technical articles discuss modifications in the catalytic system and process variables in order to achieve a reduction in process severity in order to increase the average yield and reduce the aromatic content in this fraction. Operating conditions include the following: - reduction of reaction temperature; - reduction of the catalyst oil ratio; - reduction of catalytic activity.

All these measures lead to a reduction in conversion, with consequent increase in the production of decanted oil.

Some important references on this subject are listed below. 1-Distillate yield from the FCC: process and catalyst changes for maximization of LCO: Catalysts Courier, R. W. Peterman; 2- Hydrocarbon Publishing company: Advanced Hydrotreating and hydrocarbon technology to produce ultra-clean diesel fuel, 2004; 3- Studies on maximizing diesel oil production from FCC: Fifth International Symposium on advances in fluid catalytic cracking, (218th National meeting, American Chemical Society, 1999); 4- New development boosts production of middle distillate from FCC: Oil and Gas Journal (August, 1970). LCO is one of the by-products of the FCC, representing from 15% to 25% of yield and corresponding to the distillation range typically between 220 ° C and 340 ° C. Normally LCO has a high concentration of aromatics, exceeding 80% of the total. In some situations, it is interesting to operate the FCC to maximize the LCO current, in which case it is desired to incorporate the LCO into the diesel oil pool. The high concentration of aromatics in the LCO makes it have a bad detonating quality on the diesel engine (low cetane number) and high density. The high content of aromatics also makes it difficult to improve their properties through hydrotreating.

In the most common form of FCC midrange maximization, the reaction temperature is reduced to extremely low values (from 450 ° C to 500 ° C), catalyst circulation is minimized and a low catalyst is used. activity. All these measures can increase the yield and improve the quality (reduce aromatics) of the produced LCO. The problem with this type of operation is that at the same time it promotes an increase in the residual fraction (cut-off 340 ° C +) of the FCC, typically for low value fuel oil.

This problem can be partially remedied by using an injected cooling current above the main load injection. Even so, problems of increasing the Rectifier Hydrocarbon Drag Regenerator temperature may persist, limiting the unit and preventing it from operating in even milder conditions. This dragging of hydrocarbons is due to the loss of rectifier efficiency, significantly impaired by the low rectification temperature, a function of the reaction temperature, which is closely monitored. The technology of the Applicant, object of PI 9303773 (corresponding to US 5,569,435) comprising a rapid separation system at the end of the ridge between the catalyst and the reaction products, called PASS, incorporated herein by reference, is important in this context. by reducing the hydrocarbon charge to the rectifier, making the FCC unit less sensitive to the problem.

One way around the problem of low rectification temperatures in low severity operation would be to work with a rectifier heated by an external heat source. One way of performing this heating is, for example, the total or partial replacement of the steam injected into the rectifier with a warmer current, for example the effluent flue gas from the regenerator in the case of full combustion operation or the boiler. CO in case of partial combustion. This N2 and CO2 rich current would have the secondary benefit of alleviating the thermal load of the top fractionator top condenser as well as allowing for a refinery acid water balance clearance.

However, the gas mass flow required to cool the rectifier by a few degrees would be of high magnitude, comparable to the catalyst flow rate circulating through the unit. This gas flow does not contain recoverable hydrocarbons and would be much higher than the flow that normally circulates through the wet gas compressor and the entire gas recovery section of the unit, making this option economically unfeasible.

Other patents propose heating the rectifier with regenerated catalyst, but it is a system of some complexity.

These are probably the reasons why there is no known industrial application of either the regenerator or catalyst gas for heating the rectifier. Operating at low temperatures in the post-riser region, in addition to impairing catalyst grinding efficiency, causes heavy fractions of the FCC product to condense on the surface of the reactor walls and internals, leading to coke formation on the walls. of the separating vessel. The phenomenon of coke formation is characteristic in reactors equipped with rapid separation systems, especially in units that process heavy loads. Coke formation from thin condensate films continues throughout the unit campaign, and it is common for several tons of coke to be found at the end of the vessel occupying much of the interior of the vessel. The coke presents a serious risk of ignition and fall, causing major damage to the refiner as it prevents maintenance work on the unit for a few days until it is completely removed. Their fall during the campaign tends to block catalyst runoff, often causing the unit to stop. In both cases it is cause of lost profits. The technology of the so-called Hydrocarbon Vapor Collection Tubes is described in Applicant's PI 0204737-3 and in conjunction with the technology called Slide Joints, which is the subject of the same Applicant's PI99011484-0, both incorporated in full by the present application for reference, It takes the above-mentioned Applicant's rapid separation technology immune to the problem of coke formation by preventing the FCC product from encountering cold surfaces in the reactor, enabling low temperature operation.

A natural consequence of the reduction in the aromatic content in the LCO range, which is the objective of the operation to maximize averages, is the reduction, also in the gasoline range, of the aromatic content, as well as the increase in olefins. In the case of gasoline these changes affect the specification of olefin content, stability (potential gum, induction period) and motor octane number.

Another problem of operating under soft conditions is the loss of yields of light olefins in the C3-C4 range, which may impact the unit's economy, given the high added value of these products that can later be sold as inputs to the petrochemical industry. referred to MTBE alkylation or production units. US 5,234,578 utilizes a riser solely for conveying catalyst from the regenerator to the rectifier as a means of heating the catalyst. The concept of the invention encompasses two simultaneous advantages: cracking and heat exchange in a single device, as a high-severity process riser is provided containing a very heated catalyst which at the end of the reaction falls into the separator. cold catalyst from low severity riser and heat exchange. US 6,416,656 teaches a process for simultaneously increasing diesel and LPG yield. In this process, the gasoline is depressed to increase the LPG yield and is injected below the nozzle. The process load is injected at multiple points along the riser, reducing contact time and thereby increasing LCO yield. However, the reduced severity of the FCC riser for medium distillates makes the cracking of naphtha under these conditions ineffective. International publication WO / 0160951 deals with a process for maximizing middle distillates in yields of 50 and up to 65% by weight using a system of two risers operating at different severities. It is claimed that heavy naphtha is also produced with high yield, while gas and coke are minimized as well as unconverted funds, and the cetane quality of the middle distillate is improved. The process is performed in the presence of solid zeolitic catalysts and large pore acid components for selective bottom cracking. Although this document states the excellence of the cracking process under these conditions, a detailed study of the process conditions described therein reveals that: The experiments cited in said publication WO / 0160951 were performed in modified MAT type unit with search for later emulation in pilot unit, seeking connection to business unit. The MAT type unit does not operate in thermal balance, unlike an FCC industrial unit, it is a fixed bed unit unlike a reaction riser industrial unit nor does it reflect the tendency of coke and gas formation of these units. . The attempt to emulate the industrial unit with a pilot unit comparative test, while valid for observing yield trends, does not reproduce the thermal balance. An industrial rectifier under the recommended reaction temperature conditions would operate with very low efficiency, causing hydrocarbons to be carried to the regenerator. Similarly, vaporization and charge dispersion in the injection region would be deficient, considerably increasing the tendency for coke formation. This situation, coupled with the low thermal demand by the risers, would lead to a thermal equilibrium situation in the industrial unit where the regenerator would operate very hot and extremely low catalyst circulation. The use of a catalyst cooler could correct the problem of high regeneration temperature but not rectification deficiency.

In addition low reaction temperatures are also unsuitable for conversion of derivatives of naphthenic-aromatic characteristics. Applying these loads would result in extremely low conversions resulting in high slurry oil production, even if a catalyst cooler was used. It also results in a low quality gasoline, the result of thermal cracking and non-catalytic, not meeting the specifications of octane index, olefin content and stability.

Another difficulty related to publication WO / 0160951 relates to the recycling of heavy fractions. Such recycles, especially if they come from naphthenic-aromatic fillers, would not be converted at the low temperatures and catalyst circulations recommended for riser 2 where they are injected, again leading to the high production of slurry.

Given these facts, and in accordance with the Claimant's industrial experience, it is clear that this publication has its application restricted to highly paraffinic, high cost and scarce loads in countries such as Brazil. For the same reasons it is not applicable to heavy loads containing atmospheric residue fractions with boiling point above 570 ° C, typical situation, for example, in Brazilian refineries. In the case of the present invention, the reaction products and the catalyst being sent by the two rails to different separating vessels allows the products to be routed to different fractionation sections, but with the two catalyst streams being directed to the same rectifier. Thus, the spent catalyst of the low temperature first riser is mixed with the spent catalyst of the high temperature second riser such that the mixture has a temperature similar to that of conventional rectifiers. In this case, the new FCC configuration of two risers operating at different temperatures is also used to solve the problem of low rectification efficiency in low severity operation, solving with the catalyst itself, ie with an intrinsic process fluid , an ancient difficulty in fluid catalytic cracking technology. Rectifying the spent catalyst mixture of the two risers into a single vessel thus ensures better overall grinding efficiency.

Advantageously and unlike the state of the art, the use of two separating vessels in the process of the invention allows the delivery of high severity riser products and low severity riser products to separate separation systems, thus preventing products from the range of Distillation of LCO produced in the high severity riser mixes with the low aromatic LCO produced in the low severity riser.

Another aspect of the invention is the high severity riser production of BMCI high index clarified oil. The use of an independent separator vessel ensures that this noble oil with high market value can be destined for an exclusive tank for commercialization. The study of the cited references shows that the literature does not reveal or suggest, individually or in combination, the system and process characteristics resulting from the research conducted by the Applicant and which allowed the preparation of this application.

Thus, the technique still requires a mixed-charge fluid catalytic cracking process, in the absence of added hydrogen, using a two-riser system, a first diesel riser operating in low-severity mode, generating gasoline with low drag. hydrocarbons for the regenerator, which overheats with reduced circulation and increased decanted oil production, and a second riser; for dampening the gasoline produced in said first riser, said second riser acting simultaneously as a catalyst cooler, correcting the Regenerator's high temperature problem, converting gasoline olefins and dienes and improving stability and octane, and further said ríser being the origin of a decanted oil recycle or a light fraction (HCO), in order to increase the conversion of funds, the overall result of the process being the high obtaining of middle distillates, cracked naphtha and light olefins, such process. and the apparatus used to perform said process being described and claimed in the present application.

SUMMARY OF THE INVENTION

Broadly speaking, the invention relates to a process for maximizing FCC middle distillates comprising cracking mixed loads in a two riser system, a first low-severity ridge where diesel is cracked and a second high-riser. severity where gasoline is depleted, said second riser while simultaneously acting as a catalyst cooler, correcting the regenerator's high temperature problem, converting gasoline olefins and dienes while improving stability and octane and recovering the LPG yield, the catalyst spent from said first riser being mixed with the spent catalyst of said second riser before the rectifier, and then directed to the regenerator, from where the cycle begins again addressing said second riser.

Thus, the invention provides a process for maximizing middle distillates by fluid catalytic cracking of mixed loads using a dual-ridge system operating at different severities, where the second ridge acts as a catalyst cooler. The invention also provides a process for maximizing middle distillates by fluid catalytic cracking of mixed loads using a double riser system where the second riser is the origin of a decanted oil recycle or a light decanted oil fraction (HCO), aiming at increased fund conversion. The invention further provides a process for maximizing middle distillates by fluid catalytic cracking of mixed loads using a double riser system leading to high octane cracked naphtha. The invention also provides a process for maximizing middle distillates by fluid catalytic cracking of mixed loads using a double riser system, which leads to the production of light olefins. The invention also provides an apparatus consisting of two risers, each causing the load to be cracked to an independent separator, such separators being connected via a common rectifier to a regenerator for spent catalyst regeneration and cracking cycle restart.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying FIGURE 1 schematically illustrates a flowchart of the invention in which the separators communicate with each other and only one of them is connected to the regenerator. The accompanying FIGURE 2 schematically illustrates a flowchart of international publication WO 01/60951 using two risers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is therefore a process for maximizing middle distillates from mixed hydrocarbon fillers, while also producing high octane cracked naphtha and light olefins useful as petrochemical inputs, the process employing a technology. A / double cracking, where the severity conditions are different in each of the risers. The present invention provides solutions to a number of problems arising from low severity FCC operation.

According to the concept of the invention, low severity conditions mean reaction temperature in the range of 460 ° C to 520 ° C. This reaction temperature range when dealing with heavy loads, has the pronounced effect on grinding efficiency loss, having significant effects on the hydrocarbon dragging to the regenerator and, therefore, on its heating. This is associated with the low thermal demand for the riser, resulting in a catalyst / oil ratio in the range of 3.0 to 6.0, increasing the production of decanted oil, and cumulatively increasing the regenerator temperature.

Also according to the invention, high severity conditions mean reaction temperature in the range of 560 ° C to 620 ° C. Applied to light loads, with a low tendency to coke formation, it results in extremely high riser thermal demand caused by high endotherm cracking reactions resulting in very high catalyst / oil ratio in the range of 15 to 50 ° C, drastically reducing the temperature of the coke. regenerator.

When operating the FCC unit in low severity mode to allow for improved quality of the average distillate produced, low temperatures compared to traditional operation for maximum gasoline are used.

As a result yields of light products and gasoline are minimized. The lower reaction temperature contributes to lower grinding efficiency and the dragging of hydrocarbons to the Regenerator, which tends to overheat. This fact causes a decrease in circulation and an increase in the production of decanted oil. Another effect of medium operation is the increase of olefins and dienes in gasoline, which may lead to product stability problems.

In the invention, the first riser is low severity and the second riser high severity.

Thus, the present invention describes the use of a second riser in addition to the diesel riser for gasoline downtime, said second riser while simultaneously acting as a catalyst cooler, correcting the high temperature problem of the Regenerator, converting olefins and dienes in the range. gasoline while improving stability and octane and recovering LPG yield.

In the second riser, a decanted oil or light fraction (HCO) recycle is made to increase the conversion of funds. In order to favor the reduction of the dense phase temperature and to interrupt the secondary cracking reactions (hydrogen transfer), a low-severity riser coolant is injected in order to maintain the necessary circulation to the maximum cracking of the load with reduced increase of the load. aromaticity. The spent catalyst rectification step for the removal of residual hydrocarbons has a direct impact on reducing the dense phase temperature, increasing product recovery and causing greater catalyst circulation to the riser. As in medium operation the reduced riser temperature is observed a worsening in the rectification step.

However, in the present invention this problem is also overcome.

In the two-riser system, in the first riser the main load of the unit is fed, typically consisting of vacuum gas oil or atmospheric residue, but also including heavy hydrocarbons of the same distillation range from other refinery processes.

In the first ridge, the injection of a cooling current may optionally be used.

In the second riser is injected a light cracked naphtha recycling chain. Recycling cracked naphtha converts a substantial part of the olefins to lighter products, reversing the gasoline specification problems mentioned above and successfully recovering a significant portion of the C3-C4 olefin yields sacrificed by operation in the condition of minimizing aromatic content. at the LCO.

At the same time as the quality adjustment, the cracked naphtha recycle for the second riser acts as a catalyst cooler, acting correctly on the Regenerator overheating. Naphtha recycling requires a large amount of energy from the regenerator for vaporization and endothermic cracking reactions, which produce very little fuel coke for the regenerator. The balance of these two effects is a net energy withdrawal from the regenerator, with the consequent cooling of it.

To reduce the production of decanted oil, it is proposed to recycle or recycle an intermediate product with a 370-470 ° C (HCO-Heavy Cycle Oil) distillation range. This product should be inserted into the second riser (high severity or secondary riser2) at a height higher than the middle of it. The optimal injection point should be in the range H / 2 to H / 3, where H is the height of the riser. Regenerator cooling could be achieved by installing a catalyst chiller, however, the chiller would not solve the difficulty of rectifying the low temperature reaction products needed to achieve the desired quality LCO. The present invention also proposes a way to increase grinding efficiency even though the main riser is operating at low reaction temperatures. Increasing the grinding temperature is achieved by mixing the naphtha cracking riser 2 effluent catalyst with the heavy duty cracking riser 1 effluent catalyst, which is performed prior to feeding to the rectifier.

This temperature rise is possible for two reasons. First, the reaction temperature of riser 2 controlled at the end of the riser is significantly higher than that of riser 1 or of low severity. The second: the circulating catalyst mass in riser1 is equivalent to the circulating catalyst mass in riser 1. The following example is illustrative of this situation.

A typical naphtha yield to unit load of 30% by weight is allowed. This naphtha at a temperature in the range of 30 ° C to 50 ° C is fully recycled to riser 2 or high severity, whose reaction temperature is controlled in the range of 550 ° C to 620 ° C, preferably 580 ° C to 600 ° C. ° C by adjusting in the present example to 590 ° C.

In the riser 1, which processes the heavy load, the reaction temperature is controlled in the range of 460 ° C to 520 ° C, preferably 480 ° C to 500 ° C, in the present example setting 490 ° C. The regenerator bed temperature is preferably adjusted in the range of 685 ° C to 710 ° C by adequate load temperature control for riser 1 in the range 150 ° C to 300 ° C.

The respective thermal demands of risers 1 and 2 result in catalyst mass flow rates such that the circulation in riser 2 becomes equivalent to that of riser 1, although the riser 2 loading rate is one third of the riser 1 flow rate. The temperature of the catalyst in the rectifier is therefore close to 540 ° C typical of conventional operations, providing high efficiency grinding, eliminating the drawbacks of low severity grinding. catalytic cracking for maximizing middle distillates, obtaining high octane naphtha and obtaining light olefins. The invention comprises a second aspect with respect to the system of rissers, separators, rectifiers, regenerator and recycle lines for carrying out the process of the invention. The invention comprises a third aspect regarding the use of a low acid cracking catalyst and low hydrogen transfer, so that the aromatic content is as low as possible. The use of this type of catalyst allows good LCO selectivity with moderate catalyst / oil ratios of 6-7 without reducing the reaction temperature below 490 ° C. This aspect is essential for the processing of cargo with naphthenic-aromatic characteristics, as it avoids the excessive production of decanted oil even in the first riser. The C / O ratio in the first low severity riser is between 3.0 and 7.0, and in the second riser; high severity, between 15.0 and 50.0.

The payloads for the process include heavy loads such as vacuum heavy gas oil (GOPDD), or heavier than the previous one, from the bottom of atmospheric towers, called atmospheric residue (RAT), or mixtures thereof.

The products obtained are in the percentage of by weight, gas between 3 and 7, LPG 9 to 15, cracked naphtha between 15 and 23, average distillate between 37 and 45, LCO diluent between 4.5 and 7.5, oil decanted between 3.5 and 6.5 and coke, 7 to 10.

The properties of the products as naphtha and medium distillate comprise IC (cetane index) between 30 and 38 and MON between 82 and 85. The process for maximizing FCC middle distillates using the double riser system of the invention will be described hereinafter with respect to to Figure 1.

According to Figure 1, where numeral 100 generally represents the proposed system, a load 10 is injected into a low-severity first riser21, meeting the hot regenerated catalyst coming from regenerator 50 through duct 22. No riser 21 cracking reactions occur at temperatures between 460-520 ° C, typically 480-500 ° C, the catalyst / oil ratio being between 3.0 and 7.0, with hydrocarbon production lighter than the load: gasoline, LPG, gas and LCO. In the first riser2 \ it is possible to inject a cooling stream 25, which may be water or naphtha. The vapor product of the first riser21 is separated from the catalyst in vessel 30 and directed via transfer line 32 to the fractionating tower 60. The catalyst from vessel 30 is routed to rectifier 43 where it joins the second riser catalyst 23. A duct valve 44 prevents vapor product from second riser 23 from contaminating that of first riser 21.

In the fractionating tower 60, the vapor product is condensed and fractionated according to the hydrocarbon distillation ranges. At the top of tower 60 the most volatile products are removed via 61, which are separated into total gas 63 and light naphtha 64 at the top condenser 62 of tower 60. Light naphtha 64 is routed to the base of the second riser 23 where it continues to flow. react by removing heat from the system. Fractionating tower 60 also produces low-aromatic heavy naphtha 65 and LCO 66 which are sent to hydrotreating for incorporation into the diesel pool. HCO 67 is optionally withdrawn and routed to or in place of decanted oil 68 to an intermediate point of the second riser 23. The second riser 23 works at high severity at temperatures between 560-620 ° C, typically 580-600 ° C and oil catalyst ratio between 15.0 and 50.0, converting the bottom 60 heavy hydrocarbons shipped via line 67 and the light naphtha olefins shipped via line 64, which improves the quality of these hydrocarbons. The catalyst for the second riser 23 is fed from the regenerator 50 through the duct 24. The steam product of the second riser 23 is separated from the catalyst in vessel 40, following the transfer line 42 to the second fractionating tower 70 where the products are condensed and fractionated.

The light products are removed from the top of the fractionating tower 70 via the transfer line 71 to the top condenser 72. The noncondensed fraction of the light products (fuel gas and LPG) is removed via the transfer line 73 and the liquid fraction ( light naphtha) joins the heavy naphtha withdrawal line 74 and is then routed to the refinery's gasoline / well. In the lower regions of tower 70, high severity LCO streams 75 and decanted oil 76 are withdrawn, both of which are routed to fuel oil. The second riser catalyst 2Z, separated from the products in vessel 40, joins the first riser21 spent catalyst from vessel 30 and proceeds to rectifier 43. The mixture of the second riser23 warmer catalyst and the first riser colder 21 allows a higher average temperature to be reached, contributing to the good rectification of the latter. The average rectifier temperature is about 540 ° C, similar to the usual FCC processes, providing high efficiency rectification. The resulting coke-coated rectified catalyst is routed to regenerator 50 through duct 41. In regenerator 50 the coke is burned, cleaning the catalyst for a new cycle and generating most of the energy required by the process.

Pipelines 22, 24, 41 and 44 are fitted with (unnumbered) valves to prevent product contamination with one another. The low severity employed in riser 21 is a natural requirement of the midrange maximization process, with drawback being increased production of decanted oil (non-market fuel oil), low octane gasoline production and low stability , besides the low production of LPG. The reduction in gasoline production is assimilable considering the market trend towards dieselization.

Thus, the high severity riser 23 has four functions: transforming surplus recycled fuel oil and gasoline into light derivatives, mainly LPG, where propylene is a product of high value for petrochemicals; correct the unacceptable quality of gasoline produced in the low severity operation of the riser 21; allow operation of rectifier 43 at temperatures that ensure good efficiency, as discussed earlier in this report, through the high circulation defined by naphtha cracking; and adjust the thermal balance of the unit. The cracking of the decanted oil, current 68, tends to heat the regenerator, which is circumvented by the fourth function of riser 23 which allows the use of a catalyst cooler to be avoided, thanks to the high reaction endotherm of naphtha and its high vaporization heat. ensure a catalyst / oil ratio in the range of 15 to 50. The combined cracking of cracked naphtha and decanted oil or recycled HCO allows cracking to be carried out under favorable conditions for the decanted oil, as the catalyst that already has a small The amount of coke deposited reduces catalytic activity, minimizing the production of coke generated from the decanted oil.

Due to the energy demand generated by naphtha cracking, the high severity riser will have a high catalyst / oil ratio, which also favors the cracking of decanted oil, as well as reducing the dense phase temperature of the regenerator. And Figure 2 is a flowchart concerning the fractionation of reaction products obtained from the process object of WO 01/60951. This flow chart is not contained in said publication and is intended to illustrate emphatically some differences between said publication and the present application. The flowchart of Figure 2 comprises two towers. The first tower T1, a primary fractionator, receives the products of riser R1 which receives the load F from the unit. Said fractionator T1 produces only two streams B and C. The current B contains the LCO and lighter, and is sent to the second tower T2. Current C, heavier than LCO, is sent to riser R2. The second tower T2 is the main fractionator where all FCC currents are obtained.

The currents heavier than the LCO (> 370 ° C), HCO and sludge (the decanted oil is called sludge) from tower T2 are gathered together to form current E, sent to riser R2 where it comes into contact. elevation below current C. The current D resulting from the cracking of these heavy currents in riser R2 is mixed with current A from the top of tower T1, the junction of the two currents A and D constituting current G, fractionator load main T2.

In the configuration of this international publication, current D obtained from heavy load cracking in a second riser is mixed with current B, the unit's main product, obtained from unit load cracking and fed to the main fractionator. Stream D contains a low quality LCO due to the nature of the riser load R2 in which stream D is produced. The poor payload quality of the Riser R2 is evident from the fact that its two payloads C and E are recycled from cracked chains. Chain C can be said to be a heavy recycle, PIE 370 ° C, the result of cracking on riser R1. The current E also with PIE> 370 ° C, reflects in its composition the presence of the current D cracking fruit in risers R1 and R2, therefore extremely high aromaticity.

Thus, the alleged high yield of LCO is impaired in quality due to the non-segregation of current D from riser R2, which would require a third tower, increasing the complexity of the process. In any case, the inclusion of the third tower would improve product quality but, as mentioned, would reduce the alleged LCO yield. Already in the present order, with only two towers, 60 and 70 is obtained the segregation of the loads. The PIE products> 370 ° C obtained in the main fractionator 60 are sent to riser 23, in this case a high severity riser, since cracking naphtha also comes from said main fractionator, injected at a lower point. Secondary fractionator 70, smaller than the first, has the function of separating riser 23 products that are segregated and sent to tanks. The process of the invention will be illustrated below by an illustrative Example which is not to be construed as limiting.

EXAMPLE

Several runs were performed in laboratory FCC unit (ACE) with appropriate catalytic system (high matrix content) to simulate the process reaction system. The load used for the first riser, medium or low severity riser, was a 85/15 mixture of vacuum heavy diesel and coke diesel. The main properties of this load are as follows: API = 18.5, Basic nitrogen = 1338 ppm, Aniline point = 80, S = 0.65% weight. The reaction temperature adopted was 480 ° C and the catalyst / oil ratio ranged from 3 to 9 (severity).

In the second, high severity riser, a mixture containing 50% cracked naphtha and 50% decanted oil from a low severity FCC operation was used as a filler. The reaction temperature was 595 ° C for decanted oil and naphtha, with C / O ranging from 3 to 9. The overall yield profile is shown in Table 1 below.

Based on the results of the instrumental analysis, SFC and PIANIO, some properties of cracked naphtha and middle distillate were estimated.

Average distillate: cetane index (IC) 35, aromatic content 47% Naphtha: MON = 84.5, RON 92.5 and olefin content 19.7% As can be verified using the proposed process, It is possible to produce a medium distillate with low aromaticity compared to the aromatic content present in the LCOs from a conventional FCC operation (IC = 20).

In addition, high quality gasoline is produced, ie high octane and low olefin content, which provides good chemical stability. It is important to note that the yields of the other products are similar to the yields achieved in a conventional FCC unit, ie none of the problems inherent in a low severity operation, which would be low fund conversion, low yield of LPG and the production of unstable low-octane gasoline.

A second aspect of the invention is an apparatus composed of a riser system generally designated numeral 100 employed to carry out the process of the invention. Apparatus 100 comprises, as shown in Figure 1: a) a reaction section consisting of: i) a low-severity first ridge 21, where a load 10 is injected to undergo low-severity fluid catalytic cracking reactions, and a optional cooling stream 25, the upper end of said riser 21 being connected to a first separator 30, said first separator 30 being connected via a duct 44 to a second separator 40, while at the bottom of said separator 30 the spent catalyst is directed via duct 44 to separator 40 where it combines with the separate catalyst in said separator 40, the separated spent spent catalyst fraction being accumulated in the common rectifier 43 and thereafter directed via duct 41 34 to the catalyst coke firing regenerator 50; (ii) a second, high severity riser2Z, where a bottom stream 67 from the fractionating tower 60 is injected at H / 2 or H / 3 together with or in the place of the decanted oil stream 68 from the fractionating tower 60 and also being in the same riser 2Z the bottom light naphtha 64 of the top vessel 62, said riser 23 receiving catalyst from the regenerator 50 via the duct 24; b) a separation / purification section consisting of: i) a main fractionating tower 60 connected to the separator 30 to receive the separating products from said separator via the transfer line 32; ii) a top separator 62 connected to the fractionating tower 60 for receiving top products via transfer line 61 and releasing LPG and GC gases; iii) a grinding tower 70 connected to separator 40 for receiving top products via line 42 and releasing LCO via transfer line 75 and decanted oil via transfer line 76 at the bottom of said tower; iv) a top separator 72 connected to said tower 70 for receiving top products from said tower via transfer line 71 and releasing gases at the top via transfer line 73 while at the bottom of said separator is recovered naphtha via line 74 , which joins the naphtha stream also from the same tower 70; and wherein the operation of said system 100 allows: i) to produce average distillate in proportion above 37 wt% relative to the load with reduced density and aromaticity compared to the conventional FCC process from cracking refractory heavy loads; (ii) cooling the catalyst by recycling cracked naphtha 64 to the second riser 23, caused by the energy demand of said regenerator 43 for naphtha vaporization and endothermic cracking reactions, acting correctly on the overheating of the naphtha. regenerator 60; iii) reduce the production of decanted oil by directing a recycle of an intermediate 67 or a light fraction thereof with a 370-470 ° C (HCO-Heavy Cycle Oil) distillation range, said product being introduced into the second riser 23 at a higher height in the range H / 2 to H / 3; iv) increasing the rectification efficiency by heating of rectifier 43 with the catalyst from the high severity riserlZ, which allows the reduction of the dense phase temperature; v) reduce fuel oil (decanted oil) production as a consequence of decanting decanted oil along with naphtha in a high severity riser 23.

Claims (10)

A process for maximizing FCC middle distillates by cracking in the absence of added hydrogen, said process comprising the steps of: a) directing a charge 10 to a low-severity first riser 21, wherein said charge enters contact with the hot regenerated catalyst from regenerator 50 through duct 22; b) in riser 21, cracking said load 10 at temperatures between 460-520 ° C, the catalyst / oil ratio being between 3.0 and 7.0, producing lighter hydrocarbons; c) separating the first riser vapor product 21 from the catalyst into a vessel 30 and directing the product thus separated via the transfer line 32 to the fractionating tower 60, while the catalyst from the vessel 30 is routed to the rectifier 43 where it joins the second riser catalyst 23; d) condensing and fractionating the vapor product in the fractionating tower 60, removing from the top the most volatile products via line 61, said products being separated into total gas 63 and light naphtha 64 in the top condenser 62 of tower 60; e) directing light naphtha 64 to the base of a second riser 23 where it continues to react by removing heat from the system; f) converting, in a second high severity riser 23, said riser acting simultaneously as a catalyst cooler and operating at temperatures between 550-620 ° C and with an oil catalyst ratio between 15.0 and 50.0, the bottom heavy hydrocarbons. 60 units sent via HCO stream 67 along or in place of decanted oil, stream 68, streams 67 and 68 being injected into riser 23 H / 2 or H / 3, and light naphtha olefins, stream 64, the conversion reaction being performed in the presence of catalyst fed from regenerator 50 through duct 24; g) separating the vapor product from said riser 23 from the catalyst in vessel 40, following the transfer line 42 to the second fractionating tower 70 where the products are condensed and fractionated; h) remove light products from top of fractionator tower 70 via transfer line 71 to top condenser 72, removing non-condensed fraction of light products, fuel gas and LPG via transfer line 73 and liquid fraction of light naphtha attached to heavy naphtha withdrawal line 74 being routed to the refinery's gas pool, while at the bottom of tower 70, high severity LCO streams 75 and decanted oil 76 are routed to fuel oil; i) separating spent catalyst from second riser 23 from products in vessel 40, combining said spent catalyst with spent catalyst from first riser 21 from vessel 30 and directing the mixture to rectifier 43 resulting in an average rectification temperature of about 540 °. Ç; j) routing via the duct 41 the rectified and coke-coated catalyst resulting from the process to the regenerator 50 where the coke is burned, cleaning the catalyst and generating most of the energy required by the process; Process according to claim 1, characterized in that the charge 10 comprises vacuum heavy gas oil (GOPDD), atmospheric residue (RAT), heavy hydrocarbons of the same distillation range from other refinery processes or mixtures of these streams in any proportion. Process according to Claim 1, characterized in that the temperature in riser 21 is preferably between 480 and 500 ° C. Process according to Claim 1, characterized in that the temperature in riser 23 is preferably between 580 and 600 ° C. Process according to Claim 1, characterized in that the light products resulting from riser cracking 21 include gasoline, LPG, gas and LCO. Process according to Claim 1, characterized in that, alternatively, the first riser 21 is injected with a cooling stream 25 of water or naphtha. Process according to Claim 1, characterized in that the fractionator tower 60 additionally produces heavy naphtha 65 and low aromatic LCO 66, both of which are hydrotreated for incorporation into the diesel pool. Process according to Claim 1, characterized in that the ducts 22, 24, 41 and 44 are provided with valves to prevent product contamination with one another. Process according to Claim 1, characterized in that the catalyst used is a catalyst having low hydrogen transfer. Apparatus for carrying out the process according to claim 1, characterized in that it comprises: a) a reaction section consisting of: i) a first low severity riser 21, where a load 10 is injected to undergo catalytic cracking reactions low severity fluid, and an optional cooling stream 25, the upper end of said riser 21 being connected to a first separator 30, said first separator 30 being connected via a duct 44 to a second separator 40, while at the bottom of said separator 30 the spent catalyst is directed via the duct 44 to the separator 40 where it combines with the separate catalyst in said separator 40, the combined fraction of the spent spent catalyst being accumulated in the common rectifier 43 and thence directed via the duct 41 to the regenerator 50 to catalyst coke firing; ii) a high-severity second riser 23, where a bottom stream 67 from the fractionating tower 60 is injected at H / 2 or H / 3, either in or in place of the decanted oil stream 68 and the bottom light naphtha 64 is depleted. top vessel 62, said riser 23 receiving catalyst from regenerator 50 via duct 24; b) a separation / purification section consisting of: iii) a main fractionating tower 60 connected to separator 30 for receiving the separating products from said separator via transfer line 32; iv) a top separator 62 connected to the fractionating tower 60 for receiving top products via transfer line 61e releasing LPG and GC gases; v) a grinding tower 70 connected to separator 40 for receiving the top products via line 42 and releasing LCO via transfer line 75 and decanted oil via transfer line 76 at the bottom of said tower; vi) a top separator 72 connected to said tower 70 for receiving top products from said tower via transfer line 71 and releasing gases at the top via transfer line 73 while at the bottom of said separator is recovered naphtha via line 74 , which joins the naphtha stream also from the same tower 70;