DE3904435C2 - Process for the catalytic cracking of a hydrocarbon batch in a fluidized bed - Google Patents

Description

The invention relates to a method for cracking a swiss ren hydrocarbon batch in the fluidized bed according to the Oberbe handle of claim 1.

As is well known, the petroleum industry usually uses crackers start off in which hydrocarbon molecules with high moles molecular weight and increased boiling point in smaller molecules with lower boiling point that is appropriate for the sought Use are to be split.

One of the most common procedures at the moment is, for example so-called catalytic cracking in a fluidized bed (also called FCC). This type of process uses the hydrocarbon batch by contacting at high temperature with a cracking catalyst evaporated in the vapors of the batch in suspension is held. After cracking the desired mole has reached the specific weight range, with appropriate absences kung boiling points, the catalyst is obtained from the Products separated, stripped, in one or more stages regenerated by burning the coke formed and then brought back into contact with the batch to be cracked.

The batches to be cracked are usually added to the reaction zone introduced at a temperature which, depending on the starting dimension material generally between 75 ° C and 450 ° C under a re latent pressure of, for example, 0.7 to 3.5 bar, wäh rend the temperature of the regenerated catalyst, which in this zone reaches, in the order of 600 ° C to 950 ° C can be.

The catalyst is either on the foot or on the head of one in the introduced essentially vertical tubular zone which serves as a reaction zone. The catalyst granules are then This means that the pipe can be moved upwards or downwards that a gaseous or ver  vaporisable fluid is blown in. This blowing in or on pressing takes place by means of a suitable fluid distributor. The batch to be cracked is introduced downstream and so completely as possible with the help of a suitable device evaporated in the suspension of catalyst granules.

At the end of the tube, a chamber is formed in which one the separation of the cracked batch from the catalyst grains and on the other hand stripping the deactivated kata lysator expires through the separation of hydrocarbons. The outflow is from the Ka entrained by the gas stream Talysator cleaned in a cyclone system.

With newer FCC processes, two regeneration zones can be used, through which the used catalyst circulates. In this regenerator, the coke separated on the catalyst particles is partially burned with the help of air; this combustion step leads to the generation of CO and CO ₂ . The combustion gas is cleaned of all the catalyst entrained by the gas flow in cyclones and treated separately to recover any possible energy.

The particles of the catalyst which have undergone a first regeneration partial treatment are then transferred to a second stage of the regenerator which is different from the first. The total combustion of the remaining coke is carried out in the form of CO ₂ by means of excess air in this regenerator. The entrained catalyst is separated from the combustion gases by cyclones which are arranged outside of this generator, for example.

In the foregoing context, U.S. Patent 4,414,101 describes a method and apparatus for regulating the intensity of catalytic conversion of hydrocarbons in a transmission line conversion system using a catalyst. The described method essentially has the features according to the preamble of claim 1. The US-PS 4,332,674 describes a regeneration method for a conversion catalyst for hydrocarbons. Here, a CO-rich exhaust gas is obtained from a regeneration stage with a low temperature and a CO ₂ -rich exhaust gas from a regeneration stage with a high temperature.

Suitable hydrocarbon batches boil between 200 ° C and 550 ° C or more; their density can be between 10 and 35 ° API va riieren; but you can also contain heavy hydrocarbons Use batches with a boiling point of up to 750 ° C and more can go and their density between 10 and 35 ° API or also can vary between 0 and 25 ° API.

For example, the following can be mentioned as batches: vacuum gas oils, heavy oils, such as raw and / or stabilized Oils and residues from atmospheric distillation or Vacuum distillation; these batches can, if necessary previous treatment, for example a so-called hydrotreatment in the presence of cobalt-molybdenum or nickel-molybdenum type catalysts and / or have undergone deasphalting.

The batches according to the invention are those which are fractions contain, which usually boil up to 750 ° C or more and which contain increased proportions of asphaltenic products can and contain Conradson carbon that can go up to 10% and above. These batches can if necessary, be diluted by lighter usual cuts, which can include hydrocarbon cuts that be have already experienced the cracking process and how, for example as the heavy cycle oils (H.C.O.), in Cycle.

The crystalline aluminosilicates can be in the natural Condition or can be synthetically known per se process. They can be chosen from the synthetic zeolites or the clays, such as Fau jasite, certain mordenites, the montmorillonite, the bridge  forming clays, the aluminophosphates or the like Offretites, the A, L, Y, X, omegazeolites, the erionites Etc.

The invention relates to an improvement in the separation zone for catalytic particles and their cracking effluents, d. H. a ver improvement of the stripping zone (or "stripping"). These improvements tion enables the performance of the process to be increased catalytic cracking of heavy hydrocarbons in Fluidized bed. In the prior art, the used from the actual cracking stage emerging catalyst from the adsor Free hydrocarbons and in the inter and in traparticular space through countercurrent contact in the dense vortex bed with a strip essentially containing water vapor entrained pergas, such as in EP-A-191695 be wrote. You can also use nitrogen, for example, Use flue gases or gaseous hydrocarbons. Erfin According to the invention, this is generally at the bottom of the stripper zone injected stripper gas a mixture of water vapor and moles molecular oxygen (e.g. pure oxygen). The way separate (or stripped) catalyst then becomes active generation zone (s) according to known techniques sends (see for example EP-A-191695). One has invented In accordance with the invention found that the addition of oxygen (before preferably pure oxygen and water vapor) to the stripping gas, a little expensive investment, it enabled the Ver Increase the burning capacity of the coke on the kataly table particles is deposited by more effectively the adsorbed hydrocarbons are desorbed without disrupt fluidization in the stripper zone. Predicted sets, one chooses the contents of oxygen in carefully controlling way, on the one hand you can see the lack of acid determine the substance in the gases emerging from the stripper, even if you have a relatively large amount of oxygen, the added in the stripper gases, used, and others the disappearance of hydrogen, methane and higher Hydrocarbons in the flue gases from the regenerator  put. Improving the desorption on the catalyst adsorbed hydrocarbons can be realized among the usual conditions of catalytic cracking processes. The effect of this oxygen addition becomes noticeable as soon as the Addition 1 vol .-% of the total oxygen (expressed as moleku larer oxygen), which in the unit (a closed regeneration zone (s)). The upper Limit of the use of oxygen is set by the Considerable and disruptive oxygen levels in the Reaction products. Appropriately you arrange in the device an oxygen probe adjacent to the bed surface or in Fluidized bed in the stripper zone. This upper one The limit is at 50 vol.% Total oxygen (excl presses as molecular oxygen), which ver in the unit is needed. They are preferably located in the stripper zone performed proportions of oxygen between 10 and 22%, based on the whole in the cracking unit (included rain rationszone (n)) of oxygen consumed. The volume ratio from stripper gas to additional oxygen (expressed as oxygen) is between 1 and 31 and preferably between 2 and 18. The oxygen introduced as an additional gas lies not too high in terms of its salary and does not appear in the stripped gases. This oxygen is calling actually start a burn of heavy and at what Hydrogen hydrocarbons, which are associated with the coke are deposited on the catalytic particles, and leads thus essentially to carbon dioxide gas and water. About that in addition, the oxygen transfers heat to the stripper zone and the floor temperature of this zone can be between 480 ° C to Bring 600 ° C. This results in the catalyst being heated, thereby possibly and preferably making it possible for the Temperature of the regenerator or the first regenerator to lower, which is penetrated by the considered catalyst, if there are several regeneration zones.  

The stripper zone preferably operates in the form of a dense fluidized bed, if desired using a gas / solid countercurrent. According to a particular embodiment, the stripper zone can be formed on the side of the tubular reaction zone (as in FIG. 3) and not concentrically to this zone, as in FIGS. 1 and 2.

When working in accordance with the invention, the yield of high-quality products: C ₃ -C ₄ , gasoline, LICO (light cycle oil) can be improved, as the example below shows. In addition, the process makes it possible, on the one hand, to increase the treatment capacity thanks to a reduction in the production of dry gases (H ₂ , N ₂ , CO, CO ₂ , C _2- ) and, in particular, to reduce the blower air requirement, and on the other hand to offer heavier and treat more contaminated batches thanks to a possible reduction in regeneration temperatures.

The process also enables the hydrothermal Stability of the catalyst due to the reduction in Temperature and water content of the regeneration flue gases to improve.

It has been found that the beneficial effects of Realization of the invention the more in the Foreground as low as the strength of cracking lies (maximum run LCO) and that the hydrogen content of the hydrocarbons deposited with the coke is high (Paraffin batches).

For example, embodiments of the invention will now be explained in more detail with reference to the accompanying drawings, in which FIGS. 1 to 4 represent four types of apparatus, for example.

According to a first embodiment, a catalytic cracking device is shown in FIG. 1. It essentially comprises a column 1 , the so-called batch elevator or "riser", which is fed at its base via line 2 with granules of regenerated catalyst in a certain amount by opening or closing a valve 3 . The temperature and the density of the grains of this regenerated catalyst are made homogeneous in that a first gaseous fluid supplied via line 4 is pressed in or pressed in at the foot of the riser with the aid of a first diffuser 5 . The catalyst which has been reinserted in this way and kept in a dense and homogeneous fluidized bed phase is then accelerated in a homogeneous manner in the "riser" by new introduction or pressing in with the aid of a second diffuser 8 which is located in the "riser" above the feed line for regenerated catalyst. This process is supported by a second gaseous fluid, which may be the same as the previous one and is supplied via line 7 . The batch to be cracked is then introduced into the riser with the aid of one or more injectors 6 .

The column 1 opens at the top into a chamber 9 , which in turn is concentric, for example, in which, on the one hand, the cracked batch is separated and, on the other hand, the deactivated catalyst is stripped. The treated batch is separated in a cyclone system 10 , which is stored in a chamber 9 , at the head of which a discharge line 11 is provided for the cracked batch, while the particles of the deactivated catalyst at the foot of the chamber 9 are injected or reinjected. The lines 32 and 12 feed with stripping gas, generally water vapor, diffusers 13 , which are regularly arranged at the foot of the chamber 9 . Additional oxygen, preferably pure oxygen, is here added to the stripping gas via line 31 . A probe 26 makes it possible to measure the presence of oxygen in the gases emerging from the stripper zone. There are also analysis systems 37 and throughput measurement systems 36 for the oxygen in question. Additional oxygen can also be introduced either via another line, not shown in the figure, independently of the lines 32 and 12, or via a line 31 and an independent line, or via an equivalent method.

The particles of the deactivated oxygen stripped in this way are drawn off at the foot of the chamber 9 to a regenerator 14 by means of a line 15 to which a control valve 16 is attached. In the regenerator 14 , the coke deposited on the particles of the catalyst is burned with the aid of air which was blown in at the base of the regenerator via a line 38 which feeds regularly distributed diffusers 17 . The particles of the treated catalyst and the combustion gas are separated in cyclones 18 , from where the combustion gas is drawn off in a line 19 , while the granules of regenerated catalyst are sent back to the base of the regenerator, from where they are sent via line 2 , which is connected to a control valve 3 can be recycled to feed the elevator or "riser".

Fig. 2 shows another catalytic cracking arrangement which is equipped with the stripper system according to the invention and in which a two-stage regeneration chamber is used.

In this figure, the organs already described with reference to FIG. 1 have been given the same reference numerals. The regenerator y is of the type with an increasing current and comprises two stages 14 and 20 .

After the deactivated catalyst has undergone stripping in the chamber 9 , it is led via line 15 to the lower stage 14 of the regenerator.

At the bottom, the first combustion stage is supplied with air via line 16 ; Air is distributed via regularly spaced diffusers 17 . In this stage, cyclones 18 separate the combustion gas withdrawn via line 19 from the partially regenerated catalyst particles.

The catalyst particles, which have undergone a first partial regeneration treatment, are then transported to the second floor 20 of the regenerator via the central line 21 using a so-called airlift.

Stage 20 is again fed with air via line 22 and injectors 23 . The particles of the regenerated catalyst are drawn off laterally to a buffer chamber 24 and are recirculated via line 2 to feed the elevator. The combustion gases drawn off at the upper part of stage 20 are treated in at least one outer cyclone system 25 , which is thus able to be completely resistant to elevated temperatures which result from complete combustion of the coke and at the foot of which the particles of the catalyst pass line 39 is returned to stage 20 while the combustion gases are withdrawn via line 27 .

This catalytic cracking arrangement, equipped with a two-stage regenerator with rising current and an injection device according to the invention, has the following advantages:

• - Double regeneration of the catalyst, the one integral combustion of the coke without changing the allows catalytic properties,
• - no limit on the temperature of the second Regenerator, which allows the catalyst that required temperature to evaporate the batch achieve, especially if the latter is a heavy batch
• - Improve thermal stability and Resistance of the catalyst to metals.

In the case of the embodiment of the

Fig.

3 and 4 according to the invention comprise these two characteristics

• - On the one hand, the stripper zone is designed such that it is not in the upper or lower part of the reaction tube. FIGS. 3 and 4 explain such a design, where the stripping zone is located laterally next to the tube.
• - And on the other hand, the stripping gas, essentially at Blown or inserted bottom of the stripper zone Mixture of a gas (generally water vapor) as well molecular oxygen (e.g. pure Oxygen).

The catalyst separated or stripped in this way then becomes sent to the regeneration zone (s).

Fig. 3 is thus a variant of a catalytic cracking, which is carried out in an elevator tube or "riser" 1, which carries a batch from bottom to top, which arrives via line 6, is injected or injected via line 35 in a mixture with atomizing water vapor is fed via line 7 and on the other hand of catalyst particles derived via line 2 from a regeneration zone 20th A simple modification of tube 1 would allow the mixture of charge and catalyst particles to be guided from top to bottom (“dropper”).

The reaction effluent is separated from the catalyst in the stripper zone 9 . The effluent is recovered via line 11 and distilled in a column 27 in order to obtain several adequate sections, which are summarized schematically in the form of lines 28 and 29 .

The stripping gas originating from the lines 32 and 12 is introduced via the diffusers of the injection system 13 . Additional oxygen is added to the stripping gas via line 31 . A probe 26 makes it possible to determine the presence of oxygen in the gases in the stripper zone. There are also locations for analysis 37 and throughput 36 of the oxygen in question. The deactivated catalyst flows via line 15 against a first regeneration zone 14 , which is fed with oxygen via lines 30 and 16 (with valve 33 ). The flue gases are withdrawn via line 19 and the partially regenerated catalyst flows via line 21 to a second regenerator 20 which is fed with oxygen via lines 30 and 22 (with valve 34 ). The flue gases are withdrawn from the second regenerator via line 40 , while the regenerated catalyst is returned via line 2 to the "riser" or dropper 1 .

According to FIG. 4, the stripper zone is also, as in FIG. 3, on the side of the tubular reaction zone (and not concentric to this zone, as in FIGS. 1 and 2).

FIG. 4 describes a catalytic cracking which is carried out in an elevator or "riser" 1 , which on the one hand carries a batch from bottom to top which arrives via line 6 and generally via line 35 in a mixture with atomizing steam (and / or an elevator gas, the so-called gas lift), which was fed in via line 7 (with control devices 8 and 9 ) and on the other hand carries catalyst particles which come from line 2 of a regeneration zone 20 . A simple modification of the tube 1 enables the mixture of charge and catalyst particles to be guided from top to bottom (“dropper”).

In the upper part 4 of the elevator 1 , a device 5 , generally called a "T" device, makes it possible to send the reaction effluent and the catalyst into a cyclone 3 , where on the one hand the reaction effluent (collected via line 11 ) and the catalytic particles are collected, which is withdrawn from the cyclone 3 via the line 8 . The catalytic particles are sent to the stripper zone 22 . The axis of this zone 22 differs from the axis of the tube, which means that the stripper zone is not arranged concentrically to the tube but on the side of the reaction tube.

The reaction effluent, separated from the catalyst, is thus recovered via line 11 and distilled with the aim of obtaining several adequate cuts.

At least part of the effluent or one of these cuts can preferably be recirculated into the reaction tube via line 10 .

The stripping gas coming from lines 32 and 12 is introduced via the diffusers of injector system 13 . Additional oxygen is added to the stripping gas via line 31 . A probe 26 makes it possible to determine the presence of oxygen in the gases in the stripper zone. There are also points for analysis 37 and throughput 36 , 29 , 34 , 28 of the oxygen used. The stripping gases are withdrawn into line 18 , flow through cyclone 41 and are withdrawn via line 20 . The fine catalyst particles are sent back to zone 22 via line 21 . The deactivated catalyst flows via line 15 provided with valve 16 against at least one regeneration zone 20 which is fed with oxygen via lines 30 and 38 (with valve 33 ), the oxygen or the gas containing oxygen being introduced into the catalyst bed via the distributors as 13 and 14 occurs. The flue gases are drawn off via line 19 through cyclones which are provided with the reference numerals 23 , 24 and 25, for example; the regenerated catalyst flows via the line 2 provided with valve 27 to the "riser" or "dropper" 1. This figure shows only a single regenerator. Very often, however, two regenerators are provided.

For the four methods generally and illustratively described in Figures 1 and 4, the dimensional and operational characteristics (industrial scale) can usually be as follows:

• - Height of the rising column or the down column ("riser" or "dropper"): 5 to 40 meters,
• - temperature of the batch to be cracked: 75 to 450 ° C,
• - Feed throughput of the column of catalyst: 3 to 50 Tons per minute,
• - Dwell time of the batch in the column: 0.05 to 10 Seconds,  
• - Regeneration temperature of the catalyst: 600 to 900 ° C even up to 950 ° C if there are two regeneration zones acts,
• - Dwell time of the catalyst in the regenerator 9 : 5 to 20 minutes.

To ensure a uniform distribution of the atomized batch in to ensure the reaction zone is preferably used several injectors distributed over the circumference of the reactor.

The injected or injected into the reaction zone atomized batch can be introduced at a rate be between 10 and 600 m / s and preferably between 50 and 200 m / s can vary. To achieve this, you can the atomization and pressing in advantageously Use an auxiliary fluid, which is Water vapor or gaseous fluids can act that relatively rich in hydrogen or containing hydrogen Connections from other units of the refinery stem from, are.

The required amount of auxiliary fluid may preferably be used between 0.5 and 20 wt .-%, based on the weight of the cracking batch.

The temperature of the batch to be cracked at its Introduction to the reaction zone can be between 80 and 400 ° C or vary 75 and 450 ° C according to the batches.

The stream of catalyst granules into which the batch is injected is generally a homogeneous stream of catalyst in a dilute fluidized batch, ie with a density which is generally between 15 and 700 kg / m ³ . The linear velocity of this stream is preferably between 0.01 m / s and 10 m / s.

The stream of catalyst granules is preferably with Realized with the help of an auxiliary fluid Hydrocarbons that are five or less than five Have carbon atoms or mixtures thereof, can exist. This current can be a Have a hydrogen concentration that goes up to 35 vol%, while blowing or injecting water vapor can take place up to 10 wt .-%, based on the batch, can be achieved.

The flow of catalyst granules can be at one temperature between 550 and 750 ° C if the too cracking batch is of the usual type, for example a Batch of gas oil. With so-called heavy batches, however, that completely are useful in the method according to the invention, d. H. Batches containing more than 10% by volume Hydrocarbon compounds with a higher boiling point than 550 ° C, the temperature may be preferable between 650 and 950 ° C such that the complete Evaporation of the heavier molecules as well as their selective ones thermal cracking in the injection zone to the reactor is ensured.

The from the mixture of the catalyst stream with the atomized batch resulting equilibrium temperature can be selected by choosing a suitable temperature injected batch or by any other means be sure to make it the subsequent catalytic Allow response under optimal Expire temperature conditions, which in general between 450 and 550 ° C depending on the case.

An increased temperature of the catalyst stream can namely preferably take place with the aid of a double regeneration system, as shown in FIGS. 2 and 3. The following example explains the invention without limiting it:
The batch is an atmospheric residue (résidumosphérique) from the North Sea of the following composition and characteristics:

In order to clarify the importance of adding oxygen to the stripping gas, a device according to FIG. 2 of the "pilot type" was used, ie one with reduced dimensions. In all experiments, the batch throughput was kept constant at 22 liters per hour (528 liters per day) or 20.5 kg / hour. The amount of steam used to atomize and dilute the batch is 1 kg / hour (55.5 moles / hour). The catalyst throughput is 105 kg / hour (1.75 kg / minute). The temperature at the top of the "riser" is maintained at 515 ° C in all experiments by acting on the preheat temperature of the batch to compensate for the changes in the return temperature of the regenerated catalyst. The only table lists the other working conditions, in particular the amount of pure oxygen added to the stripper steam. In the stripper zone, the amounts of water vapor and oxygen are selected such that the stripping takes place in the dense fluidization zone formed in the stripper zone. The stripping steam throughput is set to 1 kg / hour (55.5 mol / hour) for all tests. The heat balance of the installation sets itself automatically, since the design compensates for the heat losses of each of the pilot facility elements.

The different results and analyzes of the outflows are also included in the only table below for different amounts of oxygen entering the stripper gas be given listed. The entirety of this Results enables a material balance to be drawn up which is representative of that of an industrial plant, including the amount and elemental analysis of the coke, the one from the stripper zone to the one or more regenerators was transported.

An analysis of the table gives rise to the following comments:
The influence of the introduction of oxygen at the bottom of the stripper zone leads to operational improvements of the unit which are much higher than those foreseen by the expert:

• 1. Introducing oxygen, even at relatively low flow rates, negates the emission of hydrogen and hydrocarbons in the flue gas from the first regenerator.
  • Without oxygen (experiment no. 1), about 1% hydrogen, 0.9% methane and 0.4% of C ₂ - or higher hydrocarbons are measured.
  • - With oxygen, only negligible traces of such products are found.
• 2. The introduction of oxygen leads to a clear reduction in the throughput of dry gases (C _2- ) despite the increasing production of CO-CO ₂ . This result is contrary to what was foreseen.
• 3. The conversion, expressed conventionally as the sum of the yields of gas, petrol and coke, drops slightly (up to 1.1% in experiment No. 4), is compensated for by the production of liquids with a high economic value (C ₃ - C ₄ , gasoline, LCO), which increases considerably (about 2.2% in experiment no. 3).
• 4. The net production of coke and its hydrogen content decrease strongly (30 to 35% according to the experiments 2 to 4).
• 5. The temperatures in the regenerators drop what a favorable increase in the preheating temperature of the batch brings or, more desirably, an increase the catalyst circulation.
• 6. The air requirement for the regeneration of the catalyst drops proportionally with the proportion of coke formed. The total consumption of oxygen (O ₂ pure + air) was calculated for each experiment. It is surprising to find that this need drops by about 15%, although the cracking conditions remain unchanged.
• 7. During these four experiments, the measurement of the oxygen content on the surface of the catalyst bed in the stripping zone led to values of zero (less than the detection limit, ie less than 0.1%). Complementary experiments were carried out in order to fix zone 1 a at about 1000 l / h, where noticeable oxygen occurs in the reaction products.

In summary: the above experiments show that the Improve the desorption of the adsorbed Hydrocarbons on the catalyst were realizable under Process conditions of catalytic cracking thanks to a Addition of preferably pure oxygen to the stripping steam.

The result of this addition becomes industrially useful as soon as this addition 1% of consumed in the unit Total oxygen exceeds.

As previously stated, the upper consumption limit determined by the appearance of noticeable levels Oxygen in the reaction products. Arranging one Oxygen lance on the surface of the bed or in the So catalyst bed is recommended to top this To demonstrate the limit that applies to those in the examples pilot installation used on about 50% of the total used oxygen.

The main beneficial effects of adding oxygen are as follows:

• - Improve the yield of high quality products (C ₃ -C ₄ , gasoline, LCO).
• - Increase in treatment capacity thanks to a decrease in Production of dry gases and a lowering of the Air requirement.  
• - Possibility of heavier or more dirty batches thanks to a reduction in regeneration temperatures to treat.
• - Improvement of the hydrothermal stability of the catalyst by lowering the temperatures and the water content of the regeneration flue gases.

Claims (3)

1. Process for catalytic cracking of a heavy charge of hydrocarbon in a fluidized bed according to FCC methods known per se, the heavy batches up to 750 ° C. and higher-boiling fractions or more than 10% of their volume of hydrocarbon compounds with a boiling point higher than 55 ° C contain the process, a contacting zone with ascending current in a column under cracking conditions of the batch and of particles of a cracking catalyst, and a separation zone for the deactivated catalyst and the cracked batch behind the introduction zone for this batch, at least one stripping zone for the deactivated catalyst With the aid of a stripping gas and then a catalyst regeneration zone and combustion conditions of the coke deposited on the catalyst and finally a recycling zone of the regenerated catalyst for feeding the column, characterized in that

• a) optionally introducing a molecular oxygen containing additive gas separately with or to the stripping gases, the oxygen content being between 1 and 50%, based on the total oxygen consumed in the cracking process,
• b) the ratio of stripping gas to oxygen used in the make-up gas is between 1 and 31% by volume and
• c) the stripping gas is water vapor.

2. The method according to claim 1, characterized in that the Additional gas is pure oxygen.   3. The method according to any one of claims 1 to 2, characterized shows that the stripper zone works in a dense fluidized bed.