JPS6018814B2 - Improved method for recovering power from regeneration gas under turndown conditions - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regenerating spent catalyst from a fluid catalytic cracking unit (FCCU).

In particular, the present invention relates to a method for recovering power from the thermal regeneration gas recovered in such a regeneration process. In a typical FCCU, spent catalyst is continuously removed from the reactor, sent to a regenerator, and then recycled to the reactor.

In the regenerator, the dirty catalyst is contacted with an oxidizing regeneration gas at high temperature and pressure, and the catalyst is combusted of coke or other carbonaceous deposits. Combustion of such carbonaceous deposits can be accomplished in a fluidized chamber containing solid catalyst particles. Through the fluidization chamber, a fluidizing gas passes upwardly at a rate that maintains the solid particles in a fluidized bed.
The fluidized bed contains a perceptible relatively upper level and is a turbulent state of quasi-liquid nature. The fluidized catalyst forms a flow with a dilute layer at the bottom and a dilute layer at the top. Typically, the fluidizing gas is or at least includes an oxidizing regeneration gas. Combustion or regeneration gas is typically produced by combustion of carbonaceous deposits at high temperature and pressure. For example, if the regeneration gas is 537.800 (10000F) or more, 815.
It is not uncommon for the gas to have temperatures as high as 0 (15,000 F) or even higher. On the other hand, the pressure is 0.7
0k9/ground (1 Cape sig) to 2.5kg/(35p
sig) and above. This gas, commonly called flue gas, leaving the regeneration zone thus represents a large potential energy, which is used in the system to compress the air used as the oxidizing regeneration gas. Used to compensate for part of the power. If sufficient energy is released in the regeneration process and the energy is properly recovered, there will be a net gain in regeneration, thus:
Excess energy can be combined to generate power or electricity for use in other operations.

It is common to use an expansion turbine or turboexpander to recover energy from the hot Katsuodo gas from the regenerator. Typically, the high temperature and pressure gas is passed through an expansion turbine.
Here, the gas provides shaft power to an air compressor, which produces compressed air for the regeneration process. The excess power of the air compressor is used to drive a motor generator suitable for generating electricity.
Recently, fluidized catalytic cracking catalysts have been introduced which cause the carbonaceous material on the spent catalyst to be combusted almost entirely into carbon gas in the dense steel bed of the regenerator, with little carbon monoxide being produced.

The use of this type of catalyst is highly desirable since it does not cause undesirable "after-combustion" in the lean zone of the regenerator. "After-combustion" is a condition caused by the presence of regeneration gas and carbon monoxide in the lean layer. Additionally, all combustion heat associated with the use of these catalysts is either completely lost or not used externally in the generator of the carbon monoxide boiler (Fluid Catalytic Cracking (hereinafter referred to as FCC)). ) is used within the system. The latter method is disclosed in US Pat. Nos. 3,1371 and 3,139,726. The use of a complete combustion catalyst that can increase and recover the heat of combustion allows the dense steel beds in the regeneration zone to operate at relatively high temperatures, allows the employment of relatively low catalyst-to-oil ratios in the cracking zone, and It therefore improves yield. As mentioned above, the hot flue gas from the regeneration zone is used for expansion to recover energy from the flue gas. Turbine-conf. It is passed through the Lesser Set Extract/Gunjon Turbine expander and expanded. Although centrifugal flow compressors or turbo blowers could alternatively be used in such power recovery sets, the Fuji Air compressor offers certain advantages due to its high efficiency and high capacity. However, the use of axial compressors in such systems is clearly problematic. The spiral compressor has relatively steep performance characteristics (ephead-Capacity-ch in S).
aracteristics), the pumping point (pmmplngpoint) described below is
The flow rate can be reduced to within 10% to 30% of the design flow rate (DESI flow).

The characteristics of this bag flow compressor are surging (smg)
ng) or pumping (p mountain mpjng). For example, unless a free-flow compressor is operated under conditions that require it to compress more air than is needed on the discharge side, the compressor will begin to surge. Fujiryu blower (axial blo
There is a minimum capacity (capacity) below which operation becomes unstable, for example, surging occurs. Surging occurs when the pressure in the discharge line of the compressor exceeds the discharge pressure that the machine can produce.
Since the compressed gas cannot enter the outlet or exhaust line, it gives a back shock wave to the compressor.
This momentarily lowers the pressure in the outlet line and the compressor begins discharging into the outlet line again. However, this pressure will soon become so high in the outlet line that no air will be discharged from the compressor again. So,
The gas returns to the compressor as a back shock wave, and the complete cycle repeats. Continuous operation of the compressor under surging conditions will eventually cause the compressor to truly fail. Axial compressor surging is sometimes referred to by the FCC as a “turndown condition.”
This poses a serious problem since it is desirable to operate the plant under ion.

Under turndown conditions, the feedstock fed to the FCCU' is reduced below design capacity, resulting in a reduced flow of spent catalyst to the regenerator via line 10. This is based on the amount of regenerated catalyst and the compressed regenerated gas used in the regenerator (
This means that less hot flue gases are produced. It also means that less compressor capacity is required. When using a gray-flow compressor under turndown conditions, the compressor compresses more gas than is needed for the regeneration process and vents excess gas via line 32 and discharge valve 34 on the compressor discharge side. This has been the usual practice up until now. Although conventional methods eliminate compressor surging, this results in a loss of recoverable energy in the system. This venting of excess gas from the compressor discharge side also avoids excessive post-combustion of CO gas in the regenerator lean layer and can result in overheating of the lean layer when the regenerator is not operated at high temperatures. To prevent. In conventional methods, the spent catalyst is contacted with a regeneration gas, typically containing oxygen, at high temperature and pressure in a regeneration zone;
The carbonaceous material deposited on the spent catalyst was combusted.

The hot regeneration gas and regenerated catalyst were then separated and the hot flue gas was recovered. This hot flue gas is transferred to an expander
Expanding through a turbine-axial gas compressor set, the energy recovered in the expander is used to drive the compressor, which also compresses the oxygen-containing gas, and the oxygen-containing gas is sent to the regenerator as regeneration gas. Supplied. The production rate of flue gas in the regeneration zone is generally in the range of 50 to 100% of the design capacity of the expander turbine-parallel gas compressor system to ensure that sufficient expander inlet volume is utilized. It is an object of the present invention to provide an improved method for regenerating spent catalyst from fluid catalytic cracking.

A further object of the present invention is to provide an improved method for recovering power under turndown conditions from thermal regeneration gas obtained from a process for regenerating spent fluid catalytic cracking catalysts. The present invention reduces the amount of air discharged from the compressor by at least 1% less than the rate at which surging occurs when regenerating a used FCC catalyst.
Adjust to above 0%, and typically 10% of the design ratio
The surge rate exceeds 100%.

This requires an amount of air in excess of the regeneration requirement to be compressed. All of this compressed air flows to the amphigens. A complete combustion catalyst is used in the process. Complete combustion occurs when the carbon-fouled catalyst is exposed to excess air, substantially all the carbon is oxidized during post-combustion in the steel-tight catalyst bed, and the flue gas is substantially CO-free. generate. All produced flue gas is used to drive an expander power recovery turbine, which drives an air compressor and electrical power generator. As a result, the recovery power is increased. In the present invention, an axial flow air compressor is driven by an expander power recovery turbine, and the drive source of the motor generator is either the expander power recovery turbine, or the motor generator is used to assist in driving the koji flow air compressor. Perform one of the steps, compress the air with an axial air compressor, supply the compressed air to the lower part of the regenerator,
In the fluid catalytic cracking method, this regenerator regenerates a partially inactive catalyst contaminated with carbonaceous materials, and the catalyst inside the regenerator is exposed to water from the lower part of the regenerator in the dense layer and dilute layer. Fluidized by upwardly flowing air, the air oxidizes the carbonaceous material in the trough dense and lean layers, regenerates the partially inactivated catalyst, and produces hot flue gas by oxidation of the carbonaceous material. The hot-path gas drives an expander power recovery turbine, which drives an axial air compressor, and supplies the carbon-contaminated and partially inactivated catalyst to a regenerator; Turndown conditions in the fluid catalytic cracking process where the amount of catalyst feed is kept at an incomplete amount so that the amount of air for complete oxidation of the carbon purchasing material is lower than the amount of anti-surge air in the axial flow air compressor. In the method for incremental power recovery from a motor generator/expander power recovery turbine/axial air compressor device, a. Adjusting the air flow set point of said axial air compressor to a point at which the air flow is at least 10% above the surge line; b) increasing the amount of air to an excess of the amount required for regeneration; c) compressing and feeding all the air to the regenerator; and d) using a complete combustion catalyst in the fluid catalytic cracking process to eliminate carbonaceous material fouling. The total carbon content on the partially inactivated catalyst is oxidized to carbon dioxide gas in the dense layer of the regenerator, producing hot flue gas that is substantially free of carbon monoxide. , e) The generated fully heated flue gas drives an expander power recovery turbine, and f) drives a motor generator to generate electric power. be.

Next, the present invention will be explained based on the drawings. FIG. 1 is a flow sheet of the method of the present invention, and FIGS. 2-4 are operational diagrams of a typical expander power recovery turbine/axial air compressor system to explain turndown conditions and pumping points.

In FIG. 1, the FCCU introduces dirty or spent catalyst from (not shown) via line 10 to regenerator 12.

Spent catalyst from this typical FCCU contains coke and tarry carbonaceous materials that interfere with the cracking activity of the catalyst. Oxidizing regeneration gas, such as compressed air or other oxygen-containing gas, is introduced into regenerator 12 via line 16.

The oxidizing regeneration gas passes upwardly through the regenerator 12 at a rate such that the fluidized or turbulent catalyst particles with quasi-liquid properties maintain a lower level within the regenerator 12 known as a dense bed. It's fast enough. The regeneration conditions in the regenerator 12 are as follows:
Conditions are such that nearly all of the carbon monoxide produced by combustion of carbonaceous materials is converted to carbon gas. As previously mentioned, in one method this can be accomplished using a so-called complete combustion catalyst. Such a catalyst almost completely burns the carbonaceous material deposited on the spent catalyst into carbon dioxide gas in the dense steel wall of the regenerator. In this way, the thermal regeneration gas leaving the regenerator's maple dense layer is
Contains little or no carbon monoxide. Carbon monoxide must be removed beforehand because it undergoes after-combustion in the top of the regenerator, in the lean layer, or in the gas-solid separator 36 used to remove entrained catalyst from the thermal regeneration gas. . in general,
The temperature of the regenerator is 593.3 to 815.600 (1100
~15000F). Additionally, the oxidizing regeneration gas conventionally provided contains an excess of oxygen over the stoichiometric amount of oxygen required to convert the carbonaceous material to carbon dioxide. The thermal regeneration gas produced by combustion in the regenerator 12 passes through a separation system 18 .
may consist of one or more cyclones that remove entrained catalyst particles from the thermal regeneration gas. The regenerated catalyst has improved cracking activity and is returned to the fluid catalytic cracking reaction tower via line 14. Hot flue gases, i.e. those produced by combustion in the regenerator 12, are separated by the separation system 1.
8, the gas containing almost no solid catalyst particles leaves the regenerator 12, passes through the line 20, the solid separator 36, and is sent to the expander turbine.
) enters 22. expander. Turbine 22 exhausts the expanded gas via line 24 to the atmosphere or to other energy recovery equipment, such as a steam generator or the like. The expander turbine 22 serves to generate rotating power that is proportional to the system pressure level of the entire device. In the case shown, the expander turbine 22
is an expander compressor set (exp
forming part of the axial gas compressor (undercompressorset) and via a direct drive connection
axial gas compressor) 26. A gas compressor 26 takes atmospheric air or other oxygen-containing gases via line 28 and directs them to the regenerator 1.
Step 2 is necessary to compress it to the pressure level. Sufficient oxygen-containing gas, ie air, is compressed by compressor 26 to prevent surging. Generally speaking, the amount of oxygen-containing gas or air that is compressed maintains the velocity of the compressed gas discharged from the gas compressor 26 at least 10% below the velocity at which the compressor surge occurs. It is sufficient that the amount is sufficient. Next, the compressed gas is transferred to the compressor 26
is discharged into line 16. A ventilation line 32 with a valve 34 attached is attached to line 16. In the method described here, valve 34 is closed. expander·
The power developed by the turbine 22 is transferred to the compressor 26
The excess power is used to generate electricity via a motor generator auxiliary system 30 connected to the expander turbine 22. If the energy developed is insufficient for the expander turbine 22 to drive the compressor 26 at the desired capacity, the motor generator auxiliary system 30 is used as an auxiliary drive to provide the insufficient power. It is easy to see that it can be used as As can be seen, all the oxygen-containing gas (air) in the compressor 26 is sent to the regenerator 12, and with the booster power generation system closed, the compressed air is routed from the exhaust port of the compressor 26 to the line 32 valve. I won't let you run away after 34 years.

This condition is preferentially adopted regardless of whether the regenerator 12 is operated under turndown conditions. Under such turndown conditions, compressor 26 causes regenerator 12 to
The air supplied to is in excess of the amount of air required to combust the carbonaceous material on the spent catalyst in the regenerator 12. Prior art methods using free flow gas compressors operate at non-surge capacities and simply vent excess air to avoid after-combustion, rather than passing the excess air through a regenerator. It was normal. That is, the presence of excess air in the regenerator is not allowed because the regenerator is not operated in a manner that completely burns out the CO.
This resulted in a loss of energy from the system, with the excess air escaping. In the method of the present invention,
Excess air is not allowed to escape, so energy is continuously recovered under turndown conditions in the expander-compressor system. As will be noted, in the preferred case, the catalyst is of the complete combustion type, which serves to ensure that the carbon buy material is combusted to carbon dioxide in the dense zone of the regenerator 12. The complete combustion catalyst provides excellent stability for complete combustion operation, so that under turndown conditions, even in the presence of excess oxygen in the regenerator 12,
No after-combustion in the regenerator lean layer or cyclone. This is because during the regeneration gas leaving the Nukamitsu layer,
This is because there is almost no carbon monoxide. However, it is readily apparent that the method of the present invention can be applied to all regeneration methods in which almost all the carbon monoxide produced in the combustion of carbon-purchased materials is converted to carbon dioxide in the regeneration zone. This is understandable. Under these conditions, the presence of excess oxygen ensures that no after-combustion occurs in the separator, especially in the downstream equipment. Figures 2-4 show the range in which the compressor and expander operate.

FIG. 2 is a diagram showing the relationship between the compressor inlet flow rate and the crushing power of the compressor, and FIG. 3 is a plot of the discharge pressure versus the inlet flow rate of the same compressor.
Figure 3 shows the surge line (1) and 10 from the surge line.
The desired operating line (D) and throttle line (m) in % are shown, and the numbers indicate the stator setting in degrees. In both FIGS. 2 and 3, point D is the designed operating point of the compressor and is the aforementioned pumping point.

Point A in both figures is the air velocity that satisfies the stoichiometric air requirement corresponding to a 75% design turndown. Point A is further away from the figure, indicating that the compressor is inoperable.

The meaning of point A indicates the surge of the compressor. Point B in both figures is due to the desired design operation line,
The minimum amount of air desired from the axial compressor is shown when the regeneration requirement is at point A. The difference between points A and B is the amount of air that would normally be released into the atmosphere.

The process of the present invention utilizes a fully combusted catalyst and directs the amount of air released in the conventional manner to a regenerator. FIG. 4 is a diagram showing the operation of a typical expander-power recovery bin when the expander is loosely fitted to the axial flow air compressor of FIGS. 2 and 3 shown in FIG.

Figure 4 is a plot of expander flow rate and sea bream horsepower. ” Points D, A, and B are points ○ in Figures 2 and 3,
Corresponds to A and B. Point ○ is the design operating point.The additional power recovered by implementing the present invention is the horsepower difference between points A and B in FIG. As shown in Figure 3, 1 from the surge line.
The point above 0% is the lowest flow operating point.

The location of the lowest flow operating point is the desired lowest flow operating line. When the surge line is exceeded by 10%, stable operation can be applied to manufacture, and reliability and very good power recovery can be achieved. Operation beyond the surge line by less than 10% is of questionable reliability. 125 of the design from more than 10% of the surge
% is the entire range of operation. From 10% of the surge to 100% of the design improves operational stability and yields the highest power recovery. The present invention will be described below based on Examples.

〔Example〕

The advantages of the present invention are shown in the table below, which is for a typical FCCU.
This is appropriate operational data for the power recovery system.

Table 1 shows the design of the reactor side of the FCCU and operating conditions in the turndown state, and Tables 2 and 3 show the design and power recovery system conditions in the turndown state. Note that tests A and B were conducted at a 75% turndown, that is, 75% of the design capacity, and tests C and D were conducted at a 50% turndown. Table 1*(1) The regenerator bed temperature decreases due to the presence of excess air, but the feed preheat temperature was increased at B' to keep the catalyst/oil weight ratio constant.

*(2) Ratio to new feed is also *(3) The exit temperature is lowered to maintain a constant conversion rate by reducing the ratio of new feed from the design capacity.

*(4) Temperature 204.4℃ (4000F) according to ASTM method
is the ratio to new supply measured at .

In Table 2*(1), the compressor operating map shows that under these conditions the air velocity from the compressor is 10% away from the surge line,
．． 2% (236.7/274.3〒0.8627).

This value deviates slightly from the value calculated in the heat and mass balance based on the input value of 02 in the flue gas. *(
The value in parentheses in 2) is the deficit in horsepower produced by the expander turbine compared to the horsepower required by the compressor.

In Table 3 *1), the compressor operation map shows that the air velocity from the compressor under these conditions is 86.8% of the design speed (238.1/274 .3=0.
868).

*The value of (2) was due to the small volume of the expander turbine inlet, so these conditions
This was much lower than the range covered by the turbine operation map. Therefore, in this case, the operation could not be carried out o*(3)
The value in parentheses in is the value where the horsepower produced by the expander turbine is compared with the horsepower required by the compressor and the former is insufficient.

As seen in Table 2, for case A, a new feed rate of 75% turndown, the excess air required by the compressor is transferred to the regenerator in order to keep the air volume safely away from the surge point. Rather than let it pass, valve 34 was opened to allow it to escape. Under these circumstances, there was a significant shortfall (23 horsepower) between the 11,500 horsepower produced by the expander turbine and the 93 total horsepower required by the compressor. This shortage requires input from another drive, such as the motor-generator 30. However, for fresh feed rate B, also at 75% turndown, the excess air is fed to the regenerator, so the 14,260 horsepower recovered is equal to the 13 hp required by the compressor.
It can be seen that 266 horsepower exceeds 994 horsepower. In Table 3, for case D, which is a fresh feed rate of 50% turndown, excess air for combustion is admitted through the regenerator.

In ○, it must be supplied from another drive device573
Although there is a horsepower deficit, it is notable that even under such severe turndown conditions very little additional power is required. Also, in case C with 50% turndown, excess air was vented for combustion. Under these circumstances, the volume at the expander turbine inlet was so small that the system could not be operated. As the above data shows, the present invention provides a method for maximizing the recovery of energy from the FCCU from a continuous and stable stream of hot flue gas. Additionally, this method allows the use of high efficiency Tairyu air compressors under turndown conditions to reduce compressor surging or pumping without venting compressor discharge gases. In addition, an advantage of the method is that an improved air distribution is obtained in the dense zone of the regenerator by passing excess air through the regenerator without letting it escape.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet of the method of the present invention, and FIGS. 2 to 4 are operational diagrams of a typical expander power recovery turbine/axial flow air compressor system. 12... Regenerator, 18... Separation system, 22...
・Expander turbine, 26...Mari flow gas compressor, 30...Motor generator auxiliary system, 34
...Valve, 36...Solid separator. Traditional drawings 2 drawings 3 drawings 4 drawings

Claims (1)

[Claims] 1. An axial flow air compressor is driven by an expander power recovery turbine, and the drive source of a motor generator is the expander power recovery turbine, or the motor generator is used to drive an axial flow air compressor. The compressed air is compressed by an axial flow air compressor, and the compressed air is supplied to the lower part of the regenerator. The catalyst in the regenerator is fluidized in the dense and lean layers by the upward flow of air from the bottom of the regenerator; oxidizing the carbonaceous material therein, regenerating the partially deactivated catalyst, oxidizing the carbonaceous material to produce hot flue gas, driving the expander power recovery turbine on the hot flue gas, The expander power recovery turbine drives the axial air compressor, and when the carbonaceous material-contaminated and partially inactivated catalyst is supplied to the regenerator, the amount of air that completely oxidizes the carbonaceous material is transferred to the axial air compressor. Motor-generator/expander power recovery turbine/
In a method for recovering incremental power from an axial air compressor device, a) adjusting the air flow set point of the axial air compressor to a point at which the air flow is at least 10% above the surge line; and b) regenerating the required amount. By increasing the amount of air to a higher excess amount, c. Compressing all the air into the regenerator, and d. Using a complete combustion catalyst in the fluid catalytic cracking process, the carbonaceous material fouling and partially All carbonaceous material on the activated catalyst is oxidized to carbon dioxide gas in the dense bed of the regenerator, producing hot flue gas substantially free of carbon monoxide, e. An improved method for recovering power from regenerated gas under turndown conditions, comprising using hot flue gas to drive an expander power recovery turbine to drive an f-motor generator to generate electrical power.