JPS5951654B2 - Fluid catalytic cracker combustion waste gas power recovery device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power recovery device for guiding combustion waste gas generated when regenerating and heating a catalyst to a turbine to recover power in a fluid catalytic cracking unit (hereinafter referred to as FCC). .

FCC is equipped with a reaction tower and a combustion tower (regeneration tower),
A granular catalyst is circulated between compartments, and the catalyst with carbon attached in the reaction tower is sent to a combustion tower, where the carbon is burned off and regenerated, and the catalyst is heated.

Since the combustion waste gas generated at this time has a pressure of about 2 to 3 kg/Cm2 and is quite large, it is conducted to a gas expander turbine to recover power.

However, with respect to this power recovery system, the process side is always operated with priority, and even if a problem occurs in the turbine or generator, the process is often designed so that it can continue to operate as it is.

In this case, the variation on the process side must be kept to a small value below the allowable value.

On the other hand, large-diameter butterfly valves are usually used as variable control valves in FCC, but the control operation is very slow. It took about seconds.

Further, even if a system with good responsiveness is installed, for example, the stability range of the system is narrow and the deviation signal from the adjustment system cannot be increased, so the responsiveness of the system as a whole is poor.

On the other hand, the turbine
In order to prevent a sudden increase in rotational speed, the artificial valve of the turbine must be closed rapidly, for example, in a short period of about 1 degree, using an accuno, a rotor, or the like.

Therefore, the bypass valve was selected so that it could flow almost the same amount of gas as the inlet valve (the inlet valve is connected to the turbine, so the bypass valve's capacity is much smaller than the inlet valve).
, deployed in parallel.

At the time of turbine 1 rip, the inlet valve is rapidly fully closed, and at the same time, the bypass valve is rapidly opened, bypassing the entire amount. This is designed to prevent the turbine rotational speed from increasing and at the same time to suppress fluctuations on the process side as much as possible. .

However, when the turbine is put on standby at the rated rotational speed without any load or excitation after the load is cut off, the turbine rotational speed is controlled by the inlet valve, so the turbine artificial valve is reopened from the fully open state.

In this case, if the restart speed is high and the opening is sudden, it will be extremely difficult to keep the variable small due to the relationship with the operating speed of the variable control valve.

Therefore, in conventional equipment, the turbine is stopped once and then the inlet valve is gradually opened and adjusted, or the inlet valve is operated at a slow speed so that the fluctuation can be suppressed. .

Restarting the large mouth valve at a small speed in this way has the disadvantage that it takes a long time to reach a normal standby state, and it is still difficult to keep the differential pressure between the regeneration tower and the reaction tower within the permissible range. However, there was a drawback that the rotational speed fluctuated drastically.

In addition, especially in FCC, the volumes of regeneration towers and reaction towers are small, and a slight change in differential pressure has a large effect on the circulation and flow of the catalyst, making the reaction likely to become unstable. is extremely small.

Conventionally, with this type of control, for large reactors, the turbine rotation speed was brought to a no-load standby rotation speed by simply controlling the rotation speed, but for small-volume delicate reactors such as FCC. In a reactor, rotation speed control alone cannot
The differential pressure fluctuates wildly, exceeding the allowable range, and the turbine speed fluctuates wildly.In order to avoid these fluctuations, the artificial valve must be restarted slowly, and the time it takes to reach standby speed is shortened. It had the disadvantage that it was very long.

The present invention eliminates the above-mentioned drawbacks of the conventional ones, allows the turbine to return to the standby state in one stage, does not cause significant fluctuations in the process side state or the rotational speed of the turbine, and does not cause sudden changes in load. It is an object of the present invention to provide a power recovery device for combustion waste gas for a fluid catalytic cracking device that can stably cope with fluctuations and safely continue process operation.

The present invention provides a power recovery device that recovers power by guiding combustion waste gas from catalyst regeneration heating of a fluid catalytic cracking apparatus having a reaction tower and a regeneration tower to a turbine equipped with an inlet valve. A turbine circuit is formed by a turbine and a bypass valve provided in parallel with the turbine provided with the inlet valve, and the turbine circuit includes a variable control valve provided in the flow path of the combustion waste gas on the downstream side. The valves are arranged in series or in parallel, and rotate the partial opening required to perform a rapid closing operation on the artificial valve and keep the turbine on standby at the rated rotation speed in an emergency such as a turbine load cutoff. When setting the opening degree to hold the number of revolutions, when the opening of the inlet valve reaches the provisional opening, which is an opening within the range from zero opening to the rotational speed holding opening, it is held as it is, and then the opening is held as it is. The inlet valve control mechanism is provided with an inlet valve control mechanism that performs a restart operation to open the inlet valve at any time, and in response to the closing operation of the artificial valve, the bypass valve is rapidly opened to a fully open or intermediate opening degree, and the bypass valve is rapidly opened to a full open degree or to an intermediate degree of opening to maintain the rotation speed. Correspondingly, bypass valve control that controls the bypass valve so that the opening degree of the bypass valve is set to a corresponding opening degree that allows the differential pressure at the top of both the regeneration column and the reaction column to be approximately constant. This is a power recovery device for combustion waste gas of a fluidized catalytic cracking device characterized by being equipped with a mechanism.

That is, in the present invention, when performing a rapid closing operation of a turbine artificial valve, the inlet valve opening is first set to a provisional opening that does not exceed the rotational speed holding opening (the partial opening required to keep the turbine on standby for rotation at the rated rotational speed). (including the opening at zero), at the same time the bypass valve is set to an intermediate opening or fully open, and then the inlet valve is opened again and the opening is set to the rotation speed holding opening,
At the same time, the bypass valve is controlled to a corresponding opening degree corresponding to the rotational speed maintaining opening degree.

The present invention will be described with reference to the drawings in accordance with an embodiment. In FIG. 1, the FCC 1 is comprised of a reaction tower 2, a regeneration tower 3, and communication pipes 4 and 5 that connect these.

6 is raw oil, 7 is air, 8 is steam, and reaction tower 2
A generated gas 9 is obtained from the upper part of the tank.

The catalyst to which carbon is attached in the reaction tower 2 enters the regeneration tower 3 via the connecting pipe 5, where the carbon content is burned and removed, and at the same time, the catalyst itself is heated by the combustion.

The regenerated catalyst enters the reaction tower 2 again through the connecting pipe 4.

The waste gas generated by combustion in the regeneration tower 3 is
It is discharged from the top through a discharge passage 10, passes through a dust removal device 11 such as a cyclone, and further passes through a pipe line 12 to reach a variable control valve 13.

On the downstream side of the variable control valve 13, a branch point 15 is provided at the rear end of the conduit 14.

Reference numeral 16 indicates a pipe line as a waste gas passage after the confluence point 17, and a turbine circuit 18 is connected between the branch point 15 and the confluence point 17.
is inserted.

The turbine circuit 18 includes a turbine 20 equipped with a large mouth valve 19.
and a bypass valve 21 are provided in parallel.

The turbine 20 drives a generator 23 as a driven machine via a transmission 22.

24 is a pressure detector that detects the top pressure of the regeneration tower 3, the top pressure of the reaction tower 2, or the differential pressure between the two towers and operates the variable control valve 13; 25 is a bypass valve control mechanism; A signal from the pressure detector 24 (one or more of the top pressure of the regeneration tower 3, the top pressure of the reaction tower 2, or the differential pressure between the two towers), or the state quantity at the inlet of the turbine circuit 18 (pressure , temperature, flow rate), stores the signals, performs calculations, and performs a re-closing operation to give the bypass valve 21 a corresponding opening that can keep the state quantity at the inlet of the turbine circuit 18 or the differential pressure at the top almost constant. It is something to do.

In the bypass valve control mechanism 25, a target opening degree can also be set in advance.

Reference numeral 26 denotes a load detector that detects the load state of the turbine 20, and the control mechanism 27 opens and closes the large mouth valve 19 and the bypass valve 21 according to a corresponding pattern depending on the load state.

For example, when the turbine is stopped, the large mouth valve 19 is fully closed, and at the same time, the bypass valve 21 is fully opened.

In addition, when the load is cut off, the control mechanism 27 acts as an inlet valve 19 closing mechanism and a bypass valve 21 opening mechanism in response to a signal from the load detector 26, and rapidly starts closing the large mouth valve 19 using an accumulator or the like, and at the same time, the bypass valve 21 is closed. valve 2
In response to a signal from the speed controller 28, the opening operation of the large mouth valve 19 is started, and the re-closing operation of the bypass valve 21 is started.

After that, the large mouth valve 19 is controlled by the signal from the speed controller 28.
The opening degree is converged to the rotational speed maintaining opening degree.

29 is a resistor such as a barrier pull orifice.

During steady operation, the bypass valve 21 is closed, the large mouth valve 19 is fully opened, and the energy of the waste gas is recovered by the turbine 20.

The differential pressure at the top of the tower is adjusted by a variable control valve 13.

When the turbine 20 is stopped, a stop signal is given to the control mechanism 27, the large mouth valve 19 is fully closed, and the bypass valve 21 is fully opened.

No-load operation of the turbine 20 and synchronization of the generator 23 with an external power source are performed by operating the inlet valve 19.

The large mouth valve 19 may be formed by one valve, or may be of an oyakodon type in order to ensure controllability at a small flow rate.

The operation during load shedding will be explained.

Figure 3a. b and C are different operation examples, and in both cases, the solid line shows the opening degree of the large mouth valve 19, and the dotted line shows the variation in the opening degree of the bypass valve 21.

It is assumed that the inlet valve 19 is 100% open in a steady state.

The starting point for time is the time of load shedding.

The size of the bypass valve 21 is selected such that it can flow the same flow rate as the large mouth valve 19, or a slightly larger flow rate.

It is preferable that both opening degree-flow rate characteristics have substantially the same linearity.

The control shown in FIG. 3a will be explained.

After the load is cut off, the large mouth valve 19 is activated by the signal from the load detector 26.
and the bypass valve 21, the large mouth valve 19 rapidly closes and becomes fully open at A1, and the bypass valve 21 rapidly opens and becomes fully open at B1.

The fluctuation in the rotational speed of the turbine 20 in this case is almost the same as that shown by the solid line in FIG.

In other words, the rotation speed rises rapidly immediately after load shedding, but large mouth valve 1
9 begins to close rapidly, the rise is suppressed, and the large mouth valve 19
It almost reaches the apex E when it reaches full opening, and then decreases due to mechanical loss and reaches the rated rotation speed F.

In this case, "fully closed", that is, "opening degree zero" corresponds to a case where "temporary opening degree", which will be described later, is "opening degree zero".

Up to this point, the bypass valve control mechanism 25 has already detected and memorized the pressure, temperature, and flow rate of the turbine circuit input immediately before the load cutoff, and has also detected and memorized the rotation speed holding opening degree a predicted in advance.
% and the corresponding opening degree is obtained, and although the speed controller 28 is operating, the bypass valve 21
And no signal is issued to operate the inlet valve 19.

The point in time when the rotation speed has decreased to the rated rotation speed and reached point F in FIG. 5 is t2 in FIG. is activated, the large mouth valve 19 starts its restart operation from point A2, and the bypass valve 21 starts its re-closing operation from point B2.

The B2 point may be determined by a timer from the time of load shedding or from the B1 point.

At the same time, in response to a signal from the speed controller 28, the control mechanism 27 causes the inlet valve 1 to maintain the rotation speed of the turbine 20 at the rated rotation speed.
9 is controlled to converge to the rotational speed holding opening a% (for example, 15%), and accordingly the rotational speed increases again as shown in Fig. 5 G, speed control is performed, and the rotational speed is converged to the rated rotational speed. .

At the same time, the bypass valve 21 has a bypass valve control mechanism 2.
5, the corresponding opening degree b% is instructed, and the bypass valve 21
The opening degree is set to the corresponding opening degree b% (for example, 70%).

The rotational speed holding opening a% is almost determined by the performance of the turbine 20, so when the amount of waste gas from the regeneration tower 3 changes, the bypass valve control mechanism 25 calculates a new corresponding opening b% based on this. , and operate the bypass valve 21.

Conventionally, the bypass valve 21 was not reclosed and remained fully open, as indicated by the two-dot chain line in FIG.

The opening degree of the bypass valve 21 may be set to the same opening degree from point B1, such as an average opening degree between 100% and b%, as long as it falls within an allowable range.

In the control example shown in FIG. 3, the opening degree of the bypass valve 21 is not kept constant, but the opening degree of the large opening valve 19 and the interlocking valve are controlled, and are made to vary symmetrically for compensation.

In the control example shown in Fig. 3C, the large mouth valve 19 is not fully opened, but is opened at a provisional opening of 0% (preferably an opening slightly smaller than a%) that does not exceed the rotational speed holding opening a%. Let it stop.

On the other hand, the bypass valve 21 starts from the time t1 at the rotation speed holding opening a
%, the corresponding opening degree is set to b%.

At time t2, the large mouth valve 19 is restarted, and the speed controller 28 causes the rotational speed of the turbine 20 to converge to the rated rotational speed.

The bypass valve 21 is maintained at the opening degree b% by a self-holding device or the like even after t2.

A comparison between the embodiment of the present invention in which the control shown in FIG. 3a is performed and a conventional example is shown in FIGS. 4 and 5.

In both cases, the solid line shows the example of the present invention, and the dotted line shows the conventional example. Fig. 4 shows the temporal change in the top differential pressure fluctuation between the regeneration tower 3 and the reaction tower 2, and Fig. 5 shows the rotation speed of the turbine 20 (rated (ratio to rotation speed)
shows the temporal change of

In the conventional example, it takes a long time of about 60 seconds to bring the large mouth valve 19 from the fully closed state to the rotation speed maintaining opening, but even this does not satisfy the tolerance range of differential pressure fluctuation. .

Further, the rotational speed of the turbine 20 is abnormally reduced because the restart speed of the large mouth valve 19 is small, and normal operation cannot be performed.

In contrast, in the embodiment of the present invention, b-near is set to 0%, and the differential pressure fluctuation is extremely small, and the turbine 2
The fluctuation in the rotational speed at 0 is also small, the influence on the process side is small, and stable operation of the turbine 20 can be ensured.

FIG. 2 shows another embodiment, in which the turbine circuit 18 is arranged in parallel with the variable adjustment valve 13, and the turbine 20
The flow rate of the waste gas supplied to the exhaust gas is lower than in the example shown in FIG. 1, but the pressure is high.

Similar to the example shown in FIG. 1, the influence on the process side is small, and the rotational speed of the turbine 20 also changes little.

With the present invention, even in emergency situations such as load shedding,
It does not cause disturbance to the process side, prevents abnormal increases in turbine rotation speed, and quickly returns the turbine to a standby state, stably responding to sudden changes in load.
It is possible to provide a power recovery device for combustion waste gas of a catalytic fluid cracking device that allows process operation to continue safely, and has an extremely large effect in terms of practical energy recovery.

[Brief explanation of drawings]

1 and 2 are flowcharts of different embodiments of the present invention, FIGS. 3a, l), and c are diagrams showing control methods of different embodiments of the present invention, and FIGS.
The figure is a diagram comparing the performance of the embodiment of the present invention and the conventional example. 1...FCC12...Reaction tower, 3...Regeneration tower, 4
... Communication pipe, 5 ... Communication pipe, 6 ... Raw material oil, 7.
...Air, 8...Steam, 9...Produced gas, 10
...Discharge path, 11...Dust removal device, 12...Pipe line,
13... Variable control valve, 14... Pipe line, 15... Branch point, 16... Pipe line, 17... Confluence point, 18...
Turbine circuit, 19... Inlet valve, 20... Turbine, 21... Bypass valve, 22... Transmission, 23...
- Generator, 24... Pressure detector, 25... Bypass valve control mechanism, 26... Load detector, 27... Control mechanism, 28... Speed controller, 29... Resistor .

Claims (1)

[Scope of Claims] 1. A power recovery device that recovers power by guiding combustion waste gas from catalyst regeneration heating of a fluid catalytic cracking apparatus having a reaction tower and a regeneration tower to a turbine equipped with an inlet valve, wherein the inlet valve A turbine circuit is formed by a turbine equipped with the inlet valve and a bypass valve provided in parallel with the turbine equipped with the inlet valve, and the turbine circuit has a bypass valve provided in the flow path of the combustion waste gas. , a part that is arranged downstream in series or in parallel and is necessary for performing a rapid closing operation on the inlet valve in an emergency such as a load cutoff of the turbine, and keeping the turbine on standby at the rated rotation speed. When the opening degree is defined as the rotational speed holding opening degree, when the opening degree of the inlet valve reaches the provisional opening degree, which is an opening degree within the range from zero opening to the rotational speed holding opening degree, the opening degree of the inlet valve is held as it is, and then the A large-mouth valve control mechanism is provided that performs a restart operation to open the inlet valve to an opening degree that maintains the rotational speed, and in response to the closing operation of the inlet valve, rapidly opens the bypass valve to a full open or intermediate opening degree to maintain the rotational speed. A bypass that controls the bypass valve so that the opening degree of the bypass valve is set to a corresponding opening degree that allows the differential pressure at the top of both the regeneration column and the reaction column to be substantially constant in accordance with the holding opening degree. A power recovery device for combustion waste gas of a fluid catalytic cracker, characterized by being equipped with a valve control mechanism. 2. The bypass valve control mechanism stores the turbine circuit inlet pressure immediately before the start of the closing operation of the inlet valve as a target inlet pressure, and adjusts the corresponding opening so that the inlet pressure becomes approximately the same as the target inlet pressure. 2. A device as claimed in claim 1 for controlling the temperature. 3. The apparatus of claim 1, wherein the initiation of the re-closing operation of the bypass valve is indicated by a signal that initiates the re-opening operation of the inlet valve. 4. The device according to claim 1, wherein the start of the re-closing operation of the bypass valve is instructed by a timer.