JPS5951653B2 - 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.

The combustion waste gas generated at this time is 2 to 3 kg/cm□
Since it has a pressure of about G G and is a considerable amount, it is conducted to a gas expander turbine to recover the 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 action is very slow. For example, the normally used valves do not fully open or close during control operation. It took about 25 seconds.

Further, even if a system with good responsiveness is installed, 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 large mouth valve of the turbine must be closed rapidly, for example in a short period of about one second, using an accumulator or the like.

Therefore, we selected a bypass valve that could flow almost the same amount of gas as the artificial valve (the artificial valve is connected to the turbine, so
(The capacity of the bypass valve is much smaller than that of the inlet valve) and are arranged in parallel.

When the turbine trips, the inlet valve is rapidly fully closed, and the bypass valve is rapidly opened to completely bypass the turbine, thereby preventing an increase in the turbine rotation speed and at the same time suppressing fluctuations on the process side as much as possible.

However, after the load is cut off, when the turbine is placed on standby at the rated rotation speed without any load or excitation, the turbine rotation speed is controlled by the on-off valve, so the turbine artificial valve is opened again from the fully closed 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 temporarily stopped and then the large mouth valve is gradually opened to control the speed, or the large mouth valve is operated at a slow speed so that the fluctuation can be suppressed. Ta.

Restarting the inlet valve at such a low speed 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 an acceptable 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 rotational speed fluctuates wildly.In order to avoid these fluctuations, the large opening 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 quickly return to the standby state, does not cause large fluctuations in the process side state or the rotational speed of the turbine, and can withstand 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 the above problems and safely continue process operation.

The present invention provides a power recovery device for recovering power by guiding combustion waste gas from catalyst regeneration heating in a fluid catalytic cracking apparatus having a reaction tower and a regeneration tower to a turbine equipped with a large-mouth valve. A turbine circuit is formed by a turbine provided with the inlet valve 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. A partial opening degree that is arranged downstream in series or in parallel and is necessary in an emergency such as a turbine load cutoff to cause the inlet valve to perform a rapid closing operation and keep the turbine on standby at the rated rotation speed. 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, the opening of the inlet valve is held as it is, and then the rotational speed is maintained. An inlet valve control mechanism is provided that performs a restart operation of opening the inlet valve to a maintained opening degree, and rapidly opens the bypass valve in response to the closing operation of the inlet valve, in response to a condition immediately before occurrence of a load cutoff or the like. a bypass valve control mechanism that controls the opening degree to maintain the opening degree as it is when the opening degree corresponding to the setting calculated by the calculation is reached, and maintains the opening degree of the bypass valve at the opening degree corresponding to the setting even if the restart operation of the inlet valve is started; This is a power recovery device for combustion waste gas of a fluidized catalytic cracker, characterized by comprising:

That is, in the rapid closing operation of the turbine artificial valve, the present invention rapidly closes the inlet valve to maintain a temporary opening (full opening) that does not exceed the rotational speed holding opening (partial opening for keeping the turbine on rotation standby at the rated rotational speed). (including closed), then restarts the rotation speed and maintains the opening, and at the same time as the large mouth valve starts to close quickly, the bypass valve is set according to the calculated setting according to the situation immediately before a load cutoff, etc. It opens to the opening degree and then controls to maintain the same opening degree.

The present invention will be described with reference to the drawings in accordance with an embodiment. In FIG. 1, the FCCI 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 .

The catalyst to which carbon has adhered 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 heat of 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.
has been 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.

A pressure detector 24 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, which receives a signal (
The top pressure of the regeneration tower 3, the top pressure of the reaction tower 2, or one or more of the differential pressure between the two towers), or a signal of the state quantity (pressure, temperature, flow rate) at the inlet of the turbine circuit 18. The state quantity at the inlet of the turbine circuit 18 or the corresponding opening that can make the top differential pressure almost constant is calculated in advance as the set corresponding opening, and the opening of the bypass valve 21 is set to this value. is set and maintained.

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 inlet 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 a closing mechanism for the artificial valve 19 and an opening mechanism for the bypass valve 21 in response to a signal from the load detector 26, so that the accumulator or the like rapidly starts closing the large mouth valve 19, 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 opening degree of the bypass valve 21 is maintained.

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 closed, 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, synchronization of the generator 23 with an external power source, etc. are performed by operating the large mouth 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.

The solid line in Fig. 3 is the opening of the large mouth valve 19, and the dotted line is the opening of the bypass valve 2.
1 shows the variation in opening degree.

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

The time starts from the time of load shedding t. shall be.

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. 3 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 reaches the opening degree C at A1, and the bypass valve 21 rapidly opens and reaches the opening degree at B1.

This opening degree C is a temporary opening degree that is selected from within the range from opening degree zero to rotation speed holding opening degree a and is temporarily maintained.

The degree of opening C is preferably slightly smaller than the degree of opening a.

In addition, the opening degree corresponds to the rotational speed holding opening degree a, and is selected so that the differential pressure at the top of the tower falls within the allowable range based on the detected values of pressure, temperature, and flow rate at the turbine inlet immediately before load cutoff. This is the corresponding opening degree of the bypass valve 21.

For example, it is 70%, and the opening degree of the bypass valve 21 is set to this value.

In this case, the rotation speed of the turbine 20 increases rapidly immediately after the load is cut off, but the increase is suppressed as the large mouth valve 19 rapidly begins to close, and reaches its peak when the inlet valve 19 reaches the opening degree C. The speed almost reaches , and then decreases due to mechanical loss and reaches the rated speed.

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 population immediately before the load cutoff, and has also detected and memorized the rotation speed holding opening a% which is predicted in advance.
The corresponding opening degree S is determined by calculation, and the bypass valve 21 is set to the set opening degree without fully opening, using this corresponding opening degree S as the set value.

When the rotational speed has decreased to the rated rotational speed, V is t2 in FIG. 19, the restart operation is started from point A2.

The bypass valve 21 is kept open even after t2 by a self-holding device or the like.

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 degree a% (for example, 15%), and the rotational speed increases again accordingly, speed control is performed, and the rotational speed is converged to the rated rotational speed.

Conventionally, the bypass valve 21 was kept fully open from time B1 onwards.

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 on-off valve 19 and the crossing valve are controlled, and are made to vary almost symmetrically for compensation.

In the control example shown in Fig. 3C, the inlet valve 19 is not fully closed, but is opened at a provisional opening of 6% (preferably an opening slightly smaller than a%) that does not exceed the rotational speed holding opening a%. Let it stop for a while.

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 brings the rotational speed of the turbine 20 up to the rated rotational speed.

The bypass valve 21 is maintained at the opening degree of 1)% even after t2 by a self-holding device or the like.

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 is the embodiment of the present invention, and the dotted line is the conventional example. Fig. 4 shows the temporal change in the pressure difference at the top of the reaction tower 2 with the regeneration tower 3, and Fig. 5 shows the rotation speed of the turbine 20 ( (ratio to rated rotational speed) over time.

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 inlet valve 19 is low, and normal operation cannot be performed.

On the other hand, in the embodiment of the present invention, b = 70%, the differential pressure fluctuation is extremely small, the rotational speed fluctuation of the turbine 20 is also small, and the influence on the process side is small, and the turbine 20 stable operation can be ensured.

FIG. 2 shows another embodiment in which the turbine circuit 18 is arranged in parallel with the variable control 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 rises in turbine rotation speed, quickly returns the turbine to standby status, stably copes with sudden changes in load, and ensures safe process operation. It is possible to provide a power recovery device for combustion waste gas of a fluidized catalytic cracker that can be continued, 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, and FIG. 3 is a diagram showing a control method thereof. 1...FCC12...Reaction tower, 3...
・Regeneration tower, 4.5... Connecting pipe, 6...
Raw material oil, 7...air, total...steam,
9...Produced gas, 10...Discharge path, 1
1...dust removal device, 12...pipe line, 13
... Variable control valve, 14 ... Pipeline, 15
... Branch point, 16 ... Conduit, 17 ...
...merging point, 18...turbine circuit, 19
...population valve, 20...turbine, 21
...Bypass valve, 22...Transmission, 2
3... Generator, 24... Pressure detector,
25... Bypass valve control mechanism, 26...
...Load detector, 27...Control mechanism, 28...
...Speed controller, 29...Resistor.

Claims (1)

[Claims] 1. A power recovery device that recovers power by guiding combustion waste gas from catalyst regeneration heating of a fluid catalytic cracker having a reaction tower and a regeneration tower to a turbine equipped with an inlet valve, the turbine equipped with the inlet valve; A turbine circuit is formed by a bypass valve provided in parallel with the turbine provided with the inlet valve, and the turbine circuit is connected in series on the downstream side with respect to the variable control valve provided in the flow path of the combustion waste gas. , or are arranged in parallel, and in an emergency such as a turbine load cutoff, the inlet valve is rapidly closed and the rotational speed is maintained at the partial opening degree necessary to keep the turbine on standby at the rated rotational speed. When setting the 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 rotation speed holding opening degree, it is held as it is, and then the opening degree is maintained at the rotation speed holding opening degree. An inlet valve control mechanism is provided that performs a restart operation of opening the inlet valve until the inlet valve closes, and rapidly opens the bypass valve in response to the closing operation of the inlet valve. A bypass valve control mechanism is provided which maintains the opening degree as it is when the opening degree corresponding to the setting is reached, and controls the opening degree of the bypass valve to maintain the opening degree corresponding to the setting even if the restart operation of the inlet valve is started. A power recovery device for combustion waste gas of a fluidized catalytic cracker, characterized by: