AU627999B2 - Flow rate control device for slurry fluid - Google Patents

Description

62/ 9 6-

AUSTRALIA

PATENTS ACT 1990 P/00/011 Rogulation 3,2 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

TO BE COMPLETED BY APPLICANT Name of Applicant: NIPPON BROWN COAL LIQUEFACTION CO., LTD.

Actual Inventor(s): Takuo SHIGEHISA and Masachika FUJITA Address for Service: CALLINAN LAWRIE, 278 High Street, Kew, 3101, Victoria, Australia Invention Title: "FLOW RATE CONTROL DEVICE FOR SLURRY FLUID" The following statement is a full description of this invention, including the best method of performing it known to me:- TITLE OF THE INVENTION FLOW RATE CONTROL DEVICE FOR SLURRY FLUID BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a flow rate control device for slurry fluid which can prevent a restriction in flow passage caused by an adhesion of solid substances near a flow rate adjusting valve arranged in the flow passage of slurry fluid such as coal liquified heavy oil containing a substantial amount of solid substances and further which can control smoothly the flow rate of the fluid.

UEscriotion of the Prior Art oo As an example of the present invention, a valve control performed through a liquid surface collected at a bottom part of a distillation tower when the coal liquified heavy oil is to be extracted from the bottom part of the tower (refer to a Fig.3) will be described, wherein the 0al liquified heavy oil having a substantial amount of solid materials accumulated at 44 the bottom part of the tower is extracted through the flow passage 1 under an operation of a slurry pump 7, sent to a 4 S belt type solidifying machine 8 through a flow rate adjusting valve 2 and the like and processed.

During this process, as the rate of solid material in respect to the liquid component contained in the aforesaid coal liquified heavy oil is increased, the solid materials are adhered to a flow rate adjusting valve 2 or a wall surface of the flow passage 1 near the valve 2 so as to restrict a cross I sectional area of the flow passage.

As the cross sectional are of the flow passage is restricted, an amount of fluid flowing in the flow passage is reduced and finally the flow passage is closed and an operation of the distillation tower can not be continued.

In view of the fact, in the conventional prior art, a degree of reduction in flow rate of the fluid sent to the solidifying machine 8 was detected in response to a degree of increasing of the level of the liquid surface of the bottom part of the distillation tower 6 (for example, a difference between an actual level and a target level) and a degree of opening of the flow rate adjusting valve 2 was increased in response to the degree of increasing level so as to perform an automatic valve control to feed a specified flow rate in a normal state.

As shown by a broken line of a large wave in Fig.2, the S opening or closing of the valve 2 under this control is S carried out in response to a gradual variation in the liquid Ssurface level, resulting in that the operation is performed Sgradually. In addition, the flow rate of the fluid is not rapidly varied, so that the adhered solid substances may scarcely be peeled off the wall surface or the like. Due to this fact, new solid substances are adhered onto the adhered solid substances. Then, the cross sectional area of the flow passage is gradually reduced and the degree of opening of the valve 2 can not accommodate for the reduction in size of the cross sectional area, the liquid surface level at the bottom of the distillation tower 6 exceeds over the target level, resulting in that it may exceed an allowable level.

-2- As the degree exceeds the allowable level, a fluid pressure within the flow passage reaches its maximum value, a large block of solid substances adhered to the wall surface and the like is peeled off at once due to that fluid pressure and then the large amount of fluid passes through the valve 2 and flows down toward the solidifying machine 8. Then, this flow is continued for a while (due to the fact that it takes a certain time for the level of the liquid surface at the bottom part of the tower to decrease down to the target level and a degree of opening of the valve to return to its original state).

As a result, the large amount of fluid exceeding a 0 0 °solidifying capability was discharged to the solidifying machine 8, the solidifying of the solid substances could not be sufficiently carried out and so it showed a problem that the entire system should be stopped and a repairing work was needed.

In view of the fact above, in the prior art system, the automatic valve control of the valve 2 was changed over to a manual valve control when the aforesaid level of liquid S surface was apt to exceed the allowable level and then the valve 2 was rapidly and manually released through ON-OFF operation. Then, the flow rate of the fluid flowing in the flow passage was rapidly increased and the adhered solid substances were peeled off from the wall surface under its striking force and finally pushed away. In addition, since the aforesaid state occurred while keeping the valve 2 being released and then the valve 2 was returned immediately to its original state after the rapid flowing stream was stabled and 11,~.1 then the manual valve controlling operation was changed over to its automatic valve control.

Since the solid substances adhered in the flow passage could not be peeled off only with the automatic valve control of the flow rate adjusting valve in response to a variation in level of the liquid surface, as described above, the manual valve control should be applied together with the automatic valve control in the prior art. In addition, even in case of performing the manual valve control, in order to operate a rapid opening or closing of the flow rate adjusting valve o manually, this operation required a certain experience, a guess work and a 1X0. concentration in mind, so an operation should be relied upon those skilled in the o4 "4 art and is addition this prior art system had a disadvantage that the exceeding of the aforesaid level of the liquid surface over the allowable level should always be monitored and waited.

4t* 4 44 44 9r 4 44 4" 44 I t4 4 44 o 44 .4 4 *44 0I 0 4 SUMMARY OF THE INVENTION i It is an object of the present invention to resolve the aforesaid various 4 t problems. This can be done by making automatically a flow which can peel off the solid substances adhered in the flow passage gradually before the solid substances are grown up the larger blocks without changing-over into the manual control.

In accordance with the present invention there is provided a flow rate control device for slurry fluid, comprising a flow rate adjusting valve adapted to be arranged in a flow passage of a slurry fluid containing solid substances and means for giving said flow rate adjusting valve a valve control output in which an analogue output of a degree of opening of the valve based on a PID control signal is synthesized with an output of an alternating rectangular wave-form for -4r ft I 0 a f 4 i r*0 00 440 0 0 f, 0 00 generating an alternative positive or negative pulse of which pulse amplitude is about 3 to 10% of the analogue output of said degree of opening of valve corresponding to a full-opened valve and of which the pulse period is about several seconds.

The flow rate control device preferably is made such that the pulse amplitude and pulse period of the alternating rectangular wave output can be adjusted in the device of the invention.

The device of the present invention has been accomplished on the basis of a simple principle of experience that a so-called living valve moving precisely in response to a clogging in the slurry line is much stronger than a dead valve showing less movement, wherein as shown by a broken line of a large wave-form in Fig. 2, the valve control for applying a minute opening or dosing operation is added to the valve control for making a slow opening or dosing operation.

The valve control for making a gradual opening or dosing of the valve is carried out in response to an analogue output of a degree of opening of the valve based on the PID (proportional-integral-differential) control signal.

That is, the valve shows a gradual opening or dosing state in response to the signal analogously outputted in reference to a difference between the liquid surface level of the slurry fluid and the predetermined value (this is defined as "PID control signal"). Then, the system may always keep a constant flow rate in the flow passage.

The valve control for applying a minute opening or closing operation to the valve is carried out in response to an output of alternating rectangular wave for generating an alternative positive or negative pulse of which amplitude is about 3 to 10% of the analogue output of the degree of opening of the aforesaid valve corresponding to a full opening of the valve and of which period is about several seconds. That is, the valve is applied with the minute opening or closing operation in response to this output.

Since the aforesaid analogue output of a degree of opening and the aforesaid output of the alternating rectangular wave-form are synthesized to make a valve control output and given to the valve, the valve opening or closing operation is substantially varied while continuing the minute Smovement. In view of the variation of flow rate of the fluid passing through the valve, it means that the flow rate is Sgradually increased or decreased within a short time interval S while keeping a substantial constant flow rate.

0 Then, the solid adhered substances is applied with a striking force due to an increased or decreased flow rate at this short time interval and the solid substances may easily be peeled off the wall or the like. In other words, it is possible to prevent the flow passage from being restricted through an adhesion and a growing of the solid substances on the pipe wall or the like due to a minute increasing or decreasing of flow rate.

I i- -I SIn the preferred device of the invention, the pulse amplitude and the pulse period of the output of the aforesaid alternating rectangular wave can be adjusted in particular, wherein, they are rapidly accommodated for the nature of the fluid or a state of the adhered solid substances and then either the value of the increasing or decreasing flow rate or an increasing or decreasing time interval are adjusted optionally and further the action of the device is further reinforced.

The present invention has the aforesaid preferred configuration and 0 provides the aforesaid action, wherein the minute opening and closing operation of the valve are carried out together while performing the minute opening or 0041~0 closing operation of the flow rate control valve, thereby the restriction in the flow 0 0 0 passage 1 can be automatically prevented and the flow rate controlling operation can be smoothly carried out. In addition, it can be optionally adjusted in such a way as the most suitable control can be carried out in response to the nature of the o o fluid to be handled or the state of the adhered solid substances.

In addition, since the minute opening or closing operation is automatically a 004004 carried. out, it is not necessary to perform the manual valve control in the prior art, o o resulting in that the operation can be rationally carried out and at the same time a 0 a a certain trouble caused by an operator's erroneous action to make an over-opening or the like can be eliminated and a high reliable operation can be stably continued.

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1 BRIEF DESCRIPTION OF THE DRAWINGS Fig.l is a block diagram for schematically illustrating a configuration of the present invention.

Fig.2 is a timing chart for showing an output of a valve control which the controller shown in Fig.l may generated.

Fig.3 is a circuit diagram for showing the device of the preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the example shown in Fig.l, as the valve control L outputs to be applied to the driving part of the flow rate adjusting valve installed in the midway of the flow passage 1 of the slurry fluid, the outputs are used which are generated by the controller in which the PID controller 4 for receiving a sensing signal (PV) and a set signal (SV) and generating the analogue output of the degree of opening of the valve in response to a difference between them, i.e. the PID control signal and an operating program setting device 5 for overlapping the rectangular wave outputs for performing the minute opening or closing operation to the flow rate adjusting valve 2 are connected in series.

In this case, the analogue output of the degree of opening of the valve generated by the controller 4 are a stepless value in which an output to be applied to the actuator in the aforesaid driving part 3 is in a range of 0 to a value corresponding to a full-open position of the valve and this is expressed by the broken line of large wave form in I Fig.2.

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In turn, the operation program setting device 5 has a function capable of making a program for an operation corresponding to the aforesaid curved broken line and is provided with a pulse generator which can output an alternative positive and negative pulse having a pulse wave high value of about 3 to 10 of an analogue output of the aforesaid degree of opening of the valve corresponding to a full-opening of the valve and a pulse width of about several seconds and further output an alternating rectangular wave output. This alternating rectangular wave output can be placed over an analogue output of the degree of opening of the valve outputted by the PID controller 4 (overlapped) and the output of the valve control after overlapping is indicated by a saw-tooth like solid curved line in Fig.2.

It is preferable that the PID controller is provided with an upper limiter so as to enable an analogue output of the degree of opening of the valve lower than the value corresponding to the full-opened state of the valve, for example, a value less than an upper limit output restricted to 90% to be produced. In turn, the aforesaid program setting 0 device 5 is constructed such that the constant values of a pulse up-amplitude a pulse down-amplitude (X 2 and a pulse period (X 3 can be applied optionally within a predetermined range from an external side.

In this way, the valve may perform a minute opening or closing operation together with a gradual opening or closing operation to enable a prevention of a restriction of the flow passage bear the valve to be attained while controlling a flow rate in response to the variation in level in the liquid -9surface. In addition, it is also possible to make a proper variation of the constant if the alternating rectangular wave output in response to the state, resulting in that the manual valve control can be eliminated and then a severe trouble of flowing a large amount of flow rate under an erroneous manual operation can be prevented.

In addition, the overlapping of the output of the alternating rectangular wave can be performed not only continuously but also intermittently (for example, the output of the alternating rectangular wave is overlapped only when the liquid surface level exceeds a specified level) while the analogue output of the degree of opening cf the valve is being Sgenerated and so any of them can be optionally selected as required.

A programming can be set through a variation in design of the circuit in such a way as the degree of opening of the valve is low, the pulse amplitude and the period can be reduced and in turn if the degree of opening is high, they can be increased or vice versa. As a result of various practical measurements, no trouble occurred and a stable operation was c; ried out with the pulse amplitude being and a pulse period being about 5 seconds.

Referring now to Fig.3, a preferred embodiment of the present invention applied to the practical device will be described.

The illustrated system is a facility concerning a distillation tower in the line generating a coal liquified heavy oil from a coal of raw material, wherein to an outlet port opened at a bottom part of the distillation tower 6 is lo-

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oa ao a ol 0 9 4 4 o4 v a 9 4 09941 9 04O 04O 0 connected a flow passage (a pipe) 1 for use in extracting the coal liquified heavy oil containing solid substances of the slurry fluid. Slurry pump 7, flow rate adjusting valve 2 and emergency shielding valve 10 are arranged in the midwa' of the flow passage 1 from an upstream side, and in turn the solidifying device 8 having as its element a conveyor belt is arranged adjacent to the outlet end of the flow passage 1. A pipe is branched and connected to the midway part of the flow passage 1 connected to the outlet of the flow rate adjusting valve 2. Emergency releasing valve 11 is installed in the midway part of the pipe and at the same time the outlet end of the pipe is communicated with the slop tank 9.

Reference numeral 12 denotes a liquid surface sensor for the liquid surface at the bottom part of the distillation tower 6, wherein a signal corresponding to the detected liquid surface is inputted to the PID controller 4 of the aforesaid controller as the sensing signal (1V) and the valve control output from this controller is given to the driving part 3 of the aforesaid adjusting valve 2. At this time, the valve control output is a wave-form in which the output of the alternating rectangular wave-form is overlapped on the .,nalogue output f the degree of opening of the valve based on the PID control signal. In the case that the upper limiter is provided, an application of the upper limiter so as to restrict the maximum value with respect to the output of the wave-form after overlapping may cause all the rectangular wave-forms to be dclipped to make a mere flat output, whereby it is preferable that a certain restriction is provided by the upper limiter in such a way that the analogue output of the degree of opening of the valve may not exceed the predetermined value before it may overlap the output of the rectangular wave-form.

-11 The aforesaid controller of the preferred embodiment does not provide j any detailed circuit. However, there is provided a mode selection switch for selecting an operation mode of the solidifying machine 8 and an op.--ition mode of the slop tank 9. When the operation of the solidifying machine 8 is selected, the normal operation of the flow rate control is performed in which the output of the alternating rectangular wave-form is overlapped on the PID control signal corresponding to the liquid surface level and in turn the operation mode of the slop tank 9 is selected, either the slop tank operation or the aforesaid normal flow rate control operation can be carried out in response to a presence or a nonpresence of the trouble of the dogged state.

In the case that the solidifying machine 8 is in its bad condition and the operation of the slop tank 9 only is carried out, there is provided a countermeasure to remove the upper limiter at the PID controller 4.

8 8 As described above, since the minute opening or dosing operation is automatically overlapped during a slow opening or dosing operation of the flow rate adjust.ng valve under the control of the conventional automatic valve in S. 08 respect to the flow rate adjusting valve in the flow passage 1 through which the o 8, coal liquified heavy oil containing solid substances exceeding by 10% or more, a tremendous dangerous state of discharging a large amount of flow caused by the valve dogging in the conventional system and in turn accord' g to the method described above, the adhesion of the solid substances can je prevented and a stable iow rate control can be carried out.

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Claims (3)

1. A flow rate control device for slurry fluid, comprising a flow rate adjusting valve adapted to be arranged in a flow passage of a slurry fluid containing solid substances and means for giving said flow rate adjusting valve a valve control output in which an analogue output of a degree of opening of the valve based on a PID control signal is synthesized with an output of an alternating rectangular wave-form for generating an alternative positive or negative pulse of which pulse I amplitude is abot 3 to 10% of the analogue output of said degree of opening of S valve corresponding to a full-opened valve and of which the pulse period is abett 10, several seconds.

2. A flow rate control device for slurry fluid according to claim 1 in which the pulse amplitude and the pulse period of the output of the alternating rectangular wave-form can be adjusted.

3. A flow rate control device for slurry fluid substantially as hereinbefore 15 described with reference to the accompanying drawings. C I, 44 Ir DATED this 27 day of November 1991. NIPPON BROWN COAL LIQUEFACTION CO., LTD. By their Patent Attorneys: SCALLINAN LAWRIE (XOov^ I -n: I1l I~~ ABSTRACT A control device for slurry fluid capable of preventing a restriction in a flow passage caused by an adhesion of solid substances near the flow rate adjusting valve installed in the flow passage for the slurry fluid and capable of performing a smooth flow rate control by making automatically a flow capable of peeling off the solid substances adhered in the flow passage without changing-over to a manual valve control. 1 4 4 1 V 0 /^^TR^TX