GB2178198A - Control for sterilizers in a palm oil mill - Google Patents

Abstract

A sterilizer control apparatus for a plurality of sterilizers (1-1, 1-2, 1-3, 1-4) in a palm oil mill includes control signal generating means (20) which successively generates control signals at preselected intervals, and starting means (18-1, 18-2, 18-3, 18-4) for generating a start signal upon simultaneous receipt of both a ready signal generated when the associated sterilizer is ready for sterilization, and a control signal from the control signal generating means (20). To prevent overload of the steam generating means which supplies the sterilizers, if the number of sterilizers in operation exceeds a certain number, then the generation of further control signals is inhibited. <IMAGE>

Description

SPECIFICATION Control for sterilizers in a palm oil mill The present invention generally relates to a palm oil mill process which produces palm crude oil from the raw material, i.e. fresh fruit bunches (F.F.B), and more particularly to sterilizers in which the fruit bunches are subjected to a steam-heat treatment for easier further processing of the fruits, such as separation of fruits from bunch stalks, these sterilizers being sequentially and cyclically put into operation.

More specifically, the present invention relates to an improvement of a control for a set of such sterilizers, and aims to avoid the occurrence of an abrupt increase in the overall steam load demand required by the sterilizers which would otherwise occur because of a lag in manual operation for loading and unloading the cage loaded by the fruit bunches into and from the sterilizers.

Fig. 1 shows an arrangement of a typical palm oil mill.

Disposed in front of a plurality of sterilizers 1, only one of which is shown in the figure, is a cage handling yard 2 in which sterilizer cages 2a are movably provided to carry fresh fruit bunches to the sterilizers 1. Cage cranes 3 are disposed in the back of the sterilizers to uplift and transfer the sterilized fruits to strippers 4 which are disposed within the range of the crane movement.

Disposed downstream of the strippers 4 are digesters 5 which serve to mash the fruits and are coupled to screw presses 6. Fruit elevators 7 communicate the strippers 4 with the digesters 5.

Channels 8 extending below the screw presses 6 respectively carry the crude oil and nuts/fiber. The discharge end of the crude oil carrying channels open to the inlets of the vibrating screens 9. The outlets of the vibrating screens 9 communicate with crude oil tanks 10 which, in turn, communicate with clarification tanks 11.

Disposed downstream of the nuts/fiber carrying channels are nuts/fiber separators 12 (depericarpers) having separate discharge tubes 13a and 13b, the ones for nuts and the others for fiber. These fiber bearing tubes 13b extend to fiber cyclones 14 which outlets are in communication with the inlets of fiber conveyers 15. The outlets of the fiber conveyers 15 communicate with fuel inlets 16a of steam boilers 16.

Steam supply lines 1 6b extend from the boilers to respective sterilizers 1 through associated control devices 17. Control valves 1 7a are interposed between the respective sterilizers and the control devices. The steam supply lines 1 6b have branches which supply steam to the digesters 5 and further to hot water tanks T. Hot water lines Ta from the tank T are connected to the screw presses 6.

In operation, fresh fruit bunches are loaded into the cages 2a in preparation for the next transfer of the loaded cages 2a into the predetermined one of the sterilizers 1.

Within the sterilizers 1, the fresh fruit bunches are subjected to a steam-heat treatment in a sterilizing cycle during which the steam is intermittently supplied in accordance with the predetermined pattern, as will be described hereinafter in more detail. This sterilization makes the bunches come off easily, thus facilitating the next separation process by the strippers 4 at higher efficiency.

After sterilization, the cages 2a are unloaded from the sterilizer, and by means of the cranes 3, uplifted and moved above the strippers 4 at which the cages are overturn, thus allowing the sterilized fruit bunches to fall into the strippers 4.

In the strippers 4, the fruits are broken off from the bunch-stalks. Thus, the empty bunches are removed, while the stripped fruits are sent to the digesters 5 by the elevators 7 and are thrown thereinto.

The digesters 5 mash the fruits, depericarp them and break up them into nuts, crude oil and fruit pulp. These nuts, crude oil and fruit pulp are discharged and fed down to the screw presses 6 which, in turn, squeeze the oils and fats from the fruit pulp.

The crude oil, squeezed fibers and remaining nuts fall into separation channels 8. The discharge ends of the channels 8 supply the crude oil containing a great amount of oils.

This crude oil is fed to the vibrating screens 9 where solids and other impurities contained therein are removed. The screened crude oil is then poured into the crude oil tanks 10. After this, the crude oil is introduced into the clarification tanks 11 where the oils are separated from the sludge and extracted, thus palm crude oil being obtained. The palm oil is used for food after refining.

On the other hand, the remaining nuts, the squeezed fiber and other solids are taken off from the outlets of the nut-fiber channels 8, and are fed to the depericarpers 12 where the nuts are separated from the fiber. The separated fiber is sent through the tubes 13b and the fiber cyclones 14, conveyed by the fiber conveyers 15 and finally thrown, as fuel, into the water tube boilers 16. The separated nuts are discharged through the nut carrying tubes 13a for further processing.

In this manner, the byproducts, i.e. the fiber are burned in the boilers 16 to generate steam which is then supplied through the steam supply lines 16b to the digesters 5, and also to the hot water tanks T for generation of hot water by means of heat exchange.

The hot water is supplied to the screw presses 6 by way of the hot water supply lines Ta. The generated steam is also supplied to the sterilizers 1 through the associated control devices 17 which control the introduction of steam into the sterilizers in accordance with the predetermined intermittent pattern.

Such intermittent patterns are exemplified in Fig. 2 by the reference symbols (I), (K), (M) and (0). It is empirically and experimentally known that the steam-heat treatment based on such an intermittent pattern makes it easier to separate the fruits from the bunch-stalks (see "Tropical Agriculture" 20 (2), pp 101-110, 1976).

In order to carry out such a steam-heat treatment based upon an intermittent pattern, each of the sterilizer control devices 17 includes a valve control circuit 30 as shown in Fig. 3 which controls the control valve 1 7a disposed in the steam supply line 16b.

More specifically, the valve control circuit 30 includes an input terminal 31 connected to an input of a first monostable multivibrator 32 having a quasi-stable time t,. The first monostable multivibrator 32 is connected to a second monostable multivibrator 33 having a quasistable time t2 and which is connected to a third monostable multivibrator 34 having a quasi-stable time t3. The third multivibrator is connected to a fourth monostable multivibrator 35 having a quasi-stable time t4 and which is connected to a fifth monostable multivibrator 36 having a quasi-stable time t,. A cascaded chain of these monostable multivibrators 32-36 forms a pulse distributor. The output of the fifth monostable multivibrator 36 is connected to a reset terminal of a flip-flop 38.

The set terminal of flip-flop 38 is connected to the input terminal 31 and its output is connected through a buffer amplifier 39 to an output terminal 40 for indication of a state where the steam is being supplied to the sterilizer.

The output of the fourth monostable multivibrator 35 is also connected to the sixth monostable multivibrator 37 having a quasi-stable time t6. The output of multivibrator 37 is connected through a buffer amplifier 43 to an output terminal 44 for indication of a state where the sterilizer is held pressurized.

Each output of the first, third and fifth monostable multivibrators 32, 34 and 36 is connected to an input of an OR gate 41 whose output is applied to the control valve 1 7a through a buffer amplifier 42.

In operation, a control signal S, is fed to the input terminal 31. In response to this signal, the first monostable multivibrator 32 transfers to the quasi-stable state, thus generating a pulse having a duration of t, and supplying the same to one of the inputs of the OR gate 41 [(A) in Fig. 2]. After the period t, has elapsed, the monostable multivibrator 32 returns to the stable state and the second monostable multivibrator 34 transfers to the quasi-stable state. The second monostable multivibrator 34 remains the state for the period of t2 [(B) in Fig. 2].

Similar operation spreads to the following monostable multivibrator. The third monostable multivibrator 34 supplies a pulse to the OR gate 41 during the quasi-stable period of t3 [(C) in Fig. 2], after which the fourth monostable multivibrator 35 goes to the quasi-stable state for the period of t4 [(D) in Fig. 2]. After this period the fifth monostable multivibrator 36 generates and supplies a pulse to the OR gate 41 for the quasi-stable period of t5 [(E) in Fig. 2].

The OR gate 41 will, therefore, output a sequence of pulses that are "high" when the first, third and fifth monostable multivibrators 32, 34 and 36 remain their quasi-stable states and are "low" when the second and fourth monostable multivibrators 33 and 35 are in their quasi-stable states. Since this sequence of pulses is applied to the control valve 1 7a through the buffer amplifier 42, the control valve 1 7a correspondingly opens or closes, as shown by an intermittent pattern (I) in Fig. 2.

Thus, the first sterilizer consumes the steam intermittently introduced by the control valve 1 7a in accordance with the profile of steam load demand as indicated by (G) in Fig. 2.

During this steam loading period, the flipflop 38 is set upon the receipt of the control signal S1 and is reset when the fifth monostable multivibrator 36 returns to its stable state [(H) in Fig. 2].

Accordingly, the output signal from the flipflop 38 is supplied through the buffer amplifier 39 to the output terminal 40 indicating a state where the steam demand by the sterilizer 1 exists.

On the other hand, the sixth monostable multivibrator 37 transfers to the quasi-stable state when the fourth monostable multivibrator 35 returns to its stable state. The quasi-stable state of the sixth monostable multivibrator 37 continues for the period of t6 which is longer than the quasi-stable period t5 of the fifth monostable multivibrator 36. This means that pressurized steam is confined within the sterilizer 1 by keeping the control valve 1 7a closed longer than the period t5. The preserved-pressure-state signal from the sixth monostable multivibrator 37 is supplied through the buffer amplifier 43 to the output terminal 44 and turns on an indication lamp or the light (not shown) in order to facilitate to unload the processed material from the sterilizer 1.

After that, the period is set for manual operation of carrying the material out of the sterilizer and loading new material into the sterilizer 1. In the shown example, the sterilization cycle period is 100 minutes.

Assuming that four sterilizers are involved in the mill, these four sterilizers would be to run one after another with a time difference of 25 minutes by successively supplying the control signals Si to the respective sterilizer control devices 17, at an interval of 25 minutes.

Since the four sterilizers run in accordance with this scheme [(K), (M) and (0) in Fig. 2], and correspondingly the associated loadedstate signals S2 are successively present at an interval of 25 minutes as indicated by (J), (L) and (N) in Fig. 2, then the overall steam load demand required by the four sterilizers would trace a smooth profile (P) in Fig. 2, and there is no significant increase in the overall steam load demand.

However, as evidenced in actual cases, if some of the sterilizers 1 and put into operation later than the predetermined point of time, as shown in Fig. 4, the overall steam load demand will no longer trace a relatively smooth profile, but will experience an abrupt increase as indicated by (P) in Fig. 4.

In the palm oil mill, the loading and unloading of the material into and from the sterilizers are done by manual operation. Possible time lag in such manual operation will necessarily defer the start of the actual operation of the associated sterilizer. The delayed operation of one sterilizer will overlap the operation of the subsequent sterilizer, thus resulting in an abrupt increase in the overall steam load demand as indicated by (P) in Fig. 4.

Such a sudden increase in the overall steam load demand needs steam boilers having a larger capacity capable of supplying steam to the sterilizers, and makes the fuel control devices more complicated, thus rendering the system to be more expensive.

The primary object of the present invention is, therefore, to provide improved sterilizer control devices which assure to avoid any occurrence of abrupt increase in the overall steam load demand as experienced in the prior art due to time lag in manual loading and unloading operation, while enabling use of relatively compact boilers with a relatively simple fuel controls.

In accordance with the present invention, a sterilizer control device includes means which successively generates control signals at preselected intervals, and manually operable means each of which generates a ready signal indicating that the associated one of the sterilizers has been prepared for sterilization. There is also provided a starting means which generates a start signal in response to a simultaneous occurrence of the control signal and the ready signal and supplies the same to the associated steam supply control means which in turn energizes the associated steam supply means, thus initiating the sterilization cycle of the associated sterilizer.Inhibiting means is also provided which monitors the number of the sterilizers 1 in the process of sterilization and operatively inhibits the control signal generating means from generating further control signals when the number of the sterilizers exceeds the preselected number.

In one embodiment, the inhibiting means includes: loaded-state determining means which generates a loaded-state signal indicating that the associated sterilizer 1 is under sterilization, the steam being introduced; overload determining means which analyzes the loaded-state signals from the respective loaded-state determining means and generates an overloadedstate signal indicating that the number of the sterilizers under sterilization exceeds the preselected number; and means which prevents, in response to the overloaded-signal, the control signal generating means from generating a further control signal.

The above and other objects, the features and advantages of the present invention will be apparent from the following descriptions taken in conjunction with the accompanying drawings in which: Fig. 1 is a schematic diagram of a typical palm oil mill including a plurality of sterilizers and the associated control devices which are subject matter of the present invention; Figs. 2-4 relate to the prior art, more specifically, Fig. 2 being a time chart of various signals associated with sterilization in an ideal case, Fig. 3 being a block diagram of a valve control circuit of a steam supply control device for each of the sterilizers in the prior art, and Fig. 4 being a time chart similar to Fig. 2 but indicating an abrupt increase in the overall steam load demand as experienced in actual cases in the prior art; and Figs. 5-7 relates to an embodiment of the present invention, more specifically, Fig. 5 being a block diagram of a sterilizer control device in accordance with the present invention, Fig. 6 being a block diagram of a valve control circuit of a steam supply control device for each of the sterilizers, and Fig. 7 is a time chart similar to Fig. 4 but the overall steam load demand traces a relatively smooth profile in accordance with the present invention.

In Fig. 5, there is shown an embodiment of a sterilizer control device for a plurality of four sterilizers 1-1, 1-2, 1-3 and 1-4 each of which receives steam via the associated steam supply lines 16b-1, 16b-2, 16b-3 and 16b-4.

Valve control circuits each having an similar arrangement with one another are incorporated with the respective steam supply lines. Fig. 6 shows an arrangement of such a valve control circuit designated by a reference numeral 30'.

More specifically, each valve control circuit 30' includes an AND gate 41a having two inputs, one connected to the output of the OR gate 41 and the other connected to the non inverting output of the flip-flop 38. The start signal input terminal 31 is connected to the set input of the flipflop 38 via a delay circuit 38a, and also connected to the second reset input of the flip-flop 38 via an inverter 38b.

The remaining portions of the valve control circuit 30' is similar to the prior art valve con trol circuit 30 as shown in Fig. 3 taken in conjunction with the descriptions of the prior art. In Figs. 3 and 6, like components are designated by the same reference numerals or symbols.

In the valve control circuit 30', a steam supply control means 1 7A is formed by the first to sixth monostable multivibrators 32-37, OR gate 41, AND gate 41a, inverter 38b and buffer amplifier 42, while a loaded-state determining means 1 7B comprises the flip-flop 38, delay circuit 38a and buffer amplifier 39.

Turning back to Fig. 5, each of the steam supply control devices 17-1, 17-2, 17-3 and 17-4 includes the above-mentioned valve control circuit 30'. The signal input terminals thereof 31-1, 31-2, 31-3 and 31-4 are connected to the outputs from NAND gates 18-1, 18-2, 18-3 and 18-4, respectively. Each of these NAND gates serves as means for generating a start signal for the sterilization cycle of the sterilizer.

One input of each of NAND gates 18-1 to 18-4 is connected to an corresponding one of switches 19-1, 19-2, 19-3 and 19-4 each of which serves as means for generating a ready signal S4 in response to closing operation of the cover of the sterilizer or manual operation by an operator who confirms that the preparation has been completed for the sterilizer.

Each of the second inputs of NAND gates 181 to 18-4 is connected to an associated output terminal of a programmable sequence controller 20 which functions as means for successively outputting control signals S1 at a preselected interval, here 25 minute interval.

The sequence controller 20 includes further output terminals connected to respective indication iamps 21-1, 21-2, 21-3 and 21-4 for indicating which sterilizer should be prepared next.

On the other hand, the respective loadedstate signal terminals 40-1, 40-2, 40-3 and 40-4 of the steam supply control devices 171 to 17-4 are connected to control inputs of constant current switch elements 22-1, 22-2, 22-3 and 22-4, respectively. One sides of these switch elements 22-1 to 22-4 are connected to a power supply, while the other sides thereof are connected together to be coupled to an inverting input of a comparator 23 in the form of an operational amplifier, and grounded through a resistor 24. The comparator 23 has a non-inverting input coupled to the intermediate junction of a bleeder comprising of series-connected resistors 25 and 26.

The output of the comparator 23 is connected to a control terminal of a gate circuit 28 in the programmable sequence controller 20.

The combination of the above-mentioned constant current switches 22-1 to 22-4, comparator 23 and resistors 24, 25 and 26 form a means for detecting an overloaded-state 29.

Description will now turn to operation of the above-mentioned arrangement by referring to Fig. 7 which corresponds to Fig. 4 with respect to the profile of the overall steam load demand.

The programmable sequence controller 20 starts advancement in response to clock pulses supplied thereto from a clock generator 27 through the enabled gate circuit 28. Then, the sequence controller 20 outputs a control signals S1 at the predetermined point of time, for example 25 minutes after the start to the second sterilizer 1-2. Thus the logic level ''1" is applied to one input of the NAND gate 182 of the second sterilizer 1-2.At this time, if the F.F.B. (fresh fruit bunches) loading operation to the second sterilizer 1-2 has been completed and the switch 19-2 has been turned on to supply a ready signal S4 having the logic level "1" to the other input of the NAND gate 18-2, the output signal of NAND gate 18-2 changes the level from "1" to "O" in response to concurrent receipt of the control signal and the ready signal to its inputs.

This output signal is transmitted as a start signal S5 to the second sterilizer control device 17-2 at the expiration of 25 minutes.

In response to the start signal S5,the monostable multivibrators 32 to 37 operate in the same manner as the prior art, and cooperate with the OR gate 41 and the buffer amplifier 42 so as to open and close the control valve 1 7a in accordance to the preselected intermittent pattern, thus supplying steam to the second sterilizer intermittently [(K) in Fig. 7].

The negative going transition of the start signal S5 is inverted by means of the inverter 38b to level "1" and triggers the flip-flop 38 to the reset state. After that, the flip-flop 38 receives a set input signal from the delay circuit 38a. The output of the flip-flop 38 is fed to one input of the AND gate 41a which does not influence to the steam-loaded-state because the AND gate 41a is controlled by the output from the OR gate 41.

Thus, the output signal from the flip-flop 38 defines a steam-loaded-state signal S2 [(J) in Fig. 7] which remains the logic level ''1'' for a period during which the second sterilizer 1-2 is under sterilization. This signal S2 passes through the buffer amplifier 39 and is outputted from the loaded-state signal terminal 40-2 to the second constant current switch 22-2. The signal S2 keeps the switch 22-2 in the conduction state. Thus, a constant current flows through the resistor 24 to generate a voltage drop of one unit value thereacross.

This voltage drop is applied to the inverting input of the comparator 23.

It is assumed, here, that a reference voltage applied to the non-inverting input of the comparator 23 has a level three times of the unit value. Under this condition, the voltage in question supplied at the inverting input of the comparator 23 is lower than the reference voltage at its non-inverting input. Accordingly, the output of the comparator 23 remains the logic level "1", keeping the gate circuit 28 enabled to pass the clock pulses from the clock generator 27 to the programmable sequence controller 20 which is thus allowed to continue its advancement.

Meanwhile, the programmable sequence controller 20 generates and supplies an indication lamp activating signal S6 to the third indication lamp 21-3 of the third sterilizer 1-3.

The lamp 21-3 is turned on to indicate that the third sterilizer 1-3 is to be put into operation, thus facilitating the manual loading of the F.F.B. into the third sterilizer 1-3.

The programmable sequence controller 20 generates and supplies a positive going control signal S, to the third NAND gate 18-3 of the third sterilizer 1-3 at the point of time when 25 minutes has passed from the start of the operation of the second sterilizer 1-2 [(K) in Fig. 7]. In case that the manual F.F.B.

loading into the third sterilizer 1-3 is deferred behind the predetermined point of time, the signal from the third switch 19-3 to the second input of the third NAND gate 18-3 remains the "0" level that indicates the third sterilizer is still unprepared for the sterilization.

Thus, the output of the NAND gate remains the same level "1" until the ready signal S4 from the third switch 19-3 goes "1". When the output signal of the third NAND gate 18-3 makes transition from the level "1" to the level "0", the third sterilizer 1-3 starts its operation ((M) in Fig. 7]. In the illustrated example, the sterilization cycle of the third sterilizer 1-3, which should commence at the predetermined point of time of "50 minutes", actually begins at the point of time of "72 minutes" with 22 minute lag with respect to the predetermined point of time [(L) in Fig. 7].

Also the positive going transition of the steam-loaded-state signal S2 associated with the third sterilizer 1-3 renders the third constant current switch 22-3 into conduction. At this point of time, however, the loaded-state signal S associated with the second sterilizer 1-2 has already returned to its normal level "0", and the second constant current switch 22-2 is in the non-conductive state [(J) in Fig.

7]. Thus, only one of the switches, here the third switch 22-3, is being switched on.

Therefore, the output of the comparator 23 remains the logic level "1", keeping the programmable sequence controller 20 advancing.

The controller 20 then generates and supplies a lamp activating signal S6 to the fourth indication lamp 21-4, and thereafter supplies a control signal S1 of the logic level "1" to the NAND gate 18-4 associated with the fourth sterilizer 1-4 at the predetermined point of time of "75 minutes". Since the manual loading of F.F.B into the third sterilizer 1-3 was deferred well behind the predetermined point of time, delay is also introduced in F.F.B.

loading into the fourth sterilizer 1-4. Accord ingiy, the ready signal S4 does not arrive at the predetermined point of time "75 minutes". When the belated ready signal S4 arrives at the point of time "90 minutes", this initiates operation of the fourth sterilizer 1-4 [(O) in Fig. 7]. The associated loaded-state signal S2 also goes to the level "1" at this point of time ((N) in Fig. 7]. As is noted from the comparison between the signals (L) and (N) in Fig. 7, a period during which loaded-state signal S2 associated with the fourth sterilizer is supplied to the fourth constant current switch 22-4 partly overlaps with a period during which the loaded-state signal S2 associated with the third sterilizer 1-3 is supplied to the third constant current switch 22-3.Since two switches 22-3 and 22-4 are placed in conduction during this overlapping period, the inverting input of the comparator 23 receives twice of the unit value. This value is still lower than the reference voltage at the non-inverting input, so the output of the comparator 23 remains the logic level ''1'', keeping the programmable sequence controller 20 advancing.

After sending a lamp activating signal S6 to the first indication lamp 21-2 to indicate that the first sterilizer 1-1 is to be prepared for sterilization, the programmable sequence controller 20 generates and supplies a control signal S1 of the logic level ''1'' to one input of the first NAND gate 18-1 associated with the first sterilizer 1-1 at the predetermined point of time "0 minute" in Fig. 7. At this point, the second input of the NAND gate 18-1 is also provided with the ready signal S4 of the logic level "1" from the switch 19-1, so the output of the NAND gate 18-1 goes to "O" and this transition is transmitted to the start signal terminal 31-1 of the first steam supply control device 17-1.Correspondingly, operation of the first sterilizer 1-1 is initiated, and the loaded-state signal S2 is supplied to the first constant current switch 22-1 to render the switch 22-1 into conduction.

As is noted from the comparison between the signals (H), (L) and (N) in Fig. 7, at the start time of the first sterilizer 1-1, both the third and fourth sterilizers 1-3 and 1-4 have already been in operation, so the total number of the sterilizers under sterilization reaches to three. Then, the three loaded-state signals S2 associated with the sterilizers 1-1, 1-3 and 14 are applied to the first, third and fourth constant current switches 22-1, 22-3 and 224. This means that a signal having three times of the unit value is applied to the inverting input of the comparator 23. Since the signal level of the inverting input reaches the signal level of the non-inverting input, the output of the comparator 23 goes to the logic level "0" which indicates an overioaded-state signal S7.

In response to this signal S7, the gate circuit 28 continues to count the clock pulses and controls the programmable sequence controller 20 such that the control signal S1 of the level "1" for the sterilizer 1-1 has been stopped and the signal level of the control signal S, is kept at the logic level "0" until the predetermined point of time of the second sterilizer 12 arrives. Thus, at the time of changing of the output from comparator 23 to "0", the start signal S5 outputted from the NAND gate 18-1 also turns to the logic level "1". This signal is inverted by means of the inverter 38b to the level "0" and supplied to the second reset input of the flip-flop 38. The flip-flop 38 is locked to the reset state and remains this reset state until the next control signal S5 of the level "0" arrives at the start signal input terminal 31.

As long as the flip-flop 38 remains the reset state, the output of the flip-flop 38 also remains the logic level "0" and disables the AND gate 41a. Then the signal of the level "1" from the OR gate 41 is inhibited by the AND gate 41a, thus keeping the control valve 1 7a closed irrespective of operation of the monostable multivibrators 32 to 36.

Accordingly, the first sterilizer 1-1 does not actually start its operation at the predetermined point of time "0 minute" [see (I) in Fig.

7], thus avoiding any significant overload of the steam demand. Twenty five minutes later therefrom, the second sterilizer 1-2 comes into operation. At this point of time, no other sterilizer is held in the steam loaded state.

Thus, the ready signal S4 from the switch 192 associated with the second sterilizer 1-2 is accepted so that the actual sterilization of the second sterilizer 1-2 is initiated.

The pattern (P) in Fig. 7 shows the overall steam load demand.

While the present invention has been described with respect to a particular embodiment for the purpose of illustration only, various modifications and alternations can be easily carried out without departing from the scope of the invention defined by the accom

Claims (4)

panying claims. For example, a microprocessor can be used instead of the overloaded-state detecting means in the embodiment. Such a microprocessor may read the state of each steamloaded-state signals at every predetermined time and check the number of the occurrence of the steam-loaded-state signals. CLAIMS

1. A sterilizer control apparatus for a plurality of sterilizers in a palm oil mill including steam supply means for supplying steam to the sterilizers and steam supply control means operative in response to start signals for controlling the steam supply means such as to supply the steam to the respective sterilizers in accordance with the predetermined intermittent pattern, said apparatus comprising:: control signal generating means for successively generating control signals at predetermined time intervals; starting means for generating the start signal upon simultaneous receipt of both reedy signal generated when the associated sterilizer is ready for sterilization, and the control signal from the control signal generating means, and supplying the start signal to the steam control means; loaded-state determining means for generating a loaded-state signal by deciding whether the sterilizer is in the loaded state; overload determining means operable in response to the loaded-state signals from the loaded state determining means for producing an overloaded-state signal when the number of the sterilizers in the loaded state is not smaller than the preselected number; and inhibiting means responsive to the overloaded-state signal for preventing the control signal generating means from generating further control signal.

2. Apparatus according to Claim 1, said control signal generating means is a programmable sequence controller.

3. Apparatus according to Claim 1, said control signal generating means is a microprocessor.

4. Apparatus according to Claim 1 substantially as described in this specification with reference to and as illustrated by Figs. 5 and 6 of the accompanying drawings.