OPERATION OF A COOLING UNIT WITH A MINIMAL WORKING PRESSURE

TECHNICAL FIELD

The present invention starts from an operating method for a cooling unit for cooling a hot rolled material made of metal,

wherein the cooling unit has a header line, into which a liquid coolant is fed by means of a pump assembly and from which a plurality of branch lines branch off to application units,
wherein the pump assembly has a number of pumps, a control valve is arranged in each of the branch lines, and the coolant is applied to the rolled material by means of at least some of the application units,
wherein setpoint flows which are to be fed to the application units are communicated to a control unit of the cooling unit,
wherein the control unit actuates the pump assembly in accordance with a final actuation state and the control valves in accordance with actuation values.

The present invention furthermore starts from a computer program which comprises machine code which can be executed by a control unit of a cooling unit for cooling a hot rolled material made of metal, wherein the execution of the machine code by the control unit causes the control unit to operate the cooling unit in accordance with an operating method of this kind.

The present invention furthermore starts from a control unit of a cooling unit for cooling a hot rolled material made of metal, wherein the control unit is programmed with a computer program of this kind, with the result that the control unit operates the cooling unit in accordance with an operating method of this kind.

The present invention furthermore starts from a cooling unit for cooling a hot rolled material made of metal,

wherein the cooling unit has a header line, a pump assembly and a plurality of application units,
wherein a liquid coolant is applied to the rolled material by means of at least some of the application units,
wherein the application units are connected to the header line via a respective branch line,
wherein the pump assembly has a number of pumps, by means of which the liquid coolant is fed into the header line,
wherein a control valve is arranged in each of the branch lines,
wherein the cooling unit has a control unit of this kind, which operates the cooling unit in accordance with an operating method of this kind.

PRIOR ART

The abovementioned subject matter is common knowledge.

For example, WO 2013/143 925 A1 discloses a cooling unit for cooling a hot rolled material made of metal in which a liquid coolant is fed by means of a pump assembly into a header line, from which branch lines branch off to application units, by means of which the coolant is applied to the rolled material. Control valves are arranged in the branch lines. On the basis of setpoint flows which are known to it and which are to be fed to the application units, the control unit determines an actuation state for the pump assembly and actuation values for the control valves and actuates the pump assembly and the control valves accordingly. In WO 2013/143 925 A1, the header line is either under high pressure or under low pressure. The higher pressure of the coolant is generated only when this is actually required. The requirement for the high pressure is considered to be present if, at low pressure, the open position of at least one valve would exceed a certain open position specified as a limit value.

WO 2014/124 867 A1 likewise discloses a cooling unit for cooling a hot rolled material made of metal in which a liquid coolant is fed by means of a pump assembly into a header line, from which branch lines branch off to application units, by means of which the coolant is applied to the rolled material. Control valves are arranged in the branch lines. Setpoint flows which are to be fed to the application units are communicated to a control unit of the cooling unit. The control unit determines corresponding actuation values of the control valves and also actuates them in this way. No statements are made in WO 2014/124 867 A1 about — optionally variable — actuation of the pump.

WO 2014/124 868 A1 likewise discloses a cooling unit for cooling a hot rolled material made of metal in which a liquid coolant is fed by means of a pump assembly into a header line, from which branch lines branch off to application units, by means of which the coolant is applied to the rolled material. Control valves are arranged in the branch lines. On the basis of setpoint flows which are to be fed to the application units, a control unit of the cooling unit determines a total flow and, on the basis of the total flow, an actuation state of the pump assembly. The working pressure in the header line can be set between a minimum value and a maximum value. The control valves can be adjusted between fully closed and fully open positions. In order to set the individual setpoint flows, the control unit varies both the open positions of the valves and the line pressure which the pump generates in the header line.

WO 2019/115 145 A1 likewise discloses a cooling unit for cooling a hot rolled material made of metal in which a liquid coolant is fed by means of a pump assembly into a header line, from which branch lines branch off to application units, by means of which the coolant is applied to the rolled material. Control valves are arranged in the branch lines. As a function of the setpoint flows which are to be fed to the application units, a control unit determines an actuation state for the pump assembly. In addition to the total quantity of water to be fed, the control unit takes into account a change in the quantity of water and a line resistance. If the open positions of the control valves fall below minimum distances from a minimum possible open position and a maximum possible open position, the actuation state of the pump and thus also the working pressure are adapted.

WO 2020/020 868 A1 discloses a cooling unit for cooling a hot rolled material made of metal in which a liquid coolant is applied to the rolled material by means of a plurality of application units. The application units are each fed by means of a dedicated pump. Valves between the respective pump and the respective application unit are kept continuously in a fully open state. The quantities of coolant delivered are set exclusively by corresponding time-variable actuation of the pumps.

SUMMARY OF THE INVENTION

Particularly in the case of intensive cooling, but sometimes also in the case of laminar cooling, the control valves are fed by means of pumps. In this case, a typical arrangement is a supply to a plurality of control valves via a header line, the header line being supplied with coolant by a pump assembly. The pump assembly can have one pump or a plurality of pumps.

The coolant is applied to the rolled material by means of the application units (these are often designed as spray bars). In some cases, additional application units may be present which do not apply the coolant to the rolled material but discharge the coolant at some other point. This can be useful, for example, to make the quantity of coolant which is delivered as a whole more uniform.

It is the object of the present invention to provide ways in which a conventional cooling unit, that is to say a cooling unit in which the metering of the coolant applied to the rolled material takes place via the actuation of control valves, can be operated in an improved manner.

The object is achieved by means of an operating method having the features of claim 1. Advantageous refinements form the subject matter of dependent claims 2 to 5.

According to the invention, an operating method of the type mentioned at the outset is configured in such a way that, to determine the final actuation state of the pump assembly and the actuation values of the control valves, the control unit

determines a respective individual working pressure for the control valves for a respective limit modulation value of the respective control valve, which working pressure must prevail in the header line so that the respective setpoint flow flows in the respective branch line,
determines a provisional actuation state of the pump assembly, with the result that a total flow of coolant which corresponds to the sum of the setpoint flows is fed to the header line by means of the pump assembly, and at the same time a provisional working pressure which is at least as high as the highest of the individual working pressures prevails in the header line,
determines the final actuation state of the pump assembly in such a way, using the provisional actuation state of the pump assembly, that the total flow of coolant is fed to the header line by means of the pump assembly and, at the same time, a final working pressure prevails in the header line, and
determines the actuation values of the control valves in such a way, using the final working pressure, that the respective setpoint flow flows in the respective branch line.

This ensures that the pump assembly of the cooling unit is operated at the lowest possible final working pressure and thus at the lowest possible energy consumption, and nevertheless the rolled material is at all times cooled in accordance with the required setpoint flows.

It is possible for the limit modulations of the control valves to be the maximum modulations of the control valves. In order to obtain a certain control reserve, however, it may be advantageous if the limit modulations of the control valves are slightly below this, that is to say are only in the vicinity of the maximum modulations of the control valves. In the latter case, the limit modulations of the control valves thus correspond to a high percentage of the maximum modulations of the control valves, e.g. 80%, 90% or 95%. Of course, the limit modulations can also have other values. In particular, however, a value of 80% should not be undershot. The numerical data also relate to the coolant flows, i.e. the effect resulting from the actuation of the respective control valve. On the other hand, they do not relate to the manipulated variables with which the control valves are actuated. The limit modulations can be specified individually as required for the respective control valve or can be specified uniformly for all the control valves. It is also possible to specify in groups.

As part of the determination of the provisional actuation state, the control unit preferably takes into account secondary conditions relating to the pump assembly. This makes it possible to ensure that the pump assembly is always operated in a permissible operating range. The control unit can check, for example, whether it can determine a permissible actuation state of the pump assembly, in which the pump assembly, on the one hand, delivers the required total flow and, on the other hand, brings about the highest of the determined individual working pressures in the header line. If this is the case, this working pressure or a value derived directly from this working pressure can be used as the final working pressure. If this is not the case, the control unit can increase the working pressure stepwise, starting from the provisional working pressure, until a permissible actuation state of the pump assembly is found.

As part of the determination of the provisional actuation state, the control unit preferably takes into account secondary conditions relating to the control valves. It is possible, for example, for a permissible actuation state of the pump assembly which, on the one hand, delivers the required total flow and, on the other hand, brings about a working pressure in the header line which is at least as high as the highest of the individual working pressures, for the control unit to determine the associated actuation values of the control valves and check whether and, if appropriate, to what extent unwanted states occur. If this is the case, either the unwanted states can be accepted or the actuation state of the pump assembly can be adapted. The action to be taken can be decided on a case-by-case basis.

As part of the determination of the final actuation state of the pump assembly, the control unit preferably additionally takes into account at least one previous final actuation state of the pump assembly and/or at least one provisional actuation state of the pump assembly which is expected in the future. For example, the control unit can perform a model-predictive determination of the provisional actuation state. The control unit can also, for example, set up an optimization problem which includes, on the one hand, the minimization according to the invention of the provisional working pressure and, on the other hand, further circumstances. Examples of such circumstances are a change in the provisional or final working pressure and a change in the actuation state of the pump assembly.

The object is furthermore achieved by means of a computer program having the features of claim 6. According to the invention, the execution of the computer program has the effect that the control unit operates the cooling unit in accordance with an operating method according to the invention.

The object is furthermore achieved by means of a control unit having the features of claim 7. According to the invention, the control unit is programmed with a computer program according to the invention, with the result that the control unit operates the cooling unit in accordance with an operating method according to the invention.

The object is achieved by means of a cooling unit for cooling hot rolled material made of metal having the features of claim 8. According to the invention, a cooling unit of the type mentioned at the outset has a control unit according to the invention which operates the cooling unit in accordance with an operating method according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-described properties, features and advantages of this invention and the manner in which these are achieved will become more clearly and distinctly comprehensible in conjunction with the following description of the illustrative embodiments, which are explained in greater detail in combination with the drawings. Here, in schematic illustration:

FIG. 1 shows a rolling line having a first cooling unit,

FIG. 2 shows a characteristic curve of a control valve,

FIG. 3 shows a flow diagram,

FIG. 4 shows a characteristic curve of a pump,

FIG. 5 shows a flow diagram,

FIG. 6 shows a pump assembly,

FIG. 7 shows a flow diagram, and

FIG. 8 shows a flow diagram.

DESCRIPTION OF THE EMBODIMENTS

According to FIG. 1, a rolling line has at least one roll stand 1. FIG. 1 shows only a single roll stand 1. In many cases, however, there is a plurality of roll stands 1 arranged in series, and therefore the rolling line is designed as a roll train. In the rolling line, a hot rolled material 2 is rolled, i.e. its cross section is reduced. The rolled material 2 can consist of steel or aluminum, for example. However, it can also consist of some other metal, for example brass or copper. The rolled material 2 can be a flat rolled material, for example a strip or a plate. However, it may also have some other shape, being rod-shaped or designed as a profile or as a tube.

The rolling line furthermore has a cooling unit 3. According to the illustration in FIG. 1, the cooling unit 3 is arranged downstream of the roll stand 1. However, this is not absolutely necessary. The cooling unit 3 could likewise be arranged upstream of the roll stand 1, for example in the form of a so-called inter-stand cooling means between the finishing stands of a multi-stand finishing train or in the form of a roughed-strip cooling means between the first finishing stand of a multi-stand finishing train and a roughing stand. Other arrangements are also possible.

The cooling unit 3 has a header line 4. A liquid coolant 6 is fed into the header line 4 by means of a pump assembly 5. For this purpose, the pump assembly 5 can be connected, for example, to a reservoir 7 on the inlet side. However, other embodiments are also possible, for example direct supply of the pump assembly 5 via a water distribution network. According to the illustration in FIG. 1, the pump assembly 5 can have a plurality of pumps 8. In the embodiment according to FIG. 1, the pumps 8 are connected in parallel with one another. However, the pumps 8 could also be arranged in series with one another. Combinations of this approach are also possible, for example three lines, in each of which two pumps 8 are arranged in series with one another. It is also possible for just a single pump 8 to be present. The coolant 6 is usually water or consists at least substantially (98% and more) of water.

Branch lines 9a to 9d branch off from the header line 4 to application units 10a to 10d. The application units 10a to 10d are thus connected to the header line 4 via the branch lines 9a to 9d. By means of the application units 10a to 10d, the coolant 6 is applied to the rolled material 2. The application units 10a to 10d can be designed as so-called cooling bars or spray bars, for example.

According to the illustration in FIG. 1, the application units 10a to 10d are arranged above the rolled material 2 and consequently apply the coolant 6 to the rolled material 2 from above. However, this is not absolutely necessary. The application units 10a to 10d could likewise be arranged below the rolled material 2 or arranged at some other location. It is also possible for the application units 10a to 10d to apply the coolant 6 to the rolled material 2 from different sides. It is also possible that not all the application units 10a to 10d apply the coolant 6 to the rolled material 2 but that at least one — and, if so, usually one or two — of the application units 10a to 10d does not apply the coolant 6 to the rolled material 2. Corresponding embodiments and the reasons therefor are explained in the already cited WO 2019/115 145 A1, for example.

Furthermore, a total of four application units 10a to 10d are illustrated in FIG. 1. The present invention is explained in conjunction with this number of application units 10a to 10d. However, the number of application units 10a to 10d could also be larger or smaller. It has only to be greater than 1. There are thus at least two application units 10a to 10d which are connected to the header line 4 via two branch lines 9a to 9d, wherein a control valve 11a to 11d is arranged in each of the branch lines 9a to 9d.

Control valves 11a to 11d are arranged in each of the branch lines 9a to 9d. The control valves 11a to 11d can be designed as ball valves, for example. Regardless of their specific design, however, the control valves 11a to 11d can be adjusted continuously. The term “adjust continuously” is explained below with reference to the illustration in FIG. 2 for control valve 11a. Analogous statements apply to control valves 11b to 11d.

According to FIG. 2, control valve 11a is actuated by means of an actuation value Aa. The actuation value Aa lies between a minimum actuation value Amin and a maximum actuation value Amax. The actuation value Aa can be varied continuously or at least in a plurality of steps. The actuation value Aa can thus assume a plurality of possible values between the minimum actuation value Amin and the maximum actuation value Amax - optionally within the scope of an adjustment accuracy. For example, in the case of a ball valve, the minimum actuation value Amin and the maximum actuation value Amax can be 0° and 90°, and the actuation value Aa can be adjusted in steps of, for example, 0.1° or 0.2° between these two extreme values Amin, Amax.

At a reference pressure pR, which is present on the inlet side of control valve 11a, a corresponding reference coolant flow KR flows through control valve 11a and thus through the corresponding branch line 9a, depending on the actuation value Aa. Because of the possibility of continuously adjusting control valve 11a, the reference coolant flow KR also passes through a corresponding value continuum between a minimum value KRmin (usually 0) and a maximum value KRmax (which is, of course, greater than the minimum value KRmin). The reference coolant flow KR divided by the maximum value KRmax corresponds to a modulation ka of control valve 11a. The modulation ka has a maximum value of 1 and usually a minimum value of 0.

The functional relationship of the reference coolant flow KR (or, as an equivalent thereof, modulation ka) as a function of the actuation value Aa corresponds to a characteristic curve for control valve 11a. According to the illustration in FIG. 2, the characteristic curve is often non-linear. However, there is usually a strictly monotonic relationship between the actuation value Aa, on the one hand, and the reference coolant flow KR or modulation ka. As is also known to those skilled in the art, at a given actuation value Aa, the actual coolant flow Ka — i.e. the quantity of coolant 6 actually flowing through control valve 11a — can be readily determined, provided that the working pressure pA present on the inlet side of control valve 11a is known. In particular, the value obtained from the characteristic curve itself need only be scaled with the root of the quotient of the working pressure pA and the reference pressure pR. The working pressure pA and the reference pressure pR may also have to be corrected by an offset. With a given modulation ka and a known maximum reference coolant flow KRmax and a known working pressure pA, the coolant flow Ka is thus

$K_{a} = \sqrt{\frac{p A - ρ \cdot g \cdot h a}{p R - ρ \cdot g \cdot h a}} \cdot k a \cdot K R \max$

ρ is the density of the coolant 6, g is the acceleration due to gravity. ha is the height of the valve outlet (or of the application unit 10a) relative to a reference level which is uniform for the application units 10a to 10d. Depending on the arrangement of the valve outlet relative to the reference level, hA can be greater than or less than 0. The reference level can be selected as required. It can, for example, coincide with the level of a roller table by means of which the rolled material 2 is conveyed through the cooling unit 3. The associated actuation value Aa is obtained directly from the characteristic curve after determination of the modulation ka.

The cooling unit 3 furthermore has a control unit 12, which controls and operates the cooling unit 3. In general, the control unit 12 is designed as a software-programmable unit. This is indicated in FIG. 1 by the fact that the symbol “µP” for microprocessor is drawn in within the control unit 12. The control unit 12 is programmed by means of a computer program 13. The computer program 13 comprises machine code 14 that can be executed by the control unit 12. On the basis of the programming with the computer program 13 or the execution of the machine code 14, the control unit 12 operates the cooling unit 3 in accordance with an operating method which will be explained in greater detail in the following in conjunction with FIG. 3.

In a step S1, setpoint flows Ka* to Kd* are communicated to the control unit 12. The setpoint flows Ka* to Kd* indicate, for example in liters per second, the quantities of coolant 6 which are to be fed to the respective application unit 10a to 10d and discharged by the respective application unit 10a to 10d, in particular are to be applied to the rolled material 2. For example, the setpoint flows Ka* to Kd* of the control unit 12 can be specified externally or can be determined independently by the control unit 12 on the basis of other conditions. Appropriate procedures are common knowledge among those skilled in the art.

In a step S2, the control unit 12 determines an individual working pressure pAa for a limit modulation value kLim of control valve 11a. The limit modulation value kLim is specified to the control unit 12. The limit modulation value kLim may be the maximum modulation of control valve 11a. In many cases, however, it is advantageous if, in accordance with the illustration in FIG. 2, this is a value which, although close to, is below the maximum modulation of control valve 11a. In this case, the limit modulation value kLim should be at least 80%, preferably at least 90%, particularly preferably at least 95%. However, a value of 98% should not be exceeded as a rule. The limit modulation kLim thus corresponds to a high percentage of the maximum modulation of control valve 11a. As a matter of form, it should be clarified that the limit modulation value kLim relates to the modulation ka of control valve 11a, not to the actuation Aa of control valve 11a.

The control unit 12 determines the individual working pressure pAa in such a way that, at the working pressure pAa and the limit modulation kLim of control valve 11a, the desired setpoint flow Ka* flows in the branch lines 9a. The control unit 12 determines the working pressure pAa, for example in accordance with the equation

$p A a = {(\frac{k a *}{k L i m \cdot K R \max})}^{2} \cdot (p R - ρ \cdot g \cdot h a) + ρ \cdot g \cdot h a$

In a step S3, the control unit 12 determines individual working pressures pAb to pAd in a completely analogous manner for control valves 11b to 11d. The limit modulations kLim, the maximum reference coolant flow KRmax and the reference pressure pR of the other control valves 11b to 11d can have the same values as the limit modulation kLim, the maximum reference coolant flow KRmax and the reference pressure pR of control valve 11a. Alternatively, these may be other values which, if appropriate, may also vary within the other control valves 11b to 11d from control valve 11b to 11d to control valve 11b to 11d. In each case, however, the control unit 12 determines the individual working pressures pAb to pAd of the other control valves 11b to 11d independently of one another and also independently of the individual working pressure pAa of control valve 11a.

In a step S4, the control unit 12 then determines an actuation state Z of the pump assembly 5. The actuation state Z is determined in such a way that, provided it is operated in accordance with the actuation state Z, the pump assembly 5 delivers a total flow K which corresponds to the sum of the setpoint flows Ka* to Kd*. As a result of the delivery of the total flow K, the total flow K of coolant 6 is also fed to the header line 4 by means of the pump assembly 5. At the same time, the actuation state Z is determined in such a way that a working pressure pAv which is at least as high as the highest of the individual working pressures pAa to pAd prevails in the header line 4. However, both the actuation state Z and the working pressure pAv are only provisional. The actuation state Z comprises the required rotational speed n at least for each pump 8 of the pump assembly 5.

It is important in this context that the actuation of the pump assembly 5 can be varied continuously or at least in a plurality of steps. Thus, not only is it possible to switch between two or three fixed, discrete actuation states Z, but the possible actuation states Z form a continuum or a virtual continuum. If — purely by way of example — one of the pumps 8 can be operated between a minimum rotational speed nmin of 100 revolutions/minute and a maximum rotational speed nmax of 800 revolutions/minute, the rotational speed n can also be set to intermediate values between 100 revolutions/minute and 800 revolutions/minute, e.g. 150 revolutions/minute, 227 revolutions/minute or 593 revolutions/minute in the case of infinitely variable adjustability and to at least 10 different stages of, for example, 100, 150, 200, 250, etc., up to 800 revolutions/minute in the case of adjustability in stages. Of course, the numerical values mentioned should be interpreted only as examples.

It is possible, as part of step S4, for the control unit 12 to take into account only the pressure to be generated statically by the pump assembly 5. It is thus possible, as part of step S4, for the control unit 12 to assume that the pressure generated on the outlet side of the pump assembly 8 corresponds to the pressure on the inlet side of the control valves 11a to 11d. However, it is likewise possible for the control unit 12 to take additional circumstances into account. An example of such a circumstance are changes in the setpoint flows Ka* to Kd* with respect to time and associated changes in the total flow K with respect to time and associated accelerations of water quantities. A further example of such a circumstance is a flow resistance between the pump assembly 5 and the header line 4 or in the header line 4, on the basis of which the pressure generated on the inlet side of the control valves 11a to 11d is always less than the pressure generated by the pump assembly 8. For both circumstances, there are corresponding possibilities for taking them into account in the already cited WO 2019/115 145 A1. Any difference in height between the pump assembly 8, on the one hand, and the header line 4 or the reference level of the header line 4, on the other hand, can furthermore be taken into account by means of a constant offset.

In the simplest case, in which there is only a single pump 8, it is possible, for example, for the control unit 12 to determine the rotational speed n of said pump by accessing a family of characteristic curves which, as shown in the illustration in FIG. 4, stores the rotational speed n of the pump 8 which is necessary for the pump 8 to bring about a particular pressure increase δp at a particular total flow K. In conjunction with a suction pressure pS prevailing on the inlet side of the pump assembly 5, the required pressure increase δp = pS-pAv can thus be readily determined. The suction pressure pS may be known to the control unit 12 on the basis of a measurement or in some other way.

In many cases, the actuation state determined for the highest of the individual working pressures pAa to pAd will itself already be a permissible actuation state of the pump assembly 5. In this case, this actuation state can be adopted directly as provisional actuation state Z. Other possibilities and embodiments will be discussed below.

In a step S5, the control unit 12 then determines an actuation state Z′ of the pump assembly 5. In contrast to actuation state Z, actuation state Z′ is final. The control unit 12 determines the final actuation state Z′ of the pump assembly 5 using the provisional actuation state Z of the pump assembly 5. The determination in step S5 is such that the total flow κ of coolant 6 is fed to the header line 4 by means of the pump assembly 5. At the same time — assuming that the pump assembly 5 is actuated in accordance with the final actuation state Z′ — a final working pressure pAe prevails in the header line 4. In the simplest case, the control unit 12 directly and immediately assumes the provisional actuation state Z as the final actuation state Z′. It is also possible to increase the provisional working pressure pAv by a slight additive offset or to multiply it by a factor slightly greater than 1 and thereby to determine the final working pressure pAe. These approaches are similar in their effect to the use of limit modulation values kLim slightly less than 1. Other possibilities and embodiments for determining the final working pressure pAe will be discussed below.

The final actuation state Z′ brings about the final working pressure pAe in the header line 4, provided that the desired total flow K is delivered into the header line 4 by means of the pump assembly 8. The control unit 12 therefore determines, in a step S6, using the final working pressure pAe, the actuation values Aa to Ad of the control valves 11a to 11d. The determination is carried out in such a way that the respective setpoint flow Ka* to Kd* flows in the respective branch line 9a to 9d.

As part of the determination in step S6, the control unit 12 assumes that the final working pressure pAe is prevails in the header line 4. For control valve 11a, for example, the modulation ka is thus

$k a = \sqrt{\frac{p R - ρ \cdot g \cdot h a}{p A a - ρ \cdot g \cdot h a}} \cdot \frac{K a}{K R \max}$

The circumstances are similar for the other control valves 11b to 11d. On the basis of the now known modulations ka to kd of the control valves 11a to 11d, it is thus possible, using the associated characteristic curves, to determine the required actuation values As to Ad of the control valves 11a to 11d.

In a step S7, the control unit 12 actuates the pump assembly 5 and the control valves 11a to 11d. The pump assembly 5 is actuated in accordance with the final actuation state Z′. The control valves 11a to 11d are actuated in accordance with the actuation values Aa to Ad.

With the execution of step S7, the operating method according to the invention has been executed. After executing step S7, the control unit 12 generally returns to step S1, however. That is to say that the control unit 12 carries out the sequence of steps S1 to S7 repeatedly in an iterative manner. As a rule, execution takes place with a fixed cycle time. The fixed cycle time is generally between 0.1 s and 1.0 s, usually between 0.2 s and 0.5 s, for example about 0.3 s.

One possible embodiment of step S4 of FIG. 3, that is to say one possible way of determining the provisional actuation state Z, will be explained below in conjunction with FIG. 5. As part of the embodiment according to FIG. 5, step S4 of FIG. 3 is subdivided into steps S11 to S14.

In step S11, the control unit 12 determines the operating state of the pump assembly 5 which is required to deliver the total flow K and at the same time to bring about the necessary pressure increase δp from the suction pressure pS to the highest of the determined individual working pressures pAa to pAd. If there is only one pump 8, for example, the control unit 12 can determine the corresponding rotational speed n of the pump 8.

In step S12, the control unit 12 checks whether the determined provisional state Z is permissible, e.g. the determined rotational speed n is in the permissible rotational speed range of the pump 8, i.e. the working point of the pump 8 is within the range which is not hatched in FIG. 4. Checking thus implies checking for compliance with a secondary condition relating to the pump assembly 5.

It is possible (and even the normal case) that the rotational speed n is in the permissible rotational speed range of the pump 8. For example, a working point AP1 of the pump 8 that is within the permissible speed range of the pump 8 may be determined by the total flow K and the highest of the individual working pressures pAa to pAd. If the rotational speed n is in the permissible rotational speed range of the pump 8, the control unit 12 proceeds to step S13. In step S13, the control unit 12 does not take any further measures. The determined rotational speed n can be used directly.

However, it is likewise possible (if only rarely) that the rotational speed n is not in the permissible rotational speed range of the pump 8. For example, a working point AP2 or a working point AP3 of the pump 8 may be determined by the total flow K and the highest of the determined individual working pressures pAa to pAd. Admittedly, in the case of working point AP2, the pump 8 can readily generate the highest of the determined individual working pressures pAa to pAd. However, on account of the permissible speed range of the pump 8, the volume flow delivered by the pump 8 is inevitably greater than the required total flow K. In the case of working point AP3, the situation is reversed. Admittedly, the pump 8 can readily generate the required total flow K. However, on account of the permissible speed range of the pump 8, a pressure increase δp which is greater than the minimum required is inevitably produced by the pump 8.

If the rotational speed n is not in the permissible rotational speed range of the pump 8, the control unit 12 proceeds to step S14. In step S14, the control unit 12 modifies the provisional actuation state Z.

In the case of working point AP2, the control unit 12 can determine an open state, e.g. for a short-circuit valve 15 (see FIG. 6). According to the illustration in FIG. 6, the short-circuit valve 15 is connected in parallel with the pump 8. It can be regarded as part of the pump assembly 5 or as a control valve for a further application unit. The control unit 12 determines the open state, if appropriate in such a way that the amount of coolant 6 returned directly or indirectly to the reservoir 7 via the short-circuit valve 15 is such that the resultant remaining volume flow fed to the header line 4 corresponds to the desired total flow K.

In the case of working point AP3, the control unit 12 can, for example, modify the provisional actuation state Z to the effect that, although only the pump 8 is actuated (and consequently the short-circuit valve 15, if present, remains closed), the provisional working pressure pAv generated in the provisional actuation state Z at the desired total flow K is higher than the highest of the individual working pressures pAa to pAd. In this case, the provisional working pressure pAv is preferably set to the minimum of the possible and permissible values.

A further possible embodiment of step S4 of FIG. 3 is explained below in conjunction with FIG. 7. As part of the embodiment according to FIG. 7, step S4 of FIG. 3 is subdivided into steps S21 to S24. The procedure of FIG. 7 can be combined, if required, with the procedure of FIG. 5 or can be implemented independently thereof. In the case of combination, step S21 can be omitted and steps S22 to S24 are carried out after step S13 and S14, respectively.

In step S21 — in a manner analogous to step S11 of FIG. 5 —the control unit 12 determines the rotational speed n of the pump 8 which is required to deliver the total flow K and at the same time to bring about the necessary pressure increase δp from the suction pressure pS to the highest of the determined individual working pressures pAa to pAd.

In step S22, the control unit 12 checks whether the actuations of the control valves 11a to 11d are permissible at the resulting provisional working pressure pAv. The control unit 12 can, for example, check whether adjustment speeds with which the actuation values Aa to Ad of the control valves 11a to 11d are changed comply with predetermined limits. Checking thus implies checking for compliance with secondary conditions relating to the control valves.

It is possible (and even the normal case) that the secondary conditions are met. In this case, the control unit 12 proceeds to step S23. In step S23, the control unit 12 does not take any further measures. The determined rotational speed n can be used directly.

However, it is likewise possible (if only rarely) that the secondary conditions are not met, e.g. that excessively high adjustment speeds occur. In this case, the control unit 12 proceeds to step S24. In step S24 — depending on the situation in the individual case — the control unit 12 can either accept the exceeding of the predetermined limits or adapt the provisional actuation state Z of the pump assembly 5. In particular, under certain circumstances, an increase in the provisional working pressure pAv can be used to ensure that, on account of the corresponding changes in the actuations of the control valves 11a to 11d, the predetermined limits are no longer exceeded, or at least only exceeded to a relatively small extent.

One possible embodiment of step S5 of FIG. 3, that is to say one possible way of determining the final actuation state Z using the provisional actuation state Z of the pump assembly 5, is explained below in conjunction with FIG. 8. As part of the embodiment according to FIG. 8, step S5 of FIG. 3 is replaced by a step S41. In step S41 — in addition to the provisional actuation state Z currently determined in step S4 — the control unit 12 takes into account at least one further actuation state. This may be the immediately preceding final actuation state Z′ or a plurality of preceding final actuation states Z′, for example. Abrupt changes in the final actuation state Z′ can be avoided by low-pass filtering or similar measures, for example.

It is likewise possible for the setpoint flows Ka* to Kd* to be predicted by model prediction within a forecast horizon of a plurality of cycle times — for example five, eight or ten cycle times — and it is thus also possible to determine provisional actuation states Z of the pump assembly 5 which are expected in the future for the forecast horizon. In this case, the future expected provisional actuation states Z of the pump assembly 5 can also be included in the determination of the current final actuation state Z′.

As part of the embodiment according to FIG. 8, it is possible that the final working pressure pAe obtained is lower (even if, in general, only slightly lower) than the highest of the individual working pressures pAa to pAd of steps S2 and S3. It is therefore advantageous, as part of the embodiment according to FIG. 8, if the limit modulation values kLim of the control valves 11a to 11d are smaller than their maximum possible modulations and/or if, first of all, before taking into account further actuation states, a small offset is added to the provisional working pressure pAv, or the provisional working pressure pAv is scaled by a factor slightly greater than 1.

The present invention has been explained above in conjunction with embodiments in which the pump assembly 5 has only a single pump 8. However, embodiments in which the pump assembly 5 has a plurality of pumps 8 are readily possible. In this case, the pumps 8 must be actuated in such a way that all the pumps 8 are either completely shut off, so that they can be treated as if they were not present, or generate the same provisional working pressure pAv and the same final working pressure pAe. However, there is a degree of freedom with respect to the distribution of the total flow K between the individual pumps 8. To resolve this degree of freedom, it is possible, for example, to distribute the total flow K between the pumps 8 uniformly or proportionally to the capacity of the pumps 8. Alternatively, it is possible to only ever actively operate the minimum possible number of pumps 8. In this case, the header line 4 is, if possible, supplied by means of a single pump 8. The next pump 8 is only switched on when the previously operated pump 8 is no longer capable of delivering the required total flow K at the required provisional working pressure pAv or the required final working pressure pAe. Similarly, the next pump 8 in each case is only switched on when the previously operated pumps 8 are no longer able to deliver the required total flow K at the required provisional working pressure pAv or the required final working pressure pAe.

The present invention has also been explained above in respect of a single cooling unit 3. However, it is readily possible for there to be further cooling units 3. In this case, the further cooling units 3 can be controlled by control unit 12 or by some other control unit, depending on requirements. In the case of control by control unit 12, the cooling units 3 can be operated independently of one another.

The present invention has many advantages. In particular, very low energy consumption is achieved. In comparison with operation of the cooling unit 3 with a constant final working pressure pAe, savings of at least 25% and sometimes far more than 80% are obtained. Even in comparison with approaches in which the final working pressure pAe is adapted individually for each rolled material 2 and is kept at a constant level only during the cooling of the respective rolled material 2, there is still a significant energy saving. Admittedly, it is conceivable in theory for the reduction in the final working pressure pAe to lead to such a large deterioration in the efficiency of the pump assembly 5 that energy consumption increases. However, this does not occur in practice. Furthermore, both the mechanics of the control valves 11a to 11d and the mechanics of the pump assembly 5 are preserved. This is because, as a rule, it is advantageous for the control valves 11a to 11d if they are operated so as to be open as wide as possible. It is likewise advantageous for the pump assembly 5 if it is operated at as low a speed as possible. On the other hand, there are no adverse effects on the cooling of the rolled material 2 as such.

Although the invention has been illustrated and described more specifically in detail by means of the preferred illustrative embodiment, the invention is not restricted by the examples disclosed, and other variants can be derived therefrom by a person skilled in the art without exceeding the scope of protection of the invention.

List of reference signs

1

Roll stand

2

Rolled material

3

Cooling unit

4

Header line

5

Pump assembly

6

Coolant

7

Reservoir

8

Pumps

9
a to 9d
Branch lines

10
a to 10d
Application units

11
a to 11d
Control valves

12

Control unit

13

Computer program

14

Machine code

15

Short-circuit valve

Aa to Ad
Actuation values

Amax
Maximum actuation value

Amin
Minimum actuation value

AP1 to AP3
Working points

K
Total flow

ka to kd
Modulations

Ka to Kd
Coolant flows

Ka* to Kd*
Setpoint flows

kLim
Limit modulation value

KR
Reference coolant flow

KRmax
Maximum reference coolant flow

KRmin
Minimum reference coolant flow

n
Rotational speed

nmax
Maximum rotational speed

nmin
Minimum rotational speed

pA, pAv, pAe
Working pressures

pAa to pAd
Individual working pressures

pR
Reference pressure

pS
Suction pressure

S1 to S41
Steps

Z, Z′
Actuation states

5
p

Pressure increase

Number	Date	Country	Kind
20169326.4	Apr 2020	EP	regional
20169741.4	Apr 2020	EP	regional

OPERATION OF A COOLING UNIT WITH A MINIMAL WORKING PRESSURE

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CPC

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