IT201600114834A1 - Control method of a compressed air production and distribution plant - Google Patents

Description

Control method of a compressed air production and distribution plant The invention concerns a control method of a compressed air production and distribution plant. The control method is arranged, in particular, to control through a central controller a compressed air production and distribution plant comprising one or more compressors connected to the central controller and intended to supply one or more service units with compressed air by means of a compressed air distribution network for example of an industrial plant.

In many sectors of the industry compressed air is commonly used as an energy vector to move machine tools or moving parts or to cool or diffuse heat in an industrial plant as it is easily accessible, easily transportable, and can be stored, for example. for example in a tank, and its use instead of electricity leads to considerably fewer safety problems.

However, the energy consumption associated with the compressed air production and distribution system in an industrial plant is considerable.

In fact, the energy consumption associated with the mere production of compressed air by the compressors can affect from 5% up to 40% of the entire energy consumption of the industrial plant.

Furthermore, the distribution of compressed air carried out by the distribution network of the compressed air production and distribution plant of the industrial plant is always associated with energy losses mainly related to pressure losses and leakage losses, which can amount up to 40% of the energy consumption of the industrial plant due to the compressed air production and distribution plant.

Pressure or load losses within the distribution network are generally divided into distributed losses and concentrated losses. The distributed losses are due, in particular, to the friction between the compressed air and the material that constitutes the pipes of the distribution network and to the speed of the compressed air itself inside the pipes. Concentrated losses refer to pressure drops introduced by components of the distribution network in well-defined critical points of the latter, such as, for example, distribution network curves, distribution network bottlenecks, various types of valves that may be present in the distribution network, T-joints of the distribution network. The pressure losses are a function of the length of the pipes (real or equivalent), the diameter of the pipes and the roughness of the materials that make up the pipes and, therefore, the friction between the compressed air flowing inside the pipes and the walls of the pipes themselves.

Leakage losses are due to a mass of air that escapes from the compressed air distribution network through openings originating, for example, from connections that are not well sealed, or caused by wear of the pipes that are not properly maintained. They too are a function of the length of the pipes and the number of connections that are not well sealed.

Due to the high impact that the compressed air production and distribution plant has on the energy consumption of an industrial plant, the need is felt in the industrial sectors that use compressed air as an energy vector to optimize the aforementioned production plant and distribution of compressed air in order to reduce energy losses so as to consequently minimize energy consumption, in particular electricity.

In order to reduce the consumption of electricity related to the compressed air distribution network, it is possible to act on the physical factors of the same, i.e. on the dimensions and physical characteristics of the distribution network pipes that can introduce pressure losses. However, it is not possible to frequently change the physical characteristics of the compressed air distribution network due to the high intervention costs and the long downtime of the compressed air production and distribution plant that each intervention would entail.

Consequently, an attempt was made to reduce electricity consumption by optimizing the production of compressed air.

In order to optimize a compressed air production and distribution plant, there are known control methods for a compressed air production and distribution plant which provide for a controller to vary an operation of each compressor of a plurality of compressors arranged in a compressor room. according to a predetermined sequence, in order to reduce the consumption of electrical energy.

However, a defect of these known control methods is that the sequence according to which the compressors are to be operated in succession is predetermined and, therefore, does not always adapt in the most efficient way to the needs of the service users. The total demand for compressed air by an industrial plant is, in fact, typically variable over the course, for example, of a day and from day to day.

Another defect of the known control methods is that the controller acts only locally at the level of a single compressor room and not the entire compressed air production and distribution plant which can include more than one compressor room, and therefore does not keep account, for example, of the location of the individual compressors in the distribution network. In fact, these control methods of a known type of compressed air production and distribution plant take into account the pressure drops distributed only indirectly, since a pressure loss associated with the length of a pipe is compensated by the production and distribution plant of compressed air by increasing the network pressure of the compressed air produced, so that a desired operating pressure reaches the service users served by this pipe.

An object of the present invention is to improve the control methods of a known type of compressed air production and distribution plant.

Yet another object is to provide a control method for a compressed air production and distribution plant which allows to satisfy the compressed air need of one or more service users with minimum energy consumption.

A further object is to provide a control method for a compressed air production and distribution plant which is economical and simple to implement even on existing plants.

According to the invention, a control method is provided for a compressed air production and distribution plant as indicated in claim 1.

Thanks to a controlled production of compressed air and to a resolution at pre-established time intervals of a consumption optimization algorithm, the control method of a compressed air production and distribution plant according to the invention is able to minimize the consumption of electricity used by the compressors of the compressed air production and distribution plant to generate a desired quantity of compressed air from the service units of the compressed air production and distribution plant.

The invention can be better understood and implemented with reference to the attached drawings which illustrate an exemplary and non-limiting form of implementation in which:

Figure 1 is a diagram of a compressed air production and distribution plant controlled by a control method of a compressed air production and distribution plant according to the invention managed by a remote central controller;

Figure 2 is a flow rate / power graph showing three operating states of a load / unload compressor;

Figure 3 is a flow / power graph showing a trend of the power as a function of the flow rate of a compressor of the type with inverter.

With reference to Figure 1, a compressed air production and distribution plant 1 controlled by a control method of a compressed air production and distribution plant according to the invention is shown, which method is implemented by a remote central controller 100 .

In the following, an exemplary and non-limiting embodiment of the compressed air production and distribution plant 1 will be described.

The compressed air production and distribution plant 1 comprises a compressed air production arrangement, arranged to compress a fluid, in particular air, so as to produce compressed air, and a compressed air distribution network 2, shown with continuous line in Figure 1.

The compressed air distribution network 2 connects the compressed air production arrangement to a service unit arrangement to supply the service unit arrangement with a flow of compressed air generated by the compressed air production arrangement.

The arrangement of service units comprises a plurality of service units, each of which is schematically shown in Figure 1 by means of a rectangle and can be, for example, a department of an industrial plant. In Figure 1 the plurality of service units comprises four service units, i.e. a first service unit 3, a second service unit 4, a third service unit 5 and a fourth service unit 6, but of course the service units they can be in a different number (both in greater and lesser numbers) than the four service units of Figure 1 and they can be placed differently with respect to their location in Figure 1.

The compressed air production arrangement includes a plurality of compressors, each compressor also being schematically shown in Figure 1 through a rectangle.

The compressed air distribution network 2 comprises pipes, passages, valves and other possible components of a known type arranged to connect the plurality of service units to the plurality of compressors.

The control method of a compressed air production and distribution plant according to the invention is implemented by the remote central controller 100 to optimize the compressed air production and distribution plant 1, so as to minimize an electrical energy consumption inherent in the plurality of compressors, this electrical energy being used to generate a desired quantity of compressed air from the plurality of service units of the compressed air production and distribution plant 1.

In Figure 1, the plurality of compressors comprises a first group of compressors 8 which can comprise, for example, three compressors, i.e. a first compressor 9, a second compressor 10 and a third compressor 11, arranged side by side and distant from the arrangement of units. of service. The first group of compressors 8 can be arranged inside a compressor room 24.

The plurality of compressors may further comprise a second group of compressors 12 each compressor being arranged, for example, in proximity to a respective service unit. In the example of Figure 1, the second group of compressors 12 comprises a fourth compressor 13 which supplies, in particular, the fourth service unit 6. This fourth service unit 6 can in any case also be powered by one or more of the compressors of the first group. of compressors 8.

Naturally, the compressors can also be in a different number (both in greater and lesser numbers) than the four compressors in Figure 1 and can be positioned differently with respect to their location in Figure 1.

Further groups of compressors equipped with one or more compressors can also be provided in the compressed air production and distribution plant 1, each further group of compressors being arranged in further compressor rooms or comprising compressors distributed and located near respective service units .

Each compressor is provided with a respective electrical power supply device 7, schematically shown in Figure 1 by means of a circle and arranged to supply a respective compressor with electrical energy.

Each compressor is associated with other components of a known type and for this reason not further described in detail, such as, for example, an engine, a cooling system and a transmission, arranged to allow obtaining a mass of compressed air suitable for the requirements of the arrangement. of service units that it has to supply. Each compressor also comprises a monitoring device, not shown in the Figures, arranged to acquire, substantially continuously and in real time, operating data of the respective compressor, such as, for example, power, flow rate, the number of hours charged, the number of hours preceding a maintenance operation on the compressor and the number of idle hours. Each monitoring device can be provided with a display arranged to show such operating data to an operator. The plurality of compressors comprises at least one compressor of the load / unload type, or also called load / unload, operating at fixed speed, for example the first compressor 9, the second compressor 10 or the third compressor 11, a typical representation of which operation is shown in Figure 2.

Considering a Cartesian reference plane having the flow rate on the abscissa and the power on the ordinate, a compressor of the load / unload type has a first operating state corresponding to a first point A of the Cartesian reference plane having coordinates (0; 0) and associated to a non-operating condition of the load / unload type compressor, i.e. compressor off, in which the load / unload type compressor does not produce a flow of compressed air or consume electricity, that is, it does not absorb power.

The compressor of the load / unload type also has a second operating state corresponding to a second point B having coordinates (0; Psc) and associated with an empty operating condition of the load / unloading type compressor, in which the compressor of the load / unload type does not produce a flow of compressed air but consumes electrical energy, ie it absorbs a power equal to the no-load power Psc. The value of the no-load power Psc is a characteristic technical data of each compressor of the load / unload type.

Finally, the compressor of the load / unload type also has a third operating state corresponding to a third point C having coordinates (Qnom; Pnom) and associated with an operating condition for the compressor of the load / unloading type, in which the load / unload type compressor produces a compressed air flow rate equal to its nominal flow rate Qnom and consumes electricity, i.e. it absorbs a power equal to its nominal power Pnom. The values of the nominal flow rate Qnom and the nominal power Pnom are characteristic technical data of each compressor of the load / unload type.

The flow rate / power graph of a load / unload compressor is therefore described by a non-continuous function. In fact, the operating states of a load / unload compressor are discrete.

The plurality of compressors may further comprise a compressor of the type with a frequency variator, so-called inverter, capable of varying the speed of the motor of a compressor 9, 10, 11, 13 by varying the power supply frequency of the motor itself. Figure 3 shows a curve of a typical trend of the power as a function of the flow rate of a compressor of the type with inverter.

The flow rate / power graph of a compressor of the type with inverter is a function that can be substantially approximated to a straight line and is therefore continuous and derivable in an interval between a minimum flow rate value Qmin and the nominal flow rate value Qnom, these minimum flow rates Qmin and nominal Qnom being characteristic of the corresponding inverter type compressor. The compressor of the type with inverter can therefore continuously assume a plurality of operating states, each of which corresponds to a point on this line, identified by an abscissa value between the minimum flow rate value Qmin and the nominal flow rate value. Qnom.

In Figure 1 the number of compressors 9, 10, 11, 13 is equal to the number of service units 3, 4, 5, 6, but this number can also differ.

The compressed air distribution network 2 is unique in that all compressors 9, 10, 11, 13 produce respective quantities of compressed air introduced on the same line. In addition, the compressors are arranged in parallel on the compressed air distribution network 2 and can supply any service unit 3, 4, 5, 6. This allows, for example, the fourth service unit 6 to simultaneously absorb compressed air (both from the first group of compressors 8 and from the second group of compressors 12) and supply compressed air to the compressed air distribution network 2. It follows that there is at least one bi-directional section 14 of the compressed air distribution network 2 in which the compressed air can flow in both directions, ie along a first direction identified by arrow F1 in Figure 1 and along a second direction identified by arrow F2 in Figure 1, the second direction being opposite to the first direction.

The compressed air production and distribution plant 1 can also comprise an accumulation plant in the form of one or more tanks, not shown in the Figures, associated with the compressed air distribution network 2 to stabilize the pressure in the distribution network. of compressed air 2 acting, in other words, as a lung.

Furthermore, the compressed air production and distribution plant 1 may further comprise an air treatment plant, also not shown in the Figures, associated with the compressed air distribution network 2 to improve the purity characteristics of the 'air.

The air treatment system may also include one or more filters, not shown in the Figures, arranged to reduce or eliminate dust and oil present in the compressed air. Furthermore, the air treatment plant may include one or more dryers arranged to reduce the water vapor content.

The compressed air distribution network 2 can comprise a plurality of valves suitable for allowing or interrupting the passage of compressed air in one or more sections of the compressed air distribution network 2, said compressed air being intended for one or more service units 3, 4, 5, 6. In use, the valves can be controlled by the remote central controller 100.

By way of example, again with reference to Figure 1, the compressed air distribution network 2 can comprise a valve associated with each service unit 3, 4, 5, 6.

Furthermore, the compressed air distribution network 2 can comprise further valves not associated with a predetermined service unit.

In order to optimize the energy consumption associated with the compressed air production and distribution plant 1, it is advisable to know and monitor in real time at predetermined time intervals the operating parameters and the values of some quantities related to the production and distribution plant. compressed air 1, such quantities including, for example, the air flow produced by each compressor 9, 10, 11, 13, the pressure of the compressed air distribution network 2, the electricity consumption of each compressor 9, 10 , 11, 13, the air flow used by each service unit 3, 4, 5, 6 and the power absorbed by each compressor 9, 10, 11, 13.

For this purpose, the compressed air production and distribution plant 1 comprises sensor means arranged to perform a measurement of one or more of the aforementioned quantities at predetermined time intervals.

The sensor means comprise a plurality of first flow sensors 20, each first flow sensor 20 being arranged in proximity to a corresponding compressor 9, 10, 11, 13 and, in particular, downstream thereof according to a flow direction of compressed air in order to detect one or more flow rate values produced by said corresponding compressor 9, 10, 11, 13 to which it is connected. The first flow sensors 20 are schematically illustrated with an oval portion in Figure 1.

The sensor means also comprise a plurality of second flow sensors 21, each second flow sensor 21 being arranged in proximity to a corresponding service unit 3, 4, 5, 6 and, in particular, upstream thereof according to a direction of flow of the compressed air flow in order to detect one or more flow rate values used by said corresponding service unit 3, 4, 5, 6 to which it is connected. The second flow sensors 21 are schematically illustrated with an oval in Figure 1.

The sensor means also comprise a plurality of first pressure sensors 22, each first pressure sensor 22 being arranged in proximity to a corresponding compressor 9, 10, 11, 13 and, in particular, downstream thereof according to a direction of flow of the compressed air flow in order to detect one or more pressure values in the vicinity, in particular downstream, of the corresponding compressor 9, 10, 11, 13 to which it is connected. The first pressure sensors 22 are schematically illustrated with an oval portion in Figure 1.

In one version, the first flow sensors 20 and the first pressure sensors 22 can be implemented in a single detection device.

The sensor means also comprise a plurality of second pressure sensors 23, each second pressure sensor 23 being arranged in proximity to a corresponding service unit 3, 4, 5, 6, in particular upstream thereof according to a direction of flow of the compressed air flow in order to detect one or more pressure values in the vicinity, in particular upstream, of the corresponding service unit 3, 4, 5, 6 to which it is connected. The second pressure sensors 23 are schematically illustrated with an oval portion in Figure 1.

In one version, the second flow sensors 21 and the second pressure sensors 23 can be implemented in a single detection device.

Further pressure sensors can be provided, arranged to detect a value of a pressure at one or more critical points of the compressed air distribution network 2, for example at a node of the compressed air distribution network 2, to check that the pressure of the compressed air distribution network 2 remains within the extremes of a predetermined range.

Furthermore, the sensor means further comprise a plurality of network analyzers, not shown in the Figures, each network analyzer being arranged in proximity to a corresponding compressor 9, 10, 11, 13 and, in particular, upstream of the same second a flow direction of the compressed air flow in order to detect one or more values of an electrical energy consumption of each compressor 9, 10, 11, 13. In particular, each network analyzer can be arranged in proximity to a corresponding power supply device 7 of the plurality of compressors 9, 10, 11, 13.

The sensor means can be integrated in the monitoring device of each compressor 9, 10, 11, 13.

In use, the remote central controller 100, schematically shown with a broken line rectangle in Figure 1, implements the control method of a compressed air production and distribution plant according to the invention to manage the production plant and compressed air distribution 1.

In particular, the remote central controller 100 is arranged to impose an operating state on a plurality of controllable components of the compressed air production and distribution plant 1. In other words, the remote central controller 100 is arranged to control the operation of the compressors 9, 10, 11, 13. In one version, the remote central controller 100 also controls the operation of the valves of the compressed air distribution network 2.

For this purpose, the remote central controller 100 is connected to each monitoring device of each compressor 9, 10, 11, 13 and possibly to each valve. The connection between the remote central controller 100 and possibly each valve and the connection between the remote central controller 100 and each compressor 9, 10, 11, 13 is schematically shown with broken lines in Figure 1.

The remote central controller 100 is also connected to the sensor means (connection not shown in the Figures) so as to be able to receive values of the aforementioned characteristic quantities of the electrical energy production and distribution plant 1 obtained by means of the sensor means in order to consequently being able to control the aforesaid controllable components (compressors 9, 10, 11, 13 and valves, if present).

The connection between the remote central controller 100 and the controllable components and the sensor means can be of the guided type or of the wireless type and allows a bidirectional communication between the remote central controller 100, controllable components and sensor means.

DESCRIPTION OF THE METHOD

The control method of a compressed air production and distribution plant comprises providing a compressed air production and distribution plant 1 comprising at least one compressor of the load / unload type and regulating the operating status of each compressor so as to ensure production of air that satisfies an expected total flow rate and at the same time minimizes the electrical energy consumption of the system.

The operating status of each compressor is determined by minimizing a function of the electricity consumption relating to each compressor 9, 10, 11, 13, in particular by solving an optimum problem in which the system's flow rate constraints are set, to satisfy the flow rate required by service units 3, 4, 5, 6.

The control method comprises detecting or measuring, in particular through the sensor means and monitoring devices, a plurality of physical quantities varying over time and characteristics of the operation of the compressed air production and distribution plant 1. These physical quantities are substantially measured with continuity, or with very frequent sampling (fine sampling), since the sampling period has a predetermined duration and varies according to the type of sensor means and monitoring device used. For example, the sampling period can be 1s. In the following, "continuous" detection or measurement means a continuous detection or a measurement performed with a fine sampling.

The values of the physical quantities characteristic of the operation of the compressed air production and distribution plant 1 are acquired, i.e. recorded, after an acquisition time interval has elapsed, which is set in the remote central controller 100.

The duration of the acquisition time interval can be set, for example, equal to 1 minute. The acquisition time interval defines how often the operating parameters of the compressors and the values of physical quantities related to the compressed air production and distribution plant 1 are acquired, i.e. recorded, in the remote central controller 100.

The sampling period with which the sensor means and the monitoring devices operate can be shorter.Therefore, among the multiple values of the time-varying physical quantities that are detected by the sensor means and by the monitoring devices, the one detected is recorded in the remote central controller 100 at each acquisition time interval.

In particular, the method includes:

- detecting by means of the first flow rate sensors 20 a value of an air flow rate produced by each compressor 9, 10, 11, 13 and acquiring it in the remote central controller 100, for example as the input data of an optimization algorithm. The optimization algorithm can be stored and executed in the remote central controller 100. The aforesaid detecting a value of a flow rate of air produced by each compressor 9, 10, 11, 13 can be carried out continuously while said acquisition is carried out after each interval acquisition time;

- detect by means of the first pressure sensors 22 a value of an air pressure measured downstream of each compressor 9, 10, 11, 13 and acquire it in the remote central controller 100, for example as an input data of the optimization algorithm. Said detecting a value of an air pressure measured downstream of each compressor 9, 10, 11, 13 can be carried out continuously while said acquiring said value of an air pressure measured downstream of each compressor 9, 10, 11, 13 it is carried out after each acquisition time interval;

- detect, by means of the second flow sensors 21, a value of an air flow used, that is required, by each service unit 3, 4, 5, 6 and acquire it in the remote central controller 100 as input data of the optimization algorithm . Said detecting a value of an air flow used by each service unit 3, 4, 5, 6 can be carried out continuously while said acquiring a value of an air flow used by each service unit 3, 4, 5, 6 it is carried out after each acquisition time interval;

- detect by means of the second pressure sensors 23 a value of an air pressure measured upstream of each service unit 3, 4, 5, 6 and acquire it in the remote central controller 100, for example as an input data of the optimization. Said detecting a value of an air pressure measured upstream of each service unit 3, 4, 5, 6 can be carried out continuously while said acquisition of said value of an air pressure measured upstream of each service unit 3, 4 , 5, 6 is carried out after each acquisition time interval;

- detect by means of the plurality of network analyzers a value of an electricity consumption used by each compressor 9, 10, 11, 13 and acquire it in the remote central controller 100 as input data of the optimization algorithm. Said detecting a value of a consumption of electrical energy used by each compressor 9, 10, 11, 13 can be carried out continuously while said acquiring a value of a consumption of electrical energy used by each compressor 9, 10, 11, 13 is carried out after each acquisition time interval.

The control method comprises calculating a profile of the total expected flow rate. This profile is calculated by applying a predictive model, for example based on multivariate regression methods. In a calibration phase, the model learns to predict the target variable, i.e. the total flow profile, on the basis of the correlation existing in the historical data between the variable itself and at least one pressure value and at least one historical flow value of the plant of production and distribution of compressed air 1. Subsequently, in a predictive phase, the model is able to predict the expected consumption of air on the basis of the values corresponding to the physical quantities varying over time acquired at each acquisition time. The expected total flow rate profile indicates, moment by moment, what is the total flow value that the compressed air production and distribution plant 1 must meet.

The profile of total flow rate expected only in a purely ideal case in which the distribution network 2 is free from losses, is equivalent to the sum of the air flow rates required by each service unit 3, 4, 5, 6.

As mentioned above, the control method further comprises acquiring, in particular after each acquisition time interval, from each monitoring device a plurality of operating data of each compressor 9, 10, 11, 13, such as, for example , the number of loaded hours, the number of hours preceding a maintenance operation on the compressor and / or the number of empty hours.

The control method also includes setting in the remote central controller 100 a duration value of an adjustment time interval within which an operating state of the plurality of compressors 9, 10, 11, 13 is kept unchanged.

In other words, the adjustment time represents a time span within which the results of the optimization algorithm are applied to the compressed air production and distribution plant 1, in particular to the compressors 9, 10, 11, 13. .

The duration of the adjustment time interval can be set, for example, equal to 15 minutes.

The duration of the adjustment time interval is a function of a computing power associated with the remote central controller 100.

The durations of the acquisition time interval and the adjustment time interval may be different.

The duration value of the acquisition time interval can be less than or equal to the value of the adjustment time interval.

The control method further comprises entering in the remote central controller 100, for example by an operator, a plurality of configuration data including nameplate data of each compressor 9, 10, 11, 13 and data relating to the layout of the compressed air production and distribution plant 1.

For example, the configuration data includes:

the nominal working pressure value pnom of each service unit 3, 4, 5, 6. The configuration data can also include a value of a maximum admissible pressure variation which guarantees the normal operation of the plurality of units of service 3, 4, 5, 6; the service units 3, 4, 5, 6, in fact, allow to be supplied with compressed air at a pressure equal to the nominal pressure ± the maximum admissible pressure variation (Δp).

Furthermore, the configuration data may include a range of tolerable flow values in addition to the required flow rate in a given adjustment time interval and a range of tolerable flow values less than the required flow rate in a given range. adjustment time; in this way a range of tolerable flow rate values at the input to each service unit 3, 4, 5, 6 is defined; - a value of a volume of air contained in the distribution network 2, which can be obtained from the sum of the volume of air occupied by the pipes of the distribution network 2 (calculated starting from the lengths and diameters of the pipes) and the volume air occupied by any accumulation systems.

The configuration data can also include technical data of the plurality of compressors 9, 10, 11, 13 such as, for example, the nominal flow rate Qnom, the minimum flow rate Qmin, the maximum flow rate, the no-load power Psc, l 'specific performance index (KPI having unit of measurement kWh / Nmc), power-flow graphs of the operating states - that is, the coordinates of the points on a Cartesian power-flow reference plane that identify the operating states of the compressors 9, 10 , 11, 13.

The control method further comprises entering into the remote central controller 100, for example by an operator, other configuration data, including graphs of energy efficiency of each compressor 9, 10, 11, 13 as the load varies, i.e. scope. The energy efficiency graphs of each compressor 9, 10, 11, 13 are indices of the relative electricity consumption.

The control method further comprises setting in the remote central controller 100, for example by an operator, a plurality of constraints that must be respected in the control of the compressed air production and distribution plant operated by the remote central controller 100 .

A constraint includes setting a total flow rate value of the compressed air production and distribution plant 1 substantially not less than the expected total flow rate of compressed air required by the service units 3, 4, 5, 6, less than the range of values of tolerable flow; in other words, said setting said value of a total flow rate allows to supply at the inlet to the service units 3, 4, 5, 6 an air flow rate that is at least equal, that is not less, to the one they are expected to use, to less than the range of tolerable flow rates.

A further constraint is that the power value of each compressor 9, 10, 11, 13 must be included between a minimum power value and a maximum power value; in the case of an inverter-type compressor, the power value is continuously variable between a minimum power value and a maximum power value, while in the case of a load / unload type compressor the power can assume discrete values, for example for example, the power value can be equal to 0 (corresponding to a value of zero flow produced), to the no-load power Psc (corresponding to a value of zero flow produced) and to the nominal power Pnom (corresponding to a value of flow produced equal to at nominal flow rate);

Another constraint concerns the number of starts of each compressor 9, 10, 11, 13 which must be less than a maximum number of starts foreseen for each compressor 9, 10, 11, 13.

Yet another constraint concerns the need for a minimum ignition time of the cooling system before a compressor 9, 10, 11, 13 is definitively turned off; this minimum time allows a cooling fluid to cool each motor associated with each compressor 9, 10, 11, 13 to prevent the compressors from overheating; the constraint includes setting that a shutdown time of at least one compressor 9, 10, 11 is greater than a minimum cooling time of at least one compressor 9, 10, 11, the shutdown time being the time interval required for the at least a compressor 9, 10, 11 to pass from a loaded operating state to an off operating state, said minimum cooling time being a time interval in which the at least one compressor 9, 10, 11 is kept in a state no-load operation required for cooling the at least one compressor 9, 10, 11.

Yet another constraint is that the network pressure is substantially equal to an operating pressure of the compressed air production and distribution plant 1, said operating pressure being predetermined. The operating pressure is generally established equal to the sum of the maximum pressure required in a point of the network, for example the nominal pressure of the service unit 3, 4, 5, 6 which has the highest nominal pressure, and a pressure variation maximum admissible, which depends on the characteristics of the service units 3, 4, 5, 6 and, for example, may be the maximum admissible pressure variation of the service unit 3, 4, 5, 6 which has the highest nominal pressure (pressure network = pnommax ± Δpmax).

The control method further comprises calculating at one end of a regulation time interval which operating state to make each compressor 9, 10, 11, 13 assume in each subsequent regulation time interval in order to satisfy the total expected flow rate of compressed air with a minimum consumption of electrical energy, satisfying at the same time one or more of the aforementioned constraints and as a function of the configuration data and the physical quantities varying over time acquired at each acquisition time interval. The aforementioned calculating the operating status of each compressor 9, 10, 11, 13 comprises using an optimization algorithm which envisages as an objective function to be minimized an indicative function of the energy consumption of the set of compressors 9, 10, 11, 13 and returns which operating state to let each compressor 9, 10, 11, 13 assume in a subsequent adjustment time interval in order to satisfy the expected total flow rate value of compressed air with a minimum consumption of electrical energy. In other words, the control method makes it possible to establish an optimal flow rate value for each compressor 9, 10, 11, 13 (based on the data available to the remote central controller 100), i.e. how much air is set for each compressor 9, 10, 11, 13 must produce. The sum of the flow rates that each compressor 9, 10, 11, 13 must produce must give the expected total flow rate value. Through the resolution of the optimization algorithm, the energy consumption of the compressed air production and distribution plant 1 is minimized by redistributing the flow rate production between the various compressors 9, 10, 11, 13 and at the same time satisfying the total flow rate value wait.

The energy consumption of each compressor 9, 10, 11, 13 as a function of the compressed air flow to be produced can be found in the energy efficiency graphs.

The control method provides that said calculating at each adjustment time interval an operating state of each compressor 9, 10, 11, 13 may comprise, in particular, an optimization algorithm with linear programming mixed to integers (MILP) for solve an optimum, or optimization problem, with mixed integer constraints, such as the optimum problem associated with the compressed air production and distribution plant 1, i.e. how to minimize the consumption of electricity used by compressors 9, 10, 11 , 13 of the compressed air production and distribution plant 1 to generate a desired quantity of compressed air from the service units 3, 4, 5, 6.

The optimum problem is solved by assuming that it is possible to use the equation of state of perfect gases in an isothermal and isochorous model, i.e. in a situation of the compressed air distribution network 2 in which the temperature and volume of the air distribution network tablet 2 can be considered a constant.

Considering the equation of state of ideal gases expressed by the following equation:

where the variables are in order: the pressure, the volume, the quantity of substance, the gas constant and the absolute temperature and by deriving equation 1.1 with respect to time, the law of conservation of mass can be obtained:

which shows how the pressure variation linearly depends on the difference in the variations in mass flow rates of air inlet (given by the inlet flow rate of compressors 9, 10, 11, 13) and outbound (given by the current flow rate of the service units 3, 4, 5, 6).

Since in equation 1.2 p is constrained, that is, a range of pressures is set so that the pressure value varies between a maximum and a minimum value, and is known through measurements made by the sensor means and are known

<R>, T and V as constants of known value by means of physical laws or by design of the compressed air distribution network 2, the only variable remains min, i.e. how much flow rate compressors 9, 10, 11, 13 must produce to meet the total flow expected in the regulation time interval in question. In particular, the optimum problem allows to obtain a min flow rate value for each compressor 9, 10, 11, 13. The sum of all min values is equal to the expected total flow rate.

An example of setting a mixed linear programming algorithm to integers applied to the compressed air production and distribution plant 1 will be shown below.

The objective of the optimal problem is to find the minimum of an objective function f <t> (x), i.e. a vector x which produces the smallest value of the objective function respecting the constraints imposed, which are expressed as a matrix product of the type Ax = b, where A is a matrix and x and b are column vectors.

The objective function f <t> (x) is instead expressed as a vector product Cx, where C is a matrix containing elements that are a function of the electricity consumption of each compressor 9, 10, 11, 13 which are calculated considering:

- the specific performance index (KPI);

- the nominal capacity of each respective compressor (Qnom);

- the percentage of electrical absorption in the UL idle state of operation of each compressor of the loading / unloading type.

The optimum problem returns a vector x containing the results of the optimization algorithm.

The vector x comprises a plurality of numbers that can be associated to a determined point, that is to a pair of Cartesian coordinates, of a Cartesian reference plane such as that of Figure 2 or that of Figure 3 depending on the type of compressor 9, 10, 11, 13. Each point identifies a corresponding operating status of each compressor 9, 10, 11, 13.

In the case of a compressor 9, 10, 11 of the load / unload type, a pair of numbers is associated to each point of the Cartesian reference system of Figure 2 which identifies a relative operating state of the compressor 9, 10, 11 of the load / unload type. unload and the vector returns those numbers as values of a pair of variables. For example, the pair of values (0, 0) can be associated with the operating state corresponding to the first point A, the pair of values (1, 1) can be associated with the operating state corresponding to the second point B and the pair of values (1, 0) can be associated with the operating status corresponding to the third point C.

Again in the case of a compressor 9, 10, 11 of the load / unload type, it is also possible to associate a different integer to each point of the Cartesian reference system of Figure 2 which identifies a relative operating state of the compressor 9, 10, 11 of the load / unload type and in this case the vector returns this number in the form of a value of a variable. For example, the number 0 can be associated with the operating state corresponding to the first point A, the number 1 can be associated with the operating state corresponding to the second point B and the number 2 can be associated with the operating state corresponding to the third point C .

In the case of a compressor 13 of the type with inverter, a different number is associated with each point of the Cartesian reference system of Figure 3 which identifies a relative operating state of the compressor 13 of the type with inverter and the vector returns this number in the form of a value of a further variable. In particular, the number is associated with the percentage of the load at which to operate the compressor 13, therefore, for example, the number 40 can be associated with an operating state in which the compressor 13 of the type with inverter works at 40% of its possibility, for example 40% of maximum power or maximum range.

The position of the numbers within the carrier is preliminarily associated by the remote central controller 100 with a certain compressor 9, 10, 11, 13.

The remote central controller 100 then adjusts each compressor 9, 10, 11, 13, based on the plurality of numbers obtained in the vector, which are associated with operating states of a given compressor 9, 10, 11, 13.

For example, the vector x can be of the type:

X = [40, 0, 0, 1, 1, 0, 0],

where, proceeding from left to right, the number "40" is associated with compressor 13 of the type with inverter which must work in an operating state corresponding to 40% of the maximum power, the first pair (0, 0) is associated with the compressor 9 of the load / unload type which must be switched off, the second pair (1, 1) is associated with the compressor 10 of the load / unload type which must work empty and the third pair (0, 0) is associated with the compressor 11 of the type loading / unloading which must be switched off.

A is a matrix that

includes the nominal flow rates of compressors 9, 10, 11, 13 while b is a vector that expresses the total expected flow rate of compressed air (Qload (i)) required in an i-th regulation interval by the service units 3, 4, 5, 6 less than a tolerable range of flow rates.

Tolerable flow rates include:

- the tolerable flow range more than that required in the i-th adjustment range (Kub (i));

- the tolerable flow rate range less than that required in the i-th adjustment range (Klb (i)).

Finally, the control method includes:

- adjusting each compressor 9, 10, 11, 13 on the basis of said operating state calculated to satisfy the total expected flow rate value of compressed air with the minimized electrical energy consumption.

The remote central controller 100 imposes on the compressors 9, 10, 11, 13 the various operating states obtained by the optimization algorithm for an adjustment time interval subsequent to an instant in which the control method has obtained said operating states. At the end of the adjustment time interval, the control method repeats the steps listed above to obtain a plurality of further operating states to be assumed by each compressor 9, 10, 11, 13 in a still subsequent adjustment time interval. In other words, at each adjustment time interval, the control method elaborates a new optimum problem with a new target value, ie a new total expected flow rate value to be satisfied with the minimum of electrical energy used.

Within the distribution network 2 the plurality of service units 3, 4, 5, 6, such as for example the fourth service unit 6, can be powered by a dedicated compressor, such as for example the fourth compressor 13, which at the same time it can supply one or more of the other service units 3, 4, 5, 6 on the basis of the indications of the remote central control 100. In this way, the production of compressed air is distributed and managed by the central controller.

Thanks to the control method according to the invention, the production of compressed air of each compressor 9, 10, 11, 13 is planned, i.e. the remote central controller 100 determines how to divide a production of compressed air flow among the compressors 9, 10, 11, 13, in order to minimize the electricity consumption of the compressed air production and distribution plant 1. This occurs at pre-established time intervals and, on the basis of real measured data, the compressed air flow to be produced and divided is up to date.

The method according to the invention can be applied to existing compressed air production plants, in particular systems in which there are load / unload compressors and also compressors with frequency variator.

By connecting the different compressors with the same remote central controller, it is possible to adjust the operation of compressors located in different points of the system layout, without making substantial structural changes to the system itself.

Claims (16)

CLAIMS 1. Method of controlling a compressed air production and distribution plant (1) implemented by a remote central controller (100) to minimize an electrical energy consumption associated with said compressed air production and distribution plant (1), called compressed air production and distribution plant (1) comprising a plurality of compressors (9, 10, 11, 13) arranged to generate compressed air and a plurality of service units (3, 4, 5, 6) using said compressed air , said plurality of compressors (9, 10, 11, 13) and said plurality of service units (3, 4, 5, 6) being connected by a compressed air distribution network (2), in which at least one compressor ( 9; 10; 11) of said plurality of compressors (9, 10, 11, 13) can only assume different discrete operating states, said control method comprising the steps of: - detecting a plurality of values corresponding to time-varying physical quantities associated with said compressed air production and distribution plant (1) and acquiring in said remote central controller (100) said plurality of values corresponding to said time-varying physical quantities; - entering in said remote central controller (100) a plurality of configuration data of said compressed air production and distribution plant (1), said plurality of configuration data including energy efficiency graphs of each compressor (9, 10, 11 , 13) as the load varies, which quantify a consumption of electrical energy as a function of a flow rate delivered by each compressor (9, 10, 11, 13); - calculating a profile of the total expected flow rate of compressed air required by the plurality of service units (3, 4, 5, 6) over time; - set in said remote central controller (100) a duration value of an adjustment time interval within which an operating status of each compressor (9, 10, 11, 13) is kept unchanged; - setting a plurality of constraints in said remote central controller (100), said constraints comprising setting that a total flow rate of said compressed air production and distribution plant (1) is equal to said total expected flow rate of compressed air required in a range of adjustment time from the plurality of service units (3, 4, 5, 6) up to a range of tolerable flow rates; - calculating at one end of said adjustment time interval an operating state to be made by each compressor (9, 10, 11, 13) during a subsequent adjustment time interval, satisfying one or more of said constraints, said calculating one operating status including minimizing a function of the electrical energy consumption relating to each compressor (9, 10, 11, 13); and - adjusting each compressor (9, 10, 11, 13) on the basis of said operating state calculated to satisfy said total expected flow rate of compressed air with said minimized electrical energy consumption. Method for controlling a compressed air production and distribution plant (1) according to claim 1, wherein said detecting and acquiring a plurality of values corresponding to physical quantities varying over time include: - detecting a value of an air flow rate produced by each compressor (9, 10, 11, 13) and acquiring it in said remote central controller (100); - detecting a value of an air pressure measured downstream of each compressor (9, 10, 11, 13) and acquiring it in said remote central controller (100); - detecting a value of an air flow rate entering each service unit (3, 4, 5, 6) and acquiring it in said remote central controller (100); - detecting a value of an air pressure measured upstream of each service unit (3, 4, 5, 6) and acquiring it in said remote central controller (100); - detecting operating data of each compressor (3, 4, 5, 6) and acquiring them in said remote central controller (100); - detecting a value of an electrical energy consumption used by each compressor (9, 10, 11, 13) and acquiring it in said remote central controller (100). Method for controlling a compressed air production and distribution plant (1) according to claim 1 or 2, and further comprising setting a duration value of an acquisition time interval, said acquiring a plurality of corresponding values with physical quantities varying in time being carried out after said acquisition time interval has elapsed. Control method of a compressed air production and distribution plant (1) according to claim 3, wherein said duration value of an acquisition time interval is less than or equal to said duration value of a time interval adjustment. 5. Method of control of a compressed air production and distribution plant (1) according to claim 3 or 4, wherein said calculating a profile of total expected flow rate of compressed air comprises applying a predictive model which, in a calibration step , learns how to predict a total flow profile on the basis of a correlation existing in historical data between a historical total flow profile and at least one pressure value and at least one historical flow value and which, subsequently, in a predictive phase, foresees the expected air consumption on the basis of said values corresponding to physical quantities which vary over time acquired at each acquisition time interval. 6. Method of controlling a compressed air production and distribution plant (1) according to one of the preceding claims, wherein said setting a plurality of constraints comprises setting that the value of the power of each compressor (9, 10, 11, 13 ) is between a predetermined minimum power value and a predetermined maximum power value. 7. Control method of a compressed air production and distribution plant (1) according to one of the preceding claims, wherein said setting a plurality of constraints comprises setting that the number of starts of each compressor (9, 10, 11, 13 ) is less than a maximum number of starts foreseen for each compressor (9, 10, 11, 13). 8. Method of controlling a compressed air production and distribution plant (1) according to one of the preceding claims, wherein said setting a plurality of constraints comprises setting that a shutdown time of said at least one compressor (9, 10, 11 ) is greater than a minimum cooling time of said at least one compressor (9, 10, 11), said shutdown time being the time interval required for said at least one compressor (9, 10, 11) to pass from a state of operation with load in an off operating state, said minimum cooling time being a time interval in which said at least one compressor (9, 10, 11) is kept in an idle operating state necessary for cooling said at least a compressor (9, 10, 11). 9. Control method of a compressed air production and distribution plant (1) according to one of the preceding claims, wherein said setting a plurality of constraints comprises setting that the network pressure is substantially equal to an operating pressure of said plant for the production and distribution of compressed air (1), said operating pressure being predetermined and equal to the sum of the maximum pressure required in a point of the network and a variation of the maximum admissible pressure. Method for controlling a compressed air production and distribution plant (1) according to one of the preceding claims, wherein said plurality of values corresponding to physical quantities varying over time, said plurality of configuration data, said expected flow rate profile , said duration of said adjustment time interval and said plurality of constraints are input data of an optimization algorithm, in which said minimize a function of the electrical energy consumption relating to each compressor (9, 10, 11, 13) comprises applying said optimization algorithm to each adjustment time interval. Method of controlling a compressed air production and distribution plant (1) according to claim 10, and further comprising obtaining a vector of operating states of each compressor (9, 10, 11, 13), said to calculate said state of operation to be made to each compressor (9, 10, 11, 13) comprising associating a point of a flow-power graph relating to each compressor (9, 10, 11, 13) to the values of said vector. Method for controlling a compressed air production and distribution plant (1) according to one of the preceding claims, wherein said configuration data further comprises a nominal operating pressure value of each unit of said plurality of service units ( 3, 4, 5, 6). 13. Control method of a compressed air production and distribution plant (1) according to one of the preceding claims, wherein said configuration data further comprises a value of a maximum permissible network pressure variation which ensures the operation of the plurality of service units (3, 4, 5, 6). Method for controlling a compressed air production and distribution plant (1) according to one of the preceding claims, wherein said configuration data further comprise a range of tolerable flow rate values at the inlet to each unit of said plurality of units of service (3, 4, 5, 6). Method for controlling a compressed air production and distribution plant (1) according to one of the preceding claims, wherein said configuration data further comprises a value of a volume of air contained in said compressed air distribution network ( 2). 16. Method of controlling a compressed air production and distribution plant (1) according to one of the preceding claims, wherein said configuration data further comprise technical data of each compressor of said plurality of compressors (9, 10, 11, 13 ), said technical data including the nominal flow rate (Qnom), the minimum flow rate (Qmin), the maximum flow rate, the no-load power (Psc), specific performance index (KPI), power-flow graphs of operating states.