1. A presage detection and recovery support system for failure of a seawater desalination plant that is provided with a high pressure pump for pressurizing seawater and an RO membrane for obtaining freshwater from the seawater pressurized by the high pressure pump, comprising: a unit that calculates mechanical performance indices based on at least one piece of information on measurement values of flow rates, pressures and temperatures of seawater or desalinated water flowing through insides of devices which constitute the seawater desalination plant; a unit that calculates chemical performance indices of water quality obtained from components of seawater or desalinated water flowing through insides of the devices which constitute the seawater desalination plant; a unit that detects a mechanical failure of a device or an abnormality of the water quality from the mechanical performance indices and the chemical performance indices; and a unit that displays a plurality of operation methods or measure methods for recovering the plant from the mechanical failure or the abnormality of the water quality.

2. The presage detection and recovery support system for failure of a seawater desalination plant, according to claim 1, further comprising: a unit that inputs a plant operation or a measure performed by an operator; and a unit that compares the mechanical performance indices or the chemical performance indices before the plant operation or the measure is performed, with the mechanical performance indices or the chemical performance indices after the plant operation or the measure has been performed, and based on a result of comparison, modifies an order of display of the measure methods, or presence or absence of the display thereof.

3. The presage detection and recovery support system for failure of a seawater desalination plant, according to claim 1 or 2, wherein the unit that calculates mechanical performance indices calculates the mechanical performance indices using information on measurement values of flow rates, pressures and temperatures of the seawater or desalinated water, the information being received from measuring instruments installed in the seawater desalination plant.

4. The presage detection and recovery support system for failure of a seawater desalination plant, according to claim 1 or 2, wherein the unit that calculates chemical performance indices calculates the chemical performance indices using information of the water quality of the seawater or desalinated water, the information being received from water quality measuring instruments installed in the seawater desalination plant. ,TagSPECI:CROSS-REFERENCE TO RELATED APPLICATION This application is based upon and claims the benefit of priority to Japanese Patent Application No. 2013-119397, filed on June 6, 2013, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD [0001] The present invention relates to a control system for a plant that produces freshwater from seawater. BACKGROUND ART [0002] For seawater desalination plants that produce freshwater from seawater to provide it for drinking or industrial uses, various methods such as an evaporation method, a reverse osmosis method and the like have been proposed by manufacturers. [0003] For example, the evaporation method is to heat seawater to obtain steam by means of a heat source such as a boiler or the like and then to cool the steam to obtain freshwater. On the other hand, the reverse osmosis method is to pressurize seawater and to pass the seawater through a filtration film called a reverse osmosis membrane (RO membrane) to filtrate freshwater (desalinated water) from the seawater. A high pressure pump is used to pressurize the seawater. Driving the high pressure pump needs a turbine or a power source such as a power-generating plant, for generating a driving force. [0004] In a seawater desalination plant using a reverse osmosis method of the methods described above, a lifting range of the high pressure pump and a filtration performance of the RO membrane greatly influence the production volume of desalinated water. For example, seawater contains microorganisms besides salt content and trace metal. In particular, the microorganisms feed on organic matters to form colony called biofilm on the surface of the RO membrane and thus inhibit the passage of seawater through the membrane. It is generally known that the production volume of desalinated water is extremely decreased in a seawater desalination plant with biofilm being developed. [0005] On the other hand, in the case where the seawater changes into high acidic property or high alkaline property, members disposed inside the high pressure pump are corroded and damaged, which causes troubles such as a decrease in pressure and flow rate, corrosion cracking and the like. The RO membrane provides a predetermined filtration performance when the seawater is pressurized up to a pressure specified by a membrane manufacturer. Accordingly, in the case where a sufficient pressure is not obtained by the high pressure pump, it is necessary to stop the plant and to take measures such as exchange of the device or repair thereof. [0006] For example, Patent document 1 describes an operation management method that includes, when a failure of an energy recovery device and/or deterioration of a reverse osmotic membrane in a seawater desalination plant is/are detected, informing the operator of the failure and/or deterioration by means of an alarm, and also taking measures such as cleaning the RO membrane in case of the deterioration, switching an operation mode for the pump in case of the failure, or the like. [0007] The operation management method in Patent document 1 is to detect presence or absence of occurrence of an abnormality based on plant measurements and mechanical characteristics of the devices. An abnormality detected by the method is informed via a control device to the operator. Moreover, the method is characterized by instructing the operator to take measures based on the abnormality and switching over to a plant control which is prepared in advance assuming occurrence of possible failures. PRIOR ART DOCUMENTS Patent document [0008] Patent document 1: Japanese Patent Application Publication No. 2010-089036 SUMMARY OF THE INVENTION Problems to be solved by the invention [0009] However, in a seawater desalination plant which is required to continuously supply drinking water and/or industrial water, it is desirable to detect an abnormality of the device as early as possible and thus to avoid occurrence of failures to continue the operation as long as possible. Failures or abnormalities of the devices originate with an extremely slight change in the pressure, flow rate, constituent of water and the like, and subsequently the change gradually expands to lead to failures of the devices or a plant outage. Therefore, as for an abnormality of the device, it is necessary to reflect not only information on measurement points for the pressure, flow rate, constituent of water and the like, but also information on regular patrol and/or maintenance check by a site operator. Thus in the seawater desalination plant, it is desirable to detect a decrease in the production volume of desalinated water and failures of the devices as early as possible and also to take the best measures quickly when a trouble occurs. [0010] Moreover, in a seawater desalination plant constituted with a plurality of devices such as RO membranes, high pressure pumps and the like, an abnormality in the upstream side of the process is transmitted to the downstream side thereof. In particular, in this plant that treats water which is incompressible fluid, an abnormality of the pressure and/or the flow rate instantaneously spreads to the entire plant. For this reason, it is necessary to specify the point at which the abnormality occurs, with good accuracy. [0011] It is therefore an object of the present invention, in a plurality of devices included in a seawater desalination plant, to detect failures or abnormalities of the devices earlier and to determine their causes based on the detected content to present appropriate measures to an operator. Means for solving the problems [0012] The present invention is provided with a unit that detects failures of devices which constitute a seawater desalination plant, a unit that detects abnormality of water quality of fluid (seawater, desalinated water) flowing through insides of the devices, and a unit that presents to an operator based on the detected results, a plurality of measure methods for recovering the plant. Advantageous effects of the invention [0013] The presage detection and recovery support system for plant failure according to the present invention detects abnormalities of the devices from chemical characteristics of the seawater and mechanical characteristics, thereby making it possible to appropriately specify a point at which the abnormality occurs, with chemicals or the like injected intermittently into the seawater and the desalinated water as disturbance. BRIEF DESCRIPTION OF THE DRAWINGS [0014] FIG.1 is a system configuration diagram illustrating a presage detection and abnormality diagnosis system according to a first embodiment of the present invention. FIG.2 is a configuration diagram illustrating a seawater desalination plant which is a target of diagnosis in the present invention. FIG.3 is a system configuration diagram illustrating a presage detection and abnormality diagnosis system according to a second embodiment of the present invention. EMBODIMENTS OF THE INVENTION [0015] The system includes a unit that calculates mechanical performance indices of devices obtained from measurement values of flow rates, pressures and temperatures in a plant, and a unit that calculates chemical performance indices of water quality obtained from components of fluid (seawater, desalinated water) flowing through the insides of the devices. [0016] Also, the system includes a unit that estimates a point of failure in the devices from the above mechanical performance indices of the devices, and a unit that estimates a point of water quality abnormality in the devices from the above chemical performance indices of water quality. [0017] Moreover, the system includes a unit that selects an appropriate operation method or a measure method from among plant operation methods or measure methods which are prepared in advance for normally recovering the plant, based on the calculated mechanical performance indices of the devices and chemical performance indices of the water quality, and the estimated point of failure in the devices and point of abnormality in the water quality, and a unit that presents the selected method to an operator. [0018] Furthermore, the system includes a unit that inputs a plant operation or a measure performed by an operator; a unit that compares the mechanical performance indices of the devices and the chemical performance indices of the water quality obtained when failures or abnormalities occur, with the mechanical performance indices of the devices and the chemical performance indices of the water quality obtained after some measures have been taken, and calculates improvement effects attained by the plant operation or the measure performed by the operator; and according to the effects, modifies an order of display of the plant operation methods or the measure methods which are prepared in advance, or presence or absence of the display thereof. [First embodiment] [0019] A description will be given hereinafter of a presage detection and abnormality diagnosis system for a seawater desalination plant according to a preferred embodiment of the present invention. [0020] FIG.1 is a system configuration diagram illustrating a presage detection and abnormality diagnosis system 1 for a seawater desalination plant 2 according to the present embodiment. [0021] The seawater desalination plant (hereinafter referred to as plant) 2 transmits (outputs) to a plant control device 3 measurement values of water temperature, pump discharge pressure, the production volume of desalinated water, water quality and the like. The plant control device 3 receives (inputs) the measurement values of water temperature, pump discharge pressure, the production volume of desalinated water, water quality and the like, and outputs to the plant 2 control input values of the number of revolutions of the pump, valve aperture and the like so that the measurement values of the plant 2, e.g., the pump discharge pressure and the production volume of desalinated water, become respective target values. [0022] The measurement values of the plant 2 and the control input values of the plant control device 3 are displayed on a display device such as a monitor or the like provided in a plant operation unit 4. The operator who has confirmed the values on the display device may directly specify control input values using a console or the like provided in the plant operation unit 4. [0023] For the plant 2 and the plant control device 3, the presage detection and abnormality diagnosis system 1 according to the present embodiment inputs the measurement values of the plant 2 and the control input values from the plant control device 3 to a device failure (D.F.) detection unit 6 and a water quality abnormality (W.Q.A.) detection unit 7. [0024] In the device failure detection unit 6, a device performance index (D.P.I.) calculation unit 11 inputs the measurement values of the plant 2 and the control input values and calculates performance indices of devices which constitute the plant 2. Moreover, a failure point (F.P.) estimation unit 12 inputs the performance indices of the devices and specifies a point of failure in the device in the plant 2. [0025] Next, in the water quality abnormality detection unit 7, a water quality index (W.Q.I.) calculation unit 9 inputs the measurement values of the plant 2 and the control input values to calculate water quality indices in the plant 2. Moreover, an abnormality point (A.P.) estimation unit 10 inputs the water quality indices and specifies a point of abnormality in water quality in the plant 2. [0026] Next, a plant recovery (P.R.) support unit 8 inputs respective values of the performance indices and the point of failure calculated in the device failure detection unit 6, and respective values of the water quality indices and the point of abnormality calculated in the water quality abnormality detection unit 7, and outputs a list of plant recovery methods for failures or abnormalities, to a recovery method candidate (R.M.C.) display unit 5. [0027] Next, the operator selects by means of the plant operation unit 4, based on the list of plant recovery methods displayed on the recovery method candidate display unit 5 and various plant states (noise, vibration and the like) collected on site, an arbitrary plant recovery method from the list for execution. Information on the plant recovery method selected by the operator is inputted to the plant recovery support unit 8. [0028] When a measure result from the operator is inputted, the plant recovery support unit 8 compares device performance indices and water quality indices obtained when a plant failure or water quality abnormality is detected, with the present device performance indices and water quality indices, and as for a measure having indices highly improved, modifies an order of display of the measure to raise the display priority on the recovery method candidate display unit 5. On the contrary, as for a measure having indices less improved, the plant recovery support unit 8 modifies an order of display of the measure to lower the display priority. Consequently, after the next time, measures having successful results are displayed at higher ranks and thus appropriate recovery methods are presented for the case where a plant failure or water quality abnormality occurs. [0029] The presage detection and abnormality diagnosis system 1 described above calculates degrees of the device failures and degrees of the water quality abnormalities as the device performance indices and the water quality indices, respectively, and based on the calculated values, detects presage and estimates effects of the measures. [0030] Next, a calculation method of the device performance index and the water quality index by the present system will be described with reference to FIG.2. [0031] FIG.2 is an exemplary system configuration diagram of the seawater desalination plant 2 which is a target of presage detection in the present system. It should be noted that FIG.2 illustrates only a high pressure pump 21, a reverse osmosis (RO) membrane 23 and a pressure recovery device 24 which are major parts of the plant 2, and auxiliary machines associated therewith. [0032] A feed-water pump 20 pumps up seawater 28 and feeds the seawater to the high pressure pump 21 and the pressure recovery device 24. [0033] The pressure recovery device 24 pressurizes part of the seawater using pressurized concentrated water from the RO membrane 23, and a booster pump 22 further boosts a pressure of the pressurized seawater. [0034] Moreover, the high pressure pump 21 also pressurizes the seawater up to a predetermined pressure. [0035] The seawater of high pressure obtained at an outlet of the high pressure pump 21 and an outlet of the booster pump 22 is fed to the RO membrane 23. The RO membrane 23 utilizes its reverse osmosis action to filtrate desalinated water 29 from the pressurized seawater. At this time, a pressure of the desalinated water 29 is reduced to almost the atmospheric pressure. Moreover, seawater after the desalinated water 29 has been filtrated transmits its pressure to the seawater on the side of the feed-water pump 20 in the pressure recovery device 24, and is then drained as concentrated water 30. [0036] It should be noted that the plant 2 further includes pipes 25, 26 and 27 for injection of chemical provided at an outlet of the feed-water pump 20, an outlet of the RO membrane 23 on the desalinated water side, and an outlet of the pressure recovery device 24 on the concentrated water side, respectively. The pipe 25 is provided for injection of acidic or alkaline chemical liquid for preventing the RO membrane 23 from fouling. Moreover, the pipe 26 is provided for injection of chemical liquid for controlling pH of the desalinated water 29 which has changed into acidic property with filtration through the RO membrane 23. Similarly, the pipe 27 is provided for injection of chemical liquid for controlling pH of the concentrated water 30, so as to minimize an influence of the concentrated water 30 on the environment when discharged as drainage. [0037] As illustrated in FIG.2, the plant 2 according to the present embodiment includes pressure and flow rate measuring instruments (PF.M) 37, 38, 39, 40, 41, 42 and 43 that measure pressures, flow rates and temperatures for use in monitoring and controlling states of the devices included in the plant 2, and water quality measuring instruments (W.M) 31, 32, 33, 34, 35 and 36 for use in monitoring and controlling water qualities in the plant 2. Note that the pressure and flow rate measuring instruments 37, 38, 39, 40, 41, 42 and 43 illustrated in FIG.2 measure pressures, flow rates and temperatures of the seawater, the desalinated water or the concentrated water. Moreover, the water quality measuring instruments 31, 32, 33, 34, 35 and 36 measure electric conductivity which is one index of water quality. [0038] As illustrated in FIG.2, a first water quality measuring instrument (W.M) 31 is arranged on the upstream side of the feed-water pump 20 (on the side of intake of the seawater 28), and measures water quality of the taken-in seawater 28. A second water quality measuring instrument (W.M) 32 measures water quality of flowing water after a first chemical has been added through the pipe 25 to the taken-in seawater 28. A third water quality measuring instrument (W.M) 33 measures water quality of flowing water after the first chemical has been added and before the water is introduced to the RO membrane 23. The first water quality measuring instrument 31, the second water quality measuring instrument 32 and the third water quality measuring instrument 33 are arranged in this order from the upstream side (on the side of intake of the seawater 28) in the flow of water flowing through insides of the plant 2, and measure water quality of flowing water before the water is treated through the RO membrane 23. A fourth water quality measuring instrument (W.M) 34 measures water quality of flowing water (desalinated water 29) after the water has been treated through the RO membrane 23. A fifth water quality measuring instrument (W.M) 35 measures water quality of flowing water (desalinated water 29) after the water has been treated through the RO membrane 23 and after a second chemical has been added through the pipe 26. The fourth water quality measuring instrument 34 and the fifth water quality measuring instrument 35 are arranged in this order from the upstream side. A sixth water quality measuring instrument (W.M) 36 measures water quality of flowing water (concentrated water 30) which has been generated by treatment through the RO membrane 23 and to which a third chemical has been added through the pipe 27. [0039] As illustrated in FIG.2, a first pressure and flow rate measuring instrument (PF.M) 37 measures pressure, flow rate and temperature of water flowing between the feed-water pump 20 and the high pressure pump 21. A second pressure and flow rate measuring instrument (PF.M) 38 measures pressure, flow rate and temperature of water flowing between the feed-water pump 20 and the pressure recovery device 24. The second pressure and flow rate measuring instrument 38 measures pressure, flow rate and temperature of the flowing water to be introduced into the pressure recovery device 24. A third pressure and flow rate measuring instrument (PF.M) 39 measures pressure, flow rate and temperature of water flowing between the pressure recovery device 24 and the booster pump 22 provided at the subsequent stage of the pressure recovery device 24. A fourth pressure and flow rate measuring instrument (PF.M) 40 measures pressure, flow rate and temperature of water flowing between the booster pump 22 and the RO membrane 23. A fifth pressure and flow rate measuring instrument (PF.M) 41 measures pressure, flow rate and temperature of flowing water (desalinated water 29) treated through the RO membrane 23. A sixth pressure and flow rate measuring instrument (PF.M) 42 measures pressure, flow rate and temperature of water (concentrated water 30) flowing between the RO membrane 23 and the pressure recovery device 24. A seventh pressure and flow rate measuring instrument (PF.M) 43 measures pressure, flow rate and temperature of flowing water (concentrated water 30) discharged from the pressure recovery device 24. [0040] For the plant 2, in the presage detection and abnormality diagnosis system 1 according to the present embodiment, the water quality index calculation unit 9 inputs respective values of pH and electric conductivity from the water quality measuring instruments 31, 32, 33, 34, 35 and 36 to calculate water quality indices in the devices included in the plant 2. [0041] For example, a water quality index X21 in the high pressure pump 21 is expressed by [Formula 1] below, from a measuring result C32 of the water quality measuring instrument 32 and a measuring result C33 of the water quality measuring instrument 33. [Formula 1] X21=C32-C33 [0042] In the plant 2, respective water qualities in the upstream side and the downstream side of the high pressure pump 21 remain unchanged in the normal operation. Accordingly, a difference is calculated between the respective water qualities in the upstream side and the downstream side of the high pressure pump 21 and when the difference fluctuates, the water quality index X21 is judged as abnormal. [0043] Moreover, a water quality index X23 in the RO membrane 23 is expressed by [Formula 2] below, from a measuring result C33 of the water quality measuring instrument 33, a measuring result C34 of the water quality measuring instrument 34, a measuring result C36 of the water quality measuring instrument 36, a flow rate measuring result G40 of the pressure and flow rate measuring instrument 40, a flow rate measuring result G41 of the pressure and flow rate measuring instrument 41, a flow rate measuring value G27 of the chemical liquid injected into the pipe 27, liquid quality C27 of the chemical liquid and a function f1. [Formula 2] X23=(G40×f1(C33)+G27×f1(C27)-(G40-G41)×f1(C36)) ÷G41-f1(C34) [0044] Here, the function f1 in the above [Formula 2] is used for calculating a rate of impurities contained in the fluid from electric conductivity of the fluid. The above [Formula 2] is directed to, from a balance of mass of respective impurities at an inlet and an outlet of the RO membrane 23, estimating the quantity of impurities on the concentrated water side of the RO membrane 23, and comparing the estimated quantity of impurities with the actual quantity of impurities, and when a difference based on the comparison fluctuates, it is judged that water quality in the RO membrane 23 is abnormal. [0045] Note that in the present embodiment, the indices represented by the above [Formula 1] and [Formula 2] are used for diagnosis of abnormality. Consequently, it becomes possible to reduce the number of measurement values for judging an abnormality. [0046] In the presage detection and abnormality diagnosis system 1 for the seawater desalination plant 2 according to the present embodiment, the abnormality point estimation unit 10 sequentially calculates water quality indices (for example, X21 and X23 in the present embodiment) during operation of the plant 2, and judges from changes of each index, presence or absence of abnormality of water quality in the respective devices. Methods of judging abnormality include a method of setting a threshold to thereby judge abnormality when water quality exceeds the threshold, a method of detecting changes in the trends (slope, average, dispersion) of a plurality of indices to judge abnormality, a method of regarding a plurality of indices as a data group and detecting a change in the trend of the data group to judge abnormality, and the like. The present system may use any of these methods. [0047] Note that, although electric conductivity is measured as the water quality in the present embodiment, a value obtained by directly measuring saline concentration may be used. [0048] Next, a description will be given of the device performance index calculation unit 11 in the presage detection and abnormality diagnosis system 1 for the seawater desalination plant 2 according to the present embodiment. [0049] The device performance index calculation unit 11 calculates a state of each device in the plant 2 as a device performance index, based on pressures, flow rates and temperatures obtained from the measuring instruments in the plant 2. [0050] For example, device performance indices in the high pressure pump 21 include [Formula 3] below, for evaluating the quantity of water leakage from the pump, and [Formula 4] below, for evaluating the pump performance. [Formula 3] Y21A=G40-G39-G37 [Formula 4] Y21B=f2(P40-P37, N37)-G37 [0051] Here, G40, G39 and G37 in the above [Formula 3] represent flow rate measurement values in the measuring instrument 40, the measuring instrument 39 and the measuring instrument 37, respectively. Moreover, P40 and P37 in the above [Formula 4] represent pressure measurement values in the measuring instrument 40 and the measuring instrument 37, respectively. N37 in the above [Formula 4] represents the number of revolutions of the high pressure pump 21. Further, the function f2 shown in the above [Formula 4] indicates a pump performance curve (Q-H curve). The Q-H curve represents in the form of a curve, a relationship with the pump discharge flow rate (or suction flow rate) when the pump is operated with a predetermined lifting range and a predetermined number of revolutions. When a vane disposed inside the pump is damaged, pressure or flow rate at the outlet of the high pressure pump 21 deviates from the curve indicated by the Q-H curve, and thus it is possible to evaluate performance of devices inside the pump. [0052] Although calculation is made as to performance indices of the high pressure pump 21 in this example, similar indices can be calculated as to the RO membrane 23, too. For example, indices for diagnosis of failures may be defined by utilizing membrane performance calculating formula which is provided by an RO membrane manufacturer or the like, to calculate a reference value of the volume of permeated water (the volume of desalinated water), and then calculating a difference between the reference value and the desalinated water at the outlet of the RO membrane 23. [0053] Moreover, the failure point estimation unit 12 sequentially calculates device performance indices described above during operation of the plant 2, and judges from changes of each index, presence or absence of failures in the respective devices. In the same way as that in the water quality, the failure point estimation unit 12 may judge failures by comparison with a threshold, or may detect an abnormality from changes in the trends of a plurality of indices. [0054] Next, a description is given of an operation of a recovery method candidate (R.M.C.) selection unit 13 in the presage detection and abnormality diagnosis system 1 for the seawater desalination plant 2 according to the present embodiment. [0055] The recovery method candidate selection unit 13 is constituted by a failure content selection unit and a recovery method selection unit. The failure content selection unit uses a table in judgment of failures, as shown in Table 1. [0056] [Table 1] Failure P1 P2 … Pn Index X21 + × … × X23 0 + … × Y21A 0 × … - Y21B 0 × … 0 : : : : : [0057] With the device performance indices and the water quality indices calculated beforehand in rows and the associated failures in columns, Table 1 qualitatively shows a change of the index in each row for the failure in each column. In Table 1, the sign of “+” represents the case where the index becomes a positive value (or increases) when the failure occurs, and the sign of “-” represents the case where the index becomes a negative value (or decreases) when the failure occurs. The sign of “0” represents the case where there is no causal relationship between the index and the failure and the index remains unchanged, and the sign of “×” represents the case where a causal relationship is recognized but the index varies irregularly. [0058] With respect to Table 1 thus set, the recovery method candidate selection unit 13 first evaluates the degree of matching between the value of each index and the column in Table 1, and outputs matched contents of failures (P1’, P2’, ……, Pn’). Note that Table 1 merely qualitatively shows a change in the value of each index, and a plurality of contents of failures may be outputted in some cases. [0059] Next, the recovery method selection unit uses a table shown in Table 2. [0060] [Table 2] Measure A1 A2 … Am Failure P1 0.5 0.5 … 0 P2 0 1.0 … 0 P3 0 0 … 0 : : : … : Pn 0 0.2 … 0.8 [0061] Table 2 has the contents of failures indicated beforehand set in rows and the associated measures set in columns. In Table 2, each of numerical values represents a weight of the measure for each failure (“1” indicates that priority of the measure for failure is the highest). The recovery method selection unit sums weights of the respective measures associated with the failures indicated beforehand, every column. [0062] Moreover, measures are outputted in descending order of the sums of respective weights to the recovery method candidate display unit 5. [0063] Note that although the signs of “+”, “-” and the like shown in Table 1 are determined from the characteristics of the devices, it is difficult to appropriately set the weights in Table 2. To cope with this, according to the present invention, a plant performance recovery quantity (P.P.R.Q.) comparison unit 14 calculates the quantity of fluctuation of the index after some measures for failures or abnormalities have been taken, and calculates again the matched contents of failures (P1’, P2’, ……, Pn’) using Table 1. [0064] Moreover, a recovery method candidate (R.M.C.) modification unit 15 compares the contents of failures (P1, P2, ……, Pn) with the contents of failures (P1’, P2’, ……, Pn’), and remodifies the weighting of a measure (for example, A1) which the operator has taken. More specifically, when the failure (for example, P1) has not been detected with the measure taken, the recovery method candidate modification unit 15 adds a constant value to the weight of the row of P1 and the column of A1, and then normalizes the values of the row of P1 with 0 to 1 so that the sum of all the weights of the row of P1 becomes 1. On the other hand, when the failure has still been detected even with the measure taken, the recovery method candidate modification unit 15 subtracts a constant value from the associated weight, and then normalizes the values of the associated row with 0 to 1 so that the sum of all the weights of the associated row becomes 1. [0065] The presage detection and recovery support system for plant failure according to the present embodiment detects an abnormality of the device which constitutes the seawater desalination system, from the chemical characteristics of the seawater and the mechanical characteristics. Consequently, it is possible to appropriately specify a point of the abnormality, with the chemicals or the like injected intermittently into the seawater and the desalinated water as disturbance. [0066] The presage detection and recovery support system for plant failure according to the present embodiment displays on the display device a plurality of measure methods for recovering the plant based on the detected result to present the measure methods to the operator, re-evaluates effects attained by the presented measure methods, and modifies the measure methods. Consequently, it becomes possible to enhance accuracy of the measure methods when failures occur, and thus to present a more appropriate measure method. [Second embodiment] [0067] A description will be hereinafter given of a presage detection and abnormality diagnosis system for seawater desalination plants according to a second embodiment of the present invention. [0068] FIG.3 is a system configuration diagram illustrating a presage detection and abnormality diagnosis system 1a for seawater desalination plants 2 according to the second embodiment. [0069] Referring to FIG.3, the system 1a is adapted to detect and diagnose failures of respective devices and abnormalities of respective water qualities in a plurality of seawater desalination plants 2 which are set up in different points, by presage detection and abnormality diagnosis units 60 which are provided for the respective plants 2; to transmit device performance indices and water quality indices which are results of the detection and diagnosis, via a communication network 50 to the plant recovery support unit 8; and to output the contents of measures to the presage detection and abnormality diagnosis units 60 for the respective plants 2 based on the failure content selection unit (Table 1) and the recovery method selection unit (Table 2) which are recorded in a failure content and recovery method recording unit 61. [0070] Moreover, the system 1a is adapted to modify the weightings of the recovery method selection unit (Table 2) based on operation by an operator for each plant and indices before and after the operation is performed. [0071] The presage detection and recovery support system 1a for plant failure according to the present embodiment detects abnormalities of the devices which constitute the seawater desalination system, from the chemical characteristics of the seawater and the mechanical characteristics. Consequently, it is possible to appropriately specify points of the abnormalities, with the chemicals or the like injected intermittently into the seawater and the desalinated water as disturbance. [0072] The presage detection and recovery support system 1a for plant failure according to the present embodiment displays on the display device a plurality of measure methods for recovering the plant based on the detected result to present the measure methods to the operator, re-evaluates effects attained by the presented measure methods, and modifies the measure methods. Consequently, it becomes possible to enhance accuracy of the measure methods when failures occur, and thus to present more appropriate measure methods. [0073] The presage detection and recovery support system 1a for plant failure according to the present embodiment makes it possible for the single plant recovery support unit 8 to consolidate information on device failures and water quality abnormalities in the plurality of plants 2. Consequently, it becomes possible to early enhance respective accuracies of the failure content selection unit and the recovery method selection unit owing to failures in the plurality of plants 2. Moreover, it becomes possible to understand and manage the failures in the plurality of plants 2 all at once by means of the plant recovery support unit 8. [0074] In the present embodiment, the device performance indices and the water quality indices are transmitted via the communication network 50 to the plant recovery support unit 8. This is because, even in the case where the types of measuring instruments and measurement positions are different from one another in the plants 2, it is possible to commonly diagnose the plants 2 because of the device performance indices and the water quality indices being common to the plants 2. INDUSTRIAL APPLICABILITY [0075] The present invention makes it possible to detect failures of devices and/or abnormalities of water qualities in a seawater desalination plant and also to present appropriate measures to an operator.

CLIAMS:We Claim:

1. A presage detection and recovery support system for failure of a seawater desalination plant that is provided with a high pressure pump for pressurizing seawater and an RO membrane for obtaining freshwater from the seawater pressurized by the high pressure pump, comprising:
a unit that calculates mechanical performance indices based on at least one piece of information on measurement values of flow rates, pressures and temperatures of seawater or desalinated water flowing through insides of devices which constitute the seawater desalination plant;
a unit that calculates chemical performance indices of water quality obtained from components of seawater or desalinated water flowing through insides of the devices which constitute the seawater desalination plant;
a unit that detects a mechanical failure of a device or an abnormality of the water quality from the mechanical performance indices and the chemical performance indices; and
a unit that displays a plurality of operation methods or measure methods for recovering the plant from the mechanical failure or the abnormality of the water quality.

2. The presage detection and recovery support system for failure of a seawater desalination plant, according to claim 1, further comprising:
a unit that inputs a plant operation or a measure performed by an operator; and
a unit that compares the mechanical performance indices or the chemical performance indices before the plant operation or the measure is performed, with the mechanical performance indices or the chemical performance indices after the plant operation or the measure has been performed, and based on a result of comparison, modifies an order of display of the measure methods, or presence or absence of the display thereof.

3. The presage detection and recovery support system for failure of a seawater desalination plant, according to claim 1 or 2, wherein
the unit that calculates mechanical performance indices calculates the mechanical performance indices using information on measurement values of flow rates, pressures and temperatures of the seawater or desalinated water, the information being received from measuring instruments installed in the seawater desalination plant.

4. The presage detection and recovery support system for failure of a seawater desalination plant, according to claim 1 or 2, wherein
the unit that calculates chemical performance indices calculates the chemical performance indices using information of the water quality of the seawater or desalinated water, the information being received from water quality measuring instruments installed in the seawater desalination plant. ,TagSPECI:CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority to Japanese Patent Application No. 2013-119397, filed on June 6, 2013, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD
[0001] The present invention relates to a control system for a plant that produces freshwater from seawater.

BACKGROUND ART
[0002] For seawater desalination plants that produce freshwater from seawater to provide it for drinking or industrial uses, various methods such as an evaporation method, a reverse osmosis method and the like have been proposed by manufacturers.
[0003] For example, the evaporation method is to heat seawater to obtain steam by means of a heat source such as a boiler or the like and then to cool the steam to obtain freshwater. On the other hand, the reverse osmosis method is to pressurize seawater and to pass the seawater through a filtration film called a reverse osmosis membrane (RO membrane) to filtrate freshwater (desalinated water) from the seawater. A high pressure pump is used to pressurize the seawater. Driving the high pressure pump needs a turbine or a power source such as a power-generating plant, for generating a driving force.
[0004] In a seawater desalination plant using a reverse osmosis method of the methods described above, a lifting range of the high pressure pump and a filtration performance of the RO membrane greatly influence the production volume of desalinated water. For example, seawater contains microorganisms besides salt content and trace metal. In particular, the microorganisms feed on organic matters to form colony called biofilm on the surface of the RO membrane and thus inhibit the passage of seawater through the membrane. It is generally known that the production volume of desalinated water is extremely decreased in a seawater desalination plant with biofilm being developed.
[0005] On the other hand, in the case where the seawater changes into high acidic property or high alkaline property, members disposed inside the high pressure pump are corroded and damaged, which causes troubles such as a decrease in pressure and flow rate, corrosion cracking and the like. The RO membrane provides a predetermined filtration performance when the seawater is pressurized up to a pressure specified by a membrane manufacturer. Accordingly, in the case where a sufficient pressure is not obtained by the high pressure pump, it is necessary to stop the plant and to take measures such as exchange of the device or repair thereof.
[0006] For example, Patent document 1 describes an operation management method that includes, when a failure of an energy recovery device and/or deterioration of a reverse osmotic membrane in a seawater desalination plant is/are detected, informing the operator of the failure and/or deterioration by means of an alarm, and also taking measures such as cleaning the RO membrane in case of the deterioration, switching an operation mode for the pump in case of the failure, or the like.
[0007] The operation management method in Patent document 1 is to detect presence or absence of occurrence of an abnormality based on plant measurements and mechanical characteristics of the devices. An abnormality detected by the method is informed via a control device to the operator. Moreover, the method is characterized by instructing the operator to take measures based on the abnormality and switching over to a plant control which is prepared in advance assuming occurrence of possible failures.

PRIOR ART DOCUMENTS
Patent document
[0008] Patent document 1: Japanese Patent Application Publication No. 2010-089036

SUMMARY OF THE INVENTION
Problems to be solved by the invention
[0009] However, in a seawater desalination plant which is required to continuously supply drinking water and/or industrial water, it is desirable to detect an abnormality of the device as early as possible and thus to avoid occurrence of failures to continue the operation as long as possible. Failures or abnormalities of the devices originate with an extremely slight change in the pressure, flow rate, constituent of water and the like, and subsequently the change gradually expands to lead to failures of the devices or a plant outage. Therefore, as for an abnormality of the device, it is necessary to reflect not only information on measurement points for the pressure, flow rate, constituent of water and the like, but also information on regular patrol and/or maintenance check by a site operator. Thus in the seawater desalination plant, it is desirable to detect a decrease in the production volume of desalinated water and failures of the devices as early as possible and also to take the best measures quickly when a trouble occurs.
[0010] Moreover, in a seawater desalination plant constituted with a plurality of devices such as RO membranes, high pressure pumps and the like, an abnormality in the upstream side of the process is transmitted to the downstream side thereof. In particular, in this plant that treats water which is incompressible fluid, an abnormality of the pressure and/or the flow rate instantaneously spreads to the entire plant. For this reason, it is necessary to specify the point at which the abnormality occurs, with good accuracy.
[0011] It is therefore an object of the present invention, in a plurality of devices included in a seawater desalination plant, to detect failures or abnormalities of the devices earlier and to determine their causes based on the detected content to present appropriate measures to an operator.
Means for solving the problems
[0012] The present invention is provided with a unit that detects failures of devices which constitute a seawater desalination plant, a unit that detects abnormality of water quality of fluid (seawater, desalinated water) flowing through insides of the devices, and a unit that presents to an operator based on the detected results, a plurality of measure methods for recovering the plant.
Advantageous effects of the invention
[0013] The presage detection and recovery support system for plant failure according to the present invention detects abnormalities of the devices from chemical characteristics of the seawater and mechanical characteristics, thereby making it possible to appropriately specify a point at which the abnormality occurs, with chemicals or the like injected intermittently into the seawater and the desalinated water as disturbance.

BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG.1 is a system configuration diagram illustrating a presage detection and abnormality diagnosis system according to a first embodiment of the present invention.
FIG.2 is a configuration diagram illustrating a seawater desalination plant which is a target of diagnosis in the present invention.
FIG.3 is a system configuration diagram illustrating a presage detection and abnormality diagnosis system according to a second embodiment of the present invention.

EMBODIMENTS OF THE INVENTION
[0015] The system includes a unit that calculates mechanical performance indices of devices obtained from measurement values of flow rates, pressures and temperatures in a plant, and a unit that calculates chemical performance indices of water quality obtained from components of fluid (seawater, desalinated water) flowing through the insides of the devices.
[0016] Also, the system includes a unit that estimates a point of failure in the devices from the above mechanical performance indices of the devices, and a unit that estimates a point of water quality abnormality in the devices from the above chemical performance indices of water quality.
[0017] Moreover, the system includes a unit that selects an appropriate operation method or a measure method from among plant operation methods or measure methods which are prepared in advance for normally recovering the plant, based on the calculated mechanical performance indices of the devices and chemical performance indices of the water quality, and the estimated point of failure in the devices and point of abnormality in the water quality, and a unit that presents the selected method to an operator.
[0018] Furthermore, the system includes a unit that inputs a plant operation or a measure performed by an operator; a unit that compares the mechanical performance indices of the devices and the chemical performance indices of the water quality obtained when failures or abnormalities occur, with the mechanical performance indices of the devices and the chemical performance indices of the water quality obtained after some measures have been taken, and calculates improvement effects attained by the plant operation or the measure performed by the operator; and according to the effects, modifies an order of display of the plant operation methods or the measure methods which are prepared in advance, or presence or absence of the display thereof.
[First embodiment]
[0019] A description will be given hereinafter of a presage detection and abnormality diagnosis system for a seawater desalination plant according to a preferred embodiment of the present invention.
[0020] FIG.1 is a system configuration diagram illustrating a presage detection and abnormality diagnosis system 1 for a seawater desalination plant 2 according to the present embodiment.
[0021] The seawater desalination plant (hereinafter referred to as plant) 2 transmits (outputs) to a plant control device 3 measurement values of water temperature, pump discharge pressure, the production volume of desalinated water, water quality and the like. The plant control device 3 receives (inputs) the measurement values of water temperature, pump discharge pressure, the production volume of desalinated water, water quality and the like, and outputs to the plant 2 control input values of the number of revolutions of the pump, valve aperture and the like so that the measurement values of the plant 2, e.g., the pump discharge pressure and the production volume of desalinated water, become respective target values.
[0022] The measurement values of the plant 2 and the control input values of the plant control device 3 are displayed on a display device such as a monitor or the like provided in a plant operation unit 4. The operator who has confirmed the values on the display device may directly specify control input values using a console or the like provided in the plant operation unit 4.
[0023] For the plant 2 and the plant control device 3, the presage detection and abnormality diagnosis system 1 according to the present embodiment inputs the measurement values of the plant 2 and the control input values from the plant control device 3 to a device failure (D.F.) detection unit 6 and a water quality abnormality (W.Q.A.) detection unit 7.
[0024] In the device failure detection unit 6, a device performance index (D.P.I.) calculation unit 11 inputs the measurement values of the plant 2 and the control input values and calculates performance indices of devices which constitute the plant 2. Moreover, a failure point (F.P.) estimation unit 12 inputs the performance indices of the devices and specifies a point of failure in the device in the plant 2.
[0025] Next, in the water quality abnormality detection unit 7, a water quality index (W.Q.I.) calculation unit 9 inputs the measurement values of the plant 2 and the control input values to calculate water quality indices in the plant 2. Moreover, an abnormality point (A.P.) estimation unit 10 inputs the water quality indices and specifies a point of abnormality in water quality in the plant 2.
[0026] Next, a plant recovery (P.R.) support unit 8 inputs respective values of the performance indices and the point of failure calculated in the device failure detection unit 6, and respective values of the water quality indices and the point of abnormality calculated in the water quality abnormality detection unit 7, and outputs a list of plant recovery methods for failures or abnormalities, to a recovery method candidate (R.M.C.) display unit 5.
[0027] Next, the operator selects by means of the plant operation unit 4, based on the list of plant recovery methods displayed on the recovery method candidate display unit 5 and various plant states (noise, vibration and the like) collected on site, an arbitrary plant recovery method from the list for execution. Information on the plant recovery method selected by the operator is inputted to the plant recovery support unit 8.
[0028] When a measure result from the operator is inputted, the plant recovery support unit 8 compares device performance indices and water quality indices obtained when a plant failure or water quality abnormality is detected, with the present device performance indices and water quality indices, and as for a measure having indices highly improved, modifies an order of display of the measure to raise the display priority on the recovery method candidate display unit 5. On the contrary, as for a measure having indices less improved, the plant recovery support unit 8 modifies an order of display of the measure to lower the display priority. Consequently, after the next time, measures having successful results are displayed at higher ranks and thus appropriate recovery methods are presented for the case where a plant failure or water quality abnormality occurs.
[0029] The presage detection and abnormality diagnosis system 1 described above calculates degrees of the device failures and degrees of the water quality abnormalities as the device performance indices and the water quality indices, respectively, and based on the calculated values, detects presage and estimates effects of the measures.
[0030] Next, a calculation method of the device performance index and the water quality index by the present system will be described with reference to FIG.2.
[0031] FIG.2 is an exemplary system configuration diagram of the seawater desalination plant 2 which is a target of presage detection in the present system. It should be noted that FIG.2 illustrates only a high pressure pump 21, a reverse osmosis (RO) membrane 23 and a pressure recovery device 24 which are major parts of the plant 2, and auxiliary machines associated therewith.
[0032] A feed-water pump 20 pumps up seawater 28 and feeds the seawater to the high pressure pump 21 and the pressure recovery device 24.
[0033] The pressure recovery device 24 pressurizes part of the seawater using pressurized concentrated water from the RO membrane 23, and a booster pump 22 further boosts a pressure of the pressurized seawater.
[0034] Moreover, the high pressure pump 21 also pressurizes the seawater up to a predetermined pressure.
[0035] The seawater of high pressure obtained at an outlet of the high pressure pump 21 and an outlet of the booster pump 22 is fed to the RO membrane 23. The RO membrane 23 utilizes its reverse osmosis action to filtrate desalinated water 29 from the pressurized seawater. At this time, a pressure of the desalinated water 29 is reduced to almost the atmospheric pressure. Moreover, seawater after the desalinated water 29 has been filtrated transmits its pressure to the seawater on the side of the feed-water pump 20 in the pressure recovery device 24, and is then drained as concentrated water 30.
[0036] It should be noted that the plant 2 further includes pipes 25, 26 and 27 for injection of chemical provided at an outlet of the feed-water pump 20, an outlet of the RO membrane 23 on the desalinated water side, and an outlet of the pressure recovery device 24 on the concentrated water side, respectively. The pipe 25 is provided for injection of acidic or alkaline chemical liquid for preventing the RO membrane 23 from fouling. Moreover, the pipe 26 is provided for injection of chemical liquid for controlling pH of the desalinated water 29 which has changed into acidic property with filtration through the RO membrane 23. Similarly, the pipe 27 is provided for injection of chemical liquid for controlling pH of the concentrated water 30, so as to minimize an influence of the concentrated water 30 on the environment when discharged as drainage.
[0037] As illustrated in FIG.2, the plant 2 according to the present embodiment includes pressure and flow rate measuring instruments (PF.M) 37, 38, 39, 40, 41, 42 and 43 that measure pressures, flow rates and temperatures for use in monitoring and controlling states of the devices included in the plant 2, and water quality measuring instruments (W.M) 31, 32, 33, 34, 35 and 36 for use in monitoring and controlling water qualities in the plant 2. Note that the pressure and flow rate measuring instruments 37, 38, 39, 40, 41, 42 and 43 illustrated in FIG.2 measure pressures, flow rates and temperatures of the seawater, the desalinated water or the concentrated water. Moreover, the water quality measuring instruments 31, 32, 33, 34, 35 and 36 measure electric conductivity which is one index of water quality.
[0038] As illustrated in FIG.2, a first water quality measuring instrument (W.M) 31 is arranged on the upstream side of the feed-water pump 20 (on the side of intake of the seawater 28), and measures water quality of the taken-in seawater 28. A second water quality measuring instrument (W.M) 32 measures water quality of flowing water after a first chemical has been added through the pipe 25 to the taken-in seawater 28. A third water quality measuring instrument (W.M) 33 measures water quality of flowing water after the first chemical has been added and before the water is introduced to the RO membrane 23. The first water quality measuring instrument 31, the second water quality measuring instrument 32 and the third water quality measuring instrument 33 are arranged in this order from the upstream side (on the side of intake of the seawater 28) in the flow of water flowing through insides of the plant 2, and measure water quality of flowing water before the water is treated through the RO membrane 23. A fourth water quality measuring instrument (W.M) 34 measures water quality of flowing water (desalinated water 29) after the water has been treated through the RO membrane 23. A fifth water quality measuring instrument (W.M) 35 measures water quality of flowing water (desalinated water 29) after the water has been treated through the RO membrane 23 and after a second chemical has been added through the pipe 26. The fourth water quality measuring instrument 34 and the fifth water quality measuring instrument 35 are arranged in this order from the upstream side. A sixth water quality measuring instrument (W.M) 36 measures water quality of flowing water (concentrated water 30) which has been generated by treatment through the RO membrane 23 and to which a third chemical has been added through the pipe 27.
[0039] As illustrated in FIG.2, a first pressure and flow rate measuring instrument (PF.M) 37 measures pressure, flow rate and temperature of water flowing between the feed-water pump 20 and the high pressure pump 21. A second pressure and flow rate measuring instrument (PF.M) 38 measures pressure, flow rate and temperature of water flowing between the feed-water pump 20 and the pressure recovery device 24. The second pressure and flow rate measuring instrument 38 measures pressure, flow rate and temperature of the flowing water to be introduced into the pressure recovery device 24. A third pressure and flow rate measuring instrument (PF.M) 39 measures pressure, flow rate and temperature of water flowing between the pressure recovery device 24 and the booster pump 22 provided at the subsequent stage of the pressure recovery device 24. A fourth pressure and flow rate measuring instrument (PF.M) 40 measures pressure, flow rate and temperature of water flowing between the booster pump 22 and the RO membrane 23. A fifth pressure and flow rate measuring instrument (PF.M) 41 measures pressure, flow rate and temperature of flowing water (desalinated water 29) treated through the RO membrane 23. A sixth pressure and flow rate measuring instrument (PF.M) 42 measures pressure, flow rate and temperature of water (concentrated water 30) flowing between the RO membrane 23 and the pressure recovery device 24. A seventh pressure and flow rate measuring instrument (PF.M) 43 measures pressure, flow rate and temperature of flowing water (concentrated water 30) discharged from the pressure recovery device 24.
[0040] For the plant 2, in the presage detection and abnormality diagnosis system 1 according to the present embodiment, the water quality index calculation unit 9 inputs respective values of pH and electric conductivity from the water quality measuring instruments 31, 32, 33, 34, 35 and 36 to calculate water quality indices in the devices included in the plant 2.
[0041] For example, a water quality index X21 in the high pressure pump 21 is expressed by [Formula 1] below, from a measuring result C32 of the water quality measuring instrument 32 and a measuring result C33 of the water quality measuring instrument 33.
[Formula 1] X21=C32-C33
[0042] In the plant 2, respective water qualities in the upstream side and the downstream side of the high pressure pump 21 remain unchanged in the normal operation. Accordingly, a difference is calculated between the respective water qualities in the upstream side and the downstream side of the high pressure pump 21 and when the difference fluctuates, the water quality index X21 is judged as abnormal.
[0043] Moreover, a water quality index X23 in the RO membrane 23 is expressed by [Formula 2] below, from a measuring result C33 of the water quality measuring instrument 33, a measuring result C34 of the water quality measuring instrument 34, a measuring result C36 of the water quality measuring instrument 36, a flow rate measuring result G40 of the pressure and flow rate measuring instrument 40, a flow rate measuring result G41 of the pressure and flow rate measuring instrument 41, a flow rate measuring value G27 of the chemical liquid injected into the pipe 27, liquid quality C27 of the chemical liquid and a function f1.
[Formula 2]
X23=(G40×f1(C33)+G27×f1(C27)-(G40-G41)×f1(C36))
÷G41-f1(C34)
[0044] Here, the function f1 in the above [Formula 2] is used for calculating a rate of impurities contained in the fluid from electric conductivity of the fluid. The above [Formula 2] is directed to, from a balance of mass of respective impurities at an inlet and an outlet of the RO membrane 23, estimating the quantity of impurities on the concentrated water side of the RO membrane 23, and comparing the estimated quantity of impurities with the actual quantity of impurities, and when a difference based on the comparison fluctuates, it is judged that water quality in the RO membrane 23 is abnormal.
[0045] Note that in the present embodiment, the indices represented by the above [Formula 1] and [Formula 2] are used for diagnosis of abnormality. Consequently, it becomes possible to reduce the number of measurement values for judging an abnormality.
[0046] In the presage detection and abnormality diagnosis system 1 for the seawater desalination plant 2 according to the present embodiment, the abnormality point estimation unit 10 sequentially calculates water quality indices (for example, X21 and X23 in the present embodiment) during operation of the plant 2, and judges from changes of each index, presence or absence of abnormality of water quality in the respective devices. Methods of judging abnormality include a method of setting a threshold to thereby judge abnormality when water quality exceeds the threshold, a method of detecting changes in the trends (slope, average, dispersion) of a plurality of indices to judge abnormality, a method of regarding a plurality of indices as a data group and detecting a change in the trend of the data group to judge abnormality, and the like. The present system may use any of these methods.
[0047] Note that, although electric conductivity is measured as the water quality in the present embodiment, a value obtained by directly measuring saline concentration may be used.
[0048] Next, a description will be given of the device performance index calculation unit 11 in the presage detection and abnormality diagnosis system 1 for the seawater desalination plant 2 according to the present embodiment.
[0049] The device performance index calculation unit 11 calculates a state of each device in the plant 2 as a device performance index, based on pressures, flow rates and temperatures obtained from the measuring instruments in the plant 2.
[0050] For example, device performance indices in the high pressure pump 21 include [Formula 3] below, for evaluating the quantity of water leakage from the pump, and [Formula 4] below, for evaluating the pump performance.
[Formula 3] Y21A=G40-G39-G37
[Formula 4] Y21B=f2(P40-P37, N37)-G37
[0051] Here, G40, G39 and G37 in the above [Formula 3] represent flow rate measurement values in the measuring instrument 40, the measuring instrument 39 and the measuring instrument 37, respectively. Moreover, P40 and P37 in the above [Formula 4] represent pressure measurement values in the measuring instrument 40 and the measuring instrument 37, respectively. N37 in the above [Formula 4] represents the number of revolutions of the high pressure pump 21. Further, the function f2 shown in the above [Formula 4] indicates a pump performance curve (Q-H curve). The Q-H curve represents in the form of a curve, a relationship with the pump discharge flow rate (or suction flow rate) when the pump is operated with a predetermined lifting range and a predetermined number of revolutions. When a vane disposed inside the pump is damaged, pressure or flow rate at the outlet of the high pressure pump 21 deviates from the curve indicated by the Q-H curve, and thus it is possible to evaluate performance of devices inside the pump.
[0052] Although calculation is made as to performance indices of the high pressure pump 21 in this example, similar indices can be calculated as to the RO membrane 23, too. For example, indices for diagnosis of failures may be defined by utilizing membrane performance calculating formula which is provided by an RO membrane manufacturer or the like, to calculate a reference value of the volume of permeated water (the volume of desalinated water), and then calculating a difference between the reference value and the desalinated water at the outlet of the RO membrane 23.
[0053] Moreover, the failure point estimation unit 12 sequentially calculates device performance indices described above during operation of the plant 2, and judges from changes of each index, presence or absence of failures in the respective devices. In the same way as that in the water quality, the failure point estimation unit 12 may judge failures by comparison with a threshold, or may detect an abnormality from changes in the trends of a plurality of indices.
[0054] Next, a description is given of an operation of a recovery method candidate (R.M.C.) selection unit 13 in the presage detection and abnormality diagnosis system 1 for the seawater desalination plant 2 according to the present embodiment.
[0055] The recovery method candidate selection unit 13 is constituted by a failure content selection unit and a recovery method selection unit. The failure content selection unit uses a table in judgment of failures, as shown in Table 1.
[0056] [Table 1]
Failure P1 P2 … Pn
Index
X21 + × … ×
X23 0 + … ×
Y21A 0 × … -
Y21B 0 × … 0
: : : : :
[0057] With the device performance indices and the water quality indices calculated beforehand in rows and the associated failures in columns, Table 1 qualitatively shows a change of the index in each row for the failure in each column. In Table 1, the sign of “+” represents the case where the index becomes a positive value (or increases) when the failure occurs, and the sign of “-” represents the case where the index becomes a negative value (or decreases) when the failure occurs. The sign of “0” represents the case where there is no causal relationship between the index and the failure and the index remains unchanged, and the sign of “×” represents the case where a causal relationship is recognized but the index varies irregularly.
[0058] With respect to Table 1 thus set, the recovery method candidate selection unit 13 first evaluates the degree of matching between the value of each index and the column in Table 1, and outputs matched contents of failures (P1’, P2’, ……, Pn’). Note that Table 1 merely qualitatively shows a change in the value of each index, and a plurality of contents of failures may be outputted in some cases.
[0059] Next, the recovery method selection unit uses a table shown in Table 2.
[0060] [Table 2]
Measure A1 A2 … Am
Failure
P1 0.5 0.5 … 0
P2 0 1.0 … 0
P3 0 0 … 0
: : : … :
Pn 0 0.2 … 0.8
[0061] Table 2 has the contents of failures indicated beforehand set in rows and the associated measures set in columns. In Table 2, each of numerical values represents a weight of the measure for each failure (“1” indicates that priority of the measure for failure is the highest). The recovery method selection unit sums weights of the respective measures associated with the failures indicated beforehand, every column.
[0062] Moreover, measures are outputted in descending order of the sums of respective weights to the recovery method candidate display unit 5.
[0063] Note that although the signs of “+”, “-” and the like shown in Table 1 are determined from the characteristics of the devices, it is difficult to appropriately set the weights in Table 2. To cope with this, according to the present invention, a plant performance recovery quantity (P.P.R.Q.) comparison unit 14 calculates the quantity of fluctuation of the index after some measures for failures or abnormalities have been taken, and calculates again the matched contents of failures (P1’, P2’, ……, Pn’) using Table 1.
[0064] Moreover, a recovery method candidate (R.M.C.) modification unit 15 compares the contents of failures (P1, P2, ……, Pn) with the contents of failures (P1’, P2’, ……, Pn’), and remodifies the weighting of a measure (for example, A1) which the operator has taken. More specifically, when the failure (for example, P1) has not been detected with the measure taken, the recovery method candidate modification unit 15 adds a constant value to the weight of the row of P1 and the column of A1, and then normalizes the values of the row of P1 with 0 to 1 so that the sum of all the weights of the row of P1 becomes 1. On the other hand, when the failure has still been detected even with the measure taken, the recovery method candidate modification unit 15 subtracts a constant value from the associated weight, and then normalizes the values of the associated row with 0 to 1 so that the sum of all the weights of the associated row becomes 1.
[0065] The presage detection and recovery support system for plant failure according to the present embodiment detects an abnormality of the device which constitutes the seawater desalination system, from the chemical characteristics of the seawater and the mechanical characteristics. Consequently, it is possible to appropriately specify a point of the abnormality, with the chemicals or the like injected intermittently into the seawater and the desalinated water as disturbance.
[0066] The presage detection and recovery support system for plant failure according to the present embodiment displays on the display device a plurality of measure methods for recovering the plant based on the detected result to present the measure methods to the operator, re-evaluates effects attained by the presented measure methods, and modifies the measure methods. Consequently, it becomes possible to enhance accuracy of the measure methods when failures occur, and thus to present a more appropriate measure method.
[Second embodiment]
[0067] A description will be hereinafter given of a presage detection and abnormality diagnosis system for seawater desalination plants according to a second embodiment of the present invention.
[0068] FIG.3 is a system configuration diagram illustrating a presage detection and abnormality diagnosis system 1a for seawater desalination plants 2 according to the second embodiment.
[0069] Referring to FIG.3, the system 1a is adapted to detect and diagnose failures of respective devices and abnormalities of respective water qualities in a plurality of seawater desalination plants 2 which are set up in different points, by presage detection and abnormality diagnosis units 60 which are provided for the respective plants 2; to transmit device performance indices and water quality indices which are results of the detection and diagnosis, via a communication network 50 to the plant recovery support unit 8; and to output the contents of measures to the presage detection and abnormality diagnosis units 60 for the respective plants 2 based on the failure content selection unit (Table 1) and the recovery method selection unit (Table 2) which are recorded in a failure content and recovery method recording unit 61.
[0070] Moreover, the system 1a is adapted to modify the weightings of the recovery method selection unit (Table 2) based on operation by an operator for each plant and indices before and after the operation is performed.
[0071] The presage detection and recovery support system 1a for plant failure according to the present embodiment detects abnormalities of the devices which constitute the seawater desalination system, from the chemical characteristics of the seawater and the mechanical characteristics. Consequently, it is possible to appropriately specify points of the abnormalities, with the chemicals or the like injected intermittently into the seawater and the desalinated water as disturbance.
[0072] The presage detection and recovery support system 1a for plant failure according to the present embodiment displays on the display device a plurality of measure methods for recovering the plant based on the detected result to present the measure methods to the operator, re-evaluates effects attained by the presented measure methods, and modifies the measure methods. Consequently, it becomes possible to enhance accuracy of the measure methods when failures occur, and thus to present more appropriate measure methods.
[0073] The presage detection and recovery support system 1a for plant failure according to the present embodiment makes it possible for the single plant recovery support unit 8 to consolidate information on device failures and water quality abnormalities in the plurality of plants 2. Consequently, it becomes possible to early enhance respective accuracies of the failure content selection unit and the recovery method selection unit owing to failures in the plurality of plants 2. Moreover, it becomes possible to understand and manage the failures in the plurality of plants 2 all at once by means of the plant recovery support unit 8.
[0074] In the present embodiment, the device performance indices and the water quality indices are transmitted via the communication network 50 to the plant recovery support unit 8. This is because, even in the case where the types of measuring instruments and measurement positions are different from one another in the plants 2, it is possible to commonly diagnose the plants 2 because of the device performance indices and the water quality indices being common to the plants 2.

INDUSTRIAL APPLICABILITY
[0075] The present invention makes it possible to detect failures of devices and/or abnormalities of water qualities in a seawater desalination plant and also to present appropriate measures to an operator.