Patent Application
20100282679
The invention relates to a method for the advanced control of a membrane filtration unit, applied to the treatment of any effluent, employing microcoagulation on a membrane according to patent EP 1 239 943, resulting from patent application WO 01/41906, the proprietor of which is the Applicant.
To prevent clogging of microfiltration, ultrafiltration, nanofiltration and hyperfiltration membranes for the treatment of liquids such as, for example, surface water, wastewater or seawater, is a major technical and economic challenge well known to those skilled in the art.
To achieve this objective, the Applicant is the proprietor of Patent EP 1 239 943 which consists in injecting, upstream of the membrane, one or more coagulants with a very low dose, much lower than is the common practice of those skilled in the art, namely 30 to 80 times lower than the optimum jar test dose (coagulation test) making the zeta potential zero. The injection of the coagulant(s) as practiced according to EP 1 239 943 results in a significant reduction in membrane fouling, resulting in an increase in permeability of the membrane, that is to say the rate of effluent flow passing per unit area (m2) of said membrane, for a transmembrane pressure normalized to 1 bar, at a given temperature.
EP 1 239 943 teaches microcoagulation over a dosage range that ensures satisfactory operation without however optimizing the dosage. As a result, for a nonoptimized dosage within said range, the performance of the membrane is inferior to that which it is possible to achieve. Furthermore, in the case of an overdosage of the coagulant within said range, there is an economic overcost and the risk of blocking the membrane.
The object of the present invention is, most particularly, to optimize, in real time, the injected dose of the coagulant or coagulants during implementation of the membrane microcoagulation process defined above, by a method that continuously integrates the variations in the quality of the effluent and/or in the backflows and by an installation for implementing this method.
The aim of the invention is to achieve these objectives so as to obtain, in real time, almost optimum membrane performance automatically, avoiding or eliminating any human intervention. To do this, the present invention relates to an optimized, reliable and safe method of controlling a membrane filtration unit.
According to the invention, a method for the advanced control of a filtration unit, applied to the treatment of any effluent, employing microcoagulation on a membrane, consists in injecting, upstream of the membrane, a dose of coagulant(s) 30 to 80 times smaller than the dose giving the effluent a zero zeta potential, and is characterized in that:
Preferably, the measured quantities for defining the quality of the effluent to be treated comprise at least one of the following quantities:
The measured quantities for defining the membrane fouling state advantageously comprise at least the following quantities:
Preferably, the operating point is located by determining the coagulant suitable for the measured effluent and by determining the range of variation of the dose of coagulant.
The operating point may be located on the basis of a parameterization table for making the suitable coagulants and appropriate dosing ranges correspond to types of effluents defined by ranges of characteristic quantity values.
The operating point may be determined by an expert system that selects the coagulant(s) appropriate to the measured effluent and from this determines, by modeling, the range of dosage variation for tending toward the optimum operating point.
The coagulant dosage may be regulated by being slaved to the treated effluent flow rate.
Advantageously, the coagulant may be dosed by regulation with injection of a minimum dose and stepwise increase in the dose for as long a time as the increase in the dose produces an increase in the membrane permeability, the increase in injected coagulant dose being stopped when a reduction in membrane permeability results from an increase in the dose.
The injection of the coagulant(s) may be regulated according to the operating backflows of the membrane, signifying the fouling thereof, in order to tend toward the optimum operating point.
When there is doubt about the validity or the representativeness of one of the input signals or when an anomaly in the backflows occurs, the membrane unit may be controlled according to a station feedback control mode. The feedback control mode is a control by feedback with a fixed degree of treatment. As a variant, the feedback control mode is one in which the implementation of said invention is stopped.
Advantageously, the membrane operating parameters are adapted according to the setpoints, with the aim of eliminating/monitoring/controlling the accumulation of matter in the vicinity of the membrane. The preferentially adjusted operating parameters are: the procedure, duration and frequency of the backwashings and washings, and the choice of associated coagulants. Thus, for example, pulsed two-phase backwashings as described by FR 2 867 394, the proprietor of which is the Applicant, could advantageously be employed. Likewise, the nature of the washing coagulant(s) will be selected for its oxidizing or chelating or acid-base properties, for example to promote the elimination of the coagulant(s) employed according to the present invention.
It is also possible to adapt, according to the setpoints, the operating parameters of the treatment plant, especially the control of the discharges containing the coagulant(s). This is because the presence of coagulant(s) in the membrane washing waters, caused by implementing the present invention, may be problematic as regards direct discharge into the environment or recycling in the treatment plant. In this case, it may be necessary to start up a specific plant for treating these washing waters. These treatments are known to those skilled in the art, for example settling or flotation or centrifugation or filtration techniques carried out over a medium, over a mesh, over a cloth or over a membrane.
The invention also relates to an installation for implementing the method, comprising at least one membrane filtration unit, applied to the treatment of an effluent, employing microcoagulation on a membrane, comprising means for injecting, upstream of the membrane, a dose of coagulant(s) 30 to 80 times lower than the dose giving the effluent a zero zeta potential, characterized in that it includes a control assembly comprising:
The unit may comprise a block assigned to the process input variables and a block to which information about input quantities specific to the membrane or membranes used, namely membrane/backflow operating data, is sent.
The block assigned to the input variables receives information delivered by the measurement of quantities characteristic of the quality of the effluent upstream of the membrane, comprising at least one of the following quantities:
The block, to which information about input quantities specific to the membrane(s) used is sent, receives information delivered by the measurement of quantities characteristic of the state of the membrane, comprising at least the following quantities:
The installation may include input means for allowing the user to input setpoints/thresholds of the variables in order to define the field of application of the membrane microcoagulation relative to the nature and the quality of the effluent and to the membrane technology.
Preferably, the module for locating, on the basis of the setpoints and the input variables, the operating point of the membrane microcoagulation process is provided for processing the information:
Advantageously, the control assembly includes a module for controlling the rate of injection of the coagulant or coagulants according to the informed requirements. The control module is made up of two control logic blocks that are activated, depending on the information availability, in order to control the equipment for injecting the coagulant(s), namely:
The invention consists, apart from the abovementioned arrangements, of a number of other arrangements, which will be more explicitly addressed below as regards illustrative examples described with reference to the appended drawings, although these are in no way limiting. In these drawings:
In
In the installation shown in
The point of intersection of curve 7 with the x-axis corresponds to the coagulant dose X that makes the zeta potential zero.
This dose X is plotted on the x-axis in
Conventionally, for the coagulant dose equal to X that makes the zeta potential zero, the permeability of the membrane increases strongly at a peak 9 which is relatively narrow along a direction parallel to the x-axis.
As patent EP 1 239 943 teaches, the permeability of the membrane shows, completely surprisingly, a strong increase, illustrated by a jump 10 in curve 8, for a coagulant dose of between X/80 and X/30. It is thus apparent that, with a well-chosen reduced coagulant dose, it is possible to obtain an improvement in the membrane permeability equivalent to or greater than that obtained when the zeta potential is zero.
In
The region to the right of the point Γ and bounded by the value X/30 is denoted by β. This region corresponds to a coagulant overdosage relative to the optimum operating point Γ, but with no improvement in membrane performance or even a deterioration thereof. Operating in the region β furthermore runs the risk of matter and coagulant accumulating in the vicinity of the membrane, with a risk of blocking it for certain membrane geometries.
The region lying between the point Γ and the lower limit X/80 is denoted by α. This region corresponds to an underdosage relative to the optimum operating point Γ with inferior membrane performance.
One difficulty in operating close to the optimum point Γ lies in the risk of the operation diverging toward the limits of the range.
The method of the invention is based on the following logic:
The method of the invention is implemented by a control assembly M (
The unit A comprises a block A1 assigned to the process input variables. The block A1 receives information delivered by sensors for measuring quantities characteristic of the effluent quality upstream of the membrane, said sensors being installed for example in the effluent intake line, said quantities being:
Of course, the method of the invention is not limited to the analytical techniques mentioned above, by way of example, for the acquisition of the process input variables.
The unit A includes another block A2 to which information about input parameters specific to the membrane(s) used is sent, namely membrane operating/backflow data. These input variables comprise at least the following quantities:
Of course, the invention is not limited to the data delivered by these examples.
As a variant, for spiral modules or what are called IN/OUT internal-skin hollow-fiber membrane modules, a measurement of the pressure drop across the module(s) will be included for example.
Setpoints/thresholds for the variables of the block A1 are input by the operator using inputting means, especially a console (not shown), in order to define the range of application of the membrane microcoagulation relative to the nature and the quality of the effluent and to the membrane technology.
The input variables of the block A1 faced with these setpoints/thresholds constitute factors triggering the use of membrane microcoagulation when the setpoints are violated.
The backflow of the installation, that is to say indicating the state of membrane fouling, estimated from the variables delivered to the block A2, is a potential second factor triggering the use of membrane microcoagulation. Thus, a reduction in permeability below a set limit threshold according to the invention and/or a significant decrease over a set time interval constitute other factors triggering the use of microcoagulation.
The triggering factors may arise in parallel, in which case the microcoagulation is triggered by one or other of the triggering factors, or may arise in series, in which case the microcoagulation is triggered when all the triggering factors indicate that the respective setpoints have been violated.
The control thus described of the factors triggering the membrane microcoagulation provides, according to the invention, the relevance of implementing the method.
The control assembly M includes a module B which makes it possible to locate, on the basis of the setpoints and input variables of the module A, the operating point of the membrane microcoagulation process in an operating space considered as a space for stable and optimum implementation of said method.
Specifically, the module B is used to select the most suitable coagulant(s) and to determine the restricted range of variation of coagulant dose or the degree of treatment according to EP 1 239 943, i.e. a dosage between X/30 and X/80 or, advantageously, between X/40 and X/60, X being the optimum jar test dose giving the effluent to be treated a zero zeta potential.
The various possible coagulants, according to the various types of effluent quality, are stored in separate containers (not shown) that may be brought into communication with the injection line 2 via valves (not shown) controlled by the module B.
Depending on the mode of operation and the availability of the information sources coming from the block A1, the treatment in the module B will be provided:
Depending on the quality of the effluent, continuously measured by sensors, the determination of the optimum dosage range X/30-X/80, or as a variant X/40-X/60, is thus automatically updated.
The assembly M further includes a module C which is a control block for controlling the rate of injection of the coagulant or coagulants according to the requirements provided by the module B. Advantageously, the module C controls a valve J (
The coagulant dose or degree of treatment is defined by:
TT=C
R
Q
R
/Q
EB
where:
The module C is designed to optimize the injected coagulant dose and is made up of two control logic blocks C1 and C2 activated, depending on the availability of the information, for controlling the coagulant injection equipment.
The logic control block C1 controls the coagulant injection operation according to a feedback control mode. The objective of the control logic is to maintain a degree of treatment TT with coagulant around a fixed setpoint lying within the region α (
This feedback control mode enables a degree of treatment with coagulant(s) to be maintained over the restricted range of variation around the setpoint value.
The advantage of this variant is that the membrane operates in a stable manner, the coagulant dose being fixed for a given effluent quality.
The module C includes another block C2 with control logic for operating in a regulating mode. The objective of this logic is to maintain a degree of coagulant treatment TT so as to continuously guarantee an optimum degree of treatment close to the point Γ according to
To do this, as illustrated in
The regulating block C2 progressively increases, stepwise, the rate of injection of the coagulant(s) for as long as:
As soon as the variation in permeability is negative, which corresponds to violation of the point Γ, or as soon as the variation in the measured pressure drop across the membrane becomes greater than the setpoint, the regulating block C2 ceases to increase the rate of coagulant injection.
The advantage of this solution lies in the membrane fouling being continuously analyzed and the resulting degree of treatment being continuously adapted. Moreover, this regulating mode allows the operation to tend toward or converge on the operating point Γ which is technically optimum (maximum improvement in membrane performance) and economically optimum since a higher dosage than that of the point Γ does not improve the membrane performance (region β) and increases the risk of membrane blockage.
Finally, this control mode makes it possible to be sure that there is no risk of the regulating system diverging, by tending toward the extremes of the X/80-X/30 or, as a variant, the X/60-X/40, operating region.
This control mode makes it possible for the membrane microcoagulation process to be implemented optimally and perfectly safely.
This flowchart starts, at the top of the chart, with a conditional step 17 that corresponds to verifying the quality of the effluent. The question posed in step 17 corresponds to “is the effluent quality insufficient?”. The effluent quality is verified in step 17 according to the abovementioned criteria.
If the answer is “NO”, there is no need for microcoagulation. If the answer is “YES”, it is possible, as illustrated in
If the answer to the question in step 18 is “NO”, that is to say if the permeability is not decreasing, microcoagulation is not triggered. However, if the answer is “YES”, meaning that the membrane permeability is decreasing, the flowchart passes to the next step 19, which determines the coagulant dosage range between X/80 and X/30, X being the dose for making the zeta potential zero.
After step 19, the procedure passes to step 20, which sets the initial value of a factor k applied to X/80 equal to 1 and determines the dosage step N, i.e. the increment in the coagulant dose at each loop.
The next step 21 corresponds to a degree of treatment TT with injection of a coagulant dose kX/80, where k is equal to 1 for the first injection.
The next step 22 verifies whether the membrane permeability increases after the injection carried out at 21. If the answer is “NO”, the factor k is increased by the step N and a dose equal to kX/80 is injected. The increase in the factor k takes place in step 23, and the injection of the increased dose takes place in step 24.
After the injection at step 24, the procedure returns to the question posed in step 22. If the answer to the question at step 22 is “YES”, indicating that the permeability is increasing, at the next step 25 the factor k is increased by the step N and the increased dose kX/80 is injected at step 26.
After the injection at step 26, it is verified in a step 27 whether the membrane permeability is increasing. If the answer is “YES”, the procedure returns to the input to step 25 in order to increase the factor k by a step N so as to rise up the ascending part G of the peak 10 shown in
When the answer to the question at step 27 is “NO”, the procedure passes to step 28, which gives the value k a value equal to the last value of k reduced by N, i.e. (k−N), which determines the optimum dose kX/80 located close to the maximum of curve 10 shown in
Steps 17 and 18 correspond to factors triggering the microcoagulation. Step 19 determines the operating range according to the effluent quality by a parameterization table or by modeling.
The next steps 21 to 28 ensure that the degree of treatment TT is optimized.
At the start of the flowchart, there are three conditional steps, 17a, 18a and 29 occurring in parallel. It is sufficient for the answer to one of these questions to be “YES” in order for the next step 19 to be triggered.
Step 17a poses a question about the effluent quality, namely “is the quality insufficient?”. If the answer is “YES”, step 19 is triggered whereas if the answer is “NO” there is no need to trigger the microcoagulation.
Step 18a corresponds to a question about the variation in permeability. If the membrane permeability is decreasing (answer “YES”), step 19 is triggered.
Finally, step 29 corresponds to an action by the user, the latter being able to trigger the microcoagulation.
Unlike
The output of step 26 is connected to the input of a conditional step 31 that also verifies whether TT is greater than X/30. If the answer is “YES”, the procedure returns to step 19 in order to determine anew the operating range. If the answer at step 31 is “NO”, the procedure passes to step 27 that verifies whether the membrane permeability is increasing. If the answer is “YES”, the procedure returns to step 25 in order to increase the coagulant dose by a step N. If the answer is “NO”, the procedure passes to step 28, which sets the value of k to the last value k reduced by a step N.
This example relates to an experiment carried out on an ultrafiltration membrane module from the French company Aquasource (encased in/out-type, or internal-skin, hollow-fiber membrane), the filtration area of which is 1 m2.
A control unit is fitted, in the feed line:
The unit is fed with Seine river water, the quality of which is well known from experiments. In this context, a parameterization table was stored in the block B1 in order to provide the setpoints for preferential use of a coagulant and the optimum dosage range, i.e. close to the optimum dosage Γ as described in the present invention.
This parameterization table indicates, in this specific case, the choice of a single coagulant (ferric chloride) and the degrees of treatment to be carried out as a function of the TOC content of the effluent:
It should be emphasized that the coagulant dosages provided in this parameterization table are always between X/30 and X/80, where X is the dose of said coagulant that makes the zeta potential zero.
The unit was thus operated over a period of 25 days with a logic for controlling the coagulant injection in a feedback control mode as described in the present invention.
Thus, depending on the feed flow rate, the rate of coagulant injection is slaved to the feed flow rate in order to obtain the coagulant dosage provided in the above table.
The results obtained are illustrated in
Over the course of the trial period, six separate periods (A, B, C, D, E and F) are thus distinguished during which the ferric chloride dosage is adjusted between 0 and 2 mg/l of pure product according to the variation in TOC content of the effluent as per the parameterization table given above.
During period A:
During periods B, C, E, F and G:
During period D, the operating conditions are similar to periods B, C, E, F and G. However, because of the increase in the coagulant dosage above the 1.5 mg/l of pure FeCl3 threshold, the two-phase backwashing frequency is increased, i.e. a backwashing every 45 minutes, and the frequency of acid injection is increased to once every 6 backwashings.
Throughout the trial period, the variation in the treatment operation is automatically controlled without human intervention. This entirely automated control method according to the present invention enables the microcoagulation to be implemented under optimum conditions that are adapted according to the variation in effluent quality.
Thus, throughout the 25-day experiment, the operation of the membrane remained stable (permeability between 185 and 195 l/h·m2·bar@20° C.) illustrating the control in implementing the microcoagulation provided by the advanced control method described by the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0707323 | Oct 2007 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR08/01438 | 10/14/2008 | WO | 00 | 7/2/2010 |
