US-12625063-B2 - Optical concentrate monitoring for membrane scaling mitigation

US12625063B2US 12625063 B2US12625063 B2US 12625063B2US-12625063-B2

Abstract

Methods and systems are described herein for early detection of scaling during processing of liquid solutions. Particularly, the methods and systems described herein provide detection of the onset of scalant crystallization, so that measures can be deployed in a way that avoids significant scaling of membranes or other separating elements.

Inventors

Johan Vanneste
Alexander Schwiebert
John Arthur Bush

Assignees

COLORADO SCHOOL OF MINES

Dates

Publication Date: 20260512
Application Date: 20230307

Claims (15)

1 . A method of detecting scaling during processing of a liquid solution, comprising: providing a separation system comprising: a separation module comprising a separating element that separates one or more solutes from a liquid solution and concentrates the one or more solutes into a concentrate stream; an optical turbidity monitor comprising an optical signal source and at least one optical sensor; supplying a feed stream of the liquid solution to the separation module at a pressure and a flow rate; measuring turbidity of the concentrate stream using the optical turbidity monitor to determine a turbidity value of the concentrate stream; calculating a first derivative of the turbidity value with respect to time to generate a turbidity derivative; determining a setpoint that corresponds to a concentration of a scalant mineral in the feed stream below which scaling of the separating element by the scalant mineral does not occur; comparing the turbidity derivative to the setpoint; and performing a preventative measure to avoid further scaling by the scalant mineral if the turbidity derivative equals or exceeds the setpoint.
2 . The method of claim 1 , further comprising applying signal conditioning to reduce noise in the turbidity value, wherein the signal conditioning comprises filtering using a coherence function between two or more turbidity signals produced by the optical turbidity monitor.
3 . The method of claim 1 , wherein determining the setpoint comprises calculating a signal-to-noise ratio (SNR) of the turbidity derivative.
4 . The method of claim 3 , wherein the setpoint is determined to be a multiple of the SNR, and wherein the multiple is about 3 to about 10.
5 . The method of claim 3 , wherein calculating the SNR comprises: calculating a moving average of the turbidity derivative over a time interval, wherein the time interval is about 10 seconds to about 1000 seconds; calculating a standard deviation of the turbidity derivative over the time interval; and calculating the SNR as: SNR = s - μ σ where s is the turbidity derivative, μ is the moving average of the turbidity derivative, and σ is the standard deviation of the turbidity derivative.
6 . The method of claim 1 , wherein the optical turbidity monitor includes: a first optical sensor positioned at an angle of about 0° relative to the path of light emitted from the optical signal source and configured to produce a transmittance measurement; and a second optical sensor positioned at about 10° to about 90° relative to the path of light emitted from the optical signal source and configured to produce a scattering measurement, wherein the turbidity value is a ratio of the scattering measurement to the transmittance measurement.
7 . The method of claim 1 , wherein the separating element comprises a membrane configured for forward osmosis, reverse osmosis, microfiltration, nanofiltration, ultrafiltration, membrane distillation or electrodialysis.
8 . The method of claim 1 , further comprising: recycling the concentrate stream through the separation module if the turbidity derivative is below the setpoint; and diverting the concentrate stream away from the separation module if the turbidity derivative equals or exceeds the setpoint.
9 . The method of claim 1 , further comprising determining an improved subsequent setpoint based upon iterative results of one or more of: measuring a pressure of the concentrate stream, analyzing the turbidity value of the concentrate stream, and assessing effectiveness of the preventative measure, wherein the preventative measure comprises at least one of: flushing with undersaturated solution, osmotic backflushing, flow reversal, chemical cleaning, adding an antiscalant to the feed stream, and adjusting a pH of the feed stream.
10 . The method of claim 1 , wherein the optical signal source generates light at a wavelength of about 250 nm to about 10000 nm, about 250 nm to about 1400 nm, about 350 nm to about 1000, about 350 nm to about 500 nm, or about 800 nm to about 1000 nm.
11 . A method of detecting scaling during processing of a liquid solution, comprising: providing a separation system comprising: at least one separation module comprising a separating element that separates one or more solutes from a liquid solution and concentrates the one or more solutes into a concentrate stream; an optical turbidity monitor comprising an optical signal source and at least one optical sensor; supplying a feed stream of the liquid solution to the at least one separation module; measuring turbidity of the concentrate stream using the optical turbidity monitor to determine a turbidity value of the concentrate stream; calculating a first derivative of the turbidity value with respect to time to generate a turbidity derivative; determining a setpoint that corresponds to a concentration of a scalant mineral in the feed stream below which scaling of the separating element by the scalant mineral does not occur; and comparing the turbidity derivative to the setpoint.
12 . The method of claim 11 , wherein determining the setpoint comprises calculating a signal-to-noise ratio (SNR) of the turbidity derivative.
13 . The method of claim 12 , wherein the setpoint is determined to be a multiple of the SNR, and wherein the multiple is about 3 to about 10.
14 . The method of claim 12 , wherein calculating the SNR comprises: calculating a moving average of the turbidity derivative over a time interval, wherein the time interval is about 10 seconds to about 1000 seconds; calculating a standard deviation of the turbidity derivative over the time interval; and calculating the SNR as: SNR = s - μ σ where s is the turbidity derivative, μ is the moving average of the turbidity derivative, and σ is the standard deviation of the turbidity, and wherein the scalant mineral is selected from gypsum, calcium carbonate, silica, calcium phosphate, strontium sulfate, barium sulfate, and ammonium nitrate.
15 . The method of claim 11 , further comprising determining an improved subsequent setpoint based upon iterative results of one or more of: measuring a pressure of the concentrate stream, analyzing the turbidity value of the concentrate stream, and assessing effectiveness of the preventative measure, wherein the preventative measure comprises at least one of: flushing with undersaturated solution, osmotic backflushing, flow reversal, chemical cleaning, adding an antiscalant to the feed stream, and adjusting a pH of the feed stream.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63/268,975, entitled “OPTICAL CONCENTRATE MONITORING ALGORITHM FOR MEMBRANE SCALING MITIGATION”, filed on Mar. 7, 2022, the contents of which are hereby incorporated herein in their entirety. GOVERNMENT RIGHTS This invention was made with Government support under Agreement Number R19AC00096 awarded by the United States Bureau of Reclamation. The Government has certain rights in the invention. BACKGROUND Water scarcity is a global problem, with several technologies and approaches being applied to solve it. Desalination has emerged in recent decades as a promising technology to compensate for the freshwater shortage. The first modern thermal desalination processes included multi-stage flash (MSF) and multi-effect distillation (MED). With the subsequent development of the modern reverse osmosis (RO) process, membrane desalination became an economic alternative to thermal desalination. However, scaling is a severe problem for membrane desalination, leading to lower water recovery. Scaling is also a problem in other processes that lead to concentration of scalants. SUMMARY Disclosed herein are methods and systems for mitigating scaling during separation processes through early detection of scaling. In some embodiments, the disclosed methods of detecting scaling can comprise providing a separation system that includes a separation module, where said separation module comprises a separating element that separates one or more solutes from a liquid solution and concentrates the one or more solutes into a concentrate stream; and an optical turbidity monitor having an optical signal source and at least one optical sensor; supplying a feed stream of the liquid solution to the separation module at a pressure and a flow rate; measuring turbidity of the concentrate stream using the optical turbidity monitor to determine a turbidity value of the concentrate stream; calculating a first derivative of the turbidity value with respect to time to generate a turbidity derivative; determining a setpoint that corresponds to a concentration of a scalant mineral in the feed stream below which scaling of the separating element by the scalant mineral does not occur; comparing the turbidity derivative to the setpoint; and performing a preventative measure to avoid further scaling by the scalant mineral if the turbidity derivative equals or exceeds the setpoint. In some embodiments, the method may comprise applying signal conditioning to reduce noise in the turbidity value, and the signal conditioning may comprise applying a low pass frequency filter to the turbidity value or filtering using a coherence function between two or more turbidity signals produced by the optical turbidity monitor, and the determining the setpoint may optionally comprise calculating a signal-to-noise ratio (SNR) of the turbidity derivative and/or the setpoint may be determined to be a multiple of the SNR, and wherein the multiple may be about 3 to about 10, or about 4 to about 6. In some embodiments, the calculating the SNR may comprises: calculating a moving average of the turbidity derivative over a time interval, wherein the time interval may be about 10 seconds to about 1000 seconds; calculating a standard deviation of the turbidity derivative over the time interval; and calculating the SNR uses Equation 1, optionally after a time delay from commencement of the measuring step, wherein the time delay may be about 1 minute to about 10 minutes, or calculating the SNR may be performed after completion of a percentage of liquid recovery, wherein the percentage may be about 5% to about 50%. In many embodiments, the scalant mineral may be selected from carbonates, sulfates, silicates, phosphates and nitrates, for example gypsum, calcium carbonate, silica, calcium phosphate, strontium sulfate, barium sulfate, and ammonium nitrate and/or the optical signal source may generate light at a wavelength of about 250 nm to about 10000 nm, about 250 nm to about 1400 nm, about 350 nm to about 1000, about 350 nm to about 500 nm, or about 800 nm to about 1000 nm, and optionally positioned at an angle of about 0° to about 90° relative to a path of light emitted from the optical signal source, wherein the optical turbidity monitor optionally includes: an optical sensor positioned at an angle of about 0° relative to the path of light emitted from the optical signal source and configured to produce a transmittance measurement; and at least one optical sensor positioned at about 10° to about 90° relative to the path of light emitted from the optical signal source and configured to produce a scattering measurement, wherein the turbidity value may be a ratio of the scattering measurement to the transmittance measurement, and further optionally, the angle of the at least one optical sensor configured to produce the scattering measurement may be about 11° or about 90°. I