Flow control for reverse osmosis filter
The disclosure relates to systems, devices, and methods for flow control in a reverse osmosis filtration system, such as within a medical device. The systems, devices, and methods can respond to changes in permeate flow rate and solute concentration by adjusting feed water and concentrate water rates. Multiple feedback loops adjust parameters to meet water flow rate and purity requirements.
1. A system for water filtration, comprising:
a reverse osmosis filter having a semipermeable membrane;
a feed line, a permeate line, and a concentrate line, each in fluid communication with the filter;
a pump at the feed line pumping feed water into the filter;
a flow sensor configured to monitor a flow rate of permeate water exiting the filter into the permeate line;
a permeate sensor configured to monitor a property of the permeate water;
an adjustable valve configured to regulate a flow rate of concentrate water exiting the filter into the concentrate line; and
a pressure sensor configured to detect a pressure that correlates with permeate water flow; and
at least one controller configured to control:
a first feedback circuit configured to 1) compare the flow rate of the permeate water with a target flow rate of the permeate water and 2) calculate a reference pressure based on a difference between the flow rate of the permeate water and the target flow rate of the permeate water,
wherein the flow rate of the permeate water is based on at least the pressure of the feed line;
a second feedback circuit configured to 1) compare the pressure from the pressure sensor to the reference pressure calculated by the first feedback circuit and 2) regulate a flow rate of the feed water to adjust a pressure of the feed line towards the reference pressure calculated by the first feedback circuit,
wherein the second feedback circuit operates at a higher frequency than at least the first feedback circuit; and
a third feedback circuit configured to regulate the flow rate of the concentrate water exiting the filter into the concentrate line based on the property monitored by the permeate sensor.
2. The system of claim 1 , the permeate sensor is a conductivity sensor measuring the conductivity of the permeate water exiting the filter into the permeate line, the conductivity of the permeate water varying according to an amount of solute present in the permeate water after filtration.
3. The system of claim 1 , further comprising an adjustable valve at the feed line, the second feedback circuit controlling the adjustable valve at the feed line to adjust the flow rate of the feed water.
4. The system of claim 1 , further comprising an electrodeionization filter downstream from the filter.
5. The system of claim 4 , wherein the reference pressure is based on one or more predetermined values for the flow rate of the permeate water, which, in turn, are based on a required water flow rate for the electrodeionization filter.
6. The system of claim 4 , wherein the reference pressure is based on one or more predetermined values for the property of the permeate water, which, in turn, are based on conditions for operation of the electrodeionization filter.
7. The system of claim 1 , the configuration of the first and second feedback circuits interrelated such that the first feedback circuit makes an adjustment based on an adjustment made by the second feedback circuit, and the second feedback circuit makes an adjustment based on the first feedback circuit.
8. The system of claim 1 , wherein the pressure sensor configured to detect a pressure that correlates with permeate water flow is located in the feed line.
9. The system of claim 1 , wherein the pressure sensor configured to detect a pressure that correlates with permeate water flow is located in the concentrate line.
10. The system of claim 1 , wherein the second feedback circuit regulates the flow rate of the feed water to adjust the pressure of the feed line towards the reference pressure calculated by the first feedback circuit by adjusting a speed of the pump.
11. The system of claim 1 , wherein the third feedback circuit regulates the flow rate of the concentrate water exiting the filter into the concentrate line by adjusting the adjustable valve configured to regulate the flow rate of concentrate water exiting the filter into the concentrate line.
12. The system of claim 1 , wherein the second feedback circuit executes multiple times per second.
13. The system of claim 1 , wherein the first feedback circuit executes at a frequency of 0.1 Hz.
14. The system of claim 1 , wherein the at least one controller is at least one proportional-integral-derivative controller.