US20130174913A1

US20130174913A1 - Method and apparatus for controlling total dissolved solids in a liquid circulation system

Info

Publication number: US20130174913A1
Application number: US13/347,093
Authority: US
Inventors: Paul Dinnage
Original assignee: Munters Corp
Current assignee: Munters Corp
Priority date: 2012-01-10
Filing date: 2012-01-10
Publication date: 2013-07-11

Abstract

A method and apparatus for controlling the total dissolved solids in a liquid circulation system having a sump to which liquid is supplied from a liquid source measures the liquid level in the sump, calculates the average evaporation rate of the liquid over time based on that measurement and also calculates the total dissolved solids level in the liquid based on sump volume, the measured liquid level in the sump, the calculated evaporation rate and the total dissolved solids content of the liquid from the liquid source and adds supply liquid to the liquid circulating system when the calculated total dissolved solids content in the liquid in the system attains a predetermined level.

Description

BACKGROUND OF THE INVENTION

The present invention relates to controlling the level of total dissolved solids in liquid circulation systems such as direct forced draft evaporative coolers and closed loop cooling towers or the like.

DESCRIPTION OF THE PRIOR ART

Conventional types of industrial cooling towers include so-called counterflow towers wherein water or other liquid falls or is sprayed downward in the tower counterflow to air moving upwardly in the tower in the opposite direction. Such systems are used for a variety of applications including water air scrubbers, dust collection equipment, air cooling towers, evaporative coolers, fluid coolers or closed loop cooling towers, evaporative condensers or the like. Typically such industrial cooling towers are quite large and permanent.
Some relatively small towers for such purposes have been built which are transportable for various applications such as roof towers. These are disclosed, for example, in U.S. Pat. Nos. 5,227,095; 5,487,531; and 5,545,356. Another improved system is disclosed in PCT/US2010/024929 (Feb. 22, 2010); Publication WO 2010/110980, the disclosure of which is incorporated herein by reference.
Historically, such cooling towers and other devices described above, both opened and closed, have been made of metal components which are prone to corrosion, fouling, and scaling of the heat transfer surfaces as a result of the dissolved solids in the liquid being circulated. Such corrosion, fouling or scaling affects the efficiency and operation of these systems. Many attempts have been made to overcome these problems, but few have been successfully implemented. Such attempts include the use of chemical additives, systems for bleeding and replenishing the liquid used in the circulation system based on measurements of makeup flow, CA ions in the liquid, conductivity of the liquid, and measurement of the ratio of the concentration of chloride ions versus calcium to determine if calcium is plating on or off of the metal surface of the system.
For example, U.S. Patent Publication No. US 2005/0036903 discloses the use of a so-called Peutt Analyzer to sample, periodically or continuously, the presence of calcium ions in the makeup water and the cooling tower water, performing a series of calculations based on that data to establish a measurement of calcium ion behavior in the water and using those calculations to increase or decrease chemical treatment and/or increase or decrease bleed-off rates from the cooling tower. Thus this device appears to be actually measuring the dissolved solids or a scale producing chemical.
U.S. Pat. Nos. 3,754,741; 3,805,880; 4,361,522; 5,213,694; and 6,740,231 each disclose variants on what is referred to as a “feed and bleed system”. Basically, these systems measure the water level in the system and supply makeup water as needed, along with chemical treatment.
U.S. Pat. No. 5,013,488 discloses measuring the density of the water in an evaporative cooling system to selectively discharge suspended solids and replace the discharge water with fresh water containing additives.
U.S. Pat. No. 6,510,368 discloses a process for measuring performance characteristics, including corrosion measurements, in order to control the supply of makeup water and appropriate chemicals.
Japanese Patent Application Publication JP 63243695 uses measurements of tower performance, i.e., water temperature in, water temperature out, and flow rate to calculate an evaporation rate which in turn is used to determine how much water to add and/or bleed. Thus, this system is dependent on simply the proportion of liquid consumed in order to supply replacement liquid.
All of these systems are relatively complex and expensive.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a simple and inexpensive method and apparatus for controlling the total dissolved solids in a liquid circulation system.
Another object of the invention is to control total dissolved solids with a system that enables the performance of diagnostics on system performance.
Another object of the invention is to replace liquid in a liquid circulating system to control dissolved solids based on calculating the dissolved solid contents in the system over time.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a method and apparatus for controlling the total dissolved solids in a liquid circulation system such as open or closed loop cooling towers or the like is disclosed. The invention is not limited to such systems, but is suitable for any type of system in which a liquid is circulated and can contaminate or affect the efficiency of the system as a result of the presence of dissolved solids which can precipitate within the system and/or produce scale. The system is connected to a liquid supply which has a known measured, or estimated, total dissolved contents and which is used to replenish liquid in the system. In operation, the method and apparatus measures the liquid level in a sump of the system, at least periodically over time, and calculates, again at least periodically over time, the average liquid evaporation rate based on the liquid level measurements. This evaporation rate is then used to calculate the total dissolved solids level in the liquid based on the sump volume, the measured or calculated solids level in the sump, the calculated evaporation rate, and the total dissolved solids content of the supply liquid. In response to that calculation, the sump is partially drained and supply liquid is added to the liquid circulation system when the calculated total dissolved solids content attains a predetermined level. Upon the addition of supply liquid, the system recalculates the total dissolved solids content in the liquid recirculating system based on the quantity of supply liquid added. These steps are repeated over time during the operation of the system. The sump is replenished periodically to replace the evaporated water, and the calculated tank total dissolved solids is corrected based on the sump volume, the measured or calculated solids level in the sump, the amount of water added, and the total dissolved solids content of the supply liquid.
The method and apparatus of the present invention is especially designed for use in liquid circulating systems that are formed primarily of polymeric components, although the invention is not limited to the use of such components. In systems having polymeric components, heat exchangers may be composed of small polymeric tube bundles, for example, rather than metallic tubes, finned or unfinned. The advantages of systems of that type is that the polymeric tube bundles have the ability to shed scale build-up based on dissolved solids. Such scale build-up is the leading cause of cooling efficiency deterioration in cooling towers. As a result, in such polymeric tube systems, some scaling can be permitted and therefore the need for precise measurement of dissolved solids or conductivity, as is attempted in the prior art, is not necessary. Applicant has found that computational methods for the determination of total dissolved contents based on sump conditions is useful.
In addition, the system of the present invention allows for the determination of chemical and biological component treatment of the liquid in the system. Thus, the feed rate of such chemical treatment and biological agents can be controlled by the system as well.
With regard to biological growth, it has been found that many of the biocides that are candidates for use in cooling towers or the like using polymeric materials are not compatible with many of the polymers, including nylon. These biocides include bromines, chlorines, and ozone. Accordingly it has been found that the addition of fresh water with batch replenishment, rather than continual replenishment, has the additional advantage of “shocking” the sump with the chlorine residual in municipal supplies and thus contains biological growth.

The above and other objects, features and advantages of this invention will be apparent to those skilled in the art from the following detailed description of illustrative embodiments thereof, when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of an exemplary direct forced draft/fluid cooler for which the method and apparatus of the present invention is adapted;

FIG. 2 is a side elevational view of the system shown in FIG. 1, with the side wall removed;

FIG. 3 is a schematic illustration of the system and apparatus of the invention;

FIG. 4 is a view similar to FIG. 3 of another embodiment thereof; and

FIG. 5 is a view similar to FIG. 3 of yet another embodiment thereof;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings in detail, and initially to FIG. 1, a direct draft fluid cooler 10 is illustrated. The cooler is designed to advantageously use the evaporation of water or other liquids to cool a second liquid in a heat exchanger located within the device. Such systems can be used with water or other suitable liquids and although the illustrative embodiments are described as utilizing water, the invention is not limited to the use of water or to a direct draft fluid cooler liquid circulation system. It is the intent that the invention is applicable to all types of liquid fluid circulation systems which may be subjected to deterioration as a result of total dissolved solids and/or scale.
The fluid cooler 10 includes an exterior housing 12 having a top 14, vertical side walls 15, end walls 17, and a bottom wall 16. As seen in FIG. 2, wherein the side wall 15 has been removed to illustrate the interior of the device, housing 12 also contains a liquid distribution system 20 at its upper end and a heat exchanger 24 which is illustrated in the drawing as a cooling coil type structure. This cooling coil and the other components of the liquid distribution system may be made of polymeric materials such as nylon as described above. The coil is formed of curved piping having an inlet end 26 for supplying a liquid to be cooled to the heat exchanger and an outlet 28 for supplying the cooled liquid (for example glycol) to an outside system, e.g. a refrigeration system.
A water collector 30 is located within the housing 12 beneath the heat exchanger coil 24 for collecting the evaporative cooling water that passes through the spaces between the coil system from the water distribution system 20. One or more fans are provided in the bottom of the housing 12, supported therein in any convenient manner, for drawing air through the bottom opening of the housing and blowing it through the water collector 30 (which has a structure as described in PCT/US2010/024929 (Feb. 22, 2010); Publication WO 2010/110980, the disclosure of which is incorporated herein by reference) and the cooling coil 24 countercurrent to the water distributed from the distribution system 20.
Water distribution system 20 further includes a collection tank or sump 34 mounted outside housing 10 at the approximate level of the fans to receive the water collected by the collection system 30. The collected water is discharged from the tank 34 through a discharge pipe 36 to a pump 38. The pump recirculates the liquid through the distribution pipe 40 to which a plurality of nozzles 42 are connected. These nozzles, which are located within the housing, as seen in FIG. 2, create a downward spray of water above the heat exchange coil 24. These nozzles may be of known construction suitable for use in fluid coolers or evaporative cooling devices.
In the type of system disclosed in FIG. 2, over time, total dissolved solids in the liquid flowing in the liquid distribution or circulation system 20 can form scale, film or other deposits on the piping of the heat exchanger 28 or in the collector 30. Some of this material will flake off of the polymer and ultimately collect in the tank or sump 34.
The system and apparatus for controlling the amount of dissolved solids in the system, in order to minimize scale build-up and to periodically remove precipitated dissolved solids from the sump, is shown in FIG. 3. That illustration depicts the device of FIG. 1 schematically, and the reference numerals therein that are identical to those in FIGS. 1 and 2 represent the same parts.
The control system illustrated in FIG. 3 includes a controller 40, which consists of a microprocessor adapted to receive information from sensors in the system and either alone or by inputting signals to a computer or the like, performs certain calculations used to control fluid flow valves in response to the calculations. More specifically, the system includes liquid supplied to the system through the valve 42 into the sump 34. The liquid is supplied from a known source 44, e.g., the public water supply system, and contains either a known total dissolved solids content (which is publicly available information from the municipality) or a total dissolved solids content which has been determined by prior testing in any conventional manner. The valve 42 is controlled by the controller 40, as described hereinafter, to periodically supply fresh liquid to the sump.
A second valve 46 is connected to the drain line 48 of sump 34. This drain valve is also responsive to the controller 40 based on calculations made in the controller or an associated computer. The structure and control of these valves 42, 46 is well known in the art, and need not be described herein in detail.
The system illustrated in FIG. 3 further includes a means 50 for determining the liquid level in the sump 34. That sump is of known dimensions and volume. These dimensions and volume are input by the operator into the memory of the controller 40, in any conventional manner, to perform the calculations described hereinafter. The sensor means 50 can be a conventional float valve, or a pressure sensor in the bottom of the sump which determines the level of the water in the sump based on the pressure measured at the sump bottom. These sensors provide a signal to controller 40 representative of the liquid level in the sump. This signal can be monitored continuously or at least periodically, over time, to allow the controller to make the required calculations. When the circulating pump is running an additional amount of liquid is contained in the tower or housing 12 as “holdback” volume. This volume is known and can be measured, and when the pumps are running this additional volume is added to the measured sump volume for calculations of total dissolved solids.
In operation, the level of the liquid in the sump 34 is continuously measured by the sensor means 50. The information about the level of the water in the sump is provided to the controller which continuously (or periodically) calculates the average evaporation rate over time and uses that calculation to in turn calculate the dissolved solids level in the liquid in the sump.
The average evaporation rate is a simple mathematical calculation over time. The entire system, when the sump is filled, contains a known volume of liquid and as the liquid evaporates, the level in the sump decreases. With the volume of the sump being known, along with the total volume of the liquid the system can hold, calculation of the evaporation rate is a simple mathematical process. Knowing the rate of evaporation, and the total dissolved solids of the liquid originally supplied to the system, the controller can compute the amount of total dissolved solids in the liquid in the sump over time based on the evaporation rate. That is, the liquid supplied from the line 44 has a known total dissolved solids (tds) content in terms of parts per million by volume. Since the tdss do not evaporate, by determining how much liquid has evaporated over time, it is a simple calculation to determine how many ppms of total dissolved solids remain in the system after it has been operating for a period of time. Thus, for example, if 50% of the liquid in the system evaporates, the originally known tds ppm in the system has doubled after a 50% evaporation rate.
In order to control the amount and rate of build-up of scale in the system, the controller will activate drain valve 46 to drain sump water which has reached the maximum tds allowed. After this partial drain the controller will activate the valve 42 to supply additional liquid to the system as necessary to keep the total dissolved solids content in the liquid below a predetermined level, for example, below 400 ppm. The controller also opens fill valve 42 as needed to replenish evaporated water and maintain the tank level between minimum and maximum levels.
The controller monitors the fill valve to determine how much liquid is added to the system, and uses that information to recalculate the tds in the system, continuously adding liquid to the system as needed. However, as liquid is replenished to the system, the tds will increase in the system over time. When the tds achieve a predetermined level, the system must be purged. Thus, when that predetermined level of tds in the sump is achieved, the controller operates the drain valve 46 to expel liquid from the system. Since, in the preferred embodiment, the materials of which the cooling tower are made include a substantial amount of polymers, scale which flakes off from the polymeric material will collect in the sump, settle to the bottom and be discharged from the system. Upon dumping a predetermined amount of liquid from the sump, the controller closes the drain valve and refills the sump, recalculates the tds in the system based on the amount of liquid discharged from the sump with its tds content, and begins the process over again.
This system, as illustrated in FIG. 3, additionally allows the operator to monitor the efficiency of the operation of the system by calculating the cooling accomplished by the evaporative load 24. This is done by a simple formula in which the calculated evaporation rate is multiplied by the heat of evaporation of the liquid (which is a known factor). When the efficiency decreases below the desired level, the system can be shut down for cleaning
In another embodiment, illustrated in FIG. 4, the controller 40 is used to perform diagnostics on the performance of the system. In this embodiment, a sensor 60, located adjacent the air discharge at the upper end of the housing 12, which measures the leaving air enthalpy (i.e., the enthalpy of the air that leaves the cooling tower or housing 12) and provides a signal representative of the measured leaving air enthalpy to the controller. Another, similar sensor 62 is provided to measure the ambient air enthalpy and provides a signal representative of the measured ambient air temperature to the controller. These signals are used by the controller to determine the air side cooling performance of the system By comparing the air side cooling performance of the tower based on these measurements with the water side cooling performance calculated by the controller, the controller can provide information about how the measured operation compares to predicted performance.
FIG. 5 illustrates another embodiment of the invention wherein the measured feed rate of water by the controller is used to calculate the amount of chemical or biocide treatment which is to be provided by a supply 70 to the sump 34. The controller 40 operates the valve 72 to dispense a predetermined amount of chemical or biocide to the system based on the amount of liquid being replenished in the system in response to the sensor 50 and actuation of fill valve 42. Alternatively, the controller can use the calculated total dissolved solids and the measured feed water to determine the chemical feed rates.
Although the invention has been described herein with reference to the specific embodiments shown in the drawings, it is to be understood that the invention is not limited to such precise embodiments and that various changes and modifications may be effected therein without departing from the scope or spirit of the invention.

Claims

What is claimed is:

1. A method for controlling the total dissolved solids in a liquid circulation system using a liquid supply having a known, measured, or estimated total dissolved solids content and including a sump, said method comprising the steps of;

a) measuring the liquid level in the sump at least periodically over time;

b) calculating at least periodically the average liquid evaporation rate over time based on the liquid level measurements;

c) calculating at least periodically the total dissolved solids level in the liquid based on the sump volume, the measured calculated liquid level in the sump, the evaporation rate and the total dissolved solids content of the supply liquid;

d) draining a portion of the sump volume when the calculated tds reaches a predetermined limit;

e) adding supply liquid to the liquid circulation system to replenish the sump volume and reduce the tds and to maintain the sump level between maximum and minimum levels;

f) recalculating the totals dissolved solids content in the liquid circulatory system after the addition of supply liquid based on the quantity of supply liquid added; and

g) repeating steps a) through e) over time during operation of the system.

2. The method as defined in claim 1 wherein steps a); b) and c) are performed continuously.

3. The method as defined in claim 1 or claim 2 wherein the step of measuring the liquid level is performed using a liquid level sensor.

4. The method as defined in claim 3 wherein said liquid level sensor is a pressure transducer.

5. The method as defined in claim 1 or claim 2 wherein the liquid circulation system is an evaporative cooling system and the method includes the step of calculating the cooling load performance of the evaporative cooling system based on the calculated evaporation rate and the heat of evaporation of the liquid.

6. The method as defined in claim 5 including the step of comparing the calculated cooling load performance with the predicted air side cooling performances of the evaporative cooler based on the values of the enthalpy of the surrounding ambient air and the enthalpy of the air leaving the evaporative cooler.

7. The method as defined in claim 6 including the step of measuring the enthalpy of the ambient air and leaving air.

8. The method as defined in claim 1 or claim 2 including the step of measuring the amount of liquid supplied to the system in step e) and supplying at least one liquid treatment chemical to the liquid circulating system based on that measurement.

9. The method as defined in claim 1 or claim 2 including the step of measuring the amount of liquid supplied to the system in step e) and using that measurement and the content calculated total dissolved solids to supply liquid chemical treatment to the liquid in the system.

10. The method as defined in claim 1 or claim 2 including the step of periodically draining the sump near its bottom to flush precipitated solids there from.

11. A liquid circulation system connected to a source of liquid for circulation therein, in which total dissolved solids in the liquid circulating in the system is controlled, said system comprising:

a) a liquid circulation path in the system including a sump for liquid;

b) means for measuring the liquid level in the sump, at least periodically, while the system is in operation;

c) controller means for calculating, at least periodically the average evaporation rate over time based on the liquid measurements in the sump; and for calculating the total dissolved solids level in the liquid based on the sump volume, the liquid level in the sump, the calculated average evaporation rates and the total dissolved solids content of the supply liquid;

d) means responsive to said controller for draining of portion of the sump volume when the calculated total dissolved solids reaches a predetermined level

e) means responsive to said controller for supplying liquid from said liquid source to the system in order to reduce the level of total dissolved solids and to maintain sump levels between predetermine minimum and maximum levels; and

e) said controller being adapted to recalculate the total dissolved solids content in the liquid circulating in the system after the addition of liquid to the system based on the quantity of liquid added and the total dissolved content calculated before the liquid additive.

12. The system as defined in claim 11 wherein said means for measuring the liquid level in the sump is a liquid level sensor.

13. The system as defined in claim 11 wherein said means for measuring the liquid level in the sump is a pressure transducer.

14. The system as defined in claim 11 wherein said liquid circulation system includes an evaporative cooling section and said controller means is adapted to calculate the cooling load performance of the evaporative cooling section based on the calculated liquid evaporation rate and the heat of evaporation of the liquid.

15. The system as defined in claim 14 wherein said controller means is adapted to compare the calculated cooling load performances of the evaporative cooling section with the predicted air side cooling performance of the evaporative cooler section based on the values of the enthalpy of the surrounding ambient air and the enthalpy of the air leaving the evaporative cooler section.

16. The system as defined in claim 14 including means for measuring the enthalpy of the ambient air and for measuring the enthalpy of the air leaving the evaporative cooler.

17. The system as defined in claim 11 including means for measuring the amount of liquid supplied to the system in response to the calculated total dissolved solids content of the liquid and supplying at least one liquid treatment chemical to the liquid circulating system based on that measurement.

18. The system as defined in claim 11 including means for measuring the amount of liquid supplied to the system in response to the calculated total dissolved solids content and for using that measurement and the calculated total dissolved solids content to supply liquid chemical treatment to the liquid in the system.

19. The system as defined in claim 11 including means responsive to said controller for periodically draining the sump near its bottom to flush precipitated solids therefrom.

20. The system as defined in claim 13 wherein said means for draining the sump is responsive to the controller means calculation of a total dissolved solids content in the liquid that is higher than the total dissolved solids content at which liquid is added to the system.

21. The system as defined in claim 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 wherein said means for measuring the liquid level in the sump operates continuously and said controller continuously calculates the average evaporation rate and total dissolved solids level of the liquid.

22. A method for controlling the total dissolved solids in a liquid circulation system using a liquid supply having a known measured or estimated total dissolved solids content and including a sump, said method comprising the steps of;

a) measuring the liquid level in the sump at least periodically over time;

d) draining a portion of the sump periodically when the calculated tds reaches a predetermined limit; and

e) adding supply liquid to the liquid circulation system to maintain a predetermined liquid level in the sump and reduce sump tds.

23. A liquid circulation system connected to a source of liquid for circulation therein, in which total dissolved solids in the liquid circulating in the system is controlled, said system comprising:

a) a liquid circulation path in the system including a sump for liquid;

c) controller means for calculating, at least periodically the average evaporation rate over time based on the liquid measurements in the sump; and for calculating the total dissolved solids level in the liquid based on the sump volume, the liquid level in the sump, the calculated average evaporation rates and the total dissolved solids content of the supply liquid; and

d) means responsive to controller to partially drain sump when the calculated tds reaches a predetermined level; and

e) means responsive to said controller for supplying liquid from said liquid source to the system when the calculated total dissolved solids content attains a predetermined level.