Patent Application
20130174913
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.
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.
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.
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:
Referring now to the drawings in detail, and initially to
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
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
In the type of system disclosed in
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
The control system illustrated in
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
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
In another embodiment, illustrated in
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.
