Field of the invention

The subject of the invention is a system and method for measuring the properties of humid air in cooling towers from above the drift eliminators across the plan area of the cooling towers. The technical problem, solved by the invention, is an improved method of measuring and an improved precision of measuring the properties of the humid air in the cooling tower with enhanced security of such measurements.

Cooling towers are used in industrial and energy systems for the cooling of water, mostly in the electrical generation industry and also in other industries for production of cement, iron, the chemical industry and the oil industry. In the electrical generation industry, they are present in practically all kinds of electro plants utilizing fossil fuels, this is coal, natural gas, oil and nuclear energy, as well as with renewable sources like biomass, and waste material.

The cooling of water with cooling towers can be used in industrial processes directly or indirectly. With direct usage it is the same water that is used in the process as is cooled in the cooling tower, for example, in the steel industry for the cooling of a hot body where it is in direct contact with the material and is thus a so-called open-circuit. With an indirect operation the cooling water cools another liquid via a heat-exchange within the process and as part of a closed circuit and thus does not mix. An example of indirect usage of cooling water from a cooling tower are power plants, where the cooling water cools a condenser in separated cooling pipes and thus does not mix with the expanding steam from the turbine.

There are many classifications of cooling towers. These are often divided depending on the method of drawing the cooling medium through the tower, thus are either of forced or natural draft. Towers of the forced draft type are also named mechanical cooling towers, because ventilator(s) are used to enable the draft of the air. With natural-draft cooling towers, the draft occurs naturally as a result of the difference in the density of the warm air in the tower and cool air in its surroundings.

The second common classification of towers relates to the contact between the water and the air. Those in which the water and air are in the direct contact, are described as wet cooling towers, other towers are named dry cooling towers. Depending on the air-flow or the cooling medium, cooling towers are divided into counter-flow, cross- flow and through-flow. In counter-flow cooling towers the water and air are flowing in opposition to each other, in this case the water falls vertically downwards and the air flows vertically upwards, for example through a system of fills and falling water droplets. With through-flow cooling towers the water and air flow in the same direction. With cross-flow cooling towers, the water flows vertically down whilst the cooling air flows transversely or horizontally with respect to the falling water droplets.

There are many other categories of cooling towers, for example air flow-characterised cooling towers, shape-characterised cooling towers, hybrid cooling towers, divided with regard to the mode of heat and mass transfer, etc. The invention described in this paper can be used in all types of industrial cooling towers.

The technical problem

The conventional cooling tower, shown in figure 1, includes the following key components:

- Drift eliminators 1 or separators of water droplets, which limit the quantity of water leaving the tower carried by the air flow,

- Spray nozzles 2 or water sprayers, which disperse the water in small droplets,

- Fills 3 which increase the contact area and the time between the falling water droplets and the air that flows through the cooling tower,

- Rain zone 4,

- Cold water basin 5 where the water is collected,

- At least one water pump 6,

- Valve 7 for controlling the make-up water,

- Entry inlet 8 to allow the surrounding air to enter the base of the tower,

- Tower exit 9 to allow the humid air flow from the tower,

- Shell of the tower 10 allowing the flow of surrounding air to pass through the cooling tower,

Precast concrete structure or iron construction 11 to support the elements described above. From the above described elements, the following is crucial for the heat (and mass) transfer: drift eliminators 1, spray nozzles 2, fills 3 and rain zone 4. Figure 1 illustrates a schematic presentation of an example of a cooling tower and its cross-section. The cooling tower illustrated is a hyperbolic counter-flow wet cooling tower with natural draft. The water that flows in the distribution water system to the nozzles 2 disperses on them and drops vertically down. Due to the natural draft of air, buoyancy is present that causes air flow vertically u pward. This air flows over all the elements of the tower: the rain zone 4, fills 3, spray nozzles 2, drift eliminators 1, etc., and thus carries all the information of the condition and performance of the tower components. A similar case is valid for a mechanical cooling towers, where a forced draft of air is created with one or more fan ventilators.

The thermal efficiency of a cooling tower is measured by standardised performance or guarantee tests. Such tests involve a procedure showing whether or not the technological demands on the tower are met or they show the level of degradation of an operating tower in comparison with its originally planned designed conditions. Performance tests are therefore limited to precisely defined thermal demands and ambient parameters that reflect the average values of weather at a specific location or region over a long period of time. Flowever, there are drawbacks of the performance tests in that they measure only the integral or general parameters of the cooling towers and do not provide information on the condition of their individual components.

The functioning of the components of a cooling tower is determined on the basis of measurements within the tower, where the properties of the humid air are measured above the drift eliminators 1 across the whole plan area of the tower, as shown in the velocity profile 18, as an example of the result of the measurements. According to current research, the local efficiency and diagnostics of a cooling tower's components can be determined based on measurements of the temperature and velocity of the h umid air [1] - [3] to define the efficiency of the tower on a local level and to diagnose the state of the components of the tower. This is possible because the air and water that flow into the tower flow over all the key components of the tower. Thus, the air bears information on the performance of its components, also referring to the water, for instance the spray nozzles 2. For example, if a nozzle 2 is blocked, it means that the flow of warm water will be significantly decreased and consequently the temperature of the air, that flows through the area above the drift eliminators 1 where measurements of the humid air take place, will be significantly lower. Similarly, if the fills 3 over which water and air flow, are blocked, it means that due to the obstruction, a greater pressure loss will be present resulting in a decreased velocity of humid air measured above the drift eliminators 1. This is valid for all types of cooling towers. To plan upgrades of cooling towers that fulfil the defined thermal loads, the designer must have a vast database on the thermal performances, pressure drops and other characteristics of the components. These data can be acquired only by measurements inside an operating cooling tower or a test cooling tower. Such measurements are then used for identification and diagnostics of problems in cooling towers and in mathematical calcu lations considering the cooling towers' repair, refurbishments or upgrades. Particularly in wet cooling towers, where heat and mass transfer take place due to evaporation, the mathematical models are especially complex (two-phase flow) as opposed to dry cooling towers, where there is no direct contact between water and air. Namely, the calcu lation of wet cooling towers involves simultaneous heat and mass transfer (sensible and latent heat transfer), where these two processes cannot be quantified independently. In simple terms, energy transfer includes simultaneous heat transfers due to the temperature difference between air and water and mass transfer due to the evaporation of some of the water flow that is dragged through the tower. Hence, for a designer of a cooling tower, it is often hard to predict and guarantee the effectiveness of cooling at specific thermal loads of the tower. Because of this, accurate measurements of the properties of humid air that are ensured by the invention are of extraordinary importance for diagnostics and calculations of cooling towers based on which repairs, refurbishments, upgrades are to be performed, as well as designing new cooling towers.

Changes in the weather conditions throughout the seasons, daily and even hourly changes, or when the temperature of the surroundings changes from day to night or from cloudy into sunny weather (and vice-versa), strongly influence the functioning of a cooling tower. Because cold air is denser than warm air, the potential for draft and flow of air is increased at night. For the same reason the potential of the air is significantly increased in cold winter days than in hot summer days. This is especially valid for natural-draft cooling towers, which are, because of these effects, quite unpredictable devices, as their thermal performance is completely dependent on micro-meteorological conditions. Due to the extreme variability of the thermal performances of natural-draft cooling towers, it is very difficult to achieve repeatability of results of their thermal tests. In the case of mechanical cooling towers, the influence of the environment is also important, but slightly smaller, because it is possible to control or to compensate for the influence of the surrounding air via the use of the ventilators. In both, the time to perform the measurements is crucial for reducing their uncertainty with regard to the measured properties of humid air. The described invention resolves this with the simultaneous use of several mobile devices and many measuring units. As mentioned, the functioning of cooling towers is highly dependent on weather conditions, to be more specific, on temperature, precipitation, relative h umidity, wind speed, wind direction and the pressure of the surrounding air. Each of these variables influence the functioning of a cooling tower. In the case of long and possibly interrupted measurements of the humid air in the cooling tower, the conditions of the surrounding air can significantly change which increases the uncertainty of measurements. For example, currently it is common that measurements take two or more days, especially in wet natural-draft cooling towers, due to the complexity and extensiveness of the measurements. During this time the circumstances of the surrounding air will certainly have changed from that of the first day, the start of performing measurements of the humid air in the tower. J ust like the surrounding conditions, the system with cooling tower can also change significantly; for example, the quality of coal in power plants can significantly change during a day. Fast and efficient measurements, that this invention enables, essentially reduces measurement uncertainty providing more valuable results for humid air measurements in cooling towers.

In wet cooling towers, where there is direct contact between the water and air or between the cooled and cooling mediums, there is also present a transfer of mass or latent heat. This is characterised in that approximately 80 % of the transfer of heat energy in wet cooling towers occurs through the process of evaporation, this is a process of the transfer of mass. It is important in such cases, that the air above the drift eliminators 1 is saturated, as this means that the potential of the cooling air was used most efficiently. Therefore, it is important that in wet cooling towers the humidity of the air is measured above the drift eliminators 1. With this information the precision of diagnostics and resultant calculations of cooling towers operation is increased. Unsaturated air usually occurs at the inlet, at the mouth of the cooling tower where air resistance is lowest. Because the whole circumference of the cooling tower represents a vast surface, an ability to make accurate measurements of the humid air is exceptionally important. This invention also enables measurement of the h umid air at the circumference and across the whole plan area of wet cooling towers.

Industrial cooling towers are devices with high temperatures that can reach up to about 70°C (dry cooling towers). In wet cooling towers the temperature may reach up to about 45°C, but as well as the high temperatures there is always present one hundred or greater percentage humidity, because small water droplets are carried out of the tower due to the strong updraft. H igh levels of droplets in the air represent thick fog and, in many cases, practically zero visibility. High humidity and a warm environment will inevitably contribute to the development of bacteria, which in spite of strict preventative measures, is impossible to avoid one hundred percent. Cooling towers, particularly hyperbolic ones, are very big devices; the diameter at the base can reach 120 m, which represents a huge surface for heat and mass transfer. Taking measurements in cooling towers thus represents quite high levels of danger, where there are not only high temperatures, high humidity, poor visibility, possibility of bacterial infection but also working at height. This invention with its automated procedures and mobile devices further solves the problem of safety, as human presence at the time of measurements in an operating cooling tower is not necessary or is reduced to a minimum level.

As cooling towers can be large devices, as their performance depends on the weather conditions and as safety in operating cooling towers may be reduced, it is very important that the measurements within the cooling towers are performed in an automated way without or with minimum human intervention, continuously, in the shortest possible time with all required measuring sensors, all of which is solved by this invention.

Technical overview in the area of the invention

There are few advanced solutions for measuring the properties of humid air in cooling towers. Basically, the measurements are manual or with one device. This represents a problem of measurement accuracy with a limited number of sensors and also the problem of safety at work. One known solution is [1] where the measuring in the cooling tower is done manually, where one or two people measu re the temperature and velocity of humid air above the drift eliminators 1, and where the humidity of the air is not measured. In the case of hyperbolic natural-draft cooling towers, such measurements happen with interruptions over two or more days. The measurement is dangerous as a human is continuously present in the operating tower, which increases the possibility of bacterial infection. The further danger of falling from a height, that is present for such measurements, means that in certain cooling towers and states such a practice is forbidden.

The second known solution is [2] where one device with a set of sensors is used; that is one temperature sensor and one sensor for measuring the velocity of the humid air. This one device method does not measure the humidity of the air, further it does not enable simultaneous measurement of properties of the air at many points and in several areas of the cooling tower; it is manually guided within the cooling tower; it has an outdated wire positioning system for determining the location of the device within the tower and in hyperbolic natural-draft towers it does not continuously perform the measurements within eight hou rs. The third solution, which addresses the problem of measuring the properties of humid air is patent SI21817A. This solution measures temperatures in cooling towers following a thermo-visual method. The downside of this method is that it measures the temperature of the drift eliminators as it cannot directly measure the temperature of the humid air in the cooling tower, which burdens the method with significant measurement uncertainty. Measurement uncertainty is also increased with an optic system as it measures the temperature of the drift eliminators at an angle. Further this method does not measure the velocity and humidity of the air in the cooling tower.

The fourth known solution, that is in general use, is the so-called net measurement. This measurement is also predominantly performed manually, rather than automated, with a limited number of sensors and without the measurement of air humidity. It utilises a net system of points that include sensors that are connected in a truss. The measurement is performed in a limited, small area of the cooling tower. When the measurement is completed in one area of the tower, the system is manually moved to the next point and the procedure is repeated. The measurements can be smoothly implemented only near walkways 17, they are usually not implemented within the tower because the drift eliminators 1 could be damaged. In this case the method would also be very dangerous. The requirement for human presence at the time of measurement also increases the possibility of bacterial infection.

Disadvantages of existing methods:

- inability of simultaneous measurements of the properties of humid air at many points and areas within the cooling tower at the same time across the whole plan area of the tower,

- measurement of the properties of humid air is not performed with high resolution across the whole plan area of the tower,

- measurements of the properties of humid air are non-automated and require significant time with the necessity for human intervention,

- low accuracy of the positioning system, that determines the locations of the measurements within the cooling tower,

- location of measurements is not determined by advanced wireless methods,

- measurement across the whole plan area of the cooling tower has high measurement uncertainty, - measurements of the properties of humid air demand the presence of staff within the tower at the time of the measurements,

- low safety of existing methods of measurements in cooling towers,

- mathematical calculations of cooling towers and systems to which cooling towers belong using existing methods of measuring the properties of humid air, result in high calculation u ncertainty and

- in the case of hyperbolic cooling towers, measurements of the properties of humid air are performed intermittently over two or more days.

Description of the invention

According to the invention, the technical problem is solved by a system that includes at least one mobile assembly or a mobile unit and a method for measuring the properties of humid air in cooling towers. The system of the invention preferentially includes, many (two or more) mobile assemblies, from which every assembly includes at least one measuring unit with sensors for measuring the temperature, velocity and humidity of the air. Mobile assemblies simultaneously measure at several locations and areas within the cooling tower and use advanced wireless technology for the determination of position and navigation. Measurements are conducted independently, where each of the assemblies, travels on a pre-determined path with the assistance of an innovative positioning and navigation system. In this innovation the method does not require human presence in the cooling tower at the time of measurements and the measurements of the properties of the humid air are performed, in the case of hyperbolic cooling towers, without interruption within an eight-hour period, representing a significant increase in safety during the time of taking measurements in an operating cooling tower and enabling improved measurement certainty with high resolution.

The invention is described further below and is presented with an implementing example and in the figures that illustrate: figure 1 shows a schematic presentation of a cooling tower with key components and included mobile assembly

figure 2 shows a schematic presentation of a cooling tower at cross section A-A, above the drift eliminators 1 with mobile assemblies 12 and results of measurements with mobile assemblies, which in this case represents the velocity field 18 of the h umid air above the drift eliminators 1.

figure 3 shows a mobile assembly 12 with components figure 4 shows the elements of the drive mechanism of the mobile assembly

figure 5 shows a measuring unit.

The measuring system and method of the invention enable safe, without, or with minimum human assistance, uninterrupted, automated, over a short time interval, with high definition, operating simultaneously at several points and areas and over the whole plan area of the cooling tower, performance of measurements of humid air above the drift eliminators. The invention thus ensures a significantly improved precision of measurements of the humid air and with that an evaluation of the operation of the cooling tower as well as increasing the safety of performing measurements in a cooling tower. In wet cooling towers the accuracy of the measurements of the properties of humid air is further improved by the adapted sensors added in this invention for measurements of the humidity of air across the whole plan area of a cooling tower, which up to now has not been performed.

The system for measuring the properties of humid air in cooling towers defined by the invention includes:

- at least three positioning reference points 14 located on the walkways 17 of the surface of the drift eliminators 1 within the cooling tower;

- at least one mobile assembly 12 that includes a driving mechanism 40, positioning - navigation unit 23, communication unit 24 with a local processing unit with memory 24a, at least one measuring unit 13 and a unit for sampling of measurements;

- a programme module for positioning, navigation and controlling of the mobile assemblies 12;

- a programme module for executing, converting, recording and transmitting of measurements and

- an external computer 50. wherein the programme module, for positioning, navigating and controlling of the mobile assemblies 12 is executed on the external computer 50 and on the local processing unit with memory 24a, and is configured for controlling of the drive mechanism 40 of each mobile assembly 12, and which, depending on the current location of the mobile assembly 12 and each pre-determined reference measuring location, controls the driving mechanism 40 for each single mobile assembly 12; wherein the programme module for executing, converting, recording and transmitting of measurements is executed on the external computer 50 and on the local processing unit with memory 24a and is configured for performing of measurements with the measuring units 13, depending on the location and on pre-determined sequences of measurements, including the acq uisition of the measured results from the measuring units 13, processing of the results, recording and transmitting of the results together with each location to the external computer 50.

The term »location« relates to the coordinates of the mobile assembly 12 in the horizontal plane of the coordinate system and the direction of mobile assembly 12 in the horizontal plane, this is in the plane of the surface of the drift eliminators 1 or in the plane of fills 3 of the cooling tower.

The positioning-navigation unit 23 includes a local module 23a that, on the base of wireless triangulation with reference positioning points 14, determines the exact coordinates of the mobile assembly 12, and a magnetic compass, that determines the direction of the mobile assembly 12 in the horizontal plane. In one of the implementing examples a wireless triangulation is performed through reference points 14 and a local module 23a through measurements of the power of an RSSI signal. Preferentially a magnetic compass is included in a nine-degree-of-freedom inertial sensor. Optionally the positioning - navigation unit 23 also includes other motion sensors from the nine- degree-of-freedom inertial sensor, like gyroscope, accelerometer; wherein the nine-degree-of- freedom inertial sensor enables the determination of the orientation of the mobile assembly 12 on X, Y and Z axis, the angular velocity of the mobile assembly 12 around the axis and the acceleration of the mobile assembly 12 around mentioned axis.

Optionally the system includes at least one external stationary measuring unit 16 with an external communication unit for measuring the properties of the air surrounding the cooling tower and the transmission of this information to the external computer 50. The external stationary measuring unit 16 could be a weather station, that is in the vicinity of the associated installation.

Optionally the system includes at least one reference stationary measuring unit 15 for measuring the properties of humid air and water in the cooling tower, where each stationary measuring unit 15 at least includes sensors for measuring temperature, velocity and humidity of air above the drift eliminators 1. Optionally each stationary measuring unit 15 can also include sensors for measuring the temperature of water and air above the fills 3 or under the spray nozzles 2 and sensors for measuring the temperature of both water and air below the fills 3.

The mobile assembly 12, capable of performing measurements according to the methods of measuring, is part of the invention. The mobile assembly 12 is formed as a hollow chassis. A measuring unit 13 is installed on an arm 22 fixed to the chassis of the mobile assembly 12. The preferential implementation is a telescopic arm 22 on which a measuring unit 13 is fixed. The hollow chassis of the mobile assembly 12 enables the flow of air through the mobile assembly 12. The hollow chassis of the mobile assembly 12 thus ensures a minimum influence on the flow and temperature of flowing humid air in the surroundings of the mobile assembly 12 and thus improves the accuracy of measuring the properties of humid air in the surroundings of the mobile assembly 12. The telescopic measuring arms 22, that carry the measuring units 13, also make a significant contribution to increased accuracy, ensuring that the measuring units 13 are clear of the ground plan or footprint of the mobile assembly 12 which is moving over the surface of the drift eliminators 1. Besides temperature and humidity, the measuring unit 13 measures the vertical component of the velocity of the humid air without disturbing this flow. In this way every one of the measuring units 13, that are fixed to each single mobile assembly 12, enable accurate measuring of the properties of the humid air.

The drive mechanism 40 of the mobile assembly 12 comprises two caterpillar tracks 19, with associated elements for operating the caterpillar tracks 19, a power supply 20 and a drive unit 21. Every mobile assembly 12 moves on the surface of the drift eliminators 1 within the cooling tower by means of the drive unit 21, which is preferentially operated by an electric motor. The electric motor 21, via reduction propulsion gears 25 and rear cylinder 26, drives caterpillar tracks 19 with a large rotational torque. The power supply 20, which provides the energy for the movement of the mobile assembly 12 and for operating the positioning-navigation unit 23 and communication unit 24, is provided by a lithium or other similarly capable battery that is installed in each mobile assembly 12. A single charging cycle of the battery 20 is sufficient for a whole day operation. The mobile assembly 12 is manufactured in such way that it is extraordinarily light in proportion to its size and rigidity. As a result of this it is possible to drive it via the electric motors 21, using only a small amount of electric energy for movement. This additionally enables the measurements on a single segment of the cooling tower to be performed without the need to change or recharge the batteries 20 during the complete execution of measurements and without losing time. Therefore, it is possible to carry out the measurements of the whole cooling tower continuously and within a short time interval. With these, amongst other capabilities, the invention reduces the influence of weather and other inherent influences of a system with a cooling tower and improves the accuracy of measurements of the humid air. The mobile assembly 12 has sprung adjustable caterpillar tracks 19 with supporting wheels 28 and adjustable elements 31 for adjusting the forces of the springs. The advantage of an adjustable suspension is that it enables an adaptation of the caterpillar tracks 19 to the surface of all types of drift eliminators 1. Supporting wheels 28 support the caterpillar tracks 19 in such way that ensures good tension of the caterpillar tracks 19 and good grip of the caterpillar tracks 19 on the area of the drift eliminators 1. The supporting wheels 28 are placed on swinging arms 27 that are tensioned by springs 29. As a result, slippage of the caterpillar tracks 19 does not occur and the mobile assembly 12 can travel on the surface of the drift eliminators 1 in any desired direction. The transverse profiles 33 used on the caterpillar tracks 19 are designed in the shape of a trapezium. These transverse profiles 33 enable turning of the mobile assembly 12 and at the same time ensuring good traction in the required direction of motion. In this way, for measuring, it is possible to select the optimal path in each segment of the cooling tower, which enables the performance of measurements in the shortest possible time. Thus, a precise measurement of the properties of humid air is ensured, which significantly improves the accuracy of diagnostic and mathematical calculations of cooling towers and consequently the energy systems with the cooling towers.

The mobile assembly 12 is, with all the instruments for operating and measuring the properties of humid air, lighter than 20 kg. With the use of wide caterpillar tracks 19 the loading on the drift eliminators 1 is further reduced, so practically damage to the surface cannot occu r; this is an advantage of the invention over manual measurements conducted by a person. The mobile assembly 12 with its hollow chassis does not influence the properties of air flow around the mobile assembly 12. Currents of humid air can flow unobstructed as they pass around and through the mobile assembly 12 and further does not affect the measurements of the properties of the humid air that are being recorded via the sensors on the measuring unit 13. In this way precise measurements of the properties of the humid air are ensured with low measurement uncertainty.

Every mobile assembly 12 is preferentially equipped with several measuring units 13 at several locations at once. All the existing methods are based on measuring with each sensor individually, which prevents measuring in the desired short period of time, something that is crucial for efficient performance of measurements with low measurement uncertainty. According to this invention the simultaneous operation of several mobile assemblies 12 is planned, these together will enable quick and efficient methods of measuring the properties of humid air in a cooling tower. Significantly shorter measurement times can be enabled with a larger number of measuring units 13 placed on each mobile assembly 12 where the measuring units 13 are fitted on telescopic arms 22. In the example of figure 2 five mobile assemblies 12 are shown, each moving in a cooling tower on the drift eliminators 1, where every mobile assembly 12 has four telescopic arms 22 fitted with measuring units 13; the number of mobile units 12 and measuring units 13, is not limited. In the example in figure 3, a mobile assembly 12 with four telescopic arms 22 is shown, here each of the arms 22 has a measuring unit 13 fitted; the number of telescopic measu ring arms 22 and measuring units 13 is not limited. Every measuring unit 13 can measure several variables or properties of humid air, with which the operation of the cooling tower can be evaluated; for example, temperature, velocity and relative humidity of the humid air. For this purpose, the measuring unit 13 consists of a housing 34, where the sensor for temperature 38, sensor for measuring the velocity of air flow 39, and a sensor for measu ring relative humidity 37, have all been fitted. A preferential version is shown in figure 5, where the velocity of air flow is measured by the sensor that measures the frequency of blade rotation of the vane anemometer 35, this frame 36 is fixed to the housing 34 of the measuring unit 13. Telescopic measuring arms 22 enable the measurements of humid air in the cooling tower with variable resolution of measurements. Thus, it is possible, as defined by this invention, to measure properties of the humid air across the whole plan area of the cooling tower to a resolution of two meters or less.

The measuring units 13 fitted on the mobile assemblies 12 enable continuous measurement of the properties of the humid air. The measurements of the properties of the humid air are performed across the whole plan area of the drift eliminators l. The measurements are executed with measuring units 13 that enable simultaneous measurements of all three quoted parameters of the humid air. Preferentially the measuring units 13 are made with a 3D printer or other production method, that enables an optimal aerodynamic design of the measuring unit 13 regarding the conditions in cooling towers so that their presence does not disturb the air flow. In this way precise measurements of the properties of the humid air are ensured with low measurement uncertainty. Measurements are performed across the whole horizontal or plan area of the cooling tower, where the process of energy transfer or cooling of water takes place. Measurements are possible on all, especially non-walking surfaces of the cooling tower, this includes on the d rift eliminators 1 and also on the surface of the fills 3 of the cooling tower. Due to the possibility of utilising telescopic arms 22 measurements can take place at a height of up to 3 m above the surface of the drift eliminators 1. The unit for sampling the data of measurements from all the sensors on all of the measuring units 13 provides simultaneous and regular communication either to the external computer 50 over the communication unit 24, or to the local processing unit with memory 24a. When the measurements are communicated to the local processing unit with memory 24a the local processing unit with memory 24a digitizes and stores the data whilst simultaneously and regularly communicating the measurements to the external computer 50 over the communication unit 24. Preferentially the external computer 50 is a process computer that is located outside the cooling tower.

Measurement of humidity is not limited to relative humidity lower than 100%, because with the use of sensors for measuring relative humidity in the special conditions of a cooling tower, it is possible to measure moisture content over 100% where droplets have occurred. This is performed with a sensor, that with heating reduces the relative humidity within it so absolute humidity is preserved. With the heating of a chosen control volume of humid air, the quantity of steam within it does not change and absolute humidity remains the same. Heating is performed for a specific temperature difference. Due to the increased temperature this control volume is capable of absorbing more water as its relative humidity reduces. As a result of this it is possible to measure relative humidity up to and over 100% humidity. Measurement certainty is thus significantly improved compared to established measurement methods currently employed in cooling towers.

The reference positioning points 14, located on the walkways 17 of the drift eliminators 1 within the cooling tower and the positioning- navigation unit 23 located on the mobile assembly 12, always ensure the precise positioning of every mobile assembly 12 and its navigation to the pre-defined reference measuring locations. For every mobile assembly 12 the operator pre-determines the coordinates of reference measuring locations to which each single mobile assembly 12 will travel and this data is inserted into the external computer 50 prior to the commencement of performing the measurements. This data from the external computer 50 is communicated to the communication u nit 24 of each mobile assembly 12 and on the basis of this data, controls its positioning via the positioning-navigation unit 23 and according to the data, drives the mobile assembly 12 on its pre determined reference measuring locations.

For determining the precise position of the mobile assemblies 12 triangulation, or other similar method is used, enabling precise positioning in buildings up to a distance of 150 m, the method enables a determination of the location of mobile assemblies 12 to within ± 30 cm. Precise positioning of the mobile assemblies 12 and with them, the measuring units 13 to less than ± 30 cm is necessary due to various obstacles and structures, like for example, barriers, railings, supporting elements, chimney, delivery tubes, sprayers, etc., that are more than 30 cm in size.

The coordinate system, based on which the coordinates of the reference measuring locations and each location of the mobile assemblies 12 and the border of the relevant area, are determined prior to measurements with regard to the technical documentation of the tower. The center point (0, 0) used for the precise determination of positioning is preferably the middle of the tower, other locations might also be used if there are different obstacles or structures in the middle of the tower.

All currently known methods of positioning in a cooling tower are based on wire methods. Amongst them were methods with taut wires or measurement via a track gauge of the distance. However existing methods do not enable quick and precise determination of the location of the mobile assembly 12 and so, by this method, it is not possible to perform measurements in the required short time interval, which is crucial for a precise performance of the measurements, and which is crucial to reduce measurement uncertainty due to the influence of weather and the influence of changes of the system's characteristics.

Communication between the external computer 50, reference positioning points 14, positioning - navigation units 23, and the communication unit 24, is performed employing a wireless method, for example over a Wi-Fi connection. This wireless method takes place automatically using a high frequency of sampling of signals and continuously sending the information of each position to the external computer 50 outside the cooling tower. This invention uses wireless, light and transportable measuring systems for the determination of distance according to the triangulation method which enables wireless positioning of an unlimited number of mobile assemblies 12.

The position of the measuring units 13 is then determined on the basis of the location of the mobile assembly 12 and geometry of the mobile assembly 12 within the space, as the geometry of the mobile assembly 12 includes the distance of each single measuring unit 13 from the positioning - navigation unit 23 on the mobile assembly 12.

In one possible case continuous recording of the data of the location of each single mobile assembly 12 within the tower and the wireless transfer of data from the tower to the external computer 50 is performed for every mobile assembly 12 and measuring unit 13. Among the currently used methods not a single one enables the measuring of the positions of several mobile assemblies 12 and simultaneous recording using wireless transfer of data of the position of mobile assemblies 12 to an external computer 50. Further, with current existing tech nology it is not possible to simultaneously and automatedly send all data regarding the position of mobile assemblies 12 to the external computer.

The invention enables simple installation of the reference positioning points 14. The positioning elements or positioning points of current measuring systems for the positioning of mobile units are large and clumsy. Consequently, simple installation, moving and calibrating of position sensors is not possible. Methods with track metering are time consuming. In this way it is not possible to conduct these measurements in the required short time interval, something that is essential for continuous and precise execution of measurements. As defined by this invention, a possible installation of the reference positioning points 14 is on the railings of the pathways 17, which is undemanding from a time point of view.

In a cooling tower, according to the currently known methods, only a single mobile assembly 12 is used, which was connected to a single position sensor. For the purpose of accurate measurement, it was not possible nor practical to add reference positioning points 14 and mobile assemblies 12 with positioning - navigation units 23 that would increase the accuracy of measurements. As defined by the invention, it is possible to add mobile assemblies 12 with positioning - navigation units 23 and reference positioning points 14 in any desired number. With this ability simultaneous, continuous and quick measurements in a foreseeably short time interval can be achieved, something that is crucial for the precise execution of measurements across the plan area of the tower. In the case of hyperbolic natural-draft cooling towers, regardless of their size, a time for measurements shorter than eight hours can be assured. In the case of forced-draft cooling towers, this can be achieved within two hours.

In a cooling tower, droplets occur. Droplets in the current of the humid air do not affect the measurement uncertainty of the positioning. As defined by the invention specifications the wireless positioning system is designed in such way that it works within a frequency range such that the presence of droplets in the air will not interfere with the wireless signal. In this way it is able to measure position with a measurement uncertainty within ± 30 cm.

None of the currently known systems for measurements in cooling towers enable automated navigation. Existing solutions are based on manual remote control of a single mobile assembly 12. As defined by the invention independent or automated control of an arbitrary number of mobile assemblies 12 is possible in a cooling tower with reference positioning points 14 and positioning - navigation units 23. Navigation is executed on the basis of a pre-determined reference measuring locations, which the operator initially (before the commencement of the measurements of the properties of the humid air) feeds into the software of the external computer 50 outside the cooling tower on the basis of the technical documentation of the tower. Without the automated navigation of the mobile assemblies 12 it is not possible for a cooling tower of any type or any size to perform measurements in a short time interval, which is the essential advantage of the solution provided by the invention.

The software for the navigation of mobile assemblies 12 is run on the external computer 50. The external computer 50 sends a signal with the instructions to drive each mobile assembly 12 simultaneously and wirelessly, for example, via Wi-Fi communication. Instructions for the navigation at any given moment include the next location in the area for each mobile assembly 12, for instance, the coordinates of the next reference measuring location. Each mobile assembly 12 can then, by its internal control system (PI, PID or other suitable control method) in combination with the reference positioning points 14, autonomously travel from one reference measuring location to the next reference measuring location. The procedure of instructions of the navigation then repeats until each of the mobile assemblies 12 finishes the measurements at every reference measuring location. The navigation algorithm prevents any of the mobile assemblies 12 that might approach the edge of any individual part of the cooling tower by getting nearer than a pre-set distance, thus preventing any possible collision of a mobile assembly 12.

This technical solution enables autonomy of driving; therefore, the mobile assemblies 12 are, as defined by the invention, capable of avoiding obstacles or going arou nd them in an effective way. The design of the mobile assemblies 12, as represented in figure 2, enables full mobility, this is they can move equally forwards and backwards and can thus transit the area in any required direction. Due to this design, the mobile assemblies 12 are capable, with the help of the navigation system, to adapt or avoid obstacles that are present on the surface of the d rift eliminators 1. With this system it is possible to measure on any required path and as a resu lt the time of measurements is shortened to the minimum possible level.

Preferentially the navigation of mobile assemblies 12 is based on the reference positioning points 14, measuring the position with positioning - navigation unit 23, and the fitted nine-degree-of-freedom inertial sensor. The mobile assemblies 12 have an inbuilt nine-degree-of-freedom inertial sensor that is capable of ensuring reliable positioning and navigation even in the case that a signal of the reference positioning points 14 is missed. The nine-degree-of-freedom inertial sensor includes a 3D accelerometer, 3D gyroscope, 3D magnetometer in 32byte microprocessor with Kal man or similar filtering to process the signals of the nine-degree-of-freedom inertial sensor. A lack of signal of the reference positioning points 14 can happen in extraordinary circumstances when, in cooling towers, there are present surfaces or objects that prevent a visual connection between the mobile assembly 12 and the reference positioning points 14 that are usually placed on the railings of the walking surfaces 17 at the inner edge of the cooling tower.

Optionally every mobile assembly 12 can also include a unit for video surveillance, that is preferentially fitted on the communication unit 24. The unit for video surveillance is, through the external computer, con nected to the positioning- navigation unit 23 on every mobile assembly 12. The unit for video surveillance enables the detection of irregularities, for example holes in the drift eliminators 1 and avoidance of them by the mobile assemblies 12 which happens manually or automatically on the basis of the algorithms for fau lt detection in cooling towers, installed on the external computer 50. Based on the video surveillance an operator can also take control over the navigation and by manual control, guide a single mobile assembly 12 onto a changed path.

The automated navigation system of the mobile assemblies 12 enables their autonomy. As defined by the invention measurements with use of mobile units 12 are not performed manually, therefore there is no need for human presence in an operating cooling tower or it is reduced to a minimum level, which significantly increases safety during the time of the measurements.

Method of measurement as defined by the invention

The method of measurement as defined by this invention provides the possibility to perform, with the suggested technical solution, continuous simultaneous measurements by the use of several mobile assemblies 12 and measuring units 13 in the shortest possible time over the whole cooling tower regardless of the type of cooling tower or system with cooling tower or the circumference of the cooling tower, or the distribution of segments within it. In the case of hyperbolic natural-draft cooling towers, the invention ensures continuous measurements in less than eight hours. The whole method of measurements must be performed continuously and in a short time interval, because in a short time interval the surrounding parameters and characteristics of the operating system, for example power plant, will not have dramatically changed. By this method more precise measurements of the operation of the cooling tower and the whole power plant is possible.

The method of measurement as defined by the invention is composed of the following steps:

- A) defining the coordinate system and relevant area, defining the number of mobile assemblies 12, defining and entering the starting position and the reference measuring locations for each mobile assembly 12 and defining and entering the sequence of measurements of each single measuring unit

13 included in a mobile assembly 12, into the external computer 50, wherein the coordinate system, relevant area, number of mobile assemblies 12, reference measuring locations and programme for the execution of measurements for each single mobile assembly 12, are defined on the basis of the technical documentation of the cooling tower or on the basis of preliminary executed measurements of the dimensions of the plan area of the cooling tower above the d rift eliminators 1;

- B) installing of the measuring equipment that includes:

- installing of at least one reference stationary measuring unit 15 for measuring the properties of humid air in the cooling tower, where the mentioned unit includes sensors for measuring temperature, velocity and humidity of air above the d rift eliminators 1;

- installing of reference positioning points 14 within the cooling tower;

- setting of mobile assemblies 12 to their starting positions on the surface of the drift eliminators 1 defined in accordance with step A;

- C) executing of measurements in the cooling tower, wherein every mobile assembly 12 moves to its pre-defined reference measuring locations, determined in step A, and each single measuring unit 13 executes measurements according to the sequence of executing measurements defined in the step A, whereby the measured values of each individual measuring unit 13 are transmitted either directly to the external computer 50 or in the local processor unit 24a over the unit for sampling and the communication unit 24, whereby the measured values are simultaneously digitised and the digitised data is wirelessly communicated by the communication unit 24 to the external computer 50;

D) ending the execution of measurements, including the dismantling of the measuring equipment.

In the case, where the associated industrial system does not have a weather station to measure the properties of ambient air (temperature, velocity, direction of wind, humidity, pressure) around the cooling tower, the step of installing of the measuring equipment additionally includes installing of a least one stationary measuring unit 16 for measuring the properties of the ambient air (temperature, velocity, direction of wind, humidity, pressure) around the cooling tower.

Every mobile assembly 12 moves from one reference measuring location to the next reference measuring location. When a single mobile assembly 12 reaches a pre-determined reference measuring location it stops and the measuring units 13 execute measurements of temperature, humidity and velocity of air. The time of the measurements at a single reference measuring location depends on the conditions in the cooling tower and its size and takes from 30 seconds to 10 minutes. Then the mobile assembly 12 autonomously moves itself to the next reference measuring location, it stops, and the measuring units 13 execute the measurements. This procedure is repeated until the mobile assembly 12 completes the measurements at every reference measuring location. This procedure is valid for each mobile assembly 12.

The method, as defined by the invention thus enables an execution of measu rements above the drift eliminators 1 and across the whole plan area of the cooling tower with a high spatial resolution (50x50 cm); as a result of the continuous execution of measurements and simultaneous measurements over several areas in the cooling tower, a high measuring certainty of the measured properties of humid air is ensured, this is within 0.3 m/s accuracy for measuring velocity and within 0.3°C accuracy for measuring the temperature and within 5 % accuracy for measuring the humidity. This high measurement certainty also includes the influences of the surrounding ambient air parameters, positioning and the measuring equipment.

As defined by the invention, the measurement method has the following advantages:

- application of multiple mobile assemblies 12 that move automated ly, simultaneously and autonomously above the drift eliminators 1 while performing the measurements,

- measurement of properties of humid air in the cooling tower is conducted using several mobile assemblies 12, each one includes several telescopic arms 22 with measuring units 13, with sensors for measuring properties of humid air, this is temperature, velocity and humidity, enabling simultaneous measurements at a large number of locations and with high resolution across the whole plan area of the cooling tower,

- application of several measuring units 13 for measuring of the properties of humid air on one mobile assembly 12 where the measuring units 13 are installed at suitable locations on the mobile assembly 12 in such way that they do not disturb the measured current of humid air,

- hol low chassis of the mobile assemblies 12 and the use of telescopic arms 22 enable an undisturbed current of humid air, of which the properties are measured,

- application of state-of-the-art materials and a hollow chassis for the mobile assemblies 12 that with all the instruments for its operation and measurement of the properties of humid air weighing less than 20 kg and ensuring that drift eliminators 1 cannot be compressed or damaged, which could increase measuring uncertainty and decrease the performance of the cooling tower, - application of reference positioning points 14 that enable the precise determination of position or location of all the mobile assemblies 12 and measuring units 13 during every moment of performing the measurements,

- application of navigation with video surveillance enabling automated, independent and simultaneous control of all the mobile assemblies 12 together, over pre-determined paths and avoiding dangers, for example gaps in the drift eliminators 1,

- system for measuring according to the invention includes communication units 24 on the mobile assemblies 12 and an external computer 50 where all the operational data from the mobile assemblies 12 and measuring units 13 are stored and available for later calculations and analysis,

- ensuring high resolution of measurements of the properties of humid air across the whole plan area of the cooling tower,

- simultaneous and fast measurements of the properties of humid air within a time interval of a few hours during which the surrounding ambient parameters and operation of the system, for example power plant, do not significantly change, ensuring the smallest possible uncertainty of measurements of the properties of humid air,

- high resolution of measurements and low measurement uncertainty are suitable for diagnostics of the components, evaluation of the operation of the tower and enable precise mathematical calculations of cooling towers and systems with cooling towers,

- increased safety of execution of measurements in an operating cooling tower, as human presence is not necessary at the time of measurement in the operating cooling tower or is reduced to a minimum level.

An example of implementation

The example assumes an application of a hyperbolic natural-draft wet cooling tower as is schematically presented in the example of the figure 1. The procedure is similar to other types of cooling towers with drift eliminators 1 or a type of fills 3, on which it is possible to drive the mobile assemblies 12. As is shown in figure 2, the area above the drift eliminators 1 is divided into four parts or segments. In the case of a smaller hyperbolic tower, that is up to approximately 60 m in diameter above the drift eliminators 1, four mobile assemblies 12 are used, one per segment. In general, for smaller cooling towers, regardless of type, one mobile assembly 12 is used per segment. In the case of a larger cooling tower, that is where the diameter of the tower above the d rift eliminators 1 is 60 m or greater, two or more mobile assemblies 12 per individual segment are used.

Prior to the start of measurements, an examination of the cooling tower is carried out with the intention of discovering any anomalies and possible problems in the tower that could in any way prevent the execution of measurements according to the invention. In case of problems, the operator of the system is notified or if the problem cannot be solved, it has to be considered at the execution of the measurements. For example, in the case that there are objects like branches, debris, etc above the drift eliminators 1 they need to be removed or at the planning of the paths of the mobile assemblies 12 the path is redefined to by-pass the mentioned obstructions. Thus, in the planning, potential problems can be avoided and the time of measurements also optimised. Pre-determining the reference measuring locations of mobile assemblies 12 is conducted on the basis of the technical documentation of the cooling tower, provided by the operator. In the case that such documentation is not available, a measurement of the dimensions of appropriate segments in the tower above the d rift eliminators 1 is carried out. Then on the basis of documentation, reference measuring locations for every mobile assembly 12 are defined on the external computer 50 that is located outside of the cooling tower. After this, reference positioning points 14 are installed within the cooling tower. They are usually fitted on the walkways 17 at the edge of the cooling tower. Then all the mobile assemblies 12, with measuring units 13, are set to their starting locations. After this all the instruments for the execution of measurements, that is the mobile assemblies 12, including the positioning-navigation u nit 23, sensors and communication unit 24, are activated. Following this the system with the cooling tower is stabilised at the agreed pre-determined operational point, set in advance by the operator. After the stabilisation of the system, the measurements are carried out in the cooling tower. The measurements of all physical quantities, that is temperature, velocity and humidity of air in the tower, are performed throughout the whole period of the measurement. Each mobile assembly 12 independently moves from one reference measurement location to the next reference measurement location and according to the programme of measurements, the measuring units 13 perform the measurements. The programme of measurement includes the duration of stops on each given location, this is for each reference measuring location . The duration of the stop varies from 30 seconds to 10 min utes. For example, when a mobile assembly 12 reaches a certain location, it stops, for example for 5 minutes. Measurements are carried out and then after 5 minutes it moves to the next reference measuring location and the procedure repeats until each mobile assembly 12 completes the whole pre-defined path completing the measurements on every reference measuring location. The time of measurement may vary; in the case that the examination of the tower revealed certain anomalies, a longer time for the mobile assembly, or assemblies 12 can be defined for a specific area. The distance between any two locations, where the mobile assembly 12 stops, depends on the size of the tower and is from 1 to 5 meters. This procedure is valid for every mobile assembly 12. When all the mobile assemblies 12 have completed the pre-determined path of reference measuring locations, the measurements are finished and the dismantling of the measuring equipment begins. After this the system with the cooling tower returns to normal operation.

LISTING REFERENCES, THAT DO NOT INCLUDE PATENTS

[1] J.W. Cooper, Jr. Counter-flow Cooling Tower Diagnostic Testing. EPRI Cooling Tower Technology Conference, Louisville Kentucky, 2015.

[2] M. Novak, B. Sirok, B. Blagojevic, M. Hocevar, M. Rotar. CTP Method - Diagnostic Method for Control of Cooling Tower Operation. VGB PowerTech ½, 2003.

[3] E. Hampe: KCihltCirme; VEB Verlag fur Bauweses, Berlin 1975.