Evaporative cooler and its use, as well as gas-turbine plant with evaporative cooler

The invention relates to evaporative coolers for cooling the gas stream, in particular an air flow, comprising several cooling elements arranged in the flow channel, which is fed by a feeding device to be evaporated or vaporized liquid, preferably water. The invention further relates to the use of such evaporative cooler, as well as to a gas turbine plant with evaporative cooling.

Energy conversion efficiency in a gas turbine and, in particular, its capacity depends inter alia on the temperature of suction air required for combustion of supplied by the compressor to the combustor. The lower the temperature of the air entering from the environment, the higher, usually, the efficiency of the compressor. Increased total power of the gas turbine can be attributed to the higher density of the cooled intake air and thereby increase the mass flow of cooling air. Hence it is usually the output of energy, which is available in the summer months, significantly less than in the winter. Accordingly, due to the cooling of the intake air can often significantly increase the total capacity and the overall efficiency of the gas turbine, even taking into account the energy consumed for cooling. Side positive effect on the environment can thus consist in reducing the emission of oxides of nitrogen and / or CO2.

In particular, in regions or areas of relatively low humidity of the ambient air temperature of the intake air can be reduced relatively efficiently by means of evaporative cooling and thus can increase the efficiency and power of the gas turbine: with spray or distribution on large surfaces substantial amounts of an evaporating liquid, it is advisable to water in dry, warm air. The required evaporation energy is taken from the ambient air, which consequently cools. Thus, depending on the location and system temperature difference is from 5 K to 20 K. At the same time increasing the moisture content of the air. The investment costs for this type of cooling systems, although not significant, but it is usually characterized by the depreciation for the time period of 1 to 3 years, which has led to the use of these advanced systems.

Compared with direct and direct intake air humidified by spraying water in the air stream, for example, via spray arrays arranged in front of the compressor, while evaporative cooling water in an adiabatic evaporation or vaporize the absorbed air. Thus, the risk of over-saturation or spraying with water compared with humidified air is markedly reduced. The principle of evaporative cooling for reducing the temperature of the intake air in a gas turbine technically embodied and implemented in an evaporative cooler having a honeycomb structure with cooling elements, which are arranged, for example, before or between the stages of the intake filter for filtering fresh air. To this end, a certain number, usually the upright, arranged in a cascade cooling elements or cooling plates, also called irrigated sinkers or plates with a gravity bed via corresponding feed mechanism on top of supplied water (e.g., in the form of droplets or dust) so that the water comes down the possibilities to form a water film on the corresponding element or plate.

Vertically them fed into the flow channel bounded by walls of the housing, the intake air (the so-called cross-flow). Part flowing water evaporates or is converted to steam under the influence of relatively warm return air entering the evaporative cooler, whereby the temperature of the airflow exiting from the cooling apparatus is lowered. Excess, evaporates water collected in the bottom portion of the cooling plates and the pumping unit via the low pressure is pumped back to the starting point, so that the whole forms an open-shaped cascade circuit cooling water.

Like the evaporative cooler are arranged so called evaporators standpipe film, in which, however, is usually the main purpose is not cooling the gas stream, and the production of steam and which is usually somewhat sunk plates or dipleg from input to be cooled with water heated by an electric heating device.

The cooling elements or cooling plates existing evaporative coolers are usually made of stainless steel, but sometimes they are made of synthetic material or paper-based material, wherein the feed water is distributed over the available surfaces are relatively poorly and unevenly. If the entire surface of the respective cooling element to be used for evaporation, i.e. for effective cooling of the intake air flow, it is necessary to irrigate a large excess of water. This leads to the formation of water films with a relatively large thickness. However, the presence of water films of large thickness increases the likelihood of entrainment of air and water flow in blade dripping lattice gas turbine (which is its compressor), which may result in undesirable erosion phenomenon.

Therefore, for all evaporative coolers or chillers using the effect of evaporation from the open-loop cooling water in practice is a problem of determining the proper amount of water so that the water drops do not fall into the scapular lattice, but at the same time there is enough water in the evaporative cooler to provide for the possibility of optimal cooling intake air. In the conservative, the calculated reliability embodiment, the amount of water usually is adjusted so as to prevent kick drops. Thus theoretically possible cooling potential is not obtained, since the evaporation surface or the surface on which the evaporation is not used optimally.

In connection with this object of the invention is to provide an evaporative cooler of this type, by means of which at non-critical modes of operation and simplicity of operation is achieved by a high efficiency in terms of the evaporation or vaporization inputted to it a cooling fluid, and thus provides a particularly efficient cooling of passing therethrough a flow of gaseous medium, in particular air. In particular, when applying an evaporative cooler such as cooler suction gas turbine should be reduced risk for erosion installed at the fluid flow elements of the unit, especially for a compressor blade lattice. It is further proposed gas turbine having evaporative cooler of this kind, with a very high efficiency and with a high total capacity.

According to the invention, the problem regarding the evaporation cooler is achieved in that the surface of at least one of the cooling elements, at least in one part of the area reserved for forming the liquid film has a hydrophilic property resistant.

The invention proceeds from the consideration that liquid film, which is to be vaporized or converted to steam, in particular water, which is formed on the surface of the cooling element must have such a thickness that, despite the permissible fluid loss by evaporation or conversion of liquid to vapor of any one place moistened surface does not break the liquid film occurs. This would, in general, to deterioration of evaporation and thus to reduce the cooling effect. On the other hand, for effective evaporation or transformation from liquid to vapor liquid film should not be thicker than it is certainly necessary. This applies in particular to the evaporative cooler, used to cool the intake air stream of the gas turbine in order to reduce the danger of possible ingress of liquid droplets in the scapular grating compressor.

To create these conditions, even with uneven supply of liquid or simple irrigation surface is typically shaped honeycomb cooling elements or cooling plates must be of such a nature in which due to the specific interaction of the fluid with a solid to a certain degree of self-generated special uniform homogeneous liquid film, respectively, at least supported the formation of such a film. At the same time the possibility to be used at the disposal of the entire surface of the cooling element, i.e. surface wetted evaporating liquid.

Consequently, according to the concept proposed by deliberate imparting hydrophilic properties (the ability to absorb water or "water-demanding properties") or modifying the surface improves the wettability of the cooling elements - at least in a zone which is especially important for wetting. Appropriate surface treatment to impart hydrophilic properties it is also called hydrophilization. Due to such processing liquid droplet, which comes into contact with a hydrophilized surface extends, occupies a large area, such as a flat disc or a flat spherical segment, respectively, at the oblique or vertical (vertical), and a cascade arrangement of the respective cooling element flows into a flat strip and it adheres well to the surface. Due to the good action of the attracting reliably prevents the entrainment of droplets gas or air stream. For a complete wetting of the cooling elements requires a much smaller excess of water in comparison with untreated or not surface modified, which significantly reduces the required thickness of the film and, moreover, equally reduces the risk of entrainment or separation of liquid drops.

As a quantitative measure for the hydrophilicity of the surfaces thus treated can thus serve as a so-called contact angle that a drop of liquid is formed on the surface of the cooling element with the cooling surface element. In general, the hydrophilic surface has a contact angle against water, the quantity of which is less than 90 °. Preferably, however, the machined surface of the cooling element has a corresponding relatively water contact angle less than 40 °, in particular smaller than 20 °, and particularly preferably less than 10 °. Preferably, the method gidrofilirovaniya selected so that the hydrophilicity of the treated surfaces during subsequent operation persists for a long or a persistent nature, so that the first adjusted angle of contact is not increased or is increased only marginally.

Preferably, the exposed surface hydrophilizing all walls and internals evaporative cooler, which, when the liquid supply is maintained evaporation process or vaporize, regardless of their form, their position and their orientation, and on the respective substrate material. For example, along with attached in the flow channel-shaped honeycombs cooling elements include the impact on the water disposed within the channel for limiting flow of gaseous fluid cooler housing wall portions and accordingly executed purposefully supplied hydrophilic surfaces.

In a preferred embodiment, the respective cooling element comprises a base portion, for example made of metal, which before installation in an evaporative cooler, or prior to the commissioning of a process accordingly selected coating process is coated with a hydrophilic surface layer.

The first coating process, provide particularly advantageous results, in particular smaller contact angle in relation to water, is the so-called sol-gel method.

By the term "sol-gel coating" is currently defined as any coating applied to a sol-gel method for a metal, ceramic or synthetic material consisting of a substrate (substrate). When the sol-gel method in the first step is usually a colloidal suspension or dispersion of solid particles of small diameter - from 1 to 100 nm (so-called nanoparticles) in aqueous or organic solvent from the transition sol gel (gelation) is translated into an amorphous, nanostructured gel state. The sol-gel transformation leads to the formation of a three dimensional network of nanoparticles in a solvent, whereby the properties of the gel becomes solid. Then in a second step the gel, respectively helium coating applied to the substrate by heat treatment or photochemically cured (baked) and thus is transformed into a material or a resistant and durable coating with the characteristic properties of ceramic materials such as glass or transparent.

The starting material (so-called precursor) for preparing a colloidal solution coating, which is also called the sol are applied, e.g., tetraethoxysilane, tetramethylorthosilicate, sodium silicate or glycol ether, as well as various other organometallic polymers, particularly metal alkoxides and / or complexes esters with metals. By mixing additional organic molecules to various functional groups and / or by adding the inorganic microparticles and / or nanoparticles can be targeted to modify a well managed and controlled manner chemical and physical properties of the future coating. In the embodiment described here, the application obtaining coatings with a strong, if possible, the hydrophilic nature is the main aim in selecting the precursor to a colloidal solution. Secondary objectives include high strength of the coating on the substrate and its high resistance to scratching, resistance to high temperature and also provide sufficient protection against corrosion of the metal, typically a substrate coated with a coating.

The sol usually resulting from this set of reactions occurring during the hydrolysis or polymerization is applied onto the substrate, for example, by spraying, dipping or centrifugation. For the coating of very large, mostly flat surfaces is used mainly the so-called method of deep immersion. In this method, the substrate to be coated, in this case - the respective cooling element is immersed in the sol again and removed from it at a constant speed, so that the sol liquid film adheres to the substrate surface. Being initially liquid sol film after a short drying into a more or less thick gel film which is subjected to, for example, followed by heat treatment in an oxygen atmosphere (air). At temperatures up to about 400 ° C, the organic components decompose organometallic polymers with the release, mainly carbon dioxide and water. And remaining amorphous nanoporous metal oxide film begins to be sintered at temperatures above 500 ° C. Simultaneously the nucleation and crystal growth, so that an amorphous and porous gel film formed nanocrystalline more dense oxide-film.

The chemical composition of the sol, conditions of depositing a layer (e.g., the extraction rate), as well as the parameters of heat treatment (heating rate, temperature, duration of exposure) have a significant effect on the properties of the layer may be adjusted in accordance with the above given values. Due to the formation of covalent bonds between the layer and the substrate to achieve high performance adhesive that is beneficial to the long-term durability of the coating and its resistance to high mechanical loads.

Alternatively, or in addition to the pure oxide-sol-gel layers can be applied as an organic-inorganic hybrid layers, which can be coupled to obtain coatings of greater thickness and with higher extensibility. In certain cases, there may be used the treatment temperature considerably below 300 ° C. Alternatively, or in addition to the heat treatment may also be provided with UV curing or visible light.

Alternatively, the sol-gel method for hydrophilizing surfaces of the evaporation or vaporization may use other methods of applying coatings or treatments that are easier to use, less costly and result in a minor release of unwanted byproducts such as solvents.

For example, the application may be provided on the main part of the cooling element layer corresponding water- chemical varnish to obtain the desired hydrophilic surface. Suitable for this purpose, for example, acrylic paints or lacquers based on polyester resins, polysiloxanes, epoxides, polyurethane or polysilazanes. A prerequisite hydrophilization, and therefore, the wettability with water is a polar surface. The polar groups contribute to increase lacquer resin surface energy and thus better surface wettability by water. Preparation for the manufacture of hydrophilic coatings is also based on the incorporation of appropriate chemical groups such as, for example, -OH, -COOH, -NH2, -SH. Moreover, the lacquer can acquire hydrophilic properties when added in a special filler particles, in particular hydrophilic aerosil (Aerosile) (anhydrous silica powders with high specific surface). Relevant details should be known experts from other fields of application or administration of this kind of varnish, which include, for example, a coating to prevent fogging glasses, lights and special helmets. Moreover, such hydrophilic coatings are applied, for example, certain medical and technical devices.

Another possibility to achieve the required surface properties provide different methods of plasma coating in atmospheric conditions or in a vacuum. In the so-called chemical vapor deposition (CVD) (CVD-method) may be deposited on surfaces in the form of a layer compound reactive silanes (silanes saturated). Thus as a result of a chemical reaction occurs precipitation of solid components from the gas phase onto a heated substrate surface. With appropriate silane precursor can be prepared by the above method, and hydrophilic coatings. Deposition may occur in plasma of low pressure and at atmospheric conditions. Currently, such techniques are also used in waterproofing coatings, including for medical purposes. In the so-called physical vapor deposition (CVD) (PVD-method) the layers can be deposited in vacuum forming, in particular on substrates of synthetic material, metal or organometallic coatings to increase surface energy and improve thereby the wettability of the substrate . Unlike CVD-PVD process in-process layer is formed directly by condensation of the starting material.

Yet another possibility of purposeful modification of the surface properties of the material, in particular increasing the surface energy and hydrophilization provides flaming coating method, also known as Pyrosil-method, or a flame-pyrolytic process for depositing an amorphous silicate layer with a highly developed network structure under the action of fuel silane-containing gas on the substrate material. For this purpose the surface to be treated is passed through the oxidizing zone of a gas flame, wherein pre-determined dose administered siliceous substance, so-called precursor. Thus produced silicate layers generally have a thickness from 20 nm to 40 nm and provide strong expression hydrophilizing surface.

Furthermore, there are various methods that can be grouped under the general name "natural oxidation" and which due to purposeful surface oxidation leads to an increase in the polar component of the surface energy and improves thereby the wettability of the surface water. In this sense, the oxidizing effect is, for example, reactive plasma for plasma treatment in the presence of oxygen, argon or air. These processes can be carried out in vacuum or under atmospheric conditions. In the method of corona treatment, which also belongs to the methods of physical oxidation, and is currently used, for example, for processing of synthetic materials to improve the suitability of polymeric films for printing and gluing the substrate is processed by electric discharge, which leads to ionization of the gas surrounding electrodes and a substrate, such as air. Flame treatment is also an oxidation process surfaces of synthetic materials with which the latter may be given hydrophilic properties. The electrolytic oxidation, on the contrary, is suitable primarily for modifying the aluminum surface.

Processing strongly oxidizing liquids, such as hydrogen peroxide, or strongly oxidizing gases, such as ozone, it may also enhance the polarity and therefore, the hydrophilic surface. It is now known, for example, the use of ozonation by treatment of fluorination or synthetic materials, such as the production of films, as well as the fuel tanks in the processing of synthetic material. Such methods can be grouped under the general name "chemical oxidation."

Finally, also possible to provide the desired regulation of the hydrophilic properties of the surface of the cooling element evaporative cooler by chemical etching or "cauterization" or by phosphating surfaces. By etching, which is currently used mainly for the removal of contaminants such as rust, scale, et al., Refers to treatment of metal surfaces acids such as hydrochloric acid, sulfuric acid or nitric acid (acid etching), or alkalis such as sodium hydroxide (alkaline etching). When phosphatizing metal substrates treated with an aqueous solution of phosphate. Thus on the metal surface by chemical reaction produced inorganic exposed conversion layers which have a corrosion-inhibiting action and can serve as a good coating, i.e. They are hydrophilic.

Provided by the invention advantages are, in particular, that by focusing surface treatment and hydrophilizing embedded elements and cooling elements evaporative cooler intended for vaporization or evaporation of the liquid, in particular cell cooling plates, widening or more efficient use of surface active heat transfer due to improve wettability. When using this type of evaporative cooler for cooling a gas stream, such as a suction refrigerant gas turbine can be achieved, even at relatively economical raw water inlet, a very high cooling effect. Simultaneously, prevented or significantly reduced entrainment of liquid droplets from the gas flow, thereby reducing, for example, the danger of corrosion or erosion of the evaporative cooler is placed after the heat or thermal piston machines vane machine, in particular a gas turbine. Due to the high efficiency of the cooling intake also increases the efficiency and the output power to place him of the gas turbine.

Another advantage of the concept presented here is to reduce the depth of insertion of the evaporative cooler resulting in better utilization of the surfaces with the same cooling capacity as compared with the prior art. By reducing the depth of insertion becomes possible to more compact housing and reducing thereby the manufacturing costs. Furthermore, the suction-side pressure drop is significantly reduced compared to the prior art.

Therefore, the concept hydrophilizing surfaces vaporization or evaporation may also be employed in vaporizers standpipe film, preferably to increase their efficiency, the main purpose of which is not cooling the gas stream, and steam production itself, for example in the technology of liquid mixtures by distillation, etc. Instead of heating a hot gas flow, or in addition thereto can be provided in this case, for example, electric heating plates or downcomer pipes.

Example of a practical embodiment of the invention in more detail on described with reference to a figure, which shows a partial section of the evaporative cooler.

FIGURE evaporative cooler 2 serves as a coolant intake side of the intake for the cooling of the environment and not shown here supplied gas turbine air compressor. For this purpose it is provided with flow channels 6, surrounded by a closed body 4, air inlet 8 and outlet 10 of air, which is a large part of the cooling elements or cooling plates 12 respectively combined in groups or cooling modules. The flat cooling elements 12 respectively oriented vertically and parallel to the air flow 14 generated during operation, and thereto through the region or the housing cover 4 feeding device 16 located on the upper side of the respective cooling element 12, both sides of the water may be supplied. Thus, when operating as a "front side" and the "back side" of the respective cooling element formed downward flowing film of water, which passes over more guided through the flow channel 6 takes air. According to the principle of evaporative cooling, wherein vaporized or converted to steam the water flowing downwards part, whereby on the one hand increases the relative humidity of the air flow and on the other hand, its temperature is lowered. Evaporable part flowing down through the cooling elements 12, the water is collected in the bottom region, not shown in detail here the book and then opening a circuit returns using is not shown pump to the supply device 16, and fluid loss due to evaporation, offset by the addition to the circuit fresh water, preferably ordinary tap water.

Cooling effect is achieved, the higher the land entering the evaporative cooler 2 (ambient) air. In addition, to ensure high efficiency as possible should be used as the evaporator surface available to the entire surface of the cooling elements 12, the water film formed in spite of the desired evaporation must not be interrupted at any place. On the other hand being applied by a unit time amount of water should be kept as low as possible, so that from the cooling elements 12 never left any water droplets that airflow can be carried away in a blade grid set after evaporative cooler 2 compressor where they could bring due erosion damage.

To match these conflicting objectives in the best match with each other, cooling elements 12 of the evaporative cooler 2 are provided for an especially good wettability with coolant, in particular water, sol-gel coated on the surface of the base material - in this embodiment stainless steel. In particular, when the standard or normal operating conditions, for example at air intake 15 ° C and a pressure of 1013 mbar of air, the contact angle to water is achieved less than 40 °, preferably less than 20 ° or even less than 10 °. The hydrophilic coating contributes to a particularly uniform distribution of water on the surface of the cooling elements 12, even when applying a relatively small amount of water. Formation of a uniform, relatively thin film of water is maintained even or uneven wetting and high efficiency of vaporization or evaporation and also reduces the risk of entrainment of water droplets airflow.

According to the above embodiments is meant that the sol-gel coating can be formed, for example, a number of other ways in which a targeted manner can be achieved hydrophilization important for evaporating surfaces of the cooling elements 12. They include, in particular, the hydrophilic coating liquid chemical paints, plasma coating, flame coating method, physical and chemical oxidation of surfaces, as well as chemical etching and surface etching acids and alkalis. Of course, the selection process is particularly suitable hydrophilizing determined (main) material of which the cooling elements 12, as well as other aspects, such as cost and the cost and durability of the coating or modified surface under the operating conditions, etc. Particularly preferred methods, which do not require expensive vacuum equipment and hence they can be used very flexibly and locally at the site.