Patent Application
20170276386
The invention relates to media pads in an evaporative cooler and specifically evaporative coolers in an inlet duct for an industrial gas turbine.
Industrial gas turbines ingest air, compress the air, mix it with fuel, burned the mixture and used the resulting combustion gases to drive a turbine which generates power. The power generated by a gas turbine is related, in part, to the water content and temperature of the air ingested by the turbine. The higher the water content and lower the temperature of the air, the greater the power output of gas turbine.
Evaporative coolers increase the water content and lower the temperature of the air ingested by a gas turbine. They are typically used while the ambient air dry bulb temperature is high, e.g., greater than 80 degrees Fahrenheit (25 degrees Celsius), and the relative humidity is low, e.g., below forty percent. Under conditions of high temperature and low humidity, evaporative coolers can increase the power output of a gas turbine by five percent, ten percent or more.
An evaporative cooler adds water to the inlet air flowing into a gas turbine. Water flows over pads of media that extend across an inlet air duct. Air flowing through the duct evaporates the water on the media. The evaporation cools the air and increases its humidity of the air. The cooled, humid air has a greater density than the hot, dry air. The higher density increases the mass flow rate of the air which increases in power output and efficiency of the gas turbine.
Conventional media pads are most commonly formed of paper. Recent efforts have been made to form media pads from synthetic materials. These efforts have not been entirely successful due to the inability to form a synthetic material having that does not create excessive pressure loses in the inlet while maintain appropriate cooling effectiveness.
An evaporative cooler has been conceived and is disclosed herein that is configured for a gas turbine or other device, the cooler includes a stack of synthetic media pads configured to be mounted in an inlet chamber having an inlet open to atmospheric air and an outlet coupled to an air inlet to the gas turbine or other device, wherein the synthetic media pads include high density synthetic media pads and low density synthetic media pads.
Synthetic media pads have been conceived are disclosed herein that are configured to be arranged in a stack to be mounted in an air inlet chamber having an inlet open to atmospheric air and an outlet coupled to an air inlet to the gas turbine, wherein the synthetic media pads include high density synthetic media pads and low density synthetic media pads.
A method has been conceived and is disclosed herein to form a stack of synthetic media pads for an evaporative cooler, the method includes: arranging in the stack high density synthetic media pads of synthetic fibers, wherein a density of fibers in the high density media pads is above a first threshold density; arranging in the stack low density synthetic media pads of synthetic fibers, wherein a density of fibers in the low density media pads is below a second threshold density which is lower than the first threshold density, and positioning the stack in the evaporative cooler such that a front surface of the stack faces air drawn into an inlet chamber and a rear surface faces an air passage leading to an inlet to a gas turbine.
The industrial gas turbine is shown as an exemplary device using the evaporative cooler. Other devices, such as air conditioning units, that need cool, moist air may benefit from the evaporative cooler disclosed herein.
Unfiltered atmospheric air 22 enters the inlet duct 10, is filtered and the filtered air passes through the evaporative cooler 20 as the air flows 24 to the gas turbine 12. The air is used as a working fluid by the gas turbine to generate power. Exhaust air 26 is discharged by the gas turbine.
The evaporative cooler includes one or more stacks 28 of evaporative media pads. The stack(s) are arranged as a wall 30 that spans an entire cross section of the airflow passage in the inlet chamber. The wall 30 may be formed of two, three or more stacks 24 end-to-end is a vertical array. The stacks 28 may each have similar heights, depths and widths.
A water nozzle(s) 32 and a water distribution pad 34 are at the upper edge of the top stack 28. A water tank 36 is below the bottom edge of the lower stack. A water pump 38 moves water from the tank 36, up through a water pipe 40 and to the water nozzle. Downstream of the airflow 24 may be demisting pads 42 that capture water droplets from the airflow before the flow enters the compressor of the gas turbine.
Water from the nozzle(s) 32 and distribution pad flows down over the outer surfaces of the media pads in each of the stacks 28 towards the drain. As the water flows over and through the media pads, the filtered atmospheric air flows through the stacks 30 of media pads. The air is cooled by the water in the media pads as some water evaporates into the air. The evaporation increases the density of the air which results in an increased mass of the airflow as compared to the atmospheric air entering the inlet chamber. Increasing the density and cooling the airflow increases the ability of the gas turbine to efficiently produce power.
The medial pads of the stack 28 are oriented vertically such the upper edges 30 of the pads face upward and the lower edges 32 face downward. The front edges 34 of the pads face the incoming airflow and the rear edges 36 of the pads face towards the rear of the inlet chamber and downstream of the air flow. Each pad may have the same height (H) and depth (D), which corresponds to the height and depth of the stack. The length (L) of the stack is formed by the stack 28 of pads arranged side by side. The height and length of the stack may correspond to a cross section of the airflow passage through the inlet chamber.
By way of example, each synthetic media pad may have a depth (D) of 12 to 18 inches (0.3 meter to 0.5 m), and a height (H) and width (W) each of six to feet (1.8 m to 10 m). The depth is the distance between the front edge 34 and the back edge 36 of the pad. The height (H) and width (W) are the dimensions of the pad in a cross section perpendicular to the flow of air through the pad. The height and width of the pad may be selected to correspond, e.g., equal, the cross sectional dimensions of the air passage through the air duct.
The media pads are formed of synthetic materials, such as fibers of polyester or glass fibers. The fibers may be coated with polymer materials. Synthetic materials tend to be less rigid than corrugated paper which is used to form conventional media pads. Synthetic media pads have been formed of densely packs synthetic fibers to provide rigidity to the pads. However, dense synthetic material pads when stacked together create an excessive pressure drop in the air flowing through the inlet chamber.
The stack 28 is formed of low density synthetic media pads 38 formed of fibers packed in a low density arrangement and high density synthetic media pads 40 formed of fibers packed in a high density arrangement. The low density pads allow air to flow through and past the pads with minimal pressure drop across the stack. The high density pads provide rigidity to the stack. In the stack, the low density pads may alternate with high density pads in the stack.
The high density pads may be at the opposite sides of the stack, and alternate with low density pads within the pact to ensure that both sides of the low density pads are supported by a high density pad. In another alternative, the high density pads may be separated by two or more low density pads within the stack. The arrangements of low and high density pads in the stack may be determined to achieve goals of minimal air pressure drop through the stack and sufficient structural rigidity such that the pads in the stack do not unduly flutter or otherwise deform as air passes through the stack.
The low density pads may be formed of loosely packed polyester or glass fibers and the high density fibers may be formed of tightly packed polyester or glass fibers. By way of example, the density of fibers across a cross section of the high density pads may be in a range of one-half (50%) to four times (400%) greater than the density of fibers across a cross section of the low density pads.
The width (W) of the low and high density synthetic media pads 38, 40 may be generally uniform, such as within twenty percent. The principal difference between the low density and the high density pads may be the density of polyester fibers in each type of pad. Alternatively, the width of the high density synthetic pads may be narrower than the width of the low density synthetic pads, especially if narrower high density pads impart sufficient structural rigidity to the stack to ensure the stack fills the cross sectional area of the inlet chamber and does not droop or sag.
The density of the pads affects the ability of the pad to adsorb water. The pad's water absorption rate (also referred to as the water soaking capability) is an important parameter for the evaporative cooler. The pads should soak water in quite high degree to keep all pads surfaces area wet for higher cooling efficiency. High density media pads typically have lower water absorption rate than do lower density pads and higher stiffness than low density pads. The low density pads typically have high water absorption rates and tend to be soft and lack rigidity.
Hydrophilic treatments may be applied to the fibers in the pads to increase the water adsorption rate of the pads. Hydrophilic treatments are conventional and typically increase the wicking characteristic of the media, such as fibers, in the pads. Examples of hydrophilic treatments are those that change the three dimensional (3D) orientations of fibers in the pads, and coat the fibers, or other media, in the pads with a coating that attracts water. Increasing the water adsorption rate of the pads tends to increase the cooling efficiency of the evaporative cooler.
The selection and arrangement in a stack of high and low density pads can have advantages of overall good water absorption (such as wherein all surfaces, including fiber surfaces, in the pads are always wet) and a stiff stack structure that holds the stack shape while the stack is in the evaporative cooler. A stiff stack typically has a lower air pressure drop through the pads than a stack with pads that sag, droop or otherwise deform during operation of the evaporative cooler.
The density of the pads, the depth (D) of the media pads and the number of pads in a stack affects the air pressure drop through the pad. The pressure drop increases as the media pad increases in depth. Similarly, an increase in the number of pads and, especially, high density pads, increases the pressure drop through the evaporative cooler. The pressure drop through the evaporative cooler is preferably less than one half of one inch (0.5 inch) of water or 125 pascal, and more preferably 0.3 inch or 75 pascal.
The depth of the media pad and the number of high and low density media pads also affects the efficiency of the evaporative cooler. The efficiency is the ability of the evaporative cooler to increase the water content in the air to one-hundred percent (100%) saturation. An evaporative cooler achieving an efficiency of at least 85% water saturation is desired. The synthetic media pads are selected and arranged in the stack with a goal to minimize the pressure loss through the evaporative cooler and increase the water content of the air to the extent practical.
The sides of the low density pads may have ridges 42 and grooves 44 that form an undulating, e.g., wave-like, surface on the pad. The ridges and grooves increase the rigidity of the pad. The ridges and grooves may also be formed in the sides of the high density pads, or may be formed on one side but not the other of either type of pads. The depth between a groove and a ridge may be a quarter to one half of an inch (60 mm to 130 mm).
To form the grooves and ridges, the sides of the low density pad may be shaped by applying a heated press to the side. The heated press has a heated surface shaped with grooves and ridges. The heated surface forms a mold that shapes the side of the pad into grooves and ridges. The heated press softens and may partially melt the fibers at the side of the pad. The heated fibers deform into the shape of the heated surface of the press and may bond together. The heated fibers cool as the press is cooled or after the press is removed from the side of the pad. The cooled fibers retain the shape of the heated surface of the press.
The grooves and channels distribute water throughout the pad and guide air to flow from the front to the rear of the pad. Water may flow through the gaps 46 between the grooves 44 of the low density pad and the adjacent side of one of the high density pad. The gaps 46 form channels that guide the water and air across the sides of the pads. The gaps may have a width of one quarter to one inch (60 mm to 250 mm), where the width is a distance between adjacent grooves forming the gap.
The grooves and ridges may be inclined to distribute more of the water towards the front edges 34 of the pads and less water towards the rear edges 36. Distributing more water to the front of the pads reduces the risk that water drops enter the airflow downstream of the evaporative cooler. To distribute more water towards the front of the pads, the peaks of the ridges 42 may be towards the downstream edges 36 of the pads. For example, the peaks may be offset from the downstream edges 36 one-third to one-quarter the depth (D) of the pads.
The sinusoidal, horizontally aligned groves and ridges shown in
The pad side 70 has ridges 72 and grooves 74 that are straight and parallel over the entire surface of the side of the pad. The straight ridges and grooves 72, 74 are sloped at an angle 76 of ten (10) degrees. The angle may be sloped downward from the rear edge 78 of the pad to the front edge 80 of the pad. The slope may be downward, as shown in
The side pad 74 shown in
The side 96 of one of the pads has a checkerboard pattern of ridges 98 and grooves 100, e.g., depressions, between the ridges. The side 102 of the adjacent pad has grooves and ridges arranged in straight lines, such as shown in
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
