Process for cleaning gas turbine inlet air and apparatus therefor

Abstract: Contaminants are cleaning from inlet air passing to a gas turbine by contacting the air with a stream of water at a rate and spray pattern sufficient to reduce contaminants present in the air. Suitable air cleaning apparatus (10) comprises a first section of straightening blades (11), a second section of spray streams of water (12) a third section of a coalescing medium (13), and a fourth section of moisture separators (14).

Description: This invention relates to cleaning air passing to the inlet of a gas turbine and, more particularly, this invention relates to reducing contaminants present in air passing to the inlet of a gas turbine. The operation of a gas turbine is well known. In the initial phase of a gas turbine's cycle, an air compressor stage consumes approximately 60 percent of the work done by the power turbine. As such, the efficiency of the compression stage has a large effect on the efficiency of the whole cycle. To maintain peak efficiency, the compressor would have to be kept extremely clean and the blades would have to maintain their original design profile and surface smoothness. However, with these compressors pulling in ambient air laden with particulate material and in some environments corrosive volatile material, peak efficiency cannot be maintained. The compressor blades are eroded by the larger particles. Smaller particles stick to the blades changing the shape and smoothness of the blades. This is called "fouling." Both the small particles and corrosive volatiles work to corrode the blade surface. Gas turbines, therefore, require "clean" air to prevent fouling, corrosion, and erosion of the gas turbine internal components such as the compressor blades. The "state-of-the-art" method for cleaning inlet air to gas turbines is to use a combination of filters for removing particulate in the air. However, air filters, alone, have not been successful in eliminating the fouling, erosion, and corrosion damage to the compressor. The result is loss of efficiency and damage to expensive compressor blading. The air contaminants in either particulate or gaseous form penetrate even the best filter systems on the market, and enter the compressor section of a gas turbine engine. The particulates which make their way to the compressor will erode the compressor blades, or stick to the blades which cause fouling and often corrosion and pitting. The corrosion can weaken a blade to the failure point or, as a minimum, degrade airfoil performance. In addition, both solid and gaseous contaminants which make it through the compressor will enter the turbine section, causing a buildup of material which degrades the machine performance and causes hot corrosion of the hot end parts. The costs to a gas turbine operator from degraded performance and worn and/or corroded parts replacement due to contaminated inlet air can exceed a million dollars per year per turbine. EP-A-0087229 (Parmatic Filter Corporation) discloses a method of removing contaminants from the gas stream to a gas turbine by spraying liquid into the gas adjacent separating means and then removing the liquid from the gas by said separating means. Preferably, the liquid is sprayed on to an impact filter pad to saturate an area with droplets of sufficient size to maximize small particle capture by collision with and encapsulation of contaminants. The document also discloses a separating device for putting this method into effect. The device is provided with spray nozzles for spraying sea water droplets of at least 10 micrometer mass mean diameter into the gas stream and on to an impact filter pad located upstream of a separator for removing the liquid from the gas before the gas is fed to the turbine. US-A-4508555 discloses the scrubbing of effluent gases from the production of mineral fibers, particular the production of glass fiber insulating blankets or mats. The scrubbing is conducted by the use of opposed jets of water which are inclined relative to each other and interact to produce a planar dispersion of water droplets across the path of the effluent gases. It is desirable to clean the inlet air directly downstream of particulate filters used in conjunction with gas turbines. More particularly, it is desired to remove gaseous and solid contaminants from air passing to a gas turbine which can cause corrosion of turbine parts. It is further desired to reduce buildup of solid materials in the turbine. It is further desired to provide intense air scrubbing action not present in any evaporative coolers in gas turbine inlet systems. In addition, it is desired to remove particles and gaseous contaminants which get through the dry filter systems on the market today. It is further desired to provide air cleaning at a relatively low operating cost. One aspect of the present invention is directed to a process for removing particulate and volatile components from a gas stream selected from gaseous process streams and feed gas streams for a gas-using apparatus, comprising contacting the gas stream with a stream of solvent at a rate and spray pattern sufficient to remove particulate and volatile components present in the gas stream, characterised in that said solvent stream is at least one substantially flat wall of finely atomised solvent formed by at least one pair of diametrically opposing spray streams impacting head on, through which wall the gas stream passes. Another aspect of the present invention is an assembly of a gas-using apparatus and an apparatus for removing particulate and volatile components from an gas feed thereto comprising means for contacting the gas with a stream of solvent at a rate and spray pattern sufficient to remove particulate and volatile components in the gas, characterised in that said means for contacting the gas forms at least one substantially flat wall of finely atomised solvent from at least one pair of diametrically opposing spray streams impacting head on, through which wall the gas stream passes. A further aspect of the present invention is an air-cleaning apparatus comprising a first section of gas straightening blades, a second section of solvent spray streams, a third section of a coalescing medium and a fourth section of moisture separators, characterised in that the spray streams of said second section are diametrically opposed to impact head on to form at least one substantially flat wall of finely atomised solvent, through which wall the air stream passes. Still another aspect of the present invention is a gas turbine having a particulate filter to remove contaminant particles from the inlet air, characterised in that, upstream or downstream of said filter, means are provided to contact the air with a stream of water at a rate and spray pattern sufficient to reduce contaminants present in the air, said stream being at least one substantially flat wall of finely atomised water formed by at least one pair of diametrically opposing spray streams impacting head on, through which wall the air stream passes. The present invention is primarily directed to cleaning air entering the inlet of a gas turbine. One objective of the present invention is to remove and reduce the contaminant level in air passing to the inlet of a gas turbine by contacting the air with water stream or streams to carry out a "scrubbing" action, i.e., removal of contaminants. "Contaminants" herein means particles and/or volatiles. The volatiles may be, for example, corrosive gases. The drawing is a top schematic view showing an air scrubber apparatus of the present invention. In a preferred embodiment of the present invention and with reference to the drawing, there is shown an air cleaning apparatus, generally indicated by numeral 10. The air cleaning apparatus 10, herein referred to as the air scrubber 10, comprises a first section of straightening blades 11, a second section of spray streams of water 12, a third section of a coalescing medium 13, and a fourth section of moisture separators 14, all sections preferably enclosed in a housing 15. The air scrubber 10 enhances the function of conventional inlet air filters which, if desired, can be installed prior to or after the air scrubber 10 to aid further in the removal of air contaminants from the air flow to the inlet of a gas turbine. Advantageously, the air scrubber 10 provides a water scrubbing stage, not present in conventional filters. If, for example, the air scrubber 10 is placed downstream of the filters, it can be used to wash the air of particles which pass through the filters or which shed from the filter media itself. The air scrubber 10 further washes the air of corrosive volatiles which will not be picked up or captured by a conventional particle filter. In carrying out the one embodiment of the process of the present invention, an air flow containing particulate contaminants and volatile contaminants therein passes through the straightening blades 11 to assure a uniform flow velocity. A uniform flow velocity is required to assure maximum water scrubbing in the water scrubbing section 12 next described. The average velocity of the air through the blades 11 may be, for example, in the range of from 800 feet (250 meters) per minute to 1500 feet (450 meters) per minute. However, the velocity at any one point measured downstream of the blades should be within 10% of the average velocity of the air passing through the blades. Straightening blades 11 for this application are commercially available from any number of vendors in the industrial air humidification industry such as Carrier Corp. of Syracuse, New York. After the contaminated air flow passes through the straightening blades 11, the contaminated air flow is intimately contacted with water sufficient for the water to dissolve contaminants therein, absorb volatiles therein, and/or catch particles therein. The air flow is contacted with water by passing the air flow through one or more scrubbing sections 12. The scrubbing sections 12 are made up of flat walls of finely atomized spray streams of water formed by opposing fine atomizing spray nozzles. More preferably, the atomized spray streams include atomized spray streams of water defining a plurality of flat walls of water made up of fine particles of water. The walls of water are formed by a system of nozzles which are located in pairs with each nozzle in a pair diametrically opposed, i.e., facing the other nozzle of that pair in mirror-like fashion, such that the two water streams impact head on. Nozzles which are used to form the water walls and which may be used in the present invention are manufactured by and available from, for example, Pneumafil Corporation of Charlotte, N.C. The spray density of the water in this stage is between 1 and 30 gallons per minute per square foot (50 and 1200 1/min/m²) of cross-section. At the required nozzle pressure of between 10 psig (70 kPa gauge) and 50 psig (350 kPa gauge), the required horsepower for pumping is between 0.1 and 1.0 hp/ft² (800 and 8000 W/m²). The water walls scrub the air as well as evaporatively cool the air. The contaminants present in the air are removed or extracted from the air by the water. For example, contaminants may be dissolved in the water, volatiles may be absorbed into the water, and/or particle contaminants may be caught by the water to reduce the contaminants from the air. The water containing contaminants falls to the bottom of the air scrubber 10 into a reservoir. Substantially all or a portion of the water may be recirculated through this stage with a circulating pump 16. The chemical components in the water may be carefully monitored with, for example, conventional conductivity probes. An automatic blowdown is carried out with valves according to a signal from the conductivity probes to assure optimum water chemistry. It is preferred that the chemistry of this water be maintained such that no contaminants will be reabsorbed into the air or carried over into the turbine to cause fouling. It is contemplated that the entrainment of organics and suspended solids from the air into the water will require additional blowdown based on water testing. In addition, it is contemplated that biological fouling may occur in the water requiring treatment of the water to remove or reduce such fouling, for example, by ozone or ultraviolet treatment of the water. After the air flow is passed through the scrubbing section 12, the air flow passes through a coalescing stage 13 in which fine water droplets in the air are agglomerated into larger particles to facilitate higher efficiency removal in the separator stage 14 next described. Coalescing pads are commercially available from any number of vendors in the air filtration industry such as Farr Company, Los Angeles, California. From the coalescing section 13, the air flow continues through a fourth section comprising blade moisture separators 14. The moisture separators 14 are designed to remove free moisture from the air so that droplets present in the air will not be carried into the turbine. The pressure drop in the coalescing section 13 and separating section 14 should be minimized such that the overall pressure drop of the air going through the scrubber 10 does not significantly reduce turbine output, while removing moisture down to a critical particle size of approximately less than 20 micrometers. Blade type moisture separators are commercially available from any number of vendors in the industrial air humidification industry such as Munters Corp., Ft. Myers, Florida. Generally, the inlet pressure drop of the air going through the scrubber 10 is less than 2 inches (50 mm) of water (500 Pa) and the power loss of the turbine should be less than 1 percent. Depending on the composition and size of contaminants in the incoming air, and the equipment operation, the apparatus of the present invention will reduce the contaminants in the incoming air by 10 percent to 100 percent. These contaminants are counted both upstream and downstream of the apparatus with, for example, conventional sophisticated laser type particle counters accurate down to 0.19 micrometers. In addition, contaminant removal may be determined by measuring the conductivity of a sample of air which is bubbled through a column of water. Ions typically removed from the air using the apparatus of the present invention include, but are not limited to, chloride, nitrate, sulfate, sodium, ammonium, potassium, magnesium, and calcium. While the apparatus of the present invention has been described with reference to gas turbines for air contaminant removal, it is contemplated that the apparatus could also be used for furnaces, reactors using air, air stripping separators, and other apparatus wherein contaminant removal from air or gases is desired. In addition, a selected solvent may be substituted for water and used for cleaning air or other gases or for recovering particulate in various process streams.

Claims: A process for removing particulate and volatile components from a gas stream selected from gaseous process streams and feed gas streams for a gas-using apparatus, comprising contacting the gas stream with a stream of solvent at a rate and spray pattern sufficient to remove particulate and volatile components present in the gas stream, characterised in that said solvent stream is at least one substantially flat wall of finely atomised solvent formed by at least one pair of diametrically opposing spray streams impacting head on, through which wall the gas stream passes. A process as claimed in Claim 1, wherein said solvent stream is a plurality of said substantially flat walls of finely atomized solvent. A process as claimed in any one of the preceding claims, wherein the solvent is water. A process as claimed in Claim 3, wherein the spray density of water is from 50 to 1200 1/min/m² (1 to 30 US gallons/min/ft²). A process as claimed in any one of the preceding claims, wherein the gas stream has a uniform flow velocity on contact with the solvent wall(s). A process as claimed in any one of the preceding claims, wherein a major portion of the solvent is recirculated. A process a claimed in any one of the preceding claims, wherein the gas stream is passed through a particulate filter upstream of the solvent wall(s). A process as claimed in any one of the preceding claims, wherein the cleaned gas stream is passed through a particulate filter downstream of the solvent wall(s). A process as claimed in any one of the preceding claims, further comprising the subsequent steps of forming fine droplets of solvent in the contacted gas stream into larger drops and separating the gas and said larger drops of solvent. A process as claimed in any one of the preceding claims, wherein the gas stream is feed air to an air-using apparatus. A process as claimed in Claim 10, wherein the solvent is water and the feed air is inlet air for a gas turbine. A process as claimed in Claim 10 or Claim 11, wherein the air is simultaneously cooled and humidified. A method of operating a gas turbine, characterised in that the inlet air is cleaned by a process as claimed in Claim 11. An assembly of a gas-using apparatus and an apparatus for removing particulate and volatile components from an gas feed thereto comprising means (12) for contacting the gas with a stream of solvent at a rate and spray pattern sufficient to remove particulate and volatile components in the gas, characterised in that said means (12) for contacting the gas forms at least one substantially flat wall of finely atomised solvent from at least one pair of diametrically opposing spray streams impacting head on, through which wall the gas stream passes. An assembly as claimed in Claim 14, further comprising means (13) for forming fine solvent droplets in the contacted gas stream into larger drops; and means (14) for separating the gas stream and said larger drops of solvent. An assembly as claimed in Claim 14 or Claim 15, wherein said gas-using apparatus is an air-using apparatus. An air-cleaning apparatus comprising a first section (11) of gas straightening blades, a second section (12) of solvent spray streams, a third section (13) of a coalescing medium and a fourth section (14) of moisture separators, characterised in that the spray streams of said second section (12) are diametrically opposed to impact head on to form at least one substantially flat wall of finely atomised solvent, through which wall the air stream passes. An assembly of an air-cleaning apparatus as claimed in Claim 17 and an air-using apparatus arranged to receive clean inlet air from said air-cleaning apparatus. An assembly as claimed in Claim 16 or Claim 18, wherein the air-using apparatus is a furnace. An assembly as claimed in Claim 16 or Claim 18, wherein the air-using apparatus is a reactor using air. An assembly as claimed in Claim 16 or Claim 18, wherein the air-using apparatus is an air stripping separator. An assembly as claimed in Claim 16 or Claim 18, wherein the air-using apparatus is a gas turbine. An assembly as claimed in Claim 16, wherein said air-using apparatus is a gas turbine having a particulate filter to remove contaminant particles from the inlet air, and said means (12) is provided, upstream or downstream of said filter. An assembly as claimed in Claim 23, wherein said filter is located upstream of said water wall(s).

Inventors: DONLE DAVID W, DONLE, DAVID W.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1989
Main classification: F02C7
IPC codes: B01D50, F02C7