Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
  • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
  • B03C3/017—Combinations of electrostatic separation with other processes, not otherwise provided for
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D50/00—Combinations of methods or devices for separating particles from gases or vapours
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02C—GAS-TURBINE PLANTS; AIR INTAKES FOR JET-PROPULSION PLANTS; CONTROLLING FUEL SUPPLY IN AIR-BREATHING JET-PROPULSION PLANTS
  • F02C7/00—Features, components parts, details or accessories, not provided for in, or of interest apart form groups F02C1/00 - F02C6/00; Air intakes for jet-propulsion plants
  • F02C7/04—Air intakes for gas-turbine plants or jet-propulsion plants
  • F02C7/05—Air intakes for gas-turbine plants or jet-propulsion plants having provisions for obviating the penetration of damaging objects or particles
  • F02C7/052—Air intakes for gas-turbine plants or jet-propulsion plants having provisions for obviating the penetration of damaging objects or particles with dust-separation devices

Definitions

• the present invention relates to a method according to the preamble of claim 1 for cleaning the intake air to gas turbine equipment employed in electric power genera ⁇ tion.
• the method also concerns an arrangement suited for imple- menting the method.
• the intake air to the compressor section of a gas tur ⁇ bine that is, the combustion air of the turbine is cleaned with the help of mechanical fiber filters.
• the purpose of intake air filtration is to obstruct the entry of abrasive and contaminating particles into the com ⁇ pressor and the turbine, thus preventing the wear of equipment and reducing the need for cleaning and mainte ⁇ nance.
• large gas turbines employed in electric power generation also require extremely large amounts of combustion air, very small concentrations of contaminat ⁇ ing particulates result in heavy internal build-up of dirt in the equipment during running, which means that the filtration of the combustion air should be as effec- tive as possible.
• the design value of filtration efficiency will always be a compromise dictated by local circumstances.
• Such output power reduction is caused by a number of different factors including wear due to the particles, inefficiency of methods used for internal cleaning of equipment leading to gradual accu ⁇ mulation of dirt and extra wear due to such cleaning as well as increase of tolerances in seals resulting in higher leak rates. Even the smallest degradation of output power over the service life of the equipment causes significant economic losses. Also the efficiency of the turbine degrades with the internal dirt build-up, which necessitates cleaning of the compressor and the turbine at scheduled intervals. Cleaning is carried out by washing with water complemented with different kinds of crushed material. Such water wash in particular is hampered by freezing under low-temperature conditions. Extra operating costs associated with dirt build-up in equipment are traceable to increased fuel consumption, loss of output power capacity and compressor cleaning costs.
• the goal of the invention is achieved by complementing the mechanical filtration of intake air with at least one electrostatic filtering stage an a stage in which the electrical properties of particles suspended in the air are improved electrically or chemically.
• the invention offers significant benefits.
• Electrostatic precipitation methods have not been used in the prior art for cleaning large-volume air flows, because conventional filtering would have required such a high electric power to be expended for charging the suspended particles that the cost-efficiency of filtration would have been lost.
• electrostatic precipita ⁇ tion may advantageously be used, because essentially lower charging voltages can then be used in such a com ⁇ bination without compromising a good degree of separa- tion.
• the pressure losses of filtration may be reduced and mechanical filtration can be implemented using a filter of a lower degree of separation, whereby the pressure drop over the filter is smaller and the fouling rate of the filter in use is lowered, which permits less frequent replacement of the filters. Resultingly, process shutdowns and replacement costs of filters are reduced.
• the filtration arrangement may also be designed so that the system comprises a partially or entirely duplicated parallel filter system, whereby maintenance of the filtration system may be performed off-line, while the power generating system is run continuously.
• the electro- static stage achieves separation of smaller particles from the intake air than is possible with conventional filtration methods, whereby the total mass of contaminating particles passing through the filter is reduced essentially. Such improvement in filtration effi- ciency is truly significant as if a relative value of
• a relative value as good as 50 is attained by combining mechanical coarse filtration with two stages of filtration based on electrostatic methods.
• the intake air consumption of a gas turbine may easily be as high as 120 rnVs, it is obvious that the intake air flow carries along a great quantity of con ⁇ taminating particles that must be removed.
• An electrostatic precipitator is an apparatus comprising planar parallel plates connencted to a voltage source.
• One type electrostatic fiber filter is a filter comprising electrically charged fibers which have a permanent electric polarization.
• the fibers or a porous filtering media is not permanently charged but an active electric fied is used to activate the filter. All these types of apparatuses are commonly called electric filters.
• the filter arrangement shown therein comprises a mechanical fiber filter 1, an elec ⁇ trostatic precipitator 3 having corona wires 2 in the front of the unit and followed by an electrostatic fibre filter 4.
• the filter arrangement also incorporates a framework 5 to which the filter units are attached.
• the farmeworm is shown herein only diagrammatically.
• the mechanical filter 1 comprises a fiber layer, wherein the fibers may be formed to a fabric.
• the fiber layer is permeable to the air flow, and when and during the passage a portion of the suspended particles passing through the fiber layer adhere thereto.
• the mechanical filter 1 is followed by two more filtering stages, its filtering separation capability need not extend down to the smallest particles, whereby a filter 1 of lower separation capability and higher air permeability can be used.
• the function of the mechanical filter l is to separate a major portion of the total mass of contaminating particles thus protecting the subsequent filter stages.
• corona wires 2 Following the mechanical filter 1 in the filter arrange ⁇ ment are adapted corona wires 2. These wires 2 are taken to a high DC voltage so that an electric field is created around the wires.
• the purpose of the corona wires 2 is to charge the passing particles.
• the corona wires are fol ⁇ lowed by an electrostatic precipitator 3 comprising planar, parallel oriented plates disposed at a short distance from each other. Also these plates are taken to a DC high-voltage supply, whereby an electric field is created between the plates.
• such a filter When properly operated, such a filter is capable of separating at least more than 80 %, under favourable conditions even more than 90 %, of the suspended particles having a size in the range 0.1 - 1 urn. An even better degree of separation can be attained for particul- ates of larger size.
• the principal operating parameters of such a precipitator are the corona wire current, collecting current applied to the plates, and in particular, the air stream velocity which may not be so high that the adhesion of the particulates to the plates would be impaired.
• the electrostatic precipitator 3 is followed by an electrostatic fiber filter 4.
• a filter 4 is comprised of fibers which are charged so as to hold a permanent electric charge such that the fibers are polarized. Therefore, this kind of filter requires no external power supply and have an extremely simple structure.
• the electrostatic fiber filter is given a pleated form so that the mouths of the pleats are oriented to face the impinging air flow.
• the electrostatic fiber filter 4 is placed as the last filter element along the path of the air flow, because due to the relatively high price of such a filter, its replacement costs represent a substantial investment, and on the other hand, under adverse operating conditions, the efficiency of electrostatic fiber filters may be lost very rapidly.
• the optimum use of this filter type is in the separation of the smallest particulates representing a small quantity of contaminating dirt mass.
• the present invention may have alternate embodiments.
• the intake air flow is taken first through such a filter that is capable of separating the major portion of particulates from the air, thus protecting the successive filtering stages intended for separating the particulates of smaller size against damage by overload or premature clogging.
• the first filtering stage is advantageously a coarse mechanical filter or an electrostatic precipitator.
• One alternative for a filter to be used in the first or successive filtering stage is electrostatic fiber filter based on an active electric field that polarizes both the particles as well as the filter media comprised of fibers or porous material.
• Such a filter must be provided with corona wires or similar elements such as chemical means or charging plates for charging the particles suspended in the air prior to their passage toward the actual filter element.
• a cyclone separator may be combined with the arrangement according to the invention, the cyclone is arranged before the mechanical filtering stage and if some kind of electric filtration is performed before the mechanical filtration, before that stage also.
• the number of filter units and their mutual order may be varied provided that the filter arrangement comprises at least one mechanical filter and, placed after the mechanical filter, an electric filter capable of separating small suspended particles that have passed the mechanical filter. If an electric fiber filter is used, it must be located as the last unit due to its susceptibility to damage.
• the filter arrangement according to the above-described embodiment has been found the most advantageous combination in practice.
• the filter arrangement must be dimensioned so that the pressure loss over it will not exceed that of conventional filter arrangements. In most cases it is even possible to lower the pressure loss below conventional values.
• the design of the filters and the entire filter arrangement may be varied flexibly.
• An important accessory in the filter system comprises the different cleaning means of which the most important is the washing apparatus of the electrostatic precipitator. Such means makes it possible to lengthen the maintenance interval of the filter arrangement. Additional improvement to the operating reliability can be imparted by providing heater elements for heating filter insulations of the electrostatic percipitator and by partially duplicating the filter system.
• one electrostatic stage may receive air selected to pass through one of two parallel mechanical coarse filters, for instance, whereby the replacement of the mechanical filters will be easier.
• the filter system is provided with a plate-type electrostatic precipitator, the filter system achieves a high availability as the washing of the percipitator plates may be readily automated.
• the system may also comprise two parallal mechanical filters, two parallel electrostatic percipitators and one common electrostatic fiber filter.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Electrostatic Separation (AREA)

Applications Claiming Priority (3)

Publications (1)

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Family Applications (1)

Country Status (6)

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• 1995
  • 1995-02-09 FI FI950576A patent/FI101318B1/fi not_active IP Right Cessation
• 1996
  • 1996-01-12 CN CN 96191843 patent/CN1173908A/zh active Pending
  • 1996-01-12 JP JP8524015A patent/JPH11501096A/ja active Pending
  • 1996-01-12 EP EP96900619A patent/EP0808417A1/en not_active Withdrawn
  • 1996-01-12 WO PCT/FI1996/000027 patent/WO1996024760A1/en not_active Application Discontinuation
  • 1996-01-12 AU AU44500/96A patent/AU4450096A/en not_active Abandoned

Non-Patent Citations (1)

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