Abstract:
A method for cleaning a number of turbine blades of a turbine under operation conditions by means of a cleaning fluid which is sprayed onto the turbine blades by a number of nozzles is disclosed. The method is characterised in that the cleaning fluid is distributed to the nozzles such that only a fraction of the nozzles is used at any one time to spray the cleaning fluid onto the turbine blades. Furthermore, a turbine comprising a number of rotor blades, a number of stator blades and a number of nozzles is described. Each nozzle is connected to a cleaning fluid supply. The turbine further comprises at least one distribution unit which is configured such that the cleaning fluid can be distributed to only a fraction of the nozzles at any one time. Moreover, a turbocharger comprising an inventive turbine is disclosed.

Description:
CROSS-REFERENCE TO RELATED U.S. APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT 
       [0003]    Not applicable. 
       REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC 
       [0004]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0005]    1. Field of the Invention 
         [0006]    The present invention relates to a method for cleaning turbine blades under operation conditions, a turbine and a turbocharger. 
         [0007]    2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98. 
         [0008]    Industrial diesel engines use a variety of fuels, including heavy fuel oil. Such lower grade fuels have many impurities which lead to the formation of ash and other compounds. Some of these are transported from the diesel engine exhaust manifold to the turbocharger turbine and may form a thick hard deposit on the turbine blades. Such deposits cause a reduction in turbocharger efficiency, a reduction in flow capacity of the turbine, and an increase in the engine combustion temperatures. If this build-up is allowed to grow unchecked, the engine power capacity will reduce and damage to hot engine components may ensue. Damage can also occur to the turbocharger components. 
         [0009]    To avoid the build-up of deposits, turbocharger turbines are fitted with a cleaning device. This can use solid particles, such as walnut shell fragments or rice, as a cleaning medium. In this case the cleaning mechanism uses the impact of the medium on the ashy deposit to dislodge the deposit. Such a “dry washing” device can be effective, but the actual cleaning medium is hard to control worldwide since, for instance, walnut shells may not be available in many countries. Moreover, the size of rice grains may determine how much rice is used and for how long. Also the cleaning medium generally causes some damage of the turbine blades themselves, so turbocharger components have to be changed regularly. 
         [0010]    The main cleaning medium used in the industry is water. This is generally available at all staffed sites, is easy to specify and to control. The mechanism by which water cleans the hard ashy deposit is not entirely clear, however it is viewed as a combination of dissolving some of the compounds, providing an impact of water droplets to dislodge ashy particles and cracking the deposit by providing a thermal shock. 
         [0011]    The method of use of water as a cleaning medium is well-known in the industry. For instance, in U.S. Pat. No. 5,944,483 and U.S. Pat. No. 5,938,402 methods and devices for cleaning of the nozzle ring of a turbocharger turbine are disclosed. In U.S. Pat. No. 5,938,402 the cleaning device includes only one nozzle for injecting a cleaning agent into the exhaust gas flow. In U.S. Pat. No. 5,944,483 a method is described, wherein a cleaning cycle is activated which runs automatically. In the cleaning cycle the water is briefly injected repeatedly into the region upstream of the nozzle ring and an injection pause for reheating the nozzle ring is maintained between the injection operations. The configuration of the used gas-inlet casing enables the water to be injected into the region directly upstream of the nozzle ring. 
         [0012]    Typically one or a multiplicity of nozzles, usually three, are used which cause the water to form a spray. The spray nozzles are configured so that the spray forms a fan which causes a single nozzle to wash a multiplicity of turbine blades. The spray nozzles have to be placed far enough upstream of the blades so that the largest number of turbine blades is cleaned by the fewest number of nozzles. This means that the flow rate of water is kept to a minimum. The injection of large quantities of cold water into the turbocharger turbine reduces the power capacity of the turbine which in turn reduces the turbocharger boost. The turbocharger may possibly stall or the engine control system, trying to maintain a constant engine power, will increase the fuel supply and increase the engine combustion temperatures. 
         [0013]    Since water injection nozzles are placed upstream of the blades, the droplets of water evaporate in the hot turbine gas stream and their effectiveness as a cleaning medium is reduced. It is found that water droplets have to strike the turbine blades to be effective, rather than allowing steam to reach the blades. To allow effective cleaning, the engine load is reduced while cleaning is performed. This means that the turbine inlet gas stream is cooler, which causes reduced droplet evaporation, and slower, which allows a wider spray fan than it would be at full engine load. The water flow rate and supply pressure, the position of the nozzles and the engine load during washing have to be specified to ensure an effective cleaning process. Typically an engine load of 20% is specified. 
         [0014]    Particularly for power station applications, which are increasingly using low-grade fuel, there are strong economic arguments to avoid washing at low loads. Every minute not generating power at full load causes a reduction in revenue. This can cause pressure on the operators to wash less frequently than necessary and consequently may cause damage and an impression of unreliability of the engine and turbo-charger. There is therefore an urgent need for a reliable method for cleaning turbines which is not intrusive on the operation of the engine and can be performed at high engine loads. 
         [0015]    It is thus an objective of the present invention to provide an advantageous method for cleaning turbine blades of a turbine under operation conditions. It is a second objective to provide an improved turbine. A last objective is to provide an improved turbocharger. 
       BRIEF SUMMARY OF THE INVENTION 
       [0016]    The first objective is solved by a method for cleaning a number of turbine blades of a turbine under operation conditions as claimed in claim  1 . The second objective is solved by a turbine as claimed in claim  13 , and the third objective is solved by a turbocharger as claimed in claim  28 . The depending claims define further developments of the invention. 
         [0017]    The inventive method for cleaning a number of turbine blades of a turbine under operation conditions by means of a cleaning fluid which is sprayed onto the turbine blades by a number of nozzles is characterized in that the cleaning fluid is distributed to the nozzles such that only a fraction of the nozzles are used at any one time to spray the cleaning fluid onto the turbine blades. The turbine blades to be cleaned are preferably turbine stator blades since the flow passage between stator blades may be constricted by ashy deposit, if the deposit is not removed. However, turbine rotor blades, on which ashy may also be present but to a lesser degree than on the turbine stator blades, can be cleaned, as well. 
         [0018]    Preferably the cleaning fluid is distributed to the nozzles such that only one nozzle is used at any one time. By washing with only a fraction of the nozzles or only one nozzle at a time, the water flow rate is kept to a minimum and the thermodynamic effect on the engine during washing is also minimized. This offers the possibility to install a washing cycle in which different sections of the turbine blades or turbine blades of different sections of the turbine are washed sequentially. Hence, the respective actual thermodynamic load to the turbine due to the cleaning process at any time is reduced to the fraction which corresponds to the fraction of the actual cleaned blades to the total number of blades or to the fraction of the actually cleaned surface of a blade to the total surface of the blade. With the reduced load it becomes possible to clean while the turbine is running at full load. Since the cleaning can be done at full load a possible lengthening of the duration for fully cleaning all turbine blades is of no severe consequence. 
         [0019]    The cleaning fluid can, for example, be distributed by means of a distributor valve. The distributor valve can be driven by compressed air. 
         [0020]    The cleaning fluid can advantageously be led for a specified time to each of the nozzles in turn. Each of the nozzles can be connected to a water distributor valve whereby water can be allowed to flow down a particular nozzle while the other nozzles have no water flow. In operation, high pressure water may be supplied to the water distributor valve, and a control mechanism may ensure that water is piped for a specified time to each of the nozzles in turn. 
         [0021]    Preferably water can be used as cleaning fluid, especially high pressure water. Moreover, a chemical cleaning agent can be added to the cleaning fluid to increase the fluid&#39;s cleaning performance. 
         [0022]    Furthermore, each nozzle may be flushed out in turn by means of compressed air. For example, the unused nozzles can be supplied with clean high pressure air to ensure that they remain unblocked by the ashy deposit. Flushing out each nozzle in turn by compressed air increases the efficiency of the turbine and the turbocharger compared with continuously flowing of compressed air through each nozzle. 
         [0023]    The cleaning fluid flow can be controlled by a control means depending on the speed of the turbine and/or the temperature of the turbine and/or the elapsed time since the previous cleaning. The control means can especially be activated by a control system. For example, the cleaning may be started when the turbine speed has increased by more than 1.5% over a reference speed recorded at full engine load. Moreover, the control means can react to changes in the turbocharger speed at a given load. The control means can be related to engine temperatures in a similar way. It can be activated by an engine control system, related to turbocharger speed, engine temperature, or elapsed time since last clean. 
         [0024]    The inventive turbine comprises a number of rotor blades, a number of stator blades and a number of nozzles. Each nozzle is connected to a cleaning fluid supply. This may be realized either by a common cleaning fluid supply for all nozzles or a number of cleaning fluid supplies where each supply supplies one single nozzle or a subdivision of nozzles of the number of nozzles. The turbine further comprises at least one distribution unit which is designed such that the cleaning fluid can be distributed to only a fraction of the nozzle at any one time. 
         [0025]    The turbine may comprise at least one distributor valve which is placed between the nozzles and the cleaning fluid supply such that the cleaning fluid can be distributed to only a fraction of the nozzle at any one time. Preferably the nozzles are placed in the casing close to the turbine blades in upstream direction. Each nozzle can be designed to form a spray which impacts a small number of turbine blades under high engine load conditions. The nozzles should be placed in a close distance to the blades so that the droplets do not evaporate under high load conditions, and there is a larger number of nozzles since the spray fan is narrower than in standard configurations, yet in total each of the turbine blades must be impacted by water droplets. 
         [0026]    Preferably each of the nozzles is connected to a separate distributor valve. The distributor valve can be driven by compressed air. 
         [0027]    The ratio between the number of nozzles and the number of rotor blades and/or the ratio between the number of nozzles and the number of stator blades may be between 1:1 and 1:6. Advantageously the ratio between the number of the nozzles and the number of rotor blades and/or the ratio between the number of nozzles and the number of stator blades is between 1:2 and 1:4. Preferably the ratio between the number of the nozzles and the number of rotor blades and/or the ratio between the number of nozzles and the number of stator blades is 1:2. For example, the turbine may comprise a turbine row with 24 turbine blades. In this case the turbine may, for instance, comprise between 8 and, advantageously, 12 nozzles. 
         [0028]    The cleaning fluid may be water, preferably high pressure water. Advantageously the cleaning fluid can comprise a chemical cleaning agent to aid the cleaning of the turbine blades. 
         [0029]    The nozzles can be connected to a compressed air supply. The compressed air can be used in the same way as the water while the washing system is not used. For example the compressed air may flush out each nozzle in turn rather than continuously flowing through each nozzle. This increases the turbocharger efficiency. 
         [0030]    The distribution unit may be connected to a control means for controlling it depending on the speed of the turbine and/or the temperature of the turbine and/or the elapsed time since the previous cleaning. The turbine can further comprise a control means which ensures that the cleaning fluid is led for a specified time to each of the nozzles in turn so as to perform a repeating cleaning cycle. The control means can be connected to a control system for activating the control means. 
         [0031]    The turbine may comprise a number of stator blades and a number of rotor blades. The ashy deposit, which is wanted to clean away, is mainly found on the stator blades. The flow passages between some of the stator blades may become entirely blocked. The rotor blades also can become fouled by the same deposit, although the degree of fouling is usually much less. The present invention can preferably be used to clean the stator blades. 
         [0032]    The inventive turbocharger comprises an inventive turbine as previously described. The turbocharger may comprise an axial turbine or a radial turbine. The turbocharger turbine can especially comprise at least one row of stationary blades and at least one row of rotating blades. 
         [0033]    The invention allows the turbine and the turbocharger turbine, especially the stator blades of the turbine, to be washed at full load and the cleaning process has little or no effect on the engine operation. This is achieved by using a distribution unit which makes sure that only a fraction of the nozzles or only one nozzle is used at any one time. The consequence is that a low flow rate of cleaning fluid, for instance water, is used despite the increase in the number of washing nozzles. Furthermore, the turbine blades are cleaned effectively and this can be done at full engine load conditions. The increased cost of the water washing system, i.e. extra nozzles, extra piping, distributor valve, and control system, is economically viable since the engine operator can sell more power and the engine and the turbocharger are more reliable. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0034]    Further features, properties, and advantages of the present invention will become clear from the following description of an embodiment in conjunction with the accompanying drawings. 
           [0035]      FIG. 1  schematically shows a turbocharger in a sectional view. 
           [0036]      FIG. 2  schematically shows part of an inventive turbine in a sectional view. 
           [0037]      FIG. 3  schematically shows a possibility as to how to connect the nozzles to a water supply and to a compressed air supply. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0038]    An embodiment of the present invention will now be described with reference to  FIGS. 1 to 3 . 
         [0039]      FIG. 1  schematically shows a turbocharger in a sectional view. The turbocharger comprises a turbine  11  and a compressor  10 . The turbine  11  and the compressor  10  are connected by a shaft  20 . 
         [0040]    The turbine  11  includes a rotor  4  which is located inside a turbine casing  3 . The turbine casing  3  has an exhaust inlet  5  which leads to the rotor  4  so that the exhaust entering the exhaust inlet  5  activates the rotor  4 . Further the turbine casing  3  has an exhaust outlet  6  through which the exhaust coming from the rotor  4  leaves the turbine casing  3 . The arrows  18  indicate the exhaust stream entering the turbine casing  3  through the exhaust inlet  5 , activating the rotor  4  and leaving the turbine casing  3  through the exhaust outlet  6 . 
         [0041]    The compressor  10  includes an impeller  12  which is located inside a compressor casing  1 . Moreover, the compressor  10  has an air inlet  7  which air leads to the impeller  12  and an air outlet  8  through which the air coming from the impeller  12  leaves the compressor casing  1 . The arrows  19  indicate the air stream entering the compressor casing  1  through the air inlet  7 , being compressed by the impeller  12  and leaving the compressor casing  1  through the air outlet  8 . 
         [0042]    The impeller  12  comprises a hub  2  and vanes  9 . The hub  2  is connected to the shaft  20 . Further, the hub  2  is generally conical in shape and a plurality of circumferentially spaced arcuate vanes  9  are formed about its periphery. 
         [0043]    The rotor  4  of the turbine  11 , which comprises a number of turbine rotor blades  13  and a number of turbine stator blades  28 , is connected to the shaft  20  so that the activated rotor  4  activates the shaft  20 . The shaft  20  is further connected to the impeller  12  inside the compressor  10 . Hence, the rotor  4  activates the impeller  12  by means of the shaft  20 . The rotation axis of the rotor  4  is indicated by reference numeral  17 . 
         [0044]    In operation of the turbine  11  the exhaust stream  18  entering the exhaust inlet  5  activates the rotor  4  and leaves the turbine through the exhaust outlet  6 . The arrows  18  indicate the direction of the exhaust stream. Meanwhile, the impeller  12  in the compressor  10  driven by the rotor  4  sucks atmospherically fresh air into the air inlet  7  and compresses it to precompressed fresh air, which enters the air outlet  8 . The compressed air is then used for example in a reciprocating engine like e.g. a diesel engine. The arrows  19  indicate the air stream direction. 
         [0045]      FIG. 2  schematically shows part of an inventive turbine  11  in a sectional view. In  FIGS. 1 and 2  a radial turbine is shown, because the exhaust stream  18  enters the turbine in radial direction with respect to the rotation axis  17 . Instead of a radial turbine also an axial turbine can be used, where the exhaust stream enters the turbine in axial direction with respect to the rotation axis. Regarding the construction of an axial turbine it is referred to U.S. Pat. No. 5,944,483, where an example for an axial turbine is described. 
         [0046]    The inventive turbine  11 , which is shown in  FIG. 2 , comprises a number of nozzles  14  which are located inside the turbine casing  3  and which protrude into the exhaust inlet  5 . Instead of protruding into the exhaust inlet  5  the nozzles  14  can flush with the inner surface of the exhaust inlet  5 . The nozzles  14  are located close to the turbine stator blades  28  in upstream direction. Each nozzle  14  is connected to a flow channel  16  via a distribution unit, which is a distributor valve  15  in the present embodiment. However, each of the nozzles  14  can be also connected to a respective separate distributor valve  15 . Alternatively, two or more nozzles  14  can be connected to the same distributor valve  15 . The use of only one nozzle  14  or only a fraction of the nozzles  14  at any one time makes it possible to clean the turbine blades  13 ,  28  under high load conditions. The distributor valve(s)  15  can, for example, be driven by compressed air. 
         [0047]    A cleaning fluid is led through the flow channel  16  to the nozzles  14  where it is sprayed into the exhaust inlet. The cleaning fluid can be sprayed into the exhaust inlet  5  in the direction of the exhaust stream  18  or perpendicular to the direction of the exhaust stream  18 . The cleaning fluid, which is sprayed into the exhaust inlet  5 , impinges mainly on the turbine stator blades  28  but also on the turbine rotor blades  13  and cleans the blades  13 ,  28 , in particular the stator blades  28 . 
         [0048]    The cleaning fluid can, for example, be water  21 , as in the present embodiment, or any other suitable cleaning liquid. Especially high pressure water can be used as cleaning fluid. Moreover, a chemical cleaning agent can be added to the cleaning fluid to aid cleaning the turbine blades  13 . 
         [0049]    Generally, the ratio between the number of nozzles  14  and the number of rotor blades  13  and/or the ratio between the number of nozzles  14  and the number of stator blades  28  maybe between 1:1 and 1:6, preferably 1:2. In the present embodiment, the turbine  11  comprises a turbine row with 24 turbine stator blades  28  and 12 nozzles  14 . 
         [0050]      FIG. 3  schematically shows an example for a connection between a number of nozzles  14  to a water supply  24  and to a compressed air supply  25 .  FIG. 3  exemplary shows three nozzles  14   a ,  14   b ,  14   c . Each nozzle  14   a ,  14   b ,  14   c  is connected to a flow channel  26  which is connected to a compressed air supply  25 . Moreover, each nozzle  14   a ,  14   b ,  14   c  is connected to a flow channel  16  which is connected to a water supply  24 . Between each nozzle  14   a ,  14   b ,  14   c  and the respective flow channels  16 ,  26  a distributor valve  15   a ,  15   b ,  15   c  is located. The distributor valves  15   a ,  15   b ,  15   c  are each formed such that the nozzles  14   a ,  14   b ,  14   c  can be provided with compressed air or water. Each of the valves  14   a ,  14   b ,  14   c  is further connected to a control means  23  by leads  27   a ,  27   b ,  27   c.    
         [0051]    The distributor valves  15   a ,  15   b ,  15   c  can be controlled by the control means  23  depending on the speed of the turbine  11  and/or the temperature of the turbine  11  and/or the elapsed time since the previous cleaning. The control means  23  can, for instance, react to changes in the speed of the turbocharger at a given load. For example, if the turbocharger speed has increased by more than 1.5% over a reference level recorded at full engine load, the washing cycle can begin. 
         [0052]    Alternatively or additionally the control means  23  can be related to the engine temperatures in a similar way. Moreover, the control means  23  can be activated by an engine control system, related to turbocharger speed, engine temperature, or elapsed time since last clean. 
         [0053]    The washing cycle or cleaning cycle can be performed such that only a first nozzle  14   a  sprays water into the exhaust inlet  5  for a specified time. Then the valve  15   a  of the first nozzle  14   a  is closed and only a second nozzle  14   b  sprays water into the exhaust inlet for a specified time. Then the valve  15   b  of the second nozzle  14   b  is closed and only a third nozzle  14   c  sprays water into the exhaust inlet  5  for a specified time, and so forth. It is also possible that two or more nozzles  14  spray water into the exhaust inlet  5  at the same time. In the case that two nozzles  14  are in operation at the same time it is advantageous if these nozzles  14  are located opposite to each other related to the rotation axis  17 . 
         [0054]    The nozzles  14   a ,  14   b ,  14   c  in  FIG. 3  are further connected to a compressed air supply  25 . This allows for flushing out each nozzle  14   a ,  14   b ,  14   c  in turn by means of compressed air. In  FIG. 3  the nozzle  14   a  sprays water  21  into the exhaust inlet  5 , the nozzle  14   b  is flushed out by air  22 , and the nozzle  14   c  is not in operation. This means that the valve  15   c  is completely closed, while the valve  15   b  is closed in regard to the flow channel  16  which is connected to the water supply  24  and open in regard to the flow channel  26  which is connected to compressed air supply  25 . At the same time the valve  15   a  is closed in regard to the flow channel  26  which is connected to the compressed air supply  25  and open in regard the flow channel  16  which is connected to the water supply  24 . 
         [0055]    The distributor valves  15  are used so that only one nozzle  14  or only a fraction of the nozzles  14  is in use at any one time. Thus, a low flow rate of water is used despite the increase in the number of nozzles  14  compared to the state of the art. Moreover, all turbine blades  13 ,  28  can effectively be cleaned at full engine load conditions.