Patent Publication Number: US-2009217888-A1

Title: Apparatus for the cleaning of high-pressure boilers

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application is a Continuation of International Patent Application No. PCT/EP2007/058938 filed on Aug. 28, 2007, entitled, “DEVICE FOR CLEANING HIGH PRESSURE TANKS”, the contents and teachings of which are hereby incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an apparatus for the cleaning of a boiler by means of a cleaning fluid, with at least one cleaning appliance which comprises means for aligning a fluid distributor device with inner regions of the boiler. Particular consideration is given, in this context, to boilers which are intended for the treatment of a gas at high pressure and high temperature. Such boilers serve, for example, as heat exchangers for coal gasification plants. 
     BACKGROUND 
     Coal gasification is understood as series of methods for coal conversion, in which ground coal is reacted with steam and oxygen at temperatures of 650° C. to 2000° C. and at pressures of up to 100 bar. Depending on the method, synthesis gases are obtained, having different fractions of hydrogen, carbon monoxide and methane. This synthesis gas serves, for example, as an initial substance for the chemical industry, but it is also possible, for example in the case of high methane fractions, that the synthesis gas is employed as a natural gas substitute. 
     Recently, however, there has been the desire, under some circumstances, to burn other substances in addition to lignite, hard coal, peat, wood and sewage sludge. There is therefore also a need, for example, to gasify heavy oils or similar materials when this is appropriate. 
     After gasification, the synthesis gas or crude gas is cooled in at least one heat exchanger. In this case, if appropriate, additional fluids (vapor, gases, etc.) may be added, but this is not absolutely necessary. Care must be taken, however, to ensure that this synthesis gas or crude gas, when it enters such a heat exchanger, for example of the type of a tube-bundle heat exchanger, still always has temperatures markedly above 1000° C., for example of approximately 1400° C. In this case, if appropriate, even pressures in the region of 50 bar or above are maintained in the heat exchanger boiler. 
     In conventional coal gasification plants, appreciable contamination of the heat exchange surfaces did not occur, and therefore, for example, an average run time (operation without interruption) of more than nine weeks could be implemented. In the stoppage times, the contamination was then either knocked off or removed by means of a gaseous blasting medium. 
     SUMMARY 
     In view of the changing combustion conditions, however, markedly higher contamination levels are to be expected, which sometimes also adhere very firmly and consequently have properties which obstruct heat exchange. To ensure a sufficiently long run time for such a plant, therefore, it is desirable to make a subsequent cleaning possible here while the boilers are in operation. 
     Therefore, the object of the present invention is at least partially to solve the problems outlined with regard to the prior art. In particular, apparatuses and methods are to be specified which, even under the abovementioned ambient conditions inside such a boiler, ensure an, if appropriate, selective, effective cleaning of the heat exchange surfaces during operation. Moreover, the apparatuses and methods are to be capable of being employed as flexibly as possible. This applies particularly to a heat exchanger which directly follows such a coal gasifier (“syngas cooler”). 
     These problems are solved by means of an apparatus according to the features of patent claim  1 , a plant according to the features of patent claim  6  and a method according to the features of patent claim  11 . Advantageous configurations of the invention are specified in the in each case dependently formulated patent claims. It should be pointed out that the features listed individually in the patent claims may be combined with one another in any desired technologically expedient way and indicate further configurations of the invention. Furthermore, particularly preferred embodiments of the invention are also specified in the description and in the figure description. 
     The apparatus according to the invention for the cleaning of a boiler by means of a cleaning fluid, with at least one cleaning appliance which comprises means for aligning a fluid distribution to inner regions of the boiler, has at least one cleaning appliance which is surrounded by a container and which is mountable onto a connecting nipple of the boiler by means of at least one connection piece. 
     With regard to the cleaning appliance, it is preferred that the means for alignment can cause pivoting, movement and/or rotation of the fluid distribution device, if appropriate also positioning adjacently to various inner regions of the boiler. Thus, the fluid distribution device may be designed, for example, as a type of water, steam and/or gas lance, in particular with a nozzle, which can discharge a directed jet of the cleaning fluid. The means for alignment in this case allow a relative movement with respect to the boiler or to its inner regions, so that, if appropriate, various inner regions can be sprayed with the cleaning fluid. 
     In this case, then, it is proposed that the at least one cleaning appliance be surrounded by a preferably gas-tight container. The meaning of container is in particular a container, in the inner space of which pressures (markedly above atmospheric pressure) can be maintained, which, in particular, still lie above the (if appropriate, even maximum) operating pressure inside the boiler. Such a pressure container may be produced, for example, from high-strength steel. The components, such as, for example, the cleaning appliances, parts of the fluid distribution device and the like, which are positioned inside the container, then, are positioned essentially in it while, if appropriate, drive, monitoring and sensor components and the like are routed, pressure-tight, outwardly. The accesses to this container are all designed with a high-pressure seal. 
     This container or pressure container has at least one connection piece which can be mounted (likewise pressure-tight) on a connecting nipple of the boiler. Particularly preferably, this connection piece is designed in the manner of a tubular attachment on the container, so that the projecting connection piece can easily be positioned with respect to the connecting nipple of the boiler. The connection piece may be designed with connecting elements, so that it can be aligned exactly in position with the connecting nipple. 
     A configuration variant is preferred in which only exactly one cleaning appliance is provided. In this case, it is also preferable that only one connection piece is present. Nevertheless, for example, a plurality of connection pieces may be provided, for example in order to realize a plurality of connections with the boiler simultaneously or so that different connection variants or connecting nipples of the boiler can be contacted with an exact fit. In the last-mentioned case, the connection pieces are provided with a closing-off seal so that only the connection piece just being used is open. 
     With the cleaning appliance being encased by the pressurized container, it becomes possible, even while the boiler is operating at high pressures, for a connection between the cleaning appliance and the interior of the boiler to be possible, so that the cleaning fluid can be administered to inner regions of the boiler. The result of this, then, is that there is no longer any need for separate stoppage times of the boiler in order to allow cleaning of the heating surfaces or other inner wall regions of the boiler. 
     Particularly preferably, the apparatus is provided as a construction kit, in which case the container having different reception structures may be provided, in order, if appropriate, to include a plurality of cleaning appliances and/or cleaning appliances different from one another. 
     According to a further configuration variant of the apparatus, it is also proposed that the latter is connectable to a pressure increasing plant, by means of which the pressure in the container can be varied. The pressure increasing plant comprises, in particular, a gas supply device, if appropriate also a gas blow-off device. By means of the pressure increasing plant, therefore, it is possible, in particular, to introduce a gas, in particular what is known as a scavenging gas, into the container, in order to increase the pressure there. What may be considered as scavenging gas is, for example, nitrogen, but it is also possible to introduce other gases, for example those which are also present in the boiler, into the pressure container. For this purpose, the pressure increasing plant may be connected to the container, in particular by means of a pressure line and, if appropriate, by means of a pressure sensor. 
     Furthermore, it is also proposed, that the fluid distribution device be designed to be movable or pivotable at least through the at least one connection piece. The design variant is particularly preferred in which the fluid distribution device both can be moved through the connection piece and is additionally also designed to be pivotable or even additionally also rotatable. To that extent, in particular, means are provided which allow a relative movement of at least a subcomponent of the fluid distribution device through the at least one connection piece. In the event of a plurality of connection pieces being provided, positioning means are also provided which first align the fluid distribution device with the connection piece desired in each case and then lead said fluid distribution device at least partially through the latter. In particular, parts of the cleaning fluid line, of the fluid lance (for example a heavy tube-like component with an extent of at least one meter) and/or of the nozzle may in this case be moved through the connection piece. Most particularly preferred is a subcomponent of the fluid distribution device can then be moved through the connection piece only when the connection piece makes essentially a vertical connection to the boiler, such that the fluid distribution device can be introduced vertically from above into the boiler as a result of gravitation. A pivoting of the fluid distribution device is preferred when the fluid distribution device is introduced through an essentially horizontal connection via the connection piece into inner regions of the boiler. 
     Furthermore, it is considered to be advantageous that the fluid distribution device comprises a flexible hose which can be arranged on a hose drum, and the hose drum is provided in the container. In this configuration, the fluid distribution device comprises, for example, a nozzle which can penetrate vertically in the direction of the boiler and which is arranged on a flexible hose (for example a metal hose) which withstands the temperatures and pressures. The fluid distribution device is in this case designed such that it discharges the cleaning fluid onto the inner regions of the boiler approximately horizontally and/or, preferably, also upwardly counter to gravity, in particular so that it is distributed uniformly in an essentially rotationally symmetrical way. In order, then, to allow penetration into the boiler over, for example, 20 or 30 m, the hose is arranged on a corresponding hose drum, such that it can be unwound to a differing extent, depending on the desired cleaning height. This relatively large hose drum is in this case also positioned in the pressure container. The advantage of this is that the routing of the hose takes place within the same pressure level. Sensors for operating the hose drum (position measuring systems, hose limit stop control, etc.) are in this case preferably positioned outside the container. 
     Moreover, it is also preferred that the apparatus, where the fluid distribution device comprises a flexible hose which can be moved through the at least one connection piece by means of a drive, is equipped with a drive arranged in the container. In order to ensure a path-accurate movement of the hose and therefore also of the fluid distribution device, the metal hose is, for example, driven frictionally by means of driven rollers. The rollers can advantageously be operated in both directions, so that a path-accurate fluid distribution device is implemented. This drive, too, is advantageously arranged in the container, and the embodiment outlined here, with the driven rollers, can readily withstand the conditions prevailing during operation. 
     In addition, it should be pointed out that, for example, the drive for the hose drum and/or the positioning measuring system for controlling the movement of the hose are positioned outside the container. Suitable leadthroughs through the container are provided for this purpose. 
     A plant, too, then, is most particularly preferred which comprises at least one boiler for the treatment of a gas at high pressure and high temperature, in which at least one heat exchange surface is provided in the boiler and at least one apparatus according to the invention and also a corresponding connecting nipple are provided on the outside of the boiler, the fluid distribution device being positionable such that it can convey a cleaning fluid onto the at least one heat exchange surface. 
     Whereas a description of the separate mountable apparatus for cleaning is essentially provided hereinabove, then, the latter is in actual fact connected at this point to a corresponding plant. This is, in particular, a heat exchanger boiler which follows a combustion plant for coal gasification. This boiler, which is designed, for example, as a cylindrical pressure vessel with diaphragm walls and bulkhead heating surfaces (tube material Inconell 800, AC66) and in this case has a diameter of, for example, 3 to 5 m and a height of 30 to 50 m, is operated with a gas pressure in the range of 30 to 50 bar, the inlet temperature of the gas into the boiler lying in a range of 1000° C. to 1600° C. In plants of corresponding size, mass flows of the gas of 15 to 25 t/h are implemented. These are, in particular, plants in which even non-coal substances are burnt, in particular heavy oils and the like. 
     Precisely in the plants outlined above, it is preferable that a plurality of apparatuses are mounted or mountable on the boiler at the top, so that fluid distribution devices can then be introduced vertically into the boiler such that these can reach with their cleaning fluid at least subregions of the heat exchange surface implemented there. Most particularly preferred, the heat exchange surfaces are formed by a plurality of heat exchanger tubes, through which, for example, a cooling medium, such as water, flows. These heat exchange surfaces are positioned, in particular, in the upper third of the boiler. In this case, then, as seen over the cross section of the boiler, the tubes can be arranged in a pattern. Such a pattern comprises, for example, a circular arrangement of the tubes at a certain distance from the boiler casing, from which arrangement there are rows oriented radially inward are provided so as to extend into a central region, so as to form in the circumferential direction a plurality of heat exchanger sectors, for example 10, 12, 14, 16, 18 or 20 in number. It is preferred, then, that at least one connecting nipple is provided for each of these heat exchanger spaces, so that a cleaning appliance (or a plurality of cleaning appliances) or a fluid distribution device (or a plurality of fluid distribution devices) can penetrate vertically into the boiler in a directed manner via the connecting nipple and can move down the desired heat exchanger sector and clean it selectively. Highly directed and thorough cleaning is thereby possible. 
     Furthermore, it is also proposed that the boiler has a plurality of connecting nipples and that at least one apparatus be alignable with a plurality of connecting nipples. This describes, in particular, the situation where there is only one apparatus, such that the fluid distribution device is aligned, together with the container, with the respective connecting nipple, a pressure-tight connection is generated and the cleaning appliance is then activated. 
     It is most particularly advantageous that closing means are provided on the at least one connecting nipple. These closing means serve, in particular, for sealing the connecting nipple with respect to the external surroundings, such that, for example, gas exchange from inside the boiler into the surroundings or the container is no longer possible. What is achieved thereby is that the container can be uncoupled, and, in particular, the pressure contained in it can then be eliminated. As a result, on the one hand, careful treatment of the internal component is achieved and, furthermore, for example, a mounting flap of the container can be opened in order to carry out maintenance and/or repair of the components arranged inside the container. 
     As a result of a further development of the plant, at least sensors for determining a degree of contamination of the heat exchange surface or of the ambient conditions in the boiler are provided. It is preferred that both of the abovementioned types of sensors are present. With regard to the arrangement of the sensors for determining a degree of contamination of the heat exchange surface, it should be noted that, although these may basically be optical or non-contact sensors, they are preferably heat flow sensors which are brought at specific horizontal levels into heat-conducting contact with the heat exchange surface. Heat exchange between the gas flowing past and the heat exchange means inside the heat exchanger tubes can be detected by means of the temperature difference, so that the degree of slagging can thereby be determined. If a specific limit value is in this case reached or overshot, directed selective cleaning of the contaminated regions of the heat exchange surface is carried out. The provision of sensors for determining the ambient conditions in the boiler is helpful, for example, in determining or regulating the pressure inside the container for the next cleaning operation. 
     According to a further development of the plant, it is also proposed that a control unit be provided for at least one of the following functions: supply of the cleaning fluid, positioning of the apparatus with respect to the boiler, variation of the ambient conditions in the container, detection of operating data of the boiler. For this purpose, the control unit is connected to at least one of the following components: the apparatus, the cleaning fluid supply line, the hose drum, the drive, the connecting nipple, a sensor, the pressure increasing device. The control unit can thus, for example, supply the cleaning fluid or deactivate the supply of cleaning fluid. In consideration of the slagging the positioning of the apparatus or of the fluid distribution device can also be carried out, for example taking into account the determined slagging of the heat exchange surface. What is meant by this, on the one hand, is, for example, that the apparatus is aligned with the corresponding connecting nipple but, on the other hand, the position of the fluid distribution device or of the nozzle with respect to the cleaning surface can also or alternatively be undertaken and influenced. 
     According to a further aspect of the invention, a method for the cleaning of a plant which is in operation, with at least one boiler for the treatment of a gas at high pressure and high temperature, is proposed, which comprises at least the following steps:
     (a) adaptation of an ambient condition in the container of an apparatus of the type described according to the invention here to the ambient condition in the boiler;   (b) connection of the container in the boiler via the connection piece and the connecting nipple;   (c) alignment of the fluid distribution device with inner regions of the boiler;   (d) conveyance of a cleaning fluid onto the inner regions of the boiler.   

     This method can be implemented, in particular, by means of the plant described according to the invention here. 
     The ambient conditions in the container refer, in particular, to the pressure. Therefore, particularly when the pressure in the container is being adapted, such a pressure as lies above the pressure in the boiler must be selected, for example an overpressure of approximately 50 kPa. As a result of the slight overpressure, the scavenging gas (for example nitrogen) flows through the connection piece and the connecting nipple into the boiler, such that penetration of the synthesis gas into the pressurized container is avoided. Contamination of the components lying in the container is thus counteracted at the same time. 
     By means of step (b), in particular a fluidic connection between the container and the boiler is implemented, for example as a result of the opening of corresponding shut-off and/or closing means. 
     In the alignment of the fluid distribution device according to step (c), in particular the vertical penetration of a hose with a lance or nozzle into the boiler is meant, the fluid distribution device then particularly preferably being positioned selectively at (only) the contaminated sectors and commencing cleaning there. 
     Step (d) means, in particular, the supply of a cleaning medium at a pressure which is sufficient for reaching the heat exchange surfaces to be cleaned. Where liquids are concerned, in particular the pressure must be selected such that only wetting (essentially without abrasive action) is implemented, whereas, where gases are concerned, the kinetic energy must be sufficiently high to blow away the contamination, and therefore, here, as short a distance as possible between the fluid distribution device and the heat exchange surface should be implemented. 
     Now that, in particular, the initiation of the cleaning method has been explained above and can be ended in any known way, a particularly preferred configuration variant of the method end is illustrated below. Accordingly, the ending of the cleaning operation comprises at least one of the following steps:
     (e) identification of a cleaning condition;   (f) positioning of the fluid distribution device in the container in a latching position;   (g) separation of the container from the boiler via the connection piece and the connecting nipple;   (h) adaptation of the ambient condition in the container to the external surroundings of the plant.   

     Identification of a cleaning condition means, in particular, that the current cleaning condition is detected or measured. Basically, although it is also possible to adopt a specific cleaning intensity or cleaning duration as a fixed (time) limit for ending the cleaning operation, for example on the basis of experimental values, nevertheless a cleaning result of higher quality can be achieved by means of the first-mentioned variant. 
     In order to allow (temporary) separation and/or repositioning of the fluid distribution device, it is proposed to return the fluid distribution device into a latching position (or reference position) inside the container, from which position the alignment of the apparatus can regularly be started. 
     The fluid connection between the container and the boiler then needs to be separated, in particular, such that, for example, motor-driven shut-off and/or closing means are activated. 
     For assembly and/or maintenance activities, the ambient condition in the container is adapted to the normal atmosphere again. 
     This method is most particularly advantageous when the container is provided in step (a) with a pressure of at least 30 bar, in particular, for example, even 50 bar. The container and also the corresponding seals must be suitably selected for this purpose. 
     As already indicated, it is advantageous, precisely in the coal gasification plants described above, that the container is acted upon in step (a) with nitrogen gas. In this case, in particular a slight overpressure (approximately 30 to 80 kPa) with respect to the pressure in the boiler must be implemented. 
     Finally, it is also proposed that the cleaning fluid used is a liquid, this being introduced at an overpressure of 1 to 10 bar, preferably 1 to 5 bar, with respect to the pressure in the boiler. This is just sufficient, even taking into account the flow velocities of the synthesis gas, to make it possible to wet the regions of the boiler which, for example, are at distance of more than 200 mm. By the liquid impinging or acting upon the slag, abrupt evaporation occurs, the sudden change in volume which accompanies this causing the slag to crack open or flake off. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention and the technical background are also illustrated in connection with the accompanying figure. This figure shows a particularly preferred embodiment variant of the invention, to which, however, the latter is not limited. 
         FIG. 1  shows schematically the set-up of a coal gasification plant with an apparatus according to the invention for implementing the method according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , in the lower region, the boiler  2  is in this case illustrated, which is designed here with two connecting nipples  8  which are in each case designed with closing means  15 . In the case of the left connecting nipple  8 , the connection means  15  are designed with a motor (illustrated by a circle with an M), while the right connecting nipple  8  has a closing means  15  in the manner of a flap which can be opened only manually. 
     Inside the boiler  2 , in the left region, a heat exchange surface  14  is illustrated, for example with a row of heat exchange tubes through which water flows. The tubes or the heat exchange surface  14  extending in the vertical direction have or has, at various horizontal levels, sensors  16  for determining the temperature. By means of these sensors  16 , conclusions can be drawn as to the degree of slagging or of contamination of the heat exchange surface  14 . When high contamination is identified, the cleaning process commences, in which case, advantageously, cleaning is actually carried out selectively only in the sufficiently heavily contaminated sectors of the heat exchange surface  14 . 
     The cleaning itself is implemented here by means of the apparatus  1  according to the invention. The apparatus  1  comprises a cleaning appliance  4  which comprises a hose drum  11 , a hose  10 , a drive  12  and a fluid distribution device  5 . Moreover, these components are arranged in a container  6  which withstands pressures of up to, for example, 60 bar. The container  6  is designed essentially in the form of a boiler, a side wall closed in a pressure-tight manner being separable as a mounting flap for mounting the individual components. The container  6  has a connection piece  7  which can be connected to the connecting nipple  8  of the boiler  2 . This may, on the one hand, take place directly or, as illustrated here, by means of an (in particular tubular) intermediate piece. 
     Here, then, it is illustrated that the fluid distribution device  5  has been led out of the container  6  through the connection piece  7  and the connecting nipple  8 , such that the fluid distribution device  5  is positioned with respect to the corresponding sectors of the heat exchange surface  14  to be cleaned. As a result of a corresponding discharge of the cleaning fluid  3 , the heat exchange surfaces  14  are wetted and are also cleaned due to the expansion of the liquid. After the end of the cleaning operation, the fluid distribution device  5  is returned to the interior of the container  6  into a latching position again, the hose  10  at the same time being rolled up on the hose drum  11 . The closing means  15  can then be activated motively, such that the boiler  2  is closed, leak-tight, again. 
     During cleaning, the container  6  is acted upon with a scavenging medium, in particular nitrogen. This is introduced into the interior of the container  6  by means of the pressure increasing plant  9 . With the aid of a sensor  16  in the connection between the pressure increasing plant  9  and the container  6 , the pressure inside the container  6  can be exactly set or (for example also as a function of the pressure in the boiler) regulated. When the desired pressure is present, the closing means  15  can be opened once again. In addition to the supply of scavenging agents, the supply of cleaning fluid can also be monitored by means of corresponding sensors (to monitor the pressure, pressure sensors are provided which are identified by a P). Moreover, for the conveyance of fluids or for the operation of closing means, valves and similar equipment, a plurality of servomotors  19  are provided. 
     The servomotors, sensors and the like are, moreover, connected to a control unit  17  via various connections  18 , in order to implement data exchange and/or control and/or regulation of various components. 
     This entire plant  13  serves, in particular, for cooling a synthesis gas which flows into the boiler  2  at temperatures of above 1300° C. and at a pressure of above 40 bar. The apparatus  1  illustrated here makes it possible for the first time to clean heat exchange surfaces in those boilers which are operated at high pressure and high temperature, specifically online, that is to say during operation. 
     LIST OF REFERENCE SYMBOLS 
     
         
           1  Apparatus 
           2  Boiler 
           3  Cleaning fluid 
           4  Cleaning appliance 
           5  Fluid distribution device 
           6  Container 
           7  Connection piece 
           8  Connecting nipple 
           9  Pressure increasing plant 
           10  Hose 
           11  Hose drum 
           12  Drive 
           13  Plant 
           14  Heat exchange surface 
           15  Closing means 
           16  Sensor 
           17  Control unit 
           18  Connection 
           19  Servomotor