DESCRIPTION

[0001] The object of the present invention is a steam 5 apparatus for cleaning the outer surface of tube bundles of a heat exchanger; in particular, the object of the present invention is a steam apparatus for eliminating slag adhering to the outer surface of the tube bundles, typically formed by the residues carried by the

10 combustion fumes.

[0002] As is known, in heating systems provided with boilers, the use of heat exchangers is enormously widespread, which, by exploiting the heat energy still possessed by the hot combustion fumes, has the purpose of

15 further heating a process fluid, for example diathermic oil or water, passing through a tube bundle.

[0003] The hot fumes, however, contain many powders deriving from combustion, which tend to accumulate on the outer surface of the tubes of the bundle, forming

20 deposits that have an extremely negative impact on the efficiency of the exchanger, creating a barrier to heat exchange between the fluids.

[0004] For the elimination of such deposits, in cases wherein the heating system already provides steam (for 25 example in water/steam boilers), it is known to use lances provided with nozzles, arranged between the tubes of the bundle, which at predetermined time intervals emit a jet of steam that hits the surface of the tubes.

[0005] In the cases wherein the heating system does not provide steam, such as in the case of oil (fluid) diathermic boilers, compressed air lances are used, which need suitable compressors to ensure a flow of air and sufficient pressure to clean the surface of the exchanger. However, as the expanding air cools, it may cause harmful effects on the exchanger or on the external surface of the tube bundle, for example due to reaching the localized dew point for aggressive substances, if present (for example sulfuric acid) .

[0006] Precisely for these reasons, the use of such compressors is particularly disadvantageous, due to the related system and management costs. Furthermore, for a cleaning cycle using compressed air, it is necessary to use large-volume air storage tanks capable of withstanding high pressure, which are generally very expensive.

[0007] According to a further aspect, in the case of using heat exchangers that use flammable fluids (such as hydrocarbons, diathermic oils or other organic fluids), it is necessary to guarantee an adequate fire-fighting system to be activated in the event that flammable liquid leaks due to the exchanger breaking.

[0008] Also in this case, the fire-fighting systems associated with boilers of the known art, require expensive and cumbersome systems for storing inerting gases such as carbon dioxide or nitrogen, to be delivered immediately in the event of a fire.

[0009] One of the objects of the present invention is that of providing a steam apparatus capable of obviating the aforementioned drawbacks of the known art, particularly for those cases wherein steam provided by the boiler is not already available.

[0010] Such purpose is achieved by a steam apparatus, a cleaning system, a tube bundle cleaning plant, a tube bundle cleaning and water treatment plant, an inerting system, a steam generation method and a tube bundle cleaning method according to the attached independent claims. The claims dependent thereon describe preferred variant embodiments.

[0011] The features and advantages of the cleaning system, the apparatus, the systems and the methods according to the present invention will be evident from the following description, given by way of non-limiting example, in accordance with the attached drawings, wherein:

[0012] - figure 1 is a schematic view of a steam apparatus connected to a tube bundle cleaning apparatus of a boiler heat exchanger, forming a cleaning system according to an embodiment of the present invention;

[0013] - figure 2 is a schematic view of a steam apparatus according to a second embodiment of the present invention connected to a tube bundle cleaning apparatus of a boiler heat exchanger;

[0014] - figure 3 is a schematic view of a pipe bundle cleaning and water treatment plant according to an embodiment of the present invention.

[0015] With reference to the accompanying figures, a steam apparatus for generating steam for cleaning the outer surface of tube bundles 100 of a heat exchanger, according to an embodiment of the present invention is indicated collectively at 1.

[0016] It is clear that, even if hereinafter reference will be made to the cleaning of tube bundles of an exchanger, the term "tube bundles" is understood to mean equally any other type of exchange surface, known per se to a person skilled in the art and implemented in a surface-type exchanger, wherein the fluids involved in the heat exchange are separated from said exchange surface (for example finned tubes, finned pack, micro channels and the like) . In an equivalent way, therefore, "outer surface" means the surface affected by the hot fumes of a boiler on which the deposits to be cleaned accumulate. [0017] The apparatus 1 is suitable to be associated with a system 200 for the production of high temperature diathermic oil, for example a boiler 201 with diathermic oil comprising a heat exchanger with diathermic oil, or, in any case, with a heating system wherein it is heated a high temperature circulation fluid (for example hot fumes) by means of a known type of boiler.

[0018] By way of example, the steam apparatus 1 may therefore be associated with a boiler comprising a burner arranged in a combustion chamber, below which, for example, an ash pan is provided, usually below the furnace grid, wherein the combustion ash accumulates (if the fuel is solid) . Above the burner there is generally a chimney for the evacuation of exhaust combustion fumes. Generally, between the burner and the chimney there is a set of tubes (or tube bundle) wherein the fluid to be heated (for example, diathermic oil) circulates.

[0019] The steam apparatus 1 comprises an oil-water heat exchanger 2, supplied with high temperature diathermic oil D.O. from an oil supply system 300 and with water H20 from a water supply unit 4. The oil supply system 300 is, for example, a series of pipes which transport diathermic oil heated to a high temperature; in the same way, the water supply unit 4 comprises, for example, a water tank and a series of pipes which carry water H20, preferably already purified.

[0020] The exchanger is suitable to heat water H20 due to a first heat exchange between the diathermic oil D.O. and the water H20. This heat exchange is suitable to store a quantity of heat in water H20, obtaining superheated water, such as to allow the generation of steam S by flash evaporation (also known as partial evaporation) of superheated water H20.

[0021] The steam S generated by flash evaporation is supplied by a steam delivery device, for example a valve 531, connected to the oil-water heat exchanger 2 and which may be activated to supply the steam according to certain conditions inside the oil-water exchanger 2. Preferably, the steam S is delivered as a function of a predetermined pressure and temperature level reached by the water H20 inside the oil-water exchanger 2.

[0022] In a preferred embodiment, the steam apparatus 1 comprises a diathermic oil tank 10, a water tank 11 and the oil-water exchanger 2.

[0023] Advantageously, the water tank 11 is suitable to contain simultaneously superheated H20 water in equilibrium with steam S. In this regard, preferably, a water level regulator (not shown in the figures) is installed on the water tank 11 suitable to regulate the entry of water into the water tank 11 from the water supply unit 4 so as to maintain a certain level of water and steam S in equilibrium with each other.

[0024] Preferably, the diathermic oil tank 10 and the water tank 11 are enclosed in a single tank and divided and mutually sealed between them by a wall 600 inside the tank .

[0025] Preferably, the oil-water exchanger 2 and the water tank 11 are made as a single device, wherein the tube bundle 2' which carries the diathermic oil D.O. is immersed in the water H20 of the water tank 11.

[0026] Even more preferably, the diathermic oil tank 10, the water tank 11 and the oil-water exchanger 2 are integrated in a single device.

[0027] In one embodiment, a condensate separator is enclosed within the water tank 11, preferably a cyclone separator .

[0028] The water tank 11 comprises an outlet port 111, for the outlet of steam S from the water tank 11 to a steam cleaning apparatus 7, suitable to clean the outer surface of tube bundles of a heat exchanger, for example a heat exchanger for a boiler.

[0029] It is therefore clear that it is the object of the present invention both the steam apparatus 1 and a cleaning system comprising such steam apparatus 1 and the steam cleaning apparatus 7. [0030] When the dispensing device is activated, for example when at least one first delivery valve 531 (or thermal expansion valve) installed near the outlet port is opened, the steam S is delivered from the outlet port 111 and continuously regenerated by means of flash evaporation, exploiting the pressure drop inside the tank 11. In other words, this drop in pressure leads to a flash evaporation of the liquid heated in the tank 11. The outlet port 111 is connected to a steam superheating circuit 5 suitable to superheat the steam S generated by the evaporation of the water contained in the tank 11. The steam S is superheated by means of a further heat exchange between the steam S and the diathermic oil D.O. Alternatively or simultaneously with the heat exchange between the steam S and the diathermic oil D.O., the superheated steam circuit 5 is suitable to superheat the steam S by means of further heat exchange between such steam S and the water H20 heated by the oil-water exchanger 2 contained in the tank 11.

[0031] In this way, the further heat exchange (steam-oil and/or steam-water) allows the temperature of the steam S supplied by the tank 11 to be raised so as to generate superheated steam S' . Preferably, the superheated steam S' is superheated to a superheated temperature suitable to allow one to obtain a vapor quality of at least 70% or greater, preferably at least equal to 85% or higher, even more preferably at least equal to 90% or higher, once such steam S is expanded by the nozzles for cleaning the outer surface of the tube bundles 100. Preferably, the superheating takes place at constant pressure (or with a pressure variation linked only to the pressure drops of the exchangers, which may be considered negligible) .

[0032] Preferably, on the superheating circuit 5 is installed a steam-oil exchanger 51 immersed in the oil of the diathermic oil tank 10 and/or a steam-water exchanger 52 immersed in the water of the water tank 11. Depending on the speed, efficiency and superheating level required, the superheating circuit performs a heat exchange only with the diathermic oil D.O. (by means of the steam-oil exchanger 51) or only with the water H20 (by means of the steam-water exchanger 52) or with both (i.e. either by means of the steam-oil exchanger 51 or by the steam-water exchanger 52 ) .

[0033] Preferably, the steam apparatus 1 comprises a steam channeling path 6 suitable to be interfaced on one side with the cleaning apparatus 7 of the outer surface of the tube bundles 100 of a boiler exchanger and on the other side with the superheating circuit 5 and/or with the outlet port 111 of the oil-water heat exchanger 2. This channeling path 6 (for example one or more pipes) is suitable to convey a flow of steam coming from the oil- water heat exchanger 2 towards the cleaning apparatus 7.

[0034] The cleaning apparatus 7 is, for example, a high- pressure steam delivery system by means of steam lances 71, 72.

[0035] Moreover, in a preferred manner, the channeling path 6 is suitable for channeling a flow of steam coming from the steam superheating circuit 5, so as to send a flow of superheated steam S' to the steam lances 71, 72.

[0036] In other words, the steam S (preferably saturated steam) delivered by the outlet port 111 is conveyed directly to the channeling path 6 or, before being sent to the channeling path 6, is diverted towards the superheating circuit 5, so as to be superheated. The path followed by the steam flow is adjusted by adjustment means 53 of said steam flow (for example at least one valve) , suitable to channel the flow of steam from the oil-water heat exchanger 2 to the channeling path 6 or to the steam superheating circuit 5.

[0037] In particular, for example as shown in figure 1, the adjustment means 53 are installed either on a connection path 8, which connects the outlet port 111 with the channeling path 6, or on the steam superheating circuit 5. For example, a second valve 532 is installed on the connection path 8 between the inlet 54 of the superheating circuit 5 and the outlet 55 of the superheating circuit, in a portion of the path which bypasses the steam superheating circuit 5. A third valve 533 is, for example, installed on the superheating circuit 5, between the inlet 54 of the superheating circuit 5 and the outlet 55 of the superheating circuit 5, for example near such outlet 55. As already mentioned, the first valve 531 is suitable to enable the delivery of steam from the water tank 11 towards the downstream system sections, that is towards the superheating circuit 5 and the channeling path 6. The second valve 532 is suitable to enable the passage of steam S from the connecting path 8 directly towards the channeling path 6. The third valve 533 is suitable to enable the passage of superheated steam S' from the superheating circuit 5 towards the channeling path 6.

[0038] In other words, the adjustment means 53 are configured so as to allow a first supply of steam S coming from the outlet port 111 towards the channeling path 6 so as to preheat the pipes of such path 6. Moreover, the same adjustment means 53 are suitable for allowing the delivery of superheated steam S' coming from the steam superheating circuit 5 towards the channeling path 6 (and therefore towards the cleaning apparatus 7) .

[0039] Preferably, the superheated steam S' delivered towards the lances 71, 72 provides a constant supply pressure to the lances.

[0040] Furthermore, preferably, the temperature of the superheated steam S' being fed to the nozzles 711, 721 is such as to avoid that during the condensation phase (during the expansion of the steam from the nozzles) the steam quality exiting the nozzles is too low and is such as to form water droplets harmful to the surface of the tube bundle 100.

[0041] Preferably, a control system (not shown in the accompanying figures) is suitable for modulating the opening/closing of the valves 532 and 533 such that a predetermined pair of pressure and temperature values of the superheated steam S' feeds the lances 71, 72.

[0042] It is therefore clear that the embodiment illustrated in figures 1 to 3 and which provides for the use of three valves 531, 532, 533 also may be achieved by means of equivalent adjustment devices, known to the person skilled in the art and arranged in such a way as to carry out the same function described in the preceding paragraph. For example, an alternative variant may provide, in place of the valve 532, a simple bottleneck, or more generally a pressure drop, suitably calibrated such that the steam S is preferentially routed through such bottleneck only during the preheating step, when the valve 533 is closed.

[0043] It is moreover the object of the present invention a method of steam generation for the cleaning of tube bundles of a boiler exchanger. This method comprises the step of generating steam S (preferably at least saturated steam) by means of flash evaporation of superheated water due to a heat exchange between diathermic oil (at high temperature) and water.

[0044] Preferably, the method also comprises the step of superheating the steam S generated by flash evaporation by means of heat exchange between this steam S and diathermic oil and/or water, for example to obtain superheated steam.

[0045] It is clear that the method preferably also comprises the step of associating a steam apparatus 1 as described in the preceding paragraphs with a cleaning apparatus 7 of tube bundles and with a system for the production of high temperature diathermic oil, for example a diathermic oil boiler.

[0046] More particularly, with reference to the attached figures, hereinafter a sequence of steps is described which carry out the cleaning of tube bundles of a boiler exchanger by means of a steam apparatus 1 and a cleaning apparatus 7 as previously described (and therefore forming the cleaning system) . [0047] The method provides that in a first step a mass of liquid water is heated by means of heat exchange with a high temperature diathermic oil (between 150°C and 250°C inclusive), for example in the water tank 11.

[0048] Heating the mass of water inside the closed water tank 11 leads to an increase in the temperature and pressure inside the tank.

[0049] In this first step, the water tank 11 is an isochoric system, wherein the steam delivery device (for example the valve 531) is kept closed for a certain time interval, necessary to obtain superheated water. In other words, in this step, preferably flash evaporation is not generated and inside the water tank 11 superheated water H20 is at the same time present in equilibrium with steam S .

[0050] Subsequently, the opening of the valve 531 and the consequent reduction of pressure and temperature leads to the flash evaporation of a part of the superheated liquid water in the tank 11.

[0051] Preferably, therefore, the steam generation method does not generate steam continuously, but discontinuously ("batch" mode) : a first step involves the accumulation of heat without generating steam for a certain time interval suitable for superheating the water contained in the water tank 11; a second step involves the generation of flash steam, with a consequent reduction in pressure and temperature inside the water tank 11.

[0052] Preferably, the method provides for preheating the pipes of the channeling path 6 by channeling a first flow of steam S coming from the oil-water heat exchanger 2, for example before the steam S is superheated in the superheating path 5. Although not appreciable in the attached figures, the channeling path 6 may also comprise pipes of considerable length, depending on the size and type of system. In particular, in these cases, therefore, the preheating phase minimizes the formation of condensate inside the pipes of the channeling path 6, which is harmful during cleaning.

[0053] Preferably, the preheating step is performed by closing the third valve 533 and opening the second valve 532. Moreover, preferably valve means 700 are suitable to prevent the flow of steam S from being delivered into the cleaning apparatus 7. The steam S delivered during this preheating step is finally dispersed or discharged in an area specially designed for this purpose (cooling and drainage area) or is channeled towards a steam recovery path 9. This steam recovery path 9 is for example connected to a water treatment system 20, for example as shown in figure 3, or to a steam/condensate recovery tank. [0054] In particular, figure 3 illustrates an embodiment of the invention in which the steam apparatus 1 is also connected to a water treatment system 20. In such embodiment, the steam recovery path 9 is connected to a water treatment system comprising a steam in water bubbler 21. In this way the steam S used for the preheating phase of the pipes is bubbled into the water treatment system 20. The bubbling of hot steam in the water thus contributes to the process of water treatment and purification.

[0055] This water treatment process preferably involves the removal of gases dissolved in water H20 and potentially harmful in the subsequent steps of use of the water itself. For example, oxygen may be particularly aggressive/corrosive to pipes/tanks, while carbon dioxide is a precursor of encrusting carbonates.

[0056] In one embodiment, the water treatment system 20 also includes other treatment apparatuses 22, 23 suitable for further chemical-physical treatments for water purification.

[0057] Subsequently (or simultaneously) to the preheating phase, the method comprises the superheating step of the steam S by means of heat exchange between the steam S and the diathermic oil and/or the water to obtain a superheated steam S' (for example by means of heat exchange inside the exchangers 51 and/or 52) .

[0058] Following the preheating phase, the superheated steam S' is delivered into the channeling path 6, and then to the cleaning apparatus. The supply of superheated steam S' takes place, for example, by opening the third valve 533 and closing the second valve 532. In addition, suitable nozzle valves 710, 720 ad ust/enable the delivery of superheated steam S' into the cleaning lances 71, 72.

[0059] Preferably, the superheated steam S' upstream of the lances 71,72 has a high pressure of between 2 and 20 bar, preferably between 5 and 15 bar, and a temperature of between 150° and 300°, preferably between 180° and 250°. The nozzles 711, 721 present on the lance are suitable to expand the superheated steam S' (at high pressure) to the working pressure of the boiler (generally at a pressure very close to atmospheric pressure) , transforming the potential energy (high pressure and temperatures) into kinetic energy (high speed expanded steam jet, for example about 300-500 m/s) .

[0060] Consequently, the superheated steam S' is delivered in the form of a high kinetic energy steam jet from the cleaning lances 71,72 through the nozzles 711, 721 and acts on the outer surface 101 of the tube bundles 100 of the exchanger to be cleaned. [0061] The steam apparatus 1, the cleaning apparatus 7 and the water treatment system 20 by means of steam bubbling, when connected to each other, create therefore a single tube bundle cleaning and water treatment plant.

[0062] A further variant embodiment of the steam apparatus 1 (for example as shown in figure 2) is particularly suitable to be associated with heating systems or boilers which do not per se provide for the generation of diathermic oil or a hot fluid in circulation. In such variant, the steam apparatus 1 comprises an oil-fume heat exchanger 12, suitable to exchange heat between hot fumes H.F. (for example coming from a burner of a boiler or a small burner installed for this purpose) and diathermic oil D.O. circulating in an oil supply system 300. In this case, the oil supply system 300 is for example made up of only the diathermic oil tank 10 or is a diathermic oil circulation system between the diathermic oil tank 11 and the oil-water exchanger 2. This embodiment is particularly indicated in the case wherein the steam apparatus 1 is associated with a boiler which does not provide for the use of high temperature diathermic oil (for example a saturated steam boiler, or a pressurized water boiler, or any particular diathermic oil boilers which for any reason cannot be used directly in the apparatus according to the present invention) . [0063] Preferably, alternatively or concurrently with the oil-fume heat exchanger 12, the steam apparatus 1 comprises a water-fume heat exchanger 13, suitable for exchanging heat between hot fumes coming from a burner of a boiler and water H20 present in the steam apparatus 1. For example, the water-fume heat exchanger 13 is connected in series to the oil-fume heat exchanger 12 (as illustrated in figure 2) .

[0064] More particularly, the oil-fume exchanger 12 is immersed in the oil D.O. of the diathermic oil tank 10 and the water-fume exchanger 13 is immersed in the water H20 of the water tank 11.

[0065] Innovatively, the steam apparatus according to the present invention makes it possible to compensate for the lack of dry steam for cleaning tube bundles of boilers which do not per se provide steam generation. Furthermore, the present invention allows the generation of dry steam with a higher yield compared to the yields of the prior art which provide for the use of compressed air.

[0066] Further advantageously, the production of steam by flash evaporation allows to considerably reduce the volumes of the pressure vessels typically used when compressed air is used as a cleaning fluid.

[0067] Advantageously, the use of the same hot fluid (diathermic oil or hot fumes) coming from the boiler allows to drastically increase the efficiency of the boiler-cleaning system.

[0068] Furthermore, due to the superheating phase of the steam after flash evaporation, higher steam quality values may be obtained during expansion from the nozzles of the cleaning lances, avoiding the formation of water droplets harmful to the surface of the tube bundle and, at the same time, increasing the thermodynamic efficiency.

[0069] In an even more advantageous way, the use of preheating steam for the treatment of water, allows the otherwise lost steam to be recuperated and, therefore, allows the efficiency of the entire heat and water treatment system to be improved.

[0070] Moreover, according to a further advantageous aspect of the present invention, the steam apparatus is configured to inert the combustion chamber of the boiler to which it is associated, in such a way as to dampen and/or extinguish possible fires. In effect, according to a variant embodiment of the present invention, the steam S is delivered directly inside the combustion chamber of the boiler through the same lances used for cleaning, or through dedicated dispensing means. The result is a fire protection system integrated into the cleaning system, which eliminates the use of cumbersome and expensive inerting gas tanks. In this variant, the steam is supplied in such a way as to supply a sufficient amount to inert the entire combustion chamber.

[0071] It is clear that a person skilled in the art, in order to meet specific needs, may make changes to the invention described above, all contained within the scope of protection defined by the following claims.