Cleaning installation for removing soot

Abstract: The present invention relates to a device (1) for use in a cleaning installation for removing soot or similar inside deposits in a flow channel (9) in a processing system such as a boiler, heat exchanger, flue gas filter or the like, by intermittently blasting a fluid or gaseous medium into the processing system, said device (1) comprising a flow passage (5) between the associated valve (1) means and the flow channel (9), wherein the flow passage (5) is provided with an inlet (8) allowing for a continuous flow of protective gas around the flow passage (5) into the flow channel (9) in the processing system. By the present invention, corrosion is reduced since a cushion of air is generated at the end (15) of the flow passage during off-cycles of the cleaning operation as air is constantly drawn or forced in through the inlet (8). This means that the components are covered by this cushion and protected against corrosive gasses in the heat exchanger or the like. Hereby, the valve means (1) are protected from corrosion and tests have shown that durability of the exposed components facing the inside of the boiler or the like has been significantly improved.

Description: The present invention relates to a device for use in a cleaning installation for removing soot or similar inside deposits in a flow channel in a processing system such as a boiler, heat exchanger, flue gas filter or the like, by intermittently blasting a fluid or gaseous medium into the flow channel in the processing system, said device comprising a flow passage between associated valve means and the flow channel, said valve means intermittently admitting blasting fluid or gaseous medium into the flow passage. The invention also relates to a cleaning installation of such kind. Boiler installation sediments of soot or the like often occur on the inside of heat surfaces and on tubes that are in contact with flue gasses. This seriously reduces the thermal conductivity and thereby also the efficiency of the boiler if not removed. For removal of these deposits, methods are known, such as mechanical cleaning or blast cleaning using stream, water or air as cleaning means for the removal of soot. Some of these cleaning methods require shut-down of the boiler installation whilst other methods allow for the boiler to remain in operation at a reduced level of efficiency. By a few methods such as blast cleaning with air, the cleaning process can be performed during ordinary operation of the boiler. An example of another of such systems is known from EP-A-0 865 023 where a sound generator is used for loosening the sediments. The cleaning equipment is often subjected to a heat and corrosive impact from the gasses inside the boiler installation. This results in a limited durability of the cleaning equipment due to the aggressive environment in the flue gasses. For this reason, the cleaning equipment is often mounted on the outside of the gas chamber of the boiler. Equipment for blast cleaning for the removal of soot by pressurised air, is attractive in use since the equipment only requires a small amount of space outside the boiler and none at all inside the boiler. The cleaning equipment typically comprises a pressure vessel from which pressurised air is fed to a number of diaphragm valves. The valves are controlled by control means. The control means activates the valves in a pre-programmed sequence and the pipes in the boiler governed by the associated valve are blasted with the pressurised air. The air is blasted for 0,1-1 second at an interval of approx. 2-10 minutes. This cleaning cycle, i.e. the duration and the frequency, can be adjusted according to requirements, such as the type of fuel, the amount of fouling and the boiler output. The pressure vessel is usually operated at about 7-8 bars. However, this can also be adjusted in accordance with the actual needs of the boiler installation. However, permanent mounting of the blasting tubes in the boiler wall causes a deterioration of the components in the soot removal equipment exposed to the gasses inside the boiler and in particular to valve and membrane components. There are many different types of boilers in power plants. Particularly municipal waste burning plants, bio-mass fuelled plants and waste heat recovery installations generate corrosive flue gasses during the burning process. The components are in particular subject to corrosion due to the hot, aggressive flue gasses during the off-cycles, i.e. when no air is blasted through the valve assembly, the associated tube passage and into the boiler. When there is no forced air flow in the valve assembly, flue gas will escape from the main gas stream in the boiler and fill the passage space. This causes mechanical wear and corrosion of the exposed components of the cleaning equipment which, in turn, reduces the cleaning efficiency and again causes a drop in the efficiency of the boiler installation. Therefore, the object of the invention is to provide a device that reduces corrosion of the exposed components of the cleaning equipment in a soot cleaning installation. This object is achieved by a device and a cleaning installation of the initially mentioned kind wherein the flow passage is provided with a further inlet allowing for a continuous flow of protective gas into the end section of the flow passage into the flow channel in the processing system. By the present invention, corrosion is reduced since a cushion of air is generated at the end of the flow passage during the off-cycles of the cleaning operation, as air is constantly drawn or forced in through the inlet. This means that the components are covered by this cushion and protected against the corrosive gasses in the heat exchanger or the like. Hereby, the valve means are protected from corrosion and tests have shown that durability of the exposed components facing the inside of the boiler or the like has been improved significantly. This also means that the components, such as the valve housing, may be produced in a cheap material such as cast iron without compromising the durability of the valve means. In the preferred embodiment of the invention, the flow passage comprises an annular space between an inner tubular and an outer tubular member, where the outer tubular member is provided with an air inlet generating a continuous air flow around the flow passage into the processing system. Hereby, an even distribution of the air flow is ensured resulting in a particularly well-covering cushion of air. In a first embodiment of the invention, the air is simply drawn in around the flow passage and into the inside end region of the flow passage utilising the Venturi effect due to the speed of the gas flow in the boiler, heat exchanger or the like. However, in an alternative embodiment, the air inlet is provided with an injector for the supply of air into the flow passage. This means that air can be forced into the air inlet for the creation of the protective air cushion at the inside end section, even if the subpressure created by the flow rate of the gasses or the like is insufficient for the creation of an air cushion. In another embodiment, the device is provided with a plurality of air inlets. Hereby, the amount of air can be enhanced and the shape of the air cushion can be adjusted according to the radial position of the air inlets around the flow passage. In a preferred embodiment of the invention, the air inlet is provided with replaceable flow restriction means. In a particular embodiment, the replaceable flow restriction means may consist of a cover plate provided with one or more apertures through which air is allowed to flow into the annular spacing. Hereby, the continuous inlet air flow can be restricted so that the amount of incoming air is not influencing the gasses inside the boiler. In another aspect of the invention, a valve assembly is provided for use in a cleaning installation for removing soot or similar inside deposits in a flow channel in a processing system such as a boiler, heat exchanger, flue gas filter or the like, by intermittently blasting a fluid or gaseous medium into the processing system, said valve assembly comprising a diaphragm valve including a first and second chamber, said first chamber receiving pressurised air from an air supply, and said second chamber being provided with valve control means and an outlet for release of air in the chamber when activating the diaphragm valve, and a valve outlet connected with a flow passage device according to the first aspect, wherein flow communication means is provided between the outlet of the second chamber and the inlet of the flow passage of the device. When the diaphragm valve releases pressurised air which is typically up to 8 bars or perhaps more, the diaphragm retention air is released from the second chamber through the outlet and into the atmosphere. This creates a loud explosion-like noise, that can be more than 100 dBA. However, by a valve assembly according to the invention, a silencer is provided whereby noise emission is reduced considerably. In the preferred embodiment of a valve assembly according to the invention, the flow communication means includes a tubular pipe. Hereby, the noise reduction may be obtained in a simple and reliable manner, just as a tubular pipe is relatively easy to incorporate in existing valve arrangements. In another embodiment of the valve assembly, the flow communication means includes an additional supply of external air to the inlet of the flow passage device and this additional air supply preferably consists of cool air. Hereby, a constant air flow to the flow passage may be ensured, just as heat generated during the retention pressure release may be removed by an additional supply of cool air. The invention is described in detail in the following with reference to the accompanying drawings, in which Fig. 1 shows a schematic view of a cleaning installation, fig. 2 shows a schematic view of a cleaning device according to a preferred embodiment of the invention, fig. 3 shows a schematic view of another type of cleaning device according to prior art, and figs. 4 and 5 show two embodiments of a valve assembly with silencing means according to the invention. Figure 1 shows a cleaning installation for pressurised air blast cleaning for removal of sediments inside a heat exchanger, boiler or similar preferably tubular installation. The installation comprises a number of valve assemblies 1 connected to a vessel 2 of pressurised air. The vessel 2 is in communication with the individual valve assemblies 1 through a main line 3 and associated supply lines 4. The valve assemblies are controlled by a control system (not shown) by which the operating cycle of the individual valve assemblies 1 and the cleaning cycle as a whole is commanded. The valve assembly 1 is shown in detail in figures 2 and 3. As shown in figure 2, the valve assembly 1 comprises a solenoid valve 10 which is provided control means 11 for controlling the valve 10. The valve 10 is supplied with pressurised air from the supply lines 3, 4. When the valve 10 is opened, pressurised air is blasted into a flow passage 5 and into a flow channel 9 of a processing system, such as a boiler or the reverse chamber in a heat exchanger. The flow passage 5 comprises in the preferred embodiment of the invention a double walled tubular structure comprising an inner tubular member 7 and an outer tubular member 6 arranged concentrically. The outer member 6 is provided with an air inlet 8 through which air can be drawn or forced (not shown) into the annular space between the two tubular members 6, 7. From this annular space, air is drawn into the end section of the flow passage 15 where a cushion of air is formed, thus preventing the flue gasses in the flow channel 9 from entering the flow passage and coming into contact with the components of the valve 10. Air or any similar protective gas can be sucked in towards the flow channel 9 due to the flow of gas in the flow channel 9. Alternatively, air can be supplied by connecting an air or a gas supply with the air inlet 8. In figure 2, the valve assembly 1 is shown in a fixed installation. In figure 3, a removable installation according to prior art is shown. The valve 10 is connected with the flow channel 9 by a flexible tubular piece 12 secured by tightening means 13 at the two ends. In figure 4, a valve assembly 1 is shown. The diaphragm valve 10 comprises a first and a second chamber separated by a diaphragm or a membrane (not shown). The valve 10 is operated by control means, such as a solenoid valve or the like. When the valve is activated by moving the diaphragm, pressurised air flows from the first chamber to the valve outlet and into the flow passage 5. The diaphragm is provided with a small aperture through which the pressurised air flows into the second chamber and fills this chamber with air, so that equal pressures are established on both sides of the membrane/diaphragm. The pressure in the second chamber is applied to the entire surface of the membrane whereas only a minor portion of the membrane is subjected to the pressure in the first chamber. This presses the membrane against the valve exit and keeps the valve shut. The second chamber is in communication with atmospheric pressure through a ventilation opening in the control valve. In its resting position, a piston of the control valve will keep the ventilation opening shut by retaining pressure in the second chamber and thereby keep the valve shut between the blast-cleaning shuts. When the control valve is activated, the piston is retracted and the pressurised retention air of the second chamber is quickly released out through the ventilation opening 18. The opening 18 is provided with an air flow tube 16 connected to the inlet 8 of the flow passage device 5 at the opposite end. Hereby, an explosion-like sound is avoided from the quick release of air when the valve is activated. Instead, the air is led into the flow passage, whereby the blasting effect of the valve may even be slightly enhanced. In figure 5, a modification of the embodiment of figure 4 is shown. Here, the tubular pipe 16 is provided with an external supply of cool air through a conduit 17. When the valve is shut and no air is released through the flexible tube 16, external air may still be sucked into the flow passage through the inlet 8. The external air may either be atmospheric air or any other gaseous air supply. By the invention it is realised that, apart from drawing in atmospheric air through the air inlet, other protective gasses can be used without departing from the scope of the invention as defined in the claims.

Claims: A device for a cleaning installation for removing soot or similar inside deposits in a flow channel (9) in a processing system such as a boiler, heat exchanger, flue gas filter or the like, by intermittently blasting a fluid or gaseous medium into the processing system, said device comprising a flow passage (5) between associated valve means and the flow channel (9), said valve means intermittently admitting blasting fluid or gaseous medium into the flow passage, characterised in that the flow passage (5) is provided with a further inlet (8) allowing for a continuous flow of a protective gas "into the end setion of" the flow passage (5) into the flow channel (9) in the processing system. A device according to claim 1, wherein the flow passage (5) comprises an annular space between an inner tubular and an outer tubular member (7, 6), where the outer tubular member (6) is provided with the inlet (8) providing a continuous gas flow "into the end section of" the flow passage into the flow channel in the processing system. A device according to claim 1 or 2, wherein the inlet (8) is provided with an injector for the supply of air or a similar protective gas into the flow passage (5). A device according to any of claims 1 to 3, wherein the device is provided with a plurality of air inlets. A device according to any of claims 2 to 3, wherein the air or gas inlet is provided with replaceable flow restriction means. A device according to claim 5, wherein the replaceable flow restriction means is a cover plate provided with one or more apertures through which air is allowed to flow into the annular spacing. A valve assembly (1) comprising a device according to any of the claims 1 to 6 for a cleaning installation for removing soot or similar inside deposits in a flow channel in a processing system such as a boiler, heat exchanger, flue gas filter or the like, by intermittently blasting a fluid or gaseous medium into the processing system, said valve assembly (1) further comprising: a diaphragm valve (10) including a first and second chamber, said first chamber receiving pressurised air from an air supply, and said second chamber being provided with valve control means (11) and an outlet for release of air in the chamber when activating the diaphragm valve, (10) and a valve outlet connected to the device, wherein flow communication means (16) is provided between the outlet of the second chamber and the inlet (8) of the flow passage (5) of the device. A valve assembly according to claim 7, wherein the flow communication means (16) includes a tubular pipe. A valve assembly according to claim 7 or 8, wherein the flow communication means (16) includes an additional supply of external air to the inlet (8) of the device where this additional air supply preferably consists of cool air. A cleaning installation for removing soot or similar inside deposits in a flow channel in a processing system such as a boiler, heat exchanger, flue gas filter or the like, by intermittently blasting a fluid or gaseous medium into the processing system, said cleaning installation comprising a pressure vessel and one or more valve assemblies according to any of claims 7 to 9, said valve assemblies each being connected by a device according to any of the claims 1 to 6 to the flow channel in the processing system, characterised in that the device includes at least one flow passage (5) provided with a further inlet (8) allowing for a continuous flow of protective gas "into the end section of" the flow passage (5) into the flow channel (9) in the processing system. A cleaning installation according to claim 10, wherein the flow passage (5) comprises an annular space between an inner tubular and an outer tubular member, (7, 6) where the outer tubular member (6) is provided with a continuous gas flow around the flow passage (5) into the processing system. A cleaning installation according to claim 10 or 11, wherein the inlet (8) is provided with an injector for the supply of air or a similar protective gas into the flow passage. A cleaning installation according to claims 10 to 12, wherein the device is provided with a plurality of air inlets. A cleaning installation according to claims 11 to 12, wherein the air or gas inlet (8) is provided with replaceable flow restriction means. A cleaning installation according to claim 14, wherein the replaceable flow restriction means is a cover plate provided with one or more apertures through which air is allowed to flow into the annular spacing.

Inventors: SUNDGAARD KNUD, SUNDGAARD, KNUD
Applicants: OKR CLEANING
Application year: 2001
Main classification: F28F19
IPC codes: F28F19, F28G9