Patent Grant
8495783
1. Field of the Invention
The invention relates to a method and apparatus for cleaning of burners.
The invention is especially directed to remove soot and other kinds of dirt, which deposit on inner surface of burners installed in fired, tubular reformers.
2. Description of Related Art
It is known that impurities are formed in burners, and that these impurities deposit on the inner surface of the burners, which affects performance of the burners.
In the publication issue of DE 3149550 a method for removing deposit during combustion is described. Small particles of sand are blown into the burner in such a way that they remove the deposit. They are collected at the end of the burner and removed from there. However, this method is unsuitable for a fired, tubular reformer with hundreds of burners.
In a report from Ammonia Plants & Related Facilities Symposia, 2001, B. R. Fisher describes cleaning of burners in a fired, tubular reformer with bronze wire brushes and cupper wires. He recommends avoiding steel wire brushes, as they can damage the ports of the burners.
However, brushes are not efficient for cleaning burners installed in tubular, fired reformers, as the burners comprise a venturi for air suction. A brush cannot clean an inner surface of a narrow pipe, which is enlarged in the other end than the end where a brush can be inserted.
Accordingly, it is an object of the invention to provide a method and an apparatus for effective and easy cleaning of burners, especially burners installed in fired, tubular reformers.
Pursuant to the above object, the present invention relates to a method for cleaning a burner by a burner cleaner. The burner comprises an inlet pipe, a venturi and a burner nozzle with a threaded connection to the inlet pipe. The method comprises that the burner nozzle is removed; that the burner cleaner is partly inserted into the burner; that the burner cleaner having a threaded guide is connected to the burner at the thread of the inlet pipe; that a shaft being a part of the burner cleaner and partly surrounded by the guide is brought to rotate by a motor being connected to one end of the shaft; that a flare brush connected to the other end of the shaft thereby is brought to hit inner surface of the burner and remove deposit from the inner surface; and that the shaft with the flare brush is moved in the guide enabling the flare brush to clean at least a part of the inner surface of the burner.
The invention further provides a burner cleaner, which comprises a shaft; an annular guide mounted around and co-axially with the shaft, the guide being threaded to connect it to a threaded end of the burner, and the guide being shorter than the shaft enabling the shaft to move in the guide; a flare brush connected at one end of the shaft, the brush being equipped with a plurality of wire ropes with spherical bodies and the brush being inside the burner when connected to the burner; and a motor connected to other end of the shaft.
Further embodiments are described in the sub-claims.
The present invention is suitable for efficient cleaning of a high number of burners with difficultly accessible inner surface.
A fired, tubular reformer is a big and important piece of equipment in plants producing ammonia, hydrogen, town gas synthesis gas and similar and comprises a high number of burners. A fired, tubular reformer often comprises hundreds of burners.
Dirt and impurities in combustion air deposit on the inner surface. Deposit changes the nature of the surface, which affects the flow pattern of fuel gas and combustion air and thereby the shape of flame.
Each burner must operate correctly, as it has to create a flame with the correct shape. If the combustion in one or more burners is not complete for instance due to wrong fuel/air ratio, the flame hits one or more tubes and damages them. Furthermore, a reformer burner must create the correct amount of heat. The heat flux is important in a reformer, as both the amount of heat and the heat distribution on the surface of reformer tubes are important in order to obtain the required endothermic reaction in the reformer.
Thereby, clean burners are needed and an easy and efficient cleaning method is important.
In a typical burner in a fired, tubular reformer fuel gas enters through an inlet nozzle surrounded by a tube, which then is enlarged to form a venturi. The venturi ensures proper aspiration of combustion air.
However, a burner with an inner surface in shape of a venturi cannot be cleaned by a simple brush or pressurised air. The cleaning is performed from the inlet end of the burner and a brush cannot reach the entire surface. Neither can pressurised air.
The invention provides a method and apparatus for cleaning such burners. The apparatus, burner cleaner, comprises a brush mounted on a shaft with a motor connected to the other end. The brush, a flare brush, comprises 3-5 wire ropes, each of which has a small spherical body at the end. The spherical bodies can be kept close to each other, when the burner cleaner is pushed into a burner. Flare brushes are commercially available.
A threaded guide is arranged around the shaft, this keeps the cleaner in position during the cleaning procedure.
The burner cleaner is of such a size that it can be held by hand when operated.
When a burner is going to be cleaned, it is removed from the equipment, typical a reformer, and taken to workshop. The burner nozzle is screwed off and the burner cleaner is screwed on by using the nozzle thread on the inlet pipes and the thread of the guide.
When the motor of the cleaner is switched on, the spherical bodies of the rotating brush hit the inner surface of the burner and knock off the deposit. The shaft is moved in the guide, so the entire surface of the burner is cleaned.
The loosened dirt is thereafter simply poured out of the burner.
In this way the entire surface of a burner is cleaned, even the venturi of the burner. This cleaning method is thorough, quick, easy and efficient, which is especially important when cleaning a high number of reformer burners.
Optionally, a burner can be cleaned in-situ.
The burner cleaner is in more detail described by the drawings.
The cleaner inserted into a burner is shown in
Before cleaning, the brush 1 and the shaft 7 are inserted through the pipe 13 into the burner. When motor 9 is switched on, shaft 7 and brush 1 rotate so quickly that the spherical bodies 5 are flung out to the burner surface, where the deposit is knocked off. This will happen regardless how deeply the cleaner is inserted into the burner.
The guide of the cleaner is shown in
The teflon annular tube 23 and a wider part of the metal union 25 are inserted around burner inlet pipe 13 and fixed by a threaded connection 29. The thread of the burner inlet pipe 13 is the thread, which is used for connecting the above mentioned fuel nozzle.
The invention is useful for cleaning all kind of burners, and especially advantageous for burners, which do not have an inner surface in a form of a straight tube.
One embodiment of the invention is a cleaner, where the shaft is 800-1200 mm, OD is 10-12 mm and made from SS 316, stainless steel.
The guide is 120-150 mm long with OD and ID according to inner diameter of inlet fuel pipe and diameter of shaft, respectively.
The annular part of the guide is made from Teflon and the threaded union is galvanic or from SS 316.
The brush fixed on the shaft has 3-5 wire ropes covering 38-102 mm inner diameter.
The flare brush has a cobalt base hard facing, which is flame-coated to the end of the stainless steel wire rope. The spherical bodies may further contain tungsten carbide or silicon carbide.
The motor rotates 1000-2000 rpm.
A preferred embodiment of the invention is a burner cleaner, where the shaft is 900-1100 mm long.
The guide is 130-140 mm long. The annular tube has an OD of 36-40 mm and an ID of 10.2-12.2 mm.
The union is 50-60 mm long and can be a 1¼/1½ inch standard union with inner thread.
The brush fixed on the shaft has 5 wire ropes covering an inner diameter of 100 mm when rotating.
Test Results
Measurements of flue gas composition were taken in a fired, tubular reformer in an 1100 MTPD ammonia plant. The burners had been in operation for 10 years and had been cleaned by a traditional method only half a year earlier without any significant effect. The fuel was natural gas, normally mixed with synthesis off-gas.
A probe was inserted through the furnace wall, i.e. through the hole for burner ignition, and samples of the flue gas were taken near three different burners.
The flue gas was analysed for the volumetric concentrations of O2, CO and CO2.
Then the burners were removed, taken to the workshop and cleaned in accordance with the invention.
The burners were 710 mm long and having inner diameter between 50 mm and 100 mm.
A burner cleaner according to the invention was used. The shaft was 1000 mm long with OD 10 mm and connected to a flare brush with five spherical bodies and a drilling machine, rotating 1300 rpm. The guide around the shaft being 140 mm long with 37/10.5 mm OD/ID was connected to the burner.
When the motor was switched on and the brush was rotating, the shaft was moved in the guide and the inner surface of a substantial part of the straight inlet fuel pipe and all the venturi part of the burner was cleaned.
After cleaning and re-installation of the burners, the flue gas was analysed in the same way as before the cleaning. The results are given in Table 1.
Measurements before cleaning show low oxygen contents or even zero and high content of CO. This clearly indicates that the dirty venturi in the burner was unable to suck-in sufficient combustion air to ensure complete combustion.
After cleaning, an oxygen surplus was measured and CO was not present, indicating that the burner was efficiently cleaned and able to provide the required amount of combustion air.
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