JP2006183902A - Method for collective chemical cleaning of once-through boiler and system therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of cleaning tubes of a superheater, a reheater, steam tubes and the like in a once-through boiler in a collective and simultaneous manner without cutting them. <P>SOLUTION: The method for collective chemical cleaning of a once-through boiler includes using a superheater inlet valve as a cleaning fluid inlet and a main steam stop valve as a cleaning fluid outlet, and cleaning a portion therebetween by means of a cleaning device by causing circulation of a chemical cleaning solution containing a chelating compound, an organic acid and a reducing agent, the cleaning device comprising a sludge collector, a chemical cleaning solution injection device, and a circulating pump. The method also includes using a reheater inlet valve as a cleaning solution inlet and a reheated steam stop valve as a cleaning solution outlet, and cleaning a portion therebetween by means of the cleaning device by causing circulation of the chemical cleaning solution containing the chelating compound, the organic acid, and the reducing agent, the cleaning device comprising the sludge collector, the chemical cleaning solution injection device, and the circulating pump. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a batch chemical cleaning method for a once-through boiler used in a thermal power plant or a general industrial boiler, and a system therefor.

  In boilers such as once-through boilers, steam oxidation scales (hereinafter sometimes referred to as “scales”) may be generated on the inner surfaces of main steam pipes, superheaters, reheaters and the like during plant operation. When the generated scale is scattered along with the steam to the turbine, there is a problem that nozzle erosion is caused and the soundness of the turbine is lost.

  Conventionally, in order to avoid such a problem, it has been performed in advance to remove the scale in the piping such as the main steam pipe by chemical cleaning, this chemical cleaning method, for example, by cutting the superheater outlet piping, In general, this is performed by using this as a cleaning liquid inlet and a main steam stop valve or a reheat steam inlet stop valve as a cleaning liquid outlet, and circulating the cleaning liquid between them using a cleaning device.

  However, since the outlet pipe of a superheater or the like has a high temperature and a high pressure, the thickness of the pipe is as thick as several tens of millimeters, and there has been a problem that much labor and cost are required for this cutting. Moreover, in order to cut this, the approval of a regulatory authority is required, and also after the said piping restoration | repair, it is necessary to carry out the inspection of a regulatory authority, The labor and expense concerning these were also great.

  In order to avoid these efforts, a balloon-type closing jig is inserted from the main steam pipe safety valve, the closing jig is installed upstream of the safety valve, and a cleaning liquid account is taken into account from the safety valve flange and cleaning is also considered. It has been. However, this method has a problem that the superheater section cannot be cleaned and the purpose cannot be achieved sufficiently.

  In addition, even if the superheater inlet pipe is cut and washed together, there is a problem that it is difficult to recover the removed sludge, and the cleaning purpose cannot be achieved completely. There is also a problem that the vessel has a bent tube such as a U tube, and it is impossible to confirm the sludge removal effect of the portion during cleaning.

  The present invention aims to solve the above-mentioned problems, and an object of the present invention is to provide a method capable of simultaneously cleaning the superheater, the reheater, each steam pipe and the like without cutting them. Is.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have taken a predetermined position of the once-through boiler as a cleaning liquid inlet and a cleaning liquid outlet, and circulated and cleaned between them with a cleaning liquid having a specific composition. The present invention has been completed by finding that it can be removed and discharged in a fine powder state and can be cleaned even in a superheater that has been conventionally difficult to perform chemical cleaning.

  That is, the present invention uses a superheater inlet valve as a cleaning liquid inlet and a main steam stop valve as a cleaning liquid outlet, and uses a cleaning apparatus equipped with a sludge collecting device, a chemical cleaning liquid injection device and a circulation pump in the meantime, It is a collective chemical cleaning method for a once-through boiler, characterized by circulating cleaning with a chemical cleaning agent containing an organic acid and a reducing agent.

  The present invention also uses a reheater inlet valve as a cleaning liquid inlet and a reheat steam stop valve as a cleaning liquid outlet, and uses a cleaning apparatus equipped with a sludge collecting device, a chemical cleaning liquid injection device and a circulation pump in the meantime, to form a chelate. A batch chemical cleaning method for a once-through boiler, characterized by circulating cleaning with a chemical cleaning agent containing a compound, an organic acid and a reducing agent.

  Furthermore, the present invention is a cleaning device equipped with a sludge trapping device, a chemical cleaning liquid injection device and a circulation pump, wherein a superheater inlet valve is used as a cleaning liquid inlet and a main steam stop valve is used as a cleaning liquid outlet. This is a collective chemical system for a once-through boiler that can be circulated and cleaned with a chemical cleaning agent containing a reducing agent.

  Furthermore, the present invention is a cleaning device equipped with a sludge collecting device, a chemical cleaning liquid injection device, and a circulation pump, wherein a reheater inlet valve is used as a cleaning liquid inlet and a reheat steam stop valve is used as a cleaning liquid outlet, and a chelate forming compound, This is a collective chemical cleaning system for a once-through boiler that can be circulated and cleaned with a chemical cleaning agent containing an organic acid and a reducing agent.

  According to the present invention, the superheater, the reheater, the main steam pipe, and the high / low temperature reheat steam pipe can be cleaned in a lump without performing costly and labor-intensive cutting work, and deposited on these pipes. It is possible to remove the scales at the same time, and in particular, it is possible to remove scales present in the bent pipes in the superheater and the reheater.

  Therefore, by the method of the present invention, the above-mentioned piping is subjected to batch chemical cleaning, whereby the scale is peeled and dropped when the boiler is started or stopped, and this prevents the scale from being scattered and flowing into the turbine, thereby generating nozzle erosion. It is possible to prevent and maintain the soundness of the turbine.

  The present invention uses a superheater (secondary superheater) inlet valve as a cleaning liquid inlet and a main steam stop valve as a cleaning liquid outlet, and uses a cleaning device equipped with a sludge collecting device, a chemical cleaning liquid injection device and a circulation pump in the meantime, A chemical cleaning method for a once-through boiler that circulates and cleans with a chemical cleaning agent containing a chelate-forming compound, an organic acid and a reducing agent (hereinafter referred to as "first aspect invention") and a reheater inlet valve as a cleaning liquid inlet, reheat A steam stop valve is used as a cleaning liquid outlet, and a cleaning apparatus equipped with a sludge collector, chemical cleaning liquid injection apparatus, and circulation pump is used for this period, and a circular cleaning is performed with a chemical cleaning agent containing a chelating compound, an organic acid and a reducing agent. And a chemical cleaning method for a once-through boiler (hereinafter referred to as “first aspect invention”).

  Hereinafter, the first aspect invention and the second aspect invention of the present invention will be described with some drawings.

  FIG. 1 schematically shows a cleaning system according to the first aspect of the present invention. In the figure, 1 is a superheater inlet valve joint seat, 2 is a main steam stop valve joint seat, 3 is a sludge collecting device, 4 is a heater, 5 is a circulation pump, 6 is a chemical dissolution tank, 7 is a chemical dissolution injection pump, 8 is a sludge measuring device, 9 is a secondary superheater, and 10 is a main steam pipe.

  In order to implement the first aspect of the invention, it is first necessary to set the superheater inlet valve as the cleaning liquid inlet and the main steam stop valve as the cleaning liquid outlet. The superheater inlet valve is generally a gate valve. When the valve is connected with the valve, the valve bonnet is opened and the valve pair is removed. It is only necessary to connect the closing plates to the side to be closed with tan buckles, and close the closing side with the thrust that stretches both sides. Further, the chemical cleaning liquid can be circulated by attaching and mounting the temporary flange to the valve flange portion.

  The chemical cleaning liquid is circulated using a cleaning device. This cleaning device includes at least a sludge collecting device 3, a chemical cleaning liquid injection device 8 including a chemical dissolution tank 6 and a chemical dissolution injection pump 7, and a circulation pump 5.

  Among these, the sludge collection device 3 collects mainly iron sludge components removed, dropped, and dissolved from each pipe in a cleaning process with a chemical cleaning solution as fine particles by subsequent forward or reverse water washing. A cyclone separator or the like can be used.

  The cleaning device is preferably provided with a heater 4 for heating the chemical cleaning liquid. As the heater 4, a mixing heater for directly heating the chemical cleaning liquid with steam, or a panel type for indirect heating is used. A heater is available.

  Furthermore, it is preferable to attach a non-destructive measuring device 8 in order to constantly grasp the remaining state of sludge in the piping, particularly the sludge accumulation state of the bent pipe portion such as the U tube of the secondary superheater 9. As such a non-destructive measurement apparatus, an apparatus using ultrasonic waves, an apparatus using X-rays, or the like can be used.

  On the other hand, the chemical cleaning liquid used in the present invention contains a chelate-forming compound, an organic acid and a reducing agent as its main components. Among these, the chelate-forming compound is intended to make the sludge particles finer after the adhesion scale is dissolved, and facilitates the removal of sludge in the subsequent water washing step. As such a chelate-forming compound, ethylenediaminetetraacetic acid (EDTA) or a salt thereof is preferable, and a sodium salt and an ammonium salt of EDTA are particularly preferable. The amount of the chelate-forming compound added is preferably about 2.5 to 12.5% by mass.

  Moreover, as an organic acid, a citric acid, gluconic acid, etc. are preferable, and it is preferable to make PH of a chemical cleaning agent into the range of 4-10, especially 4-6 by addition of this organic acid. The organic acid is preferably used in a weight ratio of 0.4 to 0.7 with respect to the chelate-forming compound 1.

  Furthermore, it is preferable to use L-ascorbic acid, erythorbic acid or the like as the reducing agent contained in the chemical detergent. This reducing agent reduces trivalent Fe into a divalent which is easy to dissolve. The blending amount of the reducing agent is preferably 0.2 to 2 w / v% of the chemical detergent liquid amount.

  In addition, by adding a corrosion inhibitor to the chemical cleaning agent, it is possible to suppress the corrosion of the piping to be cleaned during cleaning.

  Chemical cleaning using the chemical cleaning agent can be performed at a cleaning temperature in the range of 80 to 95 ° C. Further, in principle, the washing time varies depending on the scale adhesion amount and the component composition, and is preferably carried out until the Fe elution concentration in the washing liquid is saturated. Furthermore, it is preferable that the linear flow velocity at the superheater tube U tube portion at the time of cleaning is at least 1.3 m / sec.

  On the other hand, FIG. 2 schematically shows the cleaning system of the second aspect of the invention. In the figure, 3 to 8, 13 and 14 are the same as in FIG. 1, 21 is a reheater inlet valve mating seat, 22 is a reheat steam stop valve mating seat, 23 is a reheater, and 24 is reheat. Each steam pipe is shown.

  In order to implement the second aspect of the present invention, it is first necessary to use the reheater inlet valve as the cleaning liquid inlet and the reheat steam stop valve as the cleaning liquid outlet. When engaging with the reheater inlet valve, the reheater inlet valve is also generally a gate valve. Therefore, after opening the valve bonnet and extracting the valve pair, the cleaning liquid water-flowing side of the valve has a plate with an opening. In addition, it is only necessary to connect the closing plates to the side that closes the cleaning liquid with tumbles and close the closing side with the thrust that stretches both sides. Further, the chemical cleaning liquid can be circulated by attaching and mounting the temporary flange to the valve flange portion.

  The circulation of the chemical cleaning solution is basically performed in the same manner as described in the first aspect of the invention. That is, the cleaning apparatus is the same as that used in the first aspect invention, and each device constituting the apparatus has the same function as described in the first aspect invention.

  Similarly, it is preferable to attach a non-destructive measuring device 8 in order to always grasp the sludge accumulation state in the bent pipe portion in the reheater pipe.

  Furthermore, the chemical cleaning liquid used in the second aspect invention is also the same as that used in the first aspect invention, and the components constituting the chemical cleaning liquid, the blending amount thereof, or the action thereof are also the same.

  Furthermore, chemical cleaning conditions may be substantially the same as in the first aspect of the invention, although depending on the degree of scale generation in the reheater or reheat steam pipe.

  EXAMPLES Next, although an Example, a comparative example, and a test example are given and this invention is demonstrated in more detail, this invention is not restrict | limited at all by these Examples.

EXAMPLE Preparation of the present chemical cleaning solution:
EDTA-4NH ₃ the 8w / v%, citric acid 4w / v%, L- ascorbic acid 0.2 w / v%, was added a corrosion inhibitor, each water so as to be 0.3 w / v%, chemical cleaning An agent (product of the present invention) was prepared.

Comparative Example Preparation of a comparative chemical cleaner:
Formic acid was added to water at 2 w / v%, glycolic acid at 4 w / v%, L-ascorbic acid at 0.2 w / v%, and corrosion inhibitor at 0.3 w / v%. Comparative product) was prepared.

Test example Scale cleanability test:
About the present invention product obtained in Example 1 and the comparative product obtained in the comparative example, the scale removability was examined using the same reheat steam pipe in which the scale was generated as a sample. The test was performed by maintaining the temperature of the product of the present invention and the comparative product between 85-95 ° C., immersing the sample in this for 44 hours, and examining the amount of corrosion of the sample, the amount of sludge generated and the form of sludge. . The results are shown in Table 1.

  As is apparent from the results, the sludge form when using the product of the present invention is fine powder, and it was judged that the sludge flowed out easily. Sludge was observed, and it was considered difficult to drain them. Further, when the comparative product was used, the amount of corrosion and sludge of the sample was larger than when the product of the present invention was used.

  According to the method of the present invention, the pipes of the system to be cleaned such as the superheater / reheater / main steam pipe / high / low temperature reheat steam pipe of the once-through boiler can be cleaned at the same time without being cut. This makes it possible to improve the cleaning efficiency.

  In addition, the chemical cleaning agent used in the present invention contains a reducing agent in addition to the chelate-forming compound and the organic acid, so that sludge can be removed by a method different from the conventional adhesion scale dissolution mechanism. . That is, it is possible to make the sludge particles after dissolution finer and facilitate the sludge unloading in the subsequent water washing step.

  Therefore, the present invention can be advantageously used as a method for cleaning a once-through boiler.

Cleaning system diagram at the time of batch cleaning of the superheater and main steam pipe of the first aspect invention Cleaning system diagram for batch cleaning of reheater and reheat steam pipe of the second aspect invention

Explanation of symbols

1…… Superheater inlet valve mating seat 2…… Main steam stop valve mating seat 3…… Sludge collector 4…… Heater 5…… Circulation pump 6…… Chemical dissolution tank 7…… Chemical dissolution injection pump 8…… Sludge measuring device 9…… Secondary superheater 10…… Main steam pipe 11…… Primary superheater 12…… Cage wall 13…… High pressure turbine 14…… Medium pressure turbine 21…… Reheater inlet valve mating seat 22… ... Reheat steam stop valve joint seat 23 ... ... Reheater 24 ... ... Reheat steam pipe
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Claims (15)

  A superheater inlet valve is used as a cleaning liquid inlet and a main steam stop valve is used as a cleaning liquid outlet, and a chelating agent, an organic acid, and a reducing agent are used in the meantime using a cleaning device equipped with a sludge collection device, a chemical cleaning solution injection device and a circulation pump. A batch chemical cleaning method for a once-through boiler, characterized by circulating cleaning with a chemical cleaning agent containing   The reheater inlet valve is used as a cleaning liquid inlet, and the reheat steam stop valve is used as a cleaning liquid outlet. Between these, a cleaning device equipped with a sludge collector, a chemical cleaning liquid injection device and a circulation pump is used. A batch chemical cleaning method for a once-through boiler, characterized by circulating cleaning with a chemical cleaning agent containing a reducing agent.   3. The once-through chemical cleaning method for a once-through boiler according to claim 1 or 2, wherein, after circulating cleaning of the cleaning liquid, cleaning is further performed by flowing water in a forward or reverse direction with respect to the cleaning liquid.   The method of batch chemical cleaning of a once-through boiler according to any one of claims 1 to 3, wherein the cleaning device further includes a heating means.   5. The batch chemical cleaning method for a once-through boiler according to claim 1, wherein the chemical cleaning liquid injection device of the cleaning device includes a chemical dissolution tank and a chemical injection pump.   Furthermore, the non-destructive measuring device is used to confirm whether or not the sludge that has been peeled off and removed from the object to be cleaned on the bent pipe in the secondary superheater or reheater is accumulated. Batch chemical cleaning method for once-through boilers.   The method for batch chemical cleaning of a once-through boiler according to any one of claims 1 to 6, wherein the chemical cleaning liquid further contains a corrosion inhibitor.   The method for batch chemical cleaning of a once-through boiler according to any one of claims 1 to 7, wherein the chelate-forming compound contained in the chemical cleaning solution is an ammonium salt or sodium salt of EDTA.   The method for batch chemical cleaning of a once-through boiler according to any one of claims 1 to 8, wherein the organic acid contained in the chemical cleaning liquid is citric acid or gluconic acid.   The method for batch chemical cleaning of a once-through boiler according to any one of claims 1 to 9, wherein the reducing agent contained in the chemical cleaning liquid is L-ascorbic acid and / or L-sorbic acid.   The method for batch chemical cleaning of a once-through boiler according to any one of claims 1 to 10, wherein the pH of the chemical cleaning solution is 4 to 10.   A cleaning device equipped with a sludge collector, a chemical cleaning liquid injection device, and a circulation pump, with a superheater inlet valve as a cleaning liquid inlet and a main steam stop valve as a cleaning liquid outlet, containing a chelating compound, an organic acid and a reducing agent A batch chemical system for once-through boilers that can be circulated with chemical cleaners.   Furthermore, the collective chemical cleaning system for a once-through boiler according to claim 12, wherein water can flow in a forward direction or a reverse direction with respect to the cleaning liquid.   A cleaning device equipped with a sludge collector, a chemical cleaning fluid injection device, and a circulation pump. The reheater inlet valve is used as a cleaning fluid inlet, and the reheat steam stop valve is used as a cleaning solution outlet, and a chelating compound, organic acid, and reducing agent are mixed. A batch chemical cleaning system for once-through boilers that can be circulated and cleaned with chemical cleaning agents. Furthermore, the collective chemical cleaning system for a once-through boiler according to claim 14, wherein water can flow in a forward direction or a reverse direction with respect to the cleaning liquid.

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