JP4912380B2 - Debris removal method for denitrification equipment - Google Patents

Description

  The present invention relates to a deposit removal method performed in a denitrification apparatus for treating wastewater containing ammonia nitrogen to remove ammonia nitrogen in the wastewater.

  In general, in a thermal power generation facility, wastewater containing ammonia nitrogen is discharged from various devices such as a condensate demineralizer and an electric dust collector. If such wastewater containing nitrogen is released into the ocean as it is, it will cause eutrophication of the ocean, and therefore it is required to discharge after removing the nitrogen by some means.

  As methods for removing nitrogen components from wastewater containing nitrogen components, methods such as biological treatment methods and physicochemical treatment methods are known, but in order to efficiently treat a large amount of wastewater. It is preferable to use a physicochemical treatment method.

  As a denitrification apparatus for treating waste water containing ammonia nitrogen by a physicochemical treatment method, for example, a denitrification apparatus using an ammonia stripping method is known. Specifically, an ammonium salt contained in the wastewater is converted to ammonia by adding a strong base to the wastewater, and ammonia is separated from the wastewater in a stripping tower (ammonia stripper). The ammonia stripper is a so-called ammonia vaporizer, and heats wastewater containing ammonia with water vapor to vaporize and separate ammonia contained in the wastewater.

By the way, when the waste water containing ammonia nitrogen is treated using the denitrification apparatus using the ammonia stripping method, deposits called scales adhere to the inside of the denitrification apparatus piping, and the piping is blocked. There are things to do. The scale is mainly a hydroxide of hardness components and metal ions contained in the waste water. Specifically, Ca (OH) ₂ , Mg (OH) ₂ , Fe (OH) ₂ , and Ni ( OH) _{2 and the} like.

  Such scale generation in the denitrification apparatus is considered to be mainly caused by the presence of hardness components in the waste water. That is, in general, industrial water may contain calcium and magnesium, and calcium is also detected from the waste water of a flue gas desulfurization device used for removing sulfur dioxide from boiler exhaust gas. In addition to the hardness component, iron ions and the like may be mixed into the waste water due to corrosion of piping in the power plant.

  It is considered that the hardness component and metal ions mixed in the waste water are precipitated as hydroxide when a strong base is added in the denitrification apparatus, and this adheres to the inside of the pipe and closes the pipe.

  As described above, in the denitrification apparatus using the ammonia stripping method, generation of scale has been a problem in the past. As means for solving such a problem, Patent Document 1 discloses ammonia. The raw water containing the water is poured into an evaporation tube having a substantially hollow interior, and after the ammonia vapor is distilled by stirring with steam, the introduction of the steam is stopped, and the treated water is then released by opening the inside of the evaporator to the atmosphere. An ammonia treatment method is disclosed, in which ammonia distillation is performed by repeating a batch treatment operation for discharging to a stage evaporator or out of the system.

According to the invention described in Patent Document 1, hydroxides are used when ammonia nitrogen and SS content, hardness components (Ca, Mg) or pH are increased for batch processing using an internal cavity evaporator. Even in the treatment of wastewater and sludge containing metal ions that generate slag, scaling and clogging are not caused. Further, since the evaporator groups are connected in series, a high removal ability can be obtained with a small amount of steam blowing.
JP 2003-181444 A

  However, in the invention described in Patent Document 1, although the clogging of the piping due to the adhesion of the scale can be suppressed, the adhesion of the scale itself is not prevented, and a separate removing means is required for removing the scale. Is. That is, when a large amount of scale adheres, even in the invention described in Patent Document 1, the piping may be blocked, and in this case, the scale must be removed.

  In addition, the invention described in Patent Document 1 does not prevent the scale from adhering in the existing denitrification apparatus, and requires a new capital investment.

  Furthermore, as a specific means for removing the scale, there is a method of cleaning the inside of the denitrification apparatus using a chemical. However, such a method requires a large amount of industrial water and chemicals, and requires a large amount of cost. Is required.

  The present invention has been made in view of the above-described problems, and provides a scale removal method performed in an existing denitrification apparatus, which can be performed without much expense. The purpose is to do.

  The inventors of the present invention have intensively studied to solve the above problems. As a result, in the denitrification device, when the raw water containing ammonium salt is filled in the stripping tower and the piping associated therewith and left for a predetermined time, a part of the scale attached to the inside of the denitrification device is removed, and the piping is The present inventors have found that the occlusion state can be improved and have completed the present invention. Specifically, the present invention provides the following.

(1) A denitrification relay tank for reacting an ammonium salt with a strong base to generate ammonia, a stripping tower for removing ammonia generated in the denitrification relay tank from the treated water, and removing ammonia A purified water discharge path for discharging the treated water, a denitrification relay tank that connects the denitrification relay tank and the stripping tower, a stripping tower connection path, the purified water discharge path, and the denitrification relay tank and stripping tower A denitrification circulation bypass path that short-circuits a connection path; a denitrification bypass branch point that branches into the purified water discharge path and the denitrification circulation bypass path in the purified water discharge path; and the denitrification relay tank-dispersion tower connection A denitrification bypass junction where the denitrification relay tank-dispersion tower connection path and the denitrification circulation bypass path merge, and purified water provided after the denitrification bypass branch point in the purified water discharge path A denitrification relay tank-divergence tower connection path valve provided between the denitrification bypass confluence and the denitrification relay tank in the denitrification relay tank-dispersion tower connection path; A denitrification circulation bypass path valve provided in the circulation bypass path, the denitrification apparatus for removing the ammonium salt from the ammonium salt-containing raw water containing the ammonium salt in a basic attachment attached to the denitrification apparatus. A denitrification apparatus deposit removal method for removing kimono, the first step of discharging treated water remaining in the purification water discharge path, the denitrification relay tank-dispersion tower connection path, and the diffusion tower And a second step of leaving the stripping tower filled with acidic ammonium salt-containing raw water and leaving the stripped water, the denitrification relay removal of deposits, Method.

  According to the invention described in (1), deposits such as scale can be dissolved in the ammonium salt-containing raw water by filling the ammonium salt-containing raw water inside the denitrification apparatus. This is presumably because the ammonium salt-containing raw water is acidic and has an action of dissolving calcium hydroxide, magnesium hydroxide, iron hydroxide, nickel hydroxide and the like. Moreover, since the deposit removal method of the denitrification apparatus which concerns on this invention does not require a lot of industrial water, a special chemical | medical agent, etc., it can be implemented at low cost. Furthermore, the deposits such as the scale are dissolved, so that the clogging of the piping is temporarily eliminated, and the number of times the inside of the denitrification apparatus is cleaned with chemicals can be reduced.

  Here, “ammonium salt-containing raw water” refers to wastewater from various devices provided in the plant, which contains an ammonium salt, and has a pH of about 4. In the present invention, it particularly refers to waste water in a thermal power generation facility. Further, “treated water” refers to water related to wastewater treatment by a denitrification device and water that has been subjected to wastewater treatment by a denitrification device, and the latter is particularly referred to as “purified water”.

  (2) In the second step, the deposit removal method for a denitrification apparatus according to (1), wherein the deposit is allowed to stand for 1 hour to 10 hours.

  According to the invention described in (2), since the denitrification device is filled with ammonium salt-containing raw water and left for one hour or longer, deposits such as scale can be dissolved, and the piping and the like are temporarily blocked. Can be resolved. Moreover, since the time to leave is 10 hours or less, the influence on the plant due to the stoppage of the denitrification apparatus can be minimized.

  (3) After the second step, the denitrification circulation bypass path valve is opened, the purified water discharge path valve and the denitrification relay tank-dispersion tower connection path valve are closed, and the ammonium salt The deposit removal method for a denitrification apparatus according to (1) or (2), wherein a third step of circulating the raw raw water for 1 hour to 5 hours is performed.

  (4) The deposit removal method for a denitrification apparatus according to (3), wherein the second step and the third step are repeated.

  According to the invention described in (3), since the ammonium salt-containing raw water is circulated through the purified water discharge path, the denitrification relay tank-dispersion tower connection path, the stripping tower, and the denitrification circulation bypass path, deposits such as scales are present. The efficiency of dissolving in the ammonium salt-containing raw water can be increased. Thereby, obstruction | occlusion of piping etc. can be eliminated more efficiently. Further, according to the invention described in (4), since the standing and the circulation of the ammonium salt-containing raw water are repeatedly performed, it is possible to remove more deposits.

  According to the deposit removal method of the denitrification apparatus according to the present invention, the ammonium salt-containing raw water is filled inside the denitrification apparatus, and the deposits such as scales are removed by leaving it alone. Without obstructing the piping or the like. At the same time, by carrying out the deposit removal method of the denitrification apparatus according to the present invention, the number of times the inside of the denitrification apparatus is cleaned with chemicals or the like can be reduced, which is economical.

  Moreover, since ammonium salt containing raw water shows acidity, deposits, such as a scale, can be removed partially, and blockage | clogging of piping can be eliminated temporarily.

  Next, the deposit removal method of the denitrification apparatus according to the present invention will be described with reference to the drawings.

<Denitrification equipment>
First, the denitrification apparatus according to the present embodiment will be described.

[Configuration of denitrification equipment]
FIG. 1 shows a denitrification apparatus according to this embodiment. The denitrification apparatus according to this embodiment includes a denitrification relay tank 16 for reacting an ammonium salt in a treated water with a strong base to produce ammonia, and ammonia produced in the denitrification relay tank 16 in the treated water. And a stripping tower 11 for removing from the water.

  Further, in the denitrification apparatus according to the present embodiment, the denitrification relay tank 16 and the stripping tower connection path 20 that connects the denitrification relay tank 16 and the stripping tower 11 as pipes that connect each device, and the treatment that removes ammonia. It has a purified water discharge path 23 for discharging water, and a denitrification circulation bypass path 29 that short-circuits the purified water discharge path 23 and the denitrification relay tank-dispersion tower connection path 20. Here, for convenience, a branch point where the purified water discharge path 23 and the denitrification circulation bypass path 29 branch on the purified water discharge path 23 is referred to as a denitrification bypass branch point 25, and on the denitrification relay tank-dispersion tower connection path 20, A junction where the denitrification relay tank-dispersion tower connection path 20 and the denitrification circulation bypass path 29 join together is referred to as a denitrification bypass junction 24.

  Furthermore, the denitrification apparatus according to the present embodiment is provided with a valve on each pipe. That is, the denitrification apparatus according to this embodiment includes a denitrification bypass on the purified water discharge path 23, a purified water discharge path valve 26 provided after the denitrification bypass branch point 25, a denitrification relay tank-dispersion tower connection path 20, and a denitrification bypass. Denitrification relay tank-dispersion tower connection path valve 17 provided between the junction 24 and the denitrification relay tank 16, and a denitrification circulation bypass path valve (not shown) provided on the denitrification circulation bypass path 29. And having.

  In addition, the denitrification apparatus according to the present embodiment adds the electrolyte to the first drainage storage tank 12 for storing the ammonium salt-containing raw water and the ammonium salt-containing raw water, and diffuses it into the wastewater. A denitrification reaction tank 14 for salting out insoluble components, a denitrification settling tank 15 for precipitating the insoluble components, a denitrification circulation pump 18 provided at a denitrification bypass junction 24, and a stripping tower 11 From the preheater 19 for exchanging heat between the inflowing treated water and the purified water flowing out of the diffusion tower 11, the second drainage storage tank 30 for storing the wastewater from the diffusion tower 11, and the purified water discharge path 23 And a drainage discharge path 31 that branches and guides the drainage discharged from the diffusion tower 11 to the second drainage storage tank 30. Here, selection of the flow path between the purified water discharge path 23 and the drainage discharge path 31 can be performed by a valve provided on each path.

[Operation of denitrification equipment]
The denitrification apparatus according to the present embodiment operates as follows. That is, the ammonium salt-containing raw water flowing out from each device of the thermal power generation facility is collected in the first drainage storage tank 12 and then sent to the denitrification reaction tank 14. In the denitrification reaction layer, an electrolyte such as sodium hydroxide is added to the ammonium salt-containing raw water to salt out insoluble components dispersed in the waste water. The treated water to which the electrolyte has been added is sent to the denitrification precipitation tank 15, where the salted out insoluble components are precipitated. The treated water after the insoluble component is precipitated is sent to the denitrification relay tank 16, and a strong base such as sodium hydroxide is added to convert the ammonium salt into ammonia.

  The wastewater containing ammonia is sent to the stripping tower 11 and vaporizes ammonia by an ammonia stripping method. Prior to this, the treated water containing ammonia passes through the preheater 19 and is preheated by exchanging heat with the high-temperature purified water discharged from the diffusion tower 11. Thereby, when implementing the ammonia stripping method, the thermal energy required for heating the treated water can be reduced. The ammonia vaporized in the stripping tower 11 is condensed into ammonia water by the condenser 21 and recovered in the recovery tank 22.

  The purified water from which ammonia has been removed by the diffusion tower 11 passes through the preheater 19 again, exchanges heat with the treated water containing ammonia, and is discharged through the purified water discharge path 23.

<Debris removal method of denitrification equipment>
The deposit removal method of the denitrification apparatus according to the present embodiment includes the first step of discharging the treated water remaining in the purified water discharge path 23, the denitrification relay tank-dispersion tower connection path 20, and the diffusion tower 11, and the purified water. And a second step of leaving the stripping tower 11 filled with ammonium salt-containing raw water and leaving it after the second step, if necessary, after the second step. The denitrification circulation bypass route valve is opened, the purified water discharge route valve 26 and the denitrification relay tank-dispersion tower connection route valve 17 are closed, and the third step of circulating the ammonium salt-containing raw water is included. .

[First step]
In the deposit removal method of the denitrification apparatus according to the present embodiment, firstly, the treated water remaining in the purified water discharge path 23, the denitrification relay tank-dispersion tower connection path 20, and the diffusion tower 11 is discharged. At this time, the treated water remaining in the denitrification relay tank 16 may be discharged at the same time. When discharging the treated water, the purified water discharge path 23 and the valves (valves 27 and 28 in FIG. 1) provided in the drainage discharge path 31 are opened and closed, so that the treated water from the diffusion tower 11 is supplied to the purified water discharge path. The flow path may be set so as to flow into the drainage discharge path 31 via 23. Thereby, the treated water remaining in the purified water discharge path 23, the denitrification relay tank-divergence tower connection path 20, and the diffusion tower 11 flows into the second drainage storage tank 30. The 2nd waste water storage tank 30 is connected with the 1st waste water storage tank 12, as FIG. 1 shows. For this reason, the treated water discharged to the second drainage storage tank 30 is treated again by the denitrification device when the denitrification device resumes operation.

[Second step]
After draining the treated water remaining in the purified water discharge path 23, the denitrification relay tank-dispersion tower connection path 20, and the diffusion tower 11, the purified water discharge path 23, the denitrification relay tank-dispersion tower connection path 20, and the diffusion tower 11 is filled with raw water containing ammonium salt. The ammonium salt-containing raw water is preferably stored in the first drainage storage tank 12 and filled by sequentially feeding water to the denitrification reaction tank 14, the denitrification precipitation tank 15, and the denitrification relay tank 16. That is, the filling of the ammonium salt-containing raw water can be usually performed using a water supply system used in the denitrification treatment.

  After the purified water discharge path 23, the denitrification relay tank-divergence tower connection path 20, and the diffusion tower 11 are filled with the ammonium salt-containing raw water, it is left for a predetermined time. Since the ammonium-containing raw water is acidic and contains acids such as sulfuric acid derived from acidic ammonium sulfate produced in the flue, these acids react with hardness components and metal ion hydroxides to form soluble salts. Form. For this reason, the deposit | attachment adhering to the inside of a denitrification apparatus, such as a scale, can be dissolved. The time to leave after filling the ammonium ion-containing raw water is preferably 1 hour or more and 10 hours or less, more preferably 2 hours or more and 5 hours or less. By leaving it to stand for 1 hour or more, a sufficient amount of deposits such as scale can be dissolved. Since the leaving time is 10 hours or less, the influence on the plant due to the stoppage of the denitrification apparatus can be minimized.

[Third step]
In the deposit removal method for the denitrification apparatus according to the present embodiment, after the second step, if necessary, the denitrification circulation bypass path valve is opened, and the purified water discharge path valve 26 and the denitrification relay tank are opened. -It may include a third step of closing the stripping tower connection path valve 17 and circulating the ammonium salt-containing raw water. That is, in the third step, using the denitrification circulation pump 18, ammonium salt-containing raw water is added to the denitrification relay tank-dispersion tower connection path 20, the stripping tower 11, the purified water discharge path 23, and the denitrification circulation bypass path 29. Is to circulate. By circulating the ammonium salt-containing raw water, deposits such as scales attached to the inside of the denitrification apparatus can be efficiently dissolved. The circulation is preferably performed for 1 hour or more and 5 hours or less, more preferably 1 hour or more and 3 hours or less. By circulating for 1 hour or more, deposits such as scale can be sufficiently dissolved in the ammonium salt-containing raw water. Since the circulation time is 5 hours or less, the influence on the plant due to the stop of the denitrification apparatus can be minimized.

  The second step and the third step are preferably performed repeatedly. Thereby, many deposits, such as a scale, can be dissolved with ammonium salt containing raw water.

[Cleaning of denitrification equipment with chemicals]
The deposit removal method of the denitrification apparatus according to the present embodiment is more effective when performed together with the cleaning of the denitrification apparatus with chemicals. That is, it is preferable to select and perform the deposit removal method of the denitrification apparatus of the present invention and the cleaning of the denitrification apparatus with chemicals according to the transition of the wastewater treatment amount by the denitrification apparatus.

  The chemical denitrification apparatus cleaning method includes a process of discharging the treated water remaining in the purified water discharge path 23, the denitrification relay tank-divergence tower connection path 20, and the diffusion tower 11 and filling industrial water, and the purified water discharge path. 23, the step of adding an acid to the industrial water filled in the denitrification relay tank-divergence tower connection path 20 and the diffusion tower 11, the denitrification circulation bypass path valve is opened, the purified water discharge path valve 26 and the denitrification The relay tank-dispersion tower connection path valve 17 is closed, the process of circulating industrial water to which acid has been added, the denitrification circulation bypass path valve are closed, the purified water discharge path valve 26 and the denitrification relay tank -Opening the stripping tower connection path valve 17 and discharging the industrial water to which the acid has been added.

(acid)
In the method for cleaning a denitrification apparatus using chemicals, by adding an acid to industrial water, a hydroxide such as a hardness component or a metal ion, which is a main component of the deposit, is dissolved. As the acid added to industrial water, weak acids are preferable, and organic acids and inorganic acids that are weak acids can be suitably used. Specifically, acetic acid, citric acid, and oxalic acid are examples of the organic acid, and sulfuric acid, hydrochloric acid, and nitric acid are examples of the inorganic acid. Of these organic acids and inorganic acids, those that form an insoluble salt with the hydroxide that is a component of the deposit are not preferred. For example, carbonic acid, fatty acid, and the like are acids added to industrial water in the present invention. Can not be used as. Of these, organic acids can be preferably used.

  Among organic acids, there are those that can act as chelating agents, such as polyvalent carboxylic acids typified by ethylenediaminetetraacetic acid. In this embodiment, as the weak acid that can be used in the deposit removal method of the denitrification apparatus, an organic acid having a chelating power can be used.

  As a reference when performing the deposit removal method of the denitrification apparatus according to the present embodiment and the cleaning method of the denitrification apparatus using chemicals, for example, the processing amount of the denitrification apparatus with a rated capacity of 4 t / h is 3.5 t. It is preferable to carry out the deposit removal method of the denitrification device when the denitrification device becomes less than / h, and when the treatment amount of the denitrification device becomes 2 t / h or less, It is preferable to perform a cleaning method.

It is drawing which shows the outline of the denitrification apparatus by which the deposit removal method of the denitrification apparatus which concerns on this embodiment is implemented.

Explanation of symbols

11 Desorption tower 12 First drainage storage tank 14 Denitrification reaction tank 15 Denitrification precipitation tank 16 Denitrification relay tank 17 Denitrification relay tank-Stripping tower connection path valve 18 Denitrification circulation pump 19 Preheater 20 Denitrification relay tank- Stripping tower connection path 21 Condenser 22 Recovery tank 23 Purified water discharge path 24 Denitrification bypass junction 25 Denitrification bypass branch point 26 Purified water discharge path valve 27 Valve 28 Valve 29 Denitrification circulation bypass path 30 Second drainage storage tank 31 Drainage Discharge route

Claims (4)

A denitrification relay tank for reacting an ammonium salt with a strong base to produce ammonia;
A stripping tower for removing ammonia generated in the denitrification relay tank from the treated water;
A purified water discharge route for discharging treated water from which ammonia has been removed,
A denitrification relay tank-divergence tower connection path connecting the denitrification relay tank and the stripping tower;
A denitrification circulation bypass path that short-circuits the purified water discharge path and the denitrification relay tank-dispersion tower connection path;
In the purified water discharge path, a denitrification bypass branch point that branches into the purified water discharge path and the denitrification circulation bypass path;
In the denitrification relay tank-stripping tower connection path, a denitrification bypass junction where the denitrification relay tank-stripping tower connection path and the denitrification circulation bypass path merge,
In the purified water discharge path, a purified water discharge path valve provided after the denitrification bypass branch point, and
In the denitrification relay tank-stripping tower connection path, a denitrification relay tank-stripping tower connection path valve provided between the denitrification bypass junction and the denitrification relay tank,
A denitrification circulation bypass path valve provided in the denitrification circulation bypass path, and a denitrification apparatus for removing ammonium salt from ammonium salt-containing raw water containing ammonium salt,
A denitrification apparatus deposit removal method for removing basic deposits attached to the denitrification apparatus,
A first step of discharging the purified water discharge path, the denitrification relay tank-divergence tower connection path, and the treated water remaining in the diffusion tower;
A denitrification apparatus deposit removal method comprising: the purified water discharge path, the denitrification relay tank-divergence tower connection path, and a second step in which the stripping tower is filled with acidic ammonium salt-containing raw water and allowed to stand.   The deposit removal method for a denitrification apparatus according to claim 1, wherein the second step is allowed to stand for 1 hour to 10 hours.   After the second step, the denitrification circulation bypass path valve is opened, the purified water discharge path valve and the denitrification relay tank-dispersion tower connection path valve are closed, and the ammonium salt-containing raw water is removed. The deposit removal method for a denitrification apparatus according to claim 1 or 2, wherein a third step of circulating for 1 hour to 5 hours is performed.   The deposit removal method for a denitrification apparatus according to claim 3, wherein the second step and the third step are repeated.

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