JP6285773B2 - Wastewater treatment method for exhaust gas treatment equipment - Google Patents

Description

  The present invention relates to a wastewater treatment method for an exhaust gas treatment apparatus that purifies exhaust gas by bringing seawater into contact with the exhaust gas.

Engines and boilers using fossil fuels are used in thermal power plants, chemical industrial plants, waste incineration facilities, ships, and the like. The exhaust gas discharged from such engines and boilers contains sulfur (mainly SO ₂ ), and it is necessary to remove SO ₂ to a certain level by an exhaust gas treatment device from the viewpoint of environmental protection. Here, in the exhaust gas treatment apparatus, a method (wet desulfurization) that uses an alkaline absorbent and absorbs and removes SO ₂ by contact between the exhaust gas and the alkaline absorbent in a scrubber (absorption tower) is performed. (See, for example, Patent Documents 1 and 2).

In Patent Documents 1 and 2, when the removal of SO ₂ in the flue gas, the scrubber were washed seawater is introduced as alkaline absorbent agents, pH by the cleaning seawater absorbs SO ₂ (hydrogen ion concentration) of 3 About ~ 5 drainage occurs. This waste water is introduced from the scrubber to the waste water treatment tank. In the wastewater treatment tank, wastewater and diluted seawater pumped up via a seawater pump are mixed, and then aerated (aerated) through a nozzle or the like. By this aeration treatment, the pH of the wastewater is increased, and in the sea area excluding the emission control sea area (ECA), it can be discharged into the sea as treated water with improved water quality.

JP 2013-244465 A JP 2013-158734 A

  However, in the methods of Patent Documents 1 and 2, the amount of diluted seawater is as large as about 2 to 6 times the amount of washed seawater (“Exhaust Gas Scrubber” published in 2011 by the US Environmental Protection Agency). (See "Washwater Effect"). Since a large amount of diluted seawater is pumped up and used, there is a problem that the energy consumption of the device driven by the aeration process becomes large, or the tank for aeration of the mixed waste water becomes large. Such a problem becomes apparent particularly in a ship because the energy that can be supplied in the ship is limited during navigation and the installation space in the ship is limited.

  This invention is made | formed in view of this point, and can provide the wastewater treatment method of the waste gas treatment apparatus which can reduce the energy consumption for wastewater treatment and can reduce the volume of a wastewater treatment tank. Objective.

The waste water treatment method of the exhaust gas treatment apparatus of the present invention is a method in which SO ₂ contained in the exhaust gas introduced into the scrubber is brought into contact with the washing sea water to purify the exhaust gas to a purified gas and to wash the washing sea water that has absorbed SO _2. a purification step of discharging the waste water treatment tank, the flow rate and SO ₂ concentration of the exhaust gas before being introduced into the scrubber, SO ₂ concentration of the purge gas, and the flow rate of cleaning the seawater to be introduced into the scrubber measured as waste In the wastewater treatment tank, in the wastewater treatment tank, the treatment step of mixing the air into the wastewater to obtain aeration treated water, and after the treatment step, the aerated treated water discharged from the wastewater treatment tank, A supply step of supplying and mixing an alkaline substance in an amount corresponding to the measurement value of the measurement step.

  According to the waste water treatment method, the timing of mixing the aerated treated water with the alkaline substance is after the discharge from the waste water treatment tank. Thereby, it is not necessary to introduce an alkaline substance into the wastewater treatment tank while sufficiently improving the quality of the treated water, so that the volume of the wastewater treatment tank can be reduced. Further, the amount of waste water to be aerated in the waste water treatment tank can be reduced, the energy consumption of the device driven for the aeration treatment can be reduced, and the treatment time can be shortened.

  In the wastewater treatment method, in the supplying step, the alkaline substance may be introduced into a dilution tank into which the aerated treated water is introduced, and the alkaline substance and the aerated treated water may be mixed. According to this method, the alkaline substance and the aerated water can be better mixed in the dilution tank, and the water quality improvement effect can be enhanced.

  According to the present invention, since the timing of mixing the aerated treated water with the alkaline substance is after the discharge from the waste water treatment tank, the energy consumption for the waste water treatment can be reduced, and the volume of the waste water treatment tank can be reduced. Can do.

1 is a schematic configuration diagram of an exhaust gas treatment apparatus according to a first embodiment. It is a flowchart for demonstrating the flow of a waste water treatment method. It is a schematic block diagram of the waste gas processing apparatus which concerns on 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of an exhaust gas treatment apparatus according to the first embodiment. Note that an apparatus for purifying exhaust gas discharged from an engine used in a ship is considered as the exhaust gas treatment apparatus according to the present embodiment. However, the present invention is not limited to this, and the exhaust gas treatment apparatus according to the present embodiment can be applied to the treatment of exhaust gas in thermal power plants, chemical industrial plants, and waste incineration facilities.

  As shown in FIG. 1, the exhaust gas treatment apparatus introduces a scrubber 10 to which exhaust gas g1 from the engine 20 is supplied, a first seawater pump 30 that supplies cleaning seawater a1 to the scrubber 10, and drainage a2 from the scrubber 10. And a wastewater treatment tank 40. In addition, when applying the exhaust gas processing apparatus of this Embodiment to various plants etc., it may replace with the engine 20 and a boiler may be used.

The exhaust gas g1 discharged from the engine 20 is introduced into the scrubber 10 through the exhaust gas pipe 21. The exhaust gas g1 contains SO ₂ (sulfur dioxide) and CO ₂ (carbon dioxide). In addition, the cleaning seawater a <b> 1 is introduced into the scrubber 10 through the cleaning seawater pipe 31 by driving the first seawater pump 30. The washed seawater a1 introduced into the scrubber 10 is sprayed by a plurality of nozzles (not shown) and comes into gas-liquid contact with the exhaust gas g1 rising in the scrubber 10.

As shown in the following formula (1), SO ₂ in the exhaust gas g1 is absorbed by the washed seawater a1, and dissociates into hydrogen ions (H ⁺ ) and sulfite ions (HSO ₃ ⁻ ). Further, CO ₂ in the exhaust gas g1 is absorbed by the washed seawater a1 as shown in the following formula (2). A part of the hydrogen ions react with hydrogen carbonate ions (HCO ₃ ⁻ ) in the washed seawater a1, as shown in the following formula (3).
SO ₂ (gas) + H ₂ O → H ₂ SO ₃ → H ⁺ + HSO ₃ ⁻ (1)
CO ₂ (gas) → CO ₂ (aq) (2)
H ⁺ + HCO ₃ ⁻ → H ₂ O + CO ₂ (aq) (3)

In the scrubber 10, SO ₂ in the exhaust gas g1 is absorbed and removed by the cleaning seawater a1. Therefore, the exhaust gas g1 becomes the purified gas g2 purified in the scrubber 10, and is exhausted from the upper part of the scrubber 10 to the atmosphere. In the scrubber 10, the washed seawater a1 that has absorbed SO ₂ and CO ₂ becomes drainage a2, and sulfite ions (HSO ₃ ⁻ ) and carbonic acid (CO ₂ ) are dissolved in the drainage a2. Accordingly, the pH (hydrogen ion index) of the waste water a2 is about 3 to 5. The drainage a2 in the scrubber 10 falls by its own weight along the inner wall surface of the scrubber 10, is stored in a storage section below the scrubber 10, and then discharged to the wastewater treatment tank 40 through the drainage pipe 11.

The wastewater a2 introduced into the wastewater treatment tank 40 needs to neutralize the acid in order to be discharged into the sea. Therefore, in the waste water treatment tank 40, the aeration process in which air is mixed into the waste water a2 through the blower 41 as an air supply device is performed. As an aeration process, the air supplied from the blower 41 can be ejected as fine bubble air from the nozzle 42 in the wastewater treatment tank 40 and brought into contact with the wastewater a2 in the wastewater treatment tank 40. The reaction formula in the aeration process in the wastewater treatment tank 40 is as shown in the following formulas (4) and (5).
HSO ₃ ⁻ + (1/2) O ₂ → H ⁺ + SO ₄ ²⁻ (4)
CO ₂ (aq) → CO ₂ (gas) ↑ (5)

As shown in the equation (4), in the wastewater a2 in the wastewater treatment tank 40, hydrogen ions (H ⁺ ) and sulfate ions (SO ₄ ²⁻ ) are obtained by oxidation of sulfite ions (HSO ₃ ⁻ ) by aeration treatment. ) And dissociate. Further, as shown in the equation (5), the dissolved CO ₂ in the waste water a2 is degassed by the aeration process and exhausted from the waste water treatment tank 40 to the atmosphere. By the reactions shown in the equations (4) and (5), the wastewater a2 in the wastewater treatment tank 40 is discharged from the wastewater treatment tank 40 as aerated treated water a3. Instead of exhausting directly from the wastewater treatment tank 40 into the atmosphere, it may be configured to be introduced into the outlet side of the scrubber 10 and then exhausted into the atmosphere.

The exhaust gas treatment apparatus of the present embodiment further includes a second seawater pump (supply means) 50 for supplying diluted seawater a4 (alkaline substance) to the discharge path 43 of the aerated treated water a3 discharged from the wastewater treatment tank 40. ing. The diluted seawater a4 is mixed with the aerated treated water a3 from the wastewater treatment tank 40 to dilute the aerated treated water a3. The reaction formula by this mixing is as shown in the following formula (6).
H ⁺ + HCO ₃ ⁻ → H ₂ O + CO ₂ (aq) (6)

  As a result of the reaction, the aerated treated water a3 is neutralized, and the treated water a5 is improved in water quality and can be discharged into the sea. In addition, the measuring device 44 which measures pH in the treated water a5 is provided in the discharge path 43 through which the treated water a5 flows.

  Next, the configuration for controlling the supply flow rate of the diluted seawater a4 by the second seawater pump 50 in the exhaust gas treatment apparatus of the present embodiment will be described. In order to perform such control, the exhaust gas treatment apparatus includes first to fourth measurement units 61 to 64 and a control unit 65.

The first measuring means 61 is a mass flow meter that is installed in the exhaust gas pipe 21 and measures the flow rate of the exhaust gas g1 before being introduced into the scrubber 10. The second measuring means 62 is configured by a laser gas analyzer that is installed in the exhaust gas pipe 21 and measures the SO ₂ concentration of the exhaust gas g1 before being introduced into the scrubber 10. The third measuring means 63 is a laser gas analyzer that is installed on the outlet side of the purified gas g2 in the scrubber 10 and measures the SO ₂ concentration of the purified gas g2 that has passed through the scrubber 10. The 4th measurement means 64 is comprised in the washing | cleaning seawater pipe 31, and is comprised by the mass flow meter which measures the flow volume of the washing | cleaning seawater a1 introduce | transduced into the scrubber 10. FIG. Each measuring means 61-64 is comprised so that the fluctuation | variation of a measuring object can be measured continuously. In addition, the structure of each said measurement means 61-64 shows an example, Comprising: Arbitrary structures are employable on the assumption that the fluctuation | variation of a measuring object is measurable.

  The control unit 65 is, for example, a programmable controller (PLC) including a processor that executes various processes necessary for controlling the supply of the diluted seawater a4, and a storage medium such as a ROM (Read Only Memory) and a RAM (Random Access Memory). Composed. The control means 65 is connected to each measuring means 61 to 64 and the second seawater pump 50 via a predetermined signal line. The measurement results of the measuring units 61 to 64 are output to the control unit 65 as electric signals. The control means 65 calculates the optimum supply flow rate of the diluted seawater a4 by the second seawater pump 50 based on the measurement results output from the measurement means 61 to 64. And the control means 65 outputs the electric signal according to the result of the said calculation to the 2nd seawater pump 50, and controls the drive of the 2nd seawater pump 50. The second seawater pump 50 is preferably inverter-controlled by the control means 65.

  Next, the configuration of the control means 65 will be described. In FIG. 1, the control means 65 is shown as a functional block diagram. The functional block of the control means 65 shown in FIG. 1 shows only the configuration related to the present invention, and the other configuration is omitted.

  As shown in FIG. 1, the control means 65 is comprised including the input part 65a, the calculating part 65b, and the output part 65c. The input unit 65a inputs the flow rate and concentration measurement values of the first to fourth measurement units 61 to 64 as electrical signals. The calculating part 65b calculates the flow volume of the appropriate diluted seawater a4 from each measured value input into the input part 65a. The output unit 65c outputs an electrical signal for controlling the driving of the second seawater pump 50 in accordance with the flow rate calculation result by the calculation unit 65b.

  Next, a waste water treatment method in the exhaust gas treatment apparatus will be described with reference to FIGS. 1 and 2. FIG. 2 is a flowchart for explaining the flow of the wastewater treatment method. As shown in FIG. 2, in the wastewater treatment method of the present embodiment, a purification step (ST1), a measurement step (ST2), a treatment step (ST3), and a supply step (ST4) are performed.

First, in the purification step (ST1), the exhaust gas g1 from the engine 20 is introduced into the scrubber 10 through the exhaust gas pipe 21. On the other hand, in the scrubber 10 by driving the first seawater pump 30, the cleaning seawater a <b> 1 is sprayed through the cleaning seawater pipe 31. As a result, the SO ₂ and CO ₂ contained in the exhaust gas g1 and the mist-like washed seawater a1 come into contact with each other to absorb the SO ₂ and CO ₂ into the washed seawater a1, and the exhaust gas g1 is purified to be scrubbed as purified gas g2. 10 is discharged. Washed seawater a1 that has absorbed SO ₂ and CO ₂ is introduced into the wastewater treatment tank 40 from the scrubber 10 as wastewater a2.

While performing the purification process, the measurement process (ST2) is performed. In the measurement step, the flow rate of the exhaust gas g1 before flowing through the exhaust gas pipe 21 and being introduced into the scrubber 10 is measured by the first measuring means 61, and the SO ₂ concentration of the exhaust gas g1 is measured by the second measuring means 62. The Further, the SO ₂ concentration of the purified gas g2 that has passed through the outlet side of the purified gas g2 of the scrubber 10 is measured by the third measuring means 63, and the fourth measuring means 64 flows into the scrubber 10 through the washing seawater pipe 31. The flow rate of the washed seawater a1 is measured.

  When the purification step is performed, a processing step (ST3) is performed. In the treatment process, the wastewater a2 is aerated in the wastewater treatment tank 40 and discharged from the discharge path 43 as aerated treated water a3.

  When the processing step is performed, a supply step (ST4) is performed. In the supply process, the control unit 65 controls the second seawater pump 50 to supply the diluted seawater a4 in an amount corresponding to the measurement value in the measurement process to the discharge path 43. As a result, the aerated treated water a3 discharged from the wastewater treatment tank 40 and the diluted seawater a4 are mixed, and the aerated treated water a3 is discharged into the seawater as treated water a5 having improved water quality.

  As described above, according to the wastewater treatment method according to the present embodiment, the diluted seawater a4 is mixed with the aerated treated water a3 discharged from the wastewater treatment tank 40. Therefore, the diluted seawater a4 is added to the wastewater treatment tank 40. Does not need to be introduced. Since the diluted seawater a4 is not introduced, the wastewater treatment tank 40 can be reduced in size. In addition, the amount of seawater to be aerated can be reduced, power consumption for driving the blower 41 can be suppressed, and the aeration process can be shortened.

  Next, a second embodiment of the present invention will be described in detail with reference to FIG. Note that, in the second embodiment, components that are the same as those in the first embodiment are denoted by the same reference numerals, and illustration and description thereof are omitted.

  FIG. 3 is a schematic configuration diagram of an exhaust gas treatment apparatus according to the second embodiment. As shown in FIG. 3, in the exhaust gas treatment apparatus according to the present embodiment, a dilution tank 100 is provided in the discharge path 43. A dilution treated seawater a3 discharged from the wastewater treatment tank 40 is introduced into the dilution tank 100, and diluted seawater a4 is supplied via the second seawater pump 50. Therefore, in the second embodiment, the aerated treated water a3 and the diluted seawater a4 are mixed in the dilution tank 100 to obtain treated water a5. Thereby, diluted seawater a4 and aeration treated water a3 can be mixed better, and the water quality improvement effect of treated water a5 can be enhanced. Note that a stirring device (not shown) that stirs the aerated treated water a3 and the diluted seawater a4 is preferably provided inside the dilution tank 100.

  Next, an experiment conducted for confirming the energy saving effect in the wastewater treatment method according to the first embodiment and the miniaturization of the wastewater treatment tank will be described. In Examples 1 and 2 and the comparative example of this experiment, the output of the engine 20 is 10 MW, Examples 1 and 2 have the same configuration as that of the first embodiment, and the comparative example is compared to Example 1. The supply point of the diluted seawater a4 was changed to the wastewater treatment tank 40. In Example 1 and the comparative example, the operation was performed under the conditions (1) to (7) in Table 1 below.

From the conditions of (7) in Table 1 and the results of (8), Example 1 shows that the SO ₂ concentration of the exhaust gas g1 and the pH of the treated water a5 are less than the comparative example, even though the aeration flow rate is half. It was equivalent. Therefore, the power consumption of the blower 41 necessary for the aeration process can be reduced.

In Example 2, the volume of the wastewater treatment tank is changed to 2.5 m ³ , which is half of that in Example 1, and the aeration flow rate is changed to the same conditions as in the comparative example (1 in Table 2 below) ) To (7).

In Example 2 and the comparative example, the inflow of seawater into the wastewater treatment tank 40 is as follows.
Inflow rate of Example 2 = (2) in Table 2 = 500 m ³ / h
Inflow amount of comparative example = (2) + (5) = 500 + 786 = 1286 m ³ / h in Table 2
Accordingly, the amount of seawater inflow into the wastewater treatment tank 40 is less than half that of the comparative example, and the size of the wastewater treatment tank 40 can be reduced by half. Furthermore, the amount of seawater to be aerated in the wastewater treatment tank 40 can be reduced to increase the efficiency of the treatment.

  In addition, this invention is not limited to the said embodiment, It can implement variously. In the above-described embodiment, the size, shape, and the like illustrated in the accompanying drawings are not limited thereto, and can be appropriately changed within a range in which the effect of the present invention is exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

For example, in the above supply step, another alkaline substance may be supplied instead of the diluted seawater a4. Examples of alkaline substance, seawater, or _{NaOH, Mg (OH) 2,} Ca (OH) 2, an aqueous solution containing CaCO _3, or _NaOH, Mg and _{(OH) 2, Ca (OH} ) 2, CaCO 3 It is at least one of the contained solid or powder, or alkaline water produced by electrolysis. By using the alkaline substance, the supply flow rate can be greatly reduced as compared with the case where the diluted seawater a4 is supplied.

10 Scrubber 40 Wastewater treatment tank 50 Second seawater pump (supply means)
61 1st measuring means 62 2nd measuring means 63 3rd measuring means 64 4th measuring means a1 Washed seawater a2 Drainage a3 Aerated treated water a4 Diluted seawater (alkaline substance)
a5 treated water g1 exhaust gas g2 purified gas

Claims (4)

A purification step of purifying the exhaust gas into purified gas by bringing SO ₂ contained in the exhaust gas introduced into the scrubber into contact with the washed seawater, and discharging the washed seawater that has absorbed SO ₂ into the wastewater treatment tank;
Flow rate and SO ₂ concentration of the exhaust gas before being introduced into the scrubber, SO ₂ concentration of the purge gas, and a measuring step of measuring the flow rate of cleaning the seawater to be introduced into the scrubber,
In the wastewater treatment tank, a treatment step for aeration treatment water in which air is mixed into the wastewater and aerated.
After the treatment step, an exhaust gas comprising: a supply step of supplying and mixing the aerated treated water discharged from the waste water treatment tank with an alkaline substance in an amount corresponding to the measurement value of the measurement step. Wastewater treatment method for treatment equipment.   The exhaust gas treatment apparatus according to claim 1, wherein, in the supplying step, the alkaline substance is introduced into a dilution tank into which the aerated treated water is introduced, and the alkaline substance and the aerated treated water are mixed. Wastewater treatment method. In the measuring step, the flow rate of the exhaust gas before being introduced into the scrubber is determined by the first measuring means using the SO gas of the exhaust gas. ₂ The concentration is measured by the second measuring means in the purified gas SO. ₂ The waste gas treatment method for an exhaust gas treatment apparatus according to claim 1 or 2, wherein the concentration is measured by a third measurement means, and the flow rate of the washing seawater introduced into the scrubber is measured by a fourth measurement means. . The wastewater treatment method for an exhaust gas treatment apparatus according to any one of claims 1 to 3, wherein the alkaline substance is seawater.

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