JP2009148684A - Method of treating drainage containing ammonia - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of inexpensively and surely treating a drainage containing ammonia, which dispenses with equipment for further treating the drainage containing ammonia. <P>SOLUTION: The method of treating the drainage containing ammonia in a boiler flue to which flue gas treatment apparatuses such as an exhaust gas denitrizer, an electrostatic precipitator and an exhaust gas desulfurizer are disposed serially through a flue duct comprises once storing the drainage in a storage tank, thereafter taking out the drainage, and quantitatively injecting the drainage as a liquid state to at least one of flue ducts connected to the upstream side of the each flue gas treatment apparatus. Injection is carried out preferably by atomization or dripping. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for treating ammonia-containing wastewater that can treat wastewater containing ammonia by a simple and inexpensive method.

  If the wastewater generated from the plant contains ammonia, etc., the nitrogen content in ammonia is transferred to the relevant plant or other plant because the drainage standards are defined by the nitrogen and phosphorus emission regulations of the pollution prevention agreement value. It is necessary to dispose of the wastewater after performing the specified wastewater treatment to meet the wastewater standards.

  Such ammonia-containing wastewater may be generated as follows, for example, in a flue gas treatment facility of a thermal power plant. FIG. 2 shows a system diagram of a flue gas treatment system in a coal-fired boiler of a coal-fired power plant. In this figure, a flue 31 extending from the outlet of the boiler 30 to the chimney 37 is sequentially connected in series via a flue duct, a flue gas denitration device 32, and an electrostatic precipitator (hereinafter sometimes referred to as EP) 34. And a flue gas desulfurization apparatus 36 are installed, and an air heater 33 and a gas gas heater (hereinafter referred to as GGH) 35 are installed as heat exchangers accompanying the flue gas treatment equipment. Here, the flue gas denitration device 32 removes nitrogen oxides (NOx) from the exhaust gas, the electrostatic precipitator 34 removes soot and the flue gas desulfurization device 36 removes sulfur oxides (SOx).

Among them, the flue gas denitration device 32 is currently mainly of the ammonia selective catalytic reduction method. In this method, ammonia is used as the reducing agent, and nitrogen oxide (NOx) in the exhaust gas is selectively brought into contact with ammonia in the presence of a predetermined catalyst to reduce it to nitrogen and water, and the process is simple. It has advantages such as easy operation and excellent denitration performance. Ammonia used as a reducing agent in this apparatus is normally supplied as liquefied ammonia and is once received in the receiving tank 10 via the receiving valve 9 in a liquid state as shown in FIG. During operation of the boiler 30, the liquefied ammonia is extracted from the receiving tank 10 through the extraction valve 11, then vaporized by the vaporizer 13, and transferred to the flue duct upstream of the denitration device via the accumulator 14 through the pipe 15. Then, it is injected into the flue duct by the ammonia injection device 17 provided at the location.
In addition, the sulfur content in the fuel is mostly sulfur dioxide (SO ₂ ) in the combustion process and is removed by the desulfurization unit, but part of it is sulfur trioxide (SO ₃ ) and has a high dew point. In order to combine with moisture and turn into sulfuric acid, causing corrosion damage to the flue and electrostatic precipitator, ammonia is injected into the air heater outlet flue and neutralized. The ammonia storage tank and vaporizer are also used for denitration equipment.

  Since the system from the receiving facility such as the liquefied ammonia receiving valve 9 and the receiving tank 10 to the injection device 17 corresponds to the high-pressure gas facility, it is necessary to undergo legal inspection every predetermined period. When undergoing this legal inspection, it is necessary to discharge the liquefied ammonia remaining in each facility device to make it completely empty, to pass nitrogen gas through these devices, and to wash with water. In this way, residual liquefied ammonia and its washing water are generated as ammonia-containing waste water (unsteady waste water) immediately before the legal inspection time.

  As a treatment of this ammonia-containing wastewater, for example, Patent Document 1 proposes a method of separating ammonia gas from wastewater by a denitrification technique such as an ammonia stripping method. There is a problem that additional equipment such as a temperature device is required, and the equipment cost is high.

There is also a method of diluting ammonia-containing wastewater with water and discharging it to the outside of the plant, but not only a large amount of water is required, such as when high-concentration ammonia is contained, but also a storage tank The processing cost becomes expensive, such as the necessity to install a very large one, which is not practical.
JP-A-3-258388

  Therefore, in view of the above circumstances, an object of the present invention is to provide a treatment method that reliably and inexpensively treats ammonia-containing wastewater without requiring equipment for further treatment.

  According to the present invention, the above object is to provide ammonia-containing wastewater in a boiler flue in which a flue gas treatment device such as a flue gas denitration device, an electrostatic precipitator, and a flue gas desulfurization device is arranged in series via a flue duct. The wastewater is once stored in a storage tank, then extracted from the storage tank, and in a liquid state in at least one of the flue ducts connected to the upstream side of each of the smoke treatment devices. This is achieved by a method for treating ammonia-containing wastewater, which is characterized by a constant injection.

  The treatment method of the present invention injects ammonia-containing wastewater in a liquid state into a boiler flue system in which a flue gas treatment device is disposed, and evaporates there, and ammonia gas generated by this evaporation is contained in the flue gas. It is used for reaction with SOx and the like, and is consumed by the subsequent flue gas desulfurization apparatus.

  The ammonia-containing waste water in the present invention may contain other components such as nitrite nitrogen and nitrate nitrogen as long as it mainly contains ammonia (ammonia nitrogen). Moreover, it is not restricted to the above nitrogen compounds, The other compound which shows water solubility may be included. Furthermore, the waste water may contain a solid content such as sludge. In this case, a solid-liquid separator such as a filter can be installed at an arbitrary position in the middle of the piping from the wastewater storage tank to the flue. By removing the solid content from the waste water in this way, it is possible to prevent clogging of the liquid injection means described later, and to reduce wear of components of each flue gas treatment device due to an increase in dust in the flue gas. Can do.

  For injection of the ammonia-containing wastewater into the flue duct, it is preferable to use liquid injection means such as liquid spraying means or liquid dropping means. By using such a liquid injection means, when ammonia-containing wastewater is injected into the flue duct, the wastewater is in the form of droplets with a small diameter, and the contact area with the flue gas is increased, so that the shortage in the flue It can be evaporated in time. As the liquid spraying means or the liquid dropping means, a known spray or injection nozzle can be used.

  The ammonia-containing wastewater is injected through the liquid injection means from at least one of the flue ducts connecting the respective flue gas treatment devices disposed in the boiler flue. Ammonia-containing wastewater may be injected from any flue duct. However, if a flue gas denitration device with a denitration catalyst layer formed inside is installed, the wastewater from the flue duct in front of the device is installed. It is preferable to inject from the flue duct provided in the upstream of the electrostatic precipitator or the flue gas desulfurization apparatus, avoiding the injection of the waste water. A denitration catalyst is usually a very expensive catalyst made of a precious metal such as platinum, a metal oxide that supports titanium dioxide, alumina oxide, etc., and the wastewater injected under high-temperature conditions evaporates. This is because it is necessary to prevent the catalyst from being damaged by being attached to the surface of the catalyst in the meantime. Needless to say, when other types of flue gas denitration devices are installed, there is no such limitation.

  In the present invention, in the flue duct leading to the chimney on the downstream side of the last flue gas treatment device in the boiler flue system, the flue gas temperature is low, the evaporation time of the ammonia-containing wastewater is increased, and the vapor is evaporated. It is added that the concentration of SOx capable of reacting with ammonia gas is extremely low and there is no means for removing the reaction product, so that the injection of ammonia-containing wastewater into the flue duct is not included.

  According to the treatment method of the present invention, since a small amount of ammonia-containing wastewater is injected into the flue for treatment, only a drainage storage tank, a pump, an injection device for the flue, and piping for connecting them are prepared. Therefore, it is possible to treat the waste water without the necessity of ancillary equipment such as a heating device or an alkaline agent addition device. Therefore, the construction cost and operation cost are very low.

  In addition, according to the present invention, an auxiliary effect of removing ammonia gas and SOx by reacting ammonia gas generated by evaporation of waste water with SOx in a flue duct or in each device disposed after an injection point is obtained. be able to.

  The boiler to which the method for treating ammonia-containing wastewater of the present invention can be applied is not particularly limited.For example, if it is by use, it may be a power generation boiler or an industrial boiler, and by fuel, oil cooking, coal burning, Any of gas burning may be used. After these fuels are burned in the furnace, if superheaters, reheaters and economizers are installed, the combustion exhaust gas passes through these into the flue duct connected to it from the boiler outlet. Discharged. Hereinafter, the flue gas discharged into the flue system is particularly referred to as “flue gas”.

  The flue gas treatment apparatus in the present invention refers to an apparatus related to dedusting, denitration and desulfurization of flue gas discharged from the boiler furnace, specifically, dry or wet flue gas denitration apparatus; dry or wet Electric dust collectors, dust filters such as bag filters or cyclones; dry or wet flue gas desulfurization devices; flue gas denitration desulfurization devices that perform denitration and desulfurization of flue gas using activated carbon. These flue gas treatment devices are appropriately selected and installed in the flue system in consideration of the flue gas amount, the flue gas temperature, the dust amount, and the like.

  The flue gas denitration device and the flue gas desulfurization device are not particularly limited to the denitration and desulfurization methods, and any known method may be adopted. In the case of a flue gas denitration device, for example, a selective catalytic reduction method or an activated carbon method can be used. In the case of a flue gas desulfurization apparatus, a wet method having a process such as a lime-gypsum method, a dry method using activated carbon, and the like can be given.

  The dry electrostatic precipitator may be a so-called high-temperature EP, low-temperature EP, or low-low-temperature EP that is operating in thermal power plants in various places. Of these, the high temperature EP is usually installed between the boiler outlet and the flue gas denitration device (high temperature range of flue gas temperature of about 320 to 360 ° C.). The low temperature EP is a downstream of the air heater, and is installed upstream of the flue gas desulfurization apparatus (exhaust gas temperature of about 130 ° C.). Further, the low and low temperature EP is installed between the GGH (reheater) and the wet flue gas desulfurization apparatus (the exhaust gas temperature is about 90 ° C.). Thus, in the case of an electrostatic precipitator, although the installation position in a flue changes, in any case, the processing method of this invention is applicable.

  Hereinafter, the method for treating ammonia-containing wastewater of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is a system diagram for implementing the ammonia-containing wastewater treatment method of the present invention in a flue system of a coal-fired boiler in a coal-fired power plant. In this figure, an ammonia selective catalytic reduction type flue gas denitration device 32, an air heater 33, a low temperature EP 34, a GGH 35, and a flue gas desulfurization device 36 are arranged in this order in a flue 31 leading from a boiler 30 to a chimney 37. Yes.

The ammonia gas supplied to the flue gas denitration device 32 is withdrawn from the liquefied ammonia receiving tank 10 and sent to the vaporizer 13 with the valves 11 and 12 being opened. After being vaporized by the device, the accumulator 14 and the ammonia gas pipe 15 And is injected into the flue gas flowing through the flue from the ammonia injection point 17 of the flue duct 31. In the middle of the ammonia gas pipe 15, an ammonia gas flow rate control valve 16 is installed. Further, ammonia gas supplied for neutralization of sulfur trioxide (SO ₃ ) is branched from the middle of the ammonia gas pipe 15 (upstream of the flow control valve 16) from the accumulator 14 toward the flue gas denitration device 32, and ammonia. It is injected into the flue gas flowing in the flue from the ammonia injection point 17 ′ at the outlet of the air heater 33 in the flue duct 31 via the gas pipe 15 ′. An ammonia gas flow rate adjusting valve 16 'is installed in the middle of the ammonia gas pipe 15'. The liquefied ammonia is transported by a tank lorry (not shown) and supplied to the liquefied ammonia tank through the receiving valve 9.

  The apparatus for carrying out the method for treating ammonia-containing wastewater of the present invention sends an ammonia-containing wastewater storage tank 20, an extraction valve 21 of the tank 20, a pump 22, and ammonia-containing wastewater discharged from the pump 22. From the liquid feeding pipe 23, the branch pipes 241, 242, 243, 244 branched from the middle thereof, and the liquid injection means 261, 262, 263, 264 to the flue ducts arranged at the ends of the respective branch pipes Become. The ammonia-containing wastewater storage tank 20 can receive liquefied ammonia and its washing water, as well as other ammonia-containing wastewater through the receiving valve 18. The branch pipes 241 to 244 are provided with flow control valves 251, 252, 253, and 254, respectively. If it is necessary to determine the injection amount, return pipes (not shown) are provided for returning the waste water from the upstream of the flow rate control valves 251 to 254 in the branch pipes 241 to 244 to the ammonia-containing waste water storage tank 20, respectively. You can also. These flow control valves need only be controlled so that at least one of them opens when the pump 22 is operated and wastewater is sent. The drainage flow rate of each branch pipe is set by a flow meter and a controller (not shown). A predetermined amount of waste water that has passed through at least one of the flow control valves 251 to 254 is injected into the flue duct by liquid injection means (261 to 264) disposed downstream of the flow control valve. In FIG. 1, the liquid supply pipe 23 for the ammonia-containing waste water is branched into a plurality of branch pipes 241 to 244, but such a branch pipe is not provided, and the drainage is determined in advance by a single liquid feed pipe. The liquid can be fed to the liquid injection means of the flue duct.

  The injection amount of the ammonia-containing wastewater can be determined in consideration of the ammonia concentration, flue gas amount, moisture amount, NOx concentration, etc. in the wastewater.

  The ammonia-containing wastewater injected into the flue evaporates in the flue gas, and ammonia gas is separated and generated. This ammonia gas is consumed for reaction with SOx and the like in the flue gas.

  As described above, according to the method for treating ammonia-containing wastewater of the present invention, the ammonia-containing wastewater can be treated inexpensively and reliably, and the ammonia gas generated in the flue can be treated.

It is a systematic diagram for implementing the processing method of the ammonia containing waste_water | drain of this invention. 1 is a system diagram of a general flue gas treatment system in a coal-fired boiler of a coal-fired power plant.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid ammonia receiving tank 11, 12, 19 Liquid ammonia extraction valve 13 Evaporator 14 Accumulator 15, 15 'Ammonia gas piping 16, 16' Ammonia gas flow control valve 17, 17 'Ammonia injection point 20 Ammonia containing waste water storage tank 21 Ammonia Contained drainage extraction valve 22 Pump 23 Liquid feed pipes 241, 242, 243, 244 Branch pipes 251, 252, 253, 254 Flow control valves 261, 262, 263, 264 Injection means (liquid spraying means or liquid dropping means)
30 Boiler 31 Flue 32 Flue gas denitration device 33 Air heater 34 Electric dust collector 35 GGH
36 Flue Gas Desulfurizer 37 Chimney

Claims (4)

  A method for treating ammonia-containing wastewater in a boiler flue in which flue gas treatment devices such as a flue gas denitration device, an electric dust collector and a flue gas desulfurization device are arranged in series via a flue duct, Once stored in a storage tank, it is extracted from the storage tank and metered in a liquid state into at least one of the flue ducts connected to the upstream side of each of the flue gas treatment devices. Wastewater treatment method.   The processing method according to claim 1, wherein the ammonia-containing wastewater is injected into the flue duct through a liquid spraying unit or a liquid dropping unit.   When the flue gas denitration device includes a denitration catalyst layer, the ammonia-containing wastewater is removed from the electric dust collector or the flue gas desulfurization device except for the flue duct connected to the upstream side of the flue gas denitration device. The treatment method according to claim 1, wherein the treatment is injected into a flue duct connected to the upstream side.   The method for treating ammonia-containing wastewater according to any one of claims 1 to 3, wherein the ammonia-containing wastewater is unsteady wastewater of a boiler facility equipped with an ammonia selective catalytic reduction type flue gas denitration device.

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