JPS62502388A - How to purify flue gas - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] How to purify flue gas The present invention applies to flues from fossil fuel heated boilers of power plants and dust combustion plants. This invention relates to a method for separating gases into HC, SO2 and NOx'.

It is known to simultaneously scrub the flue gas with lime and EDTA after the power plant. Ru. This known method has economical disadvantages due to too high EDTA consumption and non-stable NoX It was not popular because it was characterized by a high degree of separation.

Minutes as well as to achieve a high degree of separation of these hazardous substances! @ very economically In order to make this possible, according to the present invention, HCl and So2'i are also thoroughly washed in the first step. In the second step, NOx and residual S02 are removed, and the cleaning solution in the first step is or hydrated lime and carboxylic acids that do not interfere with the oxidation of CaSO3 to CaSO4 and the cleaning solution of the second step contains caustic soda, EDTA and/or sodium sulfite. Fully containing thorium and/or pyrosulfite, HCl is washed out in the first washing step. Then, in the second cleaning step, a partial amount of S02 is cleaned. However, for example, chlorine-poor coal In the case of burning, in the first washing step HC/= and SO2 are Cleaned to a percent value.

Limestone or hydrated lime is especially used in this cleaning process, which dissolves lime well. In order to Monobasic or polybasic carboxylic acids are used that tolerate oxidative action, i.e. In this cleaning process, Ca5O,f is created by adding air to the bottom of the washer. I can do it.

In the subsequent cleaning process, EDTA is mixed with caustic powder and S○2 cleaning is performed. This strongly prevents oxidation in the cleaning water for NOx cleaning that is placed after cleaning. , thereby adding a carboxylic acid that prevents the oxidation of ■valent iron to ■■valent iron. A cleaning solution made of

This is an example of tartaric acid and/or citric acid, thus polybasic carboxylic acids? , achieved by adding foil together as an antioxidant when mixing if desired. In the cleaning solution, very small amounts of iron ([[) enter the EDTA compound. This guarantees that it will be reduced to iron(I).

E used in the cleaning solution, especially when stabilizing to PH4i' greater than 6. DTA is, for example, larger than 1o:yit, and for each coal-fired boiler. More than 2g of alcohol per liter due to the NOx content and excess oxygen in the flue gas Washing water, caustic soda, EDTA or NTA, added with tartaric acid and thus formed This cleaning solution is made of carboxylic acids, especially tartaric acid, which have antioxidant properties. is a cheaper way to extract raw gas from raw gas than is possible using traditional cleaning methods or catalysts. It has been found that it is possible to make NOx separation economically acceptable.

Below, the chemical reactions of HC1 cleaning and s02 cleaning, as well as the S02 and NOx A reaction equation for simultaneous cleaning is shown, in which case according to the present invention, in the NOx cleaning step to the extent necessary to form the alkali sulfite needed as a reactant in the Only S02 is introduced into the NOx separation process.

According to the invention, contrary to what is described in the literature, 2 A two- to three-fold molar excess of SO2 is not used. That is because in this case there are many This is because an amount of sulfite is produced which is economically unacceptable for the process.

Reaction formula: %formula% Furthermore, depending on the excess oxygen in the gas, for the calomel electrode (3 molar KC4 evaluation) Measure the negative redox potential to keep it greater than -iomv. Add a small amount of sodium onate.

According to the working method according to the invention, the content of sodium pentathionite is extremely small. Therefore, the main amount of S02 is cleaned in the main cleaning process, and a small amount is cleaned in the second cleaning process. A two-step method of cleaning amounts of SO2 and NOx is economically unacceptably expensive. It doesn't cost much.

The course of the method described above is explained in detail in FIGS. 1 and 2.

In these figures, 1 represents the SO2 and HC1 scrubber and 2 represents the NOx scrubber. 3 represents a washing machine separated from the first washing process, for example, the first S02 washing machine. Represents oxidized gypsum in the bottom of the purifier.

4 is caustic soda storage or sodium sulfite or sodium pyrosulfite This represents 5, that is, 6 is mixed with EDTA or NTA at the proper charging mix ratio. be done. Depending on the excess oxygen in the raw gas and the NOx value, these substances can be mixed, 7 into the wash circulation limb 12. In 7, carboxylic acids that inhibit oxidation, especially Tartaric acid is stored and this acid is added to the cleaning solution at 8.

9 represents the sodium thionite reserve, which is 10 and oxygen is added as needed. Added to the cleaning solution depending on content and NOx value.

Waste water 11 is added to an oxidizing tank 13, and oxidizing air 14 is heated to a pH value of 6.5, for example. Then, the resulting gypsum is charged into a filter 15 and transformed into unfired wet gypsum at 16. Consideration should be given to ensure that the waste is discharged.

The partial amount of water required for washing the gypsum is added to the iron settling tank 17, and the washing water is separated from the filter. The water is pumped to washer 2 as filtrate reflux.

The filtrate is represented by 18, and the precipitated iron hydroxide 19 from the iron settling tank 17 is deposited. or, if the gypsum can contain all of this iron for a specific purpose, the gypsum It can also be kept in a plaster.

Excess water from the filtration and cleaning device 15 generated from the iron precipitation tank 17 is subjected to EDTA precipitation. It is supplied to tank 20. Here, by adding sulfuric acid 21 p) 1 @ 1ik about 1 ~ The clear water flowing out by overflow from the EDTA settling tank 22 adjusted to 24) is added in particular to the biological purification device 25.

In another embodiment of the invention, the iron (TI) chelate solution absorbs Nitric oxide is reduced to elemental nitrogen and sodium sulfate by sodium sulfite. The sodium sulfate content in the cleaning solution is advantageously below the saturation limit. It was found that the amount of reducing agent added was very small. does not participate in the oxidation process and therefore maintains its activity, e.g. from 0.5 I/t of cleaning solution. However, with the addition of a small amount of sodium dithionite, the amount of cleaning liquid can be reduced to 1Nm3 of raw gas. In the case of 3t, the NO concentration in raw gas is 1600~9/Nm3f IQ Q It has been found that cleaning can be performed to 9/Nm''.

Furthermore, the cleaning liquid not only has a correspondingly high sodium sulfate content, but also Useful for gas residence times greater than seconds, in which case air and water sing in the raw gas. A ratio of so-called L:G-3 to 517 m3 is used.

The height of the packing bed is 8 to 10 m, but at least 50% of the volume of the washing tower is the contact surface. should be filled into the structure of the packing body.

Sodium sulfate that has become concentrated in the cleaning solution has a concentration of 500 mg NOz/~3. and 02 content in the gas 30-40 g/l for a raw gas load of 5-8% 500-800 rvNOx/-3 and 02 content in the gas 5-8 % raw gas load is 40-609/l, 800-1200"9NOx/-3 and 0□ content in gas 5-8% raw In the case of gas load, it is 60 to 809/l, 1200-2000 m1i’NOx/m” and 5-8% 02 content in the gas. In the case of gas loading it is 80-120 g/l.

Furthermore, in order to stabilize iron (II) ions against the oxygen action of the cleaning solution in the second step, We suggest adding carbon dioxide to the

In another embodiment of the invention, the original residual 5O2- and NOx cleaning In the final cleaning step called process, cleaning is carried out using limestone, hydrated lime and ED Caustic soda for this purpose is not carried out using TA- or NTA-iron chelates. to maintain a pH value of about 7 and suppress carboxylic acid to EDTA- or NTA-iron chelates. We suggest that a cleaning solution supplied in a mixture with a tartaric acid, such as tartaric acid, is optimal. . Sufficient S02 is absorbed to reduce it through the formation of sodium sulfite. If pyrosulfite is not available, the present invention adds pyrosulfite to the cleaning solution.

Fe(If) quenching by flue gas oxygen to adjust the negative redox potential In addition to acids, the present invention also allows the use of acids in the raw gas to inhibit oxidation to Depending on the NOx content, the amount of sulfur dioxide (IJum) in the cleaning circuit is at least 209/l. Added in the amount available.

This alkali sulfite content is No. in raw gas, N in flue gas up to 800 In the case of Ox values, adjustments had to be made. This is the NOx concentration in raw gas. If the temperature is also high, for example, 20Q　Q　rn9/ Sodium notothionite which cannot contain the NOX content of Nm3 with a resolution higher than 95% In order to avoid the need to supply It was necessary to increase the amount of cleaning liquid from 20g per ton6 to a maximum of 100g.

In order to avoid too high a salt concentration, a small amount of the cleaning solution according to the invention is present during the cleaning process. amount is added to the next wash solution work-up for EDTA or NTA work-up and recovery. used.

The method sequence described above is explained in detail in FIGS. 3 and 4.

In these figures 31 is for example an HCt washer and/or an S02 pre-vacuum. Depending on the load, 32 represents a HCl- and SO2 scrubber, and 32 represents a NOx- and SO2 scrubber. 2 Represents a washer. In this washer, due to the NOx content in the flue gas, A sufficient amount of S02 is washed to produce the required 11 degrees of sulphite greater than 209/l. be purified.

33 is the washer bottom of the first S02 cleaning process, which is separated from the first cleaning process. 34 represents oxidized gypsum; 34 represents caustic soda storage tank and sodium sulfite etc. 35 represents a sodium pyrosulfite mixing device: EDTA- or NTA It represents a mixing device, in which 36 mixes at the proper mixing ratio for charging, and 37 performs cleaning circulation. 42.

Carboxylic acids that prevent oxidation, especially tartaric acid, are stored in 37a. is added to the cleaning solution at step 38.

At 41, the wastewater from the cleaning liquid treatment device 40a is added, and in the device 40b is hydrated. Since lime is added, it consists of dilute caustic soda, EDTA complex chelate, and additional The cleaning liquid with reducing and oxidation inhibitors is fed to the dewatering station 4 in this tank 40a. Passes through as 0ct calcium sulfite or calcium sulfate, for example, remaining It is added to the oxidation tank 43 at a moisture content of 20%.

The cleaning liquid from the dewatering station 40C becomes 40d and becomes the cleaning liquid in the washer 32. Since the cleaning liquid is returned to the circulation path, there is little loss of the cleaning liquid.

The oxidizing air 44 has a pH value of, for example, 6.5, taking into consideration the formation of gypsum, and Toeha 7 p) Monovalent cleaning is done with sulfuric acid or with a chlorine-containing cleaner called HC1 cleaner. The acid from the cleaner 31 reduces the market price to, for example, 3.5~ Used to lower the number to 4. The generated gypsum can be filtered through 45 and 7 different filters. It is discharged with a relatively valuable moisture content of less than 8%, which is necessary for example for transverse distortion of plaster. The necessary partial amount of water is supplied to the iron settling tank 47, and the water separated from the filter 45 is filtered water. 48 to the washer 32 as well.

The iron hydroxide 49 precipitated from the iron precipitation tank 47 is sent to a deposit or left behind. It can also be left in plaster as there is only a trace amount, and the plaster can be used for specific purposes. can hold iron.

Excess clear water from the filtration and cleaning device 45 produced from the iron settling tank 47 is treated with EDT. It is supplied to the A sedimentation tank 50.

Here, when adjusting the pH value to 1 to 2 by adding sulfuric acid or hydrochloric acid, EDTA is precipitated, iron(II) salts are added as iron(11) chelates and the mixture is mixed with reflux water. is returned into the process cleaning circuit (eg to washer 32).

The purified water from the EDTA settling tank 52 exits from the overflow pipe (represented by 54). According to the invention, the washer 31 is provided with mixed water for limestone and/or hydrated lime. or can be used as a biological purification device 55 if necessary. Ru.

In another embodiment of the invention, a portion of the wash liquid from the second step is Suggest to play it continuously like this: a) Add Ca(OH)zk to adjust the pH value to r11-12, add iron hydroxide (I Precipitation of ll and iron(I) hydroxide and C of Na2SO3 and Na2SO4 a) Conversion to SO3 and CaSO4 b) Separation of precipitated solids C) Solids? Washed with fresh water, diluted to 50% solids content and added with sulfuric acid. ripHll1t1. ’t” by adjusting to about 4 and adding air to reduce the C of CaSO3. Oxidation to aSO4, d) Further addition of sulfuric acid to adjust monovalent k to 0.8-1.5 , iron hydroxide (1) precipitated by Ca compound becomes iron sulfate (n) and dissolves, e) Separation of CaSO4.H2O as a by-product of flue gas cleaning, g) EDTA separation of iron (Ifl + Il reduction of iron (It) to iron (It) chelates (regenerated scrubber for the second step of flue gas scrubbing) for the production of purification liquid).

The method sequence described above is explained in detail in FIG.

The waste water 62 from the wash water circuit according to FIGS. 6 and 4 is fed to a gravity separator 61. be provided. At the same time, in the wastewater stream 62, to adjust the monovalent value of 1 liter of wastewater to 111-12 For this purpose, lime milk (Ca(OH)2 ) 63 is added. In this case, iron is iron hydroxide (■) / iron hydroxide (Ill) The sodium sulfate and sodium sulfite contents precipitate as solid sulfate. Lucium and calcium sulfite are formed, up to 20% in the gravity separator. Concentrated.

The solid matter 66 concentrated in this way is dehydrated through a belt filter 64, and is then dehydrated in an oxidation tank. 65, diluted again with fresh water 67 to 50% solids per ton of water, and sulfur The addition of acid 68 and air 68a reduces the calcium sulfite content to sulfuric acid at a monovalent value of about 4. Oxidized to calcium dihydrate.

After oxidation, iron hydroxide (IN) still present in the gypsum is converted into iron sulfate (I). The pH value is further lowered to pH 0.8-1.5 using sulfuric acid in order to dissolve the mixture.

Subsequently, the gypsum is dehydrated using a belt alpha filter 76.

The dewatered gypsum 77 is removed, stored, and filtered with dissolved iron(II) sulfate. Liquid 78 is supplied to mixing tank 74 .

A specific filtrate volume 71 is determined from the filtrate volume 69 after the belt α filter 64. 70 and subjected to addition 72 of hydrochloric acid p)io, s~1.0 pH adjusted to the value.

The precipitated H4EDTA is dehydrated by a belt filter 73 and supplied to a mixing tank 74. and merges with iron sulfate (Ill) solution.

Additionally, a conduit 81 into the mixing tank 74 allows a pH of 11- A certain amount of the filtrate having 12% of ．． Supplied with 1 adjusted to 5.

For this purpose, sodium methionite 83a is added to the mixing tank 74 as a reducing agent.

After the reduction has taken place, the iron(II) chelate solution enters the wash circuit via conduit 80. It will be sent back.

The filtrate after the belt filter 73 is sent to a biological purification device or evaporator as waste water 75. Supplied to a concentrator.

Iron sulfate (Illk) is reduced to iron sulfate (n) by a reduction device placed in front of the mixing tank 74. carried out in tank 79 by adding sodium dithionite 83 or iron powder 82 be able to.

According to another feature of the invention, the second substream of the liquid from step 1)) contains sulfuric acid. Add iron (It) and EDTA of step g) to obtain equimolar iron (It) at a pH value of 6-8. ■) Make a chelate bath liquid and use it as a new cleaning liquid for the second flue gas cleaning. Propose to supply it to the process.

The course of the method described above is explained in detail with reference to FIG.

A partial stream of the S02/NOx removal wash water 91 is reacted with milk of lime 92 in a mixer 93. Concentration of the solids is accomplished in gravity separator 94. Precipitation reaction in 93 The response is particularly carried out in the PI (11-12).

After filtration of the solids using a belt filter or centrifuge 95, CaSO3, CaSO A solid substance 96 consisting of 4 and iron hydroxide (II/I) is mixed with fresh water 97 and sulfuric acid 98 And under the influence of air 99, it is oxidized to CaSO4.2H20, and all the iron is iron sulfate. It exists as a dissolved substance. This suspension 101 is transferred to a belt α filter or a centrifuge 1. Since CaSO4・2H20(103) is filtered using 02, it is a commercially available product. Obtained as a product. The iron sulfate-containing filtrate 104 is fully or partially heated according to the present invention. or S02/NOx removal equipment without being returned to the O2/NOx absorption process. Typically used in external power plants or post-processed separately. pH The filtrate 105 (sedimentation tank 93) of No. 12 is used in the cleaning circuit for SO2/NOx absorption. Contains EDTA corresponding to the concentration of iron ([ 1) -EDTA - Added to the extent necessary for the production of chelate complex . Additionally, one portion of water stream 109 is precipitated with H2SO4 or HC4 in tank 110. , H4EDTA 113 made by belt filter or centrifuge 112 is F e-chelate is sent to the back road 116A, and from now on it has a pH value of 6 to 8. The Fe(II) EDTA complex solution is back-channeled into the S○2/NOx absorption process. will be returned to.

The filtrate in the H4EDTA precipitation tank 114 is neutralized and the biological! Scientifically purified Kamatake It is fed to an evaporative concentration or spray drying device 115.

The solid residue from this device 15 is 300~<SOO'C1, especially 450~500 heat-treated at °C (116) and then a 95-100% Na2SO4 A usable final green product 117 is produced.

The advantage of this method is that the Fe(II)/Fe(m ) containing filtrate is put to another use, in order to compensate for this iron discharge from the absorption circuit. A new low-cost product, Fe2SO4.7H20, will be added. This results in , easy to maintain high Fe(u)m degree in the cleaning water circulation path, The dosage of sodium acid can be further reduced or completely discontinued.

In another embodiment of the method, in step C) flue gas is used instead of air. adding a portion, liberating SO2 and reducing iron(I) to iron(It)K; It is also proposed to recirculate the flue gas with increased S02 concentration into the flue gas stream.

Free S02 in the flue gas stream results in a 4:1 weight ratio of S02 to NOx. Ru.

Adding the flue gas withdrawn before the flue gas desulphurization device instead of oxidizing air As a result, a reducing phase is generated, and iron (i) present in the washing water is reduced to iron (If). be done.

The liberated SO□ is returned from the tank 100 into the flue gas line by a conduit not shown. The supply pipe 99 therefore supplies a quantity of flue gas instead of air; Depending on the amount of flue gas, the ratio of 802 to NOx in the flue gas stream is approximately Depending on the amount, 8024m9 for 1 mg of NOx is a simultaneous cleaning of SO□ and NOx. 802 is liberated to the extent that it is supplied cleanly.

This is especially true for bath melter combustion where the NOx to S02 ratio is often 1:1. This flue gas induction according to the invention without the addition of pyrosulphites to the A guarantee is given that the concentration of NOx in the gas vs. S02 can be controlled.

Advantageously, calcium formate or potassium formate is used instead of Ca(OH)2 in step a). A mixture of lucium and calcium hydroxide is added. Thus, Na2SO3/ Significantly increases the reaction rate of Na2SO4 to CaSO3+CaSO4・2H20. , the diversion flow can be significantly reduced under the production of sodium formate, which is Like caustic soda, it absorbs SO2'2.

If the decrease in pH value due to the addition of sulfuric acid is sufficiently large, within the PH range smaller than 6. It has surprisingly been found that iron(1) is reduced to iron(II). to this discovery Therefore, the addition of an additional reducing agent to convert iron(I) to iron([1) is almost unnecessary. Depending on the demand for iron(II), it is no longer necessary.

Additionally, other substitutes for sulfuric acid can be used to reduce the pH value to below 3, especially to about 1.5. agents can be used, in which case the reduction of F (III) to F (If) is carried out without addition of reducing agent. Each of the factors that can cause a decrease in PI-1 titer Drugs can be used.

The entire reduction process of Fe(if) to Fe(II) by addition of reducing agent and Optimization of intermediate reduction at low pH values, while minimizing investment and operating costs. In order to minimize the 4.2, in particular 4, and the CaSO4 of CaSO3 is adjusted to 4. partial oxidation to PI (value 1.5-2. 5, in particular it is advantageous to lower it further to 2.0, without being oxidized. CaSO3 decomposes while producing S02, and Fe (m) is reduced to Fe (b). I found out what happens. During the reduction process, the supply of gaseous oxidant is stopped and its replacement KS○2? Pump in circulation. CaSO3 is 10-90%, especially 50% oxidized and the remainder is the part of cCaS03 that is utilized for decomposition under the production of S○2. The chemical oxidation and decomposition are controlled by the pH value, with the reaction being carried out in individual baths or The gas is guided through the tank channel and subsequently introduced into the flue gas stream in the second stage of flue gas cleaning. Ru. The flue gas containing S02 and/or S○2 generated in this process is guided in the circulation path. be done.

The S02-containing flue gas is removed from the flue gas stream before and/or after the air preheater. Served. The ratio of oxidation of CaSO3 to decomposition of Ca5O3 is It is controlled depending on a predetermined value of the return to e (It). Step C) (Patent claim Range 12) is carried out at 10-80°C1, in particular at 50°C.

The temperature adjustment is performed by a correspondingly selected extraction of the flue gas according to claim 28. It is done by

The above method sequence is explained in detail with reference to FIG.

The S02 and NOx removal substream 121 is in a tank 122 at a pH of 12 to 13. With Ca(OH)2, all iron is converted into hydroxide, sulfite and sulfate are Partially precipitated as CaSO3 and CaSO4 respectively. It will be done. After filtration, the solids 123 enter a reaction vessel 124 where they are treated with mineral acids, especially sulfuric acid. The pH value of 6.8 to 4.2, especially 4.0, is adjusted by adding air or acid. Ca5O3 is partially converted, in particular 50%, to CaSO4 by bare injection. It will be done.

This oxidation is coupled with the further decrease in the pH value to 1.5-2.5. , the oxidizing air is discontinued when a pH number of 2.5 is reached, thereby removing the produced acid. The acid alone or added in addition liberates S02 due to the decomposition of CaSO3, and the SO2 is particularly effective in the generator state, causing the reduction of Fe (ml) to Fe (old). Ru.

To further improve the reduction, the free so2'1 circulating air blast @127 S02 and NO are introduced into the reactor again, and then the flue gas is supplied with S02 and NO through conduit 128. x is supplied before the removal process. Furthermore, this S02 circulation path is connected to the S02-containing flue gas. It is taken out through a conduit 129 in front of S02 and the NOx removal device, and then transferred to the reaction tank 124. This contained SO2 participates in the reduction of Fe (Ill) to Fe (II). , causing a decrease in the partial pressure in the gas phase of the reactor, resulting in a reduction in S02 from CaSO3. Free can be used or substituted to advantage. Flue gas collection Ejection is selectively performed before or after LUVO.

The advantage of this method is that CaSO3 is used for the reduction of Fe(Ill) to Fe(■). Only a portion, in particular 50%, of the mineral acid is present at ambient temperature under the liberation of SO2 or in particular CaSO3 is heated to 50℃ and decomposed, but the undecomposed CaSO3 is exposed to air or is oxidized by oxygen to CaSO4.2H20, thus reducing the addition of mineral acids. That is.

For the optimization of the above-mentioned process, the loading of Ca(OH)2 k Solids should be stirred particularly vigorously or washed with fresh water and/or the absorption circuit. It has been found to be particularly effective when administered as a suspension in purified water. did.

Furthermore, in the cleaning circuit S03 concentrations of 5 to 151/l and 60 to 809/l Adjusting S04 concentration can limit CaSO3 precipitation and increase CaSO4 precipitation. It turned out to be a mistake. Furthermore, CO2-containing flue gas and/or pure Co2 When supplied to As a result, the reaction course is improved, particularly in the direction of increasing the precipitation rate of CaSO4.

Thus, the purpose of this precipitation step (to reduce the precipitation of CaSO3 to a relatively small amount in the subsequent F e (III) Precipitation of CaSO4 is increased only to the extent necessary for reduction and relatively high. ) can be achieved to a degree of technical and economic interest, and Suspended because the proportion of Ca5O3 is small compared to aSO4 and Fe(OH)3 Efficient filtration of liquids is possible.

Experience has shown that vvtc-formed CaSO4 in wash water treatment contains traces of iron oxide and and possibly other trace contamination! i71' (because it contains r, the whiteness of CaSO4 is be damaged.

This phenomenon occurs especially when the necessary steps for post-treatment of the wash water are not carried out as specified. Appears in

On-trace impurities are complexed, thus producing a result that can ensure the full whiteness of CaSO4. It was found that the

In another embodiment of the invention, a substream of the cleaning solution is based on polycarboxylic acids. A short-lived dispersant is added to the and the precipitation of iron hydroxide (n) and iron hydroxide (1) in the subsequent wash water after-treatment. We propose improvements without interfering with the reaction. EDTA precipitation according to step g) The acidic wastewater of the , the preparation of a strongly acidic bath solution of a salt of a sulfonic acid such as N(SO3Na)3 and by decomposition into sulfates and sulfites, possibly at elevated pressures. It is processed. The liberated SO□ is utilized as a reducing agent for NOx in the flue gas.

Ammonia is removed from the solution by making alkaline, heating and partially distilling. a is removed. Ammonia is concentrated to a 25% solution. Furthermore, ammonia Treated with sulfuric acid to produce ammonium sulfate. 1 part of a solution containing sodium sulfate The substream is returned to step C) (claim 12) and the other substream is the flue gas The result of washing is put into the bottom of the vessel in step 1, where the Ca of the washing water in the presence of N20 is CaSO4.N20 and and NaCt are produced.

The above method sequence is explained in detail with reference to FIG.

In particular, a further embodiment of the method sequence according to FIG. A short-lived dispersant mainly composed of polycarboxylic acid is added to the CaSO3・l/ 2H20, CaSO4・2H20 and iron hydroxide (■)/iron hydroxide (1[) solid The sedimentation of substances can be increased without interfering with the subsequent wash water treatment reaction. Kirito points out all. The acidic filtrate 114 from the EDTA precipitation tank is evaporated or concentrated. The solids thereby produced are treated in a spray dryer 115, which absorbs another heat After processing unit 116, pure final product consisting of 95% to 100% sodium sulfate It is post-processed at 117.

In the case of the process sequence according to FIG. 8, instead of an evaporative concentration device for the waste water from the storage tank The decomposition device 141 includes a heat exchanger 137, a once-through heater 152, and a circulation and guiding conduit. 134.135.136.138.139.140 and return of harmful substances to raw gas A conduit 142 allows a salt of dithionite and sulfonic acid, such as HON ( SO3Na)s+, NH(SO3Na)2, N(SO3Na)sk, sulfuric acid connected to convert a strongly acidic solution of such salts into salts and sulfites. , with or without applying pressure, by heat exchangers 137 and 152 at specific times. This is possible by heating for a while to decompose.

S02, optionally escaping together with the own steam via line 142, is e.g. It can be used again as a reducing agent for NO. Alkaline, heated and partially distilled By doing so, NH3 from the solution passing through conduit 143 is also removed in stripper 145. Removed by aOH addition 144 and steam addition 146 to normal 25% aqueous solution Concentrated to Ammonium sulfate is recovered as ammonium sulfate-151 using sulfuric acid through Only the N+S salts are reduced, and a partial stream 153 is CaC2z of the water from the alkaline precipitation step. Calcium sulfate dihydrate and sodium chloride are formed.

CaCt2+Na2SO4+2H20-+ CaSO4' 2N20+2NaC According to another feature of the invention, the acidic reconstituted water of the EDTA precipitation according to step g) Na2S○4 is converted into Na It is returned to the second stage of flue gas cleaning with the formation of OH and CaSO4, and is then evaporated and concentrated. The residual product w' from spray drying is post-treated with heat, and the gaseous product is removed. is introduced into the flue gas stream, resulting in a second step of flue gas scrubbing of the remaining Na2SO4k. I suggest sending it back to.

The method sequence described above is explained in detail with reference to FIG.

The acidic solution 161 from the EDTA precipitation step can be evaporated or concentrated directly or after neutralization. The pure Na2SO416 is evaporated and concentrated stepwise in the rfX fog dryer 162. 3 is formed, and from Na2SO4, all the components containing organic substances and 5-N-compounds are formed. A residue 164 remains.

The Na2SO4 is returned directly to the washing step 168 and converted to Ca(OH)2 in a settling tank. CaSO4 and NaOH are produced. The evaporation concentration residue is heated at 300 to 600℃, especially Thermal post-treatment 165 at 450-550°C, in which organic substances and 5- The N-compounds escape in gaseous form as C02, N2, S02, SO3 and are released into the flue gas. route 169. The remaining Na2804166 is pure Na2SO41 63 from the evaporative concentration into the washing process. Gaseous compounds are boiler Added to hot or partially cooled flue gas before S02 cleaning , whereby SO2 and SO3 are combined into CaSO4.

The advantage of this invention is that the simultaneous SO2 and NOx cleaning method does not release wastewater into the drain. and all salt-like components of the wastewater from H4gDTA precipitation are converted into usable product. is used within the entire process.

Therefore, no product deposit is required.

The NOx load in the flue gas can be reduced electrochemically using nitrogen monoxide and iron nitrogen in the cleaning solution. The filler metal is supplied to form a complex such as the trosyl complex, and the complex is formed by iron hydroxide (Il[) With the addition of formic acid as a precipitation inhibitor, the original cumulative nitrogen and water are added at a potentiostatically connected cathode. It can be done in such a way as to be repaid.

In order to prevent the precipitation and reduction of iron (It), tartaric acid and/or Alternatively, it is proposed to utilize citric acid in the cleaning solution during NOX reduction. this is , compared to the use of formic acid, has a significant advantage in maintaining the redox potential complex. Show points.

For example, in the case of 600 m9 of NOx, in order to reduce it to 200 m9 of NOx, It has been found that 1.5 to 2 g"t of tartaric acid and/or citric acid are used, in particular are doing.

For high NOx values, e.g. 1000-2000 m9, NOx increases in the raw gas. Depending on the condition, a correspondingly large amount of washing water, especially 2 to 5.9. /t citric acid and and/or tartaric acid.

NOx separation is carried out behind the flue gas cleaning equipment already installed for 802 separation. In order to make it possible, the present invention provides a It is possible to use the so-called purification gas passage already installed without installing special equipment in the form of a cleaning device. For use as a cleaning device, this passage can be used in a horizontal or vertical structure. can. Therefore, the so-called raw gas channel and/or the purge gas channel can be used as a cleaning pipe. A droplet collector is inserted into the tube. The water discharged from the droplet collector is It is fed to a filtration device in which the solids are separated. From this filtration device, water is The decomposition tank is supplied from there to the regeneration tank with a correspondingly applied redox potential. be done. The appropriate residence time in the regeneration tank is determined depending on the required degree of cleaning. is provided, in which case the redox potential is equal to that of calomel with a 3 molar KC1 bath solution. Recognized as negative with respect to the electrode, the oxygen content of the flue gas has an adverse effect on the reduction process. It has no use. In the cleaning section, the pump passes the cleaning water through the nozzle and then to the redox tank. A corresponding cleaning liquid is then injected. A predetermined portion of electrolysis is supplied from the cleaning system to the So2 cleaning device. Divided amount of water is supplied. The cleaning solution is used to remove acidic droplets from the aforesaid cleaning system. It is made neutral or alkaline. The reduction takes place in a redox tank and the flue gas carried out without the influence of oxygen from

The method sequence described above is explained in detail with reference to FIG.

Is 171 the raw gas coming from the cleaner or coming from the NOx generator? Representation, 1 72 designates the raw gas passage, which is also configured as a cleaning pipe, and 173 the supply pipe. 174 represents the droplet separator arranged in the raw gas passage circle; 75 represents the electrolyzer containing the wash water from the wash tube and droplet collector; Since the combined wash water is guided through the filter 179 in advance, the wash water is passed through the pump. 180 can be used for drop separator 174.

Of course, this water is recognized as necessary for spraying the droplet separator and for cleaning the gas. Due to the redox potential generated, it can also be extracted by pump 176.

176 is a calomel electrolyte in a 3 molar solution pretreated in an electrolyzer according to the present invention. A port that pumps water having a negative potential with respect to the poles to the regeneration tank 177 for a desired residence time. Here, after regeneration of Fe (Iff) to Fe (II), pump 1 78 actually circulates the water into the cleaning water nozzle 173 NO! Cleaning liquid for cleaning Supplied.

The nozzle surface may be configured in a multi-stage or multi-nozzle type depending on the size of the system. Drop collectors etc. may be configured as flow rectifiers or contact fittings.

In the present invention, the EDTA is mixed with EDTA in the electrolyzer or in a tank adjacent to the electrolyzer. The cleaning water is supplied to a regeneration tank for producing Fe(II) after electrolysis, and then after regeneration, Only after a certain residence time, depending on the size of the device and the amount of flushing water, pump 17 8 to the cleaning system together.

The electrolyzer can also be guided by bypass to the regeneration tank 177.

Another idea according to the invention is that the cleaning process 181, for example for S02 cleaning A part of the washing water is taken out as waste water and supplied to the electrolyzer 175, where it is electrolyzed. It is recognized that it decomposes due to In this case, hydrogen, oxygen, chlorine gas, nitric acid and When using sulfuric acid, crystals are deposited on the cathode and/or anode.

Depending on the amount produced, these materials can be recovered and fed to other processes.

Therefore, the acidic droplets that would otherwise form after the flue gas desulphurization device are particularly harmful to the chimney and/or Or, it is ensured that no damage can be caused even after dissipation from the cooling tower.

After this NOx cleaning with PH number control (neutral to alkaline) according to the present invention, Therefore, harmful acid moieties are eliminated.

Furthermore, during the induction of the wash water the reducing components are constrained to a lower oxygen content, i.e. Reduction is not adversely affected by oxygen from the gas.

international search report A) INEX To T! :E INTERNATIONAL SE entering RCHR EPORT ON

Claims (50)

[Claims] 1. HCl and SO from the flue gas of fossil fuel-fired boilers such as power plants and dust combustion equipment. 2 and NOx, in the first step HCl and mostly SO2 In the second step, NOx and remaining SO2 are removed, and the cleaning solution in the first step is is limestone or hydrated lime as well as calcium that does not interfere with the oxidation of CaSO3 to CaSO4. The cleaning solution in the second step contains caustic soda, EDTA and/or N TA and a carboxylic acid that inhibits the oxidation of CaSO3 to CaSO4; Contains sodium dithionite, sodium sulfite and/or pyrosulfite. A method for purifying flue gas, comprising: 2. Claim 1, characterized in that formic acid is advantageously used in the first step. Method described. 3. 2. The process as claimed in claim 1, wherein tartaric acid is advantageously used in the second step. 4. feeding wastewater from the SO2 and NOx wash water (2) to an oxidizer (13); In this, oxidation is caused by adding air or oxygen, and from the filter (15) to the (1 6) Drain the wet plaster with residual moisture of approximately 10%, and remove the water filtered from the plaster (18%). ) is supplied to the washing water (2) as a filtrate reflux, and at this time washing is carried out to wash the plaster. Water is supplied to the iron precipitation tank (17), in which iron hydroxide (19) is reduced by increasing the pH value. The excess water from the iron precipitation tank is fed to the EDTA precipitation tank (20). In this, EDTA was removed by adding H2SO4 [represented by (21)]. The clear water (24) can be sent back to the process and transferred to the biological septic tank (25). or use it in the washing tower (1) or (2) until it no longer pollutes the environment. Specially designed for use as mixing water for mixing limestone and/or hydrated lime. The method according to any one of claims 1 to 3, characterized in that: 5. The sodium sulfate concentration in the wash water of the second step is close to saturation, at least about 20 Claims 1 to 4, characterized in that the amount is adjusted to 0 g/l. The method described in any one of the above. 6. The concentration of sodium sulfate in the washing water in the second step was adjusted to the oxygen content in the flue gas of 5 to 8. %, in proportion to the NOx content in the flue gas 500-2000mg/Nm3 Claims 1 to 5, characterized in that the amount is adjusted to 30 to 120 g/l. The method described in any one of the above. 7. The residence time of the flue gas in the cleaning water of the second step is at least 10 seconds, and Claim 1, characterized in that the ratio of purified liquid to flue gas is maintained between 3 and 5 l/m3. The method described in any one of paragraphs to paragraphs 6 to 6. 8. characterized in that at least 50% of the volume of the cleaning water is filled with a packing body. A method according to any one of claims 1 to 7. 9. Claim 1, characterized in that carbon dioxide is added to the cleaning liquid in the second step. The method described in any one of paragraphs to paragraphs 8 to 8. 10. A partial stream of the washing liquid from the second stage is continuously regenerated as follows: a) Addition of Ca(OH)2 and CaSO3 of Na2SO3 and Na2SO4 and conversion to CaSO4, b) separation and washing of the CaSO3/CaSO4 mixture. Return of purified water to the second stage of flue gas cleaning, c) Oxygen and H2SO4 or CaSO3 in the cleaning liquid of the first step of flue gas cleaning /CaSO4 addition to the CaSO4 mixture and CaSO3 min at reduced pH value d) separation of CaSO4 and return of the waste water to the second stage of flue gas cleaning. sending, e) washing of CaSO4 in fresh water and separation of CaSO4, f) in washing water increase in pH value, precipitation and separation of iron hydroxide, g) addition of H2SO4 to the wash water, precipitation and separation of EDTA; h) return of the cleaning water to the first stage of flue gas cleaning. to the method described in any one of paragraphs 9 to 9. 11. Claims characterized in that the wash water of step g) is fed to a separate after-treatment. The method according to item 10. 12. A partial stream of the washing liquid from the second stage is continuously regenerated as follows: a) Adjust the pH value to 11-12 by adding Ca(OH)2, iron(II hydroxide) and and precipitation of iron(III) hydroxide and Ca of Na2SO3 and Na2SO4 conversion to SO3 and CaSO4; b) separation of precipitated solids; c) Washing of the solid with fresh water and dilution to a solids content of 50% and addition of sulfuric acid. Adjust the pH value to about 4 by adding air and convert CaSO3 to CaSO4 by adding air. oxidation, d) further adding sulfuric acid to adjust the pH value to 0.8-1.5, with Ca compound decomposition of precipitated iron(III) hydroxide to iron(II) sulfate; e) separation of CaSO4.H2O as flue gas by-product; f) step b) odor; The pH number in a partial stream of the resulting liquid is adjusted to between 0.5 and 1 by adding hydrochloric acid. EDTA precipitation, g) separation of EDTA and separate work-up of the liquid, h) second part from step b) Stream, wastewater of step e), EDTA of step g), adjustment of pH value of about 6.5, smoke Sodium dithionite to produce recycled cleaning fluid for the second stage of road gas cleaning. Reduction of iron(III) chelate to iron(II) chelate by addition of The method according to any one of claims 1 to 11, characterized in that: . 13. Claim 1, characterized in that the liquid of step g) is biologically post-treated. The method described in Section 2. 14. The liquid of step g) is thermally worked up, with sodium sulphate as product. 13. A method according to claim 12, characterized in that: 15. E of iron(II) sulfate and step g) in the second part stream of the liquid from step b) Add DTA to make an equimolar iron(II) chelate solution with a pH value of 6 to 8, and A claim characterized in that the liquid is supplied as a new cleaning liquid in the second step of flue gas cleaning. The method according to any one of items 1 to 14. 16. In step c), instead of air, a portion of flue gas is added, with S Frees O2, reduces iron(III) to iron(II), and smoke with increased SO2 concentration 13. Process according to claim 12, characterized in that the flue gas is returned to the flue gas stream. . 17. The liberated SO2 adjusts the SO2 to NOx weight ratio of 4:1 in the flue gas stream. 17. The method according to claim 16, characterized in that: 18. In step a), calcium formate or potassium formate is used instead of Ca(OH)2. Claim 1, characterized in that a mixture of lucium and calcium hydroxide is added. The method according to item 12. 19. The pH number in step c) is adjusted to below 3, in particular to about 1.5, by the addition of sulfuric acid. , simultaneously reducing Fe(III) to Fe(II) The method according to paragraph 12. 20. Instead of sulfuric acid, other drugs may be used to lower the pH value below 3, especially around 1.5. Reduction of Fe(III) to Fe(II) using a product without the addition of other reducing agents 13. A method according to claim 12, characterized in that the method comprises: 21. Step c) is carried out batchwise and the pH value is adjusted to between 3.5 and 4.2 by addition of sulfuric acid. In particular, the conversion of CaSO3 to CaSO4 by the addition of a gaseous oxidizing agent oxidation or by supplying mineral acids to a pH value of 1.5 to 2.5, especially 2, and the unoxidized CaSO3 decomposes while producing SO2. , the reduction of Fe(III) to Fe(II) occurs. The method according to paragraph 12. 22. During the reduction process, the addition of gaseous oxidant is stopped and instead SO2 is added in the circulation. 22. A method according to claim 21, characterized in that the method is carried out under pressure. 23. CaSO3 is oxidized by 10-90%, especially 50%, and the residue is oxidized under SO2 production. 22. The method according to claim 21, wherein the method is used for decomposition. 24. The partial oxidation and decomposition of CaSO3 is controlled by the pH value, and the reaction is Claim 21, characterized in that the process proceeds in a tank or a tank cascade. the method of. 25. The gaseous oxidizer is air, air with increased oxygen concentration, or oxygen. 22. The method according to claim 21, characterized in that: 26. The SO2 is guided through the circulation path, and then the flue gas is removed before the second step of flue gas cleaning. 23. A method according to claim 22, characterized in that it is introduced into a stream. 27. The SO2 and/or SO2-containing flue gas produced in this process is induced in the circulation path. 23. A method according to claim 22, characterized in that: 28. SO2-containing flue gas is removed from the flue gas stream before and/or after the air preheater. 28. A method according to claim 27, characterized in that the method comprises: 29. The ratio of oxidized CaSO3 to decomposed CaSO3 is determined by Fe(III) Claims characterized in that the reduction of Fe(II) to Fe(II) is controlled depending on a predetermined value. The method according to paragraph 23. 30. Step c) (claim 12) is carried out at a temperature of 10 to 80°C, in particular 50°C. , temperature control for the correspondingly selected flue gas withdrawal according to claim 28. 22. A method according to claim 21, characterized in that the method is carried out by: 31. A sulfite concentration of 5 to 159/l in the cleaning liquid of the second stage of flue gas cleaning and a sulfuric acid concentration of 30-80 g/l, Ca(OH)2 was added in a portion of the washing solution. A claim characterized in that the addition of CaSO3 and CaSO4 causes precipitation of CaSO3 and CaSO4. The method according to any one of items 1 to 30. 32. characterized by the introduction of flue gas and/or CO2 during the precipitation step 32. The method of claim 31. 33. Ca(OH)2 in solid form or in fresh water and/or during flue gas cleaning. Claim 31, characterized in that it is added as a suspension in a two-step cleaning solution. or the method described in paragraph 32. 34. EDTA or NTA in the entire cleaning solution or partial stream of the second stage of flue gas cleaning Any one of claims 1 to 33, characterized in that Method described. 35. Addition of EDTA or NTA is required for 1:1 molar Fe/chelate formation. 35. The method of claim 34, wherein: 36. Additionally, EDTA or NTA may be added at other points in the wash water post-treatment. 35. A method according to claim 34, characterized in that: 37. Adding a short-lived dispersant based on polycarboxylic acids to a partial stream of the cleaning solution. , which allows CaSO3 and CaSO4 as well as iron(II) hydroxide and hydroxide To improve the precipitation of iron(III) oxides without interfering with subsequent reactions in the wash water post-treatment. 13. The method according to claim 12, characterized in that: 38. The acidic wastewater of step g) EDTA precipitation is treated with dithionite and HON (S Sulfonic acids such as O3Na)2, NH(SO3Na)2, N(SO3Na)3 A strongly acidic solution of the salt of and a sulfite. The method according to item 37. 39. Specially designed to utilize the liberated SO2 as a reducing agent for NOx in the flue gas stream. 39. The method according to claim 37 or 38, characterized in that: 40. Ammonia is removed by making it alkaline, heating and partially distilling it. Any of claims 37 to 39, characterized in that the method is removed from the solution. The method described in item 1. 41. Claim 40, characterized in that the ammonia is concentrated to a 25% solution. Method described. 42. characterized by treating ammonia to ammonium sulfate using sulfuric acid 42. The method according to claim 41. 43. A partial stream of the solution containing sodium sulfate is added to step c) (Claim 12). ), and another partial stream is sent to the bottom of the column in the first stage of flue gas cleaning, where it is The combination of CaCl2 in the wash water from the first step and Na2SO4 in the partial stream sent to the bottom of the column to form CaSO4H2O and NaCl by reaction in the presence of H2O between The person according to any one of claims 37 to 42, characterized in that Law. 44. The acidic wastewater of the EDTA precipitation from step g) is evaporated and concentrated with the formation of Na2SO4. By condensing or spray drying, Na2SO4 is converted into NaOH and CaSO4. Therefore, the residual products of evaporation concentration or spray drying are returned to the second stage of flue gas cleaning. is thermally worked up and the gaseous products formed are introduced into the flue gas stream and The remaining Na2SO4 is returned to the second process of flue gas cleaning. The method according to claim 12. 45. Tartaric acid is added to the cleaning solution to electrochemically reduce the NOx load in the flue gas. Claims 1 to 4, characterized in that: and/or citric acid is added. The method described in any one of items 4 to 4. 46. Addition of acid, e.g. 2-4 g with a NOx loading of 600-2000 mg 46. The method according to claim 45, characterized in that the method is carried out between /l. 47. A so-called raw gas and/or purge gas channel (172) is used as a cleaning pipe. the droplet collector (174) is inserted into it and the droplet collector (174) is discharged from the droplet collector (174). The water is supplied to a filtration device, where solids are separated, and the water is supplied to an electrolyzer (175). From here, the loaded redox potential is supplied to the regeneration tank (177), where it is regenerated. A corresponding residence time, measured depending on the required degree of cleaning, is installed in the raw tank (177). In this case, the redox potential is calculated using a calomel solution with a 3 molar KCl solution. Considered negative to the electrode, the oxygen content of the flue gas has an adverse effect on the reduction process. In this case, the cleaning zone is supplied by the pump (178) to the cleaning water nozzle (173). A corresponding cleaning liquid is injected from the redox tank (177) by the 47. A method according to any one of claims 1 to 46. 48. A predetermined partial amount of water is transferred from the SO2 cleaning system (181) to the electrolysis device (175). 48. A method according to claim 47, characterized in that the method is transferred to: 49. Claims characterized in that the cleaning liquid is made to flow in a neutral or alkaline state. The method according to paragraph 47 or paragraph 48. 50. Claim 47, characterized in that the reduction is carried out in a regeneration tank (177) The method according to any one of paragraphs to 49.