FR2573673A1 - PROCESS FOR TREATING WASTE GAS. - Google Patents

Abstract

FOR THE REDUCTION OF THE CONTENT OF PRIMARY POLLUTANTS CONTAINING ORGANICALLY BOUND NITROGEN AND OR HYDROCYANIC ACID IN RESIDUAL GASES, THE RESULTING GAS CURRENT IS TREATED CATALYTICALLY AFTER A FIRST STEP OF OXIDIZING TREATMENT, WITH ADDITION OF OXIDIZING.

Description

The present invention relates to a method of

  waste gas treatment to reduce the concentration

  tration of pollutants, a process for the installation of

  thermal and / or catalytic waste gas treatment

  lytique as well as a treatment facility for

waste gases.

  As a process for degradation by oxidation

  pollutants in waste gases, we know the post-

thermal combustion (TNV).

  It emerges from a series of fundamental studies on

  the pollutants TNV which, in the majority of the cases of application-

  tion, the design of the TNV installation must be based on the oxidation conditions of the intermediate products (pollutants

  secondary), especially carbon monoxide (CO) and ne-

  consequently high net working temperatures cease

above 750 C.

  It is in particular with pollutants of emission class III of the technical regulations of the FRG for air purification, hereinafter referred to as TALuft - that the residual admissible concentrations of primary pollutants (300 mg / m3 )

  (m3 under normal conditions) are already reached at tem-

  peratures between 500 and 600 C, while a concentration

  dual CO of 100 mg / m3 maximum considered as admitted-

  sible, can only be reached above 800 C.

  For the elimination of secondary pollutants, the waste gas must therefore be treated at temperatures significantly higher than those necessary for the elimination of primary pollutants. As a result of this constraint, the conventional treatment of waste gases becomes, both on the

  technically than economically, much more expensive

  as much as it should be for the real reason.

  If waste gas containing organic nitrogen compounds and / or hydrocyanic acid is to be treated

  in a TNV installation, additional problems arise

  silences due to the formation of other secondary pollutants.

  As annoying secondary pollutants, mention may be made of

  especially nitrogen oxides (NOX) which are preferential-

  also at high temperatures, partly from nitrogen

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  elementary present in the waste gas.

  When treating a waste gas containing

  organic compounds of N, it appears cyanhy-

  as another dangerous secondary pollutant. In the soul-

  sure o hydrocyanic acid does not escape into the resulting gas stream, it is more or less transformed into NO during the usual waste gas treatment processes

  so NOx is also formed from cyanid

  water - whether in the form of a primary pollutant or se-

condaire.

  Due to the opposite effects - elimination of pol-

  primary gleams, respectively secondary only to

  high temperatures, but with increasing NO formation -

  x TNV is not suitable for the treatment of waste gases containing organic nitrogen compounds and / or hydrocyanic acid. Another known process for degradation by

  oxidation of pollutants in waste gases is the post-

  catalytic combustion (KNV) which generally makes it possible to

  work at lower temperatures than TNV. During the

  waste gas treatment containing organic compounds

  Nitrogen and / or hydrocyanic acid, it pre-

  feel the same difficulties as with TNV: at temperatures

  relatively low tures, the emission of primary pollutants cannot be lowered sufficiently, at temperatures which make it possible to reduce the emission of primary pollutants, there is on the other hand an increasing formation of nitrogen oxides

  (NOx). Therefore, even the KNV is not suitable for this use.

  There was therefore the problem of making available a waste gas treatment process which makes it possible to limit the emission of pollutants to the admissible range and which is suitable for the treatment of waste gas,

  containing organic nitrogen compounds and / or cyanidic acid

  water. A particular problem consisted in improving by simple measures in the indicated direction of the installations of TNV

and / or existing KNVs.

3 2 2573673

  The problem posed is solved by the charac-

terified in the claims.

  The waste gas treatment process con-

  The invention is a multi-step process.

  In a first step, the polluted gas is oxidized in a manner known per se, thermally and /

or catalytic.

  In this first step, the operation is carried out, in the case of heat treatment, at temperatures of 400 to 1000 ° C., in the case of catalytic treatment, at temperatures of

  280 to 600 C and in the case of heat treatment and cat-

  lytic combined between 400 and 600 C for the thermal part

  and between 280 and 600 C for the catalytic part.

  The gas stream from the first step which already constitutes in the traditional process pure gas, is catalytically treated, in accordance with the invention, during

  a subsequent step (KSR step) with addition of ammonia.

  The addition of ammonia can take place directly during the next stage or can be carried out in the pipe

  connecting the first floor and the next floor.

  -In a preferred variant, the addition of ammonia

  is adjusted according to the nitrogen oxides (NO x) content of the

  rant gas from the first stage. For this variant,

  appropriate measurement and regulation devices are provided

  prayers known per se. For example, for the continuous determination

  naked of NOx, a partial stream can be derived from the resulting gas stream in which the NOx content is continuously determined by chemiluminescence analysis and this value

  is used to adjust the ammonia dosage.

  It has proven advantageous to introduce by dosage

  from 0.3 to 3, preferably from 0.5 to 2 parts by volume of ammonia

  niac per part by volume of nitrogen oxide (NOx). For high levels of NO2 in NOx, the metered addition of ammonia should

  rather lie in the. upper part of the domain

  diqued - whereas for high NO contents in NOx, we

  instead choose a value at the bottom.

  In the subsequent step, it will preferably be carried out at temperatures of 130 to 320 C, in particular from 150 to

250 C.

  As catalysts for the first milking stage

  oxidant as well as for the next step, use is made of oxidation catalysts known per se. These can be used in all known forms, for example in the form of fabrics, nets or screens or shaped or unshaped particles in bulk. Preferably, catalysts deposited on porous supports will be used, in which case

  the support is preferably constituted by beads, ex-

  trudates or alveolar bodies. The active component of the cat-

  lyser is based on a noble metal, preferably based on a noble metal from the group of platinum and / or vanadium. Preferred is a catalyst containing as the noble metal platinum and / or

  palladium. Such catalysts are commercially available.

  Waste gases containing nitrogen compounds or-

  ganiques and / or hydrocyanic acid as primary pollutants can be treated by the process according to the invention. In addition, other pollutants containing carbon, hydrogen and / or oxygen may possibly be present in

  waste gases. It is in particular one or more

  sieurs of the following organic nitrogenous compounds: - primary, secondary, tertiary aliphatic amines with alkyl radicals having in particular 1

  with 6 C atoms, such as for example mono-, di-, tri-

  methyl-, ethyl, n-propyl-, n-butylamine, mono-, diisopro-

  pyl-, isobutyl-, sec-butylamine, tert-butylamine; - Cycloalkylamines such as cyclohexylamine, N-methyl-, N, N-dimethyl-cyclohexylamine, dicyclohexylamine;

  - di- and polyamines such as mono-, di-, tri-

ethylenediamine;

  - cyclic amines such as pyridine, morpho-

  line, N-methyl-, N-ethylmorpholine;

  - aromatic amines such as aniline, toluines,

  dines, xylidines, aminophenols, benzylamines;

  - nitriles, in particular alipha nitriles-

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  ticks like aceto-, propio-, butyronitrile, acryloni-

trile, methacrylonitrile;

  - nitro compounds, e.g. nitro ali- compounds

  phatics such as nitromethanç -ethane-, propane or e.g. aromatic nitro compounds such as nitrobenzene, nitrotoluenes; - nitrogen heterocyles such as pyridine, pyrrole

  - amide derivatives such as, for example. N, N-dimethyl-

  formamide. From primary pollutants, it is formed by partial oxidation and / or by degradation reactions of

  secondary pollutants such as formaldehyde or V'acé-

  taldehyde, in particular carbon monoxide, oxides

  nitrogen (NOx), ammonia, hydrocyanic acid. The process con-

  form of the invention makes it possible in particular to effectively limit

the content of secondary pollutants.

  The schematic diagram of an installation in accordance with

  the invention is shown in Figure 1. The exhaust gas

  rer is sent through a pipe (1), passing through a

  heat exchanger - (2), in a first milking stage -

  waste gas (3). This gas treatment stage

  waste (3) can be a waste gas treatment

  mique, catalytic or thermal (3a) and catalytic (3b) combined.

  If the first treatment stage is a purely thermal stage (TNV), the residual gas is purified by

  oxidation in the chamber (3a) under the action of an ex-energy

  later. For this, a fuel, e.g. (a mix of

  propane / air) is preferably routed through the pipeline

  tion 4 and burned simultaneously with the waste gas in an open flame. The resulting gas stream containing the primary and secondary pollutants enters the heat exchanger (2) through the pipeline (5) and from there to the treatment stage

  next through the pipe (5a).

  If the first treatment stage is a purely catalytic stage (KNV), the waste gas is conveyed

  by the pipe (la) to the catalytic stage (3b) in the-

  what is a catalyst (6) and from there reaches the stage of

  further processing via the pipe (7).

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  The first stage is preferably a ther-

  combined mique / catalytic (TNV / KNV). In this case, the current

  gas from the thermal stage (3a) arrives in the thermal stage

  talytic (3b) either by line (5), or directly by line (4a). The catalytically post-treated gas (resulting gas) is conveyed, via the pipe

  (7 / 7a) j to the next stage (8) comprising a catalyst (9).

  Alternatively, the resulting gas stream can be directed to

  a heat exchanger (2) through the pipe (7 / 7b). Ammonium

  niac is introduced by metering into the stage (8) through the pipe (11). It is obviously possible to introduce, by metering, ammonia into the pipe (7a), respectively (7b). The purified gas stream leaving the stage (8) is sent, by

  the pipe (12), in the exhaust chimney (not shown

  tee). The purified gas leaving the second stage (8) can, in

  variant, be routed, with sufficient heat capacity

  high, towards the heat exchanger (10) via the

  valuation (12a) and be used for additional valuation

  loss of heat, for example through

  the superheated steam line (13).

  Thanks to the process according to the invention, it is possible to obtain

  hold substantial advantages over known methods: elimination of primary pollutants containing organically bound nitrogen and / or hydrocyanic acid from exhaust air streams with an emission of nitrogen oxides ( NOx) reduced; - elimination of nitrogenous intermediate products forming as secondary pollutants in conventional air cleaning processes, - elimination of the formation of nitrogen oxide (NO)

  from nitrogen in the air when using the combination

  its TNV / KNV, by lowering the combustion temperatures; - simple adaptation of the existing thermal and / or catalytic exhaust air combustion installations to the modified official regulations by adding an additional treatment stage;

7 2573673

  - reduction of nitrogen oxides (NOx) in the

  waste gas is not disturbed by the oxygen in the pre-

smells in the waste gas.

  The following examples will better illustrate the process.

  die according to the invention without limiting its scope. The results presented in Tables 1 and 2 were obtained on an installation whose first treatment stage was a combined thermal / catalytic stage (TNV / KNV). According to Figure 1, the waste gas has been routed through line (la) to the combustion chamber at open fire (3a) and from there to the catalytic stage (3b) through line

  (4a). The resulting gas stream was directed through the canali-

  sation (7 / 7b) through the heat exchanger (2) in order to

  heat recovery and routed to the KSR stage (8).

  A commercially available oxidation catalyst based on platinum was used as catalyst both in the KNV stage (3a) and in the KSR stage (8) (KNV: catalyst KCO-WK-220ST; KSR: catalyst KCO-1934K / M, manufacturer: firm

Kali-Chemie AG).

  For the analysis of gas mixtures, samples

  were sampled each time before and after the operating phases

individual roofs.

  Tables 1 and 2 show the corresponding pollutant concentration (in percent by volume) as a function of temperature (T measured in C at the outlet of the combustion chamber). The composition relates in this case to bound carbon (balance-C), respectively to bound nitrogen (balance -N) in the

primary pollutant.

  The other abbreviations indicated have the following meaning: S = pollutant, C-ZP = free organic intermediates

  nitrogen, V = NH3 / NOxi molar ratio, c = pol-

primary glow, D = flow.

  From the results indicated, we clearly perceive

  a decrease in primary pollutants, respectively second

  thanks to the implementation of the process according to the invention

tion.

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  Similar tests with hydrocyanic acid, nitro-2-toluene and acrylonitrile as pollutants

  primary have given good, comparable results.

Table 1

  n-propylamine as primary pollutant a) balance. -VS

  TNV; '. I TNV + KNV I TNV + KNIV + KSR

  I S I C-ZP Icol C v. Clo0 I s Ic -zPI C-P COl iCNi C02 I S IC-ZPICO IHCNICO,

  I I - --- 1 1 I - ± 1-1- 1 I I I i -

  400 I 50 I 21 1101 2 I 1.7'I 6.1 0 a 0 I 0 I 94 J 2 I 0 I0 0 98

  450 1 44 1 7 1141 4 1 21.I 4 1 0.10 1 0 I96 I I I1

  500 1 38 1 9 1211 7 I 25 1 3 I 0'1 0 I 0 1 97 I I I

  550 I 31 1 0 1341 10 1 25 1 2 I 0l 0 I 0 I 98 I I I

  600 I 21 I 0 1351.10 I 34 1 2 I. 0 1 0 1 0 198 I I I

b) balance sheet -N

TNV | TNV + KNV [TNV + KNV + KSR

Z I

  I S. HCN INHj I NO. [N2 [S IHCN 1NH1 I NO, I N2 I S I iICNNI 1110N. I N

I 'I I I I III I I I II I --.--

  400I5 1..7 1. 0 3. 40 I 6 I o 1. 0.151 I 43 I2 I 0 I 0 I 3 95

  450 I 44 I 11 0 '5.140 1 4 I 1 O I 57 I39 I I I I

  500 138. 20 10 9 1 33 13 1 00 159 1 38 I I. I

  550 I 31 I 32 i 7 I 12 1 18 I 2 I 0 I 0 I 61 I 37 I I I I

  600 I 21 I 30 111 15 I 23 I 2 I 0 10 I60 I 38 I. I I I

  c = 750 ppm, D = 74.5 Nm3 / h, V = 1.4 "cw4 i,%

S Z = A 'q /' wN 8L = a 'wdd oZZ'.

  I I I I I o I 56 oI o 1 a 1 '' 1 :: oI '"." .. L- I IZI. -Lt009 I I I I I o 1 o6 1 o Io 10 1 ot l "a I'ss1 i, 'I S9 l sz Ioss I I I I I oIO D06I 0 I o 1 OtI: C.ISV ,, IcI ,. SV o08,

  L 'tZO t O Io tIt I t O IO 6.1 Lt. I z O t ú c 6S OZ ,.

  It- II.I-I I I I "l I I 'I. I.I [N' oRt m ol 'II tlDI iS t I' V ONt CHNI g {Iî3 S! I N 'ON CHN t t It. S I. 1

SA + ANN + AN1I AN + AN & | * ANL

  N- ueITq (q o-4 '..', IIII I S6lo ol 0IS Ic I s 'EI:, SO t.Lt l009 II I o6 t O l ol ot o.OI. OI O' ... 4.1 Os IOt SZ 1 oss IIII to6 Io I olt0 .. Iot "'l: OZ I *" t I 6ZtS IF "t I os, Z6t OI olo I 18 o Iol oI6' OZ .. t0 tt I o01 65I OZ, IHt- HI -I I. 1 - III t I ODIND1I ODild? .- DStOD IN [DHIoDldZ-DIS.1 'OD I; NDIHO0I. DZ-D'S t

* ____ I _I "

  dSx + Atm + ANl ANN + ANI AN. ANM D- ueq (e: eWTa.ad: uenTlod awwoD.u.lçuV 2 neelqel

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Claims (11)

Claims   1. Method for reducing the concentration of   brighteners in a waste gas by oxidative treatment,   mique and / or catalytic, characterized in that, during the introduction of a waste gas containing organic nitrogen compounds and / or hydrocyanic acid and after the oxidative, thermal and / or catalytic treatment step, we catalytically treats the resulting gas stream during   a later step with the addition of ammonia.   2. Method according to claim 1, characterized in that, in the oxidative heat treatment step,   we operate at temperatures of 400 to 1000 C.   3. Method according to any one of the claims   above, characterized in that, in the catalytic, oxidative treatment stage, the operation is carried out at temperatures of 280 to 600 C.   4. Method according to one of the preceding claims,   characterized in that one operates at temperatures of 400 to 6000C in the heat treatment step, oxidizing and between 280 and   6000C in the oxidative catalytic treatment stage.   5. Method according to one of the preceding claims,   characterized in that, in the next step, one operates at   temperatures from 130 to 320 C, preferably from 150 to 250 C.   6. Method according to one of the preceding claims,   characterized in that the following addition of ammonia is regulated   the content of nitrogen oxides (NO) in the gas stream   sultant. 7. Method according to claim 6, characterized in that intr duit- by dosing-0.3 ′ to 3 V preferably 0.5 to 2 parts by volume of ammonia per part by volume of nitrogen oxides.   8. Method according to one of the preceding claims,   characterized in that in the treatment step ca-   talytic, oxidizing and / or in the next step a catalyst based on a noble metal, preferably a noble mnetal of the group platinum and / or vanadium. 12 25? 3673   9. Method according to claim 8, characterized in that a catalyst containing platinum is used   and / or palladium as a noble metal.   10. Method for fitting out existing thermal and / or catalytic waste gas treatment plants for the treatment of waste gas containing   organic nitrogen compounds and / or hydrocyanic acid, ca   characterized in that the catalytic current is treated catalytically   zeux resulting in a subsequent step by addition ammonia.   11. Waste gas treatment plant   for carrying out a process according to one of the claims   1 to 9, comprising an oxidative treatment stage,   mique and / or catalytic and an additional stage in   which the resulting gas stream is catalytically treated- ment with addition of ammonia.