GB1572211A – Method of producing nitrogen oxides
– Google Patents
GB1572211A – Method of producing nitrogen oxides
– Google Patents
Method of producing nitrogen oxides
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Publication number
GB1572211A
GB1572211A
GB3818/77A
GB381877A
GB1572211A
GB 1572211 A
GB1572211 A
GB 1572211A
GB 3818/77 A
GB3818/77 A
GB 3818/77A
GB 381877 A
GB381877 A
GB 381877A
GB 1572211 A
GB1572211 A
GB 1572211A
Authority
GB
United Kingdom
Prior art keywords
oxygen
organic compound
process according
functional group
parent hydrocarbon
Prior art date
1976-01-30
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB3818/77A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Mitsubishi Heavy Industries Ltd
Original Assignee
Mitsubishi Heavy Industries Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
1976-01-30
Filing date
1977-01-31
Publication date
1980-07-30
1977-01-31
Application filed by Mitsubishi Heavy Industries Ltd
filed
Critical
Mitsubishi Heavy Industries Ltd
1980-07-30
Publication of GB1572211A
publication
Critical
patent/GB1572211A/en
Status
Expired
legal-status
Critical
Current
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MWUXSHHQAYIFBG-UHFFFAOYSA-N
nitrogen oxide
Inorganic materials
O=[N]
MWUXSHHQAYIFBG-UHFFFAOYSA-N
0.000
title
claims
description
90
238000000034
method
Methods
0.000
title
claims
description
47
OKKJLVBELUTLKV-UHFFFAOYSA-N
Methanol
Chemical compound
OC
OKKJLVBELUTLKV-UHFFFAOYSA-N
0.000
claims
description
45
QVGXLLKOCUKJST-UHFFFAOYSA-N
atomic oxygen
Chemical compound
[O]
QVGXLLKOCUKJST-UHFFFAOYSA-N
0.000
claims
description
41
239000001301
oxygen
Substances
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claims
description
41
229910052760
oxygen
Inorganic materials
0.000
claims
description
41
239000007789
gas
Substances
0.000
claims
description
37
150000002894
organic compounds
Chemical class
0.000
claims
description
31
WSFSSNUMVMOOMR-UHFFFAOYSA-N
Formaldehyde
Chemical compound
O=C
WSFSSNUMVMOOMR-UHFFFAOYSA-N
0.000
claims
description
21
125000000524
functional group
Chemical group
0.000
claims
description
20
230000008569
process
Effects
0.000
claims
description
20
150000002430
hydrocarbons
Chemical class
0.000
claims
description
19
238000010521
absorption reaction
Methods
0.000
claims
description
13
VNWKTOKETHGBQD-UHFFFAOYSA-N
methane
Chemical group
C
VNWKTOKETHGBQD-UHFFFAOYSA-N
0.000
claims
description
12
IJGRMHOSHXDMSA-UHFFFAOYSA-N
Atomic nitrogen
Chemical compound
N#N
IJGRMHOSHXDMSA-UHFFFAOYSA-N
0.000
claims
description
11
ATUOYWHBWRKTHZ-UHFFFAOYSA-N
Propane
Chemical compound
CCC
ATUOYWHBWRKTHZ-UHFFFAOYSA-N
0.000
claims
description
10
230000001590
oxidative effect
Effects
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claims
description
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239000000203
mixture
Substances
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claims
description
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229930195733
hydrocarbon
Natural products
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claims
description
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239000004215
Carbon black (E152)
Substances
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claims
description
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239000007864
aqueous solution
Substances
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claims
description
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OTMSDBZUPAUEDD-UHFFFAOYSA-N
Ethane
Chemical compound
CC
OTMSDBZUPAUEDD-UHFFFAOYSA-N
0.000
claims
description
5
-1
aliphatic aldehyde
Chemical class
0.000
claims
description
5
239000003638
chemical reducing agent
Substances
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claims
description
5
238000002485
combustion reaction
Methods
0.000
claims
description
5
229910052757
nitrogen
Inorganic materials
0.000
claims
description
5
239000001294
propane
Substances
0.000
claims
description
5
MGWGWNFMUOTEHG-UHFFFAOYSA-N
4-(3,5-dimethylphenyl)-1,3-thiazol-2-amine
Chemical compound
CC1=CC(C)=CC(C=2N=C(N)SC=2)=C1
MGWGWNFMUOTEHG-UHFFFAOYSA-N
0.000
claims
description
4
XEEYBQQBJWHFJM-UHFFFAOYSA-N
Iron
Chemical compound
[Fe]
XEEYBQQBJWHFJM-UHFFFAOYSA-N
0.000
claims
description
4
PXHVJJICTQNCMI-UHFFFAOYSA-N
Nickel
Chemical compound
[Ni]
PXHVJJICTQNCMI-UHFFFAOYSA-N
0.000
claims
description
4
150000001335
aliphatic alkanes
Chemical class
0.000
claims
description
4
229910052751
metal
Inorganic materials
0.000
claims
description
4
239000002184
metal
Substances
0.000
claims
description
4
JCXJVPUVTGWSNB-UHFFFAOYSA-N
nitrogen dioxide
Inorganic materials
O=[N]=O
JCXJVPUVTGWSNB-UHFFFAOYSA-N
0.000
claims
description
4
XLYOFNOQVPJJNP-UHFFFAOYSA-N
water
Substances
O
XLYOFNOQVPJJNP-UHFFFAOYSA-N
0.000
claims
description
4
239000012736
aqueous medium
Substances
0.000
claims
description
3
239000013522
chelant
Substances
0.000
claims
description
3
DNIAPMSPPWPWGF-GSVOUGTGSA-N
(R)-(-)-Propylene glycol
Chemical compound
C[C@@H](O)CO
DNIAPMSPPWPWGF-GSVOUGTGSA-N
0.000
claims
description
2
RYGMFSIKBFXOCR-UHFFFAOYSA-N
Copper
Chemical compound
[Cu]
RYGMFSIKBFXOCR-UHFFFAOYSA-N
0.000
claims
description
2
KCXVZYZYPLLWCC-UHFFFAOYSA-N
EDTA
Chemical compound
OC(=O)CN(CC(O)=O)CCN(CC(O)=O)CC(O)=O
KCXVZYZYPLLWCC-UHFFFAOYSA-N
0.000
claims
description
2
239000012670
alkaline solution
Substances
0.000
claims
description
2
239000003795
chemical substances by application
Substances
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claims
description
2
229910052802
copper
Inorganic materials
0.000
claims
description
2
239000010949
copper
Substances
0.000
claims
description
2
229910052742
iron
Inorganic materials
0.000
claims
description
2
229910052759
nickel
Inorganic materials
0.000
claims
description
2
LSNNMFCWUKXFEE-UHFFFAOYSA-L
sulfite
Chemical compound
[O-]S([O-])=O
LSNNMFCWUKXFEE-UHFFFAOYSA-L
0.000
claims
description
2
238000007254
oxidation reaction
Methods
0.000
description
12
239000007791
liquid phase
Substances
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description
11
239000007792
gaseous phase
Substances
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description
10
GEHJYWRUCIMESM-UHFFFAOYSA-L
sodium sulfite
Chemical compound
[Na+].[Na+].[O-]S([O-])=O
GEHJYWRUCIMESM-UHFFFAOYSA-L
0.000
description
8
239000000243
solution
Substances
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oxidation
Effects
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230000009467
reduction
Effects
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description
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238000006722
reduction reaction
Methods
0.000
description
6
CBENFWSGALASAD-UHFFFAOYSA-N
Ozone
Chemical compound
[O-][O+]=O
CBENFWSGALASAD-UHFFFAOYSA-N
0.000
description
5
238000002474
experimental method
Methods
0.000
description
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239000003054
catalyst
Substances
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description
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238000006243
chemical reaction
Methods
0.000
description
4
235000010265
sodium sulphite
Nutrition
0.000
description
4
HEMHJVSKTPXQMS-UHFFFAOYSA-M
Sodium hydroxide
Chemical compound
[OH-].[Na+]
HEMHJVSKTPXQMS-UHFFFAOYSA-M
0.000
description
3
150000001875
compounds
Chemical class
0.000
description
3
238000005259
measurement
Methods
0.000
description
3
WSFSSNUMVMOOMR-NJFSPNSNSA-N
methanone
Chemical compound
O=[14CH2]
WSFSSNUMVMOOMR-NJFSPNSNSA-N
0.000
description
3
QGZKDVFQNNGYKY-UHFFFAOYSA-N
Ammonia
Chemical compound
N
QGZKDVFQNNGYKY-UHFFFAOYSA-N
0.000
description
2
BDAGIHXWWSANSR-UHFFFAOYSA-N
Formic acid
Chemical compound
OC=O
BDAGIHXWWSANSR-UHFFFAOYSA-N
0.000
description
2
RAHZWNYVWXNFOC-UHFFFAOYSA-N
Sulphur dioxide
Chemical compound
O=S=O
RAHZWNYVWXNFOC-UHFFFAOYSA-N
0.000
description
2
229910052783
alkali metal
Inorganic materials
0.000
description
2
229910052799
carbon
Inorganic materials
0.000
description
2
238000010531
catalytic reduction reaction
Methods
0.000
description
2
229910001873
dinitrogen
Inorganic materials
0.000
description
2
235000019253
formic acid
Nutrition
0.000
description
2
229910017604
nitric acid
Inorganic materials
0.000
description
2
OKTJSMMVPCPJKN-UHFFFAOYSA-N
Carbon
Chemical compound
[C]
OKTJSMMVPCPJKN-UHFFFAOYSA-N
0.000
description
1
UGFAIRIUMAVXCW-UHFFFAOYSA-N
Carbon monoxide
Chemical compound
[O+]#[C-]
UGFAIRIUMAVXCW-UHFFFAOYSA-N
0.000
description
1
RWSOTUBLDIXVET-UHFFFAOYSA-N
Dihydrogen sulfide
Chemical compound
S
RWSOTUBLDIXVET-UHFFFAOYSA-N
0.000
description
1
MYMOFIZGZYHOMD-UHFFFAOYSA-N
Dioxygen
Chemical compound
O=O
MYMOFIZGZYHOMD-UHFFFAOYSA-N
0.000
description
1
238000004435
EPR spectroscopy
Methods
0.000
description
1
GRYLNZFGIOXLOG-UHFFFAOYSA-N
Nitric acid
Chemical compound
O[N+]([O-])=O
GRYLNZFGIOXLOG-UHFFFAOYSA-N
0.000
description
1
NINIDFKCEFEMDL-UHFFFAOYSA-N
Sulfur
Chemical compound
[S]
NINIDFKCEFEMDL-UHFFFAOYSA-N
0.000
description
1
239000002253
acid
Substances
0.000
description
1
239000003513
alkali
Substances
0.000
description
1
229910021529
ammonia
Inorganic materials
0.000
description
1
125000004429
atom
Chemical group
0.000
description
1
229910002091
carbon monoxide
Inorganic materials
0.000
description
1
229940125810
compound 20
Drugs
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description
1
229940125846
compound 25
Drugs
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1
238000010276
construction
Methods
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1
239000000356
contaminant
Substances
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description
1
238000011161
development
Methods
0.000
description
1
229910001882
dioxygen
Inorganic materials
0.000
description
1
239000000428
dust
Substances
0.000
description
1
229910052736
halogen
Inorganic materials
0.000
description
1
150000002367
halogens
Chemical class
0.000
description
1
125000005842
heteroatom
Chemical group
0.000
description
1
239000001257
hydrogen
Substances
0.000
description
1
229910052739
hydrogen
Inorganic materials
0.000
description
1
125000004435
hydrogen atom
Chemical class
[H]*
0.000
description
1
239000004615
ingredient
Substances
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description
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239000000543
intermediate
Substances
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229910000765
intermetallic
Inorganic materials
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239000007788
liquid
Substances
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239000000463
material
Substances
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230000004048
modification
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238000012986
modification
Methods
0.000
description
1
150000002823
nitrates
Chemical class
0.000
description
1
239000007800
oxidant agent
Substances
0.000
description
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239000012071
phase
Substances
0.000
description
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239000012286
potassium permanganate
Substances
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description
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230000009257
reactivity
Effects
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description
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238000011084
recovery
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spray
Substances
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239000000126
substance
Substances
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sulfur
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239000011593
sulfur
Substances
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239000004291
sulphur dioxide
Substances
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235000010269
sulphur dioxide
Nutrition
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238000007669
thermal treatment
Methods
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waste gas
Substances
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1
Classifications
B—PERFORMING OPERATIONS; TRANSPORTING
B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
B01D—SEPARATION
B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
B01D53/34—Chemical or biological purification of waste gases
B01D53/46—Removing components of defined structure
B01D53/54—Nitrogen compounds
B01D53/56—Nitrogen oxides
Description
PATENT SPECIFICATION ( 11) 1 572 211
( 21) Application No 3818/77 ( 22) Filed 31 Jan 1977 ( 19) By ( 31) Convention Application No 51/008378 ( 32) Filed 30 Jan 1976 in,4 @’ ( 33) Japan (JP)
g ( 44) Complete Specification Published 30 Jul 1980
I ( 51) INT CL 3 C Oi B 21/36 B 01 D 53/34 ( 52) Index at Acceptance C 1 A 2 B 521 X 521 Y 5410 541 Y 544 Y 5450 5451 5456 5457 545 X 546 X 546 Y 5471 5491 5645 5682 5683 SA SB ( 54) METHOD OF PRODUCING NITROGEN OXIDES ( 71) We, MITSUBISHI JUKOGYO KABUSHIKI KAISHA, of 5-1 Marunouchi 2-chome, Chiyoda-ku, Tokyo, Japan, a Japanese Body Corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described, in and by the following statement:
This invention relates to a method of producing nitrogen oxides (N Ox) in combustion waste gases, e g from boilers.
Methods in use or under development for the removal of N Ox from the exhaust gases leaving boilers and the like, which contain nitric oxide (NO) as the major ingredient and a small proportion of nitrogen dioxide (NO 2), are roughly divided into two, i e, removal by (A) dry catalytic reduction and by (B) wet absorption In either case, the low reactivity and 5 low concentrations of NO (usually ranging from only tens to hundreds of parts per million) in the gases have presented difficulties in finding an economical process for N Ox removal, which is now a subject of intense developmental efforts throughout the industry.
Dry catalytic reduction (A) is a process in which N Ox reacts with a reducing agent in the presence of a bed of a catalyst consisting of a metal or metallic compound whereby the N Ox 10 is selectively or nonselectively reduced to harmless N 2 In the case of selective reduction, ammonia or hydrogen sulphide is employed as the reducing agent, and, in the case of the nonselective reduction, hydrogen, methane, carbon monoxide or the like is used Disadvantages of the process are the short catalyst life under the influence of sulphur dioxide ( 502) in the exhaust gases and the difficulty of determining the catalyst life In addition, the 15 reducing agent recovered in the unreacted state must be treated to make it harmless.
Another problem of practical importance, not yet solved, is the release of untreated exhaust gases due to clogging of the catalyst bed with the dust from the gases.
Wet absorption (B) is generally carried out in one of three different ways One of the methods uses an oxidizing aqueous solution to oxidize NO to nitric acid ions (NO 3-) which 20 are absorbed in the solution, and is therefore called the liquid-phase oxidation-absorption method Another method consists of oxidizing NO in a gaseous phase to NO 2 and N 205 which can be more readily absorbed, and then taking up the products into an absorbing solution of water and an alkali in the form of nitrates (the gaseousphase oxidation-liquid phase absorption method) A modification of the latter method uses an aqueous solution of 25 a reducing substance in which the NO 2 and N 205 obtained in the manner described above are reduced to N 2 (the gaseous-phase oxidation liquid-phase reduction method).
In the liquid-phase oxidation-absorption method, a mixture of potassium permanganate and sodium hydroxide is most often employed as the absorbing solution However, the solution is expensive and the treatment for recovery of the NO 3 containing used solution 30 involves technical difficulties.
The gaseous-phase oxidation-liquid phase absorption is accomplished generally by either thoroughly oxidizing NO to N 205 with ozone and then absorbing the product in water to recover the same in the form of nitric acid, or oxidizing NO to NO 2 and then absorbing the same in an aqueous solution of an alkali metal salt such as sodium sulphite to form nitric 35 acid and an alkalimetal nitrite.
The gaseous-phase oxidation liquid-phase reduction method typically comprises having NO 2 co-ordinated by a metal chelate of iron, nickel, copper with EDTA or the like, and then reducing the product to N 2 with a sulphite or the like.
Major economic and technical difficulties common to these methods of oxidizing NO to 40 1,572,211 NO 2 in a gaseous phase and absorbing the NO 2 in a liquid phase arise from the fact that no effective substances have thus far been found, except for ozone, as agents for oxidizing NO to NO 2.
The most economical of the processes for oxidation with ozone is by oxygen corona discharge However, the process nevertheless necessitates a large power consumption and an ozoniser which can account for as much as half of the initial investment on a denitrifying plant Thus ozone cannot be an optimum oxidizing agent for treating a large volume of effluent gases.
U K Specification No 1,435,317 discloses a method for the thermal treatment of a combustion effluent stream containing an oxide of nitrogen (NO) as a contaminant, which 10 comprises the step of adding to, and contacting the said stream with a compound selected from hydrocarbons and hydrocarbon compounds containing heteroatoms selected from:
oxygen, nitrogen, halogen, and sulfur, in the presence of oxygen for at least 25 milliseconds at a temperature in the range of from 400 C to 2700 C, the amount of said added compound being such as to provide a ratio of C to N Ox of from 0 02:1 to 400:1 and a ratio of 02 15 to C of between 0 01:1 to 12:1 thereby to cause a substantial reduction of N Ox to molecular nitrogen.
In the course of experiments on oxidation of NO to NO 2 in a gaseous phase, we have found that oxygen is activated by the addition of an organic compound having an oxygencontaining functional group, such as methanol or formaldehyde, and becomes able to 20 oxidize NO to NO 2 effectively This is a behaviour in the gaseous phase in striking contrast to the generally known strong reducibility of the methanol, formaldehyde, and other such organic compounds having an oxygen-containing functional group in the liquid phase.
The present invention resides in a method of producing NO 2, comprising reacting in the gas phase and at a temperature higher than 200 C NO, oxygen, and an organic compound 25 having an oxygen-containing functional group and/ or a parent hydrocarbon compound of such an organic compound the ratio of the oxygen to the said compound and/or parent hydrocarbon being sufficiently high that the oxygen and the said organic compound and/or parent hydrocarbon form an oxidising mixture.
The invention provides a process for oxidizing NO to NO 2 using instead of the expensive 30 ozone, very inexpensive oxidizing means, well suited for the gaseousphase oxidation-liquid phase absorption or for the gaseous-phase oxidation liquid-phase reduction technique.
The present invention also resides in a process for controlling N Ox in combustion exhaust gases, which comprises adding an organic compound having an oxygencontaining functional group and/ or its parent hydrocarbon compound thereof to exhaust gases and thereby oxidizing at a temperature higher than 200 C NO in the exhaust gases to NO 2 in the presence of oxygen, the ratio of the oxygen to the said organic compound and/or parent hydrocarbon being sufficiently high that the oxygen and the said organic compound and/or parent hydrocarbon form an oxidising mixture.
The nitrogen dioxide may be removed from the exhaust gases by absorption in an aqueous medium, which may be water or an alkaline solution.
The term “organic compound having an oxygen-containing functional group” as used herein indicates an aliphatic alcohol (for example, methanol) or an aliphatic aldehyde (for example, formaldehyde) The term “parent hydrocarbon compounds” indicated alkanes (for example, methane, ethane, or propane) 45 The oxidation reaction employed in the invention is thought to consist of the following elementary reactions (taking methanol as an exemplary organic compound having an oxygen-containine functional group):
CH 3 OH + 02 – HCHO + H 202 ( 1) 50 HCHO + 02->HCOOH+ O ( 2)( 2) HCOOH + 02 H 202 + CO 2 ( 3) H 202 +NO N 2 + H 20 ( 4) 55 0 + NO -NO 2 ( 5) ( activated atoms) It is presumed that, in the elementary reactions ( 1) to ( 5), H 202 and O are formed as 60 intermediates, which then oxidise NO.
Since the oxidation reaction takes place where the organic compounds having an oxygen-containing functional group such as methanol or formaldehyde, and oxygen coexist, it is possible to use, as a parent hydrocarbon compound of the organic compound having an oxygen-containing functional group, methane, ethane, or propane, or other said 65 1,572,211 parent hydrocarbon compound which can produce the organic compound having an oxygen-containing functional group in the presence of oxygen.
The aforesaid reaction is governed by factors including the temperature, concentration of the organic compounds having an oxygen-containing functional group, and oxygen concentration, as will be specifically indicated in experimental examples to be given later 5 Other objects and advantages of the invention will become apparent from the following description when taken in conjunction with the accompanying drawing, wherein:
Figure 1 is a flow sheet of an experimental arrangement for the oxidation reaction in accordance with the invention; Figure 2 shows graphs summarizing the results of experiments conducted with the 10 arrangement of Figure 1; and Figure 3 is a flow sheet of an arrangement for practicing the process of the invention for the removal of N Ox from exhaust gases.
As shown in Figure 1, the experimental arrangement includes cylinders la, lb lc containing, respectively, carrier nitrogen gas, NO gas, and oxygen gas These gas cylinders are 15 connected, through respective flow control valves 2 a, 2 c, 2 d and flowmeters 3 a, 3 c 3 d to a mixer 4 The cylinder la is also connected through a flow control valve 2 b and a flow-meter 3 b to a bubble tower 5 in which an organic compound having an oxygencontaining functional group is stored and which is connected to the mixer 4 As nitrogen gas from the cylinder la is admitted to the bubble tower 5, the latter delivers the organic compound 20 having an oxygen-containing functional group at a concentration corresponding to the temperature and vapour pressure in the tower, to the mixer 4.
The gas mixture flows from the mixer 4 into a reactor 7, which is set to a temperature between room temperature and 1500 ‘C 50 C by a PID temperature controller 6 to carry out an oxidation reaction Gas-absorbing bottles 8 installed downstream from the reactor 7 25.
contain an aqueous solution of sodium sulphite which can absorb NO 2, from the gases leaving the reactor 7 A chemiluminescence analyser 9 determines the NO content of the.
gases downstream from the bottles 8 and transmits the results into a recorder 10.
The experiments were performed by adjusting the flow control valves 2 a 2 d and the flowmeters 3 a 3 d so that the mixed gas composition at the inlet of the reactor 7 was 150 30 ppm NO, 1 4 % 02, 75 1500 ppm organic compound having an oxygencontaining functional group, and the balance 96 99 % N 2 The gas flow rate was set to 2 Ne/min and the residence time in the reactor 7 to 1 5 5 sec The temperature in the reactor 7 was set at different values between 100 and 700 C by the PID temperature controller 6.
It can therefore be seen that the experiments were performed under oxygenrich condi 35 tions, with the number of moles of oxygen in the exhaust gas to the number of moles of carbon-containing organic compound to be added l 02 l / lCl ranging from 4 %/75 ppm (i e.
533) to 1 %/1500 ppm (i e 6 6) It is desirable for the ratio l 02 l / lCl to be greater than 6.6.
It can also be seen that the experiments were performed with the ratio of the number of 40 moles of oxygen in the exhaust gas to the number of moles of NO l 02 ll lNOl ranging from 4 %/o 150 ppm (i e 266 7) to 19 da 150 ppm (i e 66 7).
In all runs the NO and NO 2 contents of the treated gases were determined by the chemiluminescence analyser 9 while maintaining the material balance with cross checking of two measurements, i e, ( 1) measurement of the unreacted NO amount after the com 45 plete absorption of NO 2 by the aqueous solution of sodium sulphite in the gas absorbing bottles 8, and ( 2) measurement of the NO 2 amount by an electron-spin resonance meter.
The experimental results are graphically represented in Figure 2.
In the graph, the rate (%) of oxidation of NO to NO 2 is plotted as ordinate and the temperature ( C) as abscissa The “X” curve represents formaldehyde (HCHO/NO 1 25, 50 02 = 1 %), the “O” curve represents methanol (CH 3 OH/NO 1 0, 02 = 1 %), the ” U” curve represents formaldehyde (HCHO/NO 1 25, 02 = 0 1 %), and the “A” curve represents methanol (CH 30 H/NO 1 0, 02 0 1 %) The percentage rate of oxidation of NO to NO 2 is defined as Inlet NO conc (PPM) outlet NO conc (PPM) X 100 55 Inlet NO con (PPM) It will be appreciated from Figure 2 that the oxidation reaction starts at 200 C, at an 02 concentration of 1 % or more, and with the addition of an organic compound having an oxygen-containing functional group, and that the reaction proceeds faster as the tempera 60 ture increases.
Next, an example of the use of the invention for controlling nitrogen oxides in exhaust gases will be described in connection with the flow sheet of Figure 3.
Figure 3 shows the body 1 of an LNG-fired boiler incorporating a furnace la A boiler of this type emits gases usually containing from 100 to 150 ppm of N Ox 65 A 1,572,211 4 The exhaust gas stream that has left the furnace la passes through various heat exchangers arranged in series, such as superheaters lb, reheater lc, economizer id, and air heater le After the heat exchange, the effluent is discharged from the system to the atmosphere through a stack 1 f.
When the process of the invention is to be applied to a boiler, it is ideal to inject methanol 5 vapour into the boiler at the inlet of the economizer Id therein, for reasons related to the temperature conditions, boiler construction, and convenience in handling the organic compound having an oxygen-containing functional group The methanol vapour is supplied from a methanol storage tank 2 through a methanol line 3 and a bank of nozzles 4, and is thoroughly mixed with the effluent in the economizer id, thanks to the bundle of tubes 10 therein serving as baffles, whereby the NO in the gas mixture is rapidly oxidized to NO 2.
An NO 2 absorption column 5 uses an absorbing solution of sodium sulphite, for example, and injects this in the form of droplets through spray nozzles 5 a for gas-liquid contact and absorption of NO 2 from the exhaust gases The column is equipped with a circulating pump 5 b and a blow-down line Sc Since the absorbed NO 2 in the liquid phase mostly occurs as 15 N 02 and NO 3 -ions, the p H of the absorbing solution will gradually decrease When the p H has dropped to 5 or below the solution is blown down through the line 5 c.
The exhaust gases, having being stripped of NO 2 in the NO 2 absorption column and thus made harmless, are released from the system to the atmosphere via the stack if.
The concentration of oxygen is not specified herein because almost all the boilers in 20 operation today emit exhaust gases containing 1 to 10 % oxygen If the exhaust gas is exceptionally free from oxygen, then oxygen may be injected in the same manner as methanol into the exhaust gas or, alternatively, the combustion conditions may be shifted towards a higher percentage of excess air.
Claims (21)
WHAT WE CLAIM IS: 25
1 A method of producing NO 2, comprising reacting in the gas phase and at a temperature higher than 200 C NO, oxygen, and an organic compound having an oxygencontaining functional group and/or a parent hydrocarbon of such an organic compound the ratio of the oxygen to the said organic compound and/or parent hydrocarbon being sufficiently high that the oxygen and the said organic compound and/or parent hydrocarbon 30 form an oxidising mixture.
2 A method as claimed in claim 1 wherein the organic compound having an oxygencontaining functional group is an aliphatic alcohol or an aliphatic aldehyde.
3 A method as claimed in claim 1 wherein the organic compound is methanol or formaldehyde 35
4 A method as claimed in claim 1 wherein the parent hydrocarbon compound is an alkane, which yields an organic compound having an oxygen-containing functional group in the presence of oxygen.
A method as claimed in claim 4 wherein the alkane is methane, ethane or propane.
6 A method as claimed in claim 1, comprising reacting NO, oxygen and methanol or 40 formaldehyde.
7 A method as claimed in claim 1 comprising reacting NO, oxygen and at least one of:
methane, ethane, or propane.
8 A method as claimed in any one of the preceding claims, in which the ratio l 021/lCl ranges from 533 to 6 6 45
9 A method as claimed in any one of the preceding claims, in which the ratio l 02 l/lNOl ranges from 266 7 to 66 7.
A method as claimed in claim 1, substantially as herein described.
11 A process for controlling nitrogen oxides in combustion exhaust gases, which comprises adding an organic compound having an oxygen-containing functional group and/or a 50 parent hydrocarbon compound thereof to the exhaust gases and thereby oxidizing at a temperature higher than 200 C nitric oxide in the exhaust gases to nitrogen dioxide in the presence of oxygen, the ratio of the oxygen to the said organic compound and/or parent hydrocarbon being sufficiently high that the oxygen and the said organic compound and/or parent hydrocarbon form an oxidising mixture 55
12 A process according to claim 11, wherein said organic compound having an oxygen-containing functional group is methanol or formaldehyde.
13 A process according to claim 11 wherein said parent hydrocarbon compound is at least one alkane selected from the group comprising methane, ethane, or propane.
14 A process according to claim 11, 12 or 13 wherein the nitrogen dioxide is removed 60 from the exhaust gases by absorption in an aqueous medium.
A process according to claim 14 wherein the aqueous medium is water or an alkaline solution.
16 A process according to claim 14 wherein the NO 2 is absorbed in an aqueous solution of a reducing substance and is reduced to nitrogen 65 1,572,211 5
17 A process according to claim 14 wherein the NO 2 is co-ordinated by a metal chelate, and the product is reduced to nitrogen with a sulphite.
18 A process according to claim 17 wherein the metal chelate comprises iron, nickel, copper with EDTA.
19 A process as claimed in any one of claims 11 to 18 in which the ratio lO 2 l/lCl ranges from 533 to 6 6.
A process as claimed in any one of claims 11 to 19, in which the ratio l 02 l/lNOl ranges from 266 7 to 66 7.
21 A process according to claim 11 substantially as herein described 10 For the Applicants MARKS & CLERK Chartered Patent Agents 57-60 Lincoln’s Inn Fields London WC 2 A 3 LS 15 Printed for Her Majesty’s Stationery Office, by Croydon Printing Company Limited, Croydon Surrey, 1979 Published bythe Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.
GB3818/77A
1976-01-30
1977-01-31
Method of producing nitrogen oxides
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Treatment of nitrogen oxides in exhaust gas
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1982-01-27
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1997-02-19
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