DE2018518A1 - Nitrogen oxide removal from industrial waste gases by reduction with - andcarbon monoxide - Google Patents

Abstract

Outlet gas is freed from N2O3, N2O4, NO2 and N2O5 by adsorption with alkaline reagents, pref. milk of lime, is (a) contacted wtih pyrite (FeS2) in a way such that the gas is led downwards through the pyrite layer at a rate such that =0.25 mole NO/hr. are charged per 1 sq.m. pyrite particle surface, and main part NO is reduced to N2. During contact of the gas with pyrite, the pyrite layer is scrubbed with water to remove the pyrite oxidation products formed, such as Fe2(SO4)3 and H2SO4. The residual small amount of N oxide in gas is reduced by (b) contact with a gas containing CO in an amount sufficient to reduce NO to N2. Pref. pyrite has particle size >=2, more pref. 3-10, mm. Pref. in water-scrubbing step, water is charged at 0.3-6 l./mole NO in gas to be purified. Pref. CO-containing gas used is producer gas, and contact time in (b) is 10-15 secs.

Description

Des chre ibun PROCEDURES FOR THE REMOVAL OF NITROGEN OXIDES FROM EXHAUST GASES The present invention relates to those areas of the chemical industry where the gases containing nitrogen oxides are formed, especially their removal processes of nitrogen oxides from #### exhaust gases.

The gases mentioned are formed during the extraction of weak and concentrated nitric acid, from sulfuric acid by the nitrogen process, from various nitro compounds including intermediates for color die Regarding and explosives, purifying these gases up to the required standard remains a difficult one problem to be solved.

There are several methods of removing nitrogen oxides the end proposed to the exhaust gases, some of which are used in industry.

Anhydride-like nitrogen oxides (N 2O3, NO2, N2O4, N2O5) are eliminated Absorption with alkaline reagents obtained from the gases relatively easily (French Patent Specification No. 1387207 from 07/16/63).

The most difficult thing is to bind nitric oxide, which is difficult in water is soluble and does not react with alkalis or acids.

Most sorption processes for NO scavenging are based on the Application of the reducing properties of nitrogen oxide: By exposure to a or the other oxidizing agent, it is oxidized to nitrogen dioxide, that afterwards is absorbed with alkaline reagents. Nitric acid is used as an oxidizing agent (G.A. Skvortsov, 1. P Kirillov, M.M. Karavaev. News from the universities, series: Chemistry and chemical technology, 9, No. 1, 80-85, 1966), mixture of nitric acid and manganese dioxide (USSR authorship No. 226568 of December 6, 1966), ozone, atmospheric oxygen when the gas mixture is irradiated with UV light (patent specification, Die der FRD No. 1111600 from 02.15.62), used. Oxidation of nitrogen oxide with subsequent absorption the product has the advantage that the nitric oxide is used and that there is no waste attack. Disadvantages of the process of nitric oxide oxidation are insufficiently effective NO binding when using cheap oxidizing agents and increasing the cost of the Procedure when using the strongest oxidizing agents to the High purification of the gases. Because of this, the researchers consider removing the Nitrogen oxides from the exhaust gases through oxidation and absorption up to a content of 0.02-0.0l practically unsuitable because of the high procedural costs.

In recent times the greatest attention has been paid to exploitation The process based on the oxidation properties of nitrogen oxide: the Nitric oxide is used for the catalytic or thermal oxidation of various fuels materials used, the oxygen in the nitrogen oxide oxidizes flammable components and elemental nitrogen develops.

During the catalytic decomposition of nitrogen oxide, the process at a temperature of 250-7000C, under increased gas pressure (1-6 at) using a fuel gas carried out (V.E, Gorfunkel In the anthology "Cleaning and Use of sewage and industrial waste ", Kies, 1964, ische S. 13-103; A.K Cher.D. Zaichko "Chemical Industry Abroad" NIITEChIW, Moscow, No. 1, 20-24, 1966).

Palladium and platinized nickel are used as catalysts (M.N. Nabiev, -N.A. Kulik and aridere. Lectures of the Academy of Sciences of the Uzbek SSR, No. 11, 17-20, 1963). The presence of oxygen in the gases is disruptive the process. If the oxygen content is above 5%, there is a two-stage gas combustion required with the intermediate cooling of the gases after the first combustion stage.

Advantages of the process of decomposing nitric oxide to Elementary nitrogen are relatively high effectiveness and no accumulation of Waste that requires further processing. Disadvantages of catalytic decomposition of nitrogen oxide are relatively high consumption of a very expensive catalytic converter (Palladium, platinum) high consumption of reducing gas, the need for heating the entire amount of gas to be cleaned to 250-700 ° C, a great energy requirement and difficulty the apparatus design of the process of compressing large volumes more corrosive-aggressive Gases up to 6 at.

In order to exclude catalyst losses, a thermal process was used Decomposition of nitrogen oxides at a temperature of 1500-2300 ° C without a catalyst suggested.

The gases containing nitric oxide have to be adjusted to the above Heat up temperature.

As a fuel that removes the oxygen from the nitric oxide during the reduction bind the same at a high temperature, natural gas, the hydrogen and serve Gases containing carbon monoxide (CSSR patent specification, No. 104395 of July 15, 1962), glowing layer of a carbon-containing blue rial (copyright certificate of the USSR No. 223794 of June 5, 1967).

Recently, other methods of removing the Nitrogen oxides from the exhaust gases have been proposed by means of the freshly precipitated Einsensulids applied to a Einsatæ body (copyright of the USSS No. 191033 dated 04/13/64) or with the help of the anion exchange resins (V.F. Plekhotkin and others. Journal of Applied Chemistry XYII, No. 7, 1492-1496, 1969).

Disadvantages of the sulphide process is the need to keep it fresh Prepare precipitated iron sulfide more often, labor expenditure of the processes of application the sulphide on the insert body and the replacement of the insert body the depletion of the sorbent.

Anion exchange process is because of the high prices for organic Anion exchange resins are expensive.

The aim of the invention was to develop a method for removing the nitrogen oxides from the exhaust gases, which makes it possible to purify the gases up to the content of the same of nitrogen oxide of at most 0.02-0.05 vol. So that these gases are in the air can.

Another object of the invention was to develop a simple one economical process, in which no expensive catalysts and not a large one Energy expenditure for the cleaning process are required.

Another goal was also to use a cheap accessible one Reducing agent for the decomposition of nitrogen oxides.

The above and other goals were met through the removal process the nitrogen oxides from the exhaust gases by absorption of the output gas for the purpose of removal the more oxygen-rich nitrogen oxides N203 NO2, N204, N205 with an alkaline reagent achieved. The following substances can be used as the alkaline reagent: Soda, soda, tækali, Potash, lime (CaO), ammonia; it is recommended to take them as aqueous solutions. Of the reagents mentioned, is preferred Use lime milk because it is cheaper compared to the other reagents and is more accessible and because its sorption products are processed into calcium nitrate can turn.

According to the invention, that of the mentioned becomes more oxygenated Nitrogen oxides-free starting gas with pyrite - Fes2 broken in contact. This the The contact is made in such a way that the gas mentioned is passed through pyrite from above is directed downwards and at such a speed that the supply of a maximum of 0.25 mol of nitrogen oxide per hour per 1 m2 of surface area of the pyrite parts guaranteed. The height of the pyrite layer is a calculable value that is due to the above-mentioned maximum amount of nitrogen oxide supplied per 1 m² of pyrite surface is determined.

It is desirable to use pyrite not smaller than 2 mm spike size, so that the sheet resistance is not too great (maximum s 100 mm WS). It is it is best to use pyrite with a grain size of 3 to 10 mm. Application of the pyrite particles with a grain size of more than 10 mm lead to a reduction in the specific contact surface.

While the gas is in contact with pyrite, the main proportion (70-80%) of the nitrogen oxide is reduced to elementary nitrogen according to the summary equation: While the gas is in contact with pyrite, the pyrite layer is sprinkled with water in order to remove the pyrite oxidation products formed - ferric sulfate and sulfuric acid - from the surface of the pyrite particles. In addition, the water contributes to the efficient progress of the above-mentioned reaction.

It is recommended to sprinkle with water when supplying the same in an amount of 0.3-6 liters per 1 mol of nitrogen oxide in the gas to be cleaned, preferably 1.3-3 1. The sprinkling with an amount of water of less than 0.3 1 each 1 mol of NO does not guarantee complete removal of the reaction products from the Pyrite surface, which slows down the process. When using amounts of water, which exceed 6 1 per 1 Eol NO, forms on the surface of the pyrite particles Liquid film that prevents the gas from coming into contact with pyrite.

After most of the nitrogen oxide has been removed through contact with pyrite, the gas containing the residues of nitrogen oxide to be cleaned is mixed with the gas, the carbon monoxide in a lung sufficient for the reduction of the nitrogen oxide to elementary nitrogen according to the equation contains.

Usually this amount of carbon monoxide makes 1.15-1.25 moles per 1 mole Nitric oxide that remains in the gases.

As containing carbon monoxide and used in this process coming gases can be industrial gases, for example Water gas, generator gas, Lieuchtgas come into question. In the present invention, the generator gas is Recommended as it is the cheapest and easiest to access.

It is desirable to have the time of cleaning the gas to be cleaned with carbon monoxide in the range of 10-15 sec to keep the process complete can run.

The proposed method for removing nitrogen oxides from the Exhaust gases are introduced in all of its stages at the temperature of the cleaning agent output gas, i.e. gas heating or cooling is not required.

The process allows the exhaust gases to be reduced to their residual content To purify nitrogen oxides from 0.02 - 0.05 vol.

According to the invention, the method is practically implemented as follows.

into gas from which nitrogen oxides are to be removed is through a packed column or another with an alkaline sorbent, for example, milk of lime, sprinkled mass transfer apparatus sucked through.

The more oxygen-rich nitrogen oxides are removed from the gases and form with the alkaline reagent those for processing, for example, in Fertilizers suitable nitrite and nitrate solutions.

The nitrogen oxide-containing gas to be cleaned is fed into the contact apparatus where there is pyrite in the form of particles from 3 to 10 mm in size, and flows through the water-sprinkled Pyritsciicht in the direction from above after below. The pyrite sprinkling with water takes place under the feed of the water in an amount of 0.3 to 6 liters per 1 mole of nitrogen oxide, preferably 1.3 - 3 1.

The speed of the gas passed through the pyrite layer must be so great that not more than 0.25 mol of nitrogen oxide is supplied per hour per 1 m 2 of pyrite particle surface. On the pyrite part ohenoYer surface there is chemosorption of the nitrogen oxide by yyrite, Syrite oxidation products - iron (III) sulphate and sulfuric acid - which are washed away with water, are formed. The one after nitric oxide; Elementary nitrogen formed in the reduction is carried away with the gas flow. A gas containing carbon monoxide, for example generator gas, is added to the gas stream emerging from the contact zone with pyrite. The introduction of the same into the gas flow is realized either in a special apparatus or in the gas flue.

no After 10-15 seconds of contact of the animals with carbon monoxide the reduction of nitrogen oxide by means of carbon oxide, whereby elementary nitrogen and form carbon dioxide.

Both components are released into the atmosphere with the gas flow, As can be seen from the cited description, the present invention has a range of advantages.

The main advantage is the substantial simplification process engineering, although three mass transfer devices are required: one - for the implementation the sorption of the more oxygen-rich nitrogen oxides, the other - for the contact of the gases with pyrite and the third - for the contact with carbon monoxide (in the event that this contact is not made in the throttle cable). There is no need to heat and compress the gases to be cleaned, the use of the catalysts is also not necessary. So they fall Processes, the realization of which is associated with a high expenditure of heat and energy and more complex technological equipment is needed. A major reduction the operating costs are achieved by reducing the main share of nitrogen oxide (70-80ffi) a cheap natural reducing agent - pyrite is used. The presence of oxygen in the gases does not disturb the course of the process, because the oxygen at the operating temperature of the process neither with moistened pyrite still reacts with carbon monoxide.

For a better understanding of the present invention, a concrete one will be made Example of the execution of the process given.

Example.

A gas flow in an amount of 7900 m3 / h with the content of NO 3.84 g / m3, of N02 3.16 g / m3 was in a packed column sprinkled with milk of lime 1.75 m in diameter and 6 m wide. After the absorption of the starting gas with milk of lime its nitric oxide content remains the same, i.e.

3.84 g / m3 and the content of NO2 sinks to 0.316 g / m3, the out The gases escaping from the packed column are in a multi-day Contact apparatus with the entire surface of the residues supporting the pyrite layer managed by 220 m2. Pyrite layer is 23 cm high, the grain size of the pyrite particles is the 3-10 mm. The gases pass through a layer of pyrite in the direction from top to bottom at a speed of 0.1 m / sec, which equates to 0.25 kol of nitrogen oxide per 1 m of pyrite surface corresponds, sucked through. The pyrite layer is mixed with water in an amount of 0.3 - 0.5 1 sprinkled per 1 m3 of the gases to be cleaned, which is calculated for 1 kol of nitrogen oxide Standard. The gases are vests of NO and 72% by volume of nitrogen oxide NO removed. The residual nitrogen oxide content of the gas is after contacting with pyrite 1.07 g / m3.

When water is sprinkled with pyrite, the particles on the surface of the pyrite Pyrite oxidation products formed - iron (III) sulfate and sulfuric acid - removed.

Those leaking out of the machine where nitric oxide and PGrrit come into contact Safe wastewater is neutralized by lime up to pil-Nert 9, according to the Contact with Ycrit 1.07 g / m3 NO containing gas stream flowing in the gas draft in the amount of 79000 m3 / h, 315 m3 / h generator gas with the carbon monoxide supply of 25%. After the gases (NO and CO) come into contact for 10 seconds, the Nitrogen oxide content up to 0.2 g / m3 (0.02%).

Eg is allowed to open such gas into the air through chimneys to drain.

Claims (8)

PATENT CLAIMS: 1. Process for removing nitrogen oxides from exhaust gases by Absorption of the source gas with an alkaline reagent to remove more oxygenated ones Stiekoxiban N2O3, N2O4, NO2, N2O5, d a d u h e k e n'n z e i e h -n e t that that after absorption with the alkaline reagent of the said more oxygen-rich Starting gas freed from nitrogen oxides is brought into contact with pyrite FeS2 in this way is that the gas mentioned through the pyrite layer from top to bottom with such a speed is passed that no more per 1 2 pyrite particle surface than 0.25 mol of nitric oxide per hour is supplied that the reduction of the main portion of nitrogen oxide and elementary nitrogen takes place during the processing of the gas with pyrite the pyrite layer for the purpose of removing the pyrite oxidation products formed -Iron (III) sulphate and sulfuric acid - is sprinkled with water and that the rest small amount of nitrogen oxides in the gas through contact with; a carbon monoxide in an amount sufficient to reduce the nitrogen oxide to elementary nitrogen containing gas is reduced. 2. The method according to claim 1, d a d u r o h g e -lr e n n z e i c N e t that milk of lime is used as the alkali reagent. 3. The method according to claim 1-2, d a d u r c h g e -k a n n Z e i c h n e t that prit in the form of particles with Grain size at least 2 mm is used. 4. The method according to claim 3 d a d u r e h g e k e n n Z 0 1 o h n e t that pyrite is used in the form of particles with a grain size of 3 to 10 mm. 5. The method according to claim 1-4, d a d u r c h g e -k e n n z e i c h n e t that pyrite sprinkling with water when adding water in an amount of 0.3 - 6 1 per 1 mole of nitrogen oxide in the gas to be cleaned. 6. The method according to claim 5, d a d u r c h g e k e n -n z e i c n e t that pyrite sprinkling with water when the same is supplied in an amount of 1.3-3 l per 1 mole of nitric oxide is made. 7. The method according to claim 1-6, d a d u r c h g e -k e n n t e i Notwithstanding that generator gas is used as the gas containing carbon monoxide. 8. The method according to claim 1-7, d a d u r c h g e -k e n n z e i c h n e t that the time of the stirring of the gas to be purified with carbon monoxide 10-15 seconds.