RU2296000C1 - Method of cleaning flue gases from nitrogen oxides - Google Patents

Abstract

FIELD: cleaning waste flue gases of tubular furnaces used in power technological plants of ammonia production process from nitrogen oxides.

SUBSTANCE: proposed method includes mixing flue gases with air and ammonia-containing reductant. Used as ammonia-containing reductant are synthetic gases of ammonia production process of the following composition, mass-%: ammonia, 20-30; methane, 18-24; hydrogen, 25-35; argon, 3.8-4.8; the remainder being nitrogen. Selective catalytic reduction of nitrogen oxides of flue gases is performed in reactor at temperature of 240-450°C with the use of tungsten-vanadium catalyst. Proposed method makes it possible to clean flue gases to 91%.

EFFECT: high degree of cleaning.

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Description

The invention relates to methods for purification from nitrogen oxides of the exhaust flue gases of tube furnaces used in energy-technological installations for the production of ammonia.

A known method of non-catalytic purification of flue gases from nitrogen oxides [SU No. 1811993, class. In 01 D 53/34], including their homogeneous reduction with ammonia when it is introduced into the zone with a temperature of 900-1000 ° C, and in order to reduce costs while maintaining a high degree of purification from nitrogen oxides, ammonia is introduced into the zone with ammonia stripping gases hearth channels. The achieved positive result is due to the presence of methane, carbon monoxide, ammonia, methanol, water vapor and other components in the stripping gases.

A significant drawback of this method is the low concentration of ammonia in the stripping gases (about 18%) and the high temperature of the process in the hearth channels located between the rows of reaction tubes in the radiant part of the furnace, which creates increased difficulties for its practical implementation. In addition, an overflow of ammonia is possible in quantities exceeding sanitary standards.

The closest in technical essence can be considered a method of selective hydrogenation [Reference nitrogen. 2nd ed. recycled. M .: Chemistry. 1986. P.220] waste nitrous gases of ammonia and methanol production on aluminum-vanadium and aluminum-manganese-vanadium catalysts in cylindrical type reactors at a temperature of 200-320 ° C in the presence of an excess amount of ammonia.

Its disadvantages include the need to transfer liquid ammonia to a gaseous state and to purify it from oil and catalyst dust in a special apparatus, which significantly complicates the technological scheme of the process.

An object of the invention is to optimize the conditions for cleaning flue gases from nitrogen oxides while maintaining a high level of high efficiency.

The problem is achieved in that the stream of purified gases is mixed with air and an ammonia-containing reducing component, which is used as tank gases for the production of ammonia, and selective catalytic reduction is carried out in a reactor at a temperature of 250-450 ° C on a block-type catalyst manufactured by impregnating fiber ceramic carrier based on TiO ₂ with vanadium and tungsten compounds followed by heat treatment of the carrier to convert them to the oxide form V ₂ O ₅ and WO ₃ , respectively Tween.

The essence of the proposed technical solution is a method of purification of flue gases from nitrogen oxides by mixing them with air and an ammonia-containing reducing component, and tank gases of the production of ammonia composition, vol.%, Are used as the ammonia-containing reducing component.

ammonia 20-30 methane 18-24 hydrogen 25-35 argon 3.8-4.8 nitrogen rest,

and selective catalytic reduction of flue gas nitrogen oxides is carried out in a reactor at a temperature of 250-450 ° C on a tungsten-vanadium oxide catalyst.

The NO _x removal efficiency on this catalyst can reach 90% or more with an ammonia slip below 50 ppm, while non-catalytic methods have a much lower degree of purification, and ammonia slip can hardly be adjusted to an acceptable level.

It is important to note that in the case of the proposed purification method, along with ammonia, nitrogen oxides also interact with other components of the reducing system, in particular with hydrogen and methane.

In this case, catalytic chemical reactions occur, the final products of which are nitrogen, water and carbon dioxide.

With the complete oxidation of ammonia, methane and hydrogen, the potential temperature increase in the reaction zone will be 5-10 ° C.

Example. The proposed method is carried out according to the following scheme.

Flue gases from tube furnaces containing

O ₂ 6.2-8.2 vol.% H ₂ O 10.0-13.0 vol.% NO _x 200-700 mg / m ³ CO ₂ 4.9-6.9 vol.% With 70-150 mg / m ³ SO ₂ 4.9-11.3 mg / m ³ N ₂ rest

and having a temperature of 290-300 ° C, are mixed with air and an ammonia-containing reducing component of the above composition heated to the same temperature and sent to a selective catalytic reduction reactor.

The required mass ratio between nitrogen oxides in flue gases and ammonia in the ammonia-containing reducing component is regulated by flow sensors, as well as gas analyzers of the content of ammonia and nitrogen oxides output to the control unit of the installation. The volume of the reactor block and the mass of the catalyst are calculated based on the amount of flue gas to be cleaned. Air consumption depends on the content of nitrogen monoxide in the flue gas and is achieved using a blower.

The advantages of the proposed method include the fact that the degree of purification of nitrous gases is regulated by the rate of their supply to the reaction zone and the volume ratio of flue gases: ammonia-containing reducing component.

Example 1

25 thousand m ³ / h of flue gases with a temperature of 290 ° C, containing

About ₂ 7.93 vol.% H ₂ O 12.20 vol.% NO 100 mg / m ³ NO ₂ 400 mg / m ³ CO ₂ 5.9 vol.% With 110 mg / m ³ SO ₂ 9 mg / m ³ N ₂ rest,

50 m ³ / h of tank gases composition, vol.%:

NH ₃ 26.9 CH ₄ 22.3 H ₂ 34.9 Ar 4.3 N ₂ rest

and 5 m ³ / hour of air.

Using flow sensors and analyzers of ammonia and nitrogen oxides, the flue gas: ammonia-containing reduction component volume ratio of 500: 1 is maintained.

The degree of purification of flue gases from nitrogen oxides was 91%.

From the description of the invention it is seen that according to the claimed technical solution, it is possible to achieve a high degree of purification of flue gases from nitrogen oxides, while significantly simplifying the process flow diagram.

Claims (1)

The method of purification of flue gases from nitrogen oxides by mixing them with air and an ammonia-containing reducing component, characterized in that tank gases of production of ammonia composition, vol.% Are used as the ammonia-containing reducing component Ammonia 20-30 Methane 18-24 Hydrogen 25-35 Argon 3.8-4.8 Nitrogen Rest and selective catalytic reduction of flue gas nitrogen oxides is carried out in a reactor at a temperature of 250-450 ° C on a tungsten-vanadium oxide catalyst.