RU2792608C1 - Device for neutralization of toxic components of flue gases without introduction of external reagent - Google Patents

Abstract

FIELD: energy engineering.

SUBSTANCE: invention relates to a device for processing gaseous combustion products and can be used to remove toxic components of CO and NO_x emissions in the heat and power industry. The invention is intended for neutralization of toxic NO_x and CO components in flue gases without introducing an external reagent and can be applied in the heat and power industry. In the device for neutralization of toxic components of flue gases NO_x and CO from boiler plants without the introduction of an external reagent, neutralization reactions take place in a catalytic module of a honeycomb design with square channels, which has optimal overall dimensions to reduce the hydraulic resistance of the catalytic layer. It also includes the determination of a reasonable location for the reactor module in the gas path of the boiler plant, which maintains high thermal and environmental efficiency of the boiler.

EFFECT: reducing energy consumption during flue gas cleaning.

4 cl, 4 dwg

Description

The invention relates to a device for processing gaseous combustion products and can be used to remove toxic components of CO and NO _x emissions in the heat and power industry.

Currently, in the process of cleaning emissions from power equipment, granular catalysts are used / see. Pat. EN 83945 U1. IPC (2006) B01J21/00. B01J23/10/, which have significant hydraulic resistance and cannot provide effective cleaning at high emission rates. The solution to this problem is to replace granular catalysts with catalysts of a block honeycomb structure with numerous channels located in the direction of the gas flow.

Known catalyst block for purification of exhaust gases from nitrogen oxides /see. Pat. UA 90106 U. IPC (2014.01) B01J35 / 00, B01J37 / 00 /, including the formation of a block of pre-corrugated titanium plates leaning in the form of square channels, covered with a porous oxide layer, on which a catalytically active substance is applied.

A significant disadvantage of this device is the high consumption of expensive metals due to the use of titanium sheets and the increase in the time of oxidative reactions due to insufficiently fast heating of the carrier, which reduces the cleaning efficiency, as well as a rather high hydraulic resistance due to the small cell size.

The closest, in terms of technical essence and the achieved result to the proposed device, is a device for controlling emissions from boilers, which consists of a boiler containing a furnace, means for introducing fuel, primary and secondary air, a superheater, an economizer, a smoke channel with a catalyst section, a heater for air heating, dust collector and chimney / see Pat. RU 2299758 C2.MPK (2006.01) B01D 53/86, F23J 15/02, F23C 7/00, F23N 3/00/. Taken as a prototype.

The disadvantages of this device are the regulation of the total amount of air entering the combustion zone by controlling the CO / NO _x ratio, including the control of general and local temperatures inside the combustion chamber, as well as modifying the design of the primary ignition zone or the design of the burners, which leads to additional capital costs. In addition, the proposed device considers the use of a wide range of catalyst configurations, including various substrate and catalytic layer materials, without taking into account the hydraulic resistance of carriers, which can lead to an increase in pressure losses in the boiler flue, as well as affect the purification efficiency.

Also, in the description of this device, there are no indicators of cleaning efficiency in the catalytic module, which depend on the type of fuel burned (solid, liquid or gaseous) and the mode of operation of the device.

The technical result of the invention is to increase the level of flue gas cleaning from toxic emissions of nitrogen oxides and carbon monoxide, reduce the hydraulic resistance of the catalytic reactor without reducing the efficiency of flue gas cleaning, increase the efficiency and simplify the device for neutralizing toxic components of flue gases.

This technical result is achieved by the fact that in a known device for neutralizing toxic components of flue gases NO _x and CO without introducing an external reagent, containing a flue gas channel for directing flue gas into the atmosphere, a catalyst section located in the flue gas channel, including a catalyst, the active substances of which selected from the group consisting of platinum, palladium together with rhodium, basic transition metal oxides, and mixtures thereof and deposited on a ceramic honeycomb substrate, an air preheater located downstream of the catalyst section, and a smokestack, the feature is that that the catalyst section is a prefabricated catalytic module with overall dimensions L⁄D equiv in the range of 0.6÷1.4, formed from monolithic blocks of a square-section honeycomb cellular structure with unit cell dimensions of 8 × 8 mm with a deposited layer of a catalytically active substance . The catalytic module blocks have parallel channels aligned in the direction of the flue gas flow. The active substances in the channels of the catalytic module are applied with a peripheral arrangement. The catalytic module is located in the flue zone of the boiler unit with flue gas temperature in the range of 250÷350°C.

Neutralization of toxic components of flue gases NOx and CO without the introduction of an external reagent is carried out in a device containing a flue gas channel for directing flue gas into the atmosphere, a catalyst section located in the flue gas channel, including a catalyst whose active substances are selected from the group consisting of platinum, palladium along with rhodium, basic transition metal oxides, and mixtures thereof, and deposited on a ceramic honeycomb substrate, an air preheater located downstream of the catalyst section, and a chimney. In this case, the catalyst section is a prefabricated catalytic module with overall dimensions L⁄D equiv in the range of 0.6÷1.4, formed from monolithic blocks of a square-section honeycomb cellular structure with unit cell dimensions of 8 × 8 mm with a deposited layer of a catalytically active substance . The catalytic module blocks have parallel channels aligned in the direction of the flue gas flow. The active substances in the channels of the catalytic module are applied with a peripheral arrangement.

Neutralization of toxic components of flue gases, in the claimed device, is carried out in a catalytic module located in the rational zone of the boiler flue, selected taking into account the complex effect of oxygen content, flue gas velocity along the duct and flue gas temperature on the hydraulic resistance of the catalytic layer and purification efficiency.

The principle of operation of the device is based on the catalytic thermal neutralization of nitrogen and carbon oxides in the reactor layer, neutralization reactions occur in the design of the catalytic module.

The main share of _NOx emissions in the flue gases of boiler plants falls on thermal and fast scenarios of nitrogen oxidation in the air. The concentration of NO _x released during the combustion of carbon fuel is mainly determined by stoichiometric parameters and temperature in the combustion zone. One of the promising technologies for neutralizing toxic components of exhaust gases is selective catalytic oxidation without the introduction of additional reagents. The key element of the present invention is the definition of a rational zone for installing a catalytic module in the gas path of the boiler in order to increase the efficiency of neutralizing toxic components of emissions.

A special objective of the present invention is the development of a design for a device for a prefabricated catalytic module, including the determination of the geometric parameters of the unit cell of a block catalyst on a ceramic carrier, taking into account the degree of external diffusion of toxic components, limited by the rate-limiting stage of the oxidative process on the surface of the catalytic cells of the reactor block, determined by the change in its kinetic velocity when varying the load of the boiler.

The material, size and geometry of the catalytic module is determined so that most, or preferably all, of the NO _x emissions in the flue gases is neutralized on the catalyst to atomic nitrogen. Moreover, any excess CO in the flue gas was preferably further oxidized to CO ₂ on the catalyst surface by the excess oxygen in the flue gas.

The choice of platinum as a catalysis activator (an alloy of 0.5÷0.6 wt.%) is justified by its ability to increase the degree of purification due to the transition of oxidative reactions to the first order (for platinum catalysts n=1; for vanadium n=1, 8; for iron oxide n=2.5). The choice of ceramics (cordierite) as a honeycomb substrate material is based on a reduction in the time of oxidative reactions due to accelerated heating and taking into account the lower cost of a ceramic carrier compared to a metal one.

It is acceptable to replace the catalysis activator - platinum, with palladium or rhodium deposited on a ceramic substrate. Alternatively, the catalyst may be made from some other materials, such as oxides of basic transition metals such as iron, nickel, aluminium, cobalt or copper, or mixtures thereof.

и

_х с атомарным кислородом на поверхности ячеек

Oxidative reactions on the surface of the catalytic module are the interaction

And

_x with atomic oxygen on the cell surface

(1)

(1)

(2)

(2)

(3)

(3)

(4)

(4)

(5)

(5)

(6)

(6)

(7)

(7)

(8)

(8)

(9)

(9)

The rate of catalytic reactions on the surface of the catalytic module is determined taking into account the influence of the process temperature and is limited by the kinetic rate of the slowest reaction in the chain based on the Arrhenius equation:

(10)

(10)

- предэкспоненциальный множитель, не зависящий от температуры и определяемый только видом реакции;

- энергия активации реакции, показывающая избыток энергии, необходимый для осуществления реакции,

; R - газовая постоянная.where k is the reaction rate constant, numerically equal to the observed reaction rate at a fixed temperature and concentration 1/c; _T to the temperature on the surface of the catalyst, K;

- pre-exponential factor, which does not depend on temperature and is determined only by the type of reaction;

- activation energy of the reaction, showing the excess energy required to carry out the reaction,

; R is the gas constant.

The design of the catalytic module for the purification of exhaust gases from boiler plants that burn gaseous fuel from toxic components includes monolithic blocks of a square-section honeycomb structure assembled into a module so that parallel non-intersecting channels are formed, aligned in the direction of the flue gas flow. The technical result, namely the reduction of hydraulic resistance at a high degree of purification, is achieved by creating a design of a catalytic module of a honeycomb structure with square channels 8 × 8 mm in size, formed from monolithic ceramic blocks, on which a uniformly distributed catalytically active substance is applied.

и

_х с атомарным кислородом на поверхности катализационного модуля.The choice of a rational zone for the location of the catalytic module in the boiler flue, taking into account the complex effect of the operating modes of the boiler unit, the speed of movement of flue gases along the duct and the flue gas temperature on the cleaning efficiency, was made as a result of solving the equations of the algorithm describing the interactions

And

_x with atomic oxygen on the surface of the catalytic module.

(11)

(eleven)

(12)For

(12)

– время протекания реакции, с;.

- концентрация NO_x на поверхности катализатора,

,

- концентрация СО на поверхности катализатора,

;

- порядок реакции;

- константа реакционной скорости

,

;

- число реакций;

- удельная площадь поверхности катализатора,

;

- коэффициент массоотдачи,

;

коэффициент теплоотдачи,

;

- тепловой эффект реакции

,

;

– высота катализационного слоя,

;

- скорость потока газа,

.Where

is the reaction time, s;

- concentration of NO _x on the surface of the catalyst,

,

is the CO concentration on the catalyst surface,

;

- reaction order;

- reaction rate constant

,

;

- number of reactions;

is the specific surface area of the catalyst,

;

- mass transfer coefficient,

;

heat transfer coefficient,

;

- thermal effect of the reaction

,

;

is the height of the catalytic layer,

;

- gas flow rate,

.

The most optimal conditions for the neutralization of toxic components of flue gases, using a catalytic module for the oxidation of NO _x and CO without the introduction of an external reagent, taking into account the hydraulic resistance of the reactor layer, are determined by the results of experimental studies carried out by the inventors and are based on the following conclusions:

- the highest conversion efficiency for toxic components is observed at flue gas temperature at the inlet to the catalytic module T=250÷350°C;

- the maximum efficiency of purification of exhaust gases by toxic components is observed at the relative sizes of the catalytic module L⁄D _equiv in the range [0.6÷1.4];

- optimal indicators of the degree of neutralization for all types of toxic components are observed when the content of the oxidizer in the zone of installation of the catalytic module is from 3 to 5%.

The effectiveness of the proposed device was evaluated on a typical boiler equipment of enterprises of the energy complex (KA TGME-464), using data from regime maps at NO _x concentration in the range of 168-286 mg/m ³ , CO up to 80 mg/m ³ , flue gas flow rate gases at the inlet to the catalytic module in the range of 5.68-10.64 m/s, emission temperature in the range of - 275-333°C, while varying the load of the boiler unit from 220 to 500 t/h. The obtained research data demonstrate the degree of reduction of nitrogen oxides up to 96%, carbon monoxide up to 90%, with a hydraulic resistance of the catalytic module from 4500 to 12000 Pa. The proposed honeycomb-type block catalytic module provides a high degree of purification, has a relatively simple manufacturing technology and low hydraulic resistance.

In FIG. 1 shows the layout of the device, by means of which flue gases are cleaned in the gas path of the boiler plant, consisting of a convective shaft of the boiler 1, flue 2 connected to the upper branch pipe of the regenerative air heater 4, flue 5, which discharges gases into the chimney 6. At the section of flue 2 from the convective shaft 1 to the regenerative air heater 4, a catalytic module 3 is installed, which is a prefabricated structure of monolithic catalytic blocks of a honeycomb structure on a ceramic carrier.

In FIG. 2 shows a cross-section of the design of the catalytic module for flue gas purification, consisting of a monolithic block 7 in the form of a parallelepiped (optionally in the form of a cylinder) with a honeycomb structure of a square section of a monolithic carrier 8 with parallel non-intersecting channels.

In FIG. 3 shows a profile longitudinal section of the design of the catalytic module for flue gas cleaning, which shows: a monolithic block 7, a monolithic carrier 8.

In FIG. 4 shows an enlarged fragment of the honeycomb structure of a monolithic block with unit cell 9, which has dimensions of 8 × 8 mm.

Cleaning flue gases from NO _x and CO is as follows.

Flue gases generated during the combustion of gaseous fuels, for example, natural gas, from the convective shaft of the boiler 1 through the flue 2 are sent to the catalytic module 3 for flue gas cleaning, where, using the method of catalytic thermal decontamination, the nitrogen and carbon oxides contained in them are neutralized. After neutralization, the purified flue gases are sent to the regenerative air heater 4, and then the chimney 6 is discharged through the gas duct 5. Neutralization proceeds when the oxidant content is from 3 to 5%, the oxidizer is oxygen.

The proposed technical solution improves the efficiency of the device by achieving a high (up to 99% and higher) level of flue gas purification from toxic emissions of nitrogen oxides and carbon monoxide and minimizes the hydraulic resistance of the catalytic reactor without reducing the purification efficiency.

Claims (4)

1. A device for neutralizing toxic components of flue gases NO _x and CO without introducing an external reagent, containing a flue gas channel for directing flue gas into the atmosphere, a catalyst section located in the flue gas channel, including a catalyst whose active substances are selected from the group consisting of platinum , palladium together with rhodium, oxides of the main transition metals, and their mixtures and deposited on a ceramic honeycomb substrate, an air heater located downstream of the gas flow than the catalyst section, as well as a chimney, characterized in that the catalyst section is a prefabricated catalytic a module with overall dimensions L⁄D equiv in the range of 0.6-1.4, formed from monolithic blocks of a square-section honeycomb cellular structure with unit cell dimensions of 8 × 8 mm with a deposited layer of a catalytically active substance. 2. Device according to claim 1, characterized in that the catalytic module blocks have parallel channels aligned in the direction of the flue gas flow. 3. The device according to claim 1, characterized in that the active substances in the channels of the catalytic module are applied with a peripheral arrangement. 4. The device according to claim 1, characterized in that the catalytic module is located in the zone of the gas duct of the boiler unit with a flue gas temperature in the range of 250-350°C.

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