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СATALYTIC CARBON MONOXIDE IN THE INDUSTRIAL GAS EMISSIONS

СATALYTIC CARBON MONOXIDE IN THE INDUSTRIAL GAS EMISSIONS
Сергей Кузнецов, старший преподаватель, ph.d. технических наук, доцент

Херсонский национальный технический университет, Украина

Участник конференции

A new method for catalytic reduction of carbon monoxide is offered. Highly developed structure of Zn-Cu-Cr-catalyst pumice concrete and its application to the tubular supports is designed. A device - a tubular reactor in which the catalytic neutralization of industrial waste gases contaminated with carbon monoxide is suggested.

Keywords: neutralization of the catalyst, pumice concrete, tubular reactor.

 

Introduction.It is known that human body passes through the lungs about 20 m3 of air a day, and during the whole life this number is about 600000 m3. It is obvious that air pollution, even in small doses can make serious damage to health.

Nowadays in the MAC data there are more than 4.5 thousand harmful air pollutants and carbon monoxide has a leading position in this list. Its global emissions account is 177 million tons per year. The main source of carbon monoxide formation is the heat power industry. This gas is 300 times faster soluble in blood than oxygen and its concentration in air of more than 0.1% is lethal for man. It takes three to six months for carbon monoxide to become carbon dioxide,

The purpose of this study was to develop new types of catalysts and equipment for the effective neutralization of carbon monoxide included in the exhaust gas heat energy and industrial facilities. Now the combustion products are emitted into the atmosphere without treatment, and large volumes of flue gases and the presence in their structure of associated impurities, such as dust and sulfur dioxide complicates process of gases neutralization.

Development of new catalysts- one of the possible solutions for this problem. Catalytic methods have a number of significant advantages over other methods of sanitary cleaning of gases, however, this requires the availability of cheap and effective catalysts. Mass production of the catalysts is only possible if raw materials used are available and of low cost.

From the experience of using  catalysts for final oxidation of carbon monoxide it is known that as the catalytically active substances can be used compounds of Cu, Cr, Fe, Mn, Pt, Ag, Sn, Co, Pd, Zn, Cd, Th, Be, et al. To obtain the catalysts it’s necessary to impregnate a porous carrier with catalytically active substances. Then, the filler is added, and residue, drying and tableting the resulting mixture is held. However, the catalysts obtained by the described technologies are expensive and have limited amounts of release, therefore, it can not be recommended for sanitary cleaning of large volumes of gas.

These studies have led to the development of catalysts for the new types of neutralization carbon monoxide. They have a high level of productivity, activity, selectivity, mechanical strength and heat resistance, low poisoning and low aerodynamic resistance. To form the contact mass cheap and available substances are used.

The most highly active catalysts are shown having the following composition:. The weight ratios of catalytically active substance, aluminum powder and cement 1: 2.5: 3.

The manufacturing method of the catalyst is a mixture of catalytically active substances and aluminum metal (powder), ammonia water and cement. The porous structure of the catalyst is formed by reacting of the intensive flowing ammonia water with aluminum metal and the catalytically active substances, resulting in foaming of the reactants. The catalyst mass in a pasty state is applied to the inner surface of pipe with a punch.

1 - pipe; 2 - catalyst mass; 3 - punch head; 4 - punch body; 5 - guide ribs; 6 - gauge skirt; 7 - supported catalyst layer; 8 - rod.

Figure 1.  Applying of catalyst device on the inner surface of pipes.

 

Once hardened, the contact mass is dried and calcined at 350°C temperature. The resulting composition forms a solid porous layer inside the pipes - pumice concrete. The pipes are mounted on the tube sheets and placed in a common housing forming a tubular reactor.

 

1 case; 2 cover; 3-tube catalyst; 4-tube sheet; 5 bottom.

Figure 2. The tubular reactor

 

Experimental data shows that the catalyst starts to be active at t = 150oC. With increasing temperature, the degree of conversion increases, reaching a maximum at gas velocity 10000-20000 h-1 is 86-96%. Followed temperature increasing does not lead to a marked increase in the degree of conversion, because in the gas mixture is set close to the equilibrium concentration of the residual carbon monoxide which value depends on the temperature.

Since the reaction is exothermic, the reactor temperature may rise, reaching critical point. Studies showed that on heating the reactor to 350 - 400°C  followed spontaneous temperature rises. It means that the initial gas temperature should not be above the critical value defined by the formula:

,

where: - the critical temperature in the reactor (t = 350oC);

- the temperature rise in the reactor due to the heat of reaction, oC

,

where: Q - heat of reaction, kJ/mol  ;

  - CO content of the gas, % (vol.);

  - specific heat of gas, kJ/kg∙deg;

 - gas density kg/m3.

From the formula given above, it follows that for every percentage entered into the carbon monoxide reaction gas mixture temperature will rise , consequently: .

The exhaust gases of several industries, in addition to carbon monoxide in its composition contain sulfur compounds, dust and other impurities. In this regard, it is reasonable to study the influence of these impurities on the catalyst activity.

It is known that the presence in the gas of 0.1% after 10 hours, the catalyst begins to show signs of decreased activity. After 20 hours, the degree of purification,  decreases from 90% to 75% and in 70 hours - 43%. This is an indication of "poisoning" of the catalyst.

The slower fall in activity is observed in the presence of dust in the cleaned gases. After 70 hours of continuous operation the activity of the catalyst is reduced by 10% in the presence of gas in 3 - 5 g/m3 of dust. Dust causes a temporary decrease in the catalyst activity due to its mechanical clogging. Removing dust from the reaction zone restored the catalyst activity completely.

Continuous operation of the catalyst in the laboratory showed that its activity within 70 hours of continuous operation does not change. Water vapor in the gas don´t not reduce catalyst activity. The synthesized catalyst shows higher activity than the commercial low-temperature catalyst LTC-4.

The main parameters that allow you to complete a comprehensive assessment of the developed catalysts have been identified in the study of reaction kinetics. These include temperature coefficient, reaction order, and rate constant.

The relatively low values ​​of the temperature coefficient and the activation energy leads to the conclusion that the oxidation reaction of carbon monoxide on the catalyst takes place in the diffusion region. This is evidenced by the first-order reaction. Moreover, the excess oxygen at the process rate is limited by diffusion of carbon monoxide in the catalyst pores. It is assumed that the conversion of one broken-bond in the molecule and CO connection between hydrogen and oxygen in the water molecule. The total energy breaks the bonds is 1178 kJ/mol, which virtually eliminates leakage without a catalyst reaction. In catalytic reacting carbon oxide consuming oxygen from the catalyst, and the water returns the catalyst, both processes occur simultaneously. The reaction mechanism fused interaction leads to a considerable reduction of the energy barrier. This allows the process at relatively low temperatures and high space velocities, as observed in the present studies. The most effective means of accelerating the processes occurring in the diffusion region (internal transfer), is to reduce the grain size of the catalyst, as well as the use of catalysts with high surface area, in which the pores are large transport routes to the surface of the highly produced fine pores of small length.

The theoretical time necessary for the diffusion of carbon monoxide in the catalyst pores is determined by Einstein formula;

where: L - penetration depth (grain radius), cm;

 De - the effective diffusion coefficient.

The mean free path of molecules of CO (58 nm), far smaller than the diameter of the catalyst (3000 nm), the diffusion coefficient in the operating conditions given by Arnold.

,

where: - the molar mass of the components, g/mol;

- molar volume of the components cm3/mol;

T - temperature boiling componentsоК;

P - pressure, MPa;

- constant Sutherland.

If you do not use a large three-dimensional velocity of the gas, the degree of conversion of CO will be reduced by minimizing the using of inner surface of the catalyst. The bulk gas velocity can be increased by using a smaller catalyst pellet, but this increases the flow resistance layer. The equilibrium conversion rate is determined from the relationship:

The maximum conversion rate in the diffusion region is 90 - 93.5%, which is 92 - 96% of the theoretical.

For tubular reactors designed activity investigated catalysts per unit volume (volume of the catalytic activity VCA), a unit of mass (the mass of the catalytic activity MCA) and the specific surface of the catalyst (surface catalytic activity SCA). The determination of these values is carried out according to the formulas:

Table 1. Active zinc-copper-chromium catalysts - pumice concrete

 

The tubular reactor has a high capacity, can handle dusty gases and provides a high degree of purification, without requiring a large operating costs.

 

References:

  • 1. Patent of invention UKRAINE UA 62855A, IPC 7 V01D47 / 00, C10K1 / 00. Way of cleaning exhausted gases of boiler houses from oxide of carbon and device for doing it.  / Kuznyetsov S.І. (UKRAINE); Zayavl.04.09.03; Publ. 15.12.03, Bul. №12, 2003.
  • 2. Patent of invention UKRAINE UA 62856A, IPC 7B01D47 / 00, B01D47 / 08, C10K1 / 00, C10K1 / 34. Way of cleaning exhausted gases of boiler houses in textile industries / Kuznyetsov S.І. (UKRAINE); Stated. 04.09.03; Publ. 15.12.03. Bull. №12, 2003.
  • 3. Patentofinvention №67180 MKBF23J11 / 00. Device for cleaning and heatrecycling of exhausted gases / Mikhailik V.D. Mikhailik S.V. Kuznyetsov S.І. HDTU., Bull. №6, 2004.
Комментарии: 4

Карлов Владимир Анатольевич

Уважаемый Сергей Иванович, работа по созданию устройств и методик очистки выхлопных промышленных газов от окиси углерода актуальна, т.к. будет способствовать улучшению экологии, а значит сохранению здоровья людям и всего животного и растительного мира. Оценка доклада высокая. Желаю успехов в Ваших трудах. Владимир Карлов.

Трещалин Михаил Юрьевич

Уважаемый Сергей! Безусловно, актуальная разработка. Весьма показательны сравнительные результаты эффективности существующих устройств и предлагаемой установки на протяжении 70 часов. Конечно, надо повсеместно внедрять. С уважением М.Ю. Трещалин

Кузнецов Сергей Иванович

Спасибо за проявленый интерес и высокую оценку работы. С уважением Сегей Кузнецов

Симонян Геворг Саркисович

Уважаемый Сергей хорошая экологическая и техническая работа. Вами предложен новый метод каталитического восстановления -нейтрализации газов промышленных отходов,пили и окиси углерода на катализаторе на основе высоко развитих структур Zn-Cu-Cr- пемза бетона в устройстве - трубчатый реактор. Желаю успехов. Геворг
Комментарии: 4

Карлов Владимир Анатольевич

Уважаемый Сергей Иванович, работа по созданию устройств и методик очистки выхлопных промышленных газов от окиси углерода актуальна, т.к. будет способствовать улучшению экологии, а значит сохранению здоровья людям и всего животного и растительного мира. Оценка доклада высокая. Желаю успехов в Ваших трудах. Владимир Карлов.

Трещалин Михаил Юрьевич

Уважаемый Сергей! Безусловно, актуальная разработка. Весьма показательны сравнительные результаты эффективности существующих устройств и предлагаемой установки на протяжении 70 часов. Конечно, надо повсеместно внедрять. С уважением М.Ю. Трещалин

Кузнецов Сергей Иванович

Спасибо за проявленый интерес и высокую оценку работы. С уважением Сегей Кузнецов

Симонян Геворг Саркисович

Уважаемый Сергей хорошая экологическая и техническая работа. Вами предложен новый метод каталитического восстановления -нейтрализации газов промышленных отходов,пили и окиси углерода на катализаторе на основе высоко развитих структур Zn-Cu-Cr- пемза бетона в устройстве - трубчатый реактор. Желаю успехов. Геворг
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