UDC546.273.325 +344.3
Ponomarenko O. I.*, Matveyeva I. V., Beisembayeva L. K., Romanova S. M.
al-Farabi Kazakh National University, Almaty, Kazakhstan
*E-mail: Oksana. *****@***kz
Purification of gas emissions of TPP from sulphurous substances
Stoichiometric equations of processing of exhaust gases of TPP into secondary chemical products are presented. Use of effective metal-polymeric catalyst for purification of exhaust gases of TPP, which allows to dispose sulfur dioxide simultaneously with its oxidation in sulfuric acid is shown.
Keywords: exhaust gases, sulfuric acid, TPP, atmosphere
Очистка газовых выбросов ТЭЦ от сернистых веществ
Приведены стехиометрические уравнения переработки отходящих газов ТЭЦ во вторичные химические продукты. Показано использование эффективного металл - полимерного катализатора, для очистки отходящих газов ТЭЦ, который позволяет утилизировать диоксид серы с одновременным его окислением в серную кислоту.
Ключевые слова: отходящие газы, серная кислота, ТЭЦ, атмосфера
Күкіртті заттардан ЖЭО шығаратын газ қалдықтарын тазалау
ЖЭО шығатын қалдық газдарды екіншілей химиялық өнімге өңдеудің стехиометриялық теңдеулері берілген. ЖЭО шығатын қалдық газдарды тазалау үшін тиімді металл – полимерлі катализаторды қолдану жолы көрсетілді, ол күкірт диоксидінің күкірт қышқылына тотыға отырып пайдаға асуына мүмкіндік береді.
Түйін сөздер: шығатын қалдық газдар, күкірт қышқыл, ЖЭОб атмосфера
1. Introduction
The largest number of the world's electricity is generated by thermal power plants, which burn different types of mineral fuel.
In Kazakhstan, 75% of electricity is produced by coal power plants, more than 12% - by gas-heavy fuel oil and 9% - by hydroelectricity.
Cogeneration plant (CHP) is a kind of thermal power plants, which produces not only electricity, but also is a source of thermal energy in centralized heating systems (in the form of steam and hot water, including hot water and heating for residential and industrial objects). Wherein a large amount of flue gas, wastewater contaminated with various water-soluble substances and solid precipitate in the form of ash and sludge appear.
At present, a large number of different methods of flue gas cleaning from pollutants are developed and tested. Specialists, working in the field of industrial emissions purification technology, note that there is no technology of separation of sulfur dioxide from exhaust gasses with significant advantages.
Methods of desulfurization of exhaust gases of TTP based on removal of sulfur oxides by washing with a solution of lime or limestone to produce gypsum as final product are widespread in world practice. Usage of this technique requires a large continuous flow of additional materials (lime) and treatment of large quantities of waste (gypsum).
Therefore, a new approach to solve problem of utilization of sulfur compounds contained in exhaust gases of TPP is required.
The aim of this study is to develop general theoretical bases and patterns of utilization of exhaust gases of TPP with production of sulfuric acid.
2. Experiment
To achieve this goal the most affordable and effective ways for converting of waste gases of TPP (SO2, NO2, NO, CO) into complete secondary products (carbon dioxide, sulfuric acid, nitrogen and ammonia) have been previously considered [1].
The technological parameters of installation for purification of exhaust gases of CHP, allowing to remove up to 95% of sulfur and carbon oxides by low temperature (60-80 °C) liquid-phase catalytic oxidation under atmospheric pressure.
The installation consists of a mixing chamber, an emulsifier with a drop-settler and water tanks, catalyst solution and finished products, blowers, pumps, gas-wires, water and sewage systems, power supply (electricity and heat), ventilation.
Proposed installation for recycling of exhaust gases of TPP includes a vortex "Emulsifier" with eight-paddle swirler. Swirl is intended for crushing and mixing of liquid in turbulent regime. It is known that installations of this type provide an intensive mass transfer “gas – liquid”, allow to remove diffusion deceleration by dissolving of gaseous mixture containing sulfur dioxide.
3. Results and discussions
According to air conditions Almaty refers to cities with very high degree of contamination. The level of air pollution is determined by the index of air pollution. When comparing the data for the last four years, the level of air pollution in Almaty city is gradually increasing and is defined as very high.
The largest sources of air pollution of Almaty are TPP-1, TPP-2 and AHPP, which have six chimneys. They use coal, gas and heavy fuel oil. Mainly natural gas is used in summer season and in winter (heating) season heavy fuel oil and coal are used. Also on the territory of Almaty a series of district heating plants (north-east, west, south-east), which use gas and heavy fuel oil, are located. TPP-2 and AHPP are outside city boundaries. However, their smoke plumes effect on northern and even central areas of the city.
Out of the total amount of impurities contained emissions of TPP to the atmosphere of Almaty, 98% form five most common. Among them are sulfur dioxide, particulate matter (dust), carbon monoxide, hydrocarbons and nitrogen oxides. The products of combustion of solid, liquid and gaseous fuels are transformed into wastes with masses in a few times larger than masses of used fuel due to inclusion of nitrogen and oxygen from the air in the combustion process (5 times during combustion of gas and 4 times during combustion of coal). The amount and composition of pollutants of waste gases of TPP is considered on the example of TPP-1 of Almaty city.
Table 1 presents data on fuel consumption and characteristics of pollutants contained in the waste gases of TPP-1 over the last four years.
Table 1 - Emissions of pollutants, resulting from fuel combustion at TPP-1 of Almaty city
Year | Fuel consumption | Content of pollutants | ||||||
Coal, t/y | Gas, ths. nm3/y | Heavy fuel oil, t/y | СО, t/y | SO2, t/y | NO2, t/y | NO, t/y | Dust with SiO2, t/y | |
2012 | 330260 | 99160 | 15 562 | 110 | 2880 | 2010 | 320 | 620 |
2013 | 160730 | 155536 | 409 | 123 | 1309.5 | 1019.8 | 165.7 | 346.9 |
2014 | 93213 | 188820 | 1235 | 116.9 | 797.6 | 843.5 | 137.1 | 214.4 |
1st quarter of 2015 | 25136 | 91645 | 1332 | 48.608 | 212.6 | 328.6 | 53.4 | 55.9 |
Table 1 shows that the contents of exhaust gases (CO, SO2, NO2) is much greater than their maximum allowable concentration in atmospheric air.
Therefore, in this work we examined and evaluated various options of alternative technologies of joint production of carbon dioxide, sulfuric acid, nitrogen and ammonia from pollutants (SO2, NO2, NO, CO), contained in exhaust gases of TPP [2]. The stoichiometric equations of their formation are shown in Figure 1. The essence of utilization is to obtain mentioned products from exhaust gases of TPP as a result of hydrogenation reaction with steam in presence of catalyst.
Figure 1 – Schematic diagram of utilization of exhaust gases into sulfuric acid (step I), carbon dioxide (step II) and ammonia (step III)
As shown in Figure 1, at first step at oxidation of sulfur dioxide by nitrogen dioxide at presence of water sulfuric acid forms.
It should be noted that the presented equations, despite their simplicity, require thorough research beforehand in laboratory and then enlarged - in production testing.
In [3,4] a catalytic solution was developed. It consists from immobilized catalyst FeCl3 on polyethyleneimine and allows to clean exhaust gases of boiler houses and diesels of drilling rigs from the most harmful gases (SO2, NO, NO2, CO) in a wide range of concentrations of gases. Similar catalyst was used for purification process of exhaust gases of TPP from sulfurous compounds. Preliminary studies were carried out: in emulsifier a certain amount of the catalyst solution was placed, and a gas mixture passed through it at a rate of 1 m3/h.
Sulfur dioxide at the reactor inlet and after purification was determined quantitatively by iodometric method. The aqueous solution after absorption of exhaust gases was separated from catalytic solution by TBP and analyzed for the major components (SO2 and sulfuric acid). The results of these studies are presented in Table 2.
To remove the reaction product (sulfuric acid) a two-phase system was used, where in aqueous solution of catalyst tributylphosphate was added. Good extraction properties of the system “water – TBP” promotes their low mutual solubility (3.4 g/l of TBP in water and 64 g/l of water in TBP) [5]. Using of system “TBP – water” (1: 3) allows to extract catalyst and modifying additives in active form, and 95% of oxidation products remain in the free phase.
Table 2 - Results of catalytic purification of exhaust gases of TPP from SO2
The composition of the catalyst solution, mol/l | Content of SO2, mg/m3 | Result of cleaning of gas mixture, % | ||
FeCl3 | polyethyleneimine (CH2-CH2-N-) | before cleaning | after cleaning | |
0.5·10-3 | 2.3·10-3 | 1511 | 200 | 87 |
1.0·10-3 | 2.3·10-3 | 1511 | 150 | 90 |
2.0·10-3 | 2.3·10-3 | 1511 | 120 | 92 |
1.0·10-3 | 1.15·10-3 | 1511 | 215 | 85 |
1.0·10-3 | 4.6·10-3 | 1511 | 170 | 88 |
1.0·10-3 | 9.2·10-3 | 1511 | 130 | 91 |
Analyses, carried out after the cleaning of gas mixture, showed that aqueous solution of sulfuric acid with a concentration of 65-70% was obtained, purification of the gas mixture from sulfur dioxide is 85-92%. Carrying out of repeated tests in order to establish activity of test catalyst showed that after multiple experiments of gas purification from sulfur dioxide according to the proposed method, the activity of catalyst did not change.
Thus, the usage of an effective metal-polymer catalyst for purifying of exhaust gases of TPP allows to utilize sulfur dioxide, while its oxidation to sulfuric acid.
4. Conclusions
Different options of alternative technology of joint ways to get carbon dioxide, sulfuric acid, nitrogen and ammonia from the exhaust gases of TPP were analyzed and evaluated.
A technology of purification of exhaust gases of TPP from sulfurous compounds by low-temperature liquid-phase oxidation at highly-effective iron-immobilized catalysts with simultaneous separation of the product (sulfuric acid) from the reaction zone and separation of the catalyst solution was developed.
The optimal composition of the catalyst at carrying out of hydration reaction with water vapor in the presence of a catalyst (iron oxide with effective additive), allowing to obtain sulfuric acid, was found.
Developed technological scheme significantly simplifies the process of production of sulfuric acid at a sufficiently high concentration (70%). Moreover there is no need to carry out a contact oxidation of SO3 to SO2 at high lphuric acid is formed directly in the catalytic solution and then separated due to the developed methods.
5. References
, , кологохимические проблемы утилизации газовых выбросов топливно-энергетических предприятий // Материалы международной конференции «Актуальные проблемы экологии и природопользования». – Москва, 2013. – С. 225-229. , , Способы утилизации отходящих газов ТЭЦ в полноценные вторичные продукты // Материалы Международного симпозиума «Современные проблемы высшего образования и науки в области химии и химической инженерии. – Алматы, 2013. – С. 180-182. Низкотемпературное жидкофазное окисление диоксида серы кислородом на железо-иммобилизованных катализаторах. Диссертация на соискание ученой степени кандидата химических наук. –Алматы, 1999. – С. 143 Окисление сульфита натрия кислородом в присутствии закрепленных на полиэтиленимин комплексов кобальта, никеля и железа. Диссертация на соискание ученой степени кандидата химических наук.– Алматы, 2001. – С. 136 Справочник об экстракции. – Киев: Техника, 1972. – 460 с.References
