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AZERBAIJAN CHEMICAL JOURNAL № 4 2022 ISSN 2522-1841 (Online)
ISSN 0005-2531 (Print)
UDC 661.844.66.01
DEVELOPMENT OF A STATISTICAL MATHEMATICAL MODEL OF THE PROCESSING OF SULFUR-CONTAINING GASES (H2S, SO2)
*A.A.Ibrahimov, R.M.Vakilova, *F.V.Yusubov
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan *Azerbaijan Technical University
Ali.ibrahimov_i@mail.ru
Received 16.08.2022 Accepted 19.09.2022
On the basis of the proposed new principal technological scheme, research work has been carried out to improve the processing of low-concentration sulfur-containing gases and to neutralize atmospheric emissions. At the beginning of this technological process, the reduction of natural gas with water conversion products on the proposed alumocobaltmolybdenum (ACM) catalyst of SO2 was studied to achieve high yield of sulfur and then a method of neutralization of the real gas mixture with chlorinated lime was developed. Initially, the optimal parameters of the process of SO2 reduction with water conversion products of methane on the ACM catalyst were found: temperature 4000C, volume velocity 1000 s-1, ratio of initial reagents 2.1. After SO2 is reduced to sulfur, sulfur and water vapor are separated in condensers and the gas mixture containing H2S and SO2 is absorbed in a chlorinated lime suspension.The optimal parameters of the absorption process were as follows: solid:liquid ratio S:L= 2.5, gas delivery rate 75 ml\min, temperature 500C. As a result, a statistical mathematical model has been created that adequately describes the process in the range of optimal parameters of both technological processes.
Keywords: hydrogen-sulfide, sulfur-dioxide, chlorinated lime, mathematical modeling.
doi.org/10.32737/0005-2531-2022-4-114-121 Introduction
Neutralization of sulfur-containing gases is known to attract attention not only for the solution of environmental problems, but also as a source of free sulfur and other products[1-3]. In general, it is estimated that about 40% of the world's gas reserves are usable. 70 trillion-nm3 of these gases are acid gases (about 10% containing H2S) [4, 5]. To date, 100 billion m3/y of sulfur-containing gas have been processed of which up to 60% is H2S [6, 7].
The concentration of SO2 obtained during the combustion of sulfide ores during pyro-metallurgical processing can be up to 80%, depending on thecombustion furnace [8]. Therefore, mainly sulfur is released and then other products are obtained from such solid gases. In the presented work, the optimal parameters of the process of catalytic reduction of SO2 from natural gas to water with sulfur products, as well as the process of conversion of residual gases (H2S and SO2) into chlorinated lime with chlorinated lime have been determined and a statistical mathematical model of both processes has been established [9].
The literature review shows that it is more expedient to carry out the treatment of
such residual gases in the liquid phase in absorbers [10]. Therefore, due to its low viscosity, oxidative absorption methods are preferred for the treatment of waste gases remaining after the Claus process [11, 12]. It should be noted that the preparation of the absorbent used for this purpose should be easy to complete, highly effective, easy to find, non-toxic. Alkalis or their carbonates are known to be mostly used for the utilization of sour gases [13]. However, the use of alkalis, especially slaked lime is not suitable for the capture and neutralization of gases containing H2S and SO2. In addition, the products of H2S interaction with alkalis - sulfide and hy-drosulfide - need to be re-purified.
In view of all this, in the present work [14, 15] it is considered more expedient to use chlorinated lime produced on an industrial scale, meeting the above requirements and proposed for the first time as an absorbent for neutralization of sulfur-containing gasesand a new principal technological scheme has been proposed to improve the technical and economic performance of the processing of sulfur-containing gases and to minimize atmospheric emissions [8] (Figure 1).
The technological scheme consists of two main stages. First, sulfur dioxide is reduced to sulfur, free sulfur is separated and then the residual gases (H2S, SO2) are completely neutralized with chlorinated lime and transformed into a new product - gypsum.
Complex technological processes are known to be labor intensive [16]. Increasing the efficiency of scientific research, development, application, research and operation of new technological processes require optimization of these processes. In this case, the main means of calculating, analyzing, optimizing and forecasting chemical-technological processes are computers [17]. Computers operate on the basis of a mathematical model [18].
A deterministic mathematical model is constructed when there is complete information about the mechanism of the process (kinetics, hydrodynamics, thermodynamics, etc.).
During the construction of the mathematical model, the physical and chemical properties of the chemical and technological process are expressed by mathematical equations.
Experiments are carried out to check the adequacy of the unknown coefficients and the
mathematical model included in the system of differential equations to the object.
In the absence of complete information about the mechanism of the process, the studied technological process is studied functionally. Figure 2 illustrates the input, output, excitation effects and control parameters of the process. That is, input and output parameters are recorded during the experiment.
Here xi, x2, ... , Xn and yi, y2, ... , yn are the input and output parameters respectively; u1, u2, ... , un management effects; f1, f2, ... , fn -exciting effects.
The input parameter includes the composition of the processed raw material, temperature, pressure, economic indicators, etc., the quality of the product obtained as the output parameter, economic indicators, etc. can be shown.
Exciting (random) quantities may include a decrease in the activity of the catalyst and the absorbent over time and a change in ambient temperature.
It is known that there are five main technological parameters: temperature, pressure, flow, level and quality.
Fig. 1. Principled technological scheme of neutralization of the gas mixture remaining after reduction of S02 with conversion gas with chlorinated lime.
Exciting effects
■s a
it s er
OD .g
s
S
HI III*
r -o X* c Object M
1,1,1 ! ! I».
-s
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re S C
on
.a
o
Oïl
«M
3
o
Control effects
Fig. 2. Schematic description of the chemical and technological process (object).
When technological processes are studied, these technological parameters are changed to one degree or another or kept stable at certain prices. The establishment of a statistical mathematical model of experiments helps to reduce the impact of errors that can be made during experiments on the processes carried out and to make the experiments performed better [19, 20].
Therefore, despite the fact that both the catalytic reduction of SO2 to sulfur and the effect of various parameters on the process of capturing residual gases (H2S and SO2) with chlorinated lime, it is necessary to compile a mathematical modeling of this process using statistical methods.
Experimental part
First, research was conducted to find the optimal values of the parameters found experimentally, which affected the construction of a statistical mathematical model for the process of catalytic reduction of SO2 to sulfur gas conversion.
Initially, the effect of temperature on the reduction of sulfur dioxide methane with water conversion products on the catalyst ACM (alumocobaltmolybdenum) was studied.As can be seen from Figure 3, the conversion rate of sulfur dioxide was the maximum at 4000C.
a, °/400 -
90 -80 -70 -60 -50 -
200 250 300 350 400 450 500
t, 0c
Fig. 3. Temperature dependence of the rate of conversion of sulfur dioxide during the reduction of sulfur dioxide by conversion products. Volume velocityW=1000 S-1, N =2, Here N= (CO+H2):SO2is the ratio of the initial components.
0 500 1000 1500 2000 2500
W, time-1.
Fig. 4. The effect of the volume velocity of the initial gas mixture on the rate of its conversion during the reduction of sulfur dioxide with the conversion products of methane (T = 4000C, N = 2).
The effect of the volume velocity of the gas mixture on the yield of the reaction products was carried out at the optimum temperature. When the volume rate is increased to 500-2000 s-1, the conversion rate of SO2 decreases due to the reduction of the contact time of the reagents (Figure 4). At relatively low (500-1000 s-1) volumetric velocities (T - 350-4500C), the amount of sulfur produced is close to the equilibrium yield and the amount of H2, SO2 and COS in the obtained gases is relatively small.In subsequent studies, 4000C was taken as the optimal temperature and 1000 s-1 as the volume velocity.
The effect of initial component ratios (CO+H2):SO2=N and concentration on the reduction of SO2 by water conversion products was studied on an alumocobaltmolybdenum (ACM) catalyst at optimum temperature (4000C) and volumetric velocity of the gas mixture (1000 s-1).
As can be seen from Figure 5, the maximum sulfur yield is obtained when N=2.0-2.15. As the ratio increases, the amount of hydrogen sulfide increases, along with a 10-12% decrease in sulfur yield. When N>2.2, complete conversion of sulfur dioxide to sulfur and hydrogen
sulfide occurs. This is due to the high content of H2 and CO in the reaction medium as the ratio increases, which causes some of the sulfur obtained to be converted to H2S.
A formal mathematical description of the process was obtained on the basis of the above-mentioned experimental results. The effect of various factors on the degree of conversion of sulfur dioxide in the first stage was studied.
As a result, the mathematical model of the technological process is obtained as follows: Y = 1.3-0.089• X3 -0.113-Xj • X2 + 0.124• X2 (1) X1 - temperature, X2 - volume velocity, X3 -ratio of primary reagents
Optimal conditions: Ymin = 1.1, X1 = 55, X2 = 63, X3 =0.31.
In order to achieve the maximum yield of the final product, an attempt was made to create a mathematical model of the process under optimal conditions. The following ranges of factors were selected for this purpose: temperature (250-4500C), volume velocity (500-2000 s-1), ratio of primary reagents (CO+3H2 )/SO2 - 2.02.4. The interval of change of the main level factors is given in Table 1.
—His —so, -■— s
Fig. 5. The dependence (W=1000 s"\ cp (so2)= 20 %, T=400°C)of the yield of sulfur-containing products(S, H2S, SO2)on the ratio(CO+H2):SO2=N.
Table 1. Level change intervals and designation areas
Factors Levels Change interval Destination area Unit of measurement
-1 0 1
1 250 350 450 100 250-450 0C
2 500 1500 2500 1000 500-2000 s-1
3 2:1 2.2:1 2.4:1 0.2 2:1-2.4:1 -
In subsequent experiments, the effect of the ratio of chlorinated lime and water (S:L) on the absorption capacity of a mixture of hydrogen sulfide and sulfur dioxide gas was studied. As shown in Figure 6, as the S:L ratio increases, the absorbency of the absorbent increases. When S:L=1:2.5, the absorption capacity of the absorbent due to sulfur is 34 grams of sul-
3
fur/dm per hour. Experiments show that when the ratio of S:L is more than 1:2.5, it is difficult to mix the solution in the laboratory and therefore further studies are carried out in the ratio of S:L=1:2.5.
When the rate of delivery of the gas mixture to the solution is increased from 10 ml/min to 100 ml/min, absorption time is reduced due to the large amount of hydrogen sulfide and sulfur dioxide given per unit time (Figure 7). The same can be seen when the concentration of the gas in the mixture increases. Thus, the greater the concentration, the shorter the absorption.
Then, the temperature dependence of the absorption time was studied (Figure 8). It was found that when the temperature rises to 500C, the absorption time decreases and then changes very little. This is explained by the fact that at up to 500C the interaction of hydrogen sulfide and sulfur dioxide with the absorbent components is completed.
The distribution of sulfur in the reaction products depending on the temperature has been studied in the conducted experiments. As can be seen from Figure 9, reaction products up to 500C contain sulfur, calcium sulfite and calcium sulfate. With further increase in temperature, the amount of sulfur obtained decreases and above 500C the sulfur is oxidized to a higher degree of oxidation. This is explained by the fact that an increase in temperature causes the decomposition of HClO obtained from the hydrolysis of Ca(ClO)2: HClO^HCl+O'. Since the obtained atomic oxygen is a stronger oxidizer, it oxidizes H2S to sulfite and sulfate ions.
Sulfur/dm^tim
35
30
25
20
15
10
5
0
1:2,5 1:5
1:10 1:20
Fig. 6. Absorption capacity of the absorbent due to sulfur, depending on the ratio of solid:liquid (S:L).
T, 111 in 500 450 400 350 300 250 200 150 100 50
10 20 30 40 50 60 70 80 SO 100 V, ml/time
Fig. 7. The dependence of the absorption time of the absorbent on the rate of delivery of the gas mixture.S:L=1:2,5, t=500C.
t , min 350
300 250 200 150 100 50 0
—I-1-1-1-1-1-1-1-1-1
0 10 20 30 40 50 60 70 80 90 100 T, °C
Fig. 8. Temperature dependence of the absorption time of the absorbent. S:L=1:2.5.
Fig. 9. Distribution of sulfur in reaction products depending on temperature (in% of mass); (V=100ml/min; S:L = 1:10); 1-S, 2- CaSO3, 3- CaSO4
Diagram. Absorption time of H2S and SO2, depending on the gas transfer rate and temperature.
Subsequent experiments studied the absorption time of H2S and SO2 depending on the gas transfer velocities and temperature (Diagram). As the gas delivery rate increases, the absorption time decreases since the contact time of the gas with the liquid decreases. Therefore, the absorption of SO2 does not occur completely at a gas delivery rate of 0.3 m/s.
The optimal conditions of absorption in the ratio S:L = 1:2.5, the linear velocity of the gas mixture was 0.1-0.2 m/s, the temperature was 500C. It has been shown that the slowest stage of the process is physical absorption. It is proposed to transfer CaSO3 completely to CaSO4 by adding air to the absorbent solution to obtain a gypsum product and to use CaCl2 formed during the process to restore the absorbent.
Then, the factors and optimal parameters influencing the course of the process were determined in order to obtain a formal mathematical description of the processes going on in the second stage. Temperature - (25-750C), so-lid:liquid ratio - 1:2.5-1:30, gas transfer rate -50-100 ml/min (Table 2).
Table 2. Level change intervals and designation areas
Fac- Levels Change Destination Unit of measu-
tors -1 0 1 interval area rement
1 25 50 75 25 25-75 0C
2 50 75 100 25 50-100 ml/min
3 1:2.5 1:16.25 1:30 13.75 1:2.5-1:30 -
As a result, the mathematical model of the technological process has been obtained as follows:
Y = 75.2 - 0.112 • X1X2 - 0.183 • X? - 0.115 • X2 (2)
Optimal conditions: Ymax = 75.63, X1 = 368, X2 = 2154, X3 =2.21.
Thus, using the experimental planning method, the optimal technological parameters of the technological process covering the reduction of sulfur dioxide to free sulfur by gas conversion and absorption of the remaining gas mixture (H2S, SO2) with chlorinated lime were determined on the basis of statistical mathematical model.
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KÜKÜRD TORKiBLi QAZLARIN (H2S, SO2) EMALI PROSESiNiN STATiSTiK RiYAZi MODELiNiN
YARADILMASI
Taklif olunmu§ yeni prinsipal texnoloji sxem asasinda az qatiliqli kukurd tarkibli qazlann emalinin takmilla§dirilmasi va atmosfer tullantilannin zararsizla§dirilmasi uzra tadqiqat i§lari hayata kegirilib. Bu texnoloji prosesin avvalinda yuksak kukurd giximina nail olmaq ugun SO2-nin taklif olunmu§ alumokobaltmolibden (AKM) katalizatoru uzarinda tabii qazin su konversiyasi mahsullan ila reduksiyasi tadqiq edilmi§, sonra isa alinan sanaye tullanti qazlannin tarkibina uygun real qaz qan§iginin xlorlu ahangla zararsizla§dirilmasi usulu i§lanib hazirlanmi§dir. Ovvalca AKM katalizatoru uzarinda SO2-nin metanin su konversiyasi mahsullari ila reduksiyasi prosesinin optimal parametrlari tapilmi§dir: temperatur - 4000C, hacmi surat - 1000 s-1, ilkin reaktivlarin nisbati - 2.1. SO2-nin kukurda qadar reduksiyasindan sonra kukurd va su buxari kondensatorlarda ayrildiqdan sonra tarkibinda H2S va SO2 olan qaz qan§igi xlorlu ahang suspenziyasinda udulur. Udulma prosesinin optimal parametrlari bela olmu§dur: bark:maye nisbati - B:M= 2.5, qazin verilma surati - 75 ml/daq, temperatur - 500C. Naticada har iki texnoloji prosesin optimal parametrlari intervalinda prosesi adekvat ifada edan statistik riyazi modeli yaradilmi§dir.
Agar sozlzr: hidrogen-sufid, kukurd-dioksid, xlorlu 3h3ng, riyazi modelh§m3.
РАЗРАБОТКА СТАТИСТИЧЕСКОЙ МАТЕМАТИЧЕСКОЙ МОДЕЛИ ПЕРЕРАБОТКИ
СЕРОСОДЕРЖАЩИХ ГАЗОВ (H2S, SO2)
А.А.Ибрагимов, Р.М.Вакилова, Ф.В.Юсубов
На основе предложенной новой принципиальной технологической схемы проведены исследовательские работы по совершенствованию переработки низкоконцентрированных газов и обезвреживанию выбросов в атмосферу. В начале этого технологического процесса было изучено восстановление диоксида серы продуктами паровой конверсии метана на алюмокобальтмолибденовом (АКМ) катализаторе, для достижения высокого выхода серы, а затем разработан способ утилизации оставшейся реальной серосодержащей газовой смеси хлорной известью. Первоначально были найдены оптимальные параметры процесса восстановления SO2 продуктами паровой конверсии метана на АКМ катализаторе: температура - 4000C, объемная скорость - 1000 ч-1, соотношение исходных реагентов - 2.1. После восстановления SO2 до серы, сера и водяной пар конденсируются в конденсаторах. Газовая смесь содержащая H2S и SO2 поглощается суспензией хлорной извести. Были установлены оптимальные параметры процесса: соотношение твердое:жидкое (Т:Ж)-2.5, скорость подачи газа -75 мл/мин, температура - 500C. В результате была создана статистическая математическая модель, адекватно описывающая процесс в диапазоне оптимальных параметров обоих технологических процессов.
Ключевые слова: сероводород, диоксид серы, хлорная известь, математическое моделирование.
O.A.ibrahimov, RM.Vakilova, F.V.Yusubov
