RU2174945C2 - Method of processing concentrated sulfur dioxide - Google Patents

Abstract

FIELD: inorganic compounds technology. SUBSTANCE: concentrated sulfur dioxide is oxidized into sulfur trioxide according to cyclic flowsheet including sulfur dioxide oxidation stage performed in multi-bed contact apparatus, wherein initial al 50% sulfur dioxide is distributed together with oxygen stream between beds of contact material and then divided into separate contact gas streams (two streams from one contact bed). Sulfur trioxide is isolated from inter-bed contact gas and part of contact gas preliminarily freed from sulfur oxides is blown away from recycle. Stream, from which sulfur trioxide is not isolated, is mixed with distributed stream of initial sulfur dioxide and with distributed oxygen stream and combined stream is conveyed into the next oxidation stage. Sulfur trioxide is isolated from all streams after division of inter-bed contact stream and stream from the last contact stage in a single stage. Invention increases specific productivity of contact material, reduces temperature at the inlet of oxidation zone, while outlet temperature is higher. Reaction load on beds in apparatus is leveled. EFFECT: enhanced process efficiency. 2 cl, 10 dwg, 10 tbl

Description

 The invention relates to a method for processing concentrated sulfur dioxide gas, including the oxidation of sulfur dioxide, and can be used in the chemical industry for the production of liquid sulfur trioxide, sulfuric acid, oleum by contact method.

 In the contact method, a gaseous stream containing sulfur dioxide and oxygen, as well as ballast components, in particular nitrogen, passes sequentially several catalyst beds located in one or more contact devices. Several catalyst layers are used to achieve the most complete conversion of sulfur dioxide to trioxide. Usually used are vanadium, less often platinum catalysts. In order to avoid overheating of the catalyst, the gas stream is cooled between the layers using heat exchange equipment located inside or outside the apparatus with adiabatic catalyst layers. It is possible to directly cool the catalyst bed, which in practice is not widespread.

 The efficiency of the contact apparatus is an additive quantity determined by the operation of each layer of the contact apparatus. The effectiveness of the contact mass layer is primarily the specific productivity of the contact mass of the layer. The specific productivity of a layer is understood to mean the amount of sulfur trioxide obtained during the residence time of the reaction gas in the layer, referred to the volume occupied by the contact mass of the layer. By the performance of the contact mass layer is meant the amount of sulfur trioxide obtained during the residence time of the reaction gas in this layer.

In known methods for the contact oxidation of sulfur dioxide to trioxide, the efficiency decreases from layer to layer. The contact oxidation methods of SO ₂ are unknown, which provide alignment of the specific productivity of the contact mass at the given productivity of the contact mass layer over the device layers. Among the known methods, either the task of increasing the specific productivity of the contact mass of the second and subsequent layers is sharply solved, while the productivity of the second and subsequent layers drops sharply, or the task of increasing the productivity of the second and subsequent layers, while the specific productivity of the contact mass of the second and subsequent layers drops sharply.

A known method for the catalytic oxidation of SO ₂ to SO ₃ by the method of double contacting, intermediate absorption of SO ₃ from the contact gas after the third layer, oxidation of SO ₂ at the second contacting stage and final absorption of SO ₃ (Handbook of sulfuric acid. - M .: Chemistry, 1971, p. 559-570 [1]). In this method, a gas stream is processed in which the SO ₂ content is 9% and the O ₂ content is not higher than 15% of the total number of moles of the stream. The remaining volume of the flow is nitrogen, which, as a ballast component, removes excess heat from the contact apparatus. An example of the processing of SO ₂ by this method is presented in table. 1.

The disadvantages of this method are:
- a decrease in comparison with the first layer of productivity of the second and subsequent layers of the contact mass and, consequently, the low productivity of the whole contact apparatus;
- a decrease in the specific productivity of the contact mass of the second and third layers;
- the inability to process gas streams with a concentration of sulfur dioxide above 9-12 vol.%.

A known method of producing sulfuric acid by multi-stage oxidation of sulfur dioxide to sulfur with an intermediate absorption of the latter with the formation of sulfuric acid, dividing the gas stream after the first or subsequent stages of oxidation into two streams, one of which is subjected to intermediate absorption, followed by mixing it with a second stream before applying to the next stage of oxidation (SU 346852 A, 07/28/72 [2]). The gas is divided in such a ratio that the heat content of the stream after intermediate absorption and the heat content of the unabsorbed stream provide the operating temperature of the subsequent oxidation step. In this method, a gas stream is processed in which the SO ₂ content is 9% and the O ₂ content is not higher than 15% of the total number of moles of the stream. The remaining volume of the flow is nitrogen. An example of processing by the method [2] is presented in table. 2.

The disadvantages of this method are:
- reduced productivity of the second and subsequent layers of the contact mass and, therefore, low productivity of the contact apparatus, due to the need to maintain a high degree of conversion of SO ₂ to SO ₃ in the contact apparatus;
- the inability to process gas streams with a concentration of SO ₂ above 9-12 vol.% due to the high requirements for the degree of conversion.

A known method of processing concentrated sulfur dioxide (Boreskov G. K. Catalysis in the production of sulfuric acid. - M .: Goskhimizdat, 1954, p.331 [3]), which is based on an intermediate dosage of the components of the gas mixture in layers. In this method, the source sulfur dioxide is divided into two streams, the first stream is diluted with air to a content of 7-8% SO ₂ in it, this gas is processed to an oxidation state of SO ₂ in SO ₃ of 0.7, and the second stream of the source sulfur is diluted with this contact gas gas.

The disadvantage of this method is the reduction in the specific productivity of the contact mass of the second and subsequent layers due to the accumulation of SO ₃ in the gas stream from layer to layer.

A known method of producing sulfuric acid in a cyclic manner (SU 301985 A, 03.11.85 [4]). The method includes the steps of producing concentrated sulfur dioxide, oxidizing SO ₂ to SO ₃ , absorbing SO ₃ , recirculating the absorption exhaust gas, blowing part of the exhaust gas containing SO ₂ from the cycle, and then releasing it and returning it to processing. The oxidation efficiency of SO ₂ in SO ₃ also decreases from layer to layer.

The closest to the claimed method known technical solutions to a similar problem are a method for producing liquid SO ₃ in a cyclic manner (US 4046866 A, 1977 [5]) and a method for producing sulfuric anhydride in a cyclic manner (US 563115 A, 10.08.77 [6]). Methods [5] and [6] are based on the production of liquid SO ₃ , sulfuric acid and oleum from gas mixtures with a high concentration of SO ₂ and O ₂ in them and include the following stages:
- obtaining concentrated SO _{2 by} oxidation of sulfur O ₂ with the supply of recycled gas to the reaction chamber to lower the temperature of oxidation;
- catalytic oxidation of SO ₂ with dilution of the contact mixture with the initial mixture with an intermediate dosage of it over the layers of the contact apparatus and heat removal between the layers;
- the allocation of liquid SO ₃ by condensation and absorption from the contact gas obtained at the outlet of the multilayer apparatus;
- exhaust gas recirculation to the sulfur burning stage;
- removing from the cycle part of the exhaust gas.

In the method [5], a gas stream containing (from the total number of moles of the stream) 15 to 45% sulfur dioxide, 20 to 40% oxygen, 15 to 25% nitrogen and 2 to 25% sulfur trioxide is supplied to the contact apparatus. Between the layers of the catalyst to reduce the temperature of the contact gas, it is envisaged to dilute it with a mixture of source and recycle gas. In one pass through the contact apparatus, a degree of conversion of SO ₂ to SO ₃ of 60% is achieved. An example of oxidation by this method is presented in table. 3 and 4.

In the method [6], all oxygen is supplied to the first layer of the contact mass of the contact apparatus. The source sulfur dioxide is distributed between the layers and dosed into each layer of the contact mass. From the output of each layer, except the last, the contact gas flow is fed to the input of the next layer, pre-cooled. From the output of the last layer of the contact apparatus, the contact gas is directed to the SO ₃ separation step.

The disadvantages of the methods [5, 6] are:
- low specific productivity of the contact mass due to the presence of SO ₃ in the reaction gas;
- unproductive recirculation of SO ₃ , which is returned to the furnace and to the contact apparatus to lower the temperature.

A common disadvantage of the known methods of multi-stage oxidation of SO ₂ in SO ₃ in a multilayer apparatus with fixed layers of contact mass is that there is a decrease in the efficiency of using the contact mass of the catalyst from layer to layer. The decrease in the efficiency of using the contact mass of the catalyst occurs either due to a decrease in the productivity of the contact mass layer, or due to a decrease in the specific productivity of the contact mass of the layer, or for both reasons.

The decrease in the productivity of the contact apparatus from layer to layer corresponds to a decrease in the adiabatic heating of the gas during the stay in the contact mass layer, which is due to a change in the amounts of moles of SO ₂ , O ₂ and SO ₃ in the reaction gas at the inlet to each contact mass layer, as well as due to lack of contact mass in the layer. In the known methods [4] - [6], the productivity of the second and subsequent layers of the contact mass is improved by distributing the initial sulfur dioxide gas over the layers of the contact apparatus with the simultaneous use of SO ₃ in the reaction gas as an accumulator of heat released during the oxidation of SO ₂ . However, in these methods, the specific productivity of the contact mass from layer to layer decreases sharply, which requires an additional volume of contact mass and increases capital costs.

The specific productivity of the contact mass in the contact apparatus from layer to layer decreases due to the accumulation of SO ₃ in the contact gas, and also due to a change in the ratio of the number of moles of SO ₂ to the number of moles of O ₂ in the reaction gas at the inlet of each layer compared to the reaction gas at the entrance to the first layer. This leads to a decrease in the rate of a chemical reaction and, as a result, to a decrease in the specific productivity of the contact mass from layer to layer.

Analysis of known methods from the standpoint of productivity and specific productivity shows the following:
- in the method [1], the absorption of SO ₃ from the interlayer gas from the output of the third layer increases the specific productivity of the fourth layer of the contact mass. In the method [2], the absorption of SO ₃ from the interlayer contact gas increases the specific productivity of the second and third layers of the contact mass. However, in the methods [1] and [2] the problem of increasing the productivity of the contact mass layer is not solved in any way. Therefore, the total productivity of the contact mass drops from layer to layer (Tables 1 and 2) due to the need to achieve the complete conversion of SO ₂ to SO ₃ .

- in methods [4-6], as a result of using concentrated SO ₂ and O _{2, the} productivity of each contact mass layer is increased, that is, the problem of increasing the productivity of the contact mass layer is solved and the problem of increasing the specific productivity of the second and subsequent contact mass layers is not solved. Therefore, the specific productivity of the contact mass drops from layer to layer (Tables 3 and 4).

 In the methods of [1, 2], an increase in the productivity of the second and subsequent layers of contact mass can be achieved by distributing and dosing into these layers a source of sulfur dioxide and using a recycling of exhaust gas with nitrogen blowing from the exhaust mixture.

In the methods [4-6] increasing the contact mass specific capacity can be achieved by extracting from the interlayer contact with the gas exit of each layer SO _3, and also changing the ratio of amounts of SO ₂ and O ₂ in the reaction mixture at the inlet to the bed.

Another disadvantage of the known methods [1, 2] is the complex hardware design stage of the allocation of SO ₃ from interlayer flows of contact gas. First, it is necessary to cool the interlayer contact gas, separate it by absorption of SO _3, and heat the gas again to the temperature of the SO ₂ oxidation reaction in the contact mass layer.

 The above indicates the imperfection of known technologies for processing sulfur dioxide in a multilayer contact apparatus.

The objective of the invention is to improve the processing technology of concentrated sulfur dioxide in a multilayer contact apparatus and obtain the following effects:
- increase the specific productivity of each layer of contact mass and, as a result, increase the productivity of each layer and the entire apparatus as a whole;
- increase the controllability of the contact apparatus.

The problem is solved by the present method of processing concentrated sulfur dioxide gas into sulfur trioxide in a cyclic manner by oxidizing sulfur dioxide in a multilayer contact apparatus in a series-parallel manner with the distribution of the source sulfur dioxide gas W and oxygen V across the layers of the contact apparatus and dividing the contact gas flow Z _i with the output of each i-th layer for i = 1, 2, ..., m, where m is the number of layers to the flows X _i and Y _i supplied: X _i - to the input of the next (i + 1) -th layer, with the last layer output stream of recycled X _m and the entrance of the first layer; Y _i - to the stage of separation of sulfur trioxide and then to recycling, while the composition of the reaction gas, including the content of sulfur dioxide N _SO2нi , oxygen N _O2нi , sulfur trioxide N _SO3нi , is supported at the entrance to each layer based on the joint fulfillment of the following conditions:
T _i ^k - T _i ⁿ + Δ1 _i = T _pi - T _zi ; (1)
T _zi ≤ T _i ⁿ <T _i ^k ≤ T _pi ; (2)
τ _pri = (1 + Δ2 _i ) • τ $\genfrac{}{}{0ex}{}{\text{0}}{\text{ci}}$ ; (3)
0≤Δ2 _i ≤0.5, (4)
the values of the values of W _i , V _i , X _i and Y _{i are} determined by the material balance of the layer, by the material balance of the process of dividing the stream Z _i from the output of the (i-1) th layer, and by the material balance of the process of mixing the flows W _i and V _i according to the following equations:
X _i-1 = Z _i-1 • N _SO3нi / N _SO3кi-1 ; (5)
Y _i-1 = Z _i-1 - X _i-1 ; (6)
W _i = N _{SO2н i} + N _O2 ^W _i - N _SO2кi-1 • X _i-1 / Z _i-1 ; (7)
V _i = N _{O2н i} - N _O2 ^W _i - N _O2кi-1 • X _i-1 / Z _i-1 , (8)
moreover
W _i + V _i + X _i-1 = N _SO2ni + N _O2ni + N _SO3ni ; (9)
∑W _i = W; (10)
∑V _i = V; (eleven)
W _i = N _SO2 ^W _i + N _O2 ^W _i ; (12)
V _i = N _O2 ^V _i , (13)
where T _i ⁿ , T _i ^k - temperature of the reaction gas at the inlet and outlet of the i-th catalyst layer, K;
T _zi , T _pi - temperature, respectively, of ignition and the beginning of thermal destruction of the contact mass of the i-th layer, K;
Δ1 _i - stock thermal stability of the contact mass, K;
τ _pri is the residence time of the reaction gas in the i-th layer of the contact mass, s;
Δ2 _i is the dimensionless margin taking into account the decrease in the activity of the contact mass of the layer;
τ _ci is the theoretical contact time of the reaction gas with the surface of the contact mass of the i-th layer, s;
τ $\genfrac{}{}{0ex}{}{\text{0}}{\text{ci}}$ - theoretical contact time with the surface of the contact mass of the i-th layer for the volume of the reaction gas without sulfur trioxide at the inlet of the layer and with the ratio of the number of moles of sulfur dioxide to the number of moles of oxygen, s, as for τ _ci ;
X _i-1 , Y _i-1 - flows arising from the division of the flow Z _i-1 , mol / s;
Z _i-1 — contact gas flow leaving the (i-1) th layer, mol / s;
N _SO2нi , N _O2нi , N _SO3нi — SO ₂ , O ₂ , SO ₃ content in the gas stream at the entrance to the i-th layer, mol / s;
N _SO2кi-1 , N _O2кi-1 , N _SO3кi-1 - content of SO ₂ , O ₂ , SO ₃ in the stream Z _i-1 , mol / s;
W _i - distributed in the i-th layer stream of the source of concentrated sulfur dioxide gas, mol / s;
N _SO2 ^W _i , N _O2 ^W _i - the content of sulfur dioxide and oxygen in the stream W _i , mol / s;
V _i - oxygen flow distributed in the i-th layer, mol / s;
W, V — streams of the initial concentrated sulfur dioxide and oxygen supplied to the input of the contact apparatus, mol / s;
N _O2 ^V _i - the oxygen content in the stream V _i , mol / s,
and blowing from the recycle part of the exhaust gas, previously purified from sulfur oxides returned to the processing, at the stage of oxidation of SO ₂ using technical or technological oxygen or oxygen-air mixture, while:
V _i = N _O2 ^V _i + N _N2 ^V _i , (14)
where N _N2 ^V _i is the nitrogen content in the stream V _i , mol / s.

Distinctive features of the proposed method are:
- a series-parallel oxidation scheme of SO ₂ in SO ₃ in a multilayer contact apparatus;
- carrying out the process of oxidation of sulfur dioxide to trioxide in each layer of the contact apparatus in the mode τ _pri = (1 + Δ2 _i ) • τ $\genfrac{}{}{0ex}{}{\text{0}}{\text{ci}}$ ;
- joint application of techniques: distribution of the initial concentrated sulfur dioxide gas in layers with a sulfur dioxide concentration of at least 50%; distribution over the layers of the flow of oxygen; the allocation of SO ₃ from the interlayer contact gas;
- mixing the stream, which has not undergone the evolution of SO ₃ after separation of the interlayer contact gas before feeding to the next oxidation stage with a distributed stream of the source sulfur dioxide and with a distributed stream of O ₂ ;
- the use of a single stage of separation of SO ₃ for all flows after the division of the interlayer contact gas and for the stream from the last stage of contacting;
- dividing the contact gas from the output of the layer into two streams as a method for controlling:
reaction loading of layers;
gas contact time with the catalyst;
the amount of recycle gas;
the amount of SO ₃ emitted;
the ratio of recycle and the amount of allocated SO ₃ .

In the inventive method, new features improve the technology of processing sulfur dioxide in the production of sulfuric acid. Their use provides the following properties:
- increase the performance of the contact apparatus;
- an increase in the specific productivity of the contact mass;
- intensification of the process of processing SO ₂ with a significant reduction in the size of technological equipment;
- the possibility of the oxidation process at a lower gas temperature at the inlet to the contact mass layer and at a higher temperature at the outlet of the layer;
- equalization of the reaction load of the layers of the apparatus and the ability to control the load of the layers in a wide range;
- an increase in the controllability of the SO ₂ processing process due to the possibility of an invariant effect on the composition and volume of the reaction mixture, which is ensured by a combination of the following effects: distribution of the initial sulfur concentrated gas over the layers, distribution over the oxygen layers, fission of the contact gas from the output of each layer;
- reducing the number of stages of allocation of SO ₃ to one;
- the flexibility of technology in the face of variability in demand for the range and quantity of products.

 Based on the above, the claimed technical solution meets the criterion of "novelty." Analysis of the known technical solutions in the study area allows us to conclude that there are no signs in them that are similar to the distinctive features of the proposed method for the processing of concentrated sulfur dioxide in a cyclic manner, and to recognize the proposed technical solution meets the criterion of "inventive step".

In the known methods in a contact apparatus, the operation of the first layer of the contact mass most meets the condition of maximum efficiency and specific productivity. In subsequent layers, either the margin Δ1 _i has a high value, therefore condition (1) is not fulfilled, which negatively affects the productivity of the contact mass layer (see Tables 1, 2, 4), or the margin Δ2 _i is outside the boundaries (4 ), increasing the value of τ _ci . which reduces the specific productivity of the contact mass of the layer (see table. 3).

The specific productivity Ym _{i of the} contact mass of the i-th layer is
Ym _i = M _SO3i / Vк _i , (15)
where Vк _i is the volume occupied by the contact mass of the layer, m ³ ;
M _SO3i = N _SO3кi - N _SO3нi - productivity of the i-th layer of contact mass, mol / s.

где ω_i- скорость химической реакции в i-м слое, моль/(с•м³). Скорость химической реакции определяется, например, по формуле [1]

где P_SO2i, P_O2i, P_SO3i - парциальные давления SO₂, O₂, SO₃ в i-м слое, Па;
K_i, Kр_i - константы скорости [моль/(Па•с•м³)] и равновесия [Па^-0.5] реакции в i-м слое;
N_SO3нi, N_SO3кi - количество SO₃ в газовом потоке на входе и выходе i-го слоя, моль/с.The volume that the ith layer of the contact mass occupies is determined by the following formula:

where ω _i is the rate of a chemical reaction in the i-th layer, mol / (s • m ³ ). The chemical reaction rate is determined, for example, by the formula [1]

where P _SO2i , P _O2i , P _SO3i are the partial pressures of SO ₂ , O ₂ , SO ₃ in the i-th layer, Pa;
K _i , K p _i are the rate constants [mol / (Pa • s • m ³ )] and the equilibrium [Pa ^-0.5 ] of the reaction in the i-th layer;
N _SO3нi , N _SO3кi - the amount of SO ₃ in the gas stream at the inlet and outlet of the i-th layer, mol / s.

The partial pressures of the components in the reaction gas at the entrance to the i-th layer are related to the molar flow rate of these components in the following relationships:
N _SO2нi = N _нi • P _SO2нi / P _нi , (18)
N _O2нi = N _нi • P _O2нi / P _нi , (19)
N _SO3нi = N _нi • P _SO3нi / P _нi , (20)
where P _ni is the pressure of the reaction gas at the entrance to the i-th layer, Pa;
P _SO2ni , P _O2ni , P _SO3ni - partial pressure of SO ₂ , O ₂ , SO ₃ in the gas stream at the inlet of the i-th layer, Pa;
N _SO2нi , N _O2нi , N _SO3нi — SO ₂ , O ₂ , SO ₃ content in the gas stream at the inlet of the i-th layer, mol / s;
N _нi is the flow rate of the reaction gas through the i-th layer, mol / s.

 Equation (16) determines the nature of the dependence of the volume of contact mass required in the layer on the composition of the reaction gas at the inlet to the layer. The specific productivity and volume of the contact mass of the layer are inversely related (15).

In FIG. 1-3 (table. 5) shows the dependence of the required volume of contact mass, specific productivity of the contact mass of the layer and productivity of the layer on the content of SO ₃ in the reaction mixture at the inlet of the layer, the ratio of the amount of SO ₂ to the amount of O ₂ is 1: 1. The flow rate of the reaction gas at the inlet to the bed is 100 mol / s.

The absence of SO ₃ in the reaction gas at the inlet to the bed allows the oxidation of SO ₂ at the minimum required volume of contact mass, which favors the value of specific productivity. Extraction of SO ₃ from the interlayer contact gas provides an increase in the specific productivity of the contact mass of the layer.

 The specific productivity of the contact mass of the layer is explicitly affected by the performance of the layer of contact mass. According to the formula (15), the specific productivity is directly proportional to the productivity of the layer. An increase in the productivity of the layer favorably affects the value of the specific productivity of the contact mass.

 Let us prove that if condition (1) - (2) is fulfilled, the productivity of the contact mass layer is maximum if the flow rate and composition of the reaction gas through the contact mass layer are constant. With a constant flow rate and composition of the reaction gas, the temperature regime depends on the presence or absence of the required amount of contact mass volume, which is determined during design. The presence of the required volume of the contact mass provides the necessary time for the contact temperature of the reaction gas to come into contact with the contact mass.

The contact mass of the layer has a certain ignition temperature (lower temperature boundary of the oxidation reaction) and a certain temperature of the onset of thermal destruction (upper temperature boundary of the oxidation reaction). Heat is released in the contact mass layer as a result of SO ₂ oxidation to SO ₃ , which leads to an increase in temperature along the height of the layer. The heat released in the layer should not warm the layer to the temperature of the onset of thermal destruction of the contact mass. Therefore, there is a temperature limit on the productivity of the contact mass layer, and to determine the possible productivity of the contact mass layer, it is necessary to use the heat balance equation of the i-th layer
(N _SO2нi • C _SO2нi + N _O2нi • C _O2нi + N _SO3нi • C _SO3нi ) • T _i ^н + M _SO3i • Qp = [(N _SO2нi - M _SO3i ) • C _SO2кi + (N _O2нi - M _SO3i / 2) • C _O2кi + (N _SO3нi + M _SO3i ) • C _SO3кi ] • T _i ^к , (21)
where Qp is the thermal effect of the reaction, J / mol;
N _SO2ni , N _O2ni , N _SO3ni - flow rate of SO ₂ , O ₂ , SO ₃ , mol / s;
_SO2ni C, C _O2ni, C _SO3ni, C _SO2ki, C _{O2ki, SO3ki} C - heat capacity of SO _2, O _2, SO ₃ at the inlet and outlet layer, J / (mol • deg);
M _SO3i — productivity of the contact mass layer, mol / s;
T _i ⁿ , T _i ^k - temperature at the inlet and outlet of the i-th layer, K.

From (21) it follows:
M _SO3i = N _SO3кi - N _SO3нi = [(N _SO2нi • C _SO2кi + N _O2нi • C _O2кi + N _SO3нi • C _SO3кi ) • T _i ^к - (N _SO2нi • C _SO2нi + N _O2нi • C _O2нi + N _SO3нi • C _SO3нi ) • T _i ^н ] / [Qp + T _i ^к • (C _SO2кi + C _O2кi / 2 - C _SO3кi )]. (22)
In FIG. 4 and 5 (Tables 6 and 7), the dependence of the solvable heat balance on the temperature of the reaction gas at the outlet of the contact mass layer is plotted. It is assumed that the temperature regime is provided with the necessary amount of contact mass. The upper line is constructed for the reaction gas with a temperature at the inlet of the layer equal to 673 K, the middle line is 723 K, the lower line is 753 K. FIG. 4 shows graphs for the reaction gas with a flow rate of 100 mol / s of the composition SO ₂ = 43 vol.%, O ₂ = 57 vol.%, And in FIG. 5 composition SO ₂ = 38 vol.%, O ₂ = 52 vol.%, SO ₃ = 10 vol.%. According to the constructed dependences, the productivity of the adiabatic layer is greater, the higher the gas temperature at the outlet of the layer and the lower the gas temperature at the entrance to the layer.

The temperature T _i ^{n of the} reaction gas at the entrance to the i-th layer cannot be lower than the temperature T _{zi of} ignition of the reaction mixture on the catalyst. The temperature T _i ^{k of the} reaction gas at the outlet of the i-th layer cannot be higher than the temperature T _{pi of the} onset of thermal decomposition of the contact mass. For various types of vanadium catalysts, according to [6], the ignition temperature varies in the range of 623–723 K, and the temperature of the onset of thermal decomposition in the range of 873–923 K.

The presence of SO ₃ in the reaction gas raises the ignition temperature due to a chemical reaction between vanadium on the surface of the catalyst and SO ₃ . This negatively affects the temperature range (1) - (2). The presence of O ₂ in the reaction gas, on the contrary, reduces the ignition temperature of the vanadium contact mass.

Based on the foregoing, it becomes apparent that the maximum performance of the adiabatic layer of the contact mass is ensured by such a temperature regime at which T _i ^k = T _pi , and T _i ⁿ = T _zi . However, carrying out the oxidation of SO ₂ in this temperature regime is dangerous, on the one hand, due to the possibility of overheating the catalyst, and on the other hand, applying cold gas to the entrance to the contact mass layer and extinguishing the SO ₂ oxidation reaction in the bulk of the contact mass layer. The temperature regime of the oxidation process in the adiabatic layer of the contact mass, which ensures close to maximum productivity of the contact mass layer and avoids overheating or cooling of the catalyst, is determined by condition (1) - (2). The reserve Δ1 _i is introduced in order to avoid overheating of the contact mass. The range of variation Δ1 _{i is} selected from the operating experience of a particular type of catalyst. Each type of catalyst has its own range of variation Δ1 _i . The fulfillment of condition (1) - (2) provides the maximum productivity of the contact mass layer for the reaction gas of a given composition, and therefore, the growth of the specific productivity of the contact mass of the layer, which is a distinctive property of this method.

The influence of the flow rate of the reaction gas when constructing the contact oxidation scheme can be ignored. This follows from the following considerations. The volume of the contact mass Vк _i , the residence time in the i-th layer τ _pri and the flow rate of the reaction gas through the Q _qi layer are related by
Vк _i = Q _гi • τ _pri . (23)
Performance can be expressed in terms of the flow rate of the reaction gas and the partial pressures of the components and can be represented as follows:
M _SO3i = N _нi • [(C _SO2нi • P _SO2нi / P _нi + C _O2кi • P _O2нi / P _нi + C _SO3кi • P _SO3нi / P _нi ) • T _i ^к - (C _SO2нi • P _SO2нi / P _нi + C _O2нi • P _O2нi / P _нi + C _SO3нi • P _SO3н / P _нi ) • T _i ^н ] / [Qр + T _i ^к • (C _SO2кi + C _O2кi / 2 - C _SO3кi )]. (24)
If we substitute equations (23) and (24) in (15) and take into account that the molar flow rate and volumetric flow rate are related by the relation Q _gi = 0.0224 • N _нi • T _i ^н / 273, then the flow rate of the reaction gas through the layer in (15) is reduced . However, it must be taken into account that with an increase or decrease in the flow rate of the reaction gas through the contact mass layer, it is necessary to increase or decrease in proportion to the volume of the contact mass of the layer, which is solved when designing the contact apparatus. In the operating mode of the contact apparatus, the flow rate is a regime parameter of the oxidation process and differs from the maximum possible during the start-up and shutdown periods of the plants, and at other times it is close to the maximum, therefore, we can assume that the contact mass volume corresponds to the flow rate and does not affect the specific contact mass performance of the layer.

It was shown above that the specific productivity of the contact mass of the layer is favored by the absence of SO ₃ in the reaction mixture at the entrance to the contact layer. This means that the equality τ _pri = τ $\genfrac{}{}{0ex}{}{\text{o}}{\text{ci}}$ , and the value of the margin Δ2 _i is zero, that is, Δ2 _i = 0. This condition is provided by extracting all SO ₃ from the interlayer contact gas.

The separation of SO ₃ from the interlayer contact gas, as in the methods of [1, 2], requires for each interlayer contact gas stream from which SO _{3 is released} , its own absorber and its heat exchange equipment, which is necessary in order to cool the gas and then heat it again.

In the proposed scheme for organizing the work of the layers of the contact apparatus, the process of separating SO ₃ from the contact gas from the outlet of each layer is simplified. In the proposed method, SO _{3 is} extracted in a common separation unit, therefore, the step of heating the contact gas after the separation step is not required, as for example in the methods [1, 2]. As a result of the use of a common SO ₃ extraction unit, parallelization of the layers of the contact apparatus is performed, which is a distinctive property of the present invention.

Sulfur trioxide has some positive properties. For example, SO ₃ has a higher heat capacity than SO ₂ and O ₂ , and SO ₃ slows down the oxidation rate of SO ₂ . In the oxidation of concentrated sulfur mixtures, these properties play a positive role.

It is known that during the operation of the contact mass, a decrease in activity occurs. When the activity of the contact mass decreases, condition (1) with Δ2 _i = 0 is not satisfied. The range (4) takes into account the variability of the properties of the contact mass in real operating conditions and thereby ensure the fulfillment of condition (1). For a new contact mass, the quantity Δ2 _{i is} taken as the maximum, that is, for example, Δ2 _i = 0.3. If during the operation of the contact mass with a constant flow rate and composition of the gas, the contact mass activity decreases and condition (1) ceases to be fulfilled, then Δ2 _{i is} reduced. In addition, by the value of Δ2 _i, various kinds of disturbances arising during the oxidation of SO _{2 are} neutralized. Such disturbances include temperature fluctuations and the composition of the reaction mixture, a change in flow rate, and others.

The value Δ2 _i is the excess contact mass. When working on concentrated SO ₂ and O _{2, the} excess contact mass overheats. In order to avoid overheating of the contact mass, the presence of SO ₃ in the reaction gas at the entrance to the contact mass layer is used. To this end, the contact gas stream Z _i from the outlet of the previous layer is divided into two flows X _i and Y _i in a ratio that provides the necessary amount of SO ₃ at the input of the (i + 1) layer, the flow X _{i is} directed to (i + 1 ) th layer, flow Y _i to the stage of separation of SO ₃ . Instead of a stream Y _i directed to the sulfur trioxide separation step, a fresh oxygen stream V _{i + 1} and a fresh stream W _{i + 1 of} concentrated sulfur dioxide are fed to the input of the (i + 1) th layer. This technique provides incomplete parallelization of the layers of the contact apparatus and allows you to increase or decrease the degree of parallelization. The contact device operates in a serial-parallel circuit.

The distribution of the flows of the initial sulfur dioxide gas and oxygen over the layers of the contact apparatus with the simultaneous release of SO ₃ from the interlayer contact gas equalizes the operating modes of all layers of the contact apparatus and brings it closer to the operating mode of the first layer, and therefore to the most effective one. The distribution of flows and the release of SO ₃ provide equalization of the reaction load of the layers of the contact apparatus, as well as the fulfillment of conditions (1) - (2). The equalization of the reaction load of the layers of the contact apparatus and the implementation of the oxidation process of SO ₂ in compliance with conditions (1) - (2) are the distinguishing feature of the invention.

A parallel-serial circuit allows you to neutralize not only the above disturbances, but also the disturbance that occurs due to a decrease or increase in the flow rate of the reaction gas through the contact mass layer due to a change in the production program. A change in the flow rate of the reaction gas through the layer means a change in τ _pri , which requires a change in the value of τ $\genfrac{}{}{0ex}{}{\text{0}}{\text{ci}}$ while maintaining Δ2 _i . By the value of τ $\genfrac{}{}{0ex}{}{\text{0}}{\text{ci}}$ act using the ratio of SO ₂ : O ₂ and the content of SO ₃ in the reaction gas at the entrance to the layer.

Since the value of Δ2 _i determines the flow rate X _i-1 , and the gas flow rate through the ith layer of the contact mass is reliably measurable, the volume occupied by the contact mass is known, in order to calculate the required composition of the reaction gas at the inlet to the layer , it is necessary to set the values of Δ1 _i and Δ2 _i . The value of the sought quantities N _SO2нi , N _O2нi , N _SO3нi is determined by the following procedure.

Таким образом, реакционный газ без SO₃ с расходом Q_гi должен соприкасаться с контактной массой меньшее время, чем он на самом деле пребывает в слое. Объем контактной массы, соответствующий времени соприкосновения τ $\genfrac{}{}{0ex}{}{\text{0}}{\text{ci}}$ , меньше, чем действительный объем слоя контактной массы, и равен
Vк $\genfrac{}{}{0ex}{}{\text{0}}{\text{i}}$ = Q_ri•τ $\genfrac{}{}{0ex}{}{\text{0}}{\text{ci}}$ = 3,8 м³. (28)
Этот объем контактной массы был бы необходим для реакционного газа с расходом Q_гi, если бы в его составе не было SO₃. С другой стороны объем контактной массы можно определить по уравнению (16). Для объема Vк_i ⁰ можно записать

Нижняя граница интеграла (29) равна нулю. Верхняя граница этого интеграла определяется уравнением теплового баланса слоя
N_SO3кi = [(N_SO2нi•C_SO2кi + N_O2нi•C_O2кi + N_SO3нi•C_SO3кi)•T_i ^к - (N_SO2нi•C_SO2нi + N_O2нi•C_O2нi + N_SO3нi•C_SO3нi)•T_i ^н] /[Qр + T_i ^к•(C_SO2кi + C_O2кi/2 - C_SO3кi)] + N_SO3нi. (30)
Скорость химической реакции ω определяется по уравнению (17). Температуру реакционного газа T_i ^н на входе в слой и T_i ^к на выходе из слоя определяет условие (1-2). Изменение температуры в самом слое подчиняется закону

где N_SO2i= N_SO2 ^н _i-dN_SO3i; N_O2i=N_O2 ^н _i-dN_SO3i/2; N_SO3i=N_SO3 ^н _i+dN_SO3i. Изменение температуры в самом слое необходимо знать, чтобы определить величины констант скорости и равновесия K_i(T) и Kр_i(T), которые входят в уравнение (17).Let the volume of the contact mass of the ith layer be equal to Vк _i = 4.9 m ³ . The value of the flow rate of the reaction gas Q _gi at the entrance to the i-th layer is measured, that is, it is known. Let Q _i = 5.93 m ³ / s. Then the residence time of the reaction gas in the contact mass layer is also known:
τ _pri = Vк _i / Q _Гi = 4.9 / 5.93 = 0.83 s. (25)
According to condition (3-4), the residence time is expressed in terms of the contact time as
τ _pri = (1 + Δ2 _i ) • τ $\genfrac{}{}{0ex}{}{\text{0}}{\text{ci}}$ . (26)
Taking the value Δ2 _i = 0.3, from (3) we obtain the value of the contact time for the reaction gas without SO _{3 with the} flow rate Q _gi , which is equal to

Thus, a reaction gas without SO ₃ with a flow rate of Q _gi must come into contact with the contact mass less time than it actually resides in the layer. Contact mass volume corresponding to contact time τ $\genfrac{}{}{0ex}{}{\text{0}}{\text{ci}}$ less than the actual volume of the layer of contact mass, and is equal to
Vk $\genfrac{}{}{0ex}{}{\text{0}}{\text{i}}$ = Q _ri • τ $\genfrac{}{}{0ex}{}{\text{0}}{\text{ci}}$ = 3.8 m ³ . (28)
This volume of the contact mass would be necessary for the reaction gas with a flow rate of Q _gi if SO ₃ were not _present in its composition. On the other hand, the volume of the contact mass can be determined by equation (16). For volume Vк _i ⁰ we can write

The lower boundary of the integral (29) is equal to zero. The upper boundary of this integral is determined by the equation of the heat balance of the layer
N _SO3нi = [(N _SO2нi • C _SO2кi + N _O2нi • C _O2кi + N _SO3нi • C _SO3кi ) • T _i ^к - (N _SO2нi • C _SO2нi + N _O2нi • C _O2нi + N _SO3нi • C _SO3нi ) • T _i ⁿ ] / [Qp + T _i ^k • (C _SO2кi + C _O2кi / 2 - C _SO3кi )] + N _SO3нi . (thirty)
The chemical reaction rate ω is determined by equation (17). The temperature of the reaction gas T _i ⁿ at the entrance to the layer and T _i ^to at the exit of the layer determines the condition (1-2). The temperature change in the layer itself obeys the law

where N _SO2i = N _SO2 ⁿ _i -dN _SO3i ; N _O2i = N _O2 ⁿ _i -dN _SO3i / 2; N _SO3i = N _SO3 ⁿ _i + dN _SO3i . The temperature change in the layer itself must be known in order to determine the values of the rate and equilibrium constants K _i (T) and Kр _i (T), which are included in equation (17).

Thus, in equation (29), P _SO2нi and P _O2нi remain unknown. Using (18-19) partial pressures, we express as:
P _SO2i = P _i • (N _SO2iн - dN _SO3i ) / N _i ; (32)
P _O2i = P _i • (N _O2iн - dN _SO3i / 2) N _i . (33)
Given that
N _SO2нi = N _нi - N _SO3нi - N _O2нi , (34)
and gas volumetric flow rate is known and is associated with a molar ratio
Q _gi = 0.0224 • N _ni • T _i ⁿ / 273. (35)
Equations (32-35) allow in (29) to express and measure the partial pressure of SO ₂ through the partial pressure of O ₂ using equations (32) - (35). One unknown quantity remains in equation (29) - this is N _O2нi . One equation, one unknown quantity - the equation has a solution. Equations (17), (29) - (35) and conditions (1) - (2) are enough to find N _O2нi . Knowing N _O2нi , by equation (34) we find N _SO2нi and then we find their ratio N _SO2нi : N _O2нi .

Preserving the obtained relation SO ₂ : O ₂ = N _SO2нi : N _O2нi , again using equations (17), (29) - (35) and conditions (1) - (2), but we substitute the actual volume of the contact mass Vk _i into these equations = 4.9 m ³ and the above ratio of SO ₂ : O ₂ . Now unknown is the required amount of sulfur trioxide N _SO3нi . One equation - one unknown. The equation has a solution. Having determined the required amount of sulfur trioxide N _SO3ni and knowing the ratio of SO ₂ : O ₂ , we find the actual amounts of sulfur dioxide N _SO2ni and oxygen N _O2ni in the reaction mixture with the amount of sulfur trioxide N _SO3ni at the entrance to the contact layer.

In FIG. 6 (Table 8) shows the dependence of the contact mass on the SO ₂ : O ₂ ratio for the reaction mixture without SO ₃ constructed according to equations (17), (29) - (35) and condition (1) - (2). When the straight line intersects Vк _i ⁰ = 3.8 m ³ with this dependence, the desired SO ₂ : O ₂ ratio is obtained. Knowing the SO ₂ : O ₂ ratio, already on the straight line Vк _i = 4.9 m ³ we get a point that determines the required amount of sulfur trioxide N _SO3нi in the reaction mixture at the inlet of the layer (Fig. 7). If we construct the dependence of the contact mass volume on the SO ₂ : O ₂ ratio for the reaction mixture with the found amount of sulfur trioxide N _SO3нi , then the straight line Vк _i = 4.9 m ³ intersects the dependence at this point (Fig. 7).

 Since in equation (29) there is an integral dependence in which all variables are interconnected, it is difficult to obtain an analytical solution to the system of equations (17), (29) - (35). The solution is well obtained using computer technology, numerical methods, using finite-difference approximation.

 In the table. 9 shows the results of calculating the composition of the reaction gas at the inlet to the contact mass layer according to a known flow rate. The value of the flow rate of the reaction gas of the two extreme cases is 2 times different. The volume of the contact mass of the layers varies slightly. The inner diameter of the cylindrical contact apparatus is 6 m.

 The fulfillment of conditions (1) - (4) determines the composition of the reaction gas at the entrance to the contact layer by its flow rate and favors both the value of the productivity of the contact mass layer and the specific productivity of the contact mass of the layer.

According to the known composition of the reaction gas at the entrance to the i-th layer, the values of the flows entering the layer are determined. For example, according to equations (25) - (31) and condition (1) - (4), it was determined that N _SO2нi mol / s SO ₂ , N _O2нi mol / s O ₂ should be present in the reaction gas at the entrance to the i-th layer and N _SO3ni mol / s SO ₃ . The flow rate of the reaction gas through the bed can be represented as
N _ni = N _SO2ni + N _O2ni + N _SO3ni . (36)
On the other hand, the flow rate of the reaction gas consists of flows entering the bed
N _ni = V _i + W _i + X _i-1 . (37)
At the input of the ith layer, a stream of V _{i of} pure O ₂ is supplied, this stream contains V _i = N _O2 ^V _i mol / s of oxygen, the stream W _{i of the} initial sulfur dioxide gas, this stream contains N _SO2 ^W _i mol / s SO ₂ and N _O2 ^W _i mol / s O ₂ and the relation W _i = N _SO2 ^W _i + N _O2 ^W _i is observed.

At the input of the i-th layer, the flow X _i-1 from the output of the (i-1) -th layer is fed. With this stream, the required amount of N _SO3нi mol / s SO _{3 is} supplied to the input of the ith layer. As with the flow of X _i-1 is supplied to the layer N _SO2 ^X _i = _{N-1 SO2ki SO3ni} • N / _{N-1 SO3ki} mol / with SO ₂ and N _O2 ^X _i = _{N-1 O2ki SO3ni} • N / N _{SO3ki- 1} mol / s O ₂ .

The remaining amount of SO ₂ in the i-th layer comes with a stream of W _i . The amount of SO ₂ supplied with the stream W _i will be found as N _SO2 ^W _i = N _SO2нi - N _SO2 ^X _i mol / s. With a stream of W _i comes N _O2 ^W _i = W _i - N _SO2 ^W _i mol / s of oxygen.

The missing oxygen is supplied with a stream of V _i in the amount of N _O2 ^V _i = V _i -N _O2 ^W _i mol / s.

Since the composition of the flows is known, the values of the flows themselves are known:
V _i = N _O2 ^V _i ; (38)
W _i = N _SO2 ^W _i - N _O2 ^W _i ; (39)
X _i-1 = N _O2 ^X _i + N _SO2 ^X _i + N _SO3нi . (40)
Using the equations of material balance, the fluxes entering the contact layer were calculated.

В случае использования в качестве окислителя технического или технологического кислорода или кислородно-воздушной смеси для определения значений величин потоков используют такую же методику расчетов с включением в уравнения материальных балансов величины содержания азота.The flow Z _i-1 leaving the (i-1) th contact layer is Z _i-1 = N _нi-1 - 0.5 (N _SO3кi-1 - N _SO3нi-1 ), where N _SO3кi-1 is determined from the equation

If technical or technological oxygen or an oxygen-air mixture is used as an oxidizing agent, the same calculation procedure is used to determine the values of the flux values, including the nitrogen content in the equations of material balances.

As can be seen from the table. 9, a small difference in the volumes of the contact mass of the layers corresponds to sufficiently large possible ranges of variation in the flow rate and composition of the reaction gas. As is known, in the process of SO ₂ oxidation, there are fluctuations in flow rate and changes in the composition of the reaction gas at the inlet to the bed, which are associated both with the operating modes of the equipment and the production task (demand for products). In the proposed method, a change in the composition can react to a change in the flow rate of the reaction gas at the inlet to the layer.

For example, in the absence of SO ₃ in the reaction gas at the inlet, a change in the composition of the reaction gas from SO ₂ = 8.26%, O ₂ = 91.74% to SO ₂ = 17.9%, O ₂ = 82.1% allows you to change the flow rate by 1.91 times, and the change in composition reaction gas from SO ₂ = 94.64%, O ₂ = 5.36% to SO ₂ = 17.9%, O ₂ = 82.1% allows you to change the flow rate 56.5 times. The introduction of a small amount of sulfur trioxide at the entrance to the bed expands the boundaries of a possible change in the flow rate of the reaction gas through the bed.

The controllability of the SO ₂ processing process is increased and the flexibility of the technology is ensured under the conditions of variability of demand for the assortment and quantity of products, which are also distinctive properties of this method.

To provide a range of changes in the flow rate and composition of the reaction gas at the entrance to the contact layer, presented in table. 9, distributing only the initial concentrated sulfur dioxide gas, as in the methods of [5, 6], is impossible. It is necessary to have the possibility of a separate effect on the content of both SO ₂ and O ₂ in the reaction gas. Thus, it is necessary to supply oxygen to the bed separately from the source sulfur dioxide. Adding to this the process of fission of contact gas from the output of the previous layer allows you to invariantly affect the content and consumption of SO ₂ , O ₂ and SO ₃ at the entrance to the layer.

 In FIG. 8 to 10 are flow charts for implementing the proposed method. Schemes include: oven (P); unit for utilization of heat of combustion of sulfur (BUT); contact device (KA); a sulfur trioxide (BV) separation unit as a part of a heat exchanger (T), a condenser-cooler (KX), an absorber (A); exhaust gas purification unit (O).

 Sulfur is burned in an oven in an atmosphere of oxygen in the presence of recycle gas and an initial concentrated sulfur dioxide gas is obtained. Recycling gas is needed in the furnace to lower the sulfur burning temperature. The starting concentrated sulfur dioxide gas forms a reaction gas stream W. If the contact compartment has a recycling separate from the sulfur burning step (FIG. 8), then the contact compartment recycling is added to the flow W. The flow of reaction gas W is distributed between the contact layers of the apparatus. At the same time, oxygen flow V is distributed between the contact layers of the apparatus.

 By mixing the flows of sulfur dioxide from the furnace, the contact gas from the outlet of the previous layer and the oxygen stream, the required temperature of the gas mixture at the inlet of the next layer is established. The possibility of using interlayer heat exchangers is also possible.

The oxidation process in each layer is carried out in the range from the temperature of the beginning of the reaction T _zi (ignition temperature of the mixture) to the temperature T _pi , above which the thermal decomposition of the catalyst begins. At the entrance of each layer, reaction gas is supplied with a minimum predetermined sulfur trioxide content in its composition. From the output of the i-th layer, the contact gas stream Z _i is divided into two flows X _i and Y _i . The stream Y _i , i = 1, 2, ..., m, m is the number of layers of the contact apparatus, fed to the stage of SO ₃ extraction common to all layers.

In the proposed method, combining the distribution of the source gas and oxygen with the division of the contact gas, they affect the composition of the reaction mixture at the inlet of the layers and the flow rate of the reaction mixture through the layers and thereby control the rate of oxidation of SO ₂ , the productivity and specific productivity of the layer and the contact apparatus.

After separation of the contact gas stream Z _i from the output of each layer into two streams X _i and Y _{i, the} stream X _{i is} supplied to the input of the next layer of the contact apparatus, and the stream Y _i , like the contact gas from the output of the last layer, is sent to the condenser-cooler. In the condenser-refrigerator from contact gas, cooling it in the temperature range 17 - 44 ^o C, liquid SO _{3 is} isolated by condensation. From the outlet of the condenser-cooler, the exhaust gas is sent to the recycling line, and liquid SO _{3 is} sent to the finished goods warehouse or for processing into acid (oleum).

In the proposed method, sulfuric acid can be obtained from the gas discharged from the condenser-cooler, as shown in FIG. 8. For this, the gas from the outlet of the condenser-cooler is fed into the absorber, in which this gas is washed with concentrated sulfuric acid, which ensures almost complete extraction of SO ₃ from the gas and at the same time eliminates sulfuric acid fog in recycling. So, when the absorber is irrigated with sulfuric acid, in particular 98.3% concentration, there are practically no water vapor in the apparatus, and the partial pressure of acid vapor at 25 ^o C is 3.29 • 10 ^-8 MPa.

This technique, which consists in sequential processing of the contact gas by condensation and absorption, can reduce the requirements for the composition of the gas discharged from the condenser-cooler to the presence of SO ₃ in it and thereby soften the regulatory requirements for the condenser operating modes and at the same time, unlike the prototype, eliminate SO ₃ in recycle.

The serial-parallel scheme of SO ₂ processing makes it possible to obtain liquid SO ₃ , sulfuric acid, and oleum as a finished product, which provides the flexibility of the proposed technology in the face of varied demand for the range and quantity of products.

The presence of SO ₃ in recycling is not practical; on the one hand, this negatively affects the economic indicators of the cyclic scheme, and on the other hand, it is a disturbing effect on the oxidation process. Fluctuations in the concentration of SO ₃ in recycling destabilizes the process of processing sulfur dioxide, which complicates the control of the contact apparatus.

 When using technical (technological) oxygen in the system, the accumulation of ballast components (nitrogen) occurs, their blowing from the technological cycle is necessary. In FIG. 10 shows a diagram for implementing this technique, according to which part of the recycle gas is taken to the purification step. Here, sulfur oxides are extracted from gas, returned to processing, and the purified gas is taken to the atmosphere.

 An example implementation of the proposed method.

 In FIG. 9 is a flow chart of the implementation of the proposed example.

Into the furnace (P) serves: liquid sulfur in an amount of 39.73 mol / s, recycle gas 189.28 mol / s, which contains 37.3 vol.% SO ₂ and 62.7 vol.% - O ₂ . From the furnace, 189.28 mol / s concentrated sulfur dioxide gas with a concentration of SO _{2 of} 58.3 vol.%, O ₂ - 41.7 vol.% Is removed. The furnace gas is cooled to a temperature of 723 K in the heat recovery unit of the sulfur burning stage (BFC) and distributed over the layers of the contact apparatus (SC), providing the necessary amount of sulfur dioxide at the entrance to each layer. The first layer is fed with a flow of W ₁ furnace gas in an amount of 41.34 mol / s, on the second - W ₂ in an amount of 47.95 mol / s, on the third - W ₃ in an amount of 49.25 mol / s, on the fourth - W ₄ in an amount of 50.63 mol / from.

The flow V = 60.03 mol / s of oxygen is distributed among the layers of the contact mass as follows: the flow V ₁ = 23.05 mol / s is fed to the first layer; on the second - V ₂ = 14.3 mol / s; on the third - V ₃ = 12.36 mol / s; on the fourth - V ₄ = 10.32 mol / s.

The contact apparatus has a diameter of 2 m and four layers of contact mass; the height of the first layer is 0.17 m, the second layer is 0.18 m, the third layer is 0.18 m, the fourth layer is 0.19 m. The molar flow rate of the reaction gas through each layer is 100 mol / s (5.93 m ³ / s at 723 K).

 The composition of the reaction gas at the entrance to each layer of contact mass and the operating parameters of the oxidation of sulfur dioxide in each layer are presented in table. 10.

Sulfur trioxide in an amount of 6.3 mol / s is supplied to the inlet of the first layer by flow X ₄ . With a flow of X ₄ , 11.97 mol / s SO ₂ and 17.34 mol / s O ₂ enter the first layer. The missing 24.1 mol / s SO ₂ , as well as 17.24 mol / s O ₂ are fed to the first layer with a stream of W ₁ . The missing 23.05 mol / s O _{2 is} fed by stream V ₁ . Stream X _{4 is} formed by dividing the stream leaving the fourth layer Z ₄ = 94.99 mol / s in the ratio X ₄ : Y ₄ = 6.3: 10.52.

From the output of the first layer, the flow Z ₁ = 95.1 mol / s is divided in the ratio X ₁ : Y ₁ = 6.4: 9.70. Sulfur trioxide is supplied to the inlet of the second layer with a stream of X ₁ in an amount of 6.4 mol / s. With a stream of X ₁ 10.42 mol / s SO ₂ and 20.93 mol / s O ₂ . The missing 27.96 mol / s SO ₂ and also 19.99 mol / s O ₂ are supplied with a flow of W ₂ . The missing 14.3 mol / s O _{2 is} fed by a stream of V ₂ .

From the output of the second layer, the flux Z ₂ = 95.02 mol / s is divided in the ratio X ₂ : Y ₂ = 6.6: 9.76. Sulfur trioxide is supplied to the inlet of the third layer by a stream of X ₂ in an amount of 6.6 mol / s. With a flow of X ₂ , 11.45 mol / s SO ₂ and 20.34 mol / s O _{2 are} supplied. The missing 28.71 mol / s SO ₂ as well as 20.54 mol / s O ₂ are supplied with a W ₃ stream. The missing 12.36 mol / s O ₂ served as a stream of V ₃ .

From the output of the third layer, the flow Z ₃ = 95.02 mol / s is divided in the ratio X ₃ : Y ₃ = 6.8: 9.75. Sulfur trioxide is supplied to the inlet of the second layer by a stream of X ₃ in an amount of 6.8 mol / s. With a flow of X ₃ , 12.42 mol / s SO ₂ and 19.83 mol / s O _{2 are} supplied. The missing 29.52 mol / s SO ₂ as well as 21.11 mol / s O ₂ are supplied with a flow of W ₄ . The missing 10.32 mol / s O ₂ served as a stream of V ₄ .

Streams Y _i formed after separation of the stream Z _i leaving the i-th layer are cooled in a heat exchanger (T) and enter the SO ₃ (BV) separation unit. The following gas streams enter the SO ₃ separation step:
After the first layer, 15.84 mol / s SO ₂ , 31.8 mol / s O ₂ , 9.7 mol / s SO ₃ .

After the second layer, 16.97 mol / s SO ₂ , 29.59 mol / s O ₂ and 9.76 mol / s SO ₃ .

After the third layer, 17.79 mol / s SO ₂ , 28.43 mol / s O ₂ and 9.75 mol / s SO ₃ .

After the fourth layer, 19.95 mol / s SO ₂ , 28.91 mol / s O ₂ and 10.52 mol / s SO ₃ .

Total separation step SO ₃ gas stream enters composition:
SO ₃ = 39.73 mol / s, SO ₂ = 70.55 mol / s, O ₂ = 118.73 mol / s.

Compare the table. 10 s. 4. In the table. 4 presents the results of the calculation of the processing of sulfur dioxide according to a sequential scheme, as in the method [5]. The dimensions of the layers of contact mass in the method [5] are the same as in the example (table. 10). At the inlet of the first layer of contact mass, reaction gas was supplied with a flow rate of 100 mol / s and a content of SO ₂ = 51 mol / s, O ₂ = 49 mol / s (Table 4). Then this gas was sequentially processed in all layers of the contact apparatus, cooling between the layers of the contact mass to 723 K. In the first layer of the contact mass in table. 4 the specific productivity of the contact mass of the layer and the productivity of the layer is slightly lower than in table. 10. And the overall performance of the contact apparatus and the specific productivity of the contact mass of the apparatus in the example (Table 10) are higher than in the method [5] of the Table. 4, much. As can be seen from the table. 4, in the contact apparatus, a decrease in productivity and specific productivity from layer to layer occurs. Starting from the second layer, the value Δl _i increases and conditions (1) - (4) cease to be satisfied. In the method [4], it is possible to achieve the fulfillment of condition (1) - (2) (see table. 3), which will increase the performance of each layer and the entire contact apparatus by increasing at least 2 times the amount of contact mass in the apparatus, but the condition (4) - (5) will not be executed. Therefore, in a serial-parallel scheme, the process of processing sulfur dioxide oxidation proceeds at least 2 times more intensively and requires 2 times less contact mass than in the method [4], which ensures a reduction in the size of technological equipment. This fact is also a distinctive property of a series-parallel circuit.

 Compare the table. 10 s. 2. In the table. 2 presents the results of the calculation of the processing of conventional sulfur mixtures according to a sequential scheme, as in the method [2]. As can be seen from the table. 2, in the contact apparatus there is a decrease in productivity in the layers of the contact mass, while the specific productivity decreases slightly. However, the productivity of the contact apparatus in the method [2] is 4.7 times less than in the claimed method, and the specific productivity of the contact mass of the apparatus is 7.8 times less than in the claimed method, which requires 7.8 times more contact mass.

 The comparison results of the table. 10 s. 2-4 confirm that the inventive method has better performance indicators than the methods [5, 6] and the method [2].

Claims (2)

1. A method of processing concentrated sulfur dioxide gas into sulfur trioxide according to a cyclic scheme, comprising the steps of oxidizing sulfur dioxide in a multilayer contact apparatus by distributing the initial sulfur dioxide gas between the layers of the contact mass, dividing the contact gas from the output of the layers into streams, separating sulfur trioxide from the contact gas, and blowing from recycling of the part of the exhaust gas, previously purified from sulfur oxides returned to processing, characterized in that the process of oxidation of sulfur dioxide into a multilayer contact ohm apparatus is performed by a series-parallel circuit by distributing the initial sulfur dioxide and oxygen flows W V over the layers contactor contact and dividing the gas flow from the output Z _i of each i-th layer for i = 1, 2, ..., m, where m is the number of layers to flows X _i and Y _i supplied: stream X _i to the input of the next (i + 1) th layer, from the output of the last layer stream X _{m is} returned to the input of the first layer, stream Y _i to the stage separation of sulfur trioxide, then recycled and the composition of the reaction gas comprising sulfur dioxide content of N _SO2ni, sour N _O2ni kind of sulfur trioxide N _SO3ni, at the inlet of each i-th layer support, starting from the joint the following conditions:
T _i ^k - T _i ⁿ + Δ1 _i = T _pi - T _zi ; (1)
T _zi ≤ T _i ⁿ <T _i ^k ≤ T _pi ; (2)
τ _pri = (1 + Δ2 _i ) • τ $\genfrac{}{}{0ex}{}{\text{0}}{\text{ci}}$ ; (3)
0 ≤ Δ2 _i ≤ 0.5, (4)
the values of W _i , V _i , X _i and Y _{i are} determined by the material balance of the layer, by the material balance of the process of dividing the stream Z _i from the output of the (i-1) th layer, and by the material balance of the process of mixing the flows W _i and V _i according to the following equations:
X _i-1 = Z _i-1 • N _SO3нi / N _SO3кi-1 ; (5)
Y _i-1 = Z _i-1 - X _i-1 ; (6)
W _i = N _SO2нi + N _O2 ^W _i - N _SO2кi-1 • X _i-1 / Z _i-1 ; (7)
V _i = N _O2нi - N _O2 ^W _i - N _O2кi-1 • X _i-1 / Z _i-1 , (8)
moreover
W _i + V _i + X _i-1 = N _SO2ni + N _O2ni + N _SO3ni ; (9)
∑W _i = W; (10)
∑V _i = V; (eleven)
W _i = N _SO2 ^W _i + N _O2 ^W _i ; (12)
V _i = N _O2 ^V _i , (13)
where T _i ⁿ , T _i ^k - temperature of the reaction gas at the inlet and outlet of the i-th catalyst layer, K;
T _zi , T _pi - ignition temperature and the beginning of thermal destruction of the contact mass of the i-th layer, K;
Δ1 _i - stock thermal stability of the contact mass, K;
τ _pri is the residence time of the reaction gas in the i-th layer of the contact mass, s;
Δ2 _i is the dimensionless margin taking into account the decrease in the activity of the contact mass of the layer;

theoretical time of contact of the reaction gas with the surface of the contact mass of the i-th layer, s;

theoretical time of contact with the surface of the contact mass i-th layer for the volume of the reaction gas, without the presence of sulfur trioxide in the inlet layer and with the same as for τ _ci, a molar ratio of sulfur dioxide to the number of moles of oxygen with;
X _i-1 , Y _i-1 - flows arising from the division of the flow Z _i-1 , mol / s;
Z _i-1 — contact gas flow leaving the (i-1) th layer, mol / s;
N _SO2нi , N _O2нi , N _SO3нi — SO ₂ , O ₂ , SO ₃ content in the gas stream at the entrance to the i-th layer, mol / s;
N _SO2кi-1 , N _O2кi-1 , N _SO3кi-1 - content of SO ₂ , O ₂ , SO ₃ in the stream Z _i-1 , mol / s;
W _i - distributed in the i-th layer stream of the source of concentrated sulfur dioxide gas, mol / s;
N _SO2 ^W _i , N _O2 ^W _i - the content of sulfur dioxide and oxygen in the stream W _i , mol / s;
V _i - oxygen flow distributed in the i-th layer, mol / s;
W, V — streams of the initial concentrated sulfur dioxide and oxygen supplied to the input of the contact apparatus, mol / s;
N _O2 ^V _i is the oxygen content in the stream V _i , mol / s. 2. The method according to p. 1, characterized in that at the stage of oxidation of sulfur dioxide using technical or technological oxygen or oxygen-air mixture:
V _i = N _O2 ^V _i + N _N2 ^V _i , (14)
where N _N2 ^V _i is the nitrogen content in the stream V _i , mol / s.

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