RU2516635C1 - Method of controlling process of reducing sulphurous flue gases - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of controlling the process of reducing sulphurous flue gases with natural gas in the presence additional oxygen, involving treatment of flue gases to obtain sulphur in a thermal step and at least one catalytic step, involves controlling the flow rate of natural gas and total flow rate of oxygen into the thermal step based on a preset empirical functional relationship between concentration values of components of the tail gas, flow rate of components of the flue gas and temperature in the thermal reactor chamber. To this end, the method involves measuring the current temperature in the thermal reactor chamber, determining volume flow rate of O₂ and N₂ in the flue gas and concentration of H₂S, COS and SO₂ in the tail gas and calculating compensation factors, based on which the flow rate of natural gas and oxygen into the thermal step is adjusted simultaneously. Flow rate of oxygen is defined as the difference between the calculated total flow rate of oxygen and the flow rate of oxygen coming in with the flue gas.

EFFECT: improved method.

1 dwg, 2 tbl

Description

The invention relates to the field of chemistry and can be used to control the process of recovery of oxygen-containing sulfur dioxide gases to produce elemental sulfur in non-ferrous metallurgy, chemical and oil refining industries.

The process of producing sulfur by reducing sulfur dioxide with natural gas from waste gases of metallurgical production is characterized by a variable composition of raw materials. This is due to the different intensity of sulfur dioxide evolution at different stages of smelting, which leads to a change in time of the content of sulfur dioxide, oxygen and other substances entering the sulfur production unit.

Working under conditions of variable consumption of raw materials and their composition leads to a decrease in the efficiency of sulfur production, which is reflected in a decrease in the degree of sulfur extraction, an increase in the emission of sulfur dioxide into the atmosphere, an excessive consumption of natural gas and technical oxygen, and the likelihood of producing substandard sulfur - green or brown.

A known method of controlling the process of recovery of sulfur dioxide by natural gas (A.S. USSR No. 1125187, IPC C01B 17/02, G05D 27/00) by supplying natural gas and an oxidizing agent for combustion and controlling the temperature in the reactor depending on the flow rate and temperature of sulfur dioxide filed for recovery. Moreover, the temperature in the reactor is controlled by changing the flow rate of natural gas supplied for combustion, depending on the oxygen content in sulfur dioxide.

In this invention, control is based on the semi-empirical calculation of the amount of natural gas that needs to be fed into the furnace of a thermal reactor to process the original gas mixture fed for reduction. Moreover, as an object of the invention, an increase in reactor productivity due to a decrease in temperature fluctuations is indicated. Using the formula indicated in the invention, it is probably possible to stabilize the temperature in the furnace chamber of a thermal reactor, however, achieving the required optimal ratio of sulfur-containing components of the tail gas is doubtful. This is compounded by the fact that the empirical coefficients described in the description have more than twofold scatter without decoding the algorithm for choosing the desired coefficient value.

The closest in technical essence and the achieved result is a method of controlling the recovery of oxygen-containing sulfur dioxide gases by natural gas according to the patent of the Russian Federation No. 2091297, IPC C01B 17/04, G05D 27/00. In accordance with the method, natural gas immediately before reduction is supplied to the process gas stream pre-mixed with an oxygen-containing gas (air or technical oxygen), the flow rates of natural and oxygen-containing gases are measured, the content of hydrogen sulfide and sulfur dioxide in the gas is measured before the Claus stage, and the gas temperature is measured in the reaction zone of the recovery reactor. Depending on the sign and magnitude of the difference between the current reduction temperature and the set one, the flow rate of oxygen-containing gas and natural gas is proportionally adjusted. At the same time, in proportion to the difference between the current and set values of the ratio of the components of hydrogen sulfide and sulfur dioxide, depending on the sign of the difference, the flow rate of natural and oxygen-containing gases is adjusted.

In the known method, the temperature is controlled by changing the flow rates of oxygen and natural gas, and the composition of the reduced gas is controlled by changing only the flow rate of natural gas. In this description, a methodological flaw is laid: the oxygen flow rate is regulated in the circuit associated with the stabilization of the temperature in the furnace of the thermal reactor, and the natural gas flow rate is controlled in the circuit associated with the stabilization of the concentration ratio of the specified components of the tail gas. Meanwhile, the analysis of the equilibrium states of the SO ₂ —N ₂ —H ₂ O — O ₂ —CH _{4 system} , including all possible reaction products, shows that such a division of the control system into loops is illegal. For example, with a certain fixed ratio of the components of SO ₂ —N ₂ —H ₂ OO ₂ , depending on the flow rate of CH ₄ , a specific temperature in the furnace of the thermal reactor and a specific ratio of the concentrations of the components of the tail gas will be recorded. Moreover, a small increment in the flow rate of CH ₄ can lead to both an increase and a decrease in the adiabatic temperature in the furnace. The same applies to the ratio of the concentrations of the components of the tail gas. Similar observations relate to a small increment in the supply of oxygen to the furnace at a fixed flow rate of the remaining components, including methane. This behavior of the system is due to the competition of exothermic and endothermic reactions in the furnace of a thermal reactor when the oxidant-reductant balance changes at the reactor inlet and depends on the ratio of reactants and inert substances specific to the input mixture.

Thus, the ability to establish a separate functional relationship between temperature and oxygen and natural gas consumption, on the one hand, and only the consumption of natural gas and the composition of the reduced gas, on the other hand, is unlikely. In this regard, the control of the installation to achieve the optimal mode according to the invention is problematic.

The technical problem that the present invention solves is to optimize the control of the recovery process of sulfur dioxide flue gases by the methane method by simultaneously controlling two control variables, namely, oxygen and natural gas consumption.

The technical problem is solved in that the control process for the recovery of sulfur flue gases containing SO ₂ , O ₂ and N ₂ , natural gas in the presence of additional oxygen, which includes the processing of flue gases to produce sulfur in the thermal and at least one catalytic stages, carried out by controlling the temperature in a thermal reactor, changing the flow of oxygen and natural gas, as well as the composition of the tail gas at the outlet of the catalytic stage. To do this, analyze the impact on key process parameters of its input, variable parameters. The key parameters are the temperature in the furnace of the thermal reactor and the ratio of the concentrations of the components in the tail gas: (H ₂ S + COS) / SO ₂ . Under the input process parameters are taken the costs of the components SO ₂ , N ₂ , O ₂ and CH ₄ at the entrance to the thermal reactor. For this purpose, the flow rate and concentration of SO ₂ in the flue gas are preliminarily measured and the volumetric flow rate of SO ₂ and the volumetric flow rate of O ₂ and N ₂ in the flue gas are determined, the current temperature value in the thermal stage chamber, the concentration of H ₂ S, COS and SO ₂ in tail gas and calculate the correction factors, based on which at the same time correct the flow of natural gas and the flow of oxygen to the thermal stage. Moreover, the oxygen flow rate is defined as the difference between the calculated total oxygen flow rate and the oxygen flow rate that comes with the flue gas.

Calculation of correction factors is carried out on the basis of a preliminary (before the start of the production control procedure) computer analysis of the system performance in the optimal area and near it for all possible ranges of changes in the composition and flow of flue gas.

Computer analysis is based on a process model that has been repeatedly tested under industrial conditions, which is based on the calculation of the thermodynamically equilibrium states of the gas mixture for individual devices and for the installation as a whole.

A generalization of the results of the model made it possible to establish an empirical functional relationship between these key parameters and the input parameters of the process in the form of a system of equations of the following form:

, $$\left\{\begin{array}{l}|\; |\; |T(V_{O_2},V_{C{H}_{\mathrm{four}}},V_{N_2},V_{S{O}_2})-T_{\mathrm{to}\mathrm{about}n}|\; |\; |\le {\delta }_T\\ |\; |\; |R(V_{O_2},V_{C{H}_{\mathrm{four}}},V_{S{O}_2})|\; |\; |\le {\delta }_R\end{array}\right\}\left(\mathrm{one}\right)$$

,

in which

функциональное описание зависимости температуры в топке выходных параметров процесса от его входных параметров, °C, а $$\begin{array}{l}T=T(V_{O_2},V_{C{H}_{\mathrm{four}}},V_{N_2},V_{S{O}_2})={\alpha }_0+{\alpha }_{\mathrm{one}}\times V_{S{O}_2}+{\alpha }_2\times V_{O_2}+{\alpha }_3\times V_{C{H}_{\mathrm{four}}}+{\alpha }_{\mathrm{four}}\times V_{N_2}+\\ +{\alpha }_5\times V_{C{H}_{\mathrm{four}}}\times V_{S{O}_2}+{\alpha }_6\times V_{O_2}\times V_{S{O}_2}+{\alpha }_7\times V_{N_2}^2\end{array}$$

functional description of the dependence of the temperature in the furnace of the process output parameters on its input parameters, ° C, and

функционал, входящий в критерий оптимального управления процессом и определяющий его достижение, который зависит от расходов кислорода, метана и диоксида серы в термический реактор и рассчитывается по уравнению $$R=C_{H_{2}S}-C_{COS}-2C_{S{O}_2}$$

, мол.%, где $$\begin{array}{l}R=R(V_{O_2},V_{C{H}_{\mathrm{four}}},V_{S{O}_2})=b_0+b_{\mathrm{one}}\times V_{S{O}_2}+b_2\times V_{O_2}+b_3\times V_{C{H}_{\mathrm{four}}}+b_{\mathrm{four}}\times V_{C{H}_{\mathrm{four}}}\times V_{S{O}_2}+\\ b_5\times V_{O_2}\times V_{S{O}_2}\end{array}$$

functional that is included in the criterion of optimal process control and determining its achievement, which depends on the consumption of oxygen, methane and sulfur dioxide in a thermal reactor and is calculated by the equation $$R=C_{H_{2}S}-C_{COS}-2C_{S{O}_2}$$

, mol.%, where

- расходы соответствующих веществ на входе установки, нм³/ч; $$V_{O_2},V_{C{H}_{\mathrm{four}}},V_{N_2},V_{S{O}_2}$$

- the costs of the relevant substances at the inlet of the installation, nm ³ / h;

T _con - temperature in the combustion chamber of the thermal stage, ° C;

δ _T - the required accuracy of maintaining the temperature in the furnace of the combustion chamber of a thermal reactor relatively optimal, ° C;

δ _R - the required accuracy of maintaining the parameter R relative to the optimal value, mol.%;

α ₀ ÷ a ₇ and b ₀ ÷ b ₅ are the coefficients of empirical regression equations describing the process;

, $$C_{S{O}_2}$$

, C_COS - концентрации соответствующих компонентов в хвостовом газе процесса, мол.%. $$C_{H_{2}S}$$

, $$C_{S{O}_2}$$

, C _COS - concentration of the corresponding components in the tail gas of the process, mol.%.

Thus, two equations are obtained that relate the input parameters of the process with two output parameters. The type of equations in this case can be any, it is only important that the obtained equations adequately and with a minimum error reflect the relationship between the input and output variables in the entire range of input variables.

Process control takes place in the following sequence.

. Измеряют текущую температуру Т в термическом реакторе. Если |R|<δ_R и |T-T₁|<δ_T, считают, что процесс эксплуатируется вблизи оптимальной области. Следовательно, регулирование не требуется.The current concentrations of H ₂ S, COS, SO ₂ in the tail gas of the sulfur recovery process are determined. The measured concentrations of these components determine the value $$R=C_{H_{2}S}-C_{COS}-2C_{S{O}_2}$$

. Measure the current temperature T in a thermal reactor. If | R | <δ _R and | TT ₁ | <δ _T , consider that the process is operated near the optimal area. Therefore, regulation is not required.

и $$V_{C{H}_4}$$

, при этом остальные переменные, входящие в систему, известны.In case of non-compliance with at least one of these conditions, the following regulatory actions are performed. Determine the costs of sulfur dioxide, oxygen, inert substances, which together with the flue gas are fed for processing. Jointly solve a system of nonlinear equations for unknown variables $$V_{O_2}$$

and $$V_{C{H}_{\mathrm{four}}}$$

, while the remaining variables included in the system are known.

Correction coefficients are determined, which are the ratio of the operating costs O ₂ and CH ₄ supplied for processing to the required (calculated) costs. Regulate the supply of natural gas and oxygen to the furnace in accordance with the found values of their costs. In this case, the consumption of additional oxygen is determined as the difference between the value calculated and the amount of oxygen that enters the thermal reactor together with the flue gas.

To illustrate, below is an example implementation of the above method, not limiting the scope of the invention.

Example.

The operation of the installation for producing sulfur from SO ₂ -containing flue gas of metallurgical production by the natural gas reduction method was analyzed. The installation includes thermal and catalytic stages. The ranges of changes in the consumption of raw materials and their composition are given in table 1. In addition to these components, flue gas also contains nitrogen, water vapor, carbon dioxide. Preliminary calculations found that these components can be converted to nitrogen without a noticeable loss in the accuracy of subsequent calculations. When deriving the dependences, the inert components of the flue gas were converted to nitrogen.

.The analysis of this system was carried out using computer simulation, which included the calculation of optimal and similar operating modes in the ranges of all flue gas indicators shown in table 1. For each mode, the adiabatic temperature in the furnace of the thermal reactor was calculated and $$R=C_{H_{2}S}-C_{COS}-2C_{S{O}_2}$$

.

The calculation results in graphical form for one of the modes are presented in the drawing, which shows the dependence of R (mol.%) And adiabatic temperature in the furnace (° C) on the consumption of natural gas (nm ³ / h) and oxygen (nm ³ / h) in thermal reactor, where R - dashed contours, adiabatic temperature in the furnace - solid contours.

Table 1 The flue gas entering the thermal reactor Minimum value Maximum value Consumption, nm ³ / h 26000 31000 The content of O ₂ mol.% 7.5 11.5 The content of SO ₂ , mol.% 23 42

Further, the calculation results were approximated using the following empirical equations:

$$\begin{array}{l}T=T(V_{O_2},V_{C{H}_{\mathrm{four}}},V_{N_2},V_{S{O}_2})={\alpha }_0+{\alpha }_{\mathrm{one}}\times V_{S{O}_2}+{\alpha }_2\times V_{O_2}+{\alpha }_3\times V_{C{H}_{\mathrm{four}}}+{\alpha }_{\mathrm{four}}\times V_{N_2}+\\ +{\alpha }_5\times V_{C{H}_{\mathrm{four}}}\times V_{S{O}_2}+{\alpha }_6\times V_{O_2}\times V_{S{O}_2}+{\alpha }_7\times V_{N_2}^2\end{array}$$

$$\begin{array}{l}R=R(V_{O_2},V_{C{H}_{\mathrm{four}}},V_{S{O}_2})=b_0+b_{\mathrm{one}}\times V_{S{O}_2}+b_2\times V_{O_2}+b_3\times V_{C{H}_{\mathrm{four}}}+b_{\mathrm{four}}\times V_{C{H}_{\mathrm{four}}}\times V_{S{O}_2}+\\ b_5\times V_{O_2}\times V_{S{O}_2}\end{array}$$

In this case, the unknown coefficients a ₀ ÷ a ₇ and b _o ÷ b ₅ equations were selected using the least squares method, their values for the case under consideration are given in table 2.

table 2 Parameter Rating Parameter Rating a ₀ 1174,370 b ₀ 2,949 a ₁ 0.003 b ₁ -0.004 a ₂ 0.159 b ₂ -0.006 a ₃ -0.066 b ₃ 0.008 a ₄ -0.007 b ₄ -1.084 × 10 ^-7 a ₅ 2,415 × 10 ^-6 b ₅ 1,899 × 10 ^-7 a ₆ -5.123 × 10 ^-6 a ₇ -1.899 × 10 ^-7

Consider the operation of the installation with the following input parameters. The input of the thermal reactor of the installation receives 31000 nm ³ / h of flue gas of the following composition, mol.%: SO ₂ - 23; O ₂ - 11.5; H ₂ O - 9.2; N ₂ - the rest. To process this gas, air in an amount of 2300 nm ³ / h with a corresponding fuel gas flow rate (250 nm ³ / h) is fed to a furnace of a thermal reactor, technical oxygen is supplied (O ₂ - 95.5%, N ₂ - 4, 5%) in the amount of 2452 nm ³ / h and natural gas, so that the total consumption of natural gas in a thermal reactor (including the gas flow to a separate burner) is 7859 nm ³ / h, and the total oxygen consumption (including oxygen from flue gas, air, fed to the burner of a thermal reactor, and additional oxygen) is 6325 nm ³ / h. In this case, the adiabatic temperature in the furnace of the thermal reactor is 1333 ° C, and the concentrations of sulfur-containing components of the tail gas are the following, mol.%: H ₂ S - 2,44; SO ₂ - 0.51, COS - 0.40, which corresponds to a value of R = 1.02 mol.%.

To operate the unit in optimal mode, it is necessary that the temperature in the thermal reactor and R be limited by the following limits:

$$\{\begin{array}{l}|\; |\; |T-1350|\; |\; |\le 5\\ |\; |\; |R|\; |\; |\le 0.05\end{array}$$

The temperature value in the optimal operation mode (1350 ° C) is determined in advance for this installation, based on the design of the furnace and the operating experience of the installation, the value R = 0 in the optimal operation mode is determined by the stoichiometry of the sulfur production reaction (Claus reaction). Values of permissible dispersion of indicators are relatively optimal in temperature ± 5 ° C and in component concentrations ± 0.05 mol%, taken from considerations of practical attainability of indicators and their effect on sulfur recovery and sulfur dioxide emissions at the installation.

The indicated costs of natural gas and oxygen supplied to the installation do not ensure the processing of flue gas of the indicated flow rate and composition in the optimal mode, since

$$\{\begin{array}{l}|\; |\; |T-1350|\; |\; |=|\; |\; |1333-1350|\; |\; |=7>5\\ |\; |\; |R|\; |\; |=|\; |\; |\mathrm{1,02}|\; |\; |>0.05\end{array}$$

, $$V_{S{O}_2}$$

, коэффициентов уравнений (таблица 2) относительно неизвестных расходов кислорода и топливного газа, сочетание которых при заданных входных условиях обеспечит эксплуатацию установки в режиме, близком к оптимальному. В результате определяют требуемые расходы кислорода - 6424 нм³/ч и природного газа - 7630 нм³/ч.In this case, calculations are carried out in accordance with the algorithm described above. The calculations consist in the joint solution of the system of equations (1) with known parameter values $$N_{{}_{V_2}}$$

, $$V_{S{O}_2}$$

, coefficients of equations (table 2) with respect to unknown oxygen and fuel gas flows, the combination of which under given input conditions will ensure operation of the installation in a mode close to optimal. As a result, the required oxygen consumption is determined - 6424 nm ³ / h and natural gas - 7630 nm ³ / h.

Together with the flue gas, 31000 × 0.115 = 3565 nm ³ / h of oxygen and 2300x0.21 = 483 nm ³ / h of air enter the furnace of the thermal reactor. Total 4048 nm ³ / h of oxygen. Thus, in addition to the furnace of a thermal reactor, it is necessary to supply (6424-4048) /0.955 = 2488 nm ³ / h of technical oxygen with a basic substance content of 95.5 mol.%.

After establishing the flow rates of oxygen and natural gas in accordance with the found values, at a constant flow rate and composition of the processed flue gas in the steady state, the temperature in the thermal reactor will be 1354 ° C (adiabatic temperature), and the equilibrium concentrations of sulfur-containing components of the flue gas are as follows, mol.% : H ₂ S -1.73; SO ₂ - 1.05; COS - 0.38, which corresponds to a value of R = 0.045 mol.%.

$$\{\begin{array}{l}|\; |\; |T-1350|\; |\; |=|\; |\; |1354-1350|\; |\; |=\mathrm{four}\le 5\\ |\; |\; |R|\; |\; |=|\; |\; |\mathrm{0,045}|\; |\; |\le 0.05\end{array}$$

Correction of oxygen and natural gas consumption for the installation led to the operation of the installation in a near optimal mode.

Thus, the present invention ensures the achievement of both optimal temperature in a thermal reactor and an optimal ratio of reactive sulfur-containing components.

At the same time, for processing this flow rate and flue gas composition, the minimum consumption of fuel gas and technical oxygen is ensured, the maximum possible sulfur yield, minimum sulfur dioxide emissions are achieved, and the risk of producing substandard sulfur is minimized.

Claims (1)

The method of controlling the recovery process of sulfur dioxide flue gases containing SO ₂ , O ₂ and N ₂ , natural gas in the presence of additional oxygen, including the processing of flue gases to produce sulfur in the thermal and at least one catalytic stages, by controlling the temperature in the thermal reactor by changing the flow rates of oxygen and natural gas, as well as the composition of the tail gas at the outlet of the catalytic stage, in which the flow rate and concentration of SO ₂ in the flue gas are measured and the volumetric flow rate of SO _{2 is} determined, characterized in that the flow rate of natural gas and the total flow rate of oxygen to the thermal stage are controlled based on a pre-established empirical functional relationship between the concentrations of the tail gas components, the flow rates of the flue gas components and the temperature in the thermal reactor chamber, for which the current temperature value in the thermal chamber is measured stage, determine the volumetric flow rate O ₂ and N ₂ in the flue gas and the concentration of H ₂ S, COS and SO ₂ in the tail gas and calculate correction factors on the basis of SRI are simultaneously corrected gas flow rate and oxygen flow rate in the thermal stage, the oxygen consumption is determined as the difference between the calculated total oxygen flow rate and the flow rate of oxygen which is supplied with the flue gas.

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