RU2081893C1 - Method for controlling process of high-temperature heating of heavy oil residues in tube furnace - Google Patents

Abstract

FIELD: petroleum processing. SUBSTANCE: fuel is fed in amount in accordance with following inequalities:

where K(T,τ), K $\genfrac{}{}{0ex}{}{\text{*}}{\text{L}}$ , K $\genfrac{}{}{0ex}{}{\text{*}}{\text{u}}$ , respectively, are current, permissible lower and permissible upper limiting values of coefficients of heat transfer from reaction mixture to inner surface of coil pipeline; T_R(τ), T $\genfrac{}{}{0ex}{}{\text{*}}{\text{R,l}}$ , T $\genfrac{}{}{0ex}{}{\text{*}}{\text{R,u}}$ , respectively, are current, permissible, lower and permissible upper limiting values of reaction mixture temperature; and τ is time. EFFECT: optimized operation conditions. 2 dwg

Description

 The invention relates to processes in the refining, petrochemical, oil and gas, chemical and other industries using tube furnaces.

A known method of controlling the process in a tubular furnace and adjusting its operation mode, based on measuring the temperature or composition of the finished product at the outlet of the furnace, which is used to judge the characteristics of the process and introduce the appropriate adjustment of the furnace operation mode by affecting the fuel supply to the furnace [1]
There is also a method of controlling a process in a similar object, including stabilization of the pyrolysis temperature at the entrance to the radiation zone of the furnace by changing the amount of raw materials supplied to the end of the convection zone [2]
There is also known a method of controlling the thermal regime of a tubular pyrolysis furnace containing a pyrolysis coil, burners, pipelines for supplying fuel to them, a common pipeline, and pipelines for supplying fuel to the burners located in the initial section of the pyrolysis coil, and the common pipeline is equipped with adjustable valves, including temperature measurement and the effect on the total fuel consumption, the effect on the fuel supply to the burners at the initial level of the pyrolysis coil in such a way that, when the pressure in the common pipeline decreases, reduce the fuel supply sequentially, starting from the lower burner, and with increasing pressure in the reverse sequence [3]
A known method of controlling the thermal regime of the process of high-temperature heating of heavy oil residues in a tubular furnace, comprising measuring the temperature of the reaction mixture at the outlet of the furnace and at the point preceding the zone of intense carboid formation, and affecting fuel consumption by the magnitude of the difference in measured temperatures with a constant ratio of raw materials and turbulator [4]
The known method does not allow direct determination of the totality of the process characteristics in a tubular furnace, but only measures the temperature of the reaction mixture in the controlled sections of the pipeline and their ratio as one of the characteristics of the process (the known method involves determining the temperature difference measured at the outlet of the furnace and the control point preceding the zone of intense carboid formation), determine the moment of the onset of coke formation.

 However, the temperature is only a consequence of external thermal influences and the thermophysical characteristics of the reaction mixture, and a change in the temperature difference can be achieved as a result of a change in the intensity of thermal effects from the heating elements of the furnace or the products of the burner washing the pipeline to separate sections of the pipeline. In addition, it is impossible to determine exactly how the carboid formation zone will develop in certain specific operating conditions of the furnace. It is possible to tentatively distinguish only the proposed zone of possible intense coke formation, before which measurement at the control point is carried out. In this case, coke deposition is also possible on the thermocouple cover installed at the control point, which reduces the accuracy of the known method.

 Therefore, the known method makes it possible only to roughly estimate the beginning of the process of intense coke formation, does not allow determining the distribution of coke deposition intensity over sections of the pipeline during pyrolysis, and identifying areas with possible local overheating of the walls. Therefore, the known method does not include the possibility of emergency burnout of coked tubes, does not sufficiently effectively increase the overhaul time of the furnace.

где K(T,τ), K $\genfrac{}{}{0ex}{}{\text{*}}{\text{н}}$ , K $\genfrac{}{}{0ex}{}{\text{*}}{\text{в}}$ соответственно текущее, допустимые нижний и верхние пределы значения коэффициента теплопередачи от реакционной смеси к внутренней поверхности трубопровода;
T_p(τ), T $\genfrac{}{}{0ex}{}{\text{*}}{\text{р,н}}$ , T $\genfrac{}{}{0ex}{}{\text{*}}{\text{р,в}}$ соответственно текущее, допустимые нижний и верхний пределы значения температуры реакционной смеси;
τ время.The invention allows to eliminate the disadvantages of the closest analogue [4] due to the fact that in the method of controlling the process of high-temperature heating of heavy oil residues in a tubular furnace, which includes measuring the temperature of the reaction mixture at a point preceding the zone of intense carboid formation, and the effect on fuel consumption with a constant ratio of raw materials and turbulator, determine the heat transfer coefficient from the reaction mixture to the inner surface of the pipeline at a point preceding the zone of intense boidoobrazovaniya, and the corresponding temperature of the reaction mixture, and the influence on the fuel consumption based on the condition of inequalities provide

where K (T, τ), K $\genfrac{}{}{0ex}{}{\text{*}}{\text{n}}$ , K $\genfrac{}{}{0ex}{}{\text{*}}{\text{in}}$ accordingly, the current, permissible lower and upper limits of the coefficient of heat transfer from the reaction mixture to the inner surface of the pipeline;
T _p (τ), T $\genfrac{}{}{0ex}{}{\text{*}}{\text{p, n}}$ , T $\genfrac{}{}{0ex}{}{\text{*}}{\text{p in}}$ accordingly, the current, permissible lower and upper limits of the temperature of the reaction mixture;
τ time.

 Figure 1 presents a control system for the process of high-temperature heating of oil residues in a tubular furnace that implements the proposed method; figure 2 placement of a device for determining the coefficient of heat transfer from the reaction mixture to the inner surface of the pipeline and the temperature of the reaction mixture in the pipeline coil.

 Figure 1 presents a control system for the process of high-temperature heating of heavy oil residues in a tubular furnace, containing a tubular coil 1, pipelines for supplying raw materials 2, turbulator 3 and fuel 4 to the burners, flow controllers of raw materials 5 and turbulator 6, device 7 for determining the heat transfer coefficient from the reaction mixture 8 to the inner surface and block 9 calculating the amount of correction of fuel consumption.

Figure 2 shows the placement of the device for determining the coefficient of heat transfer from the reaction mixture to the inner surface of the pipeline and the temperature of the reaction mixture containing heat-supplying elements 10 and 11, temperature sensors 12, figure 2 also shows the direction of heat fluxes q ₁ and q ₂ , temperature teplopodvodyaschih surface elements T _1N, T _1vn, T _2N and T _2vn.

 The heat flux from the burners (not shown in FIG. 1) is transferred to the outer surface of the pipeline 1, then it is distributed by heat conduction to the heat-conducting elements 10 and 11, and then the reaction mixture 8 is transferred either directly or through a layer of deposits on the inner surface of the pipeline 1.

In the case, for example, when heat exchange between the inner surface of pipeline 1 and reaction mixture 8 is determined by convective and conductive (through a layer of coke formation deposits in the pipeline), the temperature T _p (τ) and thermal conductivity coefficient K (T, τ) from the reaction mixture are unknown and unknown 8 to the inner surface of the pipeline 1, and between the outer surface of the latter and the heated burners of the atmospheric furnace there is convective heat transfer, it is possible to limit ourselves to two heat-conducting elements.

Since the thermal conductivity coefficients of the heat-conducting elements 10 and 11 are different, the heat fluxes q ₁ (τ) and q ₂ (τ) removed from them will also be different (in the example of implementation, the heat-conducting elements are made of niobium, thermocouples XA are thermocouples) and are also different at the installation sites heat-conducting elements 10 and 11 temperature T _{1 VN} (τ), T _{2 VN} (τ) of the inner surface of the pipeline 1.

где T_p(τ) температура реакционной смеси,
F площадь поперечного сечения теплопроводящих элементов,
τ время,
находят коэффициент теплопроводности от реакционной смеси 8 к внутренней поверхности трубопровода 1, характеризующий толщину слоя коксообразования на стенке трубопровода 1:

и температуру реакционной смеси 8

Значения тепловых потоков q₁(τ) и q₂(τ) находят, решая обратную задачу теплопроводности в следующей постановке:

где ρ_i, C_i(T_i), λ_i(T_i) плотность, теплоемкость и коэффициент теплопроводящего элемента;
T_i температура;
τ время;
x координата точки в теплопроводящем элементе;
x_j координата точки измерения температуры в теплопроводящем элементе;
i=1,2 номер теплопроводящего элемента;
j=1,2 количество точек измерения температуры.Solving equations together

where T _p (τ) is the temperature of the reaction mixture,
F the cross-sectional area of the heat-conducting elements,
τ time
find the coefficient of thermal conductivity from the reaction mixture 8 to the inner surface of the pipeline 1, characterizing the thickness of the coke formation layer on the wall of the pipeline 1:

and the temperature of the reaction mixture 8

The values of heat fluxes q ₁ (τ) and q ₂ (τ) are found by solving the inverse heat conduction problem in the following formulation:

where ρ _i , C _i (T _i ), λ _i (T _i ) density, heat capacity and coefficient of the heat-conducting element;
T _i temperature;
τ time;
x coordinate of the point in the heat-conducting element;
x _j coordinate of the temperature measuring point in the heat-conducting element;
i = 1.2 is the number of the heat-conducting element;
j = 1.2 the number of temperature measurement points.

The temperatures T _{1, vn} and T _{2, vn are} found by direct measurement.

Sources of information
1. Auto USSR N 181624, class C 10G 9/20, 1966.

 2. Auto USSR N 292366, class B 01C 3/00, 1968.

 3. Auto USSR N 446536, class C 10G 9/20, 1972.

 4. Auto USSR N 430650, class C 10G 9/20, 1973.

Claims (1)

A method of controlling the process of high-temperature heating of heavy oil residues in a tubular furnace, including measuring the temperature of the reaction mixture at a point preceding the zone of intense carbide formation, and affecting fuel consumption with a constant ratio of raw materials and turbulator consumption, characterized in that they determine the heat transfer coefficient from the reaction mixture to internal the surface of the pipeline at the point preceding the zone of intense carbide formation, and the corresponding reaction temperature B, and the impact on fuel consumption on the basis of conditions to ensure the inequalities
K $\genfrac{}{}{0ex}{}{\text{*}}{\text{n}}$ ≅ K (T, τ) ≅ K $\genfrac{}{}{0ex}{}{\text{*}}{\text{in}}$ ,
T $\genfrac{}{}{0ex}{}{\text{*}}{\text{p, n}}$ ≅ T _p (τ) ≅ T $\genfrac{}{}{0ex}{}{\text{*}}{\text{p in}}$ ,
where K (T, τ), K $\genfrac{}{}{0ex}{}{\text{*}}{\text{n}}$ , K $\genfrac{}{}{0ex}{}{\text{*}}{\text{in}}$ accordingly, the current, permissible lower and upper limits of the value of the heat transfer coefficient from the reaction mixture to the inner surface of the pipeline;
T _p (τ), T $\genfrac{}{}{0ex}{}{\text{*}}{\text{p, n}}$ , T $\genfrac{}{}{0ex}{}{\text{*}}{\text{p in}}$ accordingly, the current, permissible lower and upper limits of the temperature of the reaction mixture;
τ time.

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