RU2111429C1 - Device for check of completeness of fuel burning and decarburization - Google Patents

Abstract

FIELD: ferrous metallurgy; check of $$$ ratio in steel-making and heat treatment. SUBSTANCE: device is additionally provided with three electrolytic elements of different diameters inserted into other and located inside first electrolytic element forming laminated structure; electrodes made from molybdenum wire are mounted between electrolytic elements; outputs of electrodes are connected to measuring circuit. EFFECT: independence of accuracy of measuring temperature on change of relationship of components in hot gases. 2 dwg

Description

The invention relates to ferrous metallurgy and can be used, in particular, to control the completeness of fuel combustion by the ratio of CO / CO ₂ in steel production and heat treatment.

 A device for monitoring the gas phase of an open-hearth furnace, containing a tubular electrolytic element of zirconium oxide with platinum electrodes as current collectors, a platinum rhodium thermocouple, porcelain and glass tubes with a bronze cap (The use of solid electrolytes in ferrous metallurgy, Metallurgy, M., 1989, p. 52).

The disadvantage of this device is that it is made with indirect heating, the responsible elements of the tubular sensor are noble metals: platinum, rhodium, the mass of which is 0.02 g. In addition, the sensor design involves the forced supply of the analyzed gas inside the tubular element using a pump, which requires additional purification of the gas from mechanical impurities, while the gas temperature should not exceed more than 60 ^o C. From the method of implementation of the current collector electrodes on the external and internal The characteristics of the electrolytic cell depend on the reliability of the measurement results. The device in difficult operating conditions and increased requirements for measurement accuracy cannot be used, because it cannot provide the required reliability and accuracy. This circumstance limits the scope of use of the device.

 The closest technical solution is a device for measuring the gas phase in the melting mode in an open-hearth furnace (auth. St. USSR 4750282. "A device for monitoring the melting mode of an open-hearth furnace. VP Zolotov, V. I. Syrov, A. G. Fokhtin et al. Containing a sensor made of solid electrolytic ceramics, collet clamp, molybdenum rod measuring circuit, shaped flange, photocells placed in two channels of the collet clamp housing.

 The disadvantage of this device is that the temperature measurement of hot gases is carried out using photocells, the accuracy of which depends on the degree of transparency of the atmosphere in the furnace. The opacity of the atmosphere of hot gases is due to the combustion mode, especially when using gas-oil burners operating on solid fuel. Frequent slag filling of holes in the clamp eliminates the assessment of the actual temperature of hot gases. The error of temperature measurement in such cases leads to an incorrect choice of the flow rate of the introduced air, to a malfunction in the automatic control system of the combustion mode and, consequently, to a mismatch of the thermal regime with technological requirements.

 The basis of the invention is the creation of a device with structural elements that would ensure independence of the accuracy of temperature measurement from changes in the ratio of components of components in hot gases.

 The problem is solved in that the device containing the solid electrolytic cell and the measuring circuit, according to the invention, is additionally equipped with three electrolytic cells of different diameters, mounted one inside the other and placed inside the first electrolytic cell, forming a layered structure, and molybdenum wire electrodes are installed between the cells, whose outputs are connected to the measuring circuit.

 In FIG. 1 shows a block diagram of the design of the device, and in FIG. Figure 2 shows the graphs obtained from practical measurements in an open-hearth furnace with a capacity of 130 tons.

The device is made of four caps (electrolytic cells) of different diameters of the same length of 60-100 mm, closed on one side and installed one on the other. Before assembly, the outer surface of each of the caps 1-4 was coated with a paste of zirconium oxide ZrO ₂ and chlorovinyl alcohol, prepared in a 4: 1 ratio, and then subjected to drying at a temperature of 200-220 ^o C for 4-5 hours, after which in caps 2 ^° C4, a longitudinal recess was made in the coating along its entire length and a molybdenum wire 0.3-0.35 mm in diameter and 200-250 mm in length was used as electrodes 5-8 in the recess. The electrode 8 was placed inside the element 4, the volume of which was pre-filled with graphite powder, then the assembly of caps 1-4 together with the electrodes on the open side was covered with a paste prepared from zirconium oxide and silicate glue in a ratio of 3: 1 and placed in a thermal furnace for drying a temperature of 850-900 ^o C during the day. After drying, the assembly of caps 1-4 was connected to the fireclay tube 9 using an alumina paste and silicate glue, the length of the tube 9 was 600 mm, the inner diameter was 12 mm, and it was dried at a temperature of 600-650 ^o C. The electrodes 5-8 were connected with flexible wires 10-13, insulated between each other by a tube 14-17 of ceramic with an outer diameter of 3-4 mm and an inner diameter of about 1 mm. Each wire 10-13 was connected by soldering with single-pole plugs 18-21. The end face of the tube 9 and the single-pole plugs 18-21 were coated with a paste of aluminum oxide and silicate glue, followed by drying at a temperature of 600-650 ^o C, and the plugs 18-21 should be about 18-20 mm from the end of the tube 9. Unipolar plugs 18-21 through voltage dividers 22 and 23 were connected to the inputs of secondary devices 24. 25 type KSP-3. The division coefficient for the divider 24 is 1:40, for the divider 25 1:10, the divider is made of resistors of the type MLT-0.25, with R1 = 1 kOhm, R2 = 41 kOhm for the divider 24 and R3 = 1 kOhm, R5 = 10 kOhm for the divider 25.

 The device operates as follows.

,
или в удобной для вычисления форме при контролируемых параметрах: температура на электродах 6, 7 и парциальное давление на электродах 5,8

,
где
F - число Фарадея, 96580 Кл/моля;
R - газовая постоянная, 8,31441 Дж/(моль•К);
T - температура горячих газов, ^oC;
P_x', P_x'' - парциальное давление газовой составляющей в контролируемой и сравниваемой средах, мс/м•с²;
E - ЭДС, мВ
Формирование сигналов на электродах 5,8 и 6,7 происходит следующим образом: по мере разогрева колпачков 1^oC4 концентрация термически активируемых точечных дефектов в структуре окислов колпачков сборки 1^oC4 возрастает, вместе с этим увеличивается их подвижность которая обуславливает электрическую проводимость. Чувствительность твердой электролитической керамики (1-4) к кислороду и другим газовым составляющим, в частности CO, заключается в том, что существует равновесие между их парциальным давлением над поверхностью окисла и таковыми в газовой фазе твердого электролита, так при меньшей величине давления составляющей в газовой фазе имеет место переход газа из окисла в окружающую среду, при большем давлении одной из составляющей в газовой среде, имеет место обратный процесс - переход из газовой среды в окисел. Заполнение внутреннего объема колпачка 4 сохраняет свое значение в течение длительного времени и может быть выбрано в качестве сравнивающего относительно потенциала, наводимого на внутренней поверхности колпачка 1. Таким образом, на внутренней поверхности колпачка 3, внутренний объем которого заполнен графитом, возникает электрический потенциал, пропорциональный парциальному давлению газа, образующегося в результате реакции углерода и кислорода, выделяющегося из окисла. Кислород из окисла в значительной мере зависит от температуры разогрева сборки 1^oC4, парциальное давление внутри колпачка 4 составляет менее 1•10^-13 МПа, что значительно ниже, чем парциальное давление составляющей в атмосфере над сборкой 1-4, вследствие этого электрические потенциалы, наводимые в структурах колпачков 1^oC4 будут отличны друг от друга по величине, а разность между ними обусловливает появление ЭДС как по температуре, так и по величине соотношения lgP_x'/P_x'', которые в полной мере характеризуют содержание контролируемой составляющей в атмосфере газов топочного пространства. Сигнал, формирующийся на электродах 6, 7 электролитов (колпачков) 2, 3 отражает изменение температуры разогрева, а сигнал на электродах 5, 8 отражает изменение парциального давления контролируемой газовой составляющей. Таким образом, наличие 4-х колпачков 1^oC4, образующих слоистую структуру из однородных твердых электролитов, можно использовать в качестве индикатора содержания кислородосодержащих составляющих в топочном пространстве теплового агрегата при температурах, соответствующих режиму горения топлива. Электроды 5, 8 и 6, 7 защищены от непосредственного контакта с газовой фазой, поэтому не подвергаются интенсивному разрушению, что и обусловливает длительную эксплуатацию индикатора при температурах горячих газов, составляющих не менее 1660^oC. Заполнение внутреннего объема колпачка 4 графитом обеспечивает стабильность парциального давления газа на низком уровне, сохраняя свое значение на длительное время, и служит в качестве сравнивающего относительно потенциала, наводимого на внутренней поверхности колпачка 1. ЭДС, появляющаяся на электродах 6, 7 обусловлена только электрической проводимостью структуры твердых электродов, поскольку они полностью изолированы от контакта с газовыми фазами. Тарирование индикатора (сборки колпачков 1-4) по кислороду или по окиси углерода и др. газовым составляющим позволяет получить четкие зависимости содержания газов и составляющей в контролируемой среде в зависимости от температуры горячих газов, что является наиболее объективным отображением режима горения.The assembly of caps 1 ^o C4 is placed in the refractory masonry of the furnace chamber (compartment) of the heat unit, so that its end face protrudes from the inner wall of the masonry at a distance of 100-150 mm, and then the devices 24, 25 are turned on. As the caps are heated, 1 ^o C4 to the temperature of the hot gases at the electrodes 5 ^o C8 there are signals that enter the inputs of the devices 24, 25 through the dividers 22, 23. In this case, the signal appearing on the electrodes 5, 8 reflects the thermal process inside the unit and characterizes the completeness of fuel combustion, and the signal on the electrodes 6, 7 synchronously with p The first signal reflects the temperature of hot gases, i.e. temperature corresponding to the current mode of fuel combustion. The signal on the completeness of combustion is generated on the basis of the difference in the partial pressures of the gas components, in particular CO, in the controlled environment of the furnace compartment and in the gas phase inside the cap 4. The temperature of the flue gases is controlled using caps 2, 3, which do not have direct contact with the gas medium , the resulting signal on the electrodes 6, 7 reflects the change in the temperature of the hot gases in accordance with the changing electrical conductivity of the structure of the caps 2, 3. Simultaneous control of the signals on the electrodes 5, 8 and 6, 7 allows you to most fully express the current state of the combustion mode in accordance with the well-known Nernst equation

,
or in a form convenient for calculation with controlled parameters: temperature at electrodes 6, 7 and partial pressure at electrodes 5.8

,
Where
F is the Faraday number, 96580 C / mol;
R is the gas constant, 8.31441 J / (mol • K);
T is the temperature of the hot gases, ^o C;
P _{x '} , P _x'' is the partial pressure of the gas component in the controlled and compared environments, ms / m • s ² ;
E - EMF, mV
The formation of signals at the electrodes 5.8 and 6.7 occurs as follows: as the caps 1 ^° C are heated, the concentration of thermally activated point defects in the oxide structure of the caps of the 1 ^° C4 assembly increases, and their mobility increases, which causes electrical conductivity. The sensitivity of solid electrolytic ceramics (1-4) to oxygen and other gas components, in particular CO, lies in the fact that there is an equilibrium between their partial pressure above the oxide surface and those in the gas phase of the solid electrolyte, so at a lower pressure component in the gas phase, there is a transition of the gas from the oxide to the environment, at a higher pressure of one of the components in the gaseous medium, the reverse process takes place - the transition from the gaseous medium to the oxide. Filling the internal volume of the cap 4 retains its value for a long time and can be chosen as a comparison with respect to the potential induced on the inner surface of the cap 1. Thus, on the inner surface of the cap 3, the inner volume of which is filled with graphite, an electric potential proportional to the partial the pressure of the gas generated by the reaction of carbon and oxygen released from the oxide. Oxygen from the oxide largely depends on the heating temperature of the assembly 1 ^o C4, the partial pressure inside the cap 4 is less than 1 • 10 ^-13 MPa, which is much lower than the partial pressure of the component in the atmosphere above the assembly 1-4, due to this electric potentials, induced in the structures of caps 1 ^o C4 will be different from each other in magnitude, and the difference between them determines the appearance of EMF both in temperature and in the ratio logP _{x '} / P _x'' , which fully characterize the content of the controlled component her in the atmosphere of the gases of the furnace space. The signal generated at electrodes 6, 7 of electrolytes (caps) 2, 3 reflects a change in the heating temperature, and the signal at electrodes 5, 8 reflects a change in the partial pressure of the monitored gas component. Thus, the presence of 4 caps 1 ^o C4, forming a layered structure of homogeneous solid electrolytes, can be used as an indicator of the content of oxygen-containing components in the furnace space of a thermal unit at temperatures corresponding to the fuel combustion mode. The electrodes 5, 8 and 6, 7 are protected from direct contact with the gas phase, therefore, they are not subjected to intensive destruction, which leads to long-term operation of the indicator at hot gas temperatures of at least 1660 ^o C. Filling the inner volume of the cap 4 with graphite ensures partial pressure stability gas at a low level, retaining its value for a long time, and serves as a comparison with respect to the potential induced on the inner surface of cap 1. EMF that appears on the electric rows 6, 7 due only to the electric conductivity of solid electrode structure, since they are completely isolated from contact with the gas phase. Calibration of the indicator (assembly of caps 1–4) with respect to oxygen or carbon monoxide and other gas components allows us to obtain clear dependences of the gas content and component in a controlled environment depending on the temperature of hot gases, which is the most objective display of the combustion mode.

 An example of a specific implementation.

The assembly of caps 1-4 was installed in the nozzle channel of the open-hearth furnace. The oxidation potential and temperature of the exhaust gases were measured continuously from the beginning of loading to the release of metal from the furnace. In the course of the bar, the flow rate of fan air was regulated in accordance with the current value of the oxidizing potential and temperature of hot gases. In FIG. 2 graphically presents one of the steel melts of the grade st. 45x. At the beginning of furnace loading, the value of the EMF and temperature according to the readings of devices 24, 25 is 237 mb and 1460 ^o C, respectively, which corresponded to 0.285 sb% in the CO content in the exhaust gases, and the fan air flow rate was 15 • 10 ³ m ³ / h . During melting, a decrease in the EMF to 124 mV and an increase in temperature to 1600 ^o C were observed, the flow rate of fan air was increased to (19-21) • 10 ³ m ³ / h. On the curve of changes in the oxidative potential of the exhaust gases, the beginning of boiling of the melt was noted by an additional increase in the EMF. According to the current records on the diagrams of devices 24, 25, we observed changes in temperature and oxidative potential of the gas phase and carried out technological measures for introducing deoxidizers and additives with simultaneous regulation of the flow of fan air in the range (18-27) • 10 ³ m ³ / h. in accordance with the intensity of boiling of the melt. Before the release of the melt from the furnace, the EMF of the oxygen potential was 67 mV, and the temperature was 1690 ^o C, the CO content in the exhaust gases was 0.05 93 vol.%. As a result of monitoring the progress of the smelting using the proposed device, it was possible to reduce the melting time by 35 minutes, fuel economy was 9.2%.

 The proposed device can also be used to control the combustion mode, maintaining the ratio of fuel-air consumption in accordance with the stoichiometry of the process.

Using the proposed device in comparison with the prototype allows you to get the following technical and economic advantages:
- 100% eliminate the use of platinum for the manufacture of current collector electrodes;
- increase the efficiency of maintaining the combustion mode in the optimal mode, while saving fuel up to 9.2%;
- eliminate 100% use of thermocouples.

Claims (1)

 A device for monitoring the completeness of fuel combustion and decarburization, containing a solid electrolytic cell made in the form of a cap, and a measuring circuit, characterized in that it is additionally equipped with three solid electrolytic cells made in the form of caps of various diameters, mounted one inside the other and placed inside the first solid electrolytic cell with the formation of a layered structure, electrodes made of molybdenum wire are installed between solid electrolytic cells, which Some are connected to the measuring circuit.

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