SU1708887A1

SU1708887A1 - Method of measuring gas temperature in furnace

Info

Publication number: SU1708887A1
Application number: SU884489486A
Authority: SU
Inventors: Петр Леонидович Шмачков; Михаил Леонидович Хазнаферов; Елизавета Васильевна Змазнева; Владимир Николаевич Смоляной; Анатолий Иванович Киселев
Original assignee: Мариупольский металлургический институт
Priority date: 1988-10-06
Filing date: 1988-10-06
Publication date: 1992-01-30

Abstract

Изобретение относитс к теплотехнике, преимущественно »? нагревуизделий в печах, а именно к контро- . лю температуры в печах. Цель изобретени - повышение точности измерени за счет оптимального выбора места размещени термопары. Размещение термопары в канале на'участке, заэкранированном от излучени , расположенном параллельно внутренней по- вехности стенки печи на рассто нии в пределах The invention relates to heat engineering, mainly "? heating products in furnaces, namely to control. Liu temperature in furnaces. The purpose of the invention is to improve the measurement accuracy due to the optimal choice of the location of the thermocouple. Placement of the thermocouple in the channel on the section shielded from the radiation, located parallel to the internal surface of the furnace wall at a distance within

Description

Изобретение относитс к теплотехнике , преимущественно к нагреву изделий в печах, а именно к контролю температуры в печах.The invention relates to heat engineering, mainly to heating products in furnaces, namely, to control the temperature in furnaces.

Цель изобретени - повышение ТОЧНОСТИ измерени -за счет- оптимального выбора места размещени термопары .The purpose of the invention is to increase the ACCURACY of the measurement - due to the optimal choice of the location of the thermocouple.

На фиг.1 дана схема размещени термопар в Г-образном канале на участке, параллельном внутренней поверхности стенки рециркул ционной камерной печи дл обработки крупных слитков; на фиг. 2 - схема попадани лучистого потока на термопару при размещении ее в канале отход щих дымовых газов на недостаточном рассто нии от Г-образного поворота.Fig. 1 shows the layout of thermocouples in the L-shaped channel in a section parallel to the inner surface of the wall of the recirculation chamber furnace for the treatment of large ingots; in fig. 2 is a diagram of the radiant flux entering the thermocouple when it is placed in the flue gas channel at an insufficient distance from the L-shaped turn.

Схема (фиг.1) содержит смеситель 1 ин«екционного устройства, горелку 2, термопары 3-6, рециркул ционный The circuit (Fig. 1) contains a mixer 1 of the injection device, a burner 2, thermocouples 3-6, recirculation

00 СХ) канал 7, кладку 8 печи, рабочее пространство 9 печи, нагреваемые 00 издели (слитки) 10, жаропрочные 00 СХ) channel 7, laying 8 furnaces, working space 9 furnaces, heated products 00 (ingots) 10, heat resistant

подставки 11, выкатной под 12. В кладке печи имеютс рециркул ционные Каналы 7, через которые газ отбираетс ИЗ рабочего пространства и поаетс в смесители инжекционных уст ройств.supports 11, withdrawable under 12. In the laying of the furnace, there are recirculation channels 7, through which gas is withdrawn from the working space and fed into the mixers of the injection devices.

На фиг.2 прин ты следующие дополнительные обозначени : 13 - изгГучающа поверхность, наход ща с в рабочем пространстве печи, 1 - луч.In Fig. 2, the following additional designations are adopted: 13 is the extinguishing surface located in the working space of the furnace, 1 is the beam.

Пр мое излучение от излучающей поверхности 13, наход щейс в рабочем простронстое печи, попадает на участок стенки канала, наход щийс сразу же за первым Г-образным поворото и частично поглощаетс , а частично рассеиваетс . ТТоэтому указанный ума ток в свою очередь служит и сточни ком излучени , которое попадает на чувствительный элемент 5. В св зи с тем, что угловой коэффициент излучени в данном случае очень мал, таюхе очень Мала отражательна спо-. собность шероховатых стенок канала 7 уже на определенном рассто нии от поворота вли ние излучени становит с посто нно малым, так что оно пра тически незаметно ка фоне конвектив ной теплоотдачи от движущегос потока газа к стенкам канала. При проведений экспериментов в камерной печи в процессе нагрева ус тановлена зависимость св зывающа параметры потока газа с MectoM оптимального размещени чувс гвительнбго элемента - термопары. Минимальное рассто ние за первым Г-образным ПОВОРОТОМ, на котором ре коменду етс устанавливать термопа| У составл ет 1.5ф, расход га за, м/с/ средн скорость газового потока в Канале, . Если разместить чувствительный элемент за первым поворотом канала на рассто нии, меньшем Lfnnu , то вли ние лучистых потоков из рабочей камеры про вл етс дак(е на фоне кон вективной теЛлоотдачи от газа к сте кам канала. Л так как ввести постЬ ную поправку, учитывающую это вли ние , практически невозможно (расположение изделий в печи, их темпе ратура, степень черноты, длина факела посто нно Измен ютс ), то нег вЬзможно также обеспечить точность контрол температуры газа, требуемую технологией. . Максимальное рассто ние за первы Г-образным ПОВОРОТОМ определено в виде следующей зависимости: и Oiff Lte 3,5() . i Если чувствительный .элемент термометра установлен на большем рассто нии от поворота , то изме ренна температура обличаетс от средней температуры Газового потока. Следовательно, невозможно обеспечить точность контрол температуры газа, требуёму технологией нагрева, Таким образьм, размещение термопары на рассто нии 1. .5(2) за первым поворотом канала позвол ет избех ать погрешностей, выносимых лучистыми потоками из рабочего пространства и температурным расслоением потока газа. Сущность предлагаемого способа заключаетс в следующем. В стенке печи (фиг.2) выполн ют канал 7 имеющий по крайней мере один поворот, и отбирают через этот канал газы из рабочего пространства печи. В частности, указанный канал может быть рециркул ционным. Экспериментально или расчетным путем определ ют расход газа U и среднюю скорость V потока а канале . Расчетным путем наход т значени : 1-., з.зфЕсли параметры notoKa-. измен - . ютс , то наход т максимальное зна чение нижнего предела (l.|J ) и минимальное значение верхнего предела (Ь ). Устанавливают чув- ствительный элемент термометра в канал за первым 6т рабочего пространства поворота на рассто нии L от этого поворота, причем iLu, и производ т измерение температуры . П р им,ер. Используют рециркул ционную камерную печь с садкой ZbO т (фиг.1), предназначенную дл крупных слитков электрошлакового переплава. Каналы имеют Г-образную форму. Дл реализации предлагае «эго -способа проведено экспериментальное исследование газового потока в рециркул ционном канале на участке, параллельном внутренней поверхности стенки печи. -В таблице представлены параметры газового потока в рециркул ционном канале при различных режимах работы печи. На основании данных таблицы опре л ют минимальное и максимальное зна ичО,5 ченил величины (-) п ,5и . П 71ft (ii (|W- 0.218; () 0,232. Определ ют границы участка, на к ром возможно измерение температуры /соответствии с предлагаемым способо , ижн граница: b5(y)«4tu 0, м Верхн граница: 0,763 м. ()щиц Таким образом, чтобы обеспечить сокую точность измерени температур газа в данном случае измерейие долж но производитьс на участке, паралЛ1вльном внутренней поверхности стен ки печи за поворотом канала на рассто нии от него не менее OjStO м, н не более 0,7бЗ м, счита .от рабочег пространства. В рециркул ционном канале за пов ротои на рассто нии 0,450 м, счита от рабочего пространства, установле на термопара. , . Дл сравнени производ т измер ние температуры известным способом . Дл него устанавливают термопару во входном сечении канала Одно временно производ т измерение термопарами , установленными за пределами обусловленных предлагаемым способом границ, дл чего в рециркул ционном канале на рассто нии соответственно 100 и 1000 мм за первым от раСЗочего пространства првор1отом установлены i термопары 3 и 5.1 Измерени провод т ка)|шый час в течение 18 ч нагрева. При применении предлагаемого способа , а также известного, в котором термопару устанавлввают в сквозном проходе дл отход щих газов, выполненном в стенке печи, получёнь следующие результаты. В качестве контрольной используют отсасывающую термопару , установленную в канале Относительна средн погрешность предлаг аемого способа,Не превыйиет 1,1%, а абсолютна погрешность соетавл ет 5,. В то же врем в известном , способе относительна средн погрешность составл ет 4,3 а абсолютна - 2l,. Дл термопар, установленных с нарушением границ, получено соответственно 3,7 и 17, (нижн граница) и Лj3 и 19,12 (верхн граница). Нарушение нижней и верхн ей границ приводит к значительному снижению точности измерени . На основе исследований, которые производили в пор дке опытно-промышленных , испытаний предлагае к го способа, разработаны новые режимные карты, обеспечивающие более точный режим нагрева при меньшем расходе инжектирующего воздуха. Работа по этим режимным картам обеспечивает снижение удельного расхода топлива на 5,9. . :-, . V Ф. о р м у л а и 3 о б р е т е н и Способ кбнтрол температуры газов ; в печи, включающий измерение температуры в выполненных в стене печи отвод щих газ израбо1чего пространства каналов, о т л и ч а ю щ и и с тем, что, с цепью повышени точности измерени , температуру измер ют в канале на участке, заэкранированном от пр мого излучени из рабочего пространства , причем измерение провод т на рассто нии (1,5.. .3,5)(U/V) от входа в канал, где U - расход гЬза, м/с; V - средн скорость газового потока, м/с.Direct radiation from the radiating surface 13, which is located in the working space of the furnace, falls on the wall section of the channel immediately behind the first L-shaped turn and is partially absorbed, and partially scattered. Therefore, the current indicated in turn also serves as the source of radiation that falls on the sensitive element 5. Since the angular coefficient of radiation in this case is very small, the tube is very small reflective. Even at a certain distance from the turn, the influence of the radiation of the rough walls of channel 7 becomes permanently small, so that it is almost imperceptible against the background of convective heat transfer from the moving gas flow to the walls of the channel. When conducting experiments in a chamber furnace in the process of heating, the dependence of the parameters of gas flow with the MectoM of the optimal placement of the thermocouple sensing element was established. The minimum distance is beyond the first L-shaped TURN, at which a thermopa | Y is 1.5f, gas flow rate, m / s / average gas flow velocity in the Channel,. If the sensitive element is placed behind the first turn of the channel at a distance less than Lfnnu, then the effect of radiant fluxes from the working chamber appears dak (against the background of convective transfer of gas from the gas to the channel stack. this effect is almost impossible (the location of the products in the furnace, their temperature, the degree of blackness, the length of the torch is constantly changing), then it is also possible to ensure the accuracy of gas temperature control required by the technology. The rotation is determined by the following relationship: and Oiff Lte 3.5 (). I If the sensitive thermometer element is set at a greater distance from the turn, then the measured temperature is different from the average temperature of the Gas stream. The required heating technology, Thus, placing the thermocouple at a distance of 1. .5 (2) behind the first turn of the channel allows us to avoid errors brought about by radiant fluxes from the working space and temperature separation of the flow ka gas. The essence of the proposed method is as follows. A channel 7 having at least one turn is made in the wall of the furnace (Fig. 2), and gases are taken through this channel from the working space of the furnace. In particular, said channel may be recycled. The gas flow rate U and the average velocity V of the flow in the channel are determined experimentally or by calculation. By calculation, they find the values: 1-., 3. 3. If the parameters are notoKa-. treason -. then the maximum value of the lower limit (l. | J) and the minimum value of the upper limit (b) are found. The sensing element of the thermometer is installed into the channel beyond the first 6 tons of the turn working space at a distance L from this turn, moreover, iLu, and the temperature is measured. For them, er. A recirculating chamber furnace with a ZbOt boil (Fig. 1) is used for large electroslag remelting ingots. The channels are L-shaped. For the implementation of the proposed ego method, an experimental study of the gas flow in the recirculation channel in the area parallel to the inner surface of the furnace wall was carried out. - The table shows the parameters of the gas flow in the recirculation channel under various operating conditions of the furnace. On the basis of the data in the table, the minimum and maximum values of the values of (-) n, 5i were determined. P 71ft (ii (| W- 0.218; () 0.232. Determine the boundaries of the section, it is possible to measure temperature / compliance with the proposed method, if the boundary is: b5 (y) "4tu 0, m Thus, in order to ensure the low accuracy of the gas temperature measurement in this case, the measurement should be carried out on the section parallel to the inner surface of the furnace wall after the channel is rotated at a distance of at least OjStO m, n .from the working space. In the recirculation channel for rotation at a distance of 0.450 m, For a comparison, a thermocouple is measured in a known manner. A thermocouple is installed in the inlet section of the channel. Thermocouples installed outside the boundaries of the proposed method are measured simultaneously, for which the recirculation channel is They are 100 and 1000 mm, respectively, and thermocouples 3 and 5.1 are installed for the first time from a wide area. Measurements are carried out at an hour for 18 h of heating. When applying the proposed method, as well as the well-known one, in which the thermocouple is installed in the through-passage for flue gases made in the furnace wall, the following results are obtained. As a control, a suction thermocouple installed in the channel is used. The relative average error of the proposed method does not exceed 1.1%, and the absolute error is 5 ,. At the same time, in the known method, the relative average error is 4.3 and the absolute error is 2l. For thermocouples installed in violation of the boundaries, 3.7 and 17, respectively, (lower limit) and Лj3 and 19.12 (upper limit) were obtained, respectively. Violation of the lower and upper bounds leads to a significant decrease in measurement accuracy. On the basis of studies that were performed in the order of pilot-industrial tests of the proposed method, new regime maps were developed that provide a more accurate heating mode with less injecting air consumption. Work on these regime cards provides a reduction in specific fuel consumption by 5.9. . : -,. V f. O rm u l a and 3 o b ete n i n Method of combusting gas temperatures; in the furnace, which includes temperature measurement in the gas exhaust ducts of the exhaust ducts made in the furnace wall, and it is measured in the channel in the area shielded from the my radiation from the working space, and the measurement is carried out at a distance (1.5 .. .3.5) (U / V) from the entrance to the channel, where U is the flow rate, m / s; V - average gas flow rate, m / s.

Claims

The invention relates to heat engineering, mainly to heating products in furnaces, 'and in particular to temperature control in furnaces. The purpose of the invention is to improve the accuracy of measurement due to the optimal choice of placement of the thermocouple. Figure 1 shows the layout of thermocouples in the L-shaped channel in a section parallel to the inner surface of the wall of the recirculation chamber furnace for processing large ingots; in FIG.

1 injection device, burner 2, thermocouples 3-6, recirculation channel 7, masonry 8 of the furnace, working space 9 of the furnace, heated products (ingots) 10, heat-resistant supports 11, withdrawable under 12. In the masonry of the furnace there are recirculation channels 7 through which gas is taken from the working space and fed into the mixers of the injection devices.

In Fig.2, the following additional designations are adopted: 13 ~ a radiating surface located in the working space of the furnace, 14 is a beam.

Direct radiation from a radiating surface 1.3, which is in operation £> and „„ 1708887

Irennoy temperature is denounced from the average temperature of the gas stream.

Therefore, it is impossible to provide>

read the accuracy of gas temperature control required by heating technology.

Thus, placing the thermocouple at a distance of 1

Ϊ7Ο8867 than the space of the furnace, falls on a section of the channel wall located immediately after the first L-shaped turn) and is partially absorbed, and partially 5 / is scattered. Therefore, this section, in turn, serves as a source of radiation, which falls on the - sensitive element 5. Due to the fact that the angular coefficient of radiation in this case is very small, and also the reflectance is very small. In fact, the rough walls of channel 7, already at a certain distance from the rotation, the effect of radiation becomes constantly small, so that it is almost imperceptible against the background of convective heat transfer from a moving gas stream to the channel walls.

When conducting experiments in a chamber furnace during heating, a relationship was established that relates the gas flow parameters to the place of optimal placement of the sensing element - thermocouples.

The minimum distance behind the first L-shaped turn, at which it is recommended to install a thermocouple, · is t 1 b _Mn =, where U is the gas flow, m '/ s;

V is the average gas flow rate in the channel.

If a sensitive element is placed behind the first bend of the channel at a distance shorter than Ld, ^{then the} effect of radiant fluxes from the working chamber is manifested even against the background of convective heat transfer from gas to the channel walls. And since it is practically impossible to introduce a permanent amendment taking into account this effect (the location of products in the furnace, their temperature, degree of blackness, and torch length are constantly changing), it is also impossible to ensure the accuracy of gas temperature control required by technology 7 / ... The maximum distance behind the first. L-shaped rotation is defined as the following relationship:

and

LD4KS ^{= 3} » ⁵ (y)«., ₅ φ '· ^β <ΪΖ 3, ₅ (ϊ) ⁴⁵ behind the first turn of the channel avoids the errors made by the radiant fluxes from the working space and the temperature stratification of the gas flow.

The essence of the proposed method is as follows.

In the wall of the furnace (figure 2) performs channel 7 _? having at least one rotation, and gases are taken through this channel from the working space of the furnace. In particular, said channel may be recirculated.

Experimentally or by calculation, determine the gas flow U and the average velocity V of the flow in the channel. By calculation, find the values:

i If the sensor is installed while the sensor is installed at a larger turn of the channel, then change 1 * 4 ⁼ 1 ”-lift 7 ^s

If the gas flow parameters change, then the maximum value of the lower limit (L * ^arc ) and the minimum value of the upper limit (L £) are found. The sensitive element of the thermometer is installed in the channel behind the first ότ of the working space of the turn At a distance L from this turn, with L ^ ^atc <L- £, and the temperature is measured.

P r and measures. Use a recirculating ⁴⁵ chamber furnace with a charge

200 tons (Fig. 1), intended for large ingots of electroslan remelting. The channels are L-shaped. To implement the proposed method, an experimental study was made of the gas flow in the recirculation channel in a section parallel to the inner surface of the furnace wall.

The table shows the parameters of the gas flow in the recirculation channel for various modes of operation of the furnace.

Experiment Consumption, And * / h Average speed, m / s IT OD (H) V 5 one 622 3.2 0.232 2 782 4.2 0.227 3 998 5.8 0.218 10

Based on the data in the table, the minimum and maximum values are determined, / U ₄ C, 5 values of (-) p ”, 5 U 15

0.218; = 0.232.

The boundaries of the area where temperature measurement is possible are determined. according to the proposed method. 2θ!> Lower bound:

’•’ Fmm - 0.348 m

Upper bound: 25

2 is a diagram of a radiant flux getting onto a thermocouple when it is placed in an exhaust flue gas channel at an insufficient distance from the L-shaped turn, '/ products in furnaces, namely to the control; Liu temperature in furnaces. The purpose of the invention is to improve the accuracy of measurement due to the optimal choice of placement of the thermocouple. Placing a thermocouple in a channel in a 'section shielded from radiation located parallel to the internal surface of the furnace wall at a distance of (1, 5 .. .3.5) (U / V) ^{0, ff} from the entrance to the rotation channel, where U is the flow gas, m ^e / s ^ V - average gas flow rate, m / s. This allows us to provide an average relative measurement accuracy over a heating period of the order of 1%. 1 tab., E 2 ill. ®

Scheme (figure 1) contains a mixer

$ 3.5 ™, = 0.763 m.

Thus, in order to ensure high accuracy in measuring the temperature of ₃₀ gas in this case, the measurement should be performed on a section parallel to the inner surface of the furnace wall behind the rotation of the channel at a distance of at least 0.348 m, but ₃₅ no more than 0.763 m, counting from the worker space.

In the recirculation channel, turning at a distance of 0.450 m, counting from the working space, set ₄₀ on a thermocouple.

For comparison, measure the temperature of the gas in a known manner. For it, a thermocouple is installed in the input section of the channel. At the same time, thermocouples are installed that are outside the boundaries determined by the proposed method, for which purpose in the recirculation channel ₅₀ at a distance of 100 and 1000 mm, respectively, behind the first turn from the working space, <

thermocouples 3 and 5. |

Measurements are carried out every hour for 18 hours of heating.

When applying the proposed method, as well as known, in which the thermocouple is installed in through. the passage for exhaust gases made in the wall of the furnace, the following results are obtained. As a control, a suction thermocouple installed in the channel is used.

The relative average error of the proposed method does not exceed f 1.1%, and the absolute error is 5.3 ° C. At the same time, in the well-known. the method, the relative average error is 4.3%, and the absolute - 21.5 ° C. For thermocouples installed with violation of the boundaries, 3.47% and 17.65 ° C (lower limit) and 4p% and 19.12 ° C (upper limit), respectively, were obtained.

Violation of the lower and upper boundaries leads to a significant decrease in measurement accuracy.

Based on studies that were carried out in the pilot trial of the proposed method, new mode maps have been developed that provide a more accurate heating mode at a lower flow rate of injecting air. Work on these regime cards provides a reduction in specific fuel consumption · 'by 5.9%. ''

Claim

A method of monitoring the temperature of gases in a furnace, including measuring the temperature in the ducts made in the wall of the furnace, exhausting gas from the working space of the channels, so that, in order to increase the accuracy of measurement, the temperature is measured in the channel on a section shielded from direct radiation from the working space, and the measurement is carried out at a distance of (1.5 ... 3.5) (U / V) ® · ⁵ from the entrance to the channel, where U is the gas flow, m ^e / s; V is the average velocity of the gas * stream, m / s.