RU2138365C1 - Method for drying and heating of steel-teeming ladle multilayer lining - Google Patents

Abstract

FIELD: metallurgy and other branches of industry. SUBSTANCE: method involves heating of multilayer lining in three modes: drying mode, nominal and forced modes; dipping multibarreled burning device into ladle for depth H=(6-10)d(r), where d(r) is diameter of burning device outlet section; prior to initiating drying process, covering ladle with closure and leaving gap of 50-100 mm size; removing moisture by means of multibarreled air ejectors during drying process. All heating modes are performed with different coefficients of excessive oxidizers, flare temperatures and gas mass flow rate of burning device. EFFECT: increased efficiency and improved quality of drying and heating processes. 5 dwg

Description

 The proposed method can be used for drying and heating multi-layer linings of steel casting or any other industrial ladles and furnaces in the metallurgical, chemical, machine-building, power machine-building, construction, oil, food and other industries.

 High-level technical solutions on this topic are contained both in scientific publications and in the descriptions of patents and copyright certificates of the Russian Federation, Germany, the USA, France, Great Britain, Switzerland and other countries.

 There is a method of drying and heating 130-ton steel pouring ladles used at the Moldavian Metallurgical Plant (MMZ) in Rybnitsa [1,2]. This method is adopted as a prototype. The main nodes and blocks of the stand, which implements the prototype method, are a stationary bed, a metal cover with an inner lining, an air-gas burner with gas and air supply systems, a fan and a smoke exhauster.

The prototype method includes the following series-parallel operations:
- installation of the bucket in a horizontal position on a stationary bed and placement of a lined metal lid with gas-air burners and a power supply system on a controlled movable bucket of the bucket near the bucket (note that in some cases the buckets are dried in the inverted steel mill, i.e. upside down );
- the supply of natural gas and air to the burner, while the air supply (air flow up to Q _in = 6000 m ³ / h or G _in = 2.04 kg / s at T _in = 288 K and a pressure of 7.5 Pa (very low pressure ; 0.1 kgf / cm ² = 9.8 kPa)) to the burner is carried out using a fan;
- ignition of the gas-air mixture flowing into the working volume of the steel pouring ladle;
- inclusion of a smoke exhauster and removal with its help of the combustion products of the gas-air mixture from the working volume of the steel pouring ladle into the suction shop system through a single hole in the lower half of the bucket volume;
- the implementation, according to the authors of [1], of the "optimal multi-stage drying regime for a steel pouring ladle using the P-130" Remicont "foreign multi-program controller, which allows providing a predetermined heating program with automatic change in energy consumption depending on the temperature of the gases leaving the ladle cover "

 Analysis of the prototype method shows that along with the known advantages of this method has several serious disadvantages. Consider these shortcomings in more detail.

 So, when installing a steel-pouring ladle with an updated multilayer lining from a vertical to a horizontal position, and even more so, upside down, a lining collapse can occur, which will result in long-term repair work, large material losses, huge lost profit. For large-capacity steel casting ladles, for example, 385-ton, horizontal installation is probably completely unacceptable, since the upper tier of the lining near the edge of this ladle is left loose due to its large temperature deformations.

 Further. When drying and heating a gas-air burner of the internal volume of the bucket, installed horizontally, cold air can flow (suck) into the lower part of this volume through the gap between the metal cover and the edge of the bucket, as a result of which the bucket lining will be unevenly heated, which is unacceptable.

 One of the main devices on the stand in which the prototype method is implemented is an air-gas burner operating on natural gas entering the burner from the gas pipeline and air supplied to the burner forcibly by a fan.

It can immediately be noted here that the forced air supply to the burner by means of a fan, compared, for example, to the air supply by means of an ejector, leads to large energy consumption of only one technical air. Indeed, when air is supplied to the burner with a flow rate of Q _in = 6000 m ³ / h (or G _in = 2.04 kg / s at T _in = 15 ^o C = 288 K) for drying the ladle lined with high-alumina bulk concrete, for τ = 32 hours [1] mass of air required
m _in = Q _in • τ = 6000 m ³ / h • 32 h = 192000 m ³
One cubic meter of high-pressure technical air currently costs about C _in = 411 rubles / m ³ , which implies that the cost of technical air alone when heating one of the above-mentioned ladles at MMZ [1] will be equal.

З _в = C _в • m _в = 411 rub / m ³ • 192000 = 78912 thousand rubles = 78.9 million rubles

 It should be borne in mind that all 32 hours at the stand, which implements the prototype method, a smoke exhauster is also operated, driven by an electric motor; this is another component of the energy consumption for the prototype method.

 We continue to criticize the prototype method according to [1]. The design of a gas-air burner used with the prototype method with a two-stage supply at low air pressure and external, in the bucket volume, crushing of the gas and air jets does not allow to organize a homogeneous mixture of fuel components - natural gas and air and their stable complete combustion.

 The problem of a uniform stoichiometric distribution of fuel components over the cross section of a gas-air jet was not solved by the authors [1]. The consequence of the uneven distribution of fuel components over the cross section of the gas stream in [1] is the non-optimal completeness of fuel combustion and not the maximum possible heat generation in the volume of the steel ladle.

 Note that one of the main signs of homogeneous mixing of the "natural gas + air" components and their optimal combustion is a blue torch at the outlet of the burner.

 The use of the foreign multi-program regulator P-130 "Remicont" when drying and heating the steel pouring ladle does not solve the problem of organizing a homogeneous mixing of fuel components at the outlet of the gas-air burner and optimal burning of natural gas in the internal volume of the ladle.

 True, as the authors of [1, p. 18] indicate, when using the aforementioned burner, “a torch is not knocked out of the bucket’s working cavity”, but the absence of burning flashes of unburned portions of fuel in the gap between the lid and the bucket edge does not indicate their absence internal volume of the bucket and does not confirm the course of complete and high-temperature combustion in this bucket. Here I would also like to draw attention to another statement by the authors [1, p. 18]: "... carbon monoxide is practically absent in the products of combustion, characterized by a minimum set temperature." This statement of the authors of [1] is incorrect: carbon monoxide (ie CO) is always present in the products of combustion of the “natural gas + air” mixture, and the higher the flame temperature, the higher the volume content of carbon monoxide in the products of combustion of this mixture (see ., for example, Menshikova TS, Ivanov NN, Ivanov AN "An economical burner for heating steel casting ladles." Steel magazine, 1996, N8, p. 22 - 24).

 Another disadvantage of the prototype method according to [1,2], according to the authors of this application, is the explicit orientation (“binding”) of the shop equipment to foreign equipment and materials [at the MMZ, the stop valve of the Interst company, high-alumina concrete of the Ancokst brand are used -SV70 of the company "Vaitscher-Radex", multi-program controller P-130 "Remicont", etc.]. The practice of domestic enterprises working with foreign partners has clearly proved that foreign companies sell equipment to their partners relatively cheaply, but very expensively - spare blocks for this equipment. The final result of such a technical policy is an increase in the final price of products.

The technical effect of the proposed method consists in increasing the efficiency and quality of the drying and heating processes of the lining of a steel pouring ladle, uniformly symmetrically-forced removal of moisture and combustion products formed during drying in the internal volume of the bucket, increasing the lining's service life and its turnover cycle, saving the flow to the ejector burner gas and air. To achieve the specified technical result in the method of drying and heating a multilayer lining of a steel pouring ladle, the lining of the ladle is subjected to continuously sequential three-mode heating of different intensity of heat and time — minimum, nominal and forced burning, controlled by the coefficient of excess of oxidizing agent torch formed by a homogeneously mixed gas-air mixture flowing out of a multi-barrel ejector burner (abbreviated as EHU), rigidly fixed to the bottom a fresh lid and immersed in the internal volume of the bucket to a depth of H = (6-10) d _g , where d _g is the diameter of the outlet cross section of the ejector burner, and a hot stream of combustion products of this torch, and the torch is ignited before drying, cover the bucket cover, leaving a gap of L = 50 ... 100 mm, the dehumidifying multi-barrel air ejectors are launched, installed, like the ejector burner, on the movable lid of the bucket uniformly and symmetrically with respect to the ejector burner and with respect to each other in quantity, n For example, 4-6 pieces, after which the ejector burner is put into operation in the drying mode of the ladle lining with the oxidizer excess coefficient α $\genfrac{}{}{0ex}{}{\text{c}}{\text{OK}}$ = 3 ... 5, the torch temperature T ^with _f = (1100 ... 800) K, the mass flow of gas through the ejector burner device G ^with _egu = (0.03-0.04) kg / s, and the bucket lining is dried for τ _c = (5-10 ..) hours with simultaneous removal of moisture and combustion products through multi-barrel air ejectors, after which the air ejectors are turned off, their output sections are closed with shutters, the ejector burner device is put into operation in the nominal mode of heating the lining of the bucket at the coefficient of excess oxidizer α $\genfrac{}{}{0ex}{}{\text{n}}{\text{OK}}$ = 1.05 ... 1.1, torch temperature T ⁿ _f = (2000 ... 1800) K, mass gas flow through the ejector burner device G ⁿ _egu = (0.05-0.06) kg / s and operating time τ _n = 9 ... 15 hours, after which the ejector burner is put into operation in the last forced mode with the same oxidizer excess coefficient and flame temperature as in the nominal mode, but with an increased gas mass flow through the ejector burner G ^f _egu = 0.07 kg / s and operating time τ _f ≤ 2 ÷ 3 h, after which the heated ladle is fed under the melt drain from the converter a.

 The proposed method is illustrated by drawings and photographs, where: in FIG. 1 shows a diagram of a stand for drying and heating a steel pouring ladle, made by the proposed method, a longitudinal section; in FIG. 2 is the same, view along arrow A in FIG. 1; in FIG. 3 shows a general view of a working ejector burner mounted on a movable bucket lid with a torch formed by a homogeneously mixed gas-air mixture (EHU operation in the nominal heating mode of a steel pouring ladle); in FIG. 4 shows a steel-pouring ladle heated by an ejector burner before being sent to drain the melt from the converter; in FIG. Figure 5 presents the results of calculating the change in the temperature of the lining (various refractory materials) of the bucket when it is heated by multi-barrel EGU depending on time.

 The main functionally interconnected nodes of the stand, which implements the inventive method of drying and heating the multilayer lining of a steel pouring ladle, are a steel pouring ladle 1, a movable cover 2 of a ladle 1 rotating around a hinge 3, a controlled multi-barrel ejector burner 4, dehumidifying multi-barrel air ejectors 5 s dampers 6.

 The steel-pouring ladle 1 includes the actual metal casing 7, reinforcing (usually chamotte brick) layer 8, a working layer (it may be an acid lining, main lining or bulk concrete) layer 9 and a slide gate 10. A slide gate 10 is designed to drain the melt from the ladle 1.

 The movable cover 2 of the bucket 1, rotating around its axis on the hinge 3, in turn, includes a metal base 11 and an internal heat-shielding cover 12.

A controlled multi-barrel ejector burner 4, rigidly mounted on a movable cover 2 and recessed into the internal volume of this bucket to a depth of H = (6-10) d _g , where d _g is the diameter of the outlet section of the EHU, contains a multi-barrel ejection module 13 with nozzles 14, mixing chamber 15, aft diffuser 16, annular forced air supply block 17, flame stabilizer 18, air intake 19. The flow of air flowing into the EHU through the air intake 19 is controlled by a small full-pressure tube 20 (pressure P _o ) and a piece RA 21 for measuring static pressure (pressure P). Data on this air flow rate is necessary to configure the EHU to the required mode of operation.

 A set of interchangeable nozzle nozzles of various bore diameters is provided for the nozzles 14, these nozzles allow, if necessary, changing the flow rate of natural gas entering the multi-barrel ejecting module 13; for access to the nozzles 14, the mounting of the multi-barrel ejecting module 13 and the mixing chamber 15 is made detachable, for example flanged.

The determination of the recession parameter H = (6-10) d _{g of a} multi-barrel EGU into the internal volume of the steel pouring ladle was carried out on the basis of the analysis of various experimental and design factors, the main among which, according to the authors of the proposed method, were reliable operation of the EGU in the required regulation range by coefficient excess oxidizer α _ok = 1.05 ... 5 and a high heat transfer coefficient α ≈ 210 W / (m ² • K), which characterizes the heat transfer intensity in the bottom area and on the side surfaces of the steel pouring ladle.

 The dehumidifying multi-barrel air ejectors 5 with shutters 6 are similar in design to the multi-barrel ejector stripper device 4, however, they do not have a forced air supply unit and flame stabilizer.

 The work of the stand, which implements the inventive method of drying and heating the multilayer lining of the steel pouring ladle, is performed in accordance with a given cyclogram.

P_о/P_кр=1,83, где P_о - полное давление природного газа на входе в эжектирующий модуль 13 ЭГУ, P_кр - статическое давление природного газа в критическом сечении форсунок 14. При таком перепаде давления будет обеспечиваться истечение природного газа со скоростью звука из прямоструйных форсунок 14 в камеру смешения 15. Далее срабатывает газовая задвижка, природный газ начинает поступать в форсунки 14 и истекать из них со звуковой скоростью в камеру смешения 15. Во входном сечении камеры смешения 15 ЭГУ сразу же устанавливается статическое давление, которое всегда ниже полного давления окружающей среды - атмосферного воздуха перед воздухозаборником 19. Под действием этой разности давлений окислитель - атмосферный воздух - устремляется в воздухозаборник 19 заранее рассчитанного диаметра и далее поступает в камеру смешения 15, где перемешивается с высокоскоростными струями природного газа, образуя при этом однородную по составу, гомогенную стехиометрическую газовоздушную смесь, которая через кормовой диффузор 16, обтекая стабилизатор пламени 17, истекает во внутренний объем сталеразливочного ковша 1. Производится поджиг этой газовоздушной смеси с помощью, например, дежурного факела запальника. Для настройки многоствольного эжекторного горелочного устройства 4 на режим сушки ковша 1 в кольцевой блок принудительной подачи воздуха 17 ЭГУ подают дополнительный расход воздуха в количестве, равном (3...5)(G_в)_стех, где (G_в)_стех - массовый стехиометрический расход воздуха, эжектируемого через воздухозаборник 19 ЭГУ 4. По окончании этой операции многоствольное эжекторное горелочное устройство полностью настроено на режим сушки футеровки ковша при коэффициенте избытка окислителя α $\genfrac{}{}{0ex}{}{\text{c}}{\text{ок}}$ = 3...5, температуре факела T^с _ф=(1100...800)K.First, using the automation unit at the entrance to the ejection module 13 of the EGU 4, the operator sets the required pressure (or rather the differential pressure) of natural gas. Natural gas required pressure drop

P _o / P _cr = 1.83, where P _o is the total pressure of natural gas at the inlet to the ejector module 13 of the EHU, P _cr is the static pressure of natural gas in the critical section of the nozzles 14. With this pressure drop, the flow of natural gas will be ensured at a speed sound from the straight-blown nozzles 14 to the mixing chamber 15. Then a gas valve is triggered, natural gas begins to flow into the nozzles 14 and flow out of them at a sound velocity into the mixing chamber 15. Static pressure is immediately established in the input section of the mixing chamber 15 of the EHU, it is always lower than the total pressure of the environment - atmospheric air in front of the air intake 19. Under the influence of this pressure difference, the oxidizing agent - atmospheric air rushes into the air intake 19 of a predetermined diameter and then enters the mixing chamber 15, where it mixes with high-speed jets of natural gas, forming homogeneous in composition, homogeneous stoichiometric gas-air mixture, which through the feed diffuser 16, flowing around the flame stabilizer 17, flows into the inner volume of the steel-pouring 1st bucket 1. This gas-air mixture is ignited using, for example, the pilot ignition torch. To adjust the multicore ejector burner 4 in drying mode ladle 1 in the annular unit purge servo valves 17 serves an additional air flow in an amount equal to (3 ... 5) (G _{a) stoich} where (G _{a) stoich} - mass stoichiometric flow rate of air ejected through the air intake 19 of the EHU 4. At the end of this operation, the multi-barrel ejector burner is fully configured for drying the ladle lining with an oxidizer excess coefficient α $\genfrac{}{}{0ex}{}{\text{c}}{\text{OK}}$ = 3 ... 5, torch temperature T ^with _f = (1100 ... 800) K.

где km = (G_в/G_г)_g - действительное соотношение массового расхода окислителя - воздуха - к массовому расходу горючего - природного газа;
km_o = (G_в/G_г) стех - стехиометрическое соотношение массового расхода окислителя - воздуха - к массовому расходу горючего - природного газа.Note that the coefficient of excess oxidizer is the ratio

where km = (G _in / G _g ) _g is the actual ratio of the mass flow rate of the oxidizing agent - air - to the mass flow rate of fuel - natural gas;
km _o = (G _in / G _g ) stoich is the stoichiometric ratio of the mass flow rate of the oxidizing agent - air - to the mass flow rate of fuel - natural gas.

For a pair of "natural gas + air" the stoichiometric ratio km _o = (G _in / G _g ) _stoich = 17.28; this number means that for complete combustion of 1 kg of natural gas (~ CH ₄ ), 17.28 kg of air is required.

By setting the ejection end of the burner 4 is started vlagoudalyayuschie multila air ejectors 5, for which high-pressure gas is air at a pressure P _a = 2 kgf / cm ² of plant low pressure network. The principle of operation of the multi-barrel air ejectors 5 is the same as that of the EGU 4. The multi-barrel air ejectors 5 are mounted on the movable cover 2 of the bucket 1 motionless, uniformly and symmetrically with respect to the EGU 4 and relative to each other in an amount of, for example, 4-6 pieces (see. Fig. 2). The purpose of multi-barrel air ejectors 5 is to remove moisture released during the convective drying of the multilayer lining of the steel pouring ladle 1, as well as combustion products (including water vapor) generated during the combustion of a gas-air torch in the internal volume of this bucket. Note that crystallized water intensively evaporates from the multilayer lining of the steel pouring ladle at the last temperature T _with ≤500 ^o C = 773K. In the absence of a uniform symmetrically-forced removal of moisture (and combustion products) in the internal volume of the steel pouring ladle, the “steaming” process can be implemented, i.e. periodic alternation of processes "evaporation-condensation" of moisture in the bucket. The negative consequences of the “steaming” process are a significant increase in the drying time of the multi-layer lining of the bucket and the large additional costs of an expensive energy carrier - natural gas. It can be noted here that with the combustion of 1 m ^{3 of} natural gas, approximately 2 m ³ of water vapor is formed. The drying process ladle of 385 tons, as shown by calculations and the accumulated production experience, has continued for the time τ _c = 5-10 hours at a mass flow of natural gas through the ejector G burner device ^of _EHP = (0.03-0.04) kg /with.

It can be noted here that the total amount of heat Q, which must be brought to the layer of the refractory mass of the lining in the process of drying it using a multi-barrel EHU, is determined by the thickness of the lining δ and its moisture content β:
Q = ρδ [C (T $\genfrac{}{}{0ex}{}{\text{kin}}{\text{in}}$ -T _o ) + βH].
In this approximate formula:
ρ is the density of the refractory mass of the lining;
δ is the thickness of the lining;
C is the heat capacity of the refractory mass of the lining;
T _in ^bale = 100 ^o C the boiling point of water;
T _about - the initial temperature of the refractory mass of the lining;
β is the moisture content in the refractory mass of the lining;
H is the specific heat of evaporation of water.

The drying time τ _c using an EHU should be sufficiently large due to the low thermal conductivity of the refractory mass and its significant thickness. The calculations showed that with the lining thickness δ = 200 mm, the value of τ _c is at the level of 20-30 hours depending on the coefficient of thermal diffusivity of the refractory mass. The dependence of the drying time τ _c on the thickness of the lining δ is quadratic; Thus, a decrease in the thickness of the lining from 250 mm to 150 mm leads to a decrease in the drying time τ _{c by} approximately 3 times.

At the end of the drying process, the multi-barrel air ejectors 5 are turned off, their output sections are closed with shutters 6, and the ejector burner 4 is put into operation in the nominal mode — the mode of heating the lining of the bucket with an oxidizer excess coefficient α $\genfrac{}{}{0ex}{}{\text{n}}{\text{OK}}$ = 1.05 ... 1.1 and the torch temperature T ⁿ _f = (2000. ..1800) K. The new operation mode of the multi-barrel ejector burner is organized by reducing the air supply to the ring unit 17 of forced air supply to the EHU to a flow rate of (0.05 ... 0.1) (G _in ) _stoich , where (G _in ) _stoich is mass stoichiometric flow rate of air ejected through the EHU. The process of heating a steel-pouring ladle with a capacity of 385 tons, as shown by calculations (see Fig. 5) and accumulated production experience, should continue in time τ _n = 9-15 hours at a mass flow of natural gas through an ejector burner device G ⁿ _egu = (0, 05-0.06) kg / s.

At the end of the heating mode, the ejector burner is transferred to the last - forced heating mode of the steel pouring ladle with the same oxidizer excess coefficient and torch temperature as in the nominal mode, by the increased gas mass flow through the ejector burner G ⁿ _egu = 0.07 kg / with and operating time τ _f ≤ 2-3 hours, after which the heated ladle is fed under the melt drain from the converter.

 Currently, the proposed method of drying and heating the multilayer lining of the steel pouring ladle is undergoing pilot testing in the converter production of Severstal OJSC, Cherepovets. (see Figs. 3 and 4).

Sources of information used in compiling the application materials:
1. Saprygin A.N., Leontiev T.S., Konyukhov V.V. and others. Improving the technology of preparation of steel pouring ladles. The Steel magazine, 1996, N 2, p. 16 - 18.

 2. Chernovol VN, Leontiev TS, Konyukhov VV and others. Improving equipment and technology for drying and heating the lining of steel pouring ladles. The journal "Metallurg", 1995, N 1, p. 29 - 30.

Claims (1)

A method of drying and heating a multilayer lining of a steel pouring ladle, including installing the ladle on a stand, covering the ladle with a lid attached to it, supplying natural gas and air to the burner, igniting it, continuously heating the lining with a torch, the temperature of which is controlled by the coefficient of excess oxidizer, removal gaseous products of combustion and moisture from the bucket, characterized in that the heating is carried out in three modes: drying for 5 to 10 hours with an excess coefficient of oxidizing agent equal to 3 to 5, tamper round of the torch 1100 - 800K, mass gas flow through the burner 0.03 - 0.04 kg / s and with simultaneous removal of combustion products and moisture, rated mode for 9 - 15 hours with an oxidizer excess ratio of 1.05 - 1 , 1, a torch temperature of 2000 - 1800K and a mass gas flow through the burner, 0.05 - 0.06 kg / s and forced mode for 2 - 3 hours at the same oxidizer excess ratio and torch temperature as in the nominal mode but increased gas mass flow rate of 0.07 kg / s, while buildings use a multi-barrel ejector device, which is immersed in a bucket to a depth of (6 - 10) d _g , where d _g is the diameter of the outlet section of the burner device, the removal of combustion products and moisture is carried out through multi-barrel air ejectors, which are placed uniformly and symmetrically in the lid relative to the burner, and the lid is covered with a gap relative to the end of the bucket, comprising 50 - 100 mm

Images