TECHNICAL FIELD

Present disclosure generally relates to a field of material science and metallurgy. Particularly, but not exclusively, the present disclosure relates to annealing furnace. Further embodiments of the present disclosure disclose a system and a method for detecting leakage in a radiant tube in a continuous annealing furnace.

BACKGROUND OF THE DISCLOSURE

Annealing, is a heat treatment process which may be carried out to alter physical and sometimes chemical properties of material. The annealing process may increase ductility and may reduce hardness of the material making it more workable. Generally, the annealing process may involve heating a material above its recrystallization temperature, maintaining at a suitable temperature, and then cooling the material to room temperature. Annealing is carried out in a furnace which may be commonly termed as annealing furnace. Normally, different annealing processes like batch (or box) annealing and continuous annealing may be employed, depending on the type of material to be subjected for the annealing process.

The continuous annealing process may be carried out in a continuous annealing furnace. The continuous annealing furnace includes four sections like preheating zone, heating zone, soaking zone and cooling zone. Out of these, the heating elements like radiant tubes are employed in the heating and soaking zones. The furnace atmosphere of the continuous annealing furnace is maintained in a reducing atmosphere by injection of H2 and N2, and a very low dew point is maintained in the furnace so that there is practically no free O2 available. Radiant tubes are fuelled with Carbon monoxide (CO) gas and Propane gas.

One application of the continuous annealing process includes annealing of cold rolled steel sheets. The cold rolled steel sheets may be annealed to relieve internal stresses, soften the steel, develop new texture, and improve mechanical properties such as formability, drawability and ductility of the steel. The continuous annealing furnace forms an integral part of cold rolled steel processing. In continuous annealing, a single strand of cold rolled steel strip is passed through a furnace in a relatively short time, during which it is subjected to a rapid heat treatment cycle. The steel strip is heated to the annealing temperature very quickly, the soaking time is short and the cooling rate is relatively rapid. Hence, the cycle takes only a few minutes. The short heat cycles minimise the carbide coarsening and grain boundary precipitation. Hence, the annealing temperatures required are higher than batch annealing so that re-crystallisation and grain growth can be promoted.

The continuous annealing furnaces may use different types of heating elements, like radiant tubes for quick heating of the steel strips. A reducing atmosphere is maintained inside the furnace using a proportionate mixture of hydrogen and nitrogen in the form of HNx. Heat transfer from the radiant tubes to the strip is through radiation and convection. The radiant tubes in the annealing furnace may have susceptibility to fail due to creep, carburization, thermal shock, tube fracture, loss of carbon control, melt – through, weld failure and oxidation. As a result of failure, the furnace throughput may be severely affected. The normal failure mode of radiant tubes is crack or rupture at weld joints. Since the atmosphere inside the furnace is at higher pressure than the negative suction pressure inside each radiant tube, HNx tends to ingress into the radiant tubes through these damaged points. As such, an appreciable drop in furnace pressure may be witnessed which prevents increasing the temperature of the furnace to higher levels depending upon production requirement.

Conventionally, several techniques have been developed for identifying leakage in radiant tubes. One such conventional technique makes use of an inert tracer gas, which when injected into the furnace environment, tends to seep through damaged radiant tubes. This tracer gas mixed with flue gases is then detected by manually moving the detector to collect gas sample from individual radiant tubes and determine leakage in the radiant tubes. However, in conventional techniques, parameters –like size of the annealing furnace are not considered for injection of inert tracer gases. Therefore, volume of inert tracer gas injected may affect the gaseous mixture inside the furnace, making it unstable and can make the HNx mixture flammable.

Further, the conventional technique may not be practical for all applications, since there are furnaces with common fume collector leading out of the radiant tubes arranged around the furnace in orientations where detectors cannot be connected without any significant design modifications in the connections to the sample chamber. Also, the equipment available for detecting concentration of tracer inset gas is found to be temperature sensitive and extremely delicate. Therefore, transferring the detector from one level to another can be cumbersome and time consuming. This would further downgrade the concentration of tracer inset gas inside the furnace atmosphere, since furnace atmosphere is an open system which excess HNx continuously being discharged through drain valve.
The present disclosure is intended to overcome one or more limitations stated above.

SUMMARY OF THE DISCLOSURE

One or more shortcomings of the conventional techniques are overcome by method and system, as disclosed and additional advantages are provided through the method as described in the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

In one non-limiting embodiment of the disclosure, a system for detecting leakage in a radiant tube of an annealing furnace having a plurality of radiant tubes arranged in one or more groups is disclosed. The system comprises a plurality of first isolation valves, each of the plurality of first isolation valves is coupled with one of the plurality of radiant tubes. The system further comprises one or more second isolation valves which are configured to fluidly connect at least one group of the one or more groups to a sampling chamber. The sampling chamber is configured to collect mixture of fluids from the plurality of radiant tubes upon selectively opening at least one second isolation valve of the one or more second isolation valves and at least one first isolation valve of the plurality of first isolation valves. The system also includes a detector provisioned in the sampling chamber to detect concentration of tracer gas in the mixture of fluids collected in the sampling chamber. The leakage in the radiant tube of the plurality of radiant tubes is identified when the concentration of the tracer gas detected by the detector from the radiant tube is higher than a predetermined threshold concentration of the tracer gas.

In an embodiment of the disclosure, the system comprises one or more first channels and each of the one or more first channels are configured to interconnect radiant tubes in at least one group of the one or more groups. The system also comprises at least one second channel interconnecting the one or more first channels.

In an embodiment, the system further comprises a nitrogen purging unit fluidly connectable to the at least one second channel to selectively flush out residual fluids from the one or more first channels.

In an embodiment of the disclosure, the system comprises a vacuum pump connectable to the at least one second channel to create a negative pressure in the one or more first channels, the at least one second channel and the sampling chamber.

In an embodiment of the disclosure, the at least one second isolation valve of the one or more second isolation valves are selectively opened to identify a defective group of the plurality of groups. Also, the first isolation valve coupled with each of the plurality of radiant tubes in the defective group is selectively opened to identify leakage in the radiant tube.

In an embodiment of the disclosure, the system further comprises a tracer gas injection unit fluidly connected to the annealing furnace to inject a pre-determined quantity of tracer gas into a furnace atmosphere. The tracer gas is helium and threshold concentration of the tracer gas is 6-7 ppm (parts per million).

In another non-limiting embodiment of the disclosure, a method for detecting leakage in a radiant tube of an annealing furnace, having a plurality of radiant tubes arranged in one or more groups is disclosed. The method comprises step of injecting a pre-determined quantity of tracer gas into a furnace atmosphere of the annealing furnace and creating a negative pressure in a one or more first channels and a sampling chamber by a vacuum pump. The one or more first channels are configured to interconnect radiant tubes of at least one group of the one or more groups, and the sampling chamber is fluidly connected to the one or more first channels through a one or more second isolation valves. The method further comprises operating, first isolation valves coupled with each radiant tube of the plurality of radiant tubes and the second isolation valve corresponding to at least one group of the one or more groups to open position, such that mixture of fluids flowing through the first channel is collected in the sampling chamber. Further, a defective group is identified of the one or more groups based on concentration of the tracer gas detected by a detector provisioned in the sampling chamber. After identifying the defective group, the first isolation valve coupled with each of the plurality of radiant tubes in the defective group is selectively operated to pass the fluid mixture from each of the the plurality of radiant tubes to the sampling chamber. Then the leakage in the radiant tube is identified based on change in concentration of the tracer gas detected by the detector in the corresponding radiant tube.

In an embodiment of the disclosure, the method further comprises, allowing the tracer gas to spread in the furnace atmosphere for a pre-defined time.
In an embodiment of the disclosure, the method further comprises purging nitrogen through the one or more first channels to flush out residual fluids after identifying at least one of the defective group of radiant tubes or leakage in the radiant tube.

In an embodiment of the disclosure, the method further comprises, creating a negative pressure in the one or more first channels and the sampling chamber through a vacuum pump after the purging of nitrogen. The tracer gas is helium and the pre-determined quantity of tracer gas is injected into the furnace atmosphere through a flow path of HNx mixture gas.

In an embodiment of the disclosure, the pre-determined quantity of tracer gas is determined by comparing entropy of mixture of tracer gas and HNx with entropy of HNx mixture. The entropy of mixture of tracer gas is maintained greater than the entropy of the HNx mixture.

It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the disclosure.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

The novel features and characteristics of the disclosure are set forth in the appended description. The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:

FIG.1 illustrates a schematic representation of a continuous annealing furnace.

FIG.2 illustrates a schematic representation of a system for detecting leakage in a radiant tube of an annealing furnace, according to some embodiments of the present disclosure.

FIG.3 illustrates a schematic representation of a circuit for injecting HNx gas and tracer gas into atmosphere of the annealing furnace, according to an embodiment of the present disclosure.

FIG.4 illustrates a schematic representation of a circuit for injecting HNx gas and tracer gas into atmosphere of the annealing furnace, according to alternate embodiments of the present disclosure.

FIG.5 illustrates a flowchart depicting a method for detecting leakage in the radiant tube of the annealing furnace, according to an embodiment of the present disclosure.

The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION

The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the description of the disclosure. It should also be realized by those skilled in the art that such equivalent system and method do not depart from the scope of the disclosure. The novel features which are believed to be characteristic of the disclosure, as to method of operation, together with further objects and advantages may be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.

In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the figures and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure.

The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a method that comprises a list of acts does not include only those acts but may include other acts not expressly listed or inherent to such method. In other words, one or more acts in a method proceeded by “comprises… a” does not, without more constraints, preclude the existence of other acts or additional acts in the method.

Embodiments of the disclosure relates to a system and method for detecting leakage or defect in a radiant tube in a continuous annealing furnace. In the continuous annealing furnace, radiant tubes are employed in heating and soaking zones as heating elements for heating the steel strip. After a prolonged operation, the radiant tubes may start leaking which would affect the furnace throughput. The disclosure discloses a system and a method to detect leakage or defect in the radiant tube using a tracer gas. The tracer gas may be an inert gas such as but not limited to helium. Helium may be selected as the tracer gas due to its high diffusivity. The helium may ingress into the radiant tube of the continuous annealing furnace when there is a defect or leakage in the radiant tube. The system disclosed in the present disclosure is used for detecting amount of tracer gas that ingresses into the radiant tubes and thus in turn to detect leakage or defect in the radiant tubes.

The system includes a plurality of first isolation valves, each one coupled to one of the radiant tube of the plurality of radiant tubes. In an embodiment of the disclosure, the plurality of radiant tubes is arranged in one or more groups in the continuous annealing furnace, each group will have at least two radiant tubes. Further, the radiant tubes in each of the one or more groups are interconnected by a first channel, such that first isolation valve coupled to each radiant tube selectively allows fluid connection of the corresponding radiant tube to the first channel. The one or more first channels may be connected to a common outlet through at least one second channel. The second channel may be provided with one or more second isolation valves, such that, each second isolation valve isolates a group of radiant tubes from the remaining group of radiant tubes.

The system further comprises a sampling chamber configured to collect the fluid mixture from the radiant tubes when the at least one first isolation valve of the plurality of isolation valves and the one of the one or more second isolation valves are operated. Further, a detector may be employed in the sampling chamber. The detector is configured to detect the amount of tracer gas in the fluid mixture.

In operation, a pre-determined amount of tracer gas like helium may be injected into the furnace atmosphere, so that if there is a leakage or defect in the radiant tube, the tracer gas ingresses into the corresponding radiant tube. The furnace atmosphere is a mixture of hydrogen (H2) gas and nitrogen (N2) gas forming a HNx mixture. The amount of helium to be injected into the furnace atmosphere depends on the entropy of HNx mixture and entropy of mixture of is determined by comparing entropy of mixture of helium and HNx with entropy of HNx mixture. In an embodiment, the entropy of mixture of helium and HNx is maintained greater than the entropy of the HNx mixture.

Subsequently, a negative pressure may be created in the one or more first channels by a vacuum pump. Now, the defective group of the one or more groups of radiant tubes is identified by operating the first isolation valves of the corresponding group and the second isolation valve of the corresponding group to open position. This allows the fluid mixture to be collected in the sampling chamber where concentration of tracer gas is examined. If the tracer gas concentration is more than pre-set threshold in any of the one or more groups, then the corresponding group of radiant tubes may be identified as defective group and each radiant tube of that group is tested for leakage or defect. Then, individual test of each of the radiant tubes in the defective group may be performed. By operating a first isolation valve of the individual radiant tube thus allowing fluid connection between the radiant tube and the sampling chamber. The detector in the sampling chamber measures the concentration of the tracer gas in the radiant tube under consideration. The defect in the radiant tube may be identified if there is a change in concentration of the tracer gas detected by the detector.

In the following detailed description, embodiments of the disclosure are explained with reference of accompanying figures that form a part hereof, and in which are shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.

FIG.1 illustrates a schematic representation of continuous annealing furnace (AF) and its components. The continuous annealing furnace (AF) may include multiple zones like preheating zone (PH), heating zone (H), soaking zone (S) and cooling zone (C). The steel sheets to be annealed may be passed through each of the zones may undergo preheating and rapid heating, in the pre-heating and heating zone (PH and H) respectively. This is followed by soaking the steel sheets in the soaking zone (S), and then rapid cooling in the cooling zone (C). In the continuous annealing furnace (AF), heating elements like radiant tube (101) may be employed in the heating and soaking zones (H and S).

Referring now to FIG.2, which is an exemplary embodiment of the present disclosure showing schematic diagram of a system (100) for detecting leakage in a radiant tube (101) of the continuous annealing furnace (AF). The continuous annealing furnace (AF) includes a plurality of radiant tubes (101a – 101n) arranged in rows or groups such that each row will have more than two radiant tubes. The system (100) of the disclosure includes a monitoring circuit (102) which is configured on the furnace to detect leakage or any form of failure in the radiant tube (101) of the annealing furnace. The monitoring circuit (102) allows continuous monitoring of the radiant tubes in running line condition without the requirement of shut down. The monitoring circuit (102) includes a plurality of first isolation valve (103). Each first isolation valve (103) of the plurality of first isolation valves (103a -103n) is coupled with one of the plurality of radiant tubes (101a – 101n). This results in each of the radiation tube (101) in connection with a first isolation valve (103). The monitoring circuit (102) further includes a plurality of first channels (104). Each of the plurality of first channels (104) is configured to fluidly interconnect the radiant tubes (101a – 101n) arranged in one group or row, such that the first isolation valve (103) coupled with each radiant tube (101) will fluidly connect the corresponding radiant tube (101) with the first channel (104). Accordingly, depending on the number of groups or rows of the radiant tubes in the continuous annealing furnace, there may be equivalent number of first channels (104). The first channel(s) (104) allow flow of fluid or gas from the plurality of radiant tubes (101a – 101n) to other components of the system (100). The one or more first channels (104) connect to a common outlet pipeline, herein referred to as second channel (105). In an embodiment, there is at least one second channel (105) connecting to the one or more first channels (104). Further, the monitoring circuit (102) includes one or more second isolation valves (106a – 106m), such that at least one second isolation valve (106) may be provided at an outlet portion of each of the one or more first channels (104). The one or more second isolation valves (106a – 106m) are configured to selectively connect a particular group of radiant tubes to the second channel (105). Here ‘m’ indicates number of groups formed. In an embodiment of the present disclosure, there may be a separate second channel (105) coupled to each of the one or more first channels (104).

In an embodiment of the disclosure, the first and second channels (104 and 105) referred herein above and below are fluid connection lines including pipes, tubes, hoses, and the like.

Further, the system (100) comprises a sampling chamber (107) connectable to an outlet portion (105b) of the second channel (105). The sampling chamber (107) is adapted to collect a mixture of fluids from the radiant tubes (101) for analysis. The one or more first channels (104) or a particular group of the plurality of radiant tubes (101a – 101n) may be selectively coupled with the sampling chamber (107) by the operation of corresponding second isolation valve (106). The sampling chamber (107) may be disposed in communication with a detector (108) to detect the amount of tracer gas content in the mixture of fluids collected from radiant tubes due to leakage or failure. In an embodiment, the detector (108) may be a helium sniffer probe. Ideally, the sniffer probe may show a helium concentration of 6-7 ppm, any reading above that is interpreted as a failure or leakage in the radiant tube (101). In an embodiment, the helium sniffer probe may be associated with spectrometer magnetic deflection mass system for identifying any peak in helium concentration. Thus, with selective operation of the second isolation valve (106) of a particular group of radiant tubes and first isolation valves (103) in the corresponding group, a defective group of the one or more groups of radiant tubes may be identified. Once, the defective group of radiant tubes is identified, the first isolation valve (103) of individual radiant tube (101) of the defective group may be operated to identify the defective radiant tube (101). For example, upon operation of the first isolation valves of the group G and corresponding second isolation valve (106), the tracer gas concentration detected by the detector (108) of the group G may be more than threshold tracer gas or helium concentration. Then such group G may be identified as defective group. Once, the defective group G of the one or more groups has been identified, individual radiant tubes of the defective group G are tested for leakage through operation of corresponding first isolation valve (103). In an embodiment, during test for leakage, the radiant tube R may be detected as defective radiant tube [as highlighted in FIG.2], when the detector (108) detects any change in concentration of tracer gas or helium content.

The system (100) further comprises a nitrogen purging unit (109) fluidly connectable to the second channel (105) through a third isolation valve (109a). The nitrogen purging unit (109) is configured to selectively purge nitrogen into the monitoring circuit (102) to flush out any residual fluids from the one or more first channels (104) and the second channel (105). In an embodiment, the nitrogen purging unit (109) is operated to flush out residual fluids from the one or more first channels (104) once the defective group of radiant tubes have been identified. The nitrogen purging unit (109) thus allows proper detection of concentration of tracer gas and hence leakage (if any) in the radiant tubes, by flushing out any residual fluids in the one or more first channels (104). The system (100) also consists of a vacuum pump (110) connectable to the monitoring circuit (102) and the sampling chamber (107) to selectively create negative pressure in the monitoring circuit (102). As shown in FIG.2, the system (100) may include a mixing tank (111) fluidly connected to the continuous annealing furnace. The mixing tank (111) is configured to mix H2 and N2 gas proportionately and form a HNx mixture, and then let into the furnace atmosphere to form a reducing atmosphere in the annealing furnace.

Now referring to FIG.3 which is an exemplary embodiment of the present disclosure illustrating a schematic representation of a circuit for supplying a mixture of HNx gas and helium tracer gas into furnace atmosphere of the annealing furnace (AF). As shown in FIG.3, the circuit comprises a H2 gas pipeline for injection of hydrogen gas into the mixing tank (111) and a N2 gas pipeline for injection of nitrogen gas into the mixing tank (111). The hydrogen and nitrogen gases are mixed proportionately to form a HNx gas mixture. This mixture HNx gas is let into the annealing furnace atmosphere (AF) through a HNx gas pipeline (114). The HNx gas mixture let into the furnace atmosphere (AF) forms a reducing atmosphere.

Further, the tracer gas such as but not limited to helium gas may be injected into the annealing furnace (AF), which penetrates into the radiant tube (101) in case of any leakage, thereby assisting to detect leakage or failure of the radiant tube (101). For effective detection as well as to ensure a safe furnace atmosphere optimum volume of helium gas must be injected such as to balance the HNx proportion inside the furnace (AF) while ensuring adequate concentration of the helium gas within the furnace for a given time. To optimize the volume of helium gas injection, entropy of the gaseous mixture of HNx and helium (or tracer gas) must be greater than or equal to the entropy of the mixture of HNx gas. This ensures ability of the injected volume of helium to effectively spread throughout the furnace (AF).

Initially, the annealing furnace atmosphere (AF) may have a mixture of HNx and subsequently helium may be injected into the annealing furnace (AF) to form a gaseous mixture of HNx + He. According to embodiments of the disclosure, the total entropy of the gaseous mixture (HNx + He) is maintained greater than the present gas mixture (HNx). As a result, helium would easily diffuse in the furnace atmosphere (AF). In an exemplary embodiment, if x% of He is being incorporated in the mixture, then subsequently x% of N2 is being reduced keeping the percentage of hydrogen constant. The amount of hydrogen is kept constant since hydrogen is already present in very less quantity i.e. around 5%. Moreover, hydrogen has higher rate of heat transfer capacity. It tends to neutralize the oxygen ingression into furnace and maintains dew point at optimum level inside the furnace.

Thus, the total entropy change of gas mixture of HNx is given by -

?S(HNx) = ?S(N2) + ?S(H2)

where the ?S(N2) and ?S(H2) on right hand side are change in entropy of Nitrogen and Hydrogen respectively, and Left hand side term is entropy change of the gaseous mixture after it enters the furnace (AF).
?S(HNx) = m_N2 R ln (v_f(N2) / v_i(N2)) + m_H2 R ln (v_f(H2) / (v_i (H2))

where m_N2 and m_H2 are the mass rate in kg/s of Nitrogen and Hydrogen gas respectively. R is the Universal Gas Constant. V_f(X) and v_i(X) are the final and initial volumes of the gas X in Nm3/h.

Using standard values of Volume, pressure, temperature existing in the status quo, the total change in entropy of the mixture inside the furnace may be determined.

After incorporation of He (Helium) in the annealing furnace -

Let x% of He be injected into the system.
Subsequently x% of N2 is reduced.
As the percentage of hydrogen would remain unchanged, thus the flow rate of H2 and the percentage of final H2 as indicated by the H2 analyzer would be same.
Now,

?S(HNx+He) = ?S(N2) + ?S(H2) + ?S(He) = m_N2 R ln (v_f(N2) / (v_i (N2))) +m_H2 R ln (v_f(H2) / (v_i (H2))) + m_H2 R ln (v_f(He) /(v_i(He)))

Thus, for optimum volume of helium injection, ?S(HNx+He) = ?S (HNx)

Using the above conditions, HNx circuit with elements incorporated for injection of helium may be designed. As shown in FIG.3, to inject helium into the annealing furnace (AF), there is a helium source (113a) of pre-determined size. The helium source (113a) is selected such that there is continuous availability of helium during injection phase. Further, hand valves (113b and 113e) may be selectively operated to ensure pressure in helium circuit is always greater than pressure in HNx circuit to prevent any backflow of hydrogen into the furnace atmosphere (AF). Also, pressure gauges (113f) are used to measure pressure at different places in the circuit and accordingly assist in maintaining the pressure at required level. The flow transmitter (113d) along with flow control valve (113c) ensures that calculated amount of tracer gas is injected in controlled environment.

Referring to FIG.4 which is an alternate embodiment of the present disclosure illustrating a schematic representation of a circuit for injection of tracer gas (helium) into the annealing furnace (AF). As shown in FIG.4, helium gas may be injected into the annealing furnace atmosphere (AF) in multiple ways. In an embodiment, helium gas may be injected into mixing tank (111) along with the hydrogen (H2) and nitrogen (N2) gases.

In an embodiment, the tracer gas or helium may be injected into the furnace directly through a new set of pipelines (115), or may be injected into HNx pipeline (114) after the mixture of HNx gas is outlet from the mixing tank (111) leading into the annealing furnace (AF).

FIG.5 is an exemplary embodiment of the present disclosure which illustrates a flowchart depicting a method for detecting leakage in the radiant tube (101) of the annealing furnace (AF).

At block 116, a pre-determined amount of tracer gas such as helium is injected into the furnace atmosphere of the annealing furnace (AF). An optimum volume of tracer gas is to be injected such as to balance the HNx proportion inside the furnace (AF) while ensuring adequate concentration of the tracer gas within the furnace (AF) for a given time. Accordingly, volume of tracer gas to be injected is determined using the condition that entropy of gaseous mixture of HNx and He is greater than or equal to entropy of HNx mixture. In an embodiment, the helium injected into the furnace atmosphere (AF) through a HNx pipeline (114) which may be considered as optimum point of injection. After injecting the helium into the furnace atmosphere (AF) it is allowed to spread in for a pre-defined time period. In an embodiment, the predetermined time period may be 7-15 minutes, for example 10 minutes.

At block 117, once the helium is injected into the furnace atmosphere (AF), the vacuum pump (110) may be fluidly connected to the monitoring circuit (102), and a negative pressure is created in the one or more first channels (104) and the sampling chamber (107). With this, the fluid mixture from the plurality of radiant tubes (101a – 101n) may flow into the one or more first channels (104) when the first isolation valves (103) are operated.

At block 118, a defective group of radiant tubes is identified. Once the negative pressure has been created in the one or more first channels (104), the first isolation valves (103) coupled to each of the radiant tubes of a particular group is operated to open position and corresponding second isolation valve (106) of that group is operated to open position. When the first isolation valve (103) and the second isolation valve (106) is operated to open position, that group is fluidly connected to the sampling chamber (107) while other first isolation valves (103) and the second isolation valves (106) are in closed position. The sampling chamber
(107) collects the mixture of fluids, and a detector (108) in the sampling chamber (107) detects the tracer gas concentration of the group and if the concentration of tracer gas is more than 6-7 ppm, that group of radiant tubes may be identified as defective group of radiant tubes.

At block 119, leakage in the radiant tube (101) is detected. Once, the defective group of radiant tubes are identified, nitrogen purging unit (109) may be connected to the monitoring circuit (102). The nitrogen purging unit (109) purges nitrogen into the corresponding first channel (104) and the second channel (105) to flush out any residual fluids in the first channel (104). Further to nitrogen purging, negative pressure is created in the first channels (104) and the sampling chamber (107) by the vacuum pump (110). Then, the first isolation valve (103) coupled to each radiant tube (101) in the defective group or row may be selectively operated to open position while other first isolation valves (103) of the defective group is in closed position. This way, the individual radiant tube (101) under consideration is fluidly connected to the sampling chamber (107), and the sampling chamber (107) may collect fluid mixture from individual radiant tube (101). The detector (108) in the sampling chamber (107) measures the tracer gas concentration of the radiant tube (101), and if a change is detected in the concentration of the tracer gas, then the radiant tube (101) is identified as defective radiant tube.

If no helium peak is observed in corresponding group, nitrogen may be purged in the monitoring circuit (102), and both the sample chamber (107) and monitoring circuit (102) are restored to negative pressure by the vacuum pump (110). Then process shown in blocks 118 and 119 are repeated for the remaining groups to completely identify the leakage in the radiant tube (101).

In an embodiment of the disclosure, the system (100) may be associated with a control unit [not shown]. The control unit may be configured to operate elements of the system (100) automatically to monitor and detect leakage in the radiant tubes. The defective radiant tube (101) may be accordingly indicated to an operator on a display unit [not shown] about the defect in the radiant tube.

Advantages

The present disclosure discloses a system and method for detecting leakage in a radiant tube of an annealing furnace with continuous monitoring of the radiant tubes without need for shut down of the annealing furnace or any individual radiant tube for monitoring. Thereby, furnace throughput will not be affected.

In the method of the present disclosure, the amount of helium injected into the annealing furnace is optimized, thus enabling detection of leakage in the radiant tube while ensuring safety by not affecting the proportion of mixture of H2 and N2 gas.

Equivalents

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc. It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Referral Numerals

Referral Numerals Description
AF Continuous annealing furnace
PH Pre-heating zone
H Heating zone
S Soaking zone
C Cooling zone
100 System to detect leakage in radiant tube of annealing furnace
101 Radiant tube
101a – 101n Plurality of radiant tubes
102 Monitoring circuit
103 First isolation valve
103a – 103n Plurality of first isolation valves
104 First channel(s)
105 Second channel
106 Second isolation valves
106a – 106m One or more second isolation valves
107 Sampling chamber
108 Detector
109 Nitrogen purging unit
109a Third isolation valve
110 Vacuum pump
111 Mixing unit
111a Hydrogen (H2) gas pipeline
111b Nitrogen (N2) gas pipeline
113a Helium source
113b, 113e Hand valves
113c Flow control valve
113d Flow transmitter
113f Pressure gauges
114 HNx pipeline / flow path
115 Direct pipeline to the annealing furnace
G Defective group of radiant tubes
R Defective radiant tube

Claims:

1. A system (100) for detecting leakage in a radiant tube (101) of an annealing furnace having a plurality of radiant tubes (101a – 101n) arranged in one or more groups, the system (100) comprising:
a plurality of first isolation valves (103a – 103n), wherein, each of the plurality of first isolation valves (103) is coupled with one of the plurality of radiant tubes (101a – 101n);
one or more second isolation valves (106a – 106m), wherein each of the one or more second isolation valves (106a – 106m) is configured to fluidly connect at least one group of the one or more groups to a sampling chamber (107);
wherein, the sampling chamber (107) is configured to collect mixture of fluids from the plurality of radiant tubes (101a – 101n) upon selectively opening at least one second isolation valve of the one or more second isolation valves (106a – 106m), and at least one first isolation valve of the plurality of first isolation valves (103a – 103n); and
a detector (108) provisioned in the sampling chamber (107) to detect concentration of tracer gas in the mixture of fluids collected in the sampling chamber (107);
wherein, the leakage in a radiant tube (101) of the plurality of radiant tubes (101a – 101n) is identified when the concentration of the tracer gas detected by the detector (108) from the radiant tube (101) is higher than a predetermined threshold concentration of the tracer gas.

2. The system (100) as claimed in claim 1 comprises one or more first channels (104), wherein, each of the one or more first channels (104) is configured to interconnect radiant tubes in at least one group of the one or more groups.

3. The system (100) as claimed in claim 1 comprises at least one second channel (105) interconnecting the one or more first channels (104).

4. The system (100) as claimed in claim 3 comprises a nitrogen purging unit (109) fluidly connectable to the at least one second channel (105) to selectively flush out residual fluids from the one or more first channels (104).

5. The system (100) as claimed in claim 3 comprises a vacuum pump (110) connectable to the at least one second channel (105) to create a negative pressure in the one or more first channels (104), the at least one second channel (105) and the sampling chamber (107).

6. The system (100) as claimed in claim 1, wherein the at least one second isolation valve of the one or more second isolation valves (106a – 106m) is selectively opened to identify a defective group of the plurality of groups.

7. The system (100) as claimed in claim 6, wherein the first isolation valve coupled with each of the plurality of radiant tubes (101a – 101n) in the defective group is selectively opened to identify leakage in the radiant tube (101).

8. The system (100) as claimed in claim 1 comprises a tracer gas injection unit (111) fluidly connected to the annealing furnace to inject a pre-determined quantity of tracer gas into a furnace atmosphere.

9. The system (100) as claimed in claim 1, wherein the tracer gas is helium.

10. The system (100) as claimed in claim 1, wherein the threshold concentration of the tracer gas is 6-7 ppm (parts per million).

11. The system (100) as claimed in claim 1, wherein the detector (108) is a sniffer probe.

12. A method for detecting leakage in a radiant tube (101) of an annealing furnace, having a plurality of radiant tubes (101a – 101n) arranged in one or more groups, the method comprising:
injecting, a pre-determined quantity of tracer gas into a furnace atmosphere of the annealing furnace;
creating, a negative pressure in a one or more first channels (104) and a sampling chamber (107) by a vacuum pump (110), wherein, each of the one or more first channels (104) is configured to interconnect radiant tubes (101) of at least one group of the one or more groups, and the sampling chamber (107) is fluidly connected to the one or more first channels (104) through a one or more second isolation valves (106a – 106m);
operating, first isolation valves coupled with each radiant tube (101) of the plurality of radiant tubes (101a – 101n) and the second isolation valve (106) corresponding to at least one group of the one or more groups to open position, such that mixture of fluids flowing through the first channel (104) is collected in the sampling chamber (107);
identifying, a defective group of the one or more groups based on concentration of the tracer gas detected by a detector (108) provisioned in the sampling chamber (107);
operating, the first isolation valve (103) coupled with each of the plurality of radiant tubes (101) in the defective group selectively to pass the fluid mixture from each of the the plurality of radiant tubes (101) to the sampling chamber (107); and
identifying, the leakage in the radiant tube (101) based on change in concentration of the tracer gas detected by the detector (108) in the corresponding radiant tube (101).

13. The method as claimed in claim 12 further comprises, allowing the tracer gas to spread in the furnace atmosphere for a pre-defined time.

14. The method as claimed in claim 12 further comprises, purging nitrogen through the one or more first channels (104) to flush out residual fluids after identifying at least one of the defective group of radiant tubes or leakage in the radiant tube.

15. The method as claimed in claim 12 further comprises, creating a negative pressure in the one or more first channels (104) and the sampling chamber (107) through a vacuum pump (110) after the purging of nitrogen.

16. The method as claimed in claim 12, wherein the tracer gas is helium.

17. The method as claimed in claim 12, wherein the pre-determined quantity of tracer gas is injected into the furnace atmosphere through a flow path of HNx mixture gas.

18. The method as claimed in claim 12, wherein the pre-determined quantity of tracer gas is determined by comparing entropy of mixture of tracer gas and HNx with entropy of HNx mixture.

19. The method as claimed in claim 18, wherein the entropy of mixture of tracer gas and HNx is maintained greater than the entropy of the HNx mixture.

20. A continuous annealing furnace comprising a system as claimed in claim 1.