FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention. - A NON-CONVENTIONAL SYSTEM AND METHOD
TO MEASURE DUST CATCHER LEVEL USING RTD (A TEMPERATURE
MEASURING DEVICE)
2. Applicant(s)
(a) NAME : STEEL AUTHORITY OF INDIA LIMITED
(b) NATIONALITY : A Govt, of India Enterprise.
. (c) ADDRESS : Bhilai Steel Plant, Bhilai - 490001,
State of Chattisgarh, India
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is
to be performed:

FIELD OF THE INVENTION
The present invention relates to a system for intelligent dust level measurement in blast furnace dust catcher using non conventional method which is particularly directed toward planned emptying of dust catcher and avoids any gas poisoning during that period.
BACKGROUND AND PRIOR ART OF THE INVENTION
A well known practice of periodical emptying of dust catcher is followed in all the blast furnaces worldwide without knowing the exact level of dust.
It is known to use ultrasonic, Radar, Capacitance, Admittance, Radio Frequency or lesser type level measuring instrument for continuous level measurement for any solid/liquid level in bunker, hopper etc. or liquid level in water tank, vessel etc. All type of level measuring instruments is having their own technology to measure level and has to be installed at the top of bunker, vessel etc.
It is experienced that the above mentioned convention types of installations especially at hazardous locations where a person/operator cannot go without proper shut down of the unit and proper safety precautions, reliable working of instruments and its proper maintenance is very difficult. Secondly the dust is entering from centre top of the dust catcher with a pressure of 1.0 to 2.5 Kg/cm2, with density of more than 15 gm/Nm3 and with a temperature of around 300 °C to 500°C and its outlet is again at the top, which creates a cyclone of heavy dust as shown in Figure 1.1 & 1.2. This dusty cyclone is the root cause of non working of any type of conventional level measuring instrument. It has to be noted that under such conditions we are blindly emptying dust from dust catcher. If dust level is more than the admissible then it affects the furnace efficiency and pollute environment by generating more disposable dust through water used in wet scrubber and also result in frequent chocking of water impulse lines used for various measurement in water line. Similarly if the dust level goes low while discharging dust catcher, fatal accident due to gas poisoning can take place. After such an accident in the year 2007 it was decided to have a reliable dust level measuring systems in blast furnace dust catcher so as to ensure human safety and at the same time furnace productivity can be improved.

The newly developed system took care of the complexities and problems of safety concerns of the general peoples and operators and it can be safely and effectively maintained during furnace in running condition also effective maintenance of dust level helps improving efficiency of gas cleaning plant. This would also favor in improving furnace efficiency, create clean environment by better recycling of dust generated from furnace and most importantly ensure human safety.
OBJECTS OF THE INVENTION
The basic object of the present invention is to overcome the disadvantages / drawbacks of the prior art.
Another object of the present invention is to provide a system for dust level measurement in dust catcher which adapted to avoid the discussed limitations and safety concerns of conventional instruments used for level measurement at various locations.
Another object of the present invention is to provide a system for dust level measurement in dust catcher adapted to avoid the problems concerning of reduced recycling of dust and excess dust generated for disposal through gas cleaning plant water outlet and polluting environment.
Yet another object of the present invention is directed to provide a system for dust level measurement in dust catcher, which would be simple and safe to install and would at the same time be effective and reliable in as far as ascertaining the dust level in dust catcher.
Also the present invention is directed to a simple and cost effective system for dust level measurement in dust catcher, which could be easily obtained cost effectively and readily installed without involving technical complexities and/or avoid safety hazards while installing and/or during use.
Yet another object of the present invention is to provide a system for dust level measurement in dust catcher where there is high temperature and most of the conventional type level measuring instrument either get burned or need foolproof cooling system.

SUMMARY OF THE INVENTION
According to one of the aspect of the present invention the system is provided a system for dust level measurement in blast furnace dust catcher at high temperature with dust cyclone at high pressure, said system comprising
a bunker/hopper means;
plurality of temperature sensor means mounted at different positions on side walls of said bunker/hopper of the blast furnace dust catcher adapted to measure temperature variation inside the dust catcher or adapted to measure temperature signal;
a controller means operatively connected with said plurality of sensor means to convert such temperature signals to plurality of digital level signals;
plurality of Gas Flow transmitter operatively connected with said controller means to provide with Gas generation from blast furnace;
a pressure and flow transmitter operatively connected with said controller means adapted to calculate Hot Blast pressure and Flow;
an open limit switch operatively connected with said controller means adapted to calculate discharge gate open position where the Level will start decreasing at the rate of Dl%/Min and D2%/Min for conical and cylindrical portion respectively only when discharge gate is open; and

a close limit switch operatively connected with said controller means adapted to provide discharge gate Close position where Stop decreasing level and start increasing level at the rate of (X21% per Nm3/hr and X22% per Nm3/hr for conical and cylindrical portion respectively during furnace running.
According to another the aspect of the present invention there is provided A method for dust level measurement in blast furnace dust catcher at high temperature with dust cyclone at high pressure using the system as claimed in claim 1 , said method comprising:
mounting of plurality of temperature sensors at various levels on side wall of dust catcher in safe location.;
averaging out the four numbers of furnace top gas temperature and utilizing the same for generating reliable digital signal for dust level in blast furnace dust catcher;
providing opening and closing feedback of dust discharge gate so that; firstly it will help in calculating the dust discharge and filling rate during model development stage and secondly during normal course it will be the point from dust level will either start decreasing or increasing based on the type of feedback available to the system;and
utilization of existing Blast Volume (Hot Air flowing to blast furnace) and Gas Make (gas generated from blast furnace) to estimate the amount of dust generated in the dust catcher and also furnace status. This signal is utilized in the model during dust catcher filling condition by

changing filling rate during low blast case and stop filling when there is no gas generated from blast furnace.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a non-conventional system and method to measure dust catcher level using RTD (a temperature measuring device).
As the furnace is directly connected to the dust catcher the temperature inside dust catcher varies more or less in accordance to that of furnace top temperature and the level of dust inside it.
Particularly the present invention relates to a system for dust level measurement in dust catcher using non conventional element like contact type temperature measuring instrument i.e. RTD, Thermocouple or any similar device which have enough physical strength to remain protected from erosion due to continuous friction with metallic dust generated from blast furnace which will be installed at different levels on side wall of dust catcher to measure continuous temperature inside it. In the present case four numbers of RTD with SS306 protection sheet having thickness of 8 mm is used.
Based on the concept of temperature variation level is detected which is explained as below, where T1, T2, T3 & T4 are the temperature sensed by the RTD1, RTD2, RTD3 & RTD4 where RTD1 is the bottom most one, as the sequence goes from bottom to top most level of the dust catcher. Tavg is the average furnace top temperature calculated in PLC logic by taking the average of 4 number of uptake temperature which is already available in the PLC system. Average Top Gas Temperature = (Tempi + Temp2 + Temp3 + Temp4)/4 't' is the time in seconds, so that Tl(t=0) is the first sample, T2(t=1) the second sample and so on.
Case-I:

When bunker/hopper is completely empty, then temperature at all the four location will vary according to average furnace top gas temperature as shown in figure 3. Logic is made for this condition and very low level signal is generated as per equation given below: T4(t=0) # T4(t=1) # T4(t=2) # T4(t=3)
T3(t=0)) # T3(t=1) # T3(t=2) # T3(t=3)
T2(t=0) # T2(t=1) # T2(t=2) # T2(t=3)
Tl(t=0) # T1(t=1) # Tl(t=2) # Tl(t=3)
If there is continuous variation in all the four temperature w.r.t last value then level is below bottom most RTD and Very Low level signal is generated as shown in figure-3.
Case-II:
As the dust level inside the catcher increases and when the bottom most RTD gets submerged in the dust, then the sensor will not have any temperature variation or will have negligible variation and the rest of the RTDs will vary according to average furnace top temperature as shown in figure 4. Logic is made for this condition and low level signal is generated as per equation given below:
T4(t=0) # T4(t=1) # T4(t=2) # T4(t=3)
T3(t=0)# T3(t=l) # T3(r=2) # T3(t=3)
T2(t=0) # T2(t=l) # T2(t=2)# T2(t=3)
(Tl(t=0) # Tl(t=l) # Tl(t=2) # Tl(t=3) < 1°C} and
{Tavg(t=0) # Tavg (t=l) # Tavg (t=2) # Tavg (t=3) > 3°C}
If there is no temperature variation in 1st RTD for 30 minutes and continuous variation of temperature in all the other three RTDs and Average Top Gas then level is between 1st & 2nd RTD and Low level signal is generated.

Case-III:
When the catcher is not completely empty but dust level is above 2nd (2nd from bottom) sensor, then both 1st and 2nd temperature sensor will not have any temperature variation or will have negligible variation but other two RTD will vary in accordance with the average furnace top temperature as shown in figure 5.
Logic is made for this condition and level Normal signal is generated as per equation given below:
T4(t=0) # T4(t=l) # T4(t=2) # T4(t=3)
T3(t=0) # T3(t=1) # T3(t=2) # T3(t=3)
T2(t=0) = T2(t=l) = T2(t=2) = T2(t=3) < 1°C and
Tl(t=0) = Tl(t=l) = Tl(t=2) = Tl(t=3) < l°C and
{Tavg(t=0) # Tavg (t=l) # Tavg (t=2) # Tavg (t=3) > 3°C}
If there is no temperature variation in 1st & 2nd RTD for 30 minutes and continuous variation of temperature in other two RTDs and Average Top Gas than level is between 2nd & 3rd RTD and Normal level signal is generated.
Case-IV:
In this case as the catcher is neither completely empty nor completely full, but dust level is above 3rd (3rd from bottom) sensor, then those three temperature sensor will not have any temperature variation or will have negligible variation except for the 4th one which is installed for the maximum level as shown in figure 6. Logic is made for this condition and level High signal is generated as per equation given below:
T4(t=0) # T4(t=l) # T4(t=2) # T4(t=3)

T3(t=0) = T3(t=l) = T3(t=2) = T3(t=3) < 1°C and
T2(t=0) = T2(t=l) = T2(t=2) = T2(t=3) < 1°C and
Tl(t=0) = Tl(t=l) = Tl(t=2) = Tl(t=3) < l°C and
{Tavg(t=0) # Tavg (t=l) # Tavg (t=2) # Tavg (t=3) > 3°C}
If there is no temperature variation in 1st, 2nd & 3rd RTDs for 30 minutes and continuous variation of temperature in 4th RTD and Average Top Gas than level is between 3rd & 4th RTD and High level signal is generated.
Case-V:
When the dust catcher is completely filled all the sensors will get submerged in dust and hence they will not show any temperature variation or will have negligible variation even when there is wide variation in average furnace top temperature as shown in figure 7. Logic is made for this condition and level very High signal is generated as per equation given below:
T4(t=0) = T4(t=l) = T4(t=2) = T4(t=3) < 1°C and
T3(t=0) = T3(t=l) = T3(t=2) = T3(t=3) < 1°C and
T2(t=0) = T2(t=l) = T2(t=2) = T2(t=3) < 1°C and
Tl(t=0) = Tl(t=l) = Tl(t=2) = Tl(t=3) < l°C and
{Tavg(t=0) # Tavg (t=l) # Tavg (t=2) # Tavg (t=3) > 3°C}
If there is no temperature variation in any of the RTDs for 30 minutes and continuous variation of temperature in Average Top Gas than level is above 4th RTD and Very High
level signal is generated.

Further if due to any reason the furnace is down (stopped) that is either for maintenance or due to any breakdown, then steps are included in the logic utilizing the blast volume parameter- which is the cold blast volume measured using orifice plate method- to pause the mathematical model and to hold the current level so that it will not generate the level Very High signal as all the RTDs will be showing no/negligible variations during down time. Like in the case where there is no temperature variation in any of the RTDs for 30 minutes and there is no variation in average furnace top temperature, or the Air flow to Blast Furnace is less than 500 Nm3/hr. then the last status holds. When the furnace restarts the model starts off from the status at which it was held.
The above described system only generates alarms at different dust levels and the dust filling rate is slow that it used to take a minimum of 40-50 hours for the status to shift from one level to another. As this system was not possible to indicate the exact dust level inside the catcher this model was not sufficient.
In order to develop a system which is enabled for continuous level indication of dust inside the catcher the above described model is further enhanced to generate a continuous level measurement signal, making use of the above mentioned alarm signals, the dust filling and rate- which is directly proportional to the blast furnace gas generation (a parameter measured using flow transmitter)- of the conical (X21%/Nm3) & the cylindrical ( X22%/Nm3) shape of the dust catcher and discharging rate- calculated by taking multiple readings of the time taken for the level to jump from one level to its next lowest level while emptying of dust catcher
For a more refined 1 model the discharge gate opening and closing feedback which is generated with the help of open limit switch and close limit switch is also included for dust discharging and filling time calculation.
Based on discharge gate opening and closing time picked from the PLC with respect to the feedback signal received from the limit switches installed at the screw conveyor for the discharge gate, furnace running status/condition and discreet dust level signal generated as explained earlier, the dust filling rate and dust discharging rate was calculated.

• Dust generated from blast furnace is 13-15 gm/Nm3/hr. approximately.
• Dust transferred from dust catcher to gas cleaning plant is 15-20 gm/Nm3/hr. approximately.
• Hence dust settled inside the dust catcher is 11.5 - 13.5 gm/Nm3/hr. approximately.
• If dust settling inside the dust catcher is taken as 13.0 gm/Nm3/hr. and Y Nm3/hr. is the blast furnace gas generated; than dust deposited in the dust catcher in one hour is 13.0* Y.
• Converted this amount of dust deposited into % level by knowing the density (p) of dust and dimension of the dust catcher (Height (h) & Diameter (d)).
Based on all this information gathered as indicated in Table 1.1 a software model was developed to indicate continuous dust level in dust catcher on PLC screen online. A general formula is derived for dust filling rate calculation based on above parameters and same is as given below:
Filling Rate ((%/min) =1.667*10-8*(DW*F*S)/(V*D)
Where:
Dw = dust concentration in gas make (gm/m3) = 13.0 (for Bhilai Steel Plant)
F = Gas Make in (Nm3/Hr.) = On-line value
D = density of dust (T/m3)= 1.16 (for Bhilai Steel Plant)
S = Span (%) = 98 (in our case)
V = Volume to be measured (m3) = 312.1275 (for Bhilai Steel Plant)
Very Low Level (Below RTD1) : LL = below 24% (for Bhilai Steel Plant)
Low Level (Between RTD 1 & RTD2) : L = 24% to 47% (for Bhilai Steel Plant)
Normal Level (Between RTD2 & RTD3) : N = 47% to 77% (for Bhilai Steel Plant)
High Level (Between RTD3 & RTD4) :H = 77% to 98% (for Bhilai Steel Plant)
Very High Level (Above RTD4) : HH= above 98% (for Bhilai Steel Plant)
Flowchart for the dust filling and discharging is shown in the Figure-16 and Figure-17.

Table 1.1
SL Information Collected Hardware Device used Purpose
No.
01 Temperature at four Contact type temperature Generate digital signal based on
different location measuring Device temperature variation.
02 Gas generation from Gas Flow transmitter Calculate gust generation per
blast furnace. minute (W gm/Nm3)
03 Hot Blast pressure and A pressure and Flow To know the Blast Furnace running
Flow. Transmitter condition.
04 Discharge gate open Open Limit switch Level will start decreasing at the
position rate of Dl%/Min and D2%/Min
for conical and cylindrical portion respectively only when discharge gate is open.
05 Discharge gate Close Close Limit Switch Stop decreasing level and start
position increasing level at the rate of (X21% per Nm3/hr and X22% per Nm3/hr for conical and cylindrical portion respectively during furnace running.
Any mismatch in actual level detected by the sensor and level calculated through model is corrected at all the level where sensor is mounted. If calculated value reaches first at a point where sensor is installed than it will wait till actual signal comes, similarly if actual signal comes first than calculated signal will jump to actual position and from there once again it will start increasing level based on software model thus makes correction at every level if any. A complete one cycle from dust filling to dust discharging is shown with the help of various snap shots taken from PLC screen as shown from Figure 8 to Figure 14.

According to another embodiment of the present invention there is provided a method for dust level measurement in blast furnace dust catcher at high temperature with dust cyclone at high pressure using the above system comprising:
Mounting of temperature sensors like RTD, Thermocouple and any such type of sensor at various levels on side wall of dust catcher in safe location.
Averaging out the four numbers of furnace top gas temperature and utilizing the same for generating reliable digital signal for dust level in blast furnace dust catcher.
Providing opening and closing feedback of dust discharge gate so that; it helps in deciding the time when to start or stop the decrease or increase of dust level in dust catcher. Explained in the Table 1.1
Utilization of existing Blast Volume (Hot Air flowing to blast furnace) and Gas Make (gas generated from blast furnace) to estimate the amount of dust generated in the dust catcher and also furnace status. This signal is utilized in the model during dust catcher filling condition by continuous changing of filling rate depending on gas generated from'the blast furnace and stop filling when there is no gas generated from blast furnace.
It is thus possible by way of the above disclosed system for level measurement at hazardous locations for human and equipment using simple and low cost temperature measuring device like RTD, Thermocouple and any other similar contact type sensor to achieve simple cost effective and reliable dust level measuring system in a blast furnace dust catcher, which can be installed safely away from vicinity of the hazardous locations and facilitate safety related shut down of operations and/or for maintenance purposes of such measuring systems.
Advantageously, the above system of the invention could be developed after extensive studies of the sensor behavior in dust, pressure and temperature. Importantly, apart from facilitating safe measure of dust level in blast furnace dust catcher at hazardous locations the maintenance of the installed system, which is favorably located at safe location, as also been made safe and simple.

A second advantage is its cost effectiveness; cost of one RTD is only Rs;4000/- compare to a radar level sensor which can work at this temperature only if dust turbulence or cyclone of dust is not present is minimum Rs.40,00,000/-.
A third advantage of the present system does not need any cooling arrangement as it is made up of solid SS316 Bar stock of thickness 8 mm compare to radar or any conventional type level sensors needs continuous nitrogen and water cooling, recurring cost for nitrogen and water, which is not required in this case.
A fourth advantage of the present system is maintenance free system fit and forget type compare to other convention level instrument need periodical inspection and cleaning time to time. This is because present system is rugged and having no electronic component present inside the sensor compare to other conventional type level measuring instrument.
The level measurement involving the system of the invention thus ensures safety of the instruments and also of the human being responsible for maintenance of such instruments. Importantly, while the system of the invention takes care of the drawbacks and limitation associated with the conventional level measuring systems also more importantly further ensures that the effectiveness and reliability of level measurement is maintained.
The possible horizontal mounting of sensor on side wall of blast furnace dust catcher as compared to the vertical mounting of the instruments taught under the conventional art; ensure safe locations for the instruments as well as the user. The instrument under the present system is thus approachable with safety by any operating/maintaining personnel at any time as and when required. Importantly also, the maintenance and checking of the instrument in the system of the invention will be possible without requiring shut down.
The details of the inventions, its objects and advantages are explained hereunder in greater detail through illustrations as per the following accompanying drawings:

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Other features as well as the advantages of the invention will be clear from the following description. In the appended drawing:
Figure 1.1 illustrates Construction of Dust Catcher
Figure 2 illustrates Location of Dust Catcher Level
Figure 3 illustrates Level Very Low
Figure 4 illustrates Level Low
Figure 5 illustrates Level Normal
Figure 6 illustrates Level High
Figure 7 illustrates Level Very High
Figure 8 illustrates Increasing of dust level at the rate of X21%/Nm3 /hr
Figure 9 illustrates Increase in level from Low Level
Figure 10 illustrates Dust discharging started from 71% Level
Figure 11 illustrates Change in filling rate as per change in dust catcher shape
Figure 12 illustrates Zero dust filling rate when furnace stopped intermittent
Figure 13 illustrates Offset Adjustment during filling if actual signal is delayed
Figure 14 illustrates Offset Adjustment during filling if calculated value is delayed
Figure 15 illustrates Conventional type level Measuring Device
Figure 16 illustrates flow chart for filling of dust catcher.
Figure 17 illustrates flow chart for discharging of dust catcher.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWING
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and illustrate the best mode presently Contemplated for carrying out the invention. Further functioning of the system and method has been discussed below to describe the way it operates. However, such description should not be considered as any limitation of scope of the present system. The structure thus conceived is susceptible of numerous modifications and variations, all the details may furthermore be replaced with elements having technical equivalence. In practice the materials and dimensions may be any according to the requirements, which will still be comprised within its true spirit.
Figure 2 illustrates the system of measurement of dust level in blast furnace dust catcher where there is continuous variation of temperature and pressure at hazardous locations using RTD, Thermocouple of any other similar contact type temperature measuring device in accordance with the present invention.
Figure 15 illustrates the arrangement and installation of a conventional type level measurement using Ultrasonic, Radar, Laser, capacitance or Radio frequency type instrument;
Reference is first invited to accompanying figure 15 which illustrates in detail a conventional system for level measurement involving the Ultrasonic, Radar, Laser, capacitance or Radio frequency type instrument. Such instruments used for level measuring are conventionally known to be, used to measure solid level in bunker, hopper etc. or liquid level in water tank/vessel. As shown in.said figure the installation of such conventional level instrument is recommended at the top of the bunker/hopper. In such system for non contact type sensor, the sensor is thus required to be positioned at the center of the outflow funnel so that an echo is received till silo is empty.
In the second case for contact type level sensor, the sensor is either rope or rod type required to be positioned at the center of the outflow funnel or any other location hanging from top and in any case it should not touch the side wall of the hooper so that dielectric of material should be measured without any interference (a false signal will be generated if goes near to wall or touches side wall).

It would be apparent from the above conventional type level measuring instrument Installation that such installations are hazardous, being directly facing possible contents and the operator/person installing/using can not reach the sensor installed without arranging proper shut down and following proper safety precautions. This necessarily affect the working of such instrument as well as its proper maintenance and it is found that even in case of shut down working in such an environment is highly unsafe. Apart from this no conventional level sensor (Contact type or non contact type) can work under this environment where temperature is some time going as high as 600 °C and dust cyclone/turbulence with a pressure variation from 1.0 Kg/cm2 to 2.5 Kg/cm2.
Figure 2, discloses the safe and user friendly horizontal installation of said temperature sensor on the side wall of dust catcher in the level measuring system of the invention. As clearly illustrated in the figure the four temperature measuring sensor is installed on the side wall of the dust catcher. For the purpose in the system of the invention the sensors (T1, T2, T3 & T4) gives Very Low Level, Low Level, Normal Level, High Level and Very High Level signal as per logic developed in the PLC.
Importantly, as clearly apparent from the above the present system illustrated in figure 2 clearly avoids the vertical mounting of instrument at the center top of the bunkers/hoppers and make possible the mounting of the instrument horizontally away from the direct vicinity of the hazardous locations w.r.t human and Instrument. Such an arrangement also favors approaching the instruments safely as and when required and enables maintenance of the instrument without requiring shut down.
• Dust Catcher-Low = T1;
• Dust Catcher-Normal = T2;
• Dust Catcher-High = T3;
• Dust Catcher - High High = T4;
• Uptake Avg = Average Top Gas Temperature

As per Figure-3 all the four temperature (Tl, T2, T3 & T4) is fluctuating continuously as per average furnace top temperature and hence very low level signal is generated.
As per Figure-4 all the Three temperature (T2, T3 & T4) is fluctuating continuously as per average furnace top temperature but Temperature (Tl) is constant that means RTD (Tl) is buried inside dust and hence Low Level signal is generated.
As per Figure-5 temperature (T3 & T4) is fluctuating continuously as per average furnace top temperature but Temperature (Tl & T2) is constant that means RTD (Tl) and RTD (T2) is buried inside dust and hence Normal Level signal is generated.
As per Figure-6 temperature (T4) is fluctuating continuously as per average furnace top temperature but Temperature (Tl, T2 & T3) is constant that means RTD (Tl), RTD (T2) & RTD (T3) is buried inside dust and hence High Level signal is generated.
As per Figure-7 all the four temperature (Tl, T2, T3 & T4) is constant though average furnace top temperature varying continuously and hence Very High Level signal is generated.
Figure 8 shows normal filling of conical portion of dust catcher at the rate of X21%/Nm3/hr after getting emptying up to 7.3% level.
In our case below 11% level it is taken as very low level (Tl). It can be seen from the figure-9 that once calculated value reaches 11%, this reading holds and only after getting feedback of actual level reached 11% from RTD (Tl) level starts increasing at the rate of X21%/Nm3/hr. depending upon gas generation from blast furnace and shape (volume) of the dust catcher.

Figure 10 shows discharging of dust catcher which started from 71% level when discharge gate was opened at 10:42 hrs. at the rate of Dl% per minute & D2% per minute as per shape of the dust catcher and level came down from 71% to 11% in 40 minutes at 11:22 hrs.
Figure-11 is again a filling cycle where increasing trend of level changes from existing X21%/Nm3 /hr to X22%/ Nm3 /hour, depending upon change in shape (volume) of duct catcher. It can be seen from above figure that vassal shape changes from conical to cylindrical from 40%.
Figure-12 is again a filling cycle where it can be sheen that there is no change in level signal when furnace stops due to any reason. During stop condition (16:50 hrs to 17:14 hrs.) as per above figure there is no gas generation and hence no dust accumulation.
Figure-13 is again a filling cycle where increasing trend of level based on calculated value reaches first to 2nd RTD (T2) that is 54% than this reading holds till digital signal from RTD (T2) is received confirming actual signal reached 54% level.
. Figure-14 is again a filling cycle where increasing trend of level based on calculated value reached only to 89.7% but the actual level reached first which was confirmed by the third RTD (T3). Hence the there is sudden jump in the reading from 89.7% to 90% to adjust the offset or calculation error for the next cycle.
Figure 15 illustrates the arrangement and installation of a conventional type level measurement using Ultrasonic, Radar, Laser, capacitance or Radio frequency type instrument;
Features:
• A system for dust level measurement in a blast furnace dust catcher especially at hazardous locations w.r.t human and Instrument where dust comes with high gas pressure and temperature varies from 1.0 Kg/cm2 to 2.5 Kg/cm2 and 200 °C to 600 °C.

• Use of four numbers of temperature measuring devices like RTD, Thermocouple or and contact type temperature sensor in place of conventional level measuring instrument to detect the level at four different level;
• Conversion of available temperature signal into a reliable digital level signal (Very Low, Low, High and Very High) in the dust catcher with the help other signal like furnace top gas temperature and hot blast pressure.
• Conversion of available digital dust level into reliable continuous level in terms of percentage (%) in the dust catcher with the help of other signal like dust catcher opening and closing status, Blast Volume rate, amount of gas generation and blast furnace running status
• Three month data collected with various conditions like low blast, intermittent furnace stoppages etc. and calculated dust filling rate and dust discharge rate.
• Introduction of dust catcher discharge gate position for starting point of increasing or decreasing the dust level in the dust catcher during filling or discharging of dust catcher.
• Accuracy of dust level is achieved by Introducing air blast volume and dust catcher discharge gate position, discharge gate operating thermal relay status and screw conveyor running status.

WE CLAIM
1. A system for dust level measurement in blast furnace dust catcher at high temperature with dust cyclone at high pressure, said system comprising
a bunker/hopper means;
plurality of temperature sensor means mounted at different positions on side walls of said bunker/hopper of the blast furnace dust catcher adapted to measure temperature variation inside the dust catcher or adapted to measure temperature signal;
a controller means operatively connected with said plurality of sensor means to convert such temperature signals to plurality of digital level signals;
plurality of Gas Flow transmitter operatively connected with said controller means to provide with Gas generation from blast furnace;
a pressure and flow transmitter operatively connected with said controller means adapted to calculate Hot Blast pressure and Flow;
an open limit switch operatively connected with said controller means adapted to calculate discharge gate open position where the Level will start decreasing at the rate of Dl%/Min and D2%/Min for conical and cylindrical portion respectively only when discharge gate is open; and

a close limit switch operatively connected with said controller means adapted to provide discharge gate Close position where Stop decreasing level and start increasing level at the rate of (X21% per Nm3/hr and X22% per Nm3/hr for conical and cylindrical portion respectively during furnace running.
2. System as claimed in claim 1 wherein said temperature sensors comprises RTD, Thermocouple and like.
3. System as claimed in claim 1 wherein said plurality of temperature sensor are four in number(Tl, T2, T3 & T4).
4. System as claimed in claim 1 wherein said sensors gives Very Low Level, Low Level, Normal Level, High Level and Very High Level digital signal.
5. System as claimed in claim 1 wherein said dust level measurement in a blast furnace dust catcher especially at hazardous locations w.r.t human and Instrument where the dust has high gas pressure from 1.0 Kg/cm2 to 2.5 Kg/cm2 and temperature varies from 200 °C to 600 °C.
6. System as claimed in claim 1 wherein said plurality of sensors are mounted horizontally away from direct vicinity of hazardous locations.
7. A method for dust level measurement in blast furnace dust catcher at high temperature with dust cyclone at high pressure using the system as claimed in claim 1 , said method comprising:

mounting of plurality of temperature sensors at various levels on side wall of dust catcher in safe location.;
averaging out the four numbers of furnace top gas temperature and utilizing the same for generating reliable digital signal for dust level in blast furnace dust catcher;
providing opening and closing feedback of dust discharge gate so that; firstly it will help in calculating the dust discharge and filling rate during model development stage and secondly during normal course it will be the point from dust level will either start decreasing or increasing based on the type of feedback available to the system; and
utilization of existing Blast Volume (Hot Air flowing to blast furnace) and Gas Make (gas generated from blast furnace) to estimate the amount of dust generated in the dust catcher and also furnace status. This signal is utilized in the model during dust catcher filling condition by changing filling rate during low blast case and stop filling when there is no gas generated from blast furnace.
8. Method as claimed in claim 1 wherein said temperature sensors comprises RTD, Thermocouple and like.
9. A system for dust level measurement in blast furnace dust catcher at high temperature with dust cyclone at high pressure as herein substantially described and illustrated with the accompanying drawings.

10. A method for dust level measurement in blast furnace dust catcher at high temperature with dust cyclone at high pressure as herein substantially described and illustrated with the accompanying drawings.