FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
1 TITLE OF THE INVENTION :
A SYSTEM FOR PRESSURE MEASUREMENT OF GAS IN HIGH DUSTY AREA/HIGH DUST AND/OR HUMID AREA.
2 APPLICANT (S)
Name : STEEL AUTHORITY OF INDIA LIMITED.
Nationality : A Govt, of India Enterprise;
Bhilai Steel Plant, Bhilai-490001, State of Chattisgarh,India.
3 PREAMBLE TO THE DESCRIPTION
COMPLETE
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 pressure measurement of gas in high dusty area or high dusty and humid area. More particularly, the present invention is directed to providing a system for pressure measurement with high accuracy and minimum error in a reliable manner using selectively a three layer tapping point configuration with purging of high pressure Compressed air or Nitrogen without requiring any Rota-meter as in case of backpressure measurement type tapping point based conventional method, ensured improved performance and reliability with respect to choking of the pressure measuring impulse lines. The system is equally efficient for pressure measurement in high dust area including both high positive pressure such as in blast furnace intermediate pressure, Blast Furnace top gas pressure/Bin pressure and/or very low pressure such as Coke Oven gas pressure respectively. Advantageously, the measured pressure is compensated for the known constant error measured due to nitrogen back pressure using an error compensation software in the level-I computer (PLC or DCS) before displaying the correct reading on HMI screen or for use in control action. Use of three layered multi hole tapping point as per the system of pressure measurement in high dust medium according to the present invention ensure accuracy better than 0.1% free of any chances of choking, making the system effective for precise and reliable pressure measurement in high dust area in a variety of industry.
BACKGROUND OF THE INVENTION
Precise measurement of pressure in air/gas medium for requirement of industrial process and its control is essential in a number of industrial applications. In steel plants, Blast furnace and Coke oven are the equipments which need constant monitoring of operating pressure within the equipments under working condition and in a high dust or high dust plus humid environment. Accuracy in measurement of pressure/parameter under such highly dusty atmosphere requires special equipments to minimize error and reliable functioning.

Well known practices of pressure measurement for different site condition are as given below:

Si. No. Methodology Site Condition
01 Conventional "y"'type tapping. No dust and clean gas or dusty environment in Suction mode.
02 Conventional "Y" type tapping with Dry dusty medium with positive
controlled air or nitrogen purging with the help of Rota-meter. pressure.
03 Remote seal pressure transmitter Pressure measurement in dusty liquid, Tar or other chemical.
It is known to use pressure transmitter connected to various above mentioned methodology to measure pressure of different medium. It is experienced that frequent problem of fine choking occurs with the above mentioned conventional types of installations especially at locations like:
(i) Blast furnace top pressure or blast furnace body pressure at various levels, where heavy dust is present and some time even molten metal/slag can also come at the mouth of tapping point and block the hole.
(ii) Raw Coke Oven gas pressure measurement where traces of Tar, Heavy Benzol, Naphtha etc. are present.
Blast furnace body pressure measurement and monitoring helps in controlling the differential pressure at various levels as it is very important for smooth operation of blast furnace, This helps the operator to know the burden permeability at different levels, burden movement and hot air path inside the blast furnace and thus enables him to take corrective action accordingly. More the number of pressure points along the furnace height better the burden movement control and hence improved productivity. Similarly blast furnace top gas pressure and Bin/Gas Seal pressure measurements are very important for material charging and burden movement inside the furnace. Normally, presence of high positive pressure with heavy dust inside the blast furnace process, causes choking of pressure tapping points very frequently. Rectification/cleaning are not possible without shutdown. To overcome this type of problem, many industries worldwide use nitrogen for continuous purging through a Rota-meter and measure its back pressure near tapping. But this also

causes problem due to insufficient flow/pressure to prevent dust or liquid material entering inside the tapping.
Similarly coke oven gas generated from coke oven batteries consists of many chemicals like Tar, Heavy Benzol, Naphtha and many more chemicals which results in frequent choking of impulse line. As this measurement is very important multiple tapping points are provided and regular cleaning of tapping points fs done. Because of very low range of measurement even nitrogen purging with rotameter is also not possible.
Presently a pressure measurement by back measuring pressure of purged nitrogen through rotameter is installed in one of blast furnace. But the same is getting choked and required periodical cleaning which is not possible in case of blast furnace body pressure measurement due to high temperature and high carbon monoxide present in the gas necessitating maintenance with shutdown of the furnace and consequent loss of production.
There has been therefore a persistent need in the field of pressure measurements in high dust gas medium to developing a system involving appropriate tapping point which would ensure precise and reliable pressure measurement required for process control and monitoring without the problem of choking of tapping point holes or induce error as usually occur in case of conventional rotameter based back pressure related error in measurement. The system would work with required accuracy, efficiency and reliability for both high positive pressure and very low positive pressure.
The newly developed system by way of the present invention is an attempt to providing a system of accurate pressure measurement of dusty gas environment which will take care of the complexities and problems of pressure measurement in both the above described conditions with minimum error in reliable manner.
OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to providing a system for pressure measurement involving selectively deployed three layered taping point

configuration adapted to overcome the disadvantages/drawbacks of the existing apparatus and method of pressure measurement in high dust medium.
Another object of the present invention is to provide a system for pressure measurement of blast furnace body and top gas or any other medium consists of heavy dust which is adapted to avoid the discussed limitations avoiding choking or using rotameter and improve furnace operation.
Another object of the present invention is directed to provide a system for pressure measurement of gas medium such as in Coke Oven gases consisting of many hazardous gases/chemicals which is adapted to maintain desired measuring accuracy avoiding the problem of choking or error due to rotameter based back pressure sensing and thus ensure improved process control.
Yet another object of the present invention is directed to provide a system for pressure measurement in dusty gas medium, which would be simple and safe to install and would at the same time be effective and reliable in ascertaining the gas pressure measurement.
A further object of the present invention is directed to a simple and cost effective system for pressure measurement in a dusty gas medium, which could be easily obtained cost effectively and readily installed without involving technical complexities and avoiding safety hazards during installation or use.
A still further object of the present invention is directed to provide a system for pressure measurement in dusty gas medium where there is high temperature and high dust medium present at the tapping point and where most of the conventional back pressure measured Rota-Meter type nitrogen purging pressure measuring instrument fails and requires frequent cleaning,
Yet another object of the present invention is directed to provide not only a reliable but accurate system for pressure measurement in dusty gas medium where there is high temperature and high dust, involving an improved three layered tapping point configuration which not only takes care of accuracy of the measurement but at the same time ensures its reliability.
A further object of the present invention is directed to provide a safe system for pressure measurement in dusty gas medium at high temperature and with presence

of high percentage of carbon monoxide in the gas in the atmosphere maintaining safety of both for the instrument as well as the operating personnel.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to a system for pressure measurement of gas along the height in high dusty area/ high dust and/or humid area comprising
a three layer tubular coaxial tapping point comprising an inner central first tubuler layer having diameter of less than 10 mm, an intermediate tubular second layer with multiple holes selectively dispensed on surfaces of said first and second layer; and an outer third tubular layer welded to furnace body for installation wherein the dimensions of tubes and holes are variable depending on process conditions, accuracy and reliability of measurement required;
means for continuous purging with high pressure nitrogen ;
said three layer coaxial tapping points with multiple holes in said first and second layers adapted to reduce error during said pressure measurement for display and/or process control.
A further aspect of the present invention is directed to said system for pressure measurement comprising an orifice placed in the flow path of inlet nitrogen for purging through said inner first layer at required pressure and having means adapted to sense and convert the raw pressure signal of measured process pressure and nitrogen back pressure to corrected signal by compensating for error for displaying on HMI screen or for said process control.
A still further aspect of the present invention is directed to said system for pressure measurement wherein said first layer diameter is maintained in the range of 6 mm to 10 mm and preferably 8 mm resulting in nitrogen purging with high pressure even at the tip of the tapping point for low flow rate, favouring continuous nitrogen purging

and measuring its back pressure to generate high purging pressure and low flow near end of the tapping point with constant minimum error.
A still further aspect of the present invention is directed to said system for pressure measurement wherein the sum of the area of holes on the said second layer is maintained at least 1.5 times more than the sum of the area of the holes on the first layer to ensure minimum measuring error;
A still further aspect of the present invention is directed to said system for pressure measurement wherein said three layer coaxial tapping point to measure intermediate pressure of blast furnace comprising coaxial tubular stainless steel involving said first layer (Inner) pipe having inner diameter of 8 mm and outer diameter of 12 mm with 12 hole of size 3 mm; said second layer having inner diameter of 18 mm and outer diameter of 22 mm with 8 hole of size 5 mm and said third layer having inner diameter of minimum 30 mm welded on furnace body or Pipe body and total length of said first layer of the tapping point shall be as per thickness of furnace body and site condition.
A still further aspect of the present invention is directed to said system for pressure measurement wherein said three layer coaxial tapping point to measure Blast furnace top gas/Bin pressure comprising said first layer (Inner) pipe having inner diameter of 8 mm and outer diameter of 12 mm with 12 number holes of size 3 mm; said second layer having inner diameter of 18 mm and outer diameter of 22 mm with 8 number holes of size 5 mm and said third layer having inner diameter of minimum 30 mm welded on furnace body or Pipe body and total length of said first layer of the tapping point shall be from 450 mm to 600 mm approximately.
A still further aspect of the present invention is directed to said system for pressure measurement wherein said three layer coaxial tapping point to measure coke oven low gas pressure comprising said first layer (Inner) pipe having inner diameter of 8 mm and outer diameter of 12 mm with 9 number holes of size 3.5 mm; said second

layer having inner diameter of 18 mm and outer diameter of 22 mm with 8 number holes of size 5 mm and said third layer having inner diameter of minimum 30 mm welded on furnace body or Pipe body and total length of said first layer of the tapping point shall be from 450 mm to 600 mm approximately.
A still further aspect of the present invention is directed to said system for pressure measurement wherein for pressure measurement of blast gas at different level along the body of blast furnace, Nitrogen at 3 to 5 preferably about 4 Kg/cm2 is passed through an orifice having inner diameter of 3.5 mm whereby nitrogen goes inside the blast furnace and do not allow chocking of tapping.
A still further aspect of the present invention is directed to said system for pressure measurement wherein for pressure measurement of blast gas for blast furnace top and bin/gas seal, Nitrogen at 4 Kg/cm2 is passed through an orifice having inner diameter of 2 mm to 4 mm preferably about 3.5 mm or 2.5mm, whereby nitrogen goes inside the blast furnace and do not allow chocking of tapping.
A still further aspect of the present invention is directed to said system for pressure measurement as claimed in anyone of claims 1 to 9, wherein for pressure measurement of coke oven low gas pressure, Nitrogen at 0.5 to 2.0 preferably about 1 Kg/cm2 is passed through an orifice having inner diameter of 1.5 mm to 2.5 mm preferably about 2.0 mm which goes inside the blast furnace and do not allow chocking of tapping.
Yet another aspect of the present invention is directed to a method for pressure measurement of gas along the height in high dusty area/ high dust and/or humid area involving the system as described above comprising carrying out said pressure measurement involving preferably:

for pressure measurement of blast gas at different level along the body of blast furnace, Nitrogen at 4 Kg/cm2 is passed through an orifice having inner diameter of 3.5 mm whereby nitrogen goes inside the blast furnace and do not allow chocking of tapping due to any reason and wherein at a differentia! pressure (Nitrogen pressure before orifice and process pressure) of 2.2 Kg/cm2, maximum error occurring for a measured pressure of 2 Kg/cm2 is 13.24 mmWC;
for pressure measurement of blast gas for blast furnace top and bin/gas seal, Nitrogen at 4 Kg/cm2 is passed through an orifice having inner diameter of 3.5 mm or 2.5mm, whereby nitrogen goes inside the blast furnace and do not allow chocking of tapping due to any reason and wherein at a differential pressure (Nitrogen pressure before orifice and process pressure) of 2.2 Kg/cm2 maximum error occurs for a measured pressure of 2 Kg/cm2 is 9 mmWC for 3.5 mm diameter orifice and 2.15 mmWC for 2.5 mm diameter orifice; and
for pressure measurement of coke oven low gas pressure, Nitrogen at 1 Kg/cm2 is passed through an orifice having inner diameter of 2.0 mm which goes inside the blast furnace and do not allow chocking of tapping due to any reason and wherein at a differential pressure (Nitrogen pressure before orifice and process pressure) of 1.0 Kg/cm2 maximum error occurs for a measured pressure of 20 mmWC is 0.69 mm for 3.5 mm diameter orifice and 0.24 mmWC for 2.0 mm diameter orifice.
A still further aspect of the present invention is directed to said method wherein known constant error measured due to nitrogen back pressure is adjusted in the Level-1 computer (Automation System, PLC or DSC) before the correct reading on HMI screen or used for controlling action of the field device.
The various other objects and advantages of the present invention is described in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1A & IB: is the schematic drawing of a conventional tapping point of pressure measurement apparatus showing its longitudinal sectional view (1A) using back measuring pressure of purged nitrogen and its connection through rotameter (IB) for installation on blast furnace.
Figure 2A: is the schematic drawing showing longitudinal section of the pressure measuring apparatus with three layered tapping point according to the present invention for intermediate pressure measurement of blast furnace body at high temperature with heavy dust at high pressure, showing the disposition of holes in the first and second layer.
Figure 2B: is the schematic drawing showing longitudinal section of the pressure measuring apparatus with three layered tapping point according to the present invention for pressure measurement furnace top gas and bin pressure measurement at high temperature with heavy dust at high pressure.
Figure 2C: is the schematic drawing showing longitudinal section of the pressure measuring apparatus with three layered tapping point according to the present invention for pressure measurement at very low pressure medium consisting of many impurities like Tar, Heavy Benzol, Neptha etc responsible for impulse line choking such as raw Coke Oven gas.
Figure 3: is the graphical piot of percent error vs differential pressure showing superimposition of result obtained with conventional as well as modified pressure tapping for Blast Furnace Intermediate Pressure.
Figure 4: is the graphical plot of percent error vs differential pressure showing superimposition of result obtained with Conventional and modified pressure tapping for Blast Furnace Top/Bin Pressure with 3.5 mm orifice Id.
Figure 5; is the graphical plot of percent error vs differential pressure showing superimposition of result obtained with conventional and modified pressure tapping for Blast Furnace Top/Bin Pressure with 2.5 mm orifice Id.

Figure 6: is the graphical plot of percent error vs differential pressure showing superimposition of result obtained with compression of result between conventional and modified pressure tapping for Very Low Pressure measurement with 3.5 mm Orifice Id.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES
The present invention relates to a system for accurate and reliable pressure measurement involving three layer Tapping Point installed to measure pressure of high dusty medium such as in blast furnace and/or coke oven, without using Rota-Meter for measuring back pressure of purged nitrogen.
Reference is first invited to the accompanying Figure 1A & IB that show the conventional tapping point configuration of pressure measurement apparatus showing its longitudinal sectional view(lA) using back measuring pressure of purged nitrogen and its connection through rotameter(lB) for installation on blast furnace. In the existing tapping point configuration, presently back pressure is measured at the inlet as shown in Figure 1.2, so that the pressure measured is having more error. As for example, to minimize the error, differential pressure should be reduced to very low level (e.g. 0.00121Kg/cm2 approx) and for this rotameter is used for constant flow at low pressure even in case of inlet pressure variation to keep error constant. Thus in the conventional pressure measurement system for dusty gas atmosphere Rotameter is essentially used to keep the flow constant even in case of inlet pressure variation so that error can be constant. Hence, under conventional system, required reduction in line pressure means cause more dust or moist dust to deposit on the holes of tapping point with higher possibility of choking.
In order to overcome the limitations and disadvantages of the conventional tapping point, a pressure measurement system has been designed and developed by way of the present invention involving a three layer coaxial tubular tapping point wherein the 1st layer (Inner) pipe having inner diameter of d11 mm and outer diameter of d12 mm with 12 hole of size 3 mm, 2nd layer(intermediate) having inner diameter of d21 mm and outer diameter of d22 mm with 8 hole of size 5 mm has been configured and a 3rd layer(outer) having inner diameter of d31mm is welded on furnace body or Pipe

body. The modified configuration of tapping point is customized for accurate pressure measurement of Bias furnace intermediate pressure/ body pressure, Blast Furnace top gas/Bin pressure and Coke Oven gas pressure and the corresponding schematic figures are shown in accompanying Figure-2A, Figure-2B and Figure-2C respectively. The dimensions are variable depending on process conditions, accuracy and reliability of measurement required.
There is high pressure drop in perforated sheet hence holes in the first layer helps in passing of some quantity of nitrogen with reduced pressure from centre path to middle chamber (between 1st and 2nd layer). Making hole of less then 3.5 mm is very difficult on Stainless Steel pipe hence 3mm hole was made, but smaller the hole on 1st layer better will be the result. Number and size of holes on the second layer is selected such that in any case minimum passage (hole) area on the 2nd layer should not be more than 1.5 time the passage area on the 1st layer to minimize the error.
Thus the sum of the area of holes on the second layer is selectively maintained at least 1.5 time more than the sum of the area of the holes on the 1st layer which ensure minimum measuring error.
Importantly, Rotameter is not required in the tapping point configuration according to the present invention unlike the conventional back pressure measuring type tapping point, which resulted in better performance and reliability with regard to choking of the pressure measuring impulse lines. Rotameter is used to keep the flow constant even in case of inlet pressure variation so that error can be constant. Eliminating the rotameter in modified tapping helps in keeping error variation minimum even with high variation of differential pressure ranging from 0.4 Kg/cm2 to as high as 2.2 kg/cm2 with corresponding error ranging from 0.21 mmWC to 1.1 mmWC
1st layer tube diameter is reduced drastically from 50 mm to less than 10 mm which resulted in purging with high pressure even at the tip of the tapping point for low flow rate. This involves use of continuous nitrogen purging and measuring its back pressure without using rotameter to generate high purging pressure and low flow near end of the tapping point with constant minimum error.

A clear technical advancement resides in choking of tapping holes by the use of continuous purging with high pressure nitrogen in place of low pressure nitrogen as it was done earlier. If Nitrogen pressure is blowing at a high pressure of 0.5 Kg/cm2 through a hole of 8 mm (Main centre hole) even hot metal or mud will not able to block this hole.
A transmitter is installed in the inlet of nitrogen line and a relation is developed for inlet pressure and error transmitted and the same is compensated in the PLC or DCS before display or control action.
The known constant error measured due to nitrogen back pressure is adjusted in the Level-1 computer (Automation System) before display on screen or controlling the field device.
Normally in case of blast furnace for body pressure measurement, the maximum measurable pressure available at any point of time at any location will not be more than 3.0 Kg/cm2, hence nitrogen pressure is decided to be kept at 4.0 Kg/cm2 and a tapping point is designed in such a way, so that the error due to back nitrogen pressure should not be more than 16 mmWC, even with a differential pressure of up to 2.4 Kg/Cm2 (N2 Pr. - Furnace Pr.);
In case of blast furnace for top gas and bin pressure measurement, the maximum measurable pressure available at any point of time at any location will not be more than 2.0 Kg/cm2, hence nitrogen pressure is decided to be kept at 4.0 Kg/cm2 and a tapping point is designed in such a way, so that the error due to back nitrogen pressure should not be more than 11 mmWC even with a differential pressure of up to 2.4 Kg/Cm2 (N2 Pr. - Furnace Pr.);
In case of raw Coke Oven gas pressure measurement the maximum measurable pressure available at any point of time at any location will not be more than 15 mmWC, hence nitrogen pressure is decided to be kept at 0.5 Kg/cm2 and a tapping point is designed in such a way, so that the error due to back nitrogen pressure should not be more than 0.4 mmWC and the known constant error measured due to nitrogen back pressure is adjusted in the Level-1 computer (Automation System) before display on screen or controlling the field device;

When inlet pressure is 4.0 Kg/cm2 and back pressure is 0.0 Kg/Cm2, then pressure at point A (after orifice) is P11 (pressure measurement as per conventional method), pressure at point B is P12 Kg/cm2 and pressure at point C is P13 mmWC which is the error reflected on transmitter reading.
When inlet pressure is 4.0 Kg/cm2 and back pressure is 2.0 Kg/Cm2 than pressure at point A (after orifice) is P21 Kg/cm2 (pressure measurement as per conventional method), pressure at point B is P22 Kg/cm Kg/cm2 and pressure at point C is P23 Kg/Cm2 (2.0 Kg/cm2 + Perr) Perr is the error reflected on transmitter reading.
Further the error measure is directly proportional to the pressure measured before and after orifice plate. Relation between pressure measured after office plate and error measured is established and the same is compensated using in the level-I computer (PLC or DCS) before displaying the correct reading on HMI screen or used for control action.
Accompanying Figure 2A illustrates an embodiment of three layer coaxial tubular tapping point of the system of pressure measurement according to the present invention with improved tapping point for intermediate pressure measurement of blast gas at different level along the body. Nitrogen at 4 Kg/cm2 is passed through an orifice having inner diameter of 3.5 mm, nitrogen goes inside the blast furnace and do not allow chocking of tapping due to any reason. At a differential pressure (Nitrogen pressure before orifice and process pressure) of 2.2 Kg/cm2, maximum error occurs for a measured pressure of 2 Kg/cm2 is 13.24 mmWC which is 0.066% of the measured value compared to an error of 1785 mmWC (8.93%) if it would have been measured through conventional system.
Accompanying Figure 2B illustrates another embodiment of the three layer coaxial tubular tapping point configuration of the system of pressure measurement with improved tapping point for Blast Furnace top gas/Bin pressure for pressure measurement of blast gas for blast furnace top and bin/gas seal. Nitrogen at 4 Kg/cm2 is passed through an orifice having inner diameter of 3.5 mm, nitrogen goes inside the blast furnace and do not allow chocking of tapping due to any reason. At a differential pressure (Nitrogen pressure before orifice and process pressure) of 2.2 Kg/cm2, maximum error occurs for a measured pressure of 2 Kg/cm2 is 9 mmWC for 3.5 mm dia orifice and 2.15 mmWC for 2.5 mm dia orifice which is 0.045% and

0.011% of the measured value respectively. This error could have been of magnitude 417 mmWC (2.09%) and 90 mmWC (0.45%) if it would have been measured through conventional system.
Accompanying Figure 2C illustrates the system of pressure measurement with improved tapping point for Coke Oven Low Gas pressure for pressure measurement of coke oven gas. Nitrogen at 1 Kg/cm2 is passed through an orifice having inner diameter of 2.0 mm which goes inside the blast furnace and do not allow chocking of tapping due to any reason. At a differential pressure (Nitrogen pressure before orifice and process pressure) of 1.0 Kg/cm2, maximum error occurs for a measured pressure of 20 mmWC is 0.69 mm for 3.5 mm dia orifice and 0.24 mmWC for 2.0 mm dia orifice which is 3.45% and 1.2% of the measured value respectively. This error could have been of 757 mmWC (3785%) and 143.4 mmWC (717%) if it would have been measured through conventional system.
Laboratory experimental results are presented in the following Table-1, Table-2 (a), Table-2 (b) and Table-3 for intermediate pressure, Blast Furnace top gas pressure/Bin pressure and Coke Oven gas pressure respectively.
Accompanying Table 1 presents the data relating to pressure measurement result using a tapping point for intermediate pressure with 12 numbers 3 mm holes on 1st layer and 8 numbers 5 mm holes on 2nd layer. Table 1:

Pressure after orifice with 3.5 mm orifice
SI. No. Diff Pr. (Kg/cm2) Erl = Pll
(mmWC)
(Conventional) Pr. drop across Orifice Error-1 (%) Error-2 (mmWC) Modified Meas. Pr. (Kg/Cm2} Error-2 (%)
1 0.4 190 0.381 0.95% 2 2.0002 0.010%
2 0.6 380 0.562 1.90% 3 2.0003 0.015%
3 0.8 473 0.7527 2.37% 3.85 2.000385 0,019%
4 1 663 0.9337 3.32% 5.3 2.00053 0.026%
5 1.2 852 1.1148 4.26% 6.4 2.00064 0.032%
6 1.4 1042 1.2958 5.21% 7.48 2.000748 0.037%
7 1.6 1231 1.4769 6.16% 8.76 2.000876 0.044%
8 1.8 1352 1.6648 6.76% 10.05 2.001005 0.050%
9 2 1548 1.8452 7.74% 11.76 2.001176 0.059%
10 2.2 1785 2.0215 8.93% 13.24 2.001324 0.066%
11 2.4 1904 2.2096 9.52% 14.76 2.001476 0.074%
12 2.6 2159 2.3841 10.80% 16.46 2.001646 0.082%

Accompanying Table 2(a) presents the data relating to pressure measurement result using a tapping point for Blast Furnace top gas pressure/Bin pressure, with 12 numbers 3 mm hole on 1st layer and 8 numbers 5 mm hole on 2nd layer for 3.5 mm orifice Id.
Table 2(al:

Pressure after orifice with 3.5 mm orifice
SI. No. Diff Pr. (Kg/cm2) Erl = Pll
(mmWC)
(Conventional) Pr. drop across Orifice Error-1 (%) Error-2 (mmWC) Modified Meas. Pr. (Kg/Cm2) Error-2 (%)
1 0.2 28.1 0.19719 0.14% 0.65 2.000065 0.003%
2 0.4 56.8 0.39432 0.28% 1.2 2.00012 0.006%
3 0.6 89.1 0.59109 0.45% 2.1 2.00021 0.011%
4 0.8 125.3 0.78747 0.63% 2.77 2.000277 0.014%
5 1 160 0.984 0.80% 3.6 2.00036 0,018%
6 1.2 196 1.1804 0.98% 4.27 2.000427 0.021%
7 1.4 236 1.3764 1.18% 5.17 2.00051^ 0.026%
8 1.6 275 1.5725 1.38% 5.98 2.000598 0.030%
9 1.8 321 1.7679 1.61% 7.04 2.000704 0.035%
10 2 368 1.9632 1.84% 7.9 2.00079 0.039%
11 2.2 417 2.1583 2.09% 9 2.0009 0.045%
12 2.4 472 2.3528 2.36% 10 2.001 0.050%
2.6 528 2.5472 2.64% 11.4 2.00114 0.057%
Accompanying Table 2(b) presents the data relating to pressure measurement result using a tapping point for Blast Furnace top gas pressure/Bin pressure with 12 numbers 3 mm hole on 1st layer and 8 numbers 5 mm hole on 2nd layer for 2.5 mm orifice Id.
Table 2(b):

SI. No. Diff Pr. (Kg/cm2) Erl=P2 mmWC Pr. Drop across Orifice Error-1 (%) Error-2 mmWC Meas. Pr. (Kg/Cm2) Error-2 (%)
1 0.2 5.6 0.19944 0.03% 0.2 2.00002 0.001%
2 0.4 12 0.3988 0.06% 0.42 2.000042 0.002%
3 0.6 19 0.5981 0.10% 0.61 2.000061 0.003%
4 0.8 26 0.7974 0.13% 0.75 2.000075 0.004%
5 1 34 0.9966 0.17% 0.85 2.000085 0.004%
6 1.2 42 1.1958 0.21% 0.95 2.000095 0.005%
7 1.4 50 1.395 0.25% 1.18 2.000118 0.006%
8 1.6 60 1.594 0.30% 1.4 2.00014 0.007%
9 1.8 69.5 1.79305 0.35% 1,71 2.000171 0.009%

10
2 79 1.9921 0.40% 1.92 2.000192 0.010%
11 2.2 90 2.191 0.45% 2.15 2.000215 0.011%
12 2.4 101 2.3899 0.51% 2.36 2.000236 0.012%
13 2.6 115 2.5885 0.58% 2.5 2.00025 0.012%
Accompanying Table 3 presents the data relating to pressure measurement result using a tapping point for Coke oven Low gas Pressure measurement with 9 numbers 3.5 mm hole on 1st layer and 8 numbers 5 mm hole on 2nd layer.
Table 3:

Readings with single 3.5 mm orifice Readinqs with two 2.0 mm orifice in series
SI. No. Diff Pr. (Kg/cm2) Erl=Pll (mmWC) (Conven.) Error-1 (%) Error-2 mmWC Meas. Pr. (Kg/Cm2) Error-2 (%) Er3=P2 (mmWC) (Conven.) Error-3 (%) Error-4
mmWC Meas. Pr. (Kg/Cm2) Error-4 (%)
2 0.4 225 1125.00% 0.21 0.002021 1.050% 52.8 264.00% 0.11 0.002011 0.550%
3 0.6 389 1945.00% 0.38 0.002038 1.900% 82.3 411.50% 0.16 0,002016 0.800%
4 0.8 568 2840.00% 0.55 0.002055 2.750% 112.6 563.00% 0.21 0.002021 1.050%
5 1 757 3785.00% 0.69 0.002069 3.450% 143.4 717.00% 0.24 0.002024 1.200%
6 1.2 933 4665,00% 0.8 0.00208 4.000% 179.1 895.50% 0.27 0.002027 1.350%
7 1.4 1108 5540.00% 0.89 0.002089 4.450% 216.5 1082.50% 0.31 0.002031 1.550%
8 1.6 1340 6700.00% 0.95 0.002095 4.750% 251.7 1258.50% 0.34 0.002034 1.700%
9 1.8 1529 7645.00% 1.01 0.002101 5.050% 293.4 1467.00% 0.37 0.002037 1.850%
10 2 1750 8750.00% 1.06 0.002106 5.300% 337.5 1687.50% 0.4 0.00204 2.000%
11 2.2 2000 10000.00% 1.1 0.00211 5.500% 382.7 1913.50% 0.44 0.002044 2.200%
Graphical representation of experimental results are shown graphically with the help of Figure 3, Figure 4, Figure 5 and Figure 6 for intermediate pressure, Blast Furnace top gas pressure/Bin pressure and Coke Oven gas pressure respectively.
Figure 3: is the graphical plot of percent error vs differential pressure showing superimposition of result obtained with conventional as well as modified pressure tapping for Blast Furnace Intermediate Pressure.
Accompanying Figure 4 shows the graphical plot of percent error vs differential pressure showing superimposition of result obtained with Conventional and modified pressure tapping for Blast Furnace Top/Bin Pressure with 3.5 mm orifice Id.

Accompanying Figure 5 illustrates the graphical plot of percent error vs differential pressure showing superimposition of result obtained with conventional and modified pressure tapping for Blast Furnace Top/Bin Pressure with 2.5 mm orifice Id.
Accompanying Figure 6 illustrates the graphical plot of percent error vs differential pressure showing superimposition of result obtained with conventional and modified pressure tapping for Very Low Pressure measurement with 3.5 mm Orifice Id.
The above figures show that the error in pressure measurement with modified tapping is substantially reduced as compared to conventional method.
Advantageously, the above system of the invention could be developed after extensive studies of the material movement in the blast furnace, material charging, availability of dust density & moisture in the gas, and impurities available in the raw coke oven gas. Importantly, apart from accurate measurement achieved 100% reliability of the measurement.
Another advantage is improvement in safety of human being, as location of tapping point is prone to gas leakages and hot environment. It is not advisable to attend the problem or remove the tapping point for cleaning when gas is available in the line or in furnace.
Further advantages of the present system is maintenance free system of fit and forget type as compared to other convention tapping point which need periodical inspection and cleaning from time to time.
The pressure 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 pressure measuring systems also more importantly further ensures that the effectiveness and reliability of pressure measurement is maintained.
It is thus possible by way of the present invention to providing a system for pressure measurement of high dusty gas medium involving a coaxial three layered multihole tapping point free of any choking problem due to dust, whereby precise and reliable pressure measurement is possible in a heavy dusty process such as blast furnace body pressure at different level along the height especially at hazardous locations where dust comes with high gas pressure and temperature in the range of about 1,0

Kg/cm2 to 2.5 Kg/cm2 and 200 °C to 600 °C respectively in a safe manner without needing any human intervention. The system according to the present invention can be employed for pressure measurement in a heavy moist dusty process such as blast furnace gas seal pressure where pressure changes from 0 - 2.0 Kg/cm2 after every charging cycle as well as for low pressure gas such as in coke oven.
The invention thus provides a cost effective and maintenance free system avoiding use of delicate rotameter for flow control of purged nitrogen in the line involving three layered multi hole tapping point so that better accuracy of better than 0.1% is achieved. The raw signal from the field is converted to corrected signal before using it for control or monitoring wherein occurrence of known error due to nitrogen is compensated in the level-1 automation system before displaying in control room and taking control action.

We Claim:
1. A system for pressure measurement of gas along the height in high dusty area/
high dust and/or humid area comprising
a three layer tubular coaxial tapping point comprising an inner central first tubuler layer having diameter of less than 10 mm, an intermediate tubular second layer with multiple holes selectively dispensed on surfaces of said first and second layer; and an outer third tubular layer welded to furnace body for installation wherein the dimensions of tubes and holes are variable depending on process conditions, accuracy and reliability of measurement required;
means for continuous purging with high pressure nitrogen ;
said three layer coaxial tapping points with multiple holes in said first and second layers adapted to reduce error during said pressure measurement for display and/or process control.
2. A system for pressure measurement as claimed in claim 1 comprising an orifice placed in the flow path of inlet nitrogen for purging through said inner first layer at required pressure and having means adapted to sense and convert the raw pressure signal of measured process pressure and nitrogen back pressure to corrected signal by compensating for error for displaying on HMI screen or for said process control.
3. A system for pressure measurement as claimed in anyone of claims 1 or 2, wherein said first layer diameter is maintained in the range of 6 to 10 mm and preferably 8 mm resulting in nitrogen purging with high pressure even at the tip of the tapping point for low flow rate, favouring continuous nitrogen purging and measuring its back pressure to generate high purging pressure and low flow near end of the tapping point with constant minimum error.

4. A system for pressure measurement as claimed in anyone of claims 1 to 3 , wherein the sum of the area of holes on the said second layer is maintained at least 1.5 times more than the sum of the area of the holes on the first layer to ensure minimum measuring error.
5. A system for pressure measurement as claimed in anyone of claims 1 to 4, wherein said three layer coaxial tapping point to measure intermediate pressure of blast furnace comprising coaxial tubular stainless steel involving said first layer (Inner) pipe having inner diameter of 8 mm and outer diameter of 12 mm with 12 hole of size 3 mm; said second layer having inner diameter of 18 mm and outer diameter of 22 mm with 8 hole of size 5 mm and said third layer having inner diameter of minimum 30 mm welded on furnace body or Pipe body.
6. A system for pressure measurement as claimed in anyone of claims 1 to 5, wherein said three layer coaxial tapping point to measure Blast furnace top gas/Bin pressure comprising said first layer (Inner) pipe having inner diameter of 8 mm and outer diameter of 12 mm with 12 number holes of size 3 mm; said second layer having inner diameter of 18mm and outer diameter of 22 mm with 8 number holes of size 5 mm and said third layer having inner diameter of minimum 30 mm welded on furnace body or Pipe body and total length of said first layer of the tapping point ranges from 450 mm to 600 mm approximately.
7. A system for pressure measurement as claimed in anyone of claims 1 to 6, wherein said three layer coaxial tapping point to measure coke oven low gas pressure comprising said first layer (Inner) pipe having inner diameter of 8 mm and outer diameter of 12 mm with 9 number holes of size 3.5 mm; said second layer having inner diameter of 18 mm and outer diameter of 22 mm with 8 number holes of size 5 mm and said third layer having inner diameter of minimum 30 mm welded on furnace body or Pipe body and total length of said first layer of the tapping point ranges from 450 mm to 600 mm approximately.

8. A system for pressure measurement as claimed in anyone of claims 1 to 7, wherein for pressure measurement of blast gas at different level along the body of blast furnace, Nitrogen at 3 to 5 preferably about 4 Kg/cm2 is passed through an orifice having inner diameter of 3.5 mm whereby nitrogen goes inside the blast furnace and do not allow chocking of tapping.
9. A system for pressure measurement as claimed in anyone of claims 1 to 8, wherein for pressure measurement of blast gas for blast furnace top and bin/gas seal, Nitrogen at 4 Kg/cm2 is passed through an orifice having inner diameter of 2 to 4 preferably about 3.5 mm or 2.5mm, whereby nitrogen goes inside the blast furnace and do not allow chocking of tapping.

10. A system for pressure measurement as claimed in anyone of claims 1 to 9, wherein for pressure measurement of coke oven low gas pressure, Nitrogen at 0.5 to 2.0 preferably about 1 Kg/cm2 is passed through an orifice having inner diameter of 1.5 mm to 2.5 mm preferably about 2.0 mm which goes inside the biast furnace and do not allow chocking of tapping.
11. A method for pressure measurement of gas along the height in high dusty area/ high dust and/or humid area involving the system as claimed in anyone of claims 1 to 10 comprising carrying out said pressure measurement involving preferably:
for pressure measurement of blast gas at different level along the body of blast furnace, Nitrogen at 4 Kg/cm2 is passed through an orifice having inner diameter of 3.5 mm whereby nitrogen goes inside the blast furnace and do not allow chocking of tapping due to any reason and wherein at a differential pressure (Nitrogen pressure before orifice and process pressure) of 2.2 Kg/cm2, maximum error occuring for a measured pressure of 2 Kg/cm2 is 13.24 mmWC;
for pressure measurement of blast gas for blast furnace top and bin/gas seal, Nitrogen at 4 Kg/cm2 is passed through an orifice having inner diameter of 3.5 mm or 2.5mm, whereby nitrogen goes inside the blast furnace and do not allow chocking of tapping due to any reason and wherein at a differential pressure (Nitrogen

pressure before orifice and process pressure) of 2.2 Kg/cm2 maximum error occurs for a measured pressure of 2 Kg/cm2 is 9 mmWC for 3.5 mm diameter orifice and 2.15 mmWC for 2.5 mm diameter orifice; and
for pressure measurement of coke oven low gas pressure, Nitrogen at 4 Kg/cm2 is passed through an orifice having inner diameter of 2.0 mm which goes inside the blast furnace and do not allow chocking of tapping due to any reason and wherein at a differential pressure (Nitrogen pressure before orifice and process pressure) of 1.0 Kg/cm2 maximum error occurs for a measured pressure of 20 mmWC is 0.69 mm for 3.5 mm diameter orifice and 0.24 mmWC for 2.0 mm diameter orifice.
12. A method as claimed in claim 11 wherein known constant error measured due to nitrogen back pressure is adjusted in the Level-1 computer (Automation System, PLC or DSC) before the correct reading on HMI screen or used for controlling action of the field device.