FIELD OF THE INVENTION:

The present invention relates to a boiler tube leak detection system and method for detection of tube leakage in boiler. More particularly, the present invention relates to a boiler tube leak detection method where leakage is analyzed with respect to analyzing operating parameters therefore the method is much simpler and requires less hardware so it will be a much cheaper.

BACKGROUND OF THE INVENTION:
Boiler is one of the most important components of Power-Plant/Process Industry. Reliability, availability of the plant is greatly influenced by condition and reliability of the main boiler and its associated system. One of the most prominent reasons of Boiler Fault is tube Leakage. Early or timely detection of leakage helps to plan an outage reduce secondary damages as well as down time cost and time.
Till date Acoustic Leak Detection system is the only proven methodology to identify a leakage. In a Boiler if high-pressure steam or water leak occurs, abnormal noise is generated at or around the rupture. The frequency curve of this noise is different from that of the background noise generated by combustion in the furnace or by the spraying of fuel in the burner. The background noise generally has more power at lower frequencies. The system accurately identifies and locates a boiler tube leak in its early stage against the noise of an operational boiler.
The concept of Acoustic Leak Detection was first introduced by US Babcock and now there are few suppliers of Acoustic Leak Detection System like Green-bank Mistras, Mitsubishi Hitachi Power Systems, Acoustic -Monitoring International. Traditionally, for any Power-plant the operator can analyse any leakage by observing the Steam Flow and Feed Flow trend with time. When a leak occurs the trend changes from its inception but it is difficult to detect it at its emergence point and it takes quite some time to detect it depending on quantum of leakage. Further, Leak Detection system is mostly used for utility boilers and very limited application in Industrial boilers. In utility boiler only Acoustic Leak Detection is the most popular way of detecting Leakage. There are number of suppliers who can offer Acoustic Based Leak Detection System.
US 5363693: discloses a method for detecting leakage from a chemical recovery boiler system of the type which includes a recovery boiler and associated output steam piping, comprising steps of: a) periodically measuring fluid input to a recovery boiler system to obtain data; b) periodically measuring fluid output from a recovery boiler system to obtain data; c) periodically calculating short term average drum balances from data obtained in steps (a) and (b); d) periodically calculating the long term average drum balances from the data obtained in steps (a) and (b); e) calculating the standard deviation for said short term average drum balances; f) calculating a standard deviation for said long term average drum balances; g) using said standard deviation of said short term average drum balances and said long term average drum balances to determine whether a significant difference exists between said short term average and said long term average; and h) indicating an error condition if a significant difference is determined to exist.
The systems of prior art mostly operates on the principle that if the boiler /pressure vessel fails and a high-pressure steam or water leak occurs, abnormal noise is generated at or around the rupture. The frequency curve of this noise is different from that of the background noise generated by combustion in the furnace or by the spraying of fuel in the burner. The background noise generally has more power at lower frequencies. Higher frequency noise is generated by high-pressure leaking at ruptures. Pressure vessel leaks can be detected by monitoring for this higher frequency component and uses Acoustic principle with the enhanced sound wave sensors to capture the sound signal within the boiler. The sensors convert the sound signal into electrical current signal. The monitoring system uses FFT technique to convert the sound signal into frequency spectrum and display in the form of bar chart. The analysis is based on the continuous intensity of the sound at a particular frequency to confirm whether it is a tube leak.
Acoustic Leak Detection system is one of the most common method for detecting tube leakage. This system had passed through several changes and achieved a level of technical maturity but still sensitive to operating condition design/engineering. Filtering-method, Spectrum-analysis are two common methods of Acoustic Leak Detection system but both methods have low sensitivity and sensor fails frequently. The leak detection capability is affected by the following factors that is the level of background noise depends on the structure of the boiler and the positioning of the sensors., the level of leak noise depends on the direction or angle of the ejected spray as well as whether or not the spray strikes anything, eddy formation inside boiler due to high ash coal gives false alarm.

The advantages of the present system over the said prior arts is that it considers the effects of swelling and sinking. Correction mechanism is used in the feed water flow monitoring. The system is also provided with program calculated auto set point operation. Soot blowers and start up vent operations are routine and emergency operations which happen in boiler operation every day and result in difficulties to judge the feed input and steam output deviations. In the present application this limitation is given due care by adjusting the calculation programme to stop observing these operations and start adjusting calculations once these valves operations stabilized to normal close condition. In view of the foregoing, a simple yet an accurate method for the boiler tube detection is required.

OBJECTIVE OF THE INVENTION:

An object of the present disclosure is to provide boiler tube leak detection system and method for detection of tube leakage in boiler with accuracy.

SUMMARY OF THE INVENTION:

An aspect of the present disclosure relates to providing a method for detecting a leakage in a boiler system comprising the steps of: periodically measuring fluid feed flow value (FWF) in the boiler by a field device (1) to obtain data set D1; periodically measuring steam flow value (MSF) in the boiler by a field device (1) at the same point of time as fluid feed flow to obtain data set D2; periodically measuring mandatory variables by a field device (1); computing a variable TOTDIFF by a server (5); calculating a predetermined value and standard deviation for each mandatory variable and TOTDIFF by the server (5); wherein the mandatory variables are selected from the group consisting of main steam pressure (MSP)*, drum pressure (DP), main steam temperature (MST)*, drum level (DL), continuous blowdown valve % opening (CBP), intermittent blowdown valve % opening (IBP), soot blower on/off (SBO), soot blower control valve % opening (SBP), and start up vent % opening (SVP) characterized in that incidence of leakage is detected by analyzing the TOTDIFF with respect to the predetermined value and the standard deviation value.
In an embodiment of present disclosure, the data is captured by a distributed control system (DCS) (3) from the field devices (1) via a Modbus protocol or Ethernet protocol (2) and transferred to the server (5) through a gateway (4).
In yet another embodiment of present disclosure, the field devices (1) are selected from the group consisting of pressure transmitter, temperature transmitter, flow Nozzle and transmitter, RTD thermocouple, Level Transmitter, and position feedback transmitter.

In still another embodiment of present disclosure, the field device (1) for periodically measuring the fluid feed flow value (FWF) is a flow nozzle and transmitter.

In another embodiment of present disclosure, the field device (1) for periodically measuring the steam flow value (MSF) is a flow nozzle and transmitter.

In yet another embodiment of present disclosure, the field device (1) for periodically measuring the main stream pressure (MSP), drum pressure (DP) is a pressure transmitter.

In still another embodiment of present disclosure, the field device (1) for periodically measuring the main stream temperature (MST) comprises temperature transmitter and RTD thermocouple.

In another embodiment of present disclosure, the field device (1) for periodically measuring the drum level (DL) is level transmitter.

In yet another embodiment of present disclosure, the field device (1) for periodically measuring the continuous blowdown valve % opening (CBP), intermittent blowdown valve % opening (IBP), soot blower on/off (SBO), soot blower control valve % opening (SBP), and start up vent % opening (SVP) is position feedback transmitter.

In an embodiment of present disclosure, the server (5) has an in-built artificial intelligence architecture to detect leakage based upon incoming data flow.

In still another embodiment of present disclosure the data is analyzed in the server (5) on continuous basis for detecting leakage in the boiler system.

These and other features, aspects, and advantages of the present subject matter will become better understood with reference to the following description. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the subject matter, nor is it intended to be used to limit the scope of the subject matter.

BRIEF DESCRIPTION OF DRAWINGS:-
Figure 1 shows the leak detection system.
Figure 2 shows the leak detection flow chart.
Figure 3 shows the curve without leakage.
Figure 4 shows the curve with leakage.

DETAILED DESCRIPTION OF THE INVENTION WITH RESPECT TO ACCOMPANYING DRAWINGS:

In the present disclosure, as shown in Figure 1 the field devices (1) periodically measuring fluid feed flow value (FWF) (via flow nozzle and transmitter) a in the boiler to obtain data set D1, further periodically measuring steam flow value (MSF) (via flow nozzle and transmitter) in the boiler at the same point of time as fluid feed flow to obtain data set D2 and furthermore periodically measuring mandatory variables. Plant Distributed control system (DCS) Data (3) is captured from Modbus or Ethernet (2) and through a Gate way (4) transferred to the working server (5). Working server (5) has an inbuilt AI based architecture to detect leakage based on Incoming data flow. For the same, station with pre-loaded software is connected to plant DCS system through Gate-way in between on Mod-Bus (or Ethernet) Protocol with single way data transfer mode so that any un-wanted signals (in form of Virus ) should not travel to Plant control system making it safer and secured. Data Transferred to the station is stored in SQL based database and is analysed on continuous basis for any leakage in the Boiler system. The architecture ensures continuous data flow. In totality, the disclosed combined architecture with analytical software is a State of Art product and would be a trend setter in the industry. For this Detector, continuous data flow is required from plant control system to the station with pre-loaded software.
The disclosure of present invention provides a tool which can be plugged into boiler control system for extraction of real time data and to develop a software which contains parameter based analytical model to predict leakage in system based on Parametric Variation. Normally in a typical boiler, variation in Feed Water Flow and Steam Flow is coined as a new term (TOTDIFF). The variable TOTDIFF is a function of a few variables, which have been coined as Mandatory Variables.
Referring to Figure 2 which shows the flow diagram of the invention. The main parts of the leakage detection method include feed water flow, super heater, start up vent position feedback, soot blower valve position feedback, circulation block blow down valve position feedback, program to calculate the standard deviation and an alarm. The blow down value position feedback and calculation for swelling and sinking correction is given to the calculation block as input. Further the calculation block is also provided with start-up vent and soot blower valve position feedback. The data is compared with the flow difference for past 1hr/ past 2hr indicating the deviations. The alarms are generated to alert the operator if the leakage is suspected.
As described earlier accuracy of Acoustic Leak Detection system depends on operating condition. Due to high cost, its application is mostly limited in utility boilers. In the disclosure of the present invention, leakage quantity is measured with respect to (Steam Flow – Feed Flow) difference. Theoretically it is safe to assume that Leakage quantity is fairly similar irrespective of size of boiler. So in a smaller capacity boiler percentage change of flow with respect to the variable (Steam Flow – Feed Flow) will be higher and it will be easier to detect.
Data collected from boiler control system is captured and analyzed using a computer program which works based on below logic. The software works on the fundamental principle of calculating the totalizer flow difference of water and steam flow.
Flow Total Difference (TOTDIFF) = Feed water flow total (D1) – Steam Flow total (D2)------?
With reference to the above calculation, the TOTDIFF value shall be taken on graphical representation showing the continuous trend of comparison between instant/ past 1hr/ past 2hr readings indicating the deviation (if any).
Looking at the deviation from the existing trend, leakage is suspected and alarms generated to alert the operator. But, the above case indicates an ideal condition in which the plant is running at stable load with all parameters constant including no variation in drum level and no drain/vent valve being operated. In actual conditions, plant is subjected to fluctuation in load which leads to change in other variables whose effect has to be taken into account.
All these variable plays an important role and affect the totalizers readings which are being calculated by DCS totalizer. Also these variables keep on changing in running plants as per the process requirements. To achieve the actual or minor leakage loss from the boiler boundary all these are being considered meticulously to get the desired output.
Variables (Measured at field via field devices and sent to DCS) for which the system shall take the readings directly from DCS are:
• Main Steam Pressure (Measured via Pressure Transmitter)
• Drum Pressure (Measured via Pressure Transmitter)
• Main Steam Temperature (Measured via Thermocouple and Temperature Transmitter)
• Main Steam Flow (Measured via Flow nozzle and transmitter)
• Feed water flow (Measured via Flow nozzle and transmitter)
• Drum level (Measured via Level transmitter)
• Continuous Blow Down(CBD) % Opening (Measured via Position transmitter)
• Intermittent Blow Down (IBD) % Opening (Measured via Position transmitter)
• Soot Blower % opening (Measured via Position transmitter)
Now Equation 1 shall be modified as:
Variable Flow Total Difference (TOTDIFF) = [(Feed water flow total – Steam Flow total) – {(Quantity of water in drum) – (Quantity of water before 2sec)} + k * (Density difference of present and 2sec before)]
Where,
k = Quantity of water in (waterwall + Downcomer + headers) i.e. Quantity of water except drum
The above value shall be defined manually according to the boiler design.
Quantity of water in drum = Density of water in drum X Volume of drum;
Now the volume of drum shall be calculated as,
Drum vol. = [r * r *{Cos-1 ((r-h)/r) – (r – h)} * sqrt(2rh – h2 )] * L
r = Inner diameter of Drum
L = Length of Drum
h = Dist. between two ports of level gauge + Drum level (in mtr)
Density shall be calculated according to the pressure.
As shown in Figure 3, the variable flow totalizer difference value shall be plotted on a curve. Now this curve can be seen with instant flow totalizer, Flow totalizer of prevailing last 1hr and Flow totalizer of prevailing last 2hr.
When the actual flow totalizer reading exceeds a certain limit, then the system shall indicate a leakage as shown in Figure 4,
Variable Flow Totalizer Difference (TOTDIFF) > Predetermined value of TOTDIFF + Standard Deviation value of TOTDIFF ---------?
The plotted curve will show the deviation from the normal trend if the leakage is there and the flow difference shall keep on increasing.
If this value is greater than the predetermined value, continuously for last one hour, the probability of leakage is moderate.
If this value is greater than the predetermined value continuously for last two hours, the probability of leakage is high and the leakage is confirmed.
In Equation 2, predetermined value is the manually entered value which will be fed based upon the boiler operation behavior.
Moreover Equation 2 can be executed in either manual or Auto mode;
In Manual Mode, both the values – predetermined value & standard deviation value shall be entered manually.
In Auto Mode, predetermined value shall be constant as entered but standard deviation shall get changed according to the flow changing per unit time.
In table 3, 4 and curve plots of Figure 4 and 5, minimum difference is a tunable value and Standard deviation is calculated by program, it can be entered manually also. B is minimum possible leakage detection value. In curve plots, it is 200 kg. It can be further reduced according to boiler operation stability.
In case of operation of IBD/Soot blower/Start up Vent valve, the system shall not record the data during the transition duration of opening of valve. In case of CBD valve operation, the system shall modify the standard deviation according to the excess flow through the valve and shall consider it a new data. Hence in all the cases of operation of drain/vent valves, the system shall not indicate a leakage. It will either don’t consider that data or shall add extra flow to the system which ultimately will not affect the actual flow totalizer difference and the plotted curve shall not deviate due to this disturbance.
The software works on the fundamental principle of generating multiple operating patterns based on few Mandatory Process Variables. Mandatory Process variables are identified as those variables having influencing effect on Steam Flow and Feed Flow Difference (TOTDIFF) value.
A few Mandatory Variables are listed below in Table 1 to exemplify pattern generation procedure.

Feed Water Flow FWF
or
Steam Flow MSF
Main steam temperature MST*
Main Steam Pressure MSP*
Continuous Blowdown (CBD) Valve % Opening CBP
Intermittent Blowdown (IBD) Valve % Opening IBP
Soot Blower On/Off SBONOFF
Soot Blower Control Valve % Opening SBP
Start Up Vent % Opening SVP
Drum level DL
Drum Pressure DP
Table 1

Table 2 is an example of generation of Pattern:-
Variable Lower Limit Upper Limit Incoming Data Pattern Upper Limit Pattern Lower Limit
MSF 5 6 150 145 156
MSP 2 2 76 74 78
CBP 5 5 56 51 61
IBP 5 5 72 67 77
SBONOFF Binary 0 or 1 1 1
SBP 5 5 34 29 39
SVP 5 5 56 51 61

Table 2

MSF=Main Steam Flow;
MSP=Main Steam Pressure;
CBP= CBD Valve % Opening;
IBP= IBD Valve % Opening;
SBONOFF=Soot blower ON/OFF;
SBP=Soot blower control valve Position;
SVP=Start Up Vent Position.

ADVANTAGES:
• More accurate detection of leakage;
• Less sensitive to operating condition;
• Simpler design;
• Less hardware required;
• Detect general operational issues.

Although the subject matter has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible. As such, the scope of the disclosure should not be limited to the description of the preferred embodiment contained therein.

We Claim:

1. A method for detecting a leakage in a boiler system comprising the steps of:
periodically measuring fluid feed flow value (FWF) in the boiler by a field device (1) to obtain data set D1;
periodically measuring steam flow value (MSF) in the boiler by a field device (1) at the same point of time as fluid feed flow to obtain data set D2;
periodically measuring mandatory variables by a field device (1);
computing a variable TOTDIFF by a server (5);
calculating a predetermined value and standard deviation for each mandatory variable and TOTDIFF by the server (5);
wherein the mandatory variables are selected from the group consisting of main steam pressure (MSP), drum pressure (DP), main steam temperature (MST), drum level (DL), continuous blowdown valve % opening (CBP), intermittent blowdown valve % opening (IBP), soot blower on/off (SBO), soot blower control valve % opening (SBP), and start up vent % opening (SVP).
characterized in that incidence of leakage is detected by analyzing the TOTDIFF with respect to the predetermined value and the standard deviation value.

2. The method as claimed in claim 1, wherein the data is captured by a distributed control system (DCS) (3) from the field devices (1) via a Modbus protocol or Ethernet protocol (2) and transferred to the server (5) through a gateway (4).

3. The method as claimed in claim 1, wherein the field devices (1) are selected from the group consisting of pressure transmitter, temperature transmitter, flow Nozzle and transmitter, RTD thermocouple, Level Transmitter, and position feedback transmitter.

4. The method as claimed in claim 1, wherein the field device (1) for periodically measuring the fluid feed flow value (FWF) is a flow nozzle and transmitter.

5. The method as claimed in claim 1, wherein the field device (1) for periodically measuring the steam flow value (MSF) is a flow nozzle and transmitter.

6. The method as claimed in claim 1, wherein the field device (1) for periodically measuring the main stream pressure (MSP), drum pressure (DP) is a pressure transmitter.

7. The method as claimed in claim 1, wherein the field device (1) for periodically measuring the main stream temperature (MST) comprises temperature transmitter and RTD thermocouple.

8. The method as claimed in claim 1, wherein the field device (1) for periodically measuring the drum level (DL) is level transmitter.

9. The method as claimed in claim 1, wherein the field device (1) for periodically measuring the continuous blowdown valve % opening (CBP), intermittent blowdown valve % opening (IBP), soot blower on/off (SBO), soot blower control valve % opening (SBP), and start up vent % opening (SVP) is position feedback transmitter.

10. The method as claimed in claim 2, wherein the server (5) has an in-built artificial intelligence architecture to detect leakage based upon incoming data flow.

11. The method as claimed in claim 1, wherein the data is analyzed in the server (5) on continuous basis for detecting leakage in the boiler system.