FIELD OF THE INVENTION

The present invention relates to an improved online leakage detection system for machine cooling water circuit for reducing caster roll breakage due to thermal fatigue as a sequel to under cooling. More particularly, the present invention relates to water leakage detection system across the rotary joints of caster rolls and development of water mass flow monitoring system for identification of caster segments prone to roll failure due to thermal fatigue.

BACKGROUND AND PRIOR ART OF THE INVENTION

Research & Development Centre for Iron and Steel (RDCIS), Ranchi and Rourkela Steel Plant (RSP), Rourkela have designed, installed and commissioned “An improved online leakage detection system and water flow monitoring for machine cooling water circuit for caster rolls.” System is being utilized successfully since commissioning from March 2010 at Casting Machine, SMS-2, Rourkela Steel Plant.
Rourkela Steel Plant has two slab casters that produces slab of width between 800-1500mm. Each caster has thirteen segments. These segments have solid guide and drive rolls. The Internal cooling holes of these rolls vary from 28mm to 30mm. Each caster has soft water machine cooling water circuit, which supplies water for cooling the rolls, bearing housings, etc. in the different segments of the caster. The machine cooling water circuit is a closed loop circuit. The existing monitoring system for machine cooling water circuit was flow switch based having low flow alarm. This system was having only orifice type flow meter for measuring the flow in the segments. The display of the flow was available only in the water distribution room of the casters. There were no instruments for monitoring the temperature or pressure of machine cooling water circuit.

Lack of proper monitoring system led to problems like roll breakage due to thermal fatigue . This resulted in higher roll consumption and interruption in casting sequence leading to lesser availability of caster. Due to cracks in rolls and improper cooling, surface defects are generated on the product / slab.

The present inventors have designed , installed and commissioned an improved online leakage detection system and water flow monitoring for machine cooling water circuit for caster rolls in CCM-2 , Rourkela Steel Plant to circumvent the above mentioned problems. The improved PLC based monitoring system gives the operator in the main control room real time data related to flow, mass flow , pressure and temperature of water in the inlet line and through different segments of the caster. Through the trending features of the Human Machine interface (HMI) screen the operator can also get the data of the above parameters of machine cooling water for the last one month. This helps in quicker identification of the zone or segment, whenever leakages occur. Proactive action can be taken to reduce the roll breakage due to thermal fatigue as a result of under cooling. This will help in reducing the roll consumption and thereby reducing the interruption in casting sequence.

US7039552 discloses a new start-up operation of a continuous caster is monitored by comparing itself with the normal start-up operation, which is benchmarked by a multivariate statistical model using selected historical operation data. If the new operation is statistically different from the benchmark, then alarms are generated to indicate an impending start cast breakout and at the same time, the process variables that lead to process excursions from the normal operation are identified as the most likely root causes of the predicted breakout. The model is built using Mult-way Principal Component Analysis technology to characterize the operation-to-operation variance in a reduced dimensional space (also known as latent variable space) based on a large number of process trajectories from past normal start-up operations. The process trajectories over the entire start cast duration are predicted based on the current observations.

The above prior art is for caster operation which depends on many variable. on the contrary the present invention is related to on line detection of water leakage flowing through internal cooling holes of caster rolls through rotary joints , etc . It is not directly related to caster operation. As a sequel to under cooling the rolls will fail due to thermal fatigue. Measurement of mass flow , pressure and differential temperature help in analysis and indicate towards the segments ( rolls) prone to failure due to under cooling in the present invention , which is not a part of the cited prior art.

OBJECTS OF THE INVENTION

One object of the present invention is to overcome the disadvantages / drawbacks of the prior art.

A basic object of the present invention is to provide online leakage detection system for machine cooling water circuit for caster rolls.
Another object of the present invention is to provide an improved water flow monitoring for machine cooling water circuit for caster rolls.

Yet another object of the present invention is to provide the operator in the main control room real time data related to flow, mass flow, pressure and temperature of water in the inlet line and through different segments of the caster for monitoring the health of the machine.

Yet another object of the present invention is to provide an improved system that helps in quicker identification of the zone or segment prone to roll failure due to thermal fatigue as a result of under cooling.

These and other advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

According to one of the aspect of the present invention there is provided An improved system for online leakage detection and water flow monitoring in machine cooling water circuit for caster rolls reduce roll failure because of thermal fatigue due to under cooling , said system comprising :

at least one controller means adapted for calculation for differential temperature , mass flow with density compensation and differential flow;

at least two flow sensor means substantially installed in the inlet and outlet water line in the horizontal portion of the pipe line and operatively connected with said controller means adapted to measure the water flow through the each segment of caster;

at least two temperature sensor means substantially installed in the inlet and outlet water line and operatively connected with said controller means adapted to measure the water temperature of the inlet and outlet water after passing through the each segment of the caster ;

at least two pressure sensor means substantially installed in the inlet and outlet water line and operatively connected with said controller means adapted to measure the water pressure of the inlet and outlet water after passing through the segment of caster;

at least one human machine interface screen means operatively connected with said controller means via an Ethernet module adapted to monitor the caster machine health through different parameters such as said mass flow , said temperature differential , said differential flow.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates an improved online leakage detection and water flow monitoring system for machine cooling water circuit for caster rolls.

The present system consists of the electro-magnetic flow meter (EM) , resistance temperature detector (RTD), pressure transmitter , programmable logic controller (PLC) and human machine interface (HMI).

The components such as PLC and Sensors are a part of the system . They are the instruments on the basis of which the system has been implemented. The present invention is for the online leakage detection system which comprises of hardware’s such as PLC and Sensors.

The online leakage detection system compares the water flow rate through each segment of the caster with desired flow rate through the segment. If the difference between the actual and desired is more than 20% , it generates an alarm. Volumetric flow is the water flow rate. The word differential means difference between inlet and outlet flow rate.

It also calculates the differential temperature between inlet and outlet water temperature through the segment. If the difference is more than 15 ˚ Celsius, it generates an alarm.

Thirdly it also gives the differential mass flow between inlet and outlet.
The differential flow rate will indicate water leakage in the circuit which will indicate towards leakage. It provides alarm if the difference between inlet & outlet flow is more than 20%.

The three parameters along with pressure indications in the control room helps the operator in control room pin point the segments prone to roll failure due to thermal fatigue. It also indicates the leakage condition of the different segments so that these segments can be changed during planned shutdown.

The differential temperature and differential flow is the mathematical difference of the inlet and outlet water temperature and flow respectively.

The inlet and outlet water temperature is fed to PLC through RTD input card in the PLC. Through the embedded program of PLC this difference is calculated and data is displayed in HMI screen.

Similarly for differential flow , the inlet and outlet flow is fed to PLC through RTD input card in the PLC. Through the embedded program of PLC this difference is calculated and data is displayed in HMI screen.

The water density varies with temperature , to calculate the mass of water , the density at different temperature are fed to PLC program. Based on the temperature input , it gives the mass of water flowing through the segment. This have been incorporated in the system to help detect the leakage as mass of water entering the segment should equal mass of water leaving the segment if there are no leakages. The volume may change with temperature but mass remains constant. That is why the terminology used is mass flow with density compensation.

The segments of the caster have number of rolls. These rolls have holes for internal cooling. The external cooling is achieved through water sprays nozzles for which prior art is there. The water circuit through the internal cooling holes is a closed loop circuit. Since the rolls rotate , they are connected to water line through rotary joints. Impairment of internal cooling circuit is due to leakage of water through rotary joints or blockage of these holes if the water circuit filters are not working properly.

If water flow is less than the designed value, water temperature through these holes may rise to 70-80 ˚ Celsius which will cause fire cracks to develop in the inner portion of the roll. The parameter mentioned help in pinpointing the cause. For lower temperature range the water density does not vary much and hence water flow and mass flow rate is almost same. The difference is there when the temperature goes beyond 80˚ Celsius .

If the flow is as per norm but the differential temperature is high then this would indicate the blockage roll cooling hole.

If the water flow through the segments is less than desired on the outlet side but the inlet water flow is as per desired value then , this would indicate leakages through the rotary joints of the segments. This would also be indicated by pressure drop on the outlet side.

The electro-magnetic flow meters are installed in the horizontal portion of the water line with appropriate expanders and reducers for keeping the water velocity through the flow meter in the range for best accuracy .

The water flow velocity through electromagnetic flow meter should be between 2-3m/s for best accuracy. Expanders and reducers are used in case the pipe line size are different from the electro magnetic flow meter size. The flow meter size is selected based on the flow range and the meter size is calculated by formula that area of meter divided by maximum flow should be between 2-3m/s.

The resistance temperature detectors are installed in the vertical portion of the pipeline. The selection of temperature sensor has been done to measure even 0.1˚ Celsius variation in the water temperature.

The pressure transmitters are installed at an appropriate location to give the correct pressure of the inlet and outlet. Inlet pressure transmitter is installed at a point before the branching to different segments. Outlet pressure transmitter is installed after the branching join into common outlet.

The field sensors send the data to the controller installed in the main control room. The field devices are connected to the controller through signal cables which are terminated at the respective input module of the controller. The controller does the mathematical calculation for differential temperature , mass flow and differential flow gives the indication of the net loss of water after passing through the segments.

The calculations are difference in the inlet and out let water temperature , mass flow and volumetric flow, These are simple mathematical calculation done by the controller.

The computer based human machine interface screen acts as tool for the operator to monitor the health of the machine through these parameters.

Through trends of flow and temperature also the operator can predict the segments prone to roll failure due to thermal fatigue.

Through report generation facility the flow trend can also be analyzed and water flow through different segments can be optimized as per requirement.

The Oil cooler line is one of the branch lines of the water circuit. It is not directly related to the caster segment but since it is a closed loop water line circuit flow of water through this line has been shown.

The following design parameters were taken into consideration in designing the improved online leakage detection system and water flow monitoring for machine cooling water circuit for caster rolls.

According one of the embodiment of the present invention there is provided an improved system for online leakage detection and water flow monitoring in machine cooling water circuit for caster rolls reduce roll failure because of thermal fatigue due to under cooling . The system comprises at least one controller means for calculation for differential temperature , mass flow with density compensation and differential flow; at least two flow sensor means substantially installed in the inlet and outlet water line in the horizontal portion of the pipe line and operatively connected with controller means to measure the water flow through the each segment of caster; at least two temperature sensor means substantially installed in the inlet and outlet water line and operatively connected with controller means to measure the water temperature of the inlet and outlet water after passing through the each segment of the caster ; at least two pressure sensor means substantially installed in the inlet and outlet water line and operatively connected with controller means to measure the water pressure of the inlet and outlet water after passing through the segment of caster; at least one human machine interface screen means operatively connected with controller means via an Ethernet module to monitor the caster machine health through different parameters such as mass flow , temperature differential , differential flow.

No. of slab casters in CCM-2 Two

Inlet water line size 300 NB

Inlet water Flow rate 7700 Lpm (maxm.)

Inlet Water Pressure 5.5 bars

Inlet Water Temperature 30ºC - 40ºC

Outlet Water Temperature 60ºC -80ºC

Outlet water line size & flow rate in different segments
Segment 0 : 80NB : 350 L.P.M
Segment 1 : 100NB : 600 L.P.M
Segment 2-3 : 125NB : 1000 L.P.M
Segment 4-5 : 125NB : 1000 L.P.M
Segment 6-7 : 125NB : 1000 L.P.M
Segment 8-13 : 200NB : 2600L.P.M

Water Quality
Softened water
Calcium hardness < 18 ppm
Suspended solids < 10 ppm
Sulphate < 150ppm
Chloride < 150ppm
pH value 7.5 – 9.0
Total dissolved solids < 400ppm

The design of the system was based on these criterion. The selection of electromagnetic flow meters for line size and maximum flow were based on the above criterion. Selection of Resistance temperature detector was based on inlet and outlet temp. Water quality has a role on conductivity on which the electro-magnetic flow meter is based.

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 illustrates the schematic arrangement of the system.

Figure 2 illustrates the schematic arrangement of field devices in water circuit.

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.

The field devices are connected to analog input cards in the programmable logic controller panel by means signal cables ( Figure 1).

A programmable logic controller panel comprises controller , analog input and output card, resistance temperature detector input card, digital input and output cards and Ethernet module.

The controller takes all the data from the field sensor and does the mathematical calculation for differential temperature , differential flow etc as shown in Figure 1 . A computer based human machine interface screen is installed in the main control room. The controller and the computer are connected through networking by means of Ethernet module. The screen display the real time data to the operator for flow, mass flow , temperature , pressure of inlet and outlet water line. The past data can also be visualized through the data enquiry system and report generated for analysis. A Block Diagram of the scheme with various components are shown in Figure 1.

Figure 1: The schematic arrangement of the field devices, controller, and human machine interface screen . The field devices like electro-magnetic flow meter , Resistance temperature detector , Pressure transmitter are connected to analog input cards and RTD input cards. The analog signals are transmitted through signal cables. These cards are connected to Processor of PLC. The HMI is connected to the PLC through Ethernet module. The Ethernet module connects the PLC and HMI through communication cable.

The electro-magnetic flow meters , resistance temperature detector and pressure transmitter are installed in the inlet water line and outlet water line of the different segments( Figure 2).

Figure 2 depicts the position of field devices in the system. Inlet water line has one electro-magnetic flow meter (EM) , Resistance temperature detector ( RTD) and Pressure transmitter. The outlet line of the Segment 0 , 1 , 2-3 , 4-5, 6-7 , 8-13 and oil line has electro-magnetic flow meter and RTD installed. The pressure transmitter is installed in the outlet line. The Field devices sends signal to PLC . The Double arrow between PLC and HMI indicates two way communication between them .
Table 1
Table 1 : Data Available on Main HMI Screen
Inlet Water Line Volumetric Flow (V1) Desired
Flow 6550lpm Inlet Temp
( T1) Differential Temp. Mass Flow
M1 Inlet Pressure P1
5.5bar
Segment 0 Volumetric Flow(V2) 350lpm Outlet temp(T2) T2-T1 M2
Segment 1 Volumetric Flow(V3) 600lpm Outlet temp(T3) T3-T1 M3
Segment 2-3 Volumetric Flow(V4) 1000lpm Outlet temp(T4) T4-T1 M4
Segment 4-5 Volumetric Flow(V5) 1000lpm Outlet temp(T5) T5-T1 M5
Segment 6-7 Volumetric Flow(V6) 1000lpm Outlet temp(T6) T6-T1 M6
Segment 8-13 Volumetric Flow(V7) 2600lpm Outlet temp(T7) T7-T1 M7
Outlet line V2+…+V7 Differential V1-(V2+..+V7) M2+..+M7 P2
2.5bar

Table 1: the data depicted in HMI. The data available on the main HMI screen like Differential temperature, Differential Flow help in analyzing the condition of the cooling circuit.

The above table is the main screen for the operator which depicts the flow, temperature, pressure on the inlet and outlet side of the machine. It also gives the flow and mass flow difference and also the temperature differential of the inlet and outlet water flowing through the machine. Through this screen the operator can visualize the health of the machine. The health of the machine is analyzed based on the differential flow & differential temp and also pressure. This has been explained in the earlier paragraphs too. The higher outlet temperature will be there if the flow through the segment is less than the desired flow as water takes the heat while caster rolls have hot metal flowing over it. If the differential temperature increases beyond 15 ˚Celsius an alarm is given which gives an indication for the operator to check for the flow rate.
If the flow rate is okay , then blockage may have occurred in the internal hole. This segment required to be maintained during the schedule maintenance. This is how the health of the machine is monitored.
The desired flow rate requirement through different segments will change with the slab width & thickness size. Through this monitoring system , the water flow rate can be adjusted through globe valve in each segment as per the differential temperature. The flow rate can be increased if the differential temperature exceeds permissible limit of 15 ˚C. If the differential temperature very much less than the desired then the water flow rate can be reduced . The flow rate can be increased in the other segment where differential temperature is high. In this way the input water can be redistributed through different segments .

The online leakage detection system is part of water flow monitoring system as it through the observations of flow and temperature together , the leakage through the rotary joints is analyzed and detected .

WE CLAIM

1. An improved system for online leakage detection and water flow monitoring in machine cooling water circuit for caster rolls reduce roll failure because of thermal fatigue due to under cooling , said system comprising :

at least one controller means adapted for calculation for differential temperature , mass flow with density compensation and differential flow;

at least two flow sensor means substantially installed in the inlet and outlet water line in the horizontal portion of the pipe line and operatively connected with said controller means adapted to measure the water flow through the each segment of caster;

at least two temperature sensor means substantially installed in the inlet and outlet water line and operatively connected with said controller means adapted to measure the water temperature of the inlet and outlet water after passing through the each segment of the caster ;

at least two pressure sensor means substantially installed in the inlet and outlet water line and operatively connected with said controller means adapted to measure the water pressure of the inlet and outlet water after passing through the segment of caster;

at least one human machine interface screen means operatively connected with said controller means via an Ethernet module adapted to monitor the caster machine health through different parameters such as said mass flow , said temperature differential , said differential flow.

2. System as claimed in claim 1 wherein said controller means adapted for inputting data from the flow sensor , temperature sensor and pressure sensor .

3. System as claimed in claim 1 wherein said flow sensor comprises plurality of expanders and plurality of reducers adapted for keeping the water velocity through the flow meter in appropriate accuracy.

4. System as claimed in claim 3 wherein said flow sensors is in range of 2 to 3 m/s.

5. System as claimed in claim 1 wherein said temperature sensor measure even 0.1˚ C of temperature.

6. System as claimed in claim 1 wherein said controller means compares the water flow rate through each segment of the caster with desired flow rate through the segment adapted to generate alarm if the difference between the actual and desired flow rate is more than 20% for leakage detection through rotary joints across caster rolls.

7. System as claimed in claim 1 wherein said controller means calculates the differential temperature between inlet and outlet water adapted to generate an alarm if the difference is more than 15 ˚ C for leakage detection through rotary joints across caster rolls.

8. System as claimed in claim 1 wherein said controller means calculates the differential flow rate adapted to generate alarm if the difference between inlet and outlet flow is more than 20%.

9. System as claimed in claim 1 wherein said human machine interface screen adapted for determining the blockage condition of internal cooling holes.

10. An improved system for online leakage detection and water flow monitoring in machine cooling water circuit for caster rolls reduce roll failure because of thermal fatigue due to under cooling as herein substantially described and illustrated with the accompanying drawings.

ABSTRACT

The present invention relates to an improved system for online leakage detection and water flow monitoring in machine cooling water circuit for caster rolls reduce roll failure because of thermal fatigue due to under cooling . The system comprises at least one controller means for calculation for differential temperature , mass flow with density compensation and differential flow; at least two flow sensor means substantially installed in the inlet and outlet water line in the horizontal portion of the pipe line and operatively connected with controller means to measure the water flow through the each segment of caster; at least two temperature sensor means substantially installed in the inlet and outlet water line and operatively connected with controller means; at least two pressure sensor means substantially installed in the inlet and outlet water line and operatively connected with controller means; at least one human machine interface screen means .