TEMPERATURE CONTROL SYSTEM

Abstract

A temperature control system used for cooling a rolling mill product is provided. The temperature control system includes a plurality of isolation valves that are directly coupled to one or more water boxes. At least one pump is coupled to the isolation valves. The at least one pump provides the pressure needed for cooling. The isolation valves are positioned to reduce the time required to build up pressure for cooling and reducing the metallurgical property transition length of the rolling mill product.

Claims

1. A temperature control system used for cooling a rolling mill product comprising: a plurality of isolation valves that are directly coupled to or approximately near one or more water boxes; and at least one pump that is coupled to the isolation valves, the pump provides the pressure needed for cooling, wherein the isolation valves are positioned to reduce the time required to build up pressure for cooling and reducing the metallurgical property transition length of the rolling mill product.

2. The temperature control system of claim 1, wherein the isolation valves are located outside the one or more water boxes.

3. The temperature control system of claim 1, wherein the one or more water boxes comprise a plurality of cooling nozzles for cooling the rolling mill product.

4. The temperature control system of claim 3, wherein each of the cooling nozzles correspond to one isolation valve.

5. The temperature control system of claim 1, wherein the pump comprises a Variable Frequency Drive (VFD) pump.

6. The temperature control system of claim 1, wherein the pump delivers the required set point pressure without additional control.

7. The temperature control system of claim 1, wherein the one or more water boxes are grouped into a plurality of zones.

8. The temperature control system of claim 7 further comprising a plurality of zone VFD control pumps that modulate the rolling mill condition parameters based on the zones and finishing temperatures.

9. The temperature control system of claim 7 further comprising a plurality of zone pressure reducing valves that modulate the rolling mill condition parameters based on the zones and finishing temperatures.

10. The temperature control system of claim 9, wherein the zone pressure reducing valves deliver the required zone pressure set point.

11. The temperature control system of claim 7 further comprising a plurality of pressure transmitters are positioned at each zone to detect its pressure.

12. A method of configuring a temperature control system used for cooling a rolling mill product comprising: positioning a plurality of isolation valves that are directly coupled to one or more water boxes to reduce the time required to build up pressure for cooling and reducing the metallurgical property transition length of the rolling mill product; and coupling at least one pump to the isolation valves to provide the pressure needed for cooling.

13. The temperature control system of claim 12, wherein the isolation valves are located outside the one or more water boxes.

14. The temperature control system of claim 12, wherein the one or more water boxes comprise a plurality of cooling nozzles for cooling the rolling mill product.

15. The temperature control system of claim 14, wherein each of the cooling nozzles correspond to one isolation valve.

16. The temperature control system of claim 12, wherein the at least one pump comprises a Variable Frequency Drive (VFD) pump.

17. The temperature control system of claim 12, wherein the at least one pump delivers the required set point pressure without additional control.

18. The temperature control system of claim 12, wherein the one or more water boxes are grouped into a plurality of zones.

19. The temperature control system of claim 18 further comprising a plurality of zone VFD control pumps that modulate the rolling mill condition parameters based on the zones and finishing temperatures.

20. The temperature control system of claim 18 further comprising a plurality of zone pressure reducing valves that modulate the rolling mill condition parameters based on the zones and finishing temperatures.

21. The temperature control system of claim 20, wherein the zone pressure reducing valves deliver the required zone pressure set point.

22. The temperature control system of claim 18 further comprising a plurality of pressure transmitters are positioned at each zone to detect its pressure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a schematic diagram illustrating the inventive temperature control system used in accordance with the invention;

[0014] FIG. 2 is a graph illustrating the performance of a fixed speed centrifugal pump used in accordance with the invention;

[0015] FIG. 3 is a graph illustrating the performance of a zone pressure reducing valve (PRV) used in accordance with the invention;

[0016] FIG. 4 is a graph illustrating the performance of a Variable Frequency Drive (VFD) pump used in accordance with the invention;

[0017] FIG. 5 is a graph illustrating the activation response of multiple isolation valves used in accordance with the invention;

[0018] FIG. 6 is a graph illustrating the second response of a Ross Dale CX Valve using 4.1 bar pilot air pressure and no downstream resistance;

[0019] FIG. 7 is a graph illustrating the second response of a ASCO 8290 With 90 mm Operator 4.1 bar pilot air pressure and 17.5 mm cooling nozzle downstream resistance; and

[0020] FIG. 8 is a graph illustrating a fixed speed pump using a downstream control valve.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The invention involves a system that increases front end uniformity of metallurgical properties and scale control for inline heat treatment of long rolling products by moving isolation valves closer to the cooling operation. Isolation valves are mounted to the waterbox or within close proximity of the cooling nozzle. Each isolation valve is associated with a single cooling nozzle. This offers a more discrete control of cooling length which will increase cooling efficiency. The isolation valve is able to open and close full stroke in less than a second which minimizes the time required for the cooling nozzle to achieve set point pressure. A pressure reducing valve may be incorporated to alleviate supply pressure differentials due to operation of other cooling zones or equipment. A variable frequency drive pump is able to adjust the supply pressure to meet the set point temperature in order to achieve target temperature for single and/or multiple zones.

[0022] FIG. 1 is a schematic diagram illustrating the inventive temperature control system 2 used in accordance with the invention. Valve reaction time is improved by reducing the distance of the current location of 3-Way Divert Valve (3 m) from the process. The new isolation valve 4 is to be located on the outside of each water box 6 (<0.5 m) that corresponds to a number of nozzles. This reduction in distance improves the acceleration of water pressure to reach steady state at the cooling nozzle by approximately 1 second; for an average mean ring diameter of 1060 mm this equates to 36 Rings at 120 M/s. Each zone 1, 2, and 3 includes their respective water boxes 6.

[0023] The isolation valve 4 response, from fully closed to fully open (290 ms), matches closely to the guaranteed of the modified Fisher 3-Way Divert Valve (300 ms) used in the prior art. This is possible since the size of the 2 isolation valve is significantly smaller than the 4 to 8 Fisher 3-Way Divert Valve. Since the isolation valve's 4 maximum dimension is 2; it can only effectively process water suitable enough for one cooling nozzle. This means that there can only be one (1) secondary valve for each cooling nozzle. This greatly increases process control by giving the ability to uniformly predict how much pressure/flow is changed when a valve is actuated.

[0024] When the isolation valve 4 is closed the water pressure will be slightly higher than the required cooling set point. This increase in water pressure will change depending on the set point pressure. It has been observed that for 2.0 bar set point; the increased change in pressure is 0.5 bar.

[0025] Since the water is no longer being diverted, the process will now stop the flow (dead head) rather than divert the flow. When the downstream valves offer more resistance; the pressure after the pump will increase. Using a fixed speed pump, the pressure can only be increased by a factory determined set tolerance before the shut-off pressure is reached, as shown in FIG. 2. Once this upper limit has been obtained the pump must shut down or divert some flow to prevent damage to the pump. In order to keep the process running an Automatic Recirculation Control valve 14 is installed.

[0026] With a Variable Frequency Drive (VFD) pump 8, the process can continue to run for short periods of time while the system is dead headed to protect the water pumps from electrical/mechanical overload. Utilizing a VFD pump 8 reduces waste by only providing the pressure required; rather than having a fixed speed booster pump designed only for the worst case scenario water pressures and flows. The VFD 8 pumps provide the rolling mill with better energy efficiency and reduced water consumption that requires filtration and cooling. The VFD 8 pumps also provide better set point pressure stability. An Armstrong VFD Pump, as shown in FIG. 4 offers better control of water pressure for the same degree of change in process variable compared to the pressure reducing valve (PRV), as shown in FIG. 3.

[0027] For typical rod mill systems: only a single VFD pump per strand is needed. Having separate supply pumps allows each strand to run independent of each other's processing conditions. Installing a standby pump is recommended to maintain production capability.

[0028] By removing the standard 3-Way Divert Valve and utilizing the VFD pump 8; the Back Pressure Valve (BPV) and its control loop is no longer required. This reduces the complexity of the system by delivering the required set point pressure without additional controls.

[0029] By treating an entire zone 1, 2, and 3 as a single water box, only one pressure set point (initial set point 2.0 bar) is needed. This eliminates the requirement for modulating valves at each water box and their corresponding flow transmitters and flow loops. The overall recipe and ETCS system will only require: number of cooling nozzles per zone, zone pressure set point (with corresponding position of the zone pressure reducing valve (PRV) 12), and the strand's pressure set point (with corresponding torque of VFD Pump 8).

[0030] The zone PRVs 12 can modulate the pressure as rolling condition parameters change based on zone entry and finishing temperatures. The zone entry temperature can help predict what is required while the zone exit pyrometer can fine tune the required finish temperature. Since the process needs to maintain the pressure between a range (0.5 and 3.0 bar for rod mills) a pressure transmitter is needed for each zone. In the event the water pressure falls below the required minimum for the zone the isolation valve will close to consolidate the cooling toward the finishing end of the zone.

[0031] The zone PRVs 12 are used to set the water pressure for the zones 1, 2, and 3. Each zone 1, 2, or 3 is able to have different set points depending on processing conditions. It is critical that the supply pressure for each zone is maintained so that the process has the correct pressure set points for each zone.

[0032] The pressure transmitters 10 offer <1 millisecond response time which is much faster than the 145 millisecond response rate of the Rosemount 2088. However, the accuracy of the pressure 10 is <+/0.17 bar typical (+/0.34 bar max) a comparison to the standard Rosemount 2088 (+/0.14 bar) transmitter must be further evaluated. The Rosemount 2088 transmitter requires an expensive HART 475 communicator to set the device. The accuracy should be sufficient enough for the process. By focusing the modulation control to be based on temperature with a pressure reference the overall cost of the system can be drastically reduced. The expensive flowmeter with HART 475 communicator is no longer required.

[0033] Several types of valves were tested in order to find the best fit for the invention. FIG. 5 shows the existing 3-Way Divert Valve response rate against the two (2) leading contenders. In total six (6) valves were evaluated. Data points have been averaged to show comparative response rate to each other Actual data displays an overshoot and recovery before reaching steady state pressure. A key difference in response time is the location of the valves. In this test; the ASCO and Ross Dale CX isolation valves are located close to the process where as the Fisher 3-Way Divert Valve is located 8 m away. When the valves are closer to the operation the response is improved.

[0034] Fisher 3-Way Divert Valve claims to have 0.300 second actuation time. Through testing it was found that the valve does actuate within the 0.300 seconds however; the response rate to achieve steady state pressure is significantly longer than initially expected. Due to the distance of the pipe length (7.7 m) and increased resistance of altitude (2.3 m) the response rate is delayed significantly. In the test setup 1.3 seconds was required to achieve design pressure (2.0 bar).

[0035] Ross Dale CX valve claimed to have 0.014 second response rate. Although some testing proved this to be true the valve can only operate if the pilot air supply is higher than the working pressure of the medium. Therefore for 2.0 bar water operating conditions the typical design of 4.1 bar of air is sufficient. However, as the conditions change and higher water pressures are required, the 4.1 bar air pressure is not strong enough to consistently close the valve. After cycle testing, half year (250,000) cycles, the response rate was diminished and the seals needed to be replaced. In FIG. 6, the downstream outlet is connected to a globe valve which is fully open. When the valve is open (between seconds 10.25 and 12.5 seconds) the inlet to the valve pressure drops 3.5 bar and outlet pressure after the valve is 3 bar. When the valve closes the inlet pressure increases and the outlet pressure never completely drops to 0 bar. At 4.1 bar pilot air supply, there is insufficient air pressure to close the valve.

[0036] This valve is an industrial valve used in paper mill applications to process thick slurries. It has a piston, 90 mm operator, which creates a positive seal when closed. The valve is available in fail open or fail closed default positions. The valve requires an externally mounted actuator; the ASCO 8317 was selected for its fast response rate and high flow coefficient value. The actuator is operated by a 24 Volt DC electrical supply and 4.1 bar instrument air supply, which is typical of rolling mill conditions. The valve data sheet claims to have 0.290 second response rate. Throughout testing this appeared to be consistently true even after cycle 500,000 cycles (1 year of typical production). Technical professionals at ASCO have claimed that this valve should be able to operate 1 million cycles without maintenance. The standard design of 4.1 bar of pilot air pressure is sufficient to close the valve to the guaranteed 6.2 bar incoming water pressure. Higher operating water pressures of 8.0 bar have been observed and the valve continues to perform as designed. In FIG. 7, the downstream outlet is connected to a 17.5 mm bore cooling nozzle. When the valve is open (between seconds 9 and 11.25 seconds) the inlet to the valve pressure drops 1.5 bar and outlet pressure after the valve is 5.6 bar, when the valve closes the inlet pressure increases and the outlet pressure drops to 0 bar at 4.1 bar pilot air supply, the valve is able to close

[0037] With a fixed speed pump, as the downstream control valve begins to close to decrease product cooling; the water pressure begins to increase as the total water requirement is reduced. In FIG. 8, the pressure starting at operation point 1 (Op.1) increases to operation point (Op.2) as the downstream water requirement is reduced. The motor power remains relatively constant and the flow decreases.

[0038] The VFD Pump 8 is used to control torque when flow change is required while maintaining stable supply pressure. Pump selection discussed in this report only account for variable head. When the static head speed is reduced to a point where the flow is 0 LPM; the system pressure is equal to static head pressure. The static head pressure will vary depending on piping and elevation.

[0039] The VFD Pump 8 selected allows the process to deadhead for short period of time (<30 seconds) without increasing pressure. When the system must deadhead for more than 30 seconds the pump can shut off. In FIG. 10, the flow decreases with the change in speed from point A to point B. Due to affinity laws: motor speed is proportional to the cube root of the motor power. Therefore the power consumption decreases with decreasing flow demand.

[0040] By installing a pressure transmitter 10 downstream of the pump 8 and relaying information back to the drive, constant pressure can be maintained while the flow is decreasing. Through extensive testing of flow characteristics of the cooling nozzles the pressure vs flow relationship for various bore sizes has been defined. Using this data as the pump system curve; electrical and automation can map the required speed (or torque) to meet the E&A process set point.

[0041] In order to optimize pump selection, the Best Efficiency Point (BEP) is used. The BEP is a point on the pump curve where the efficiency is the highest. At this point, the impeller is subjected to minimum radial force promoting a smooth operation with low vibration and noise. When the flow conditions change the efficiency is degraded for that pump. Armstrong double volute pump with VFD is selected increase process capabilities as flow requirements change.

[0042] The invention improves acceleration of water pressure to reach steady state conditions to minimize transition length and achieve desired metallurgical properties of the final product. First, the invention replaces the large and expensive 3-Way Divert Valves with several smaller isolation valves close to the rolling process. By strategically placing the isolation valves closer to the cooling process, the lag time to achieve desired set point temperatures has been decreased significantly. Furthermore, the supply pumps must be variable frequency driven in order to accommodate the dead heading and maintain pressure set points with increased accuracy.

[0043] Although the present invention has been shown and described with respect to several preferred embodiments thereof, various changes, omissions and additions to the form and detail thereof, may be made therein, without departing from the spirit and scope of the invention.