Tirpur Area Water Supply Project A Report on Transient Modeling Study

Transcription

1 y February of 81

2 y INTRODUCTION: The report presents results from a transient modeling study conducted on the clear water transmission main of Tirpur Areas Water Supply Project, Tamilnadu, India. The main objectives of the study were: 1. To evaluate adequacy of the existing protection measures against extreme transient pressures that are likely to occur during normal shutdown, power failure and pump startup scenarios and 2. To reinforce protection measures that can withstand transient pressures resulting from occasional abnormal operating procedures i.e., less than adequate compliance to recommended pump and valve operation. BACKGROUND: There are two pumping stations (Clear Well Pump House or CWPH and Booster Station) on the clear water transmission main modeled in this study. Each station has three pumps two duty pumps and one for standby operation. The original design included protection measures for the pipeline against severe transient pressures resulting from power failure scenario in which all four pumps (two at CWPH and two at Booster Station) operating at their rated conditions get tripped. The protection included 4 one-way surge tanks, two of which are located between CPWH and Booster station (Figure 3). In addition, the original design included 91 air release valves (120 mm orifice diameter) on the pipeline to facilitate air release during pump startup operation. Although the primary purpose for these air valves is to let air out of the system during pipe filling operation, they 2 of 81

3 y can become active during normal operation if there is air entrainment in the pipeline for some unforeseen reasons. The air valves can also let the air into the pipeline when pressures in the pipeline at air valve drop below atmospheric conditions. Proper selection and sizing of these air valves becomes essential when there is a potential for air entrainment during normal operation of the pipeline (Funk et,al.,1992 and Lingireddy et.al, 2004). Improper selection and sizing could potentially lead to unwanted secondary pressure spikes which in turn could damage the pipeline either at the location where they were generated or elsewhere as the pressure waves travel through the pipeline system. Damages to the pipeline systems have been reported after the pipeline was commissioned. Some of those damages were attributed to transient generated pressures during abnormal pump operation. Much of the damage appears to be between Clearwater Pump House and Booster Station. The sluice valve that was ruptured on June 25 th, 2006 was located around a chainage of 4400m from CWPH and was between CWPH and Booster station. There were two similar incidents of sluice valve ruptures prior to June 25 th, 2006 and both locations were close to CWPH and were between CWPH and Booster station. A pressure relief valve that opens at 40m of head has been recently added at a location close to suction side of the Booster station to prevent excessive pressure rise in that area. The flow is predominantly by gravity towards the discharge end of the pipeline (last 6.3 km) and there is a standpipe arrangement at the beginning of the gravity portion of the treated water main. 3 of 81

4 y DATA SUMMARY: Data for the clear water transmission main of was obtained from HCC. Data obtained from HCC included as-built pipeline profile drawings in electronic format, intake structure and pump station details, pump control and check valves, tank and connecting pipe sizes for all four oneway surge tanks (OSTs). Figure 1 shows the schematic of the pipeline profile for the clear water transmission main. Other physical and hydraulic characteristics of the pipeline system are listed in the following. o Low water level(intake sump) o Water level at Discharge o Number of working pumps (CWPH) o Number of working pumps (BPS) : 175m : 327m : 2 (+1 standby) : 2 (+1 standby) o Pump rated speed for Both CWPH & BPS): 990 rpm o Rated discharge per pump (CWPH) : m 3 /s o Rated discharge per pump (BPS) : m 3 /s o Rated pump head (CWPH) : 108.2m o Rated pump head (BPS) : 120 o o Pump and Motor Inertia (GD 2 ) Pump and Motor Inertia (GD 2 ) o Pump efficiency (CWPH) : 89% o Pump efficiency (BPS) : 90% o Pump file : 1 o NRV closure time o Cavitation head : 360kgf-m 2 (CWPH) : 560kgf-m 2 (Booster) : 0.5 s (linear closure) : -9.5m 4 of 81

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6 y TRANSIENT MODEL RUNS: In tune with stated objectives of the study, initial model runs were geared towards verifying adequacy of the existing protection measures. A Surge2000 model was built for the clear water transmission main based on the information obtained from HCC. Steady state analysis was carried out to ensure that the flows and pressures match the design values. Figure 2 shows steady state hydraulic gradeline (HGL) for the clear water transmission main while all 4 pumps (two at each station) are operating at their rated speed. The existing protection for the pipeline system comprises four one-way surge tanks (OSTs). These tanks were sized to protect the system against most severe transient pressures resulting from simultaneous failure of all four operating pumps. Although there are 91 air valves on the pipeline, the original design did not explicitly consider these air valves as part of baseline protection. A transient analysis was run on this model to simulate simultaneous failure of all four operating pumps. This transient model run included existing OSTs but not the air valves. Likewise, the pressure relief valve that has been recently placed on the suction side of Booster station was not included in the model. The model, however, did include the vacuum breaking arrangement located towards the discharge end of pipeline. Figure 3 shows a pressure envelope following pump trip during a 200 second transient simulation. The corresponding pressure profile from the original design report is shown in Figure 4. As evident from Figures 3 and 4, the pressure profiles from the current model run and the original design agree fairly well. Model runs pertaining to the original design allowed the pressures to drop below cavitation limit (Figure 4). To be consistent with the results reported earlier, the current model run allowed the pressures to drop below the cavitation limit as well. This is why the low pressures at certain locations shown in Figure 3 have dropped below the cavitation limit of - 9.5m. 6 of 81

7 y Figures 5 and 6 show pressure head variation at discharge headers of CWPH and Booster Station respectively, for the current model run. Figures 7 and 8 show the pump speed variation curves. Figure 9 shows pressure head variation at two representative nodes where the low pressures dropped below cavitation head. Figure 10 shows pressure head variations at OSTs. The highest pressure head over the entire system was about 130m and occurred right around the Booster Station. Based on the diameter (1400 mm) and thickness (12 mm) of the pipeline and assuming manufactured/fabricated grade C steel for pipe material, the highest allowable transient pressure for this pipeline is 180m (AWWA M11). The 12 mm thickness for the pipeline also allows it to withstand significantly large negative pressures (theoretical limit of -20m). The lowest pressures in the system were around -20m. The low pressures in the system are within the theoretical allowable pressure limits even without considering the air valves for surge protection. There are air valves at all places along the pipeline where pressures drop below zero and are expected to provide relief against low pressure conditions provided they are of good quality and are maintained in good condition. The model was updated to simulate the effect of existing two-stage air valves on the negative pressures. In addition, the cavitation head was limited to -9.5m (i.e., pressures were not allowed to drop below vapor pressure). Figure 11 shows the pressure envelope corresponding to this model run. As evident from this figure, the negative pressure condition improves without a significant impact on the positive pressures when the effect of air valves was taken into account. Based on the results presented in Figures 3 through 11, it is clearly evident that the existing OST based protection is adequate to protect the system against adverse transient pressures resulting from simultaneous failure of all four operating pumps. Since, the pressure relief valve (PRV) on the suction side of 7 of 81

8 y Booster Station is currently part of the existing pipeline system, the model was updated to incorporate the PRV and was analyzed for the worst case scenario. Figure 12 shows the pressure envelope corresponding to this model run. No undue positive pressures were noticed for this run either. Maximum pressure between CWPH and Booster Station has dropped by a few meters indicating the benefits of adding the PRV. The flowrate through the pressure relief valve is shown in Figure 13. For most pipeline systems, simultaneous failure of all operating pumps results in most severe transient pressures. Occasionally, however, other operating scenarios and events can trigger more sever pressure transients. Therefore, it is important to verify if the existing OSTs can adequately protect the pipeline system from such operating scenarios. One such scenario is a pump startup operation when the OSTs and pipeline are filled with water (e.g. after a normal pump shutdown condition and after charging the OSTs). Figure 14 shows the pressure envelope corresponding to this model run. This modeling scenario did not consider the effect of air valves on transient response. The highest pressure in the system was slightly less than 160m and it occurs on the discharge side of the Booster Station confirming the adequacy of the existing protection for pump startup condition following a normal pump shutdown operation. Next, a single pump startup operation within a few minutes of power failure condition has been simulated. Figure 15 shows the pressure envelope corresponding to this model run. This model run did not consider the influence of air valves on the transient pressures. As evident from this figure, the highest pressure is no more than 160m and occurs between the CWPH and Booster Station. Therefore, the pipeline appears to be safe for normal pump startup operation a few minutes after a pump trip event when presence of air valves is ignored. However, presence of air valves that are not equipped with surge suppressing mechanism may pose additional problems during a pump startup 8 of 81

9 y condition immediately after a pump trip event. Air entered the pipeline during a pump trip event exits through the same orifice during a pump startup event and can result in a secondary transient air slam pressure (Lingireddy et.al., 2004). Though the secondary transient may not be strong enough to damage the air valve where air slam pressure occurs, propagation of secondary pressure wave to low elevation regions may increase the pressures in those regions sufficient enough to damage the air valves and/or other devices. Transient analysis was repeated considering the existing 2-stage air valves. Figure 16 shows the pressure envelope corresponding to this model run during a 500 second transient simulation. As evident from Figure 16, pressure heads in the initial portions of the pipeline went up by nearly 50m from the previous runs. Highest pressure in the system was about 20 bars and occurs near CWPH. Note that this run included the newly installed pressure relief valve upstream of the Booster Station. Figure 17 shows pressure head variation at the first air valve location (Air-1) immediately downstream from CWPH. Figure 18 shows pressure head variation at Air-26 (chainage 13885) which is located at the highest elevation point between CWPH and Booster Station. Being at the peak location, this air valve tends to ingress most air into the pipeline during low pressure conditions. Figure 19 shows the air volume curve at this location. About 3m 3 of air enters the pipeline at this location during the pump trip event. Complete expulsion of this air occurs at 236 seconds from the start of simulation (Figure 20). Figure 21 shows the variation in flowrate at the time of complete expulsion of air which results in a fairly significant air slam pressure as seen in Figure 18 (at 236 seconds). This modeling run did not take into account any mal-functioning valves (leaking NRVs, flow bypass valves, discharge BFVs etc) at pump station that will allow continuous draining of the pipeline after the pump trip event and before starting up the pump. If such continuous draining conditions exist, the volume of air entering the pipeline would be much higher than 3m 3 and consequently much higher magnitude of flow change at the time of complete expulsion of air. Higher flow change at the time of complete expulsion results in higher air slam pressure. 9 of 81

10 y It is in this context, the use of surge suppressing air valves help reduce the air slam pressures and therefore reduce the overall positive pressures associated with rapid expulsion of unintended and unwanted air. The model from the previous run was modified replacing the existing 2-stage air valves with 200 mm 3-stage surge suppressing air valves. Figure 22 shows the pressure envelope for this simulation. Comparing pressures from this figure with those presented in Figure 16, it is evident that the use of three stage air valves of uniform size (200 mm) did not provide much relief for maximum positive pressures although they appeared to have reduced the occurrences of low pressures and cavitation conditions. Figures 23 and 24 show the pressure head and air volume curves respectively, at air valve located at highest elevation point between CWPH and Booster Station. Although the air slam pressure is slightly lower compared to 2- stage air valve case (Figure 18), it is still very significant indicating that the size of air valve at this location being too large to alleviate the air slam pressure. Other air valves, being same size, could be causing additional air slam pressures as well. Therefore, the approach of one size fits all appears to not help reduce the air slam pressures for this pipeline system. Attempts were made to optimize the air valve sizes such that the air slam pressures would be minimized and consequently minimizing the overall maximum pressures in the entire system. After several attempts, an optimal set of two and three stage air valves were arrived. Data used for these air valves came from A.R.I. Flow Control Accessories, Israel. Figure 25 shows the pressure envelope corresponding to this model run. Figure 26 shows the pressure head variation at Air-26 (air valve at peak location between CWPH and Booster Station). Air slam pressure at this location is about 25m less than the case with existing 2-stage air valves (Figure 18). Figure 27 shows the air volume curve at Air-26 and Figure 28 shows the close up view of the air volume curve at the time of complete expulsion of air. Comparing the air volume curve shown in 10 of 81

11 y Figure 28 with that in Figure 20, it is evident that the use of an optimal threestage air valve slows down the expulsion of air towards the end thereby reducing the secondary transient due to air slam. Figure 29 shows the variation in flowrate at the time of complete expulsion of air. Figure 30 shows pressure head variation at the first air valve location (Air-1) immediately downstream from CWPH. Maximum pressure at this location was brought down to 150m from about 200m corresponding to non surge-suppressing air valves. Now that the efficiency of optimal combination of 3-stage surge suppressing air valves of ARI has been established, it is important to verify if that combination (along with the existing OSTs) can also provide adequate protection against transient pressures arising from other critical operating scenarios. The following critical operating scenarios were identified and transient modeling runs were conducted to verify the sufficiency of the proposed air valve combination along with existing OSTs and Pressure Relief Valve. A. Two pumps at each station (full capacity) are working under steady state conditions and a power failure occurs tripping all 4 operating pumps simultaneously. B. Two pumps at each station (full capacity) are working under steady state conditions and a power failure occurs at CWPH tripping both of the CWPH pumps simultaneously. This calls for turning the Booster Station pumps off before the down surge generated at CWPH reaches Booster Station. Booster pumps are turned off 14 seconds (travel time between CWPH and Booster Station) after power failure at CWPH. C. Two pumps at each station (full capacity) are working under steady state conditions and a power failure occurs at Booster Station tripping both of the operating pumps simultaneously. CWPH pumps are turned off 14 seconds (travel time between CWPH and Booster Station) after power failure at Booster Station. 11 of 81

12 y D. One pump at each station is working under steady state conditions and both get tripped simultaneously. Within a few minutes both pumps are restarted one after the other. Operating Scenario A Figure 31 shows the steady state hydraulic grade line (HGL) for this pipeline system while all 4 pumps are operating at their rated speed. Figure 32 shows pressure envelope for this transient scenario (all 4 operating pumps trip simultaneously) during a 500 second simulation. Highest transient pressure in the system was about 130m (Figure 33) and the lowest pressure was about -7m. Figure 34 shows pressure head variation at a few representative nodes where the pressure drops below atmospheric pressure. Figure 35 shows pressure head variations at OSTs. As evident from these figures, the optimal combination of 3- stage air valves (along with existing OSTs and pressure relief valve) provides adequate protection for this operating scenario. Operating Scenario B Figure 36 shows the steady state hydraulic grade line (HGL) for this pipeline system while all 4 pumps are operating at their rated speed. Figure 37 shows pressure envelope for this transient scenario (Booster Pumps trip 14 seconds after CWPH pumps get tripped) during a 500 second simulation. Highest transient pressure in the system was about 130m (Figure 38) and the lowest pressure was about -7m. Figure 39 shows pressure head variation at a few representative nodes where the pressure drops below atmospheric pressure. Figure 40 shows pressure head variations at OSTs. As evident from these figures, the optimal combination of 3-stage air valves (along with existing OSTs and pressure relief valve) provides adequate protection for this operating scenario. 12 of 81

13 y Operating Scenario C Figure 41 shows the steady state hydraulic grade line (HGL) for this pipeline system while all 4 pumps are operating at their rated speed. Figure 42 shows pressure envelope for this transient scenario (CWPH trips 14 seconds after Booster Pumps get tripped) during a 500 second simulation. Highest transient pressure in the system was about 140m (Figure 43) and the lowest pressure was about -8.5m. Figure 44 shows pressure head variation at a few representative nodes where the pressure drops below atmospheric pressure. Figure 45 shows pressure head variations at OSTs. As evident from these figures, the optimal combination of 3-stage air valves (along with existing OSTs and pressure relief valve) provides adequate protection for this operating scenario. Operating Scenario D Figure 46 shows the steady state hydraulic grade line (HGL) for this pipeline system when one pump at each station is operating at its rated speed. Figure 47 shows pressure envelope for this transient scenario during a 500 second simulation. Highest transient pressure in the system was about 150m (Figure 48) and the lowest pressure was about -4m. Figure 49 shows pressure head variation at a few representative nodes where the pressure drops below atmospheric pressure. Figure 50 shows pressure head variations at OSTs. As evident from these figures, the optimal combination of 3-stage air valves (along with existing OSTs and pressure relief valve) provides adequate protection for this operating scenario. Model Runs with Air Valve Sizes Recommended by Black and Veatch: The contractor has requested to evaluate the adequacy of air valve sizes recommended by Black and Veatch International Ltd., for this pipeline project. 13 of 81

14 y Models created for different critical operating scenarios were updated with the air valve location, type and size information provided by the contractor per Black and Veatch Recommendations. Air valve characteristics provided by ARI Flow Control Systems (Israel) were employed for modeling both three-stage (air valves with anti-slam device) and two-stage valves. Nominal size for all air valves (with and without anti-slam device) was specified as 200mm. Figure 51 shows pressure envelope from the transient run corresponding to scenario B, described in the previous sections. Comparison of this pressure envelope with that from an earlier run with optimal air valve sizes (Figure 37) indicates potential cavitation conditions at several locations in the system when uniform size air valves are used. Although, the thickness of pipeline allows it to withstand higher negative pressures (well below the vapor pressure of water), limiting the high negative pressures allows much smoother operation and minimizes unwanted secondary transients due to collapse of vapor cavities. After several attempts, occurrences of extremely low pressures conditions were minimized by replacing five of the 200mm anti-slam air valves (AV-13, AV-25, AV-35, AV-50, AV-79) with 150mm anti-slam air valves. Figures 52 through 55 show the corresponding pressure envelopes for scenarios A-D. DYNAMIC CHARACTERISTIC OF CHECK VALVES: Although it is difficult to model the exact closure characteristics of a check valve for lack of reliable closure characteristics data, one could verify the validity of check valve modeling assumptions with the help of manufacturer suggested deceleration vs. reverse velocity data. The proposed check valves for this project are VAG SKR slanted seat valves. The manufacturer suggested deceleration vs. reverse velocity data for these check valves is shown in Figure 56. Reverse velocity at the time of complete closure of check valve can be assessed based 14 of 81

15 y on the deceleration at the time of flow reversal. Deceleration at the time of flow reversal can be determined by analyzing Surge2000 model of the pipeline system with NO check valves at pumps thereby allowing flow reversal. Pumps at CWPH: Figure 57 shows the flowrate at pump discharge (with NO check valves) following pump trip, along with the corresponding deceleration of flow. From Figure 57, the deceleration at the time of flow reversal is roughly 0.2 m/s 2. This deceleration may be used to determine the potential reverse flow velocity at the time of complete closure of check valve from manufacturer suggested data. For a deceleration of 0.2 m/s 2 at the time of flow reversal, SKR valve gives a reverse velocity of about 0.02 m/s at check valve closure (Figure 58). Knowing the celerity of MS pipe (1200m/s) and the velocity change of 0.02 m/s, the change in pressure head (pressure spike) at the time of complete closure of check valve may be determined using Joukowsky s equation as H = (c/g) V H = (1200/9.81) 0.02 H = 2.45m This change in pressure head at the time of complete closure may be compared with change in pressure computed by the Surge2000 model to determine if the assumed check valve closure characteristics are reasonable. Figure 59 shows the flow and head variation at pump discharge for the first few seconds of Surge2000 simulation. It may be noted that all Surge2000 models for the pipe 15 of 81

16 y system under consideration used a 0.5 second linear closure time for the check valves. From Figure 59, the change in pressure head at the time of complete check valve closure (zero flowrate though the pump) is around 5m. Since the change in pressure head computed by the Surge2000 model is significantly higher than the value computed from the deceleration characteristics (2.45m), the assumed check valve closure characteristics provide conservative (worse than what s possible in reality) estimates for the transient pressures. So the assumed linear closure characteristics for the check valves will results in conservative estimates for the transient pressures as the actual closure characteristics reduce the flow area very rapidly in the first half of the closure time. Pumps at Booster Station: Figure 60 shows the flowrate at pump discharge (with NO check valves) following pump trip, along with the corresponding deceleration of flow. From Figure 60, the deceleration at the time of flow reversal is roughly 0.2 m/s 2. This deceleration may be used to determine the potential reverse flow velocity at the time of complete closure of check valve from manufacturer suggested data. For a deceleration of 0.2 m/s 2 at the time of flow reversal, SKR valve gives a reverse velocity of about 0.02 m/s at check valve closure (Figure 61). Knowing the celerity of MS pipe (1200m/s) and the velocity change of 0.02 m/s, the change in pressure head (pressure spike) at the time of complete closure of check valve may be determined using Joukowsky s equation as H = (c/g) V 16 of 81

17 y H = (1200/9.81) 0.02 H = 2.45m This change in pressure head at the time of complete closure may be compared with change in pressure computed by the Surge2000 model to determine if the assumed check valve closure characteristics are reasonable. Figure 62 shows the flow and head variation at pump discharge for the first few seconds of Surge2000 simulation. It may be noted that all Surge2000 models for the pipe system under consideration used a 0.5 second linear closure time for the check valves. From Figure 62, the change in pressure head at the time of complete check valve closure (zero flowrate though the pump) is around 12m. Since the change in pressure head computed by the Surge2000 model is significantly higher than the value computed from the deceleration characteristics (2.45m), the assumed check valve closure characteristics provide conservative (worse than what s possible in reality) estimates for the transient pressures. So the assumed linear closure characteristics for the check valves will results in conservative estimates for the transient pressures as the actual closure characteristics reduce the flow area very rapidly in the first half of the closure time. SUMMARY: The existing protection based on the one-way surge tanks appears to be more than adequate for protecting the pipeline system from adverse transient pressure generated during a pump trip event. Abnormal operation and inadequate maintenance conditions that may results in excessive accumulation of air at peak points may result in secondary pressure transients from air slam pressures during a pump startup event immediately after a pump trip event. Pressures in excess of 17 of 81

18 y 20 bars were noted close to the clear water pump station as a result of air slam pressures at peak air valve locations. Use of one size 3-stage surge suppressing air valve did not appear to help reduce the air slam pressures. An optimal combination of sizes for 3-stage surge suppressing air valve provided adequate relief for different operating scenarios. Use of 200mm two-stage and three-stage (anti-slam) air valves at all locations as recommended by Black and Veatch provide adequate protection to the pipeline against high pressure transients. However, they appear to cause cavitation and other low pressure conditions at several locations. Although the pipeline is capable of withstanding very high negative pressures (based on its thickness), it is advisable to avoid cavitation and the associated secondary transient pressure problems. Replacing five of the anti-slam 200mm air valves (AV-13, AV-25, AV-35, AV-50, AV-79) with 150mm anti-slam air valves appear to minimize the extreme low pressure conditions thereby allowing much smother operation. The VAG SKR Slanted disk check valves provide satisfactory operation against flow reversal through pumps. RECOMMENDATIONS: Based on an extensive transient modeling runs, the study recommends the use 200mm two-stage and three-stage (anti-slam) air valves as recommended by Black and Veatch except for the air valves at AV-13, AV-25, AV-35, AV-50, AV- 79. At these locations, 150mm anti-slam valves are recommended in place of 200mm anti-slam valves to minimize the occurrence of extensive low pressure conditions. The recommended protection is in addition to the OST protection per original design and a newly installed pressure relief valve. The recommended protection can only work if the OSTs are maintained properly and are ensured to 18 of 81

19 y have water to their design capacity prior to running all the pumps at their rated speed. REFERENCES: Funk, J.E., Wood, D.J., Lingireddy, S. and D.C. Denger, Pressure Surges due to Rapid Expulsion of Air, International Conference on Unsteady Flow and Fluid Transients, Sept-Oct 1992, Durham, England. Lingireddy, S., Wood, D.J., and Zloczower, N. (2004) Pressure Surges in Pipeline Systems Due to Air Release. Jl. American Water Works Association, 96 (7), of 81

20 Elevation (m) System Profile 0 1.0E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Figure 1. Schematic of clear water transmission main profile 20 of 81

21 HGL (m) System Profile 0 1.0E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Figure 2. Pipeline schematic between CWPH and Booster Station. 21 of 81

22 HGL (m) 380 Baseline Model E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Figure 3. Max/Min Pressure Envelope with Existing OST Protection (Pressures allowed to drop below vapor pressure) 22 of 81

23 Figure 4. Max/Min Pressure Profile Original Design (obtained from HCC) 23 of 81

24 Head (m) Time (s) Figure 5. Pressure Head Variation on Discharge Side of CWPH (Existing OST Protection) 24 of 81

25 Head (m) Time (s) Figure 6. Pressure Head Variation on Discharge Side of Booster Station (Existing OST Protection) 25 of 81

26 Speed (rpm) Time (s) Figure 7. Pump Speed Variation at CWPH (Existing OST Protection) 26 of 81

27 Speed (rpm) Time (s) Figure 8. Pump Speed Variation at Booster Station (Existing OST Protection) 27 of 81

28 Head (m) Time (s) J-110 J-91 Figure 9. Pressure Head Variation at Representative Nodes where Pressures Dropped Below Cavitation Head 28 of 81

29 Head (m) Time (s) OST-1 OST-4 OST-3 OST-2 Figure 10. Water Level Drawdown Curves for Different OSTs 29 of 81

30 HGL (m) 380 Baseline Model (OSTs + Air Valves) E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 11. Max/Min Pressure Envelope with Existing OST Protection + Air Valves (Low Pressures were Limited to Vapor Pressure) 30 of 81

31 HGL (m) 380 Baseline Model (OSTs + Air Valves + PRV) E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 12. Max/Min Pressure Envelope with Existing OST Protection + Air Valves + Pressure Relief Valve 31 of 81

32 Flow (m^3/s) 1.2 Flow Through PRV Time (s) Figure 13. Flow through Pressure Relief Valve 32 of 81

33 HGL (m) 400 Pump Startup E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 14. Pressure Envelope for Pump Startup Operation (OSTs and Pipeline are filled with water) 33 of 81

34 HGL (m) _ E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 15. Pressure envelope ignoring existing Air Valves single pump startup following pump trip 34 of 81

35 Pressure (kpa) _ E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 16. Pressure envelope WITH existing Air Valves pump startup following pump trip 35 of 81

36 Head (m) 200 Air Time (s) Figure 17. Pressure head variation at Air-1 (chainage 361) 36 of 81

37 Head (m) 90 Air Time (s) Figure 18. Pressure head variation at Air-26 (chainage 13885) 37 of 81

38 Volume (m^3) 3.5 Air Time (s) Figure 19. Air volume curve for Air-26 (chainage 13885) 38 of 81

39 Volume (m^3) Air Time (s) Figure 20. Close up view of air volume curve at the time of complete expulsion of air 39 of 81

40 Flow (CMS) 1.0 Air Time (s) Figure 21. Variation in flowrate in the pipeline at Air-26 at the time of complete expulsion of air 40 of 81

41 HGL (m) _ E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 22. Pressure envelope with all 200 mm 3-stage air valves 41 of 81

42 Head (m) 90 Air Time (s) Figure 23. Pressure head variation at Air-26 (200 mm 3-stage air valves) 42 of 81

43 Volume (m^3) 3.5 Air Time (s) Figure 24. Air volume curve for Air-26 (200 mm 3-stage air valves) 43 of 81

44 HGL (m) Optimal Sizes for 3-Stage Surge Suppressing Air Valves E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Time Lower Limit Cavitation Figure 25. Pressure envelope with optimal combination of 3-stage air valves 44 of 81

45 Head (m) 70 Air Time (s) Figure 26. Pressure head variation at Air-26 (optimal combination of 3-stage air valves) 45 of 81

46 Volume (m^3) 3.0 Air Time (s) Figure 27. Air volume curve for Air-26 (optimal combination of 3-stage air valves) 46 of 81

47 Volume (m^3) 2.0 Air Time (s) Figure 28. Close up view of air volume curve at the time of complete expulsion of air 47 of 81

48 Flow (m^3/s) 1.0 Air Time (s) Figure 29. Variation in flowrate in pipeline at Air-26 at the time of complete expulsion of air 48 of 81

49 Head (m) 160 Air Time (s) Figure 30. Pressure head variation at Air-1(optimal combination of 3-stage air valves) 49 of 81

50 HGL (m) 450 Steady State E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Figure 31. Steady State HGL for Operating Scenario A 50 of 81

51 HGL (m) 450 _ E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 32. Pressure envelope for operating scenario A 51 of 81

52 Head (m) 140 Booster Pump Discharge Time (s) Figure 33. Pressure head variation at Booster Pump discharge (highest pressure in the system occurs at this node) 52 of 81

53 Head (m) Time (s) J-170 J-177 J-178 Figure 34. Pressure head variation at a few representative nodes where the lowest pressure dropped below atmospheric pressure. 53 of 81

54 Head (m) 26 OST Water Levels Time (s) OST-1 OST-2 OST-3 OST-4 Figure 35. Water Level Drawdown Curves for OSTs 54 of 81

55 HGL (m) 450 _ E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Time Lower Limit Cavitation Figure 36. Steady State HGL for Operating Scenario B 55 of 81

56 HGL (m) 450 _ E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 37. Pressure envelope for operating scenario B 56 of 81

57 Head (m) 160 Booster Pump Discharge Time (s) Figure 38. Pressure head variation at Booster Pump discharge (highest pressure in the system occurs at this node) 57 of 81

58 Head (m) Time (s) J-223 J-292 Figure 39. Pressure head variation at a few representative nodes where the lowest pressure dropped below atmospheric pressure. 58 of 81

59 Head (m) 26 OST Water Levels Time (s) OST-1 OST-2 OST-3 OST-4 Figure 40. Water Level Drawdown Curves for OSTs 59 of 81

60 HGL (m) 450 Steady State E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Figure 41. Steady State HGL for Operating Scenario C 60 of 81

61 HGL (m) 450 Min and Max E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 42. Pressure envelope for operating scenario C 61 of 81

62 Head (m) 160 Chainage = 1000m Time (s) Figure 43. Pressure head variation at Booster Pump discharge (highest pressure in the system occurs at this node) 62 of 81

63 Head (m) Time (s) J-118 J-309 J-626 J-66 Figure 44. Pressure head variation at a few representative nodes where the lowest pressure dropped below atmospheric pressure. 63 of 81

64 Head (m) Time (s) OST-1 OST-2 OST-3 OST-4 Figure 45. Water Level Drawdown Curves for OSTs 64 of 81

65 HGL (m) 400 Steady State E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Figure 46. Steady State HGL for Operating Scenario D 65 of 81

66 HGL (m) E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 47. Pressure envelope for operating scenario D 66 of 81

67 Head (m) Time (s) Figure 48. Pressure head variation at Booster Pump discharge (highest pressure in the system occurs at this node) 67 of 81

68 Head (m) Time (s) J-178 J-223 J-66 Figure 49. Pressure head variation at a few representative nodes where the lowest pressure dropped below atmospheric pressure. 68 of 81

69 Head (m) Time (s) OST-1 OST-4 OST-3 OST-2 Figure 50. Water Level Drawdown Curves for OSTs 69 of 81

70 HGL (m) 400 Pressure Envelope Cavitation conditions E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 51. Pressure envelope for operating scenario B with 200mm size two and three stage air valves recommended by Black and Veatch 70 of 81

71 HGL (m) 400 _ E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 52. Pressure envelope for operating scenario A 71 of 81

72 HGL (m) 400 Pressure Envelope E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 53. Pressure envelope for operating scenario B 72 of 81

73 HGL (m) 400 Pressure Envelope E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 54. Pressure envelope for operating scenario C 73 of 81

74 HGL (m) 450 Max/Min Pressure Head Envelope E+4 2.0E+4 3.0E+4 4.0E+4 5.0E+4 Distance (m) Pipeline Envelope Min Max Lower Limit Cavitation Figure 55. Pressure envelope for operating scenario D 74 of 81

75 Figure 56. Dynamic characteristics of VAG non-return valves (courtesy: VAG) 75 of 81

76 Decceleration (m/s^2) Flowrate (m^3/s) Decceleration Calculations Decceleration(m/s^2) Flowrate(m^3/s) Flow Reversal Point (No CV at Pump) Decceleration = 0.25m/s^ Time (s) -0.2 Figure 57. Flow deceleration at pump discharge following pump trip pumps were modeled with NO check valves(cwps) 76 of 81

77 Reverse Velocity = 0.02m/s Deceleration = 0.25m/s 2 Figure 58. Reverse velocity based on calculated deceleration(cwps) 77 of 81

78 Head (m) Flowrate (m^3/s) Head Increase due to CV Closure Head(m) Flowrate(m^3/s) Check Valve Closure Head Increase = 5m Time (s) -0.2 Figure 59. Pressure head variation from Surge2000 model pumps modeled with check valves (CWPH) 78 of 81

79 Decceleration (m/s^2) Flowrate (m^3/s) Decceleration Calculations Flow Reversal Point (No CV at Pump) Decceleration(m/s^2) Flowrate(m^3/s) Decceleration = 0.2m/s^2 0-4 Time (s) -0.2 Figure 60. Flow deceleration at pump discharge following pump trip pumps were modeled with NO check valves(booster) 79 of 81

80 Reverse Velocity = 0.02m/s Deceleration = 0.2m/s 2 Figure 61. Reverse velocity based on calculated deceleration(booster Station) 80 of 81

81 Head (m) Flowrate (m^3/s) Head Increase due to CV Closure Head(m) 0.8 Flowrate(m^3/s) Head Increase = 12m Check Valve Closure Time (s) Figure 62. Pressure head variation from Surge2000 model pumps modeled with check valves (Booster) 81 of 81