Steam System Safety Operation and Maintenance

Transcription

1 A Short Refresher on Water Hammer as related to Steam System Safety Operation and Maintenance 21st IDEA Distribution Workshop Miami, FL February 21, 2011 Mark Vogler Superintendent Thermal Engineering

2 Water Hammer as related to Steam System Safety, Operation, and Maintenance is: Little known Often misunderstood Can yield catastrophic results

3 Trap Piping and VFD Cabinet (out-of-sight out-of-mind)

4 Sequence of Events Trap out-of-sight due to drip shield placement Trap valve was closed at some point due to continued leakage on VFD Created a manometer Net-zero system flow thru period leading up to event Halloween night, 2008 Change in steam demand around 8:30 pm 3 loud bangs heard in basement

5 Net-Zero Steam Flow Pipe Filled with Condensate

6 RESULT >> Support attachment and anchor welds pull from pipe

7 Support pulled from ceiling Expansion joint pulls apart

8 Result of Incident Steam discharged into mechanical room and up pipe chase to upper floors Sprinklers discharge at 35 heads Building incurred significant water and steam damage Adverse affect on research projects Major analysis, redesign, and repair effort required

9 Goal today is to Increase awareness and understanding of Steam System: Safety, Operation, and Maintenance as related to water hammer Provide information to prevent a similar incident at your facility

10 So What is water hammer? ** Basic definition Water hammer is an impact load created by the sudden starting or stopping of a liquid in a piping system ** NOT a WATER HAMMER

11 About water hammer Complex Phenomenon Multiple factors Numerous causes Varying dynamics Result of a transient condition (e.g. rapid change from moving to not moving) Wide variety of types ranging from simple to complex Household washing machine, dish washer, icemaker Plants pumps, valves, process machinery Piping Systems Facility (house), process, distribution, service, etc

12 True or False? To create a water hammer in a steam system, you must have high-velocity steam to push a slug of water fast enough to cause damage to the system. FALSE

13 Low steam flow with this incident

14 Near-zero Flow here only 1.3 psid Imbalance Needed

15 True or False? You can bleed condensate past a gate valve if you go slow. FALSE

16 The results can be disastrous

17 True or False? Only higher-pressure steam can create a really dangerous water hammer. FALSE

18 Water hammer can occur even with lower-pressure steam

19 So What is needed to create condensate-induced (aka bubble collapse ) water hammer in a pipe? Closed piping system Sub-cooled Condensate (>40 F) Flowing Steam

20 How is CIWH caused? Pipe Begin with pipe and condensate Condensate

21 Add flowing steam Pipe Steam Condensate

22 As condensate level rises, steam velocity and turbulence increases Pipe Steam Condensate

23 As steam velocity and turbulence increase, waves develop Pipe Steam Developing waves Condensate

24 Eventually, steam becomes trapped, and resultant steam bubble collapses Pipe Trapped steam bubble Steam Condensate

25 When steam bubble collapses BANG!! Pipe Steam As void collapses BANG!! Condensate BANG!!

26 Collapsing bubble is what makes condensate induced water hammer dangerous Void created from condensing steam Steam BANG!! and creates a (Dp) pressure pulse where Dp =.5(rcDV) or Dp =.5rV 2 Is rapidly closed KEY ELEMENTS: Density (r) Volume of void Velocity generated in closing void (approaches speed of sound in water) BANG!!

27 Steam Bubble Collapse w/initial Net-Zero Flow

28 Steam Bubble Collapse Creates Pressure Pulse Loading

29 Pressure Pulse Ruptures Pipe

30 Potential causes of excess condensate buildup Live steam sloped against a closed valve Riser Live Steam Low spot in system Un-insulated piping Cold-Starts Re-Starts Clogged/isolated steam trap

31 Steps to avoid Water Hammer: Keep systems drained Keep systems properly maintained Perform routine inspections Keep steam piping insulated Keep insulation DRY During start-ups ALWAYS drain water before introducing steam NEVER mix steam with sub-cooled condensate Provide venting Do not get in a hurry, Energize Slowly Drain, Drain, Drain

32 Some key points Water Hammer is: A Complex Phenomenon Caused by Multiple Factors Varying Dynamics Different Types Numerous Causes

33 Beyond Complex Water Hammer can be: Damaging to property

34 Also Water Hammer is: Very Dangerous it can KILL

35 Good News Though Water Hammer is: Preventable Drain bottom of risers Live Steam Avoid sloping live steam against a closed valve Drain low spots in system Start-up Slowly Ensure proper trap placement Keep piping insulated and dry Keep traps working

36 Special Consideration Drain Downstream Side of Valve Live Steam If valve closed for long period of time Provide drain of downstream side of valve before energizing system

37 Remember ALWAYS keep water drained from steam system piping If you re unsure, ASK DO NOT Guess Credits: - ABS Consulting - Con Edison, New York, NY - Kirsner Consulting - MIT Utilities - Vanderweil Engineering Additional Resources: Trade Associations International District Energy Association Consulting Engineers (training) Energy Service Provider Equipment Suppliers Mark Vogler Supt Thermal Engineering Citizens Energy Group (317) mvogler@citizensenergygroup.com

38 Questions? 21st IDEA Distribution Workshop Miami, FL February 21, 2011 Mark Vogler Superintendent Thermal Engineering

39 Citizens Steam Generation 1.99 million lb/hr mlb/hr steam from trash over 6 billion lbs 28 Miles Dist Piping ~250 customers 5 hospitals Research laboratories University Campus Lucas Oil Stadium

40 Citizens Chilled Water West Street Chilled Water Plant 74,800 Total Tons WSCW 36,000 tons ISCW 8,500 tons IUPUI (North Plant) 5,500 tons 2 Satellite Plants 4,800 tons 2010 over 121 mil THr 14 Miles Dist Piping ~50 customers 2 hospitals Research laboratories University Campus Lucas Oil Stadium

41 An Example of a Bubble Collapse Incident Manhattan Skyline July 18, 2007

42 East 41 st & Lexington Ave

43 Aftermath