Presentation on theme: "Centrifugal Pump Isolation Hazards: Case Histories and Prevention Methodologies Peter N. Lodal Eastman Chemical Company."— Presentation transcript:
Centrifugal Pump Isolation Hazards: Case Histories and Prevention Methodologies Peter N. Lodal Eastman Chemical Company
What is a B.L.E.V.E.? Boiling Liquid Expanding Vapor Explosion Boiling liquid expanding vapor explosion, often referred to by the acronym BLEVE, is a phenomenon which occurs when a vessel containing a pressurized liquid substantially above its boiling point is ruptured, releasing the contents explosively.
3 Heat P Liquid Vapor Pressure Increases Temperature Increases T What Causes a BLEVE? Closed System
What can BLEVE? Tanks Tanks External pool fire If flammable, fireball is enormous Hot water heaters Hot water heaters BLEVE does not necessarily involve flammables Drums External pool fire 15-20 minutes Launch Cylinders Cylinders Launch like a missile Railcars Railcars External pool fire Launch over 1 mile in the air Pumps Running isolated (suction & discharge closed) As little as 20-30 minutes
Case 1 Sludge Pump
Case 1:Description of Incident 7 A loud sound was heard and a 20 foot long white to whitish-gray cloud was seen in the area of Sludge Pump. Inspection showed Pump was fractured and small pieces were found as far away as 35 feet. Pump suction and discharge valves were found closed and the local pump run switch was found in the auto position.
Case 1: Data 12 Pump suction & discharge valves were closed. Pump local hand switch was set in Auto. DCS was set telling the pump to run. Electrical evaluation of the pump power breaker indicated the pump was running until some “incident” tripped the breaker.
Case 1: Data (continued) 13 Pump fracture analysis suggests approximately 200-210 psig pressure was generated. Pegged pressure gauge on pump discharge suggests pressure reached 200-210 psig. Vapor pressure data suggests temperature required to reach 200-210 psig was approximately 230 C.
Case 1: Data (continued) 14 Differential Scanning Calorimeter (DSC) on actual pump sample showed no exotherm until 376 C. Autoignition temperature on actual pump sample was measured at 485 C.
Case 1:Conclusions 15 No evidence of deflagration. Material does not appear to be thermally sensitive at our temperatures. Autoignition does not appear to be credible. Root Cause -- Pump was inadvertently started by DCS and left running with process material blocked into the pump head which built up enough temperature to raise the vapor pressure to 200-210 psig which caused the pump to fail.
Case 2 Caustic Pump
Case 2: Data 26 Pump suction & discharge valves were closed. Pump was inadvertently started when operator threw a hand switch thinking it was for a ventilation fan.
Case 2: Conclusions 27 Material was non-flammable, so deflagration was ruled out. Root Cause = Pump was inadvertently started and left running with process material blocked into the pump head which built up enough temperature to raise the pressure to a point which caused the pump to fail.
Case 3 Condensate Pump
Case 3: Data 35 Pump suction & discharge valves were closed during a power interruption and system shutdown. Pump was started remotely 3 days after the shutdown.
Case 3: Conclusions 36 Material was non-flammable, so deflagration was ruled out. One 5-lb piece of the casing was found 400 feet from the pump installation. Root Cause = Pump was started automatically and left running with condensate blocked into the pump head which built up enough temperature to raise the pressure to a point which caused the pump to fail.
Common Features 37 1. Complete Isolation (Suction and Discharge Blocked), not deadheaded (discharge only blocked). 2. Fluid Filled 3. Remote Start Capability 4. Seal Failure did not provide adequate pressure relief
38 Case Pump Summaries Case 13500 RPM, 15 HP, 140 psig Organic Acids & decomposition solids Case 21750 RPM, 10 HP, 55 psig 50% Sodium Hydroxide solution Case 32600 GPM, 75 HP, 110 psig Steam condensate
Conclusions 39 Pump Explosions can occur with completely isolated fluids, even when those fluids are non-flammable Damage potential increases as horsepower increases (increasing inability to dissipate energy) Seal failure as a relief mechanism is NOT a safe assumption
Recommendations 40 So, what are the best ways of preventing pump explosions? 1. Use local start only (remote shutoff is not an issue) 2. Avoid the ability to isolate the pump Lock open or remove valves on the suction and/or discharge 3. Train operators on the significance of this issue
Centrifugal Pump with Remote Stop
Recommendations 42 If local start and lock open valving are not options (e.g., spared pump installations with auto-throwover), there are a number of control options that can be evaluated on a case-by-case basis for adequacy of risk reduction: Relief device (rupture disc or relief valve) High Temp Shutdown High Pressure Shutdown Limit switches on isolation valves to ensure they are open (or at least not closed) Low flow interlock Low power draw interlock (limited application—reliability issues) Next
Centrifugal Pump with Relief Back
Centrifugal Pump with SIF Back
Pump Protection Selection Matrix 45 Pump Protection Selection Guidance Type of Pump Hazard Pump Service Types Version: B 3/2/2011 By KBYount (HPCC) PRELIMINARY DRAFT <- Protection Method Centrifical Pumps Variable Speed Drive Centrifical Pump Positive Displacement Pump Reactive Chemical Exotherm Liquid Vapor Pressure Expansion Hazard (Bleve) Thermal Expansion Hazard (Casing Bust Open) Pump Seal/Bearing Failure Safety Rated Protection Required (SIL 1- 3) Batch (ON/OFF) Pumping Service Analog Control Valve/Loop Involved Auto Pump Throwover Service Variable Process Composition Variable Process Temp Slurry Service Interlock On-line Testing Required Pump Type, Process Service/Conditions -> ABC DEFGH IJKLMNO Low Power Monitor Interlock 1YNN NYCCY YNCNN Low Amps Interlock 2YNN NY CC YNCNN Low Flow Interlock (transmitter or switch) 3YCN YYYY YCYYC High Temperature Interlock (Pump Casing) 4YYN YYNYY YYYYYY High Pump Discharge Pressure Interlock 5YYY NYYCY YYYYYY C Overpressure Relief Valve 6YYY CNC YYYYYC N Minimum Flow/Recirculation Line 7YNna YN YYCYYC Y Minimum Flow Control Loop (DCS or Mechanical FC) 8YNna YN YYC C Y Block Valve Position Indication Interlock 9YYY YYYC YCCYY Operational Locks on Manual Isolation Valves 10YYY YYYYN NNNYYYna Local Only Operator Start Switch (New) 11 Y = Yes, Typically good for this service N = No, Typically not a good fit for this service C = Conditionally good for the service, additional design details are required, see notes na = Not Applicable
46 Share Learnings Communicate the hazard Identify potential pump explosion hazards in our areas Remote start capability Evaluate each potential pump explosion hazard Make recommendations to mitigate risk