Presentation on theme: "Peter N. Lodal Eastman Chemical Company"— Presentation transcript:
1 Peter N. Lodal Eastman Chemical Company Centrifugal Pump Isolation Hazards: Case Histories and Prevention MethodologiesPeter N. LodalEastman Chemical Company
2 Boiling Liquid Expanding Vapor Explosion What is a B.L.E.V.E.? 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.What is a BLEVE?Boiling Liquid Expanding Vapor Explosion
3 What Causes a BLEVE? Pressure P Increases Vapor Closed System TemperatureIncreasesTWhat Causes a BLEVE?Closed system with any liquid (doesn’t have to flammable or reactive, can even happen with just water)As heat is applied, temp and press increasePressure keeps bulk of fluid liquid stateEventually the bulk liquid temp increases significantly above normal atmospheric boiling pointHeatLiquid
4 Vessel Ruptures Pressure Rapidly P Decreases Vapor 1600x Vapor VolumetricExpansionLiquidFlashVaporizesThe Vessel wall exposed to increasing temp and pressureFinally the vessel wall failsSystem pressure is rapidly decreasedCauses the bulk liquid to instantly flash vaporizeLiq to Vap has a 1600 times volumetric expansionThis expanding vapor is the energy that rips the vessel apart and throw fragments considerable distancesIn some cases it can propel the vessel itself long distancesIf liquid if flammable, in addition to the physical energy, can also have enormous fire ballHeatLiquid
5 What can BLEVE? Tanks Hot water heaters Drums Cylinders Railcars Pumps External pool fireIf flammable, fireball is enormousHot water heatersBLEVE does not necessarily involve flammablesDrumsExternal pool fire minutesLaunchCylindersLaunch like a missileRailcarsLaunch over 1 mile in the airPumpsRunning isolated (suction & discharge closed)As little as minutesWhat can BLEVETanks pool fireIf liquid is flammable, the resultant fireball can be enormous2:24 videoHot Water Heater 1:45Drums approx min in pool fire(Aniline Plant 1:30)BLEVE can launch 55 gal steel drum several hundred feetRailcars derailments exposed to pool fire from another carCan be launched over 1 mile in the air1:45The heat source for each of these was pool firePumps can BLEVE if started and left running isolated (suction & discharge closed so fluid is bottled up)Our onsite case histories indicate this can happen in as little as minsI’d like to review 3 our onsite case histories with you
7 Case 1:Description of Incident 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.
12 Case 1: Data 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.
13 Case 1: Data (continued) Pump fracture analysis suggests approximately psig pressure was generated.Pegged pressure gauge on pump discharge suggests pressure reached psig.Vapor pressure data suggests temperature required to reach psig was approximately 230 C.
14 Case 1: Data (continued) 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.
15 Case 1:Conclusions 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 psig which caused the pump to fail.
26 Case 2: Data Pump suction & discharge valves were closed. Pump was inadvertently started when operator threw a hand switch thinking it was for a ventilation fan.
27 Case 2: ConclusionsMaterial 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.
35 Case 3: DataPump suction & discharge valves were closed during a power interruption and system shutdown.Pump was started remotely 3 days after the shutdown.
36 Case 3: ConclusionsMaterial 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.
37 Common FeaturesComplete Isolation (Suction and Discharge Blocked), not deadheaded (discharge only blocked).Fluid FilledRemote Start CapabilitySeal Failure did not provide adequate pressure relief
38 Case Pump Summaries Case 1 3500 RPM, 15 HP, 140 psig Organic Acids & decomposition solidsCase 21750 RPM, 10 HP,55 psig50% SodiumHydroxide solutionCase 32600 GPM, 75 HP,110 psigSteam condensateCase Pump Summaries:All relatively small centrifugal pumpsNo special chemical properties, non-flammable, non-reactive, one just water
39 ConclusionsPump Explosions can occur with completely isolated fluids, even when those fluids are non-flammableDamage potential increases as horsepower increases (increasing inability to dissipate energy)Seal failure as a relief mechanism is NOT a safe assumption
40 RecommendationsSo, what are the best ways of preventing pump explosions?Use local start only (remote shutoff is not an issue)Avoid the ability to isolate the pumpLock open or remove valves on the suction and/or dischargeTrain operators on the significance of this issue
41 Centrifugal Pump with Remote Stop A centrifugal pump is shown with a local start / stop switch but with only the capability to stop the pump remotely. This is the preferred set up for a centrifugal pump and should be used unless process necessity dictates a different design requirement.
42 RecommendationsIf 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 ShutdownHigh Pressure ShutdownLimit switches on isolation valves to ensure they are open (or at least not closed)Low flow interlockLow power draw interlock (limited application—reliability issues)Next
43 Centrifugal Pump with Relief In this case, the remote stop capability has been replaced with start / stop capability from the BPCS. This type of set up will normally require some additional protection with the reliability indicated by a LOPA of the pump. In this case a relief valve on the discharge of the pump has been provided to relieve building pressure. The relief from the pump should be sent to a safe location which, depending on the chemical, could be the floor, a relief stack, or some other form of secondary containment.Back
44 Centrifugal Pump with SIF A SIF has been added to the pump to cause it to stop in the event of high discharge pressure. All symbols with a darkened corner are part of the SIF and are tied to the safety PLC or hardwired.Because there is now an interlock that can stop the pump from running, a local Jog – Off - Auto Switch has been added. The Jog function is spring loaded to return but the Jog bypasses all interlocks as a positive test that power has been locked out when required for LOTO purposes.A variety of instrumented options could be used to trip the pump based on the requirements of the process including pressure (as shown), flow, temperature, and power.Back
45 Pump Protection Selection Matrix Pump Protection Selection GuidanceType of Pump HazardPump Service TypesVersion: B 3/2/2011 By KBYount (HPCC) PRELIMINARY DRAFT<- Protection MethodCentrifical PumpsVariable Speed Drive Centrifical PumpPositive Displacement PumpReactive Chemical ExothermLiquid Vapor Pressure Expansion Hazard (Bleve)Thermal Expansion Hazard (Casing Bust Open)Pump Seal/Bearing FailureSafety Rated Protection Required (SIL 1-3)Batch (ON/OFF) Pumping ServiceAnalog Control Valve/Loop InvolvedAuto Pump Throwover ServiceVariable Process CompositionVariable Process TempSlurry ServiceInterlock On-line Testing RequiredPump Type, Process Service/Conditions ->ABCDEFGHIJKLMNOLow Power Monitor Interlock1YLow Amps Interlock2Low Flow Interlock (transmitter or switch)3High Temperature Interlock (Pump Casing)4High Pump Discharge Pressure Interlock5Overpressure Relief Valve6Minimum Flow/Recirculation Line7naMinimum Flow Control Loop (DCS or Mechanical FC)8Block Valve Position Indication Interlock9Operational Locks on Manual Isolation Valves10Local Only Operator Start Switch (New)11Y = Yes, Typically good for this serviceN = No, Typically not a good fit for this serviceC = Conditionally good for the service, additional design details are required, see notesna = Not Applicable
46 Communicate the hazard Share LearningsCommunicate the hazardIdentify potential pump explosion hazards in our areasRemote start capabilityEvaluate each potential pump explosion hazardMake recommendations to mitigate riskShare our Learning’s:We need to communicate this hazard to everyone who works around pumpsEach area needs to identify their potential pump explosion hazardsDo you have remote start capability?Each area needs to evaluate each potential pump explosion hazard and make recommendations to mitigate the risk