static electricity and cleaning of equipment presented by: dhairya mehta shamel merchant shashank...
TRANSCRIPT
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STATIC ELECTRICITY AND CLEANING OF EQUIPMENT
Presented by:Dhairya MehtaShamel MerchantShashank MaindarkarManish Medar
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OVERVIEWWhat is Static ElectricityMajor Sources in IndustrySome Calculations for Spark IgnitionMinimum Ignition EnergyHazard AssessmentPrecautions to be takenCase Study
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What is Static Electricity?Electrical Imbalance on the surface of a
materialTransfer of Electrons Causes Spark ignition, which under
favorable (?) conditions can lead to explosion
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Major Sources of Static in Industry
Use of Power / Conveyor beltsPulverized materials / dusts
pneumatically transportedThe flow of fluids through pipes or
conduits, or from orifices into tanks or containers
The flow of gases from orificesThe use of rubber-tyred vehicles
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Typical NumbersCharge production in typical operations for non-accumulators[C/kg]:
Non-Accumulators: Conductivity < 50 pico - mhos/cm
Sieving: 10-11 - 10-9
Pouring: 10-9 - 10-7
Micronising: 10-7 - 10-4
Pneumatic Transport: 10-6 - 10-4
Calculation example:Pouring operation of 100 kg Product: (10-8 C/kg)Charge on product: 10-6 CSpark energy: E = 0.5 x C x VC = 10-6 C; V = 10 kV (typical value for spark discharge) Then discharge energy E = 5 mJ
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Minimum Ignition Energy
Ene
rgy
for
Igni
tion
C o ncen tra tion (v.p ; tem p )
M in (ox ygen)
M in (a ir)
MIE the minimum energy that can ignite a mixture of a specified flammable material with air or oxygen, measured by a standard procedureTypical minimum ignition energy values for Combustible Vapors:Soot: > 4000 mJ Natural products: > 10 mJ Organic chemicals: 1-10 mJ Aluminium, Sulphur: < 1mJ Methane: 0.3 mJ Carbon disulphide: 0.068 mJ Hydrogen: 0.012 mJ
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Electrostatic Hazard Assessment - logic
◦ Is there a flammable atmosphere?◦Will charge be generated?◦Can charge accumulate?◦ Is the field strength high enough to
breakdown the surrounding air?◦ Is there sufficient energy to ignite the
flammable atmosphere – discharge type?If the answer is YES, then there is a risk of
ignition!
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General Means of Control Bonding and earthing of stationary
conductive equipment.
Increasing the conductance of floors, footwear, wheels and tyres
Increasing the conductivity of non-conductors
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Fig. Filling a Tanker with a Flammable Liquid
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PrecautionsMINIMISE CHARGINGFluids
◦ Keep Flow Velocity Low◦ Avoid 2nd Phase entrainment◦ Avoid Pumps, Filters etc. specially near vessels
AVOID CHARGE ACCUMULATIONEarth All Conducting Parts - e.g. plant & itemso Generally <10 ohmo Special cases <106 ohm
Earth Personnel
MAXIMISE CHARGE DISSIPATIONLiquidsIncrease Conductivity (e.g. ‘improver’ Stadis 450)
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Barton Solvents Wichita facility Case - Study
Flammable Liquid: VM & P NaphthaIncident: While Transferring VM & P
Naphtha to a storage tank, an explosion occurred. (July, 2007)
Investigated by: U.S. Chemical Safety and Hazard Investigation Board
Main Cause: Static Electricity Spark Ignition
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Key Findings
Tank Contained ignitable vapor-air mixture in the head space Stop-start filling, trapping air in the transfer piping The tank had a liquid level gauging system float with a loose linkage The MSDS for the VM&P naphtha involved in this incident did not adequately communicate the explosive hazard.
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RecommendationsAdd a Nonflammable, Nonreactive (inert)
gas to tank head SpaceModify or Replace Loose Linkage tank
level floats Use Anti-Static Additives Reduced flow (Pumping) Velocity
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CLEANING OF EQUIPMENT IN PROCESS INDUSTRIES
Main methods:
1. Chemical
2. Mechanical
3. Combination of chemical and mechanical
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Chemical cleaning to removeDeposits build up due to:
1. Carbonaceous or organic structure molecules
2. Algae and slime organisms
3. Degradation deposits
4. Preoperational deposits
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CHEMICAL CLEANING SOLVENTS• Alkaline Cleaners - Degreasing of metal surface - Caustic Soda-Surfactant - Caustic Soda plus potassium permanganate (for sulfide
deposits)• Organic Acids - Remove oxides, mill scale and other impurities - Monoammoniated Citric Acid Citric Ion – Chelating agent for iron (pH 3.5)• Inorganic Acids - Remove water side deposits, iron oxides and calcium
scales - Inhibited Muriatic Acid (HCl), Inhibited Sulphuric Acid
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CHEMICAL CLEANING SOLVENTS• Organic Solvents - Removal of grease and oil spots - Spent solution might be recyclable - M-Pyrol for PVC Reactors• Complexing, chelating or sequestering agents - React with hardness ions, forming water soluble
complexes - Expensive but selective complexation - Ease and safety - EDTA, gluconates and polyphosphonates
Solvent Cleaning Methods• Circulation - Circulation of solvent • Cascade Method - Used for towers - Chemical pumped through reflux line
and cascade down over trays and interior tower
- Soils at bottom of tray –unremoved - High pumping capacity of solvents
Solvent Cleaning Methods• Fill and Soak - Vessel filled with solvent and let to soak - 15 min – 1 hour - Proper flushing to remove loose soil - Vent – to remove gases produced during reaction between soil and
deposit• On stream Cleaning - Steam Vapor phase cleaning – solvents introduced at high
pressure, soils carried with vapor - Foam Cleaning – Foamed solvent solution to increase contact time - Foam also has characteristic property of reducing static electricity - Cost effective compared to fill and soak - Aeration reduces total weight – important when structural integrity
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Solvent Cleaning Methods• Gel Cleaning - Similar to foam cleaning - Gel type cleaning agent sprayed or brushed
on surface - Remove iron oxide prior to painting - Eg. naval gel• Pickling and passivating - Agents act as corrosion inhibitors and
passivators - CS use HCl, Alloy use ammoniated citric acids
Mechanical MethodsWater jetting - Hyperblasting water used at 1000-10000 psi - Sheer force remove deposits - Consists of lances and specially designed nozzle - Extremely dangerous
Mechanical Methods
Hydrodrilling, Plugs, Crawlers - Special drills used with water to cut
through heavy deposits in tube walls - Water –Lubricant and flushing
Case StudiesXerox670000 pounds of emissions Replacement of chlorinated solvents with
citric acidReduction of emissions by 90%Saves USD 40000/yr in hazardous waste
disposal
Case StudiesDuPont-MerckInstalled integrated ultrasonic transducer
and rod-shaped tubular ultrasonic resonator
Eliminates the need to buy cleaning solvents and to dispose of solvent waste
Vapor emissions on site were reduced by 80%
8 cleaning cycles to pay for the system
Case StudiesParr PaintsInstalled high pressure systemReduction in latex adhering to wallsCost of high pressure unit, $800. Savings in waste disposal, $3000/yr. Payback, 1.7 months
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THANK YOU