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STATIC ELECTRICITY AND CLEANING OF EQUIPMENT

STATIC ELECTRICITY AND CLEANING OF EQUIPMENT. Presented by: Dhairya Mehta Shamel Merchant Shashank Maindarkar Manish Medar. OVERVIEW. What is Static Electricity Major Sources in Industry Some Calculations for Spark Ignition Minimum Ignition Energy Hazard Assessment

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STATIC ELECTRICITY AND CLEANING OF EQUIPMENT

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  1. STATIC ELECTRICITY AND CLEANING OF EQUIPMENT Presented by: Dhairya Mehta Shamel Merchant ShashankMaindarkar Manish Medar

  2. OVERVIEW • What is Static Electricity • Major Sources in Industry • Some Calculations for Spark Ignition • Minimum Ignition Energy • Hazard Assessment • Precautions to be taken • Case Study

  3. What is Static Electricity? • Electrical Imbalance on the surface of a material • Transfer of Electrons • Causes Spark ignition, which under favorable (?) conditions can lead to explosion

  4. Major Sources of Static in Industry • Use of Power / Conveyor belts • Pulverized materials / dusts pneumatically transported • The flow of fluids through pipes or conduits, or from orifices into tanks or containers • The flow of gases from orifices • The use of rubber-tyred vehicles

  5. Typical Numbers Charge 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 C • Spark energy: E = 0.5 x C x V C = 10-6 C; V = 10 kV (typical value for spark discharge) Then discharge energy E = 5 mJ

  6. Minimum Ignition Energy MIE the minimum energy that can ignite a mixture of a specified flammable material with air or oxygen, measured by a standard procedure Typical 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

  7. 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!

  8. 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

  9. Fig. Filling a Tanker with a Flammable Liquid

  10. Precautions MINIMISE CHARGING Fluids • Keep Flow Velocity Low • Avoid 2nd Phase entrainment • Avoid Pumps, Filters etc. specially near vessels AVOID CHARGE ACCUMULATION Earth All Conducting Parts - e.g. plant & items • Generally <10 ohm • Special cases <106 ohm Earth Personnel MAXIMISE CHARGE DISSIPATION Liquids Increase Conductivity (e.g. ‘improver’ Stadis 450)

  11. Barton Solvents Wichita facility Case - Study • Flammable Liquid: VM & P Naphtha • Incident: 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

  12. 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.

  13. Recommendations • Add a Nonflammable, Nonreactive (inert) gas to tank head Space • Modify or Replace Loose Linkage tank level floats • Use Anti-Static Additives • Reduced flow (Pumping) Velocity

  14. CLEANING OF EQUIPMENT IN PROCESS INDUSTRIES • Main methods: • Chemical • Mechanical • Combination of chemical and mechanical

  15. Chemical cleaning to remove • Deposits build up due to: • Carbonaceous or organic structure molecules • Algae and slime organisms • Degradation deposits • Preoperational deposits

  16. 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

  17. 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

  18. 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

  19. 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 ?

  20. 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

  21. Mechanical Methods • Water jetting - Hyperblasting water used at 1000-10000 psi - Sheer force remove deposits - Consists of lances and specially designed nozzle - Extremely dangerous

  22. Mechanical Methods • Hydrodrilling, Plugs, Crawlers - Special drills used with water to cut through heavy deposits in tube walls - Water –Lubricant and flushing

  23. Case Studies • Xerox • 670000 pounds of emissions • Replacement of chlorinated solvents with citric acid • Reduction of emissions by 90% • Saves USD 40000/yr in hazardous waste disposal

  24. Case Studies • DuPont-Merck • Installed 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

  25. Case Studies • Parr Paints • Installed high pressure system • Reduction in latex adhering to walls • Cost of high pressure unit, $800. • Savings in waste disposal, $3000/yr. • Payback, 1.7 months

  26. THANK YOU

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