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

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Presentation on theme: "STATIC ELECTRICITY AND CLEANING OF EQUIPMENT Presented by: Dhairya Mehta Shamel Merchant Shashank Maindarkar Manish Medar 1."— Presentation transcript:

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

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 2

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 3

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 4

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 5

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 6

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! 7

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 8

9 Fig. Filling a Tanker with a Flammable Liquid 9

10 Precautions MINIMISE CHARGING Fluids ◦ Keep Flow Velocity Low ◦ Avoid 2 nd Phase entrainment ◦ Avoid Pumps, Filters etc. specially near vessels AVOID CHARGE ACCUMULATION Earth All Conducting Parts - e.g. plant & items o Generally <10 ohm o Special cases <10 6 ohm Earth Personnel MAXIMISE CHARGE DISSIPATION Liquids Increase Conductivity (e.g. ‘improver’ Stadis 450) 10

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 11

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. 12

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 13

14 CLEANING OF EQUIPMENT IN PROCESS INDUSTRIES Main methods: 1. Chemical 2. Mechanical 3. Combination of chemical and mechanical 14

15 Chemical cleaning to remove Deposits build up due to: 1. Carbonaceous or organic structure molecules 2. Algae and slime organisms 3. Degradation deposits 4. Preoperational deposits 15

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 16

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 17

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


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