STATIC ELECTRICITY AND CLEANING OF EQUIPMENT

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```					    STATIC ELECTRICITY AND
CLEANING OF EQUIPMENT

Presented by:
Dhairya Mehta
Shamel Merchant
Shashank Maindarkar
Manish Medar
1
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
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
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
Typical Numbers
Charge production in typical operations for non-
accumulators[C/kg]:

Non-Accumulators: Conductivity < 50 pico - mhos/cm
-11    -9
Sieving:                  10 - 10
-9    -7
Pouring:                  10 - 10
-7    -4
Micronising:              10 - 10
-6    -4
Pneumatic Transport:      10 - 10

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
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
Min (air)

Energy for Ignition
values for Combustible Vapors:
Soot:                   > 4000 mJ
Natural products:       > 10 mJ
Organic chemicals: 1-10 mJ
Min (oxygen)
Aluminium, Sulphur: < 1mJ
Methane:                0.3 mJ
Carbon disulphide: 0.068 mJ                               Concentration (v.p; temp)
Hydrogen:               0.012 mJ
6
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
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
Fig. Filling a Tanker with a Flammable Liquid

9
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
o Generally                 <10 ohm
o Special cases             <106 ohm

Earth Personnel

MAXIMISE CHARGE DISSIPATION
Liquids
Increase Conductivity (e.g. ‘improver’ Stadis 450)
10
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
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
 The MSDS for the VM&P naphtha involved in this incident did
not adequately communicate the explosive hazard.                  12
Recommendations
 Add a Nonflammable, Nonreactive (inert)
 Modify or Replace Loose Linkage tank
level floats
 Reduced flow (Pumping) Velocity

13
CLEANING OF EQUIPMENT IN
PROCESS INDUSTRIES
    Main methods:

1.    Chemical

2.    Mechanical

3.    Combination of chemical and
mechanical

14
Chemical cleaning to remove
    Deposits build up due to:

1.    Carbonaceous or organic structure
molecules

2.    Algae and slime organisms

4.    Preoperational deposits

15
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
16
- Inhibited Muriatic Acid (HCl), Inhibited Sulphuric Acid
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
Solvent Cleaning Methods
•   Circulation
- Circulation of solvent
- 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 ?
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 Methods
   Water 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 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
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
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
THANK YOU

26

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