Static Electricity and Cleaning of Equipment (36-40)

8/13/2019 Static Electricity and Cleaning of Equipment (36-40)

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STATIC ELECTRICITY AND

CLEANING OF EQUIPMENT

Presented by:

Dhairya MehtaShamel Merchant

Shashank Maindarkar

Manish Medar

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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

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What is Static Electricity?

Electrical Imbalance on the surface of amaterial

Transfer of Electrons

Causes Spark ignition, which underfavorable (?) conditions can lead to

explosion

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Major Sources of Static in Industry

Use of Power / Conveyor belts

Pulverized materials / dusts

pneumatically transported

The flow of fluids through pipes orconduits, or from orifices into tanks or

containers

The flow of gases from orifices The 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: (10-8C/kg)Charge on product: 10-6CSpark energy: E = 0.5 x C x VC = 10-6 C; V = 10 kV (typical value for spark discharge) Thendischarge energy

E = 5 mJ 5


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Minimum Ignition Energy

n

ergy

or

gn

on

Concentration (v.p; temp)

Min (oxygen)

Min (air)

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 energyvalues for Combustible Vapors:

Soot: > 4000 mJ

Natural products: > 10 mJ

Organic chemicals: 1-10 mJAluminium, 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 tobreakdown the surrounding air?

Is there sufficient energy to ignite the

flammable atmospheredischarge 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 stationaryconductive 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 CHARGING

Fluids

Keep Flow Velocity Low

Avoid 2ndPhase entrainment

Avoid Pumps, Filters etc. specially near vessels

AVOID CHARGE ACCUMULATIONEarth All Conducting Parts - e.g. plant & items

oGenerally


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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 SparkIgnition

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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. 12


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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

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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 remove

Deposits build up due to:

1. Carbonaceous or organic structuremolecules

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 IonChelating agent for iron (pH 3.5)

Inorganic Acids

- Remove water side deposits, iron oxides and calcium

scales- Inhibited Muriatic Acid HCl Inhibited Sul huric 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

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Solvent Cleaning Methods

Circulation- Circulation of solvent

Cascade Method

- Used for towers- Chemical pumped through reflux lineand cascade down over trays and interiortower

- Soils at bottom of trayunremoved

- High pumping capacity of solvents


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Fill and Soak- Vessel filled with solvent and let to soak

- 15 min1 hour

- Proper flushing to remove loose soil

- Ventto remove gases produced during reaction between soil and

deposit On stream Cleaning

- Steam Vapor phase cleaningsolvents introduced at highpressure, soils carried with vapor

- Foam CleaningFoamed 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 weightimportant when structuralintegrity ?


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Gel Cleaning- Similar to foam cleaning

- Gel type cleaning agent sprayed orbrushed on surface

- Remove iron oxide prior to painting- Eg. naval gel

Pickling and passivating

- Agents act as corrosion inhibitors andpassivators

- CS use HCl, Alloy use ammoniated citricacids


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Mechanical Methods

Water jetting- Hyperblasting water used at 1000-10000 psi

- Sheer force remove deposits

- Consists of lances and specially designed nozzle

- Extremely dangerous


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Mechanical Methods

Hydrodrilling, Plugs, Crawlers

- Special drills used with water to cut

through heavy deposits in tube walls

- WaterLubricant and flushing


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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


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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 by80%

8 cleaning cycles to pay for the system


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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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THANK YOU

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Documents

Static Electricity and Cleaning of Equipment (36-40)