User talk:Plakhapate
FUGITIVE EMISSIONS
ABSTRACT: The purpose of this article is to create public awareness in general .It also provides decision makers reference information for maintaining better environment.
Key words: Fugitive Emissions, Environment Impact, Clean Air Act
About Author: Mr P.J. Lakhapate is a Chemical Engr. from UDCT (Mumbai). He
has 30 years of industrial experience. He has published more than 30 articles. He is
working as a consultant. He can be contacted at NL-6-1-5, Sector –9 , Nerul , Navi-Mumbai ,India -400706 . Phone: 91-22-27702655 .
Email:plakhapate@ rediffmail.com.
FUGITIVE EMISSIONS
Introduction
Most of the fugitive emissions cases are invisible to the eye. The fugitive emissions of the toxic/hazardous/corrosive substances are silent killers to human beings ,other living species, flora and fauna . Hence it is essential to know everybody about the fugitive emissions.
What is fugitive emissions ?
It is defined as “ Any chemical or mixture of chemicals, in any physical form, which represents an unanticipated or spurious leak, from anywhere on an industrial site “
The emission from the stack of the fired heater are not fugitive emissions. However emission from valve packing or pump seal are examples of fugitive emissions.
Why is fugitive emissions important?
Fugitive emissions in USA have been estimated to be in excess of 300,000 tones per year, accounting for about one third of the total organic emissions from chemical plants and inevitably mirrored in Europe.
Volatile Organic Compounds (VOC’s) emissions are of significant environmental concern because some have the potential for Photochemical Ozone Creation Potential (POCP), Ozone Depletion Potential (ODP), Global Warming Potential(GWP), Summer smog, Toxicity, Carcinogenicity , Mutagenicity, Odour nuisance etc.
Apart from Safety, Health & Environment aspects , it also represents a huge loss of potentially valuable materials and cause of plant efficiency.
Visible cost - Loss of material
Invisible costs - Labour to repair leaks
- Material to repair leak
- Wasted energy
- Low plant efficiency
- Environmental clean up
- Environmental fines
- Lost sale due to poor image
- Claims for personal injury
On what factors depend the values of fugitive emissions?
Many process streams in petrochemical refineries are “light”(containing at least 20% of substances with a vapour pressure greater than 0.3kPa at 20 deg C) and at high pressure (1500- 3000 kPa) conditions which encourage fugitive losses.
The values of fugitive emissions depend upon,
• Equipment design
• Age and Quality of equipment
• Standard of installation
• Vapour pressure of the process fluid
• Process temperature and pressure
• Number and type of sources
• Method of determination
• Inspection and maintenance routine
• Rate of production
How are fugitive emissions measured?
At present many end users prefer a leak –tightness result expressed in terms of ppm measured by sniffing, since this is the format of Environmental Protection Agency (EPA) targets in the USA and is widely used across the world.
However ppm does not measure leakage rate., but indicates leakage severity Further research is being done to correlate ppm concentration with the leakage rate.
What are the sources of fugitive emissions?
1)Atmospheric tanks with/without breather valve 2)Tank lids 3)Seals of rotary equipment e.g.PumpBlower,Compressor,Turbine,Agitator 4)Flange joints 5)Valve stem seals 6)Sample points 7)Leakage thro’ vent & drain.
What is the distribution of fugitive emissions in a large petrochemical complex? Studies in various refineries indicate the following approximate distribution of fugitive emissions
%
Valves 60
Relief Valves 15
Tanks 10
Rotary Equipment. 10
Flanges 5
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What is the breakup for fugitive emissions of valves?
ISO-15848-1 is a standard for Measurement, Test & Qualification procedures for Fugitive Emissions for Industrial Valves.
Study differentiates fugitive emissions based on type of valve
% Leaking per type
1) Regulating Control Valve 70
2) Automatic Gate Valve 27
3) Gate Valve 26
4) Globe Valve 20
5) Plug Valve 20
6) Ball Valve 1
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Also note that less than 1% of valves in gas/vapour service account for major fugitive emissions in the refinery.
How fugitive emissions can be reduced?
Integrated Pollution Prevention Approach is necessary. A life cycle cost for environmentally safe design must be evaluated at the beginning of the project.
For Valves:
The fugitive emission can be substantially reduced by proper a) selection of type of valve (Plug or Ball instead of Gate or Globe) b) selection of packing material based on process parameters c) type of packing ( Diagonal interlock braided or flexible Graphite type,) d) packing with bellow seal or with lantern ring e) installation f) maintenance
For Control Valves:
PTFE stem gaskets are sensitive to thermal cycles to 350 deg F. In the case of ordinary graphite gaskets the loading force requirement is high. This increases the stem friction and affects stem movement. These problems can be solved by perfluoroelastomer packing .(Perfluoroelastomers are polymerized from TFE and several other monomers including perfluoromethyl vinyl ether)
For Relief Valves:
It is difficult to reduce the emissions through the relief valves since in most of the cases it is linked with upset process conditions. However following guidelines can be used.
a) Keep adequate margin between operating pressure and set pressure. b) For VOC emissions ,connect to flare header (If possible provide voc recovery system)
For Rotary Equipments
Rotary equipments include Pumps, Compressors, Blowers, Turbines, Agitators, Mixers, Blenders etc.
The fugitive emissions for rotary equipment depend upon
Design - Process Parameters
- Speed
- Seal selection
Installation - Fixing with base plate
- Piping connection forces
- Shaft & Casing alignment
- Coupling alignment
- Balancing of shaft & impeller
Commissioning- Poor priming
Operation - Beyond performance range
- Poor NPSHa
Maintenance - Inadequate
An approximate leakage rate for various sealing options are given below
gm/hr ppm Gland Packing >1 >1000 Single Mech . Seal 0.01 – 1.0 10 – 1000 Double Mech . Seal < 0.01 < 10 Sealless 0 0
For Bolted Flanged Connections:
The factors affecting the leakages are
a) Non parallel flanges
b) Non smooth surfaces
c) Surface waviness
d) Quality of gasket
e) Type of gasket (Non metallic, Semi –metallic, Metallic) f) Form of gasket (Plane Sheet, Rectangular, Spiral wound) g) Type of joint involved ( flat, tongue & groove) h) Process parameters(Pressure , Temperature) i) Fluid handled j) No. of Bolts k) Installation Procedure (placement of gasket, tightening of bolts) l) Maintenance
A study conducted by Pressure Vessel Research Council (PVRC) of USA indicate that most flange joint failures resulting in leak are due to
%
a) Improper installation 26
b) Flange Damage 25
c) Gasket 22
d) Loose Bolts 15
e) Flange Misalignment 12
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What are the statutory regulations/requirements?
The 1990 Clean Air Act Ammendments (CAAA) lists 189 volatile hazardous air pollutants(VHAP) including 150 volatile organic compounds(VOC).If process contains 5%(or more) by weight of one or more VHAP it comes under CAAA legislation.
In April 1997, CAAA incorporated Quality Improvement Program(QIP) with earlier Leak Detection and Repair (LDAR) concept.
If greater than 2% of tested valves are leaking (more than 500 ppm), monthly inspections are required for all the valves or the the facility stays at a quarterly inspection frequency by committing to a QIP programme.
Further leaking valves must be repaired within 5 days, repaired and retested within 15 days or identified for repair during the next shutdown. Inspection timing intervals can be reduced to quarterly if leaking valves are less than 2% , semiannually if leaking valves are less than 1% or annually if less than 0.5% of the total no. of valves.
In a large refinery or petrochemical complex may have more than 100,000 components on various monitoring schedules for compliance with Environmental Regulations. This is a major task for the maintenance team if implemented in right spirit.
What is the path forward ?
“Elimination is better than minimization technique”. This requires “Thinking out of the box ”.
Few examples are given below:
Excess flow valve (spring loaded valve) does not have stem hence there is no fugitive emissions. The automatic recirculation valve is already being used in recirculation line of centrifugal pump. Thus wherever possible this valve can be used instead of control valve.
If the line or equipment is kept under shade , then thermal relief valve for solar exposure can be eliminated.
If the line is above 8m height then external fire case can be eliminated for the liquid trapped between two isolation valves.
If possible design the equipment for higher pressure rating and eliminate the requirement of thermal relief valve.
If possible select a low pressure process so that total emission can be reduced substantially.
Seal less pump (Peristaltic Pump) is better than pump with seal as far as fugitive emission is considered. However we need to improve the efficiency of the pump.
Use of monobloc pump also eliminates seal requirement.
Thus “ inherent environment safe design “ is the key for future survival.