Fugitive Emissions - the bad guys of the pollution world who avoid even the toughest seals

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Fugitive Emissions - the bad guys of the pollution world who avoid even the toughest seals!

For many of us, the idea of a fugitive emission sounds deeply sinister and conjures up images of dangerous, smelly chemicals skulking around behind our backs, meaning to cause us harm. Well, not to anthropomorphasise pollutants, but that is pretty much what these pollutants do. Mr P.J Lakhapate, a Chemical Engineer and consultant who works in the field of fugitive emissions helps us understand what these dangerous pollutants are and how to deal with them.

What are fugitive emissions ?

Most fugitive emission cases are invisible to the eye. The fugitive emissions of toxic/hazardous/corrosive substances are silent killers to human beings, other living species, flora and fauna.

They are defined as emissions of "Any chemical or mixture of chemicals, in any physical form, which represent an unanticipated or spurious leak, from anywhere on an industrial site".

In other words, a fugitive emission could be that little hissing sound you hear as you walk past an old looking valve at the dry cleaners. In reality, that valve is releasing things into the environment that should stay in the machine - for many reasons, not least of which that they are poisonous to you and your environment.

Why are fugitive emissions important?

Fugitive emissions in the 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. This situation is mirrored in Europe, and is probably much worse in other parts of the world where environmental standards and levels of policing are lower.

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 fugitive emissions also represent 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 do the values of fugitive emissions depend?

Many process streams in petrochemical refineries are "light" (containing at least 20% of substances with a vapour pressure greater than 0.3kPa at 20 °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 parts per million (ppm) measured by sniffing, since this is the format of the Environmental Protection Agency (EPA) in the USA. These systems are widely used across the world.

However ppm does not measure leakage rate, but indicates leakage severity. Further research is being done to correlate concentration (in parts per million - ppm) with the leakage rate.

Sources of fugitive emissions?

Atmospheric tanks with/without breather valve
Tank lids
Seals of rotary equipment e.g. Pump Blower, Compressor, Turbine, Agitator
Flange joints
Leakage through vents & drains.
Valve stem seals
Sample points

Studies in various refineries indicate the following approximate distribution of fugitive emissions:

Valves - 60%
Relief Valves - 15%
Tanks - 10%
Rotary Equipment - 10%
Flanges - 5%

ISO-15848-1 is a standard for Measurement, Test & Qualification procedures for Fugitive Emissions for Industrial Valves.

Studies differentiate fugitive emissions based on the type of valve. The likelihood of leaking for the following types of valves are:

Regulating Control Valve 70%
Automatic Gate Valve 27
Gate Valve 26
Globe Valve 20
Plug Valve 20
Ball Valve 1

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

An 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 emissions 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 at high temperature. 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 emissions through the relief valves since in most of the cases these are linked with upsets in process conditions. However the following guidelines can be used.
a) Keep an adequate margin between the operating pressure and set pressure.
b) For VOC emissions connect to a flare header
(If possible provide voc recovery system)

For Rotary Equipment
Rotary equipment 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
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 the Pressure Vessel Research Council (PVRC) in the USA indicated that most flange joint failures resulting in leaks were due to
a) Improper installation - 26%
b) Flange Damage - 25%
c) Gasket - 22%
d) Loose Bolts - 15%
e) Flange Misalignment - 12%

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, the 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.
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 the right spirit.
What is the path forward? Elimination is better than minimization. This requires thinking out of the box.
A few examples are given below:
An excess flow valve (spring loaded valve) does not have a stem hence there are no fugitive emissions. This automatic recirculation valve is already being used in recirculation lines of centrifugal pumps. Thus wherever possible this valve can be used instead of a control valve.
If the line or equipment is kept under shade, then a 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 pumps ( eg a Peristaltic Pump) are better than pumps with seals as far as fugitive emissions are considered. However we need to improve the efficiency of these pump.
Use of a monobloc pump also eliminates seal requirement.

Inherent environmentally safe designs are the key for future survival.

More information:

About Author: Mr P.J. Lakhapate is a Chemical Engr. from UDCT (Mumbai). He has 31 years of industrial experience and currently consults in the field. He has published more than 30 articles. Contact information Phone: 91-22-27702655. Email: plakhapate@rediffmail.com.