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 -                                                          100 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 ---                                           100

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                                    ---                                      100

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.