Fugitive Emissions

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Fugitive Emissions

Gestión Ambiental Tema 5
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Fugitive Emissions

• An average sized manufacturing plant have
  3000-30.000 components (pumps, valves,
  compressor, seals pipe flanges) that can leak
• Even well maintained equipment there is some
  unintentional releases (Fugitive emissions)
• These emissions may be
• Continual leakage of small amounts of process
  fluids due to faulty process equipment
• Sudden, major leaks due to equipment failure

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Standards normally define

• Chemical streams that must be monitored
• Types of components (pumps, valves,
  connections,) to be monitored
• Measured concentrations that indicates a leak
• Frequency of monitoring
• Actions to be taken is a leak is discovered
• Length of time in which an initial attempt and an
  effective repair of the leak must be made.
• Actions that must be taken if a leak cannot be
  repaired within guidelines.

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Sources and amounts

• Fugitive emissions can originate
• At any place where equipment leaks may occur.
• Pipe connections
• Evaporation of hazardous compounds from
  open-topped tanks or reservoirs
• Dust from activities as construction, demolition,
  traffic, waste collection, agriculture
• The cumulative impact from the thousands of
  components with small emissions can be
  staggering.

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Typical distribution of fugitive emissions in
process plants
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Measuring fugitive emissions

• Use of direct measurement equipment
• Time consuming
• Methods for estimating the fugitive emissions
• Average emission factor approach
• Screening ranges approach
• EPA correlation approach
• Unit-specific correlation approach

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Average emission factor approach

• Based on knowledge on the number and type of each
  component, the service of each component is in,
  the total organic concentration of the stream,
  and the time period each component was in
  service.
• ETOC FA WFTOC
• ETOC TOC emission rate from a component (kg/h)
• FA Average emission factor for the component
  (kg/h)
• WFTOC Average mass fraction of TOC in the
  stream serviced by the component
• The calculation should be used only to determine
  whether the aggregate of units is emitting more
  VOCs than allowable
• It does not account for specific differences at
  an individual facility

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Emission factors
SOCMI Industria química orgánica
SOCMI, Synthetic Organic Chemical Manufacturing
Industries
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Screening ranges approach

• It is more exact than the average emission
  approach because it relies on screening data from
  the facility, rather than on industrywide average
  values.
• It is assumed that components with screening
  values greater or lesser than 10.000 ppmv have a
  different average emission rate.
• The application of this method is similar to the
  previous one, except that the number of
  components leaking less and more than 10.000 ppmv
  are calculated separately.

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Screening ranges approach

• ETOC (FG NG) (FL NL)
• ETOC TOC emission rate for an equipment type
  (kg/h)
• NG Units with screening values gt10.000 ppm
• NL Units with screening values lt10.000 ppm
• FG emission factor for sources with screening
  values gt10.000 ppm, kg/h source
• Fl emission factor for sources with screening
  values lt10.000 ppm, kg/h source

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Screening ranges approach factors
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EPA correlation approach

• Predict mass emission rates as a function of
  screening values for a particular equipment
  value. Correlations relating screening values to
  mass emissions rates for SOCMI process units and
  for petroleum units are listed.
• The default-zero leak rate is the mass emission
  rate associated with a screening value of zero.
  This provides an emission rate for components
  where the screening rate was below the detection
  limit of the organic vapour analyser.

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EPA correlation approach
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Unit-specific correlation approach

• More exact and expensive method
• It requires the collection of screening values
  and corresponding mass emissions data for a
  statistically significant number of each piece of
  process unit equipment.
• It is necessary to obtain data for different
  screening ranges. 1-100, 101-1,000, 1,001-10,000,
  10,001-100,000, gt100,000 ppmv

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Controlling fugitive emissions

• Two primary techniques are used for reducing
  fugitive emissions from equipment
• Modifying or replacing existing equipment
• Implementing a leak detection and repair program.

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Equipment modification

• Installing additional equipment that eliminates
  or reduce emissions
• Replacing existing equipment with sealless types
• Most fugitive emissions come from leaking valves,
  due to deterioration of the packing material. To
  control these emission must be considered
• - Component monitoring
• - Stem sealing
• - Mechanical conditions
• Use of sealless diaphragm valves

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Valves
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Valves
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Other equipment

• Pumps and compressors
• Routing leaking vapours to a closed vent system
• Dual mechanical seal between which a barrier
  fluid is circulating at a pressure higher than
  the pumped fluid
• Sealless pumps (diaphragm pumps, magnetic drive
  pumps,)
• Pressure relief valves
• These emissions are not considered fugitive
  emissions
• Used of closed vent systems and a flare or by use
  of rupture disk-pressure relief valve combination
• Flanges and other types of pipe connectors
• The emissions rate per connector is usually low

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Equipment modifications to reduce fugitive
emissions
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Fugitive emissions from storage tanks

• Important source of fugitive emissions
• There are 6 basic tanks design
• Fixed-roof tanks
• External floating roof tanks
• Internal floating roof tanks
• Domed external floating roof tanks
• Variable vapour space tanks
• Pressure tanks

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Fixed-roof tanks

• Vertical or horizontal
• Constructed above or below ground
• Steel or fibreglass
• Freely vented to the atmosphere or equipped with
  a pressure/vacuum vent
• Fugitive emissions are caused by changes in
  pressure, temperature and liquid level.
• They are the least expensive , but are generally
  considered the minimum acceptable equipment for
  storing liquids because of their potential to
  release fugitive emissions.

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External floating roof tanks

• Open-topped cylindrical steel shell equipped with
  a plate roof that floats on the surface of the
  liquid.
• The roof rises and falls with the liquid level in
  the tank. The floating roof is equipped with a
  rim seal system, which contacts the tank wall and
  reduces evaporative losses of the stored liquid.
• Fugitive emissions should be limited to
• Imperfect rim seal system
• Fittings in the floating deck
• Exposed liquid on the wall when liquid is
  withdrawn and the roof lowers.

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Internal floating roof tanks

• Has a permanent fixed roof and a floating roof
  inside
• Evaporative losses are minimized by installing a
  floating roof inside.
• The space between the fixed and the floating roof
  is generally freely vented, so any vapours that
  moves into the space will be vented to the
  atmosphere.

Domed external floating roof tanks

• Similar to the previous one
• Is usually the result of retroffiting an existing
  floating roof with a fixed roof to block the wind
  and minimize evaporative losses.

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Variable vapour space tanks

• Equipped with expandable vapour reservoirs to
  attributable to temperature and pressure changes.
• Use a flexible diaphragm membrane to provide
  expendable volume.
• May be either separate gasholder units or
  integral units mounted on a fixed roof tank
• Losses are limited to tank filling times when
  vapour is displaced by liquid and the tanks
  vapour storage capacity is excedeed.

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Pressure tanks

• Used for storing organic gases and liquids with
  high vapour pressure
• Equipped with a pressure/vacuum vent that is set
  to prevent venting loss from boiling and
  breathing loss from temperature and barometric
  pressure changes.
• Losses from these tanks should be minimal,
  provided that the vent is well maintained and the
  tanks are not overpressurized.

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Tanks
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Tanks
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Emissions estimations

• Looses from fixed-root tanks can occur
• Continually while the liquid is standing in the
  tank
• Working losses when liquid is being added or
  withdrawn from the storage tank
• Assuming that the tanks are substantially liquid
  and vapour tight and operate at atmospheric
  pressure
• LT LS LW
• LT total losses
• LS standing storage losses
• LW working losses

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Standing storage losses

• Ls 365 VVWVKEKS
• VV vapour space volume, ft3
• WV vapour density, lb/ft3
• KE vapour space expansion factor, dimensionless
  
• KS vented space saturation factor,
  dimensionless
• KE DTV/TLA (DPV DPB)/(PA PVA)
• DTV daily temperature range, ºR
• TLA daily average liquid surface temperature,
  ºR
• DPV daily pressure range, psi
• DPB breather vent pressure setting range, psi
• PA atmospheric pressure, psi
• PVA vapour pressure at daily average liquid
  surface temperature, psi
• KS 1/ (1 0,053 PVA HVO)
• HVO vapour space outage, ft

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Working losses

• LW 0.0010 MV PVA Q KN KP
• Mw Vapour molecular weight, lb/ft3
• Q annual net throughput (tank capacity (bbl)
  times annual turnover rate), bbl/yr
• KN Turnover factor, dimensionless
• For turnover gt 36/year, KN (180 N)/6N
• For turnover lt 36/year, KN 1
• KP working loss product factor, dimensionless
• For crude oils 0,75
• For all other liquids 1,0

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Emissions control

• Emissions from organic liquids in storage occurs
  by
• Evaporative losses during liquid storage
• Changes in the liquid level during filling and
  emptying operations
• Emissions from fixed-roof tanks can be controlled
  by
• Installing an internal floating roof and seals
  (60-99 efficiency)
• Vapour exchange (90-98 efficiency)
• Vapour recovery systems to convert them to a
  liquid product (96-99)

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Fugitive emissions from waste treatment and
disposal

• Many units require vigorous mixing and turbulence
• Other units contain more quiescent liquid but
  require large expanses of surface area exposed to
  the air.
• Land application of wastewater is another
  significant source of fugitive emissions.
• Options
• Cover the equipments
• Minimizing turbulence at points where is not
  needed