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Understanding the Revised Subpart W Regulation
Greg Gasperecz, VP, EHS
Enviance, Inc.
2
Overview
Subpart W Revisions - Federal Register 12/23/11
• Definitions
• Calculation methods and Errors
Important: Significant Error in Eq. W-36 !!
• Reporting
• Calculation Tips and Techniques
• Emission Factor Tables Quick Look
3
Definitions Subpart A
Subpart W Definition of Source Category
• Clarified that “Owner” and “Operator” used in Subpart A have the
same definition as defined at 98.238 (Subpart W)
• Continuous and Intermittent Bleed Pneumatic Devices – meaning
clarified (Subpart A)
• Onshore Petroleum and Natural Gas Production (Subpart W 98.230)
Includes dehydrators and vessels on well pads or associated with a
single well pad
EOR operations that use CO2 are included
• Onshore Natural Gas Processing (Subpart W 98.230)
Recovery of separated gases not required to be part of this segment
Identifies the included processes in generic terms
25 MM scf/day threshold applies to plants that do not fractionate
4
Definitions Subpart W Definition of the Source Category
• Onshore Natural Gas Transmission Compression (Subpart W 98.230)
Defined “transmission pipeline” at 98.238 to consistent with intent at 98.230
Clarified what Transmission Compression includes
Removed term “natural gas dehydration”
• Natural Gas Distribution (Subpart W 98.230)
Replaced “city gate station” with “metering-regulating station”
Defined “metering-regulating station” at 98.238 to consistent with intent at 98.230
Defined “distribution pipeline” at 98.238 to consistent with intent at 98.230
Local Distribution Company description was made consistent with Subpart NN
5
Definitions Subpart W – Specific Terms at 98.238
• “Associated with single well pad” – newly added; for consistency
with source category definition
• “Facility…Onshore Petroleum and Natural Gas Production” –
revised to reflect single well pad approach, and clarifying
• “Facility…Natural Gas Distribution” – revised to clarify all distribution
pipelines operated by an LDC in a single state are included
• “Farm taps” – revised to eliminate reference to city gate
• “Flare” – newly added; ground level or elevated; energy recovery
not required
• “Forced extraction of natural gas liquids” – newly added; describes
removal of C2+ hydrocarbons; excludes dehydration and other
water removal activities
6
Definitions Subpart W – Specific Terms at 98.238
• “Gas well” – removed; now addressed in “sub-basin category”
definition
• “Natural gas” – newly added; includes field quality, pipeline quality
or process gas
• “Oil well” – removed; now addressed in “sub-basin category”
definition
• “Pressure groups” – newly added; used in revised calculations for
Well Venting for Liquids Unloading
• “Tubing diameter groups” – newly added; used in revised
calculations for Well Venting for Liquids Unloading
• “Sub-basin category” – Newly added; main concept in the change
from measurements at field level to sub-basin level. Note the county
overlay in this definition.
7
Definitions Subpart W – Specific Terms at 98.238
• “Transmission-distribution (T-D) transfer station” - newly added;
defines what was previously termed custody transfer
• “Transmission pipeline” – revised; clarified to be consistent with
FERC or state rate-regulated pipelines or those covered by the
Hinshaw Exemption of 1994 Natural Gas Act
• “Horizontal well” – newly added; used in calculations for well
completions and workovers
• “Vertical well” – newly added; used in calculations for well
completions and workovers
• “Well testing venting and flaring” – newly added; defined as
occurring at the time production rate is determined; if production
rate determined upon completion, then that activity would be part of
completions and workovers.
8
Calculation Methods Revisions
• 58 separate changes to calculation definitions or the terms used in the calculations
• Most are clarifications and technical improvements
• Standard Temperature = 60o F
• Emission factors changes often due to shift to STP change
Table 1A – onshore production; most new factors are lower; Pneumatic devices now different for Eastern vs. Western; Western US appears to be changed due to STP shift; Eastern changes due to new information?
Table 2 – natural gas processing; All changes due to STP
Table 3 – transmission compression; All changes due to STP
Table 4 – underground storage; All changes due to STP
Tables 5 & 6 – LNG storage and import/export; All changes due to STP
Table 7 – natural gas distribution; All changes due to STP
9
Calculation Methods Revisions Significant Actions
• Pneumatic devices and pneumatic pumps
Eq. W-1 and W-2 now use Tt (Average estimated number of operational
hours); Default is 8760 hours.
Eq. W-1 and W-2 use correct factors to convert scf to CO2e
• CH4: 0.000403 metric tons CO2e per scf CH4 at 60F
• CO2: 0.00005262 metric tons CO2e per scf CO2 at 60F
• Acid gas removal - Eq. W-4A and W-4B added in place of W-4 to
clarify inlet vs. outlet measurement approaches
10
Calculation Methods Revisions Significant Actions
• Well venting for liquids unloading - now uses the tubing diameter
and pressure group combination approach in Eq. W-7
• Gas well venting completions/workovers with hydraulic fracturing
Sub-basin category aggregation for measurements
Eq. W-10A and W-10B added in place of W-10 to reflect whether
backflow is metered
11
Calculation Methods Revisions Significant Actions
• Gas well venting completions/workovers with hydraulic fracturing
Renamed equations and added Eq. W-11C to determine is flow is sonic
Eq. W-12 now defines FRM – the ratio of backflow rate to average
production rate
12
Calculation Methods Revisions Significant Actions
• Blowdown vent stacks
Applicable only to manually activated operations
Uses “unique physical volume” concept
Eq. W-14A used when Ta and Pa are same for all blowdowns
Eq. W-14B used when Ta and Pa vary for each event
• Onshore production storage tanks-
10 bpd threshold is based on annual average daily throughput
Eq. W-15 modified corrected to add factor of 1,000
Note: e-CFR does not display the factor of 1,000 in W-15
Eq. W-16 revised to reflect yearly emissions rather than hourly
13
Calculation Methods Revisions Significant Actions
• Well testing venting and flaring
Replaced Eq. W-17 with W-17A (for oil well) and W-17B (for gas well)
• Flare stack emissions - 98.233(n)
Onshore natural gas processing plants that solely fractionate a liquid
stream use GHG mole percent in feed natural gas liquid for all streams
Tier 4 (CEMS)method allowed if CEMS is present
14
Calculation Methods Revisions Significant Actions
• Leak detection and leaker emission factors - 98.233(q)
Eq. W-30 A and W-30B added in place of W-30
• Use W-30A for natural gas processing, transmission compression, underground storage, and LNG storage and import/export
• Use W-30B for natural gas distribution
For underground storage and transmission compression GHGi use 0.975 for CH4 and 0.011 for CO2
For LNG storage and import/export GHGi use 1.0 for CH4 and 0 for CO2
For natural gas distribution GHGi use 1.0 for CH4 and 0.011 for CO2. CO2 value is likely a mistake, since total should not exceed 1.0
For natural gas distribution, monitoring for leaks can be done over a multiple year period, not to exceed 5 years.
Eq. W-30B is a multiple year, rolling sum (even if all monitoring done in first year)
15
Calculation Methods Revisions Significant Actions
• Population count and emission factors - 98.233(r)
“meter/ regulator runs” at above grade “metering-regulating stations”
term used in place of “non-custody transfer city-gate”
Eq. W-31 - underground storage and transmission compression GHGi
use 0.975 for CH4 and 0.011 for CO2
Eq. W-31 - LNG storage and import/export GHGi use 1.0 for CH4 and 0
for CO2
Eq. W-31 - natural gas distribution GHGi use 1.0 for CH4 and 0.011 for
CO2. Mistake?
Eq. W-32 now yields an emission factor with unit of measure of scf per
meter-regulator run per hour
Potential mistake in the combined use of W-30B and W-32 to produce
the emission factor in W-31 (double use of GHGi).
16
Calculation Methods Revisions Significant Actions
• Volumetric emissions - 98.233(t)
Set standard temperature as 60 F
Retained standard pressure as 14.7 psia
• GHG volumetric emissions - 98.233(u)
Mole fraction (Mi) should be an annual average value when measuring
Default mole fraction set at 0.95 for CH4. Note inconsistency with GHGi
values at 98.233(q)
Segment 98.233(u) 98.233(q)
TC 0.95 0.975
Und. Storage 0.95 0.975
LNGs 0.95 1.0
Distribution 0.95 1.0
17
Calculation Methods Revisions Significant Actions
• GHG mass emissions - 98.233(v)
ρ i= Density of GHGi. Use 0.0526 kg/ft3 for CO2and N2O, and 0.0422
kg/ft3 for CH4at 60 F and 14.7 psia
DENSITY OF CH4 IS INCORRECT – CORRECT VALUE = 0.01919
kg/ft3
Caution: Eq. W-36 is applied to results from numerous other
calculations
Mr. Gasperecz,
Thank you for pointing out the conversion error in the CH4 density value defined in
Equation W-36 in 40 CFR part 98 subpart W. EPA is considering ways to address
this issue. If the EPA decides to issue guidance on this topic, it will be posted here:
http://www.epa.gov/climatechange/emissions/subpart/w.html
EPA Response to notice that Eq. W-36 value for CH4 density is incorrect
Notice and response dated January 13, 2012
18
Calculation Methods Revisions Significant Actions
• Onshore production and distribution combustion – 98.233(z)
External fuel combustion sources with a rated heat capacity equal to or
less than 5 mmBtu/hr are exempt
Internal fuel combustion that are not compressor drivers and with a
rated heat capacity equal to or less than 1 mmBtu/hr are exempt
Clarifies when to use Subpart C methods:
• Fuel is listed in Table C-1 or blend thereof
• Fuel is pipeline quality natural gas with minimum HHV of 950 Btu/scf
• Can use any tier of Subpart C
• Reporting as required in Subpart W - 98.236(c)(19)
Clarifies when to use Subpart W methods:
• Field gas, process vent gas or blend thereof, or not pipeline quality
• Use calculation method at 98.233(z)(2) – carbon content approach
• Reporting as required in Subpart W - 98.236(c)(19)
19
Reporting Significant Actions
• Reporting rollup required by equipment /component type is common
• Population emission factor reporting had a significant rollup change
Original rule required rollup by equipment type
Revision requires rollup by component type (valve, connector, etc.)
• For gas sent to a flare, report amount to unlit flare, and to lit flare.
Report emissions under the equipment source type, not at the flare.
• Unique name or ID required for:
Blowdown vents for all segments (unique blowdown volume)
Acid gas recovery units in onshore processing segment
Dehydrators in onshore processing segment
Flares in onshore processing segment
Storage vessels in transmission compression segment
20
Reporting Significant Actions
• Well venting for liquids unloading – for each tubing diameter group
and pressure group combination in each sub-basin category, report
Count of wells vented to the atmosphere for liquids unloading
Count of plunger lifts
Whether the selected well from the tubing diameter and pressure group
combination had a plunger lift
Cumulative number of unloadings vented to the atmosphere
Average flow rate of the measured well venting in cubic feet per hour
Internal casing (or tubing) diameter, and well depth of each well in that
tubing size and pressure combination
Casing pressure in that tubing size group and pressure group
combination that does not have a plunger lift.
Tubing pressure in a tubing size group and pressure group combination
that has a plunger lift.
Annual CO2 and CH4 emissions, expressed in metric tons Coe for each
gas
21
Reporting Significant Actions
• Reporting by sub-basin category also applied to
Workovers and completions
Storage tanks for onshore production
Enhanced oil recovery
• For each oil sub-basin category, also report best estimate of
API gravity
Gas to oil ratio
Average low pressure separator pressure
22
Calculation Tips and Techniques Use Templates to Leverage Your Work
• Templates are sets of calculations that are applicable across
facilities and (in most cases) segments
• Correspond to 40 CFR 98.233 (a) through (z)
• Advantages – Consistency, Transparency, Minimize time and data
Consistency
Quality assurance
Transparency
Speed of delivery
Reduce data entry
23
Calculation Tips and Techniques Monthly/Quarterly Estimates from Annual Results
• Why?
Corporate sustainability updates
California Cap & Trade planning and trading
• Typical Processing, TC, and Distribution source types that collect
data once per year
Pneumatic devices
Equipment leaks
Dehydrators, AGRs, Transmission Storage Tanks
Estimating monthly emissions from annual results
24
Calculation Tips and Techniques Example Template for Single Calculation (Es,i CH4)
25
Calculation Tips and Techniques Example Template for Transmission Compression
Tables and Tidbits
27
Emission Factor Comparison
Table 1A
Eastern US December 23, 2011 November 30, 2010
28
Emission Factor Comparison
Table 1A
Western US
December 23, 2011 November 30, 2010
29
Emission Factor Comparison
Table 2
December 23, 2011 November 30, 2010
30
Emission Factor Comparison
Table 3
December 23, 2011 November 30, 2010
31
Emission Factor Comparison
Table 4
December 23, 2011 November 30, 2010
32
Emission Factor Comparison
Tables 5 & 6
December 23, 2011 November 30, 2010
33
Emission Factor Comparison
Table 7
December 23, 2011 November 30, 2010
34
Equation W-15
Incorrect in e-CFR
As of 2/7/2012
Federal Register 12/23/2011 E-CFR 2/7/2012
35
Detailed Guide to Subpart W Revisions
36
Exclusive Offer - Subpart W Revisions Guide
• Lists each revision and EPA’s
explanation by subject matter and
citation, including reporting
revisions
• Combines revisions to calculations,
monitoring, and reporting into
grouped sections
• Organized by equipment and
activities that are subject to rule
Contact John at 760-496-0200 x215
to receive your copy