DATE: February 12, 2009 

SUBJECT: Methodology for Estimating LNG Storage Emissions Using GTI Data 

 

This memorandum describes the method used to estimate greenhouse gas emissions from 

liquefied natural gas (LNG) storage facilities. These emission estimates are used to 

support the threshold analysis for Subpart W - Oil and Natural Gas Systems. Gas 

Technology Institute (GTI) data serves as the basis for these estimates. 

LNG storage comprises two types of facilities: peakshaving plants and smaller satellite 

storage facilities. The GTI data consists of a list of approximately 60 LNG peakshaving 

storage facilities and their liquefaction capacity, storage capacity, and vaporization design 

capacity1

. Using this data, ICF used methods developed in a previous memorandum (see 

Appendix) to derive energy usage for liquefaction, boil-off liquefaction, and 

vaporization/sendout processes. ICF used assumptions from the Appendix to estimate 

emissions from the approximate 100 satellite facilities. 

Fugitive and onsite combustion greenhouse gas emissions are estimated separately. 

Fugitive greenhouse gas emissions are estimated for each facility by distributing the 

national inventory emissions2

 for all LNG storage to each facility. These emissions 

include fugitive methane and carbon dioxide from all three processes – liquefaction, 

storage, and vaporization/sendout. Onsite carbon dioxide and nitrogen oxide combustion 

emissions are estimated for each process by multiplying the calculated energy usage by 

an emissions factor. The next three sections describe our approach for calculating energy 

usage for each process using the data on liquefaction, storage, and vaporization capacities 

provided by GTI. The final section describes our approach for estimating fugitive and 

onsite combustion emissions. 

Energy Used for Liquefaction

EIA estimates 38,706 million cubic feet (MMcf) of LNG to storage in 20063

. Using the 

assumption outlined in the Appendix, the horsepower required to liquefy this volume and 

add it to storage is estimated using Equation 1 below. 

Equation 1: Liquefaction Energy Usage for LNG Storage 

4,800 50%

1,000,000

1

/

750

200

38,706 = × × × hours ×

Hp

MMHp

MMcf day

Hp

days

MMcf LHP

 

1

 GTI(2007) The World Energy Source Book – Fourth Edition, An Encyclopedia of the World LNG 

Industry, GTI 07/0002 2

 EPA. Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990 – 2006. 

<http://epa.gov/climatechange/emissions/usinventoryreport.html>. 

3

 EIA. Liquefied Natural Gas Additions to and Withdrawals from Storage. 

<http://tonto.eia.doe.gov/dnav/ng/ng_stor_lng_dcu_nus_a.htm>. 
2 

Where, LHP is the total liquefaction energy usage, in million horsepower-hours 

(MMHPhr), for the entire LNG storage sector. This equation assumes the LNG was 

added over a 200-day “fill” season (equal to 4,800 hours), with 750 horsepower (Hp) 

used per million cubic feet per day of liquefaction, where 50% of compressors are driven 

by gas-powered engines or turbines. The result is a total sector usage of approximately 

348 MMHPhr. This total is apportioned to each individual facility based on its portion of 

the industry’s liquefaction capacity (provided by GTI1

) by using Equation 2. 

Equation 2: Apportionment of LNG Storage Liquefaction Energy Usage to 

Individual Peakshaving Plants 

LHP

LC

LC

LHP plant

plant = ×

Where, LHPplant is the liquefaction energy usage for an individual peakshaving plant, 

LCplant is the liquefaction capacity for an individual peakshaving plant (provided by GTI), 

LC is the liquefaction volume for 2006 (provided by EIA), and LHP is calculated in 

Equation 1. None of the approximately 100 satellite LNG storage facilities are assumed 

to have liquefaction capacity. 

Energy Used for Boil-off Liquefaction

Similar to liquefaction, the Appendix provides a method to estimate boil-off liquefaction 

energy usage based on storage capacity. The method assumes that 0.05% of the energy 

required to liquefy added gas to LNG storage is necessary for boil-off liquefaction. This 

method is shown in Equation 3. 

Equation 3: Boil-off Liquefaction Energy Usage 

8760 50%

1,000,000

1

/

750 0.05%

365 = × × × × hours ×Hp

MMHPhr

MMcf day

Hp

days

SC

BOLHP plant

plant

Where, BOLHPplant is the boil-off liquefaction energy usage in MMHPhr at a given 

facility, and SCplant is the LNG storage capacity at a given facility (provided by GTI1, in 

MMcf). This equation assumes that gas engines are used for 50% of boil-off 

compressors. The required energy for boil-off liquefaction at the 100 satellite LNG 

storage facilities is estimated using the assumption that the total storage of these facilities 

is 8.7 billion cubic feet (Bcf), described in the Appendix. 

Energy Used for Vaporization and Sendout

As indicated in the Appendix, an average sendout absolute pressure of 300 pounds per 

square inch (psia) and an inlet pressure of 15 psia requires 1.86 MMHPhr to compress 1 

MMcf/day for sendout using 2-stage compression. EIA estimates that 33,743 MMcf in 
3 

withdrawals were taken from LNG Storage in 20063

. Using this data, Equation 4 is used 

to estimate the total vaporization and sendout energy usage for the LNG storage sector. 

Equation 4: Vaporization and Sendout Energy Usage for LNG Storage 

MMcf day

MMHPhr

days

MMcf SOHP

/

1.86

365

33,743 = ×

Where, SOHP is the total sendout energy usage for the LNG storage sector in 2006 in 

MMHPhr. The result is 172 MMHPhr was used for sendout of the 33,743 MMcf 

withdrawn from LNG storage facilities in 2006. The total sendout energy usage was 

apportioned amongst individual facilities based on their designed vaporization capacity, 

provided by GTI, using Equation 5. 

Equation 5: Apportionment of LNG Storage Sendout Energy Usage to Individual 

Peakshaving Plants 

SOHP

VC

VC

SOHP plant

plant = ×

Where, SOHPplant is the sendout energy usage of an individual facility, VCplant is the 

vaporization capacity of the individual facility (provided by GTI), VC is the total 

vaporization capacity of the LNG storage sector, and SOHP is calculated in Equation 4. 

This analysis uses the approach provided in the Appendix to determine the amount 

apportioned to satellite facilities. The required energy for vaporization and sendout at the 

100 satellite LNG storage facilities is estimated using the assumption that the total 

storage of these facilities is 8.7 billion cubic feet (Bcf), described in the Appendix. 

Calculating Facility Greenhouse Gas Emissions

Fugitive and combustion greenhouse gas emissions were calculated using two 

methodologies. Each of these is described separately below. 

Fugitive Emissions

Fugitive methane and carbon dioxide emissions were apportioned to each facility using 

the total LNG storage sector emissions as provided in the EPA Inventory of U.S. 

Greenhouse Gas Emissions and Sinks 1990 – 20062

. The total fugitive emissions were 

distributed to each facility based on its portion of total storage capacity for all facilities 

(provided by GTI1). 

Combustion Emissions

Combustion carbon dioxide and nitrogen oxide emissions were calculated for each 

facility using combustion emissions factors for each greenhouse gas. Engine 
4 

horsepower-hours were used to drive these emissions. The emission factor for carbon 

dioxide is 719 tonnes/MMHPhr and for nitrogen oxide is 0.0187 tonnes/MMHPhr. 

REFERENCES

EIA. Liquefied Natural Gas Additions to and Withdrawals from Storage. 

<http://tonto.eia.doe.gov/dnav/ng/ng_stor_lng_dcu_nus_a.htm>. 

EPA. Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990 – 2006. 

<http://epa.gov/climatechange/emissions/usinventoryreport.html>. 

GTI(2007) The World Energy Source Book – Fourth Edition, An Encyclopedia of the 

World LNG Industry, GTI 07/0002.
5 

APPENDIX: Memorandum entitled Additional Changes to 

Activity Factors for Portions of the Gas Industry