DATE: February 12, 2009

SUBJECT: Methodology for Estimating L NG 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 cap acity, storage capacity, and vaporization design capacity 1 . 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 a ssumptions 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 emissions 2 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 lique faction, 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 2006 3 . Using the assumption outlined in the Appendix, the horse power required to liquefy this volume and add it to storage is estimat ed using Equation 1 below.

Equation 1: Liquefaction Energy Usage for LNG Storage

% 50 800

, 4 000

, 000

, 1 1

/ 750

200 706

, 38

× × × × = hours Hp MMHp
day MMcf Hp
days MMcf LHP

1 GTI(2007) The World Energy Source Book – Fourth Ed ition, 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 sect or. 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 GTI 1 ) by using Equation 2.

Equation 2: Apportionment of LNG Storage Liquefaction Energy Usage to Individual Peakshaving Plants

LHP LC LC LHP plant
plant × =

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

LC plant is the liquefaction capacity for an indivi dual peakshaving plan t (provided by GTI), LC is the liquefaction volume for 2006 (p rovided by EIA), and LHP is calculated in Equation 1. None of the approximately 100 sa tellite LNG storage facilities are assumed to have liquefaction capacity.

Energy Used for Boil-off Liquefaction

Similar to liquefaction, the Appendix provide s 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

% 50 8760 000

, 000

, 1 1

/ 750 % 05

. 0 365 × × × × × = hours Hp MMHPhr

day MMcf Hp
days SC BOLHP plant
plant

Where, BOLHP plant is the boil-off liquefaction en ergy usage in MMHPhr at a given facility, and SC plant is the LNG storage capacity at a given facility (provided by GTI 1 , 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 assump tion 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 compre ssion. EIA estimates that 33,743 MMcf in3 withdrawals were taken fr om LNG Storage in 2006 3 . 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

day MMcf MMHPhr

days MMcf SOHP / 86

. 1

365 743

, 33

× =

Where, SOHP is the total sendout energy us age 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 St orage Sendout Energy Usage to Individual Peakshaving Plants

SOHP VC VC SOHP plant
plant × =

Where, SOHP plant is the sendout energy usage of an individual facility, VC plant is the vaporization capacity of the individual faci lity (provided by GTI), VC is the total vaporization capacity of the LNG storage sect or, 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 requi red energy for vaporization and sendout at the 100 satellite LNG storage facili ties is estimated using th e 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 em issions 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 – 2006 2 . The total fugitive emissions were distributed to each facility base d on its portion of total storage capacity for all facilities (provided by GTI 1 ).

Combustion Emissions

Combustion carbon dioxide and nitrogen oxide emissions were calculated for each facility using combustion emissions fact ors for each greenhouse gas. Engine4 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 Ga s Emissions and Sinks 1990 – 2006. <http://epa.gov/climatechange/emi ssions/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 Portio ns of the Gas Industry