[ applications ]
Carbon intensity of hydrogen and substitute products
Under the IRA , the U . S . Department of Treasury adopted a specific version of the GREET model , 45VH2-GREET , to determine GHG reductions for Section 45V . The model is used to calculate the life cycle GHG emissions from hydrogen production under a well-to-gate system boundary . GHG emissions from green hydrogen depend on the displaced incumbent fossil fuel . In the case of refinery hydrogen and process heat , green hydrogen provides a 1:1 displacement of natural gas steam methane reforming ( SMR ) hydrogen on an energy basis . For ammonia , methanol , and on-road transportation fuels , the displacement ratio is pathway-dependent . In fuel cell vehicles , one kilogram of hydrogen displaces approximately double the energy content of petroleum diesel .
Table 1 shows potential applications for green hydrogen and the displaced product . The CI of displaced products varies between 69.1 and 126.9 g / MJ of hydrogen . The hydrogen use rate per unit of product , along with CI , facilitates the calculation of GHG reductions per kilogram of green hydrogen . Considering this calculation , the GHG benefit per kilogram of green hydrogen used for ammonia , methanol , and trucking suggests they are the best sectors to achieve the GHG abatement goals of the IRA .
Displaced emissions from ammonia production are higher due to the complexities of the natural gas- to-ammonia process . Green ammonia , utilized in agriculture , promotes the advancement of lowcarbon fuels and biomaterials , contributing to the reduction of GHG emissions in the agriculture sector as ammonia is a key component of fertilizer manufacturing ( EIA , 2021 ). Nitrogen fertilizers , including urea and ammonium nitrate , constitute roughly 80 % of the total ammonia market , with only 2 % directly applied in pastures ( Saygin , et al ., 2023 ).
Methanol production , currently reliant on natural gas reforming , involves hydrogen as an interim flow . The incorporation of green hydrogen , along with waste CO 2
, introduces a novel low-carbon source for methanol or synthetic fuels through Fischer- Tropsch or methanol-to-olefin technologies . Grey methanol , an energy-intensive product , derives half of its global production from coal , potentially leading to an indirect displacement effect . Methanol ’ s applications are widespread , ranging from chemicals and other industrial applications to transport fuel ( EIA , 2019 ). The efficiency of fuel cell vehicles leads to green hydrogen displacing twice the energy in transportation fuel , resulting in a high GHG displacement rate for this application .
The effect of green hydrogen in industrial applications also depends on the displaced source of hydrogen . In oil refinery applications , for example , hydrogen SMRs often provide waste heat for the refinery , which lowers the overall CI of the grey hydrogen . Hydrogen liquefaction can add 8 kg
CO 2
e / kg of hydrogen ; so , on-site green hydrogen production can displace more GHG-intensive sources
Table 1 . Applications for green hydrogen and GHG displacement of GHG emissions |
Application |
Displaced Product |
Hydrogen Use
( M tonne / y )
|
Use Rate ( kg H 2 / kg
Product )
|
Displaced Carbon Intensity ( CO 2 e ) g / MJ Product a b kg / kg H 2 |
Ammonia |
NG Ammonia |
2.0 |
0.194 |
126.9 |
12.29 |
CO 2 to Methanol |
NG , Coal Methanol |
1.6 |
0.191 |
93.4 to 200 |
9.76 to 20 |
Fuel Cell Truck |
Diesel |
0.5 |
0.5 |
95.0 |
22.80 |
Oil Refinery Hydrogen |
H 2 by NG SMR |
6.8 |
1 |
78.7 |
9.44 |
HEFA |
H 2 by NG SMR |
0.336 |
1 |
80 to 90 |
9.5 to 10.8 |
LH 2 Delivery |
H 2 by NG SMR |
0.04 |
1 |
150 |
18.0 |
Boiler Fuel |
NG Boiler |
2.4 |
1 |
69.1 |
8.29 |
|
a
Life cycle GHG emissions from GREET
|
|
b
Displaced GHG emissions = CI ( g / MJ ) × LHV ( MJ / kg )/ Use Rate × 120 MJ / kg H 2 / 1000
|
= 126.9 g / MJ NH 3 × 18.8 MJ / kg NH 3 ) × 120 / 1000 = 12.29 kg CO 2 e / kg H 2 |
CI values from GREET ( Wang , 2023 ) and GREET 45V calculator ( ANL , 2023 ), and ( Unnasch , 2018 ). |
28 Hydrogen Tech World | Issue 17 | August 2024