Criteria Air Pollutants and Greenhouse Gas Emissions from Hydrogen Production in U.S. Steam Methane Reforming Facilities

Abstract

The global and U.S. domestic effort to develop a clean energy economy and curb environmental pollution incentivizes the use of hydrogen as a transportation fuel, owing to its zero tailpipe pollutant emissions and high fuel efficiency in fuel cell electric vehicles (FCEVs). However, the hydrogen production process is not emissions free. Conventional hydrogen production via steam methane reforming (SMR) is energy intensive, coproduces carbon dioxide, and emits air pollutants. Thus, it is necessary to quantify the environmental impacts of SMR hydrogen production alongside the use-phase of FCEVs. This study fills the information gap, analyzing the greenhouse gas (GHG) and criteria air pollutant (CAP) emissions associated with hydrogen production in U.S. SMR facilities by compiling and matching the facility-reported GHG and CAP emissions data with facilities’ hydrogen production data. The actual amounts of hydrogen produced at U.S. SMR facilities are often confidential. Thus, we have developed four approaches to estimate the hydrogen production amounts. The resultant GHG and CAP emissions per MJ of hydrogen produced in individual facilities were aggregated to develop emission values for both a national median and a California state median. This study also investigates the breakdown of facility emissions into combustion emissions and noncombustion emissions.

How green is blue hydrogen?

“…Many non peer-reviewed reports give estimates for carbon dioxide emission from gray hydrogen that are in the range of 10 tons carbon dioxide per ton of hydrogen, 1,7 although data in support of these values are generally absent, perhaps because they are based on confidential information. 11 Since the gross calorific heat energy content of hydrogen is 0.286 MJ per mole, 17 10 tons of carbon dioxide per ton of hydrogen corresponds to 70 g CO 2 per MJ. This is similar to but somewhat lower than our value of 75.6 g CO 2 per MJ.…”

“…Most of these non peer-reviewed reports do not include methane in their estimates, 1 or if they do, they provide no detail as to how they do so. The most thorough peer-reviewed analysis of carbon dioxide emissions for gray hydrogen is that of Sun et al 11 who obtained data on both rates of hydrogen production and emissions of carbon dioxide from many individual facilities across the United States. They concluded that on average, carbon dioxide emissions for gray hydrogen are 77.8 g CO 2 per MJ, remarkably close to our value of 75.6 g CO 2 per MJ.…”

“…Still, the supply of green hydrogen in the future seems limited for at least the next several decades. 2,5 Greenhouse gas emissions from gray hydrogen are high, 10,11 and so increasingly the natural gas industry and others are promoting "blue hydrogen". 5,8,9 Blue hydrogen is a relatively new concept and can refer to hydrogen made either through SMR of natural gas or coal gasification, but with carbon dioxide capture and storage.…”

Using waste CO2 from corn ethanol biorefineries for additional ethanol production: life‐cycle analysis

“…When compression is needed for H 2 storage, it does undercut the benefits of importing H 2 in terms of both cost and GHG emissions. The CIs (g CO 2 e/MJ H 2 ) of potential H 2 sources, including both production and transmission to corn ethanol plants, are calculated using the GREET model 20,35‐39 and presented in Fig. 4.…”

Feasibility analysis of a hybrid auxiliary power unit for pleasure boats

“…Emissions The annual diesel genset CO2 emissions are calculated from the diesel consumption with an emission factor equal to 3.2 kg of CO2 per kg of diesel [18]. The FCS CO2 emissions, due to the fuel processing system, are estimated with an emission factor of 0.56 kg of CO2 per kWh of produced electricity [19]. Finally, the genset NOx emissions are estimated by considering a NOx emission factor of 2 g per each kWh of produced electricity [20], while FCS NOx emissions can be assumed as negligible.…”