Energy 2: Natural Gas

This session will present latest research on life cycle GHG emissions and other life cycle metrics of natural gas for different uses including power generation, liquefied natural gas and methanol liquid transportation fuel.

LOCATION: 2309
13:30 Matthew Pellow and Sally Benson

Life-cycle CO2 emissions of synthetic methanol production by direct electrocatalytic reduction: Impact of catalyst performance
SPEAKER: Matthew Pellow

ABSTRACT. Direct electrocatalytic reduction of carbon dioxide (eCO2RR) is one of several technologies being developed as a low-emissions route to energy-dense liquid transportation fuels for a carbon-constrained future.[1,2] This technology would avoid net emissions from fuel combustion, because capturing the CO2 used to produce the fuel would fully offset the emissions from combusting it. Although extensive basic-science catalysis research is underway in this area [3,4,5], the full life-cycle emissions of this technology platform have not been quantified.

This work uses a hybrid LCA approach to estimate the relative importance of catalyst material and catalyst performance in determining the overall life cycle emissions of methanol produced using a eCO2RR process. The CO2 reduction electrocatalyst (typically a transition metal or alloy) and the carbonaceous support are incorporated using process-based LCA. For the balance of the CO2 reduction cell system, a water electrolyzer is used as a surrogate technology, and incorporated using input-output LCA.

The reference case eCO2RR system contains a nanoparticulate copper catalyst (100 nm particle diameter) that reduces CO2 to methanol with 25% current efficiency and a current density of 0.5 A cm-2. In a preliminary analysis, the total system CO2 emissions are 1.24 g CO2 / g methanol, and 99% of these emissions are from generating the electricity used to drive the electrocatalytic reduction. The CO2 capture process, the product purification process, and the embodied emissions in the process equipment each contribute 1% or less to the CO2 intensity of the methanol product. The CO2 intensity is therefore influenced by those technical parameters relevant to the generation and use of the electric power: the CO2 intensity of the electricity; the thermodynamic efficiency of the catalyst; and the catalyst’s selectivity for the desired product.

This analysis framework quantifies (1) the emissions impact of using eCO2RR to provide drop-in liquid hydrocarbon fuels, and (2) the emissions impact of specific scientific/technology advances when incorporated into a eCO2RR fuel synthesis process. This approach provides a long-term emissions impact perspective to guide priorities in catalysis research for sustainability.

AUTHOR NOTE: I will only be able to present this work on Oct. 7 or Oct. 8, as I will not be at the conference on Oct. 6. (I would prefer Oct. 8 if possible.) In addition, I am the organizer of a proposed special session on net energy analysis (submission 63) and would need to avoid a conflict if this session is approved for the conference. Thank you – MP

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References

1. Prospects of CO2 Utilization via Direct Heterogeneous Electrochemical Reduction. Whipple, D. and Kenis, P. J. Phys. Chem. Lett. 2010, 1, 3451-3458.

2. Recycling of carbon dioxide to methanol and derived products – closing the loop. Goeppert, A.; Czaun, M.; Jones, J.P.; Prakash, G. K. S.; Olah, G. Chem. Soc. Rev., 2014,43, 7995-8048.

3. Status and perspectives of CO2 conversion into fuels and chemicals by catalytic, photocatalytic and electrocatalytic processes. Evgenii V. Kondratenko, E.; Mul, G.; Baltrusaitis, J.; Larrazabal, G.; Perez-Ramırez, J. Energy Environ. Sci., 2013, 6, 3112-3135.

4. Catalysis of the electrochemical reduction of carbon dioxide. Costentin, C.; Robert, M.; Saveant, J.-M. Chem. Soc. Rev., 2013, 42, 2423-2436.

5. Conversion of carbon dioxide into methanol – a potential liquid fuel: Fundamental challenges and opportunities (a review). Ganesh, I. Renewable and Sustainable Energy Reviews, 31, 2014, 221–257.

13:45 Carla TagliaferriRoland CliftPaola Lettieri and Chris Chapman

Liquefied natural gas for the UK: a life cycle assessment

ABSTRACT. The Liquefied Natural gas (LNG) will be an increasing energy supply for the UK while the national reserves of the continental shelf are diminishing. In the context of an increased global push towards renewable and low carbon energy technology, the LNG rises controversy about the carbon footprint of the entire life cycle. Hence, this comprehensive study analysed the carbon footprint and also all other environmental impacts of the LNG supply to the UK within the new project Qatargas II. New tanker ships and facilities were assumed to be used in the analysis and the entire life cycle of the LNG supply chain, from the gas extraction to the distribution to the consumer, has been included in the assessment. The main findings of this study show how the operations specifically associated with LNG production, that includes natural gas liquefaction, transport and vaporization, significantly influence the environmental impact of the total supply chain and hence they cannot be considered negligible in a complete environmental assessment. The sensitivity analysis has analysed the influence of some key parameters, such as energy requirements of the liquefaction and vaporisation processes, fuel for propulsion, days of navigation (that is shipping distance), tanker volume and composition of raw gas. The case study here reported highlights how i) long distance for LNG transport and ii) natural gas processing including sweetening, liquefaction and vaporisation, are the key aspects that can alter the total environmental burdens.

14:00 Kourosh Vafi and Adam Brandt

GHGfrack: An open-source LCA model to estimate greenhouse gas emissions from hydraulic fracturing

ABSTRACT. Production of petroleum and natural gas from low permeability rocks is expanding quickly due to advances in hydraulic fracturing and horizontal drilling. One immediate impact of this operation on the environment is the emission of greenhouse gases (GHG) into the atmosphere. GHGs are emitted by combustion of diesel fuel to supply the required energy for rotation of the drill bit, circulation of drilling fluids, and injection of high pressure water to crack the formation. GHGs can also be emitted during the completion and “flow back” process, wherein fugitive methane emissions can be released. These emissions should be accounted to properly assess the carbon intensity of the produced fuels. We developed a detailed engineering-based model to estimate greenhouse gas emissions from drilling of oil and gas wells and from hydraulic fracturing operations. Our model includes drilling of directional wells, drilling mud circulation, and the hydraulic horsepower of fracturing operations. The mathematical sophistication of the model is comparable to the software used in drilling operations, but it is tailored for use by LCA practitioners and for the regulatory system where the transparency and accessibility by the public is a key requirement. The model is equipped with an automatic mode that intelligently suggests the torque value and other input parameters, allowing use without access to detailed geological or technical data. The user can calibrate the model with their own set of field data if available. We present the structure and construction methods for building the model. We then discuss the verification and calibration of the model with data on diesel fuel consumption during drilling of vertical and horizontal wells. We use this model to estimate GHGs emitted from hydraulic fracturing of more than 7000 oil wells in the Bakken oil field of North Dakota. Lastly, we discuss sensitivity analysis to show key input parameters.

14:15 Emily Grubert and Adam Brandt

Methane Leakage in LCA: Quantifying the Effect of Fugitive Methane Emissions on Greenhouse Gas Inventories

ABSTRACT. Natural gas is an important fuel in the global energy economy, and many hope that natural gas can serve as a lower pollution bridge fuel to a cleaner energy economy, both in terms of traditional pollutants and climate pollutants. One major question about natural gas’ climate impacts is the amount of methane leakage from the natural gas fuel cycle, and in turn, how easy reducing methane leakage might be. Life Cycle Assessment is frequently used for evaluating and comparing the greenhouse gas emissions impacts of products and processes, including many that directly or indirectly rely on natural gas. Indeed, given natural gas’ large role in the electricity and manufacturing sectors in many parts of the world, natural gas is involved in the total life cycle of an extremely large number of products and processes.

Many studies rely on emissions factors from a few impact inventories like EcoInvent or GaBi, in part because primary data gathering for every possible element of a life cycle inventory is generally not possible. Due to this common reliance, however, the importance of accuracy is even greater for inventories associated with very common inputs like natural gas.

This study investigates the current treatment of methane leakage rates for natural gas in common LCA software, including GaBi and SimaPro. We first evaluate the current level of methane leakage assumed in common inventories and compare it with best-estimate leakage rates in the recent literature. We also test sensitivity to a range of methane leakage rates based on field-verified measurements from the United States and Australia. To demonstrate the relevance of methane leakage to LCA outputs, we then use LCA software to estimate greenhouse gas impacts for a diverse set of products and processes as a function of the assumed methane leakage rate. We present results for a set of common input commodities, including electricity, steel, concrete, plastics, and grain. As an example, we also present results for several common consumer goods for which LCA studies are common in the literature.