Fuel pathways

Ultra-low sulfur diesel from Crude oil

New York State (NYS) is geographically located in Petroleum Administration for Defense District (PADD) I and its petroleum resources are associated to be consisted of 2.68% crude oil domestic extraction and 97.32% foreign import in this study (U.S. Energy Information Administration, 2011) [48]. Petro-diesel production stages (WTP) typically include crude oil extraction, crude oil transport to refinery, crude oil refining, and diesel fuel delivery. Three types of conventional crude oil extraction processes (onshore production, offshore production, and advanced onshore steam-injection) are considered both for domestic crude oil production and foreign production [42]. The Argonne GREET Model 1.8d was applied to evaluate crude oil transport mode, diesel refinery from cruel oil, and the delivery modes for the PADD I region [49]. The energy consumption and GHG emissions for each stage of diesel production was quantified as the flow diagram provided in Figure A1 in Appendix A.1. Besides diesel fuel, other products like gasoline, heavy fuel oil, jet fuel, kerosene, etc. are also produced from the cruel oil refinery process and thus the mass allocation method based on these output

products is applied to determine the contributions of energy use and GHG emissions of diesel fuel in the upstream operations (crude oil extraction, feedstock delivery, and refinery). Energy use and fugitive emissions from crude oil storage and handling in the transportation processes (e.g., crude oil loading and unloading) are not included in this study, because the report from NREL (1998) indicates only 0.02% of total energy use and 0.015% of GHG emissions occur from crude oil handling/storage in transportation stage [42], which both are negligible. In order to supply a unit of auxiliary electricity to the truck, diesel fuel can be either direct engine combusted (Figure A1) or integrated with an SOFC-based APU system (Figure A2). The SOFC stacks need to maintain relatively high hydrogen fuel utilization (68%) in order to be consistent with the previous assumption of 30% net system efficiency for the SOFC-APU. The leftover effluent gases from stacks are combusted to supply heat for the reformer. Partial steam from the exhaust stream is also recycled as an input for fuel autothermal reforming [14].

Biodiesel from waste cooking oil (WCO)

NREL has reported that the average urban waste oil (yellow grease) produced by restaurants in New York State is 3,060 kg/year/restaurant, with a total of approximately

85,400,000 kg WCO produced per year state-wide [43]. Eighty-eight restaurants

following the collection path near the Rochester Institute of Technology campus were selected to potentially provide a total of 269,000 kg/year waste oil. The WCO feedstock is collected by a light duty truck following a 19.3 km path (as shown on Figure A3) and filtered to remove organic solid wastes before being dispensed to a BioProTM 380 Automated Biodiesel Processor, manufactured by Springboard Biodiesel, LLC (Chico,

CA), which has the capacity of producing 59,000 liters of biodiesel annually. Even though it is beyond the system boundary of biodiesel production, it is noteworthy to mention that organic solid wastes filtered from WCO can serve as a potential feedstock for biogas production with anaerobic digestion.

The biodiesel processor is integrated with a two-step catalysis method [50]: WCO with high free fatty acids requires pretreatment in which the acid catalyst (e.g., sulfuric acid) mixes with methanol to reduce free fatty acids, followed by the transesterification reaction (see Eq.(5)) that requires an alkali catalyst like potassium hydroxide mixed with methanol to produce the biodiesel. For each run, it takes 13 hours for WCO to convert into biodiesel and glycerol. Water consumption and waste water off-site treatment are also quantified in this system, even though LCA does not consider water balance as environmental impact because it does not contribute impact to any traditional impact categories [29]. The remaining methanol from the distillation step is reused as the input to the next test run. For more information about the biodiesel production process flow with an SOFC-APU system, please refer to Figure A4.

(5)

Glycerol is co-produced in the process and can be used in pharmaceutical and food industries [42]. Experimental data indicate 190 L WCO mixed with 37.8 L

methanol, 380 mL sulfuric acid and 2.35 kg potassium hydroxide yield 181 L biodiesel and 14 L glycerol (Springboard Biodiesel BioPro 380). This mixture has been confirmed in laboratory experiments by the author and in other studies [51]. The electricity for system facilities is assumed to be supplied from the New York State grid and Table 4 provides the sources for the average electricity generation along with respective electricity production efficiency [41].

Table 4. New York State average electricity grid mix (2006-2007)

Average grid mix Percentage Electricity production efficiency (MJ/MJ)

Petroleum 5% 4.53 Natural gas 30% 2.83 Coal 15% 3.56 Hydroelectric 18% 1.06 Nuclear 29% 3.24 Other renewable 3% 1.13

*Distribution and transmission loss of electricity is assumed as 8%

Ethanol from corn stover (CS)

The potential production of CS feedstock in New York State is 0.25 million dry tons annually [52]. However, it has been suggested that maintaining a certain amount of CS on the soil after harvest helps maintain soil organic carbon, minimize soil erosion, and retain and recycle nutrients. Spatari et al. [30] applied Monte Carlo analysis in a CS LCA and found the available residue (i.e., removable from land) for ethanol production varies from 35% to 70% of total CS production, depending on the agricultural practice and location. For the present analysis, an average of 50% of the available CS was assumed to be used as ethanol production feedstock, without jeopardizing soil quality or introducing other unintended environmental impacts.

A research group at NREL revealed the relationships between the collection distance of CS feedstock and the economically viable plant size [44]. As they suggested, 80 km radius around the plant corresponds to a plant treatment capacity of 2,000 metric ton of CS per day. Wojnar et al. [53] also indicate that the average truck travel distance for CS feedstock delivery in New York State is 38.6 km, however, the roundtrip travel pattern should be considered even if the truck returns empty [30]. Thus it is pertinent to consider CS feedstock transport distance as 80 km and the plant size as 2,000 metric ton per day in this study. Aden et al. [44] have developed a lignocellulosic biomass treatment process to produce ethanol using co-current dilute acid prehydrolysis followed with enzymatic saccharification and co-fermentation. This treatment process is adapted in this study and further integrated with an SOFC-APU system, as Figure A5 illustrates. CS with assumed 15% moisture content is pretreated with dilute acid (sulfuric acid) and ammonia to improve the accessibility of enzyme for hydrolysis. Overliming treatment is required to remove the liberated compounds that are toxic to the fermenting organism (Zymomonas

mobilis). The cellulose enzymes are purchased from industrial suppliers and they

stimulate saccharification and co-fermentation, which help convert cellulose and xylose into ethanol [47]. Anaerobic digestion is integrated in the system with the organic condensates and waste water from pretreatment. The biogas is combusted with the insoluble lignin to gain the energy recovery and generate electricity, which would cover the electricity and heat needs of the system. The main co-product of this considered system is the remaining electricity after subtracting the electricity use in the system, which will be sent back to the grid. On-site waste water treatment is also included within this system boundary.

Compressed natural gas from municipal solid waste (MSW)

In 2010, there were 27 active MSW landfills operating in New York State that accepted 7.6 million tons of solid waste (Department of Environmental Conservation, NY) [54]. Because comprehensive data on urban wastes in New York State have not been yet reported, the present work refers to a previous study conducted by NorthEast-South Towns [55], a group of municipalities in western New York State. It is estimated that in 2000 the total biomass solid wastes were approximately 252,000 metric tons (59% of the total waste stream) with 89,000 metric tons recovered by recycling or composting, and 163,000 metric tons available as bio-fuel feedstock. Figure A6 in Appendix A.1 shows the flow diagram of CNG derived from MSW with the SOFC-APU system. When the MSW arrives at the landfill, it is sorted into one of four categories: recyclable materials, organic biomass, refuse-derived fuels, and heavy wastes. Because MSW management sites have already involved waste collection, transport and sorting even without the anaerobic digestion process, the energy use and GHG emissions for these steps are not considered in this study. Anaerobic digestion processes decompose the organic fraction of MSW to form landfill gas by controlling the operating conditions (e.g., waste composition, moisture, oxygen content, and temperature) and the effluent gases typically contains 45-50% methane (CH4), 35-40% carbon dioxide (CO2), 10-15% nitrogen (N2),

and small amounts of hydrogen (H2), oxygen (O2), hydrogen sulfide (H2S) and ammonia

(NH3) [30]. Instead of flaring to the atmosphere, the landfill gas can be captured by a

collection system and further purified to mitigate the hydrogen sulfide (down to 5 ppm) with a zinc oxide desulfurizer and remove carbon dioxide with pressure swing adsorption [28,45]. Even though the LFG is monitored and shown with undetectable hydrogen

sulfide content from the landfill site studied in this work (see in Table 1), a pre- purification process is needed to mitigate hydrogen sulfide in that the compositions of LFG are also geographically varied and the SOFC-APU system is vulnerable to sulfur- containing gases. Because LFG is lighter than air, it spontaneously diffuses and moves upward to the landfill surface. After LFG purification and carbon dioxide removal, it is compressed up to 27,571 kPa in the truck delivery tank and no additional energy is needed during the gas (named as CNG) transfer process from the truck tank to gas stations because the tank pressure is high enough as compared to the local distribution system (1,480 kPa). The electricity needs for the facilities are provided by an on-site power generation based on landfill gas combustion.