Hydrogen from biomethane; gasoline & diesel from tree residue; cellulosic ethanol among new proposed California LCFS fuel pathways
California Air Resources Board (ARB) staff posted 32 new Low Carbon Fuel Standard (LCFS) fuel pathway applications for comments at the LCFS website. Among the multiple applications for different processing pathways of corn or sorghum ethanol are four pathways from LytEn for hydrogen produced from biomethane; four pathways for renewable gasoline and diesel produced from tree residue from Ensyn; and one application for cellulosic ethanol using corn stover feedstock from POET.
The LCFS is a regulation to reduce the carbon intensity (CI) of fuels sold in California by 10% by 2020. The LCFS applies to liquid and non-liquid fuels. If a product is above the annual carbon intensity target, the fuel incurs deficits. If a product is below that target, the fuel generates credits which may be used later for compliance, or sold to other producers who have deficits. So far, fuel producers are over-complying with the regulation. (Earlier post.)
The average CI for gasoline and gasoline substitutes for 2016 is 96.50 gCO2e/MJ; for diesel and diesel substitutes it is 99.97 gCO2e/MJ.
LytEn and hydrogen from biomethane. LytEn produces hydrogen from the cracking of methane (fossil natural gas or renewable biomethane) through a proprietary process. For the LCFS pathway applications, LytEn is using landfill gas.
LytEn proposes dual hydrogen production-delivery systems: one will include a facility with a hydrogen production system that will fill tube trailers for delivery of hydrogen to stations in the Bay Area in California, and the second will include installing on-site hydrogen production systems.
As a co-product, the hydrogen process produces carbon black, which could displace the use of carbon in the commercial production of electrodes.
The hydrogen production system is anticipated to generate 200 kg H2/ day or about 6000 kg of compressed H2 per month. LytEn proposes to use either 33.3% renewable biomethane and the balance fossil natural gas or 100% renewable biomethane as feedstocks for the production of hydrogen.
LytEN is requesting CIs of 15.29 and -46.91 g CO2e/MJ for 33.3% and 100% renewable biomethane pathways, respectively, generated from on-site systems. For the tube trailers pathways, LytEn is requesting CI values of 29.84 and -32.36 g CO2e/MJ for the 33.3% and 100% renewable biomethane pathways, respectively. The CI values for these pathways are based on lifecycle analysis conducted using the CA-GREET 1.8b model.
Because limited data provided by LytEn precluded ARB staff from determining all the necessary inputs for hydrogen production, staff is imposing a number of constraints on this prospective pathway which are listed below. Further, LytEn will need to submit commercial production data to obtain an updated provisional CI for this pathway prior to generating LCFS credits. (Fuels with prospective CIs are not eligible to claim credits under the LCFS.)
Ensyn renewable diesel and renewable gasoline from forest residues. Ensyn, Tesoro and Chevron are designing a commercial process to produce renewable gasoline and diesel from the co-processing of Renewable Fuel Oil (bio-oil) obtained via pyrolysis of tree residues. (Earlier post.)
For these pathways, tree residues will be collected in the area of Renfrew County, Ontario, Canada and processed into Renewable Fuel Oil (RFO) at a facility in Renfrew, Ontario, Canada. RFO will be transported to California for co-processing in a Fluid Catalytic Cracker (FCC) unit in a refinery into finished renewable gasoline and diesel.
Ensyn, Tesoro and Chevron expect to produce a combined total of 2 million gallons per year of renewable diesel and gasoline. The renewable gasoline and diesel products meet ASTM specifications and can be blended with ethanol and biodiesel.
The applicants are requesting carbon intensities (CIs) of 20.12 and 25.03 g CO2e/MJ for renewable gasoline via rail and truck transport, respectively and prospective CIs of 21.67 and 25.58 g CO2e/MJ for renewable diesel via rail and truck transport, respectively. The CI values for these pathways are based on lifecycle analysis conducted using a modified version of the CA-GREET model.
ARB staff commented that the prospective CI values are a reasonable representation of the carbon intensities of renewable diesel and gasoline. However, again, because the co-processing operation has not begun commercial operation, ARB staff cannot determine actual inputs. Staff thus imposed a number of constraints—basically different types of supporting evidence required—on these prospective pathways.
POET cellulosic ethanol from corn stover. POET-DSM produces cellulosic ethanol at the newly constructed Project Liberty Cellulosic Ethanol Plant in Emmetsburg, Iowa (Project Liberty Plant). The facility is expected to produce over 13 million gallons per year of ethanol using corn stover as feedstock.
Corn stover comprises the dried leaves, stalks, husk, and cobs left on the ground after the harvest of the primary corn crop. In partnership with local farmers, POET-DSM will collect and bale the corn stover for subsequent transport to the Project Liberty Plant for conversion to ethanol. A polypropylene netting material is used to hold the bales together. The bales are transported to the Project Liberty Plant on tractor-trailers.
The carbon intensity (CI) determined for the corn stover pathway includes the GHG emissions impacts associated with the fertilizer/nutrients that must be applied to fields from which corn stover has been removed. This application makes up for the nutrients lost when corn harvesting residues are removed.
At the Project Liberty Plant, the corn stover is shredded and screened to remove the biomass fines, which are used as process fuel for the solid fuels boiler (SFB). The netting material used to wrap the corn stover bales are also separated in the screening process and used as fuel for the SFB.
The screened feedstock undergoes an acid pre-treatment process which begins to decompose the cellulosic biomass and primarily produce C5 (xylose) monomer sugars. The remaining biomass is then subjected to enzymatic hydrolysis which produces the C6 (glucose) monomer sugars. This process first involves neutralizing the biomass after acid pre- treatment process with Ammonia, followed by the addition of cellulase enzymes.
The C5 and C6 sugars produced are then fermented into ethanol using yeast. The fermented beer is then distilled to produce near-pure ethanol at the top of the distillation column, and stillage at the distillation bottoms.
The liquid and solids in the stillage are then sent to filter presses to further separate the stillage into filter cake and filtrate. The filter cake is used as process fuel for the SFB, while the filtrate is sent to the wastewater treatment plant where it is anaerobically digested to produce biogas and sulfur cake. The biogas produced could be used as a process fuel but is considered surplus to the corn stover pathway. Sulfur cake and ash produced by the SFB are sent to landfill for disposal.
The Project Liberty Plant is dependent upon grid-based electricity, as well as fossil-based natural gas from the pipeline. GHG impacts from grid-based energy utilization were assessed for the corn stover pathway.
In addition to anhydrous ethanol, Project Liberty produces two valuable co-products; surplus steam from the SFB, and biogas from the wastewater treatment process. Both co-products are exported to the nearby corn-starch plant in Emmetsburg (Emmetsburg), where these co-products are assumed to displace natural-gas based utilization. The GHG emissions associated with the equivalent displacement of natural gas utilization at Emmetsburg accrues as a credit to the Liberty corn stover pathway.
The ethanol produced is denatured and loaded onto rail car tankers destined for California. Once the ethanol arrives in California, it is assumed to be transported in heavy-duty diesel tanker trucks to a bulk terminal 40 miles away where it is blended with CARBOB gasoline to produce reformulated gasoline. Following blending, the reformulated gasoline is distributed to fuel dispensing stations 50 miles away from the blending terminal.
The total Well-to-Wheels CI estimate for this cellulosic ethanol is 21.58 g CO2e/MJ.
ARB staff recommended certification with the estimate CI for the Liberty corn stover pathway, subject to some specified operating conditions.