(251a) Carbon Negative Biofuel and Power Systems Via Hybrid Pyrolysis and Anaerobic Digestion Biorefineries

Carbon Negative Biofuel and Power
Systems via Hybrid Pyrolysis and Anaerobic Digestion Biorefineries

Aui
A.^b Ganguly A.^b, Mas Martin I.^b, and
Wright M. M.^ab

^aBioeconomy
Institute

^bDepartment
of Mechanical Engineering

Iowa
State University

Anaerobic Digestion
(AD) is a promising and beneficial technology for converting agricultural,
industrial, and commercial wastes into value-added products. Studies have shown
that AD is both an economical and environmentally viable option which aligns
with the Iowa Energy Plan. With the advancement in technology and developments
of policies, AD can create more opportunities for farmers and businesses to
benefit from an extra revenue stream. A previous study has investigated the
techno-economic and life cycle analysis of an Iowan farm-scale AD combined heat
and power (CHP) plant co-located with a cattle feedlot. This study investigates
two scenarios with six cases of different feedstocks – Biomass Only (BO) and
Biomass and Glycerin (BG) scenario. The feedstocks evaluated in this study is
based on regional availability which is corn stover, rye and wheat. Glycerin
was obtained as a waste stream from a soybean bio-diesel plant. The
techno-economic analysis evaluates both the capital and operating costs of the
systems, while the life cycle analysis evaluates the total greenhouse gas (GHG)
emissions released during the entire process.

The AD
system in this study has a power capacity of 950 kilowatts of electricity (kW_e).
Using a discounted cash flow rate of return (DCROR) analysis, the internal rate
of return (IRR) of the six cases varies from 3.51% to 5.57%. The addition of
glycerin into the system reduces the operating costs of the process by an
average of 32%. Life cycle analysis resulted in a GHG emissions between -82.6
to 498.52 grams of carbon dioxide equivalence per kilowatt hour (gCO_2e/kWh),
with the BG scenarios having a higher GHG emission in compared to the BO
scenarios. Sensitivity analysis suggested that operating parameters such as
power efficiency, operating capacity and waste per cattle significantly affects
the IRR, while glycerin and manure emission factors have the greatest impact
towards the GHG emissions. The commercialization risks associated with the
choice of feedstock and operating parameters were also evaluated via
uncertainty analysis.

            Future work in this
area includes combining the AD system described above with a pyrolysis unit in
a biorefinery. This process produces biofuel as a main product and electricity
as a by-product. Pyrolysis biochar feeds into the anaerobic digester leading to
significant improvements in biogas methane content. Solid and liquid effluents
from AD can be sequestered through soil application leading to a potential
strategy for carbon negative energy. Both the economics and environmental
viability of this system will be evaluated using techno-economic and life cycle
analysis.