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Recovering Valuable Bio-Based Products
from Thin Stillage in Corn Ethanol PlantsK.J. Valentas, S. Heilmann and Joseph Molde, University of Minnesota,
ACE Conference August 5, 2014
Cost of corn ethanol operations varies directly with corn prices.
The Problem
Source: Ag. Marketing
Resource Center, March
2013, Iowa State Univ.
extension ethanol model
Sometimes profits are negative
The Opportunity
• Thin stillage can potentially be converted to higher
value products than DDGS to improve cash flow and
stabilize profitability
• A “drop-in” Hydrothermal carbonization (HTC) process
unit can convert condensed distillers solubles (CDS) to
such products
• These products include phosphorous, fatty acids,
fertilizers and functional hydrochars of various types
What is HTC and how does it work in a corn ethanol plant??
How does HTC fit into the broader spectrum of Thermochemical Processing ?
The general objective of thermochemical processing is to increase the carbon:
oxygen ratio of the biomass to improve its fuel properties. There are three
regimes with the product mix determined by the thermal intensity.
(1) Hydrothermal Gasification: Temp. range of 400-8000C, w/wo
catalyst, Products are; Hydrogen, methane, carbon dioxide.
Carbon is consumed and converted to CO2. High concentration
of CO2 prevents distribution in natural gas infrastructure.
(2) Hydrothermal Liquefaction: Temp. range of 250-4500C,
products are Bio-oils (phenols), hydrogen, methane, carbon
dioxide and some char. Bio-oils are particularly problematic
since they are inherently unstable, highly corrosive and toxic.
They also are not oils and are primarily phenols.
(3) Hydrothermal Carbonization (HTC): Temp. range 170-2500C,
Products are Char, fatty acids (if lipids are in biomass), water,
Maillard reaction products, N, K, and P.
How does HTC work?
•Aqueous biomass is heated to about 4000F at
pressure of 260 psia in a confined vessel.
•Biomass solids are dehydrated by elimination
of oxygen and hydrogen in the form of water
with almost no carbon dioxide generated.
•Fatty acids in the biomass are sorbed by the
char.
•Addition of a precipitant would cause the
phosphate in the biomass to also be sorbed by
the char.
•By cooling and simple filtration the hydro- char
and filtrate are easily recovered and separated.
Hydrothermal Carbonization (HTC)
Whole Stillage Thin Stillage
Wet distillers
grain
Drier
Eva
po
rato
r
Condensed
Distillers Solubles
Corn Oil
30% of totalDDGS
Centrifuge
Centrifuge
HTC
Phosphorous
Fatty Acids
Hydrochar
Proposed “drop-in” HTC unit in the
thin stillage process flow.
Filtrate to DDGS
drier or fertilizer
Primary products from HTC processing of CDS
• HTC recovers 32% of the solids in the
concentrated thin stillage as hydrochar
to which about 70 % of the
phosphorous and residual corn oil (in
the form of fatty acids) are sorbed.
• The hydrochar with sorbed
components is readily separated
from the remaining concentrated
thin stillage (68% of the original) by
simple mechanical filtration.
• The filtrate with 68% of the
original solids is combined with wet
distillers grains and dried in the
normal manner or alternatively
converted to a liquid fertilizer
• The fatty acids are recovered
by solvent extraction and the
phosphorous by acid wash from
the hydrochar.
Secondary and higher value-added products from CDS
�
�
�
�
Hydrochar
Surface area =
2m2/gram
+ Metal Salts
Heat to 8000C in
Inert atmosphere
Chemical adsorbents
Polymer additives
Supercapacitor
electrodes
�
Surface area
= 100m2/gram
• Adsorbents are used in many applications including water purification and chemical
processing or as a phosphorous filter to reduce runoff. At the low end these are at least
$1.00/lb. Work in this area is a collaboration with colleagues in the chemical engineering
department
• The high surface area of the modified chars are thought to provide strengthening in
some polymer systems such as polylactides. A collaborative effort with colleagues in the
chemistry department is ongoing
• Micro porosity imparted to the char during post heat treatment could result in
materials suitable for use in supercapacitors. There is an ongoing collaboration with
colleagues at the University of California, Berkeley.
What about the filtrate from the HTC process?
There are at least two viable options
• The filtrate can be added back to the DG’s and dried as is done
now with the CDS
• Filtrate can be concentrated utilizing the energy that would
have been used to dry it and subsequently applied as a liquid
fertilizer for corn and other row crops.
The fertilizer option is attractive since it recycles a part of the
corn crop to the land and reduces the requirement for
conventional fertilizer. This would be viewed as
environmentally sound as it would further reduce the carbon
footprint for corn ethanol
What are the questions that need to be answered to be able to use the
HTC filtrate from CDS as a plant fertilizer?
HTC processing of CDS retains most of the nitrogen and phosphorous in
the filtrate if no steps are taken to cause phosphorous to be purposely
sorbed by the char. At the same time maillard reaction products and other
chemicals are produced that could exhibit phytotoxicity or be detrimental
to soil bacteria.
The major questions are:
• Does the addition of HTC filtrate to soil have any negative
or positive effects on soil microorganisms?
• Does HTC filtrate have any phytotoxic effect on
either seed germination or plant growth
• What is the effect of aging the filtrate prior to application?
• What is effect of concentration of the filtrate on soil
microorganisms and possible phytotoxicity
These questions are currently being addressed on a lab scale for the system
of CDS filtrate and corn. The results will be published in a Masters thesis and
peer reviewed technical papers in the near future..
Cash flow example for 100M gallon/year ethanol plant operating at 30% backset
Mass balance based on preliminary experimental results
• Phosphorous as phosphoric acid = 2700 tons/yr at net value of $540/ton
•Fatty acids = 12.8M lbs/yr. with assumed value of $0.30/lb. ( Corn oil =$0.54
and white grease =$0.34).
• Hydrochar = 20.4 M lbs/yr Value depends on application from low of $1/lb
as activated carbon to high of $7/lb as polymer additive or supercapacitor.
• Thin stillage consumed = 21,400 tons/yr @$240/ton = $ 5.14 M
Incremental Yearly Cash Flow from HTC
$1.5M phosphoric acid + $3.84M fatty acids + $20.4M hydrochar (@ $1/lb) –
< $5.14M > thin stillage = $20.6M
The installed capital cost for an HTC unit for a 100M gallon plant is about $1.5M
What is the financial benefit of adding HTC??
Financial support for this research is
provided by Minnesota Corn Growers, AURI,
and the Institute for Renewable Energy and
the Environment (IREE).
Questions ???
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