Environmental Benefits and Impacts of Pellet Production and Combustion
Chemical Composition of Grasses
Strategies to Reduce the Ash Content in Perennial Grasses
Roger Samson and Bano Mehdi.
Abstract
"Perennial grasses have been identified as the lowest cost dedicated
agricultural feedstock for energy and agri-fibre markets. However, it is of
paramount importance that the ash content of these feedstocks be reduced so as
to facilitate their commercialization. High ash contents are particularly
troublesome for achieving efficient combustion when used for bioenergy
applications, and in chemical recovery systems, in the pulp and paper industry.
The major component of ash is silica. Warm-season (C4) grasses are found to
have lower silica levels than C3 grasses, owing primarily to the fact that they
utilize water 50% more efficiently. Silica levels in grasses are also highly
influenced by the monosilicic acid content of soils. As a result, clay soils
produce higher silica-containing feedstocks than sandy soils. Silica levels are
lowest in the stem fraction of grasses, and highest in inflorescences, leaves,
and leaf sheaths. Selection for higher stem content will help to reduce the
plant's ash content, while increasing the desirable feedstock characteristics,
such as cellulose content, which is important for ethanol and pulp and paper
markets.
Reducing the potassium and chlorine contents of feedstocks grown for fuel
purposes is important to improve combustion efficiencies. The chlorine content
of feedstocks is strongly influenced by fertilization practices and can be
minimized by using chlorine-free fertilizers. Potassium and chlorine contents
can be reduced to similar levels as wood chips by overwintering the grasses;
however, there is a tradeoff in that lower yields are harvested. The feedstock
production cost of overwintered switchgrass is lower than short-rotation
forestry, and switchgrass provides similar properties for combustion as
wood."
www.reap-canada.com/Reports/Strategies to reduce the ash content in perennial grasses.htm
Combustion Emissions
Greenhouse Gas Impact
Changing the Energy Climate:
Clean and Green Heat from Grass Biofuel Pellets
R. Jannascha , R. Samsona, A. de Maioa, T. Adamsb, and C. Ho Lema
Resource-Efficient Agricultural Production — Canada,
Box 125, Ste Anne de Bellevue, Quebec, Canada J7V 7P2
www.reap-canada.com, Tel (514)
398-7743 Fax (514) 398-7972.
Presented at "Climate Change 2: Canadian Technology Development
Conference"
Canadian Nuclear Society, Toronto, Oct. 3-5, 2001
Abstract
"Volatile energy markets, concerns over energy security, and international
agreements to reduce greenhouse gas (ghg) emissions have created unique
opportunities for biofuel development. Feedstock for pelletized fuels from
warm-season grasses such as switchgrass (Panicum virgatum) can be grown for
$3-4/GigaJoule (gj) and pelletized for $3/GJ with only minor emissions of CO2.
Assuming hay prices provide a shadow price for switchgrass, the price
volatility of switchgrass appears low relative to the price volatility of
fossil fuels. Using close-coupled gasifier combustion technology, switchgrass
fuel pellets emit 85%, 91%, 87%, and 89% less CO2 than electricity,
heating oil, natural gas, and propane, respectively. Every 100 ha of
switchgrass converted into pellet form and used to displace the same fuels in
space-heating applications prevents the emission, on average, of 1800 tonnes of
CO2. Heating an average Ontario house with a 90-GJ heat demand costs
$1213 with switchgrass pellets compared to $2234, $1664, $882, and $2302 with
electricity, heating oil, natural gas, and propane, respectively. An estimated
23 and 130 million acres of agricultural land in Canada and the U.S.,
respectively, could be converted to perennial grass biofuel production. The
depressed farm sector would benefit economically from energy farming through
economic diversification and absorption of excess production capacity.
Low-grade heat energy derived from grass pellets could displace some of the
30,000 GigaWatt Hours of electricity currently used for home heating in Quebec,
Ontario, and Manitoba. Surplus electricity could be exported where it would
likely displace fossil-fired electricity. Pelletized-grass biofuels could
provide consumers without access to natural gas with less expensive heating
options than fossil-energy options. For consumers with access to natural gas,
the price premium for switching to a much lower ghg-emitting alternative would
be modest, except during natural gas price spikes when switchgrass could be
cheaper. Developing the switchgrass pellet market could help ease the political
challenges in implementing the Kyoto Protocol."
www.reap-canada.com/Reports/AECL.htm
The Use of Switchgrass Biofuel Pellets as a Greenhouse Gas Offset Strategy
R. Samson1, M. Drisdelle2, L.
Mulkins1, C. Lapointe, and P. Duxbury1
Abstract
For more than 20 years, efforts have been made to grow dedicated biomass crops
such as switchgrass, but no economically viable, energetically efficient
transformation pathway has been described to convert this material into a
usable energy form to displace fossil fuels. To meet this goal, it is proposed
that warm-season grasses such as switchgrass be used for heat-related energy
applications. This is considered to be the energy use with the highest
comparative advantage for switchgrass, as the application requires little
upgrading of the original energy quality of switchgrass, and it best matches
the widespread production of the crop in North America. To improve combustion
efficiency, the biomass quality of switchgrass can be upgraded through cultural
management practices to reduce the chlorine, potassium, and silica content of
the fuel. Densification of the grass into a pellet form appears economically
attractive and is essential to create highly controlled combustion for space-heating
applications.
Switchgrass pellets can be converted into usable heat at 82-84% efficiency in a
close-coupled gasifier pellet stove designed to handle moderately high ash
fuels. Relative to oil and natural gas systems, switchgrass pellets have the
potential to reduce fuel-heating costs and greenhouse gas emissions in eastern
Canada by approximately 30% and 90%, respectively. Compared to all other
biofuel production and energy-transformation pathways currently proposed,
switchgrass pellet heating offers the highest net energy yield per hectare, the
highest energy output-to-input ratio, the greatest economic advantage over
fossil fuels, and the most significant potential to offset greenhouse
gases."
www.reap-canada.com/Reports/bioenergy2000Aug2.html
Energy Profit Ratios (How Green Is It?)
A Process and Energy Analysis of
Pelletizing Switchgrass
R Jannasch, Y. Quan, and R. Samson
Resource Efficient Agricultural Production (REAP-Canada)
P.O. Box 125, Ste. Anne de Bellevue, QC H9X-3V9
www.reap-canada.com
Executive Summary
A commercial-scale pelleting trial using switchgrass feedstock was conducted in
Ste. Marthe, Quebec, in August 2001, to study the pellet-production process at
a commercial alfalfa-dehydrating plant and assess energy use, percent yield,
and quality of the finished product. Nine tonnes of baled switchgrass (14.5%
moisture) were pelleted.
Square bales were easier to process than round bales, and baled switchgrass
could be broken and course chopped in 30% less time than alfalfa. The crop
could be pelleted without drying, which generated a cost saving over sawdust
and alfalfa of $8-12 per tonne. A reduction in screen size from 1/8 inch to
7/64 inch for the fine-grinding process appeared to produce a modest increase
in pellet hardness. Pellet throughput was approximately 2 tonnes/h (20-22
lbs/HP), a rate similar to wood. Pellets hardness was similar to alfalfa and
wood pellets, but less than optimum binding characteristics resulted in greater
fine production during pelleting and handling. The loss of fines during the
pelleting, cooling, and temporary storage stages produced a percent yield of
91% on a dry matter basis. The percent yield of finished pellets was 57% of the
initial feedstock supply; however, fines produced during the screening and
shaking process were not re-pelleted. The binding quality of the feedstock and
pellet durability could be improved by changes to the die configuration, steam
treatment, or natural additives. If the majority of fines were reprocessed in
the pelleter, it is expected that the yield of finished product would be
increased to 95% of the original feedstock. The energy requirement for
pelleting switchgrass is estimated to be 0.416 GJ/tonne. It is expected that
energy efficiency could be increased substantially with the adoption of modern
equipment in demonstration projects or by working with large-scale western
Canadian pellet processors. Switchgrass appears to lack natural binding
properties compared to alfalfa, and improving pellet durability is a major
research and development priority for successful commercialization."
www.reap-canada.com/Reports/PelletSG.htm
Water Quality and Erosion Control
Environmental and Economic Analysis of Switchgrass Production for Water Quality Improvement and Alternative Energy Use in Northeast Kansas
Richard G. Nelson, Director
Engineering Extension
Kansas State University
Manhattan, Kansas
rnelson@ksu.edu
Executive Summary
The major goals of this project were to 1) determine reductions in sediment
yield, surface runoff, nitrogen in surface runoff, and edge-of-field erosion
(USLE) associated with producing switchgrass on conventional agricultural
acreage in northeast Kansas; and 2) evaluate the break-even cost of producing
switchgrass in the Delaware Basin versus conventional commodity crops. In
addition, from information gained in the environmental analysis, the magnitude
of a potential "switchgrass water quality" payment required to
cost-effectively produce switchgrass and utilize it as an alternative energy
source was determined.
Switchgrass production (tons/acre/year) was modeled as a function of varying nitrogen fertilizer input (0, 50, 100, 150, and 200 pounds of nitrogen per acre); between 580,000 and 1.4 million tons of switchgrass could be produced annually across the basin. In all nitrogen-input cases modeled, the reduction in sediment yield, edge-of-field erosion, and surface runoff in the basin as a result of switchgrass plantings was 99%, 98%, and 55%, respectively. Average reductions as a result of switchgrass plantings for nitrogen in surface runoff ranged from 65% to 16% (0 to 200 pounds nitrogen).
The environmental savings in the basin would cost between $20 million and nearly $36 million dollars per year, and the average annual cost per acre for switchgrass ranged from about $77 with no nitrogen applied to around $140 with 200 pounds of nitrogen applied. The edge-of-field cost per ton ranged from around $33 with no nitrogen applied to slightly over $23 at 200 pounds of nitrogen applied. A majority of the switchgrass produced had an edge-of-field cost of $25 per ton or less. Savings of at least 50% in each of the four environmental variables could be attained for an edge-of-field cost of $20 - $24.99 per ton or less.
The magnitude of switchgrass water quality payments needed to achieve delivered-energy costs of $6.00 per MMBtu ranged from a low of $10.06 per ton ($61.59 per acre), to a high of $24.71 per ton ($52.35 per acre) depending upon the switchgrass yield level.