Biomass Resources Overview
Biomass Resources include all plant and plant-derived (organic) materials that are available on a renewable or recurring basis. Plant biomass is a complex mixture of organic materials, primarily carbohydrates (~75% dry weight) and lignin (~25% dry weight) with the proportions varying by plant type, but also containing fats, proteins and minerals. The carbohydrates consist mainly of cellulose or hemicellulose fibers which give strength to plant structures with a small portion of carbohydrates in the form of starches and simple sugars. Lignin is the glue that holds the fibers together. Thus the stems, stalks, branches, and leaves of plants are the lignocellulosic components of plants which are eaten by forage animals for food, processed mechanically for bioproducts (such as wood used in buildings or furniture), or processed thermally or biochemically in many different ways to produce heat, electricity, chemicals, and biofuels. Both the primary lignocellulosic resources (trees, grasses, and stalks of food crops) and all by-products of processing (from pulping black liquor to sawdust to food waste and manure) compose the biomass resource base that can be utilized for producing various types of bioenergy. For production of liquid biofuels, some processes involve separating the lignin from the cellulose and hemicellulose in order to gain access to the carbohydrates that can be broken down into sugars. Reduction of lignocellulosic materials to sugars and other compounds is anticipated to be the major source of liquid biofuels and chemicals in the future. Examples of biomass resources that are currently used for liquid biofuels include: starches from the grain of corn (maize), wheat and other grains; sugars squeezed from the stalks of sugarcane; and oils derived from soybeans and other oilseed crops.
All biomass resources available for producing bioenergy and biofuels are expected to be produced and harvested in a sustainable manner. A recent analysis of biomass resources (US Department of Energy, 2011), includes a more rigorous treatment and modeling of resource sustainability than was done in a previous evaluation (Perlack et al. 2005). The 2011 update evaluates two scenarios—baseline and high yield. Overall, results of this update are consistent with the 2005 study in terms of the magnitude of the resource potential previously estimated to be over one billion dry tons on an annual basis.
In the 2011 baseline scenario, forest resource quantities are estimated to vary from about 33 to 119 million dry tons currently to about 35 to 129 million dry tons in 2030 over a price range of ($20-$80 per dry ton). Primary forest biomass (derived from logging, thinnings, and land clearing) is the single largest source of forest resource. The agricultural resources show considerably more supply, with the quantity increasing significantly over time. This increase is due to yield growth (assumed to be about 1% per year) and assumptions of more land managed with no-till or reduced cultivation, all of which makes more crop residue available. The increase can also be attributed to the deployment of energy crops, which are assumed to be first planted in 2014 and have yield growth of 1% per year that is due to breeding and selection and experience gained). In 2012, biomass supplies are estimated to range from about 59 million dry tons at a *farmgate price of $40 per dry ton or less to 162 million dry tons at $60 per dry ton.
The composition of this biomass is about two-thirds crop residue and one-third various agricultural processing residues and wastes. By 2030, quantities increase to 160 million dry tons at the lowest simulated price to 664 million dry tons at the highest simulated price ($60 per dry ton). At prices above $50 per dry ton, energy crops become the dominant resource after 2022.
No high-yield scenario was evaluated for forest resources except for the woody crops. Forest residues come from existing timberlands, and there is no obvious way to increase volumes other than reducing the amounts of residues retained onsite for environmental sustainability or decreasing the merchantable utilization requirements—neither option was considered. Forest residues and wastes total to 100 million dry tons by 2022.
The high-yield agriculture scenario assumes a greater proportion of corn in reduced and no-till cultivation and increased corn yields (averaging 2% per year) to about double the current rate of annual increase, all factors which increase residue levels. Agricultural residues and wastes are about 244 million dry tons currently and increase to 404 million dry tons by 2030 at a farmgate price of $60 per dry ton. For energy crops, the high-yield scenario increased the annual rate of crop productivity growth from the 1% baseline to 2%, 3%, and 4% annually. Energy crops are the largest potential source of biomass feedstock, with potential energy crop supplies varying considerably depending on what is assumed about productivity. At a 2% annual growth rate, energy crop potential is 540 million dry tons by 2030 and 658 million dry tons if an annual increase in productivity of 3% is assumed. Both of these estimates assume a farmgate price of $60 per dry ton. Increasing yield growth to 4% pushes the energy crop potential to nearly 800 million dry tons. Energy crops become very significant in the high-yield scenario—providing over half of the potential biomass.
In total, potential supplies at a forest roadside or farmgate priceof $60 per dry ton range from 855 to 1009 million dry tons by 2022 and from about 1046 to 1305 million dry tons by 2030, depending on what is assumed about energy crop productivity (2% to 4% annual increase over current yields). This estimate does not include resources that are currently being used, such as corn grain and forest products industry residues. By including the currently used resources, the total biomass estimate jumps to well over one billion dry tons and to over 1.6 billion dry tons with more aggressive assumptions about energy crop productivity.
The above results, along with estimates of currently used resources are summarized in the Data Book table entitled “Summary of Currently Used and Potential Biomass.” One important year highlighted in this table is 2022—the year in which the revised Renewable Fuels Standard (RFS) mandates the use of 36 billion gallons per year (BGY) of renewable fuels (with 20 billion gallons coming from cellulosic biofuels). The feedstock shown in the baseline scenario accounts for conventional biofuels (corn grain, ethanol, and biodiesel) and shows 602 million dry tons of potential lignocellulosic biomass resource. This potential resource is more than sufficient to provide feedstock to produce the required 20 billion gallons of cellulosic biofuels. The high-yield scenario demonstrates a potential that far exceeds the RFS mandate.
* The farmgate price is a basic feedstock price that includes cultivation (or acquisition), harvest, and delivery of biomass to the field edge or roadside. It excludes on-road transport, storage, and delivery to an end user. For grasses and residues this price includes baling. For forest residues and woody crops this includes minimal comminution (e.g. chipping).
Perlack RD, Wright LL, Turhollow AF, Graham RL, Stokes BJ, Erbach DC. 2005. Biomass as feedstock for a bioenergy and bioproducts industry: the technical feasibility of a billion-ton annual supply. DOE/GO-102995-2135 or ORNL/TM-2005/66. Oak Ridge National Laboratory, Oak Ridge, TN. 60 pp. www1.eere.energy.gov/biomass/publications.html
U.S. Department of Energy. 2011. U.S. Billion-Ton Update: Biomass Supply for a Bioenergy and Bioproducts Industry. R.D. Perlack and B.J. Stokes (Leads), ORNL/TM-2010/224. Oak Ridge National Laboratory, Oak Ridge, TN p.227. (accessed 8-15-2011 at https://bioenergykdf.net/content/billiontonupdate)
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