EME 444
Global Energy Enterprise

Biomass Applications and Processes

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Bioenergy conversion technologies
Bioenergy Conversion Technologies
Source: Wisconsin Grasslands Bioenergy Network, Biomass Conversion

A feedstock is "any renewable, biological material that can be used directly as a fuel, or converted to another form of fuel or energy product."  According to the Office of Energy Efficiency and Renewable Energy, "biomass feedstocks are the plant and algal materials used to derive fuels like ethanol, butanol, biodiesel, and other hydrocarbon fuels".

There are two basic categories of biomass material: woody & .... non-woody! "Lignocellulose" is woody biomass. (For an excellent description and discussion, see Sources of biomass from the Wisconsin Grasslands Bioenergy Network. This is not required reading.)

From the Environmental and Energy Study Institute, here is a list of some of the most "common (and/or most promising)" biomass feedstocks--

  • Grains and starch crops – Sugar cane, corn, wheat, sugar beets, industrial sweet potatoes, etc.
  • Agricultural residues – Corn stover, wheat straw, rice straw, orchard prunings, etc.
  • Food waste – Waste produce, food processing waste, etc.
  • Forestry materials – Logging residues, forest thinnings, etc.
  • Animal byproducts – Tallow, fish oil, manure, etc.
  • Energy crops – Switchgrass, miscanthus, hybrid poplar, willow, algae, etc.
  • Urban and suburban wastes – Municipal solid wastes (MSW), lawn wastes, wastewater treatment sludge, urban wood wastes, disaster debris, trap grease, yellow grease, waste cooking oil, etc.  

Logistics

Feedstock logistics encompass all of the operations necessary to harvest the biomass and move it to the conversion reactor at the biorefinery (or the heat and/or electricity generation facility), including the processing steps necessary to ensure that the delivered feedstock meets the specifications of the biorefinery conversion process. A biorefinery is where "biomass is upgraded to one or more valuable products such as transport fuels, materials, chemicals, electricity and, as a byproduct, heat" (Source: "What is a Biorefinery?" by Bernstsson, Snadén, Olsson, and Åsblad. This article provides an excellent explanation of various biorefining processes if you are so inclined!). Conventionally, facilities that generate electricity and/or heat through direct thermal conversion (combustion) are not considered biorefineries unless they first convert the biomass into a "novel" material like biogas. In the chart at the top of this page, biorefineries are used in all technologies except for thermal conversion.

Logistics includes harvest and collection, preprocessing, storage and queuing, handling and transportation, and is used in all four of the technologies in the chart above.

In its natural form, most biomass is bulky, relatively wet, and due to its low bulk-density, costly to transport. Preprocessing includes production steps, like chipping, grinding, compacting and drying, that turn biomass into what is properly called feedstock.

Biomass densification is the compression or compaction of biomass to reduce its volume per unit area. Densification is used for solid fuel applications (e.g., pellets, briquettes, logs). Drying biomass improves the grinding process, and results in smaller more uniform particles of biomass.

For cellulosic biomass, mechanical (e.g., crushing) and thermochemical (e.g., hydrolysis) pretreatments are necessary.

Many herbaceous feedstocks, for example corn stover, are only harvested over a few weeks during the year in the U.S. Corn Belt. To maintain a continuous supply of this feedstock to biorefineries, storage is required. Biological degradation can reduce the amount of biomass available for bioenergy production and also impact the conversion yield, by altering biomass chemical composition.

Unprocessed biomass leaving the field or forest is often bulky, aerobically unstable, and has poor flowability and handling characteristics. These traits can make raw biomass handling and transportation inefficient. Transport can be expensive, especially as distance increases.

The video below from the U.S. Department of Energy may help you visualize some of the processes involved with harvesting and using various feedstocks. Please watch the following (3:39) video:

Conversion

The figure at the top of this page shows four categories of biomass processing: thermal, thermochemical, biochemical, and chemical. This is a very helpful starting place for understanding the different inputs and outputs associated with biomass. (The DOE, on the other hand, groups its biomass research into biofuels, biopower ,and bioproducts.) The main differences in how biomass is processed have to do with "the temperatures used to deconstruct the biomass, the biomass derived intermediates produced from deconstruction, and the catalytic means used to upgrade those intermediates to finished fuels and products" (Source: Bioenergy Technologies Office, Processing and Conversion).

To Read Now

Visit the the Wisconsin Grasslands Bioenergy Network and read closely, Bioenergy Conversion Technologies.