Biomass Energy Lecture Notes

Modeling and Design of Energy Systems

ENVE 162– CRN 111515 Spring 2025 MW 1:30-2:45pm; Granite Pass Room 135
Abbas Ghassemi, Ph.D. Emeritus Professor Teaching Professor; Civil and Environmental Engineering SE2 372; aghassemi2@ucmerced.edu

Renewable Energy Sources

Biomass Energy Lecture Notes- April 23, 2025

Biomass Energy

  • Biofuel

  • Feedstock

  • Biofuels Life Cycle:

    • Transportation

    • Processing & Conversion

    • Biorefinery

    • Distribution

    • Consumer

  • The biofuels life cycle begins with feedstock production and ends with a fully finished product ready for the end user.

Bioenergy

  • Bioenergy is a diverse resource available to help meet the demand for energy.

  • It is a form of renewable energy (maybe even carbon neutral) that is derived from recently living organic materials known as biomass.

  • Biomass can be used to produce transportation fuels, heat, electricity, and products.

What is Biomass Energy?

  • Biomass energy is the use of living and recently dead biological material as an energy source.

  • How it works?

    • Traditional: forest management, using wood as fuel

    • Use of biodegradable waste

      • Examples: manure, crop residue, sewage, municipal solid waste

    • Recent interest in agricultural production of energy crops

      • Should be high yield and low maintenance

      • Examples: corn, sugarcane, switchgrass, hemp, willow, palm oil, and many others

      • Does not have to be a food crop

    • Recent interest in bioengineered (GM) plants as fuel sources

    • Production of a liquid or gaseous biofuel

      • Biogas due to the breakdown of biomass in the absence of O_2, Includes capture of landfill methane

      • Bioethanol from fermentation, often from corn. Cellulosic bioethanol is usually from a grass (switchgrass)

      • Biodiesel from rapeseed and other sources

Biofuels

  • It can be converted into liquid transportation fuels that are equivalent to fossil-based fuels, such as gasoline, jet, and diesel fuel

  • It can be converted into liquid fuels—known as biofuels—for transportation.

    • Biofuels include cellulosic ethanol, biodiesel, and renewable hydrocarbon "drop-in" fuels.

  • It can be converted into heat and electricity using processes like those used with fossil fuels.

    • There are three ways to harvest the energy stored in biomass to produce biopower: burning, bacterial decay, and conversion to a gas or liquid fuel.

  • A versatile energy resource, it can also serve as a renewable alternative to fossil fuels in the manufacturing of bioproducts such as plastics, lubricants, industrial chemicals, and many other products currently derived from petroleum or natural gas.

Algae as a Possible Fuel Source

  • Unlike fuel from corn and other cellulosic sources…. Algae and some other biomass fuel sources have potential to achieve near-zero net carbon emissions.

  • Cultivation of some requires very low energy inputs

  • If managed sustainably, the carbon released during fuel combustion is captured and used for various applications including re-absorption by the growth of new feedstocks.

CO_2 Emissions for Corn and Bio Based Fuels

  • Carbon Footprint of Transportation Fuels
    *Relative emissions: Diesel and Biodiesel

  • The graphic presents a comparison of emissions from various fuels. The x-axis shows different types of emissions (CO, Total Unburned HCs, Particulate Matter, NOx, Sulfates, PAHs, n-PAHs, Mutagenicity, CO2), while the y-axis represents the percent change.

  • B100 (100% biodiesel) with NOx adsorbing catalyst on vehicle

CO_2 from Biofuels

*   Crops like corn are finely ground and separated into their component sugars
*   The sugars are distilled to make ethanol
*   Only 37% of the CO_2 is reabsorbed by the original crops which can be used as an alternative fuel

Biofuel Conversion Processes

  • Producing advanced biofuels such as cellulosic ethanol and renewable hydrocarbon fuels involves a multistep process.

  • Two ways to brake down the tough rigid structure of the plant cell wall—which includes the biological molecules cellulose, hemicellulose, and lignin bound tightly together.

    • High-Temperature Deconstruction by use of extreme heat and pressure (Pyrolysis, Gasification, Hydrothermal liquefaction).

    • Low-Temperature Deconstruction makes use of biological catalysts such as enzymes or chemicals to breakdown feedstocks into intermediates.

High-Temperature Deconstruction

  • Pyrolysis, biomass is heated rapidly at high temperatures (500°C–700°C) in an oxygen- free environment.

    • The heat breaks down biomass into pyrolysis vapor, gas, and char.

    • Once the char is removed, the vapors are cooled and condensed into a liquid “bio-crude” oil.

  • Gasification follows a slightly similar process; however, biomass is exposed to a higher temperature range (>700°C) with some oxygen present to produce synthesis gas (or syngas)—a mixture that consists mostly of carbon monoxide and hydrogen.

  • When working with wet feedstocks like algae, hydrothermal liquefaction is the preferred thermal process.

    • This process uses water under moderate temperatures (200°C–350°C) and elevated pressures to convert biomass into liquid bio-crude oil.

Low-Temperature Deconstruction

  • Low-Temperature Deconstruction makes use of biological catalysts(enzymes) or chemicals to breakdown feedstocks into intermediates.

  • Biomass undergoes a pretreatment step that opens up the physical structure of plant and algae cell walls, making sugar polymers like cellulose and hemicellulose more accessible.

  • These polymers are then broken down enzymatically or chemically into simple sugar building blocks during a process known as hydrolysis.

  • Following deconstruction, intermediates such as crude bio-oils, syngas, sugars, and other chemical building blocks must be upgraded to produce a finished product.

    • This step can involve either biological or chemical processing.

Biomass Energy: Advantages and Disadvantages

Advantages
* It is renewable energy
* Carbon neutrality
* Less dependency on fossil fuels
* Can be produced domestically
* Sources for biomass energy are easily available
* Low cost in comparison to fossil fuels
* Reduces and utilizes waste
Disadvantages
* Not completely clean energy
* Economically inefficient
* Can lead to deforestation
* Requires a large amount of space
* Requires Water
* Low energy density
* Requires sustainable use and management