Using Thermochemical Processes to Handle Agricultural Waste (FS-2023-0688)

• Gasification yields syngas, which can be used for heating buildings, such as poultry houses, or used in a generator for electricity production. Other potential by-products of gasification include biochar (which can augment soil fertility), tar, and ash. Gasification operates at elevated temperatures, typically between 1500°F and 1800°F (800°C and 1000°C).
• Pyrolysis transforms biomass in an oxygen-deprived setting. The primary products are bio-oil (a potential fossil fuel substitute), syngas, and biochar. Pyrolysis typically operates at temperatures between 700°F and 900°F (350°C to 550°C).
• Combustion uses limited exposure to oxygen to mainly generate heat that can be used directly for heating or indirectly for generating electricity. The primary product of this process is ash. Combustion requires temperatures from 1500°F to 1800°F (800°C to 1000°C).
• Incineration involves direct burning organic waste materials to release energy for power generation without oxygen limitations. It can help reduce the volume of the waste. It is important to note that incineration requires careful management to avoid potentially hazardous pollutant emissions.

• Gasification: Offers cleaner syngas production with fewer contaminants, biochar as a soil amendment, and potential for carbon capture when more energy is produced than the energy used in the process.
• Pyrolysis: Helps in reducing the emission of certain greenhouse gases by avoiding complete combustion and producing bio-oil and biochar byproducts.
• Combustion: Emits CO₂, which could be considered carbon neutral since the biomass absorbed the same CO₂ during growth and can produce renewable energy in the process. Any energy used in processing and infrastructure should be calculated in carbon accounting.
• Incineration: Depending on the technology and waste processed, it can lead to the emission of various pollutants While modern municipal incinerators are designed to minimize these emissions, such controls are generally unavailable and/or cost-prohibitive for small-scale operations.

When poultry litter, wood waste, and other low-moisture solid agricultural wastes are used in thermochemical processing, the main contaminant of concern is nitrous oxide (NOₓ). Gasification has inherent advantages over combustion and incineration for emissions control because the produced syngas is produced at a higher temperature and pressure during gasification than exhaust gases produced in combustion. These higher temperatures and pressures allow for easier removal of NOₓ, sulfur oxides (SOₓ), and volatile trace contaminants.

• Gasification: High energy efficiency, with broad applications from electricity generation to producing liquid fuels and chemicals using the produced syngas.
• Pyrolysis: Energy yield is contingent upon the process temperature, with higher temperatures producing higher quality bio-oil. The syngas, biochar, and bio-oil outputs have potential to be used in renewable energy production, industry, and soil enhancement.
• Combustion: Efficient in terms of heat production but requires controlled environments to harness this heat effectively to utilize the heat directly or indirectly in electricity production.
• Incineration: Predominantly limited to heat production in small applications, with larger applications associated with municipality solid waste process with advanced emission controls to reduce emissions of harmful pollutants.

While promising, each method presents a set of challenges. All thermochemical methods can only be efficiently used with dry biomass and not with wet substrates, such as dairy manure.

• Gasification and Pyrolysis: Require sophisticated setups and advanced technology. Poultry operators considering gasification and pyrolysis will need trained individuals to keep the processes running at peak performance, due to the varying composition of poultry litter.
• Combustion: The technology for combustion ranges from basic to complex, depending on the desired efficiency and output.
• Incineration: The least technologically intensive option, but with the most environmental concerns.

Thermochemical processing and anaerobic digestion represent two diverse strategies for bioenergy conversion and energy harnessing. A thermochemical approach subjects feedstocks (ranging from wood to other low moisture biomass, such as poultry litter) to high temperatures to significantly reduce waste volume and facilitate energy recovery, either as heat or electricity. Gasification and pyrolysis processing uses a controlled oxygen setting that results in syngas, a versatile gas with applications in power generation and chemical synthesis. Combustion and incineration involve the direct burning of waste, predominantly municipal solid waste.

Anaerobic digestion depends on a biological route and utilizes microorganisms to decompose organic materials in oxygen-deprived environments. This process yields biogas - a renewable energy source rich in methane - and a nutrient-dense liquid residue called digestate used as a beneficial fertilizer. Anaerobic digestion facilities typically process biomass with higher moisture content, such as dairy manure, food waste, and sewage sludge. Anaerobic digestion is considered a more mature technology for agriculture waste products, as there are considerably more anaerobic digestion facilities in the United States than gasification and pyrolysis units.

Harnessing energy from low-moisture biomass through thermochemical processing can reduce waste volume and diminish fossil fuel dependence. Producers of low moisture waste products, such as the poultry industry, can utilize on-farm or community-based thermochemical processing to reduce waste volume and create local renewable energy production. As the technology applications in the agricultural sector are still emerging, there are a few key areas for research and technology advancement:

• Boosting Efficiency: Increasing conversion efficiency will reduce harmful emissions and increase economic gains.
• Feedstock Variations: Increasing the flexibility of thermochemical processing to changes in composition and moisture content of the feedstocks utilized.
• Biochar Value: Understanding the agronomic value of biochar created from various feedstocks and the ability of the biochar to bind nutrients and improve soil health.
• Air Emissions: Recognizing that commercial thermochemical processing systems operate under of variety of operational conditions, which impact the potential to produce and emit a wide range of toxic air pollutants. Air emissions should be monitored closely to understand potential environmental impact.
• Carbon Credits: Understanding the carbon balance of different thermochemical processing applications based on the quality of the products created (syngas, biochar, and bio-oil) and the infrastructure utilized to create these products.