Gasification

Overall Summary

Primary Application

• The primary application is for gasification of separated manure solids for production of energy and valued co-products.

• Theoretically scalable to any size of the dairy farm however economics will dictate true application to scale and a dairy. There are a couple of dairy farms located in US which treat manure by using gasification technology. Currently capital costs for installing this technology are higher especially for small to medium size dairy farms.

Economic/Return on Investment Considerations

• The capital cost of gasification systems is relatively high.
• The operating costs of these systems are low as they provide their own energy and require no additives if the feedstock is dry enough and has a high enough energy content.
• Depending on the system, gasifiers can produce a dried bedding material and biochar product which is a salable soil supplement with a limited market, at this time. Gasification co-products such as manure-biochar may not be congenial to use as bedding material for cows.
• The economic viability of gasification of dairy manure at the farm-level needs to be improved.
• Research results of the impact of biochar on crop yield and soil health testing is on-going across the country and will ultimately determine the viability of gasification projects for manure.

Industry Uptake

• This technology is being tested for smaller-scale applications to extract valuable energy and other chemical products from various waste streams, not many dairy farms have adopted this technology, with only a couple in demonstration.
• There are two dairy farms with 4,500 cows each in the U.S. where gasification units are installed to process the dairy manure. There is another gasification unit located at a demonstration site that beds heifers on deep pack bedding.

Technology Maturity

• Gasification technology has been well established for longtime to utilize lower BTU coal (e.g. lignite) as a feedstock to produce synthetic natural gas (SNG), also known as syngas, and gasification is considered one of the prominent “clean coal” technologies.
• There are enthusiastic promotors of gasification technology, but the technology and resulting products are not yet proven using dairy manure as feedstock.

Primary Benefits

• Despite economic and energy concerns, there are many significant advantages of this technology including: compact design, fast treatment times, reduction of odors, biological oxygen demand (BOD) reduction, destruction of pharmaceutically activated compounds and hormones, and elimination of sludge.
• The high heating value from gasification of dairy manure can approach 8,000-9,000 Btu, but the resulting biochar has a high ash content.
• Approximately 15% of the nitrogen resides in the ash, the rest is released to the air, causing potential concerns for air quality.
• All the original phosphorus remains in the ash. From a mass-partitioning perspective, approximately 85-95% of mass flows through the combustion gases while only 5-15% remains as ash.
• From a greenhouse gas (GHG) perspective, comparisons for baseline dry-lot land application to gasification processing shows a significant mitigation of GHG.
• From a pathogen reduction perspective, gasification and other thermal processing go well beyond pasteurization and are very effective control processes.
• Due to thermal degradation of solid by-products and avoidance of anaerobic and volatile storage conditions, odor mitigation can be significant, but air emission controls on volatiles, particulates, NOx, and sulfur must be considered.

Secondary Benefits

• Gasification is a flexible thermochemical technology with few operational risks. It is a process which handle a wide range of feedstocks such as wood waste, crop biomass, wastewater treatment plant biosolids, municipal solid wastes, livestock waste streams (stall wastes) and blends of the various feedstocks.
• Syngas can be used as feedstock to produce high-value chemical products such as ammonia (anhydrous ammonia, ammonium sulfate, urea), methanol, synthetic petroleum products, and other chemicals.
• Carbon dioxide generated by gasification process can be utilized to recover residual oil in oil mines and be sequestered permanently by pumping deep into geological formations which is one of the important IPCC’s GHG mitigation strategy (e.g. BECCS – Bioenergy and carbon capture and storage).

How it works?

• Gasification is a process that converts biomass (including manure) into syngas and biochar. Syngas can be converted into heat and electricity.
• The process takes place at temperatures between 700-1,500°C in a low-oxygen or oxygen-starved environment, using air or steam as the reaction medium.
• Gasification converts biomass into a combustible gas mixture consisting of H₂, CO, CO₂, CH₄, N₂ and traces of higher hydrocarbons.
• Gasification is being used at larger scale to produce energy at several places in the world by utilizing a wide variety of feedstocks such as coal, petroleum coke, and biomass (e.g. The Great Plains Synfuels Plant operated by Dakota Gasification Company).

Pretreatment and/or Post-treatment Required

• Dry manures like poultry litter and dry-lot manures can be processed directly via air/steam gasification technology.
• Manure solids in the liquid streams from dairy and swine operations typically need to be separated before gasification. Alternatively, these solids can be processed in a catalyzed wet gasification system, but this is a significantly more complex technology and due to high ash and sulfur contents, pretreatment of manure is necessary to promote effective operation.

Limitations

• The presence of tars and methane negatively impacts gasification efficiency and make syngas unsuitable as feedstock for other thermochemical processes such as Fischer-Tropsch synthesis (FTS) which converts a mixture of carbon monoxide and hydrogen into liquid hydrocarbons.
• The energy input requirement for a wet gasification manure treatment system is large and questions exist about the energy balance as well as cost and the potential need to pretreat the manure due to its high ash and sulfur contents.
• As a result, little to no active research or commercial application presently exists with respect to wet gasification of dairy manure.

Other Considerations

• Market share for the gasification products (syngas, heat, electricity, and biochar) is also required to create a revenue stream for farmers and potential social and environmental benefits. Considerable work is required in developing and securing these markets.