(278a) Biochar Collection Overview and Design Upgrades in Biomass Pyrolysis Pilot Plant

The Thermochemical Process Development Unit (TCPDU) at the National Renewable Energy Laboratory conducts research on a pilot plant that may be configured for biomass fast pyrolysis or gasification with the ultimate objective of creating renewable transportation fuels. Current research is focused on optimizing pyrolysis conditions for low-cost feedstock blends that are widely available and relevant on an industrial scale. Future research (2018) will focus on ex-situ catalytic upgrading of pyrolysis vapors using a riser reactor and regenerator system, similar to a fluid catalytic cracking system. The TCPDU is capable of feeding ½ ton of biomass per day and commonly operates at a feed rate of ~33 lb/h biomass while configured for fast pyrolysis. At this feed rate, the TCPDU generates ~2.2 gal/h of raw bio-oil and ~4.5lb/h of solid bio-char.

Efficient solids separation and collection is essential when thermochemically converting biomass to desirable products. Solids in the TCPDU are removed from the process stream via dual cyclonic separators. When solids are not collected efficiently, carryover to downstream operations occurs often leading to process disruption, requiring downtime and maintenance before operations resume. Whenever operators must perform maintenance that involves opening the process they are subjected to additional exposure hazards. This increased downtime is very expensive, and therefore must be minimized for a plant to operate efficiently.

While running experimental feedstocks within the TCPDU, the solids collection system was quickly determined to be insufficient for the nature of the solids generated when varying feedstocks and run parameters. In order to conduct our research, it was deemed necessary to redesign our solids collection systems. A 3-phase approach was taken in an effort to continue performing research while improving our solids collection system in a step wise manner. Phase 1 included an assessment of the system as configured with a focus on minor changes that could improve operations in the short term. Phase 2 consisted of a thorough assessment of our solids collection system in an effort to identify underlying causes of solids collection problems, with a focus on design changes that would improve flexibility across feedstocks and run conditions. Phase 3 involved looking at our current, past, and projected feedstock characteristics, and redesigning our solids collection system for maximum efficiency over an extended period of time.

Changes to date include the following: timing of automated valves, temperature of collection components, flow path of pneumatically conveyed solids, velocity of pneumatically conveyed solids, ease of maintenance of solids collection system, safety while performing maintenance on solids collection system, procedural changes, and early indicators of malfunctions within the collection system.

Modifications performed have resulted in vastly reduced down time due to solids collection issues. Since these modifications, the system has produced nearly 500 gallons of bio-oil and collected more than 1,000 lbs. of solids without a single solids collection related shut down. Future work will focus on optimal cyclone design and may assess benefits of additional solids collection strategies as we move towards catalytic fast pyrolysis.