(129b) Method for Hot Real-Time Sampling of Biomass-Derived Pyrolysis Vapors

The Thermochemical Process Development Unit (TCPDU) at the National Renewable Energy Laboratory (NREL) is a highly instrumented half-ton/day pilot scale plant capable of demonstrating industrially relevant thermochemical technologies from lignocellulosic biomass, including pyrolysis. Biomass derived pyrolysis vapors are a very complex mixture of over 400 known chemical components that undergo additional condensation reactions changing their composition as they are cooled and collected to form multiphasic oils. Added to this chemical change, up to 60% of the resulting products do not readily re‑volatilize, making off-line post analysis of condensed chemistry difficult. Real-time hot online sampling techniques, such as Molecular Beam Mass Spectrometry (MBMS), can provide real-time analysis providing operational indicators for performance.

It is difficult to obtain a representative real-time analytical sample of biomass derived pyrolysis vapors. Sampling must occur within a narrow range of temperature to reduce plugging of lines due to cooling and product composition changes due to overheating. Residence time within the sampling lines must be kept to a minimum to reduce further reaction chemistries. Solids from ash and char contribute to plugging and must be filtered at temperature. Pyrolysis vapors also form aerosols that are carried far downstream and can pass through filters resulting in build-up in downstream locations.

Experience at NREL has shown several key factors to consider when designing and installing an analytical sampling system for biomass pyrolysis vapors. They include minimizing sampling distance, effective filtering as close to source as possible, proper line sizing, even heating of all components, minimizing pressure drops, additional filtering or traps after pressure drops, and avoiding 90 degree bends to minimize vapor condensation and polymerization. Sample dilution may help with plugging but can actually cause aerosols to carry further downstream and will dilute trace analytes that may be of interest.