Black Liquor Crystallization and Viscosity Facility

A bench-scale heated pressure vessel is used to concentrate weak black liquor and determine when soluble scale precipitates. During an evaporation run, a Focused Beam Reflectance Measurement (FBRM) laser is used to monitor the size distribution of the particles in the liquor to determine the equilibrium dissolved solids content as a function of temperature. During evaporation, black liquor reaches a point where there is a sudden increase in crystal formation, known as the first critical solids point, which is also captured in this data. These evaporation curves are useful to mills in operating multiple effect evaporators. After an evaporation run, filtered samples of the crystals are collected for chemical analysis and determination of the crystal species. This information can help diagnose scaling problems in multiple effect evaporators. Further, we can pause a run and sample the crystals at several points if desired. We also have the capability to measure liquor viscosity during evaporation (noting that this is a separate evaporation run).

Portable Fouling Test Unit (PTFU)

RBI has patented a device consisting essentially of two (or more) annular flow test cells in parallel.  One cell serves as the reference while the other(s) serve as simultaneous test cases.  Each cell is made up of an electrically heated rod within an insulated tube.  Process fluid (e.g. black liquor) flows in the annulus and scale forms on the rod.  By using multiple cells, different conditions, such as Reynolds number or surface temperature, can be compared with respect to scale formation.  Anti-fouling additives can also be evaluated with direct comparison to a reference cell containing no additive.  The PTFU is designed for air transport, and would fit in two large Pelican-type cases.  We are open to collaboration to build and test a prototype in a mill.

Pressurized Entrained Flow Reactor (PEFR)

The Pressurized Entrained Flow Reactor (PEFR) at the Renewable Bioproducts Institute enables high-temperature, high-pressure studies of pyrolysis, gasification, and combustion of solid fuels under well-controlled residence times and gas environments. The system is designed for fundamental kinetic studies and applied research on biomass, coal, and related feedstocks.

This PEFR is among the largest university-operated pressurized entrained flow reactors used for research.

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Reactor Design

The PEFR is a pressurized drop-tube reactor configuration. When operated at elevated pressure, the reactor is housed within a pressure vessel.

The majority of the gas stream is preheated to reactor temperature and passed through a honeycomb ceramic flow straightener to create a uniform velocity profile at the fuel injection point (top of reaction section). Both the preheat and reaction sections are electrically heated using Super Kanthal elements.

Fuel particles travel in a laminar flow regime down the reactor centerline, enabling controlled thermal histories and residence times. The effective heated length (15–170 cm) is adjusted by positioning a moveable collector probe along the reactor axis.

Fuel Introduction & Flow Configuration

• Ground solid fuels are injected through a water-cooled fuel injector probe.
• A cool primary inert gas stream (~50°C) carries the particles into the reactor.
• A preheated secondary gas provides the reactive environment and rapid heating.
• Particle heating occurs by radiation from the tube walls and convection from the hot secondary gas.

Reactions occur in the hot gas zone and are rapidly extinguished by quenching in a water-cooled collector probe with N₂ injection.

Feedstocks Studied

Past feedstocks include:

• Various woods
• Pulverized coals
• Lignite coal char
• Switchgrass
• Bagasse
• Corn stover
• Recycled paper sludge
• Black liquor

Product Collection & Analysis

• Reacted solids (“char”) collected via small cyclone
• Condensation aerosols (“fume”) captured in glass fiber filter
• On-line gas analysis:
  • FT-IR
  • NDIR (CO, CO₂, H₂)
  • Chemiluminescence (NOx)
• Gas bag sampling available for GC or GC-MS analysis

This configuration enables real-time gas monitoring and post-run product characterization.

Example Applications

• Carbon conversion kinetics during black liquor gasification in CO₂ and steam
• Sulfur evolution (H₂S formation) during pyrolysis of black liquor
• Lignite coal char gasification rate modeling and validation at elevated pressure

Selected example datasets and figures are available upon request.