Research Article pubs.acs.org/journal/ascecg
Catalyst Residence Time Distributions in Riser Reactors for Catalytic Fast Pyrolysis. Part 2: Pilot-Scale Simulations and Operational Parameter Study Thomas D. Foust,*,§,† Jack L. Ziegler,§,† Sreekanth Pannala,‡ Peter Ciesielski,† Mark R. Nimlos,† and David J. Robichaud†
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National Bioenergy Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States ‡ Corporate Research and Development, SABIC Americas, 14100 Southwest Freeway, Sugar Land, Texas 77478, United States ABSTRACT: Using the validated simulation model developed in part one of this study for biomass catalytic fast pyrolysis (CFP), we assess the functional utility of using this validated model to assist in the development of CFP processes in fluidized catalytic cracking (FCC) reactors to a commercially viable state. Specifically, we examine the effects of mass flow rates, boundary conditions (BCs), pyrolysis vapor molecular weight variation, and the impact of the chemical cracking kinetics on the catalyst residence times. The factors that had the largest impact on the catalyst residence time included the feed stock molecular weight and the degree of chemical cracking as controlled by the catalyst activity. Because FCC reactors have primarily been developed and utilized for petroleum cracking, we perform a comparison analysis of CFP with petroleum and show that the operating regimes are fundamentally different. KEYWORDS: Catalytic fast pyrolysis, Catalytic upgrading, Riser reactor, Multiphase flow simulation, Catalyst residence time distribution
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INTRODUCTION In part one of this study, we detailed the simulation development methodology for biomass catalytic fast pyrolysis (CFP) and compared it against a validation case, Andreux et al.,1 gaining confidence in our modeling methodology. In this second stage, we use the techniques developed in part one to assess the functional utility of using this validated model to assist in the development of CFP processes in fluidized catalytic cracking (FCC) reactors to a commercially viable state. Specifically, we examine the effects of the following on the catalyst residence time distributions (RTDs): mass flow rates, inlet boundary conditions (BCs), and pyrolysis vapor molecular weight variation. The flow rates include the ratios of pyrolysis vapor, fluidizing gases, and solid catalyst. Additionally, the nonreactive model developed in part one was enhanced to incorporate a reduced order chemical mechanism for CFP. With simplified reactive 2D and 3D simulations, this study demonstrates guidelines for improving the overall performance of the CFP in FCC reactors. CFP processes for the production of fuels can be described as a three-step process: preparation of the feedstock, rapid heating in the absence of oxygen (pyrolysis), and catalytic upgrading with a catalyst. Figure 1 provides a schematic diagram of the National Renewable Energy Laboratory (NREL) CFP pilotscale reactor (NCFP-PSR). The NCFP-PSR operates in an ex situ arrangement where the biomass is pyrolyzed in a bubbling bed reactor and the vapors are upgraded in the circulating bed © 2017 American Chemical Society
Figure 1. Schematic of NCFP-PSR.
Received: October 3, 2016 Revised: January 4, 2017 Published: February 21, 2017 2857
DOI: 10.1021/acssuschemeng.6b02385 ACS Sustainable Chem. Eng. 2017, 5, 2857−2866
Research Article
ACS Sustainable Chemistry & Engineering Table 1. Model Summary grid type domain granular energy gas wall BC solids wall BC roughness cells resolution chemistry
2D
3D
Cartesian rectangular algebraic approx., full transport no slip partial slip specularity 0.001 and 0.05 96 × 5088
