Investigation of biomass gasification and effects of ammonia on producer gas combustion

Energy security and global climate change are two of the greatest challenges that face the next century and it will be up to this generation to figure out a solution to these monumental challenges. Nearly everything ranging from commerce to travel to education relies on abundant and cheap energy to function and progress. For the last 150 years, this energy has come through the combustion of fossil fuels which are limited by their very nature. As these fuels are combusted to produce heat and power, various harmful gasses are emitted into the atmosphere and can lead to acid rain, smog, depletion of the ozone layer, and even a heating of the earth\u27s surface. Gasification of biomass provides one possible solution to both of these problems by utilizing a renewable energy source that is abundant and has the potential to be carbon negative. NOx emissions are regulated by the government and could potentially be the limiting factor on the potential of biomass gasification to have a major impact in overcoming the two greatest challenges of today. It is believed one of the primary causes of NOx emissions is due to nitrogen found in the feedstock that is gasified. This work is aimed at both developing the tools necessary to understand the detailed systems involved in biomass gasification, as well as to characterize the NOx emissions that result from the combustion of the biomass-derived producer gas. In the current work, a two-fold approach is taken to address this issue. First, a process model is created utilizing the software Aspen Plus to simulate data taken from a pilot-scale gasification system utilizing maple and oak wood as the feedstock and air as the gasification medium. This model uses a mass balance approach to simulate the gasification process. A system of cyclones filter out the particulate matter in the producer gas before the gas is burned. Second, the effects of fuel-NOx are studied experimentally utilizing a newly developed lab-scale, low-swirl combustion apparatus. This combustion apparatus is first tested using natural gas that contains low concentrations of ammonia for four swirlers with varying effective areas. A single swirler is chosen to conduct tests to analyze the effect of ammonia concentration on NOx emissions from the producer gas. Results of the current work can be summarized as follows. (1) A biomass gasification model was created to model the gasification of wood feedstock. This model shows very good agreement with experimental results for all components except hydrogen in the producer gas. (2) For the swirlers studied, NOx emissions are reduced as the swirl strength increases. (3) For a natural gas flame, both the equivalence ratio and effect of thermal NOx are important considerations when trying to achieve low NOx emissions. (4) For the combustion of producer gas, higher equivalence ratios reduce the overall NOx emissions. The above results show the need for a greater understanding of producer gas combustion in low-swirl burners for a wide variety of compositions in order to better control overall emissions in the future

Investigation of fundamental transport and physicochemical phenomena in lignocellulosic fast pyrolysis

Fast pyrolysis of biomass has the potential for high-yield production of valuable fuels and chemicals from renewable biological and agricultural waste feedstocks. Optimization of this technology is dependent on developing a deeper understanding of the complex transport and kinetic phenomena which drive product formation. In this dissertation, direct, time-resolved imaging of feedstock degradation and product formation mechanisms for the pyrolysis of whole biomass and several of its components has been made inside an optically accessible pyrolysis reactor. The reactor thermal and transport characterization allows the determination of dominant mechanisms of pyrolysis product formation in the multiphase reacting environment. This novel investigation of biomass pyrolysis simultaneously captures relevant transport and kinetic phenomena including melt, agglomeration, ejection, evaporation and condensation throughout the pyrolysis of solid biomass feedstocks and the surrounding reactive environment. A novel pyrolysis reactor was developed in order to provide four-sided optical access to probe near-particle surface phenomena. The reactor and pyrolysis conditions were characterized using multiple techniques in order to better understand the relevant transport and kinetic limitations from which to interpret the imaging results. Condensed-phase products were analyzed via gas chromatography/mass spectrometry (GC/MS) to verify product compositions obtained using the optically accessible reactor match those observed in other small-scale test reactors. Acetone planar laser-induced fluorescence (PLIF) temperature measurements and multi-point thermocouple mapping provide a detailed thermal profile of the reaction environment and the convectively driven transport near the reaction filament. A line heat source conductivity measurement was developed and used to characterize the biomass feedstock effective conductivity in order to understand heat transport through the biomass sample from the heated filament strip. These studies indicate non-isothermal pyrolysis conditions with both heat and mass transfer limitations which must be accounted for in the interpretation of results - as is common in many pyrolysis reactors. Planar Mie scattering of product condensation across a well characterized thermal boundary layer allows for time resolved tracking of product formation through distinct condensation bands which are attributed to unique classes of compounds. Correlating the time-resolved condensation scattering signal to simultaneous color micro-scale imaging of feedstock morphological changes allows for developing an understanding of the physical and chemical mechanisms which drive product formation during the pyrolysis of biomass. Dominant transport appears to occur via evaporation and condensation/re-polymerization reactions with minimal contribution from ejection of large aerosols/droplets. In order to elucidate the nature and timescales of the transport of evaporated products away from the reacting biomass sample, a planar fluorescence imaging technique was utilized coincident with planar Mie scattering imaging in order to track the product stream prior to and after Mie scattering signal is apparent from chemical condensation in the thermal boundary layer. Three excitation wavelengths (532 nm, 355nm, 266nm) generated from a 10 Hz Nd:YAG laser were used to probe the volume directly above the pyrolyzing biomass. Differences in the timescales of product/intermediate formation were observed and correlated with the primary observed condensed phase products via Mie scattering. In order to further explore the nature of the primary aerosols and droplets from biomass fast pyrolysis, products were collected directly above the reacting biomass sample and electron and fluorescence microscopy were used to explore the condensed products. Through time-resolved observation of fast pyrolysis of whole red oak, cellulose, and lignin, comparisons among the mechanisms and timescales of thermal degradation and product formation have been made. Single component studies may aid in building a comprehensive understanding of whole biomass pyrolysis but the application of these results must be framed within the context of the complex physicochemical characteristics unique to each feedstock and the specific reaction and transport limitations for a given system. Observations such as those presented in this dissertation indicate that predictive modeling efforts should incorporate the full complexity of biomass pyrolysis and include dynamics of the bulk systems in addition to pure kinetic results. For the pyrolysis regime utilized in this study where kinetic and transport effects both contribute, particle size, degree of polymerization, molecular complexity of the pseudo-components and feedstock compositional and structural variations were shown to influence the phenomena governing the conversion process

Visualization of physicochemical phenomena during biomass pyrolysis in an optically accessible reactor

The thermochemical conversion of biomass via fast pyrolysis requires detailed descriptions of both the kinetic and heat and mass transport rates, which are often in direct competition. To investigate the evolution of products, whole biomass and biomass constituents (e.g. cellulose and lignin) are pyrolyzed in a novel optically accessible reactor. This enables real-time, in situ observation of the temporal evolution of light-oxygenates, volatile sugars, and phenolic compounds during melting, agglomeration, ejection, and volatilization of biomass under realistic heating rates (∼100 K/s). Both cellulose and lignin underwent liquefaction, but liquid coalescence in lignin limits vapor transport. This is overcome by dispersing extracted lignin in an inert matrix, and confirms the predominant mass transport of pyrolysis products from whole biomass, cellulose, and lignin occurs via devolatilization. These results differ from prior work on single-particle pyrolysis and reveal thermochemical mechanisms that are relevant for typical large-scale pyrolysis processes with transport limitations

Extreme hardness at high temperature with a lightweight additively manufactured multi-principal element superalloy

Materials are needed that can tolerate increasingly harsh environments, especially ones that retain high strength at extreme temperatures. Higher melting temperature alloys, like those consisting primarily of refractory elements, can greatly increase the efficiency of turbomachinery used in grid electricity production worldwide. Existing alloys, including Ni- and Co-based superalloys, used in components like turbine blades, bearings, and seals, remain a performance limiting factor due to their propensity, despite extensive optimization efforts, for softening and diffusion-driven elongation at temperatures often well above half their melting point. To address this critical materials challenge, we present results from integrating additive manufacturing and alloy design to guide significant improvements in performance via traditionally difficult-to-manufacture refractory alloys. We present an example of a multi-principal element alloy (MPEA), consisting of five refractory elements and aluminum, that exhibited high hardness and specific strength surpassing other known alloys, including superalloys. The alloy shows negligible softening up to 800°C and consists of four compositionally distinct phases, in distinction to previous work on MPEAs. Density functional theory calculations reveal a thermodynamic explanation for the observed temperature-independent hardness and favorability for the formation of this multiplicity of phases.This article is published as Kustas, Andrew B., Morgan R. Jones, Frank W. DelRio, Ping Lu, Jonathan Pegues, Prashant Singh, A. V. Smirnov et al. "Extreme hardness at high temperature with a lightweight additively manufactured multi-principal element superalloy." Applied Materials Today 29 (2022): 101669. DOI: 10.1016/j.apmt.2022.101669. Copyright 2022 The Authors. Attribution 4.0 International (CC BY 4.0). Posted with permission. DOE Contract Number(s): AC02-07CH11358; NA000352