A Radiant Flow Reactor For High-Temperature Reactivity Studies Of Pulverized Solids

Our radiant two‐phase flow reactor presents several new possibilities for high‐temperature reactivity studies. Most importantly, the thermal histories of the suspension and entrainment gas can be independently regulated over wide ranges. At low suspension loadings, outlet temperatures can differ by hundreds of degrees and gas temperatures are low enough to inhibit hydrocarbon cracking chemistry, so primary products are quenched as soon as they are expelled. With coal suspensions, tars were generated with the highest H/C ratio and lowest proton aromaticity ever reported. Alternatively, particles and gas can be heated at similar rates to promote secondary chemistry by increasing particle loading. Simply by regulating the furnace temperature, arbitrary extents of conversion of coal tar into soot were observed for fixed total mass loss. Under both circumstances heat fluxes are comparable to those in large furnaces, so relevant heating rates and reaction times are accessible. Suspensions remain optically thin even for the highest loadings of technological interest because they are only 1 cm wide. Consequently, the macroscopic behavior remains firmly connected to single‐particle phenomena. Mass and elemental closures are rarely breached by more than 5% in individual runs, so interpretations are not subject to inordinate scatter in the data. The reactor is also well suited for combustion studies, as demonstrated by extents of carbon and nitrogen burnout from 50% to 100% for various gas‐stream oxygen levels

DEVELOPMENT OF A VALIDATED MODEL FOR USE IN MINIMIZING NOx EMISSIONS AND MAXIMIZING CARBON UTILIZATION WHEN CO-FIRING BIOMASS WITH COAL

In full-scale boilers, the effect of biomass cofiring on NO{sub x} and unburned carbon (UBC) emissions has been found to be site-specific. Few sets of field data are comparable and no consistent database of information exists upon which cofiring fuel choice or injection system design can be based to assure that NOX emissions will be minimized and UBC be reduced. This report presents the results of a comprehensive project that generated an extensive set of pilot-scale test data that were used to validate a new predictive model for the cofiring of biomass and coal. All testing was performed at the 3.6 MMBtu/hr (1.75 MW{sub t}) Southern Company Services/Southern Research Institute Combustion Research Facility where a variety of burner configurations, coals, biomasses, and biomass injection schemes were utilized to generate a database of consistent, scalable, experimental results (422 separate test conditions). This database was then used to validate a new model for predicting NO{sub x} and UBC emissions from the cofiring of biomass and coal. This model is based on an Advanced Post-Processing (APP) technique that generates an equivalent network of idealized reactor elements from a conventional CFD simulation. The APP reactor network is a computational environment that allows for the incorporation of all relevant chemical reaction mechanisms and provides a new tool to quantify NOx and UBC emissions for any cofired combination of coal and biomass

Suppressed Nitrogen Evolution From Coal-Derived Soot And Low-Volatility Coal Chars

This laboratory study uses a novel furnace to resolve nitrogen evolution during the three stages of pulverized coal combustion: primary devolatilization, secondary pyrolysis, and combustion. The behavior of six coals depicts continuous rank variations, as well as suppressed nitrogen evolution from low volatility coals. During primary devolatilization of any coal, aromatic compounds in tar and oils are virtually the only shuttles for nitrogen out of the coal matrix. The small amounts of HCN observed while primary devolatilization winds down probably come from the char, because char particles are significantly hotter than tar in these experiments. Secondary pyrolysis promotes additional HCN evolution from both char and tar. Moreover, substantial fractions of the volatile-nitrogen from primary devolatilization is reincorporated into a carbonaceous soot matrix for all coal types. The fraction of coal nitrogen incorporated into soot remains constant, even while soot yields dramatically increase. Incorporation of nitrogen into soot has the potential to substantially reduce the amount of coal nitrogen amenable to aerodynamic NOx abatement strategies for coals with large tar yields. This potential limitation is compounded by another limitation for low volatility coals. Whereas one-half to two-thirds of the coal-nitrogen is expelled by thermal decomposition from other coal types, only 30 to 40% is expelled from low volatility samples. This tendency suggests that nitrogen functionalities become much more refractory as their surrounding aromatic domains become more extensive, either in high rank coals or soot. For such systems, our measurements indicate that the only way to expel the nitrogen is to burn it away

Assess Coal Quality Impacts on Your Personal Computer

In the past, utility companies that operate coal-fired boilers entered into long-term contracts with their coal suppliers to secure a steady supply of similar fuels for smooth, trouble-free, day-today operations. In today's environment long-term contracts might seem unappealing because utility strategists would rather be free to switch to different coals to lower costs or meet emissions regulations. Coal switching is often an important pan of compliance strategies that seek an optimal balance among technology upgrades, bubble-based emissions averages across several boilers, and open-market trading allowances. Although switching is now motivated by SO2 compliance, a new coal can affect many other operating characteristics, including pulverizer performance, heat rate, slagging and fouling, unburned carbon in ash, NOx emissions, and certainly cost. In light of the push for tighter NOx regulations before the turn of the century under Title I of the Clear Air Act Amendments, it is prudent for utilities to factor in the impact of a coal switch on NOx and unburned carbon emissions into their coal selection decisions

Predicting the Complete Distributions of Volatile Products from Diverse Fuel Types with Flash Chain

FLASHCHAIN is a reaction mechanism for the rapid devolatilization of solid fuels. This paper illustrates how the theory was recently expanded to predict the complete distribution of all major devolatilization products for a variety of fuel types, including any kind of coal, biomass, and petroleum coke. Noncondensible gases are now resolved into the primary hydrocarbon species (CH4, C2H9, C2H4, C3H9, C3H8), HCN, Hi, H2S, H20, C02, and CO. Tars are characterized by their complete elemental compositions (C/H/O/N/S) and their molecular weight distributions. Chars are characterized by their complete elemental compositions (C/H/O/N/S) and their sizes and densities. The theory also predicts the partitioning of chlorine and alkali species (Na and K). This paper also introduces a mechanism to describe the secondary pyrolysis of the primary devolatilization products, as occurs naturally at elevated temperatures in all combustion and gasification systems. During secondary volatiles. the volatiles are radically transformed, with complete conversion of tar into soot and conversion of all gases into H2, CH4, C2H2, HCN, H2S, CO, C02, and H20

Predicting Detailed Product Distributions For Pyrolysis of Diverse Forms of Biomass

Paper from the AFRC 2013 conference titled Predicting Detailed Product Distributions For Pyrolysis of Diverse Forms of Biomass by Stephen Niks