Mahendra P. Mathur

Co-firing of coal and cattle feedlot biomass (FB) Fuels, Part III: fouling results from a 500,000 BTU/h pilot plant scale boiler burner☆

Abstract Part I of the paper presented a methodology for fuel collection, fuel characteristics of the FB, its relation to ration fed, and the change in fuel characteristics and volatile oxides due to composting. The bench scale experiments with 30 kWt (100,000 BTU/h) facility revealed better combustion for coal: FB blends (90:10) than for coal alone and the NOx emission were slightly less with the blend (Part II). Part III concerns with larger-scale (pilot plant) experiments conducted at the 150 kWt (150,0000 BTU/h) Combustion and Environmental Research Facility (CERF) of the National Energy Technology Laboratory (NETL). Only fouling part of the results are reported in part III. The 90:10 coal:FB blend resulted in almost twice the ash output compared to coal and ash deposits on heat exchanger tubes that were more difficult to remove than baseline coal ash deposits. The increased fouling behavior with blend is probably due to the higher ash loading and ash composition of FB.

High-energy Nd-Yag laser ignition of coals: Experimental observations

Abstract Some experiments were conducted to study the interaction of the Nd-Yag laser radiation with four different coals. All coals were ground and screened to 400 mesh and then pressed into cylindrical pellets of 3 mm diameter and 2 mm length. The coal pellets were prepared by cold pressing using a stainless-steel die to a pressure of about 500 kg/cm 2 . Laser intensities ranging from 0.5 × 10 3 to 1.5 × 10 4 W/cm 2 at 1.064 μm wavelength and a pulse duration of 5 ms were used. For laser intensities less than 800 W/cm 2 , no ignition was observed for all coals. For laser intensities above this value, two ignition mechanisms were observed: the surface ignition followed by the gas-phase ignition when Wyoming subbituminous, Indian lignite, and North Dakota lignite coals were used. For the same range of the laser intensities, however, only the gas-phase ignition was observed when Pittsburgh bituminous coal was used. It was also noted that a significant amount of the external laser radiations were absorbed by the pyrolysis products during the early stages of the ignition period. This process leads to a series of nonlinear phenomena and dictates not only the processes occurring at the coal surface but also in the gas phase.

High-pressure vertical pneumatic transport investigation☆

Abstract Vertical pneumatic transport was investigated in a 0.026 m i.d. Lucite tube at various pressures. Nitrogen was the conveying gas at pressures of 101, 790, 2170 and 4238 kPa. Pressure drop, particle velocity, pressure fluctuations and flow patterns were measured or visually observed and recorded. Choking velocity, velocity at minimum pressure drop and the particle friction factor were also investigated at these elevated pressures. Glass beads (97 and 545 μm) and coal (89 and 505 μm) were used as the conveyed solids. The use of Lucite tubing was made possible by encapsulating the entire transport system in a high-pressure containment vessel and pressurizing the outside and the inside of the transport tube simultaneously. A Zenz-type diagram of pressure drop per unit length versus superficial gas velocity was plotted at all pressures investigated. As pressure increased, the curve shifted toward a higher pressure drop at a given gas velocity. Gas velocity at minimum pressure drop thereby decreases as the pressure increases. The same trend is observed for the choking velocity. Average particle velocity of the gas—solid flow mixture approaches the superficial gas velocity at higher pressures more readily than it does at lower pressures. Investigation of the friction factors for the small particles (89 and 97 μm) at elevated pressures revealed that the friction factors due to the gas and solid were dependent on the loading of the system. Expressions were developed for predicting the frictional pressure drop for the gas and solid at low loadings for small particles. Correlations for particle velocity, choking velocity, particle friction factor and velocity at minimum pressure drop are recommended for designing dilute-phase (i.e. ϵ>0.9) high-pressure transport systems.

Flow measurement in pneumatic transport of pulverized coal

Etude experimentale des facteurs influant sur les performances de 2 debitmetres massiques de suspensions de charbon pulverise dans un gaz

Transient heating of coal particles undergoing pyrolysis

Abstract Most of the studies reported to date have viewed the coal devolatilization process as occurring isothermally throughout the coal particle, and transient processes occurring in the interior of coal particle have been largely ignored. However, in pulverized coal combustion processes involving several heating rates and several particle sizes, large temperature gradients are often produced within the coal particles that are undergoing pyrolysis. Large temperature gradients inside the coal particle result in pyrolysis of the coal particle in the following manner. The pyrolysis front first initiated at the particle surface propagates inward into the particle, leaving behind a char layer that gradually thickens as the front moves inward. The present work uses the method of line to theoretically investigate the competition between the motion of the pyrolysis front and the intraparticle heating for coal particles as it undergoes heating and pyrolysis under the effects of heating rate, particle size, particle thermal conductivity, and heat of devolatilization. Two intraparticle heating mechanisms have been identified in this study. The first is the intraparticle diffusion heating where the motion of the pyrolysis front is faster than the rise in the surface temperature but is slower than the rise in the temperature of the unreacted core. As a result, the coal particle is totally pyrolized before the surface temperature reaches its oxidation value. The second mechanism is due to the thermal wave moving with the pyrolysis front where the motion of the pyrolysis front is faster than the rise in the temperature of the unreacted core but is slower than the rise in the coal surface temperature. This may lead to a situation where the surface temperature reaches its oxidation value and only a narrow outer layer close to the surface is pyrolized.

Reduction of nitrogen oxides from post-combustion gases utilizing molecular radical species

Abstract Plasma induced radicals from ammonia, methane and hydrogen have been injected into NO laden post-combustion gases to reduce pollutant concentrations. Results of chemical kinetics modelling indicate that radicals from ammonia, which are formed by interaction with an argon plasma stream, introduced into the post-combustion gases, will provide nearly complete NO removal. Laboratory investigations have shown that molecular radical reduction is capable of providing up to 94 mol% NO reduction. Streams of ammonia or combined ammonia/methane, which provide this reduction, utilize a minimum input energy and yield no substantial ammonia discharge.

MEASUREMENT OF PARTICLE VELOCITY IN PNEUMATIC TRANSPORT OF COAL USING CROSS-CORRELATION TECHNIQUE

ABSTRACT Particle velocity has been determined experimentally in a solid-gas flow using the cross-correlation technique. Signals from two flow-monitoring devices, one based on the measurement of the dielectric constant of coal/air and the other based on the rate of static charge transfer technique, have been utilized to determine the cross-correlation function and hence the time delays between the signals. Other pertinent fluid dynamic parameters have been evaluated using experimentally determined particle velocities.

High-energy Nd:YAG laser ignition of coals

One of the main purposes of the present study is to explore the use of laser radiation to initiate and support combustion of coals. Within this context, some experiments were conducted to study the interaction of the Nd-Yag laser radiation with four different coals. Laser intensities ranging from 0.5 X 103 to 1.5 X 104 W/cm2 at 1.064 micrometers wavelength and the pulse duration of 5 ms were used. For laser intensities less than 800 W/cm2, no ignition was observed for all coals. For laser intensities above this value, two ignition mechanisms were observed: the surface ignition followed by the gas phase ignition when Wyoming subbituminous, Indian lignite and North Dakota lignite coals were used. For the same range of the laser intensities, however, only the gas phase ignition was observed when Pittsburgh bituminous coal was used. It was also noted that a significant amount of the external laser radiations were absorbed by the pyrolysis products during the early stages of the ignition period.