Australian Institute of Energy 9th Australian Coal Science Conference

SOLUTIONS FOR INDUSTRY

The proceedings CD ROM $50 can be ordered by emailing the AIE 

Greenhouse

A Potential Technology for “Zero” Greenhouse Gas Emissions from Conventional Power Plants
A-K Wong and D Zhang   Curtin University of Technology, Perth
Conventional combustion of fossil fuels for power generation contributed to a large proportion of man-made greenhouse gas (GHG) emissions.  One of the key difficulties of mitigating these emissions is separating CO2 from the flue gases (consisting mainly of N2 for sequestration
This paper discusses the feasibility of a potential technology for GHG emission control.  This technology employs conventional combustion of fossil fuels (such as coal), using oxygen as the oxidant and recycling CO2 and /or H2O form the flue gases with the aim to simplify the separation of flue gases.
Mass and energy balance analysis is performed for four cases: conventional combustion, recycling H2O only, recycling CO2 only, and recycling the whole flue gas.  Aspects addressed include combustion reactions, air/oxygen requirements and flue gases.  Preliminary analysis show recycling H2O alone is most beneficial because it is simpler, less energy consuming and cheaper to pump H2O and less sensible heat is loss through flue gases.  However, further study is needed to improved sufficient heat transfer.

Non-Combustion Sources of Greenhouse Gases
M Juniper, Brisbane
The current global trends are the increase in greenhouse gas concentrations and the associated increase in the earth’s surface temperature. Both the sources and sinks of greenhouse gases are important considerations as they effectively determine the atmospheric concentrations of the greenhouse gases. While CO2 is currently the most significant greenhouse gas, CH4 is becoming increasingly important due to its rate of increase and its physical and chemical nature. Global emissions of CH4 range from 305-775 T(1012)g CH4/yr. Wetlands are the largest source of CH4, followed by rice paddies, fossil fuels, ruminants, biomass burning, land-fill, termites and CH4 hydrates. Termites are therefore not major contributors to the CH4 emissions with estimates ranging from 10-50 Tg CH4/yr. The primary methane sink is the reaction with hydroxyl radicals within the troposphere. The amount of CO2 emitted from the combustion of fossil fuels is 5500 Tg/yr and is therefore a significant source of greenhouse gases. CH4 Therefore, CH4 has the potential for greater significance, in terms of it’s contribution to the greenhouse effect in the future.

Coal Products

Development of Coal Hydrogasification Technology
K Nomura, F Norguchi, K Katsukura The Japanese Gas Association; H Maruyama and T Ohoma NEDO, Japan
Coal Hydrogasification for producing substitute natural gas (SNG) is a promising technology in Japan to secure a stable supply of natural gas by diversifying its sources.  Under agreement with NEDO, the Japan Gas Association has completed a 5-year program in which three elemental gasifier technologies and two peripheral technologies were developed using experimental apparatus.
 
In gasification tests, a wide range of carbon conversion was verified under various conditions including two-stage reaction.  A new injector, which incorporates a tip burner to generate high temperature hydrogen, was developed through the hot model test.  The optimal internal configuration was developed to generate adequate recycle of product gas and form the two-stage reaction zone through the cold model test.  Dense phase coal conveying was verified using hydrogen under high pressure between 3 and 7 MPa, and various factors for stable discharge and cooling of char, which is residue from the hyrogasifier, was confirmed using a model particle.

Low Severity Extraction of Pitch from Coal as a Precursor to Value Added Products – Revisited
A Berkovich and C Lafferty  University of Kentucky, Lexington USA
This paper reports on the production of pitch feedstocks for value added carbon materials via mild solvent extraction of coal.  Crude anthracene oil, an inexpensive coal tar distillate was shown to extract a reasonable yield of pitch from coal under mild temperatures with no over pressure.  The effect of extraction temperature, residence times and coal to solvent ratios was investigated for a suite of coals differing in rank and sulfur content.  The extraction capability of recycled anthracene oils recovered from prior extractions was also examined.  Carbon fibers were fabricated from the derived pitches and their physical properties assessed.

Ash

Dynamic High-temperature X-ray Diffraction Analysis – A New Approach to Coal Mineral Matter High Temperature Transformation
D French, L Dale and C Matulis  CSIRO Energy Technology
X-ray diffraction has been an invaluable tool for the characterization of coal mineral matter and the capability to perform dynamic X-ray diffraction (XRD) analysis under controlled atmosphere conditions and variable heating rates to 2400oC (1600oC in oxidising atmospheres) provides a powerful new tool for the study of coal mineral matter reactions at high temperature. Used in conjunction with SIROQUANTä, a quantitative XRD package developed by CSIRO Energy Technology, quantitative abundance data can be obtained not only for the crystalline phases but also for any solid or liquid amorphous phase which may be formed.
An immediate application of high-temperature XRD is investigation of the mineral reactions that occur during coal combustion in power plant boilers which lead to the formation of slagging and fouling deposits. Examples of the application of high temperature XRD to mineral reactions relevant to pf combustion are presented with studies of a synthetic ash and ashes of a high-volatile bituminous and a medium-volatile bituminous coal

Rheology of Coal Ash in Fluidised Bed Combustion of Low Rank Coal
N Tonmukayakul and Q  Nguyen  CRC for Clean Power from Lignite University of Adelaide, Adelaide
Development of more effective technologies for utilizing low rank coals for power generation has been driven by a demand for higher efficiency, low capital costs and minimal environment impacts. Fluidised bed systems are regarded as one of the most promising alternative technologies for power generation to overcome the disadvantages of the existing pulverized coal burning power generation plants for low rank coals. However, ash deposition and bed agglomeration are potential problems in fluidised bed processing of high alkali coals. Thus, in order to gain a better understanding the mechanism of agglomeration in fluidised bed technologies, a good knowledge of the rheological behavior of coal ash deposits at high temperatures and under processing conditions is necessary. This paper presents a detailed investigation of rheological characterisation of high alkali low rank coal ashes under different operating temperatures. The rheological properties of the coal ashes were measured using the unique high temperature ash rheometer recently developed in our laboratory. The experimental results obtained will be presented the effect of the alkali content on the rheological characteristics discussed in terms of the implication of coal ash rheology on agglomeration.
 
Evaluation of the Slag Flow Characteristics of Australian Bituminous Coals in Slagging Gasifiers
J H Patterson, H J Hurst, A Quintanar CSIRO Energy Technology, Brisbane; R Boyd and H Tran Pacific Power International, Sydney
The slag viscosity and crystallisation characteristics of coal ash slags have been further examined, confirming the suitability of Australian bituminous coals for use in slagging gasifiers. Data has been obtained for the reference coals of the CRC for Black Coal Utilisation. For a slag tapping temperature of 1450oC, about half the coals examined are shown to require a limestone flux addition of <3% CaCO3 by weight of coal. However, high temperatures of critical viscosity proved more of a problem than expected, particularly for Queensland coals, increasing flux requirements at 1400oC. Limitations arising from slag crystallisation appear to be associated with SiO2/Al2O3 ratios of < 2 and iron contents > 10% FeO. Empirical viscosity models have been developed for Australian bituminous coals ash slags in the range 10-15% FeO. Relative coal value modelling has been used for economic optimisation of limestone flux addition and gasification temperature. The efficacy of coal blending has been demonstrated for reducing flux requirements and lowering the temperature of critical viscosity.

Fates and Roles of Alkali and Alkaline Earth Metal Species during Gasification of Victorian Lignite
D Mody, H Wu and C Z Li   CRC for Clean Power from Lignite, Melbourne
The transformation of alkali and alkaline earth metal (AAEM) species in a Victorian lignite during the pyrolysis and subsequent gasification in CO2 was studied in a novel quartz fluidised-bed reactor. Lignite samples prepared by physically adding NaCl and ion-exchanging Na+ and Ca++ into the lignite were used to investigate the effects of chemical forms and valency of the AAEM species in the substrate lignite on their transformation during pyrolysis and gasification.   Carboxyl-bound Na was found to be less volatile than Na present as NaCl, but more volatile than carboxyl-bound Ca, during pyrolysis at temperatures between 400°C and 900°C.  However, the carboxyl-bound Na was volatilised to a much greater extent than the carboxyl-bound Ca in the same lignite during pyrolysis.  It was seen that the loading of NaCl into the lignite did not significantly affect the char reactivity in the fluidised-bed reactor at 900°C.

Predicting Coal Ash Slag Flow Characteristics (Viscosity Model in Al2O3-CaO “FeO”-SiO2 System)
A Kondratiev and E Jak   University of Queensland, Brisbane
A model has been developed which enables the viscosities of coal ash slags to be predicted as a function of composition and temperature under reducing conditions. The model describes both completely liquid and heterogeneous, partly crystallised slags in the Al2O3-CaO-“FeO”-SiO2 system in equilibrium with metallic iron. The Urbain formalism has been modified to describe the viscosities of the liquid slag phase over the complete range of compositions and a wide range of temperatures. The computer package F*A*C*T was used to predict the proportion of solids and the composition of the remaining liquid phase. The Roscoe equation has been used to describe the effect of presence of solid suspension (slurry effect) on the viscosity. The model provides a good description of the experimental data in liquid phase, and liquid + solid mixtures, over the complete range of compositions and a wide range of temperatures. This model can now be used for viscosity predictions in industrial slag systems. Examples of the application of the new model to coal ash fluxing and blending are given in the paper.
 
Application of new FACT Database for the Prediction of melting Behavior of Coal Mineral Matter
E Jak and P Hayes   University of Queensland, Brisbane
A range of technological coal utilisation issues, including prediction of the Ash Fusion Temperatures (AFT), fluxing in IGCC, coal blending, slagging and fouling in PF combustion, are related to the melting behaviour of the coal mineral matter.  A new thermodynamic database for the system Al-Ca-Fe-O-Si has recently been developed.  This new database, in conjunction with the F*A*C*T computer package, can now be used to calculate the proportions and compositions of liquid and solid phases, liquidus temperatures and other phase equilibrium information over a wide range of compositions, temperatures and atmospheric conditions.  These predictions, examples of which are given in the paper, are important for the characterisation of melting behaviour of the coal ash slags and are applied to assist in solving a range of the related coal utilisation technological issues.
AFTs are widely used as a measure of coal ash fusibility and melting behaviour, and hence is a widely used parameter in coal marketing and utilisation. The research described in the present paper examines the relationship between measured AFTs and F*A*C*T liquidus calculations for a selected set of coals. The formation of the solid phases in these coal ashes is also examined and compared with the F*A*C*T equilibrium predictions.  A model for the AFTs predictions based on the F*A*C*T calculations is developed and applied to coal blending.

Slagging in a Pulverised-Coal-Fired Boiler
G Devir, J Pohl University of Queensland, Brisbane Australia; and R Creelman RA Creelman and Associates, Sydney
This paper describes a technique to evaluate the severity of slagging of a coal in a pulverised-coal-fired boiler. From an operator’s perspective, the performance of a coal can be gauged by the time lapsed between sootblowing cycles that allows control of furnace deposits. This translates to the time taken for the superheater metal tube surface temperature to exceed a nominal value. However, to ultimately describe the slagging performance of pulverised coals in a boiler, several descriptors of deposit behaviour need to be nominated and quantified. There is precious little data in the literature on the nature of in-situ boiler slags, their rate of growth and/or their strength properties relevant to sootblowing. The latter is thought to be of more concern to boiler operators and gives rise to the significance of selecting suitable strength tests. As well as standardised methods for characterising pulverised coal performance in a boiler, several novel and less popular techniques will be discussed in detail. A suite of three sub-bituminous coals from the Callide Coalfields, Biloela (600 kilometres north of Brisbane), has been selected for slagging tests in the 350 MWe units of Callide ‘B’ Power Station. Disposable air-cooled mild steel slagging probes have been constructed to simulate the conditions for deposit formation in the boiler region. To date, tests for one of these coals has been completed and preliminary results are presented below. Once testing for the remaining coals has been completed, it is anticipated that the differences exhibited in deposit growth and strength may be correlated with typical variations in physical and chemical properties of the pulverised coal.

The Heterogeneous Nature of Mineral Matter, Fly-Ash and Deposits
R Creelman RA Creelman  and Associates; J Pohl, G Devir and S Shi University of Queensland, Brisbane
Deposits that cannot be easily removed cost the Utility Industry several billion dollars per year in reduced capacity and maintenance. These deposits are cause by complex mineral matter transformations to fly ash and the interaction of fly ash during combustion and in the deposits. This paper reports on a series of studies looking at the heterogeneous nature of mineral matter, fly ash, and deposits and how this heterogeneity affects deposition. The data comes from Low Temperature Ashing (LTA) of coal, fly ash from boilers, and deposits from pilot scale furnaces and boilers. The paper presents optical and Scanning Electron (SEM) micrographs, Electron Micro Probe Analysis (EMPA) and Energy Dispersive X-Rays Analysis (EDXA) analysis of mineral matter, individual fly ash particles, and isolated regions of the deposits. During combustion, included mineral matter is transformed into fly ash, melts and partially adheres to the char surface, and may form agglomerated masses. Excluded mineral matter has little chance of encountering another ash particle and agglomerating in the gas phase, but can react with other particles in the wall deposits. Certain fly ash particles adhere to the wall where they can combine with other fly ash particles. Analyses of molten regions of deposits have shown, so far, three types of minerals, made of mixed minerals, to be responsible for forming difficult deposits with melting points below deposit temperatures which range from 1200-1350. These compounds are iron cordierite (2FeO-2Al2O3-5SiO2) with melting points around 1100-1300 C, Juniper, et al (1993); albite (Na2O-Al2O3-6SiO2) and its silica undersaturated equivalent nepheline (Na2O-Al2O3-2SiO2) with melting points around 850 - 1100 C Su (1999), anorthite (CaO-Al2O3-2SiO2) with melting points around 1300-1400 C Pollman (1967), and compounds with ratios of CaO/P2O5 of 2.3-2.5 and melting points around 1300 C, Su (1999).

FB Systems

Distribution of Pyrolysis Products from a Set of Ion-exchanged Victorian Lignite Samples at Elevated Pressures
C Sathe and CZ Li CRC  for Clean Power from Lignite, Melbourne
A set of ion-exchanged samples prepared from Loy Yang lignite were pyrolysed in a wire-mesh reactor at elevated pressures from 1 to 61 bars. The char yields from all the samples did not show considerable sensitivities to changes in pressure at the heating rate of 1000 K s-1. The sensitivities of the tar yields to changes in heating rate and pressure were dependent of the ion-exchanged form of the sample. Analysis of the tar samples showed that the release of larger aromatic ring systems (3 or more fused rings) was greatly affected by increases in pressure for the raw lignite sample. The yields of the larger aromatic ring systems from the Ca-form and Na-form samples were lower than those from the raw lignite sample and were not significantly affected by pressure. The effects of pressure on the pyrolysis product distribution are thought to be mainly due to the changes in the transportation of volatile precursors with pressure.

Combustion

Combustion Mechanism of Single Non-porous Carbon Sphere
J. Chen, J. Pohl, V. Rudolph University of Queensland, Brisbane Australia; and D Harris CSIRO, Brisbane
This paper describes the measurements of the combustion rates of single carbon spheres. Carbon spheres, 100 mm in size, are heated in air by a laser to 1500 ~ 2000 K with a heating rate of 104 K/s. The surface temperature and weight loss of the carbon spheres are measured simultaneously during combustion. The change of particle size was recorded by two video cameras, which viewed the burning particle from two different directions. These measurements show that the combustion reaction at these conditions is controlled by the combination of diffusional and kinetic rate (regime II). Particle-to-particle variation of combustion rates could result partly from differences in the porous microstructure of each individual particle and partly from the change of combustion mode throughout the burn-off process. As reaction proceeds, the combustion rates first increases and seems to reach its maximum at around 50-60% burn-off and then decreases at higher burn-off levels. Initial results on individual coal maceral combustion rates are also presented in this paper.

Reactivity of Chars Prepared from the Pyrolysis and Gasification of Loy Yang Lignite under a Wide range of Conditions
H Wu, D Mody, C Li CRC for Clean Power from Lignite, Melbourne; J Hayashi and T Chiba,  Hokkaido University, Japan
A Loy Yang lignite sample was pyrolysed under a wide range of experimental conditions using a wire-mesh reactor, a fluidised-bed reactor, a drop-tube reformer and a thermogravimetric analyser (TGA). The reactivity of these char samples in CO2 and air was measured in the TGA as well as in the fluidised-bed reactor. A sample prepared by the physical impregnation of NaCl into the lignite was also used in order to investigate the effect of NaCl in the lignite on the reactivity of the resulting char. Our experimental results indicate that, due to the volatilisation of a substantial fraction of Na in the lignite substrate during pyrolysis, the true catalytic activity of the Na in the lignite substrate should be evaluated by measuring the sodium content in the char after pyrolysis. The char reactivity measured in situ in the fluidised-bed reactor was compared with that of the same char measured separately in the TGA after re-heating the char sample to the same temperature as that in the fluidised-bed. It was found that the re-heating of the char in the TGA reduced the char reactivity.
 
 

The Effect of Operations Conditions and Coal Type on Char Reactivity and Morphology during Combustion in a Drop Tube Furnace
R. Barranco, M Cloke and E Lester, University of Nottingham UK
Three coals from Colombia were chosen for a series of experiments using a Drop Tube Furnace (DTF). The research was undertaken to investigate possible effects of the operating temperature, particle size and coal type on char characteristics during combustion. The DTF is capable of reproducing high heating rates, high reaction temperature and the oxygen level can be regulated to simulate atmospheres similar to those found during combustion in full scale boilers. The coals were characterised using standard methods and image analysis techniques. The changes in the characteristics of the char produced were assessed using a number of different techniques including intrinsic reactivity analysis and automatic char test by image analysis.
The results showed that the operating temperature has a substantial effect on the intrinsic reactivity of the char. There is also a contribution of the particle size but this was found to be statistically significant only for one of the coals. It is clear from the results that standard characterisation techniques make poor combustion predictors. Conversely, a reactivity parameter, derived from a grey-scale histogram obtained by image analysis of the coal, provides an important parameter to predict coal combustion behaviour. This reactivity index is based on the premise that coal material which exhibits the highest reflectance is slowest to burn. On the other hand, char morphology and intrinsic reactivity play an important role when assessing coal combustion performance. Finally it may be concluded form the results that the Colombian coals used in this study burn cleanly and efficiently and therefore, they are good for combustion purposes.

Determining Coal Reactivity Parameters at Elevated Pressures using Bench-Scale Techniques
M  Kelly, D Roberts, C  Mill, D Harris, CSIRO Energy Technology, Brisbane; J  Stubington, University of NSW, Sydney; Y Otake University of Queensland, Brisbane; and T Wall, University of Newcastle, Newcastle
International interest in Australian coals for use in gasification applications is set to rise.  Already there are several coal-fired IGCC demonstration plants overseas and the use of these technologies is expected to increase, particularly in Asia and Europe.  Performance data for coals under the extreme conditions found in pressurised gasification technologies are difficult to obtain.  Fundamental coal reactivity parameters, such as volatile yield and char reactivity, need to be measured under conditions that are relevant to enable them to be successfully implemented into predictive gasification models.
 
This paper describes a bench scale technique that can be used to measure volatile yield and intrinsic char reactivity data for coals in high-pressure environments containing O2, CO2 and H2O. Coal volatile yield under fast heating rates and high pressures is determined using a wire-mesh reactor, and the intrinsic reactivity of the resulting chars at high pressure is determined using a pressurised thermogravimetric analyser.  The application of these techniques is demonstrated through the determination of volatile yield and char reactivity data at increased pressures for a suite of Australian export thermal coals.  This demonstrates the usefulness of the method as a tool for coal assessment for use in advanced utilisation technologies.

Intrinsic Gasification Kinetics at Increased Pressure: the Applications of the nth Order Rate Equation
D Roberts, D Harris  CSIRO Energy Technology, Brisbane;  and T Wall University of Newcastle, Newcastle
Pressurised char gasification models used for coal assessment and gasifier design require the input of reliable intrinsic kinetic data.  It is suggested in the literature that the nth order rate equation (that has been used extensively at atmospheric pressure) is not suitable for describing such data over a wide range of pressures.  However, there is no comprehensive analysis of char reactivity at increased pressures and low temperatures which can be used to clarify this suggestion.  Consequently, pressurised char gasification models use rate equations based on accepted reaction mechanisms.  Whilst this is a fundamentally correct approach, such expressions are complicated, poorly-quantified and difficult to apply to different coals.
 
This paper summarises the results of a wider study into the intrinsic reactivity of coal chars to O2, CO2 and H2O at pressures of 1–30 atm.  It was found that the nth order rate equation is applicable to the char–O2 reaction for pressures up to (at least) 16 atm.  For char–CO2 and char–H2O reactions, however, the reaction order (n) was found to decrease with pressure such that at above approximately 30 atm it was almost zero—consequently the nth order equation was not suitable.  The CO2 and H2O results were analysed using a TPD technique, which estimated the relative number of surface complexes on the char as a function of reaction pressure.  These results were used to model a reaction order that decreased with pressure.  This effect was incorporated into the nth order rate equation to improve its predictive capabilities over a range of pressures, and therefore simplify the incorporation of kinetic data into char gasification models.

NOx Emissions

Utility Boiler Computer Modeling Experience in the USA for Practical Furnace Air port and Low NOx Burner Field Design
B Breen ESA Pittsburgh PA USA; J Urinch ESA Pittsburgh PA USA; and B Krippene BCK  of North America Inc, USA
Practical field experience with low NOx combustion systems and equipment on existing coal-fired utility boilers has presented significant engineering challenges to the designer. Many of these boiler units have required extremely imaginative or "high tech" engineered solutions in order to accomplish the necessary field design modifications for successful NOx emissions control at minimum impact and cost to the operator. Many of these challenging units have been investigated for optimum low NOx combustion system design through the use of computer modeling.
 
One example of these engineering challenges is how to minimize the emissions of both NOx and carbon monoxide while maintaining design or lower excess combustion air levels leaving the boiler unit and simultaneously minimizing the unburned carbon content or carbon loss in the ash. With some coals, this is not a problem because the coals are fairly porous, very reactive and will burn out in almost any furnace. With other coals the low NOx burner and furnace combustion air injection port settings, as optimized to achieve acceptable carbon monoxide emissions and carbon levels in the boiler ash, often compromise the boiler unit’s true potential for NOx emissions reduction.
 
These "hard-to-burn" or un-reactive coals, therefore, need to utilize all of the available furnace volume in a very effective manner. Computer simulations lead to a better understanding of practical combustion air addition and/or air injection profiles which help to maintain good combustion through efficient burnout while minimizing NOx formation.
A second example for engineering challenge is where very low NOx emissions leaving the boiler unit are required to be achieved by way of deep air-staging of the boiler-furnace burner zone area. This results in the potential for heavy flame impingement and reducing conditions on the lower furnace pressure part enclosures with a corresponding increase in furnace slagging and corrosion of the pressure parts. This is especially a problem on the higher pressure and temperature – more thermally efficient boiler units which, because of their higher use or capacity factors, are also required to be in-service more of the time. This requirement for higher boiler unit availabilities and reliabilities
creates an incentive for both the boiler operator and the system designer to investigate design changes in the low NOx burner and air port configurations which will minimize reducing environment type flame impingement on the furnace walls. Math modeling investigations not only of operating equipment settings or adjustments but also of moving or re-sizing burner and air port configurations often leads to the most practical low NOx combustion system applications.
 
Other practical investigations include the computer modeling of Fuel Lean Gas Reburn for NOx reduction in the upper furnace as well as the effect of primary air on burner settings and adjustments for minimum NOx when coal heating value or moisture content changes. This paper presents several examples of where effective furnace and low NOx burner modeling has produced substantial advantages to the low NOx combustion system designer. Using practical boiler furnace air injection port and low NOx burner math modeling as an integral part of the design process has often made the difference between a successful low NOx combustion system field conversion project and an unsuccessful one.

Formation of HCN and NH3 during the Pyrolysis and Gasification of Coal and Biomass
Z Xie, W Zhao, J  Feng and C Li, Monash University, Melbourne; K Pratt, Swinburne University of Technology, Melbourne; and K Xie Taiyuan University of Technology, China
A small set of rank-ordered Chinese (the Northern Hemisphere) and Australian (the Southern Hemisphere) coal samples were pyrolysed in Ar and gasified in CO2. A pair of Chinese and Australian coals of identical carbon content but very different petrographic composition behaved very differently in terms of the formation of HCN and NH3 during pyrolysis. The use of CO2 instead of Ar was seen to drastically affect the formation of NOx precursors at 800°C.  The exact effects of CO2 depend on the rank of the original coal substrate as well as the freshness of the char while it is held at high temperature. Reaction mechanisms leading to the formation of HCN and NH3 during pyrolysis and gasification are discussed.

Influence of Volatile Matter on NOx Emissions Behavior of Pulverized Coals and Blends
S Pisupati  Pennsylvania State University, USA
Coal properties are known to affect NOx emissions, ash behavior in the furnace and unburnt carbon loss.  Volatile matter content is the most important coal property that affect NOx emissions.  The objective of this study was to determine the influence of volatile matter content of coals and coal blends on NOx emissions.  NOx emissions are a strong function of temperature in the flame zone and the operation conditions (ie air staging, burner configurations etc).  The study used six coals with volatile matter content ranging from 19 to 36%, and two coal blends simulating the volatile matter content of tow medium volatile coals.  This study was conducted in 1,000 lb steam/h water-tube research boiler located at the Energy Institute of The Pennsylvania State University.  The study employed two burner configurations (a high swirl and a low swirl).  Most of the combustion air was admitted in three stages (zones) near the burner
 
The results showed that for all the coals and blends tested, air staging by increasing the percentage of air admitted down stream from the coal nozzle, the NOx emissions decreased.  Even at both extreme conditions (i.e. without any air staging and with maximum possible air staging) in the study, a guner4al trend of lower NOx emissions with increasing volatile matter content was observed.  The NOx emissions ranged from 0.79 to 1.15 lb/MMBtu with no air staging, and . 0.54 to 0.74 lb/MMBtu with maximum air staging for the low swirl burner configuration.  The NOx emissions ranged from 1.1 to 1.25 lb/MMBtu with no air staging and 0.6 to0 0.84 lb/MMBtu with maximum air swirl tested for the high swirl burner configuration

Measurements of Nitrogen Species, Evolutions and Reaction in Coal-fired Utility Boiler Flames
A Williams, J Pohl, B Stanmore, D Szczepanski, University of Queensland Brisbane; S Visona Sigma Process Solutions, Brisbane
CFD modelling may become a valuable tool for prediction of nitric oxide emissions in power stations around the world. Verification of these codes is an important step to determining their usefulness, accuracy and applicability to designing and optimising industrial boilers. Currently there is a lack of data in the mainstream literature of gas species concentrations, and char properties measured in an industrial sized, coal fired utility boiler. This paper aims to present measurements suitable for CFD code verification and to examine the assumptions made about the evolution and reaction of nitrogen species within an opposed-fired, pulverized coal-fired boiler. The assumptions discussed include whether
· nitrogen evolution from char is proportional to char burnout, and
· the importance of NH3, HNCO and HCN as NO precursors.
A water-cooled probe was used to collect gas and char samples within the flame region of a coal-fired boiler. Gas species concentrations were determined on site by FTIR spectroscopy and conventional measurements. Char samples were collected and analysed off site. The data collected suggested that the nitrogen evolution is proportional to coal burnout although an accurate estimate of the proportionality constant could not be determined. An estimate of this value found was 1.2. The role of HNCO and NH3 in the formation of NO was found to be small at the power stations tested, however only bituminous coals were tested.

Utilization of Advanced Low NOx Burner for Pulverized Coal
H Makino, H Tsuji and M Kimoto, Yokosuka Research Laboratory Japan
T Hoshino and T Kig, Harima Heavy Industries Co., Ltd Japan
Y Otake  The University of Queensland Brisbane
The advanced low NOx burner for pulverized coal combustion, which can reduce both NOx concentration and unburned carbon in fly ash, was applied to an industrial boiler. Highly-intensified internal recirculation zone, which accelerates the early stage of thermal decomposition of coal and thus reduces carbon content in char, was formed in the flame generated by this advanced burner. The burner has been developed with the following procedure. The influence of the burner configuration on formation of the internal recirculation zone was investigated by cold flow tests. Combustion tests were, then, conducted with two sizes of test furnace (coal feed rate; 0.1 and 1.5 t/h) in order to evaluate the influence of burner operating conditions on the emission of NOx and unburned carbon in fly ash. The scale-up effect was also investigated in these combustion tests. For the purpose of a practical application, sixteen advanced low NOx burners were installed to an industrial boiler and an Australian coal was fired. Fuel ratio of the coal was 1.5 and ash content was approximately 10%. NOx concentration and unburned carbon in fly ash were measured under various boiler operating conditions. NOx concentration with the burner decreased to about half compared that with a conventional low NOx burner when unburned carbon in fly ash with the advanced burner was the same as that with the conventional burner.

Gas-Diesel (Dual-fuel) Modeling in Diesel Engine Environment
A Bounif, A Aris and C Mansour  University des Sciences et de la Technologie Algerie
The aim of this paper is to investigate the emission and performance characteristics of a commercial diesel engine (Deutz FL8 413F) being operated on natural gas with pilot diesel ignition. A computer program has been developed to model the experimental data using a chemical kinetic reaction mechanism of the Gas-Diesel (Dual-fuel) combustion. A detailed chemical kinetic reaction mechanism of natural gas oxidation and NOx reduction was used to predict the main combustion characteristics temperature, pressure and species concentrations) under the conditions of this study. The following sections include a description of the experimental facilities, discussion of numerical simulation and engine test results. The performance in terms of accuracy of the networks is assessed by comparison with the experiments. A reasonably good prediction of performance and emission was obtained by computation covering the whole range of the engine operating conditions. It can be summarized that the results of this study are satisfactory.

NOx Predictions
P Bennett, Energy Tactics, Brisbane
Coal properties, such as volatile and nitrogen content, influence NOx emissions but there is no simple relationship between these coal properties and NOx emissions that fits all operational power plant. To help in the understanding of the interactions that occur during NOx formation several empirical models (fitting an arbitrary equation to data), simple reaction engineering models (combinations of CSTR and PFR react ors) using simplified chemical kinetics and complex computational fluid dynamics (CFD) models for the prediction of NOx emissions have been developed by organisat ions aro und the world. All methods have their limitat ions and advantages.
In a recent ACARP project 1 several models were formulated, these were:
• Reaction Engineering Model - used to model NOx formation in a pilot scale furnace,
• Empirical Model (coal properties) - used to show the influence of coal properties on NOx formation in a pilot scale furnace, and
• Empirical Model (power plant) - used to show the influence of power plant operation on NOx formation.

Coal Blends  Bio Mass

Progress in Developing Indices for Predicting Combustion Behavior and Ash Deposition of Coals and Blends in Power Station Boilers
S Su CSIRO, Brisbane; J Pohl University of Queensland, Brisbane; D Holcombe ACRIL, Ipswich and J Hart CRC for Black Coal Utilisation, Newcastle
This paper reports the results of examining the validity of the existing indices for predicting the performance of coals and blends in utility boilers, and proposes a new index.
 
The examination of existing indices for predicting ignition, flame stability and burnout was based on the pilot-scale test data from two furnaces on 68 coals and blends. These coals and blends had a mean vitrinite reflectance between 0.25 and 1.63. The results showed that the volatile matter content can be used as an index of ignition and flame
stability. The mean vitrinite reflectance and the fuel ratio can predict the burnout. The new Maceral Index,developed by Su (1999), correlates burnout with R2=0.81-0.98, and has potential for correlating ignition and flame stability with R2=0.34-0.77.
 
Nine slagging indices and five fouling indices were examined based on pilot-scale test data on 25 coals and blends. All slagging indices, except the %Fe2O3/%CaO ratio, were unable to rank the slagging propensities for the coals and blends tested. It was found that the %Fe2O3/%CaO ratio correlates the slagging propensity with R2=0.52-0.79 for the test data. The worst slagging occurs when the ratio approaches 1.
 
Five fouling indices were tried to correlate the ratio, FGET/IDT (ox.) (flue gas exit temperature/initial deformation temperature in an oxidizing atmosphere) when tests are conducted at the same firing rate. The five fouling indices are Na2O (g/GJ), R2= 0.65-0.90 > (%Na2O+0.6589%K2O)(%ash(db)/100), R2=0.52-0.59 > (1/Q)Yash(YK2O+YNa2O), R2=0.38-0.66 > %Na2O in ash, R2=0.38-0.66 > (B/A)% Na2O, no correlation.  In addition, FGET correlates fouling deposit growth rate with R2=0.71.

Investigations into the Effects of Moisture Loss and Coal Blending on Hardgrove Grindability Index (HGI)
HB Vuthaluru, HM Yan, DK Zhang  Curtin University of Technology, Perth and J Brooke, Westfarmers Coal Limited, Perth
Investigations into the effects of moisture and coal blending on Hardgrove Grindability Index (HGI) were carried out on Collie coal of Western Australia. Experiments were conducted in a standard Hardgrove apparatus in two stages comprising three Premier seam coals  (namely P2, P4 and Hebe) and several      blends (namely Hebe/P2, Hebe/P4, Hebe/P2/P4) prepared at various blending ratios. Stage 1 experiments comprised of five days of air-drying followed by oven drying. Stage 2 experiments followed the procedure of overnight air drying with 2 and 4 hours oven drying at 40°C on successive days.
 
Among the coal seams tested in Stage 1, Hebe showed the highest HGI (58) whereas P4 was the lowest (46). Stage 2 experiments, however, showed much lower values of HGI with the new batch of Hebe samples collected from the same pit. HGI was found to correlate well with residual moisture in both stages of experiments, with correlation coefficients ranging from 0.5-0.9 depending on the type of coal seam or blend. In contrast, moisture measurements on HGI samples (0.6-1.8 mm fraction) showed erratic trends with HGI. Both Stage 1 and Stage 2 experimental results suggest that no relationship exist between HGI sample moisture and HGI. Blending showed the positive effect on both binary (P2/Hebe and P4/Hebe) and ternary (P2/P4/Hebe) blends with HGI values shifting towards those of Hebe seam (ranged 48-55). However, the effects of blending and blending ratio on HGI were not evident in Stage 2 experiments mainly due to closely spaced HGI values of coal seams. Measured HGI values of binary and ternary blends in Stage 1 and Stage experiments were found to correspond well with the weighted average values of HGI within + 2 HGI units.
 
Extension of the Operating Regime of Utility Boiler
B Singh Sigma  Process Solutions, Brisbane
The operating regime of a utility boiler is controlled by the number of burners in service and the turn down ratio of the burner. The number of burners is services varies, in steps, by a fixed number (4 or more) depending on the design of the pulveriser and the size of the boiler. The need to change in the number of burners to meet the varying demand is a costly operation and makes the unit inflexible during this period. This paper presents the results of trials in extending the operating range of a burner by controlling the size distribution of the pulverised fuel from almost micronised to normal range. Trials conducted at Swanbank B Power Station show that the lower operating output of a 120 MW boiler can be extended from 75 to 40 MW.

Thermochemical Recuperative Hydrogen Production from Brown Coal
C Fushimi, M Goto and A Tsutsumi University of Tokyo, Japan; J Hyashi and T Chiba University of Hokkaido, Japan
In this study, the fundamental research on the reactivity of Australian brown coal with the steam reforming gasifications was conducted at the heating rate of 100K/s by using a thermogravimetric reactor.  The pyrolysis (thermal decomposition) finished only 10-15 s and the steam gasifications reaction completed in very short time.  About 70-80% of coal energy was converted into hydrogen by the steam reforming

Co-firing of Bark and Industrial Coals on a Stoker Fired Combustion System
A Clemens, D Gong  CRL Energy Ltd New Zealand;  and J Gifford  Forrest Research New Zealand
Addition of biomass (a low sulphur and CO2 neutral fuel) to the fuel mix at coal-fired plant has potential benefits including reduced SO2 and CO2 emissions.  However before using biomass in existing coal plant an assessment of the performance of coal/biomass mixtures is needed to understand and minimise operational problems and optimise the properties of the fuel blend.
 
To evaluate the performance of coal/biomass mixtures, co-firing of mixtures (92.5/7.5, 85/15 and 77.5/22.5) by calorific value was undertaken on a laboratory scale (50 kW) combustion rig with a stoker firing system.  The biomass was a bark sourced from debarking operations at a saw-mill.  Samples of a typical New Zealand sub-bituminous industrial coal from the Waikato region were used.
 
Combustion performance of the mixtures varied considerably from that of the sub-bituminous coal samples alone.  In all cases there were reductions in SO2 emissions – in some instances greater than that expected solely on the grounds of reduced sulphur content in the biomass.  In some cases increased rates of fouling deposition and slag formation were observed – in some instances decreased fouling deposition rates were decreased. A study of the complex ash chemical changes accompanying combustion was undertaken and the key factors responsible for these behaviours was identified.

Themochemical Recuperative Coal Gasification Combined Cycle using Brown Coal
A Tsutsumi University of Tokyo, Japan; S Bhattacharya CRC for Clean Power from Lignite, Melbourne; J Hayshi and TY Chiba Hokkaido University, Japan
A thermochemical recuperative coal gasification combined cycle (TGCC) has been proposed based on a variation of the integrated gasification combined cycle (IGCC) for the power generation. The cycle uses an oxygen-blown fluidised bed for gasification and a shift-reactor to maximise the production of hydrogen and carbon dioxide.

Thermochemical recuperation can be considered to be energy recycling as a chemical heat pump which upgrades heat at low temperature (such as gas turbine exhaust from  combined cycle) by supplying heat and reactants for endothermic reactions, where subsequently the accumulated energy is released at a higher temperature level during combustion of the combustible gas. In this cycle, part of the gas turbine exhaust gas, is used to heat oxygen and produce steam, both of which are used as reactant in the gasifier, steam only in the shift reactor. Thermal energy held by the exhaust gas is effectively utilised to produce chemical energy of the reformed products, largely H2.and CO2, and to a minor extent CO and CH4. The cycle is expected to be suitable for use with low-rank coals, which have significant proportion of catalytic metallic species, Ca, Na, Mg, and Fe that enhance gasification.
 
This study is part of a collaborative project between researchers in Japan and Australia, and is funded by the New Energy Development Organisation (NEDO) of Japan. This paper briefly discusses the background of the project, and presents results of preliminary simulation of the proposed cycle using commercially available simulation packages. The paper also identifies the areas where scientific research and technical advances are required. A brief discussion is made on the relevant scientific research addressed by various sub- projects.