Coal Streams Research Articles

Experimental study on the effects of ammonia cofiring ratio and injection mode on the NOx emission characteristics of ammonia-coal cofiring

Ammonia (NH3) cofiring is a promising approach to reduce the CO2 emissions from coal-fired power plants. However, the potential drastic increase of NOx emissions may inhibit the wide implementation of NH3 cofiring. To explore the potential NOx control strategies, the effects of NH3 cofiring ratio (RNH3), NH3 injection mode and overfire air (OFA) rates on the NOx emission characteristics of NH3/coal cofiring are studied in a test furnace that allow for flexible control of the injection positions and combustion environment of NH3. The results show that when NH3 is injected with coal stream (top mixing mode), the NOx emissions increase and then decrease with the increase of RNH3 under all OFA rates. However, when NH3 is fed through the side port of furnace separately (side mixing mode), the NOx emissions exhibit distinct trends under different OFA rates. Under lower OFA rates, the NOx emissions show monotonical decrease with the increase of RNH3, while under higher OFA rates the NOx emissions first decrease and then increase with the increase of RNH3. Consequently, higher OFA rates could produce higher NOx emissions than lower OFA rates. This indicates that air-staging is not always effective in the NOx reduction of NH3 cofiring. Thus, although the side mixing mode of NH3 cofiring exhibits overall better performance in NOx control, caution is needed to accommodate the OFA rate with NH3 cofiring ratio. Although a variety of trends of NOx emissions were observed in this study, the results demonstrate that all these trends are in fact governed by the same mechanism – the competition between the NO-formation and NO-reduction reactions of NH3 in the varying O2 environment in the furnace. By creating appropriate O2 environment in the furnace, the NOx emissions of NH3/coal cofiring could be substantially lower than that of pure coal combustion. The findings of these paper are instrumental in the design and operation of NH3 cofiring system in full scale coal-fired boilers to achieve effective NOx control.

Методичний підхід до обґрунтування способу газифікації кам’яного вугілля для виробництва синтетичних моторних палив

The aim of the article is to substantiate the most suitable method of gasification of Ukrainian hard coal for further production of synthetic motor fuel. For this substantiation, a methodical approach has been developed, the use of which has allowed to obtain the following results. As a raw material base, the article recommends long-flame coal of the Western Donbass, located on the territory of the Dnepropetrovsk region, where powerful enterprises for the extraction and enrichment of coal operate. The most common methods of coal gasification in the world are analyzed: Lurgi (counter-current steam-oxygen gasification of large-lump coal (or briquettes) in a stationary bed), Siemens (direct-flow steam-oxygen gasification in the pulverized coal stream), Texaco (direct-flow oxygen gasification in the flow of coal-water pulp). For each of these methods, material balances have been developed; the composition and quality of the generated gas, the possibilities of organizing the production of the necessary energy resources, the level of emissions of harmful substances into the atmosphere and wastewater discharge have been evaluated. A methodology for calculating the composition of generator gas is proposed, which takes into account the composition of the blast (content of oxygen, water vapor or water). All calculations were performed for an enterprise with a coal capacity of 550 thousand tons of working weight per year. Based on the calculations and comparison of their results, the Texaco method is recommended for industrial implementation. The advantages of this method are as follows: the absence of a stage of steam production for gasification, the scarcity of the water cycle, which practically excludes the formation of wastewater, and the possibility of using contaminated water from other sources for gasification; the highest total content of hydrogen and carbon monoxide in the resulting synthesis gas; the maximum assimilated capacity of production reactors and the largest number of capacities created in the world using this technology; utilization of the heat of the resulting gas to obtain a large amount of electric and thermal energy.

Техніко-економічна оцінка різних способів газифікації бурого вугілля для виробництва синтетичного моторного палива

The aim of the article is to assess the feasibility of organizing the production of synthesis gas from brown coal, the reserves of which in Ukraine are sufficient. As a raw material base, the article considers the coal of the Novo-Dmytrivske deposit, which is located on the territory of the Kharkiv region. The balance reserves of brown coal in categories A + B amount to 284.4 million tons and in category C1 – to 95.6 million tons, that is, a total of 380 million tons. The average technical analysis data for the deposit are as follows: moisture per working weight is 51.2%; ash content per dry weight is 19.4%; the total sulfur content is 2.45%. The elemental composition of the coal of this deposit is characterized by the following data: carbon – 68.0%, hydrogen – 6.0%, oxygen – 23.0%, sulfur, nitrogen and other elements – 3.0%. To achieve the goal, the properties of coal of this deposit have been examined and the following technologies of coal gasification have been analyzed: Lurgi process (counter-current steam-oxygen gasification of coarse coal (or briquettes) in a stationary bed); Prenflo process (direct-flow steam-oxygen gasification in a pulverized coal stream); Texaco process (direct-flow oxygen gasification in a coal-water pulp stream). For each of these processes, material balances have been developed; the quality of gas synthesis, the possibility of organizing the production of the necessary energy resources, the level of emissions of harmful substances into the atmosphere, and the main technical and economic indicators have been evaluated. The calculations were made for an enterprise with a coal capacity of 9 million tons of actual weight per year. Based on the calculations made, the Lurgi process is recommended for industrial implementation. The advantages of this process are: the lowest temperature and pressure of the gasification process; a wider range of products obtained during gasification; almost optimal syngas composition in terms of H2 : CO ratio; the lowest emissions of carbon dioxide generated during coal gasification and preparation of synthesis gas for further use; the lowest production cost of prepared synthesis gas; the lowest specific capital investments (per 1 thousand m3 of prepared synthesis gas). The inexpediency of using the Texaco process for the gasification of brown coal is substantiated, as well as the directions for improving the Prenflo process for its further use in the gasification of brown coal of the Novo-Dmytrivske deposit are determined.

Retrofit of a 600 MW Down-Fired Pulverized-Coal Furnace for Low NOx Emission

Aiming at solving the problem of high NOx emissions of a down-fired boiler, a new combustion system has been proposed by means of the numerical simulation using Ansys Fluent. The coal-lean stream (tertiary air), which was originally mixed with a separated overfired air (SOFA) stream on the front and rear walls of the upper furnace, was relocated to the lower zone of the furnace after retrofit. The secondary-air slots were transformed into a new annular port type, which was injected into the furnace with a down-tilt angle to increase the residence time of the coal stream. Furthermore, the effect of secondary air distribution and velocity of coal stream on performance was studied. After retrofitting the combustion system, the NO emissions were effectively controlled, decreasing from 906 mg Nm−3 to 576 mg Nm−3, but the carbon content of fly ash increased from 2.46% to 5.78%. Aiming at decreasing the carbon content of fly ash, the effect of coal/primary air velocity on the arch was studied. Less carbon content in fly ash can be observed for the lower arch airflow velocity. The results showed that the NO emissions can be controlled below 595 mg Nm−3, and the carbon content of fly ash was reduced to 3.39% when the velocity was decreased to 18 m s−1.

Cooperative Carbon Dioxide Capture in Diamine-Appended Magnesium-Olsalazine Frameworks.

Diamine-appended Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) metal-organic frameworks have emerged as promising candidates for carbon capture owing to their exceptional CO2 selectivities, high separation capacities, and step-shaped adsorption profiles, which arise from a unique cooperative adsorption mechanism resulting in the formation of ammonium carbamate chains. Materials appended with primary,secondary-diamines featuring bulky substituents, in particular, exhibit excellent stabilities and CO2 adsorption properties. However, these frameworks display double-step adsorption behavior arising from steric repulsion between ammonium carbamates, which ultimately results in increased regeneration energies. Herein, we report frameworks of the type diamine-Mg2(olz) (olz4- = (E)-5,5'-(diazene-1,2-diyl)bis(2-oxidobenzoate)) that feature diverse diamines with bulky substituents and display desirable single-step CO2 adsorption across a wide range of pressures and temperatures. Analysis of CO2 adsorption data reveals that the basicity of the pore-dwelling amine─in addition to its steric bulk─is an important factor influencing adsorption step pressure; furthermore, the amine steric bulk is found to be inversely correlated with the degree of cooperativity in CO2 uptake. One material, ee-2-Mg2(olz) (ee-2 = N,N-diethylethylenediamine), adsorbs >90% of the CO2 from a simulated coal flue stream and exhibits exceptional thermal and oxidative stability over the course of extensive adsorption/desorption cycling, placing it among top-performing adsorbents to date for CO2 capture from a coal flue gas. Spectroscopic characterization and van der Waals-corrected density functional theory calculations indicate that diamine-Mg2(olz) materials capture CO2 via the formation of ammonium carbamate chains. These results point more broadly to the opportunity for fundamentally advancing materials in this class through judicious design.

Application of plasma burners for char combustion in a pulverized coal-fired (PC) boiler – Experimental and numerical analysis

This study considers the combustion of pulverized coal with unburned char recovered from ash of the industrial boiler. The concept of char combustion with coal is implemented by installing two plasma burners on the front wall of the combustion chamber. The main objective is to improve the boiler's efficiency by reducing the amount of unburned fuel. The behavior of the combustion process is investigated using CFD modeling of the combustion chamber with tangentially-fired burners and two plasma burners. Thermogravimetric analysis and laboratory-scale tests in a drop tube furnace are performed to obtain the combustion characteristics of the investigated char and, eventually, to assess the validity of co-firing with coal the unburned char. The CFD simulation of the non-retrofitted boiler with twelve pulverized-fired burners results in the excessive movement of coal particle streams toward the chamber walls outside of the designed swirl diameter caused by a high centrifugal force, thereby contributing to a decreased level of fuel burnout. The CFD results with plasma burners indicated that the swirl diameter is reduced improving the degree of mixing resulting in a more uniform temperature and velocity distributions. The average temperature at the combustion chamber outlet increases by approximately 40 °Creaching 1260 °C.

Effect of the primary oxidizer stream jet velocities on the ignition and combustion characteristics of pulverized coal under MILD oxy-coal combustion conditions

MILD oxy-coal combustion technology is a prospective technology with the potential for CO2 capture and storage, and it is characterized by the intense flue gas recirculation to preheat the fuel and to dilute the oxidizer due to the oxidizer or fuel jet with high velocity. The effect of the primary oxidizer stream jet velocities ranging from 1.7 m/s to 11.2 m/s on the coal ignition and combustion characteristics were experimentally investigated on a flat flame pulverized coal burner at various oxygen concentrations of 5%-21% and gas temperatures of 1473–1873 K under O2/CO2 and O2/N2 atmospheres. The coal flame images were recorded by the digital camera, and the flame structure evolution and ignition delay times of coal particles were analyzed at different primary oxidizer stream jet velocities and hot coflow conditions. The coal combustion radiation spectrum was monitored by an optical fiber spectrometer and the coal particle temperatures were derived with the two-color pyrometry. The results showed that the bright yellow soot flame gradually disappeared with the decrease of O2 concentration when CO2 replaced N2. The difference of ignition delay times between O2/CO2 atmosphere and O2/N2 atmosphere decreased from 2.8 ms to 0.2 ms when the primary air jet velocity increased from 1.7 m/s to 11.2 m/s at 1473 K and 5% O2. This meant the elevated jet velocity was beneficial to offset the delayed effect of the physicochemical properties of CO2 on coal ignition. The peak coal particle temperature increased by 68 K at 1873 K and 5% O2 under O2/CO2 atmosphere with the highest jet velocity owing to the accelerated diffusion of O2 into coal particle stream. Moreover, a dimensionless coal particle temperature parameter η was proposed to characterize the variation of the peak coal particle temperature caused by the improved heat transfer and mass transport between the coflow and coal particles under high jet velocity. The maximum value of η was 1.053 at 1873 K and 21% O2 under O2/CO2 atmosphere with the jet velocity of 11.2 m/s, indicating the increased jet velocity had the predominant effect on the increase of peak particle temperature at high gas temperature and O2 concentration.

Behavior of Cr during coal combustion: An overview

The paper overviews all essential aspects related to Cr behavior during coal combustion and was written with the aim of mitigating its negative impact on human health and surrounding environment. Attention is paid to its concentrations and modes of occurrence in coal, to its volatility and partitioning among coal combustion streams as well as to promising strategies enhancing Cr retention and mitigating its emissions. As Cr behavior is a complex phenomenon, the paper discusses also the most significant affecting factors, such as combustion temperature, flue gas composition and the presence of interacting species (Cl, S, P, major elements, H2O, O2, CO2 or N2 atmosphere), using various adsorbents/additives etc. In relation to mitigating its negative environmental impact, special attention is drawn to evaluation of its two dominant valence states – trivalent and hexavalent Cr – regarding their toxicity, modes of occurrence in coal and ashes, their behavior during combustion and namely their mobility from coal combustion ashes. Due to a world-wide trend to co-combust coal with wastes in power stations, important characteristics related to waste materials are also included in evaluation.

The effect of feed solids concentration on flotation performance using the Reflux Flotation Cell

This study examines the separation performance achieved using the Reflux Flotation Cell (RFC) when treating low economic value coal waste streams over a range of feed solids concentrations. Feed solids concentrations of 1.3, 2.4 and 5.7 wt% were examined using a fine coal suspension of nominally 50 wt% head ash, covering the typical range emerging from the overflow of a desliming hydrocyclone. This work was also extended to include much higher levels of ultrafine gangue through the addition of significant levels of silica, resulting in an extreme feed ash of 97 wt% head ash, the aim being to assess whether these levels of gangue minerals affect hydrophobic particle capture. For the actual plant feed, as the feed solids concentration was increased the flux of hydrophobic particles fed to the RFC increased in a fixed ratio to the flux of hydrophilic particles. These results showed a greater gas flux was required to maintain combustible recovery as the feed flux of hydrophobic particles increased. The relationship between bubble surface coverage and hydrophobic particle recovery was also investigated. Estimates of the average bubble surface coverages, ranging 6–18%, showed a decreasing trend between recovery and surface coverage. By establishing a strong positive liquid bias flux, ∼0.7 cm/s in magnitude, the product ash was maintained within a narrow band of 7.0–11.9 wt% ash across the series of experiments, demonstrating consistent and strong product desliming over the up to 16-fold increase in feed solids concentration.

Simultaneous investigation of coal ignition and soot formation in two-stage O2/N2 and O2/CO2 atmospheres

Due to the intermittent nature of most renewable energy sources, the flexible oxy-coal combustion technology equipped with carbon capture, utilization, and storage (CCUS) will play an indispensable role in achieving carbon neutrality. In this work, we fundamentally investigated coal stream ignition and soot evolution in a series of staged O2/N2 and O2/CO2 atmospheres for two kinds of coal samples. A novel two-stage flat-flame burner can provide a controlled temperature (1500 K) and atmosphere that are comparable to those in practical boilers. We incorporated in-situ Mie scattering of coal particles, visible light of coal flame, laser-induced incandescence (LII) of soot, as well as online soot particle sampling (in combustion) and gas analysis (in pyrolysis). Compared with conventional O2/N2 atmosphere, the O2/CO2 case under the same oxygen fraction (XO2 = 0.3) substantially delays the ignition of coal streams (i.e., 10.1 ms for lignite and 8.9 ms for bituminous coal) on the more representative two-stage burner, and reduces soot volume fraction in the coal flame (i.e., by 26% for lignite and 48% for bituminous coal). The growth and oxidation of primary soot are retarded by the O2/CO2 ambience, which might be attributed to the lowered coal/char surface temperature and the smaller O2 diffusion coefficient in oxy-mode. In particular, we find that elevating oxygen fraction reduces soot volume fraction in the O2/N2 case, but exceptionally promotes soot formation in the O2/CO2 case. When the effect of coal rank is concerned, the bituminous coal ignites much later than the lignite due to less amount of combustible light gases released during pyrolysis. The lowered local temperatures in bituminous coal combustion lead to reduced soot forming ability in the O2/CO2 ambience, but in O2/N2 conditions, burning bituminous coal is sootier.

Determine Water Quality of Barapukuria Coal Mine Company Ltd and Its Surrounding Area in Dinajpur District

The purpose of this programme is to determine water quality of Barapukuria Coal Mining Company Ltd. and its surrounding area in Dinajpur district. 36 samples of water (Coal water flow stream drain water, surrounding area Water samples of water from the surface of the surface and tube type of tube well) are collected from this study area. Current pH, Conductivity, TDS, DO, temperature Samples physical character are measured and recorded in notebooks. After marking it properly, by adding HNO₃ control the collected samples pH 500 ml Polypropylene bottles are stored in ice box samples for chemical laboratories. Besides, the information related to the impact on the area is collected by the Barapukuria Coal Mining Company Ltd. and Barapukuria Coal-based thermal power plant. The amount of Al, Fe, Ti, Cu, Co, Cd, Zn, Ca, Mn, Mg, Na, K, As of the samples collected from the Analytical Chemistry Laboratory of Geological Survey of Bangladesh was determined. Chemical analysis of the samples showed that excessive presence of any element was not exist ECR (Environment Conservation Rule). 1997 of Bangladesh Standard value.

Investigation on ignition behaviors of pulverized coal particles in a tubular swirl burner

This paper intensively investigated the ignition of turbulent coal flames in a novel fully-mixed tubular swirl burner. The Nikon D300s digital camera was used to capture the statistical ignition behavior of dispersed coal particle streams in different ambiences. Meanwhile, the combustion dynamics of individual coal particles were also recorded by means of high-speed photography. Two low-rank coal samples, Hulunbel lignite and Zhundong coal, were tested in this study. The ignition delay times of coal particles in the swirl burner were compared with those in a flat-flame burner. In contrast to previous work on a laminar flat-flame burner, the current experimental results show that the turbulent ambience significantly enhances the ignition of all coal samples, which is exceptionally pronounced under high temperature and low oxygen conditions. In addition, the sensitivity analysis suggests that both the enhanced heat and mass transfer contribute to the early ignition in turbulence. The effect of elevated mass transfer coefficient turns prominent in low oxygen fraction ambience, wherein the volatile barrier effect is suppressed by the enhanced mixing process. The combined effect of turbulence favors the shifting of ignition modes to the heterogeneous-dominant region. Last but not least, the ceased volatile flame that visualized in turbulent low oxygen ambience further confirms the important role of heterogeneous ignition.

The effects of oxygen concentration and gas temperature on coal stream ignition and particle surface temperature in reducing-to-oxidizing environments

In the near-burner region of pulverized coal burners, two zones exist, with very different oxygen concentrations. The first zone is a locally reducing environment, caused by the fast release of volatiles from a region of dense coal particles, and the second zone, which is surrounding the first zone, is a hot oxidizing environment. The transition of coal particles from the reducing zone to the oxidizing zone affects early stage coal combustion characteristics, such as devolatilization, ignition and particle temperature history. In this work, we used a two-stage Hencken flat-flame burner to simulate the conditions that coal particles experience in practical combustors when they transition from a reducing environment to an oxidizing environments. The composition of the reducing environment was chosen to approximate that of a typical coal volatile. Three oxygen concentrations (5, 10 and 15 vol%) in the “ambient” oxidizing environment were tested, corresponding to those at different distances downstream from a commercial burner. The corresponding gas temperatures for the oxidizing environments were adjusted for the different oxygen concentrations such that the “volatile” flame temperatures were the same, as this is what would be expected in a commercial combustor. High speed videography was used to obtain the ignition characteristics, and RGB color pyrometry was used to measure particle surface temperatures. Two different sizes of coal particles were used. It is found that when particles undergo a reducing-to-oxidizing transition at high temperatures, the particles are preheated such that the critical factor for ignition delay is point at which the particle is in the presence of oxygen, not the concentration of oxygen. The ignition delay of large particles is found to be 53% longer than that of small particles due to their higher thermal mass and slower devolatilization. The oxygen concentration in the ambient have a negligible effect on early-stage particle temperatures.

Influences of initial coal concentration on ignition behaviors of low-NOx bias combustion technology

In order to provide the key parameters of initial coal concentration to low-NOx bias combustion technology and enrich the pulverized-coal bias combustion theory, pilot-scale ignition experiments of bias coal streams were carried out using a 250-kW fuel input bias combustion facility. The experimental results including combustion temperature, unburned residues, gas species, and flame spectra were collected. The influences of initial coal concentration on the ignition behaviors of an Indonesian subbituminous in a reducing atmosphere were studied. Our findings show that as initial coal concentration increased, the intensity of visible light and the carbon burnout progressively increased, while the ignition distance and the fuel NOx formation continually decreased. It was observed that the region of continuous flame became successively concentrated, and the flame stability was increasingly enhanced, indicating that the ignition behaviors improved in a gradual way. Furthermore, the mechanism of the combined homo-heterogeneous ignition changed to homogeneous ignition. To be specific, at initial coal concentrations of 0.33 kg/kg and 0.41 kg/kg, the homo-heterogeneous combined ignition mechanism occurred. While at an initial coal concentration of 0.53 kg/kg, the mechanism changed to homogenous ignition. For a tangentially-fired pulverized-coal boiler burning the Indonesian subbituminous, the highest initial coal concentration of the horizontal bias combustion burners can be designed as 0.53 kg/kg, which will be beneficial to the strong ignition and low-NOx emission.

Evaluation of Pressure Filtration of Coal Refuse Slurry: Effects of pH, Filtration, and Air-Blow Times

ABSTRACT Coal refuse slurry impoundments have potential environmental concerns associated with water contamination and impoundment stability. Pressure filtration can be used as an alternative method of handling such coal waste streams as it offers an opportunity to stack the dewatered refuse solids for subsequent disposal, reducing or eliminating the need for the impoundment. A response surface methodology approach was used to evaluate the effects of pH, filtration time, and air-blow time on pressure filtration, whose response was measured in terms of final cake moisture. Cake moistures as low as 19.2% were obtained in this study. Experimental results showed a decrease in cake moisture by 13% with an increase in filtration time from 40 minutes to 50 minutes. One third reduction in cake moisture was achieved for a test with 10 minutes of air-blow after 30 minutes of filtration time compared to a test with 40 minutes of filtration time. The effect of pH was significant on both the residual moisture content and the amount of solids deposited in the cake, with acidic pH increasing the filtration performance. A linear fit was developed to relate the amount of solids deposited in the cake as a function of pH and filtration time. A regression model for the response surface with respect to the predictor variables had an R2 value of about 0.99 with almost all the main effects, their square terms, and the interaction effects statistically significant.

A Comprehensive, Three-Dimensional Analysis of a Large-Scale, Multi-Fuel, CFB Boiler Burning Coal and Syngas. Part 2. Numerical Simulations of Coal and Syngas Co-Combustion.

This paper presents the results of numerical computations for a large-scale OFz-425 CFB (circulating fluidized bed) boiler utilizing coal and syngas. Four different operating scenarios are considered, including the reference variant, corresponding to the conventional, mono-combustion of bituminous coal, and three tests involving replacement of secondary air and part of the coal stream with syngas fed by start-up burners. Pressure, gas velocity, temperature, and carbon dioxide distribution in the combustion chamber are discussed in the paper. The results indicate that the syngas supply leads to an increase in local temperature and carbon dioxide concentrations. The proposed concept is not advisable as it may lead to frequent emergency stops of the CFB boiler.

Experimental and kinetic study on the transformation of coal nitrogen in the preheating stage of preheating-combustion coupling process

Preheating-combustion of pulverized coal has been demonstrated as an effective low NOx combustion technology. This method preheats a coal stream to high temperatures before the coal stream is injected into a utility boiler for combustion. Considering the complex mechanisms during the preheating, the effects of the preheating parameters, including temperature, residence time and excess air ratio are studied in a drop-tube furnace in detail. Meanwhile, a kinetics analysis on the transformation of coal-N in gas phase is also performed by means of Chemkin-Pro coupled with mature NOx reduction mechanisms. The experimental results show that the yield of coal-N converted to NO decreases at first and then increases with increasing excess air ratio. The lowest NO yield after preheating is achieved at excess air ratio of 0.1. To reduce NOx formation effectively, the preheating zone should be under high temperature and long residence time. Kinetic modeling indicates that NO was reduced into N2 by both hydrocarbon radical and HCN. Also, the modeling results show that the increasing excess air ratio weakens the effect of hydrocarbon radical reduction, and the mole ratio of NOHCN/NOHCN+CiHj decreases from 1.99 to 1.17 with the increasing excess air ratio from 0.1 to 0.6.

Plugin energy penalty model and gypsum production for flue gas desulfurization prediction

The present paper presents two process functions for the estimation of the energy demand for $$\hbox {SO}_{2}$$ filtering from coal flue gas streams and the gypsum production by wet flue gas desulfurization (WFGD) systems. Functions are prepared to be used as plugins on conceptual design procedures of industrial processes based on coal combustion with some sulfur content without the need of modeling the complete WFGD system. An energy penalty function (EPF) is proposed as the ratio of demanded work to operate the filtering process with respect to the input flue gas volumetric flow rate, called the work ratio. Dihydrate calcium sulfate is a value product estimated by a gypsum slurry production function (GPF) based on the ratio of gypsum production to the input flue gas volumetric flow rate. Mass, energy and species balances are solved to simulate WFGD operation based on the inlet and outlet flue gas temperature, $$\hbox {SO}_{2}$$ content and cleaning efficiency, and results are compared to data from coal-fired power plants, from now on called the reference model. Design of experiment (Box–Behnken method) is used to identify main parameter weighting and cross-dependencies to finally build the EPF and GPF plugin functions. Relative deviations with respect to the reference model are of 1.41% and 0.05% for EPF and GPF, respectively. Both equations can be coupled to any kind of combustion system to quantify the energy penalty related to flue gas $$\hbox {SO}_{2}$$ removal and to predict the corresponding amount of gypsum as a by-product and to predict optimal operational conditions.

Study on ignition behaviors of bias parallel pulverized coal streams in a reducing atmosphere: Influences of exit velocity

Ignition experiments regarding the combustion of Indonesian coal were performed in a reducing atmosphere using a bias combustion simulator with a thermal power of 250-kW. Flame spectra, gas temperatures and gas species were recorded, and coal combustion residues were sampled. The influences of exit velocity on the ignition mechanism, ignition delay distance, continuous flame boundary and fuel NOx formation of bias parallel pulverized-coal streams were investigated. The experimental results reveal that as exit velocity increased, the peak value of visible-light intensity, the combustion efficiency and the flame stability gradually decreased, while the ignition delay distance, the continuous flame boundary, and the formation of fuel NOx gradually increased. Furthermore, the ignition behaviors became worse. A transition of ignition mechanism occurred with increasing exit velocity, at an exit velocity of 16 m/s, the bias parallel pulverized-coal streams ignited in a hetero-homogeneous joint mechanism; at exit velocities of 20, 25 and 29 m/s, the bias parallel pulverized-coal streams ignited in a homogeneous mechanism. For different exit velocities, the fuel-rich stream ignited in advance of the fuel-lean stream, and the continuous flame boundary leaned evidently towards the fuel-rich stream side. According to the experimental findings in the present study, the horizontal bias combustion pulverized-coal burners were designed and applied to one-sixth of the total burners in a tangentially-fired pulverized-coal boiler. At the rated electrical load of 500 MWe, the NOx concentration prior to denitrification decreased by 11%, and the ammonium consumption for denitrification decreased by 42 kg/h. The results of the present study are also beneficial to further advance ignition concepts of low NOx bias combustion of pulverized-coal and enable the related numerical simulation work.

Intensifying the PC conversion in the raceway by means of coke oven gas

Among numerous measures to accelerate the PC conversion within the blast furnace (BF) raceway, local increase of oxygen concentration is the most common one. On the other hand, the presence of cold media (oxygen) in the vicinity of the coal stream might affect its ignition and combustion negatively. A minor amount of coke oven gas (COG) may increase the temperature and consequently accelerate the coal conversion. To examine this effect, laboratory trials under blast furnace simulating conditions were performed using the Multifunctional Injection Rig for Ironmaking (MIRI). The results of the simulation testified a higher conversion degree of coal while adding the COG. The temperature increase is measurable in the reaction chamber and the off-gas stream. Optical microscopy of the original PC particles and residues after reaction confirm the findings of the off-gas analysis and the increase in temperature during the experiments with addition of COG. The thermogravimetric analysis was applied to determine and to compare the behaviour of coal in different atmospheres including an atmosphere with COG. A stand at one tuyère at a modern BF was erected and tests were performed targeting the observation of the ignition behaviour of coal at different COG rates, using a camera image analysis system. Laboratory trials under blast furnace raceway simulating conditions showed, that even a small amount of COG significantly improves the PC conversion degree. A new technology of PC injection, including addition of small amount of COG to the PC transporting gas, aimed at neutralization of the oxygen local cooling effect, elaborated, justified and tested.