Content In Flue Gas Research Articles

Experimental study on mercury content in flue gas of coal-fired units based on laser-induced breakdown spectroscopy

Accurate measurement of trace heavy metal mercury (Hg) in flue gas of coal-fired units is great significance for ecological and environmental protection. Mixed gas was used to simulate the actual flue gas of a power plant in this study. A laser-induced breakdown spectroscopy (LIBS) system for Hg measurement in mixed gas was built to study the effect of mixed gas pressure, Hg concentration in mixed gas and delay time on Hg measurement. The experimental results show that the appropriate low mixed gas pressure can obtain high Hg signal intensity and signal to noise ratio. The Hg signal intensity and signal to noise ratio increased with the increase of Hg concentration in mixed gas. The Hg signal intensity and signal to noise ratio decreased with the increase in delay time. According to the above results, the optimized measurement conditions can be determined. Different Hg concentrations in mixed gas were quantitatively analyzed by the internal standard method and traditional calibration method respectively. The relative error of prediction of the test sample obtained by the internal standard method was within 11.11%. The relative error of prediction of the traditional calibration method was less than 14.54%. This proved that the internal standard method can improve the accuracy of quantitative analysis of Hg concentration in flue gas using LIBS.

Energy conservation certification for coal layer-combustion industrial boiler

The effect of boiler load on main operation parameters and the boiler efficiency were investigated, and the thermal efficiency distribution of nearly 300 coal-fired boilers was further analyzed. The results show that the exit gas temperature decreases as the boiler load decreases, while the unburned carbon contents in ash and slag, and CO content in flue gas usually increase. Correspondingly, the loss due to exit gas decreases, and the loss due to unburned solids usually increases. The loss due to surface radiation and convection increases. Taking into account changes of all the losses, the boiler efficiency decreases at lower loads. With reference to TSG G0002, Technical Specification for Energy Conservation Certification of Coal Layer-Combustion Industrial Boiler under off-Design Conditions has been drafted and the evaluating values of energy conservation for products have been proposed, including boiler efficiency under different test loads and CO concentration in flue gas. The target efficiency values vary according to the boiler capacity and fuel type. The CO concentration value is a limit that can be achieved by most boilers.

Innovative NOx reduction from cement kiln and pilot-scale experimental verification

Nitrogen oxide emissions from cement industry have greatly promoted the formation of haze weather. Current denitration technologies can hardly meet the increasingly stringent emission requirements. Here we proposed an innovative method called “rear independent reduction” (RIR) to reduce nitrogen oxide emissions from the cement kiln. A pilot-scale experimental setup was put in place to verify its feasibility. Reduction efficiencies of 61.2% and 48.6% were obtained in the absence and presence of cement raw meal, respectively. The effects of amount of reduction pulverized coal, flue gas temperature, the addition of cement raw meal, and oxygen content in flue gas on the NOx reduction efficiency were comprehensively investigated. Increasing the amount of reduction pulverized coal cannot only enhance the reduction efficiency, but also promote the rise of flue gas temperature. The ideal flue gas temperature is around 900 °C. Oxygen content in flue gas determines the impact of cement raw meal on the reduction efficiency, and the optimal value is below 1.0%. The significant reduction of NOx in flue gas should be attributed to the reaction between reductants and nitrogen oxides. This work provides a new way to address the problem of NOx emission in cement industry.

Direct Measurement of Gaseous Sodium in Flue Gas for High-Alkali Coal

A direct measurement technique was developed to detect gaseous alkali metals in this work. It was based on the surface ionization principle. To verify the mechanism, a detector probe was designed and calibrated by NaCl samples. The calibration gives a linear correlation between the detected voltage signals and the vaporizing rates of sodium. Then, the calibrated detector probe was applied to detect the gaseous sodium content in flue gas for the prepared Zhundong coal samples during the heating process. These coal samples contained varied contents of sodium, which were classified as raw coal, washed coal, and coal with sodium additives. Results show that sodium compounds in the raw coal vaporize in the temperature range of 300–600 °C. Its highest release rate appears at 457 °C. For the coal samples with additives of NaCl or Na2SO4, higher addition ratio leads to more released sodium. Compared with SO42–, Cl– has a greater influence on sodium release. This technique may be applied to online measure the gase...

A new method for boiler combustion calculation

Fuel combustion calculation is an important basic work of boiler performance test and analysis. During the process of combustion calculation, solving excess air ratio and actual volume of dry flue gas are key objectives. Current method is to firstly calculate excess air ratio, then calculate actual volume of dry flue gas. And in order to solve excess air ratio, almost all fue gas composition need to be measured, which will not only increase the workload of measurement, but also reduce the accuracy of calculation results. To this end, a new combusion calculating method is proposed in this paper which solves actual dry flue gas ratio through oxygen content in flue gas, thus actual volume of dry flue gas is calculated. Finally, the excess air ratio is obtained through acutal volume of dry flue gas. By the new method, the flue gas composition measure items can be reduced to only oxygen content, but it will not reduce the precision of combustion calculation.

Study on the evolution and transformation of Cl during Co-incineration of a mixture of rectification residue and raw meal of a cement kiln

The co-processing of hazardous waste in cement kiln can eliminate a large number of hazardous wastes, but the excessive existence of chlorine will affect normal operation of cement kiln. In this study, the partition of Cl in flue gas, fly ash and residual solid under different experiment conditions was obtained by using tubular furnace to incinerate mixtures of rectification residue and raw meal. The chlorine content in flue gas was determined using ion chromatography and the chlorine content in fly ash and residual solid was measured by high temperature combustion hydrolyzing-ion chromatography. The results showed that chlorine mainly existed in flue gas and residual solid, and only less than 3.5% of chlorine existed in fly ash. The incineration temperature had a significant effect on the distribution of chlorine in each part. The higher the incinerating temperature, the greater the proportion of chlorine in flue gas and fly ash. While temperatures were higher than 1300 °C, the proportion of chlorine in all parts remained basically unchanged, roughly 18:14:1. With the increase of the retention time, the proportion of chlorine in the residual solid decreased gradually, and the proportion of chlorine in the flue gas increased gradually. The distribution ratio of chlorine in each part remained unchanged after about 30 min. In addition, the chlorine content of the sample and the air flow rate had a relatively slight effect on the partition of chlorine. Based on these experimental results, some suggestions on the co-processing of hazardous waste in cement kiln were put forward.

Study of Temperature Fields and Heavy Metal Content in the Ash and Flue Gas Produced by the Combustion of Briquettes Coming from Paper and Cardboard Waste

The present study focused on the combustion of four types of briquettes made from paper and cardboard waste produced in Ouagadougou (Burkina Faso). Rotary and tubular kilns were used to study the combustion. The combustion mean temperatures, nitrogen, phosphorus and potassium (NPK) content in the ash and heavy metals content in the ash and the flue gas were analyzed. The combustion steady phase mean temperatures ranged from 950 °C to 750 °C were obtained according to briquettes type. The temperature favored the transfer of the heavy metal in the flue gas comparatively to the ash mainly for Hg, Cd and Pb. The Pb, Hg and Mn content in flue gas and the ash are higher than their content in the parent wood used for paper production due to the additive during the manufacturing process. The results showed a high content of heavy metal in flue gas produced by combustion of briquette made with office paper and in the ash for the briquette made of corrugated cardboard. Furthermore, the low heavy metal contain in the ash allow their use for soil amendment. However, ash contained a low proportion of NPK (less than 2%) which does not allow their usage as fertilizer alone.

Variation of toxic pollutants emission during a feeding cycle from an updraft fixed bed gasifier for disposing rural solid waste

Abstract The variation of toxic pollutants emission during a feeding cycle was examined by field monitoring from a batch feeding updraft fixed bed gasifier for disposing rural domestic solid waste. Results showed that the content of oxygen in flue gas gradually increased, while SO2 and HCl in flue gas decreased with time after feeding in a whole feeding cycle. Although large amount of CO was produced during the gasifying, low CO content in flue gas could be obtained after the heat treatment with an electric heating device. The distribution characteristics of dioxin congeners in flue gas indicted the re-synthesis of dioxins after flue gas heating, and the increase of oxygen promoted the synthesis of dioxins. The emission content of dioxins could meet the standard (0.1 ng I-TEQ·m− 3, GB18458-2014) of China when the oxygen content was controlled below 8.3%. Hence, for a batch feeding gasifier, low oxygen condition should be offered by reducing air intake at the later stage of feeding cycle in order to decrease the re-synthesis of dioxins after the flue gas heating.

Combustion adjustment test of circulating fluidized bed boiler

To achieve optimal operation, a combustion adjustment test were carried out in a 240t/h CFB boiler. Three factors, including bed pressure drop, primary air flow and secondary air flow were studied, each of which had three values of factor levels. Results show that the sensible heat loss in exhaust flue gas is the largest part of heat loss, accounting for more than 75%. To achieve higher thermal efficiency, the bed pressure drop should be maintained around 7.2kPa, the oxygen content in flue gas around 5%, and the bed temperature around 900°C. From the point of combustion efficiency, the boiler can be operated under a relatively low bed pressure drop, around 6.7kPa. The heat losses due to the unburned combustibles are relatively small. The NOx concentration in flue gas was also studied, from which it can be concluded that the emissions targets should be set up in combination with the boiler efficiency, especially CO concentration in flue gas. Through combustion adjustments, the NOx emission can be decreased by about 50% without affecting the boiler efficiency.

Data-Reconciliation Based Fault-Tolerant Model Predictive Control for a Biomass Boiler

This paper presents a novel, effective method to handle critical sensor faults affecting a control system devised to operate a biomass boiler. In particular, the proposed method consists of integrating a data reconciliation algorithm in a model predictive control loop, so as to annihilate the effects of faults occurring in the sensor of the flue gas oxygen concentration, by feeding the controller with the reconciled measurements. Indeed, the oxygen content in flue gas is a key variable in control of biomass boilers due its close connections with both combustion efficiency and polluting emissions. The main benefit of including the data reconciliation algorithm in the loop, as a fault tolerant component, with respect to applying standard fault tolerant methods, is that controller reconfiguration is not required anymore, since the original controller operates on the restored, reliable data. The integrated data reconciliation–model predictive control (MPC) strategy has been validated by running simulations on a specific type of biomass boiler—the KPA Unicon BioGrate boiler.

Studies of Spherical Granules of the CuO-Fe2O3-Al2O3 Catalyst Prepared by Drop Molding for the Process of Fluidized Bed Burning of Brown Coal

A method of drop molding was suggested for preparation of spherical granules of CuO-Fe 2 O 3 -Al 2 O 3 catalysts. The catalysts were characterized using a set of physicochemical methods and tested for fluidized bed burning of brown coal. The influence of thermal treatment (700 and 800 °C) on the activity, strength and physicochemical properties of the spherical CuO-Fe 2 O 3 -Al 2 O 3 catalyst were studied. The prepared catalyst was shown highly active to oxidation of CO (competitive to that of the currently used industrial catalyst), high crushing and attrition mechanical strength (ca. 10–14 MPa of the minimal crushing strength and 15–23 MPa in average; attrition loss 0.8 % according to ASTM D-4058). Testing of the CuO-Fe 2 O 3 -Al 2 O 3 catalyst for the fluidized bed burning of brown coal demonstrated the attainability of high coal burnout (95 %) characteristic of the industrial catalysts (Shchkz-1, IC-12-73, IC-12-74A), the CO content in flue gas being 600 ppm that was lower of that observed with the industrial iron-containing catalyst IC-12-74A 3,000 ppm) and comparable with the catalyst IC-12-73 (700 ppm).

Effects of carbon dioxide in oxy-fuel atmosphere on catalytic combustion in a small-scale channel

The effect of CO2 dilution on oxy-fuel reaction over catalytic surface is experimentally investigated in a small-scale channel in terms of heat transfer, chemical reactivity as well as interplay between hetero- and homogeneous reaction. There are two kinds of small-scale reactors, tubular reactor and channel reactor, respectively, used in this study. In the tubular reactor, the interaction between heterogeneous and homogeneous reaction on tubular platinum reactor are addressed based on the resulting surface temperatures of the tube and fuel conversion ratios. CO2 would absorb chemically-induced heat release of hydrogen, but in the meantime heat up the flowing mixture via radiative and convective heat transfer. In the channel reactor, the results demonstrate that the segmented catalyst with cavities has minimal oxygen concentration to hold catalytically stabilized thermal flame in a channel, and performs approximately complete fuel conversion. Beside, CO content in flue gas is increased in the case of segmented catalyst with cavities. It speculates that CO2 decomposes CO through the reaction of CO2+HCO + OH in gas phase in the vicinity of the catalyst surface, and the requested H radical and thermal energy are provided by the neighboring heterogeneous reaction.

Modes of Occurrence of Fluorine by Extraction and SEM Method in a Coal-Fired Power Plant from Inner Mongolia, China

In this study, an extraction method and environmental scanning electron microscopy (SEM) are employed to reveal the changes in the occurrence mode of fluorine in a coal-fired power plant in Inner Mongolia, China. The different occurrence states of fluorine during coal combustion and emission show that fluorine in coal mainly assumes insoluble inorganic mineral forms. The results illustrate that the three typical occurrence modes in coal are CaF2, MgF2 and AlF3. The fluorine in fly ash can be captured by an electrostatic precipitator (EPS) or a bag filter. In contrast, the gaseous fluorine content in flue gas is only in the range of several parts per million; thus, it cannot be used in this study. The occurrence mode of fluorine in bottom ash and slag is inorganic villiaumite (e.g., soluble NaF, KF and insoluble CaF2) which is difficult to break down even at high temperatures. The occurrence mode of fluorine with the highest content in fly ash is physically adsorbed fluorine along the direction of the flue gas flow. The insoluble inorganic mineral fluoride content in fly ash is also high, but the gradually increasing fluorine content in fly ash is mainly caused by physical adsorption. Fluorine in the coal-fired power plant discharges mostly as solid products; however, very little fluorine emitted into the environment as gas products (HF, SiF4) cannot be captured. The parameters used in this study may provide useful references in developing a monitoring and control system for fluorine in coal-fired power plants.

Simulation Research about Impacts of Flue Gas on Surrounding Buildings

The revamping project of turning coal-burning boiler into gas-fired boiler for urban heat supply in Tianjin causes high vapor content in flue gas, which has great influences on the day lighting of surrounding buildings. In this paper, CFD software is introduced to simulate the distributions of NOx, SO2 and vapor in space after leaving the chimney and their impacts on surrounding buildings with the effect of the atmosphere. Result shows that flue gas discharged from the chimney with the height of 30 m has significant impacts on the surrounding buildings.

Multi-Model Modeling of O2 Content in Flue Gas of Power Plant Based on Affinity Propagation Clustering

Characteristics of multiple conditions and nonlinear are existed in working process of thermal power unit. To solve the problem, a LS-SVM multi-model modeling of oxygen content in flue gas method based on affinity propagation clustering is presented. In this method, affinity propagation clustering is firstly used to cluster the training samples. Then, the sub-models of LS-SVM are trained by sub-samples. The predicted value of the testing sample is estimated by the sub-model which is selected by similarity measurement. The proposed method has been applied to modeling experiment based on the field data. The experiment shows that the proposed modeling method has superior regression accuracy and better ability of generalization.

Thermochemical Wear of Refractory Linings Associated With Gas Firing in Metallurgical Plants

The present paper deals with the corrosive interaction between the atmosphere and the refractory lining as well as in one case the steel shell for two industrial facilities. In one of the following cases a magnesia carbon lining is partly decarburized by the atmosphere during preheating of a steel ladle. In the other case, the flue gas from blast furnace gas heating of a hot blast stove causes a nitric attack on the cold side of the refractory lining at the steel shell. Investigation of these mechanisms rely on computational fluid dynamics (CFD) simulations which quantify the flow and temperature field as well as the species transport during heat release from the gas combustion in both plants. Furthermore, the heat exchange between hot gas and refractory is estimated and thereby associated chemical reactions with/within the refractory material. In both CFD case studies a non‐premixed approach was applied to model the combustion process and to characterize the flue gas composition. The follow‐up reactions with refractory lining and the steel casing are discussed specifically for each case. The calculated oxygen content in flue gas during ladle preheating is estimated to 15%vol. The maximum heat transfer between hot gas and refractory takes place in the bottom region of the ladle due to convection. The radiative heat exchange plays the most important role in the zone of magnesia‐carbon lining. Within the investigation of carbon burnout kinetics limiting factors like diffusion and mass transfer coefficient of oxygen were defined and (partially) determined. The NO formation during the blast stove heating period strongly depends on the dome temperature which is an important blast process control value. Calculated NO emission loads showed promising agreement with real plant data and literature trends.

Sequestration of supercritical CO2 by mercury oxide

AbstractHgCO3·2HgO (mercury oxide carbonate), along with partly unreacted reactants, was obtained by exploring the behaviour of the Hg2Cl2/HgO binary system in supercritical CO2 (scCO2) at 200°C, 22000 kPa in the presence and absence of water, using a self-made laboratory-scale system. The reaction of pure HgO with scCO2 aimed at the synthesis of HgCO3 (mercury carbonate), also yielded the same product. Meanwhile, with a small amount of water present in the Hg2Cl2/HgO-scCO2 system, at 200°C, 22000 kPa, the mineral terlinguaite (Hg4O2Cl2) was obtained instead of mercury oxide carbonate. Repeating this reaction under the same conditions, but in the absence of CO2, again resulted in the synthesis of terlinguaite, leading to the assumption that the scCO2 had no influence on the synthesis of terlinguaite. This study reveals a new moisture-free laboratory method and conditions for the permanent fixation of CO2 by HgO. This method bears two benefits: 1) it can be introduced to reduce the Hg content in flue gas and fly ash emitted from coal-burning power plants and municipal waste incinerators; 2) it can contribute to CO2 mineralisation in montroydite (HgO) geological formations as mercury oxide carbonate.

SO3 Impact on Amine Emission and Emission Reduction Technology

Mitsubishi Heavy Industries, Ltd. (MHI) in collaboration with Kansai Electric Power Co., Inc. (KEPCO) has developed a highly efficient chemical absorbent CO2 removal process called KM CDR Process TM. This process, together with the proprietary KS-1TM solvent has been applied to ten (10) commercial CO2 capture plants with a maximum CO2 capture capacity of 450 metric tons per day (tpd). These commercial plants are providing captured CO2 to the chemical and fertilizer industries, predominantly to enhance urea production. One (1) further commercial CDR plant, 500tpd capacity, is currently under construction in Qatar. Performance data and learnings from these commercial plants are used to make further process improvements and catalyse R&D activities.To provide a greenhouse gas mitigation solution for the power industry, MHI has adapted the KM CDR ProcessTM for coal fired power plant application. Beginning in 1999, MHI have performed a number of test programs assessing plant performance and optimization with coal fired flue gas while evaluating the impact of associated impurities at the 1 tpd pilot test facility in Hiroshima R&D Center. In 2006, MHI constructed a 10 tpd CO2 capture demonstration plant at a commercial 500MW coal fired power plant in Matsushima, Japan. Between 2006 and 2008, MHI operated the 10tpd pilot plant in excess of 6,000hours, trouble shooting and developing the technology. The Matsushima plant lead to MHI successfully beginning operation of the world's largest, 500 tpd, carbon capture plant for coal fired flue gas in June, 2011. The 500tpd capture plant, dubbed Southern Company (SoCo) 500, streams the equivalent of 25MW of flue gas from a coal fired boiler at Alabama Power's Plant Barry. The SoCo 500 plant is an integral part of the world's first fully integrated coal fired flue gas CCS project.In recent years, governments and regulators have begun to examine amine emissions, from amine based CO2 capture facilities, and the associated potential impacts to the environment and human health. It is envisaged that in the near future amine emission reduction will be become a critical requirement for all amine based CO2 capture OEMs.To reduce the amine emissions, MHI introduced the first optimized washing system within an absorber column in 1994, and developed a proprietary washing system in 2003. The washing system is currently operating in ten (10) commercial plants of KM CDR ProcessTM, as a result amine emissions from these plants have been lowered to the ppm level. MHI has continued to improve this technology for further reduction of amine emissions and established “advanced amine emission reduction system”. A series of amine emission test programs have been carried out with various flue gases at the 1 tpd pilot test facility in Japan and the 0.2 tpd mobile CO2 capture test unit, which has been installed at Southern Company's plant Yates in the USA, using both KS-1TM and MEA solvents. During these test programs, MHI found that an increasing SO3 content in flue gas caused a significant increase of amine emissions. The phenomenon was also observed at the SoCo 500 plant and a commercial plant. During the several test programs, MHI applied a proprietary washing system in the commercial CO2 capture plant to remove aerosols, including SO3 mist absorbed amine vapor, from the flue gas stream and confirmed that the amine emission were drastically reduced.MHI is also currently researching amine atmospheric chemistry, i.e. behavior of emitted amine compounds in air from CO2 capture plant, to better understand the potential issues with commercialization of this technology for CCS application.

A study on the calcination and sulphation behaviour of limestone during oxy-fuel combustion

The mechanisms governing the behaviour of limestone for in-furnace desulphurisation during oxy-fuel combustion have been investigated in this paper. Apart from the use of pure limestone, the mixtures of limestone with a brown coal (i.e., lignite) at different mass ratios have also been examined to address the influence of ash on the behaviour of limestone. The combustion experiments were conducted in a drop-tube furnace at a furnace temperature of 1273K and a reactor length of 1200mm for a nominal particle residence time of approximately 1.0s. Pure air and an O2/CO2 mixture at a volume ratio of 27:73 were tested. SO2 at a concentration of 1000ppm was also doped into these two gases to examine its competition with Si and Al in the ash on the interaction with limestone. A high CO2 partial pressure has been confirmed to slow down the calcination of limestone in O2/CO2. However, mixing limestone with coal enhanced the limestone calcination by increasing the particle temperature through radiative heat transfer from flame. With a large quantity of limestone such as the 18% tested here, direct sulphation is a major route contributing to sulphur capture during oxy-fuel combustion. The importance of direct sulphation is exceeded by indirect sulphation via an initial calcination of limestone when medium and low quantities of limestone are added to coal. The Si and Al in coal undermine the calcination and sulphation of limestone in O2/CO2 because of the preferential formation of Ca aluminosilicate eutectics. These eutectics tend to melt and deposit on the unreacted limestone surface, thus providing extra resistance to the diffusion of gas through the limestone particles. Increase of SO2 content in flue gas favours the indirect sulphation of calcium over the interaction of calcium with ash, thereby increasing the extent of desulphurisation during oxy-fuel combustion.

Experimental study on removals of SO2 and NOX using adsorption of activated carbon/microwave desorption

Experimental studies on desulfurization and denitrification were carried out using activated carbon irradiated by microwave. The influences of the concentrations of nitric oxide (NO) and sulfur dioxide (SO2), the flue gas coexisting compositions, on adsorption properties of activated carbon and efficiencies of desulfurization and denitrification were investigated. The results show that adsorption capacity and removal efficiency of NO decrease with the increasing of SO2 concentrations in flue gas; adsorption capacity of NO increases slightly first and drops to 12.79 mg/g, and desulfurization efficiency descends with the increasing SO2 concentrations. Adsorption capacity of SO2 declines with the increasing of O2 content in flue gas, but adsorption capacity of NO increases, and removal efficiencies of NO and SO2 could be larger than 99%. Adsorption capacity of NO declines with the increase of moisture in the flue gas, but adsorption capacity of SO2 increases and removal efficiencies of NO and SO2 would be relatively stable. Adsorption capacities of both NO and SO2 decrease with the increasing of CO2 content; efficiencies of desulfurization and denitrification augment at the beginning stage, then start to fall when CO2 content exceeds 12.4%. The mechanisms of this process are also discussed. Implications: The prominent SO2 and NOx treatment techniques in power plants are wet flue gas desulfurization (FGD) and the catalytic decomposition method like selective catalytic reduction (SCR) or nonselective catalytic reduction (NSCR). However, these processes would have some difficulties in commercial application due to their high investment, requirement of expensive catalysts and large-scale equipment, and so on. A simple SO2 and NOx reduction utilizing decomposition by microwave energy method can be used. The pollutants control of flue gas in the power plants by the method of microwave-induced decomposition using adsorption of activated carbon/microwave desorption can meet the requirements of environmental protection, which will be stricter in the future.