Stack Flue Gas Research Articles

Mercury emission and fate characteristics in various combustion sources

In this study, we investigated the behavior and emission characteristics of Hg across diverse industrial combustion sources, such as coal-fired power plants, solid refuse fuel (SRF) power plants, medical waste incinerators, and industrial waste incinerators, as well as the development of emission factors, Among the facilities, the estimated Hg control efficiency was 86% for coal-fired power plants, 69% for SRF power plants, and over 95% for medical and industrial waste incinerators. The oxidation and regulation of elemental Hg (Hg0) are considered important factors in reducing Hg air emissions, with the flue gas HCl concentration being the primary factor affecting Hg oxidation. Particulate Hg was mainly controlled in the electrostatic precipitator (ESP) at the power plant, effectively capturing dust particles ranging from 10 to 100 μm. The emission factors estimated by measuring stack flue gas exhibited their highest values at SRF power plants, with an estimated average of 127±25 mg/ton, while the lowest values were observed for industrial waste incinerators, with an average of 2.5±0.3 mg/ton. This study is significant in that it provides a comparative analysis of various real industrial cases, and the Hg emission factors are expected to offer valuable data for estimating future national Hg air emissions.

Computational fluid dynamics numerical simulation of flue gas emission from stack and tower integration system of coal-fired power plant

ABSTRACT The method of Computational Fluid Dynamics (CFD) simulation has been extensively employed in the stack and tower integration technology (STIT) research; however, a significant number of studies overlooked the impact of thermal buoyancy on the external flow field of cooling tower. In light of this, an improved approach is proposed in this study. A model of a cooling tower and its surrounding flow field was established, and its reliability was confirmed too. Based on our model, the performance of three enhancement strategies under various crosswind speeds and ambient temperatures was simulated. The results indicate that all three enhancement strategies can effectively simulate the effects of thermal buoyancy. In the simulations, the elevation of the flue gases increased from 306 m to either 426 m or 476 m. In the present study, ambient conditions characterized by crosswind speeds below 4 m/s and temperatures below 297.15 K were deemed suitable for the dispersion of stack and tower integration (STI) flue gases. A power function distribution was identified between crosswind speed and the mean height of the plume, while a linear relationship was observed between ambient temperature and the mean height of the plume.

Study on emission factors of FCC flue gas pollutants in petroleum refineries.

Fluid catalytic cracking (FCC) unit is one of the means to lighten heavy oil in refineries, and its regenerated flue gas is also the main source of air pollutants from refinery. However, it is not clear about the type and amount of pollutants discharged from FCC units in China. The emissions of regenerated pollutants in the stack flue gases of three typical FCC units in China were investigated in this study, including a partial regeneration unit without a CO boiler (U1), a partial regeneration unit with a CO boiler (U2), and a full regeneration unit (U3). Different monitoring methods were used to analyze the concentration of sulfur dioxide (SO2) and nitrogen oxides (NOx), and the results showed that Fourier transform infrared spectroscopy (FTIR) monitoring results of SO2 and NOx are approximately 10 times and 5 times larger than those of the continuous emission monitoring system (CEMS) data, respectively. Also, the contents of characteristic pollutants such as NH3, C6H6, HCN, C8H8, C2H4, CH4, and CO were also monitored by FTIR, and the emission factors based on coke burn-off rate and throughput were investigated. The pollutants in U1 exhibited relatively higher contents with the NH3, HCN, and C6H6 of 116.99, 71.94, and 56.41 mg/Nm3 in flue gas, respectively. The emission of regenerated pollutants in U2 and U3 are significantly different from U1. Regeneration processes (including coke properties, operating modes, and presence or absence of CO boilers) affected pollutants' emission factors in varying degrees. At last, reasonable emission factors based on the different FCC regeneration processes contribute to the prediction, assessment, and control for the pollutant emission.

Experimental investigation of removal of flue gas emissions exhaust from municipal solid waste incinerator using photovoltaic-based electrostatic precipitator.

For the past decades, the flue gas emitted from municipal solid waste incinerator, power plant, and various industries is a permanent problem for the environment and has been affecting human life. Many flue gas filtration devices have been emerging out over the years. Although the electrostatic precipitator was an appropriate device due to high filtration efficiency and little pressure drop and energy efficiency, the cost and design of the electrostatic precipitator is a major restriction for manufacturers and end-users. With recent advances in technology, designing a cost-effective and less complex electrostatic precipitator has become mandatory. This article aims to design and develop a solar-powered cost-effective needle-plate type electrostatic precipitator which includes a static power converters and high-voltage transformer-rectifier (T-R) set with an input voltage as 230V AC, output voltage as 80-kV direct current (DC), and output current of 40mA for mitigation of flue gas emissions exhaust from municipal solid waste incinerator. The analysis of flue gas at ESP inlet and outlet has been performed using Ecotech stack sampler and flue gas analyzer. The obtained experimental results are validated with emission standards provided in the Solid Waste Management rules book, India, 2016.

Suppressing the formation of chlorinated aromatics by inhibitor sodium thiocyanate in solid waste incineration process

Suppressing the formation of chlorinated aromatics (Cl-aromatics) by chemical inhibitors is an important measure to reduce dioxin emission from the solid waste incineration plants. In this study, we first investigated the reduction effect of a novel inhibitor sodium thiocyanate (NaSCN) on the emission of dioxins in 2 full-scale solid waste incineration systems. Injection of NaSCN solution into the higher temperature flue gas resulted in about 60% reduction in the concentration of total tetra- to octa-chlorinated dibenzo-p-dioxins and dibenzofurans in stack flue gas. The suppression effect was further verified by a laboratory study on the chlorination of naphthalene over model fly ashes with or without NaSCN addition. By characterizing the reaction products between NaSCN and key catalysts Cu and Fe chlorides, two main suppression mechanisms were proposed: (i) reduction of highly active cupric chloride (CuCl2) and ferric chloride (FeCl3) to less active cuprous chloride (CuCl) and ferrous chloride (FeCl2), (ii) sulfidation of Cu chlorides. The laboratory study indicated that the unreacted NaSCN in the combustion flue gas could be mainly decomposed into Na2S, C3N4, Na2S2O3, NaS2, Na2SO4, CO2, SO2, NO2 and COS. These decomposition products are low toxic or can be effectively removed by the air pollution control devices. CapsuleNaSCN suppressed the formation of chlorinated aromatics in combustion flue gas mainly through inducing the reduction of highly active Cu (II) and Fe (III) chlorides.

Behavior of thallium in pulverized coal utility boiler installations in Southwest China

ABSTRACT Thallium (Tl) is a toxic element that exists in coal at trace level. Coal-fired power plants (CFPPs) consume large amounts of coal and can potentially release this element into surrounding environment. However, knowledge of fates of Tl inside CFPPs and associated atmospheric emissions is still very limited. In this study, five CFPPs with pulverized coal boilers (PC) in Guizhou province, southwest China, were selected for investigation. All input and output solid materials and the stack flue gas samples were collected simultaneously. Tl concentrations in feed coal (0.10–0.34 mg·kg−1) of the five CFPPS were only a third to one half of the national average value. Tl concentrations were obviously higher in fly ash (0.39–1.13 mg·kg−1) than in bottom ash (0.09–0.25 mg·kg−1), indicating notable redistribution of Tl during coal combustion. Tl concentrations were low in limestone (0.01–0.02 mg·kg−1), flue gas desulfurization gypsum (0.01–0.03 mg·kg−1), and the stack flue gas (0.006–0.011 μg·Nm−3). Most Tl inside these CFPPs was captured by electrostatic precipitator or electrostatic precipitator-fabric filter (ESP/ESP-FF) fly ash (88.66%–97.44%), followed by bottom ash (2.13%–10.73%), gypsum (<3.89%), and stack emissions (0.01%–0.05%). Atmospheric emission factors of Tl from different CFPPs are in the range of 0.04–0.09 mg Tl·t−1 coal, 0.02–0.04 μg·(kW·h)−1, or 0.002–0.004 g Tl·TJ−1. Using these emission factors, a total of 3.96 ± 1.32 kg (range: 2.64–5.94 kg) Tl is estimated to be released into the atmosphere annually from CFPPs in Guizhou in 2017. To avoid the cross-media contamination from the combustion products, careful treatment of the captured fly ash, bottom ash, and gypsum is needed, considering that a large amount of Tl (average: 728 kg·yr−1; range: 664–792 kg·yr−1) is retained in these solid combustion products and the possibility of formation of more toxic Tl3+ during the combustion process. Implications: Thallium (Tl) is a rare but toxic element. Identifying and quantifying its source are high priorities for controling its contamination. Coal-fired power plants (CFPPs) were thought an important source of Tl, but few field studies had been conducted for this area. In this article, we investigated the fate of Tl in five pulverized coal utility power plants in Guizhou province, Southwest China, and found the Tl concentration in stack gas is in low levels of 0.006–0.011 μg·Nm−3, and less than 0.05% of total input of Tl is escaped into the ambient atmosphere. The majority of Tl (88.7%–97.4% of the total output) is detained by the ESP/ESP-FF fly ashes. Compared to the little amount (~4 kg·yr−1) of Tl that discharged into the atmosphere from Guizhuo’s CFPPs in 2017, more Tl (over 700 kg) ends up in the solid coal combustion products each year, which makes the need of careful disposal of this solid combustion waste to prevent the mobilization of Tl into the environment.

Segment-based Volatile Organic Compound Emission Characteristics from Different Types of Coking Plants in China

ABSTRACT The source profiles, emission factors, and chemical reactivity of volatile organic compounds (VOCs) generated by two typical coking plants, one employing a non-recovery process and the other, a mechanical process, in Shanxi Province, a major coking hub in China, were determined for different segments of coke production during normal operations. The primary components in the stack flue gas were ethylene, 1-butene, benzene, acetylene, and 2,2-dimethylbutane for the non-recovery plant and styrene, benzene, and ethylene for the mechanical plant. The fugitive emissions were also monitored at the mechanical plant, and the most abundant species leaking from the oven were benzene, toluene, ethane, m-xylene, and ethylene, whereas those leaking from byproducts were benzene, propane, ethane, ethylene, n-pentane, n-butane, isobutene, 1-butene, toluene, and propylene. The stack flue gas at the non-recovery and mechanical coking plants exhibited VOC emission factors of 96 g Mg–1-coke and 0.4 g Mg–1-coke, respectively; thus, VOCs released by the former merit greater concern. Since the highest ozone formation potential (OFP) was observed for the stack flue gas at the non-recovery plant (80.26 mg m–3), followed by fugitive oven emissions at the mechanical plant (7.22 mg m–3), controlling these VOCs will significantly reduce their conversion into ozone. Overall, replacing non-recovery coking plants with mechanical coking plants will decrease VOC emissions and improve the ambient air quality in China.

Fate of cadmium in coal-fired power plants in Guizhou, Southwest China: With emphasis on updated atmospheric emissions

Coal-fired power plants (CFPPs) are important source of anthropogenic atmospheric releases of various pollutants, including cadmium (Cd). In this research, the distribution of Cd in seven CFPPs in Guizhou province, southwest China and the atmospheric Cd emissions from this source category in this province was studied. Among the boilers, one was a circulating fluidized bed boiler (CFB) and the others were pulverized coal-fired boilers (PC). All CFPPs are equipped with De-NOx, De-dust, and De-SO2 devices. Solid samples including feed fuel (coal, gangue, and coal slime), limestone, bottom ash, fly ash, gypsum, as well as stack flue gas samples were simultaneously collected and analyzed. Cd in feed coal, bottom ash, fly ash, limestone, gypsum, and stack flue gas were in the range of 0.15–0.68, 0.08–0.42, 0.43–2.03, 0.01–0.67, 0.02–0.41 mg kg−1, and 0.005–0.03 μg·Nm−3, respectively. Cd release ratio during the coal combustion in the boiler was in the range of 95.91–98.77% for PC, but only 76.94% for CFB. Cd atmospheric emission factors were in the range of 0.03–0.2 mg Cd·t−1 coal, 0.02–0.1 μg·(kW·h)−1 or 0.002–0.01 g Cd·TJ−1 for the seven CFPPs, lower values were found for CFB boiler than that of PC boilers. In 2017, the amount of Cd emitted from CFPPs in Guizhou province was estimated to be 51.4 kg y−1 (CFB: 2.4 kg y−1 and PC: 49 ± 32 kg y−1), significantly lower than previous reports.

Spatial and temporal variation, source profile of PCDD/Fs in the atmosphere of a municipal waste incinerator in China

The mass concentrations, toxic equivalent quantity (TEQ) concentrations and congener profiles of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the stack flue gas and ambient air of municipal solid waste incinerator (MSWI) were monitored in this study to evaluate the levels, emission characteristics, seasonal variation and emission sources of PCDD/Fs. Thirty-one ambient air samples were collected from four sites around MSWI during 2016–2017, and twelve stack flue gas samples were collected from one MSWI. Results showed that the PCDD/Fs concentrations of the stack flue gas ranged from 0.0077 to 0.021 ng I-TEQ/Nm3, with an average value of 0.016 ng I-TEQ/Nm3. The ambient air samples collected in 2016 and 2017 ranged from 0.017 to 0.27, and 0.035–0.27 pg I-TEQ/Nm3, with an average value of 0.078 and 0.10 pg I-TEQ/Nm3, respectively. The 2, 3, 4, 7, 8-PCDF always contributes most to toxicity both in stack flue gas and ambient air samples. PCDD/Fs in the ambient air of the study area showed significant seasonal differences, and the total concentration of PCDD/Fs was highest in winter, which was about 3.5–7.5 times that of summer. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to determine the correlation between MSWI emissions and PCDD/Fs in ambient air. It is worth mentioning that MSWI is not the main source of PCDD/Fs in ambient air.

Optimisation of fuel in fire tube saturated steam boiler

Considerable improvements have been made to minimise the fuel consumption in industrial boilers since a sizable portion of the operational cost can be reduced with fuel optimisation. In this study a combination of air preheater and condensing economiser is proposed to optimise the fuel usage in a fire tube heat boiler. The process utilises 10% excess air that is preheated to 96°C in an air preheater using the heat of stack flue gases. This improves the boilers efficiency by 3%. Moreover, makeup water is also heated to 84°C in the condensing economiser using the heat of stack flue gases coming from the air preheater. This proposed assembly extracts most of the energy from stack flue gases before it start to condense. A simulation using ASPEN HYSYS® shows that using preheated make up water and preheated combustion air, fuel demand in the boiler is reduced by 10%, thus making the process more economical.

Optimisation of fuel in fire tube saturated steam boiler

Considerable improvements have been made to minimise the fuel consumption in industrial boilers since a sizable portion of the operational cost can be reduced with fuel optimisation. In this study a combination of air preheater and condensing economiser is proposed to optimise the fuel usage in a fire tube heat boiler. The process utilises 10% excess air that is preheated to 96°C in an air preheater using the heat of stack flue gases. This improves the boilers efficiency by 3%. Moreover, makeup water is also heated to 84°C in the condensing economiser using the heat of stack flue gases coming from the air preheater. This proposed assembly extracts most of the energy from stack flue gases before it start to condense. A simulation using ASPEN HYSYS® shows that using preheated make up water and preheated combustion air, fuel demand in the boiler is reduced by 10%, thus making the process more economical.

Atmospheric mercury emissions from two pre-calciner cement plants in Southwest China

China produces the most cement product worldwide, and cement plants (CPs) have been regarded as the largest anthropogenic sources of atmospheric mercury (Hg) emissions in China since 2009. Onsite studies of this source are scarce compare to the huge numbers of CPs in China. Hence, quantifying Hg emissions from more CPs is needed in reducing the large uncertainties existed in the current Hg emission inventories and for assessing subsequent impacts of Hg on human and ecosystem health. In this study, two pre-calciner CPs in Guizhou province of Southwest China were selected for quantifying the emission factor and mass balance of Hg. Results showed that Hg emission levels in the two CPs were obviously different due to the differences in Hg input and circulation in the production system. In cement plant #1 (CP #1), the input and output of Hg reached a dynamic equilibrium condition, the emission factor was 76.1 mg Hg·t−1 clinker, and Hg concentration in the stack flue gas was in the range of 14.46–16.64 μg m−3. In cement plant #2 (CP #2), Hg was in an enriching status because it was a new plant with operation of several months and most input Hg was retained inside the production system, hence with a much lower emission factor of 1.8 mg Hg·t−1 clinker and Hg concentration of 0.15–0.49 μg m−3 in the stack gas. Kiln tail stack was the main output pathway of Hg in the clinker production process. With removal efficiency of 73.06% and 99.95% at kiln tail by ESP in CP #1 and humidifier + ESP-FF in CP #2, respectively, Hg emitted into the atmosphere was mainly in the forms of gaseous oxidized mercury (Hg2+) and gaseous elemental mercury (Hg0). Besides, the operation mode (on or off) of raw mill had great impact on the concentration and speciation of Hg in flue gas and flue gas temperature at kiln tail. In the clinker production system, limestone is the main source of Hg input (41.4–56.4%), followed by the fueled coal (15.3–32.5%). While, in the clinker to cement production process, the additives (mainly gypsum from coal-fired power plants, 83.2–94.4%) was the main source of Hg in the cement because Hg concentration in the clinker was very low.

Analisa Peningkatan Efisiensi Direct-Fired Heater

Direct-Fired Heater, usually called heater is a heat exchanger equipment that use hot gasses from combustion to rise up process fluid temperature flow through tubes coil in the heater. Debutanizer Reboiler Heater at PT Pertamina Balikpapan Refinery, having capacity 137,185,000.00 Btu/h was replaced and need efficiency improvement both in heat absorption and fuel consumption. That’s why; need to analyze the existing design. The analysis method is using Microsoft Excel Programming Software base on API 560, API 530, Direct-Fired Heater Design Handbook and literatures from journals and articles. For efficiency improvement in heat absorption and fuel consumption, need to modify heating surface area and combustion air input at elevated temperature. So, by adding Air-Preheater for rise up combustion air input by using stack flue gas, the fuel combustion can be decreased and heat liberated increased.

An effective numerical method for calculating unseparated flows in building aerodynamics

The problem of the mixing of heated gases is of interest in connection with the development of pollution-free technologies for natural-fuel combustion in modern heat and electricity generating plants. The operating principle of the tall structures designed for this purpose, which combine a smokestack and a cooling tower, is as follows. At the base of the stack flue gas, from which the sulfur has been removed, is fed into a flow of air heated in a heat exchanger. As it moves through the stack, the gas mixes with the hot air and is carried into the atmosphere by the natural draft. The design must satisfy certain requirements. The temperature of the flue gas must not fall below a certain limit at which condensation that leads to corrosion develops. The gas outlet velocity must be higher than 4 m/s to prevent downdraft. The concentrations of pollutants released into the atmosphere must be within the permissible limits. One promising means of enhancing the efficiency of such structures is to swirl the flue gas ahead of the stack inlet. Flow swirling considerably intensifies the heat and mass transfer processes, improves the mixing of the hot gases, reduces the pollutant concentrations at the stack outlet, and prevents flow separation on the walls. The general formulation of the problem of the mixing of two nonisothermal turbulent flows is based on the complete Reynolds equations. This system closed by a turbulence model (algebraic or differential) is fairly complicated and its solution is laborious. A simplified model is based on the parabolized Navier-Stokes equations, which restricts the area of applicability to unseparated flows. However, in view of the mechanical nature of the problem considered, unseparated flows are of most interest. In this paper, an effective method of solving boundary-layer equations is discussed, in which the initial system reduces to ordinary differential equations written on the streamlines.

Performance Analysis of a Combined Cycle Power Plant with Simultaneous Cooling of Inlet Air Streams to the Compressor and Condenser

Abstract: This paper presents the thermodynamic performance analysis of an existing combined cycle power plant to be retrofitted with a waste heat driven aqua lithium bromide absorption refrigerator for cooling the inlet air streams to the compressor and air-cooled steam condenser. The power plant is located in the hot and humid tropical region of Nigeria, latitude 4°45′N and longitude 7°00′E. This was achieved by performing energy and exergy analysis of the integrated system. Using the operating data of the existing combined cycle power plant, the results of the analysis showed that by cooling the inlet air streams to 15oC at the compressors, and to 29oC at the air-cooled steam condenser, the net power output, thermal and exergy efficiencies of the combined cycle plant increased by 7.7%, 8.1% and 7.5% respectively while the plant total exergy destruction rate and specific fuel consumption dropped by 10.8% and 7.0% respectively. The stack flue gas exit temperature reduced from 126oC to 84oC in the absorption refrigerator, thus reducing the environmental thermal pollution. The COP and exergy efficiency of the refrigeration cycle was 0.60 and 27.0%, respectively. Results also show that the highest rate of exergy destruction in the combined cycle power plant occurred in the combustion chamber while the highest rate of exergy destruction in the absorption refrigeration cycle occurred in the evaporator followed by the absorber.

Performance Analysis of a Combined Cycle Power Plant with Simultaneous Cooling of Inlet Air Streams to the Compressor and Condenser

This paper presents the thermodynamic performance analysis of an existing combined cycle power plant to be retrofitted with a waste heat driven aqua lithium bromide absorption refrigerator for cooling the inlet air streams to the compressor and air-cooled steam condenser. The power plant is located in the hot and humid tropical region of Nigeria, latitude 4°45′N and longitude 7°00′E. This was achieved by performing energy and exergy analysis of the integrated system. Using the operating data of the existing combined cycle power plant, the results of the analysis showed that by cooling the inlet air streams to 15oC at the compressors, and to 29oC at the air-cooled steam condenser, the net power output, thermal and exergy efficiencies of the combined cycle plant increased by 7.7%, 8.1% and 7.5% respectively while the plant total exergy destruction rate and specific fuel consumption dropped by 10.8% and 7.0% respectively. The stack flue gas exit temperature reduced from 126oC to 84oC in the absorption refrigerator, thus reducing the environmental thermal pollution. The COP and exergy efficiency of the refrigeration cycle was 0.60 and 27.0%, respectively. Results also show that the highest rate of exergy destruction in the combined cycle power plant occurred in the combustion chamber while the highest rate of exergy destruction in the absorption refrigeration cycle occurred in the evaporator followed by the absorber.

Characterization of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans of the Flue Gases, Fly Ash and Bottom Ash in a Municipal Solid Waste Incinerator

The emissions factors of PCDD/Fs from the stack flue gas, bottom ash and fly ash of a municipal solid waste incinerator (MSWI) were analyzed in this study. The congner profiles of PCDD/F mass were dominant in OCDD and OCDF; however, those of PCDD/Fs-TEQ were mainly 2,3,4,7,8-PeCDF and 1,2,3,7,8-PeCDD in all samples. The PCDD/F emission factors of MSWI per metric ton of waste incinerated from the stack flue gas, bottom ash and fly ash were at an averaged of 0.0919, 7.20 and 12.8 μg PCDD/Fs-WHO2005-TEQ ton–1, respectively. Futhermore, the emission factor of MSWI in the unit of electricity produced averaged 0.185, 14.5 and 26.3 μg PCDD/Fs-WHO2005-TEQ (MWh)–1, respectively. As the results shown in this study, the majority of total PCDD/Fs-WHO2005-TEQ were mainly in both bottom ash and fly ashes. From long-term perspective, the disposal of both bottom and fly ashes should pay more attention to this issue. The results of this study provide useful information for both further studies and environmental control strategies aimed at persistent organic compounds (POPs).

Spatial variation of PCDD/F and PCB emissions and their composition profiles in stack flue gas from the typical cement plants in China

Cement production processes are important sources of unintentionally produced persistent organic pollutants (UP-POPs), such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and polychlorinated biphenyls (PCBs). The emissions of PCDD/Fs and PCBs in the stack flue gases from eight typical cement plants in China were investigated in this study, including one wet process rotary kiln, three dry process rotary kilns and four vertical shaft kilns. PCBs exhibited relatively higher mass concentrations with the dioxin-like (dl) and indicator PCBs of 0.14–17.36 and 0.42–12.90 ng/Nm3, respectively. However, PCDD/Fs contributed most to the total toxic equivalent concentrations, with the proportions exceeding 90%. The international toxicity equivalency (I-TEQ) concentrations of PCDD/Fs varied greatly from 0.01 to 0.46 ng I-TEQ/Nm3 in stack gases, two of which exceeded the exhaust gas concentration limit of 0.1 ng I-TEQ/Nm3 established by the European Union Directive. In weight units, 1,2,3,4,6,7,8-HpCDF was the most abundant congener in the stack gases from various types of cement kilns, with the factions of 17.0–27.8%. TCDFs and PeCDFs were the first two most abundant homologue groups. 2,3,4,7,8-PeCDF was the largest contributor to the total I-TEQ. The emission factors of PCDD/Fs and PCBs in the eight cement kilns were estimated to be 0.01–1.35 μg I-TEQ/t clinker and 8.20 × 10−4∼8.23 × 10−2 μg World Health Organization TEQ (W-TEQ)/t clinker, respectively. No obvious differences of the PCDD/F and PCB emission factors were found among the varied cement production technologies.

Mercury emission from sintering process in the iron and steel industry of China

Iron and steel production is one of the most significant anthropogenic sources of atmospheric mercury emission. However, there is little information about this source in China. In this study, we focused on three typical Chinese sintering furnace processes. Mercury in flue gas was sampled using the EPA Method 30B and Ontario Hydro Method, and solid samples were also analyzed. We found that 1.12–4.66% of mercury input in sintering furnace processes was emitted into the atmosphere. The total mercury concentrations in the sintering furnace flue gas were 17.773, 31.765 and 18.275μg/m3; the major mercury species was oxidized form, which accounted for 73.4–94.7% of the total mercury. The mercury concentrations in the stack flue gas were 0.373, 0.533 and 0.465μg/m3, while its removal efficiencies by air pollution control devices (APCDs) were 97.5%, 81.1% and 96.8%, and its emission factors were 2.49, 2.71 and 1.28mg/t sinter. The main mercury inputs were iron ore, coal, coke and lime, where the iron ore input was 74.84–92.22% of the total mercury quantity. Moreover, mercury was distributed in fly ash (19.22–81.54%), gypsum (13.29–46.00%), iron ore sinter (0–11.45%), and flue gas (1.12–4.66%). An approximate mercury mass balance could be obtained from various samples in this study.

Performance analysis of an integrated gas-, steam- and organic fluid-cycle thermal power plant

This paper presents the performance analysis of an existing combined cycle power plant augmented with a waste heat fired organic Rankine cycle power plant for extra power generation. This was achieved by performing energy and exergy analysis of the integrated gas-, steam- and organic fluid-cycle thermal power plant (IPP). Heat source for the subcritical organic Rankine cycle (ORC) was the exhaust flue gases from the heat recovery steam generators of a 650 MW natural gas fired combined cycle power plant. The results showed that extra 12.4 MW of electricity was generated from the attached ORC unit using HFE7100 as working fluid. To select ORC working fluid, ten isentropic fluids were screened and HFE7100 produced the highest net power output and cycle efficiency. Exergy and energy efficiencies of the IPP improved by 1.95% and 1.93%, respectively. The rate of exergy destruction in the existing combined cycle plant was highest in the combustion chamber, 59%, whereas in the ORC, the highest rate of exergy destruction occurred in the evaporator, 62%. Simulations showed exergy efficiency of the IPP decreased with increasing ambient temperature. Exit stack flue gas temperature reduced from 126 °C in the combined cycle power plant to 100 °C in the integrated power plant.