Flue Gas Desulphurization System Research Articles

Research on enhancing separation of ultra‐fine droplets using turbulators between adjacent demister plates in WFGD systems

AbstractTo enhance the performance of demister applied in wet flue gas desulphurization systems, flow turbulators are equipped between adjacent plates to reconstruct flow field. Both experimental and numerical approaches are employed to investigate the influence of various kinds of turbulator configurations upon removal of droplets within the range of 5–50 μm obeying Rosin‐Rammler distribution. Turbulators including spoiler, square column, concave groove, perforated concave groove, and triangular and cylinder columns are compared, among which spoiler provided the highest overall efficiency while square column yields the best graded efficiency for 5 μm droplets group. Furthermore, moving the spoiler towards the core region of the demister ducts received better performance due to augmented interaction between spoiler and drainage channels, which performed an essential role in droplets collection. Based on this knowledge, spoilers are optimized by changing their angle of attack and size; the result is positive since overall separation efficiency can be improved to 100%, along with graded efficiencies for 10 and 5 μm groups achieving 95.97% and 27.26%, respectively, much higher than those of baseline demister without turbulators. This study indicates that inertial‐based demisters have great potential in separating ultra‐fine droplets through reorganizing turbulence field, thus extra system loss can be avoided by abandoning additional filter components.

Atmospheric SO2 pollutant prediction using mutual information based TCNN-GRU model for flue gas desulfurization process

Over the past several years, sulfur dioxide (SO2) has raised growing concern in China owing to its adverse impact on atmosphere and human respiratory system. The major contributor to SO2 emissions is flue gas generated by fossil-fired electricity-generating plants, and as a consequence diverse flue gas desulphurization (FGD) techniques are installed to abate SO2 emissions. However, the FGD is a dynamic process with serious nonlinearity and large time delay, making the FGD process modeling problem a formidable one. In our research study, a novel hybrid deep learning model with temporal convolution neural network (TCNN), gated recurrent unit (GRU) and mutual information (MI) technique is proposed to predict SO2 emissions in an FGD process. Among those technique, MI is applied to select variables that are best suited for SO2 emission prediction, while TCNN and GRU are innovatively integrated to capture dynamics of SO2 emission in the FGD process. A real FGD system in a power plant with a coal-fired unit of 1000 MW is used as a study case for SO2 emission prediction. Experimental results show that the proposed approach offers satisfactory performance in predicting SO2 emissions for the FGD process, and outperforms other contrastive predictive methods in terms of different performance indicators.

Uncertainty and disturbance estimator-based model predictive control for wet flue gas desulphurization system

Uncertainty and disturbance estimator-based model predictive control for wet flue gas desulphurization system

The effect of spray nozzles failure on SO2 removal efficiency

ABSTRACT This study was carried out on an absorber in the body of flue gas desulphurization system (FGD) of a coal-fired power plant. In this study, efficiency losses caused by the clogging or breaking of the spray nozzles were examined. These abovementioned problems of spray nozzles are the most common among the many factors affecting the sulfur retention efficiency. Although energy and exergy analysis is very common to optimize the system efficiency of FGD units, failure of spray nozzles in absorbers might be the main reason in terms of low FGD units efficiency and low SO2 removal rates. In this study, firstly locations of clogged or damaged nozzles are determined by examining a total of 240 nozzles (3 × 80). After the replacement of the broken spray nozzles, increase in the efficiency of A-B, B-C, A-C and A-B-C spray lines were observed as 9.14%, 3.77%, 10.56%, 9.72%, respectively. Depending on the washing zone of the nozzles, if one nozzle is damaged, it causes the efficiency to decrease between 0.24% and 0.36%.

FGD (FLUE GAS DESULPHURIZATION) SYTEM -OVER VIEW

Advantage of using dry FGD (FLUE GAS DESULPHURIZATION) System instead of the WET FGD System in terms of efficiency and cost-effective solution. Though, the high cost of expensive slaked/quick lime required as reagent in dry FGDs, considering the capital cost of the project and considering the Water saving (useful in the water scarcity area) the Dry FGD system shall be recommended.

Flexible Control of Wet Desulphurization Process Based on Frequency Retrofit

To assist in the absorption of renewable energy, coal-fired power plants need to operate over a wide range of loads, which exacerbates the challenge of the time delay in the wet desulphurization process. Therefore, this paper proposes a new control structure based on frequency retrofit and a corresponding model predictive controller to change the traditional idea of wet desulphurization control. This structure provides faster control actions, thus reducing time delay directly. And it makes the original discrete control variable continuous, enabling most control methods. The field application to the wet flue gas desulphurization system reveals the practical prospects of the proposed control structure and simulations have been conducted to verify the merits of the proposed control scheme based on data collected from a 1000 MW power plant.

Impact of ultra-low emission retrofitting on partitioning and emission behavior of chromium in a Chinese coal-fired power plant.

Due to its low vapor pressure, chromium (Cr) mostly emitted as fly ash particles (especially PM2.5) into environment in coal-fired power plants (CFPPs). The ultra-low emission (ULE) control technologies used in current CFPPs may be beneficial to reducing both the regular pollutants and hazardous trace elements (e.g., Cr), but the insight into the removal efficiency of Cr by different upgrading air pollution cleaning devices (APCDs) and the environmental stability of the Cr-bearing wastes produced from those APCDs in the ULE CFPPs has rarely reported. This study investigated and compared the distribution and emission characteristics of Cr in a Chinese CFPP before and after ULE, and the leaching behavior of Cr after ULE retrofitting in combustion byproducts was also revealed. The results showed that Cr was primarily captured in bottom and fly ashes (80.85%), followed by gypsum (0.02%) and sludge from wet electrostatic precipitator (WESP) (4.52×10-4%), with only 3.02×10-8% emitted into the atmosphere. Additional WESP had a large removal efficiency of Cr with the value of 92.04%, and the overall Cr removal efficiency of selective catalytic reduction (SCR) equipment, electrostatic precipitator (ESP), wet flue gas desulphurization (WFGD) system, and WESP equipped after ULE retrofitting was 99.99%. Notably, although the mass percentage of Cr in WESP sludge was negligible, the concentration of Cr in WESP sludge was 324.04mg/kg. The leaching concentrations of Cr in combustion byproducts were in the descending order: fly ash>WESP sludge>bottom ash>gypsum. The atmospheric emission factor of Cr in the studied power plant was 1.08mg/t coal, which was significantly lower than those of the CFPPs before ULE retrofitting. Therefore, the ULE retrofitting for CFPP was beneficial to reduce Cr emissions. More attention should be paid to the subsequent processing problem of solid combustion byproducts, especially the WESP sludge.

The Turning Point in Indian Environment

The human life in the earth may be continued without water for few days, without food for few weeks. However the human life in the earth may not be continued for few minutes without air. Air comes under. 24 ? 7 in our human system. In such condition, air plus sulphur dioxide is harmful to respiratory system which leads to premature deaths and reduction in life expectancy. It is a big shock to the nation that India becomes the highest emitter of sulphur dioxide of the world, surpassing the China. It is not a encouraging trend for us. Under these circumstances MOEF and CC has notified the norms for various pollutants including sulphur dioxide emission from thermal power plants in December 2015. The norms cover various size plants for various periods with various levels of emission, with a timeframe of two years as implementation schedule. This notification is a correct notification in correct direction, but with some time delay. This notification has put about 1800000 MW in study mode, mainly of coal fired units in nature. The sulphur dioxide emission may be well controlled by installing flue gas desulphurisation (FGD) system in boiler flue gas path. By injecting lime in the flue gas path, sulphur dioxide is converted to calcium sulphite and then by reacting with oxygen, it is converted to calcium sulphate. Thus the flue gas is purified from sulphur dioxide. India has to import this technology. Technology transfer is a difficult task especially on commercial terms. This article narrates the various happenings in the country after the publication of notification.so that the reader gets the overall picture in single presentation. The implementation of the flue gas desulphurisation (FGD) system in Indian thermal power plants as early as possible, may improve the environment prevails in the country. This paper deals with various issues related to Sulphur dioxide emission and reduction measures.

Spray Dryer Ash from Thermoelectric Power Plants as Civil Construction Materials

AbstractInstalling flue gas desulphurization systems before particulate collectors in thermoelectric plants generates spray dryer ash (SDA), a mixture of fly ash and sulfur products. SDA carries a ...

A wet type flue gas desulphurisation system used in a coal-fired power plant: a case study

A wet type flue gas desulphurisation system used in a coal-fired power plant: a case study

A wet type flue gas desulphurisation system used in a coal-fired power plant: a case study

A wet type flue gas desulphurisation system used in a coal-fired power plant: a case study

Analysis of Desulfurization Characteristics in Coal-Fired Power Plant by Numerical Simulation and Computer Simulation

In this paper, the spray tower of a wet flue gas desulphurization system in a coal-fired power plant is studied. The flue gas and slurry droplet are two-way coupled with Euler-Lagrange method. The heat and mass transfer and the ion reaction in SO2 removal are also considered. The results show that the error between simulation removal efficiency and practical value is within 5% under the above models. Adjusting liquid-gas ratio and opening spray layer are beneficial to the SO2 removal, and the optimal liquid-gas ratio is 16 L/m3. Balance gas velocity is needed, because an overlarge velocity will significantly reduce removal efficiency.

Spray drying absorption for desulphurization: a review of recent developments

Sulphur dioxide (SO2) abatement technologies, i.e. flue gas desulphurization (FGD), have proven effective in curtailing the harmful SO2 emissions resulting from coal combustion for electrical power generation. New regulations on these emissions now require some power utilities to retrofit new FGD units to existing coal-fired power plants to meet required emission standards. Wet FGD limestone scrubbing has been predominantly used over other competing technologies. However, the simplicity of the spray-drying absorption (SDA) technology has made it an attractive alternative to the wet scrubbing process. SDA offers huge savings on energy, water, operating cost and maintenance. Despite high cost of the sorbent (hydrated lime) used, recent advances in SDA process offer considerable economic and technical advantages ranging from improved sorbent utilization, better atomization and enhanced performance. Alternative sorbents and additives are continuously being explored for simultaneous removal of pollutant gases from flue gas. The performance improvement areas in a lime spray drying system include the use of inorganic salt additives, recycling of the dried product and the use of siliceous materials. This study is intended to review FGD systems applicable to coal-fired power plants, through a technical comparison between competing technologies. Additionally, a review of the spray-drying absorption process and operating parameters affecting their efficiency was carried out, together with a critical assessment of the literature published to date.

Development of arc welding technique to preclude microsegregation in the dissimilar joint of Alloy C-2000 and C-276

Hastelloy C-2000 and C-276 are widely used in Flue Gas Desulphurization (FGD) system and Chemical Processing Industries (CPI). Current work is focused on weld microstructure, and mechanical properties (structure-property relationship) of the dissimilar combination of alloy C-2000 and C-276. Multi-pass Pulsed Current Gas Tungsten Arc (PCGTA) welding was adopted for joining the dissimilar alloys using the filler ERNiCrMo-17. Microstructural characteristics of the weld joint were assessed by Optical and Scanning Electron Microscope (SEM). Weld interface microstructure examination revealed the presence of grain coarsening near the Heat Affecting Zone (HAZ) of the alloy C-276 side. SEM analysis shows the absence of secondary Topologically Closed Packed (TCP) phases in the Inter-Dendritic (ID) regions of the dissimilar weld. Micro-segregation of alloying elements in the weldment was assessed by Energy-Dispersive X-ray Spectroscopy (EDS). X-Ray Diffraction (XRD) analysis had been carried out to identify the phase constitution and average grain size. Strength, toughness, and hardness of the dissimilar weld were evaluated with the support of the tensile test, Charpy impact test, and Vicker’s hardness test. Tensile study showed that all the tensile fracture occurred at the base metal side of alloy C-276. The average toughness of the dissimilar alloy joint was noted about 84 J. Hardness test results indicated that fusion zone (FZ) hardness value was 6.19% and 2.27% superior to the candidates’ material (C-276 and C-2000) employed in this study. The refined grain structure and absence of microsegregation resulted in the highest hardness in the dissimilar weld FZ. Results revealed the substantiated use of PCGTA welding for the effective joining of dissimilar alloys of C-2000 and C-276 through the evaluation of metallurgical and mechanical characteristics.

Multimodel Anomaly Identification and Control in Wet Limestone-Gypsum Flue Gas Desulphurization System

Sulphur dioxide, as one of the most common air pollutant gases, brings considerable numbers of hazards on human health and environment. For the purpose of reducing the detrimental effect it brings, it is of urgent necessity to control emissions of flue gas in power plants, since a substantial proportion of sulphur dioxide in the atmosphere stems from flue gas generated in the whole process of electricity generation. However, the complexity and nondeterminism of the environment increase the occurrences of anomalies in practical flue gas desulphurization system. Anomalies in industrial desulphurization system would induce severe consequences and pose challenges for high-performance control with classical control strategies. In this article, based on process data sampled from 1000 MW unit flue gas desulphurization system in a coal-fired power plant, a multimodel control strategy with multilayer parallel dynamic neural network (MPDNN) is utilized to address the control problem in the context of different anomalies. In addition, simulation results indicate the applicability and effectiveness of the proposed control method by comparing with different cases.

Nitrate removal from wastewater generated in wet Flue Gas Desulphurisation Systems (FGD) in coal-fired power generation using the heterotrophic denitrification method

Abstract The article presents an assessment of the possibilities of using the heterotrophic denitrification process to remove nitrates from wastewater produced in wet flue gas desulphurisation (FGD) installations and also its optimization in the scope of basic technological parameters. This kind of wastewater is characterized by high salinity (even up to 40,000 g/m3), high temperature (up to 50°C) and low biodegradability, which is expressed by the biochemical oxygen demand (BOD5). The experimental rig consisted of a storage tank and a bioreactor in the form of a bed with an apparatus for measuring basic parameters (temperature, pH, nitrate nitrogen). After an initial adaptation period, a high degree of nitrate nitrogen removal from wastewater (exceeding 95% reduction) was obtained with a reaction time of 180 minutes during the denitrification rate test (NUR). It was also determined that the optimal loading range of the active surface of the bed of 300 m2/m3 should be between 1.5–2.5 gN-NO3/m2·d. The results of the study show that when the required conditions for the development of microorganisms are provided, it is possible to fully adapt the denitrification biomass to the adverse composition of wastewater from wet FGD unit.

Design and operational condition optimization of a rotary regenerative heat exchanger

In this study, comprehensive optimization studies of rotary regenerative heat exchangers (RHEX) used in the flue gas desulphurization system are conducted. In this context, two optimization studies are taken into consideration; the first one is the optimization for the existing design by replacing the matrix elements with corrugated – undulated (CU) plates and the second one is the design and operational condition optimization to design a RHEX for the same boundary conditions utilizing CU plates. Sinusoidal pitch, inner height and the undulation angle of the undulated plate are selected as the decision variables where effectiveness, entropy generation number, and cost are treated as the objectives in the first case. For the second case, RHEX outer diameter and length, as well as the angular velocity, are added to the design variables and RHEX volume is considered to be an additional objective. Case-specific heat transfer coefficient and friction factor based on the experimental data are adapted through the thermal–hydraulic modelling of the RHEX with the effectiveness and number of transfer unit method. NSGA-II is implemented for multi-objective optimization. It is concluded that thanks to optimized CU and RHEX geometry as well as the angular velocity, RHEX effectiveness can be augmented by 92.06% with a penalty of 66.66% increase in the total cost by only replacing the existing matrix profile with CU elements. Also, minimizing the cost by 46.11%, an increase of effectiveness by 32.02% and 16.60% decrease of entropy generation number can be obtained. A new design with the same budget can be obtained by improving the effectiveness by 53.19% and reducing the entropy generation number by 18.95% in a volume which is 8.90% smaller. Similarly, a RHEX design to have approximately the same volume with the existing RHEX is possible with 50.64% increased effectiveness, 20.65% decreased entropy generation number and 23.35% reduced cost.

Dynamic optimization oriented modeling and nonlinear model predictive control of the wet limestone FGD system

Abstract Nonlinear model predictive control (NMPC) scheme is an effective method of multi-objective optimization control in complex industrial systems. In this paper, a NMPC scheme for the wet limestone flue gas desulphurization (WFGD) system is proposed which provides a more flexible framework of optimal control and decision-making compared with PID scheme. At first, a mathematical model of the FGD process is deduced which is suitable for NMPC structure. To equipoise the model's accuracy and conciseness, the wet limestone FGD system is separated into several modules. Based on the conservation laws, a model with reasonable simplification is developed to describe dynamics of different modules for the purpose of controller design. Then, by addressing economic objectives directly into the NMPC scheme, the NMPC controller can minimize economic cost and track the set-point simultaneously . The accuracy of model is validated by the field data of a 1000 MW thermal power plant in Henan Province, China. The simulation results show that the NMPC strategy improves the economic performance and ensures the emission requirement at the same time. In the meantime, the control scheme satisfies the multi-objective control requirements under complex operation conditions (e.g., boiler load fluctuation and set point variation). The mathematical model and NMPC structure provides the basic work for the future development of advanced optimized control algorithms in the wet limestone FGD systems.

Effect of a Wet Flue Gas Desulphurization System on the Emission of PM2.5 from Coal-Fired Power Plants

Wet flue gas desulphurization (WFGD) is wildly used to control SO2 emission from coal-fired power plants. The influence of WFGD on particulate matter (PM) emission has recently drawn significant public attentions in China. In this study, PM2.5 was collected at both the inlet and outlet from three WFGD units, including a single scrubber lime-stone-gypsum FGD unit, a cascade scrubber lime-stone-gypsum FGD unit, and a seawater FGD unit. PM2.5 mass concentrations and their chemical compositions were analyzed. A method to calculate the addition and removal ratios is proposed according to the concertation of PM2.5 components, such as Ti, Pb, Cr, and V. The results indicate that the removal ratio was similar between the three WFGD units (77.1% on average). However, the addition ratio varied significantly. The performance of the cascade scrubber lime-stone-gypsum FGD unit was best, with a lower addition ratio of 8.6%, which is attributed to the weaker evaporation of desulphurization slurry droplets in their second tower under the low temperature of the flue gas. The addition ratio of the seawater FGD unit was also low (23.9%) because of its low concentration of solids in the seawater. The addition ratio of the single scrubber lime-stone-gypsum FGD system was highest, with a value of 162.3%, which was probably due to the low efficiency of the de-mister.

Understanding the impact of FGD technologies on the emissions of key pollutants in a Co-Firing power plant

The transition from limestone to lime-based flue gas desulphurisation system (FGD) was tested in a power station fired with high sulphur (S)-petroleum coke to better control the emissions of key pollutants. To this end, as a request of the power station owner to IDÆA-CSIC, we surveyed the power station fired with 70% S-petroleum coke and equipped with a slaked lime-based FGD, and compared the results with data from our previous works conducted at the same power station but operated with lower co-firing rates and a limestone FGD, the purpose being to improve the understanding on the impact that different FGD technologies may have on the fate, speciation and, ultimately, the emissions of key pollutants from the power station. Our observations suggest that the reaction pathways and speciation of key trace pollutants in the gypsum slurry including Cl, Mo, Hg and Se remained largely unchanged with the transition from limestone to lime-based FGD. By contrast, As, Cr, B, U and V speciation in the gypsum slurry was sensitive not only to the FGD sorbent, likely in response to differences in the pH, but also to the absence of ligands such as F−.The highly alkaline lime slurry neutralised the H+ released by the formation of metal-complexes. This favoured the stability of trace elements in their oxy-anionic forms or forming hydroxyl complexes, as opposed to the acidic conditions in limestone-FGD gypsum from previous works. Enrichment in Mo, V and Ni in the fly ash was primarily associated with the combustion of a petroleum coke. Other elements such as Pb, As, Zn, Cu and Se were also enriched in the fly ash relative to the boiler slag.