FGD Technology Research Articles

Numerical simulation and optimization of semi-dry flue gas desulfurization in a CFB based on the two-film theory using response surface methodology

Semi-dry circulating fluidized bed flue gas desulfurization(CFB-FGD) is a major industrial FGD technology. Assuming that only one desulfurizer particle is wrapped in each droplet for mass transfer and dissolution, this study proposed a two-film theory-based simplified desulfurization model, with which CFB desulfurization was performed. After model verification, this study simulated the hydrodynamics and desulfurization reaction characteristics and explored the effects of inlet SO2 concentration(A), gas velocity(B), circulating particle mass flux(C), and jet water volumetric flux(D) on the desulfurization efficiency. Simulation results coupling with response surface methodology (RSM) analysis could not only quantitatively reflect the effect degree of a single variable but also apply to the interaction between parameters, thus determining the optimal parameters. RSM results showed that D and CD were the independent and interaction parameters, respectively, that most significantly affected desulfurization efficiency. The simulation under the optimal operating parameters showed that the desulfurization efficiency was greatly improved, reaching 99.69%.

An overview of the energy scenario and energy storage device

With demand for the natural resources exceeds a certain threshold, it leads to a global ecological threat like the "Amphhan” catastrophe that had ravaged the eastern part of West Bengal during the month of February 2020 that resulted in the loss of lives and economic activity which is yet to be regained with its earlier momentum. The inflicted calamity has given a "blow” as well as "boost” to renewable energy sector that leads to greater seriousness on development of the energy storages devices/stations in the country. While India has already achieved 374 GW of total installed capacity of power generation in which the contribution from the thermal sector is about 62 per cent and that of the RP is about 22 per cent that comes to 90 GW as of today and 60 GW is under pipeline or under construction or under tendering process. The year 2020 is undoubtedly a year of change and the COVID-19 pandemic situation together with enforced lockdown in several parts of the country and even in globe has forced people to think differently to remain relevant against the New-Normal. In order to choose the sources of energy that does not cause pollution to the surrounding environment, the RET is the best and most favourable options to opt for along with the battery storage devices for making the power available throughout the day-long and even when the sun sets. Most of the batteries currently produced and used in our country is lithium-ion based and is mostly imported. To be on the self-reliant mode and moving towards "Atmanirbhar Bharat” through "Make in India” we need to have more and more indigenous manufacturer of Li-ion batteries. Good news is that 10 Indian companies have already procured manufacturing technology from DRDO and large scale production of indigenous Li-ion batteries is expected soon. The National Energy Mission of the Government of India has just rolled out with a focus on the Make in India and is envisioned to take all necessary formalities and policy decisions to be adopted to incentivise advanced energy storage manufacturing in India through the application of innovation and new technology options that are available. As a science communicator, the authors strongly opine that with the appropriate support from the Government of India through the policy decisions by the Niti Aayog, India will be one of the top markets for the energy storage adoptions and manufacturing and is another way forward to mitigate the climate change by producing electricity free from carbon dioxide emissions into atmosphere and provide green energy for sustainable path of development. As we see that the energy storage is a new thrust area along with introduction of FGD technology retrofitting with the thermal power plant, we look forward to the new ecosystem to be achieved by 2030.

Advances in absorbents and techniques used in wet and dry FGD: a critical review

Abstract Sulfur dioxide is considered as an extremely harmful and toxic substance among the air pollutants emitted from the lignite- and other high-sulfur-coal based power plants, old tires processing units, smelters, and many other process industries. Various types of absorbents and desulfurization technologies have been developed and adopted by the industries to reduce the emission rate of SO2 gas. The present paper focuses on the ongoing advances in the development of varieties of regenerative and non-regenerative absorbents viz., Ca-based, Mg-based, Fe-based, Na-based, N2-based, and others along with various FGD technology, viz., wet, dry or semi-dry processes. Additionally, different types of contactors viz., packed column, jet column, spray tower, and slurry bubble columns along with their significant operational and design features have also been discussed. In the existing or newly installed limestone-based FGD plants, an increasing trend of the utilization of newly developed technologies such as limestone forced oxidation (LSFO) and magnesium-enhanced lime (MEL) are being used at an increasing rate. However, the development of low-cost sorbents, particularly suitable solid wastes, for the abatement of SO2 emission needs to be explored sincerely. Many such wastes cause air pollution by way of entrainment of fine particulate matter (PM), groundwater contamination by its leaching, or brings damage to crops due to its spreading onto the cultivation land. One such pollutant is marble waste and in this work, this has been suggested as a suitable substitute to limestone and cost-effective sorbent for the desulfurization of flue gases. The product of this process being sellable in the market or may be used as a raw material in several industries, it can also prove to be an important route of recycling and reuse of one of the air and water-polluting solid wastes.

Numerical simulation of semi-dry desulfurization spouted bed using the discrete element method (DEM)

A research on semi-dry FGD technology using CFD-DEM method is conducted to study the motion of wet particles and their performance on SO2 remove. The liquid bridge force model proposed by Mikami (1998) et al. is introduced to estimate the interactionamong wet particles. The reaction rate of desulfurization is calculated depended on the two-film theory. The profiles of particle volume fractions, velocities and the main forces on particles are obtained. Simulation results indicate that liquid bridge force facilitates the formation of particle aggregation. Meanwhile, the distributions of particles are more inhomogeneous, which result in a decrease on SO2 removal efficiency. Furthermore, the effect of humidity on the desulfurization is also investigated by adjusting the parameter of dimensionless liquid bridge volume. As the humidity increases, the agglomerate grows and the SO2 removal efficiency increases first and gradually decreases. Simulation results of SO2 removal efficiency are in a good agreement with the experimental data from Kunio Kato (1999) et al.

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.

Full-Scale Evaluation of SO2 Capture Increase for a Semi-Dry FGD Technology

Tento přispěvek pojednava o zakladnich aspektech řizeni kotlů se stacionarni fluidni vrstvou, a to v porovnani se vzduchovým a oxyfuel režimem. Diskutovany jsou zakladni požadavky na parametry provozu takoveho kotle, ktere musi být navzajem splněny, zejmena požadavek na teplotu fluidni vrstvy, režim fluidace a dokonale vyhořeni paliva.

Experimental study on SO2 recovery using a sodium–zinc sorbent based flue gas desulfurization technology

A sodium–zinc sorbent based flue gas desulfurization technology (Na–Zn-FGD) was proposed based on the experiments and analyses of the thermal decomposition characteristics of CaSO3 and ZnSO3·2.5H2O, the waste products of calcium-based semi-dry and zinc-based flue gas desulfurization (Ca–SD-FGD and Zn–SD-FGD) technologies, respectively. It was found that ZnSO3·2.5H2O first lost crystal H2O at 100°C and then decomposed into SO2 and solid ZnO at 260°C in the air, while CaSO3 is oxidized at 450°C before it decomposed in the air. The experimental results confirm that Zn–SD-FGD technology is good for SO2 removal and recycling, but with problem in clogging and high operational cost. The proposed Na–Zn-FGD is clogging proof, and more cost-effective. In the new process, Na2CO3 is used to generate Na2SO3 for SO2 absorption, and the intermediate product NaHSO3 reacts with ZnO powders, producing ZnSO3·2.5H2O precipitate and Na2SO3 solution. The Na2SO3 solution is clogging proof, which is re-used for SO2 absorption. By thermal decomposition of ZnSO3·2.5H2O, ZnO is re-generated and SO2 with high purity is co-produced as well. The cycle consumes some amount of raw material Na2CO3 and a small amount of ZnO only. The newly proposed FGD technology could be a substitute of the traditional semi-dry FGD technologies.

A proposal for SO2 abatement in existing power plants using rich in calcium lignite

Under current European legislation for the abatement of SO2 emissions and the strict ELV after 2016, existing power plants need to apply flue gas desulphurization technologies. For the majority of the units operating in Northern Greece and elsewhere in the Balkans, wet FGD is not the desired option due to the high capital investment involved and the limited service life of the units (less than 20 years).The answer to the dilemma (opt out or new investment) seems to be a solution that comes from the rich calcium lignite of the region. Although local lignite is of low calorific value and loaded with mineral matter and high moisture, it carries a high calcium oxide content part of which is in the form of limestone. The calcareous fly ash is rich in free lime and under certain conditions full desulphurization of the flue gas is already achievable. The desulphurization efficiency of the flue gas due to calcium in lignite is at an average of 80% and it only needs to be boosted to 96% in order to achieve SO2 emission levels below 200 mg/Nm3 (dry, 6% reference oxygen).The scope of this research work is an effort to study the effect of the so called “natural desulphurization” and have its efficiency characterized in terms of certain lignite physical parameters. Under proper mixing and homogenization of the lignite feed to the power plants, the peak SO2 emissions can be smoothed out. Further desulphurization of the flue gas can be achieved by several dry FGD techniques already investigated in Greece and elsewhere [1]. Dry FGD is reported to have an efficiency limitation of 80% in the cool side of the combustion process (after LUVO). SO2 emission concentrations in the vicinity of 1.000 mg/Nm3 can by cooped with low investment dry FGD installation (with multiple injection points if required). Actual operation data show a clear relation between power load and flue gas velocities in the ducts as well as SO2 emission concentrations. A feasibility study carried out for a dry FGD installation is compared to wet FGD technology. It turns out that if lignite feed homogenization is employed, power plants can afford a compromising solution with power load losses in case of peak SO2 emissions and dry FGD installations instead of the classic and expensive wet FGD solution.

Flue gas desulphurisation in Serbia: Technologies, legal and economic aspects

Combustion of coal results in sulfur dioxide (SO2) emissions which cause detrimental impacts on the environment and human health. Electric power generating units account for the majority of SO2 emissions in Serbia. Environmental regulations in Serbia require gradual implementation of flue gas treatment technologies for control the emissions of pollutants into the atmosphere. As far as Serbian thermal power plants are concerned, the basic design of systems for flue gas desulphurisation has been developed for two thermal power plants. As wet limestone-based FGD technologies dominate in the world because of high SO2 removal efficiency, cost effectiveness, and gypsum as the by-product, it is expected that Serbian thermal power plants will use this technology. This paper presents a review of commercially available FGD technologies, as well as legal and economic perspective of the process. U.S. EPA's National Risk Management Research Laboratory has published the Coal Utility Environmental Cost Workbook which provides the rough-order-of-magnitude budgetary cost estimates as the starting point for the limestone forced oxidation cost model that might be a good starting point for cost estimates for Serbian electric utilities.

Population balance for CFB–FGD systems

Abstract Population balance is the basis of stable and effective operation of circulating fluidized bed flue gas desulfurization systems (CFB–FGD systems). The population balance model parameters were calibrated by comparing the calculated results for a CFB–FGD system with experimental data from a bench-scale CFB–FGD system. The relative error was less than 5.1%. The influences of the model parameters, reactor structures, operating conditions, and adhesive carrier particles on the population balance of the CFB–FGD system were then analyzed using the calibrated population balance model. The results indicated that particle segregation and the superficial gas velocity strongly influenced the particle size distribution. The cyclone separation efficiency and the selected particle draining coefficient also impacted the particle size distribution and the bottom ash ratio. The calcium to sulfur ratio and the bed temperature mainly influenced the bottom ash ratio and the desulfurization efficiency of the system. The anti-abrasion characteristics of the rapidly hydrated sorbent influenced the particle size distribution, the bottom ash ratio, and the desulfurization efficiency of the system. The population balance in the CFB–FGD system was more easily achieved when circulating ash from a CFB boiler was used as adhesive carrier particles instead of coal fly ash. This research provides guidance for stable, effective operation of CFB–FGD systems to promote industrial applications of CFB–FGD technology.

Application Status and Economic Analysis of Active Coke Flue Gas Desulfurization Technology

This paper analyzes the active coke FGD fundamental principles, structures and current applying situations, and calculates the initial investment active coke FGD and limestone-gypsum FGD. Moreover, it calculates the operating cost by raw material price and products price in China, and compares the initial investment cost and operating cost of the two FGD technologies in different usage period. This paper concludes that the high investment cost limits the wide application of active coke FGD, it can only be applied in some projects need sulfuric acid.

Prediction and Experimental Validation Studies of Wet Flue Gas Desulphurization with a Novel Type PCF Device Based on Limestone-Gypsum

A novel wet-type flue gas desulphurization process were developed and tested in this study. The process used a PCF device as the absorber where SO2 was absorbed into slurry of reactive CaCO3. A model of external mass-transfer based on the two-film theory was proposed for estimation of the SO2 absorption in the PCF device, and the theoretical SO2 removal efficiency was compared with the experimental data. The results show that the SO2 absorption rate in the spray zone is controlled by a combination of gas- and liquid-film diffusions in the range of tested operating conditions. The increase of gas flow rate and droplet size and decrease of liquid−gas ratio all can lead to a decrease in the SO2 removal efficiency. Addition of Cl− to the slurry (25 g/L) decreases the SO2 removal efficiency from 83.87 to 70.75%. when comparing the results of prediction and experiment, the data show good agreement. With droplet size equal to 2500 μm, when gas flow rate and liquid−gas ratio are changed, the relative errors of SO2 removal efficiency between the predicted and experimental data are below 3.40 and 8.67%, respectively. It demonstrates that the model proposed in the present study is an effective model to evaluate and predict the desulphurization performance of the novel type PCF device. Moreover, the theoretical model can be extended to apply in other wet FGD technologies.

Limestone dissolution in flue gas desulfurization—experimental and numerical study

AbstractBACKGROUND: Wet FGD technologies account for around 87% of such systems worldwide, particularly those that use limestone as the absorbent. This technique is widely used in large thermal power stations. Limestone reactivity is one of the parameters that most influence the yield of the FGD process. With the aim of improving the design and operation of desulfurization units, many studies have been carried out to investigate the rate of limestone dissolution.RESULTS: In this study, experimental equipment was set up to evaluate the limestone reactivity. In addition, a model to simulate the dissolution of limestone particles was developed. The proposed model considers the particle size distribution and composition, along with the pH of the liquid matrix where dissolution occurs. The average relative error between the experimental and numerically calculated results is 5%, after 10 min of experiment.CONCLUSION: A model based on film theory predicts with precision limestone dissolution as a function of the particle size distribution, chemical and physical composition of the limestone, pH and the solution composition. Copyright © 2010 Society of Chemical Industry

Prediction of SO 2 removal efficiency for wet Flue Gas Desulfurization

The wet Flue Gas Desulfurization in the coal-fired power plants has been the most widely used because of its high SO 2 removal efficiency, reliable and low utility consumption. The difficulty in the prediction of the SO 2 removal from flue gas is that the performance of the system is related to a wide range of variables. In this paper, the SO 2 was removed by absorbing and reacting SO 2 with limestone slurry, and limestone scrubbing was accomplished in a spraying reactor. Experimental investigations for effects of different operating variables on the SO 2 removal showed the reasonable process parameters such as the pH value of the liquid phase, droplet size of the spray and the flow rates of liquid and gas. The removal process was analyzed using the two-film theory of mass-transfer. Both the liquid and gas side resistances were important, and the absorption rate was controlled by a combination of both gas-film and liquid-film diffusion controls. A model of external mass-transfer with the effects of a chemical enhancement factor and sulfite concentration in the liquid phase was developed for the prediction of the SO 2 removal efficiency, and the calculated values were in reasonable agreement with the experimental values. The study is considered as the one-dimensional prediction of SO 2 removal and low-cost application of limestone slurry for commercial FGD technology.

Coal-fired Power Generation: Proven Technologies and Pollution Control Systems

During the last two decades, significant advances have been made in the reduction of emissions from coal-fired power generating plants. New technologies include better understanding of the fundamentals of the formation and destruction of criteria pollutants in combustion processes (low nitrogen oxides burners) and improved methods for separating criteria pollutants from stack gases (FGD technology), as well as efficiency improvements in power plants (clean coal technologies). Future demand for more environmentally benign electric power, however, will lead to even more stringent controls of pollutants (sulphur dioxide and nitrogen oxides) and greenhouse gases such as carbon dioxide.

Batch basket filtration centrifuges for FGD pay their way

In the majority of the developed world, legislation has been introduced to reduce sulphur emissions from coal combustion processes through flue gas desulphurization systems. On the downside, the installation of such technology is a costly business, even with governmental financial support. However, by combining the limestone gypsum FDG system with batch basket filtration centrifuges, a saleable product, i.e. high quality gypsum, can be produced, which makes the incorporation of FGD technology a much more economically viable option. Nigel Day explains.

A technical pilot plant assessment of flue gas desulfurisation in a circulating fluidised bed

Flue gas desulfurisation in a circulating fluidised bed absorber (CFBA) is quite a novel dry desulfurisation technology [6th International Conference on Circulating Fluidised Beds (1999) 601] that shows significant advantages in comparison with other dry technologies and that could also be competitive with the widely-used wet FGD technology. This experimental study analyses the performance of a flue gas treatment plant comprising a CFBA and an electrostatic precipitator (ESP). The most significant aspects considered in this study are: the effect of precollecting the fly ash, the effect of the SO 2 inlet concentration, the effect of power plant load changes, the contribution of the final particulate control equipment to the overall SO 2 removal efficiency and the impact of the desulfurisation unit on the ESP behaviour and its final dust emissions. In addition, the behaviour of the integrated CFBA-ESP system with respect to the main operating parameters was studied by means of a fractional factorial design of experiments. All this experimental work was carried out in a 3-MWe equivalent pilot plant that processes real gases withdrawn from the Los Barrios Power Plant. Processing a flue gas with up to 2000 ppm SO 2 concentration, a sulfur removal of 95–97% with a lime utilisation of 75% was achieved. A simple regression model to evaluate the efficiency of the whole system is also proposed.

Use of limestone for SO 2 removal from flue gas in the semidry FGD process with a powder-particle spouted bed

Hydrated lime is normally used as SO 2 sorbent in spray dry scrubbers, whereas limestone is considered unreactive under conditions prevailing in such a system. However, limestone is more easily available and several times cheaper than hydrated lime. We tried to use limestone to remove SO 2 from flue gas in the semidry FGD process with a powder-particle spouted bed. If limestone can be utilized in the process it would be of particular advantage. In the present study, the effects of operating parameters on SO 2 removal were investigated, such as Ca/S molar ratio, particle size of SO 2 sorbent, apparent residence time of gas in the bed and approach to saturation temperature. The comparison of reactivity with SO 2 between limestone and hydrated lime was also made based on their structural properties. The experimental results showed that SO 2 removal efficiency of limestone was considerably enhanced in the present process by increasing Ca/S molar ratio and decreasing the approach to saturation temperature and sorbent size. Thus, the present process with limestone as SO 2 sorbent may be an attractive alternative to other FGD technologies in terms of removal efficiency, price and availability of sorbent.

96/05489 Control of air toxics from coal-fired power plants using FGD technology

96/05489 Control of air toxics from coal-fired power plants using FGD technology

96/03299 - Pilot-scale testing of spray dryer/pulse-jet fabric filter FGD technology for medium- and high-sulfur coal applications

96/03299 - Pilot-scale testing of spray dryer/pulse-jet fabric filter FGD technology for medium- and high-sulfur coal applications