Industrial Application of a Deep Purification Technology for Flue Gas Involving Phase-Transition Agglomeration and Dehumidification

A moist plume forms when the flue gas emitted from wet desulfurization equipment exits into the ambient air, resulting in a waste of water resources and visual pollution. In addition, sulfur trioxide (SO₃), water with dissolved salts, and particles in the wet flue gas form secondary pollution in the surrounding atmosphere. In this study, a deep purification technology for flue gas involving phase-transition agglomeration and dehumidification (PAD) is proposed. This deep purification technology includes two technical routes: the integrated technology of phase-transition agglomeration and a wet electrostatic precipitator (PAW); and the integrated technology of phase-transition agglomeration and a mist eliminator (PAM). Industrial applications of PAW and PAM were carried out on 630 and 1000 MW coal-fired units, respectively. The results show that the average amount of recycled water obtained from wet flue gas by means of PAD is more than 4 g·(kg·°C)⁻¹. Decreasing the wet flue gas temperature by 1.5–5.3 °C allows 5%–20% of the moisture in the flue gas to be recycled; therefore, this process could effectively save water resources and significantly reduce water vapor emissions. In addition, the moist plume is effectively eliminated. With the use of this process, the ion concentration in droplets of flue gas is decreased by more than 65%, the SO₃ removal efficiency from flue gas is greater than 75%, and the removal efficiency of particulate matter is 92.53%.     

Using Taguchi method to determine optimum process conditions for flue gas desulfurization through an amine scrubber

This study was done to determine the optimum process conditions for absorption of sulfur dioxide in a mixture of flue gases. Using a selective amine-based absorber; a high amount of SO₂ was absorbed in the scrubbing process. The process was designed to reduce the amount of sulfur dioxide. The pilot plant was designed and set up in the Research Center of Petroleum University of Technology, containing absorption and desorption stages. This paper reports an investigation of the effect and optimization of parameters that improve the efficiency of the whole process. The experiments were conducted under varying levels of desorption temperature, pH of the absorber solution, concentration of SO₂ inlet gas, and flow rate of the absorbing solution. Using Taguchi experimental design method, the optimum conditions were identified for the absorption process. An efficiency of more than 99 % could be obtained by varying the parameters in which all the released SO₂ gas was absorbed from the inlet flue gas; an achievement that is much favorable for industrial purposes.     

Nitrogen oxides removed from flue gases with sulfur dioxide under the action of pulsed electron beams

The process of a model flue gas mixture purification from nitrogen oxides by microsecond-pulsed electron beam ionization in the presence of sulfur dioxide (SO₂) was experimentally studied. In mixtures with a small SO₂ content, interaction of this component with nitrogen oxides leads to a considerable increase in the specific energy consumption required for the gas purification (∼80 eV per NO molecule). In a gas mixture with approximately equal concentrations of SO₂ and NO, the energy consumption for NO removal decreases to a level close to that in the mixture free of sulfur dioxide.     

Simultaneous absorption of NOx and SO2 from flue gas with pyrolusite slurry combined with gas-phase oxidation of NO using ozone

NO was oxidized into NO₂ first by injecting ozone into flue gas stream, and then NO₂ was absorbed from flue gas simultaneously with SO₂ by pyrolusite slurry. Reaction mechanism and products during the absorption process were discussed in the followings. Effects of concentrations of injected ozone, inlet NO, pyrolusite and reaction temperature on NO_x/SO₂ removal efficiency and Mn extraction rate were also investigated. The results showed that ozone could oxidize NO to NO₂ with selectivity and high efficiency, furthermore, MnO₂ in pyrolusite slurry could oxidize SO₂ and NO₂ into MnSO₄ and Mn(NO₃)₂ in liquid phase, respectively. Temperature and concentrations of injected ozone and inlet NO had little impact on both SO₂ removal efficiency and Mn extraction rate. Specifically, Mn extraction rate remained steady at around 85% when SO₂ removal efficiency dropped to 90%. NO_x removal efficiency increased with the increasing of ozone concentration, inlet NO concentration and pyrolusite concentration, however, it remained stable when reaction temperature increased from 20 °C to 40 °C and decreased when the flue gas temperature exceeded 40 °C. NO_x removal efficiency reached 82% when inlet NO at 750 ppm, injected ozone at 900 ppm, concentration of pyrolusite at 500 g/L and temperature at 25 °C.     

High temperature removal of hydrogen sulfide using an N-150 sorbent

In this study, an N-150 sorbent was used as a high temperature desulfurization sorbent for the removal of hydrogen sulfide from coal gas in a fixed bed reactor. The results indicate that the N-150 sorbent could be used for H(2)S removal in the tested temperature ranges. Regeneration test also reveals that utilization of the N-150 sorbent maintains up to 85% compared to the fresh sorbent. No significant degeneration occurs on the N-150 sorbent. In addition, various concentrations of H(2)S, H(2) and CO were also considered in the performance test of the N-150 sorbent. Except for H(2)S, H(2) and CO act the important roles in the high temperature desulfurization. By increasing the H(2) concentration, the sulfur capacity of the sorbent decreases and an adverse result is observed in the case of increasing CO concentration. This can be explained via water-shift reaction. On the basis of the instrument analysis, X-ray powder diffraction determination and SEM images with EDS spectrum characterization, residual sulfur is found in the regenerated N-150 sorbent and this sulfur species is sulfate which resulted by incomplete regeneration. The sulfate formation and sintering effect are major reasons to cause activity loss in the sulfidation/regeneration cycles.     

Effect of nitrogen oxides on the sulfur dioxide removal from flue gases under the action of pulsed electron beams

The process of sulfur dioxide (SO₂) oxidation under the action of a microsecond-pulsed electron beam was experimentally studied in model gas mixtures with various initial concentrations of nitrogen dioxide (NO₂). It is shown that the presence of NO₂ significantly affects the process of SO₂ oxidation.     

Comparison of two different hot-gas desulfurization powder processes: Transport reactor and bubbling fluidized bed

The KIER bench-scale fluidized hot-gas desulfurization process was designed to operate two different configurations. One was a bubbling desulfurizer and a bubbling regenerator, the other was a transport desulfurizer and a bubbling regenerator. Two systems were compared each other in terms of operational parameters, hydrodynamic parameters such as gas flow rate and solid circulation rate, reaction characteristics such as sorbent sulfur sorption capacity and regeneration characteristics. Also, the fresh and used solid samples from two different modes were analyzed for density, sulfur content, size, attrition, and morphology. The transport–bubbling system was simpler and more stable in pressure balance, but a little more unstable in temperature control than the bubbling–bubbling system. The solid residence time in each reactor was 0.68 h for the bubbling–bubbling system, and 0.09 h for the transport–bubbling system.     

Effects of Nitrogen Dioxide and Carbon Monoxide on the Determination of Sulfur Dioxide by Flue Gas Analyzer

Reference materials of SO₂, NO₂ and CO were used to study the effects of different concentrations of NO₂ and CO on the determination value of SO₂ by flue gas analyzer with electrochemical sensors and UV differential optical absorption spectroscopy (DOAS). Results showed that SO₂ was affected more greatly by NO₂ than CO using the method of electrochemical sensors. The electrolytic reaction of NO₂ was the primary factor causing the lowerconcentration of SO₂. SO₂ with the concentration of 0–300 mg/m³ was affected greatly by NO₂, and the determination value was unreliable. The determination error of SO₂, with the concentration higher than 1500 mg/m³, was about 2%, and the test value was more accurate. The method of UV DOAS could improve the determination reliability of concentration of SO₂ greatly when NO₂ coexisted.     

A model on desulfurization characteristics of an entrained bed-bubbling bed hot gas cleanup system for IGCC

A mathematical model has been developed to predict performance of a continuous entrained-bed and bubbling fluidized-bed hot gas desulfurization system in IGCC. The model combines the particle residence time with the kinetic rate in each reactor. The model has been applied to the KIER’s laboratory scale fluidized bed process. The present model provided a reasonable fit in predicting experimental results that the outlet concentration of H₂S from the desulfurizer and SO₂ from the regenerator increased nearly proportionally to the inlet concentration of H₂S to the desulfurizer. The model also could predict well the outlet concentration of O₂ from the regenerator to decrease as the inlet concentration of H₂S to the desulfurizer increased. The present model predicted with reasonable accuracy mean diameter of bed particles and sulfur content of particles in desulfurizer and regenerator.     

Surface characteristics of regenerative Fe-KOH/LSB catalysts for low-temperature catalytic hydrolysis of carbon disulfide and research of the surface regeneration mechanism

In the present study, a series of regeneration conditions and the regeneration mechanism of modified lake sediment biochar (Fe-KOH/LSB) catalysts for low-temperature catalytic hydrolysis of carbon disulfide (CS₂) were investigated. The results showed that Rm-WNA method had the best regeneration effect. Under optimal regeneration conditions, the sulfur capacity (13.86 mg_[S]/g_[catalyst]) of regenerated Fe- KOH/LSB was close to that of fresh Fe-KOH/LSB (14.88 mg_[S]/g_[catalyst]). The water washing process could wash away a small number of sulfates and a large number of alkaline groups. TG-DTA and DRTFIR results indicated that the nitrogen sweeping process could decompose Fe₂(SO₄)₃ into Fe₂O₃, which partially recovered the catalytic and the adsorptive abilities. CO₂-TPD results indicated that the alkali steeping process offer -OH groups, further improving the catalytic and the adsorptive abilities. After 3 times-regeneration, the sulfur capacity of Fe-KOH/LSB reached 13.31 mg[S]/g_[catalyst], indicating that the Rm-WNA method had good stability for the recovery of the catalytic activity. BET, XPS and XRD results revealed that the decrease of the sulfur capacity for regeneration was attributed to the decrease of the adsorptive abilities of C and SiO₂.     

Aspen Plus-based simulation of a cement calciner and optimization analysis of air pollutants emission

The cement industry is a typical high energy consumption and heavy pollution industry, in which amounts of CO₂, NO, NO₂, and SO₂ discharge from the pre-calciner kiln system and cause severe greenhouse and acid rain effects. Meanwhile, reasonable division of the combustion environment in the calciner is the main method to control the formation of pollutant gases. In this article, a calciner process model in Aspen Plus is proposed based on the combustion mechanism analysis of the Dual Combustion and Denitration calciner (DD-calciner) and verified by industrial data. Then, for a concrete DD-calciner, the article studies the effects of the flow rate of coal and tertiary air on flue gas compositions and effects of the staging combustion technology on the NO _x , SO₂, and CO concentrations in the flue gas. Through comparing the model results with the relevant environmental standards, the optimization analysis for staging combustion parameters of the calciner is done, and the result shows that when the proportion of tertiary air entering the pyrolysis and combustion zone is controlled within the range of 57–65.52% (0.89 < α < 1.004), all the gas pollutants emit within accepted standards simultaneously. The calciner process model outlined in this article describes the key processes of the physical and chemical reactions in the calciner. It can be used to study the key operation and design parameters which influence the flue gas constituents, so as to provide data support for determining the pollutant emission reduction plan of the cement industries with a view to reduce air pollutant emission.     

Sulfation and attrition of calcium sorbent in a bubbling fluidized bed

A bubbling fluidized bed reactor was used as a desulfurization apparatus in this study. The height of the bed was 2.5 m, and the inner diameter was 9 cm. The bed materials were calcium sorbent and silica sand. The effects of the operating parameters of the flue gas desulfurization including relative humidity, temperature, superficial gas velocity, and the particle size of calcium sorbent on SO₂ removal efficiency and calcium sorbent conversion and attrition rate in the fluidized bed were investigated. It was found that the temperature effect in our system was negligible from 40 to 65°C. A higher relative humidity had a higher calcium conversion and a higher sulfur dioxide removal efficiency. Moreover, a smaller particle size of calcium sorbent had a lower calcium conversion in the cyclone but a higher sulfur dioxide removal efficiency. A lower superficial gas velocity resulted in a higher sulfur dioxide removal efficiency and a higher calcium conversion, thus, the total volume of the flue gas treated was maximum near the minimum fluidization velocity. Finally, an attrition rate model proposed in this study could predict the elutriation rate satisfactorily.     

离子液体中阴阳离子的特性对其吸收二氧化硫的影响

SO_2是一种无色、有强烈刺激性气味的气体,弥散在空气中的SO_2对人体健康、生态环境有着严重的危害,是导致空气质量不断恶化的主要大气污染物之一。人为造成的SO_2污染物的主要来源有燃料燃烧、工业生产、交通运输等,其中燃料燃烧占70%。因此,削减和控制燃料燃烧所产生的SO_2的排放是我国能源利用和环保领域的重要研究方向,烟气脱硫是应对烟气中SO_2排放的有效途径。湿法烟气脱硫是目前应用最广泛的方法,占世界安装烟气脱硫机组总容量的85%,采用该方法处理的烟气占总处理量的80%。在湿法烟气脱硫技术中比较实用的主要包括钙法脱硫、有机胺脱硫、海水脱硫。其中,钙法脱硫的脱硫效率高,对煤种的适应性较强,但是脱硫会产生CaSO_4沉淀,降低经济效益;有机胺脱硫的系统腐蚀性小,副产品可生产硫酸,但是胺易挥发,造成吸收剂损失和环境污染;海水法脱硫的工艺简单、运行可靠,但其应用受到地域的影响,并且对环境也会产生一定的影响。离子液体是一种新兴的绿色介质,它具有环保、可再生、结构可调控的优点,为解决传统工艺中的污染问题提供了新方案。在离子液体吸收气体的过程中,吸收液不会因其挥发性而蒸发进入气相,并且可以在较低的温度下完成吸收解吸循环。离子液体的这些优良特性使其在SO_2吸收方面有着极广阔的应用前景。目前,研究者们已合成了一系列胍盐类、咪唑类、醇胺类、吡啶类等离子液体,探究其吸收SO_2的性能与机理,并根据其结构可设计的特点,在离子液体中的阴阳离子上引入各类官能团(如氰基、醚基、氨基、卤素),合成满足特定需求的离子液体,使其高效、可逆、低耗地吸收SO_2。本文总结了近年来各类离子液体吸收SO_2的性能和机理,为系统地认识离子液体在SO_2分离领域的应用提供了帮助;重点阐明了离子液体中阴阳离子的种类、官能化,尤其是酸碱性对其吸收SO_2的影响,这为调整离子液体酸碱性、合理设计离子液体的结构,探索离子液体吸收SO_2的机理,改善其对SO_2的吸收性能有着重要的价值。最后指出了目前研究中存在的问题并且对未来新型离子液体的合成进行了展望。     

SO x emission and pollution control at Mellitah Gas Plant

Due to the increase of energy consumption, natural gas energy is becoming one of the most important sources to fulfil the world energy demand. However, normally the available raw natural gas is mixed with some heavy components such as C₃ ⁺ and/or some impurities such as CO₂, N₂ and sulfur compounds (H₂S and RSH). The raw gas should be treated in order to meet the international specifications and eliminate or at least minimize the emission of toxic and/or pollutant gases to the surrounding area. Mellitah Plant applies the latest technology in order to meet the international standards. In this paper, we will present the different process at Mellitah site in which we produce a clean natural gas for export and recover 99.8 wt% of associated sulfur compound with the raw gas and/or acid gas. The recovered sulfur is produced in liquid phase then dried for storage in solid phase. The solid sulfur is exported to international market. The emission control at Mellitah plant is optimized and controlled as per the latest available technology. The fuel gas utilized for all the process is completely clean gas; flue gas contains always less than 10 ppm of H₂S. Therefore, the burned gas produced mainly CO₂ and H₂O with a trace amount of SO _x . If SO _x emission at Mellitah is compared to any other industrial complex in Libya or any other similar plant any elsewhere utilizing fuel oil and/or diesel oil then the Mellitah emission will be the lowest. An erratum to this article can be found at     

A technical and economic evaluation of CO<Subscript>2</Subscript> separation from power plant flue gases with reclaimed Mg(OH)<Subscript>2</Subscript>

A method of inexpensively and reliably separating CO₂ from flue gases by means of using magnesium hydroxide (Mg(OH)₂) has been studied. Mg(OH)₂ may be easily reclaimed from power plants using magnesium enhanced flue gas desulfurization systems (ME-FGD). The CO₂ scrubbing system may be operated as either a once-through system which produces magnesium carbonate for sequestration of carbon, or as a regenerable system where a concentrated CO₂ gas stream is created for further processing.The experimental results indicate that CO₂ is absorbed into solutions containing reclaimed Mg(OH)₂ by mean of a first order reaction, where the activation energy of this reaction was measured to be 7.7 kcal/mol. Continuous flow experiments were performed in a bubble reactor with simulated flue gas containing 15%_V CO₂ in contact with a solution of Mg(OH)₂. Experiments have shown that up to 70% of CO₂ separation may be achieved in this system. For a system based on a typical 500 MW power plant and reclaiming the magnesium hydroxide from a ME-FGD, experiments have shown that from 7–17% of the CO₂ from the gas stream may be continuously removed through the regenerable system.The energy requirements for CO₂ separation were also evaluated for a regenerable system based on equilibrium data in the liquid phase. A liquid solution equilibrium solver, MINEQL+, was used to determine the equilibrium values. The economic evaluation is based on a 500-MW power plant burning a high sulfur coal. The calculation considered up to a 22 °C temperature difference between the absorption step and the regeneration system. These calculations show that approximately 40 to 68 MW of energy are required to separate 7% of the CO₂ from the flue gas stream. The energy required depends on the temperature and pH difference between the absorption and desorption step, and the liquid-to-gas ratio in the absorber. The details of the energy calculations are given in the paper.     

Wet flue gas desulphurization using a new O-element design

Scrubbing by liquid sprayingis one of the most effective processes used for removal of fine particles and soluble gas pollutants (such as SO₂, HCl, HF) from the flue gas. The primary function of venturi scrubber, which represents the first stage of the wet flue gas cleaning processes, such as in waste incineration plants, is to capture fine particles as well as remove HCl, HF or SO₂ as a result of the decrease in the flue gas temperature before entering the absorption column. In this paper, a newly developed four-branch O-element is proposed as a replacement for venturi scrubber. By means of this device, sulphur dioxide (SO₂) removal efficiency and pressure loss and temperature drop were experimentally calculated. The dependence of these variables on liquid–gas ratio was monitored. The simulated flue gas was prepared by the combustion of the carbon disulphide solution in toluene (1:1 vol.) in the presence of the flame in the reactor. Such prepared flue gas with temperature around 150 °C was processed in the laboratory-designed O-element scrubber. Water was used as an absorbent liquid. The maximal efficiency of SO₂ removal achieved by this process was up to 70 %, which is far better in comparison with the commonly used venturi scrubbers. The pressure drop of our proposed newly designed wet scrubber is similar to that of the commonly used venturi scrubbers; nevertheless, the influence of the amount of the liquid on pressure drop is not so significant. In parallel, a mathematical model describing the mass transfer, enthalpy balance and pH change of the absorbing solution was also developed. Enthalpy balance was calculated by numerical iteration to determine the unknown outlet liquid temperature. Mass transfer calculation was used for the determination of complete Henry constant from all the subsequent SO₂ absorption reactions.     

Oxide Catalysts with Ultrastrong Resistance to SO2 Deactivation for Removing Nitric Oxide at Low Temperature

Nitrogen oxides are one of the major sources of air pollution. To remove these pollutants originating from combustion of fossil fuels remains challenging in steel, cement, and glass industries as the catalysts are severely deactivated by SO₂ during the low‐temperature selective catalytic reduction (SCR) process. Here, a MnO_X/CeO₂ nanorod catalyst with outstanding resistance to SO₂ deactivation is reported, which is designed based on critical information obtained from in situ transmission electron microscopy (TEM) experiments under reaction conditions and theoretical calculations. The catalysts show almost no activity loss (apparent NO_X reaction rate kept unchanged at 1800 µmol g^?1 h^?1) for 1000 h test at 523 K in the presence of 200 ppm SO₂. This unprecedented performance is achieved by establishing a dynamic equilibrium between sulfates formation and decomposition over the CeO₂ surface during the reactions and preventing the MnO_X cluster from the steric hindrance induced by SO₂, which minimized the deactivation of the active sites of MnO_X/CeO₂. This work presents the ultralong lifetime of catalysts in the presence of SO₂, along with decent activity, marking a milestone in practical applications in low‐temperature selective catalytic reduction (SCR) of NO_X.     

Reforming natural gas for CO2 pre-combustion capture in combined cycle power plant

The aim of this study is to assess the conversion of a natural gas combined cycle power plant (NGCC) using an advanced gas turbine (GE9H) for CO₂ pre-combustion capture. The natural gas is reformed in an auto-thermal reformer (ATR) either with pure oxygen or with air. After water-shift conversion of CO into CO₂ and physical CO₂ recovery, the synthesis gas contains a high fraction of H₂. It is diluted with N₂ and steam to lower its low heating value (LHV) for NO _X emission control. Oxygen purity and reforming pressure have little impact on the performances. High-pressure reforming is preferred to reduce the process size. Air reforming results in a slightly higher efficiency but in a bigger process too. The CO₂ recovery rate has a big impact on the power plant efficiency since a lot of steam is required to lower the heating value (LHV) of the synthesis gas leaving the recovery process. Two values of LHV have been assessed. Steam consumption for natural gas reforming and synthesis gas dilution are the main consuming elements. An erratum to this article can be found at     

Hydrogen sulfide removal from coal gas by the metal-ferrite sorbents made from the heavy metal wastewater sludge

The metal-ferrite (chromium-ferrite and zinc-ferrite) sorbents made from the heavy metal wastewater sludge have been developed for the hydrogen sulfide removal from coal gas. The high temperature absorption of hydrogen sulfide from coal gas with the metal-ferrite sorbent in a fixed bed reactor was conducted in this study. The metal-ferrite powders were the products of the ferrite process for the heavy metal wastewater treatment. The porosity analysis results show that the number of micropores of the sorbents after sulfidation and regeneration process decreases and the average pore size increases due to the acute endothermic and exothermic reactions during the sulfidation–regeneration process. The FeS, ZnS, and MnS peaks are observed on the sulfided sorbents, and the chromium extraction of the CFR6 can fulfill the emission standard of Taiwan EPA. The suitable sulfidation temperature range for chromium-ferrite sorbent is at 500–600 °C. In addition, effects of various concentrations of H₂ and CO were also conducted in the present work at different temperatures. By increasing the H₂ concentration, the sulfur sorption capacity of the sorbent decreases and an adverse result is observed in the case of increasing CO concentration. This can be explained via water-shift reaction.     

Multi-functional sorbents for the simultaneous removal of sulfur and lead compounds from hot flue gases

A multi-functional sorbent is developed for the simultaneous removal of PbCl(2) vapor and sulfur dioxide from the combustion gases. The sorbent is tested in a bench-scale reactor at the temperature of 700 degrees C, using simulated flue gas (SFG) containing controlled amounts of PbCl(2) and SO(2) compounds. The removal characteristics of PbCl(2) and SO(2), individually and in combination, are investigated. The results show that the mechanism of capture by the sorbent is not a simple physical adsorption process but seems to involve a chemical reaction between the Ca-based sorbent and the contaminants from the simulated flue gas. The porous product layer in the case of individual SO(2) sorption is in a molten state at the reaction temperature. In contrast, the combined sorption of lead and sulfur compounds generates a flower-shaped polycrystalline product layer.