伞形罩除尘脱硫器性能模拟和实验研究

针对中小型燃煤锅炉的粉尘和二氧化硫等有害气体的污染问题,自行研制一种新型伞形罩烟气除尘脱硫器。利用计算流体力学通用软件,选择雷诺应力模型(RSM)和离散相模型(DPM)模拟其中的气固相流动;并在入口气速为10.6 m/s,粉尘质量浓度为2—22 g/m3时,对其性能进行预测;再通过实验验证模拟值,结果表明:数值模拟可视化装置内的速度、压力、DPM浓度分布;模拟预测的压降值为230—250 Pa,除尘效率为84%—86%;压降与除尘效率的模拟值和实验值吻合较好,相对误差分别为4%和10%。因此,用数值模拟来预测评价新型伞形罩洗涤器的性能方便且可行。     

Numerical prediction of dust capture efficiency of a centrifugal wet scrubber

The gas, liquid, and dust particle behavior inside a centrifugal wet scrubber was simulated and a submodel for predicting its collection efficiency was developed that also takes in account the reduction in collection efficiency due to droplet carryover. Centrifugal wet scrubbers are used in many industries and deliver a high scrubbing efficiency at relatively low capital and operational costs. However, they often experience problems such as droplet carryover at high gas flows and reduced collection efficiency at low gas flows. An improved understanding of flow processes inside the scrubbers is needed to develop a better scrubber design. An experimental test facility was setup for this purpose which also served to validate the CFD modeling results. Ideal operating parameters for maximum scrubbing efficiency and minimum droplet carryover were identified. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1001–1012, 2018     

Predictive Model of Hydrogen Sulfide Absorption by Chelate Solution in a Venturi Scrubber

In the present study, a simple model was used to predict the removal efficiency of a venturi scrubber for H₂S absorption into a ferric chelate solution. From momentum and mass balances in the scrubber, a set of first‐order, nonlinear ordinary differential equations relating predominantly the liquid velocity with the H₂S concentration in the liquid along the axial direction in the scrubber were formulated. These relationships were numerically solved to give performance profiles. The validity of the model was examined by comparing the results of the model with experimental data from the working laboratory scale. The results predicted from the model are in good agreement with the experimental data obtained in different sizes of the venturi scrubber and operating variables.     

文氏栅洗涤器除尘脱硫实验研究

采用双碱法脱硫技术 ,在自行设计的多通道文丘里洗涤器 (简称文氏栅洗涤器 )进行模拟燃煤烟气的除尘脱硫试验。其试验过程是 :先在三种不同喉部参数 (分别称为 1# ,2 # ,3 # )的文氏栅洗涤器进行除尘试验 ,经过优选后 ,在 2 #文氏栅洗涤器上进行脱硫试验。试验结果表明经过优选的 2 #文氏栅洗涤器有着较高的除尘脱硫效率。当文氏栅洗涤器的运行参数为 :pH =12、液气比为 0 .75L/m3、 [Na+ ]=0 .3mol/L、 [SO2 ]=12 0 0× 10 -6,文氏栅洗涤器的除尘效率大于 96 % ,脱硫效率大于 80 %。经过完善后可用作中小型燃煤锅炉烟气的除尘脱硫     

SO2 SCRUBBING IN A TAPERED BUBBLE COLUMN SCRUBBER

SO₂ emissions from various sources are found to occur in various concentrations and quantities. Abatement of SO₂ emission, therefore, assumes significant importance over the decades. Wet scrubbers offer great advantage over other devices for gas cleaning. That is the reason that compliance with SO₂ standards will in many cases result in the installation of scrubbing devices. This article presents results of a study on the scrubbing of SO₂ (initial concentration ranging between 400 and 1780 ppm) in a tapered bubble column scrubber using water and dilute sodium alkali. Preliminary studies reveal that the tapered bubble column is capable of generating higher fractional gas holdup than a standard bubble column under similar situations. Moreover, the tapered bubble column has generated bubbles with less power consumption than the existing columns under comparable hydrodynamical conditions. Experimental results indicate that almost 100% SO₂ removal (i.e., zero penetration) can be achieved in the scrubber developed in alkali scrubbing at an optimum Q_L/Q_G ratio of 3.0 m³/1000 ACM. The selection of any gas-cleaning device is based on the performance of the system. In view of this, empirical and semi-empirical correlations are put forward for the prediction of the performance of the scrubber in terms of different pertinent variables of the system for water as well as alkali scrubbing. Experimental results fit extremely well with the correlations. The removal efficiency achievable in the present tapered bubble column scrubber has been found to be higher than that of a single-stage standard bubble column with some modification. The present tapered bubble column is, therefore, hydrodynamically, energetically, and efficiency-wise much better than a standard bubble column.     

Growth of aerosol particles by adiabatic expansion at the throat of a venturi scrubber

The condensational growth of aerosol particles in the throat section of a venturi scrubber and the contribution of it to the dust collection efficiency were discussed.The condensable water vapor produced in the throat of venturi was quantitatively obtained for various conditions assuming the change in pressure and temperature to be adiabatic process. In terms of this condensable water vapor and the particle number concentration, the diameter of grown particles was determined, and the degree of contribution due to particle growth to the particle collection by venturi scrubber was evaluated as the change in particle collection efficiency involved in the particle growth.Experimental verification of the above results was qualitatively made by changing the humidity of the inlet gas, which is the most important property dominating the particle growth, in the particle collection by venturi scrubber.     

Development and application of a novel swirl cyclone scrubber—(1) Experimental

Conventional cyclones have a lower collection efficiency for smaller particles and conventional wet scrubbers have significant clogging and fouling problems by salt formation at the tip, the inside and outside of the nozzles, the tubes and the walls of scrubbers. Also, many companies and manufacturing sites have been in trouble for collecting their adhesive particulates. The novel swirl scrubber that we have developed consists mainly of a cyclone and a swirl scrubber with an impact cone and plates. This study reports the collection efficiency of particulates and the application of the novel swirl scrubber. The particle collection efficiency as a function of particle size was investigated with changes of plate angles, nozzle size and pressure, and volumetric flow rate of scrubbing medium. The particle collection efficiency increased with a decrease in plate angle, an increase in pressure of scrubbing medium at the nozzle tip, and an increase in volumetric flow rate of the scrubbing medium. The collection efficiency of PM₁₀ by scrubbing effect was much higher than that by cyclonic effect. In particular, the total increase in particle collection efficiency by scrubbing effect was significant (around 2.5 μm) in particle aerodynamic diameter. The developed novel swirl scrubber can be used for significantly increasing the collection efficiency of TSP, PM₁₀, and PM_2.5, in particular, which have adhesive characteristics. The costs for installation, operation and maintenance of the scrubber system are much cheaper than those of cyclones and scrubbers or other particulate collecting devices.     

Experimental investigation on removal of coal-fired fine particles by a condensation scrubber

The removal of coal-fired fine particles by heterogeneous condensation of water vapor in a scrubber was investigated. Supersaturated vapor phase necessary for the condensation growth of fine particles was achieved in the scrubbing zone as well as in the top of the scrubber by means of steam addition in the gas inlet and above the scrubbing liquid inlet, respectively. The condensation grown droplets were then removed by the scrubbing liquid and high-efficient demister. Influences of the steam addition amount, the temperature difference between the inlet gas and scrubbing liquid, and the liquid-to-gas ratio, etc. on removal efficiency were examined. The results show that with a steam addition amount of flue gas, number removal efficiencies of more than 60% and 70% can be attained for the two cases of steam addition, respectively. For the cases with steam addition in the gas inlet of scrubber, higher temperature difference between the inlet gas and scrubbing liquid enhances the removal of fine particles. Under the conditions of steam addition above the scrubbing liquid inlet, the removal efficiency decreases with increasing temperature difference. The removal efficiency can be effectively improved by increasing the liquid-to-gas ratio for both steam addition modes.     

洗涤塔脱除燃烧源超细颗粒的实验研究

在填料洗涤塔中进行了利用蒸汽相变原理促进燃煤和燃油超细颗粒凝结长大并高效脱除的实验研究;采用电称低压冲击器(ELPI)、SEM及XPS对两种燃烧源细颗粒凝结洗涤前后的数浓度、粒径分布、形貌和元素组分进行了分析测试,考察了洗涤塔进口气液温差、进口烟气含湿量及液气比等对脱除效率的影响。结果表明,燃煤和燃油产生的超细颗粒形貌和组分具有较大的差别,燃煤超细颗粒主要为硅铝矿物质,而燃油超细颗粒主要为含炭物质;在相同条件下,燃煤超细颗粒相变脱除效果优于燃油超细颗粒;脱除效率随洗涤塔进口气液温差的增大而提高,在相同进口气液温差下,增大进口烟气含湿量可显著提高超细颗粒的脱除效率;液气比的影响与填料洗涤塔内是否存在蒸汽相变有关;通过合理调节进口烟气含湿量及进口烟气与洗涤液的温差在填料塔内建立微粒凝结长大所需的过饱和水汽环境可有效脱除燃烧源超细颗粒。     

Wet scrubbing intensification applied to hydrogen sulphide removal in waste water treatment plant

Hydrogen sulphide removal in a waste water treatment plant at semi‐industrial scale in a compact wet scrubber has been investigated. The gas residence time in the scrubber was reduced to 30 ms using a NaOCl caustic scrubbing solution. The contactor is composed of a wire mesh packing structure where liquid and gas flow co‐currently at high velocity (>12 m s⁻¹). H₂S removal percentages higher than 95% could be achieved whereas a moderate pressure drop was measured (<4000 Pa). Both the hydrodynamic and chemical conditions can influence the efficiency of the process. Correlations were developed to predict both the pressure drop and the H₂S removal efficiency at given operating conditions.     

The Influence of Aerodynamic Characteristics on Mass Exchange Efficiency in FGD Scrubbers

On the basis of the model for aerodynamic characteristics of a FGD spray tower, a model for mass exchange in a single spray bank scrubber was developed. The relation for mass transfer units with respect to parameters characterizing dispersed and continuous phases was determined. Predictions of the scrubber efficiency for very fast and very slow reaction rates in the slurry are presented and discussed. The influence of sulfur dioxide concentration in gas and slurry feeds on the absorption efficiency are shown. A qualitative comparison with experimental data presented in the literature was performed.     

分子筛吸附脱除燃煤烟气硫碳硝的研究进展

煤炭是我国主要的能源,但燃煤烟气中二氧化硫(SO2)、二氧化碳(CO2)、一氧化氮(NO)等污染物会对环境和人类健康造成不利的影响。本文综述了分子筛及改性分子筛吸附脱硫、脱碳、脱硝技术和同时脱硫脱硝技术的现状;分析了温度、改性对脱硫的影响,压力、温度、改性对脱碳的影响,O2、水分、改性对脱硝的影响以及浓度、抗硫性能对脱硫脱硝的影响;并对同时脱除上述3种气体的发展趋势进行了展望,为多组分气体共吸附技术及燃煤烟气硫碳硝同时脱除的工业化应用提供理论依据和方法。     

Mathematical Modelling of Non‐Isothermal Venturi Scrubbers

A mathematical model consisting of differential equations for energy, momentum and material exchange is developed for a non‐isothermal Venturi‐type scrubber. By this model, the effects of heat and mass transfer on droplets concentration distribution and removal efficiency of particulate in a non‐isothermal Venturi scrubber can be investigated. In order to approach a realistic model, the liquid film flow on the walls and droplet size distribution are considered. The model is validated by comparing the results of mathematical model by plant and experimental data reported in the literature. The Results section of this work reveals that the inlet humidity and temperature of the gas can affect the removal efficiency of the scrubber.     

SO2 SCRUBBING IN A TAPERED BUBBLE COLUMN SCRUBBER

SO₂ emissions from various sources are found to occur in various concentrations and quantities. Abatement of SO₂ emission, therefore, assumes significant importance over the decades. Wet scrubbers offer great advantage over other devices for gas cleaning. That is the reason that compliance with SO₂ standards will in many cases result in the installation of scrubbing devices. This article presents results of a study on the scrubbing of SO₂ (initial concentration ranging between 400 and 1780 ppm) in a tapered bubble column scrubber using water and dilute sodium alkali. Preliminary studies reveal that the tapered bubble column is capable of generating higher fractional gas holdup than a standard bubble column under similar situations. Moreover, the tapered bubble column has generated bubbles with less power consumption than the existing columns under comparable hydrodynamical conditions. Experimental results indicate that almost 100% SO₂ removal (i.e., zero penetration) can be achieved in the scrubber developed in alkali scrubbing at an optimum Q_L/Q_G ratio of 3.0 m³/1000 ACM. The selection of any gas-cleaning device is based on the performance of the system. In view of this, empirical and semi-empirical correlations are put forward for the prediction of the performance of the scrubber in terms of different pertinent variables of the system for water as well as alkali scrubbing. Experimental results fit extremely well with the correlations. The removal efficiency achievable in the present tapered bubble column scrubber has been found to be higher than that of a single-stage standard bubble column with some modification. The present tapered bubble column is, therefore, hydrodynamically, energetically, and efficiency-wise much better than a standard bubble column.     

Influence of Temperature on SO2 Removal Enhanced by Water Vapor Using a Corona‐Discharge Reactor

A reactor using d.c. corona discharge of negative polarity was applied to remove sulfur dioxide from an oxygen‐nitrogen mixture in the presence or absence of water vapor for temperatures ranging from room temperature to 350 °C. It was observed that increasing the reactor temperature caused a decrease in the removal efficiency. Mixing water vapor with the process gas resulted in an increase of the removal efficiency. The effect of the presence of water vapor on improving the removal efficiency was significant under low temperature conditions, while it was relatively moderate under high temperature conditions. In addition, the solid deposit formed inside the reactor at two temperatures, room temperature and 200 °C, was analyzed with both a differential scattering calorimeter and an X ray diffractometer. The analysis indicated that SO₂ was ultimately converted to solid sulfur in both the presence and absence of water vapor in the gas flow.     

表面活性剂吸收法治理甲苯废气的中试实验

采用添加表面活性剂的填料塔来吸收治理甲苯废气，探讨了水-吸收剂的吸收机理，筛选出适合吸收甲苯的表面活性剂。考察了喷淋量、入口废气中的甲苯浓度和表面活性剂添加量这3个因素对甲苯去除率的影响。通过实验分析所得到的结果表明，对甲苯来说表面活性剂对去除率的影响最大，喷淋液体流量次之，入口浓度的影响最小。当条件满足时，最高去除效率可以达到90．6％(质量)，甲苯废气可以达标排放。     

Mercury removal from coal combustion by Fenton reactions. Paper B: Pilot-scale tests

This second paper in a series describes results of pilot-scale testing for mercury (Hg) removal from coal combustion flue gas using a scrubbing solution based on the Fenton reactions. The selected reagents contain hydrogen peroxide and iron salts. The mercury scrubbing was performed in a condensing heat exchanger (CHX) with flue gas generated by coal combustion in CANMET’s vertical combustor research facility (VCRF). Both the Ontario Hydro method and a Hg CEM were used for Hg sampling and speciation. The results, obtained with the combustion of three different pulverized coals – bituminous, sub-bituminous and lignite – showed that the CHX was very effective in removing oxidized mercury (Hg(II)). Concerning the performance of the scrubbing solutions, 30–40% of elemental mercury (Hg(0)) oxidation was achieved for the lignite coal, with the solution being preferably composed of FeCl₃ and H₂O₂ and with pH value between 1 and 3. Results also showed that better Hg removal results were achieved by combining sulphur removal and Hg removal in the same stage of the CHX. An additional test done on the pilot-scale research boiler with a conventional wet scrubber showed that the Hg removal capability using the Fenton reactions was not dependent on the configuration of the wet scrubber. Although the Hg(0) oxidation ratio was not particularly high compared to the achievements from bench-scale tests, considering the economic and non-toxic nature of the scrubbing solution and the readily available equipment, the current results are encouraging and deserve further work to develop a better understanding of the chemistry in order to determine if the method can be further optimized.     

Electrochemical sulfur dioxide concentrator for flue-gas desulfurization

A small test cell has been designed to investigate the electrochemical removal and concentration of sulfur dioxide from stack gases. The cell is a high temperature molten-salt cell which uses the ternary eutectic of lithium, potassium and sodium sulfates as the electrolyte. Simulated flue-gas having a composition similar to that resulting from burning 3.5% sulfur coal is fed to the cathode, where sulfur dioxide and oxygen are converted to sulfate ion. At the anode, the reverse reaction occurs resulting in a small volume of gas containing up to 50% sulfur oxides.     

A sustainable mediated electrochemical process for the abatement of NOx from simulated flue gas by using Ag(I)/Ag(II) redox mediators

Electrochemical removal of NO and NO₂ by using Ag(I)/Ag(II) redox mediator system in nitric acid medium by two-stage scrubbing process was investigated. Experiments were carried out for the complete removal of NO and NO₂ from the stimulated flue gas at room temperature and atmospheric pressure. The process parameters like current density, Ag(I) concentration, HNO₃ concentration, initial concentration of NO, Ag(I) concentration and temperature were studied and optimized. A removal efficiency of >99% was achieved using this sustainable redox process. Ag(II)/Ag(I) can be regenerated and reused for the scrubbing of waste gases continuously and there is no other gases emission during scrubbing.     

Simulations and process analysis of the carbonation–calcination reaction process with intermediate hydration

Several technologies are currently being developed to separate carbon dioxide from large point sources, such as coal-fired power plants. An emerging technology that shows great potential is a calcium oxide–calcium carbonate cycle. A major drawback is the calcium carbonate decreases in reactivity over multiple cycles. The Ohio State University demonstrated in 2008 the first carbonation–calcination reaction (CCR) process that includes intermediate hydration for sorbent regeneration and its feasibility over multiple cycles at the 120 kW_th scale with actual flue gas from coal combustion. The CCR Process utilizes a calcium-based sorbent to react with the carbon dioxide and sulfur dioxide in a flue gas stream to form calcium carbonate and calcium sulfate, respectively. The carbon dioxide is subsequently released from the calcium carbonate to produce a high-purity, sequestration-ready carbon dioxide stream while regenerating the calcium oxide sorbent. The sulfur dioxide is fixated as calcium sulfate and removed through a purge stream. An intermediate hydration step restores reactivity to the calcium oxide sorbent. Process analysis from computer simulations shows the CCR Process to be highly effective and efficient in removing both carbon dioxide and sulfur dioxide at low energy penalties under realistic conditions. A 20–22% decrease in electricity generation efficiency with the CCR Process is expected, compared with amine scrubbing around 27% and oxy-combustion around 25% energy penalty. A 25–28% increase in thermal energy with the CCR Process is expected to maintain a constant electrical output. Further, the CCR Process consumes half the oxygen necessary for an oxy-combustion plant and 25% less steam necessary for amine scrubbing.