Zeolite sorbent that effectively removes mercury from flue gases

The measurement and control of mercury (Hg) emissions from utility power plants continue to be the subjects of much study. In a programme funded by the Department of Energy, Physical Sciences Inc (PSI) has developed a Hg sorbent using a zeolite material with a proprietary agent for improved capture of elemental as well as oxidized Hg. Joseph R Morency, Thomai Panagiotou & Constance L Senior present some promising laboratory results.     

Degradation of concrete by flue gases from coal combustion

The effect of flue gases from coal combustion on the concrete shell of a power plant stack was analyzed and the damage to the concrete was evaluated. The compressive and tensile strengths of concrete were determined by rebound hammer test and pull-off test on the site. Samples of concrete taken from various zones of the stack shell were analyzed in detail. The examination techniques used included chemical analysis, water suspension analyses, XRD, thermal analysis, SEM and EDS. It was found that the flue gases and the acid condensate, acted very aggressively at an elevated temperature and caused severe degradation of the inside surface zone of the concrete shell. The binding material in this zone was converted into sulfur-bearing compounds. Gypsum was identified as the dominant compound in the degraded zone of concrete in the upper parts, while anhydrite in the lower parts of the stack. Carbonated zone was located below the clearly delimitated sulfated zone of the concrete. The aggressive environment in the stack did not affect the internal zones in the concrete.     

Waste heat recovery from flue gases with substantial dust load

Heat recovery is accomplished in a newly developed heat exchanger THERMOWIR. THERMOWIR consists of a large number of channels. Vortices are generated within the THERMOWIR and the dust is thrown to the walls of the THERMOWIR, thus keeping the center of the channels dust free, where the heat transfer tubes are located. A demonstration unit with 1 MWe capacity is being installed at present in a cement factory.     

Determining the coefficients of air consumption from volumetric analysis of flue gases during the breakdown of material being calcined

Conclusions A formula is proposed for determining the quantity of carbon dioxide evolved from material being burnt (dolomite, magnesite, or limestone) per 1 kg or 1 Nm³ for fuel, and also a formula for determining the coefficient of air consumption during the combustion of any fuel in the presence or absence, within the combustion products, of gases from the material being broken down (CO₂).Translated from Ogneupory, No. 7, pp. 9–12, July, 1970.Here and subsequently instead of coefficient of excess air, the term coefficient of air consumption will be used.     

Thermoneutral tri-reforming of flue gases from coal- and gas-fired power stations

The treatment of flue gases from fossil fuel fired power stations by tri-reforming with natural gas or by coal gasification could become an attractive approach for converting the CO₂, H₂O, O₂, and N₂ contained in these flue gases via syngas processing into useful products, such as methanol, hydrogen, ammonia, or urea. The present study determines the constraints for achieving such thermochemical reactions under conditions of thermoneutrality, by reacting the flue gases with water, air, and natural gas or coal at 1000–1200 K. The implications of such reactions are examined in terms of CO₂ emission avoidance, fuel saving, economic viability, and exergy efficiency.     

改性活性炭脱除模拟烟气中气态汞的实验研究

以椰壳活性炭为原料,经硝酸活化再采用NaCl或NaBr溶液化学浸渍改性制备燃煤烟气脱汞吸附剂。通过N_2吸附-脱附(BET),扫描电子显微镜(SEM),X射线光电子能谱(XPS)对制备的吸附剂进行表征,并且采用模拟烟气在管道喷射装置内考察汞吸附脱除性能。结果表明:与原始椰壳活性炭相比,经硝酸活化后的椰壳活性炭汞吸附能力得到提高;而采用NaBr改性后的椰壳活性炭脱汞效果最好。在管道喷射实验装置内,经过1 mol/L NaBr改性后的椰壳活性炭,在模拟烟气温度120℃,碳汞质量比8 000,停留时间2 s条件下,脱汞率达到92.7%。改性后的椰壳活性炭是一种具有潜在应用价值的优良脱汞吸附剂。     

SCR catalyst performance in flue gases derived from subbituminous and lignite coals

Lignite and subbituminous coals from the United States of America have characteristics that impact the performance of catalysts used in selective catalytic reduction (SCR) for nitrogen oxide removal and mercury oxidation. Typically, these coals contain ash-forming components that consist of inorganic elements (sodium, magnesium, calcium, and potassium) associated with the organic matrix and mineral grains (quartz, clays, carbonates, sulfates, and sulfides). Upon combustion, the inorganic components undergo chemical and physical transformations that produce intermediate inorganic species in the form of inorganic gases, liquids, and solids. The alkali and alkaline-earth elements are partitioned between reactions with minerals and reactions to form alkali and alkaline-earth-rich oxides during combustion. The particles resulting from the reaction with minerals produce low-melting-point phases that cause a wide range of fireside deposition problems. The alkali and alkaline-earth-rich oxides consist mainly of very small particles (<5 μm) that are carried into the backpasses of the combustion system and react with flue gas to form sulfates, and possibly carbonates. These particles cause low-temperature deposition, blinding, and plugging problems in SCR systems. These coals also contain the very low levels of chlorine that are necessary for mercury oxidation. Slipstream testing was conducted at two selected subbituminous-fired power plants and one lignite-fired power plant to determine the impacts of ash on SCR plugging, blinding, and mercury oxidation. The results indicated a high potential for blinding and plugging due to the formation of sulfate-bonded deposits and no evidence for mercury oxidation.     

碱液吸收法治理含NOx工艺尾气实验研究

为了提高碱液吸收氮氧化物废气的吸收效率,控制氮氧化物废气的排放,在直径为25 mm,高度1 000 mm的填料吸收塔内,对碱液吸收法治理含NOx工艺尾气的过程进行了研究,主要探讨了填料塔中的填料、吸收液、喷淋密度和氧化度对氮氧化物脱除效果的影响。结果表明:相对于同样的吸收条件,填料的表面积越大,空隙率越高,则吸收效果越好;NaOH溶液和Na2CO3溶液对氮氧化物都能达到较好的脱除效果,但是相对于最佳的脱除效果,NaOH溶液的质量浓度却比Na2CO3溶液的质量浓度低;碱液吸收含NOx工艺尾气的适宜喷淋密度为12 m3/(m2.h);当氧化度为50%左右时,吸收效果可以达到更好。     

催化氧化脱除垃圾焚烧烟气中二恶英类的研究

选择钒、钨等过渡金属作为催化剂的活性成分,二氧化钛为载体,偏钒酸铵,钨酸铵等作为活性成分之来源,浸渍法生产了二氧化钛载钒催化剂。并进行了以载钒型催化剂分解垃圾焚烧烟气中的二恶英类的工业侧流试验,在反应温度为240～320 ℃、气体空速为7 000～8 000 h－1的工艺条件下,二恶英类分解率可达95％～99%。     

Understanding the effects of sulfur on mercury capture from coal-fired utility flue gases

Coal combustion continues to be a major source of energy throughout the world and is the leading contributor to anthropogenic mercury emissions. Effective control of these emissions requires a good understanding of how other flue gas constituents such as sulfur dioxide (SO₂) and sulfur trioxide (SO₃) may interfere in the removal process. Most of the current literature suggests that SO₂ hinders elemental mercury (Hg⁰) oxidation by scavenging oxidizing species such as chlorine (Cl₂) and reduces the overall efficiency of mercury capture, while there is evidence to suggest that SO₂ with oxygen (O₂) enhances Hg⁰ oxidation by promoting Cl₂ formation below 100 °C. However, studies in which SO₂ was shown to have a positive correlation with Hg⁰ oxidation in full-scale utilities indicate that these interactions may be heavily dependent on operating conditions, particularly chlorine content of the coal and temperature. While bench-scale studies explicitly targeting SO₃ are scarce, the general consensus among full-scale coal-fired utilities is that its presence in flue gas has a strong negative correlation with mercury capture efficiency. The exact reason behind this observed correlation is not completely clear, however. While SO₃ is an inevitable product of SO₂ oxidation by O₂, a reaction that hinders Hg⁰ oxidation, it readily reacts with water vapor, forms sulfuric acid (H₂SO₄) at the surface of carbon, and physically blocks active sites of carbon. On the other hand, H₂SO₄ on carbon surfaces may increase mercury capacity either through the creation of oxidation sites on the carbon surface or through a direct reaction of mercury with the acid. However, neither of these beneficial impacts is expected to be of practical significance for an activated carbon injection system in a real coal-fired utility flue gas.     

Removal of carbon dioxide from flue gases in packed column using ionic liquids

The study of CO₂ absorption in ionic liquids (ILs): [Emim] [Ac], [Bmim] [Ac] in a packed column is presented. The influence of mass transfer resistances, initial CO₂ concentration, absorption temperature and 2, 5, 10% wt. water addition on CO₂ removal efficiency was investigated. The resistance in series model and estimated values of enhancement factor were used to predict with good accuracy mass fluxes of absorbed carbon dioxide for both ILs. The CO₂ absorption efficiency in packed column depends on temperature and initial CO₂ concentration. The addition of small amounts of water to [Emim][Ac] is of minor effect on CO₂ absorption.     

低浓度二氧化硫冶炼烟气处理工艺

介绍了有色冶炼行业低浓度二氧化硫烟气的处理工艺,包括烟气脱硫、非稳态转化工艺、WSA工艺、一转一吸加尾吸工艺、常规两转两吸制酸工艺。企业应结合自身的实际情况,根据冶炼系统不同的烟气浓度和烟气量,选择合适的处理工艺。     

The behaviour of phosphorus in flue gases from coal and secondary fuel co-combustion

Phosphorus compounds have been reported to be a cause of increased deactivation rates of selective catalytic reduction (SCR) DeNOx catalysts in coal fired power plants. The deactivating behaviour of phosphorus was previously verified during lab and bench scale investigations. The results have been in good compliance with other research activities on similar topics.In order to compare the results of lab and bench scale tests with the actual operating conditions, measurements at two full scale power plants were carried out. The plants co-fired either meat and bone meal or sewage sludge as secondary fuel, while both represent high phosphorus fuels with a considerable amount of volatile fractions.The results of fuel and fly ash analysis showed an increased content of phosphorus during the co-combustion conditions. The analysis of the fine particulate matter showed a high phosphorus concentration on particles smaller than 0.9 μm. A considerable phosphorus concentration on particle fractions smaller than 0.05 μm is a clear indication of the presence of gaseous phosphorus compounds. These are expected to have a high deactivation potential on the SCR catalysts.     

Removal of carbon dioxide from flue gases with aqueous MEA solution containing ethanol

Adding ethanol to an aqueous amine solution offers several advantages for post-combustion CO₂ capture. The equilibrium isotherms at higher temperatures shift towards lower loadings, leading to an easier desorption. At constant temperature in the desorber bottom, the desorber pressure is increased, leading to energy savings in the CO₂ compression. Alternatively, at constant desorber pressure, the temperature in the desorber bottom is decreased, leading to a smaller efficiency drop of the power plant. Furthermore, the absorption rate of CO₂ is enhanced by adding ethanol. In the present work, the potential of using ethanol as a co-solvent for a 0.3 g/g aqueous monoethanolamine (MEA) solution is assessed based on simulations with an equilibrium stage model. A major drawback is the volatility of ethanol. The recovery of ethanol can be achieved using a water scrubber and subsequent stripping. The recovered ethanol vapor is sent directly to the desorber for heat integration. The process with ethanol recovery results in an increased complexity of the capture plant, difficulties in controlling the water balance and higher investment costs and offers, if any, only a moderate energetic advantage. The process concept could, however, be used for other co-solvents with similar properties as ethanol but lower vapor pressures.     

Removal of nitric oxide and sulfur dioxide from flue gases using a FeII-ethylenediamineteraacetate solution

The combined absorption of NO and SO₂ into the Fe(II)-ethylenediamineteraacetate(EDTA) solution has been realized. Activated carbon is used to catalyze the reduction of Fe^III-EDTA to Fe^II-EDTA to maintain the ability to remove NO with the Fe-EDTA solution. The reductant is the sulfite/bisulfite ions produced by SO₂ dissolved into the aqueous solution. Experiments have been performed to determine the effects of activated carbon of coconut shell, pH value, temperature of absorption and regeneration, O₂ partial pressure, sulfite/bisulfite and chloride concentration on the combined elimination of NO and SO₂ with Fe^II-EDTA solution coupled with the Fe^II-EDTA regeneration catalyzed by activated carbon. The experimental results indicate that NO removal efficiency increases with activated carbon mass. There is an optimum pH of 7.5 for this process. The NO removal efficiency increases with the liquid flow rate but it is not necessary to increase the liquid flow rate beyond 25 ml min^?1. The NO removal efficiency decreases with the absorption temperature as the temperature is over 35 °C. The Fe²⁺ regeneration rate may be speeded up with temperature. The NO removal efficiency decreases with O₂ partial pressure in the gas streams. The NO removal efficiency is enhanced with the sulfite/bisulfite concentration. Chloride does not affect the NO removal. Ca(OH)₂ and MgO slurries have little influence on NO removal. High NO and SO₂ removal efficiencies can be maintained at a high level for a long period of time with this heterogeneous catalytic process.     

Mathematical modeling of desublimation of carbon dioxide from flue gases of heat power systems

A quasi-nonstationary mathematical model of the low-temperature desublimation of carbon dioxide from purified flue gases of heat power systems has been developed. Process calculation results at parameters that correspond to its integration into the power trigeneration module based on a combination of Rankine and refrigeration cycles are given. Optimal operation estimates were obtained, which could be used to select an optimal engineering solution (changing the diameter of the heat exchanger tubes or the use of parallel units).     

Energy-saving technology for scrubbing waste gases from frit furnaces

Translated from Steklo i Keramika, No. 2, pp. 14–15, February, 1992.