城市生活垃圾焚烧飞灰组成特性及重金属熔融固化处理技术研究进展

近年来,我国城市生活垃圾清运量以每年5%左右的增速发展,垃圾焚烧处理能力不断提升,而垃圾焚烧过程会产生占焚烧总量3%~5%的垃圾焚烧飞灰。随着垃圾焚烧处理能力的不断提升,垃圾飞灰产量逐年增加,飞灰处置压力越来越大。城市生活垃圾焚烧飞灰作为一种高重金属浸出毒性的危险废弃物,对环境存在较大危害。论述了城市生活垃圾焚烧飞灰的组成特性及重金属的分布和性质,从飞灰熔融过程原理、重金属转化特性、重金属固化影响因素等方面阐述了熔融处理垃圾飞灰技术的研究进展,探究了飞灰组分和熔融条件对熔融过程及重金属固化效果的影响。论述了等离子熔融技术和熔融固化重金属的效果,最后对飞灰复配熔融及冷却过程优化处理给出参考性建议,并指出飞灰熔融处理技术未来发展方向。垃圾焚烧飞灰中重金属主要以其氧化物、氯化物、硫酸盐形式存在,熔融处理可以改变飞灰组分及相态,使飞灰发生多晶转变和熔融相变过程,重金属离子发生同晶置换反应,被固化在硅酸盐的Si—O四面体晶格结构中,很大程度上降低了飞灰的浸出毒性并实现熔渣资源化利用。熔融处理过程中,熔融气氛、时间及飞灰组分对过程特性和重金属的迁移转化影响较大,冷却方式不同会影响玻璃体熔渣的物理性质。根据重金属的熔点和沸点特性,在熔融处理后,烟气和二次飞灰中会携带部分挥发性强、沸点低的重金属。在今后研究中需要对烟气和二次飞灰进行冷却或二次捕集处理,并对烟气成分进行探究。由于熔融处理过程耗能大、投资高、关键设备研发难攻关,我国垃圾焚烧飞灰熔融处理技术仍处于技术研发阶段,尚无稳定化工业运行实例,但已有部分中试研究试验。熔融处理前,应先分析飞灰组成成分,根据飞灰组成进行预处理。通过添加助熔剂、调节飞灰碱度对飞灰进行复配熔融处理,降低熔融处理的能耗,高效稳定处理重金属。在实验室稳定有效试验的基础上,可以对等离子体熔融处理装置进行技术改进和创新,提高等离子火焰稳定性,实现熔渣的高效分离,提升装置耐久性。     

Novel sorbents for mercury emissions control from coal-fired power plants

The authors have successfully developed novel efficient and cost-effective sorbents for mercury removal from coal combustion flue gases. These sorbents were evaluated in a fixed-bed system with a typical PRB subbituminous/lignite simulated flue gas, and in an entrained-flow system with air simulating in-flight mercury capture by sorbent injection in the ductwork of coal-fired utility plants. In both systems, one of the novel sorbents showed promising results for Hg⁰ removal. In particular, this sorbent demonstrated slightly higher efficiencies in Hg⁰ removal than Darco Hg-LH (commercially available brominated activated carbon) at the similar injection rates in the entrained-flow system. The other novel sorbent showed excellent Hg⁰ oxidation capability, and may enable coal-fired power plants equipped with wet scrubbers to simultaneously control their mercury and sulfur oxides emissions. In addition, fixed-bed results for this sorbent showed that co-injection of a very small amount (∼10%) of raw activated carbon could eliminate almost all of the mercury generated by reactions of Hg⁰ with the sorbent.     

SO2 removal from flue gas with dry limestone

SO₂ removal from flue gas with an efficiency of over 90% can be achieved by the furnace limestone injection (FLI) process in combination with the recently developed ash recycle activation (ARA) process. The ARA process uses a mixture of fly ash and CaO sorbent that comes out of the furnace for further SO₂ removal. The dust is separated from the flue gas, treated with low pressure steam and then added to the flue gas again. The activation of the Ca compounds occurs during steam treatment. Capillary condensation occurs and aqueous electyrolyte solution reactions within the particle become effective. A differential particle model is formulated.     

垃圾焚烧飞灰在污染物控制领域中的应用探讨

随着垃圾焚烧处置技术的推广和应用,垃圾焚烧飞灰产量逐年增加,传统填埋处置方式存在成本高、填埋场资源不足等问题,因此飞灰的综合利用问题广受关注。由于飞灰富含SiO₂、Al₂O₃等活性物质,在污染物的吸附脱除领域具有良好的应用前景。本文主要结合垃圾焚烧飞灰的理化特性,介绍了垃圾焚烧飞灰在不同废水废气中的污染物吸附脱除效果。综合近年来污染物脱除研究情况,着重介绍了原始飞灰和改性飞灰在重金属、磷盐、染料等污染物脱除中的应用效果、机理,指出了目前存在的主要问题,并对不同的应用工艺进行了成本分析和优缺点对比。最后提出了需要继续深入微波水热在提高飞灰吸附性的应用研究和进一步完善飞灰在污染物控制领域应用的全过程研究的建议与展望。     

NH4Cl改性活性炭脱除气态Hg0的特性分析

制备了原始活性炭与NH₄Cl改性活性炭,对其进行了物化特性表征,在固定床汞吸附实验台上考察了N₂气氛下颗粒粒径、NH₄Cl溶液浓度、SO₂、CO₂等因素对活性炭脱除Hg⁰性能的影响。研究结果表明：NH₄Cl浸渍改性没有造成活性炭孔隙结构的明显变化,但使得Cl元素成功担载到活性炭表面;随着颗粒粒径增大,活性炭吸附Hg⁰的外部传质速率、内部扩散速率均降低,较小的颗粒粒径有利于活性炭脱汞;由NH₄Cl改性在活性炭表面所产生的卤素官能团（AC-Cl）能够有效地氧化烟气中的Hg⁰,增强了活性炭对于Hg⁰的氧化吸附作用;SO₂能有限地促进原始活性炭的脱汞性能,对NH₄Cl改性活性炭脱汞性能则表现出先促进后抑制并主要体现抑制作用的现象,并且抑制作用随SO₂浓度的增大而增加;CO₂由于能在活性炭表面极化,且能与氨基官能团反应生成有利于吸附汞的羰基,促进了活性炭的脱汞性能。     

Laboratory study of air-water-coal combustion product (fly ash and FGD solid) mercury exchange

Recent laboratory research has indicated that coal fly ash derived from subbituminous and bituminous type coals is a sink for atmospheric mercury (Hg), however lignite-based ash was found to emit Hg to the air. Solids collected from systems with components that enhance Hg removal (i.e. activated carbon injection (ACI), flue gas desulfurization (FGD), and selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR)) may have higher Hg concentrations and therefore a higher potential for Hg release. For this study we investigated the potential for Hg release to the air and water from coal combustion products (CCPs) collected from coal-fired units with FGD equipment, SCR and SNCR equipment, and sorbent injection for Hg removal. In the laboratory study, most dry samples acted as sinks for atmospheric Hg in the dark at 25 °C. When exposed to light or increased temperature (45 °C), deposition of Hg to the fly ash substrates in most cases continued but decreased. Wet FGD samples emitted Hg. However, they became a sink for atmospheric Hg or exhibited low Hg emission rates when dried. Mercury flux in the dark at 25 °C was correlated with fly ash carbon content (LOI). Most liquid extracts derived using the synthetic precipitation leaching procedure (SPLP EPA method 1312) had very low Hg concentrations (<13 ng/l).     

模拟城市垃圾焚烧中硫化合物对重金属Cd迁移分布的影响

The effect of sulfur compounds （including sulfur, sulfide, sulfite and sulfate）, initial concentration of heavy metal and operating conditions on Cd emission in municipal solid waste （MSW） incineration were investi-gated using a simulated tubular furnace and simulated MSW spiked with Cd. The concentration of Cd was meas-ured by inductively coupled plasma-atomic emission spectrometry （ICP-AES） after digesting the samples including bottom ash, fly ash and flue gas according to related USEPA methods. The results show that S and Na2S tend to in- crease Cd partitioning in bottom ash, whereas Na2SO3 and Na2SO4 tend to reduce Cd partitioning in bottom ash. The effect of sulfur compounds on Cd partitioning in bottom ash was in the sequence of Na2S〉S〉Na2SO3〉 Na2SO4. chemical equilibrium analysis is also performed to determine the effect of sorbents on Cd adsorption. The calculations show that S presents strong affinity for Cd and restrains Cd adsorption by SiO2, whereas when temperature rises to between 830℃ and 1030℃, Cd adsorption efficiency of SiO2 is over 80% and the efficiency of Al2O3 is up to 85%.     

垃圾焚烧系统换热表面的积灰生长与控制研究进展

焚烧是我国处理城市生活垃圾的重要方式，能够实现城市生活垃圾的减量化、无害化和资源化利用。由于城市生活垃圾水分高、盐分多、热值低，导致垃圾焚烧炉普遍面临严重的积灰问题，这不仅为垃圾焚烧炉的安全运行带来隐患，还严重影响垃圾焚烧发电厂的经济效益。本文综述了垃圾焚烧炉受热面积灰生长的研究现状，介绍了垃圾焚烧炉受热面积灰生长的机理，分析了飞灰粒径、烟气流速、烟气温度、换热面温度等对垃圾焚烧炉受热面积灰生长特性产生影响的因素。在燃煤锅炉和生物质炉积灰结渣的现有积灰模型基础上，需要结合垃圾炉的积灰实验数据发展可以预测垃圾焚烧炉积灰结渣问题的模型。针对垃圾焚烧炉受热面积灰严重的现象，本文提出了设备改进、工艺优化、使用添加剂和涂层技术抑制积灰生长的一系列方法。最后总结了当前的重点研究内容，提出了建立能够准确预测垃圾焚烧炉积灰生长的模型，开发新的有效减轻垃圾焚烧炉换热面积灰的涂层等今后开展研究的方向，为垃圾焚烧电厂的合理运行提供了参考建议。     

粉煤灰负载的钙基脱硫剂的制备

针对目前干法烟气脱硫工艺吸收剡利用率低、用量大等问题,开发以粉煤灰、Ca（OH）2、活化剂为主要原材料,通过固相反应／水热化合反应过程制备粉煤灰负载的高效钙基脱硫剂,其脱硫效果采用流动床气一固催化测试装置测定,脱硫率可达93％。     

Nano-Structured Sorbent Injection Strategies for Heavy Metal Capture in Combustion Exhausts

Nano-structured sorbent injection is a promising technique for heavy metal capture in combustion systems. The importance of sorbent injection strategies, including the form of the sorbent and its injection location for metal capture and removal is investigated in this study. A multi-component tri-modal aerosol dynamic model was employed to understand the evolution of heavy metals and sorbents, as well as their interactions in the incineration system. Experiments were conducted to assess the performance of in-situ generated SiO₂, compared with bulk Ti-PICL sorbent, in capturing lead and cadmium from a demilitarization incineration system. Nano-structured SiO₂ generated in-situ was found to be more efficient than the bulk Ti-PICL sorbent because it offers a higher external surface area for condensation. The sorbent injection location is important as it affects the physical properties of the sorbent and the pathway for heavy metal capture. Extensive sintering and reduction in the surface area were observed when sorbent was injected into high temperature flue gas, i.e., directly into the combustor. However, when injected into much lower temperature flue gas, the pathway for heavy metal capture was altered from condensation to inter-particle coagulation due to the nucleation of heavy metal species. This study further revealed that new emission standards can be readily met with an optimal sorbent injection strategy.     

Evaluation of SO2 oxidation and fly ash filtration by an activated carbon fluidized-bed reactor: The effects of acid modification, copper addition and operating condition

It is expected that the simultaneous removal of acid gases and particles from flue gas, using a single process and at the same temperature, will become an economical, and thus, desirable option. Accordingly, this study investigates the potential for the utilization of a fluidized-bed adsorbent/catalyst reactor for the simultaneous removal of SO₂ and fly ash from simulated flue gas. The operating conditions for the evaluation include: (1) different pre-treatments of the adsorbent/catalyst, (2) the operating parameters of adsorption/filtration and (3) the effects of simultaneous adsorption/filtration through the fluidized-bed reactor. Based on the experimental data gathered, the Brönsted acid sites were formed on the surface of activated carbon (AC) support materials after modification with nitric or sulfuric acid and it acted as anchor. This characteristic accounts for the promotion of the effects of dispersion and adsorption of the adsorbent/catalyst. Moreover, the addition of copper facilitated the oxygen transfer of SO₂ to the carbon matrix. The concentration of SO₂ removed by the fluidized-bed adsorbent/catalyst reactor decreased from 17.9 to 14.2 mg SO₂/g of adsorbent after exposure to a high concentration of fly ash. Therefore, an acid-pre-treatment of the adsorbent/catalyst is required to hasten the removal of SO₂ in the simulated flue gas. Our result shows that the acidic groups may facilitate the adsorbent/catalyst removal of SO₂ when there exist high concentrations of fly ash in the flue gas.     

Content, mobility and transfer behavior of heavy metals in MSWI bottom ash in Zhejiang province, China

Municipal solid waste incinerator (MSWI) bottom ash samples were taken from six cities of Zhejiang province, where 1/4 incinerators of China were located. The samples were instrumentally analyzed to detect the content of heavy metals. Sequential extraction procedure (SEP) was adopted to characterize the mobility and environmental impact of heavy metals. And the transfer coefficients of heavy metals from the input MSW to the bottom ash during the incineration were also calculated. It showed that the average content of Zn, Mn, Cu, Pb and Cr in the bottom ash exceeded 300 mg/kg, which was much higher than that in the soils. SEP results showed that although the residue fraction was the primary fraction of the heavy metals in the bottom ash, there were still 1.84 mg of Cd, 86.21 mg of Cu, 83.46 mg of Pb and 939.46 mg of Zn in 1 kg bottom ash having the potential of leaching, which indicated a great threat to the surrounding environment. The result of coefficients calculation revealed that almost all the Cu, Cr, Mn and Ni in the input MSW were transferred to the bottom ash during the incineration. Bottom ash was also the main destination of Cd, Co, As, Mo, Pb and Zn though considerable amounts of those metals were transferred to the raw gas.     

Evaluation of low ash impact sorbent injection technologies for mercury control at a Texas lignite/PRB fired power plant

A sorbent injection test program was carried out at NRG Texas Power LLC's (NRG) Limestone Electric Generating Station (LMS). LMS fires a 30/70 blend of Powder River Basin (PRB) and Texas Lignite, and is equipped with a cold-side electrostatic precipitator (ESP) and wet scrubber. The plant markets its fly ash for beneficial use, so development of a low ash impact mercury control technology is important to the economics of implementing a mercury control system. In addition to standard activated carbon injection, two different low ash impact mercury control technologies were evaluated in parametric tests: low ash impact sorbents and Toxecon™ II. The parametric ACI test program conducted at LMS demonstrated that high (>90%) levels of mercury removal could be achieved with carbon sorbents. The Toxecon™ II design used at LMS did not provide for as high a mercury removal as injection upstream of the ESP, likely due to poor coverage of the cross-sectional area of the ESP. Limited concrete testing was performed with simulated ash/carbon mixtures. As expected, the amount of air-entraining additive required increased with increasing carbon content in the ash. However, it appeared that small amounts of non-passivated carbon may be acceptable in fly ash for concrete use.     

电渗析法分离医疗垃圾焚烧飞灰浸出液中重金属

采用电渗析法分离医疗垃圾焚烧飞灰浸出液中重金属,考察了电流密度、液固比、处理时间等参数对重金属移除的影响,并分析了电渗析处理对飞灰特性、重金属形态及其浸出毒性的影响. 结果表明,电流密度0.8 mA/cm2、液固比10(w)和处理时间14 d条件下飞灰浸出液中重金属分离效果最好,11.1% Pb, 42.3% Zn, 56.7% Cd, 38.7% Cu, 7.5% Cr被移除,飞灰中大量NaCl被移除,氯含量从20.43%降低到0.78%,热灼减率从11.1%升高到34.3%,可溶态和碳酸盐态重金属含量降低,飞灰基质减少及不可溶态重金属存在导致残灰中重金属含量增加,Pb和Cd浸出浓度仍超过生活垃圾填埋场的阈值.     

First full-scale demonstration of mercury control in Alberta

Alberta electricity companies, TransAlta, ATCO, and EPCOR, teamed with GE Energy to conduct full-scale evaluation of sorbent injection in Sundance Unit 5 operated by TransAlta. Sundance Unit 5 fires a Western Canadian sub-bituminous coal and is equipped with cold-side ESP for PM control. Goals of the program were to evaluate: (1) the ability of achieving 70% or greater mercury reduction using activated carbon injection in long-term tests (30 days), (2) the effect of sorbent injection on ESP performance and opacity in long-term testing, and (3) the effects of combustion conditions on “natural” mercury removal in fly ash.     

Influence of SO3 on mercury removal with activated carbon: Full-scale results

Activated carbon injection is considered one of the most cost-effective options for mercury control at PRB-fired power plants. However, roughly 30% of sites firing PRB coal use SO₃ for flue gas conditioning. The presence of SO₃ in flue gas can decrease mercury capture by activated carbon, sometimes dramatically. Overcoming activated carbon performance limitations caused by SO₃ conditioning for units with this configuration is essential to enable these plants to cost-effectively meet pending mercury emission regulations. Ameren's Labadie Unit 2 fires PRB coal and uses SO₃ to enhance particulate capture in the electrostatic precipitator (ESP). Full-scale sorbent injection tests at Labadie were conducted from 2005–2007. Six sorbents were tested at SO₃ injection concentrations ranging from 0 to 10.7 ppm. Sorbent performance was evaluated at two injection locations (the air preheater (APH) inlet and outlet). Native mercury capture on fly ash was typically less than 15%. When the mercury sorbents were injected downstream of the air preheater, the SO₃ concentration resulted in a decrease in mercury capture from 85% (no SO₃ injection) to 17% (SO₃ injection set at 10.7 ppm). Mercury sorbents were more effective when injected upstream of the air preheater. With the SO₃ system off, mercury removal increased from 75% when injecting 5.1 lb/MMacf of brominated carbon at the APH outlet, compared to 95% when injecting at the inlet. With the SO₃ system on, test results indicated an increase from about 30% injecting at the outlet to 58% injecting at the inlet. Tests evaluating the ADA-ES patented onsite milling process showed that 85% mercury capture was achieved injecting 4 lb/MMacf of milled activated carbon compared to a requirement of 10 lb/MMacf to achieve the same removal using as-received carbon, representing a 60% reduction in activated carbon consumption. No changes in opacity, APH and ESP performance, or other balance-of-plant effects were observed in these tests.     

Gaseous mercury removal in a hybrid particulate collector

Gaseous mercury removal from simulated flue gas by sorbent injection was estimated and the effect of an electric field applied to a particulate collector on mercury removal was analyzed. For this, a bench scale system which included a sorbent injection reactor and a hybrid particulate collector was made up. The hybrid particulate collector consisted of an electrostatic precipitator and a fabric filter. Activated carbon was injected into the reactor as a sorbent. According to the result of experiment using simulated gas prepared by injecting gaseous mercury into air, the mercury removal by activated carbon injection at 130°C varied from around 3.9% at C/Hg ratio of 1,000 up to around 24.4% at C/Hg ratio of 50,000 including reaction in the hybrid particulate collector. When C/Hg ratio was fixed at 10,000 and temperature was changed from 50°C to 150°C, the mercury removal decreased from 43.2% to 1.9%. In addition, when high voltage was applied to the hybrid particulate collector, the mercury removal increased up to 63.1% at a C/Hg ratio of 5,000 and at a temperature of 130°C. Considering baseline mercury removal efficiency of up to 50% in the utility boilers due to the acid gases containing in the flue gas, above results indicate that 90% or more of gaseous mercury could be removed.     

混燃石油焦循环流化床锅炉硫污染物排放特性

在3台配备了炉内脱硫+静电除尘器（ESP）/布袋除尘器（FF）+湿法脱硫装置（WFGD）的410 t·h^-1循环流化床（CFB）锅炉进行了硫污染物排放特性研究。在3个测点采用US EPA Method 8对烟气中不同形态硫污染物进行了平行取样,并同时采集了相应工况下入炉燃料、石灰石、底渣、飞灰、石膏和废水等,考察了污染物控制装置对硫污染物的影响以及硫在电厂的迁移和分布特性。结果表明,锅炉出口烟气中硫主要以颗粒态硫和SO₂的形式存在,占比分别为48.94%～55.05%和44.14%～49.07%。ESP和FF能高效脱除颗粒态硫,脱除效率均达95%以上;WFGD对SO₃/硫酸雾、颗粒态硫的脱除效率分别达62.66%～67.82%和53.06%～60.89%。燃料中硫经过燃烧和污染物控制装置脱除之后绝大部分迁移至灰渣（底渣+飞灰）和湿法脱硫产物（石膏+废水）中,分别占硫总输出的56.79%～70.12%和29.25%～41.70%,只有0.63%～1.51%的硫排放到大气环境中。     

Emission of Polycyclic Aromatic Hydrocarbons (PAH) from Solid Waste Incinerator Equipped with an After-Combustion Chamber

Abstract

Polycyclic aromatic hydrocarbons (PAH) are typical indicators of incomplete combustion during solid waste incineration. The PAH emissions caused by waste incineration vary according to waste composition and operating parameters such as furnace temperature, after-combustion conditions, excess air, carbon monoxide levels.

In this work, the content of PAH in the fly ashes (sampled upstream the flue gas treatment system) and bottom ashes produced by the combustion of a refuse derived fuel (RDF) in a rotary kiln incinerator equipped with an after-combustion chamber is determined. The emission levels of PAH are correlated with different operating conditions of the incinerator to evaluate the destruction efficiency of the after-combustion chamber for these compounds.