市政污泥中低温气化及重金属迁移转化特性

利用管式炉进行了污泥CO₂气化实验,并与N₂热解实验进行对比,系统研究了污泥中低温气化及重金属迁移转化特性。研究发现：热解过程中各可燃气体释放速率峰值出现的时间顺序为CO峰 < H₂次峰 < CH₄峰≈C_nH_m峰 < H₂主峰,气化过程中为CO主峰 < CH₄峰≈C_nH_m峰 < H₂主峰 < CO次峰。在450~550℃的区间内,气化和热解的冷煤气效率、样品失重率及残渣含碳量均相近,温度超过550℃冷煤气效率差距逐渐增大,温度超过700℃,样品失重率及残渣含碳量差距逐渐增大。气化温度为850℃时,冷煤气效率达87%。在450~700℃的区间内,气化残渣中Cr、Ni、Cu、Zn、As、Pb的残留率均随温度增加呈缓慢降低的趋势,在700~850℃区间,上述重金属的残留率下降较快。Cd的残留率在450~550℃区间缓慢下降,550~700℃区间快速降低,700~850℃区间缓慢降低。气化残渣中Cr、Ni、Zn、As、Cd的稳定形态所占比例相较于污泥原样明显提高,而Pb、Cu的稳定形态所占比例与污泥原样相近。污泥中温（700℃）气化时,冷煤气效率约为50%,气化残渣中Cr、Ni、Cu、Zn、As的残留率约为高温（850℃）下的1.2倍,Pb约为2.7倍,Cd为7.5倍,残渣中各重金属的稳定形态比例与高温时接近,环境危害性小。     

氧化钙调理污泥气化过程中重金属的迁移转化规律

以CaO为主要成分的石灰常用于污泥的调理和稳定。为探究其对污泥气化过程中重金属迁移转化规律的影响,在沉降炉-固定床反应器和固定床上于600、800、1000℃进行了污泥的热解及气化实验,并分析了不同污泥样品、热解焦和气化灰中典型重金属（Mn、Zn、Cu、Cr、Ni）的含量及形态分布。结果表明,CaO的加入将稀释调理污泥中的重金属,并使Mn、Zn、Cr向稳定态转化;CaO会使重金属离子与OH-结合生成沉淀,继而在气化反应中分解成氧化物。在气化过程中,CaO会提高重金属的残留率,也会吸收其氯化物、硫酸盐等在高温下分解生成的HCl、SO₂等酸性气体,促使氧化物的生成和抑制重金属的释放。     

城市污泥中重金属处理方法研究进展

城市污水处理中产生的剩余污泥量大且富含多种生物可利用成分,资源化利用潜力大。城市污泥中的重金属是影响城市污泥无害化和资源化的主要因素之一,如何有效去除城市污泥中重金属是环境科学、环境工程研究热点。文章介绍了络合去除、电动修复、酸化溶出、微波等污泥中重金属去除技术,分析了其中存在的问题与发展趋势。     

城市污泥中重金属稳定性的化学形态分析

以城市污水厂剩余污泥为研究对象,以连续提取法对其中8种主要重金属元素的化学存在形态进行了分析,结果表明:污泥中除Ni、Zn、Cd有超标和潜在的超标危险外,其它各金属的含量均低于国家标准的最高要求;污泥Ni、Cd具有相当的生物毒性,其余的元素生物有效部分较少,稳定性较好。总体来看城市污泥可通过降低超标重金属含量来实现农用的目的。     

城市生活垃圾中聚乙烯塑料流化床气化

引言 城市生活垃圾气化熔融作为新一代的高效低污染垃圾热处理技术,在国外已有一定发展,如Thermoselect技术[1,2]、Siemens技术[1,3]、荏原技术[4]、RCP技术[1]等.上述技术中气化温度大多控制在550～650℃,但根据垃圾组分含量不同,反应条件也随之变化.因此,非常有必要进行垃圾单组分气化研究.我国城市生活垃圾中塑料大约占总质量的8%～20%,见表1.PE大约占塑料类垃圾的50%,其发热量高达43000 kJ·kg-1,所以有效气化PE极具意义.     

微波-柠檬酸浸出城市污泥中重金属

采用微波辅助柠檬酸浸出城市污泥中的重金属,考察了升温速率、pH值、搅拌时间等对浸出率的影响。结果表明,升温速率为15℃/min,pH值调至3,前搅拌30 min,170 W功率下微波2.3 min,再反应3 h,污泥中Zn、Cu、Ni与Pb的浸出率分别达到了47.84%,11.05%,43.83%,25.59%,较无微波条件下,重金属浸出率平均提升了50.7%,反应时间缩短了8 h。处理后污泥中重金属含量远低于《农用污泥中污染物控制标准》(GB 4284—84)。     

流化床低温热解耦合输送床气化方案初探

针对煤制油项目中存在的煤炭资源利用效率低、吨油耗煤量高的问题,提出了流化床低温热解耦合输送床气化的原料煤利用方案(设想),并系统地阐述了该方案的原则流程、工艺特点和潜在的问题。该方案较好地整合了流化床低温热解技术和输送床气化技术的优点,可同时实现原料煤的高焦油收率、高合成气产率和高能量利用率,但仍存在潜在技术问题。     

污水处理污泥掺配水煤浆气化重金属迁移研究及灰渣排放评价

以典型炼油企业污水车间产出的污泥及气化灰渣为研究对象,对其组成进行分析,对掺配油泥水煤浆气化灰渣的排放进行安全性评价,并对煤及油泥中含有的重金属元素在气化处置过程中的转移规律进行了研究。结果表明,掺配5%污泥水煤浆的灰渣其灰分组成基本不变,重金属含量符合排放标准。油泥及煤中的重金属在气化过程中主要迁移至细灰及粗渣中,通过气化炉高温气化反应,可实现重金属的固化。油泥掺配水煤浆气化处置,对灰渣排放无影响,能够实现对油泥的资源化利用及无害化处理。     

污水处理污泥掺配水煤浆气化重金属迁移研究及灰渣排放评价

以典型炼油企业污水车间产出的污泥及气化灰渣为研究对象,对其组成进行分析,对掺配油泥水煤浆气化灰渣的排放进行安全性评价,并对煤及油泥中含有的重金属元素在气化处置过程中的转移规律进行了研究.结果表明,掺配5％污泥水煤浆的灰渣其灰分组成基本不变,重金属含量符合排放标准.油泥及煤中的重金属在气化过程中主要迁移至细灰及粗渣中,通...     

CFD based combustion model for sewage sludge gasification in a fluidized bed

Gasification is one potential way to use sewage sludge as renewable energy and solve the environmental problems caused by the huge amount of sewage sludge. In this paper, a three-dimensional Computational Fluid Dynamics (CFD) model has been developed to simulate the sewage sludge gasification process in a fluidized bed. The model describes the complex physical and chemical phenomena in the gasifier including turbulent flow, heat and mass transfer, and chemical reactions. The model is based on the Eulerian-Lagrangian concept using the nonpremixed combustion modeling approach. In terms of the CFD software FLUENT, which represents a powerful tool for gasifier analysis, the simulations provide detailed information on the gas products and temperature distribution in the gasifier. The model sensitivity is analyzed by performing the model in a laboratory-scale fluidized bed in the literature, and the model validation is carried out by comparing with experimental data from the literature. Results show that reasonably good agreement was achieved. Effects of temperature and Equivalence Ratio (ER) on the quality of product syngas (H₂ + CO) are also studied.     

Air-steam gasification of sewage sludge in a bubbling bed reactor: Effect of alumina as a primary catalyst

Numerous references can be found in scientific literature regarding biomass gasification. However, there are few works related to sludge gasification. A study of sewage sludge gasification process in a bubbling fluidised bed gasifier on a laboratory scale is here reported. The aim was to find the optimum conditions for reducing the production of tars and gain more information on the influx of different operating variables in the products resulting from the gasification of this waste. The variables studied were the equivalence ratio (ER), the steam-biomass ratio (SB) and temperature. Specifically, the ER was varied from 0.2 to 0.4, the SB from 0 to 1 and the temperature from 750 °C (1023 K) to 850 °C (1123 K). Although it was observed that tar production could be considerably reduced (up to 72%) by optimising the gasification conditions, the effect of using alumina (aluminium oxide, of proven efficacy in destroying the tar produced in biomass gasification) as primary catalyst in air and air-steam mixture tests was also verified. The results show that by adding small quantities of alumina to the bed (10% by weight of fed sludge) considerable reductions in tar production can be obtained (up to 42%) improving, at the same time, the lower heating value (LHV) of the gas and carbon conversion.     

A mathematical model of fluidized bed biomass gasification

A mathematical model of biomass gasification in a fluidized bed has been developed. It considers axial variations of concentrations and temperature in the bubble and emulsion phases. The mass balance involves instantaneous oxidation and equilibrium devolatilization of the biomass, kinetics of solid-gas gasification reactions as well as of gaseous phase reactions and interphase mass transfer and gas convection. The energy balance is solved locally for each vertical volume element, and globally on the reactor by iteration on the temperature at the bottom of the bed. Three parameters have been adjusted based on the experimental results: the heat transfer coefficient at the wall, the weighting of the kinetics of the water-gas shift reaction and the fraction of biomass carbon remaining as char after devolatilization. The model is used to simulate a pilot scale (50 kg/h) biomass gasifier, and its predictions compared to experimental measurements. The temperature and gaseous concentrations are estimated with good accuracy for the experiments using a wood feedstock, except for the concentration of hydrogen which is overestimated.     

重金属市政污泥固化稳定化技术研究

对某污水处理站产生的污泥进行固化稳定化处理,测定其无侧限抗压强度、水稳定性、重金属浸出毒性、渗透性等指标。实验表明,处理后污泥无侧限抗压强度可达0.2 MPa,水稳定性无明显变化,重金属浸出浓度低于毒性鉴别标准值,渗透性满足填埋指标要求。     

串行流化床煤气化试验

针对串行流化床煤气化技术特点,以水蒸气为气化剂,在串行流化床试验装置上进行煤气化特性的试验研究,考察了气化反应器温度、蒸汽煤比对煤气组成、热值、冷煤气效率和碳转化率的影响。结果表明,燃烧反应器内燃烧烟气不会串混至气化反应器,该煤气化技术能够稳定连续地从气化反应器获得不含N₂的高品质合成气。随着气化反应器温度的升高、蒸汽煤比的增加,煤气热值和冷煤气效率均会提高,但对碳转化率影响有所不同。在试验阶段获得的最高煤气热值为6.9 MJ&#8226;m^-3,冷煤气效率为68％,碳转化率为92％。     

Modeling and simulation of biomass air-steam gasification in a fluidized bed

By considering the features of fluidized-bed reactors and the kinetic mechanism of biomass gasification, a steady-state, isothermal, one-dimensional and two-phase mathematical model of biomass gasification kinetics in bubbling fluidized beds was developed. The model assumes the existence of two phases — a bubble and an emulsion phase — with chemical reactions occurring in both phases. The axial gas dispersion in the two phases is accounted for and the pyrolysis of biomass is taken to be instantaneous. The char and gas species CO, CO₂, H₂, H₂O, CH₄ and 8 chemical reactions are included in the model. The mathematical model belongs to a typical boundary value problem of ordinary differential equations and its solution is obtained by a Matlab program. Utilizing wood powder as the feedstock, the calculated data show satisfactory agreement with experimental results and proves the effectiveness and reliability of the model. __________ Translated from Chemical Engineering (China), 2007, 35(10): 23–26 [译自: 化学工程]     

生物质流化床空气-水蒸气气化模型研究

根据流化床反应器特点,结合生物质气化动力学反应机理,建立了生物质在流化床内气化的等温稳态、一维二相动力学模型。该模型所做的主要假定如下:流化床分为气泡相和乳相,在气泡相和乳相内均存在化学反应,考虑二相内的轴向气体扩散,生物质热解过程瞬时完成,主要考虑焦碳以及CO,CO2,H2,H2O,CH4等在流化床内发生的8个主要化学反应。数学模型属于常微分方程组边值问题,利用数值计算软件M atlab7.0进行编程求解。以木粉为原料,将模型结果与实验结果进行了对比,模拟结果与试验数据符合良好,在一定程度上证明了模型的有效性和可靠性。