造纸污泥流化床焚烧试验研究

在一座密相床截面积为 ０．２３ ｍ×０．２３ｍ、高度为 ５ｍ的流化床燃烧试验装置上进行了造纸污泥的焚烧试验．探明污泥水分、流化速度、二次风份额和过剩空气系数等参数对污泥燃烧性能的影响规律,为高水分造纸污泥焚烧炉的优化设计提供了依据．测试表明,在不添加脱硫剂情况下焚烧烟气中ＳＯ２、ＮＯｘ和Ｎ２Ｏ的排放浓度完全满足国家排放标准．     

垃圾焚烧炉氯源对氯化氢和二噁英排放的影响

本文研究了150 t/d垃圾与煤混烧流化床锅炉在不同含氯水平和添加钙基脱硫时氯化氢和二噁英的排放特性。实验结果表明烟气中的氯化氢和二噁英浓度随燃料中垃圾比例的增加而上升,在含氯量一定的情况下,炉内燃烧状况决定了二噁英的生成量,烟气中的二噁英随燃料中含氯量的增加而增加,飞灰中的二噁英则随燃烧状况的改善而增加。钙基的加入可以有效降低氯化氢和二噁英的排放。在我国目前的垃圾组分条件下,全煤工况和垃圾与煤混烧工况的二噁英排放量很低。     

污泥在循环流化床炉内的燃烧和污染排放特性

本文介绍了在１００吨／日循环流化床垃圾焚烧炉上进行的工业污水处理厂干化污泥和城市污水处理厂干化污泥焚烧结果。对焚烧产生的烟气中的污染物烟尘、氮氧化物、二氧化硫、氯化氢、汞、镉、铅和二恶英等排放浓度所进行的测试结果表明,采用循环流化床炉焚烧干化污泥,在炉内加石灰石情况下,烟气排放能达到我国生活垃圾焚烧污染控制标准。     

城市干化污泥循环流化床燃烧过程中NO和N2O的排放特性

在15 kW循环流化床实验台上进行了城市干化污泥的燃烧实验,研究了污泥含水率、燃烧温度、过量空气系数、二次风比率等因素对NO和N₂O排放特性的影响。实验结果表明:污泥含水率从4.5%增加至17.5%时,NO排放浓度明显降低,N₂O排放浓度明显升高;燃烧温度升高,NO排放浓度呈上升趋势,N₂O排放浓度则呈下降趋势;增大过量空气系数会促进NO和N₂O的生成;提高二次风比率可以降低NO和N₂O的排放浓度。城市干化污泥在循环流化床燃烧过程中NO和N₂O的排放浓度高于污泥与煤混烧时的排放浓度,但燃料N向NO和N₂O的转化率低于与煤混烧过程。     

流化床锅炉的燃尽程度

一、前言 本文利用燃烧煤矸石的130(T/h)流化床锅炉的实验数据,分析扬析颗粒的燃尽,以探讨提高流化床锅炉效率的途径。由于飞灰在悬浮段内的停留时间很短,悬浮段的烟气温度又不高,飞灰在悬浮段的燃尽是有限的。一般情况下,飞灰含碳量接近于颗粒从流化床中扬析时的含碳量。     

DME/LPG混合燃料HCCI燃烧模拟

根据碳氢燃料化学反应系统具有层次结构的特性,本文通过分析二甲醚(DME)与液化石油气(LPG)的详细化学反应机理,构建了反映DME／LPG混合燃料均质压燃(HCCI)燃烧的详细化学反应机理．采用该机理应用单区燃烧模型对DME／LPG混合燃料HCCI燃烧的化学反应动力学过程进行了数值计算．计算结果与试验结果对比表明,所构建的DME／LPG混合燃料氧化的详细化学反应机理能够准确预测DME／LPG混合燃料的两阶段放热特性,对低温和高温着火始点的预测很好;但高温反应过程预测欠佳,高温反应机理需要改进．     

在燃气轮机试验燃烧室内提高水煤浆燃烧强度的途径和燃烧效率的测定

本文给出了一个卧式常压燃烧装置,以CWS为燃料的试验研究结果。并根据本装置结合CWS的燃烧,给出了通过测量燃烧室出口烟气中CO_2％,以计算出燃烧效率的方法。     

煤粉再燃对600 MW锅炉NOx排放的影响

在国内某台燃用褐煤的600 MW机组锅炉上进行了煤粉再燃技术示范并进行了工业试验.机组在600 MW负荷下运行时,NOx排放可控制在274 mg/m3(烟气中氧量折算到6%,下同)的水平,比改造前下降了65.36%,同时燃烧效率没有降低.进行了常规通风、空气分级和煤粉再燃三个工况下的试验,结果表明,煤粉再燃对NOx的控制效果最好,其次为空气分级.再燃煤粉比例对NOx排放也有明显的影响,在试验条件下,随着再燃燃料比例的增加,NOx排放呈降低趋势.     

甲醇柴油比对二元燃料燃烧与排放特性的影响

在六缸电控单体泵增压中冷重型柴油机进气管上面布置电控甲醇喷嘴,采用柴油引燃甲醇均质混合气的二元燃料燃烧模式,开展了高甲醇柴油比的二元燃料燃烧特性与排放特性试验研究。研究结果表明;随着醇柴比的增加,二元燃料的滞燃期增加,放热率峰值、最大缸内压力和压力升高率峰值都变大;未燃HC和CO排放上升,NO_x排放则先下降后上升;烟度与颗粒物浓度排放都下降,低负荷下醇柴比为4.0时效果尤其显著;大负荷时二元燃料燃烧时热效率明显提高。     

10吨/时示范性煤泥沸腾燃烧锅炉

本文介绍永荣矿务局发电厂10吨/时洗煤泥沸腾锅炉的结构特性及运行性能,该沸腾炉采用浙江大学提出的异重床,高位成型给料,不溢流不排冷渣沸腾燃烧新工艺。工业试验结果表明:含水量27％左右的高灰份(A~g=52％),细颗粒(100％<0.5mm),高粘度煤泥在没有其它燃料助燃时是可以燃烧的,燃烧效率达95.4％,运行稳定,操作方便。     

Partitioning and transformation behavior of selenium during coal combustion

The partitioning of selenium in coal-fired flue gas and desulfurization wastewater is of great threat to the ecological environment and human health. However, the unclear understanding of interactions between selenium vapors and fly ash hinders the emission control of selenium from coal-fired power plants. To further illuminate the mechanism of selenium partitioning and transformation, this study carefully estimated selenium distribution characteristics in the coal combustion byproducts from several industrial power plants. The effective temperature range as well as the key ash components for selenium retention by fly ash was clarified by multiple-scale experiments and theoretical perspectives. The results showed that gaseous selenium tended to be captured by fly ash at a medium-to-low temperature range (i.e. below 650 °C). The limited residence time resulted in the incomplete capture of gaseous selenium by fly ash. Mullite, quartz, iron oxides, and anhydrite in fly ash were found to be the main trappers for gaseous selenium. Among these components, iron oxides showed excellent selenium adsorption performance at a wide temperature range of 150-700 °C, which was realized by the strong chemical adsorption. By contrast, as the dominant phases in fly ash for the physical adsorption of gaseous selenium, mullite and quartz mainly captured gaseous selenium below 300 °C. On the other hand, sulfur dioxides had priority over gaseous selenium to react with calcium-containing ash components by forming anhydrite in the high-temperature region. The formed anhydrite had a limited selenium adsorption capacity, which was confirmed to capture gaseous selenium through a combination of physical adsorption and weak chemical adsorption. For the in-depth control of selenium emitted into desulfurization system and atmosphere environment, these findings provided a comprehensive insight into the behavior of selenium partitioning and transformation into fly ash during coal combustion.     

Ash formation and deposition during combustion of pulverized torrefied wood and coal in a 100 kW downflow combustor

Torrefied wood originating from beetle-killed trees is an abundant biomass fuel that can be co-fired with coal for power generation. In this work, pulverized torrefied wood, a bituminous coal (Sufco coal) and their blended fuel with a mixing ratio of 50/50 wt.%, are burned in a 100-kW rated laboratory combustor under similar conditions. Ash aerosols in the flue gas and ash deposits on a temperature-controlled surface are sampled during combustion of the three fuels. Results show that ash formation and deposition for wood combustion are notably different from those for coal combustion, revealing different mechanisms. Compared to the coal, the low-ash torrefied wood produces low concentrations of fly ash in the flue gas but significantly increased yields (per input ash) of ash that has been vaporized. All the mineral elements including the semi- or non-volatile metals in the wood are found to be more readily partitioned into the PM₁₀ ash than those in the coal. The inside layer deposits sticking to the surface and the loosely bound outside deposits exposed to the gas both show a linear growth in weight during torrefied wood test. Unlike coal combustion, in which the concentration of (vaporized) ash PM₁ controls the inside deposition rate, wood combustion shows that the formation of porous bulky deposits by the condensed residual ash dominates the inside deposition process. Co-firing removes these differences between the wood and coal, making the blended fuel to have more similar fly ash characteristics and ash deposition behavior to those of the bituminous coal. In addition, results also show some beneficial effects of co-firing coal with torrefied wood, including reduction of the total deposition rate and the minimization of corrosive alkali species produced by wood.     

Properties of biomass vs. coal fly ashes deposited in electrostatic precipitator

This paper presents comparative experimental studies of the morphology and elemental composition of fly ash particles from coal- and biomass-fired boilers, deposited in each stage of 3-stage electrostatic precipitators (ESPs). It was shown that fly ash morphology, its physical properties, and the percentage of elements in the fly ash taken from each stage of ESP depend on the kind of fuel. The biomass fly ash contains many irregular large particles, which are pieces of unburned wood. Bulk density of biomass fly ash is on average lower than that of coal fly ash, and drastically decreases in the second and third stages of ESP. The resistivity, measured at electric field of 4 kV/cm, of fly ash from biomass-fired boilers is much lower than that from coal, and can be below 10² Ω m, whereas from coal, except the first stage, varies in the range from 10⁷ to 10¹⁰ Ω m. The low resistivity of coal fly ash in the first stage of ESP results from high carbon content, and of biomass is probably an effect of additional high percentage of potassium, calcium and sodium sulfates. The percentage of Si, Al, Na, Fe, and Ti in fly ash from coal-fired boilers is much higher than from biomass, and in the opposite, the percentage of Mg, K, Ca, Mn, Mo, S, Cl, and P in biomass ash exceeds that in coal fly ash. Potential detrimental effects of biomass combustion products (salts, acids, tar) leaving the boiler on the construction elements of the electrostatic precipitator, including electrodes and HV insulators have been discussed in this paper. It was concluded that the long-term effects of biomass co-firing on the electrostatic precipitator performance, including the collection efficiency, have not been sufficiently studied in the literature and these issues require further detailed investigations.     

Experimental study on co-firing characteristics of ammonia with pulverized coal in a staged combustion drop tube furnace

Utilizing ammonia as a co-firing fuel to replace amounts of fossil fuel seems a feasible solution to reduce carbon emissions in existing pulverized coal-fired power plants. However, there are some problems needed to be considered when treating ammonia as a fuel, such as low flame stability, low combustion efficiency, and high NO_x emission. In this study, the co-firing characteristics of ammonia with pulverized coal are studied in a drop tube furnace with staged combustion strategy. Results showed that staged combustion would play a key role in reducing NO_x emissions by reducing the production of char-NO_x and fuel(NH₃)-NO_x simultaneously. Furthermore, the effects of different ammonia co-firing methods on the flue gas properties and unburned carbon contents were compared to achieve both efficient combustion and low NO_x emission. It was found that when ammonia was injected into 300 mm downstream under the condition of 20% co-firing, lower NO_x emission and unburnt carbon content than those of pure coal combustion can be achieved. This is probably caused by a combined effect of a high local equivalence ratio of NH₃/air and the prominent denitration effect of NH₃ in the vicinity of the NH₃ downstream injection location. In addition, NO_x emissions can be kept at approximately the same level as coal combustion when the co-firing ratio is below 30%. And the influence of reaction temperature on NO_x emissions is closely associated with the denitration efficiency of the NH₃. Almost no ammonia slip has been detected for any injection methods and co-firing ratio in the studied conditions. Thus, it can be confirmed that ammonia can be used as an alternative fuel to realize CO₂ reduction without extensive retrofitting works. And the NO_x emission can be reduced by producing a locally NH₃ flame zone with a high equivalence ratio as well as ensuring adequate residence time.     

Experimental study on electrostatic removal of high-carbon particle in high temperature coal pyrolysis gas

A high-temperature electrostatic precipitator (ESP) presents a good solution for hot gas cleaning, which can remove fly ash from pyrolysis gas at temperatures higher than the tar dew point. In this paper, the characteristics of negative DC corona discharge in air and simulated coal pyrolysis gas were studied. The removal of coal pyrolysis furnace fly ash (ash A) was investigated and compared with that of coal-fired power plant fly ash (ash B) in ESP with a temperature ranging from 300?K to 900?K. The current density of simulated gas was higher than that of air under the same discharge voltage and at different temperatures. The simulated gas also had a higher spark voltage and a lower onset voltage compared with air. The fractional collection efficiency of ash A was lower for particles with diameters of larger than 0.1?µm at high temperature, compared with ash B. A lower collection efficiency in simulated gas was obtained for particles with diameters of less than 0.1?µm compared with air. The collection efficiency of submicron particles in simulated gas was usually higher than it in air, especially for particles with diameters of less than 0.04?µm. In simulated gas, the overall collection efficiency of ash A was obviously lower than that of ash B, especially at high temperature. From 300?K to 700?K, the collection efficiencies of both ash samples were as high as above 93%, but the collection efficiency of ash A in simulated gas decreased to 78.7% at 900?K.     

炉内喷钙脱硫对锅炉热效率的影响

根据炉内喷钙脱硫的化学反应过程,经过化学分析和数学推导,得出了锅炉采用炉内喷钙脱硫后化学反应热、飞灰量和烟气量的增加对锅炉热效率影响的计算公式。采用三种试样的试验结果,定量分析了煤的含硫量不同时,随着钙硫摩尔比的变化喷钙脱硫引起的热损失的变化。结果表明,化学反应热损失大于飞灰和烟气量增加造成的热损失,当煤的含硫量为3.46％时,可使锅炉热效率降低1％左右。     

中试规模的第二代增压流化床联合循环发电技术研究与开发

第二代增压流化床联合循环发电技术(2G PFBC-CC)是当前具有应用前景的洁净煤发电技术之一。东南大学热能工程研究所构建了2 MWt加压喷动流化床部分气化炉,对原有1 MWt增压流化床燃烧炉进行了改造,形成了较完整的2G PFBC-CC系统．经过二年多的调试和试验研究,验证了2G PFBC-CC工艺可行性和先进性,部分气化炉产生的煤气热值在4．2 MJ／Nm3以上,满足燃气透平的要求,排出的半焦可在PFB燃烧炉内稳定燃烧,飞灰含碳量在2％以下,系统碳利用效率在99％以上。     

CFBC混烧城市污泥与煤:N2O和NO的排放

在0.15MWth CFBC试验台上混烧城市污泥与煤,当城市污泥的含水率和混烧率分别变化在30％～60％和25％～100％之间时,可以实现稳定燃烧。分析了炉膛温度和城市污泥混烧率对NO和N_oO生成浓度的影响。结果显示,在焚烧氮含量很高的城市污泥过程中,通过适当提高炉膛温度,可以控制N_2O的生成,但是NO的生成浓度主要与混烧率有关。     

污泥吸附剂的制备及其光谱性能研究

以城市和石化污水厂生化活性污泥及剩余污泥为原料,采用热解法制备烟气脱硫吸附剂,并与商品活性炭对比进行了孔结构、扫描电镜、X射线衍射、热分析及元素分析性质表征,利用傅里叶红外光谱法研究污泥吸附剂在SO₂-O₂-N₂及SO₂-O₂-H₂O_(g)-N₂体系的吸附机理。结果表明城市污水厂剩余污泥制备的吸附剂脱硫性能较好,其次为石化活性污泥,生化活性污泥吸附剂脱硫性能较差,剩余污泥制备的吸附剂脱硫率略低于商品活性炭。SO₂-O₂-N₂体系吸附机理主要为物理吸附,SO₂-O₂-H₂O_(g)-N₂体系SO₂发生了催化氧化,以化学吸附为主。吸附过程中起吸附作用的主要是微孔结构。     

Insight of arsenic transformation behavior during high-arsenic coal combustion

The release of arsenic vapors (As³⁺) during high-arsenic coal combustion not only raises serious environmental concerns, but also causes catalyst deactivation in selective catalytic reduction (SCR) systems. To illuminate the mechanisms involved in the transformation of arsenic vapors towards less troublesome arsenates (As⁵⁺) during coal combustion, the accessory minerals in the high-arsenic coal were identified and the association relationship of these compounds with arsenic in fly ash was estimated. The results showed that Si/Al were the main inorganic elements in high-arsenic coal while the content of Ca was quite low. Ca was mostly transformed into sulfates during coal combustion and the effect of Ca on the arsenic transformation was limited. Al/Fe played a more significant role in arsenic speciation transformation and arsenic in the fly ash was predominantly bound with Al/Fe-oxides as arsenates. It was further confirmed that Al in kaolin/metakaolin showed good capacity on arsenic capture. In addition, few arsenic vapors were captured through the physical adsorption mechanism and the large fraction of As³⁺ in some fine particles was mostly attributed to the chemical reactions between arsenic vapors and Al-compounds. Meanwhile, a certain amount of arsenic vapors were converted into As₂O₅(s) under the influence of SCR catalyst and then carried by flue gas to participate in fly ash. Besides, part of arsenic distributed in the fly ash was through the stabilization of ash matrix in high temperature conditions. The transformation of arsenic from vapors towards particulate arsenic favored arsenic emission control by particulate matter control devices.