化工废液焚烧炉内积灰结渣特性

以一台化工废液焚烧炉为研究对象,研究炉内的积灰、结渣与腐蚀行为。利用X荧光光谱仪、扫描电镜、X射线衍射仪对样品的元素组成、微观相貌以及矿物组成进行分析。结果表明,化工废液中高浓度的Na、S在焚烧和换热过程中的转化机理是影响飞灰粒子沉积和管壁腐蚀的关键因素。XRF元素分析显示,沉积物样品中的元素成分基本相似,但是由于挥发性不同,表现出不同的分布、沉积特征,Na在整个取样范围内分部均匀,而Fe、Ni沿烟气流动方向逐渐降低,S则在低温段表现出富集的特征。在660~900℃,碱金属硫酸盐与气相SO₂/SO₃以及Fe₂O₃和NiO发生反应生成的低熔点共晶体,即碱-铁硫酸盐Na₃Fe(SO₄)₃和硫酸镍钠Na₂Ni(SO₄)₂,能够加剧已沉积粒子的烧结和诱发高温腐蚀;在低温段检测到的Na₃H(SO₄)₂表明低温腐蚀的出现。     

Very High Volume Fly Ash Cements. Early Age Hydration Study Using Na2SO4 as an Activator

The early age ambient temperature hydration of a hybrid cement formulation containing very high volumes of coal fly ash (~80% by dry mass) and activated by Na₂SO₄ is presented. The Na₂SO₄ salt acts as a safe and convenient in situ source of alkali to activate fly ash glassy phases without undesirable effects on cement clinker hydration. Comparison to a reference paste with gypsum instead of sodium sulfate revealed that Na₂SO₄ reduced setting times, shortened the induction period, and increased early alite hydration and compressive strength development, but also restricted ettringite formation. When replacing the active fly ash component for milled sand of a similar particle size, the Na₂SO₄‐activated pastes set even quicker, no ettringite was observed, and early strengths were considerably reduced. Possible reaction mechanisms in the hybrid pastes are discussed.     

AGGLOMERATION BEHAVIOR IN A BUBBLING FLUIDIZED BED AT HIGH TEMPERATURE

Minimum fluidization velocity and agglomeration behavior were investigated at high temperature in an 80?×?30?mm two-dimensional quartz fluidized bed and in an 82?mm i.d. circular fluidized bed. Bed materials tested were two sizes of glass beads as well as three sizes of fluidized bed combustor (FBC) ash. The minimum fluidization velocity decreased with increasing bed temperature, whereas the minimum sintering fluidization velocity increased with the bed temperature. The sintering of glass beads belongs to visco plastic sintering, the first type. FBC ash agglomerate has higher amounts of SiO₂, Al₂O₃, Na₂O, K₂O, and SiO₂ than in the original ash, indicating that low melting eutectics were formed and that the liquid phase in a silicate system was formed. The agglomeration of FBC ash belongs to the second type, an excessive quantity of liquid being formed by melting or chemical reaction.     

Prevention of bed agglomeration with iron oxide during fluidized bed incineration of refuse-derived fuels

The present study was performed to evaluate the effect of iron oxide addition on the prevention of bed agglomeration during the fluidized bed incineration of refuse-derived fuels (RDFs) having different alkali contents. To investigate the extent of bed agglomeration as a function of the Fe₂O₃/(K₂O+Na₂O) molar ratio, a simulation was performed by using a thermodynamic equilibrium model. Based on this simulation, potassium (K) component exhibited a much higher affinity for iron (Fe) component than for silicon (Si) component, and the extent of agglomeration was remarkably reduced. Therefore, a small amount of iron oxide added to the bed effectively reduced the extent of bed agglomeration in the fluidized bed incineration process. Furthermore, the extent of agglomeration decreased as the molar ratio of Fe₂O₃/(K₂O+Na₂O) increased until unity was attained. In excess Fe₂O₃, no potassium silicate melts existed in the products, while the amount of sodium silicate melts remained constant.     

The identity of the sulfur‐containing phases present in cement clinker manufactured using a high sulfur petroleum coke fuel

Cement clinker produced using a high sulfur petroleum coke fuel has been analysed to determine the identity of the sulfate‐containing phases. Quantitative X‐ray diffraction methods were used in conjunction with extraction procedures to concentrate or extract the sulfate phases. The minerals of interest were anhydrite (CaSO₄), aphthitalite (3K₂SO₄·Na₂SO₄), arcanite (K₂SO₄), calcium langbeinite (K₂SO₄·2CaSO₄) and thenardite (Na₂SO₄). Overall sulfur content of the clinker increased in proportion with the amount of sulfur in the fuel. The clinker produced using the high sulfur fuel was found to contain a significantly increased concentration of aphthitalite but a reduced amount of thenardite. Comparison of the experimental results with theoretical predictions based on the Bogue formulae shows differences in respect of calcium langbeinite, which is not detected in the clinker, and thenardite, which is detected. Copyright © 2004 Society of Chemical Industry     

Na2SO4 deposit-induced hot corrosion of BN-coated α-SiC

BN coated α-SiC was exposed to ~2.5 mg/cm² of Na₂SO₄ for 0.75-144 hours between 700°C and 1100°C in a 0.1% SO₂-O₂ gaseous environment. A combination of SEM, EDS, ICP-OES, XRD, and optical profilometry was used to determine that BN induced a previously unobserved form of Na₂SO₄ deposit-induced hot corrosion of SiC below the melting temperature of Na₂SO₄ (T_m = 884°C). Above the melting temperature of Na₂SO₄ BN did little to alter the hot corrosion behavior of SiC, due to B₂O₃ volatility. Substrate attack below the melting temperature of Na₂SO₄ was found to result in rivulet recession features, whereas deep, localized pitting occurred above the melting temperature of Na₂SO₄. Initially, the mixture of Na₂SO₄ and BN led to the formation of a Na₂O- and B₂O₃-containing liquid silicate and accelerated corrosion which after prolonged exposure, resulted in the partial crystallization into a lath-like tridymite and cristobalite mixture. Prolonged exposure resulted in a flattening of SiC consumption rates after exposure for several hours at 1000°C and after several days at 800°C, resulting in decreased SiC oxidation/corrosion kinetics.     

Role of delayed release of sulphates from clinker in DEF

Two clinkers rich in sulphate burned in the pilot plant rotary kiln and cements prepared from them were investigated. Clinker richer in sulphate (SO₃=3.6%) contained independent anhydrite grains as well as inclusions of anhydrite in belite. The mortar from it expanded after heat treatment at 90 °C and the addition of Na₂SO₄ or NaOH accelerated and increased this expansion. The expansion occurred irrespective of the fact that the clinker contained only 3% of C₃A, although the C₄AF content was 13%. The second clinker with 2.6% SO₃ contained mainly calcium langbeinite and expanded only when 2% of Na₂SO₄ was added. The SEM examination of the mortars revealed the presence of numerous bands of massive ettringite around sand grains. Agglomerates of cracked ettringite in cement gel were also present. In addition, microcracks were seen inside the darker C-S-H gel. The conclusion is that anhydrite forming inclusions in belite gives an expanding mortar after heat treatment at 90 °C independently of the tricalcium aluminate content. Such clinkers are not typical of industrial conditions. The expansion is caused by the bands of massive ettringite as well as its agglomerates present in the cement gel and nanometric ettringite in the C-S-H phase.     

Corrosion of nickel in sodium sulphate-sodium chloride melts. Part I

The corrosion behaviour of Ni in molten Na₂SO₄, NaCl, and in mixtures of these two salts, at 900° C, in laboratory air and under O₂+SO₂/SO₃ atmospheres has been examined by electrochemical curves and topochemical analysis of corrosion products.Ni passivity in pure Na₂SO₄ was observed under potentiodynamic and potentiometric conditions, the passive film corresponding to NiO. Passivity was not so easy to achieve in chloride melts as in sulphate alone, but once a thick oxide film forms on the specimen, the Cl^– addition is accompanied by an increase in the film stability. The inhibiting role of NaCl on Ni in the passive-transpassive area was also evidenced. In opposition, halide additions (especially those up to 25%) increased the dissolution current densities of Ni in the active region. These higher dissolution rates are represented by the equation Ni₃S₂+4NaCl+1/2 O₂ = 2NiCl₂+2Na₂S + NiO which is also suggested as a critical factor in the Ni passivation.The passive capability found for Ni in Na₂SO₄/NaCl melts, in air, is destroyed by SO₃ atmospheres. This corrosion-stimulation is due to the SO₃ role in promoting reactions such as NiS + 3O^2– = Ni²⁺+SO₃+8e which would be potential-determining at the Ni surface until Ni²⁺ precipitates or the conjugate oxygen cathodic reduction process takes place. Microprobe analysis also evidenced S penetration which might be the reason for the Ni embrittlement.The polarization curves for Ni in pure NaCl showed the lack of a passive region; occurrence of extensive intergranular attack was also indicated by metallographic observation. The observed dissolution must occur at the expense of the Ni interactions with the species which intervene in the reaction equilibrium between O₂ and molten NaCl (O₂, Cl^–, Cl₂ and O^2–) as well as with the Na⁺ cations, as has been discussed elsewhere. Its self-sustaining nature is enhanced by the continuous reduction of the nickel ion content of the melt by NiCl₂ evaporation.     

Reactions between sodium and silica during gasification of a low-rank coal

Laboratory experiments were conducted on samples of a prepared low-rank South Australian Lochiel coal, viz. Na⁺ ion-exchanged acid-washed and physical impregnation of NaCl samples, to study the influence of gas atmosphere on the reactions between sodium with silica during pyrolysis in nitrogen and gasification with steam or carbon dioxide. Additionally, samples of the reaction mixtures of sodium salts (sodium acetate and NaCl) and silica were made and exposed to the same reaction conditions. The characterisation of products has been quantified in terms of their water solubility in combination with mineralogical analysis (SEM, XRD). Sodium disilicate, Na₂Si₂O₅ was found to be the major reaction product formed under all three atmospheres and this is in agreement with thermodynamic equilibrium predictions. Na₂Si₂O₅ forms in a direct reaction between sodium carbonate (intermediate form of Na present in the coal) and solid silica. Steam is found to be the most important variable as it lowers the melting temperature of sodium carbonate and consequently, the temperature of formation of liquid sodium disilicate. Further silica can dissolve in the formed liquid silicates and increase the total mass of fused silicate glass. The liquid sodium silicates formed at 750 °C in steam, or at 850 °C in carbon dioxide or nitrogen, should be considered as a potential source for bed agglomeration and defluidisation during fluidised bed gasification of coal.     

Ash partitioning during the oxy-fuel combustion of lignite and its dependence on the recirculation of flue gas impurities (H2O, HCl and SO2)

Oxy-fuel combustion of a brown coal (i.e. lignite) has been carried out at 1000 °C to experimentally examine the vaporisation of organically bound metals and the agglomeration of ash particles as a function of the concentration of gaseous impurities including H₂O, HCl and SO₂ in ∼27% O₂ balanced with CO₂. The properties of bulk ash and individual metals were investigated intensively. Particularly, attention was paid to Na which is notorious for fouling and to organically bound Al which has been less studied. The results indicate that, the organically bound metals, although possessing a very low content in the raw coal, are vital for the agglomeration of ash particles, which are also highly sensitive to the loading of gas impurities in flue gas. HCl recirculation is the most crucial factor promoting the vaporisation of metals via chlorination. Apart from alkali metals, the organically bound Al and Ti were also vaporised noticeably. Recirculation of SO₂ promoted the sulfation of Na to condense into liquid droplet which increased fine ash yield. Co-existence of bulk HCl and SO₂ played a synergetic role in the sufation of Na via an initial chlorination of the char-bound Na. In contrast, co-existence of steam with HCl and SO₂ favored the formation of Na alumino-silicates, which are favorable for ash agglomeration.     

Experimental investigation of fluidised bed co-combustion of meat and bone meal with coals and olive bagasse

Meat and bone meal (MBM) was co-fired in a laboratory scale fluidised bed combustion (FBC) apparatus together with three different primary fuels: two coal types and olive bagasse residues. Several two component fuel blends were tested under different combustion conditions to study how primary fuel substitution by MBM affects flue gas emissions as well as fluidised bed (FB) agglomeration tendency. MBM, being a highly volatile fuel, caused significant increase of CO emissions and secondary air should be used in industrial scale applications to conform to regulations. The high N-content of MBM is moderately reflected on the increase of nitrogen oxides emissions, which are reduced by MBM derived volatiles. The MBM ash, although containing bone material rich in Ca, did not create any noteworthy desulphurisation effect. The observed slight decrease in SO₂ emissions is predominantly attributed to the lower sulphur content in the coal/MBM fuel mixtures. The experimental work is evaluated with bed agglomeration indices from literature. The SEM/EDS analysis of bed material samples from the coal/MBM tests revealed the formation of conglomerates of bed material debris and ash with sizes that do not greatly exceed the original bed inventory and thus are not problematic. On the contrary, the co-combustion tests of olive bagasse residues with MBM led to a prompt loss of fluidisation, as a consequence of the high potassium and silicon content of the olive bagasse, the chlorine contents in both MBM and olive bagasse, and the high phosphorus content in the MBM also forming eutectics with potassium.     

Sulfur dioxide release in fluidized bed combustion of Jorban oil shale

Due to high concentrations of sulfur and carbonates in Jordan oil shale, it was anticipated that the deposits would be a suitable burning fuel in an atmospheric fluidized bed system. The SO₂, capture by calcium oxide and calcined dolomite in spent shale prompted this experimental program to verify spent shale reactivity and SO₂ retention. Concentrations of SO₂, in effluents were analyzed vs. time in a fluidized bed material of silica sand, pure limestone rock (99.6% carbonates) and spent shale. The SO₂, release was studied in batch tests for each bed material. The effect of particle size in spent shale FBC was tested.Some model sulfur containing compounds were impregnated on limestone carrier solids and combusted to give time-release data. A sample of pyrite was charged to the bed of limestone sand in order to study its sulfur release and compare the data. A component balance was attempted to trace sulfur in the various bed materials.     

Reductive roasting of nickel laterite ore with sodium sulphate for Fe-Ni production. Part II: Phase transformation and grain growth

In Part II, the correlation between Fe–Ni grain growth and characteristic fusion temperatures of the Na₂SO₄–laterite mixtures, and phase transformations of the reduced pellets were investigated. For the mechanism of sodium sulphate, Na⁺ is able to liberate the hosted nickel and iron within lizardite, while SO₄^2– is the sulphur source for the formation of Fe–FeS eutectic compound which can decrease the characteristic fusion temperatures to promote the growth of ferronickel grains. The mean particle size of ferronickel increased from 7.4 μm to 48.6 μm with the addition of 20 wt% Na₂SO₄.     

Diesel emissions from biofuels derived from Spanish potential vegetable oils

Methyl esters obtained from the most interesting Spanish oleaginous crops for energy use—sunflower and Cynara cardunculus—were both used as diesel fuels, pure and in 25% blends with a commercial fuel which was also used pure. A stationary engine test bed, together with the instrumentation for chemical and morphological analysis, allowed to study the effect of these fuels on the engine emissions, soluble organic fraction of the particulate matter, origin of adsorbed hydrocarbons, sulphate content, particle number per unit filter surface, and mean particle diameter. Both the consideration of the thermochemical properties of the tested fuels and the computations of a chemical equilibrium model were helpful for the results analysis. These results proved that the use of these vegetable esters provides a significant reduction on particulate emissions, mainly due to reduced soot and sulphate formation. On the contrary, no increases in NO_x emissions nor reductions on mean particle size were found.     

Research on the mechanism of bed agglomeration and superheater fouling in CFB boiler fired pure petroleum coke

Circulating fluidized bed combustion is an effective method for the clean and efficient utilization of high-sulphur petroleum coke. In the actual production and operation process, there are serious problems of bed agglomeration and superheater fouling. The chemical and mineral compositions of the deposition were analyzed by X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF), and the effects of CaO sulphation and V₂O₅ on bed agglomeration and superheater deposits were studied through targeted experiments. The research results show that the sulphation process of CaO is the cause of bed agglomeration, and the superheater fouling is the result of the combined action of K₂SO₄ condensation and CaO sulphation; V₂O₅ in petroleum coke ash catalyzes the oxidation reaction of SO₂ to accelerate the sulphation of CaO, thereby accelerating the development of bed agglomeration and superheater fouling.     

Agglomeration and strength development of deposits in CFBC boilers firing high-sulfur fuels

Fluidized bed combustor (FBC) ashes from high-sulfur, low-ash fuels, can agglomerate if subjected to sulfating conditions for long enough (days to weeks). The degree of sulphation increases with both temperature and time under these conditions, and at a conversion equivalent to the production of 50–60% or more of CaSO₄ in the deposit the ashes agglomerate. Fly ash agglomerates less readily than does bed and loop seal ash and produces weaker deposits, although all of these materials will agglomerate if sufficient time is allowed. The potential for agglomeration increases if the temperature is increased from 850 to 950°C. Agglomeration also occurs at lower temperatures (down to at least 750°C), but the mechanism may be via carbonation and then sulphation of the ash. Although experiments reported here suggest that if pure CaSO₄ is compressed to the 140 kPa range it does show some tendency to agglomerate, the agglomeration of FBC ash is not produced simply by the formation of CaSO₄. Finally, the agglomeration process is only weakly influenced by the partial pressure of SO₂ in the flue gas. Attempts to identify physical parameters to differentiate the tendency of various bed materials to agglomerate have been only partially successful. Two bed materials with strong and weak agglomerating tendencies were studied. These were shown to have very similar particle shapes and only slightly different angles of repose, but quite different bulk densities. Residues with a greater bulk density appear to have a stronger tendency to agglomerate, and this may provide a method of ranking the agglomeration potential of different bed materials.     

Studies on high-performance blended/multiblended cements and their durability characteristics

Number of blends were prepared by intergrinding clinker, gypsum, fly ash, calcined clay, microsilica and limestone in laboratory ball mill in varying percentages, and their physical properties such as fineness, consistency, setting time and compressive strength have been determined. The durability tests on selected compositions were also conducted by exposing the mortar cubes separately in 5% Na₂SO₄ and 5% NaCl solutions till the age of 90 and 180 days. The performance was observed by compressive strength development criteria after various length of exposure. Results have been discussed and found that the durability of blended cement is higher than the ordinary Portland cement.     

Combustion characteristics of waste-oil produced biodiesel/diesel fuel blends

In this study, wasted cooking oil from restaurants was used to produce neat (pure) biodiesel through transesterification, and this converted biodiesel was then used to prepare biodiesel/diesel blends. The goal of this study was to compare the trace formation from the exhaust tail gas of a diesel engine when operated using the different fuel type: neat biodiesel, biodiesel/diesel blends, and normal diesel fuels. B20 produced the lowest CO concentration for all engine speeds. B50 produced higher CO₂ than other fuels for all engine speeds, except at 2000 rpm where B20 gave the highest. The biodiesel and biodiesel/diesel blend fuels produced higher NO_x for various engine speeds as expected. SO₂ formation not only showed an increasing trend with increased engine speed but also showed an increasing trend as the percentage of diesel increased in the fuels. Among the collected data, the PM concentrations from B100 engines were higher than from other fuelled engines for the tested engine speed and most biodiesel-contained fuels produced higher PM than the pure diesel fuel did. Overall, we may conclude that B20 and B50 are the optimum fuel blends. The species of trace formation in the biodiesel-contained fuelled engine exhaust were mainly C_nH_2n+2, DEP, and DPS. For the B100, B80, B50, and D fuelled engines, C₁₅H₃₂ was the dominant species for all engine speeds, while squalene (C₃₀H₅₀) was the dominant for B20. DEP was only observed in the B100, B80, and B50 fuelled engines in this study. The D fuelled engine showed a higher DPS production for engine speeds higher than 1200 rpm.     

Oxidative Coupling of Methane Over Na–W–Mn–Zr–S–P/SiO2 Catalyst: Effect of S, P Addition on the Catalytic Performance

The multi-component catalysts we prepared exhibited high performance for the oxidative coupling of methane. The highest activity of catalysts was obtained over the Na–W–Mn–Zr–S–P/SiO₂ at the temperature of 1,023 K, on which the C₂ yield was 23.5% at the methane conversion of 43.8%. XRD and XPS results showed the S, P addition could lead to the increase of lattice oxygen concentration and the formation of phase such as Na₂SO₄, Na₂Zr(PO₄)₂ on the catalysts. These phases play great roles in activity of the catalysts system.     

Influence of alkalies on the composition of belite-rich cement clinkers and the technological properties of the resulting cements

Contents of alkalies in raw meals of low lime saturation are almost completely bonded in belite-rich clinker. The volatilization rate of alkalies during clinker burning is low. In absence of SO₃, the major portion of alkalies is incorporated in the belite as main clinker phase. The latter absorbing higher concentrations of K₂O than of Na₂O. In the matrix of belite-rich clinkers alkalies are enriched with preferably orthorhombic alkali aluminate being stabilized. Increasing amounts of alkalies incorporated in the belite lattice result in a correspondingly more extensive stabilization of the hydraulically more active modifications α′- and α-belite. Rapid clinker cooling (about 3000 K/min) assists the stabilizetion of high-temperature forms of belite, the hydraulic activity of the stabilized phases is enhanced. The compressive strength of the resulting belite-rich cements after 28 days can be raised by 60 to 100% compared with alkali-free belite-rich cements.