Comparative study of nitrification performances of immobilized cell fluidized bed reactor and contact oxidation biofilm reactor in treating high strength ammonia wastewater

BACKGROUND: The immobilized cell fluidized bed reactor and contact oxidation biofilm reactor are two common choices for high strength ammonia wastewater treatment, however, comparative study of the nitrification performance of the two reactors has not been thoroughly studied. The nitrification performance of the two bioreactors when treating strong synthetic ammonia wastewater was investigated and compared. RESULTS: Results demonstrated that the immobilized cell fluidized bed reactor had a shorter acclimation period, and possessed several advantages over the contact oxidation biofilm reactor, in the form of complete oxidation of 150–360 mg L^?1 ammonia wastewater in a shorter time, higher ammonia removal rates (from 9.6 to 4.32 × 10² mgN L^?1 d^?1) over the temperature range 8 to 32 °C, irrespective of organic load. In contrast, a large reduction in ammonia removal was found in the contact oxidation biofilm reactor with chemical oxygen demand (COD) load. The immobilized cell fluidized bed reactor exhibited stable and high rates of nitrification in the long term. CONCLUSION: These facts demonstrated that the immobilized cell fluidized bed reactor is a suitable selection for high strength ammonia wastewater treatment. Copyright © 2007 Society of Chemical Industry     

Optimization fluidization characteristics conditions of nickel oxide for hydrogen reduction by fluidized bed reactor

We evaluated the optimal conditions for fluidization of nickel oxide (NiO) and its reduction into high-purity Ni during hydrogen reduction in a laboratory-scale fluidized bed reactor. A comparative study was performed through structural shape analysis using scanning electron microscopy (SEM); variance in pressure drop, minimum fluidization velocity, terminal velocity, reduction rate, and mass loss were assessed at temperatures ranging from 400 to 600 °C and at 20, 40, and 60 min in reaction time. We estimated the sample weight with most active fluidization to be 200 g based on the bed diameter of the fluidized bed reactor and height of the stocked material. The optimal conditions for NiO hydrogen reduction were found to be height of sample H to the internal fluidized bed reactor diameter D was H/D=1, reaction temperature of 550 °C, reaction time of 60 min, superficial gas velocity of 0.011 m/s, and pressure drop of 77 Pa during fluidization. We determined the best operating conditions for the NiO hydrogen reduction process based on these findings.     

Influence of Temperature on SO2 Removal Enhanced by Water Vapor Using a Corona‐Discharge Reactor

A reactor using d.c. corona discharge of negative polarity was applied to remove sulfur dioxide from an oxygen‐nitrogen mixture in the presence or absence of water vapor for temperatures ranging from room temperature to 350 °C. It was observed that increasing the reactor temperature caused a decrease in the removal efficiency. Mixing water vapor with the process gas resulted in an increase of the removal efficiency. The effect of the presence of water vapor on improving the removal efficiency was significant under low temperature conditions, while it was relatively moderate under high temperature conditions. In addition, the solid deposit formed inside the reactor at two temperatures, room temperature and 200 °C, was analyzed with both a differential scattering calorimeter and an X ray diffractometer. The analysis indicated that SO₂ was ultimately converted to solid sulfur in both the presence and absence of water vapor in the gas flow.     

Breakthrough and Sulfate Conversion Analysis during Removal of Sulfur Dioxide by Calcium Oxide Sorbents

Sorption of sulfur dioxide (SO₂) was carried out on calcium‐based sorbents under dynamic conditions in a fixed bed. The experimental conditions were reaction temperature (700 to 1000°C), SO₂ concentration (1000‐10 000 ppm), sorbent particles size (1 to 2 mm) and the types of sorbents (hydroxide or carbonate). The sorption process was found to be effective at low concentration levels (less than 10 000 ppm) as the breakthrough time significantly decreased with increase in concentration. The maximum removal of SO₂ was observed at a reaction temperature of 950°C. The hydroxide‐based sorbents of relatively smaller particle size were found to exhibit superior sorption performance in terms of longer breakthrough time and higher sulfate conversion. A mathematical model developed, assuming a porous structure of the sorbent materials, attributed the low sulfation conversion during SO₂ sorption due to a pore diffusion mechanism.     

On the high‐gasification rate of Brazilian manganese ore in chemical‐looping combustion (CLC) for solid fuels

The high rate of char gasification observed when using a Brazilian manganese ore as compared to ilmenite is investigated in a batch fluidized‐bed reactor. Experiments were carried out at 970°C using petroleum coke, coal and wood char as fuel with a 50% H₂O in N₂ as fluidizing gas. A manufactured manganese oxygen carrier was also used, however, which presented a slower char conversion rate than the manganese ore. It is concluded that decrease in H₂ inhibition and oxygen release are unlikely to be the main responsible mechanisms for the ore's unexpected gasification rate. The ore was also mixed in different ratios with ilmenite and it was observed that the presence of even small amounts of ore in the bed resulted in increased gasification rate. Thus, the high‐gasification rate for the manganese ore could be due to a contribution from the impurities in the ore by catalyzing the gasification reaction. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4346–4354, 2013     

Manganese based materials for diesel exhaust SO2 traps

The storage of SO₂ in manganese based materials was investigated in flow reactor experiments. Manganese oxide precipitated with ammonia and hydrogen peroxide stored about 76 wt.% of SO₂ at a high diffusion rate into the bulk. Doping with potassium increases the SO₂ storage rate substantially at 200 °C, but has an only minor effect at 400 °C. Kinetic studies showed that the storage of SO₂ in pure and potassium doped manganese oxide is controlled by the kinetics of the sulfate formation reaction on the catalyst surface up to complete sulfation, whereas the storage on manganese cerium mixed oxide is limited by internal diffusion of the formed sulfate. The sulfate formation reaction was found to be first order with respect to both SO₂ and manganese oxide. For the potassium doped catalyst sulfur was found to be bound on manganese sites being transferred to potassium afterwards.     

Investigations of the reduction of NO to N2 by reaction with Fe

The paper presents the results of the investigation of nitric oxide reduction by its reaction with metallic iron, within the temperature range of 750-1200 °C. Experiments were carried out in a one-dimensional tubular flow reactor externally heated in an electrical furnace. The spherical and cylindrical iron samples of well-defined and fixed surface area were placed in the center of the reactor. Mixtures NO/N₂, NO/O₂/N₂, NO/CO₂/N₂ of different molar compounds fractions were continuously fed into the reactor. The surfaces and cross-sections of partly oxidized iron samples were observed using a scanning microscope. The rate of nitric oxide reduction in the first stage of iron oxidization was measured. The obtained values lie between those presented in the literature and measured in the fluidized bed reactor and thermogravimetrically. A very strong influence of oxygen but a very weak one of carbon dioxide on the efficiency of NO reduction was observed within the investigated range of temperature.     

铁强化电解锰阳极液体系中氧化锰矿烟气脱硫和锰浸出工艺

结合电解锰生产工艺,以氧化锰矿为原料,以电解锰生产过程产生的电解阳极液废水配置烟气脱硫浆液,在其中添加FeSO₄强化电解锰阳极液体系下氧化锰矿烟气脱硫及浸锰能力,探讨铁强化氧化锰矿烟气脱硫和浸锰的工艺条件对烟气SO₂脱除和锰浸出的影响机制。研究发现FeSO₄的加入,通过FeSO₄与MnO₂之间的氧化还原反应以及产物三价铁离子和二价锰离子的协同催化作用,可同时提高锰矿烟气脱硫效率和锰的浸出率。锰矿粒径越小,脱硫及浸锰效率越高。温度升高,氧化锰矿浆液烟气脱硫率逐渐下降,浸锰率则先升高后下降,并在60℃时达到最大。浆液液固比和烟气流量的增大均会导致烟气脱硫率的下降,但会提高氧化锰矿浸锰率。进口SO₂浓度过高会导致脱硫率下降,但更有利于浸锰。采用5级逆流吸收对7%的烟气进行铁离子强化氧化锰浆脱硫,得到最终SO₂出口浓度293μL/L,溶液Mn²⁺浓度为44.72g/L,满足电解要求。铁强化电解锰阳极液体系有效回收利用了电解锰生产废水,不仅集脱硫浸锰工艺为一体,且可实现脱硫和浸锰效率的同时提升,为电解锰行业的清洁生产和资源综合利用提供理论依据和技术参考。     

Thermal decomposition of pyrite in a fluidized bed

The thermal decomposition of pyrite was investigated in a silica batch fluidized bed reactor, in the temperature range 594 to 625°C. Particles were sampled during each run and those partially reacted showed a sharp reaction front. An equilibrium between pyrite and the resulting pyrrhotite is maintained until the central core of pyrite has disappeared, after which the reaction proceeds uniformly throughout the particle forming pyrrhotites with successsively lower sulfur contents. The reaction rate was sensitive to temperature, particle size and gas velocity. Application of the shrinking core model is consistent with heat transfer as the controlling step.     

Application of the reaction kinetics and dispersion model to gas-solid reactors for removal of sulfur dioxide from flue gas

The conversions of a reactive, micro-grained limestone were studied in terms of exposure time and concentration of sulfur dioxide in the flue gas. The rates of the sulfation reaction were correlated as a function of the conversion of calcium oxide to sulfate and concentration of sulfur dioxide in the gas phase. In comparison with active sodium carbonate the sulfation of limestone particles proceeds at the rate which is substantially lower than the sulfation rate of soda particles.The empirical kinetic equation developed in this study is further applied in a two-phase dispersion model of simplified non-ideal flow behavior of the gas and solid in the reactor. The model can serve a rational basis for the conceptual design of a suitable contacting apparatus. Numerical solutions of the model equations outline possibilities and limitations of the dry lime process for the removal of sulfur dioxide from hot flue gas.     

The reaction of NiO/NiAl2O4 particles with alternating methane and oxygen

The reduction and oxidation behaviour of oxygen carrier particles of NiO and NiAl₂O₄ has been investigated in a fluidized bed reactor as well as a thermogravimetric analyzer (TGA). The particles showed high reactivity and gas yield to CO₂ with methane in the temperature interval 750–950°C. In the fluidized bed the yield to CO₂ was between 90 and 99% using bed masses corresponding to 16–57 kg/MW_fuel. Complementary experiments in a TGA at 750 and 950°C showed a clear reaction of the NiAl₂O₄ with CH₄ at the higher temperature. There was methane released from the reactor at high degrees of solid oxidation, which is likely associated with the lack of Ni‐sites on the particles which can reform the methane. There was some carbon formation during the reduction, although the amount was minor when the gas yield to carbon dioxide and degree of oxidation of the solid was high. A simple reactor model using kinetic data from a previous study predicted the gas yield during the reduction in the fluidized bed experiments with reasonable accuracy. The oxygen carrier system investigated in this work shows high promise for use in a real CLC system, provided that the particle manufacturing process can be scaled up with reasonable cost.     

Model study of the direct causticization reaction between sodium trititanate and sodium carbonate

The solid state reaction between sodium tri‐titanate and sodium carbonate, forming mainly sodium pentatitanate, was investigated. Experiments were carried out in a micro‐differential reactor made of quartz glass at various temperatures between 800°C and 880°C and in a pilot fluidized bed reactor operated in a semi‐batch mode. In the former reactor, basic kinetic data was obtained by measuring the release of carbon dioxide. Different kinetic models were considered to describe the conversion, such as the Valensi‐Carter model for diffusion controlled reaction rates and the phase‐boundary model for first‐order reaction kinetics. Furthermore, a model that included both diffusion in the solid material and the chemical kinetics was derived. This model described the experimental data obtained in the micro‐differential reactor very well. However, for the fluidized bed experiments, these different kinetic models did not accurately describe the experimental data. Therefore, an improved model was developed, which also took into account the time taken for the reactants to achieve physical contact. This model gave good agreement with the experimental data.     

A novel induction heating fluidized bed reactor: Its design and applications in high temperature screening tests with solid feedstocks and prediction of defluidization state

A novel mini induction heating fluidized bed reactor (IHFBR) is introduced which was developed to carry out screening tests of high temperature reactions up to 1500°C particularly for solid feedstocks. Despite conventional mini reactors, this reactor mimics real scenario of solid feeding in industrial reactors: cold feedstock is injected within 1 s from a lift tube, then particles reach reaction temperature in less than 5 s in a reaction zone. The lift tube (9.5 cm diameter) is also the gas distributor of the fluidized bed (2.5 cm diameter) so that the bed is completely fluidized with uniform gas distribution. Beside facilities to perform tests in a fluidized bed, another important feature of this reactor is prediction of the defluidization state in the bed. Not only reproducible data are generated, but also many tests can be conveniently carried out, that is, one test per hour. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1507–1523, 2015     

Hydrodesulfurization of diesel in a slurry reactor

The need for more complete removal of sulfur from fuels is due to the lower allowable sulfur content in gasoline and diesel, which is made difficult by the increased sulfur contents of crude oils. This work reports an experimental study on the hydrodesulfurization (HDS) of diesel in a slurry reactor. HDS of straight-run diesel using a NiMoS/Al₂O₃ catalyst was studied in a high-pressure autoclave for the following operating conditions: 4.8–23.1 wt% catalyst in the reactor, 320–360 °C, 3–5 MPa pressure, and 0.56–2.77 L/min hydrogen flow rate. It was found that the reaction rate was proportional to the catalyst amount and increased with temperature, pressure and hydrogen flow rate. The reaction kinetics for the HDS reaction in the slurry reactor was obtained. As compared with HDS in a fixed bed reactor, HDS in a slurry reactor is promising because of the uniform temperature profile, high catalyst efficiency, and online removal and addition of catalyst.     

A simplified mathematical modeling for thermo-catalytic decomposition of methane over carbon black catalyst in a fluidized bed reactor

A mathematical model for thermo-catalytic decomposition of methane over carbon black catalysts in a fluidized bed was proposed. The simplified isothermal, uniform flow model was considered and implemented into a computer code to predict the reactor performance. The experiment of methane decomposition into hydrogen and carbon was carried out in a fluidized bed of I.D of 0.055 m and height of 1.0 m. The range of reaction temperature was 850–900 °C, gas velocity was 1.0–3.0 U _mf , and catalyst loading was 50–200 g. The reaction parameters for model equation were determined from the curve fittings and the comparison of experimental data with simulation results showed good agreement for fluidized bed reactor system. From the simulation results, the fluidized bed performance with different operating conditions were obtained, and this simple model can be used to predict the performance of a larger scale fluidized bed reactor and also in determining the optimum operating conditions.     

Oxi-ammoniation of pine-bark particles

Pine-bark sawdust was oxidized with nitric acid (5-20% by weight) and further ammoniated with NH₃ or NH₄OH. Ammoniation with NH₃ was carried out in a fluidized bed reactor at 100 and 250°C and a NH, flow of 126 L/h (0°C; 101.3 kPa). Ammoniation with NH₄OH was carried out in a batch reactor by reacting the oxidized sample with NH₄OH (2 kmol/m³) at total reflux. Data on total nitrogen, ammonia nitrogen and KMnO₄ soluble nitrogen content are reported for the resulting product.     

Oxidative conversion of ethane over VMoTeNb oxide catalyst

The oxidative conversion of ethane over a multicomponent oxide catalyst with the composition V_0.3Mo₁Te_0.23Nb_0.12 was studied in the temperature range of 360–450°C. It was found that temperature did not affect the contribution from the parallel and consecutive paths of reaction product formation. The obtained data could be useful in developing applications for the process, particularly in choosing the type and design of a reactor (tubular fixed bed, fluidized bed, and so on).     

Catalytic activity of coal ash on steam methane reforming and water-gas shift reactions

The catalytic activity of Clarion 4A coal ash on water-gas shift, steam methane reforming and carbon dioxide methane reforming reactions was studied in an atmospheric fluidized bed over temperatures ranging from 370°C to 900°C. The rates of steam methane reforming and water-gas shift reactions over ash were found to be several times the corresponding non-catalytic reactions but were one order of magnitude lower than the reactions over commercial catalysts. Also, it was found that the ash affected the water-gas shift reaction more significantly than the steam methane reforming reaction probably because of the larger amount of iron oxide in the coal ash. However, there was no appreciable reaction for carbon dioxide reforming up to 900°C.     

Reactivity of calcined limestone and dolomite with sulfur dioxide

Under the conditions prevailing in in-situ desulfurization of fluidized bed combustion two types of limestone and two types of dolomite were tested for their reactivity with sulfur dioxide. Experimental variables were sorbent size, sulfur dioxide concentration and reaction temperature. In general reactivity increased with temperature with activation energy ranging 15.9 to 19.5 kcal/mol for initial reaction rate. Reaction order with respect to sulfur dioxide was close to one and reactivity decreased with increase of sorbent size. With continuous feeding of coal and sorbent sulfur dioxide concentration in the effluent gas decreased with increase of Ca/S ratio.     

Nitric oxide reduction by char and carbon monoxide: Fundamental kinetics of nitric oxide reduction in fluidizedbed combustion of coal

The reduction of nitric oxide during combustion of coal char in a fluidized-bed combustor was examined with respect to two reactions : a char-catalysed reaction; and a char-consuming reaction, which control nitric oxide emissions. The relative importance of the two reactions was investigated by measuring detailed material balances for the reactions. The product distribution was explained in terms of three fundamental parallel reaction paths. Reaction rates were investigated with a fixed-bed flow reactor over the temperature range 883–1194 K, the same as the fluidized bed combustor.