Zhong Yang Luo

High-temperature sulphur removal under fluidized bed combustion conditions — A chemical interpretation

Abstract Theoretical and experimental studies were conducted on coal sulphur removal under chaotically changing oxidizing and reducing conditions, which occur in the dense zone of bubbling fluidized beds. Experimental desulphurization trends were analyzed by comparison with multi-species (50 gas-phase, 7 solid-phase species) equilibrium calculations for coal/steam/sorbent/air system. It was shown, that under fluctuating reducing/oxidizing conditions, sulphur capture as CaS in locally reducing zones increased the sulphur retention level of the sorbent. In experiments, performed in a 8 cm i.d. bench-scale FBC boiler, effective sulphur retentions were obtained in the 800–1000 °C temperature range. As a chemical interpretation, a time history of sorbent particle calcination-sulphation is proposed, which leads to the formation of a particle structure with a sulphided (CaS) core and a sulphated (CaSO4) shell. Full-scale applications are discussed and measures for improving limestone utilization and high-temperature sulphur removal in fluidized beds are recommended.

Thermodynamic Analysis of Indirect Ethanol Synthesis from Syngas

The dependence of chemical equilibrium constant on the reaction temperature and pressure and the feed molar ratio were theoretically calculated for indirect ethanol synthesis from syngas through the coupling of CO with methyl nitrite (MN) to dimethyl oxalate (DMO) and the hydrogenation of DMO to ethanol. It shows that the coupling process and the hydrogenation of DMO to ethanol are highly favorable at all temperatures and pressures, especially at low temperature. The hydrogenation of DMO to ethylene glycol (EG) and the further reaction of ethanol with H2 to high alcohol are thermodynamically favorable at low temperatures, below 630 and 450 K, respectively. Additionally, high reaction pressure is facilitated to EG and high alcohol formation. Accordingly, moderate reaction temperature (up 538 K) and low reaction pressure (below 1 MPa) are beneficial to ethanol production.

Experimental Study on the Physico-Chemical Properties of Bio-Oil and Diesel Emulsification

Experimental study on the physico-chemical properties of bio-oil and diesel emulsification has been carried out in this paper, which was based on the preliminary experiment. The effect of surface tension and viscosity on the stability of emulsions were particular concerned. It was found that the longest stable time, the lowest viscosity and lowest surface tension can be obtained simultaneously when the hydrophile and lipophile balance (HLB) value was of the optimal value, i.e. 6.5. Experimental results indicated that the stable time of emulsion decreased rapidly with the increase of bio-oil content, while the value of surface tension and viscosity increased. Meantime, it was shown that the most stable emulsions had the lowest value of viscosity and surface tension.

Studies on the Extraction of Phenols from Coal Tar Produced in Multi-Generation System

Isolation of phenols from the middle oil fraction(170-230°C) of tar produced in the multi-cogeneration system has been investigated for the purpose of recovering valuable pure phenols, such as phenol, cresols, xylenol and ethyl-phenol. Phenolic compounds were separated from the middle oil by liquid-liquid extraction using alkali and sulfuric acid. The yield of phenolic fraction from the middle oil (170-230°C) is up to 37%, which is much higher compared with those of metallurgical coke plants. Chromatography-mass spectrometry was used to analyse phenolic compounds. The result shows that the phenol content is less than 2%, and main compounds are cresol(14%), xylenol(20%) . Phenols of the middle oil fraction(230-280°C) was also analysed, which main contain methyl naphthol(20%).

Study of Air Jet Penetration in a Fluidized Bed

This work presents experimental and numerical simulation results on secondary air jet penetration into a dense phase of a 2-D fluidized bed. Velocity measuring method and non-intrusive methods based on images were used in the experiments. Effects of secondary air nozzle size and angles, secondary air jet flow velocity and suspension density of the fluidized bed material on the air jet penetration were tested. The results show that with increasing of secondary air jet velocity, the jet range increases exponentially. Secondary air jet range decreases exponentially with increasing of average bed suspension density. The size of secondary air nozzle does not have significant impact on jet range. However, larger nozzle size may result in a lower velocity decay coefficient. It was also found the secondary air nozzle angle is not an independent parameter affecting jet range. The jet range may penetrate the most depth point into the fluidized bed with the angle of −30°. As a comparison, the numerical simulation was done with same parameters in the experiments. Comparison of experimental and numerical results shows good agreements.

Desulfurization Characteristics of Fly Ash Recirculation and Combustion in the Circulating Fluidized Bed Boiler

The experiments of the fly ash recycle combustion using Guizhou anthracite were carried out in a bench scale circulating fluidized bed (CFB) combustor. Effects of some key operating parameters such as recycle ash to coal mass ratio (Ca to S molar ratio), temperature, reactivation modeof fly ash, circulation rateand fluidization velocity on the desulfurization efficiency were intensively investigated. It is shown that thelimestone utilization efficiency could be improved about 30% with the following operating conditions: the mass ratio of fly ash (reactivated by water and dried at 90°C) to coal was 0.45, the furnace temperature was 880°C, the water to ash mass ratio was 4.5% (the water-to-calcium molar ratio was 0.55) and circulation rate was 18.

Thermochemical analysis of ACFB-based gas and power cogeneration

A first- and second-law analysis is presented for a process developed for simultaneous generation of a fuel gas and electric power (gas and power cogeneration) based on atmospheric circulating-fluidized-bed (ACFB) combustion of coal. The mathematical model has a zone structure, multi-species equilibrium calculations for applicable zone conditions at high temperatures (50 gas-phase and seven solid-phase chemical species) and the concept of freezing of the gas composition at low temperatures. Our analysis shows that the process utilizes coal in a simple, effective and environmentally clean manner. The first- and second-law efficiencies of the process are, respectively, 35.0 and 27.6% for gas generation, 15.4 and 14.6% for power generation, 50.4 and 42.2% overall. The heating value of the gas is 11 MJ/Nm3 (medium). Desulphurization is achieved by using CaS-based sulphur capture during limestone addition to the gasifier bed. Results are compared with data from a 150 kg of coal/h experimental plant.

Simulation on Coal Devolatilization Combined a Multi-Step Kinetic Model with Chemkin Software

As the first step in coal combustion and gasification, coal devolatilization has significant effect on reaction process. Previous coal devolatilization models have some disadvantages, such as poor flexibility, model complexity, and requirement of characterization parameters. Recently, Sommariva et al. have proposed a multi-step kinetic model of coal devolatilization. This model avoids the disadvantages mentioned above and can predict elemental composition of tar and char. In this paper, the mechanism of this model has been revised for simple application to Chemkin. Revision method is that some reactions are split into more reactions by using one pseudo-intermediate-product to replace several final products. Simulation results show that calculation results from revised mechanism compare quite well with that from original mechanism and have good agreement with experimental data. The revised mechanism is accurate and can be applied to Chemkin very easily, which gives it wide application to simulation of coal pyrolysis, gasification and combustion.

Experimental Study of Breakthrough Adsorption on Activated Carbon for CO2 Capture

In this study, a commercial activated carbon was assessed as adsorbent for post-combustion CO2 capture. The breakthrough adsorption experiments were conducted in a fixed-bed column with simulated flue gas of 12% CO2. The effects of feed flow rate and adsorption pressure on breakthrough time and CO2 adsorption capacity were evaluated. The column efficiency was introduced to estimate the percentage of the utilization of the bed adsorbent capacity. At a higher flow rate, the breakthrough time, breakthrough capacity and column efficiency decreased. Conversely, increasing adsorption pressure was favorable to CO2 adsorption by the increase in breakthrough time, CO2 adsorption capacity and the column efficiency. During the experiments, temperature changes were detected at three positions inside the column to track the movement of breakthrough front.

The Structure, Morphology and Catalytic Performance of a Silica Supported Cu Catalyst for Ethylene Glycol Synthesis

A silica supported Cu catalyst with good performance for ethylene glycol (EG) production was prepared by the hydrolysis of tetramethoxysilane (TMOS) in one phase solution using methanol as co-solvent, followed by the precipitation of copper on SiO2 by ammonia evaporation. XRD, SEM and TEM were carried out to characterize the structural and morphology properties of the catalyst. The results showed that Cu particles were homogeneously dispersed on the support and thus lead to the high catalytic performance.