Papers by Author: Lu Zhou

Abstract: The submerged combustion vaporizer (SCV) is a kind of equipment used for liquefied natural gas (LNG) vaporization. In order to get insights into the heat transfer of supercritical LNG, numerical simulations were carried out in this paper for investigating heat transfer of LNG in horizontal circular tubes under supercritical pressure. Numerical results showed that LNG temperature at the outlet under the design parameters was 276 K which met the demands of application. The velocity of LNG at the outlet was 12 m/s, and the pressure drop along the ducts was 120 kPa.

Abstract: The submerged combustion vaporizer (SCV) is a new kind of vaporizer for liquefied natural gas (LNG). In this paper, a numerical study has been carried out to investigate the heat transfer characteristics of supercritical LNG in horizontal tubes. The thermo-physical properties of supercritical LNG were used for this study, and the influence of inlet LNG mass flow rate on heat transfer was investigated. Numerical results showed that the LNG flow in horizontal tubes included two stages. In the first stage, the surface heat transfer coefficients increased significantly with the increase of the fluid bulk temperature and reached a maximum value when the fluid bulk temperature equaled the pseudo-critical point . After the maximum, the surface heat transfer coefficients fell rapidly with the increase of the fluid bulk temperature. With increasing the inlet LNG mass flow rate, the surface heat transfer coefficients increased due to the increased fluid velocity in horizontal tubes.

Abstract: A simulation model was developed for predicting the particle size evolution in hydrothermal synthesis of nanoparticles in supercritical water. Four elementary kinetic processes, including hydrothermal synthesis reaction, nucleation, growth, and aggregation, were involved based on the population balance equations (PBEs). The homogenous nucleation of metal oxide nanoparticles started at the operation time of 3.72μs. When the rate constant of hydrothermal synthesis reaction lnk increased from 2.8 to 6.16, the nucleation rate increased by three orders of magnitude (1021-1024particles/m3•s) and the nucleation period reduced from 0.2s to less than 0.02s. The APS decreased by approximately half when a ten-fold smaller growth rate constant was adopted in the range of 10-11-10-8.

Abstract: The oxidation of methanthiol and thiirane in supercritical water was explored by using a tubular-flow reactor system using oxygen as oxidant. No sulfur containing species existed in the gaseous effluent. Sulfide, sulfite and sulfate were detected as the sulfur containing species in the liquid effluent for supercritical water oxidation (SCWO) of methannthiol, while it was determined as thiosulfate, sulfite and sulfate for SCWO of thiirane. When reaction temperature exceeded 873K, the sulfur contained in the methanthiol or thiirane all transformed into the liquid products. Oxidant stoichiometric ratio had little effect on the conversion rate of sulfur but could promoted sulfite converted into sulfate. Sulfide and thiosulfate were determined as the exclusive sulfur containing product arising directly from methanthiol and thiirane, respectively. The transformation pathways of sulfur contained in the methanthiol and thiirane were proposed as methanthiol-sulfide-sulfite-sulfate and thiirane-thiosulfate-sulfite-sulfate, respectively.

Abstract: Oxidation of iron sulfide in supercritical water was investigated in the batch reactor. Iron sulfide was converted in two parallel processes: gasification by water and oxidation by oxygen. Assuming that the reaction order of H₂O was 0, the activation energy and pre-exponential factor of the gasification process were determined to be 43kJ mol^-1 and 22.4 min^-1, correspondingly. It is found that above 773K the oxidation process was limited by the mass transfer of O2 to particles surface. Below 773K, with an assumption of zero order in H₂O concentration and first-order reaction in oxygen concentration, the activation energy and pre-exponential factor for the rate of oxidation were estimated as154kJ mol^-1 and 1.7×10⁶m³ mol^-1 min^-1, respectively. With supercritical water oxidation under the experimental conditions, the sulfur-containing components in the product were sulfide, sulfite and sulfate, in which sulfide and sulfate were predominant. It is likely to completely convert the sulfur to the sulfate by supercritical water oxidation using high temperature and long reaction time. The reaction pathway of iron sulfide could be expressed as: iron sulfide → sulfide → sulfite → sulfate.

Abstract: A supercritical water oxidation (SCWO) reactor containing a hydrothermal flame as heat source is simulated by computational fuild dynamics (CFD) simulation. Methanol solution and oxygen are fed separately into the reactor as fuel and oxidizer, and at the same time the cold waste water is also fed into the reactor. The combustion of methanol is simulated by the eddy dissipation concept (EDC) model with an Arrhenius law kinetic. This simulation is conducted to study the behavior of the hydrothermal flame at different inlet fuel temperatures and the relationship between the ignition temperature and methanol mass fraction.

Abstract: The combustion behavior of fixed carbon in supercritical water was explored by a batch reactor. Effects of reaction parameters such as reaction temperature, time, oxygen stoichiometric ratio and stirring rate were investigated. Fixed carbon was difficult to burn out, even if in a harsh condition the conversion of fixed carbon was only 51%. It is determined that for the temperature below 450°C, the process of oxidation was limited by the reaction rate between oxygen and particle surface. For the temperature above 550°C, the rate of oxygen mass transfer to the particle surface was the rate-limiting step. In the transition zone of temperature, surface reaction was comparable to mass transfer in limiting reaction rate. Only trace amount of carbon monoxide was produced at 500°C, and no carbon monoxide was detected at 600°C.