Joule-heated Glass Melter Research Articles

Numerical modeling on the discharged fluid flow from a glass melter by a Lagrangian approach

Abstract In Japan, it is planned to use vitrification to immobilize high level radioactive liquid waste (HLLW) obtained from the nuclear reprocessing process. In the vitrification process, the HLLW will be mixed with molten glass in a joule-heated glass melter. The molten glass is then poured into a canister through a nozzle at the bottom of the melter. When some abnormalities occurred, feature of the discharged flow become different from that in normal conditions. We cannot observe the state of the molten glass inside the melter directly because of the severe environment. Accordingly, we cannot investigate the cause when the abnormalities occurred. Hence, numerical simulation of the discharged flow becomes important to understand and recover from operational problems or abnormalities with the glass melter. However, existing numerical models of the glass melter do not really simulate the discharged glass flow. In the present study, we introduce a new algorithm into an existing Lagrangian approach to efficiently simulate the discharged glass flow. To verify the model, 3D simulations were performed on a real scale system and got compared with the results of experimental validation tests. The simulation results show good agreement with the experimental results. Consequently, the new Lagrangian approach accurately simulates the molten glass flow.

ジュール加熱式ガラス溶融炉における電場・熱流動・粒子挙動の連成解析

ジュール加熱式ガラス溶融炉における電場・熱流動・粒子挙動の連成解析

CFD Modeling Coupled with Electric Field Analysis for Joule-Heated Glass Melters

A computational fluid dynamics model on a joule-heated glass melter, which is used for the vitrification process of high-level liquid waste, has been developed to simulate the operation of actual melters. Electric field simulation is coupled with the thermal and flow field calculation to investigate the effects of the joule-heating on the buoyancy-driven flow of the molten glass. The melter is operated in a cyclic sequence including a bottom-heating phase, a drain phase and a bottom-cooling phase. In order to estimate the transient behavior of actual melters, unsteady simulations for several tens hours are necessary. It is found that there is non-uniformity of the heating at the bottom of the melter during bottom-heating phases. It is generated by the asymmetrical electric current distribution due to the arrangement of the electrodes. The temperature distribution at the bottom, however, is kept almost symmetrically due to the mixing effect by natural convection of the glass. Computational results are compared with experimental data obtained by actual operations of a prototype melter. The temperature distribution and electric resistances between electrodes predicted by the simulations indicate that the characteristics of the simulated melter show good agreements with the actual melter.

Numerical Simulation of Platinum Group Metal Particles Behavior in a Joule-Heated Glass Melter

For a joule-heated glass melter, we have developed a numerical simulation scheme, which couples electric field, thermal fluid dynamics and platinum group metal particles behavior. Glass properties, especially the viscosity and electrical conductivity, widely change due to the platinum group metals included in high-level liquid waste. It is necessary to estimate the distribution of the platinum group metals in the glass, because operational conditions of the melter are strongly affected by them. In this study, the platinum group metals behavior was treated as the transport of the particle concentration by the Eulerian method in order to reduce the computational loading. Databases of glass properties with the platinum group metals were obtained by measurements of glass samples. Numerical simulation of 18 batch cycles showed that the platinum group metals not only were transported by the glass flow but also settled down and deposited on the bottom walls of the melter. Additionally, the electric current intensively converged along the bottom walls due to the increase of the electrical conductivity in the deposited layer of the platinum group metals. Numerical results agreed reasonably well with experimental data. It has been clarified that this numerical method is useful for the design and operation.

2220 ジュール加熱式ガラス溶融炉の数値解析 : 第二報 白金族粒子の沈降・堆積の数値解析(G05-3 解析モデルと解析手法,G05 流体工学)

We have developed a numerical simulation scheme which couples electric field, heat transfer, fluid dynamics and metal particles behavior in a joule-heated glass melter. The particles behavior is treated as the continuous transport of the particle concentration by the Eulerian method. It is able to evaluate the unsteady operational melter status and performance, which are strongly affected by the settling and deposition of the platinum group metals included in high level waste. Numerical simulation showed that high current density bypasses along the inclined bottom wall due to the increase of the electrical conductivity in the deposited layer of the metals. As for remaining mass of the metals in the melter, numerical results agreed reasonably well with the experimental data.

2219 ジュール加熱式ガラス溶融炉の数値解析 : 第一報 電場・伝熱・流体の連成解析(G05-3 解析モデルと解析手法,G05 流体工学)

2219 ジュール加熱式ガラス溶融炉の数値解析 : 第一報 電場・伝熱・流体の連成解析(G05-3 解析モデルと解析手法,G05 流体工学)

Electrical Power Supply and Controls for a Remotely Operated Glass Melter for Nuclear Waste

An electrical power supply and the controls and instruments used for a joule-heated glass melter for nuclear waste are discussed. Remotely replaceable interconnection wiring assemblies for the power, controls, and instruments are also described.

Incineration/vitrification of simulated low-level institutional wastes in a joule-heated glass melter

The purpose of this study was to determine the feasibility of reducing the volume of low-level institutional wastes by incineration and then converting the residual solids into glass with a single-step process. Experimental test results with simulated waste show that a joule-heated ceramic melter originally developed for high-level waste vitrification can be used for the low-level waste volume reduction process. Off gas analysis from the experiment shows that incineration of combustible solids was essentially complete. This is attributable to high combustion temperatures (>950 °C) and the introduction of excess combustion air or oxygen at the melter's glass surface. The only instance where a pyrolysis product (hydrogen) was detected was when the oxygen concentration in the process off gas depleted to 7.8%. An insulating blanket over the glass surface, which would have reduced incineration temperatures, never formed. In addition, calculations show that for scaled-up processing rates, incineration temperatures will remain high because the medicinal waste provides much of its own heat for combustion, vitrification, and process heat losses. Results of the incineration experiment indicate that process scale-up for higher capacities is quite feasible. Although feed rates in this experiment through the pilot-scale melter were low (0.5 kg/ h), they could be increased as much as tenfold, even for the laboratory-scaled unit tested here, by use of an improved feed system. The overall test results were so encouraging that we recommend further tests aimed at adapting high-level waste vitrification technology to the management of both institutional wastes and low-level wastes generated from the nuclear fuel cycle.