Data acquisition system for optimization and control of the processes from an isotopic exchange column

Transcription

1 Data acquisition system for optimization and control of the processes from an isotopic exchange column C. M. Retevoi, I. Stefan, A. Bornea & O. Balteanu National Institute of Research-Development for Cryogenic and Isotope Separation Technologies, Romania Abstract One of the problems in a tritium separation installation is controlling the temperature of the isotopic exchange column. To maintain a constant column temperature, the signal from the monitoring system (sensors) is used to control a power supply for the electrical heat exchangers. Other parameters measured in the flow circuit are the pressure, water level in the column and boiler temperature. The computer to be used for the control is equipped with LabView software, a data acquisition board, and a signal conditioner. Also, we developed a new monitoring system for detritiation installation using National Instruments products, FieldPoint Modules, LabView 6.1 and serial board, configuring for RS-485, usefully for long distance. 1 Introduction The raise of tritium level concentration in heavy water determines some problems in operation of nuclear reactor and also for the environment. Therefore it is very important to decrease the tritium level in heavy water and in this way most owners of Candu reactors are making researches and develop technologies for heavy water detritiation. As it is well known after several years of functioning the radioactive level in the moderator attained such a value that imposes heavy water detritiation. The technology developed at the Institute of Cryogenics and Isotope Separations is based on catalytic isotope exchange between water and hydrogen gas both carrying various isotopes of hydrogen: normal hydrogen, deuterium, and tritium. This isotope exchange is followed by cryogenic distillation separating the various isotopes of hydrogen gas. The é Heat Transfer VIII, B. Sund

2 382 Heat Transfer VIII detritiation process was simulated using as working fluids water with a small content of deuterium and a gaseous mixture of hydrogen and deuterium. On a successive, the experimental data obtained on catalyst isotopic exchange column on tritium or deuterium transfer from water to gas and the mathematical model to simulate the column behavior allowed to determine the performance of isotopic exchange column. After interpreting the experimental data, we determined the speed constants, which characterize the isotopic exchange for distillation, and catalyze respectively, as function of the experimental conditions: tritium or deuterium concentration in the feed water of the system, distillation and catalyst isotope exchange. The isotopic exchange between tritiated heavy water and deuterium (DTO-D 2 ), respective deuterated -water and hydrogen is realized according to the following reactions: Distillation: (1) ( ) l + ( D2 O) v ( DTO) v + ( D2 ( ) L + ( H 2 O) V ( H 2O) L + DTO O) l HDO ( HDO) V Catalytic action: (2) ( DTO ) l + ( D2 ) ( D2O) + ( DT ) g g l ( ) V + ( H 2 ) G ( H 2O) V + HDO ( HD) G The above reactions are characterized by the separation factors. For distillation, the separation factor is expressed using vapor pressures: P1( DTO ) P1( HDO ) α T = D = P2( D 2 O ) P2( H 2 O ) α (3) In order to describe the isotopic exchange process water-vapor-hydrogen gas, we consider an exchange column and described the processes: distillation and catalytic isotope exchange distinctively. The distillation layer is realized with ordered package B7 type of phosphorous bronze. The hydrogen gas with water vapor saturate is circulated in countercurrent with water on the distillation layer and it s realized the isotopic exchange by distillation. The catalyst layer is realized with the catalyst PT/C/PTFE. The hydrogen gas and the water vapors are circulated in co-current on the catalyst layer and it s realized the isotopic exchange by catalyst isotopic exchange. The distillation and the isotopic exchange alternate along the column. Also for monitoring the isotopic exchange column is necessary to control the temperature very carefully. For that we made an automation system with data acquisition and control which provide all data for analyze. The design of the process calls for a constant catalytic exchange temperature that must be maintained at a value of 9 C. To achieve this, the plant is equipped with electrical heat exchangers for heating the gas (hydrogen) and

3 Heat Transfer VIII 383 the heavy water. The control is achieved using an array of sensors and controllers. The sensors used for monitoring the process are type J thermocouples. The control systems use different sensors of the same type but better quality. The temperature control is achieved by controlling the electrical power fed to the heaters. Besides sensing the fluid temperatures at various points, we also monitor the vapor pressure and the heavy water level in the column. The level is controlled via two dosing pumps, which work alternately to feed water to the column. 2 Performances We monitored the temperature of hydrogen inside the heat exchanger and at the input of column and made sure these are lower than the maximum safe temperatures (9 C and 15 C respectively). The security system monitors the pressure of the nitrogen used for cooling the electrical resistance rods inside the heaters. For temperature measurement, we used thermocouple type J, and the FieldPoint module FP-TC-12.The new system developed has module FP 11 connected to the serial board, configured for RS-485 from computer. The real advantage is that we can connect all necessary FieldPoint modules to make the monitoring of entire installation. In this way we reduced the costs and are easy to use. The FP-11 connected to the serial port type C114H is configured with address 1. The equilibrium constants for the various reactions inside the column are calculated using the formulas: K1= *T *1-5 *T *1-8 *T 3 ; K2= *T *1-4 *T *1-7 *T 3 ; K3= *T *1-5 *T *1-8 *T 3 ; K= *T *1-6 *T *1-9 *T 3 ; The connection between FP-11 module and PC is realized through serial board C114HI, with output configuration for RS-485, in half-duplex mode. Serial board connector has 25 pines, and pine with number 8 is connected at pine Rx+ to the FP-11 module. Tx- pine is connected to the pine 2 of serial board connector. With FieldPoint Explorer we configured very quickly the parameters of FieldPoint modules, including ranges, power-up states and Ethernet IP address. We realized also interactively read and write data from I/O modules to tests and verify proper operation. Because FieldPoint Systems also include a free OPC server for industrystandard connectivity, we integrated the systems with software that has OPCclient. OPC uses DCOM technologies, so client application can access data from remote OPC server over the network. Figure 1 shows the front panel from LabView and shows how the temperature is controlled and also how we calculate the equilibrium constants, as a function of the acquired temperature.

4 384 Heat Transfer VIII Figure 1: Front Panel from LabView. Monitoring the isotopic exchange column. Figure 2 shows the front panel displaying the equilibrium isotherm and the operating line plot. The operating line of the column is obtained from the measured D/D+H ratio in the liquid and gas phase at the top and the bottom of the isotopic exchange column. Figure 2: Front panel in LabView for equilibrium isotherm. From the equilibrium isotherm and the operating line, the number of theoretical plates can be determined following the Mc-Cabe-Thiele approach.

5 Heat Transfer VIII Conclusions The experimental dates obtained at the tritium isotopic exchange proved that the speed constants are half of the deuterium speed constants. These experimental dates and the computed values of the speed constants represented an image about catalyst performances of the deuterium and tritium isotopic exchange. The mathematical model and the experimental dates permitted to design an isotopic exchange column for deuterium and tritium exchange for liquid to gas phase. Because LabView has the same development tools and language capabilities as a standard computer language such as C looping and case structure it is well suited for modeling and simulation. The purpose of this application is to accomplish the monitoring and increasing level security, for protection in detritiation installation. We realized experiments with LabView, as an OPC client by connecting to an OPC FieldPoint server through DataSocket connection. This procedure is used to connect VIs to devices on any OPC server, such as FieldPoint. With DataSocket we can efficiently pass data over the Internet, and respond to multiple users without the complexity of low-level TCP programming. References [1] Hall T. Martin & Meg. L. Martin LabView for Automotive, telecommunications, semiconductor, Biomedical and other applications, Prentice Hall PTR, Upper Saddle River, NJ 7458,2,USA, pages ,ISBN X. [2] Cohen K. - The Theory of isotope separation, Editura McGraw-Hill, New- York, [3] Masami Shimizu, T. Doi, A. Kitamoto, Y. Takashima - Numerical Analysis on Heavy Water Separation Characteristics for a Pair of Dual Temperature Multistage - Type H 2 / H 2 O - Exchange Columns. Journal of Nuclear Science and Technology, 17(6), pp (June 198). [4] Masami Shimizu, A. Kitamoto, Y. Takashima - Numerical Analysis on Heavy Water Separation Characteristics for Pair of Bithermal Trickle- Bed Type H 2 / H 2 O - Exchange Columns. Journal of Nuclear Science and Technology, 2(3), pp (March 1983).