Malaysia International NDT Conference & Exhibition 2015 (MINDTCE-15), Nov 22-24 - www.ndt.net/app.mindtce-15 Neutron Imaging System For level Interface Measurement More Info at Open Access Database www.ndt.net/?id=18667 Abstract R.M. Zain, R.Yahya, M.F.A. Rahman, N.M. Yusof Plant Assessment Technology Group Industrial Technology Division Malaysian Nuclear Agency Bangi 43000 Kajang Selangor, Malaysia rasif@nm.gov.my Level interface measurement in petroleum industries is very important for the assessment and improvement of plant performance. Inaccurate level measurement can seriously affect the production process and the entire operation. It may result in reduced performance and off-spec product. The portable neutron backscattered scan device is advanced in-situ inspection system for visualizing of the level measurement. The study has been carried out at the Vessel Test Rig facility, Malaysian Nuclear Agency to visualize and measure the interface level. System development and functionality of this device presented in this paper and also the experimental results. Keywords: Vessel, on-line measurement, radiation, neutron backscattered, level interface 1.0 Introduction Accurate level measurement inside the reactor/storage vessel is one of the important parameters to produce the best quality product in production line. Modern industrial plant operations often require accurate level measurement of process liquids in production and storage vessels. A variety of portable advanced level indicators are commercially available to meet the demand, but these may not suit specific need of situations. In the case of the pressure vessel with wall thickness up to 10 cm, toxic and corrosive chemical the portable neutron backscatter technique (NBT) is one of the best methods to measure the level without to shout down the process [1]. Currently, in the market the inspection by using portable NBT only produce two dimension graph profile to show the level measurement. Meanwhile, in this paper presents the advanced portable NBT to produce images of level measurement. The system has been tested at vessel test rig to evaluate its performance. 2.0 THEORETICAL CONSIDERATION Neutrons emitted from the radioactive source are energetic particles, with energies up to several Mev. Collectively, such energetic neutrons are referred to as fast neutrons with the energy ranges from 0.5 11 Mev. When fast neutron collides with the nuclei surrounding material, their energy is moderated through scattering. During this collision, neutron lost its energy and producing a wide range of slow neutron, which it approaches a thermal condition is known as moderation. The substance in which this process takes places is called a moderator. The energy transferred to the target nucleus is E 0 E [2]-[3],
2 ( ) 0 = 0 1 ( + ) Where E 0 is the energy of incident neutron, m is mass of incident neutron, M is the mass of scatter nucleus. It is possible that all the neutron energy be transferred on collision with a hydrogen atom. It is clear that, for this reason, the presence of hydrogen is a major factor in the slowing down of fast neutrons. It can be seen that the number of collisions required to thermalize a fast neutron is lower for elements of lower atomic number, such as hydrogen. A high proportion of chemical, oil and gas process streams contain hydrogen in one form or another. This is especially true in petrochemical, oil and gas industries where hydrogen is present in practically every process material. In portable NBT to perform inspection of level measurement, high energy neutrons from 241 Am-Be radioactive source are beamed onto a vessel. Fast neutrons are slowed down mostly by collision with hydrogen atoms of material inside the vessel [4], [5]. Parts of thermal neutron are bounced back towards the source [6],[7]. By placing a thermal detector next to the source, these backscatter neutrons can be measured. The number of backscatter neutrons is directly proportional to the concentration of the hydrogen atoms in front of the neutron detector[4]-[9]. As the source and detector move down the side of the vessel, interfaces can be detected provided they are involved a change in hydrogen atom concentration. 3.0 System Development The portable NBT consists of a neutron scanner probe and automatic winding system. Inside the neutron scanner probe located the He-3 proportional counter tube and Cf-252. Figure 1 shown the probe scanner neutron. The detector connected to the Ratemeter for slow neutron counting device through coaxial cable. Next, the Ratemeter connected to computer through RS-232. Figure 1: Neutron probe scanner The software developer is to control the movement of the probe and data analysis to produce the image. The graphic user interface software development is shown in figure 2. During the inspection
for level measurement the neutron scanner probe will be placed into the surface of the vessel. This probe can move in x-axis and y-axis control by an automatic winding system. Figure 2: GUI of the Neutron Imaging system. 4.0 Result and Discussion The study has been conducted at the Vessel test rig at Malaysian Nuclear Agency. This vessel contains of diesel and vapour. The vessel has the several windows along the height of vessel that can view the level interface through naked eyes. This function is to verify any method to measure the interface level. Figure 3 shown the experiment has been conducted. Figure 3: Experimental conducted at Vessel Test Rig. Figure 4 shows the images of interface of diesel and vapour inside vessel test rig in a dynamic process. The size of image pixel is 150 x 35 pixels. The red colour shows the vapour space and the red colour is a diesel. This location of level interface is similar by using naked eyes. Meanwhile, in figure 5 show the analysis of the raw data from the image. It can be seen that high value of the thermal neutron count at a height between 0 cm to 30 cm. It clearly shows the
presence of highly hydrogenous material. Meanwhile, at a height between 48 cm to 80 cm show a low value of thermal neutron count indicated the presence of vapour space. Besides that, observation shows that as the detector-source probe moves from 30 cm to 50 cm the count of thermal neutron changes slowly, showing the presence of different interface in that region. From the visual on the side window of the vessel test rig, the interface for hydrocarbon and vapour equator mark located at the 40 cm. Figure 4: Line image of interface of diesel and vapour. The thermal neutron count varies starting from 10 cm below and above the equator mark, i.e. 30 cm and 50 cm respectively. As the probe moves towards the 30 cm to 50 cm range, the thermal neutron count reduced drastically as the detector probe starts to enter the region which contain vapour; approaching the equator between the hydrocarbon and vapour interface. This is because as the detector approach region of vapour, less thermal neutron are produced and as a result the thermal neutron count detected by detector decreases [3], [9]. Height (cm) 90 80 70 60 50 40 30 20 10 0 500 7350 Neutron backscatter count /8 sec
Figure 5: Analysis of image 5.0 Conclusion The portable neutron backscatter technique provides easy access to determine the interface level of vessel containing different types of hydrogenous material. The most advantage features of this technique is, it only requires one side of the vessel to be scanned compared to other methods. 6.0 Acknowledgements This research was fully supported and encourage by top management of the Malaysian Nuclear Agency. This special thank also go to Commercial Technology Devision for Tabung Amanah funding. 7.0 Reference [1] Asano H et. all, Liquid two phas flowin a plate heat exchanger by neutron radiography, Nucl Instrum Method A, 542 (2005) 154. [2] Glenn f. Knoll, Radiation detection and measurement, 2 nd edition, John wiley & Sons 1998 [3] Charlton, J.S., (1985), Radioisotope Techniques for Problem-Solving in Industrial, Springer, Berlin [4] Cywicka-Jakiel, T., (2003), Fast-neutron and gamma-ray transmission method for cokehumidity determination, Applied Energy 74, 305 311. [5] Du, M., et. all, (2005), Detection of water in aluminium scrap with a fast neutron source (Cf- 252), In: Kvande, H. (Ed.), Light Metal 2005, The Minerals, Metals & Materials Society. [6] Hasan, N.M., Zain, R.M. Rahman, M.F.A. and Mustapha, I., (2009), The use of a neutron backscatter technique for in-situ water measurement in paper-recycling industry, Applied Radiation and Isotopes, 62 p.1239-1243. [7] Jonah, S.A., Zakari I.I. and Elegba, S.B., (1999), Determination of the hydrogen content of oil sample from Nigeria using an Am Be neutron source, Applied Radiation and Isotopes 50, 981 983. [8] Naqvi, A.A., (2003), Moisture measurements of wood and sugar samples using neutron transmission technique, Nuclear Instruments and Methods in Physics Research A 497, 569 576. [9] Tominaga, H., Wada, N., Tachikawa, N., Kuramochi, H., Horiuchi, S., Sase, Y., Amano, H., Okubo N. and Nishikawa, H., (1983), Simultaneous utilization of neutron and gamma-rays from Cf-252 for measurement of moisture and density, Applied Radiation and Isotopes 34 (1), 429 436.