Coal analysis using the pulsed neutron generator

Vol 14 No, 4NUCLEAR SCIENCE AND TECHNIQUESNovember 2003Coal analysis using the pulsed neutron generatorJING Shi-Wei, LIU Lin-Mao, GU De-Shan, QIAO Shuang, SANG Hai-Feng, ZHANG Yong-Xiang, ZHANG Zhong-Hua,CAO Xi-Zheng, TIAN Yu-Bing, CHI Yan-Tao, ZHAO Xin-Hui(The Radiation Technology Institute of the Northeast Normal University, Changchun 130024)Abstract A prototype of elemental analyzer for coal has been developed by using a PFTNA (pulse fast thermalneutron analysis) system. The PFTNA technology is based on the reactions such as(n, n),(n, n'y),(n, pm), etc. byexamining the characteristic gamma rays emitted. In our prototype a pulsed neutron generator provides 14 Mev pulsneutrons, which contribute to the separation of spectrum Il(the sum of capture and activation spectrum) from spectrum I(the sum of inelastic, capture and activation spectrum), and thus to the measurement of C and O contents incoal Data management is completed by computer program using the least-square regression method. The experimentin Changshan Power Plant for 3 months showed that the precision of calorific value, whole water, volatile content andash content is 0.5 k/kg, 1.0 wt%, 2.0 wt% and 1.5 wt%, respectivelyKeywords Coal, Pulsed neutron generator, PFTNA(pulse fast thermal neutron analysisCLC numbers 0571.53. TL929. TN62Introductionthe same set of detectors but stored at different memonesThe elemental analysis in coal can direct theLow resolution and high z detectors such asproduction process, improve product quality and de- bGo or gso aree employed in the PFTNAcrease the danger coefficient. As the high precision The data analysis of y-spectrachemical analysis method used previously has some least-square regression method 's completed by usingdisadvantages, there are many research institutes en-gaged in the development of analysis methods to dis- 2 Experimental systemmethofast-thermal neutron analysis) system is one of themThe experimental setup of the analyzer is shownThe basis of PFTNA is a pulsed neutron generFig 1. A 14 Mev pulsed neutron generator producedtor utilizing the deuterium-tritium(d-T)reaction. The by ourselves and a 50 mm x 50 mm BGO detectorpulsed d-T neutron generator provides 14 Mev neu- provided by the Shanghai Institute of Ceramics havetrons which in turn initiate several types of nuclear been used in the present work. The neutron tube isreactions((n, n'y),(n, pr),(n, Y), etc. )on the object placed in a stainless steel cylinder whose length is 100under scrutiny. During the neutron pulse, the y-ray cm and diameter is 8 cm. The cylinder is filled withspectrum is primarily composed of rays from the(n, silicon oil to dissipate the power in the target of then'y)and(n, py) reactions on elements such as C and O. neutron tubBetween pulses, some of the fast neutrons that stillThe coal samples were placed in a 30 cmx30stay in the object will lose energy by collisions with 30 cm polypropylene box surrounded by a 10 mmlight elements constituting the object. When the neu- thick lead reflector. The distance between neutron tubetrons have energy less than lev, they will be captured target and upside of the lead reflector was 10 cm. Toby such elements as H, N, and Fe through(n, y) reac- shield neutrons, enough paraffin with boron surtions. The y rays from these reactions are detected by rounded the neutron tube the coal sample and the deCorrespondingauthor:JINGShi-Wei:jingsw504@nenu.edu.cnSupported by the Science Foundation for Young Teachers of Northeast Normal中国煤化工Received date: 2002-10-18CNMHG266NUCLEAR SCIENCE AND TECHNIQUESVoL 14tector. The bGo detector was horizontally placed to I and II were stored by mCa in computer. The gateincrease the effective detection volume. The detector circuit was used to change the neutron pulse timeand the neutron tube are controlled by a cable con- measurement period and time distribution for spectr-nected to the control room 10 m far from the neutron um I and II optionally. Both neutron pulse time andtube.A gate circuit was employed to control the neu- measurement time we employed shown in Fig.2 weretron pulse time and the measurement time of spectrum decided by the neutron tube character and the measI(the sum of inelastic, capture and activation spec- urement requirements.trum)and spectrum II(the sum of capture and activation spectrum). The concept of these times is shown in 3 Experimental resultsFig. 2. The neutron pulse time was adjustable from 10us to 300 us and 50 us was finally chosen in this faTen bulk coal samples of 27-litre volume eachcility. The measurement time for spectrum I and ll is were prepared from coal samples collected from a150 us and 150 us, respectively. The data of spectrumthermal power plant. The samples were thoroughlymixed and analyzed for calorific value, ash contentStainless steel shellControl console ofvolatile content. and the whole water. The 4096 chan-neutron generatenel mca we used was divided into two 2048 channelSilicon oisections, one for storing data from spectrum I and theNT503neutron tubeother for data from spectrum Il. The spectrum I(sumPb reflectorof inelastic, capture and activation spectrum)occupiedBGo detector samplechannel 2049 to 4096, while the spectrum II(sum ofMCAcapture and activation spectrum) occupied channel 1to 2048. An example was given in Fig 3 and the en-Paraffin with boronergy windows for each analyzed element were shownFig. 1 The extal setup of the pulse neutron coal indusn Table 1. for c. o and pb the net counts were obial analyzer.tained from counts of spectrum I subtracted by countsof spectrum Il. For C element measurement, we canuseC=a1(Nc1-NC2)+a2(No-No2)+a3(1)where Ce is the content of C element; NcI, Nc? is thecounts of C energy window in spectrum I and Il,re-spectively; Nol, No2 is the counts of O energy windowin spectrum I and Il, respectively; al, a2 and a3 are theMeasurement timeof spectrum I 150 us Measurement timeempirical constants for the regression Eq ( 1)of spectrun150μsFor other elements analysis, similar method likeFig2 Schematic diagram of the neutron pulse time and theEq (1)was employed, and some results are shown inmeasurement timeTable 2Table 1 The energy window for each analyzed elementElementsFeCaCSWindow width inspectrum I(ch)2797-28823090-31903230-3346Window width inpectrum(h)3674295729221322-16371037-11377508351043-11431205-1321933-993TYH史No 4JING Shi-Wei et al. Coal analysis using the pulsed neutron generatorH peako peak15Fe, Al peak830001500Fig-3 An example of spectrum I and II with measurement time of 900 sTable 2 The measurement results of some parametersParametersCalorific value(kJ/kg) Whole water(wt%) Volatile(wt%)Ash(wt%)Precision1.0Accuracy1.04 Discussiongamma spectrometer should be employed in view ofits high stability and data throughput rate. We haveSeveral research institutes in some countries suchlready bought the digidaRT from ORTEC whoseas USA, Australia and China have developed thethroughput rate is 100, 000 cps. Hence the three probPFTNA system to measure the elements in coal. Our lems will be solved in our institute soon and the per-institute is the first institute in China to take part in theformance characteristics of the PFtNA system will beproject. Based on the experimental results and the apgreatly improvedplication practice in Changshan Power Plant in JilinProvince for 3 months, we believe that the PFTNA Referencessystem is suitable for the element analysis in coal, andthe measurement precision will be improved if some 1 Wirnakd M R, Clayton C G J Appl Radiat Isot, 1983problems are solved34(1):71-82Firstly, the industrial application of the PFTNA is 2 Clayton C G Wirnakd M R J Appl Radiat Isot, 198largely dependent on the neutron tube lifetime. Re34(1):83-93cently, lifetime of a neutron tube can reach 10,000 h 3 Clayton C G Wirnakd M R J Appl Radiat Isot, 1983and this is the basis to develop an industrial system. In34(1):3-22the Northeast Normal University, the NT503 tubes 4 Vourvopoulos G Nucl Instrum Method Phys Res, 1991lifetime is more than 4, 000 h and the price is low, soB56/57:917920the user of the PFTNA system can conveniently re- 5 Vourvopoulos G Womble P C Nucl Instrum Method Physfresh the neutron tube when the old one is uselessRes,1989,B36:200-205Secondly, stability of the neutron generator and the 6 Salgado J, Oliveira C Nucl Instrum Method Phys Res,whole spectroscopic system must be improved in order to increase the measurement precision. We plan to 7 Chen B X, He J Y, Liu J C Nucl Electron Detect Techndevelop a new circuit system to modulate high voltage( in Chinese),1996,16(1):6-12and beam current of the neutron tube according to the8 Liu Rdinanal NurI Chem, 1991, 151(1)data from the neutron monitor. In the end. a digital83-93中国煤化工CNMHG