Upgrading of Kutahya region lignites by mild pyrolysis and high intensity dry magnetic separation.PDF

Pergamon 0892-68750000047-9 Minerals Engineering, Vol. 13, No. 6, pp. 657-661, 2000 2000 Elsevier Science Ltd All fights reserved 0892-6875/00/ - see front matter TECHNICAL NOTE UPGRADING OF KUTAHYA REGION LIGNITES BY MILD PYROLYSIS AND HIGH INTENSITY DRY MAGNETIC SEPARATION* H. KOCA , S. KOCA and O.M. KOCKAR* , Anadolu University, Bozuyuk Technical Collage, Mining Department, Eskisehir, Turkey. E-Mail hkocaanadolu.edu.tr Osmangazi University, Mining Engineering Department, Eskisehir, Turkey “ Anadolu University, Chemical Engineering Department, Eskisehir, Turkey Received 23 September 1999; accepted 20 March 2000 ABSTRACT Lignite samph,s, taken from Kutahya-Seyitomer Power Plant, were used for devolatalisation and desulphurisation experiments, by means of mild pyrolysis followed by High Intensity Dry Magnetic Separation. Pyrolysis experiments were pered in a modified Heinze Retort and important parameters of process, temperature, heating rate and residence time, were studied to determine the optimum conditions. At optimum conditions of pyrolysis, final temperature of 450 C, heating rate of 7 C/min and residence time of 30 rain, up to 61.04 of sulphur reduction was obtained with 57.11 combustible recovery depending on particle size. Char, obtained at optimum conditions of pyrolysis experiments, was further cleaned by a Permroll HIDM separator. Sulphur reduction enhanced up to 86.55 with 22.67 ash, 0.88 sulphur content and 46.09 combustible recovery, depending on particle size. 2000 Elsevier Science Ltd. All rights reserved Keywords Coal; magnetic separation INTRODUCTION Cleaning of coals before combustion by physical s such as gravity s, flotation, flocculation and oil agglomeration have been carried out for some years with limited success, as they are effective only in reducing ash and pyritic sulphur Rawson 1986; Ersayin, et al. 1992. The increasing concern over the environmental effects of volatile matter, released from the combustion of fossil fuels, resulted in the use of semi-coking and pyrolysis technologies to obtain clean coal Cicek et al. 1996; Ersahan et al. 1997; Lin et al. 1997; Atesok et al. 1998. The pyrolysis of coal enables not only the reduction of volatile matter but also desulphurisation of coal via H2S gas release. During pyrolysis, pyrite FeS2, converts to various iron sulphides, among which the ferrimagnetic pyrrhotite Fe7Ss ation takes an important place Gryglewicz 1995; Chen 1998. Heat treatment is also effective in increasing the magnetic susceptibility of mineral matter Yildirim et al. 1996; Renda et al. 1998. Therefore the cleaning of coal by pyrolysis followed by magnetic separation appears to be a new approach to coal cleaning technology. * Presented at Minerals Engineering 99, Falmouth, Cornwall, UK, September 1999 657 658 H. Koca et al. Kutahya-Seyitomer region lignites, located in western Turkey, include high ash, sulphur and volatile matter, and therefore cannot be utilised without intensive cleaning. Laboratory work has revealed that it is difficult to reduce ash and sulphur contents of these region lignites to an acceptable level by applying conventional physical cleaning s Koca 1995. It is the objective of this study to clean Kutahya-Seyitomer region lignites by means of pyrolysis followed by magnetic separation. EXPERIMENTAL Sample Lignite samples were collected from feeders to power plant boilers. Ash, volatile matter, fixed carbon and lower calorific value of sample are 36.52, 42.74, 18.34 and 3531 Kcal/kg, respectively on dry basis. The pyritic, sulphatic, organic and total sulphur percentages of the sample were determined as 1.50, 0.56, 0.34 and 2.40, on dry basis respectively. The sample was sieved into 5 size fractions-2.36l.7; - 1.71.0; - 1.00.5; -0.50.25 and -0.25 ram. Pyrolysis experiments The experimental set-up consisted of three different units heating unit, control and display unit, and liquid product-collecting unit. The heating unit was composed of a Heinze Retort with a volume of 400 cm 3 70 mm ID and externally heated by an electric furnace. The liquid product-collecting unit consisted of a trapping system, held at 0C throughout the experiments. The Heinze retort, including 40 g of air-dried lignite sample, was placed into the electric furnace and connected to the trapping unit. Temperature was then raised at the desired heating rate to a final temperature and held for a certain period of time. The liquid phases collected in the trapping system consisted of aqueous and oil phases, which were separated and weighed. Oil was collected as a by-product of the process. After pyrolysis, the retort was taken out of the furnace and cooled to room temperature. The solid, char, was removed, weighed and analysed for ash, sulphur volatile matter and calorific value. The gas yield was calculated by difference. A Janke - 1.71.0; - 1.00.5; -0.50.25 and -0.25 mm 10, 30 60, 120 and 180 min Upgrading of Kutahya region lignites 659 The effects of temperature on pyrolysis are shown in Figure 1. Char and oil recovery was decreased with increasing temperature while the recovery of gas and decomposition water was increased Figure la. Volatile matter, weight yield and sulphur content of char were decreased while sulphur reduction and ash content were increased with increasing temperature Figure lb. 100 90- . 80- 70- 60- “ 50- o 40- 30- o 20- 10- 0 350 A Char Oil [ Gas Water I I I 450 550 650 Temperature, C a 750 -1o0 90- 80- 70- .-c - 60- . 50- -6 - 40- 7 30- eo 20- ,“ 10- .7 o 350 Weight Yield ---“- AshVlatile Matter I] Total Sulphur Reduc. n Sup. v v v 450 550 650 Temperature, C b 25 20 15 o 10 d 5 [-. 0 75O Fig. 1 The effect of temperature on pyrolysis. The effects of heating rate and residence time at different particle sizes were also studied. The optimum conditions to obtain maximum char yield and sulphur reduction were determined as following Temperature 450 C Heating rate 7 C/min Residence time 30 min The best results obtained at optimum conditions are summarised in Table 1 for different particle size ranges. The effect of pyrolysis on the changes of pyritic, sulphatic and organic sulphur is also given. Pyritic and organic sulphur were decreased along with total sulphur while sulphatic sulphur was not changed significantly. Decomposition of sulphatic sulphur was not achieved at 450 C, indicating sulphate sulphur was composed mainly of calcium sulphate which has much higher thermal stability Ersahan et al. 1997. TABLE I The summarised results of pyrolysis experiments on dry basis Particle size mnl -2.361.7 -1.71.0 -1.00.5 -0.50.25 -0.25 Head sample Ash Pyritic 47.18 0.97 47.51 0.80 49.18 0.74 48.13 0.66 49.10 0.70 36.52 1.50 ower calorific value s ofsulphur, Sulphic Organic Total 0.55 0.23 1.75 0.45 0.17 1.42 0.50 0.15 1.39 0.52 0.20 1.38 0.48 0.22 1.40 0.56 0.34 2.40 Volatile Reduc.in mat. sulp., 12.93 47.14 12.31 58.61 12.03 59.59 11.51 61.04 9.61 58.14 42.74 Comb. rec., Char Oil 58.61 6.32 56.76 7.83 54.68 7.91 57.11 8.28 61.23 8.51 LCV1, Kcal/kg Char Oil 3788 8523 3751 8476 3740 8357 3763 8311 3733 8339 The XRD spectra of the char revealed that the conversion of pyrite to various iron sulphides occurred after pyrolysis. It was determined that pyrite and marcasite are dominant constituents in the head sample while pyrrhotite and iron sulphide are the major constituents for char. It has been reported by many authors that 660 H. Koea et al. the conversion of pyrite into various iron sulphides occured between 360 and 700 degrees C Gryglewicz 1995; Cicek et al. 1996; Atesok et al. 1998; Chen et al. 1998; Renda et al. 1998. Magnetic separation experiments The solid products, char, of -1.71.0; -1.00.5 and -0.50.25 mm from the pyrolysis experiments were used in the magnetic separation experiments. Two products, non-magnetics as clean coal and magnetics as tailings, were obtained after each experiment. Combustible recoveries and reduction in sulphur were calculated according to the head sample. The effects of process parameters on the ash and sulphur content of the concentrate were uated under the following conditions. Roller speed Feed rate Angle of back splitter 30, 40, 50 rpm 50, 150, 250 g/min 90, 96, 100, 110 The optimum conditions of separation were obtained as 40 rpm roller speed, 50 g/min feed rate and 100 splitter angle for the coarse fraction and 96 for others. The best results obtained at the above condition are summarised in Table 2. TABLE 2 The summarised results of magnetic separation experiments on dry basis Particle size iron -1.71.0 Ash Tot. Sulp. Products Clean coal 32.85 1.01 84.19 75.73 2.21 15.81 Tailin Feed 47.51 1.42 100.00 Clean coal 32.77 0.96 87.44 -1.00.5 81.17 2.23 49.18 22.67 78.25 48.13 Tailing Feed Clean coal 1.39 0.88 1.97 1.38 Tailing Feed -0.50.25 According to experiment 2 According to head sample 3Lower calorific value Comb. rec., AT.Expk ATHS 2 47.79 8.97 56.76 47.81 12.56 6.87 100.00 54.68 80.71 46.09 19.29 11.02 100.00 57.11 CONCLUSIONS Reduction in sulphur, AT.Expk ATHS z 53.19 80.63 54.35 81.55 65.48 86.55 LCV 3 Kcal/kg 5112 1132 3751 5194 905 3740 6106 997 3763 Extensive research has indicate that cleaning of Seyitomer region lignites was efficiently obtained by means of pyrolysis followed by High Intensity Dry Magnetic Separation, and the following conclusions can be made -- At optimum conditions of pyrolysis, sulphur reductions and overall combustible recoveries charoil are given below. Particle size, mm Sulp. reduc., Overall comb. rec., Low. cal. val., Kcal/kg -2.361.7 47.14 64.93 3788 - 1.71.0 58.61 64.59 3751 - 1.00.5 59.59 62.59 3740 - 0.50.25 61.04 65.39 3763 -0.25 58.14 69.74 3733 -- Sulphur reductions were obtained mainly via pyritic and organic sulphur decomposition and sulphatic sulphur was not decreased significantly. Upgrading of Kutahya region lignites 661 -- The structure of the by-product of the process, oil, has been reported to be very similar to crude oil and can be directly fid to petroleum refining plants Putun et al. 1997. This allows enhancement, the overall combustible recovery by about 8 . -- Conversion of pyrite to various iron sulphides, mainly pyrrhotite, was obtained at all the studied temperature and size ranges. The XRD patterns showed that char did not contain pyrite and marcasite after pyrolysis while the lignite sample contained mainly pyrite and marcasite. -- Char, obtained from the pyrolysis of -1.71.0, -1.00.5 and -0.50.25 mm size fractions, was further cleaned with a Permroll High Intensity Dry Magnetic Separator. -- At optimum conditions of magnetic separation sulphur reductions and overall combustible recoveries including oil recovery according to head sample are given below. Particle size, nm_l Sulp. reduc., Overall comb. rec., Low. cal. val., Kcal/kg - 1.71.0 80.63 55.62 5112 - 1.00.5 81.55 55.72 5194 -0.50.25 86.55 54.37 6106 REFERENCES Atesok, G., Pen,k, K.T. and Unal, L.B., Decreasing of ash and sulphur contents of Istanbul- Yenikoy region semicoked lignite by HIDM separator. In Proceedings of the llth Turkish Coal Congress. Zonguldak, Turkey, 1998, pp. 129-138 Chen, H.K., Li, B.Q. and Zhang, B.J., Transation of sulfur during pyrolysis and hydropyrolysis of coal. Fuel, 1998, 776, 487-493. Cicek, B., Bilgesu, A.Y., Senelt, M.A. and Pamuk, V., Desulphurisation of coals by flash pyrolysis followed by magnetic separation. Fuel Processing Technology, 1996, 462, 133-142. Ersahan, H., Sara, O.N. and Boncukoglu, R., Desulphurisation of 2 Turkish lignites in an entrained flow reactor. Journal of Analytical and Applied Pyrolysis, 1997, 44 1, 65-74. Ersayan, S. mad Icli, H., Simulation of coal washing equipments; In Proceedings of the 8th Turkish Coal Congress. Zonguldak, Turkey, 1992, pp. 195-120 Garcialabiano, F., Adanez, J., Hampartsoumian,E. and Williams, A., Sulfur release during the devolatilisation of large coal particles. Fuel 1996, 755, 585-590. Gryglewicz, G., Sulfur transations during pyrolysis of a high-sulfur Polish coking coal. Fuel, 1995, 743, 356 -361. Koca, H., Washability characteristics of Seyitomer region lignites and the application of Otisca ProceSs. Ph.D Thesis, Osmangazi University, 1995, Eskisehir, Turkey. Lin, L., Khang, S.J. and Kerener, T.C., Coal desulphurisation by mild pyrolysis in a dual-auger coal Feeder. Fuel Processing Technology, 1997, 531-2, 15-29. Putun, A.E., Ozbay, N., Kokar, O.M., and Putun E., Fixed-bed pyrolysis of cottonseed cake Product yields and compositions. Energy Sources, 1997, 199, 905-915. Rawson, N.A., Desulphurisation of coal by microwave energy. Ph.D Thesis, Leeds University, 1986, Leeds, England. Renda, D., Onal, G. and Mustafaev, I., Production of ecologically clean fuel by semicoking and desulphurisation of lignites. In Proceedings of the 7 th Int. Mineral Processing Symposium. Istanbul, Turkey, 1998, pp. 417-420 Ylldxrlm, I., Yflce, H., Onal G. and Celik, M.S., Upgrading of a low-rank sernicoked lignite by high intensity dry magnetic separator. In Proceedings of the 6 th Int. Mineral Processing Symposium. Kusadasl, Ttukey, 1996, pp. 137-142 Correspondence on papers published in Minerals Engineering is invited, preferably by e-mail to bwilIlsmin-, or by Fax to 44-01326-318352