Evaluation of a hot oil immersion drying method for the upgrading of crushed low-rank coal

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1 Jurnal f Mechanical Science and Technlgy () () 99~ DOI.7/s--- Evaluatin f a ht il immersin drying methd fr the upgrading f crushed lw-rank cal Tae-In Ohm,*, Jng-Seng Chae, Jae-H Lim and Sung-Hyun Mn Department f Envirnmental Engineering, Hanbat Natinal University, San -, Duckmyung-dng, Yuseng-gu, Daejen 5-79, Krea Waste Resurce Energy Team, Krea Institute f Energy Research, Yuseng-gu, Daejen 5-, Krea (Manuscript Received August 5, ; Revised Octber, ; Accepted December, ) Abstract Cal is the mst abundant fuel n earth, and lw-rank cal (LRC) such as sub-bituminus cal and lignite makes up abut half f all cal depsits. LRC is incnvenient t use due t its lw calric value and high cntent f misture tgether with the strng tendency f spntaneus cmbustin due t these xygen rich cals, etc. Slving these prblems wuld substantially imprve the efficiency f LRC usage. In this study, we describe a drying technique utilizing ht il immersin. This upgrading prcess may be executed easily under relatively lw temperature cnditin due t the difference f heat capacity and thereby pressure gradient between cal and heating il. This results in greatly reducing its energy cst. Drying tests f Indnesian lignite were perfrmed with refined waste il and B-C heavy il, which were heated t C, C r C. Fllwing min f treatment, the misture cntent f the upgraded cal was imprved frm % t.-.%, and its high heating value frm, kcal/kg t, kcal/kg. Keywrds: Lw-rank cal; Cal drying; Oil immersin; Refined waste il Intrductin * Crrespnding authr. Tel.: +, Fax.: + 7 address: tihm@hanbat.ac.kr Recmmended by Assciate Editr Oh Chae Kwn KSME & Springer A stable security plan requires lw-cst energy surces, but the present substantial demand fr energy has elevated the prices f gasline as well as cal. The upgrading f Lw-rank cal (LRC) ffers a means t reduce ttal energy csts. LRC accunts fr abut half f the wrld's cal depsits, and is relatively inexpensive at just -% f the price f high-rank cal. Hwever, the use f LRC has been extremely limited fr several reasns. Its high misture cntent f -7% makes it mre difficult t transprt ver lng distances, and its heating value is nly,5 kcal/kg at best. Als, due t its high prsity and high carbnyl cntent, LRC has a strng tendency tward spntaneus cmbustin during lng-term strage. Overcming these disadvantages thrugh an upgrading prcess wuld cnfer a significant ecnmic benefit [, ]. In LRC upgrading prcesses, water is evaprated frm surface and interstitial spaces, the misture being replaced with il. Hence, the heating value f LRC is increased, and the cnversin frm a hydrphbic t hydrphilic cnditin serves t stabilize it [-5]. Cal drying technlgies can be categrized as evaprative r nn-evaprative, the latter categry including prcesses knwn as the K-Fuel prcess (U.S.A.), the Binderless Cal Briquettes prcess (Australia) and the Upgrading Brwn Cal prcess (Japan) [-9]. In this study, the technique f immersin in ht il was used t dry LRC thrugh heat and mass transfer mechanisms. Cals were added t il heated abve the evapratin temperature f misture, generating a strng turbulent flw n the cal surface by biling. Thrugh heat transfer, bth surface water and interstitial water evaprated rapidly [-]. By this drying technique, hereinafter called 'fry drying', LRC culd be upgraded t a misture cntent f 5% r less and a heating value f, kcal/kg r mre, wing t replacement f misture in the cal with il.. Test samples and test methdlgy Depsits f Indnesian lignite are abundant, and its advantageus gegraphic distributin helps t keep transprtatin csts lw. Fr these reasns, Indnesian lignite was selected as the test sample t be upgraded. Fr use in experiments, blck cals were mechanically crushed and then passed thrugh - mm, -7 mm and - mm screens, such that specific cal sizes culd be tested. Basic characteristics f cal samples were measured using a Truspec CHN Elemental Analyzer (LECO), SC -DR Sulfur Analyzer (DIONEX), Analyze (LECO), IC- Ana-

2 T.-I. Ohm et al. / Jurnal f Mechanical Science and Technlgy () () 99~ Table. Characteristics f Indnesian lw rank cal. Misture C Prximate analysis (as received base) Ash Fixed carbn Vlatile matter.... H Ultimate analysis (as received base) O N S Cl (ppm) nt dne nt dne Weight(cal+il) 5 79 cal input cal diameter : -mm cal weight : 5g il temp : C Calrific values High calrific value (kcal/kg) Lw calrific value (kcal/kg),.,. 7 Fry-dry time (min) Fig.. Drying curve f raw Indnesian lignite. C, r C befre the additin f 5 g f cal per litre f il. Each fry-drying experiment was perfrmed fr minutes. After drying, cals were transferred t a centrifugal separatr fr minutes, and the amunt f separated il was then measured. T assess drying efficiency under each reactin cnditin, misture cntent was measured by electric ven in samples cllected befre and after the drying prcess, and crushed t a unifrm size f.5 mm. Misture measurements were cmpleted the same day t preclude changes in misture cntent. Fr all parameters measured, the arithmetic mean f three experiments was calculated. Fig.. Batch-type cal drying apparatus. lyze (LECO) and TG A-7 Prximate Analyzer. Results f prximate, ultimate, and heating value analyses are shwn in Table. Refined waste il and B-C heavy il were used as drying media. Refined il is recycled waste il frm which misture, ashes, heavy metals and ther cntaminants had been remved. B-C heavy il, the mst viscus f the heavy ils with a minimum viscsity f 5 cst (5 C), is used as fuel fr burners equipped with a preheating and warming apparatus, such as large-scale bilers and lw-speed diesel engines [, ]. The refined waste il used in this study had a biling pint f apprximately C and a specific gravity f.5-.; the B- C heavy il had a biling pint f abut C and a specific gravity f [, ]. Fig. shws the design fr a batch-type cal drying apparatus. The cylindrical reactr (height cm, diameter cm) and a square mesh net receptacle fr cals t be fed int the reactr (width cm, length cm, height.5 cm) were made f stainless steel. The weight f the il in the reactr was measured with an electrnic scale placed under the drying apparatus. An autmatic temperature cntrller was prvided t precisely cntrl the reactr temperature. A ntebk cmputer recrded changes in temperature and weight as functins f heating time f the il and drying time f the cal. The il was preheated t a stable temperature f C,. Results and discussin. Drying curves The drying prcess f a general slid can be divided int three perids, namely, a preheating perid, a cnstant-rate drying perid and a falling-rate drying perid. In the brief preheating perid, the slid initially warms and the misture cntent slwly decreases. In the subsequent cnstant-rate drying perid, the evapratin rate at the surface f the slid is equal t the internal diffusin rate, and there is an abrupt, linear decrease in misture cntent. Lastly in the falling-rate drying perid, the evapratin rate at the surface increases while the internal diffusin rate diminishes, and thus misture cntent decreases slwly until a minimum is reached. This scenari will vary accrding t the shape f the slid and cnditins f the heated gas such as temperature and humidity. A drawback in the use f heated gas fr slid drying is the length f time required fr bth the cnstant-rate drying perid and the falling-rate drying perid. T slve this prblem, in this study we have investigated the drying characteristics f an alternative prcess that utilizes biling heat transfer. The cal drying curve in Fig. shws that mst f the misture evaprated within abut 5 minutes at an il temperature f C, much mre rapidly than ccurs using heated gas drying methds. Further, there was a stepwise reductin r irregularity in weight indicating rapid misture evapratin t its final level. This ccurred because misture was biled ff

3 T.-I. Ohm et al. / Jurnal f Mechanical Science and Technlgy () () 99~ Table. BET results f raw and upgraded LRC prepared using B-C il r refined waste il. Weight (%) raw-cal B-C il drying Refined-il drying Temp : C / min Gas : N Temperature ( C) Fig.. TGA curves f raw and upgraded Indnesian lignite in N (Heating rate C /min). Parameter BET surface area (m /g) Micrpre area (m /g) (. nm- nm) Micrpre vlume (cm /g) (. nm- nm) Average pre width (Å) Raw LRC Upgraded LRC dried in B-C il Upgraded LRC dried in refined waste il Weight (%) raw-cal B-C il drying Refined-il drying Temp : C / min Gas : air Misture(%) mm -mm Temperature ( C) B-C Oil Temperature( C) Fig.. TGA curves f raw and upgraded Indnesian lignite in Air (Heating rate C /min). at the same time that high temperature and vapur pressure in the cal led t hardening and carbnizatin [-].. Results f TGA analyses Cals - mm in diameter, befre and after drying in B-C il at C, were TGA-analyzed in nitrgen r in air at a heating rate f C /min. The results are shwn in Figs. and. Undried cal lst mass in either nitrgen r air bth befre reaching a temperature f C and after, as misture phasechanged t vapur. In cntrast, cal first subjected t the drying prcess lst mass gradually ver a temperature range f -5 C. This was apparently caused by decmpsitin f rganic material present in the cal. The reductin f mass in cal dried in B-C il tk place at slightly higher temperatures than with cal dried by refined il, due t the characteristically high viscsity and high density f B-C heavy il.. Results f BET analysis The physical structure f cal particles is an imprtant factr in mst reactins because it influences the rates f heat and mass transfer as well as the reactin surface area. BET analysis based n an absrptin methd in nitrgen was perfrmed Misture(%) using MICROMERITICS ASAP System, and the results are shwn in Table. This analysis indicated that misture ccupying fine pres was replaced by il after the drying prcess, and that pre diameter, surface area and vlume were all reduced.. Effectiveness f fry-drying Refined Oil Temperature( C) -mm -mm Fig. 5. Misture Cntents f Upgraded Cal Dried in B-C Oil (upper panel) r in Refined Oil (lwer panel). The cal cntained 7-% misture befre the drying prcess; misture cntents determined after the fry-drying prcess are shwn in Fig. 5. Misture cntent was reduced t

4 T.-I. Ohm et al. / Jurnal f Mechanical Science and Technlgy () () 99~.5 -mm -mm Oil Lss rate l(%).5.5 Oil Absrptin Amunt (g) -mm -mm B-C Oil Temperature( C ) B-C Oil Temperature( C).5 -mm -mm Oil Lss rate l(%).5.5 Fig.. Oil Cnsumptin Rates fr Upgrading Prcess Carried Out in B-C Oil (upper panel) r in Refined Oil (lwer panel). Oil Absrptin Amunt (g) Refined Oil Temperature( C) -mm -mm Fig. 7. Amunt f Oil Absrbed by Cal Upgraded in B-C Oil (upper panel) and in Refined Oil (lwer panel)..-9% after drying with B-C il, and -7% when dried with refined il. The effectiveness f fry-drying was greater at higher il temperature and with smaller cal size..5 Oil cnsumptin Fig. shws the amunt f il cnsumed during the drying prcess, expressed as percentage f the ttal amunt used. Oil cnsumptin was similar regardless f cal size, and increased slightly with drying temperature. This was due t increased vlatilizatin f il during the high-temperature drying prcess. Oil cnsumptin was smewhat greater fr - mm cals dried with B-C heavy il. It is shwn in sectin. that this was due t absrptin. Oil Seperatin rate (%).5.5 -mm -mm. Oil absrptin by cal In the drying prcess using high viscsity B-C heavy il, il absrptin became mre significant as cal size decreased (Fig. 7). This was due t absrptin f the viscus il in the pres f the smaller particles, which n a relative basis have a wider surface area. Cal size had less influence n the absrptin f refined il, which was mre readily recvered frm the smaller cal by centrifugal separatin..7 Oil recvery rate and net il cnsumptin Oil was recvered frm dried cal by centrifugal separatin Net Oil Lss rate (%).5.5 -mm -mm Fig.. Oil Recvery Rates (upper panel) and Net Rates f Cnsumptin (lwer panel) fr Centrifugal Separatin f Refined Oil.

5 T.-I. Ohm et al. / Jurnal f Mechanical Science and Technlgy () () 99~ fr minutes. B-C heavy il culd nt be recvered due t its high viscsity. Rates f refined il recvery and net cnsumptin are shwn in Fig.. The rate f recvery was independent f bth drying temperature and cal size. Net il cnsumptin increased with drying temperature, regardless f the cal size.. Misture re-absrptin after fry-drying In rder t mnitr misture re-absrptin, dried cal was stred at -5 and 7-75% humidity, and misture cntent was measured every hurs. Misture was cntinuusly reabsrbed, reaching a misture cntent f % after days..9 Summary f test results ) Drying il: B-C heavy il misture cntent:.-.% (, min) il cnsumptin:.-.5% (.-. g) il absrptin: 7- g (per sample f 5 g) misture re-absrptin ver days:.5% (misture cntent) ) Drying il: refined waste il misture cntent:.-.% (, min) il cnsumptin:.5-.7% (.5-. g) il cnsumptin taking int accunt il remval:.-.5% (.9-. g) il absrptin: -7.5 g (per sample f 5 g) misture re-absrptin ver days:.% (misture cntent). Cnclusin We have develped a new, rapid methd fr the upgrading f LRC. Drying tests were perfrmed n Indnesian lignite (misture cntent %, high heating value, kcal/kg) using immersin in either refined il r B-C heavy il that had been heated t a temperature f C, C r C. Using this fry-drying prcess, it was pssible t btain upgraded cal with a misture cntent f % r less and a high heat value f apprximately, kcal/kg. () 9-9. [] X. Renfu et al., Effects f chemicals and blending petrleum cke n the prperties f lw-rank Indnesian cal water mixtures, Fuel Prcessing Technlgy, 9 () 9-5. [] Y. Nugrh and A. McIntsh, Lw-temperature xidatin f single and blended cals, Fuel, 79 () [] A. Küçük and Y. Kadiglu, A study f spntaneus cmbustin characteristics f a Turkish lignite; particle size, misture f cal, humidity f air, Cmbustin and Flame, () 55-. [5] W. Snata and D. Zhang, Lw- temperature xidatin f cal studied using wire-mesh reactrs with bth steady-state and transient methds, Cmbustin and Flame, 7 (999) -5. [] T. Sugita et al., UBC (Upgraded Brwn Cal) prcess develpment, in, Kbe Steel Engineering Reprts () 5. [7] H. Katalambula et al., Lw-grade cals, A Review f Sme Prspective Upgrading Technlgies, Energy & Fuels, (9) 9-5. [] M. Mrimt et al., Hydrthermal extractin and hydrthermal gasificatin prcess fr brwn cal cnversin, Fuel, 7 () [9] S. J. Lee, H. Y. Shin, I. K. Bae and S. C. Chae, Reprt n upgrading technlgy fr lw-rank cal, Jurnal f the Krean Sciety fr Gesystem Engineering, 5 () 7-. [] T. I. Ohm, J. S. Chae, J. E. Kim, H. K. Kim and S. H. Mn, A study n the dewatering f the industrial waste sludges by fry-drying technlgy, Jurnal f hazardus materials, (9) 5-5. [] T. I. Ohm, J. S. Chae, H. K. Kim, K. S. Lim, M. J. Kim and S. H. Mn, An experimental study n the drying characteristics f the sludge in the EDIHO using drying curve, Jurnal f Krea Sciety f Waste Management, (9) -. [] T. I. Ohm, J. S. Chae, K. S. Lim and S. H. Mn, The evaprative drying f sludge by immersin in ht il: Effects f il type and temperature, Jurnal f hazardus materials, 7 () -. [] M. S. Shin, H. S. Kim, D. S. Jang and T. I. Ohm, Nvel fry-drying methd fr the treatment f sewage sludge, Jurnal f Material Cycles and Waste Management, (). Acknwledgement This wrk was supprted by the New & Renewable Energy Technlgy Develpment Prgram f the Krea Institute f Energy Technlgy Evaluatin and Planning (KETEP) grant funded by the Krea Ministry f Knwledge Ecnmy (N. KETEP : ). References [] M. Sakaguchi et al., Hydrthermal upgrading f Ly Yang Brwn Cal - Effect f upgrading cnditins n the characteristics f the prducts, Fuel Prcessing Technlgy, 9 Tae-In Ohm received his B.S. degree in Mechanical Engineering frm the In Ha University at Inchen, Krea, in 9, and his Ph.D in 99. Currently he is a prfessr f Envirnmental Engineering at Hanbat Natinal University at Daejen, Krea. His main research field is incineratin f wastes and waste derived fuels. Recently he has launched new research tpic fr recycling f waste vapr by cmpressin with ultra speed impeller cmpressr.