PRESSURE BALANCE OF A MULTIPLE-LOOP CHEMICAL REACTOR

Transcription

1 Refereed Proceeding The 13th International Conference on Fluidization - New Paradigm in Fluidization Engineering Engineering Conference International Year 010 PRESSURE BALANCE OF A MULTIPLE-LOOP CHEMICAL REACTOR Trevor D. Hadley Ken Chiang Nick R. Burke Kok-Seng Lim CSIRO Proce Science and Engineering, trevor.hadley@ciro.au CSIRO Proce Science and Engineering CSIRO Proce Science and Engineering CSIRO Proce Science and Engineering Thi paper i poted at ECI Digital Archive. xiii/64

2 Hadley et al.: PRESSURE BALANCE OF A MULTIPLE-LOOP CHEMICAL REACTOR ABSTRACT PRESSURE BALANCE OF A MULTIPLE-LOOP CHEMICAL REACTOR Trevor D. Hadley 1., Ken Chiang., Nick R. Burke., Kok-Seng Lim CSIRO Proce Science and Engineering. CSIRO Petroleum Bayview Avenue, Clayton, VIC 3168, Autralia For a chemical looping (CL) proce it i important to determine the optimum reactor configuration that would offer good preure balance to enure mooth tranfer of the olid between the reactor loop a well a atifying the oxygen carrier and heat requirement. A variation of the CL proce for production of enriched hydrogen tream i invetigated which adopt multiple reactor loop. A preure balance model i developed and a methodology i propoed to find a feaible reactor configuration at an indutrial cale production of hydrogen. INTRODUCTION Chemical looping (CL) i reported a a promiing technology for foil fuel combution becaue of it ability to produce a more concentrated carbon dioxide tream, enabling eaier capture and equetration. In uch a ytem a metal oxide i ued to oxidie the fuel intead of air. The reduced metal i then oxidied in a eparate chamber and returned back to the combution chamber. In thi way the air and fuel do not make direct contact with each other and the reulting CO and H O are kept eparate from the N and remaining O. The advantage of thi arrangement i that the CO i inherently eparated from the N thereby reducing the cot of eparation prior to equetration. Reearcher (1-3) have invetigated CL combution a an alternative mean of preparing a CO equetration-ready tream. Of thee, ome have invetigated the combution of natural ga (CH 4 ) (4,5) while other have conidered the combution of ynga (CO and H ) (6,7) and coal (with a NiO baed oxygen carrier) (8). Mot of thee have conidered uing two connected fluidized bed, however Noorman et al (5) have conidered utiliing two dynamically operated packed bed. CL can alo be utilied for gaification and ha been invetigated, amongt other, a a mean for gaifying coal (6,7) uing Fe/FeO or CaO. Additionally, CL ha been invetigated a a mean of producing hydrogen uing team (9,10). A hot of metal can be utilied a the oxygen carrier. However, tranition metal oxide uch a nickel, copper, cobal, iron and manganee are good candidate given their favourable reductive/oxidative thermodynamic propertie. Hoain and de Laa (11) preented a thorough review of CL combution, including conideration of the choice of oxygen carrier, and compared thee to current CO capture technique. Publihed by ECI Digital Archive, 010 1

3 The 13th International Conference on Fluidization - New Paradigm in Fluidization Engineering, Art. 64 [010] Thi paper invetigate not only the ma and energy balance requirement of the CL proce, but alo the preure balance in order to find a likely reactor geometry which will atify the many requirement including converion and olid flux. MODEL OF PRESSURE DROP One of the key factor that affect the performance of the CL proce i in achieving a good balance between olid recirculation rate required for the reaction a well a heat tranfer. From the reactor deign and operational conideration, it i important to determine the optimum reactor configuration that would offer good preure balance to enure mooth tranfer of the olid between the reactor loop a well a atifying the oxygen carrier and heat requirement. The preure balance in turn i affected by variable uch a the phyical propertie of the olid and ga, fluid velocity, olid recirculation rate and well a the geometry of the ytem. Variou methodologie have been reported to etimate the preure drop through part of a circulating fluidized bed (1,13). A one-dimenional model i ued in thi paper, a ued by Lim et al (14). The chemical looping reactor (CLR) i divided into three main ection being the rier, downcomer and bubbling fluidized bed. The key preure lo equation are ummaried in Table 1. Table 1. Key preure lo equation (14). Region Factor Equation Ref Rier Static dp / dz = ρ (1 ε g ; (15) Rier bae Rier Rier Acceleration Ga friction Solid friction tatic ) * ( ε ε ) /( ε ε ) = exp P d accel = G fg / ρ g g g dp / dz = f ρ U / D f (( z z ) / Z ) t dp / dz = f ρ (1 ε ) U / D Rier Exit bend P = f ρ 1 ε ) U where f = bend bend p ( g Cyclone P = ρ.03u {1 + φ ( r / r ) i t o bend [ 1 } ] / U cyc g 1 t e + Downcomer Static Pdown = ρ ( 1 ε mf ) gh, at U (19) mf Solid valve P = ( G A ) /( C A ) ρ (1 ε ) (13) Bubbling bed Static valve t Do o mf (16) (1) (1) (17) (18) P = ρ ( 1 ε gh (0) bubb ) HYDROGEN PRODUCTION VIA CHEMICAL LOOPING Relatively pure hydrogen can be formed from a natural ga tream uing chemical looping. The propoed arrangement i hown in Figure 1a. In thi arrangement team i reduced to form hydrogen in the Steam Reactor while natural ga i combuted in the Fuel Reactor to form CO and water vapour. In term of the circulating oxygen carrier, the Steam Reactor i often referred to a the oxidier while the Fuel Reactor i referred to a the reducer. The heat of reaction are a follow: 3FeO + H O Fe O + H H rxn (700 C) = -45 kj/mol Fe 3 O 4 (1) Fe3O4 CO + H O + CH + 1FeO H rxn (750 C) = 9 kj/mol Fe 3 O 4 ()

4 Hadley et al.: PRESSURE BALANCE OF A MULTIPLE-LOOP CHEMICAL REACTOR For thi invetigation natural ga (eentially CH 4 ) ha been choen a the fuel while iron oxide ha been choen a a likely oxygen carrier. In the Steam Reactor hydrogen i formed from team via the oxidation of FeO to Fe 3 O 4. The Fe 3 O 4 i reduced back to FeO in the Fuel Reactor in order to upply the oxygen required for the combution of the natural ga. While the reaction in the Steam Reactor i exothermic, the reaction in the Fuel Reactor i endothermic and the heat requirement in the Fuel Reactor cannot be fulfilled by any heat from the Steam Reactor, except if the hot hydrogen tream were ued to preheat the feed natural ga tream. Even if the natural ga were preheated to 50 C there would be a heat deficit. Therefore a third loop ha been propoed where a portion of the olid are heated to 900 C via oxidation of the reduced metal with air and the combution of fuel (if required). The olid return to the Fuel Reactor at an elevated temperature and therefore upply enible heat to the Fuel Reactor a hown in Figure 1b. (a) (b) Figure 1. Schematic repreentation of the CL team-iron proce (a) two loop, (b) multiple loop MASS AND ENERGY BALANCES The main aumption are contained in Table. Furthermore, the oxygen carrier wa aumed to have a particle diameter of 160 µm. The aociated minimum fluidization velocity (U mf ) wa predicted uing the approach of Wen and Yu (18) and determined a 19 mm/ temperature between 700 and 1000 C. An oxygen carrier of the form (Fe O 3 ) x (CeO ) y (ZrO ) z ha been choen (x = 0.0, y = 0.13, z = 0.67). Table. Some of the key aumption for the propoed CL proce. Steam Reactor Fuel Reactor Air Reactor Reactor type Rier Bubbling Bed Rier Temperature 700 C 750 C C Reaction 3FeO + H O Fe 3O 4 + H CH 4 + 4Fe 3O 4 CO + H O + 1FeO 6FeO + O Fe 3O 4 CH 4 + O CO + H O Converion 100% FeO to Fe 3O 4 100% Fe 3O 4 to FeO 100% FeO to Fe 3O 4 Exce 10% CH 4 8% O Fuel preheat CH 4 to 50 C CH 4 to 50 C Heat lo 10% 10% 10% CASE STUDY A methodology to evaluate the propoed CL team-iron proce and determine the likely reactor geometry i ummaried in Figure. A hydrogen production rate of 49,000 Nm 3 /h ha been choen baed on an exiting indutrial cale reformer (1). Publihed by ECI Digital Archive, 010 3

5 The 13th International Conference on Fluidization - New Paradigm in Fluidization Engineering, Art. 64 [010] Ma and Energy Balance The Steam Reactor generate light exce heat. However adiabatic condition can be achieved by cooling the returning olid tream from the Fuel Reactor from 750 C to 685 C. A predicted, the Fuel Reactor ha a heat deficit which need to be upplied via the enible heat available in hotter olid from the Air Reactor. The additional oxidied metal fed to the Fuel Reactor (from the Air Reactor) alo need to be reduced uing CH 4. The temperature of the returning olid (from the Air Reactor) trongly effect the overall CH 4 requirement, a hown in Figure 3 with le CH 4 required at higher temperature. Figure. Propoed methodology for determining a multiple-loop chemical reactor configuration. Below 1050 C the Air Reactor heat can be upplied entirely via the air oxidation of FeO. However, above thi temperature additional heat i required via the combution of CH 4. While thi doe increae the overall CH 4 requirement, it effect i minimal in the C range. However, com buting CH 4 in the Air Reactor i undeirable a it produce CO which will be in a dilute form together with the nitrogen and unreacted oxygen. The optimum temperature for thi particular arrangement i 1050 C, however a lightly more con ervative temperature of 1000 C wa adopted in thi tudy and hence the Air Reactor ha a light exce of heat. Thi i balanced by cooling the entering olid tream from the Fuel Reactor to 705 C (from 750 C) before it enter the Air Reactor. 4

6 Hadley et al.: PRESSURE BALANCE OF A MULTIPLE-LOOP CHEMICAL REACTOR Figure 3. Fuel uage a a function of the temperature in the Air Reactor. In comparion to a typical indutrial hydrogen reformer, the current CL proce configuration require more fuel with a minimum of 0.6 Nm 3 of CH 4 required per Nm 3 of H produced (compared to 0.38 ()). Becaue CL i conidered an alternative to other method of concentrating the CO tream and making it equetration-ready, thi additional cot hould be compared to the cot incurred in procee uch a ammonia crubbing. Preure Balance Baed on the cyclone geometry, the rier and bed diameter, initial etimate of the rier and bed height a well a the relative height and poition of the reactor, downcomer and loop eal, an initial preure balance can be determined acro the entire ytem uing the aumption in Table 1. The high olid flux through the Steam Reactor reulted in a high preure drop acro the rier. The taller the rier i, the more difficult it become to deign the ytem uch that the preure at the bottom of the Fuel Reactor i till ufficiently above the preure at the entrance to the team rier. The height wa et in order to achieve a olid reidence time of more than a minute. The reulting rier preure drop wa too high and wa olved by increaing the amount of exce team ued for the oxidation of the FeO. Thi exce team would need to be condened from the hydrogen produced and then recycled back to the Steam Reactor. The reultant ma balance i given in Figure 4. Finally, in order to complete the preure balance, the freeboard of the Fuel Reactor need to be operated at 1.1 bar (gauge) and the downcomer need to be operated with more than 50% of the height occupied by the dene phae. The preure balance i hown in Figure 5. However, the current preure balance give no conideration to the olid refluxing effect at the exit of the rier, or to the preure change at the entry to the rier from the loop eal. Publihed by ECI Digital Archive, 010 5

7 The 13th International Conference on Fluidization - New Paradigm in Fluidization Engineering, Art. 64 [010] Solid FeO 19% 19% Fe 3 O 4 1% 1% CeO 13% 13% 13% 13% ZrO 67% 66% 67% 66% Ga O 3% % N 77% 98% H O 100% 8% 44% H 18% CH 4 100% % CO 54% Figure 4. Poible chematic of CL arrangement, and ma balance ued for hydrogen production. Flow are in ton per hour and compoition in ma percentage. Figure 5. Preure balance obtained over the CL ytem. The ga flow rate influence the cyclone dimenion leading to height of 1.6 and 5.3 m (baed on tandard cyclone deign technique) for the team and Air Reactor repectively and hence determining the minimum height for the two rier and downcomer. The final deign i preented in Table 3. CONCLUSIONS A reactor deign methodology ha been propoed for a multiple-loop chemical reactor. The methodology take into account the ma and energy and the preure balance of the overall ytem. Thi approach ha then been applied to examine a 6

8 Hadley et al.: PRESSURE BALANCE OF A MULTIPLE-LOOP CHEMICAL REACTOR poible reactor configuration for the production of hydrogen from natural ga while imultaneouly producing a concentrated CO tream that can be equetrationready. The methodology ha hown that a feaible deign can be obtained for the team-iron proce. However, there are cot penaltie involved cooling of the olid tream to the Steam and Air Reactor; increaed methane uage for an equivalent hydrogen production when compared with an etablihed hydrogen reformer; and an increaed team uage which neceitate recondening and recycling. For true cot benefit analyi, thee additional cot hould be compared to the additional cot incurred in alternative CO concentration and capture technique. Table 3. Likely reactor configuration for CL team-iron hydrogen production. Steam Down- Fuel Air Down- Unit Rier comer Reactor Rier comer Ga flow entering Nm 3 /h exiting Nm 3 /h Superficial ga velocity m/ G entering kg/m. exiting kg/m. Internal diameter m Temperature C Preure bottom kpa,g Height top kpa,g Total internal m Ga exit m Downcomer (not including cyclone) m Bubbling bed /loop eal m Height relative to datum Bottom m Loop eal entrance to rier m Solid voidage (ε) NOTATION A cro-ectional area m C D dicharge coefficient - D t rier diameter m f friction factor - g gravitational contant m/ G olid flux kg/m. h bed height m P preure Pa Greek ρ particle denity kg/m 3 ε voidage fraction - r e radiu of exit pipe m r t radiu of circle to which centre line i tangential m U uperficial velocity m/ z height in rier m z i location of point of inflection m Z o characteritic length m ø factor ued in calculation - Subcript * aymptotic lean phae 1 inlet duct exit duct d dene phae f friction g mf t o ga minimum fluidization veel emptying out to opening/orifice Publihed by ECI Digital Archive, 010 7

9 The 13th International Conference on Fluidization - New Paradigm in Fluidization Engineering, Art. 64 [010] REFERENCES 1. P. Cho, T. Mattion, A. Lyngfelt, Comparion of iron-, nickel-, copper- and manganeebaed oxygen carrier for chemical-looping combution, Fuel, 83 9 (004) F. He, H. Wang, Y. Dai, Application of FeO3/AlO3 Compoite Particle a Oxygen Carrier of Chemical Looping Combution, Journal of Natural Ga Chemitry, 16 (007) A. Lyngfelt, B. Leckner, T. Mattion, A fluidized-bed combution proce with inherent CO eparation; application of chemical-looping combution, Chemical Engineering Science, (001) A. Abad, T. Mattion, A. Lyngfelt, M. Johanon, The ue of iron oxide a oxygen carrier in a chemical-looping reactor, Fuel, (007) S. Noorman, M. van Sint Annaland, H. Kuiper, Packed Bed Reactor Technology for Chemical-Looping Combution, Indutrial & Engineering Chemitry Reearch, 46 1 (007) L. Fan, F. Li, S. Ramkumar, Utilization of chemical looping trategy in coal gaification procee, Particuology, 6 3 (008) F.X. Li, L.S. Fan, Clean Coal Converion Procee - Progre and Challenge, Energy & Environmental Science, 1 (008) L. Shen, J. Wu, J. Xiao, Experiment on chemical looping combution of coal with a NiO baed oxygen carrier, Combution and Flame, (009) M.F. Bleeker, S.R.A. Kerten, H.J. Veringa, Pure hydrogen from pyrolyi oil uing the team-iron proce, Catalyi Today, (007) E. Lorente, J.A. Peña, J. Herguido, Kinetic tudy of the redox proce for eparating and toring hydrogen: Oxidation tage and ageing of olid, International Journal of Hydrogen Energy, 33 (008) M. Hoain, H.I. de Laa, Chemical-looping combution (CLC) for inherent CO eparation - a review, Chemical Engineering Science, (008) R.W. Breault, V.K. Mathur, High-Velocity Fluidized-Bed Hydrodynamic Modeling.. Circulating Bed Preure-Drop Modeling, Indutrial & Engineering Chemitry Reearch, 8 6 (1989) M. Horio, Hydrodynamic, In: Circulating Fluidized Bed, (Ed. J.R. Grace, A.A. Avidan and T.M. Knowlton), Springer, New York, (1996). 14. K.S. Lim, P. Peeler, R. Cloe, T. Joyce, Etimation of Solid Circulation Rate in CFB From Preure Loop Profile, 6th International Conference on Circulating Fluidized Bed. Frankfurt, Germany (1999) Y. Li, M. Kwauk, The Dynamic of Fat Fluidization, In: Fluidization, (Ed. J.R. Grace and J.M. Maten), Plenum Pre, New York, (1980). 16. H.T. Bi, J.X. Zhu, Static Intability Analyi of Circulating Fluidized-Bed and Concept of High-Denity Rier, AICHE Journal, 39 8 (1993) C.E. Cape, K. Nakamura, Vertical Pneumatic Conveying - Experimental Study With Particle in Intermediate and Turbulent-Flow Regime, Canadian Journal of Chemical Engineering, 51 1 (1973) D. Kunii, O. Levenpiel, Fluidization Engineering, Butterworth-Heinemann, Boton, (1991). 19. R.K. Sinnott, Chemical Engineering Deign, 4th ed., Elevier Butterworth-Heinemann, New York, (005). 0. D.R.M. Jone, J.F. Davidon, The flow of particle from a fluidied bed through an orifice, Rheologica Acta, 4 3 (1965) C.Y. Wen, Y.H. Yu, A Generalized Method for Predicting Minimum Fluidization Velocity, AICHE Journal, 1 3 (1966) H. Olon, P. Rudbeck, K.H. Anderen, Adding Hydrogen Production Capacity by Heat Exchange Reforming, XIV Refinery Technology Meet (RTM). Kovalam, Trivandrum, India (007). 8

10 Hadley et al.: PRESSURE BALANCE OF A MULTIPLE-LOOP CHEMICAL REACTOR Keyword: Chemical looping; Multiple-loop reactor; Hydrogen production; Preure balance; Circulating fluidized bed Publihed by ECI Digital Archive, 010 9