Reaction Characteristics of CaSO 4 / CaSO 4 1/2H 2 O Reversible Reaction for Chemical Heat Pump

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1 oi:.252/jcej.7we22; release online on October, October, 27, Kyoto, Japan IMPRES Paper ID: A9 Reaction Caracteristics of CaSO / CaSO /2H 2 O Reversible Reaction for Cemical Heat Pump Hironao OGURA *, Masairo HAGURO, Yasuiro SHIBATA, Yasufumi OTSUBO Division of Arcitecture an Urban Science, Grauate Scool of Engineering, Ciba University -, Yayoi-co, Inage, Ciba JAPAN iro_ogura@faculty.ciba-u.jp, Pone: , Fax: Keywors: Cemical Heat Storage, Reactant, termogravimetry, Waste energy utilization, Energy saving Abstract We a propose cemical eat pumps using a reversible calcium sulpate/water reaction system for effective waste energy utilization. However, more reaction kinetics stuies are necessary for tis reaction system, especially for ifferent atmospere conition an ifferent materials. As a result, te reaction equilibrium line of CaSO in te close system like CHP system was foun to be close to tat in te open system. It means tat te CHP using CaSO / CaSO /2H 2 O reversible reaction stores uner 7K level termal energy, an releases te same level ot eat an 27K level col eat. Furtermore, te effects of material size on te reaction rates coul be calculate by te propose equations, wic enable te effective CHP reactor esign. Introuction From te viewpoints of energy savings an environmental impacts, we ave been stuying on cemical eat pumps (CHPs. We a propose an evelope CHPs using a reversible calcium oxie/water reaction system for effective termal energy utilization in omestic use (Ogura et. al., 99 an inustrial use suc as electric power use (998 or rying (2. Furtermore, for lower temperature eat source, we a propose CHPs using a reversible calcium sulpate/water reaction system for effective waste energy utilization (2. Calcium sulpate as possibility of storing uner 7K level termal energy an releasing te same level ot eat an 27K level col eat. Also Calcium sulpate is easy to get, inexpensive an safe. However, more reaction kinetics stuies are necessary for tis reaction system, especially in a close system like CHP system for ifferent materials. Altoug te reaction kinetics of CaSO as been one by some researcers (Baens, et. al., 998, Huson, et. al., 996, Stryom, et. al., 995, tose were one in an open system. In tis stuy, we examine te reaction equilibrium lines of te yration of calcium sulpate an te eyration of calcium sulpate emiyrate for ifferent kins of material in an open system, a semiclose system an in a close system by consiering te eat pump operations. Semi-close system is assume to be a close system wit force convection suc as a fan unit for mass transfer AC(s + Q H A (s +C (g H Hig Temperature A (s+c (g AC(s + Q H C (g C (g B (s +C(g BC(s + Q L L Low Tem perature ( ( [ Heat Storing Step ] H Hig Temperature si e Reactor BC(s+ Q L B (s +C (g L Low Tem perature ( ( [ Heat Releasing Step ] Figure Operating principle of cemical eat pump enancement. Tese ifferent kins of conition are necessary to consier te CHP conitions. We use an improve termogravimetry for te vacuume conition experiments. Furtermore, te effects of material size on te reaction rates of te yration of calcium sulpate /te eyration of calcium sulpate emiyrate are examine in an open system.

2 oi:.252/jcej.7we22; release online on October, October, 27, Kyoto, Japan Operating Principle of CHP Figure sows a typical gas-soli CHP configuration. Te CHP is a close system of couple low an ig temperature reactors connecte to eac oter. Te eat storage an release reactions occur at ifferent pressure levels. Te low temperature sie reactor as a iger reaction equilibrium pressure line. Te CHP, as stuie earlier, operates as a batc system wit a eat storing step an a eat releasing step. In te eat storing step, te eat Q H is store in te form of termocemical energy by ecomposition of te reactant AC(s in te ig temperature sie reactor. Te release gas C(g flows into te low temperature sie reactor ue to a pressure ifference between te two reactors. Te gas C(g reacts wit te reactant B(s releasing low temperature eat Q L. As long as te reactant A(s is separate from te gas C(g, te reaction eat can be store for any lengt of time in te form of cemical energy. In te eat releasing step, te gas C(g flows from te low temperature sie reactor to te ig temperature sie reactor by opening a valve ue to te pressure ifference between te reactors. Te exotermic reaction of te reactant A(s at a ig temperature level wit te gas C(g takes place in te ig temperature sie reactor. Te low temperature sie reactor stores te low temperature eat Q L or is coole own an release col eat by its ecomposition/evaporation eat.. Experiments -. Experimental unit Figure 2 sows an example of te experimental unit. Tis figure sows te open system unit. A termogravimetry (SHIMADZU TGA-5H is connecte wit an evaporator/conenser controlle by a temperature control bat. For te open system experiments, te evaporate water vapor is introuce to te termogravimetry by N 2 gas flow. For te semi-close system experiments, it is a force convection type. Te water is evaporate an introuce to te termogravimetry by vacuuming from te termogravimetry sie. For te close system experiments, te termogravimetry an te evaporator/conenser are connecte in a vacuume an close conition. In every system, water vapor is introuce to te termogravimetry via te port close to te reactant instea of te rear port. It means te water vapor flow to balance part of te termogravimetry is reuce. -2. Working materials Termogravimetry SHIMADZU TGA-5H Evaporator/Conenser Temperature control bat Flow meter N 2 tank Work station (SHIMADZU TA-6WS Personal Computer Sample H 2O Figure 2 Experimental unit for open system For te experiments, te calcium sulpate emiyrate : CaSO /2H 2 O (Wako, mean iameter: µm an te cemical gypsym : CaSO 2H 2 O (Wako, mean iameter: µm were use as cemical materials. Also, te natural gypsums CaSO 2H 2 O (Prouce in Australia, mean iameter: m uner, -5m an 5-m were use as start materials. -. Experimental proceure For te termogravimetry experiments, mg of te CaSO /2H 2 O an natural gypsum are installe in te cell of te termogravimetry. For te open system experiments, te evaporate water vapor is introuce to te termogravimetry by N 2 gas flow (ml/min. For te semi-close system experiments, te water is evaporate an introuce to te termogravimetry by vacuuming from te termogravimetry sie. For te close system experiments, te reactor an te evaporator/conenser are vacuume to te appropriate pressures. Te reactor is eate up wit 5 - K/min an kept at constant temperature for minutes. Te joint valve connecting te reactor an te evaporator/conenser is opene, an CaSO /2H 2 O is eyrate in tis eating-up stage as a eat-storing step. After tat, te yration reaction of CaSO occurs as a eat-releasing step wit te reactor temperature cooling own wit 5 - K/min. Te yration an te eyration operations were repeate. Te reaction conversion canges an te reaction eat were calculate from te weigt canges of te reactants. Tis reaction occurs between β- CaSO /2H 2 O an γ- CaSO in our experimental temperature range (Baens, et. al.,

3 oi:.252/jcej.7we22; release online on October, October, 27, Kyoto, Japan 2. Results an Discussion 2-. Reaction equilibrium Figure sows te reaction equilibrium line of CaSO / CaSO /2H 2 O reversible reaction obtaine by te (Lee, et. al., 986 an te reaction equilibrium plots by our experimental ata in ifferent systems. All of te ata reprouce well te equilibrium line. However, for te same reaction pressure, te open system ata nees sligtly iger temperature tan te oters. It is probably because tat te water vapor reacts wit CaSO effectively in te semi-open an close system. From tese results, it can be seen tat te CHP using CaSO / CaSO /2H 2 O reversible reaction stores uner 7K level termal energy, an releases te same level ot eat an 27K level col eat. Figure sows te CaSO / CaSO /2H 2 O reaction equilibrium line of four kins of natural materials in a open-system. Te natural gypsum soul be more eco-frienly an more flexible in size tan cemical gypsum. All of te four kins of our experimental ata reprouce well te equilibrium line (Lee, et. al., 986. Te large mean iameter material reacts at iger temperature tan te small iameter material. It can be seen from tese results tat te cemical an te natural material less tan m mean iameter can use te reaction equilibrium line altoug te reaction rates nee to be consiere in ifferent ways Reaction rate At tis stage, it is not easy to get many ata on reaction rate in te close system. So, we examine reaction rates in te open system especially focuse on te effects of te reactant iameter. In te similar reaction system using CaO/H 2 O reaction, it was foun tat te reaction rate in te open system is not so ifferent from tat of te semi-close system (Sokrat et. al., 25. We believe tat even te open system ata can be important ata for CHP reactor esign. Eqs. ( an (2 are equations (Lee, et. al., 986. (yration reaction ( X = k P t ( P = ( P Pe /{ PS ( P Pe } (eyration reaction ( X = k P t (2 P = ( Pe P /{ PS ( Pe P} In orer to use Eqs. ( an (2 for reaction rate calculation, we nee to prove tat our experiment ata follow te grain moel concept. Figures 5 an 6 lnp [-] lnp [-].. open system ( open system ( semi-close system ( semi-close system ( close system ( close system ( Calcium sulpate emiyrate (cemical, m /T [/K]... Figure Reaction equilibrium line of CaSO / CaSO /2H 2 O reaction natural gypsum 5µ( natural gypsum 5µ( cemical gypsum µ( cemical gypsum µ( natural gypsum µuner ( natural gypsum µuner ( natural gypsum 5µ natural gypsum 5µ( /T [/K] Figure Reaction equilibrium line of CaSO / CaSO /2H 2 O reaction for natural gypsums sow tat te F [ ( = X ] canges an te F [ ( = X ] canges for natural gypsums. Tese figure sow tat all materials ave almost linear relationsips between F/F an time. So, all natural materials can be tougt to follow te grain moel concept. However, te influence of material iameter is not consiere in Eqs. ( an (2. We propose Eqs. ( an ( tat inclue te influence of mean iameter of material. η, η are terms of te iameter effect. (yration reaction X = ( kη r ( P t ( 8 k = 5.76 exp( 5.6 / RT (eyration reaction X = ( kη r ( P t ( k = 6.96 exp(. / RT k an k are reaction rate constants of

4 oi:.252/jcej.7we22; release online on October, October, 27, Kyoto, Japan F [-] natural gypsum,5um natural gypsum,5um natural gypsum,um uner cemical gypsum,um T=7K Tw=29K Figure 5 F canges for natural gypsums k η r [ /min] /T [/K] Figure 7 k η r for natural gypsums natural gypsum,5um natural gypsum,5um natural gypsum,um uner cemical gypsum,um F [-] T=9K Tw=29K natural gypsum,5um natural gypsum,-5 um natural gypsum,um uner cemical gypsum,um k η r [/m in] natural gypsum,5um natural gypsum,5um natural gypsum,um uner cemical gypsum,um /T [/K] Figure 6 F canges for natural gypsums (Lee, et. al., 986. We revise k te to reprouce te calculate line to te experimental ata. Figures 7 an 8 sow te k η r, k η r ata calculate by F, F in Figures 5 an 6 in comparison wit line. Tese figure sow tat te larger mean iameter of material are te smaller k η r, k η r. Tis result is expecte to be cause by te eat an mass transfer existence (Sokrat et. al., 25. We assume tat te k η r, k η r are affecte mainly by te mean iameter of material. From Figures 7 an 8, we calculate te iameter effect α by Eq. (5 α = ln( kiη ln( k i ηr (5 By Eq. (5, we got η r for η =. ηr =.2 e. r (6 Figures 9 an are example of conversion canges for natural gypsums in yration an eyration reactions. It can be seen from tese figures tat all of te calculate lines by Eqs. (, (, (5 an (6 reprouce te experimental ata well. Te ifference between calculate ata an experimental ata in te mean iameter 5~m migt be cause by using average of yration η r an eyration η r wen we calculate η i. From tese results, we can simulate te reaction rates consiering te material size by te propose Eqs. ( an ( in CHP operations, an estimate te CHP power using CaSO / CaSO /2H 2 O reversible reaction. Conclusion Figure 8 k η r for natural gypsums Te reactivity of te yration of calcium sulpate an te eyration of calcium sulpate emiyrate were stuie by an improve termogravimetry. As a result, te reaction equilibrium line of CaSO in te close system like CHP system was

5 oi:.252/jcej.7we22; release online on October, October, 27, Kyoto, Japan X[-] natural 5-µm 7K 29K natural 5-µm 6K 28K natural -5µm 7K 29K natural -5um 6K 28K natural umuner 7K 29K cemical um 7K 29K cemical um 6K 28K Figure 9 Conversion canges for natural gypsums in yration reaction close to tat in te open system. It means te CaSO / CaSO /2H 2 O reversible reaction is consiere as one of te best caniates for low-temperature CHP reactant, tat stores uner 7K level termal energy an releases ot/col eat. Furtermore, te effects of material size on te reaction rates are calculate by our propose equations. So, te cemical eat pump power using ifferent size CaSO / CaSO /2H 2 O can be estimate by te propose equations, an it enables te effective CHP esign. Nomenclature F = ( X [-] i i k i = reaction rate constant [/min] P = imensionless partial pressure of water vapor [-] P e = reaction equilibrium pressure [-] P w = saturate vapor pressure [-] P = riving pressure term [-] T = temperature [K] T w = conenser an evaporater temperature [K] t = reaction time [min] X = conversation [-] η r = term of mean iameter influence [-] Subscript = eyration g = gas = yration i =, l = liqui r = mean iameter (, 25,, 75 s = soli Literature Cite Baens, E., P. Llewellyn, J. M. Fulconis, C. Jouran, S. Veesler, R. Boistelle an F. Rouquerol, Stuy of Gypsum Deyration X [-] natural um 7K 278K naturalum 9K 298K natural -5um 9K 288K natural umuner 9K 288K cemical um 8K 279K cemical um 9K 279K Figure Conversion canges for natural gypsums in eyration reaction by Controlle Transformation Rate Termal Analysis (CRTA, J. Soli State Cemistry, 9, 7- (998 Huson-Lamb, D. L., C. A. Stryom an J. H. Potgieter, Te termal eyration of natural gypsum an pure calcium sulpate eyrate (gypsum, Termocimica Acta, 282/28, 8-92 (996 Lee, S. K., H. Matsua an M. Hasatani, Funamental Stuies of CaSO (/2H 2 O/CaSO Termocemical Reaction Cycle for Termal Energy Storage by Means of Cemical Reaction, Kagaku Kogaku Ronbunsu,2, (986 Ogura, H., M. Kanamori., H. Matsua. an M. Hasatani.; Generation of Low-Temperature Heat by Use of CaO/H 2 O/Ca(OH 2 Reaction., Kagaku Kogaku Ronbunsu, 9, 9-96 (99 Ogura, H., S. Fujimoto, H. Iwamoto, H. Kage, Y. Matsuno, Y. Kanamaru an S. Awaya, Basic Performance of CaO/H 2 O/Ca(OH 2 Cemical Heat Pump Unit for nigt- Electric Heat-Storage an Col/Hot Heat-Recovering, Kagaku Kogaku Ronbunsu, 2, (998 Ogura, H. an A. S. Mujumar, Proposal for a novel Cemical Heat Pump Dryer, Drying Tecnology, 8, -5 (2 Ogura, H., H. Hamaguci, H. Kage an A. S. Mujumar, Energy an Cost Estimation for Application of Cemical Heat Pump Dryer to Inustrial Ceramics Drying, Drying Tecnology, 22, 7-2 (2 Stryom, C. A., D. L. Huson-Lamb, J. H. Potgieter an E. Dagg, Te termal eyration of syntetic gypsum, Termocimica Acta, 269/27, 6-68 (995 Sokrat, A., H. Ogura an H. Kage, Final Conversion an Reaction Rate of CaO Hyration in Different Experimental Systems, Kagaku Kogaku Ronbunsu,, (25 5