Designing and evaluating the technical, economic and environmental performance of an adsorption cooling system operating using bioresources from waste streams of mango processing

Dzigbor, Aaron (2019-12)

Thesis (PhD)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: This study sought to improve the technical performance (coefficient of performance (COP) and specific cooling power (SCP)), environmental impacts and economic viability of employing the adsorption working pairs produced from waste streams of mango processing in the adsorption cooling system (ACS). The specific objectives were: to produce and characterize mango seed husk activated carbon (AC) using NaCl as the activation agent and compared with commercial AC; assess the performance (in terms of COP and SCP) of the mango seed husk AC (with commercial AC as the control) paired with both high-grade and low-grade ethanol as refrigerants; improve the heat and mass transfer performance of commercial AC paired with both high-grade and low-grade ethanol as refrigerants through composite formation; and evaluate the environmental and economic impacts of integrating adsorption cooling system (ACS) in dried mango chips processing in both grid and off-grid power conditions. Mango seed husk AC was produced through slow pyrolysis method using NaCl as the activation agent. About 100 g of dried mango seed husk was soaked in 250 ml of NaCl solution of concentrations (10 w/v%, 20 w/v%, and 30 w/v%) to obtain impregnation ratios of 0.25, 0.5 and 0.75 at 25 °C. The carbonization temperatures were 400 °C, 450 °C, and 500 °C. The experimental design was based on a 33 (impregnation ration, soaking time, and carbonization time) Box-Behnken fractional factorial optimization method with three center runs, giving total runs of 15. The responses analyzed were bulk density, ash content, and surface area. The optimized mango seed husk AC produced was tested in an ACS constructed in-house and its performance compared with commercial AC. The composite AC were also formed by soaking commercial AC in NaCl solution at varying concentrations of 10 w/v %, 15 w/v %, 20 w/v %, 25 w/v %, 30 w/v % and 35.7 w/v %, for 24 hours at 25 °C, dried at 105 °C for 24 hours and then tested in ACS constructed in-house with high purity (99.7%) and low-grade (60%) ethanol to evaluate the effect of ethanol grade on the performance of the composite formed. Finally, three scenarios for each power setting (on-grid and off-grid) were studied, on-grid: coal as boiler fuel and conventional chiller for cooling (Scenario 1), mango seed as boiler fuel and adsorption chiller for cooling (Scenario 2) and mango seed as boiler fuel and ACS for cooling (Scenario 3). Off-grid scenarios 4, 5 and 6 corresponded to on-grid scenarios 1, 2 and 3, respectively. Environmental impacts and economic viability for each scenario were based on material and energy balances and South African economic conditions, respectively. The results showed that mango seed husk AC had comparable ash content (6.92%) to the commercial AC. The SCP, COP and temperature drop recorded in ACS for mango seed husk AC when paired with high purity (99.7%) ethanol reduced from 40 W/kg, 0.050 and 4.46 °C to 37.3 Wkg-1, 0.048, and 4.5 °C, respectively, when paired with low-grade ethanol (60%). Moreover, the COP and SCP of commercial AC paired with high purity ethanol were 0.099 and 84.5 Wkg-1, which reduced to 0.091 and 75.5 W/kg, respectively, when paired with low-grade ethanol. In addition, the COP of the composite AC containing 20%, 25% and 30% NaCl paired with low-grade ethanol were 0.121, 0.160 and 0.146, respectively, which were higher than when paired with high purity ethanol, thus 0.082, 0.080, and 0.076, respectively. In terms of environmental and economic impacts, on-grid scenario 3 showed the greatest potential for reducing emissions and improving economic viability by emitting 7.10×105 kgCO2eq/yr and internal rate of return (IRR) of 25.33% compared to scenario 1 that had the GHG emission of 7.89×105 kgCO2eq/yr and IRR of 17.48%. In off-grid, scenario 6 had the least GHG emission of 6.90×105 kgCO2eq/yr and IRR of 24.84%while scenarios 4 had the highest GHG emission of 7.67×105 kgCO2eq/yr and IRR of 16.09%. Overall, it is possible to improve the heat and mass transfer of activated carbon paired with low-grade ethanol. The improvement in heat and mass transfer when AC + NaCl was paired with low-grade ethanol suggests that low-grade ethanol can be used as an alternative refrigerant. However, in areas where silica gel is accessible, forming composite with silica gel + NaCl paired with pure water as refrigerant would eliminate the mass transfer challenges associated with using AC+NaCl composites paired with ethanol. Furthermore, the replacement of vapour compression cooling technology with ACS and boiler fuel with mango seed has led to the reduction in GHG emission and improvement in the economic viability of dried mango chip processing. Thus, the study has improved the technical, economic and environmental performance of ACS in terms of temperature maintenance, resource consumption, and emissions.

AFRIKAANSE OPSOMMING: Hierdie studie het beoog om die tegniese werkverrigting (koëffisiënt van werkverrigting (KVW) en spesifieke verkoelingskrag (SVK)), omgewingsimpak en ekonomiese lewensvatbaarheid te verbeter deur die aanwending van adsorpsiepare geproduseer uit die afvalstrome van mango-prosessering in die adsorpsie verkoelingstelsel. Die spesifieke doelstellings was: om mangosaaddop geaktiveerde koolstof (GK) te produseer deur NaCl as die aktiveringsmiddel te gebruik, dit te karakteriseer en met kommersiële GK te vergelyk; die werkverrigting (in terme van KVW en SVK) van die mangosaaddop GK (met kommersiële GK as die kontrole) gekombineer met beide hoë suiwerheid en lae-graad etanol as koelmiddels, te assesseer; die hitte- en massa-oordrag werkverrigting van kommersiële GK gekombineerd met beide hoë suiwerheid en lae-graad etanol as koelmiddels te verbeter deur samestelling vorming; en die assessering van die omgewings- en ekonomiese impak wanneer adsorpsie verkoelingstelsel (AVS) in gedroogde mangoskyfie-prosessering geïntegreer word in beide netwerk en buite-netwerk krag kondisies Mangosaaddop GK is geproduseer deur ’n stadige pirolise metode deur gebruik te maak van NaCl as die aktiveringsmiddel. Ongeveer 100 g gedroogde mangosaaddop is in 250 ml NaCl oplossing geweek met konsentrasies (10 % w/v, 20 % w/v, en 30 % w/v) om impregneringsverhoudings van 0.25, 0.5 en 0.75 by 25 °C te verkry. Die verkolingstemperature was 400 °C, 450 °C, en 500 °C. Die eksperimentele ontwerp is gebaseer op ’n 33 (impregneringsverhouding, weektyd, en verkolingstyd) Box-Behnken fraksionele faktoriaal optimeringsmetode met drie middellope, vir ’n totaal van 15 lope. Die response geanaliseer was massadigtheid, as-inhoud, en oppervlakarea. Die geoptimiseerde mangosaaddop GK geproduseer is getoets in ’n binne-huis geboude AVS en sy werkverrigting is vergelyk met kommersiële GK. Die saamgestelde GK is ook gevorm deur kommersiële GK in NaCl oplossing by verskeie konsentrasies van 10 % w/v, 15 % w/v, 20 % w/v, 25 % w/v, 30 % w/v en 35.7 % w/v, vir 24 uur by 25 °C te week, te droog by 105 °C vir 24 uur, en dan te toets in ’n binne-huis geboude AVS met hoë suiwerheid (99.7 %) en lae-graad (60 %) etanol om die effek van etanol graad op die werkverrigting van die samestelling gevorm, te evalueer. Laastens, drie scenario’s vir elke kragstelsel (binne-netwerk en buite-netwerk) is bestudeer: steenkool as ketelbrandstof en konvensionele afkoeler vir verkoeling (Scenario 1), mangosaad as ketelbrandstof en konvensionele afkoeler vir verkoeling (Scenario 2), en mangosaad as ketelbrandstof en AVS vir verkoeling (Scenario 3). Buite-netwerk scenario’s 4, 5 en 6 stem ooreen met binne-netwerk scenario’s 1, 2 en 3, onderskeidelik. Omgewingsimpak en ekonomiese lewensvatbaarheid vir elke scenario is gebaseer op materiaal- en energiebalanse en Suid-Afrikaanse ekonomiese kondisies, onderskeidelik. Die resultate het gewys dat mangosaaddop GK vergelykbare as-inhoud (6.92 %) het as die kommersiële GK. Die SVK, KVW en temperatuurval aangeteken in AVS vir mangosaaddop GK wanneer dit met hoë suiwerheid (99.7 %) etanol gekombineer is, was 77.3 W/kg, 0.048 en 4.5 °C – ’n afname van 87.5 W/kg, 0.050 en 4.46 °C wanneer dit gekombineer word met lae-graad etanol (60 %). Verder, die KVW en SVK van kommersiële GK gekombineer met hoë suiwerheid etanol was 0.098 en 122 W/kg, wat afgeneem het na 0.091 en 111 W/kg, onderskeidelik, wanneer gekombineer is met lae-graad etanol. Daarby was die KVW van die saamgestelde GK wat 20 %, 25 %, en 30 % NaCl bevat, gekombineer met lae-graad etanol 0.121, 0.160 en 0.146, onderskeidelik. Dit was hoër as toe dit gekombineer is met hoë suiwerheid etanol – 0.082, 0.080, en 0.076, onderskeidelik. In terme van omgewings- en ekonomiese impak, het binne-netwerk scenario 3 die grootste potensiaal gewys vir die vermindering van emissies en verbetering van ekonomiese lewensvatbaarheid deur uitstorting van 7.10×105 kgCO2 ekw/jr en interne opbrengskoers (IOK) van 25.33 %, vergelyk met scenario 1 wat KHG emissies van 7.89×105 kgCO2 ekw/jr en IOK van 17.48 % gehad het. In buite-netwerk, het scenario 6 die minste KHG emissies gehad - 6.90×105 kgCO2 ekw/jr en IOK van 24.84 %, terwyl scenario 4 die hoogste KHG emissies van 7.67×105 kgCO2 ekw/jr gehad het en IOK van 16.09 %. Alles in ag geneem, is dit moontlik om die hitte- en massa-oordrag van geaktiveerde koolstof gekombineer met lae-graad etanol te verbeter. Die verbetering in hitte- en massa-oordrag wanneer GK + NaCl met lae-graad etanol gekombineer is, stel voor dat lae-graad etanol gebruik kan word as ’n alternatiewe verkoeler. In areas waar silika jel bereikbaar is, sal die vorming van ’n samestelling met silika jel + NaCl gekombineer met suiwer water as verkoeler, die massa-oordrag uitdagings geassosieer met die gebruik van GK + NaCl samestellings gekombineer met etanol, elimineer. Verder, die vervanging van damp kompressie verkoelingstegnologie met AVS, en ketelbrandstof met mangosaad, het tot die vermindering in KHG emissies gelei en die verbetering in ekonomiese lewensvatbaarheid van gedroogde mangoskyfie-prosessering. Dus het hierdie studie die tegniese, ekonomiese en omgewingswerkverrigting van AVS in terme van temperatuur handhawing, hulpbron verbruik en emissies, verbeter.

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