Development Of Composite Adsorbent For Adsorption Refrigeration Of Ammonia Powered By Ship’s Waste Heat

Activated carbon-ammonia has been considering as one of the most promising workingpairs for adsorption refrigeration powered by waste heat on board ship due to its goodperformance in anti-vibration, evaporation capacity as well as a larger temperature range of themedium for powering the system. However, the practical application of the working pair has alsobeen limited by a much lower heat conductivity of the activated carbon. In this paper, expandedgraphite was selected as the additive to improve the heat conductivity of the composite adsorbentsynthesized by monolith of activated carbon and the expanded graphite, researches included areas follows:1) Analysis of the deterioration mechanism of a new kind of composite adsorbent undermarine environment. The recycling performance for ammonia adsorption on the compositeadsorbent, which consists of SrBr2, SrCl2and LiSCN respectively about60-90%,8-31%and2-9%, was evaluated based on the experiments carried out on an adsorption refrigeration unitpowered by the steam from the boiler. Results show that the refrigeration capacity of the systemdecreased in the cooling water temperature due to the thermal resistance of adsorbent bed.Results also reveal that the duration for the liquid ammonia contained within the storage tankreaching the level in correspondence with19.9-43.5%of the net volume has been extended forabout8-24minutes after adsorption/desorption cycles. Conclusions are drawn that the physicaladsorption of ammonia should be focused while developing composite adsorbent for adsorptionrefrigeration.2) Probing into the mechanism of operating parameters of expanded graphite’s expansionprocess on the thermal conductivity and desorption performance of composite adsorbents. Theexpanded graphite was firstly developed over a temperature and time range of873.15-1073.15Kand5-90s. The composite adsorbents were synthesized by mixing SAC-02activated carbon(SBET=1408m2/g) and the expandable graphite as per the mass ratio from1:1to3:1. Thecomposite monolith was formed by taking the specific density of450kg/m3as reference, and theThermal Conductivity Analyzer and adsorption dynamics test device were respectively used tomeasure the thermal conductivity of the composite and the desorption rate of a storage tank(φ45mm×69mm×3mm) packed with the composite adsorbent. Results show that the asprepared expanded graphite samples obtained the highest heat conductivity where the temperature and the duration for expansion were respectively about973.15K and35s. The heatconductivity of the composite is anisotropic and decreases in the proportion of activated carbon;at343.15K, the rate of ammonia desorption on the2:1composite before300s was the largest.The composite absorbent’s thermal conductivity was effectively improved by adding expandedgraphite.3) Adsorption equilibrium of ammonia on the composites. Tristar II3020type automaticanalyzer was selected to characterize the structure of the adsorbent in terms of specific surfacearea, specific pore volume and pore size distribution, and isotherms of excess adsorptionamounts of high pure ammonia on the composites were volumetrically measured over atemperature range of293.15-313.15K and for pressures up to1.167MPa, the outcomes were usedto determine D-A equation through nonlinear fit. The Clausius-Clapeyron equation and D-Aequation were used to calculate the isosteric heat of ammonia adsorption on the composite.Results show that the composites’ specific surface area, micropore and mesopore volumesdecreases in the addition of the expanded graphite. The relative error of the calculated resultsfrom D-A equation is less than4%where the equilibrium pressure is higher than0.15MPa. Theisosteric heat of ammonia adsorption on the activated carbon and the composites whose mixingratio between activated carbon and expanded graphite is2:1and1:1is about13-26kJ/mol.Conclusions are drawn that the addition of the expanded graphite has little effect on the porestructure of the composite and the D-A equation is recommendable to predict the equilibriumdata of ammonia adsorption on the composites.