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- Liu, Shengchun, et al.
(författare)
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Alternative positions of internal heat exchanger for CO2 booster refrigeration system : Thermodynamic analysis and annual thermal performance evaluation
- 2021
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Ingår i: International journal of refrigeration. - : ELSEVIER SCI LTD. - 0140-7007 .- 1879-2081. ; 131, s. 1016-1028
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Tidskriftsartikel (refereegranskat)abstract
- Refrigeration systems running on transcritical CO2 cycle are considered an alternative to phase-down the use of hydrofluorocarbons (HFCs) in response to the Kigali Amendment. Responding to the need to improve the efficiency of CO2 booster systems and to identify optimum system designs, thermodynamic models of three booster systems are proposed with the use of an internal heat exchanger (IHX). Findings from this study suggest that placing the IHX with a low-temperature fluid side at the suction line of high pressure stage compressor and high-temperature fluid side at the outlet of gas cooler represents the most optimal approach in improving the coefficient of performance (COP) of the booster system. When operating in the transcritical conditions, the COP values can be improved by 6.35% at the IHX thermal effectiveness of 0.8 and by 6.48% at the ratio of medium temperature load to low temperature load of 6. Using IHX can significantly reduce the compressor discharge pressure, which can be reduced by 0.55 MPa at the ambient temperature of 40 degrees C. Furthermore, by adding IHX, the annual performance factor of CO2 system can be improved significantly by 1.68% and the annual total power consumption can be decreased by 6.48% in the tropical climate. It can be concluded that IHX can improve the COP values of a booster system when operating in the subtropical and tropical regions.
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| 2. |
- Tao, Jun, et al.
(författare)
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Catalytic cracking of biomass high-temperature pyrolysis tar using NiO/AC catalysts
- 2015
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Ingår i: International Journal of Green Energy. - : Informa UK Limited. - 1543-5075 .- 1543-5083. ; 12:8, s. 773-779
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Tidskriftsartikel (refereegranskat)abstract
- Nickel oxide supported on activated carbon (NiO/AC) catalysts were prepared and used for catalytic cracking of tars from inert high-temperature pyrolysis of biomass. Rice husk was selected as the feedstock, and pyrolyzed at 800 °C using a lab-scale pyrolysis set. The pyrolysis vapors were subjected to either thermal cracking or catalytic cracking under 500-700 °C. The results indicated the thermal cracking was not very efficient to convert the tars, while the catalytic cracking reduced both the light and heavy tars significantly. The yield of the light and heavy tars were decreased from 4.4 wt% and 1.9 wt% in the non-catalytic process to 0.2 wt% and 0.1 wt% in the catalytic process by the NiO/AC (4.3 wt%) at 700 °C. The catalytic cracking also increased the gas product remarkably, mainly the H2 and CO2. The catalytic performance of the NiO/AC catalyst could enhance at elevated catalytic temperatures and increased NiO content of the catalyst.
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