Abstract
In this article, a thermodynamic study was conducted on the energetic and exergy performance of a new configuration of liquid chemical looping gasification (LCLG) plant integrated with a power block to assess the overall performance of the system including exergy partitioned in syngas and first law efficiency (FLE). LCLG is a relatively new concept for the production of high-quality synthetic gas from solid feedstock such as biomass. As the temperature and pressure of the looping system are high, there is thermodynamic potential to co-produce chemical products, power and heat. Hence, in the present work, three different configurations of a power cycle were thermodynamically assessed. In the first proposed power cycle, the produced syngas from the gasifier was combusted in a combustion chamber and the exhausted gases were fed into a gas turbine. In the second and third proposed power cycles, the hot air was directly fed into a gas turbine or was used to produce steam for the steam turbine combined cycle. The processes were simulated with Aspen Plus and Outotec HSC chemistry software packages. The influence of different operating parameters including temperature and pressure of the air reactor and type of oxygen carrier on the first law and exergy efficiency (exergy partitioned in synthetic gas) was assessed. Results showed that the FLE for the proposed gas turbine and steam turbine combined cycles was ~33% to 35%, which is within the range of the efficiency obtained for the state-of-the-art power cycles reported in the literature. Results also showed that lead oxide was a suitable oxygen carrier for the LCLG system, which can be integrated into a steam turbine combined cycle with an FLE of 0.45, while copper oxide showed an FLE of 0.43 for the gas turbine combined cycle.
Highlights
In recent years, syngas production using gasification has received special attention as coal will continue to remain the dominant source of energy production due to its lower price and availabilityProcesses 2019, 7, 763; doi:10.3390/pr7100763 www.mdpi.com/journal/processesProcesses 2019, 7, 763 in comparison with other fuels [1,2]
Metal oxides are employed as the oxygen carrier and they are reduced in the fuel reactor and are successively oxidized in the air reactor
The produced syngas from the liquid chemical looping gasification (LCLG) system was was combusted combusted at high high pressure pressure and and temperature temperature in a combustion combustion chamber, and and the the product product gases gases were transported to a gas turbine to produce the work
Summary
Syngas production using gasification has received special attention as coal will continue to remain the dominant source of energy production due to its lower price and availabilityProcesses 2019, 7, 763; doi:10.3390/pr7100763 www.mdpi.com/journal/processesProcesses 2019, 7, 763 in comparison with other fuels [1,2]. Sarafraz and his co-workers have proposed the use of liquid metals instead of solid metal oxides to improve the thermal performance and chemical efficiency of the chemical looping gasification system [9,10]. They have shown that if the rate of oxygen in the system is limited to sub-stoichiometric quantities, the proposed system works as a chemical looping gasification. This brings immense benefits to syngas production technology as it controls the amount of carbon dioxide production, avoiding the appearance of nitrogen in the product, which addresses the nitrogen dilution problem. The outlet air from the air reactor can be used in a gas turbine combined cycle to increase the overall thermodynamic efficiency of the system by producing work
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