Optimal operation of chillers plant in academic building by using linear programming approach

The operation of chillers plant in the HVAC system is not ideally efficient in major academic buildings because the chillers are operated without accounting for the cooling load demand of the air-conditioning area of the building. The current operation of the chillers plant may fall under two cooling effects, namely excessive cooling effect that will reduce the efficiency of the chillers and inadequate cooling effect that may create an unpleasant environment inside the air-conditioning area. This is because the cooling load demand of the air-conditioning area of the building is unknown and is not numerically measured. The main aim of this study is to find the optimal operation of chillers plant in HVAC system by formulating an optimization framework with the main goal of minimizing energy consumption and electricity costs. The formulation of the optimization framework for chillers plant operation is modelled as Linear Programming (LP) to establish real representation of the chillers plant. The energy consumption profile, cooling load demand, cooling capacity and COP can be obtained by using historical data analysis. The optimization framework is modelled in GAMS v38.2.1 and solved by CPLEX solver to obtain the optimum input for the chillers plant in the HVAC system. The minimum total power consumption can be achieved by optimally coordinating the operation of chillers, cooling towers and AHUs while maintaining room temperature. From the cost comparison analysis between the current and optimal chillers plant, considerable cost reduction is expected to be less than 5 % if the chillers plant is operating efficiently or greater than 30 % if the chillers plant is not functioning effectively. Therefore, this study is beneficial to the administration of academic building to find a strategic action plan to promote cost optimization in the operation of the chillers plant

Transforming carbon-intensive coal-fired power plants into negative emission technologies via biomass-fired calcium looping retrofit

Calcium looping is a promising CO2 capture technology due to reduced energy and economic penalties compared to mature solvent scrubbing technologies and the potential for achieving negative emissions. This study examined the potential for transforming coal-fired power plants into negative CO2 emission technologies via retrofit of calcium looping with biomass co-firing in the calciner. The results confirmed that co-firing 30% biomass with coal in the calciner was sufficient for the retrofitted process to achieve negative CO2 emissions (-3.9 gCO2/kWh). Such a retrofit scenario had a net efficiency of 29.9% and a levelised cost of electricity of 81.1–81.4 €/MWh. Alternative approaches to calcium looping design were also explored to maximise the techno-economic viability of the retrofitted process. It was shown that by reducing the CO2 capture rate in the carbonator to 70%, the retrofitted process maintained the same net efficiency as the reference retrofit scenario. This modification resulted in a 1.8–5.0% reduction in the levelized cost of electricity. Moreover, reducing the fraction of flue gas fed to the carbonator to 80% resulted in a 0.6%-point reduction in efficiency penalty compared to the reference retrofit scenario. Although this adjustment led to specific CO2 emissions of 109.0 gCO2/kWh (4.0% higher than the reference retrofit), the emissions remained 86.2% lower than those of the unabated host plant. Notably, the levelized cost of electricity in this scenario was 6.2–7.5% lower than that for the reference retrofit scenario. Overall, this study demonstrated that by incorporating biomass co-firing, the calcium looping retrofits can transform the existing coal-fired power plants into negative CO2 emission technologies or, at the very least, improve the techno-economic viability of CO2 capture. Future research should address the broader environmental impact and potential challenges associated with biomass co-firing in coal-fired power plants retrofitted with calcium looping

Reaction mechanism and kinetics of the sulfation of Li4SiO4 for high-temperature CO2 adsorption

CO2 adsorption is an important approach to control the excessive CO2 emission from energy and industrial plants and mitigating the greenhouse effect. As an acknowledged high-temperature adsorbent, Li4SiO4 shows advantages in capturing a large amount of CO2 with a fast reaction rate and excellent cyclic stability. However, its CO2 adsorption capacity would be significantly affected by the flue gas impurities, such as SO2 and O2. The underlying reaction mechanism of such impurities and Li4SiO4 is still unclear. For this reason, this work studied the reaction path and kinetics between Li4SiO4 and SO2 through experiments, thermodynamic calculations, and characterizations. The results showed that Li4SiO4 reacts with SO2 to produce Li2SiO3 and Li2SO4 in the presence of O2 at 500–700 °C and forms Li2SiO3 and Li2SO3 in the absence of O2 at 500–682 °C. Furthermore, this study revealed a very low activation energy of 7.47 kJ/mol for Li4SiO4 sulfation in the presence of O2 in the kinetic-controlled stage, and the value goes up to 249.7 kJ/mol in the diffusion-controlled stage. These results will provide valuable references for the industrial applications of CO2 adsorption by Li4SiO4