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Metakaolin (MK) is one of the most sustainable cementitious construction materials, which is derived through a direct heating procedure known as calcination. Calcination process takes place substantially lower temperatures than that required for Portland cement, making it a more environmentally sustainable alternative to traditional cement. This procedure causes the removal of hydroxyl water from the naturally occurring kaolin clay (Al2Si2O5(OH)4 with MK (Al2O3·2SiO2) as its product. Kaolin naturally exists in large amount within 5°29′N–5°35′N and 7°21′E–7°3′E geographical coordinates surrounding Umuoke, Obowo, Nigeria. Alumina and silica are the predominant compounds in MK, which provide it with the pozzolanic ability, known as the 3-chemical pozzolanic potential (3CPP), with high potential as a cementitious material in concrete production and soil stabilization. Over the years, researchers have suggested the best temperature at which MK is derived to have the highest pozzolanic ability. Prominent among these temperature suggestions were 800 °C (3CPP of 94.45%) and 750 °C (3CPP of 94.76%) for 2 h and 5 h' calcination periods, respectively. In this research paper, 11 different specimens of Kaolin clay obtained from Umuoke, Nigeria, were subjected to a calcination process at oven temperatures from 350 to 850 °C in an increment of 50 °C for 1 h each to derive 11 samples of MK. The MK samples and Kaolin were further subjected to X-ray fluorescence), scanning electron microscopy (SEM) and X-ray diffraction (XRD) Brunauer–Emmett–Teller (BET) tests to determine the microstructural behaviour and the pozzolanic properties via the 3CPP as to exploit the best MK with the highest cementing potential as a construction material. The results show that the MK heated at 550 °C and 800 °C produced the highest pozzolanic potentials of 96.26% and 96.28%, respectively. The enhancement in pozzolanic potential at optimum calcination temperature is attributed to an increase in the specific surface area upon calcination of kaolinite confirmed by BET results. The SEM and XRD results further supported the above result with the strengthened crystal structure of the MK at these preferred temperatures. Generally, 550 °C is more preferred due to the less heat energy needed for its formulation during 1 h of calcination, which outperforms the previous results, that suggested 750 °C and 800 °C in addition to longer hours of heat exposure. [ABSTRACT FROM AUTHOR]

This paper presents a multi-criteria optimization of integrated power systems. Five power configurations that combines the solid oxide fuel cell (SOFC), gas turbine cycle (GTC), steam turbine cycle (STC), organic Rankine cycle (ORC), absorption refrigeration cycle (ARC), and carbon capture and sequestration (CCS) as SOFC-GTC, SOFC-GT-STC, SOFC-GT-ST-ORC, SOFC-GT-ST-OR-ARC, and SOFC-GT-ST-OR-AR-CCS were proposed, modeled, and analyzed. The proposed plants were further subjected to the Technique for Order of Preference by Similarity to the Ideal Solution (TOPSIS) optimization with technical and socio-economic parameters as the decision criteria. Important results suggest that the power of the proposed systems are within 207–281 MW, while energy and exergy efficiencies are in the range of 42.93–58.13% and 42.49–57.54%, respectively. The exergy destruction rate is within 206–322.9 MW. Furthermore, SOFC-GT-ST-OR-AR-CCS that integrates all the investigated power cycles, including the carbon capture proposes a CO2 emission factor of 0.029 ton/MWh, as against 0.332–0.401 ton/MWh for the other configurations. Unit cost of energy (UCOE) for all systems are within $0.059–0.141 per kWh, with the SOFC-GT-ST-OR-AR-CCS having the highest UCOE. The cost of CO2 avoidance of $110 per ton of CO2 suggests the minimum carbon tax that will make SOFC-GT-ST-OR-AR-CCS economically competitive with the best configuration that is without carbon capture. Also, the carbon capture integrated power system has the least efficiency of 42.93% because a portion (73.5 MW) of the power generation was used in the carbon capture process. Nonetheless, the TOPSIS results suggest that at 0.7312, the SOFC-GT-ST-OR-AR-CCS is closest to the ideal solution, when compared to the other configurations which fall within 0.2238–0.7312. It is suggested that policies in Nigeria should promote (i) the integration of CCS technology in power generation; (ii) the retrofitting of simple cycle power plants with medium- and low-grade thermal power technologies; and (iii) dual-fuel power plants (natural gas and biomass) to harness the benefit of carbon neutrality in biomass and good energy density in natural gas. [ABSTRACT FROM AUTHOR]