Thermoeconomic and thermoenvironomic modeling and analysis of selected gas turbine power plants in Nigeria

This study presents comprehensive thermoeconomic and thermoenvironomic modeling and analysis of selected gas turbine power plants in Nigeria using the first and second laws of thermodynamics (exergy) concept. Exergetic analysis was conducted using operating data obtained from the power plants to determine the exergy destruction and exergy efficiency of each major component of the gas turbine in each power plant. The results of the study showed that the combustion chamber (CC) is the most exergy destructive component compared to other cycle components. The percentage of exergy destruction in CC varies between 86.05% and 94.6%. By increasing the gas turbine inlet temperature (GTIT), the exergy destruction of this component can be reduced. The total exergy improvement potential of the selected plants varies from 54.04 to 159.88 MW. The component with the highest exergy improvement potential is the CC, which has the value that varies from 30.21 to 88.86 MW. Thermoeconomic analysis showed that the cost of exergy destruction is high in the CC, and an increase in the GTIT effectively decreases this cost. The exergy costing analysis revealed that the unit cost of electricity produced in the plants ranged from cents 1.99/kWh (N3.16/ kWh) to cents 5.65 /kWh (N8.98/kWh). Thermoenvironomic analysis showed that the CO2 emissions varied between 100.18 and 408.78 kg CO2/MWh, while cost rate of environmental impact varied from 40.18 $/h (6, 388.62 N/h) to 276.97$/h (44, 038. 23 N/h). The results further showed that CO2 emissions and cost of environmental impact decrease with increasing GTIT. The sustainability index increase with increasing GTIT. Finally, this study will assist efforts to understand the thermodynamic losses in the gas turbine cycle, and to improve efficiency as well as provide future recommendations for better performance, sustainability, and lessening environmental impact of power plant

Heat exposure in sugarcane harvesters in Costa Rica

Background Occupational heat stress is a major concern in sugarcane production and has been hypothesized as a causal factor of a chronic kidney disease epidemic in Central America. This study described working conditions of sugarcane harvesters in Costa Rica and quantified their exposure to heat. Methods Non-participatory observation and Wet Bulb Globe Temperatures (WBGT) according to Spanish NTP (Technical Prevention Notes) guidelines were utilized to quantify the risk of heat stress. OSHA recommendations were used to identify corresponding exposure limit values. Results Sugarcane harvesters carried out labor-intensive work with a metabolic load of 261 W/m2 (6.8 kcal/min), corresponding to a limit value of 26° WBGT which was reached by 7:30 am on most days. After 9:15 am, OSHA recommendations would require that workers only work 25% of each hour to avoid health risks from heat. Conclusions Sugarcane harvesters are at risk for heat stress for the majority of the work shift. Immediate action is warranted to reduce such exposures.Antecedentes El estrés térmico ocupacional es una preocupación importante en la producción de caña de azúcar y se ha planteado la hipótesis de que es un factor causal de una epidemia de enfermedad renal crónica en América Central. Este estudio describió las condiciones de trabajo de los cosechadores de caña de azúcar en Costa Rica y cuantificó su exposición al calor. Métodos Para cuantificar el riesgo de estrés térmico se utilizó la observación no participante y las Temperaturas Globales de Bulbo Húmedo (WBGT) según las directrices españolas NTP (Notas Técnicas de Prevención). Se utilizaron las recomendaciones de la OSHA para identificar los valores límite de exposición correspondientes. Resultados Los cosechadores de caña de azúcar realizaron un trabajo intensivo con una carga metabólica de 261 W/m2 (6,8 kcal/min), correspondiente a un valor límite de 26° WBGT que se alcanzó a las 7:30 am la mayoría de los días. Después de las 9:15 de la mañana, las recomendaciones de la OSHA exigirían que los trabajadores sólo trabajasen el 25% de cada hora para evitar los riesgos para la salud derivados del calor. Conclusiones Los cosechadores de caña de azúcar corren el riesgo de sufrir estrés térmico durante la mayor parte del turno de trabajo. Se justifica una acción inmediata para reducir tales exposiciones.Universidad Nacional, Costa Rica.Instituto Regional de Estudios en Sustancias Tóxica