SOUTHERN JOURNAL OF SCIENCES

Sand casting is a viable waste as an alternative raw material, regarding a good solution in the production of concrete blocks. The use of sand casting to produce concrete blocks is performed by about 80% of the productive capacity of the company considered in this study. Thus, this work aims to make an improvement by applying fuzzy logic. The methodology was applied from the formulation of ranking criteria, which improved the production process. Therefore, after the implementation of the established criteria, was achieved an improvement of about 10%. Thus, the results achieved can help companies, generating alternatives with more excellent reliability and assertiveness. Moreover, Fuzzy is a methodology that provides strong support for decision making, supporting subjective and intuitive criteria.

Carbon capture and storage (CCS) has been observed as an alternative measure to mitigate emissions from greenhouse gases. CCS systems separate CO₂ during the process of converting fuel and transport to the facilities where they are stored, e.g., under geological formation conditions. Capture and sequestration technologies are now widely used in different industries. CO₂ capture is currently a costly and energy-consumingtechnology. The costs obviously depend on the size of the plant and the type of fuel used. Generally, capture systems are categorized into three categories: pre-combustion, post-combustion, and oxy-fuel combustion. The saline aquifer, depleted oil, and gas fields are large-capacity storage sinks. The coalbeds also provide as a substitute to geological storage. One of the main advantages of coal storage is renewable methane fuel and coaldesulfurization. The studied coal reserves are located in Candiota, State of Rio Grande do Sul, Brazil. These are the largest coal deposits in the country, with a reserve of 1 billion tons. This work will represent a study on CO₂ storage in Candiota coalbed system. The use of a synthetic CO2 cylinder with a flow of 0.2 L/min varies the time of contact with the coalbed. The results from the volatile matter increase by 11%. The results of the ultimate analysis exhibited an 8% increase for carbon and oxygen after 60 minutes of CO₂ flow in the coalbed. On the other hand, there was a reduction of 32% for sulfur. The resultant phenomena occur due to the adsorption capacity of CO₂, where the compounds are released from the pores of coal.

Background: MQ-series gas sensors belong to the metal oxide semiconductor (MOS) family of sensors that can sense the presence of many gases. These sensors find their application in gas alarm systems as key components. While necessary sensor circuit output voltage value for alarm point in a stand-alone gas alarm system is desirable, but what exact combination of the sensor circuit parameters is required? Hitherto, the determination of these circuit parameters has not been given much attention in the research community. Aim: the purpose of this work is to explore a structured graphical approach of determination of MQ series gas sensor circuit parameters for a stand-alone gas alarm system that yields desired sensor circuit output voltage value for the alarm point; the main objective of the study was to develop mathematical model equations that relate the: (i) sensor resistance (RS) with the gas concentration (x) and the sensor resistance at standard calibration concentration of the sensor base gas in the clean air (Ro) and (ii) sensor circuit output voltage (VRL), load resistance (RL) and sensor resistance (RS). It is expected from the model equations developed that graphical correlations of the sensor circuits parameters will be generated. Using these graphs for a particular case of an MQ-4 gas sensor under the influence of LPG, the parameters that yield desired sensor circuit output voltage of 2V for 1000 ppm of LPG alarm point will be determined. Methods: Model equations were developed for the sensor dynamics, and based on these model equations, graphs for the determination of required sensor parameters were plotted for a case of MQ-4 gas sensor response to LPG. Results and Discussion: The results yielded optimal values for R_O,R_S and R_L of 20 kΩ, 30 kΩ and 20 kΩ respectively, for alarm settings of 1000 ppm and a desired sensor circuit output voltage of 2 V. Based on determined parameters, the calibration equation for determination of best concentration value for a given value of emulated LPG concentration was developed. Using the method proposed in this study makes the process of determining the MQ-series gas sensor circuit parameters less cumbersome as their value can easily be obtained from the resulting graphs. Conclusions: a structured graphical approach for determination of MQ-series gas sensor circuit parameters for alarm points in a stand-alone gas alarm system showed that using MQ-4 gas sensor and LPG as the target gas, and for a sensor circuit output voltage of 2 V for alarm point at 1000 ppm of LPG, the corresponding value of R_O, R_S and R_L obtained were 20 kΩ, 30 kΩ, and 20 kΩ respectively. Hence, a structured graphical approach is suitable for determining MQ series gas sensor circuit parameters for a stand-alone gas alarm system under the influence of its associated gases.