Improved Salt Quality and Reduced Energy Consumption via Hot Air Drying

This study examines the effects of hot air drying operating parameters on salt quality and energy consumption. Temperature, air velocity, and drying time were modified to evaluate their effects on NaCl percentage, water content, whiteness, and hot air drying energy consumption. The results showed that increasing temperatures, air velocities, and drying times decreased water content and increased salt temperatures. Additionally, given several operating parameters, NaCl percentage and whiteness initially increased to an optimum value and decreased, respectively. The decrease in NaCl percentage and whiteness is due to salt’s rapid decomposition with high-temperature heating to form a yellow residue. Increasing temperatures and drying times increased energy consumption and decreased drying energy efficiency. However, increasing air velocities increased both energy consumption and drying energy efficiency. The most economical values for energy consumption and drying energy efficiency for one operation cycle were 1.79 kWh and 17%, respectively. This study found that the lowest energy consumption and highest energy efficiency while maintaining high salt quality were achieved at 70ºC with an air velocity of 22.5 m/s and a drying time of 30 min.

Hot air drying; Hot air performance; Salt; Salt drying; Sodium chloride quality

        Salt is an essential material worldwide, used in many modern industrial applications (Khormali et al., 2016; Aslfattahi et al., 2019; Sofyan et al., 2019), as well as human consumption (Rochwulaningsih et al., 2019a; Rochwulaningsih et al., 2019b). Indonesia’s demand for salt has continually grown at a tremendous rate over the last few decades (Juwono, 2020). The country’s growing chemical industry and population have accelerated this growth. Consequently, demand has increased for high-quality salt with low production costs. High-quality salt requires that salt be dried to a feasible water content after processing (Zhao et al., 2008). The drying process comprises two phases: heating and drying. It occurs through changes to temperature, relative humidity, and airflow (Palamba et al., 2018). The drying process removes water from solid salt particles via evaporation. Drying helps store salt for lengthy periods and improves its quality. The challenge in drying salt is reducing the water content without sacrificing quality since natural elemental impurities—such as sulfate (SO₄^-2), calcium (Ca), and magnesium (Mg)—may adversely affect public health (Heydarieh et al., 2020). Moreover, salt drying consumes energy, so its operating parameters must be chosen correctly. For example, a high temperature during salt drying should be avoided because it turns salt yellow (McGee and Diosady, 2016). A variety of strategies are required to obtain the maximum use of positive energy flow production (Harahap et al., 2020). Various drying systems have been applied to salt drying, such as rotary dryers (Jafari and Farahbod, 2017), fluidized bed dryers (Zhao et al., 2008), and hot air dryers (Qadir et al., 2005). Hot air drying has attracted much attention because it offers a wide range of applications, such as drying herbs (Liang et al., 2020), agricultural products (Das and Arora, 2018; Deepika and Sutar, 2018; Gao et al., 2019), and wood products (Khamtree et al., 2019). Operating parameters—such as temperature, air velocity, and drying time—influence product quality when drying with hot air (Zhu, 2018). The current study aimed to investigate the effect of hot air drying parameters—such as temperature, air velocity, and drying time—on salt quality in terms of NaCl percentage, whiteness, and water content. The energy consumption and energy efficiency of hot air drying were also investigated.

    This experimental investigation showed that salt’s water content decreased with increasing operating parameters, such as temperature, air velocity, and drying time. Increased salt temperatures were associated with increased operating parameters. At several given operating parameters, the salt’s NaCl percentage and whiteness initially increased to an optimum value and then decreased. Temperature, air velocity, and drying time were found to be critical parameters for hot air drying; therefore, they should be correctly selected for better salt quality. This study also found that, by correctly setting a parameter, the energy required to produce 1 kg of dried salt (NaCl of 96.91% and whiteness of 77.74) from crude solar sea salt was 0.358 kWh. This result shows that hot air dryers are economical for drying high-water-content salt to enhance its quality.

    The authors gratefully acknowledge the research funding scheme Penelitian Penugasan from the University of Trunojoyo Madura, Indonesia (Nr.: 163/UN46.4.1/PT.01.03/2020). Also, the authors thank Mr. Hamzah Muhammad Ba’abud and Mr. Muhammad Jawad for their kind support and advice.

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