**1. Introduction**

Instant co ffee is one of the most commonly consumed drinks worldwide; around 118 billion dollars of it were sold in the global market in 2019. The worldwide market for instant co ffee has high growth expectations: projected to grow by 11.6% in the next 5 years [1]. Co ffee has a high concentration of antioxidants [2], vitamins B, and minerals [3]. It benefits physical performance and stimulates the central nervous system [4]. Co ffee is sold as whole bean, ground co ffee, instant co ffee, co ffee pods, and capsules. Among these, instant co ffee is quickly becoming popular all over the world because of cheaper transportation and convenience in preparation, which increases its demand among urban consumers [5]. Many industrial-scale plants have been established around the word to produce this kind of co ffee.

The production process of instant co ffee powder begins with roasting the co ffee beans and grinding them. Later, they pass through a liquid solid extraction. The extracted liquid is then concentrated and, finally, it is spray dried. The drying process reduces the amount of water in the co ffee and allows its shelf-life to be increased. This operation requires the most energy resources [6], and is also considered highly exergy-destructive [7]. Spray dryers are considered to be limiting units within a productive

process, and one of the operations with the highest exergy improvement potential [8]. A previous study has demonstrated that the exergy efficiency of spray dryers is lower than that of other drying technologies such as tray dryers, continuous dryers, heat pump assisted dryers, fluidized bed dryers, solar dryers, freeze dryers, vacuum dryers, and flash dryers [7].

Exergy analysis has become an important tool for the assessment of different energy-intensive industrial processes, such as spray drying [9]. These analyses have allowed for the identification of the components with the highest exergy losses, the avoidable exergy losses, and the operational conditions, which most affect the irreversibility of the systems. Erbay et al. [10] used a pilot-scale spray dryer on white cheese slurry to demonstrate experimentally that parameters like atomization pressure and drying air temperature can affect the exergetic efficiency of the spray dryer. Another study of the same scale for the drying of cherry puree showed that drying agents could reduce the exergy destruction rate of the process [11]. Some studies were done at a laboratory scale. One lab-scale study, evaluated the exergetic efficiency of spray drying of photochromic dyes and obtained efficiency below 4% [12]. Further, Aghbashlo et al. [13] studied the influence of parameters such as air and feed flow rate in the exergy destruction rate of the spray drying of microencapsulation of fish oil. Only two studies have been done on industrial-scale spray dryers, and both took place in a powdered milk factory. The first analyzed each step of the production process and concluded that the spray dryer was one of the most exergy destructive components (2196 kW) [14]. In the second study, Camci et al. [15] analyzed a spray drying system with solar collectors for preheating the drying air in a closed loop, resulting in an increase of the exergetic efficiency to 22.6%.

However, although the exergetic analysis identifies the location and magnitude of the thermal energy losses, it has limitations given that it can not quantify the cost of those losses. Furthermore, an exergy analysis is not conclusive about which components should have investment priority in order to reduce the exergy losses [16]. In order to complete an exergy analysis, an exergoeconomic analysis can be applied, which combines exergy and economic principles at the component level to identify the real cost sources in a thermal system [17]. Since the thermodynamic considerations of exergoeconomics are based on the exergy concept, the term exergoeconomics can also be used to describe the combination of exergy analysis and economics [18]. Exergoeconomic analysis has been applied in different industrial processes in order to minimize the economic losses due to irreversibility, and, consequently, provide the added benefit of reducing production costs of the entire complex energy system. Few conventional exergoeconomic analyses of different drying technologies on both the pilot and industrial scale have been found in the literature; they focused on the production of pasta [19], tea leaves [20], powdered cheese [21], and powdered milk [22,23]. Of these, only the last two refer to spray drying technology at an industrial scale. These exergoeconomic analysis performed were useful for the evaluation of the economic viability of the proposed improvements to the spray dryer in a powdered milk factory. Erbay et al. [21] also performed an exergoeconomic analysis on a pilot-scale spray dryer for cheese powder and concluded that some investments should be made in order to reduce the operational cost rates by increasing exergetic efficiency of the process.

Although the exergy and exergoeconomic analyses allow for the quantification of the exergetic and cost losses, they do not provide sufficient information about which losses are avoidable; this information is essential for industrial plants to make decisions about improvement potential. Advanced exergoeconomic analysis is a proposed tool that has been applied to different industrial processes in order to quantify the avoidable and unavoidable economic losses and determine the potential for improvement [24]. However, there have not been any studies that apply an advanced exergoeconomic analysis in spray-drying technology in order to quantify this kind of exergy destruction.

The aim of the present work is to carry out a conventional and advanced exergy and exergoeconomic analysis on the spray drying process of instant coffee at a factory in Guayaquil, Ecuador in order to quantify total operating cost rates at a component level and split into avoidable and unavoidable parts. There are two main novelties in this study: first, real data from an instant coffee plant in operation have been used; second, an advanced exergoeconomic analysis on the spray-drying system of an instant co ffee plant has been applied for the first time. This analysis will be a valuable decision-making tool for the factory for future improvements focused on operational cost reduction, and sustainability increase.

## **2. Materials and Methods**
