768 Journal of Chemical Engineering of Japan Copyright © 2017 The Society of Chemical Engineers, Japan Journal of Chemical Engineering of Japan, Vol. 50, No. 10, pp. 768–774, 2017 Industrial Spray Tower Hot Air Inlets Area Temperature Control Pawel Wawrzyniak, Marek Podyma and Ireneusz Zbicinski Faculty of Process and Environmental Engineering, Lodz University of Technology, 213 Wolczanska Str., 90-924 Lodz, Poland Keywords: CFD Simulations, Counter-Current Spray Drying, Wall Deposits, Deposit Burning An intensive deposition of powder on the walls in the counter-current spray towers develops the risk of deposits burning in the vicinity of hot air inlets. Cooling of the hot air inlets area could reduce wall temperature to avoid deposit burn- ing. CFD calculations were performed to estimate the effect and to optimize the position of cold air inlets on cooling efficiency of the hot air inflow areas in industrial spray tower. To keep the same evaporation capacity of the tower when cold air was introduced, the heat balance of the dryer was recalculated. Experimental analysis of the wall temperature distribution near air inlets enabled validation of the CFD model. Analysis of the results shows a difference in circumfer- ential cool air distribution in all analyzed configurations due to the upward and downward flows of drying gas near the inlet ring. The wall can be cooled also by the downward flow of a drying agent temporarily induced by the instable flow pattern in the whole tower. The simulation methodology developed in this work allows to select the optimal cooling air inlets construction and location. Introduction Drying is one of the most important processing opera- tions in many industries. Due to high energy consumption, the drying process assumes a significant share of the total production costs. Depending on the size of the dryer and the unit cost of the product, the value of the daily produc- tion can reach hundreds of thousands of euros. Most of the dryers operate close to maximum capacity. A further increase of the productivity oſten requires modification of the limiting performance elements of the drying system. Necessary action is exceptionally obvious, but oſten requires temporary cessation of production. No company can afford to stop the manufacturing for matters which will not be compensated by productivity growth. e counter-current spray drying process offers relatively low energy input for evaporation and integration of sev- eral unit operations in one vessel, e.g., drying, agglomera- tion and segregation (Muzammil et al., 2013; Soltani et al., 2015). However, counter-current spray drying is one of the processes for which the knowledge of the mechanism of heat, mass and momentum transport, parameters control- ling drying process, quality interactions, etc. is still limited (Rahse and Dicoi, 2001; Fletcher et al., 2006; Francia et al., 2015). Due to complex dynamics of air and dried particles, an intensive deposition of the powder on the walls in the counter-current spray towers develops the risk of deposits burning in the vicinity of hot air inlets. Decreasing gas tem- perature to avoid product deterioration, the productivity of the tower will be limited. Air cooling of areas endangered by the deposit burning area could reduce wall temperature and allow to increase the dryer capacity. e present paper presents the application of the previ- ously validated CFD model capable of predicting the air temperature in the vicinity of hot air inlets. CFD calcula- tions were performed for 5 configurations of cooling air in- lets in an industrial spray tower. e evaporation capacity of the tower was constant to estimate the effect and to optimize the position of cold air inlets on cooling efficiency. 1.ɹMotivation A CFD calculation offers the possibility to analyze and estimate the effect of cold air jets on wall temperature and to optimize the position of cooling air inlets (Zbiciński and Li, 2006; Muzammil et al., 2013). A previously developed and validated CFD model of the industrial counter-current spray drying process would allow us to evaluate the configuration of cooling air inlets and to reduce wall temperature in the vicinity of hot air inlets, leading to dryer capacity increase (Wawrzyniak et al., 2012c). 2.ɹExperimental 2.1ɹDrying tower A schematic diagram of the drying tower is shown in Figure 1. e dryer total height was 37 m and its inner di- ameter was 6 m. At the top of the drying tower, there was a sackcloth filter. From the top of sack filters to the bottom of the cone, the drying chamber was 33 m high. e dryer wall was insulated with mineral wool. A detailed description of the system has been presented earlier (Wawrzyniak et al., 2012a). Received on January 6, 2017; accepted on June 8, 2017 DOI: 10.1252/jcej.16we387 Presented at the 20th International Drying Symposium (IDS 2016), Gifu, August 2016 Correspondence concerning this article should be addressed to P. Waw- rzyniak (E-mail address: pawel.wawrzyniak@p.lodz.pl). Research Paper