Thermodynamic characterization of single-stage spray dryers: Mass and energy balances for milk drying

Abstract

Spray drying is an efficient unit operation applied in food drying that demands a high amount of energy compared to vacuum evaporation and membrane filtration. The objective of this work was to present a mathematical model-like basis for the construction of mass and energy balances. For this purpose, two lab-scale single spray dryers in milk drying with different evaporative capacities have been used as example. The values of the absolute humidity, mass and energy losses, energetic specific consumption (ESC), and the efficiency of the process were obtained by calculations developed in this work. The mathematical model was valid for the evaluation of mass and energy losses, and it allowed us to compare the efficiencies of spray dryers with different designs. From this model, it is possible to compare different drying processes and dryers. ARTICLE HISTORY

Determination of ideal water activity and powder temperature after spray drying to reduce Lactococcus lactis cell viability loss

“…Despite numerous studies that have used the inlet/outlet air temperatures as indicators of cell viability loss in the spray drying process, the combination of these parameters is specific to the equipment or operating conditions tested. In other words, using the same inlet air temperature in 2 different drying towers with different evaporative capacities will not necessarily result in the same outlet air temperature (Silva et al, 2017). In this sense, our study proposes verification of cell viability loss based on the powder properties (Aw and T°C powder ), which may be analyzed independent from the evaporative capacity and design of the spray dryer used.…”

“…The thermal energy used by the equipment to dehydrate the L. lactis cells (E inlet ) was estimated according the following equation proposed by Silva et al (2017):…”

Challenges associated with spray drying of lactic acid bacteria: Understanding cell viability loss

“…The spray dryer shown in Figure 1A operates in the batch mode and the powder concentrate remains in contact with the outlet air throughout the process (Martins, Cnossen, Silva, Cezarino, et al., 2019). This spray dryer (Figure 1A) is designed for laboratory and pilot‐scale use, with water evaporation capacity ranging from 0.5 to 30 kg/h (GEA, 2020a, 2020b; C. R. Silva et al., 2017). When LAB cultures are spray dried, the concentrate is made up of living cells dispersed in a carrier intended to immobilize and protect bacterial cells both during and after drying.…”

Produção e caracterização de produtos lácteos em pó de búfala com e sem hidrólise da lactose

“…Dentre os métodos de secagem mais usuais, a técnica de spray drying apresenta cerca de 10 vezes menos consumo energético que a liofilização (freeze-drying) e, ao contrário da técnica de secagem em tambor (drum drying), o produto não atinge altas temperaturas durante a evaporação da água (SILVA et al, 2017) A secagem via spray dryer consiste em pulverizar o líquido concentrado em pequenas gotículas através de um atomizador, em uma grande câmara de secagem contendo ar aquecido a cerca de 200 °C (essa temperatura pode variar de acordo com o produto a ser seco e irá controlar a taxa de transferência de massa e de energia entre as gotículas do produto e o ar de secagem) (BELLETTI et al, 2009;SCHUCK et al, 2005).…”

“…A temperatura do produto situa-se entre a temperatura do atomizador e a temperatura do ar de saída, ou seja, permanece abaixo de 100 °C (SCHUCK et al, 2009). Devido ao aumento da superfície de contato entre o produto e o ar, a água é evaporada rapidamente sem tratamento térmico excessivo (SILVA et al, 2017).…”