Sustainable Solar Drying of Brewer’s Spent Grains: A Comparison with Conventional Electric Convective Drying

Abstract

Spent grains from microbreweries are mostly formed by malting barley (or malt) and are suitable for a further valorization process. Transforming spent grains from waste to raw materials, for instance, in the production of nontraditional flour, requires a previous drying process. A natural convection solar dryer (NCSD) was evaluated as an alternative to a conventional electric convective dryer (CECD) for the dehydration process of local microbrewers’ spent grains. Two types of brewer’s spent grains (BSG; Golden ale and Red ale) were dried with both systems, and sustainability indices, specific energy consumption (eC), and CO2 emissions were calculated and used to assess the environmental advantages and disadvantages of the NCSD. Then, suitable models (empirical, neural networks, and computational fluid dynamics) were used to simulate both types of drying processes under different conditions. The drying times were 30–85 min (depending on the drying temperature, 363.15 K and 333.15 K) and 345–430 min (depending on the starting daytime hour at which the drying process began) for the CECD and the NCSD, respectively. However, eC and CO2 emissions for the CECD were 1.68–1.88 · 10−3 (kW h)/kg and 294.80–410.73 kg/(kW h) for the different drying temperatures. Using the NCSD, both indicators were null, considering this aspect as an environmental benefit.

Mechanical Property Comparison of Geopolymer Brick Dried by Electrical and Passive Solar Devices with Phase Change Material (Paraffin Wax)

“…Solar drying with a PCM consumes 2 h less curing time when compared to all other methods, which is in accordance with [21]. This is due to the effect of the PCM which captures more heat flux in the form of heat storage, giving rise to a hotter and more uniform atmosphereinside the solar dryer when compared to the solar dryer without a PCM.…”

“…This could be due to the effect of the ambient, which is hotter when compared to that for electric drying, which occurs inside a room. This is also evident from [21], which predicts that solar drying is more efficient and economical when compared to electric drying. Also, solar drying with a PCM shows higher compressive strength, tensile split strength, and flexural strength when compared to solar drying without a PCM, which is due to the higher heat storage capacity of the PCM and the fact that changes in the atmospheric temperature are well absorbed by the PCM, which gives rise to rough, tough, and dry conditions in the brick.…”

“…➢ GPBs constructed from fly ash waste and other ingredients undergo full curing in all four methods. ➢ A solar dryer with a PCM consumes 2 h less curing time when compared to all other methods [21]. ➢ As per modified guidelines for geopolymer concrete mix design using Indian standards, the target compressive strength is around 30 MPa [2,3], but the experimental result obtained was 38.50 MPa for solar-dried brick with a PCM.…”

“…Mohammed Rihan Maaze and Sandeep Shrivastava recommended a curing temperature between 40 and 60 • C for the efficient curing and good physical and mechanical properties of GPBs. A solar dryer was used as an alternative and compared with conventional electric convective drying [21]; it was shown that solar drying consumes less curing time when compared to conventional electric drying. Various advancements in fiber polymer composites are emerging because of their increased use in a myriad of applications, like polymer in bricks for construction applications [22,23].…”

Water Splitting by MnOx/Na2CO3 Reversible Redox Reactions

“…A 0.05 m internal vibrated fluidized bed reactor was used. The advantages of using solar concentrated as a heat source were recently highlighted in number of publications with respect of solar-topower uses [23][24][25], solar-driven thermo-chemical reactions [4,25] and solar-driven physical applications [26][27][28]. Water/steam and N2 carrier gas were preheated in a coil heat exchanger within the cavity as illustrated at the right of the reactor in Figure 4.…”