Performance and Energy Consumption of an Impinging Stream Dryer for High-Moisture Particulate Materials

Abstract

Impinging stream dryers (ISDs) are a novel alternative to flash dryers for high-moisture particulate materials. However, studies on hydrodynamics and heat/mass transfer as well as drying characteristics of an ISD are still limited or incomplete. The effects of various geometric and operating parameters of an ISD on its performance, in particular, are not conclusive. In addition, ISD was tested mainly with model materials that do not represent the real challenge of higher-moisture materials, which tend to be sticky in nature. In this study, modifications were made to an existing coaxial two-impinging stream dryer of Sathapornprasath et al. [1] to make it more suitable for high-moisture particulate materials. This newly modified dryer was then evaluated for its performance in terms of the volumetric water evaporation rate and volumetric heat transfer coefficient. Soy residue (okara), which is a by-product of a soymilk production process, was used as a test material. Particle mean residence time was also evaluated and the results were used to support and explain the performance data of the dryer. Finally, the specific energy consumption of the dryer was assessed at various geometric and operating conditions. The maximum volumetric water evaporation rate was found to be around 520 kg water /m 3 h and the maximum volumetric heat transfer coefficient was around 4,500 W/m 3 K for the mean particle residence time of approximately 0.97-1.74 s. In terms of the specific energy consumption the lowest specific energy consumption was found to be around 5.6 MJ/kg water.

Impingement drying for preparing dried apple pomace flour and its fortification in bakery and meat products

“…This phenomena is not unique to apple pomace, and as such different drying methods have been studied in various fruit pomace and vegetables (Bai et al 2013;Choicharoen et al 2009;Constenla et al 2002;de Torres et al 2010;Khanal et al 2010;Raghavan and Orsat 2007;Tseng and Zhao 2012;Yemmireddy et al 2013). Khanal et al (2010) reported that drying grape and blueberry pomaces at lower temperature for longer time (40°C for 72 h) did not cause significant losses in anthocyanins, while higher temperature drying (125°C) for a much shorter time (8 h) led to 70 % reduction.…”

“…Impingement drying (ID) offers "a novel alternative to flash dryers for high-moisture particulate materials" (Choicharoen et al 2009). ID uses high velocity streams of hot air across the product being dried, which are then circulated back across the heating element.…”

Some Recent Advances in Drying Technologies to Produce Particulate Solids

“…Nevertheless, studies on ISD are still partial or limited to very few applications. In these type of dr yers the intensive collision of opposed streams creates a zone that offers ver y huge heat, mass and momentum transfer 54) . Hence rapid removal of surface moisture is possible.…”

“…However, the design of such system is ver y important particularly the feeding arrangement and the design of the impinging pipes affect the value of volumetric heat transfer coefficient and in turn the water evaporation rate. Recently, Choicharoen et al 54) have carried out performance evaluation of impinging dryer with Okara as a ideal material and concluded that ISD gives very high volumetric heat transfer coefficient and the performance depends on the aforementioned parameters.…”

Report on comparison among current industrial scale lignite drying technologies (A critical review of current technologies)

“…Nevertheless, studies on ISD are still partial or limited to very few applications. In these type of dryers the intensive collision of opposed streams creates a zone that offers very high heat, mass and momentum transfer rates [47]. Drying air and wet solids enter concurrently from the gas inlet port and the material inlet port, respectively.…”