Quality Changes of Superheated Steam–Dried Fibers from Oil Palm Empty Fruit Bunches

Abstract

Conventional drying of the fibers from oil palm empty fruit bunches (EFB) using flue gas from diesel burners frequently causes browning and dust explosion. Replacing the drying medium with superheated steam is expected to improve the quality of EFB fibers as well as improve the safety of the dryer operation. In this study, the effects of steam temperature and steam velocity on the quality of steam-dried EFB fibers was investigated. The drying experiment was carried out at atmospheric pressure with steam superficial velocity in the range of 0.3 to 0.49 m s -1 and temperature in the range of 135 to 200 C. Three quality parameters of the EFB fibers, the color, strength, and microstructure, were used to assess the changes in EFB fiber quality as a result of superheated steam drying. The color of the EFB fiber was either improved or not significantly degraded. The strength of the superheated steam-dried EFB fibers was higher than that of undried and hot air-dried EFB fibers. The microstructure of fresh undried EFB fibers as seen by scanning electron microscopy (SEM) showed the presence of round silica particles of 10-20 mm in diameter all over the EFB fiber strand, which complicates pulping and bleaching. Superheated steam drying successfully removed the silica particles from the EFB fibers at temperatures of at least 200 C and a velocity of steam of at most 0.49 m s À1 , which is better than hammering, which can only remove 88% of the silica particles. The high temperature of the superheated steam loosened the silica particles from their craters. The EFB fibers cracked and split at steam velocities at or above 0.49 m s À1 and high superheated steam temperatures at or above 200 C and as a consequence became weaker at these conditions. The removal of silica particles by superheated steam drying makes the EFB fiber amenable to pulping and bleaching. Superheated steam drying is therefore found to improve the overall quality of EFB fibers compared to hot air drying.

Guest Editorial

“…Atmospheric freeze drying, [6] spray-freeze drying, [1] and foam mat freeze drying of egg white [7,8] are some of the interesting new concepts in drying that are worth pursuing further. These two issues also covered applications of ultrasonics, [9,10] acoustics, [11] microwaves, [12] superheated steam, [13] and pulsations [14] to enhance drying kinetics. The use of drying models to intensify innovations was also covered.…”

Basic Properties of Oven–Heat Treated Oil Palm Empty Fruit Bunch Stalk Fibers

“…The silica bodies were white in color, 11 to 16 m in diameter, arranged in regular patterns, and embedded in extracellular cavities, as previously described (Hasibuan and Daud 2009;Omar et al 2014). Silica bodies were not removed by oven-heat treatment at 100 °C or 190 °C for 15 min.…”

“…Silica bodies were not removed by oven-heat treatment at 100 °C or 190 °C for 15 min. According to Hasibuan and Daud (2009), their removal requires superheated steam drying.…”

“…Hammering (milling) and washing removes only 88% of the silica. In addition, superheated steam drying conducted at 140 °C and a velocity of 0.40 m/s dislodges silica particles without damaging OPEFB fibers (Hasibuan and Daud 2009). According to Omar et al (2014), the absence of silica bodies increases enzyme access to the OPEFB internal layer, resulting in good digestion and hydrolysis during saccharification.…”

“…Heat treatments with various temperatures have been applied to OPEFB in a superheated steam dryer (Hasibuan and Daud 2009), high-pressure autoclave , and superheated steam equipment (Bahrin et al 2012b). To reduce OPEFB moisture content to less than 10 mf wt%, a conventional oven has been used for drying pre-treatments (Khalib et al 2010).…”