Performances of Fluidized Bed Drying Integrated with Biomass Furnace for Drying of Paddy

A fluidized bed drying integrated with biomass furnace was tested for drying of paddy. The drying of 12 kg of paddy via this drying system reduced the moisture content from 23% (wet basis) to 14% (wet basis) in 1338s and 1007s with average temperature of 60°C and 70°C, respectively. The drying rate varies from 0.15 to 0.48 kg every 300s and 0.2 to 0.5 kg every 300s with the average of 0.27 and 0.335 kg every 300s for average air temperature drying of 60 and 70°C respectively. For temperature of 60°C obtained SMER maximum, minimum and average, respectively: 0.72 kg/kWh, 0.23 kg/kWh and 0.37 kg/kWh. For temperature of 70°C obtained SMER maximum, minimum and average, respectively: 0.66 kg/kWh, 0.26 kg/kWh and 0.38 kg/kWh. The thermal efficiency varies from 14.78 to 47.31% and 17 to 42.49% with the average of 24.31 and 24.93% for average air temperature drying of 60°C and 70°C respectively.


INTRODUCTION
The scientific name for paddy is Oryza sativa L. It belongs to the family of graminae and crops of rice which is the staple food of nearly 90% of Indonesia's population.Indonesia is the third biggest paddy producing country worldwide with its annual production of around 78 million ton (BPS (Badan Pusat Statistik Indonesia), 2015) and also an economic resource of more than 30 million farmers.Paddy after harvest generally have a high moisture content of about 20-23% wet basis in dry season and about 24-27% wet basis in wet season (Purwadaria, 1995).At the level of the moisture content, easily broken rice or not securely stored because it is very susceptible to attack by fungus and insect.Threfore, in order to secure long-term storage or prior to the launch, the paddy needs to be dried as soon as possible to achieve moisture content of about 14% wet basis (Badan Standardisasi Nasional, 2008).
Traditional sun drying and flat bed box dryer (artificial dryer) is commonly used for drying of paddy.Traditional sun drying, where the product to be dried is exposed direcly to the sun has many disadvantages such degradation by wind-blown debris, rain, insect infestation, human and animal interference which will result in contamination of the product and also slow process (Yahya et al., 2001).Flat bed box dryer also has many disadvantages such as cannot produce uniform moisture content and so, some parts of product will be over dried and some other parts will not be dried adequately which will result a lot of broken rice during milling process and slow process (Izadifar and Mowla, 2003).Also, some flat bed box dryers with kerosene burners (fossil fuels) as heat source.It is has many side effects, their combustion products produce pollution, acit rain and global warming.Further, prices of kerosene are steadily increasing (Fudholi et al., 2010;Bhandari and Gaese, 2008).
Recently, various design and performances of solar drying systems for agricultural and marine products were reported (Fudholi et al., 2015a(Fudholi et al., , 2015b)).Many studies have been reported on fluidized bed dryer for drying of paddy.The influence of drying temperature on quality products have been studied by Karbassi and Mehdizadeh (2008), Wiset et al. (2001), Soponronnarit (1999), Soponronnarit et al. (1995) and Bonazzil et al. (1997).The influence of final moisture content on quality products have been studied by Sutherland and Ghaly (1990).The influence of drying temperature and bed thicness on drying rate have been studied by Wetchacama et al. (2000) and Tunambing and Driscoll (1991).
Studies on drying kinetic have been reported by Khanali et al. (2012) and Law et al. (2004).However, there is little information in the literature on performances of fluidized bed drying for drying of paddy.Therefore, the pusposes of this study are to determine the experimental performances of fluidized bed drying for drying of paddy with biomass fuels as heat source.

MATERIALS AND METHODS
The photograph and the schematics diagram of the fluidized bed dryer integrated with biomass furnace as shown in Fig. 1 and 2. The drying system consists of main components such as biomass furnace, fluidized bed, cyclones and blowers.Biomass furnace consists of several main parts such as combustion chamber, heat exchanger, chimney and blower.Wall of combustion chamber uses brick, cement and still plate materials, heat exchanger pipe uses mild still with diameter and number of pipes are 2 inc and 16 unit, respectively, which dimensional of biomass furnace as shown in Fig. 3. Fluidized bed consists of drying chamber, air flow distribution, the inlet and exit of rice, the front part of The experiments are carried out at the Institut Teknologi Padang, West Sumatra, Indonesia.Paddy farmers bought freshly harvested in Padang and as much as 12 kg put into the drying column for the drying process.Biomass fuels is used Coconut shell charcoal.Incoming and outgoing air temperature biomass furnace and drying column is measured using a thermocouple and air flow rate is measured using flow meter.Paddy weight change was measured using scales.Materials were weighed and measured the temperature every 5 minutes.
The performance of drying system was calculated using the following equation.The moisture content of paddy on wet basis was calculated as: where, m w is mass of water (kg) and m d is mass of bone dry (kg).
The rate of extraction of heat from biomass furnace or heat energy that used for drying process was calculated as: where, ݉ሶ air is air mass flow rate (kg/s), C Pair is specific heat of air (J kg -1 °C-1 ) and T i and T o are inlet and outlet air tempetarures of biomass furnace (°C), respectively.
Drying rate is mass of water evaporated from the product per unit time was calculated using the following equation: .
where, m water is mass of water evaporated (kg) and t is drying time (s).
The mass of water evaporated (m water ) from wet product can be calculated as (Fudholi et al., 2014b): where, m p = Initial mass of product (kg) M i = Initial moisture content on wet basis (%) M f = Final moisture content on wet basis (%) The specific moisture extraction rate (SMER) is ratio of the moisture evaporated from wet product to the energy input to drying system and was calculated as (Fudholi et al., 2014a(Fudholi et al., , 2014b(Fudholi et al., , 2015c)): where, E input is energy input to drying system (kWh).The energy input to drying system can be calculated as: where, E bf = Thermal energy of biomass fuel (coconut shell charcoal, kW) E b = Electrical energy consumed by blower (kW) The thermal energy of biomass fuel can be calculated as: where, mሶ bf = Coconut shell charcoal consumption rate (kg/s) CV bf = Caloric value of coconut shell charcoal (kcal/kg) (CV bf was considered as 7600 kcal/kg, Triyono, ( 2006)) The electrical energy consumed by blower can be calculated as: where, V is line voltage (Volt), I is line current (Ampere) and Cosφ is power factor.
Thermal efficiency of drying system is ratio of the energy used for moisture evaporation to the energy input to drying system, was calculated as: The energy used for moisture evaporatian can be calculated as: where, H fg is laten heat of vaporization of water (kJ/kg).

RESULTS AND DISCUSSION
Figure 6 shows the temperature of the drying chamber and air temperature inlet and outlet of the biomass furnace versus drying time at mass flow rate of 0.1256 kg/s.The temperature inlet and outlet of the biomass furnace varies from 34.3 to 38°C and 59.3 to 62.3°C with average is 36.6 and 61°C, respectively for average drying temperature of 60°C.For average drying temperature of 70°C, the temperature inlet and outlet of the biomass furnace varies from 34.7°C to 36.6°C and 68.6°C to 72.7°C with average is 35.4 and 71.3°C, respectively.On the other hand, the biomass energy used varies from 2715 W to 3518 W and the average biomass energy used is 3108 W for average drying temperature of 60 o C. For average drying temperature of 70°C, the biomass energy used varies from 4210 W to 4848 W and the average biomass energy used is 4579 W. Figure 7 shows relative humidity ambient, inlet and outlet of the fluidized bed.Average relative humidity ambient found an average of 67.4% and 72.3% for air temperature drying of 60 and 70°C, respectively.The relative humidity inlet and outlet of the fluidized bed varies from 19.5 to 22.5 and 29.4 to 69.8%, respectively with average is 21.1% and 37.6% respectively for average drying temperature of 60°C.For average drying temperature of 70°C, the relative humidity inlet and outlet of the fluidized bed varies from 12.7 to 15.7% and 23.2 to 65% with average is 13.6 and 34.5% respectively.
Figure 8 shows a relationship of weight change of paddy to the drying time for average air temperature drying of 60°C and 70°C.The drying of paddy via fluidized bed drying integrated with biomass furnace at average air temperature drying of 60 o C reduced the weight from 12 to 10.74kg in 1338s.For average air temperature drying of 70°C, this system reduced the weight from 12 to 10.74 kg in 1007s.
Figure 9 shows relations moisture content of paddy to the drying time for different air temperature drying.Paddy was dried to final moisture content of 14% wet basis from 23% wet basis in 1338s and 1007s for average air temperature drying of 60 and 70°C, respectively.Figure 10 shows drying rate for drying of paddy via fluidized bed drying integrated with biomass furnace for average air temperature drying of 60°C and 70°C.For temperature of 60°C obtained drying rate maximum, minimum and average, respectively: 0.48, 0.15 and 0.27 kg every 300s.For temperature of 70°C obtained drying rate maximum, minimum and average, respectively: 0.5 kg, 0.2 kg and 0.335 kg every 300s.The SMER varies from 0.23 to 0.72 kg/kWh and 0.26 kg/kWh to 0.66 kg/kWh with the average of 0.37 kg/kWh and 0.38 kg/kWh for average air temperature

CONCLUSION
A fluidized bed drying integrated with biomass furnace was tested for 12 kg of paddy.It was dried to the final moisture content of 14% from 23% (wet basis),which mass of water evaporated is 0.126 kg/s.The drying of paddy via this system at average air temperature drying of 60°C reduced the weight from 12 kg to 10.74 kg in 1338s using firing of 1.003 kg.For average air temperature drying of 70°C, this system reduced the weight from 12 kg to 10.74 kg in 1007 s using firing of 1.12 kg.The average SMER of 0.37 kg/kWh and 0.38 kg/kWh for average air temperature drying of 60°C and 70°C respectively.The average thermal efficiency of 24.31 and 24.93% for temperature drying of 60 and 70°C, respectively.

Fig. 1 :
Fig. 1: Photograph of the fluidized bed drying system

Fig. 6 :
Fig. 6: The temperature and biomass energy used versus drying time at mass flow rate 0.1256 kg/s

Fig. 12 :
Fig. 12: The variation of thermal efficiency versus drying time 24.31 and 24.93% for average air temperature drying of 60 and 70°C, respectively.