Performance Analysis of Horizontal Tube Coffee Roaster Heated by Combustion of Producer Gas of Biomass Gasification

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1 Performance Analysis of Horizontal Tube Coffee Roaster Heated by Combustion of Producer Gas of Biomass Gasification Bambang Purwantana 1 Arjanggi Nasution 1 Nursigit Bintoro 1 and Bambang Prastowo 2 1 Faculty of Agricultural Technology, Universitas Gadjah Mada, Jl. Flora, Bulaksumur, Yogyakarta 55281, Indonesia, bambang_pw@ugm.ac.id. 2 Indonesian Center for Estate Crops Research and Development, Jl. Tentara Pelajar No. 1, Cimanggu, Bogor 16111, Indonesia Abstract Coffee roaster usually developed by use of oil fuel, LPG, or electricity as heat resources. Nowadays these resources are tends to limited and expensive. The use of gas produced from biomass gasification for coffee roasting is an appropriate alternative as it is cheap and environtmentally sound. This research was done to determine the design and operational parameters of horizontal tube coffee roaster heated by combustion of gas of biomass gasification. The experiments were conducted by modifies the LPG based horizontal tube coffee roaster to the biomass gasification stove based coffe roaster. The experimental variations were length of tube, rate of gasification air input, dimension of coffee bean, and weight of coffee per batch of roasting. The roasting performance measured were final moisture content and colour of the roasted coffee bean. The results showed that the heat of combustion of gas produced from biomass gasification could be employed to substitute the LPG. The quality of roasting was similar as light to medium roast. The heat transfer process from gasification stove to the roaster tube should more be improved by modification of stove, that is enlarging burning area of gasification stove. In the operational aspect, the rotation speed of roaster tube could be set lower to match the heat capacity of gasification stove. Keywords: roaster, coffee, biomass gasification, performance, uniformity Introduction In 2012, coffee plantation area in Indonesia was 1.31 million hectare. The national production of coffee bean was about 600,000 ton/year, and there was less than 20% are processed and marketed in secondary products. A roasting process of coffee bean is needed in developing the secondary level products such as coffee powder. Coffee roasting is a heat treatment process as a stage to develope a specific aroma and taste of coffee. There are four steps in roasting process, i.e: drying, releasing volatile, decomposition, and complete roasting. The initial change is take place at 50ºC and above, in which the protein is took apart and the water is evaporated. Browning is take place above of 100ºC due to pyrolysis processs of organics compound. At about 150ºC the volatile products (CO 2 and CO) are released. Decomposition is started at ºC, indicated by cracking of the bean, releasing bluish smoke and coffee aroma. The roasting process completed at temperature of ºC. Ridwansyah (2003), classifies the coffee roasting temperature as three categories, that are: 1) Light Roast (193ºC-199ºC). 2) Medium Roast (204ºC), and 3) Dark Roast (213ºC- 221ºC). The roasting time are vary from 7 to 20 minute depended on the moisture content of E14-1

2 bean and quality of the product needed. Degree of roasting could be determined based on the colour of bean. The roasting process is stopped when the colour of roasted bean is same with standard sample or reference. The degree of roasting is also related to the broken level or loss of roasted coffee bean. Light roast has 3-5 % loss, medium roast has 5-8 % loss, and dark roast has 8-14 % loss (Sumarsono, 2011). Roasting machines are usually use oil fuel, natural gas, electricity, or biomass combustion as heat resources. First of these three resources are tends to limited and expensive, while direct biomass combustion is not environmentally good. An alternative way to utilize inexpensife and clean energy as well as low emission is application of biomass gasification method. Biomass gasification is a degradation method of biomass into form of gases components by used of high temperature in limited of oxygen condition. The main gases produced from biomass gasification are H2, CO, and CH4 (Lim and Sims, 2003). Compared with direct biomass combustion, biomass gasification is better as it has higher energy efficiency, clean, and no emission. In energy terminology, conversion efficiency of biomass gasification was 60 70% (McKendry, 2002). Some basic design of biomass gasifiers have been developed in Faculty of Agricultural Technology Universitas Gadjah Mada, Yogyakarta (Purwantana, 2007; Purwantana et.al, 2011). The experimental results indicated that combustion of gas produced from biomasss gasification had high temperature, clean, and less emissions. Saravanakumar et. al, (2007) using a bottom lift updraft gasifier and wood as a fuel, resulted 73% of energy efficiency and temperature of gas combustion of 750ºC. Sutarjo et. al, (2002) using updraft gasifier with shell of palm oil as a fuel resulted 590ºC to 677ºC temperature of gas combustion. Purwantana et. al, (2013) conducted gasification of oil palm empty fruit bunch using updraft gasifier integrated to the low pressure stove and resulted the temperature of gas combustion of 559 C. Based on the temperature performance of combustion of gas produced from biomass gasification, it has potential to be used as heat resources in coffee roasting. This research was done to determine the design and operational parameters of horizontal tube coffee roaster heated by combustion of gas of biomass gasification. Operational parameters of coffee roaster and gasification stove will be determined to find the best roasting performance. Materials and methods The research was conducted in April to September 2012 in the Laboratory of Farm Machinery and Energy, Faculty of Agricultural Technology, Universitas Gadjah Mada, Yogyakarta. The main tools were: updraft gasifier of 140 cm in high and 60 cm in diameter, horizontal tube roasting machine with capasity of 5 kg/batch, and low pressure gasification stove. The instruments were: stop watch, K type thermocouples, digital thermometer, anemometer, caliper, and balance. The materials used were: coffee bean and rice husk as gasifier fuel. The experiments were carried out each in three variations of initial weight of coffee inputing in the roaster, diameter of coffee bean, length of roaster tube, and rate of air input of gasification respectively. The measured data were temperature of stove flame, temperature in roaster tube, decrease of moisture content, and the change of coffee colour. Configuration of the roaster, gasifier and their instrumentation is shown in Figure 1. E14-2

3 Figure 1. Configuration of machine and instrumentation The coffee bean moisture content was measured by thermogravimetry method that was by evaporating the water from the coffee using oven. The percentage of wet basis mouisture content was determined by divide the difference of weight before and after oven to the weight of bean before oven. The quality of roasted coffee bean were analyzed using RGB based colour which determined based on the average brightness level of red, green, and blue colours (Muttalib, 2011). Results and discussion Table 1 shows result of preliminary experiment on the characteristic of temperature in some point areas due to variation of air input of gasification. The result shows that high temperature of stove flame and in the roaster tube was reached at air input rate of 93 and 187 l/min. Based on this result the gasification for roasting process was set at air input of 187 l/min. Table 1. Characteristic of temperature at various air input of gasification No Rate of air input (l/min) Temperature of stove flame (ºC) Temperature in roaster tube (ºC) Temperature in exhaust (ºC) The characteristic of temperature also shows that it was still ineffective heat transfer happen in the system. From the potential temperature of 400 ºC at stove point resulted only 100 ºC to 150 ºC temperature in the roaster tube, while the temperature in exhaust area was E14-3

4 still high, that was 200 ºC to 250 ºC. Although the temperature in the roaster tube was enough to be used for roasting process, the heat transfer process from gasification stove to the roaster tube should more be improved such as by enlarging the burning area of gasification stove. An indication performance of roasting process is decreation rate of moisture content. In this research the roasting process was took in 20 minute using 5 kg capasity of horizontal roaster. The decrease of the moisture then be compared to the standard moisture content of light roast, medium roast, and dark roast coffee. Table 2 shows the moisture decrease of coffee at various weight of coffee inputing in the roaster. It shown that 20 minute periode of roasting process was not enough to produced roasted coffee at standard moisture content; there is addition time needed to reach these standards. At 50% of capasity it still produced light roast standard of roasted coffee. Table 2. Moisture decrease at various weight of coffee inputing in the roaster No Coffee weight (kg) Roasting process of small size coffee bean resulted a dark roast coffee, while roasting of medium sizes coffee bean resulted light to medium roasted coffee (Table 3). The results indicate that heat capasity available in the roaster tube was still limited for big sizes of coffee due to inefective heat transfer from the stove to the roasting plenum. Table 3. Moisture decrease at various diameter of coffee No Coffee diameter (mm) (Smal) (Medium) (Big) 5.63 Preliminary experiment resulted the bigger air input the higher temperature of gas combustion in the stove. It was linear to the decrease of moisture content, where the bigger air input the bigger decrease of moisture (Table 4). At air input of 93 and 187 l/min resulted the decrease of moisture equivalent to light roast and medium roast. Table 4. Moisture decrease of coffee at various rate of gasification air input No Rate of air input (l/min) Roasting treatment was also took in vaious length of roaster tube. Nominally, although it was not significantly difference, there were decreation of moisture content rate at longer roaster tube (Table 5). In this research the change of tube length was still not followed by the change of stove dimension. E14-4

5 No Table 5. Moisture decrease at various length of roaster tube Length of roaster tube (cm) The temperature and decreation of moisture content affects the colour characteristic of roasted coffee. The higher temperature the darker colour of roasted coffee. It was parallel to the decrease of moisture. Table 6 to Table 9 shows the colour of roasted coffee at various roasting treatments. In general the roasting by use of heat of combustion gas produced from biomass gasification resulted roasted coffee in light to medium standard. Table 6. Colour of roasted coffee at various weight of coffee in the roaster No Wight of coffee (kg) Mean of RGB Table 7. Colour of roasted coffee at various diameter of coffee bean No Cofee diameter (mm) Mean of RGB Table 8. Colour of roasted coffee at various rate of gasification air input No Rate of air input (l/min) Mean of RGB Table 9. Colour of roasted coffee at various length of roaster tube No Length of roaster Mean of RGB tube (cm) There are several options to improve the roasting performance. In the design aspect, modification of stove sholud be done in order to enlarge the heating locus on the roaster tube and minimized heat losses from the exhaust. In the operational aspect, the rotational speed of the roaster tube should be set slower to match the heat capasity of the gasification stove. E14-5

6 Conclusion The combustion heat of gas produced from biomass gasification could be employed for roasting process of coffee. In periode of 20 minute roasting resulted a light to medium standard. Effective reduction of moisture content could be done by setting the bigger flow rate of gasification air input and lower length of roaster tube. At the same duration of roasting time, the higher roasting temperature the darker roasted coffee. Modification of gasification stove is needed to focused heating locus on the wall of roaster tube. The rotational speed of the roaster tube should be set slower to match the heating capasity. References 1. Lim, K., Sims, R. (2003). Liquid and Gaseous Biomass Fuel, Bioenergy Option for Cleaner Environment. Elsevier, UK.. 2. McKendry, P. (2002). Energy Production from Biomass. Bioresource Technology Vol. 83: Muttalib, S. A. (2011). Studies on the quality of mixed Robusta and Arabica coffee by used of Neural Network method and Principle Component Analisys (in Indonesian). Faculty of Agricultural Technology, Universitas Gadjah Mada, Yogyakarta 4. Purwantana, B. (2007). Development of Gasifier for Gasification of Arenga Pinnata Wurmb (in Indonesian). Agritech Vol. 27 No Purwantana, B., Prastowo, B., Markumningsih, S., (2011). Conversion of Empty Fruit Bunch of Oil Palm for Renewable Energy (in Indonesian). Proceeding of National Seminar of Estate Crop Innovation. Indonesian Center of Estate Crop Research and Development, Jakarta October 15, Purwantana, B., Prastowo, B., Abineno, J.C., (2013). Gasification of Empty Fruit Bunch of Oil Palm by Use of Updraft Gasifier (in Indonesian). Jurnal Teknotan Vol 7 No 1: Ridwansyah Coffee Processing (in Indonesian). #hl=id&biw=1280&bih=569&q=pengolahan+kopi 8. Saranavakumar, A., Haridasan, TM., Reed, TB., (2007). Eksperimental Investigation of Long Stick Wood Gasification in Bottom Lift Updraft Fixed Bed Gasifier. International Journal Fuel Processing Technology. Elsiever. pp Sumarsono, (2011). Coffee Roaster (in Indonesian). E14-6