STUDI MEKANISME PROSES TOREFAKSI BASAH UNTUK MENGONVERSI SAMPAH KOTA TIDAK DAUR ULANG MENJADI BAHAN BAKAR PADAT

• Main Author: Triyono, Budi
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/46009
• Institution: Institut Teknologi Bandung

Municipal solid waste (MSW) is a complex problem in major cities in Indonesia and other developing countries that has not been resolved. MSW is currently only collected and disposed to final landfill. On the other hand, national energy security is also an issue to be solved. Utilization of MSW, which is dominated by organic waste, as solid fuel can be a solution for both problems. The largest obstacles in the utilization of MSW as solid fuel in developing countries such as Indonesia are its high water content, irregular size and shape, and difficulty-to-sort due to the mix of plastic and organic waste. There are several techniques to utilize MSW as fuel, i.e. direct combustion, bio-gasification, dry torrefaction (carbonization), and wet torrefaction. Based on a literature study, wet torrefaction could be an appropriate pre-treatment process for mixed MSW because it requires no initial drying and mixed organic-plastic MSW can be processed without initial sorting. Based on a field survey at temporary disposal sites and final landfill of Bandung city in 2016, the composition of the non-recycled MSW was: leaf litter (34.67%), food waste (23.33%), vegetable waste (14.33%), fruit waste (11.00%), and non-recycled plastic (16.67%). In this research, first experiments and analysis were conducted to investigate the effect of wet torrefaction on increasing the fuel properties of individual component of waste. Five types of samples were chosen to represent the five types of waste in MSW with the highest mass fraction found in a field survey: mahoney leaf, rice (starch) waste, cassava stalks, banana peels, and instant noodle packaging plastic. Each sample was treated with wet torrefaction under four conditions: 150, 175, 200 and 225 ºC with holding time 30 minutes. The experimental results showed that a higher operating temperature will increase the calorific value, followed by a decrease in mass yield as a consequence of the process severity degree. However, food waste torrefaction showed different characteristics: the increase in calorific value was followed by an increase in mass yield. This is unique and different from the results of wet torrefaction on other organic wastes. The wet torrefaction temperature of 225 °C and lower temperatures did not affect the fuel properties of plastic waste and only changed its shape into bulky size. This research stage also provide equations to predict the fuel properties of mixed MSW with no interaction assumption. Second experimental study also conducted to investigate the effect of wet torrefaction on increasing the fuel properties of mixed organic-plastic MSW. The experiments were conducted in a 2.5-L stirring reactor temperature variation (150, 175, 200 and 225 °C) and several holding times and solid loads. The result showed that wet torrefaction at a temperature of 200 °C with a holding time of 30 min and a solid load of 1:2.5 was the optimum condition, producing a solid product with a uniform physical shape, small particles and a homogeneous particle size distribution, a calorific value (HHV) of 33.01 MJ/kg and an energy yield of about 89%. The wet torrefaction process is not only suitable to convert the mixed municipal waste into renewable high energy density solid fuel, but it can also be used to produce separate organic product that can be used as solid fuel and a plastic product that can be prepared for other treatments, such as pyrolysis to produce liquid fuel or recycling. The comparison between fuel properties data resulted by experimental of mixed MSW and calculation data provided by previous non-interaction equation showed that there are significant different of results. This proves the hypothesis that there were some interactions between the components of mixed waste during the wet torrefaction process. The third experiments was carried out to investigate the interaction between waste component and showed that the interaction between leaf litter, vegetable waste and fruit waste were relatively small and negligible. However, food waste (starch) interacted significantly with leaf litter, vegetable waste and fruit waste during wet torrefaction process. The fourth experiment was conducted to get data that can be analyzed by the response surface methodology (RSM) to produce the equations of interaction correction number (ICN). By adding the interaction number equation, the final equations were proposed that can be used to predict the fuel properties of wet torrefied product: mass yield, calorific value, volatile matter, fixed carbon, ash content, carbon content, hydrogen content, oxygen content, nitrogen content, and sulfur content. A series of experiments were also conducted to validate the proposed equation. The results showed that the predicting data resulted by proposed equation generally closer to experimental (real) data than non-interaction calculation result. It proved that the proposed equations could be used to predict the fuel properties of wet torrefied product for various waste compositions and operating temperatures. This study provides at least four scientific contributions: (1) the mechanism of wet torrefaction, especially on starch-based biomass, (2) knowledge of interactions between organic wastes (lignocellulosic and starch based) during wet torrefaction, (3) proposed equations to predict the fuel properties of wet torrefied products, and (4) the alternative method for mixing or separating mixed MSW.