Biomass Gasification as a Sustainable Energy Technology for Small Food Processing Industry

Transcription

1 Biomass Gasification as a Sustainable Energy Technology for Small Food Processing Industry Nakorn Tippayawong, Chutchawan Chaichana, Anucha Promwungkwa, Prasert Rerkkriangkrai, Asira Bunkham 0189 Chiang Mai University, Thailand The Asian Conference on Sustainability, Energy and the Environment 165

2 1. Introduction Food processing industry is one of the most important sectors in Thailand. Fish balls are popular in Thai cuisine. Usually, they are fried, grilled or cooked in noodle or curry. Typical fish balls are a mixture of de-boned fish flesh, starch, salt, sugar, monosodium glutamate, and water. Once the paste is prepared, it is formed into a ball shape, put into warm water, and allowed to set. After setting, fish balls are cooked by dropping into hot water, followed by chilling with cold water. After draining, they are packed, and ready for cold storage and subsequent distribution to marketplace. Fish ball manufacturing process is energy-intensive, consuming large amount of fuels. Energy cost represents a major fraction of initial cost for fish ball processing. Normally, thermal energy is provided from wood burning which may have serious socio-environmental impacts including emissions of greenhouse gases, smoke, and tars, leading to complaints from neighboring communities. Direct firing of biomass in furnaces, semi open pits, and other open burning application is notoriously poor. Combustion efficiency is generally low with high smoke and noxious emissions, and process control is difficult and limited. This will bring about more serious air pollution and adverse effect on human health, especially those workers who are directly exposed to the emissions. Alternative utilization method is therefore needed. Gasification offers optional conversion technique for the biomass residues available that has high energy efficiency and environmental acceptability (Chopra and Jain, 2007; Kirubakaran et al., 2009). Gasification is a thermochemical processing of a fuel into producer gas. The process produces combustible gases like CO, H 2 and HCs, from the following reactions (De Bari et al., 2000); Gasification: Biomass char + tar + gases (H 2, CO, CO 2, CH 4 ) (i) Thermal decomposition: tar gases (H 2, CO, CO 2, CH 4 ) (ii) Generation of simple-to-use gaseous fuels from solid materials makes gasification very attractive. Burning of this combustible gas is cleaner, and process control is simpler than combustion of solid materials. Many kinds of biomass materials have been successfully converted, including woods, grasses, herbaceous plants, energy crops, agricultural residues, and solid wastes. The hardware involved is relatively economical for use in small scale enterprises and in rural areas. Several types of biomass gasifiers have been developed and demonstrated. Among the most popular design of gasifier adopted was downdraft system. In this work, waste woods have been utilized as a source of clean energy via gasification. A simple downdraft fixed bed gasifier system was developed. It was installed and operated at a small fish balls manufacturing factory, with the aims to reduce operating cost of current practice, and to demonstrate a cost effective and practical producer gas burner to provide process heat with appropriate gasification technology. Experimental data obtained from the operation were presented. Analysis of its energy use and operating cost was conducted, and compared with existing combustion system. 166

3 2. Methodology The fish ball factory is in Samutsakorn, Thailand. This small enterprise produces fish balls that are distributed and sell locally. Its 3-m 3 hot water container is heated by a locally made furnace, consuming about 60 ton of fuelwood a month. This costs around 1500 Euro per month (1 Euro = 40 Thai baht, exchange rate on March 2011). Cost of fuelwood tends to increase as supply is becoming difficult. Furthermore, the factory is situated near residential area where smoke and emissions may be offensive, especially during cold seasons. Existing wood fired furnace was modified to accommodate a gasifier and a gas burner. Waste woods with heating value of 16 MJ/kg were used as fuel feed. Limited test run was carried out to evaluate performance of the system. A single-stage, downdraft, throat-type, fixed-bed gasifier was designed and built (shown in Fig. 1). The gasifier components included an insulated cylindrical reactor, a rotatable grate, an air drive, and an ash pit. Loading of fuel feedstock was done from the top, piling on the grate. The reactor wall was made of firebrick and covered with a steel sheet. Air was induced through circumferential holes by a fan downstream. The gasifier core was designed such that a cross section area was reduced downstream of the air inlets to form a throat or constriction. The reactor volume was designed to require refueling once every two hours when working at rated capacity. The grate area of 0.13 m 2 was designed from specific gasification rate of 270 kg/h/m 2 and the fuel feed rate of 35 kg/h. Ash formed was removed from the gasifier by the rotatable grate and fell into a water sealed, ash pit. The volume of the ash pit was sufficiently large to allow long hour operation without ash removal. The system consists of the gasifier, a gas conditioning system and a gas burner. Bottom of the main reactor was tightly sealed by water. The gas burner was put in place beneath the existing water tank used for boling. Initially, a small amount of burning charcoal was used to establish a fire on the grate inside the gasification reactor. The induced draft fan was started, drawing air in to sustain combustion. Immediately afterwards, the waste woods were loaded, and the lit was closed. Air was regulated by valves in such a way that combustible producer gas was generated. This would take about min for a stable flame at the gas burner to be established. Producer gas was utilized to provide hot water to process fish balls. 167

4 Fig. 1 Biomass gasifier - burner system setup Measurements were taken by monitoring fuel consumption rate and amount of water used on an hourly basis. The gas flow rate was measured with a volume meter. The cool, dry, clean gas was sampled using gas bags and analyzed on a Shimadzu model GC-8A gas chromatograph for measuring volumetric concentration of H 2, CH 4, CO, CO 2, O 2 and N 2. Standard gas mixtures were used for quantitative calibration. Gas temperature at the gasifier exit and flame temperature were measured with type K thermocouples. 3. Results and Discussion Operators were trained to run the system by a team of engineers and technicians. The gasifier was able to start between 5-15 min and attain steady state operation from cold start in about min. Combustion zone in the gasifier may be viewed through an observation aperture. After attaining steady operation, the gasification system appeared to run smoothly. Producer gas fueled stable flame was established. No tar problem and no visible smoke were observed. As a precaution, the reactor was poked at regular interval to avoid biomass flow obstruction due to bridging, throat or channel formation. Several test runs on the system were carried out. Producer gas could be ignited successfully in which bright orange flame was established. Gas production rate was found to be about 450 m 3 /h/m 2. The gas temperature leaving the reactor was found to vary from o C. Composition of the producer gas was 10-15% CO, 10-15% H 2, 2-3% CH 4, 10-20% CO 2, 3-5% O 2, and balance N 2. The gaseous fuel s lower heating value was estimated to be about 3.70 MJ/m 3. This may be attributed to low percentages of CO and H 2, hence low value of the heating value of the producer gas. In comparison with those reported in the literature (shown in Table 1), CO and H 2 obtained in this work were indeed comparatively small, resulting in relatively low value of heating value. 168

5 Table 1 Comparison of gasifier performance with literature Reference feedstock CO (% v/v) H 2 (% v/v) LHV (MJ/m 3 ) This work Waste wood Dogru et al. (2002) Hazelnut shells Zainal et al. (2002) Wood chips Sharma (2009) Acacia wood Sheth and Babu (2009) Waste wood Erlich and Fransson (2011) Wood pellets Tippayawong et al. (2011) Cashew nut shells Sharma (2011) Hard wood Q in 175 kw η= 27% Q out 47 kw loss Fig. 2 Energy conversion in the gasifier boiler system About 10% of the biomass feed input was left as bottom ash. Visual inspection of ash showed some tiny bits of charcoal. It was worth noting that no clinkering or agglomeration of ash was observed. The thermal energy output was about 50 kw which was sufficient for generating hot water for fish ball processing in the factory. Fig. 2 shows energy diagram of the new system. From the rates of hot water generated and biomass fuel consumed, the system thermal efficiency was estimated to be 27%, a significant improvement from the existing hot water generator system with only 15% efficiency. The newly introduced system can save fuel woods at around 20 ton a month. Up to the time of reporting, the system has been in use for over 12 months. Results were consistent throughout the field test runs. The owners were happy, and satisfied with the installation of the gasifier system, in place of the existing furnace. Economic performance was evaluated, based on analysis of a simple period to positive cash flow, where the initial investment and additional operating costs, and the wood fuel cost savings were considered. Positive cash flow was reached when the investment and cumulative operating costs were equal to the cumulating fuel cost savings. In this simple analysis, no discount rate was taken into account. The overall installation cost included costs for an induced draft fan, gas burner, refractory and structural materials, piping, insulation, painting, engineering design and construction expenses. The additional operating cost was from maintenance cost and miscellaneous operating materials associated with the gasifier system that would not be present in the wood-fired furnace. The gasifier system required an investment of about 2800 Euro and an additional operating cost of about 20 Euro a month. Saving in fuel cost was approximately 500 Euro a month. This resulted in a simple period to 169

6 positive cash flow of less than six months. This system was economically attractive to potential users because its useful life is expected to be several years. Combustion of producer gas was much cleaner than burning waste wood directly, hence complaints from neighbors were reduced. Smoke and noxious gas emissions were expected to decrease significantly. Workplace environment was cleaner. Effect to human health, especially the factory workers was reduced. There was also skill development among the employees who trained to operate the system. There are plans to implement similar modification to other similar small and medium enterprises in the country. This factory can become a demonstration site for others to come and learn from their experience. 4. Conclusion Gasification as sustainable energy conversion technology for solid biomass materials was considered in this study. The downdraft throat-type gasifier was found to perform satisfactorily well with waste woods for hot water generation. Producer gas generated was successfully utilized to fuel a burner at required thermal output rating for processing fish balls. Overall thermal efficiency was significantly improved, leading to significant fuel saving. The operators and owners were satisfied with the system. Analysis results showed that the gasifier system operation was economically attractive. Acknowledgement This work was supported by the Fund for Energy Conservation Promotion, Thailand s Energy Policy and Planning Office, Ministry of Energy. The authors would also like to thank technical and secretarial staff from the Energy Research and Development Institute, Chiang Mai University. Kind cooperation from Mr Adul Chawalitporn was appreciated. References Chopra, S. and A. Jain (2007) A review of fixed bed gasification systems for biomass, Agricultural Engineering International: CIGR E-journal, vol. 9. Available at: De Bari, I., D. Barisano, M. Cardinale, D. Matera, F. Nanna and D. Viggiano (2000) Air gasification of biomass in a downdraft fixed bed: a comparative study of the inorganic and organic products distribution, Energy and Fuels, vol. 14, pp Dogru, M., C. R. Howarth, G. Akay, B. Keskinler and B. Malik (2002) Gasification of hazelnut shells in a downdraft gasifier, Energy, vol. 27, pp Erlich, C. and T. H. Fransson (2011) Downdraft gasification of pellets made of wood, palmoil residues respective baggase: experimental study, Applied Energy, vol. 88, pp Kirubakaran, V., V. Sivaramakrishnan, R. Nalini, T. Sekar, M. Premalatha and P. Subramanian (2009) A review on gasification of biomass, Renewable and Sustainable Energy Reviews, vol. 13, pp

7 Sharma, A. K. (2009) Experimental study on 75 kw th downdraft (biomass) gasifier system, Renewable Energy, vol. 34, pp Sharma, A. K. (2011) Modeling and simulation of a downdraft biomass gasifier I: model development and validation, Energy Conversion and Management, vol. 52, pp Sheth, P. N., and B. V. Babu (2009) Experimental studies on producer gas generation from wood waste in a downdraft biomass gasifier, Bioresource Technology, vol. 100, pp Tippayawong, N., C. Chaichana, A. Promwungkwa and P. Rerkkriangkrai (2011) Gasification of cashew nut shells for thermal application in local food processing factory, Energy for Sustainable Development, vol. 15, pp Zainal, Z. A., A. Rifau, G. A. Quadir and K. N. Seetharamu (2002) Experimental investigation of a downdraft biomass gasifier, Biomass and Bioenergy, vol. 23, pp

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