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Bio Gas Plant Green Energy From Poultry Wastes In Singapore
Available online at www.sciencedirect.com
ScienceDirect
Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia
Energy (2017) 000–000 436–441 EnergyProcedia Procedia143 00 (2017) www.elsevier.com/locate/procedia
World Engineers Summit – Applied Energy Symposium & Forum: Low Carbon Cities & Urban Energy Joint Conference, WES-CUE 2017, 19–21 July 2017, Singapore ThePlant 15th International DistrictPoultry Heating and Wastes Cooling Bio Gas Green Symposium Energy onFrom In Singapore
Assessing the feasibility of using the heat demand-outdoor temperature function for Dr a long-term district heat demand forecast Liew Kian Heng b I. Andrića,b,c*, A. Pinaa, Consultant, P. Ferrãoa, J.Liew Fournier ., B. Lacarrièrec, O. Le Correc Strategics a
IN+ Center for Innovation, Technology and123 Policy Research Técnico, Bt Merah Lane- Instituto 1#04-118Superior Singapore 150123Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France
Abstract
Singapore is a land scarce nation where farming space is very limited competing with other critical uses for a growing population. Farms taking up large tract of land and generate wastes face many unsurmountable difficulties and regulatory compliances on Abstract sustainability issues. Poultry farm is not the best type of industry due to polluted wastes generated and foul smell emissions. Yet an 800,000 chicken egg-producing farm in the last bastion of farming land in Singapore called Lim Chu Kang has evolved to District heating networks are commonly addressed in the literature asdemands, one of the most effective solutions for decreasing the overcome the space constraints, environmental regulatory, sustainability production efficiencies and green energy push gascarbon emissions from the building sector. Thesethe systems require high investments which are returned through theinto heat ingreenhouse lowering the footprint. This company has been first successful farm in Singapore to convert chicken wastes sales. as Due changed climate conditions building renovation policies, in itthe could decrease, biogas fuelto tothe generate electricity. In doing so,and it has reduced the polluted wastesheat anddemand transform intofuture energy toward selfprolonging recovering the investment return sufficiency, waste heat period. from the turbine exhaust for drying of chicken feed. The power generated is up to 1 MW while The mainwater scopeinofthe this paper digester is to assess the feasibility of using heatinto demand outdoor temperaturefertilizers. function for heat demand the waste aerobic is treated and extracted thethe sludge dried–cake for agricultural Excess energy forecast. Thesold district Alvalade, located was inused as aefforts case study. The district is consisted energy of 665 could also be to theof Singapore Power Gridinas Lisbon income.(Portugal), This company its CSR has invested this waste-to-green technology as a vary creative first construction mover while period increasing security, fighting foodscenarios scarcity (low, promoting safe high) eggs for people of buildings that in both and food typology. Three weather medium, andthe three district Singapore. initiatives on achieving international green deep). energyTo recognition and error, improving on green energy efficiencies renovationFurther scenarios were developed (shallow, intermediate, estimate the obtained heat demand values were would be the steps forward the benefits Singapore. Green energy production is anvalidated essentialby way meeting energy needs as compared with results fromfor a dynamic heatofdemand model, previously developed and theofauthors. the inevitable depletion of non-renewable energy sources coupled with climate change are now global challenges. adopted a The results showed that when only weather change is considered, the margin of error could be acceptable for someItapplications zero-waste to reduce waste stream airfor pollution with an anaerobic digester and a biogasafter power plant fuelled by 50 (the error policy in annual demanditswas lower thanand 20% all weather scenarios considered). However, introducing renovation tonnes of chicken manure day. Theupbiogas is used to generate electricity power the scenarios farm’s infrastructure, its scenarios, the error valueper increased to 59.5% (depending onheat the and weather and renovation combinationincluding considered). new co-generation feed dryer. The digester liquor is treated and treated water is recycled for the initial dilution of manure to enhance The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the the digestion process. Sludge undergoes a belt press to separate solids and liquid resulting in bio solid cake used for making decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and fertilisers. This integrated system ensures that by-products can be reused, minimizing waste and reducing emission of greenhouse renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the gases by adapting biogas for green electricity production. coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the World Engineers Summit – Applied Energy Symposium & © 2017 The Authors. Published by Elsevier Ltd. Forum: Low Carbon Cities & Urban Energy Joint Conference. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. Keywords: green energy; biogas; biomass; anaerobic digester; waste management; heat recovery; pollution control; carbon neutral; sustainability Keywords: Heat demand; Forecast; Climate change
1876-6102 © 2017 The Authors. Published by Elsevier Ltd.
Peer-review under responsibility of the scientific committee of the World Engineers Summit – Applied Energy Symposium & Forum: Low Carbon Cities & Urban Energy Joint Conference. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the World Engineers Summit – Applied Energy Symposium & Forum: Low Carbon Cities & Urban Energy Joint Conference. 10.1016/j.egypro.2017.12.708
2
Liew Kian Heng et al. / Energy Procedia 143 (2017) 436–441 Author name / Energy Procedia 00 (2017) 000–000
437
1. Introduction Renewable sources of energy have been the point of interest in the world due to climate changes and the inevitable depletion of finite resources such as coal and oil. This is one of Singapore’s main interests as there is a limited amount of natural resources to work with. Due to its geographical location and features, there is a lack of tidal and wind energy that can be used for producing electricity. On the other hand, it sits on an area that has very good geothermal activity underground but it has not been tapped on because it is unfeasible from an economical point of view [1, 2]. Biogas is a relatively new area in the energy industry in Singapore and will be the focus of this paper. Although solar energy is currently considered to be the most viable option for renewable energy in Singapore [2], biogas was not taken into consideration in the assessment as biomass is not extensively available in the highly urbanized city. However, this can be different depending on its application; places like farms creates waste products that are mostly biomass which will be able to be fuel the production of biogas. In Singapore, there has not been an integrated facility that has achieved a zero-waste policy through the utilisation of biomass yet. A project that aims to achieve this with its facilities is one co-planned between the National Environment Agency’s (NEA’s) Integrated Waste Management Facility (IWMF) and Public Utilities Board’s (PUB’s) Tuas Water Reclamation Plant (TWRP) [3]. This paper will provide information of the first poultry farm in Singapore to implement a biogas cogeneration plant for its energy needs in a sustainable manner, as well as the positive impact on the environment. 1.1. Background Information The poultry farm operated in Lim Chu Kang is home to 800,000 chickens producing 350,000 eggs per day and is a major supplier of the industry in Singapore. Consequently, this produces more than 50 tonnes of chicken manure daily. These wastes were earlier made into compost using traditional methods which put a strain on the company’s manpower and posed an occupational health and safety risk for its employees. Mixed wastes to be stored for 3 months prior to usage for this method also spread unpleasant odour to residential areas in the vicinity which resulted in fines by the National Environment Agency (NEA) due to complains by residents. Land use is also inefficient as the process also requires storage space for the mixed wastes, sawdust and woodchips needed to be mixed with chicken manure to produce the compost, and excess compost inventory due to low demand. The space is taken up and hinders the potential expansion of its core business operations. Thus, the company decided to implement an alternative measure to its waste management, keeping in line with CSR and aim for sustainable agriculture through the reduction of its waste stream. 2. Anaerobic Digester (AD)
Fig. 1. Farm Site Layout [4]; Fig. 2. Anaerobic Digester
The AD constructed is a lagoon-type liquid digester covered by a high-density polyethylene (HDPE) flexible membrane. It is used to produce biogas, digester liquor and activated sludge. The production of biogas in the AD has
438
Liew Kian Heng et al. / Energy Procedia 143 (2017) 436–441 Author name / Energy Procedia 00 (2017) 000–000
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three stages: mixing, filtration and anaerobic digestion. In the first stage, 200m3 of water is added to the chicken manure to form a sludge slurry. This maintains the conditions suitable for anaerobic digestion and increases the ease of transport. After mechanical filtering to remove feathers, sand and the content of limestone, the slurry is then fed to the AD to be digested. Through this process, the biogas is produced and accumulates between the slurry surface and the HDPE cover. The gas is a mixture of two significant components, 55-70% methane (CH4) and the remainder being carbon dioxide (CO2) [5]. This will produce 15 tons of digested sludge, a raw material to be used for making compost, which is stored in a holding tank. 3. Biogas Usage, Heat & Water Recovery The biogas will be transported to three points-of-use, namely the boiler system, dryer house and biogas power plant. The boiler system is powered by the biogas and is used to pasteurise eggs, removing Salmonella & other pathogens with heat. 3.1. Feed Dryers
Fig. 3. N & N Proposed Plan; Fig. 4. New Co-Gen Dryer Plan
Fig. 5. New Co-Gen Dryer Section; Fig. 6. New Co-Gen Dryer
Apart from the dryer house, the farm also adopted a co-gen dryer system built in the existing feed mill plant where the dryer receives heat from the biogas power plant for drying the feed; exhaust heat energy cogenerated in the plant is utilised.
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Liew Kian Heng et al. / Energy Procedia 143 (2017) 436–441 Author name / Energy Procedia 00 (2017) 000–000
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3.2. Biogas Power Plant
Fig. 7. Biogas Plant Plan; Fig. 8. Biogas Plant Front Elevation
The biogas plant uses the Micro Turbine Energy system which comprises of two compressors and a series of five micro-turbines operated in parallel to generate electricity using the biogas supplied from the AD. The biogas is first pre-treated by undergoing particulate filtration, removing any residual impurities in the gas. The moisture will then be removed before stepping up of the gas pressure from 200 mbarg to 5.4 barg in the compressors. This compressed biogas will then be combusted and the micro-turbines will generate electricity. 3.2.1. Green Energy The technology implemented will reduce carbon emissions by decreasing reliance on electricity produced by energy companies that uses natural gas. Natural gas is extracted from underground rock formations and although its CO2 emission is 60% less than coal [6], it still adds to the carbon footprint as the content was brought up to the surface and into the atmosphere. In this case, since CH4 and CO2 would have been produced by the decomposition of chicken manure, the result of producing these forms of energy is carbon neutral and is a greener approach for energy supply. 3.2.2. Benefits
Fig. 9: Section; Fig. 10: N & N Biogas Plant
Liew Kian Heng et al. / Energy Procedia 143 (2017) 436–441 Author name / Energy Procedia 00 (2017) 000–000
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Jointly, the dryers and power plant consumes 900 m3/h of biogas during operation, higher than that of its production rate at 600 m3/h; there is minimal accumulation of biogas in the AD, diminishing the need for more land use for its expansion. The production rate is higher than the expected amount to be produced due to the reuse of digester liquor and presence of manure from other sources such as pullets and hatchlings. The primary gas testing results and the estimated output of energy is 1000kWh, bringing about energy cost savings of at least SGD$60,000 per month. 3.3. Wastewater Treatment Plant The wastewater treatment facility receives the digester liquor produced by the AD where it undergoes aerobic treatment by means of dissolved air flotation. Air is released from the bottom of the flotation tank; these bubbles allow suspended matter and oil to be adhered to and brought to the surface as scum sludge, thereby decreasing the amount of pollutants and subsequently lowering the Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD). The uric acid and undigested proteins in chicken manure translates to a high nitrogen content—a hindrance to the essential fermentation process in the AD [7]. The nitrogen content, in the form of ammonia (NH 3), can be removed by stripping. It will then form ammonium sulfate ((NH 4)2SO4) when reacted with sulfuric acid (H2SO4).
Fig. 11. Dissolved Air Flotation, Aerobic Treatment; Fig. 12. Belt Press Sludge Dryer Schematic [9]
The treated wastewater can be added back into the slurry pit, enhancing the performance of anaerobic digestion with its lowered nitrogen content [8]. The resultant (NH4)2SO4 can be added to the scum sludge and piped to a holding tank with a valve leading to a feed hopper. When the valve of the feed hopper is opened, the sludge will fall onto a belt press which separate the solids and fluid. The dried sludge solids are transported from the holding area into a sheltered storage space. When needed, wet scrubber units with at least 0.5 m3/s of air exchange capacity can be placed next to the dewatering units to remove pollutants, trace NH3 and residual H2S from the AD, from the air stream. 4. Green By-products The solids (bio solid cake) will then be retained in a receiving container as raw material for the manufacture of compost and fertilisers. The production of compost from the waste solids not only provides a form of revenue, it also removes the need for waste disposal, saving at least SGD$35,000 [10] on waste disposal fees per month. The waste water will either be pumped back to the initial manure liquefying process in the slurry pit after diffused air
Fig. 13. Sludge Dryer & Dried Sludge Solids; Fig. 14. Dried Sludge Solids in Holding Area
flotation, aerobic treatment, or further treated through an ultra-filtration process comprising of sand filtration and reverse osmosis to be used for irrigation and general washing purposes.
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5. Conclusion Through the usage of this system that recycles waste products, the waste stream of the farm is minimized; waste is converted to more forms of usable resources. Chicken manure is repurposed to manufacture fertilizers while the water in this integrated biogas system is never wasted; it is recirculated for the digestion process in early stages or further treated for the farm’s essential water needs for washing and irrigation. The use of a biogas plant reduces the emissions of pollutants and greenhouse gases whilst producing electricity, allowing the farm to be self-sufficient and sustainable. By working towards a zero-waste policy with the multi-faceted approach to solving its energy and waste problems, it can subsequently provide higher revenues, cost savings and reduction of the negative impacts on the environment. This is a first initiative for such a farm in Singapore and the impact to the environment is truly exemplary. Acknowledgements This paper is made possible for the engineering fraternity and young engineers to learn about waste management, sustainability of using biomass to prevent water pollution, water and heat recovery, pollution control and green energy. The contributions and strong support by N&N Agriculture Pte Ltd have been overwhelming. NTU Students including Mr Sean Ho RX, an intern from NTU has been part of the learning process in the research, would benefit in the field of environmental engineering. We like to thank Liew Strategics in providing the researches, innovation and motivation for real-life continuing learning not available in any textbooks. In particular for preparing this paper, we like to thank Mr Liew Yuqi from NUS for his unrelentless contributions in making the entire presentation and submission seamless.
References [1] G. Oliver, A. Palmer, H. Tjiawa and F. Zulkefli, "Geothermal Power for Singapore", Innovation, vol. 10, no. 2, pp. 26-29, 2011. [2] "EMA : Renewable Energy - Overview", Ema.gov.sg, 2017. [Online]. Available: https://www.ema.gov.sg/Renewable_Energy_Overview.aspx. [Accessed: 29- Mar- 2017]. [3] "Driving Synergies Through IWMF and TWRP", Nea.gov.sg. [Online]. Available: http://www.nea.gov.sg/energy-waste/wastemanagement/solid-waste-management-infrastructure/the-development-of-the-integrated-waste-management-facility/driving-synergiesthrough-iwmf-and-twrp. [Accessed: 03- Apr- 2017]. [4] 8275E035 N & N Agriculture Development- Biogas Production QRA_Final Report, 2013. [5] T. Forster-Carneiro, R. Isaac, M. Pérez and C. Schvartz, "Anaerobic Digestion: Pretreatments of Substrates", Biogas Production, pp. 1-25, 2012. [6] National Energy Technology Laboratory (NETL). 2010. Cost and performance baseline for fossil energy plants, Volume 1: Bituminous coal and natural gas to electricity. Revision 2. November. DOE/NETL-2010/1397. United States Department of Energy. [7] T. Böjti, K. Kovács, B. Kakuk, R. Wirth, G. Rákhely and Z. Bagi, "Pretreatment of poultry manure for efficient biogas production as monosubstrate or co-fermentation with maize silage and corn stover", Anaerobe, 2017. [8] G. Markou, "Improved anaerobic digestion performance and biogas production from poultry litter after lowering its nitrogen content", Bioresource Technology, vol. 196, pp. 726-730, 2015. [9] "Belt filter", En.wikipedia.org. [Online]. Available: https://en.wikipedia.org/wiki/Belt_filter. [Accessed: 04- Apr- 2017]. [10] "Refuse Disposal Facility", Nea.gov.sg, 2017. [Online]. Available: http://www.nea.gov.sg/energy-waste/waste-management/refuse-disposalfacility. [Accessed: 03- Apr- 2017]. Footnote: The short version of the paper was presented at WES-CUE2017, Jul 19-21, Singapore. This paper is a substantial extension of the short version of the conference paper.
ScienceDirect
Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia
Energy (2017) 000–000 436–441 EnergyProcedia Procedia143 00 (2017) www.elsevier.com/locate/procedia
World Engineers Summit – Applied Energy Symposium & Forum: Low Carbon Cities & Urban Energy Joint Conference, WES-CUE 2017, 19–21 July 2017, Singapore ThePlant 15th International DistrictPoultry Heating and Wastes Cooling Bio Gas Green Symposium Energy onFrom In Singapore
Assessing the feasibility of using the heat demand-outdoor temperature function for Dr a long-term district heat demand forecast Liew Kian Heng b I. Andrića,b,c*, A. Pinaa, Consultant, P. Ferrãoa, J.Liew Fournier ., B. Lacarrièrec, O. Le Correc Strategics a
IN+ Center for Innovation, Technology and123 Policy Research Técnico, Bt Merah Lane- Instituto 1#04-118Superior Singapore 150123Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France
Abstract
Singapore is a land scarce nation where farming space is very limited competing with other critical uses for a growing population. Farms taking up large tract of land and generate wastes face many unsurmountable difficulties and regulatory compliances on Abstract sustainability issues. Poultry farm is not the best type of industry due to polluted wastes generated and foul smell emissions. Yet an 800,000 chicken egg-producing farm in the last bastion of farming land in Singapore called Lim Chu Kang has evolved to District heating networks are commonly addressed in the literature asdemands, one of the most effective solutions for decreasing the overcome the space constraints, environmental regulatory, sustainability production efficiencies and green energy push gascarbon emissions from the building sector. Thesethe systems require high investments which are returned through theinto heat ingreenhouse lowering the footprint. This company has been first successful farm in Singapore to convert chicken wastes sales. as Due changed climate conditions building renovation policies, in itthe could decrease, biogas fuelto tothe generate electricity. In doing so,and it has reduced the polluted wastesheat anddemand transform intofuture energy toward selfprolonging recovering the investment return sufficiency, waste heat period. from the turbine exhaust for drying of chicken feed. The power generated is up to 1 MW while The mainwater scopeinofthe this paper digester is to assess the feasibility of using heatinto demand outdoor temperaturefertilizers. function for heat demand the waste aerobic is treated and extracted thethe sludge dried–cake for agricultural Excess energy forecast. Thesold district Alvalade, located was inused as aefforts case study. The district is consisted energy of 665 could also be to theof Singapore Power Gridinas Lisbon income.(Portugal), This company its CSR has invested this waste-to-green technology as a vary creative first construction mover while period increasing security, fighting foodscenarios scarcity (low, promoting safe high) eggs for people of buildings that in both and food typology. Three weather medium, andthe three district Singapore. initiatives on achieving international green deep). energyTo recognition and error, improving on green energy efficiencies renovationFurther scenarios were developed (shallow, intermediate, estimate the obtained heat demand values were would be the steps forward the benefits Singapore. Green energy production is anvalidated essentialby way meeting energy needs as compared with results fromfor a dynamic heatofdemand model, previously developed and theofauthors. the inevitable depletion of non-renewable energy sources coupled with climate change are now global challenges. adopted a The results showed that when only weather change is considered, the margin of error could be acceptable for someItapplications zero-waste to reduce waste stream airfor pollution with an anaerobic digester and a biogasafter power plant fuelled by 50 (the error policy in annual demanditswas lower thanand 20% all weather scenarios considered). However, introducing renovation tonnes of chicken manure day. Theupbiogas is used to generate electricity power the scenarios farm’s infrastructure, its scenarios, the error valueper increased to 59.5% (depending onheat the and weather and renovation combinationincluding considered). new co-generation feed dryer. The digester liquor is treated and treated water is recycled for the initial dilution of manure to enhance The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the the digestion process. Sludge undergoes a belt press to separate solids and liquid resulting in bio solid cake used for making decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and fertilisers. This integrated system ensures that by-products can be reused, minimizing waste and reducing emission of greenhouse renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the gases by adapting biogas for green electricity production. coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the World Engineers Summit – Applied Energy Symposium & © 2017 The Authors. Published by Elsevier Ltd. Forum: Low Carbon Cities & Urban Energy Joint Conference. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. Keywords: green energy; biogas; biomass; anaerobic digester; waste management; heat recovery; pollution control; carbon neutral; sustainability Keywords: Heat demand; Forecast; Climate change
1876-6102 © 2017 The Authors. Published by Elsevier Ltd.
Peer-review under responsibility of the scientific committee of the World Engineers Summit – Applied Energy Symposium & Forum: Low Carbon Cities & Urban Energy Joint Conference. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the World Engineers Summit – Applied Energy Symposium & Forum: Low Carbon Cities & Urban Energy Joint Conference. 10.1016/j.egypro.2017.12.708
2
Liew Kian Heng et al. / Energy Procedia 143 (2017) 436–441 Author name / Energy Procedia 00 (2017) 000–000
437
1. Introduction Renewable sources of energy have been the point of interest in the world due to climate changes and the inevitable depletion of finite resources such as coal and oil. This is one of Singapore’s main interests as there is a limited amount of natural resources to work with. Due to its geographical location and features, there is a lack of tidal and wind energy that can be used for producing electricity. On the other hand, it sits on an area that has very good geothermal activity underground but it has not been tapped on because it is unfeasible from an economical point of view [1, 2]. Biogas is a relatively new area in the energy industry in Singapore and will be the focus of this paper. Although solar energy is currently considered to be the most viable option for renewable energy in Singapore [2], biogas was not taken into consideration in the assessment as biomass is not extensively available in the highly urbanized city. However, this can be different depending on its application; places like farms creates waste products that are mostly biomass which will be able to be fuel the production of biogas. In Singapore, there has not been an integrated facility that has achieved a zero-waste policy through the utilisation of biomass yet. A project that aims to achieve this with its facilities is one co-planned between the National Environment Agency’s (NEA’s) Integrated Waste Management Facility (IWMF) and Public Utilities Board’s (PUB’s) Tuas Water Reclamation Plant (TWRP) [3]. This paper will provide information of the first poultry farm in Singapore to implement a biogas cogeneration plant for its energy needs in a sustainable manner, as well as the positive impact on the environment. 1.1. Background Information The poultry farm operated in Lim Chu Kang is home to 800,000 chickens producing 350,000 eggs per day and is a major supplier of the industry in Singapore. Consequently, this produces more than 50 tonnes of chicken manure daily. These wastes were earlier made into compost using traditional methods which put a strain on the company’s manpower and posed an occupational health and safety risk for its employees. Mixed wastes to be stored for 3 months prior to usage for this method also spread unpleasant odour to residential areas in the vicinity which resulted in fines by the National Environment Agency (NEA) due to complains by residents. Land use is also inefficient as the process also requires storage space for the mixed wastes, sawdust and woodchips needed to be mixed with chicken manure to produce the compost, and excess compost inventory due to low demand. The space is taken up and hinders the potential expansion of its core business operations. Thus, the company decided to implement an alternative measure to its waste management, keeping in line with CSR and aim for sustainable agriculture through the reduction of its waste stream. 2. Anaerobic Digester (AD)
Fig. 1. Farm Site Layout [4]; Fig. 2. Anaerobic Digester
The AD constructed is a lagoon-type liquid digester covered by a high-density polyethylene (HDPE) flexible membrane. It is used to produce biogas, digester liquor and activated sludge. The production of biogas in the AD has
438
Liew Kian Heng et al. / Energy Procedia 143 (2017) 436–441 Author name / Energy Procedia 00 (2017) 000–000
3
three stages: mixing, filtration and anaerobic digestion. In the first stage, 200m3 of water is added to the chicken manure to form a sludge slurry. This maintains the conditions suitable for anaerobic digestion and increases the ease of transport. After mechanical filtering to remove feathers, sand and the content of limestone, the slurry is then fed to the AD to be digested. Through this process, the biogas is produced and accumulates between the slurry surface and the HDPE cover. The gas is a mixture of two significant components, 55-70% methane (CH4) and the remainder being carbon dioxide (CO2) [5]. This will produce 15 tons of digested sludge, a raw material to be used for making compost, which is stored in a holding tank. 3. Biogas Usage, Heat & Water Recovery The biogas will be transported to three points-of-use, namely the boiler system, dryer house and biogas power plant. The boiler system is powered by the biogas and is used to pasteurise eggs, removing Salmonella & other pathogens with heat. 3.1. Feed Dryers
Fig. 3. N & N Proposed Plan; Fig. 4. New Co-Gen Dryer Plan
Fig. 5. New Co-Gen Dryer Section; Fig. 6. New Co-Gen Dryer
Apart from the dryer house, the farm also adopted a co-gen dryer system built in the existing feed mill plant where the dryer receives heat from the biogas power plant for drying the feed; exhaust heat energy cogenerated in the plant is utilised.
4
Liew Kian Heng et al. / Energy Procedia 143 (2017) 436–441 Author name / Energy Procedia 00 (2017) 000–000
439
3.2. Biogas Power Plant
Fig. 7. Biogas Plant Plan; Fig. 8. Biogas Plant Front Elevation
The biogas plant uses the Micro Turbine Energy system which comprises of two compressors and a series of five micro-turbines operated in parallel to generate electricity using the biogas supplied from the AD. The biogas is first pre-treated by undergoing particulate filtration, removing any residual impurities in the gas. The moisture will then be removed before stepping up of the gas pressure from 200 mbarg to 5.4 barg in the compressors. This compressed biogas will then be combusted and the micro-turbines will generate electricity. 3.2.1. Green Energy The technology implemented will reduce carbon emissions by decreasing reliance on electricity produced by energy companies that uses natural gas. Natural gas is extracted from underground rock formations and although its CO2 emission is 60% less than coal [6], it still adds to the carbon footprint as the content was brought up to the surface and into the atmosphere. In this case, since CH4 and CO2 would have been produced by the decomposition of chicken manure, the result of producing these forms of energy is carbon neutral and is a greener approach for energy supply. 3.2.2. Benefits
Fig. 9: Section; Fig. 10: N & N Biogas Plant
Liew Kian Heng et al. / Energy Procedia 143 (2017) 436–441 Author name / Energy Procedia 00 (2017) 000–000
440
5
Jointly, the dryers and power plant consumes 900 m3/h of biogas during operation, higher than that of its production rate at 600 m3/h; there is minimal accumulation of biogas in the AD, diminishing the need for more land use for its expansion. The production rate is higher than the expected amount to be produced due to the reuse of digester liquor and presence of manure from other sources such as pullets and hatchlings. The primary gas testing results and the estimated output of energy is 1000kWh, bringing about energy cost savings of at least SGD$60,000 per month. 3.3. Wastewater Treatment Plant The wastewater treatment facility receives the digester liquor produced by the AD where it undergoes aerobic treatment by means of dissolved air flotation. Air is released from the bottom of the flotation tank; these bubbles allow suspended matter and oil to be adhered to and brought to the surface as scum sludge, thereby decreasing the amount of pollutants and subsequently lowering the Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD). The uric acid and undigested proteins in chicken manure translates to a high nitrogen content—a hindrance to the essential fermentation process in the AD [7]. The nitrogen content, in the form of ammonia (NH 3), can be removed by stripping. It will then form ammonium sulfate ((NH 4)2SO4) when reacted with sulfuric acid (H2SO4).
Fig. 11. Dissolved Air Flotation, Aerobic Treatment; Fig. 12. Belt Press Sludge Dryer Schematic [9]
The treated wastewater can be added back into the slurry pit, enhancing the performance of anaerobic digestion with its lowered nitrogen content [8]. The resultant (NH4)2SO4 can be added to the scum sludge and piped to a holding tank with a valve leading to a feed hopper. When the valve of the feed hopper is opened, the sludge will fall onto a belt press which separate the solids and fluid. The dried sludge solids are transported from the holding area into a sheltered storage space. When needed, wet scrubber units with at least 0.5 m3/s of air exchange capacity can be placed next to the dewatering units to remove pollutants, trace NH3 and residual H2S from the AD, from the air stream. 4. Green By-products The solids (bio solid cake) will then be retained in a receiving container as raw material for the manufacture of compost and fertilisers. The production of compost from the waste solids not only provides a form of revenue, it also removes the need for waste disposal, saving at least SGD$35,000 [10] on waste disposal fees per month. The waste water will either be pumped back to the initial manure liquefying process in the slurry pit after diffused air
Fig. 13. Sludge Dryer & Dried Sludge Solids; Fig. 14. Dried Sludge Solids in Holding Area
flotation, aerobic treatment, or further treated through an ultra-filtration process comprising of sand filtration and reverse osmosis to be used for irrigation and general washing purposes.
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5. Conclusion Through the usage of this system that recycles waste products, the waste stream of the farm is minimized; waste is converted to more forms of usable resources. Chicken manure is repurposed to manufacture fertilizers while the water in this integrated biogas system is never wasted; it is recirculated for the digestion process in early stages or further treated for the farm’s essential water needs for washing and irrigation. The use of a biogas plant reduces the emissions of pollutants and greenhouse gases whilst producing electricity, allowing the farm to be self-sufficient and sustainable. By working towards a zero-waste policy with the multi-faceted approach to solving its energy and waste problems, it can subsequently provide higher revenues, cost savings and reduction of the negative impacts on the environment. This is a first initiative for such a farm in Singapore and the impact to the environment is truly exemplary. Acknowledgements This paper is made possible for the engineering fraternity and young engineers to learn about waste management, sustainability of using biomass to prevent water pollution, water and heat recovery, pollution control and green energy. The contributions and strong support by N&N Agriculture Pte Ltd have been overwhelming. NTU Students including Mr Sean Ho RX, an intern from NTU has been part of the learning process in the research, would benefit in the field of environmental engineering. We like to thank Liew Strategics in providing the researches, innovation and motivation for real-life continuing learning not available in any textbooks. In particular for preparing this paper, we like to thank Mr Liew Yuqi from NUS for his unrelentless contributions in making the entire presentation and submission seamless.
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