Production of Bioenergy Using Filter Cake Mud in Sugar Cane Mill Factories
Carmen Baez-Smith, P.E. Smith Baez Consulting, Inc. Loxahatchee, Florida, USA
Sugar Processing Research Institute 2008 Conference September 29 - October 1st, 2008 Delray Beach, Florida, USA
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Objectives
Evaluation of the bioenergy-producing capability of filter cake mud Improving the energy balance of the sugar mill Improving productivity of the sugar mill Evaluation of the mathematical kinetic model for anaerobic digestion
Digester size Gas production potential Byproducts
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Advantages of Anaerobic Digestion
Methane is a useful renewable fuel High degree of waste stabilization Low production of waste biological sludge Low nutrient requirements No oxygen requirements Reduce greenhouse gas emission Control of unpleasant odors
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Anaerobic Digestion Fundamentals
Anaerobic digestion is a complex biological process that uses microorganisms to break down organic material to carbon dioxide and methane
Complex wastes are broken down in 3 basic steps :
Enzymatic Hydrolysis Conversion of higher to lower molecular weight (LMW) material. Acid fermentation (Bacterial) Conversion of LMW into fatty acids. Methanogenesis (Bacterial) Conversion of fatty acids into methane and carbon dioxide.
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Feed Analysis for Anaerobic Digestion
Total Solids (TS) Total Dissolved Solids (TDS) Chemical Oxygen Demand (COD) Biological Oxygen Demand (BOD) Fixed Solids (Ash and Mineral Content ) Crude Protein pH Temperature
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Filter Cake Composition (Wet)
Compound Name Sucrose Wax and Fats Fiber Nitrogen P2O5 K2O CaO Ash Moisture Total % 3.00 3.00 6.50 1.00 0.97 0.09 0.94 4.50 80.00 100.00
Source: Paturau, J.M., By-Products of the Cane Sugar Industry, an Introduction to their Industrial Utilization, 1982, Page 151, Elsevier, New York, USA.
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Filter Cake Composition (Dry)
Material Type Organics Ash & Mineral Composition % 70 30
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Filter Cake Composition
Parameter Total Solids COD BOD Ash and Minerals Moisture
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Feed Concentration mg/Kg % 200,040 20.0 157,025 15.7 84,042 8.4 60,188 6.0 800,000 80.0
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Source: Carmen Baez-Smiths Personal Notes
Kinetic Model for Filter Cake
Based on the Monod growth-kinetic equation for anaerobic digestion in a plug- flow digester with recycle (Equation 1)
1
Yk ( S o S ) ( S o S ) + ( 1 + ) K s ln(
Equation 1
Si ) S
kd
Where
= Solids retention time, days So = Influent concentration S = Effluent concentration Y = maximum yield coefficient, defined as the ratio of the mass of cells formed to the mass of substrate consumed Ks = Half-velocity constant, mass/unit volume = Recycle ratio Si = Influent concentration to reactor after dilution with recycle flow Kd = Endogenous decay coefficient, day-1 Smith Baez Consulting, Inc., 2008 www.smithbaez.com
Anaerobic Digestion evaluation
Model Results
Solids Retention Time = 20 Days
Parameter Cane Grinding Rate, Ton/day Filter Cake Production, Ton/day Filter Cake COD, mg/Kg Effluent COD, mg/Kg Digester Volume, ft3 Digester Volume, m3 Volume of methane produced, ft3/day Volume of Methane Produced, m3/day 3 Volume of gas produced, ft /day 3 Volume of gas produced, meter /day Power Generation, MegaWatts Value 10,000 655 157,025 23,554 392,957 11,126 885,602 25,081 1,581,432 44,776 5.2
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Biological Solids (Cell Material)
Correlation
Solids Retention Time = 20 Days Filter Cake Mud Fatty Acids* Proteins* Carbohydrates* Lb of Biological Solids Production/Lb of BOD 0.044 0.035 0.065 0.150
* Perry L. MacCarty, Anaerobic Waste Treatment Fundamentals, Part I, Public Works, Vol 95, 9, 1964.
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Gas Productivity
Correlation
Gas Production Rates COD Loading Rate, Lb COD/ft3 day 3 COD Loading Rate, kg COD/m day Methane Yield, m3/Kg COD added 3 Methane Yield, m /Kg BOD added 3 Gas Productivity, ft /lb COD Destroyed 3 Gas Productivity, m /Kg COD Destroyed
Calculated Reported * 0.52 0.10 - 0.30 8.39 1.6 - 4.8 0.27 0.13 0.50 0.36 9.04 12 - 18 0.56 0.75 - 1.12
Sources: 1) *Ghos, S, T. Liu and K. Fukushi, Anaerobic Biodegradation of Toluene in a Plug-Flow Reactor, University of Utah, Salt Lake City, UT. 2) Metcalf & Eddy, Wastewater Engineering. Treatment, Disposal and Reuse, Third Ed. 1991, New York, NY Smith Baez Consulting, Inc., 2008 www.smithbaez.com
Theoretical Methane Content of Biogas
Substrate
Chemical Composition C15H31OCOOH C4H6ON
Methane % of Total Gas
72 63 50
Fats Proteins
Carbohydrates C6H12O6
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Model Assumptions
Assumptions Parameter Filter Cake COD, mg/Kg Filter Cake Total Solids, mg/Kg Efficiency of Waste Utilization (E), % Yield coefficient (Y), mg cells/mg COD Maximum Rate of Substrate Utilization per Unit -1 Mass of Microorganisms, k, days Recycle Ratio, Temperature, F -1 Endogenous Coefficient (Kd), day Half Velocity Constant, Ks, mg/L COD Filter Cake Specific Gravity Power Process Efficiency, % Methane % in Gas Produced, % 3 Digester Methane Gas Heating Value, Btu/ft
Value 157,025 200,040 85% 0.05 2 0.5 122 0.05 40 1.07 80% 56% 600
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Overall Material Balance
Two alternatives will be presented depending on the post-anaerobic digestion sludge treatment:
Alternative #1 will separate the sludge after anaerobic digestion into process water and a thicker sludge, which subsequently is dried to produce biofertilizer Alternative #2 will just dry the sludge after anaerobic digestion to produce biofertilizer
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Overall Material Balance
Alternative #1: Sludge Dewatering and Thickening Influent Overall Material Balance Filter Cake Feed, Ton/day Bioconversion by Anaerobic Digestion, Ton/day Total Process Water Produced, Ton/day Total Water Evaporated (by Drying), ton/day Total Biofertilizer, Ton/day Total Effluent Percent of the Feed 12% 63% 16% 9% 100%
655 78 414 103 60 655
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Overall Material Balance
Alternative #1: Sludge Dewatering and Thickening
R a te, T o n /d a y 800 600 400 200 0 Filter Cake Proc. Water Evap. Water Process Stream Anaer. D Material Balance
Biofertilizer
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Overall Material Balance
Alternative #2: Sludge Drying Influent Overall Material Balance Filter Cake Feed, Ton/day Bioconversion by Anaerobic Digestion, Ton/day Total Process Water Produced, Ton/day Total Water Evaporated (by Drying), ton/day Total Biofertilizer, Ton/day Total Effluent Percent of the Feed 12% 0% 79% 10% 100%
655 78 0 515 62 655
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Overall Material Balance
Alternative #2: Sludge Drying
R a te , T o n /d a y 800 600 400 200 0 Filter Cake Evap. Water Anaer. D Process Stream Biofertilizer Proc. Water Material Balance
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Conclusions
Data seems to indicate that the kinetic model developed is adequate to quantify filter cake (FC) mud anaerobic digestion Enzymatic pretreatment of the FC increase the conversion capacity by at least 50% Applied research is needed to field-verify the results
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Conclusions
Data seems to indicate that anaerobic digestion (AD) of filter cake is an attractive alternative for an otherwise underappreciated byproduct of sugar cane mills AD has the potential of increasing productivity and portfolio diversity in the sugar mill operations
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Thank You
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