Optimizing Biowaste Material Mixing for Efficient Biogas Production via Airlift Pump-Equipped Digesters Graduation Project 2 Prepared by Tariq Malhis 1/42 Supervisor Dr. Ihab Surakji Co-Supervisor Prof. Wael Ahmad Dr. Amjad El-Qanni Outline Introduction and Background Research Objectives Literature review Methodology Results Conclusion 1/8/2024 2/42 How is Biogas Produced Biogas is produced via the anaerobic digestion process The biogas consists of CH4, CO2 and other impurities. 1/8/2024 3/42 Biogas Content Sales [VALUE] % [VALUE]% [VALUE]% Methane Carbon dioxide hydrogen sulphide 70 29 1 Phases of the Anaerobic Digestion Process 1/8/2024 4 Sources: Myint, M., N. Nirmalakhandan, and R.E. Speece, Anaerobic fermentation of cattle manure: Modeling of hydrolysis and acidogenesis. Water Research, 2007. 41(2): p. 323-332. Enzmann, F., et al., Methanogens: biochemical background and biotechnological applications. AMB Express, 2018. 8(1): p. 1. 1/8/2024 5 Research Objectives 5/42 Research Objectives This study aims to evaluate an effective method for extracting biogas from food waste (liquid sludge)using a bioreactor or digester. This is achieved by modifying the mixing methods employed in these digesters, based on evaluating the mixing rate, average velocity, and velocity contours for both liquid and gas phases within the digester. The new method involves using Airlift pumps for mixing the liquid and gas phases within the digester. 1/8/2024 6/42 Achieving the Research Objectives A survey on all theory regarding the different used mixing methods. Assessing the most ideal riser design among the Standard, Tapered, and Step designs. Utilize the air-water flow rate results obtained by Flonergia for airlift pumps. Carry an experimental work to get the best ratio between the gas and liquid phases. Comparing and evaluating the mixing rate of liquid sludge versus biogas with that of water versus air. Evaluating the rheological property of Liquid sludge at different liquid and gas flowrates. Conclude how implementing airlift pumps inside the digester would affect the mixing rate and yield product of biogas. In order to achieve the objectives, the following tasks have been done: 7/42 1/8/2024 8 8/26 8/26 Literature Review 8/42 Structure of the Literature Review The different types of mixing methods for the liquid and gas phase. Compare the different types of mixing methods and conclude which is the most convenient and would result in the highest yield product of biogas. Distinguishing between the various multiphase flow regimes within the riser. Analyze which flow regime would result to the highest mass flowrate of liquid phase. 1/8/2024 For the clarity of presentation, the literature review is divided into the following aspects: 9/42 Continuous Stirred Tank Reactors (CSTRs) This type of reactor consists of a mechanical impeller or other mechanical means to ensure maintain a good mixing rate within the digester . Advantages: Moderate mixing rate Good initial yield product Easy to operate Disadvantages: In adequate mixing in regions far from the digester High maintenance cost 1/8/2024 10/42 Sources: Sağır, E. and P.C. Hallenbeck, Chapter 6 - Photofermentative Hydrogen Production, in Biohydrogen (Second Edition), A. Pandey, et al., Editors. 2019, Elsevier. p. 141-157. Stockar, U., Biothermodynamics of live cells: A tool for biotechnology and biochemical engineering. Journal of Non-equilibrium Thermodynamics - J NON-EQUIL THERMODYN, 2010. 35: p. 415-475. Types of CSTR Axial Mixing Radial Mixing 1/8/2024 11/42 Sources Schwedhelm, I., A non-invasive microscopy platform for the online monitoring of hiPSC aggregation in suspension cultures in small-scale stirred tank bioreactors. 2019. Escarpment Renewables Digester tank and the mixer (CSTRs) Outer walls of underground digester tank 12/42 Pneumatic Bioreactors Pneumatic bioreactors are a type of bioreactors in which medium stirring is accomplished through gas bubbling. Compressed air or gas mixture is introduced at the bottom of a cylindrical column or tank using nozzles, perforated plates, or a ring sparger. The two main types are the Bubble column reactor and the Airlift reactor. 1/8/2024 Sources: Angeles, M., et al., ChemInform Abstract: A Review of Experimental Procedures for Heavy Oil Hydrocracking with Dispersed Catalyst. Catalysis Today, 2013. 220. 13/42 Airlift Pumps 14 Special effect pumps that use injected compressed air to lift the liquids Operates under the buoyancy effect (Catrawedarma et al., 2020) Advantages: Simplistic design No moving parts Low maintenance Partially submerged riser pipe Injection Point Suction pipe Riser pipe Air Inlet Airlift pump schematic (Bukhari, 2018) Source: S. Bukhari, “Improving the Airlift Pump Prediction Model for Aquaculture Applications,” the University of Guelph, 2018. G. N. B. Catrawedarma, Deendarlianto, and Indarto, “The performance of airlift pump for the solid particles lifting during the transportation of gas-liquid-solid three-phase flow: A comprehensive research review,” Proc. Inst. Mech. Eng. Part E J. Process Mech. Eng., no. 2, 2020, doi: 10.1177/0954408920951728. 14/42 Dual Injector Airlift Pump Dual injector airlift pump designed by Ahmed and Badr, 2016 It is called a dual injection as gas phase is injected in both radial and axial directions Holes are evenly distributed for both the radial and axial injection. 15 Axial gas phase Injection Enhanced liquid phase lifting Radial gas phase Injection Enhanced penetration of gas phase W. H. Ahmed, A. M. Aman, H. M. Badr, and A. M. Al-Qutub, “Air injection methods: The key to a better performance of airlift pumps,” Exp. Therm. Fluid Sci., vol. 70, pp. 354–365, 2016, doi: 10.1016/j.expthermflusci.2015.09.022. 1/8/2024 15/42 15 The Advantages of Pneumatic Reactors over Continuously Stirred Tank Reactors Quick mixing time, which is the time to reach a specific degree of homogeneity. high level of homogeneity across the fluid. maximum biomass transfer takes place at the pneumatic reactors compared to the stirred tank bubble reactor at the same adequate environmental aspects. no moving parts Vs moving parts. 1/8/2024 Sources: Zhong, J.-J., Bioreactor Engineering. 2011. p. 257-269. Kress, P., et al., Effect of agitation time on nutrient distribution in full-scale CSTR biogas digesters. Bioresource Technology, 2017. 247. 16/42 Types of Flow Regime 1/8/2024 Source: Dang, C., et al., SPECTRAL AND EIGENVALUES ANALYSIS OF ELECTRICAL IMPEDANCE TOMOGRAPHY DATA FOR FLOW REGIME IDENTIFICATION. 2019. 17/42 The Riser Design Design: Standard Riser. The Riser is 4-inch in diameter and 1.9 m in height. This design enables both churn turbulent and slug flow regime. Slug flow regime can improve mixing and reduce dead zones, due to the concave shaped bubbles. 1/8/2024 Source: Ahmed, W.H. and H.M. Badr, Dual-Injection Airlift Pumps: An Enhanced Performance. Particulate Science and Technology, 2012. 30(6): p. 497-516. . 18/42 1/8/2024 19 Methodology 19/42 Understanding CFD Simulation CFD (Computational Fluid Dynamics) simulation is a computer-based tool. Simulation software such as ANSYS is used for testing the validity of proposed digester design. Optimizing the manufacturing process Enhance the product formation Decrementing the tests running time and initial costs 1/8/2024 Sources: Hussein, A., Chapter 12 - Flow Assurance Solids Prediction and Modeling, in Essentials of Flow Assurance Solids in Oil and Gas Operations, A. Hussein, Editor. 2023, Gulf Professional Publishing. p. 503-577. Tillman, D.A., D.N.B. Duong, and N.S. Harding, Chapter 7 - Modeling and Fuel Blending, in Solid Fuel Blending, D.A. Tillman, D.N.B. Duong, and N.S. Harding, Editors. 2012, Butterworth-Heinemann: Boston. p. 271-293. 20/42 Geometry Full Size Digester 1/8/2024 The analyzed digester has a diameter of 6 m and a height of 2.1 m. The total volume is 59.38 m³. 2 m of the digester’s total height is submerged by the liquid phase. The active or working volume is equal to 56.5 m³. 21/42 Modifying the Geometry Quarter-size Digester 1/8/2024 Reduction in the size of the digester to quarter its original size. Decreasing the computational time required by the CPU. using the symmetry option when carrying out the meshing and fluent setup process. Eliminating the uncertainty in the results. 22/42 Isometric View Meshing Side View 1/8/2024 Tetrahedral meshing was carried out. elements size of 0.070 mm Total of 409,163 elements. Hurtado, F.J., A.S. Kaiser, and B. Zamora, Fluid dynamic analysis of a continuous stirred tank reactor for technical optimization of wastewater digestion. Water Research, 2015. 71: p. 282-293. 23/42 Mesh Independence Test Element sizes range from 0.0775 mm down to 0.0700 mm, decreasing by 0.0025 mm with each step. The CFD simulation results for average velocity of the liquid sludge across the digester was evaluated. The simulation results for the liquid sludge for all element sizes were within the range of 0.03m/s. The complexities of multiphase flow in CFD simulations cause fluctuations in results, even during steady flow analysis. 1/8/2024 Mesh Independence Test Element size (mm) 0.0775 0.0750 0.0725 0.0700 Number of Elements 302,585 336,268 371,391 409,163 Average Velocity (m/s) 0.0357 0.0346 0.0326 0.0378 0.0700 409,163 0.0378 The complexities of multiphase flow in CFD simulation, even steady flow analysis won’t be able to stabilize the average velocity values. 24/42 Digester Boundary Conditions 1/8/2024 The digester was divided to three main bodies. Pressure outlet at the top of the gas phase, has its liquid and mixture phase categorized as default. The backflow value in the gas phase settings was set to 1, preventing the over flow of liquid phase. 25/42 Riser Boundary Conditions Mass flow inlet to the digester set for both liquid and gas phases. Mass flow outlet from the digester set for the liquid phase. The mixture phase boundary condition set as default for both mass flow inlet and outlet. 1/8/2024 26/42 Fluent Setup (Volume of Fluid) VOF versus Eulerian Model. Differences between hybrid and Standard initialization process. Running the simulation at a steady state. 1/8/2024 27/42 1/8/2024 28 Results and Discussions 28/42 Five random point from the Flonergia results of water versus air flowrates for the 4-inch standard riser were used as input values for examining and testing water-air and liquid sludge-biogas, within the digester. Random points were utilized to cover the minimum and maximum range of flow rates for both tested liquid and gas phases. Input values for liquid and gas phases Test Liquid phase Gas phase Ratio of Liquid phase to Gas phase (L/min) (Kg/s) (L/s) (kg/s) 1 60 0.998 0.50 0.000613 2.00 2 103 1.713 0.70 0.000858 2.45 3 216 3.593 1.00 0.001225 3.60 4 451 7.502 5.14 0.006297 1.46 5 510 8.483 5.50 0.006738 1.55 1/8/2024 29/42 Source: Flonergia. FloMov: Efficient Pumping Technology. 2023 29 December 2023]; Available from: https://www.flonergia.com/. Conducted simulation for water versus air. Conducted simulation for liquid sludge versus biogas. Used same consistent liquid and gas flow rates for each test. The average velocity of liquid sludge was analyzed and compared to that of water. Then the velocity contours for each liquid and gas phases was examined. Results 1/8/2024 Test Average velocity (m/s) Water Liquid sludge 1 0.0144 0.0052 2 0.0182 0.0114 3 0.0378 0.0269 4 0.1149 0.0752 5 0.3165 0.0942 30/42 Average Velocity Trend 1/8/2024 The same average velocity trend of water. The higher viscosity and density of liquid sludge. The rheological behavior, Newtonian and/or non-Newtonian, of liquid sludge. The increase in shear rate, leads to an increase in the viscosity of the fluid. 31/42 Average velocity of water 1.436E-2 1.8200000000000001E-2 3.78E-2 0.1149 0.3165 Average Velocity of liquid sludge 5.1673500000000002E-3 1.1360800000000001E-2 2.69E-2 7.5218199999999999E-2 9.4203300000000004E-2 Test Average Velocity (m/s) Velocity Contours for Water versus Air Velocity Contours for water versus air at 4000 timesteps 1/8/2024 32/42 Velocity Contours for Liquid Sludge versus Biogas Velocity Contours for Liquid sludge versus biogas at 4000 timesteps 1/8/2024 33/42 Velocity contours of the top view for tests No. 4 and 5: (a) Water versus air (b) liquid sludge versus biogas 1/8/2024 Velocity Contours for the Initial Tests Velocity contours of the side and top view at 4000 timesteps, for Test No.3: (a) water versus air (b) liquid sludge versus biogas. Dominance of yellow and red velocity contours close to the outlet of the 4-inch riser. Higher viscosity and density of liquid sludge. More time is required for the liquid sludge to uniformly mix within the digester. 35/42 1/8/2024 36 Conclusion 36/42 Conclusion The rheological behavior, Newtonian and/or non-Newtonian, of liquid sludge, at various flow rates for both liquid and gas phases. During the intervals when the airlift pump undergoes a rest period, if the fluid exhibits a non-Newtonian behavior, residuals will start to accumulate. Having a velocity contours and Newtonian fluid behavior at digester’s bed decreases the accumulation of residuals. Emphasis the efficiency of Airlift pumps over CSTRs, in enhancing the yield product of biogas. 1/8/2024 37/42 Accepted Publication “Optimizing Biowaste Material Mixing for Efficient Biogas Production via Airlift Pump-Equipped Digesters” 26/26 Submitted Manuscript for Publication “Brief review of Biowaste Material Mixing for Efficient Biogas Production” 39/42 Acknowledgements 1/8/2024 40 40/42 Acknowledgements Dr. Ihab Surakji Head of Mechanical and Mechatronics Engineering An-Najah University , Palestine Dr. Amjad El-Qanni Assistant Professor An-Najah National University Prof. Wael Ahmed Full Professor University of Guelph, Canada 41/42 41 Questions Thank you! 1/8/2024 42/42 1/8/2024 43 1 2 3 Fluent Setup Steps Boundary Conditions 1/8/2024 44 Pressure Outlet 1/8/2024 45 Mixture Phase Gas Phase Mass flow inlet 1/8/2024 46 Mixture Phase Gas and liquid Phase Mass flow outlet 1/8/2024 47 Mixture Phase Liquid Phase Objectives Evaluate a new effective method for extracting biogas from food waste using a bioreactor or digester. integrate an airlift pump. Proposed design of the digester Carrying a CFD simulation Evaluating the Rheological property of Liquid sludge Examining the mixing rate within the designed digester. 1/8/2024 48/42 Overall View of the Escarpment Renewables Plant 1/8/2024 49 Overall View of the Escarpment Renewables Plant 1/8/2024 50 Overall View of the Escarpment Renewables Plant 1/8/2024 51 Overall View of the Escarpment Renewables Plant 1/8/2024 52 Shell and Tube Heat Exchangers 0-0.399 0-0.307 1/8/2024 53 Rheological Property 1/8/2024 54 Viscosity Measurements for liquid sludge 55 Test No. Rotational Velocity () Average Dynamic Viscosity () 1 40 0.240747160 2 60 0.217709533 3 80 0.195314031 4 100 0.175434064 5 120 0.159423297 6 150 0.145731449 7 180 0.143590414 8 200 0.128065671 The density was found to be 0.996 g/cm3 (i.e., 996 kg/m3) measurements were done at slurry temperature of 33 the liquid digestate shows a shear-thinning non-Newtonian fluid behavior 55 image1.jpeg image2.jpeg image3.png image4.jpg image5.jpg image6.jpeg image7.png image8.jpeg image9.jpeg image10.jpeg image11.jpeg image12.png image13.png image14.png image15.png media1.mp4 image16.png image17.jpeg image18.png image19.jpg image20.png image21.png image22.png image23.png image24.png image25.png image26.jpeg image27.png image28.png image29.png image30.png image31.png image32.png image33.png image34.jpg image35.png image36.png image37.png image38.png image39.jpeg image40.jpeg image41.jpeg image42.jpeg image43.png image44.png image45.png image46.png image47.png image48.png image49.png image50.png image51.jpeg image52.jpeg image53.png image54.png image55.png image56.jpeg image57.png image58.png image59.png image580.png image590.png /docProps/thumbnail.jpeg