MINLP OPTIMIZATION FOR HEAT INTEGRATION OF BIO-HYDROGEN PRODUCTION FROM PALM WASTE

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1 Journal of Engineering Science and Technology Special Issue on SOMCHE 2014 & RSCE 2014 Conference, January (2015) School of Engineering, Taylor s University MINLP OPTIMIZATION FOR HEAT INTEGRATION OF BIO-HYDROGEN PRODUCTION FROM PALM WASTE A. INAYAT 1, *, MURNI M. AHMAD 1, M. I. A. MUTALIB 1, S. YUSUP 1, Z. KHAN 2 1 Chemical Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, Tronoh, Perak, Malaysia 2 Department of Chemical Engineering, COMSATS Institute of Information Technology, Lahore, Pakistan *Corresponding Author: abrar.inayat@petronas.com.my Abstract With the current energy and environmental crisis, hydrogen economy has now gained a positive outlook. This alternative type of energy can be produced from a renewable source such as biomass. However, the thermochemical conversion of biomass into hydrogen via steam gasification can be energy intensive due to its endothermic behaviour. In this work, a mixed integer non-linear (MINLP) mathematical problem has been developed to design an energy efficient process to produce hydrogen from biomass steam gasification. The MINLP work targets to minimize the total cost subject to minimum utility cost, area cost and exchangers fixed cost. The MINLP optimization was carried out in MATLAB and able to simultaneously solve the reaction kinetics calculations, flowsheet performance and production cost along with the heat integration. Keywords: Bio-hydrogen, Optimization, Heat integration, Biomass, MINLP. 1. Introduction Hydrogen (H 2 ) has the potential to become a significant form of energy in the future as it is relatively cleaner than fossil fuels. Several alternatives and renewable sources are under considerable interest to be used for production of H 2, including biomass [1]. The usage of biomass for H 2 production is an attractive approach to be explored in Malaysia due to its abundance. Being the world largest exporter of palm oil [2], the availability of oil palm waste provides excellent feedstock for hydrogen production. Hydrogen can be produced via a few methods: thermochemical processes (i.e., pyrolysis and gasi- 50

2 MINLP Optimization for Heat Integration of Bio-hydrogen Production from Nomenclatures CCU CF CHU CP CU dt CU dt HUj d Tijk EMAT F h i j NOK Q CUi Q HUj Q ijk ST T i,k T IN T j,k T OUT Z CUi Z HUj Z ijk Unit cost for cold Fixed cost for exchangers Unit cost for hot utility, Cold path/stream Cold utility Temperature approach for match of hot stream i and cold utility Temperature approach for match of cold stream j and hot utility Temperature approach for match (i,j) at temperature location k Minimum approach of temperature Heat capacity flowrate Heat transfer coefficient Hot stream (HP) Cold stream (CP) Total number of stages Heat exchanged between hot stream i and cold utility Heat exchanged between cold stream j and hot utility Heat exchanged between hot process stream i and j in stage k Stage Temperature of hot stream i at hot end of stage k Inlet temperature of stream Temperature of cold stream j at hot end of stage k Outlet temperature of stream Binary variable to denote cold utility exchange heat with stream i Binary variable to denote hot utility exchange heat with stream j Binary variable to denote existence of match (i,j) in stage k Greek Symbols Β Exponent for area cost Γ Lower bound of heat exchanger Ω Upper bound of heat exchanger fication) or biological processes (i.e., biophotolysis and fermentation) from biomass [3]. Balat [4] reported that H 2 production via gasification process is more economical than pyrolysis due to lower production cost. For gasification, the conversion of biomass into gaseous product can be enhanced by processing at high temperature and using gasifying agent such as air, pure steam, air-steam or oxygen-steam mixtures [5]. Pure steam is used as the gasification agent for higher H 2 content in the product gas [6]. Furthermore, the purity of H 2 in a steam gasification process can be increased to more than 80% when it is coupled with CO 2 adsorption [7]. Heat integration is the systematic methodology for energy utilization within the process, which identify the energy targets and optimize the utilities. Heat is one of the most important energy especially in biomass steam gasification process with extremely endothermic behavior. Nevertheless, gasification is an energy intensive process. To make the process more cost competitive in terms of energy usage, process integration can be applied to recover and reuse as much heat as possible. Cicconardi et al. [8] used coal gasification for hydrogen production and power generation using model in ASPEN PLUS. Steam production required for the process was carried out using the heat integration application supported by

3 52 A. Inayat et al. composite curve method. Heyne and Harvey [9] reported a study on synthetic natural gas production (SNG) from biomass gasification using integrated process design in ASPEN PLUS. The authors applied pinch analysis for the optimal internal heat recovery calculation within the process. Pavlas et al. [10] applied pinch analysis on a biomass gasification plant for power generation to maximize the heat recovery. It was predicted that 33% energy saving based on the hot utility using heat pump application. Sadhukhan et al. [11] performed heat integration analysis on biomass integrated gasification combined cycle processes. They modelled a combined heat and power generation plant from gasification, fourth generation biomass waste feedstock in ASPEN simulator and performed a heat integration study to maximize the heat recovery. Calin et al. [12] presented energy and process integration study on an integrated gasification combined cycle for hydrogen production and power generation from coal with carbon capture and storage. Based on pinch analysis, it is not possible to simulate the reaction kinetics and flowsheet calculations simultaneously. Another approach to study the heat integration for flowsheet other than pinch analysis has also been reported, i.e., using mathematical programming of mixed integer nonlinear programming (MINLP). However, there is limited study on biomass-based process has been published. Baliban and Floudas [13] developed a mathematical model based on MINLP for conversion of biomass to liquid. Heat integration has been carried out using simultaneous calculations based on MINLP. The model included the heat and power integration to maximize energy recovery from the process. Martin and Grossmann [14] performed MINLP optimization for hydrogen yield based on different flowsheets. After that, heat integration applied to recover maximum energy for the optimized flowsheet. The objective of this study is to develop a mixed integer nonlinear programming (MINLP) for the flowsheet of hydrogen production process based on steam gasification from biomass (palm waste). MINLP optimization approach employed to solves simultaneously reaction kinetics and flowsheet calculations for minimum heat integration cost while integrating heat sources and sinks, to increase energy efficiency of the process. 2. Technical Approach The reaction kinetics modelling, flowsheet development and modelling have been presented by authors in earlier work [15]. The pervious study focuses on the mathematical modelling of the process design for hydrogen production from palm waste using MATLAB. The flowsheet includes steam generation, gasification and gas cleaning unit as shown in Fig. 1. The flowsheet model incorporated with the product gas composition, mass and energy balance calculations [16]. Based on Fig. 1, there are two cold streams and one hot stream available in the process flowsheet for hydrogen production from steam gasification of palm waste. Cold stream C1 is the stream that provides energy required for steam generation and cold stream C2 provides energy for the gasification process. Hot stream H1 is the stream containing the output energy from the gasifier to scrubber and pressure swing adsorption (PSA). Heat integration was carried out using stage-wise superstructure mixed integer nonlinear programming (MINLP) optimization approach [17-18]. Each stage represents the potential of exchange between both hot and cold streams. Optimization of the heat integration model consists of the following set of equations [17-18].

4 MINLP Optimization for Heat Integration of Bio-hydrogen Production from Fig. 1. Process flowsheet for hydrogen production from palm waste with hot and cold streams. Overall heat balance for each stream (1) ( T T ) F = Q + Q i HP INi OUTi i ijk CUi k ST j CP (2) ( T T ) F = Q + Q j CP OUTj INj j ijk HUj k ST j HP Heat balance at each stage ( T T ) F = Q k ST, i HP (3) i, k i, k+ 1 i ijk j CP ( T T ) F = Q k ST, j CP (4) j, k j, k + 1 j ijk j HP Assignment of superstructure inlet temperature T = T (5) INi i,1 TINj T j, NOK + 1 = (6) Feasibility of temperature T T k ST i HP (7) i, k i, k+ 1, T T k ST i CP (8) j, k j, k + 1, T T i HP (9) OUTi i, NOK + 1 TOUTj Tj,1 j CP (10) Hot and cold utility load Q ΩZ 0 i HP, j CP, k ST (11) ijk ijk

5 54 A. Inayat et al. Q ΩZ 0 i HP (12) CUi CUi Q ΩZ 0 j CP (13) HUj HUj Zijk, ZCUi, Z HUj = 0,1 (14) Logical constraints ( Ti, NOK + 1 TOUTi ) Fi = QCUi i HP (15) ( T T ) F = Q j CP (16) OUTj j,1 j HUj Calculation of approach temperature dtijk Ti, k Tj, k + Γ(1 Zijk ) k ST, i HP, j CP (17) dtijk + 1 Ti, k + 1 Tj, k Γ(1 Zijk ) k ST, i HP, j CP (18) dtcui Ti, NOK 1 TOUTCU + Γ(1 ZCUi ) i HP (19) + No stream split constrains Zijk 1 j CP, k ST (20) i HP Zijk 1 i HP, k ST (21) i CP Calculation of log mean temperature difference (LMTD) 1/3 ijk + 1 dt ijk + dt LMTD ijk = dt ijk dt ijk+ 1 i HP, j CP, k ST 2 (22) dtcui + ( TOUTi TINCU ) LMTDCUi = dtcui ( TOUTi TINCU ) i HP 2 (23) dthuj + ( TINHU TOUTj ) LMTDHUj = dthuj ( TINHU TOUTj ) j CP 2 (24) Calculation of heat exchange area 1 1 ijk i + j Q ( h h ) Aijk = i HP, j CP, k ST (25) LMTD ijk 1 1 CUi i + CU Q ( h h ) ACUi = i HP (26) LMTD CUi 1 1 HUj j + HU Q ( h h ) AHUj = j CP (27) LMTD HUj 1/3 1/3

6 MINLP Optimization for Heat Integration of Bio-hydrogen Production from Objective function TC = min CCU Q + CHU Q + CF Z + CF Z + CF Z CUi HUj ijk CUi HUj i HP j CP i HP j CPk ST i HP j HP β β β ijk CUi HUj i HP j CPk ST i HP j CP + C A + C A + C A 3. Optimization and Model Validation Optimization of MINLP was carried out according to the flow chart given in Fig. 2. The optimization has been carried out using fmincon solver in MATLAB optimization toolbox. (28) Fig. 2. Schematic diagram for MINLP optimization approach. To validate the heat integration model, the approach was applied to a case study taken from literature [17-18]. The stream data for the chosen system are given in Table 1 [17-18]. Table 1. Data for heat integration model validation [17-18]. Stream TIN (K) T OUT (K) F (kw/k) h (kw/m 2 K) Cost (USD/kW) H C C Hot Utility Cold Utility Minimum Approach of Temperature [19] = 1K Exchanger Cost = (Area) 0.83 The model is validated based on temperature s values solved for the process at minimum cost. The temperature distribution is shown in Fig. 3, while the cost difference is presented in Table 2. The values calculated using our approach shows good agreement for the chosen case study with the mean error of

7 56 A. Inayat et al. Table 2. Results for model validation. Basis Reference Current [17-18] Model Total Heat Exchanger Area (m 2 ) Area Cost (USD/ yr.) Total Utility Cost (USD/ yr.) Fixed Cost (USD/ yr.) Total Cost (USD/ yr.) mean error Fig. 3. Temperature distribution solved using MINLP approach for model validation. 4. Energy Recovery for Bio-Hydrogen Production Process The energy distribution on the flowsheet at temperature 1150K, steam/biomass ratio of 4 and sorbent/biomass of 0.87 is shown in Fig. 4 [20]. The stream data for cold and hot streams are given in Table 3. Table 3. Stream data for heat integration. No Stream Supply Target Heat Capacity T Energy Energy Temp Flowrate, F, Temp (K) (K) (KJ/h) (kw) (K) (kw/k) 1 H C C The energy recovery after applying heat integration is shown in Fig. 5. It is predicted that 97% energy can be recovered from the product gas stream. In addition, the energy required for steam production (306 kj/hr.) can totally be recovered from the recycled energy.

MINLP Optimization for Heat Integration of Bio-hydrogen Production from.... 57 Fig. 4. Energy distribution for the flowsheet [20]. Fig. 5. Energy recovery for the flowsheet at minimum heat integration cost.

reported in previous work based on pinch analysis approach used for the same flowsheet [20]. The overall energy recovered from the requirement is 78.75%.

8 MINLP Optimization for Heat Integration of Bio-hydrogen Production from Fig. 4. Energy distribution for the flowsheet [20]. Fig. 5. Energy recovery for the flowsheet at minimum heat integration cost. There is only (301.6 kj/hr.) external energy required from hot utility to fulfil the energy requirement for gasification process. The minimum hot utility required is less than the 601 kj/hr. reported in previous work based on pinch analysis approach used for the same flowsheet [20]. The overall energy recovered from the requirement is 78.75%. In terms of cost total utility cost of heat integration is 3391 USD per year and total cost of heat integration is 8410 USD per year; fixed cost of heat exchanger is USD/ yr.; area cost of heat exchanger is 220 USD/ yr. and total area covered is m 2. The temperature distribution of the heat exchanger network is shown in Fig. 6. Hot stream which is outlet from the gasifier is at 1150K to recover energy from this stream the cold stream at 303K which is inlet to gasifier and another cold stream at 303K which requires energy for steam production must be heated to specified temperature both these streams are interacted with hot stream outlet from gasifier in heat exchanger respectively in other words we can say that in the preheater for inlet to gasifier so as to achieve desired conditions. From heat exchanger 1 the cold stream leaves at 917K and hot stream at 482K this hot stream is then passed from HE2 in which cold stream enter at 303K and exit at 582K the temperature of hot stream reaches at 414K. Additionally a cold utility is installed in way of hot stream and remaining energy is recovered and finally the hot stream leaves at 400K. In way of cold stream at 917K outlet from HE1 it is interacted with hot utility and finally the temperature of cold stream reaches to 1150K. The other cold stream at 522K from HE2 is interacted with hot utility and finally its temperature reaches 523K.

9 58 A. Inayat et al. Fig. 6. Temperature distribution for the flowsheet at minimum heat integration cost. A comparison of the current study with the literature has been carried out and listed in Table 4. The comparison is not straight forward due to different flowsheet designs, feed stocks and/or products, and having different capacities. Current study has been focused on improving energy requirement of selected biomass gasification plants for hydrogen production using heat integration approach. The comparison with the previous work [20-21] based on the same flowsheet shows that in current study the energy recovery is 78.75% higher compared to previous one, i.e., 57.63%. Also, the current study has the advantage of simultaneous calculation of heat integration using MINLP optimization approach along with the reaction kinetics, mass and energy balance of the flowsheet developed for hydrogen production via biomass steam gasification with in-situ CO 2 capture. Moreover, hydrogen production cost can be analysed along with the heat integration cost. Table 4. Comparison with literature. Energy Saving Ref. (%) MINLP 10.8 kg/s 62.6 [22] Process Approach Capacity Production of ethanol from corn Stover via direct gasification and steam reforming (Thermo-chemical) Integrated coal gasification combined cycle for electricity generation Biomass gasification process for syngas production Biomass steam gasification for hydrogen production Biomass steam gasification with CO 2 capture for hydrogen production Biomass steam gasification with CO 2 capture for hydrogen production Pinch analysis Pinch analysis Pinch analysis Pinch analysis 44.3 kg/s 94 [23] 12.5 t/day 33.6 [10] 71 g/hr [24] 61.2 g/hr [20] MINLP 61.2 g/hr Current study

10 MINLP Optimization for Heat Integration of Bio-hydrogen Production from Conclusion This work encapsulates, heat integration study on flowsheet of hydrogen production from steam gasification of biomass using mathematical optimization problem MINLP for energy efficient flowsheet. Using heat integration of flowsheet, almost 97% of energy has been recovered from the product gas line. The optimization of the MINLP model showed that considerable saving can be obtained for steam production and energy requirement for the gasification process using heat integration technique. There was only 21.25% energy required from the hot utility to fulfil the energy requirement of the process. The optimization of MINLP has an advantage over the SPRINT (pinch analysis) calculations that the simultaneous calculation of heat integration can be carried out along with the reaction kinetics, mass and energy balance of flowsheet. Acknowledgement The authors gratefully acknowledge the financial support from Universiti Teknologi PETRONAS, Malaysia (STIRF 0153AA-C78) for the financial support to carry out this research. References 1. Saxena, R.C.; Seal, D.; Kumar, S.; and Goyal, H.B. (2008). Thermo-chemical routes for hydrogen rich gas from biomass: A review. Renewable and Sustainable Energy Reviews, 12(7), Sumathi, S.; Chai, S.P.; and Mohamed, A.R. (2008). Utilization of oil palm as a source of renewable energy in Malaysia. Renewable and Sustainable Energy Reviews, 12(9), Levin, D.B.; and Chahine, R. (2010). Challenges for renewable hydrogen production from biomass. International Journal of Hydrogen Energy, 35(10), Balat, M. (2008). Hydrogen-Rich Gas Production from biomass via pyrolysis and gasification processes and effects of catalyst on hydrogen yield. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 30(6), González, J.F.; Román, S.; Bragado, D.; and Calderón, M. (2008). Investigation on the reactions influencing biomass air and air/steam gasification for hydrogen production. Fuel Processing Technology, 89(8), Balat, M.; Balat, M.; Kirtay, E.; and Balat, H. (2009). Main routes for the thermo-conversion of biomass into fuels and chemicals. Part 2: Gasification systems. Energy Conversion and Management, 50(12), Florin, N.H.; and Harris, A.T. (2008). Enhanced hydrogen production from biomass with in situ carbon dioxide capture using calcium oxide sorbents. Chemical Engineering Science, 63(2), Cicconardi, S.P.; Perna, A.; Spazzafumo, G.; and Tunzio, F. (2006). CPH systems for cogeneration of power and hydrogen from coal. International Journal of Hydrogen Energy, 31(6), Heyne, S.; Seemann, M.C.; and Harvey, S. (2010). Integration study for alternative methanation technologies for the production of synthetic natural gas from gasified biomass. Chemical Engineering Transactions, 21,

11 60 A. Inayat et al. 10. Pavlas, M.; Stehlík, P.; Oral, J.; Klemes, J.; Kim, J.-K.; and Firth, B. (2010). Heat integrated heat pumping for biomass gasification processing. Applied Thermal Engineering, 30(1), Sadhukhan, J.; Zhao, Y.; Shah, N.; and Brandon, N.P. (2010). Performance analysis of integrated biomass gasification fuel cell (BGFC) and biomass gasification combined cycle (BGCC) systems. Chemical Engineering Science, 65(6), Calin-Cristian, C. (2010). Evaluation of energy integration aspects for IGCCbased hydrogen and electricity co-production with carbon capture and storage. International Journal of Hydrogen Energy, 35(14), Baliban, R.C.; Elia, J.A.; and Floudas, C.A. (2011). Optimization framework for the simultaneous process synthesis, heat and power integration of a thermochemical hybrid biomass, coal, and natural gas facility. Computers & Chemical Engineering, 35(9), Martín, M.; and Grossmann, I.E. (2011). Energy optimization of hydrogen production from lignocellulosic biomass. Computers & Chemical Engineering, 35(9), Inayat, A.; Ahmad, M.M.; Mutalib, M.I.A.; and Yusup, S. (2010). Biomass steam gasification with in-situ CO 2 capture for enriched hydrogen gas production: A reaction kinetics modelling approach. Energies, 3, Inayat, A.; Ahmad, M.M.; Mutalib, M.I.A.; and Yusup, S. (2012). Process modeling for parametric study on oil palm empty fruit bunch steam gasification for hydrogen production. Fuel Processing Technology, 93(1), Biegler, L.T.; Grossmann, I.E.; and Westerberg, A.W. (1997). Systematic methods of chemical process design. New Jersey, USA: Prestice Hall PTR. 18. Yee, T.F.; Grossmann, I.E.; and Kravanja, Z. (1990). Simultaneous optimization models for heat integration I. Area and energy targeting and modeling of multi-stream exchangers. Computers & Chemical Engineering, 14(10), Detournay, M.; Hemati, M.; and Andreux, R. (2011). Biomass steam gasification in fluidized bed of inert or catalytic particles: Comparison between experimental results and thermodynamic equilibrium predictions. Powder Technology, 208(2), Inayat, A.; Ahmad, M.M.; Mutalib, M.I.A.; and Yusup, S. (2011). Heat integration analysis of gasification process for hydrogen production from oil palm empty fruit bunch. Chemical Engineering Transactions, 25, Inayat, A.; Ahmad, M.M.; Mutalib, M.I.A. and Yusup, S. (2010). Flowsheet development and modeling of hydrogen production from Empty Fruit Bunch via steam gasification. Chemical Engineering Transactions, 21, Čuček, L.; Martín, M.; Grossmann, I.E.; and Kravanja, Z. (2011). Energy, water and process technologies integration for the simultaneous production of ethanol and food from the entire corn plant. Computers & Chemical Engineering, 35(8), Emun, F.; Gadalla, M.; Majozi, T.; and Boer, D. (2010). Integrated gasification combined cycle (IGCC) process simulation and optimization. Computers & Chemical Engineering, 34(3), Ahmad, M.M.; Aziz, M.F.; Inayat, A.; and Yusup, S. (2011). Heat integration study on biomass gasification plant for htdrogen production. Journal of Applied Sciences, 11(21),

Flowsheet Modelling of Biomass Steam Gasification System with CO 2 Capture for Hydrogen Production

ISBN 978-967-5770-06-7 Proceedings of International Conference on Advances in Renewable Energy Technologies (ICARET 2010) 6-7 July 2010, Putrajaya, Malaysia ICARET2010-035 Flowsheet Modelling of Biomass