CHEMICAL ENGINEERINGTRANSACTIONS VOL. 52, 2016 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Guest Editors: Petar Sabev Varbanov, Peng-Yen Liew, Jun-Yow Yong, Jiří Jaromír Klemeš, Hon Loong Lam Copyright © 2016, AIDIC Servizi S.r.l., ISBN978-88-95608-42-6; ISSN 2283-9216 System Analysis of Poly-Generation of SNG, Power and District Heating from Biomass Gasification System Muhammad Shahbaza, Suzana Yusupa,*, Abrar Inayatb, David Onoja Patricka, Angga Partamaa aBiomass Processing Lab, Centre of Biofuel and Biochemical Research, Department of Chemical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610, Perak, Malaysia. bDepartment of Sustainable and Renewable Energy Engineering, University of Sharjah, 27272 Sharjah, United Arab Emirates drsuzana_yusuf@petronas.com.my A transition towards synthetic fuels such as synthetic natural gas (SNG) is a requirement that can contribute to future energy security and sustainable development. Conventional coal gasification could be replaced with biomass gasification to produce synthetic natural gas that can be used in existing natural gas distribution infrastructure, transport, domestic and industrial sectors with almost no or little modifications. This study evaluates the integration of synthetic natural gas production using biomass gasification with combined heat and power plant (CHP). Various system performance indicators are used for comparing different systems such as carbon conversion, energy efficiencies, economic feasibility and commercial viability of technologies. For the evaluation of studied system, 100 MW of dried biomass is used as input for synthetic natural gas production together with power and district heating. The results obtained by integration of process showed a substantial synthetic natural gas production potential i.e. about 74.3 MW based on 100 MW biomass input. The process heat requirement of the system is about 26.60 MW and 0.60 MW for electrification. The results indicate that 27.35 MW heat is available for district heating and about 3.4 MW net amount of heat is available for power production by organic Rankine cycle (ORC). The results also show that the system is 74.3 % efficient based on lower heating value. Poly generation concept of SNG production along with power and district heating system claims its economic viability. 1. Introduction Growing environmental concerns and fossil fuel depletion are a motivation to look for alternative energy resources. Natural gas has proved to be a clean fuel among other fossil fuel like crude oil and coal (Li et al., 2014). The importance of natural gas due to its vast applications as domestic and commercial fuel, raw material of chemicals, heat and power production and specially in transport as compressed natural gas (van der Meijden et al., 2010). Natural gas has not gained importance due to abundance and low price of crude oil in past decades. Natural gas importance has increased drastically in the last few years due to fluctuation in crude oil price (Hamilton et al., 2014). The natural gas reserves are also limited and may not be enough in the next 50 to 60 y at the current pace of usage (Li et al., 2014). Research has been triggered to produce it synthetically. Synthetic natural gas (SNG) production techniques from coal were developed in the last quarter of 20th century. SNG production from coal is not attractive due to its higher GHG emission and limited reserves. Biomass is a possible option for SNG production that not only addresses the environmental issues but solves the issues of sustainability and waste utilization. Synthetic natural gas has many advantages which make it an attractive option. It can be used in existing natural gas distribution network, transport, domestic and industrial sector with almost no or little modifications (Molino et al., 2015). It can also produce new job, promote indigenous resources, lower trade deficient and huge import bills for conventional fossil fuels. DOI: 10.3303/CET1652131 Please cite this article as: Shahbaz M., Yusup S., Inayat A., Patrick D. O., Partama A., 2016, System analysis of poly-generation of sng, power and district heating from biomass gasification system, Chemical Engineering Transactions, 52, 781-786 DOI:10.3303/CET1652131 781 mailto:drsuzana_yusuf@petronas.com.my The efficient utilization of biomass for energy production is very important (Arvidsson et al., 2012) due to its competition of land utilization with food crops. Biomass is one of the largest energy source and it shares about 9 % in 2010 for world energy mix and it is expected to be 18 % in 2050 (Lauri et al., 2014). The integration of SNG production from biomass with power production and district heating is a step to enhance the efficient utilization of biomass to firm the bio refinery concept (Arvidsson et al., 2014). This cogeneration and polygeneration helps to meet the future energy requirement (Rudra et al., 2015). Combine heat and power (CHP) is considered an alternative to convention energy system in terms of energy saving. Significant work has been done for CHP especially in Europe. Biomass is the only source that can be used for both liquid and chemical products (Khan et al., 2014). The SNG production through thermochemical gasification of biomass has good impact on carbon foot print by replacing coal. The efficiency of process has increased 20 % in CHP by using thermal process integration (Mertzis et al., 2014). The integration of power production and use of waste heat for district heating with bio-SNG from biomass gasification made the process to be economical and cut GHG emission. The SNG production has been tested on pilot scale successfully in Güssing Austria for I MW plant (Rehlinget al., 2009). Biomass is used in both dried and wet form for biomass gasification. Drying is the most energy consuming part of the whole process. It almost required 10-25 % of whole process energy requirement (Görling and Westermark, 2010). The effect of integrated dryer and humidifier for SNG production from biomass with integrated power and DH is not well reported. The aim of this research work is to develop a system for SNG production from biomass gasification with combine heat and power cycle. For this purpose a process scheme is designed which includes biomass drying, SNG production, cleaning of product gas and combined heat and power cycle. A system analysis is made to evaluate the SNG production in terms of MW on LHV (lower heating value) of biomass input and determine the power and district heating (DH) potential after process integration. The effect of integrated dryer and humidifier on SNG, district heating H and power production are also analyzed. 2. Methodology This study is conducted to produce SNG from Scots pine wood biomass gasification and to find the power and district heating potential by using process integration concept. For this purpose a process was developed after evaluation of commercial and developed techniques on the basis of carbon conversion of biomass and energy efficiency. The system consists of drying, humidification, gasification, gas cleaning, methanation for SNG production, gas upgrading, CO2 removal and organic Rankin cycle (ORC) for power production as described in Figure 1. The reference capacity is selected for 100 MW of biomass on LHV basis. The LHV and composition of Scots pine find experimentally are given in Table 1. The process was developed on the basis of stoichiometric calculation of gasification, methanation reactions and considering physical operation like cooling and heating. A material and energy balance was conducted with the help of computer aided technique. The important process requirement, parameters and mass flow rate after material balance are given in Table 2. Table 1: Biomass composition and heating value Biomass Composition (wood chips 1 ~ 5 mm) Wt (%) Carbon 50.63 Hydrogen 5.94 Oxygen 42.74 Nitrogen 0.62 Sulfur 0.06 Chlorine 0.01 LHV(MJ/kg) 18.82 2.1 Process scheme The process flow was developed as shown in Figure 1. The biomass particles in the range of 1-5 mm entered into the dryer where the moisture was reduced from 50 % to 15 %. High pressure steam was used at 12 bar pressure and 350 °C. It produced 3 bar low pressure steam at 150 °C that was available for steam cycle for power and DH through process integration. Recycled CO2 from CO2 removal unit used to transport dried biomass at higher pressure into circulating fluidized bed gasifier (CGB) coupled with humidifier. Pure oxygen from air separation unit at the rate of 1.5 kg/s along with steam 1.3 kg/s was supplied for combustion and gasification reaction. Air separation unit consumed 0.9 MW energy for 100 MW biomass 782 input. The gasifier was operated at 10 bar and 850 °C in the presence of Ni-olivine based catalyst. Ni-olivine based catalyst enhanced the methane production as well as suppressed the tar formation. The produced gas obtained from gasifier consists of CO, CO2, CH4, HCl, H2O and H2S were cooled from 850 °C to 371 °C in cooling unit. This cooling process produced super-heated steam that is utilized in gasifier and methanator to fulfil energy demand. The removal of HCl and H2S was done in the cleaning section by using bauxite and zinc oxide respectively. Both units consumed 0.173 MW. The methanation of cleaned gas was carried out in the methanator and High temperature reactor (HT) at 300 °C in the presence of Ni catalyst. The high pressure steam converted the gases into methane. Heat of reaction is produced due to exothermic nature of methanation reaction. Part of the heat was utilized in high pressure steam dryer and high temperature reactor using integration concept. The CO2 removal was done by using slexol process in order to upgrade the SNG. The refrigeration of slexol consumed 0.3 MW. The SNG is ready for distribution network. Part of the high pressure steam is sent to organic Rankin cycle (ORC) for power generation and low temperature and pressure steam after process integration is sent to district heating unit. The efficiencies of turbine, compressor and pumps used in process are given in Table 2. Table 2: Process parameters and flow rates Process requirement and parameters Feed flow rates Gasifier catalyst Ni+Olivine Biomass flow(wet) 11.22 kg/s Alkali removal Bauxite Biomass flow (dry) 5.60 kg/s Sulphur removal ZnO Bed HHV 100% dry 18.85MJ/kg Compressor efficiency 0.70 LHV 100 % dry 18.80MJ/kg Turbine efficiency 0.85 CO2 recycle 1.4 kg/s Pump efficiency 0.70 Gasifying steam 1.3 kg/s Methanator Isothermal tubular O2 combustion 1.5 kg/s Methanator catalyst Nickel Steam dryer 12 bar CFB 10 bar 850 °C Water cooling unit ZnO bed HT+ Methanation 300 °C ZnS Gas cooling Unit Slexol for CO2 removal Lp Steam Steam In Biomass 50 % Lp Condensate Steam generated HCl Removal H2S removal Steam in Hp Steam Condensate Hp Steam Bio-SNG Biomass 15 % Cool gas 350 °C Hot Gas 850 °C Clean syn gas Product gases 300 °C Cool gas 25 °C CO2 to Gasifier CO2 vent Steam In Humidifier Air sepration H2O O2 Humidified O2 Figure 1: Developed process flow of SNG Production from Biomass gasification 783 3. Results and Discussion A simple input and output balance has been made to validate the process analysis. The analysis is shown in Table 3. It shows that for gasification of 100 MW biomass large amount of process steam is required. A substantial amount of energy is needed for pre heating process and 2.26 MW electric powers is required to run the whole process. The most important thing is 74.3 MW SNG (on LHV basis) being produced along with 30 MW steam and 3.4 MW power has been obtained by combine heat and power (CHP). The heat available for DH is 27.33 MW. The energy balance is given in Figure. 2. Figure 2: Energy balance of the system 3.1 SNG Production The SNG production is 74.3 MW on LHV basis from 100 MW biomass input. The use of steam at 10 bars as gasifying agent has not only increased the CH4 yield to about 93.04 mole% but also suppress the coke formation. The compression of coke formation is very important as it will deactivate the downstream catalyst. In addition the use of pressurized steam is also helpful for better fluidization that enhanced the gasification efficiency by increasing the contact between gasifying agent and bed material. In the presence of steam in gasifier also increased the H2/CO ratio in product gas due the activeness of water gas shift reactions also reported in literature (Ahmed et al., 2012).The increase in H2/CO ratio is important as the required ratio in methanation step should not be less than 3 (Jan et al., 2010). Jan et al. (2010), reported that for higher methane yield in methanator reactor the H2/CO ratio should be in the range of 3 - 5. In addition, the use of Ni- Olivine instead of sand not only acts as energy flowing medium but also provides the active sites for methanation reaction. The cold gas efficiency of 74.3 % was obtained for SNG production from biomass input LHV basis. 3.2 Energy requirement and steam generation The process steam requirement of the whole process is 26.60 MW. Energy requirements for different processes are shown in Table 3. It was observed that the dryer has the highest energy consumption about 13.04 MW. On the other hand, 9.46 MW energy is required for high temperature shift convertor (HTSC) and methanator. The amount of energy required for gasification unit is 4.10 MW is less than dryer and methanation units. This study utilized process integration so that the amount of energy generated by the system at different steps is recovered in the form of steam. Steam is produced during methanation due to exothermic reaction is about 20.67 MW and 9.33 MW from cooling of syngas. The total steam generation is 30 MW and detail is given in Table 3. The steam generation detail is given in Table 3. The use of humidifier has increased the steam generation. Energy demand of gasifier and fluidized bed dryer fulfill by acquiring energy from methanation and waste heat recover from syngas cooler. Dryer is the most energy consuming part of system. The heat load of dryer is provided to the system using heat integration concept and remaining amount is used for power production and make whole process CHP to utilize poly generation benefits. Process 100 MW LHV Steam Generation 27 . 35 MW District Heating 26 . 60 MW Process Steam Required 30 MW 5 . 86 MW Preheating 2 . 62 MW Power Needed 3 . 4 MW Power SNG 74 . 33 MW LHV 784 Table 3: Energy requirements and steam generation system Equipment Energy (MW) Steam Generation Energy (MW) High temperature shift convertor + Methanation 9.46 Heat of reaction (Methanator) 20.67 Gasification 4.10 Syngas cooler 9.33 Drying Total 13.04 26.60 30 3.3 Pre heating energy requirement The system requires energy for pre-heating in high temperature shift convertor, methanator, gasifier and dryer. From heat integration concept these demands of energy is fulfilled by recovering heat from system. 5.86 MW heat is required, 1.86 MW is obtained from condensate of flue gases during cooling of SNG while 2.10 MW is recovered from flue gases and 1.92 MW waste heat from district heating system is then integrated in the process as shown in Table 4. Table 4: Pre heating energy Process Energy (MW) Flue gas condensate 1.84 Flue gas recovered Waste heat from DH 2.10 1.92 Total 5.86 3.4 District heating and power production The utilization of waste heat is the prime focus of this study. The purpose of utilization of heat through process integration is to make SNG economical. Low pressure steam is generated at different steps from dryer, cooler and other units are utilized for district heating system. The energy available for DH was about 27.3 MW as shown in Figure 2. The energy available for power production after fulfilling dryer and gasifier energy demand is 3.4 MW. The amount of energy available is 3.4 MW for power generation and organic Rankine cycle (ORC) (Walraven et al., 2015) was used for power production. Many studies have been done to analyze the ORC and Rankine cycle for CHP (Stoppato, 2012) and more recently (Baral et al., 2015). The use of ORC is economical for lower power generation than Rankine cycle. In summer there is no requirement of district heating so the heat load used for power production increased the power production in that time. The DH and power efficiency on the LHV basis of biomass input is 27.33 % and 3.4 %. 4. Conclusions This study was conducted to analyse the process for SNG production from biomass gasification with integration of power and district heating. The SNG production is about 74.3 MW from 100 MW biomass input on LHV basis after the process integration. On the other hand, heat load for district heating is 26.7 MW and for power production is 3.4 MW. The thermal efficiency of the integrated system is 74.33 % SNG on LHV basis and district heating efficiency is 26.7 % basis. ORC is used for power production and power efficiency is 3.4 %. The Energy requirement of dryer and gasifier is fulfilled within the system using heat integration of process. The higher production of SNG is due to the use of humidifier that increased gasification process by increasing CO/H2 ratio. The Combine heat and power production with SNG production make the process economical by utilization of waste heat. In summer power production is increased by utilizing energy of district heating due to lower demand for heating. Acknowledgement The authors are grateful to Ministry of Higher Education Malaysia for financing this research under Long term Research Grant Scheme (LRGS). The authors would like to thanks the Universiti Teknologi PETRONAS Malaysia for providing facility and support. 785 References Ahmed T. Y., Ahmad M. 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