Fuel 266 (2020) 117111 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Full Length Article Techno-economic assessment of process integration models for boosting hydrogen production potential from coal and natural gas feedstocks T Usman Hamida,b, Ali Raufb, , Usama Ahmedc, , Md. Selim Arif Sher Shahd, Nabeel Ahmade ⁎ ⁎ a Department of Chemical Engineering, Texas Tech University, Lubbock, TX 79409-3121, USA Department of Chemistry and Chemical Engineering, Lahore University of Management Sciences, Lahore 54792, Pakistan c Chemical Engineering Department, King Fahad University of Petroleum & Minerals, Dhahran, Saudi Arabia d Department of Chemical and Biomolecular Engineering, Yonsei University, Republic of Korea e Department of Chemical Engineering, COMSATS University Islamabad, Lahore Campus, Pakistan b G R A PHICA L A BSTR A CT A R TICL E INFO A BSTR A CT Keywords: Gasification Steam methane reforming Heat integration H2 production CO2 emissions The elevated energy demands from past decades has created the energy gaps which can mainly be fulfilled through the consumption of natural fossil fuels but at the expense of increased greenhouse gas emissions. Therefore, the need of clean and sustainable options to meet energy gaps have increased significantly. Gasification and steam methane reforming are the efficient technologies which resourcefully produce the syngas and hydrogen from coal and natural gas, respectively. The syngas and hydrogen can be further utilized to generate power or other Fischer Tropsch chemicals. In this study, two process models are developed and technically compared to analyze the production capacity of syngas and hydrogen. First model is developed based on conventional entrained flow gasification process which is validated with data provided by DOE followed by its integration with the reforming process that leads to the second model. The integrated gasification and reforming process model is developed to maximize the hydrogen production while reducing the overall carbon dioxide emissions. Furthermore, the integrated model eradicates the possibility of reformer’s catalyst deactivation due to significant amount of H2S present in the coal derived syngas. It has been seen from results that updated model offers 37% increase in H2/CO ratio, 10% increase in cold gas efficiency (CGE), 25% increase in overall H2 production, and 13% reduction in CO2 emission per unit amount of hydrogen production compared to Abbreviations: GEE, GE Energy is a type of entrained flow gasifier; SMR, Steam methane reforming; DMR, Dry methane reforming; POX, Partial oxidation; WGS, Water gas shift; HHV, Higher heating value; LHV, Lower heating value; CGE, Cold gas efficiency; IGCC, Integrated gasification combined cycle; IPCC, Intergovernmental Panel on Climate Change; EIA, Energy Information Administration; NG, Natural gas; MFK, Mass flowrate in kg/hr; TIC, Total investment cost; HCR, Hydrogen to carbon monoxide ratio ⁎ Corresponding authors. E-mail addresses: ali.rauf@lums.edu.pk (A. Rauf), usama.ahmed@kfupm.edu.sa (U. Ahmed). https://doi.org/10.1016/j.fuel.2020.117111 Received 1 August 2019; Received in revised form 11 January 2020; Accepted 14 January 2020 0016-2361/ © 2020 Elsevier Ltd. All rights reserved. Fuel 266 (2020) 117111 U. Hamid, et al. base case model. Furthermore, economic analysis indicated 8% reduction in cost for case 2 while presenting 7% enhanced hydrogen contents. 1. Introduction the syngas. The major drawbacks of this process involve endothermic reactions that increases both operational and production costs compared to SMR process. Moreover, the H2/CO ratio is 1:1 that indicates less H2 production with respect to SMR [18]. Furthermore, DMR process causes catalyst deactivation that results in operational problem [19]. Similarly, partial oxidation (POX) is a noncatalytic process which upon combustion with pure oxygen produce syngas. The main drawbacks are high oxygen separation cost, high operating temperature i.e. 1300–1500℃, and pressure of 3–8 MPa to proceed reactions [10]. In addition, syngas produced from the POX process offer H2/CO ratio of 1:1 which is much less than the ratio offered by SMR [10,20]. Conclusively, considering prime advantages of gasification and SMR over DMR and POX, both gasification and SMR are best suited to maximize the H2 production while minimizing the greenhouse gas emissions. Most of attentions are devoted towards the standalone gasification development with and without CO2 capture assessment using coal and other feedstocks to produce H2, electricity, poly-generation, and syngas [21–24]. Cormos [25] developed the overall integrated gasification combined cycle (IGCC) with CO2 capture and storage. IGCC processes have also shown promising integration with other processes to produce H2 through various gasifier types i.e. Shell, GEE, etc. upon utilization of coal and biomass [26–29]. In addition, Cormos et al. [14] presented multi-fuel and multi-product operation for IGCC with carbon capture and storage. On the other hand, economic analysis was also being performed for H2 production through natural gas reforming with CO2 capture [30]. Szima et al. studied the DMR process for H2 production along with CO2 capture [31]. Qian et al. [32] presented an integrated model for efficient utilization of coke-oven gas and coal through gasification using tri-reforming. Yi et al. [33] studied the integration of reforming and coal gasification for CO2 utilization to minimize the water resources. Conclusively, most of the research conducted so far dealt either standalone reforming process or coal gasification. However, a few studies have been carried out recently to investigate the harmonious process integration and intensification between gasification and SMR. Adams and Barton [34] proposed techno-economic studies for several processes to produce efficient polygeneration from coal and natural gas. Cormos et al. [35] assessed the techno-economic calculation for flexible H2 and power generation through coal gasification. Ahmed et al. [36] suggested the integrated model of coal gasification and SMR to utilize syngas heat and steam from gasification process to increase H2 production. Ahmed et al. [37] also performed techno-economic assessment for both conventional coal and integrated coal gasification and SMR process, concluding the integrated model as a more efficient process. However, the earlier process integrations of gasification and reforming units in series experienced operational issues in the reforming section as the coal derived syngas contains higher sulfur content then the allowable limits of the reforming catalyst. Keeping in view the limitations in the harmonious integration between gasification and reforming technologies, new pragmatic integration approach has been demonstrated in this work to indirectly utilize the heat from the gasification derived syngas in the SMR process with the aid of radiant cooler without any risk of catalyst poisoning and deactivation. The proposed integration exploits the parallel process integration network approach to utilize the key technical and economic benefits of different technologies that can enhance the overall process sustainability without relying on the single fuel. The current article consists of four sections. The first section provide a through introduction followed by the process simulation methodology containing base case model (case 1) and the updated model (case 2). In subsequent section, a detailed analysis based on critical process variables against Since the last few decades, abrupt increase in population, industrial development, and rising living standards resulted in an enormous escalation in the energy demands. According to BP energy outlook 2019, the overall energy demands across the globe is expected to grow by 1.2% per annum [1]. Consequently, creating a pressing problem to explore new technologies and energy resources to overcome the energy gap. Although, the avid consumption of natural resources meet energy gap but at the expense of rising level of greenhouse gases especially CO2, which is a prime root cause of global warming [2]. For instance, the overall growth rate of CO2 emission is 2.1% after three years of stability from 2014 to 2016, leading to temperature rise of 2℃ [3,4]. According to Intergovernmental Panel on Climate Change (IPCC), it is expected that global temperature may rise from 1.1 to 6.4℃ by 2100 [5]. Therefore, it is need of time to explore such options that efficiently utilize the energy resources while minimizing the greenhouse gas. Presently, the primary fossil fuels available to generate power and overcome energy gap includes natural gas, crude oil, and coal [3]. Natural gas yields high efficiencies for power plants with low greenhouse gas emissions and showed a potential of growth as compared to oil [6]. According to U.S. Energy Information Administration (EIA), the natural gas prices for the projected period till 2050 are anticipated to remain low [7,8]. Therefore, it is expected to gain priority in future due to cost effectiveness and efficient production of H2 with minimum greenhouse gas emissions. Importantly, advancements through environmentally benign coal and natural gas technologies coupled with carbon capture and sequestration (CCS) will gain priority and will open doors for coal utilization [9,10]. On the other hand, natural resources survey conducted in 2013 showed an approximated 890 billion tonnes of coal reserves available across the globe [11]. Furthermore, consumption of coal indicates increasing trend from 2012 to 2040 with an average increase of 0.6% per annum [12]. Considering the fossil fuel reserves, coal reserves are much more than that of natural gas. Therefore, the abundantly available coal reserves across the globe at relatively low cost with prime applications in power and hydrogen (H2) production, coal is expected to remain potential fossil fuel in future [12]. Due to ever increasing energy demands and economic instability around the globe, it is unlikely to meet demands while solely relying on single fuel. Therefore, the need of hybrid systems to handle multiple fuels generating multiple products in environmentally benign manner will enhance the overall process sustainability. Recent developments in H2 and electricity generation processes using coal and natural gas as primary fuels have devoted more attentions to meet energy requirements while mitigating greenhouse gases emissions [13]. Some of the commercial H2 production technologies from fossil fuels includes coal gasification, steam methane reforming (SMR), dry methane reforming (DMR), and partial oxidation (POX) [10]. The gasification of low and high-quality fuels in both standalone and blending manner have been evaluated as one of the cost-effective approaches for future power and H2 generation technology with low carbon footprint. Importantly, the diversity of products that can be produced from the gasification mainly H2 make gasification technology even more prominent [14,15]. Moreover, the flexibility of gasification process for integration with other technologies signifies its future potential. SMR process uses natural gas and steam to generate syngas containing H2 and carbon monoxide with ratio of 3:1 that indicate higher H2 production potential. It is among the most developed, widespread, and least expensive technology for H2 production [16]. Moreover, the high efficiencies, low operational, and production cost along with readily available natural gas strengthen this technology [17]. On the other hand, dry methane reforming (DMR) uses CO2 and natural gas to produce 2 Fuel 266 (2020) 117111 U. Hamid, et al. product composition, cold gas efficiency (CGE), H2/CO (HCR) ratio, higher heating value (HHV), and CO2 emissions has been discussed. The last section concludes the article along with some future directions. this point, the outlet of water gas shift process contains high contents of water, which upon temperature reduction removed as a condensate with the help of flash drum in gas cooling. Subsequently, acid gas removal section is installed which separate CO2 from H2. The validation [43] of gasification and WGS models of the base case with the literature has been done and represented in the Fig. 2. 2. Simulation methodology and model development Aspen Plus V9 is used in this study as a simulation tool where the Peng-Robinson with Boston-Mathias alpha function (PR-BM) is used as an effective thermodynamic property package for gasification, scrubber, steam methane reforming (SMR), acid gas removal, and water gas shift sections [38–40]. Due to varying composition of coal from one region to another, proximate analysis, ultimate analysis, and heating value data is provided in Table 1. Prior to perform the simulation studies and convert the coal into syngas, RYield model of Aspen Plus is used to breakdown coal into its constituent elements. Subsequently, RGibbs reactor is used to model gasification process which results in syngas production and slag formation. Similarly, RGibbs model is also used to model the SMR process. The composition [36,42] of the natural gas used in the process is provided in Table 2. Concisely, RGibbs model of Aspen Plus works on the principle of Gibbs free energy minimization to calculate the equilibrium with phase splitting. Likewise, REquil model of Aspen Plus is used to calculate the equilibrium of phases when stoichiometry of the reaction is known. Therefore, water gas shift reactors are modeled based on REquil reactors. Some of the design assumptions and process streams data is presented in Tables 3 and 4. Before investigation of integration in the case 2, the base case model (case 1) is validated with the data published in the literature. 2.2. Case 2 – Integration of GEE radiant gasifier with steam methane reforming process In case 2, gasification and steam methane reforming (SMR) processes are coupled using parallel design configuration as shown in Fig. 3. Natural gas [36,42] is fed to the reforming unit where reforming reactions mentioned in Table 5 occurs to produce syngas at ~912℃ and 32 bar. In the reforming process, heavier hydrocarbons are first converted into methane, which subsequently undergoes methane reforming in the presence of steam. The developed SMR model is also validated with the published data [36] as represented in Fig. 4. Case 2 presents the heat integration of SMR section with the GEE radiant type gasifier. In GEE radiant type gasifier, significant heat can be extracted from the syngas leaving the gasifier that can efficiently be utilized to proceed SMR process. To make this heat integration possible, heat exchangers (HEX301 & MHT) are installed in such a way that heat extracted from the syngas is used for pre-heating and sustaining the endothermic reactions involved in SMR process. Subsequently, heavier hydrocarbon is converted into methane and eventually to syngas at 912°C in RS701 and RG701, respectively. The detailed flowsheet built using Aspen Plus is presented in Fig. 5. Due to high temperature of resulting syngas from reforming process, the temperature is reduced to 325°C by water quenching followed by the water gas shift section. The flowsheet of case 2 for Scrubber, water gas shift, and cool gas section remain same as depicted for case 1. A selected comparison of process streams data of case 1 (Fig. 1) and case 2 (Fig. 3) is presented in Table 4. 2.1. Case 1 (Base Case) – Syngas production from GEE entrained flow gasifier The complete process is divided into multiple sections i.e. gasification, scrubber, water gas shift, and gas cooling section. The schematic diagram of case 1 is presented in Fig. 1. The base case of gasification section, scrubber, water gas shift, gas cooling section, and steam methane reforming section has been validated [36,43]. The gasifier section is the most important section in any gasification process where syngas is produced from the coal at high pressure and temperature in the presence of water and oxygen. After decomposition of coal, resulting product is being mixed with oxygen and slurry water. Subsequently, this mixture undergoes gasification process where reactions mentioned in Table 5 resulted in syngas generation and slag leaving at 1370°C. The GE Energy (GEE) radiant entrained flow gasifier is considered in this work due to which heat is recovered from syngas to decrease the temperature from 1370°C to 760°C. Afterward, the quenching is carried out with the help of liquid water to decrease the temperature to 216°C follow by slag removal. After gasification, scrubber is used to remove particulate matters and chlorides through water to avoid fouling in the subsequent unit operations. The gas product leave from the top while waste leave from the bottom of scrubber at 211° C . The syngas is then fed to the water gas shift (WGS) reactor to convert carbon monoxide into CO2 in the presence of steam to maximize the H2 production. Also, carbonyl sulfide (COS) in the syngas is difficult to remove as compared to hydrogen sulfide (H2 S ). Therefore, in WGS section COS is converted into H2 S in the presence of steam resulting in H2 and CO2 . Steam to carbon monoxide ratio of 2.0 is maintained at the inlet of water gas shift reactor to maximize the CO conversion. First water gas shift reactor (SHFT501) decreases the CO mole fraction from 24.5% to 5% while increases the H2 mole fraction from 18.8% to 38.2%. An intermediate cooler (HEX501) is used to remove the heat generated due to the exothermic reactions before introducing to the second water gas shift reactor. Ultimately, CO mole fraction reduced to 0.8% while H2 mole fraction become as high as 42.4% and leave the shift reactor (SHFT502) at258°C. Subsequently, heat is being recovered from the product stream containing 0.8% CO, 29.9%CO2 , 42.4%H2 , 25.3%H2 O, and 1.8 ppm COS. At 3. Results and discussion 3.1. Heat integration analysis Two process models have been developed and compared in this study to analyze the syngas production and the heating requirements. Case 1 is the conventional process for generating syngas from coal Table 1 Proximate and ultimate analysis of coal [41]. Coal Type Proximate analysis (weight %) Moisture Ash Volatile Matter Fixed Carbon Total Sulfur HHV, kJ/kg (Btu/lb) LHV, Btu/lb (Btu/lb) Bituminous Illinois No. 6 As Received Dry Basis 11.12 9.7 34.99 44.19 100 2.51 27,113 (11,666) 26,151 (11,252) 0 10.91 39.37 49.72 100 2.82 30,506 (13,126) 29,544 (12,712) As Received 11.12 63.75 4.5 1.25 0.29 2.51 9.7 6.88 100 Dry Basis 0 71.72 5.06 1.41 0.33 2.82 10.91 7.75 100 Ultimate Analysis (weight %) Moisture Carbon Hydrogen Nitrogen Chlorine Sulfur Ash Oxygen Total 3 Fuel 266 (2020) 117111 U. Hamid, et al. gasification process, whereas, case 2 represents the integration of gasification and reforming technologies for enhanced syngas generation. The process flow diagram developed in Aspen Plus for case 2 showing the heat exchanger network for recovering the heat from coal derived syngas and supplying it for NG reforming is represented in Fig. 6. The syngas generated from gasification unit is typically at a temperature of 1370℃ which is being cooled enough to carry out WGS reactions. Therefore, two heat exchangers are installed in the downstream of gasification section to reduce the temperature from 1370℃ to 760℃. The outlet temperature of first heat exchanger is adjusted in such a way that the extracted heat from the coal derived syngas can efficiently be utilized in the reformer. The methane and water that will be utilized in the SMR section entered at 25℃ which undergoes pre-heating to meet reformer temperature requirement. The calculator blocks are used to control the flowrates of both methane and water in such a way that all heat recovered from the syngas of gasifier efficiently be utilized in feed pre-heating and sustaining reformer temperature. For efficient heat recovery between hot and cold streams, Aspen Energy Analyzer has been used to perform the pinch analysis and construct grid and composite diagrams. Thermal data of the process streams has been extracted through the simulation models followed by approach temperature difference (ΔTmin) of 10℃ between hot and cold streams. Moreover, the composite curves are developed for both the cases to analyze the heat recovery between hot and cold utilities. The composite diagram depicting the enthalpy vs temperature graphs are presented for case 1 and case 2 in Figs. 7 and 8, respectively. The comparative analysis showed that, an energy saving of 156.8 MW is possible in case 2 design through the heat integration which otherwise require significant flowrates of external utilities to drive steam methane reforming. Subsequently, the syngas from reformer leaves at 912℃ which is at much higher temperature and require cooling before injecting to water gas shift section. Therefore, two heat exchangers are installed to pre-heat the water to meet the quenching water requirement and steam required in water gas shift section. This heat integration resulted in reducing the utilities load of the overall process to 47 MW. Table 2 Natural gas composition [36,42]. Natural gas composition (Mole Fraction) CH4 C2H6 C3H8 C4H10 CO2 N2 Total Lower heating value (LHV) 0.939 0.032 0.007 0.004 0.010 0.008 1.000 47.76 MJ/kg Table 3 Design assumptions. Equipment Aspen model Description Coal flowrate Mixer Gasifier (GEE) RYield, RGibbs (Reactor) Pre-reformer RStoic (Reactor) Reformer RGibbs (Reactor) Air Separation Unit (ASU) Separator, Multistage compressor Water Gas Shift (WGS) Gas Cooling REquil (Reactor), Heat exchangers Flash drum Coal = 62.20 kg/sec (70% coal, 30% water) Entrained flow gasifier GE Energy (GEE) Temperature = 1370℃ Pressure = 5.6 MPa; Carbon conversion = 98% Hydrocracking of heavier hydrocarbon Natural gas flowrate = 5.5 kg/sec; Temperature = 912℃; Pressure = 3.2 MPa; Steam/CH4 ratio = 3.0; Nickel based catalyst Oxygen flowrate = 50.57 kg/sec; Temperature = 90.9℃; Pressure = 6.76 MPa; 94.97% pure oxygen (mole %) Adiabatic reactors = 2; Steam/CO ratio = 2.0 Isothermal flash vessels = 3 Table 4 Comparison of Case 1 and Case 2 process streams data. Air Temperature [°C] Pressure [MPa] Mass Flows [kg/hr] CO CO2 H2 H2O CH4 H2S N2 COS O2 Water Case 1 Case 2 Case 1 Case 2 Case 1 Case 2 Case 1 Case 2 15.0 0.1 794,515 15.0 0.1 794,515 90.9 6.8 182,048 90.9 6.8 182,048 60.0 6.0 93,188 60.0 6.0 93,188 0.0003 0.0003 0.0099 0.0099 1.0000 1.0000 0.7732 0.7732 216.0 5.5 662,874 0.2724 0.0695 0.2087 0.4323 0.0001 0.0049 0.0061 0.0002 205.6 3.2 663,234 0.2722 0.0694 0.2086 0.4326 0.0001 0.0049 0.0061 0.0002 0.0188 0.0188 Scrubber Temperature [°C] Pressure [MPa] Mass Flows [kg/hr] CO CO2 H2 H2O CH4 H2S N2 COS Syngas WGS Gas Cooling Case 1 Case 2 Case 1 Case 2 Case 1 Case 2 211.0 5.5 619,159 0.2931 0.0747 0.2245 0.3899 0.0001 0.0053 0.0065 0.0002 189.4 3.2 638,507 0.2835 0.0722 0.2172 0.4098 0.0001 0.0051 0.0063 0.0002 150.0 5.4 730,977 0.0083 0.2993 0.4243 0.2531 0.0001 0.0046 0.0054 150.0 3.2 807,548 0.0079 0.2790 0.4547 0.2418 0.0037 0.0040 0.0049 39.0 5.4 559,018 0.0111 0.3999 0.5673 0.0017 0.0001 0.0061 0.0073 39.0 3.2 616,163 0.0103 0.3670 0.5984 0.0024 0.0049 0.0052 0.0064 4 Fuel 266 (2020) 117111 U. Hamid, et al. Fig. 1. Case 1. Syngas production from coal-based gasification process. Table 5 Chemical reactions involved in the process. Gasification Reactor C(s) + H2 O CO + H2 C(s) + CO2 2CO CO H= +131MJ/kmol H = + 172 MJ/kmol H= 111MJ/kmol CO2 H= 283MJ/kmol H2 O H= 242MJ/kmol Water gas shift (WGS) reactor COS + H2 O H2 S+ CO2 CO + H2 O H2 + CO2 H= H= 34MJ/kmol 41MJ/kmol 1 2 1 CO + O2 2 1 H2 + O2 2 C(s) + O2 Steam methane reforming reactor 3 C2 H6 + H2 O 5CH 4 + CO 3C3 H8 + 2H2 O 7CH 4 + 2CO 3C4 H10 + 3H2 O 9CH 4 + 3CO CH 4 + 2O2 CO2 + 2H2 O CH4 + H2 O CO + 3H2 ΔH ΔH ΔH ΔH ΔH = = = = = +3.6460 +16.607 +41.116 −802.54 +206.12 MJ/kmol MJ/kmol MJ/kmol MJ/kmol MJ/kmol Fig. 4. Base case validation of steam methane reforming section [36]. Base Case Validation CO CO2 H2 H2O 0.45 0.40 CH4 3.2. Effect of slurry temperature and oxidant requirements on syngas composition 0.4244 0.4212 0.3931 0.3893 Coal slurry and moisture is one of the main constituents of gasification process and the temperature of slurry also plays an important role in the syngas composition and cold gas efficiency (CGE). Coal based power plants usually have large amount of waste heat which can be utilized for coal slurry pre-heating. In this study, the sensitivity analysis has been carried out at five different temperature i.e. 25℃, 60℃, 250℃, 278℃, 300℃ to evaluate its effect on syngas composition. The results presented in the Fig. 9 reveal the mole fraction, O2/Coal ratio, and CGE at five different temperature of slurry water. The results showed that increasing coal slurry temperature increases the CO and H2 mole fraction while decreases the steam and CO2 content in the syngas. CGE is an important parameter to analyze the performance of the gasifier and it typically represents the heating value of the syngas as given in Eq. (1). The results showed the CGE of the syngas increase with an increase in the temperature of coal slurry. Mole Fraction 0.35 0.30 0.3026 0.3012 0.2942 0.2993 0.2531 0.2526 0.25 0.1862 0.20 0.1807 0.15 0.1051 0.1002 0.10 0.05 0.00 0.0002 Reference 0.0002 Base Case Gasifer Product 0.0082 0.0001 Reference 0.0083 0.0001 Base Case WGS Product Fig. 2. Base case validation [43]. Fig. 3. Case 2: Heat integrated gasification and steam methane reforming. 5 Fuel 266 (2020) 117111 U. Hamid, et al. RY301 COAL(IN) H301 CH4(IN) PUMP301 S311 H2O(IN) S301 MIX301 OXY102(IN) RG301 S302 HEX301 HOTGAS VLV301 HEX302 MHT S304 S303 S312 SPL302 SNG101(OUT) S313 SSPLIT WATER(IN) SLAG S310 S701 S702 MIX701 RS701 RG701 S703 S704 S705 SNG103(OUT) H701 HEX702 S305 S306 HEX703 S307 S308 HEX704 S309 S101(OUT) SPL301 S706 Fig. 5. Integrated gasification and steam methane reforming flowsheet using Aspen Plus®. Fig. 6. Heat integration between Gasification and SMR for Case 2 Design. CGE = msyngas × LHVsyngas m fuel × LHVfuel coal slurry temperature as shown in Fig. 9. As we know that O2 production is an energy intensive process and it affects the overall process performance. The analysis showed that the O2/coal ratio can significantly be reduced at elevated coal slurry temperature. Moreover, the results indicate that with an increase in slurry water temperature, the overall load of gasifier to increase the syngas temperature to 1370°C (1) Moreover, the effect of coal water slurry’s temperature has been also observed on the consumption of oxidizing agent in the gasifier. The results showed that oxygen consumption decreases with an increase in Fig. 7. Composite curve of case 1. 6 Fuel 266 (2020) 117111 U. Hamid, et al. Fig. 8. Composite curve of case 2. Fig. 9. Effect on slurry water temperature on gasifier syngas and CGE. Fig. 11. Effect of steam to carbon monoxide ratio on WGS product. Fig. 10. Effect of reformer temperature on syngas composition and methane conversion. 7 Fuel 266 (2020) 117111 U. Hamid, et al. Table 8 Estimation of operational and maintenance expenditures. Fig. 12. Case comparison at the outlet of water gas shift reactor. O&M Cost Units Case 1 Case 2 Fixed O&M Cost Maintenance Cost Labor Cost Administrative, support & overhead cost Total Fixed O&M Cost MM MM MM MM €/year €/year €/year €/year 24.70 6.00 1.80 32.50 25.20 6.00 1.80 33.00 Variable O&M Cost Natural Gas Coal Boiler Feed Water (BFW) WGS Catalyst Solvent (Selexol) Reforming Catalyst Total variable O&M Cost MM MM MM MM MM MM MM €/year €/year €/year €/year €/year €/year €/year – 48.64 0.48 1.36 0.80 – 51.29 15.94 48.64 1.15 1.38 0.94 0.02 68.06 Total Fixed and Variable Cost Total Fixed and Variable Cost (net H2) Total Lifetime Cost Lifetime Hydrogen Cost MM €/year MM €/tonne H2 MM € €/tonne H2 83.79 2.59 2941.55 484.71 101.06 2.49 3390.52 446.14 Table 6 Case comparison against selected parameters. Parameters Case 1 Case 2 CO CO2 H2 H2O N2 H2S Others Higher Heating Value (HHV) [MJ/kmol] Lower Heating Value (LHV) [MJ/kg] Hydrogen Flowrate [tonne/hr] Hydrogen/Carbon Monoxide (HCR) CO2/H2 (CO2 emissions per unit H2 production) Cold Gas Efficiency (CGE) 0.0083 0.2993 0.4244 0.2531 0.0054 0.0046 0.0049 137.77 7.13 32.37 51.10 0.71 67.0% 0.0079 0.2790 0.4547 0.2418 0.0049 0.0040 0.0077 148.65 8.14 40.53 57.89 0.61 73.7% Table 9 Results summary. CO2/H2 (CO2 emissions per unit H2) Energy saving [MWth] Hydrogen production [tonne/hr] Cold gas efficiency (CGE) Higher heating value (HHV) [MJ/kmol] Total Investment Cost [MM €] Hydrogen Cost [€/tonne H2] 0.7 CO H2 CO2 Case 1 Case 2 0.71 – 32.37 67.0% 137.77 846.88 484.71 0.61 47 40.53 73.7% 148.65 863.96 446.14 H2 O O2 flowrate 220 0.6 Units Case 1 (MM €) Case 2 (MM €) Reformer Solid Handling Facility Gasification Island Syngas processing unit Acid Gas Removal Unit Air Separation Unit Offsite Unit and Utilities MMCUFTD tonne of coal/hr tonne of coal/hr tonne of coal/hr tonne of CO2/hr tonne of O2/hr Equipment Cost (25%) – 53.25 213.85 53.00 118.51 125.98 141.15 5.13 53.25 213.85 53.00 124.77 125.98 143.99 Total Installed Cost Contingency MM € Installed Cost (15%) Installed Cost (5%) 705.73 105.86 719.96 107.99 35.29 36.00 MM € MM €/tonne H2 846.88 26.17 863.96 21.32 Land Cost Total Investment Cost Total Investment Cost per tonne H2 Gasifier mole fraction Plant sub-system 0.5 180 0.4 0.3 160 0.2 O2 flowrate (Tonne/hr) 200 Table 7 Estimation and comparison of capital cost expenditures. 140 0.1 0.0 120 10 40 70 100 130 160 190 Water flowrate (Tonne/hr) Fig. 13. Influence of water flowrate on gasifier product. the gasification process unlike case 1. The typical pressure to carry out SMR process is around 32 bar. The second most influential parameter is the reformer’s temperature, which effects the syngas composition, CH4 conversion, and H2/CO (HCR) ratio. As depicted in Fig. 10, an increase in reformer’s temperature increases H2 and CO contents while decrease the CO2 and H2O. As SMR reactions are endothermic, the most important parameter to evaluate the reformer performance is the CH4 conversion to syngas which usually increases with an increase in the reformer temperature. For instance, at 700℃, the syngas has 12.6% methane that decreases gradually to 0.16% at 1100℃. Moreover, carbon monoxide mole fraction increases from 2.4% to 13.2% when temperature increases from 700℃ to 1100℃. Similarly, H2 mole fraction in product stream increases from 30.4% to 52.9% with increase in temperature from 700℃ to 1100℃. The reason is that reforming decreases. The results also showed that the increase in slurry’s temperature minimizes the conversion of CO and H2 to CO2 and H2O, respectively. Conclusively, pre-heating of coal slurry water not only increases the CGE of the gasification process but also decreases the oxygen requirement which ultimately reduces the load on air separation unit. 3.3. Effect of Reformer’s operational parameters on NG derived syngas In case 2, steam methane reforming (SMR) process is coupled with 8 Fuel 266 (2020) 117111 U. Hamid, et al. 560 H 2 production CO 2 emission 41.0 550 40.5 540 40.0 39.5 530 syngas at temperature around 912℃. Fine-tuning in the reformer’s temperature and recycle blocks are used to ensure maximum conversion of methane. CO2 emission (Tonne/hr) H2 production (Tonne/hr) 41.5 3.4. Comparison of steam demand requirements for case 1 and case 2 Water gas shift process in the promising technology to convert carbon monoxide into CO2 in the presence of steam to maximize the H2 production. The CGE of the syngas at the inlet of WGS reactor affects the overall H2 production and the process steam requirements. It can be seen form the process flow diagram of case 2 that the coal and NG derived syngas is mixed at the inlet of WGS reactors which significantly increase the CGE of the case 2. For instance, the CGE of case 1 and case 2 is calculated as 67.0% and 73.7%, respectively, resulting 10% increase in CGE. The syngas composition analysis also showed that H2/ CO for the case 2 is 37% higher as compared to case 1 before WGS because of an additional NG reforming. Similarly, the ratio of steam to CO ratio plays an important role in the conversion of carbon monoxide to CO2 which also effect the H2 mole fraction in the product. The ratio selected for this comparison ranges from 0.5 to 2.0 with step size of 0.5. Fig. 11 shows that with an increase in steam to CO ratio, the conversion of CO to CO2 and H2 increases. To ensure maximum conversion of CO, the steam/CO ratio of 2.0 is maintained to produce maximum H2. The comparative analysis at the outlet of WGS reactor showed that case 2 increases the H2 mole fraction in the syngas up to 7% whereas reduce the CO2 and H2O content. Lastly, comparison of case 1 and case 2 at the WGS outlet has been presented in the Fig. 12. The results indicated that case 2 provide enhanced production of H2 and 7% higher H2 contents as compared to case 1. Most importantly, the overall CO2 content for case 2 is 6.8% less than the case 1 which is beneficial for acid gas removal section because it requires less solvent and energy for hydrogen purification. Also, cold gas efficiency (CGE) of both cases reveal that case 2 present higher CGE which hint the enhance overall efficiency of the process. 39.0 38.5 0.60 0.65 0.70 0.75 0.80 0.85 0.90 520 0.95 CH4 for Reforming (MMCUFTD) Fig. 14. Comparison for CO2 emissions and H2 production. 102.0 890 CAPEX OPEX 101.8 885 101.6 880 101.2 101.0 870 100.8 865 100.6 OPEX (MM €/year) CAPEX (MM €) 101.4 875 860 100.4 855 100.2 100.0 850 20% 25% 30% 35% 40% 45% 3.5. CO2 specific emissions analysis for H2 generation Water Content Fig. 15. CAPEX and OPEX comparison against slurry water content. O2 requirement OPEX/H2 production 2.65 210 O2 requirement (Tonne/hr) 2.60 200 2.55 190 180 2.50 170 2.45 160 150 OPEX / H2 production (MM €/Tonne H 2) 220 Considering the clean and sustainable process for H2 production a comparison against conventional and integrated model is presented. Though, H2 is the main constituent of the syngas and water gas shift product but CO2 is also inevitable during H2 production. In addition, CO2 is a greenhouse gas that results in global warming and many other environmental problems. Therefore, processes which produces less amount of CO2 upon production of H2 gaining priority. Considering the CO2 emissions per unit H2 production parameter, the results of both cases have been presented. According to Table 6, case 2 showed higher potential of H2 production and less CO2 specific emissions compared to the conventional gasification process. For instance, CO2:H2 ratio for case 1 is 0.71 while for case 2 the ratio is 0.61 which indicates that case 1 causes more CO2 emission as compared to case 2. Considering the energy and environment protection indicators, case 2 has been not only evaluated as a better alternative in terms of H2 production and energy utilization but it also provides promising results towards the environmental aspects. The model developed in case 1, hydrogen purity after acid gas removal is 91.33% but case 2 it is 94.8%. Afterward, acid gas removal section is used to separate CO2 from the H2 upon using the Selexol as solvent. Precisely, comparison against various parameters indicated remarkable improvements for case 2 as compared to case 1. For example, 25% increase in hydrogen production, 14% enhanced lower heating value (LHV), 10% improved cold gas efficiency (CGE), and 13% enhanced hydrogen to carbon ratio with 13% reduced carbon dioxide emissions make case 2 significant improved process. 2.40 20% 25% 30% 35% 40% 45% Water Content Fig. 16. Comparison for O2 requirement and OPEX/H2 production cost. reactions are endothermic and require large amount of heat i.e. 206.12 MJ/kmol. According to Le Chatelier’s principle, increase in temperature promote forward rate of reaction which confirm that more and more methane conversion is possible at high temperature. Importantly, more than 85% of methane is already being converted into 9 Fuel 266 (2020) 117111 U. Hamid, et al. Fig. 17. Effect of methane flow rate on CO2 emission and economic analysis. 4. Economic analysis while case 1 offer 32.37 tonne/hr of H2. The results showed that case 2 provide better and cost-effective method to produce H2 which resulted in 25% increase in hydrogen generation with 18% reduction in total investment cost per tonne of H2 generation. 4.1. Estimation of capital expenditure (CAPEX) As described in the process description, hydrogen is a clean fuel which could be produced from gasification of coal and reforming of methane in a parallel configuration. Hence, multiple processes i.e. solid handling, gasification island, syngas processing, acid gas removal, air separation, and reformer are harmoniously integrated to maximize the hydrogen production while utilizing the heat within the overall process. Therefore, economic analysis of integrated process is essential to evaluate the capital cost of conventional gasification process (case 1) and heat integrated gasification and steam methane reforming process (case 2) that contain additional reactors. The influencing factors for cost estimation are plant capacity, raw material utilization, size of plant, plant efficiency, and some inevitable uncertainties associated with the process plant. So, Eq. (2) provides reasonable cost estimation for integrated gasification process that also known as power law of capacity where CE indicate equipment’s cost, CB represents cost of base case, Q denotes reference capacity, M is a constant, IB is the cost index of base case, and IE is the cost index of calculating year [25,44]. Through literature, the capital and variable costs for both cases were determined upon specifying the capacity of each section [45–47]. CE = CB × Q QB M × IE IB TIC per tonne of H2 = Total investment cost Hydrogen generation (3) 4.2. Estimation of operational and maintenance (O&M) expenditures Fixed and variable expenditures are represented by the operational and maintenance (O&M) expenditures. The key dependence of O&M expenditure is on fuel prices, Selexol and catalyst requirement, maintenance cost, and operational hours. The O&M expenditures for both cases are reported in Table 8 with some operational indicators extracted from the literature [45–47]. The results showed that case 2 present higher total fixed and variable cost compared to case 1 because of additional natural gas and steam methane reforming catalyst. However, total fixed and variable cost to produce per tonne of H2 indicated that case 2 is economically benign because of low cost and high H2 generation. Similarly, lifetime cost of the process is also being computed with the assumption that process construction time is three year with life span of 25 year having operational hours per year equals to 7500 h. Cost comparison indicated that case 2 has the tendency to produce H2 offer 8% life-time cost reduction as compared to case 1. Therefore, operational and maintenance expenditures revealed that case 2 is present more benefits in term of cost to produce H2. (2) Some economic analysis-based assumptions have been made that are offsite and utilities are 25% of equipment cost, contingency is 15% of installed cost, land cost is 5% of installed cost. Finally, calculations are performed to estimate the cost of each section using and ultimately total investment cost, which is sum of total installed cost and total cost. The capital cost expenditure of case 1 and case 2 is presented in Table 7. Case 1 and case 2 possess same cost for solid handling, gasification island, syngas processing unit, and air separation unit because the base remain same. As, case 2 presents higher syngas flowrates due to which acid gas removal section cost increases. Based on the equipment cost of each section, installed cost, contingency, land cost, and utilities’ cost are being computed. Afterward, comparison of total investment cost (TIC) associated with case 1 and case 2 is reported based on cost per tonne of H2, as represented in Eq. (3). The results indicated that case 2 presents higher flowrate of hydrogen production i.e. 40.53 tonne/hr 4.3. Compilation and comparison of key results Some of the key results are summarized in Table 9 to provide quick comparison between case 1 and case 2. For instance, case 2 has lower CO2 emission per unit H2 production as compared to case 1 while offering energy saving of 47 MWth and increased overall hydrogen production. Additionally, higher heating value (HHV) for case 2 is also higher than case 1 design. Besides technical assessment, economic analysis indicates that hydrogen cost can be reduced from 484.7 €/ tonne to 446.14 €/tonne due to an improved process efficiency, energy savings, hydrogen production and product purity regardless of increased capital investment. 10 Fuel 266 (2020) 117111 U. Hamid, et al. 5. Selecting optimum process variables product gas. Therefore, benefits of both processes collectively come up with more innovative option to be implemented pragmatically. Ultimately, a new heat integrated model has been developed which efficiently utilize the heat recovered from the syngas to preheat the steam methane reforming reactants and proceed the endothermic reforming reactions while maintain reformer temperature. Case 1 is a conventional coal-based gasification model, whereas, case 2 represents the strategy to utilize the gasification heat for NG reforming. Both case studies are compared based on H2/CO (HCR) ratio, cold gas efficiency (CGE), higher heating value (HHV), syngas compositions, and CO2 specific emissions. Comparative analysis showed that case 1 presents HCR ratio of 0.766 while case 2 offers 1.05, which indicates the higher H2 content as compared to carbon monoxide for case 2. Similarly, based on cold gas efficiency of process, case 2 presents 73.7% CGE, whereas, case 1 represents only 67.0% CGE. The results of HHV for case 2 and case 1 has been evaluated as 149.56 MJ/kmol and 137.75 MJ/kmol, respectively. Similarly, CO2 specific emissions analysis also showed that case 2 offers less CO2 emission compared to case 1. Besides these, economic analysis indicated that case 2 reduces both capital cost expenditures and operational and maintenance expenditure as compared to case 1. So. Case 2 design has been evaluated as the best case in terms of cold gas efficiency, H2 to carbon monoxide ratio, higher heating value, improved H2 production, and less greenhouse gas emissions as compared to case 1. Conclusively, case 2 is not only technically a valid schematic but also presents with cost-effective solution to maximize the hydrogen generation by 25%. 5.1. Optimal parameters for CO2 emission The optimum value of some important parameters is obtained upon performing the sensitivity analysis. The effect of water flowrate on gasifier product composition and oxygen requirement for gasification process is reported in the Fig. 13. The results showed that carbon dioxide content in product syngas increases with an increase in water flowrate for gasification process. Additionally, carbon monoxide and hydrogen which are essential components of syngas keep on decreasing while water content in the syngas also started to increase steadily. Besides these, oxygen requirement to maintain the gasifier temperature of 1370°C also indicates an increasing trend starting from nearly 142 tonne/hr to 208 tonne/hr. Furthermore, methane flowrate for reforming process is also being analyzed with respect to CO2 emissions and H2 production as presented in Fig. 14. The results indicate that the overall CO2 emission started to increase as methane flowrate increases while hydrogen production started to decrease. Therefore, the sensitivity analysis of these parameters indicated that 30% water in coal slurry is enough to maintain the flow of slurry and insure the feasible water content of 18% in the gasifier product syngas. Similarly, the optimum methane flowrate considered to be 0.715 MMCUFTD which result efficient heat integration to maintain reformer temperature around 912°C, minimum CO2 emission, and H2 production. 5.2. Optimal process parameters for economic analysis CRediT authorship contribution statement To obtain the optimal process values considering both capital expenditures (CAPEX) and operational expenditure (OPEX) are represented besides CO2 emissions. According to Fig. 15, slurry water contents have been evaluated against CAPEX and OPEX, which reveal that both the costs increases with an increase in water content in the slurry. Furthermore, the cost associated with hydrogen production for the overall process has been evaluated which showed that the H2 production cost increases with an increase in the slurry’s water. Moreover, the load on air separation unit (ASU) also increases to meet the process requirement which itself is an energy intensive process. The results in Fig. 16 showed that cost associated with hydrogen production can be minimized by reducing the water content in the coal-slurry while meeting the process constraints. Usman Hamid: Simulation, Validation, Formal analysis, Investigation, Writing - original draft. Ali Rauf: Writing - review & editing, Supervision, Project administration. Usama Ahmed: Conceptualization, Methodology, Supervision. Md. Selim Arif Sher Shah: Visualization. Nabeel Ahmad: Formal analysis. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements 5.3. Effect of process parameters on emissions and economics The authors would like to acknowledge the support provided by the Lahore University of Management Sciences (LUMS), Pakistan, and King Fahd University of Petroleum & Minerals (KFUPM), Saudi Arabia, for conducting this research. Coal and methane flow rates are the two components that influence the overall CO2 emissions by contributing carbon. 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