Techno-economic analysis of bio heavy-oil production from sewage sludge using supercritical and subcritical water

Journal Pre-proof Techno-economic analysis of bio heavy-oil production from sewage sludge using supercritical and subcritical water

Truong Xuan Do, Rana Mujahid, Hyun Soo Lim, Jaekon Kim, Young-Il Lim, Jaehoon Kim PII:

S0960-1481(19)31635-0

DOI:

https://doi.org/10.1016/j.renene.2019.10.138

Reference:

RENE 12507

To appear in:

Renewable Energy

Received Date:

24 January 2019

Accepted Date:

25 October 2019

Please cite this article as: Truong Xuan Do, Rana Mujahid, Hyun Soo Lim, Jaekon Kim, Young-Il Lim, Jaehoon Kim, Techno-economic analysis of bio heavy-oil production from sewage sludge using supercritical and subcritical water, Renewable Energy (2019), https://doi.org/10.1016/j. renene.2019.10.138

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Journal Pre-proof Techno-economic analysis of bio heavy-oil production from sewage sludge using supercritical and subcritical water

Truong Xuan Doa,b, Rana Mujahidc, Hyun Soo Limd, Jaekon Kime, Young-Il Lima*, Jaehoon Kimc,f,g*

aCoSPE,

Department of Chemical Engineering, Hankyong National University, Anseong 17579 Republic of Korea

bSchool

of Chemical Engineering, Hanoi University of Science and Technology, 1st Dai Co Viet, Hanoi, Vietnam cSchool

of Mechanical Engineering, Sungkyunkwan University,

2066, Seobu-ro, Jangan-gu, Suwon, Gyeonggi-do, 16419 Republic of Korea dKorea

Electric Power Research Institute,

105 Munji-ro Yuseong-gu, Daejeon, 34056 Republic of Korea eResearch

Institute of Petroleum Technology, Korea Petroleum Quality and Distribution Authority,

33, Yangcheong 3-gil, Ochang-eup, Cheongwon-gu, Cheongju, Chungcheongbuk-do, 28115 Republic of Korea fSchool

of Chemical Engineering, Sungkyunkwan University,

2066, Seobu-ro, Jangan-gu, Suwon, Gyeonggi-do, 16419 Republic of Korea gSKKU

Advanced Institute of Nano Technology (SAINT), Sungkyunkwan University,

2066, Seobu-ro, Jangan-gu, Suwon, Gyeonggi-do, 16419 Republic of Korea

*Corresponding author: Young-Il Lim ([email protected]), Jaehoon Kim ([email protected]) First author: Truong Xuan. Do ([email protected]) Coauthors: Rana Mujahid ([email protected]), Jaekon Kim ([email protected]), Hyun Soo Lim ([email protected])

1

Journal Pre-proof Highlights  Bio heavy-oil (BHO) was produced from 100 t/d sewage sludge (SS) in industrial scale  Economic feasibility was evaluated for BHO plants using super and subcritical water  Minimum fuel selling price of BHO was 0.91 $/L, higher than actual price (0.55 $/L)  A BHO plant with subcritical water is profitable if SS treatment credit is >120 t/d

Graphical Abstract

Supercritical reactor (375 ℃ , 230 bar)

Economic values of Case 1  TCI = $15.1 million  TPC =$2.1 million/yr  ROI = 5.7 %/yr  Net MSFP = 0.90 $/L Waste gas

Case 1 Sewage sludge with 80% water (100 t/d, HHV=18 MJ/kg)

Centrifuge

DCM Separators

Case 2 Subcritical reactor (325 ℃ , 120 bar)

Waste water

Solid residue

Economic values of Case 2  TCI = $14.3 million  TPC =$2.1 million/yr  ROI = 6.6 %/yr  Net MSFP = 0.92 $/L

2

H2

Bio heavy-oil (8 t/d, HHV=36 MJ/kg) Case 1

Hydrotreater Case 2 Bio heavy-oil (9 t/d, HHV=34 MJ/kg)

Journal Pre-proof Abstract The economic feasibility of a bio heavy-oil (BHO) production process from 100 t/d sewage sludge (SS) using super- and sub-critical water was evaluated. The process included a super- or sub-critical reaction, BHO recovery via a condenser and centrifuge, BHO purification via extraction, phase separation and filtration, hydrotreating desulfurization, and wastewater treatment. For technoeconomic analysis (TEA), two cases were considered: BHO production with supercritical (Case 1) and subcritical (Case 2) water. The four-level economic potential approach was used for the TEA. The minimum fuel selling price (MFSP) of the BHO plants was approximately 0.91 $/L, which was higher than the actual selling price of 0.55 $/L. Case 2 showed higher economic values than Case 1 owing to the lower capital and production costs. When the SS treatment credit is >120 $/t or the BHO price is higher than the MFSP, the BHO plant with subcritical water (Case 2) is profitable. This study shows economic potentials for the SS hydrothermal liquefaction process with an upgrading unit.

Keywords: Sewage sludge; Bio heavy-oil; Supercritical and subcritical water; Techno-economic analysis; Process modeling; Four-level economic potential.

Abbreviation 4-level EP (four-level economic potential); ASR (annual sales revenue); BHO (bio-heavy-oil); CF (cash flow); CIT (corporation income tax); DCM (dichloromethane); EIC (equipment installation cost); EP (economic potential); FC (fixed cost); FCI (fixed capital investment); GP (gross profit); HI (heat integration); HHV (higher heating value); IC (indirect cost); IRR (internal rate of return); LC (labor cost); LNG (liquefied natural gas); MFSP (minimum fuel selling price); NP (net profit); NPV (net present value); NRTL (Non-random two-liquid); PBP (payback period); PC (project contingency); PEC (purchased equipment cost); PFD (process flow diagram); ROI (return on investment); SS (Sewage sludge); subBHO (bio-heavy-oil production with sub-critical water); supBHO (bio-heavy-oil production with super-critical water); TCI (total capital investment); TEA 3

Journal Pre-proof (techno-economic analysis); TIC (total installed cost); TPC (total production cost); TRC (total rawmaterial cost); TUC (total utility cost); WC (working capital); WSOs (water-soluble organics).

1. Introduction Sewage sludge (SS) has been considered as a promising biomass resource for producing renewable and sustainable fuels [1, 2]. Because dewatered SS contains a large amount of water (75–85 wt%), toxic chemicals (e.g., pathogens and heavy metals) [3, 4], unpleasant odors, and organic compounds, the thermochemical conversion of SS for producing bio-oil offers a viable and ecofriendly alternative to landfilling and incineration [5]. Even though an appreciable amount of bio-oil can be obtained from pyrolysis (40–50 wt% on a dry ash-free basis) [6-8], the considerable energy consumption for drying SS makes pyrolysis technology unattractive for practical applications [9]. Compared with the fast pyrolysis for the production of bio-oil from dried SS, the direct use of SS containing approximately 80% water as a feed can reduce the energy consumption by 30% [10]. In this context, direct hydrothermal liquefaction of SS, which does not require the removal of water prior to conversion, is promising for producing high calorific bio heavy-oil (BHO) without the energyintensive step. Supercritical and subcritical water has the unique properties such as the low dielectric constants ( = 2–30), high solubility of organic species, high diffusivity, low or zero surface tension, and high reactivity. These properties make supercritical and subcritical water suitable for converting wet biomass into liquid fuels [11]. The yields of bio-oil from SS hydrothermal liquefaction were in the range of 40–55 wt%, and the calorific values of the bio-oil were 30–35 MJ/kg, depending on the reaction conditions and separation methods used [5, 8, 12-16]. The BHO can be utilized as a combustion fuel in an industrial boiler [1, 2]. Several studies have investigated the liquefaction of SS with supercritical and subcritical water [5, 12, 15, 17]. A supercritical water liquefaction of SS was explored, showing a maximum yield of 37 wt% at 385 C and 272 bar [17]. Xu et al. (2018) obtained BHO with a yield of 54 wt% by a fast 4

Journal Pre-proof hydrothermal liquefaction of SS at 340 C and 180 bar [18]. The effect of catalysts on hydrothermal liquefaction of SS was investigated and the highest yield of BHO (48 wt%) was obtained with 50 bar H2 at 300 C [12]. The effect of water loading, sludge moisture content, and recovery solvent was examined in a fast hydrothermal liquefaction of SS [15]. A detained kinetic model for hydrothermal decomposition of SS was reported at a temperature range of 180300 C [19]. Castello et al. (2019) presented a catalytic upgrading of crude BHO from SS producing straight-chain hydrocarbons [20]. The economic feasibility analysis of renewable energy resources is a crucial step in making sound decisions for commercial applications [21]. Techno-economic analysis (TEA) is used to evaluate the economic feasibility from both technological and economic viewpoints. Several studies have assessed the economic feasibility of SS conversion processes [22-27]. Gasafi et al. (2008) reported that supercritical gasification was competitive owing to the revenues associated with the disposal of SS as a waste product [22]. Chen et al. (2019) performed environmental, energy, and economic analyses of municipal solid waste and SS in China [24]. Olkiewicz et al. (2016) evaluated the economic feasibility of biodiesel produced directly from primary liquid sludge, using experimental data obtained with a laboratory-scale extractor. Here, the break-even price of biodiesel was 1.23 $/kg [25]. Because the drying step of sludge was eliminated from the biodiesel production process, the biodiesel price was reduced [25]. Xu et al. (2014) conducted a cost-combined lifecycle assessment in China. Here, anaerobic digestion was a suitable alternative to reduce both environmental and economic burdens. Landfill and incineration technologies had the largest and smallest environmental burdens, respectively [26]. Luz et al. (2015) reported the TEA of an SS gasification process in Brazil for electricity generation, where the net present value (NPV) and internal rate of return (IRR) were estimated according to the plant capacity (or number of inhabitants) [27]. The NPV with an interest rate of 10.6%/yr became positive from a plant capacity of 74 t/d SS [27]. Do et al. (2019) reported a TEA of solvothermal liquefaction from 100 t/d SS with supercritical methanol and ethanol [28]. The supercritical methanol liquefaction plant was economically feasible with a return on investment (ROI) of 21%/yr. However, the plant did not include a BHO upgrading unit. Although the BHO production 5

Journal Pre-proof with super- and sub-critical water (supBHO and subBHO, respectively) is considered one of the most promising ways to treat SS, economic feasibility analysis of the supBHO and subBHO processes has never been discussed. In this study, TEA is performed to investigate the economic feasibility of the supBHO and subBHO plants. The objectives of this study are (1) to develop a process flow diagram (PFD) for the two BHO plants from 100 t/d SS using super- and sub-critical water for the estimation of the total capital investment (TCI) and total production cost (TPC); (2) to evaluate the economic feasibility of the two BHO plants with regard to the return on investment (ROI), payback period (PBP), and IRR; and (3) to perform a sensitivity analysis for identifying the major factors influencing the economic values and finding situations where the BHO plant can be profitable. This study shows economic potentials for the SS hydrothermal liquefaction process including a BHO upgrading unit in the industrial scale.

2. Methodology of techno-economic analysis (TEA) From the technological viewpoint of TEA, the PFD is established for a given plant and the mass and heat balances are solved. Temperature (T), pressure (P), flow rate (Q), and composition (xi) for each stream are obtained from the mass and heat balances. The equipment type and size are determined to estimate the TCI and TPC of the plant. From the economic viewpoint of TEA, economic values such as the ROI, PBP, and IRR are calculated using the TCI and TPC, and sensitivity analysis is performed to identify the major factors influencing the economic values [28, 29]. The four-level economic potential approach (4-level EP) is a systematic and hierarchical method for TEA in the preliminary design stage. The 4-level EP includes 1) the input and output structure, 2) the flowsheet structure, 3) heat integration (HI), and 4) economic feasibility analysis [30-32]. Fig. 1 shows the TEA procedure.

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Journal Pre-proof - Experimental data - Thermodynamic properties

Process simulation (PFD)

Mass and heat balances (T, P, Q, and xi)

Technological viewpoint

Equipment selection and sizing - Equipment prices - Economic assumptions

TCI and TPC

- 4-leve EP - Economic assumptions

ROI, PBP, and IRR

Economic viewpoint

Sensitive analysis Fig. 1. Procedure of techno-economic analysis (TEA).

For two BHO plants with super- (supBHO) and sub-critical (subBHO) water, the 4-level EP was applied under the assumptions shown in Table 1. The plants were constructed with 30% equity, which was a little lower than that (40%) of Jones et al. [33] in USA. The uptime of the plants was 8,000 h/yr. The construction and start-up periods were assumed to be one year and four months, respectively. It was assumed that the plant life (Lp) and the depreciation period (Ld) were 20 and 10 years, respectively. The corporation income tax rate (β) was 22% of the gross profit (GP) [31]. The inflation rate () and interest rate () were set as 2%/yr [31] and 4.2%/yr, respectively. Thus, the net interest rate was 2.2%/yr. The  (=4.2%/yr) was an interest for a big enterprise in 2017 in Korea. It was supposed that the salvage value (Vs) was zero after the Ld, which was often used in the economic analysis [31]. These assumptions were made for both plants. Three plant capacities, i.e., 20, 50, and 100 t/d SS containing 80% water, were examined, considering the SS production rate in a city of 200,000 habitants. One supervisor ($12/h) was employed in each 7

Journal Pre-proof of the three plants, but the number of laborers was 6, 9, and 12 for the 20, 50, and 100 t/d plants, respectively. The land and civil engineering cost was assumed to be 0.25, 0.5, and 0.99 million dollars ($M) for the 20, 50, and 100 t/d plants, respectively. The annual capital expenditure was disregarded. The purchasing and installation cost of the super- and sub-critical water reactor and surrounding equipment was obtained from a Korean company, which was $1.9 million for the 100 t/d plant. The capacity exponent was set as 0.6 to estimate the purchased cost of the super- and sub-critical water reactor at different plant sizes. The costs of electricity, liquefied natural gas (LNG), and cooling water including makeup water and chemicals were set as $0.098/kWh, 0.448 $/kg, and $0.273/m3, respectively [31]. The LNG price in 2017 was lower than that of Do et al. [31]. The prices of dichloromethane (DCM) as an extraction solvent, NaOH as a base solution of the scrubber, and H2SO4 as an acid solution of the scrubber were 300, 12, and 15 $/t, respectively. The BHO obtained from the super-critical water process (575 $/t) had a higher price (by 9.5%) than that from the sub-critical one (525 $/t) owing to the high calorific value of supBHO. The BHO prices were based on the selling price to a power plant in Korea. The treatment credit for SS with 80% water content was 100 $/t in 2017 in Korea and was a source of revenue for the BHO plant. The H2 price varied significantly according to the plant location and the amount of consumption. This price was assumed to be 1,800 $/t for H2 used for hydrotreating BHO to remove sulfur and oxygen. The loss of cooling water and DCM accounted for 2% of the consumption, and the heat loss of the LNG combustor accounted for 5%. Jones et al. (2013) used 1% heat loss for the combustor [33]. The heat loss (5%) used in this study was expected to include the overall heat loss of both the combustor and the heat exchangers with the hot utility (hot gas and steam).

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Journal Pre-proof Table 1. Economic assumptions for super- and sub-critical water BHO processes (supBHO and subBHO) from SS. Parameter Debt ratio () Plant availability Construction period Startup time Plant life (N) Plant depreciation period Inflation rate ()a Corporation tax rate ()a Interest rate ()a Salvage value (Vs) Laborer salary (3 shifts/day)

Assumption 70 (30% equity) 8,000 h/yr 1 yr 4 months 20 yr 10 yr 2.0%/yr 22%/yr 4.2%/yr $0 $6/h (laborer) and $12/h (supervisor)

Land and civil engineering cost 0.25, 0.5, and 0.99 $M for 20, 50, and 100 t/d plant Annual capital expenditure ($M/yr) 0% of FCI Purchased equipment + installation costs for 100 t/d plant Slurry pump (1 bar  230 bar) 0.5 $M Heat exchanger between slurry and reactor outlet (25100 ℃) 0.9 $M 0.2 $M Heat exchanger between slurry and hot gas (100325/375 ℃) 0.3 $M Super- or sub-critical water reactor 1.9 $M Total (reactor and surrounding equipment and installation)b Electricity price 0.098 $/kWh Utility price LNG 0.448 $/kg Cooling water price 0.273 $/m3 Extraction solvent (DCM: di-chloromethane) 300 $/t 4% NaOH (in base solution) 12 $/t 5% H2SO4 (in acid solution) 15 $/t 525 $/t Raw material Subcritical BHO pricec and product Supercritical BHO pricec 575 $/t price SS treatment creditd 100 $/t H2 for hydrotreatmente 1,800 $/t Cooling water lossf 2% Extraction solvent loss 2% LNG combustor heat loss 5% aData in Korea in 2017. bPurchased equipment cost of supercritical water BHO reactor in 2017 in Korea. cPrice of BHO to be sold to the Korean power plant in 2017. dSS treatment credit in 2017 in Korea. eH price = production price from the steam methane reforming process ($1.0/kg) + 80% overcharge for transportation. 2 f2% of cooling water was assumed to be evaporated in the cooling tower [34].

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Journal Pre-proof 3. Process description and modeling The PFDs for the supBHO (Case 1) and subBHO (Case 2) with 100 t/d SS are presented in Figs. 2 and 3, respectively. The PFD is divided into (1) the supercritical or subcritical reaction area, (2) the separation area, (3) the desulfurization area, (4) the wastewater treatment area, (5) the two-stage scrubber area, (6) the hot utility area, (7) the cold utility area, and (8) the storage area. The NRTL (non-random two-liquid) model was used to calculate the mass and energy balances in the BHO plant. This model is recommended for highly non-ideal chemical systems and has been used for vapor– liquid equilibrium and liquid–liquid equilibrium applications.

Fig. 2. PFD of the supercritical water BHO plant (supBHO) with 100 t/d SS containing 80% water - Case 1

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Fig. 3. PFD of the subcritical water BHO plant (subBHO) with 100 t/d SS containing 80% water Case 2

In the reaction area, the supercritical water reaction occurred at 375 C and 230 bar, and the subcritical reaction occurred at 325 C and 120 bar. Then, the product from the reaction was fed to a two-stage condenser, and the gas and liquid products were separated. The gas stream, including acid gases, was cleaned by a two-stage scrubber and vented. The BHO was produced from the liquid stream via the separation and desulfurization areas, where H2 was used for hydrotreating the BHO. Wastewater from the two-stage scrubber, centrifuge, liquid–liquid separator, solid–liquid filter, and water–oil decanter was cleaned by an aerobic reaction in the wastewater treatment area. Detailed stream results for the two cases are presented in S1.1 and S2.1 of the Supplementary Material, respectively.

3.1 SS and BHO properties 11

Journal Pre-proof The proximate and ultimate analyses of SS, which were measured experimentally, are presented in Table 2. The dried SS contained heteroatoms (3.5 wt% S and 7.1 wt% N) and metallic/ash species (e.g., Fe, Ca, and Si, 10.8 wt%). The higher heating value (HHV) and water content of the SS were 18.3 MJ/kg and 80 wt%, respectively. Ultimate analysis and physical property analysis of the BHOs produced from the super- and subcritical water reactions were performed using a custom-built batch reactor (see Table 3). Detailed descriptions of the reactor setup and reaction procedure are provided elsewhere [35, 36]. The HHV of supBHO (36 MJ/kg) is higher than that of subBHO (33.9 MJ/kg) because supBHO has a higher C content and lower O content than subBHO. The two HHVs measured by experiment are almost the same as those values (35.3 MJ/kg and 33.2 MJ/kg, respectively) calculated from the ultimate analysis [37]. The supBHO has a higher selling price than subBHO, as discussed in the previous section. The subBHO exhibited a higher density and molecular weight (Mw) than the supBHO. The BHO having the carbon chain length from C6 to C29 contained toluene, cresol, aromatics, long-chain hydrocarbons, and alcohols. In addition, negligible amounts of inorganic species, such as Fe, Zn, Si, and Ni, were present in the produced BHO (see Table 3), indicating the efficient partitioning of ash in the SS into solid residue (SR).

Table 2. Proximate and ultimate analysis results for the SS. Ultimate analysis of dried SS (wt%)a Carbon (C) Hydrogen (H) Oxygen (O) Nitrogen (N) Sulfur (S) Fe Ca Si K Zn, Cr, Cd, Pb, Cu Cl Al, P, Mg, Na, Ti, Ba, Mn, Sr, Br, Ni Others Subtotal HHV (MJ/kg) aDry basis (105 ℃); bWet basis

38.4 5.3 26.2 7.1 3.5 3.5 2.1 1.1 0.7 0.31 0.1 3.0 8.69 100.0 18.3

Proximate analysis of SS (wt%)b Moisture 80.0 Volatiles 12.9 Fixed carbon 2.3 Ash 4.8

100.0

12

Journal Pre-proof Table 3. Ultimate analysis results and physical properties for supBHO and subBHO produced at 375 and 325 ℃, respectively. Ultimate analysis (wt%)a supBHO subBHO Element (Case 1) (Case 2) Carbon (C) 77.5 72.9 Density (kg/m3) Mean molecular Hydrogen (H) 7.2 7 weight (Mw) Oxygen (O) 3.6 4.7 Nitrogen (N) 4.2 4.2 Sulfur (S) 4.3 3.4 Main components Others Subtotal HHV (MJ/kg)

3.2 100 36

7.8 100

Physical properties supBHO (Case 1) 950

subBHO (Case 2) 1,040

458 g/mol

584 g/mol

Toluene, p-Cresol, Ethylbenzene, Phenol, Phenol, 4-ethyl-, 3Dodecene, (Z)-, Indole, Indole, 3-methyl-, 1-Decene, Cetene

Toluene, 3-Dodecene, (Z)-, pCresol, Ethylbenzene, Cholest-4ene, 5-Octadecene, (E)-, 5H-1Pyrindine, Cetene, 1-Decene, Cholest-2-ene

Fe (0.14), Zn (0.01)

Fe (0.14), Si (0.39), Zn (0.01), Ni (0.01)

33.9 Ash content (wt%)

In the process simulation, the crude BHO obtained from the super- and sub-critical water reactions was modeled by alcohols, esters, acids, and aromatics, as shown in Table 4. 1-butanol and 1-hexanol were regarded as water-soluble organics (WSOs) discharged into the wastewater. On the basis of the real BHO components shown in Table 3, the modeled BHO components were determined so that the overall yield experimentally confirmed (see Table 5) was obtained from the process simulation with the modeled components. However, the element balance with the modeled components in the gas and liquid phases could not exactly satisfy the ultimate analyses of SS and crude BHO. For sulfur (S), it was assumed that 90% of the inlet sulfur was transformed into C4H4S (thiophene) and removed in the desulfurization area. For nitrogen (N), approximately 31% of the inlet nitrogen was transformed into 2,4,6-trimethylpyridine, 2,6-dimethylpyridine, and o-ethylaniline. It was regarded that solid residue (SR) included the rests of sulfur and nitrogen.

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Journal Pre-proof Table 4. Compositions of supBHO and subBHO used in the process simulation. Mass fraction (wt%) SupBHO SubBHO a 1-butanol 22.86 21.53 a 1-hexanol 22.74 18.56 n-hexadecanoic acid 5.56 6.12 Ethyl-phenylethanoate 5.06 5.57 Diethyl-succinate 2.93 3.23 p-cresol 4.91 5.41 2,4,6-trimethylpyridine 13.28 14.62 2,6-dimethylpyridine 5.86 6.45 o-ethylaniline 10.83 11.92 n-butyric acid 3.59 3.95 Toluene 2.39 2.63 Total 100 100 aWater soluble organic (WSO) BHO component

3.2. Super- and sub-critical reaction area 100 t/d (or 4,167 kg/h) SS was mixed with recycled water (20 t/d or 833.3 kg/h) prior to being fed into the super- or sub-critical water reactor at 375 or 325 ℃, respectively. The feed was pumped and compressed to 230 or 120 bar and preheated by a heat exchanger between the feed and reactor outlet streams. The product stream was sharply condensed by two indirect heat exchangers and cooled to 25 C. The mixture of water and crude BHO was separated via the centrifuge, yielding BHO in the subsequent separation area. Most of the water (4,136 and 4,167 kg/h for Cases 1 and 2, respectively) was separated by the centrifuge. Experiments were performed using a laboratory-scale reactor. The overall mass balance based on 100 t/d SS was obtained from the experimental data, as shown in Table 4. The BHO product from the supercritical reaction had a lower yield (8.0 wt%) than that from the subcritical reaction (9.0 wt%). A larger amount of WSOs was produced in the supercritical reaction than in the subcritical reaction. The SR, which included ash and tar, was approximately 6.5 wt%. The super- and subcritical reactors were modeled by a yield reactor (Ryield) using a commercial process simulator (ASPEN Plus), where the outlet composition and yield were based on the experimental data. 14

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Table 5. Super- and sub-critical reactor yields and flow rates in BHO production from 100 t/d SS containing 80 wt%. Case BHO Water Gas WSO SRa Case 1 wt% 8.0 80.0 0.8 4.2 7.0 kg/h 335 3,334 28 177 292 Case 2 wt% 9.0 80.8 0.5 2.7 7.0 kg/h 375 3,365 23 112 292 aSR included inorganic matter and tar

Total (%) 100 4,167 100 4,167

The gas product (28 and 23 kg/h for Cases 1 and 2, respectively) was separated from the flash in the reaction area. The composition of the gas product is presented in Table 6. The gas product from the supercritical reaction had a higher content of combustible gases and a lower CO2 content than that from the subcritical reaction.

Table 6. Composition of the gas product of the supercritical reaction (Case 1) and subcritical reaction (Case 2). Case Component CH4 Case 1 wt% 2 vol% 5 0.4 Case 2 wt% vol% 1

C2H4 0.6 0.9 0.4 0.6

C2H6 1.5 2 0.2 0.4

C3H8 3.4 3.2 1.5 1.5

CO 3.7 5.4 2.2 3.4

CO2 84.1 77.6 93.7 92

others 4.7 5.9 1.6 1.1

Total 100 100 100 100

Table 7 shows the carbon distribution in the products such as BHO, WSO, gas and solid residue, which is based on the carbon content of the dewatered SS. The carbon content in BHO and WSO is a little lower for Case 1 than that of Case 2.

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Journal Pre-proof Table 7. Carbon distribution of BHO/WSO, gas and solid residue on the basis of carbon present in dewatered SS. Case 1: supBHO Case 2: subBHO aC bC

C in BHO/WSO (wt%)a 84.0 86.0

Carbon content in BHO and WSO Carbon content in SS Carbon content in gas Carbon content in SS × 100

in BHO/WSO =

C in gas (wt%)b 3.9 2.2

C in SR (wt%)c 12.1 11.8

Total 100 100

× 100

in gas = cC in solid residue = 100 ― (C in BHO and WSO + C in gas) 3.3 Separation area After the centrifuge, a mixture of BHO and SR (712 and 751 kg/h for supBHO and subBHO, respectively) was separated from the water phase containing WSOs. The mixture of BHO and SR recovered from the centrifuge was then introduced to a mixer using DCM as a solvent. Using solid– liquid filtration, the SR (292 kg/h) was eliminated from the BHO dissolved in DCM. In the process simulation, the filter was modeled as the component separator to remove the SR. The solvent (DCM) was recycled via a distillation column. Fresh solvent (8.3 kg/h) was added because of the 2% loss of the recycled solvent (408 kg/h). The crude BHO (427.7 or 467.3 kg/h) from the bottom of the distillation column entered the desulfurization area. In the distillation column, the number of theoretical stages was 13. The Murphy efficiency was set as 0.68. 98% of the DCM was recovered.

3.4. Desulfurization area The hydrotreating reactor for desulfurization was operated at 404 C and 127 bar [38]. H2 of 9.7 or 9.6 kg/h, which is 20% higher than the H2 consumption rate was supplied to this reactor. The hydrotreating reactor was modeled by a stoichiometric reactor (Rstoic). Table 8 shows nine stoichiometric reactions with a given conversion. It was assumed that S was completely converted into H2S in the 8th reaction, and eight deoxygenation reactions occurred, producing water and light hydrocarbons (mixtures C1–C4). The deoxygenation conversions of Case 2 were lower than those of Case 1 for satisfying the BHO yield (see Table 5). The gas and liquid products from the 16

Journal Pre-proof hydrotreating reactor were separated by a flash. The final product (335.4 or 375 kg/h of BHO) was obtained from the liquid product via a water–oil decanter. The gas product (96.3 or 96.6 kg/h), which included H2S and light hydrocarbons from the flash, was cleaned by a wet scrubber with a 4% NaOH solution in the desulfurization area. The cleaned gas (light hydrocarbons) from the top of the scrubber was fed to a LNG combustor in the hot utility area. The wastewater from the scrubber and the water– oil decanter entered the wastewater treatment area.

Table 8. Stoichiometric reaction modeling in the hydrotreating reactor for desulfurization. Reactions 1 2 3 4 5 6 7 8 9

H2 + C4H10O → H2O + C4H10 H2 + C6H14O → H2O + C6H14 3H2 + C16H32O2 → 2H2O + C16H34 3H2 + C3H6O2 → 2H2O + C3H8 2H2 + C4H8O → H2O + C4H10 2H2 + C4H10O → H2O + CH4 + C3H8 3H2 + C6H14O → H2O + CH4 + C2H6 + C3H8 4H2 + C4H4S → C4H10 + H2S 2H2 + C6H14O → H2O + CH4 + C5H12

Conversion Case 1 Case 2 0.12 0.088 0.12 0.088 0.25 0.088 0.25 0.18 0.25 0.18 0.25 0.174 0.12 0.088 1 1 0.12 0.088

3.5 Wastewater treatment area and two-stage scrubber area The wastewater treatment area was composed of an air fan to supply air, an aerobic reactor for the decomposition of organic matter, and a flash for the gas and liquid separation [39]. All the wastewater from the centrifuge, decanters, and scrubbers was treated in this area. The purified water was recycled to the mixer of the reaction area at a rate of 833.3 kg/h. The gas from the super- and sub-critical reaction areas was treated in a two-stage wet chemical scrubber for odor control. The wet scrubber used 5% H2SO4 in the first stage and 4% NaOH for acid gas removal in the second stage. The acid and alkaline wet scrubbers aim to remove odorous compounds such as H2S, mercaptans, organic sulfides, NH3, amines, and volatile organic compounds [31]. Although the two electrolyte solutions (4% NaOH and 5% H2SO4) were not modeled in the process simulation, the cost of the two solutions was included in the economic analysis.

17

Journal Pre-proof 3.6. Hot and cold utility area and storage area The hot utility consisted of an LNG combustor to supply the heat required for the super- or subcritical reactor, hydrotreating reactor, and distillation column. The cold utility (cooling water) included a cooling tower, where water was cooled from 47 to 25 ℃. The cold water was used in the two-stage condenser of the reaction area, the distillation column condenser of the separation area, and the cooler of the desulfurization area. Seven storage tanks were employed to store the feed SS, base and acid solutions, H2, DCM, BHO product, and SR for 7 days.

3.7. Energy consumption The energy consumptions of the two cases are listed in Table 9. The cold heat duty of Case 1 (supBHO) is higher than that of Case 2 (subBHO), which is mainly needed to cool the stream after the super- or sub-critical reaction. The hot heat duties of the two cases are almost the same owing to heat exchangers. More electricity is needed in Case 1 than in Case 2. The electricity is mainly used to pump the SS to the super- (230 bar) or sub-critical (120 bar) reactor.

18

Journal Pre-proof Table 9. Energy consumption of the super- and sub-critical BHO plant with 100 t/d SS. Utility Equipment Case 1 (supBHO) Case 2 (subBHO) Supercritical reactor 1,208.05 1,319.44 Hot utility Reboiler (distillation column) 125.38 124.64 (kWth) Hydrotreating reactor 76.59 88.20 Subtotal 1,410.02 1,532.28 Cooler 1 -2,614.66 -895.01 Cooler 2 -424.75 -425.35 -373.70 -403.80 Cold utility Cooler 3 (kWth) Cooler 4 -47.13 -47.14 Cooler 5 -191.73 -208.16 Condenser (distillation column) -100.05 -97.13 Subtotal -3,752.03 -2,076.59 Pump 1 90.44 47.19 Pump 2 0.01 0.00 Pump 3 5.96 6.60 Pump 4 0.03 0.03 Pump 5 0.00 0.00 Electricity Pump 6 0.00 0.00 (kWe) Pump 7 0.00 0.00 Air fan 1 5.28 5.28 Air fan 2 6.55 6.86 Hot gas fan 0.98 1.02 Compressor 18.05 17.87 Subtotal 127.31 84.85

4. Results and discussion The 4-level EP for the two cases was evaluated under the economic assumptions in Table 1. Sensitivity analysis was performed with regard to the plant capacity, TCI, TPC, BHO price, and SS treatment credit.

4.1. Results of 4-level EP Fig. 4 shows the results of the 4-level EP for Case 1 (supBHO) and Case 2 (subBHO). In Level 1, considering only the input and output materials, Cases 1 and 2 have almost the same economic potential (EP). However, in Levels 2–4, the EP of Case 1 is lower than that of Case 2, because Case 1 has a higher TCI and TPC, as shown in Table 10. Because the HI was incorporated in the PFDs

19

Journal Pre-proof shown in Figs. 2 and 3, the EP of Level 2 is the same as that of Level 3. In Level 4, the EPs of the two plants are $0.86 and $0.94 million/yr, respectively. 5 Case 1 - supBHO Case 2 - subBHO

EP (M$/yr)

4

3

2

1

0 Level 1

Level 2

Level 3

Level 4

Fig. 4. Variation in the EP in the 4-level EP for a plant capacity of 100 t/d SS.

The detailed results of the 4-level EP are presented in Table 10. In Level 1, the raw-material cost and the product selling profit are calculated for the production of 1 kg of BHO. The total raw-material cost (TRC) per kg of BHO is 0.059 and 0.067 $/kg for Cases 1 and 2, respectively. The total selling profit including the SS treatment credit for Case 2 (1.64 $/kg) is lower than that for Case 1 (1.82 $/kg). However, because the BHO production rate for Case 2 (3.0 kt/yr) is higher than that for Case 1 (2.7 kt/yr), the annual sales revenue (ASR) for Case 2 ($4.91 million/yr) is slightly higher than that for Case 1 ($4.88 million/yr). The SS treatment credit is double the BHO selling price. The EP of Level 1 (EP1) is obtained via subtraction of the TRC from the total selling profit. The EP1 for Case 2 ($4.70 million/yr) is slightly higher than that for Case 1 ($4.73 million/yr). In Level 2, the total installed cost (TIC), including the purchased equipment cost (PEC) and the equipment installation cost (EIC), is calculated for the PFD constructed. Additionally, the total utility cost (TUC) for electricity, LNG, and cooling water is estimated from the simulation of the PFD (see Table 8). By converting the TIC ($M) into the annual cost ($M/yr) using a capital charge factor of 0.2 yr-1 [31], EP2 ($M/yr) is obtained as follows: EP2 = EP1 – 0.2TIC – TUC.

(1) 20

Journal Pre-proof The EP2 for Case 2 ($2.68 million/yr) is higher than that for Case 1 ($2.53 million/yr), as the TIC and TUC for Case 2 are lower than those for Case 1.

Table 10. Results of the 4-level EP for Case 1 (supBHO) and Case 2 (subBHO) from 100 t/d SS. Level 1: Input–output structure Case 1 Input (supBHO) DCM NaOH H2SO4 H2 Total raw material cost (TRC) Output SS treatment credit BHO Total product selling profit EP1 ($/kg) EP1 ($M/yr) Case 2 Input (subBHO) DCM NaOH H2SO4 H2 Total raw material cost (TRC) Output SS treatment credit BHO Total product selling profit EP1 ($/kg) EP1 ($M/yr)

Raw-material costs ($/kg) 0.007 0.005 0.003 0.052 0.067 Product revenues ($/kg) 1.242 0.575 1.817 1.750 4.70 Raw-material costs ($/kg) 0.007 0.004 0.002 0.046 0.059 Product revenues ($/kg) 1.111 0.525 1.636 1.577 4.73

Amount required (kg/kg of BHO) 0.025 0.017 0.009 0.029

Cost ($/kg) 0.300 0.300 0.300 1.800

Other product (kg/kg of BHO) 12.424 BHO production rate (t/yr) ASR ($M/yr)

Price($/t) 0.100 2,683 4.88

Amount required (kg/kg of BHO) 0.022 0.014 0.007 0.026

Cost($/kg) 0.300 0.300 0.300 1.800

Other product (kg/kg of BHO) 11.112 BHO production rate (t/yr) ASR ($M/yr)

Price($/kg) 0.100 3,000 4.91

Level 2: Flowsheet structure Total installed cost (TIC, $M) EP2 ($M/yr) (Capital charge factor of 0.2)

Case 1 8.55 2.53

Case 2 8.03 2.68

Utilities Electricity Heat (LNG) Cooling water Total utilities cost (TUC, $M/yr)

Level 3: Heat integration (HI) Saving on utilities Hot utilities Cold utilities Total saving EP3 ($M/yr)

Case 1 0.10

Case 2 0.07

0.35 0.00642 0.46

0.37 0.00355 0.44

Case 1 0.00 0.00 0.00 2.53

Case 2 0.00 0.00 0.00 2.68

Level 4: Economic feasibility evaluation

Economic values

TCI (Total capital investment, $M) TPCavg (average total production cost, $M/yr) ASRavg (average annual sale revenue, $M/yr) DCavg (average depreciation cost, $M/yr) DRCavg (principal and interest for 20 yr) GPavg (average gross profit, $M/yr) CITavg (average corporation income tax, $M/yr) CFavg (average cash flow at present value, $M/yr) EP4 (NPavg at present value, $M/yr) ROI (return on investment, %/yr) PBP (payback period, yr) IRR (internal rate of return, %/yr)

21

Case 1 15.09 2.65 6.00 0.67 0.76 1.92 0.43 1.39 0.86 5.7 9.63 13.2

Case 2 14.29 2.61 6.04 0.63 0.72 2.08 0.46 1.45 0.94 6.6 8.73 14.7

Journal Pre-proof Fig. 5 presents a breakdown of the TIC for Cases 1 and 2. The reaction area and desulfurization area account for >55% of the TIC. The utility area incurs a higher capital cost for Case 1 than for Case 2, because Case 1 (with supercritical water) requires a higher heat duty than Case 2 (with subcritical water).

A600: Storage 16%

A600: Storage 17%

A100: Reaction 34%

A100: Reaction 30%

A500: Utility 12%

A400: Scrubbing & wastewater treatment 6%

A500: Utility 12%

A300: Desulfurization 24%

A400: Scrubbing & wastewater treatment 6%

A200: Separation 8%

A300: Desulfurization 26%

(a) Case 1

A200: Separation 9%

(b) Case 2 Fig. 5. Breakdown of the TIC.

The PEC and EIC were obtained from the mapping and sizing of each item of equipment using the Aspen Economic Analyzer (ASPEN Tech, USA), as presented in S1.2–S1.3 and S2.2–S2.3 of the Supplementary Material for Cases 1 and 2, respectively. In Level 3, the hot and cold utilities are saved by the HI [32]. The HI is not further exploited, as major heat networks are included in the present PFD. In Level 4, the economic values, such as the ROI, PBP, and IRR, are estimated according to the TCI and TPC. The fixed capital investment (FCI) includes the TIC, indirect cost (IC, 89% of PEC), and project contingency (PC, 10% of TIC and IC). The TCI is the sum of the FCI, working capital (WC, 5% of FCI), and land and civil engineering cost. The details of the TCI are presented in Table 11. The TPC is the sum of the TRC, TUC, and fixed cost (FC). The FC includes the operating labor cost (LC; one supervisor and 12 laborers), plant maintenance cost (2% of FCI), operating charges (25% of LC), plant overhead (50% of LC), and general and administrative cost (8% of LC), as shown in

22

Journal Pre-proof Table 12. The maintenance cost for Case 1 is higher than that for Case 2 owing to the higher FCI. The TPC in the first year of operation is 2.13 and 2.10 $M/yr for Cases 1 and 2, respectively. The TPC increases each year when the inflation is regarded as 2%/yr for 20 years. The TPC averaged for 20 years (TPCavg) is 2.65 and 2.61 $M/yr for Cases 1 and 2, respectively (see Level 4 in Table 10). The ASR also increases each year owing to inflation. The depreciation cost (DC) of the FCI is equally distributed for Ld (= 10 yr) and the DCavg is averaged for Lp (= 20 yr). When 30% equity (70% debt of TCI) is applied to the plant, the debt repayment cost (DRC) includes the fully amortized principal and interest during the plant life (Lp = 20 yr). The DRCavg is averaged over Lp. The GP is obtained as follows: GP = ASR – TPC – DC – DRC.

(2)

A corporation income tax (CIT) of 22% is applied to the GP. However, the CIT is not payed if the GP is negative for a year. The net profit (NP) is obtained by subtracting the CIT from the GP. The cash flow (CF) is the sum of the GP and the DC. The NP and CF are converted into the present value with the interest rate (=4.2%/yr) for the calculation of the ROI and PBP. For the NP and CF at the present value, the NPavg and CFavg are averaged over Lp. The NPavg is replaced by the EP4 in Level 4 of Table 10. The EP4 for Case 2 ($0.94 million/yr) is higher than that for Case 1 ($0.86 million/yr) owing to the lower TCI and TPC, as mentioned previously.

Table 11. TCI for Case 1 (supBHO) and Case 2 (subBHO) from 100 t/d SS. Case 1 Case 2 Total purchased equipment cost (TPEC, $M) Indirect cost (IC = 0.89  TPEC, $M) Total installed cost (TIC, $M) Total direct and indirect cost (TDIC = IC + TIC, $M) Project contingency (PC = 0.1  TDIC, $M) Fixed capital investment (FCI = TDIC + PC, $M) Working capital (WC = 0.05  FCI, $M) Land and civil engineering cost (6,600 m2×150 $/m2 = 0.99 $M) Total capital investment (TCI = FCI + WC + Land, M$)

23

2.96 3.66 8.55 12.20 1.22 13.42 0.67

2.95 3.48 8.03 11.51 1.15 12.66 0.63

0.99

0.99

15.09

14.29

Journal Pre-proof Table 12. FC for Case 1 (supBHO) and Case 2 (subBHO) from 100 t/d SS. FC details Operating labor cost ($M/yr) Maintenance cost Operating charges Plant overhead General and administrative cost Fixed cost (FC)

Case 1 Case 2 0.672 0.672 0.268 0.253 0.168 0.168 0.336 0.336 0.054 0.054 1.498 1.483

The ROI is the ratio of NPavg to the TCI. The PBP is the time (yr) required to recover the FCI from the CFavg. The IRR is the interest rate such that the total CF at the present value for Lp is equal to the FCI. The ROI, PBP, and IRR for Case 2 are 6.6%/yr, 8.7 yr, and 14.7%/yr, respectively, indicating improved economic performance compared with Case 1. In Table 13, the economic values of supBHO and subBHO are compared with that of the bio-solid production process from 90 t/d SS [31] under similar economic assumptions. The bio-solid plant [40] including fry-drying, torrefaction, a two-stage wet scrubber, wastewater treatment, and a steam boiler is more competitive than the super- and sub-critical BHO plants owing to a lower TCI and TPC. However, the bio-solid plant does not provide processing for desulfurization and removal of heavy metals.

Table 13. Comparison of economic values among supBHO, subBHO, and the bio-solid produced from SS. TCI TPC ROI PBP IRR ($ million) ($ million/yr) (%/yr) (yr) (%/yr) Case 1: supBHO with 100 t/d SS 15.09 2.13 5.7 9.6 13.2 Case 2: subBHO with 100 t/d SS 14.29 2.10 6.6 8.7 14.7 Bio-solid from 90 t/d SS [31] 5.42 1.37 16.0 4.8 29.5 The minimum fuel selling price (MFSP) is the mean annual cost divided by the total fuel production rate. The mean annual cost at the present value includes the TPC, CIT, DRC, DC, and 15% of the ROI. The MFSP is shown in Table 14. Because there is an SS treatment credit, the net MFSP is obtained via subtraction of the SS credit from the gross MFSP. The MFSP of upgraded bio-oil obtained from fast pyrolysis [33, 38] was 0.92 $/L for 2,000 t/d of dry-wood and 40% equity, which 24

Journal Pre-proof is the same range as the value of this study. Because the present BHO price is 0.55 $/L, the supBHO and subBHO plants with 100 t/d SS are not profitable even with the SS credit under the present economic assumptions.

Table 14. MFSP of supBHO and subBHO with 100 t/d SS. BHO Mean annual cost MFSP MFSP SS credit Net MFSP BHO price 　 (kg/h) (TPC+CIT+DC+15% ROI, $/h)a ($/kg) ($/L) ($/L)b ($/L) ($/L) Case 1 335.4 756.26 2.25 2.14 1.24 0.90 0.55 (supBHO) Case 2 375.0 732.41 1.95 2.03 1.11 0.92 0.55 (subBHO) Lp



aMean bSS

annual cost =

(TPC  CIT )(1   ) n  DRCn

n 1

(1   ) n Lp

 DCavg  0.15TCI

credit per liter of BHO

In a solvothermal liquefaction plant with alcohol [28], the water content of SS was reduced from 80% to 10%, and a heat duty of 3.2 MJ/kg-water was required for drying SS. In the hydrothermal liquefaction plant, the drying process is not used, and the two-stage scrubbing and BHO upgrading units are included. The BHO yield based on dried SS is 4047%, which is lower than that of solvothermal liquefaction [14]. However, hydrothermal liquefaction of SS does not use a huge amount of organic solvents such as methanol, ethanol, and acetone. Instead, DCM with 2% loss is used for the extraction of BHO. When the SS treatment credit increases, the net MFSP of the hydrothermal liquefaction plant is lowered.

4.2. Sensitivity analysis Sensitivity analysis allows identification of the key factors influencing the economic values and considers the uncertainty of the factors [31, 32]. The ROI and EP4 of supBHO and subBHO plants are shown according to the plant size in Fig. 6. Because a plant capacity of >100 t/d may be not practical, owing to the transportation cost of SS, the range of the plant size is set as 20–100 t/d SS. The ROI increases gradually with the increase of the plant size. The ROI and EP4 are positive over 25

Journal Pre-proof 60 t/d for both cases. Case 2 (subBHO) shows slightly higher ROI and EP4 than Case 1 (supBHO) in the entire plant size.

1.5

10

(a) ROI

(b) EP4 1.0

EP4 ($M/yr)

ROI (%/yr)

5

0 20

40

60

80

0.5

100 0.0

Plant size (t/d)

20

40

60

80

100

Plant size (t/d) -5

-0.5

supBHO

supBHO

subBHO

subBHO -1.0

-10

Fig. 6. Effect of the plant size on the ROI and EP in Level 4 (EP4).

The factors influencing the economic values are changed by 30% for the sensitivity analysis. In Table 15, the absolute values of the TCI, TPC, SS credit, and BHO price are presented according to the 30% relative changes.

Table 15. Absolute values of the factors used in the sensitivity analysis for the 100 t/d SS plant. Factors

-30 -20 Case 1 10.56 12.07 Case 2 10.00 11.43 100 t/d TPC (M$/yr) Case 1 1.49 1.71 Case 2 1.47 1.68 SS credit ($/t) 70.0 70.0 Supercritical BHO price ($/t) 402.5 402.5 Subcritical BHO price ($/t) 367.5 367.5 100 t/d TCI (M$)

Relative changes (%) -10 0 (base value) 10 13.58 15.09 16.59 12.86 14.29 15.72 1.92 2.13 2.35 1.89 2.10 2.32 80.0 90.0 100.0 460.0 517.5 575.0 420.0 472.5 525.0

20 18.10 17.14 2.56 2.53 110.0 632.5 577.5

30 19.61 18.57 2.78 2.74 120.0 690.0 630.0

Fig. 7 shows a plot of the sensitivity [30, 31]. The 100 t/d plant size was used as the base case. A greater slope of the ROI or EP4 with the relative change of the factors indicates a larger influence on the ROI or EP4. The SS treatment credit has a larger impact than the BHO price, because the major source of revenue for the BHO plant is the SS treatment credit, as shown in Table 10 (Level 1). The 26

Journal Pre-proof TCI influences the ROI more than the TPC, which is opposite for the EP4 that is closely related to the TPC. Cases 1 and 2 show the same trend. However, ROI and EP4 of Case 2 are higher than those of Case 1 for the same relative change of factors. For a solvothermal liquefaction plant of SS with methanol [28], ROI was higher than that of the hydrothermal liquefaction plant because of high BHO price (800 $/t) and no desulfurization unit.

12

SS credit-Case 2 BHO price-Case 2 TCI-Case 2 TPC-Case 2

1.6

SS credit-Case 1 BHO price-Case 1 TCI-Case 1 TPC-Case 1

SS credit-Case 2 BHO price-Case 2 TCI-Case 2 TPC-Case 2

1.2

SS credit-Case 1 BHO price-Case 1 TCI-Case 1 TPC-Case 1

Case 2

Case 2

ROI (%/yr)

EP4 ($M/yr)

8

0.8 Case 1

Case 1

4

0.4

Base line

(a) ROI

Base line

(b) EP4 0

0 -30

-20

-10

0 Relative change (%)

10

20

30

-30

-20

-10

0 Relative change (%)

10

20

30

Fig. 7. Plot of the sensitivity to the ROI and EP in Level 4 (EP4). An ROI of >10% can be achieved for the 100 t/d subBHO plant when the SS credit is >$120/t, the BHO price is >$700/t, the TCI is <$10 million, or the TPC is <$1.5 million/yr. If the subBHO price is higher than the MFSP with 15% ROI (=$0.90/kg), the 100 t/d subBHO plant is profitable.

5. Conclusion Techno-economic analysis (TEA) was performed for two bio-heavy-oil (BHO) production processes with 100 t/d sewage sludge (SS) containing 80% water. One was a BHO process with a yield of 40% based on 100 t/d SS, using supercritical water at 375 C. The other was a process with a yield of 47%, using subcritical water at 325 C. The process flow diagram (PFD) of the two plants was divided into eight areas: the supercritical or subcritical reaction area, separation area, desulfurization area, wastewater treatment area, two-stage scrubber area, hot utility area, cold utility area, and storage area. The mass and energy balances of the two PFDs were calculated using a commercial process simulator (ASPEN Plus). The four-level economic potential (EP) approach was applied for the TEA, 27

Journal Pre-proof which is a systematic and hierarchical method in the preliminary design stage. The main results were summarized as follows: -

The EP in Level 4 was $0.86 and $0.94 million/yr for BHO production with super- and subcritical water, respectively.

-

The total capital investment (TCI) of BHO production with super- and sub-critical water was $15.1 million and $14.3 million, respectively.

-

The total production cost (TPC) was $2.1 million/yr for both BHO production with superand sub-critical water.

-

The net minimum fuel selling price (MFSP) of the two plants was approximately 0.91 $/L, while the actual selling price was 0.55 $/L.

-

The return on investment (ROI) of BHO production with sub-critical water (6.6%/yr) was higher than that of BHO production with super-critical water (5.7%/yr).

-

The sensitivity analysis showed that the SS treatment credit had a larger impact than the BHO price.

-

If the BHO price is >$0.9/L or the SS credit is >$120/t, the 100 t/d BHO production with sub-critical water is profitable

The direct hydrothermal liquefaction of SS without drying has an advantage of less energy consumption than solvothermal liquefaction. However, the hydrothermal liquefaction suffers from lower yield and calorific value than the solvothermal one. It will be useful to compare the economic feasibility of biofuel conversion pathways from SS such as hydrothermal and solvothermal liquefactions, and bio-solid productions under the same economic assumptions.

Acknowledgements This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Science, ICT, and future Planning (grant number: NRF-2016-010423). Additional support from Kpetro (Korea Petroleum Quality and 28

Journal Pre-proof Distribution Authority) and the Waste-to-Energy Technology Development Program of Korea Environmental Industry & Technology Institute, which is granted financial resources from the Ministry of Environment, Republic of Korea (No. RE201807014), is also appreciated.

Appendix A. Supplementary data Supplementary data associated with this article can be found in the online version, at doi:_____________________

References [1] Fytili D, Zabaniotou A. Utilization of sewage sludge in EU application of old and new methodsA review. Renew. Sust. Energ. Rev. 2008; 12: 116-40. https://doi.org/10.1016/j.rser.2006.05.014. [2] Manara P, Zabaniotou A. Towards sewage sludge based biofuels via thermochemical conversion–A review. Renew. Sust. Energ. Rev. 2012; 16: 2566-82. https://doi.org/10.1016/j.rser.2012.01.074. [3] Huang H, Yuan X, Zeng G, Zhu H, Li H, Liu Z, Jiang H, Leng L, Bi W. Quantitative evaluation of heavy metals’ pollution hazards in liquefaction residues of sewage sludge. Bioresour. Technol. 2011; 102: 10346-51. https://doi.org/10.1016/j.biortech.2011.08.117. [4] Li L, Xu ZR, Zhang C, Bao J, Dai X. Quantitative evaluation of heavy metals in solid residues from sub- and super-critical water gasification of sewage sludge. Bioresour. Technol. 2012; 121: 169-75. https://doi.org/10.1016/j.biortech.2012.06.084. [5] Wang Y, Chen G, Li Y, Yan B, Pan D. Experimental study of the bio-oil production from sewage sludge by supercritical conversion process. Waste Manage. 2013; 33: 2408-15. https://doi.org/10.1016/j.wasman.2013.05.021.

29

Journal Pre-proof [6] Cao J-P, Li L-Y, Morishita K, Xiao X-B, Zhao X-Y, Wei X-Y, Takarada T. Nitrogen transformations during fast pyrolysis of sewage sludge. Fuel 2013; 104: 1-6. https://doi.org/10.1016/j.fuel.2010.08.015. [7] Fonts I, Azuara M, Gea G, Murillo MB. Study of the pyrolysis liquids obtained from different sewage sludge. J. Anal. Appl. Pyrolysis 2009; 85: 184-91. https://doi.org/10.1016/j.jaap.2008.11.003. [8] Huang H-j, Yuan X-z, Li B-t, Xiao Y-d, Zeng G-m. Thermochemical liquefaction characteristics of sewage sludge in different organic solvents. J. Anal. Appl. Pyrolysis 2014; 109: 176-84. https://doi.org/10.1016/j.jaap.2014.06.015. [9] He C, Chen C-L, Giannis A, Yang Y, Wang J-Y. Hydrothermal gasification of sewage sludge and model compounds for renewable hydrogen production: A review. Renew. Sust. Energ. Rev. 2014; 39: 1127-42. https://doi.org/10.1016/j.rser.2014.07.141. [10] Yang T, Liu X, Li R, Li B, Kai X. Hydrothermal liquefaction of sewage sludge to produce bio-oil: Effect of co-pretreatment with subcritical water and mixed surfactants. J. Supercrit. Fluids 2019; 144: 28-38. https://doi.org/10.1016/j.supflu.2018.10.005. [11] Peterson AA, Vogel F, Lachance RP, Fröling M, Antal JMJ, Tester JW. Thermochemical biofuel production in hydrothermal media: A review of sub- and supercritical water technologies. Energ. Environ. Sci. 2008; 1: 32-65. https://doi.org/10.1039/B810100K. [12] Malins K, Kampars V, Brinks J, Neibolte I, Murnieks R, Kampare R. Bio-oil from thermochemical hydro-liquefaction of wet sewage sludge. Bioresour. Technol. 2015; 187: 23-9. https://doi.org/10.1016/j.biortech.2015.03.093. [13] Prajitno H, Park J, Ryu C, Park HY, Lim HS, Kim J. Effects of solvent participation and controlled product separation on biomass liquefaction: A case study of sewage sludge. Appl. Energ. 2018; 218: 402-16. https://doi.org/10.1016/j.apenergy.2018.03.008.

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Journal Pre-proof [14] Prajitno H, Zeb H, Park J, Ryu C, Kim J. Efficient renewable fuel production from sewage sludge using a supercritical fluid route. Fuel 2017; 200: 146-52. https://doi.org/10.1016/j.fuel.2017.03.061. [15] Qian L, Wang S, Savage PE. Hydrothermal liquefaction of sewage sludge under isothermal and fast conditions. Bioresour. Technol. 2017; 232: 27-34. https://doi.org/10.1016/j.biortech.2017.02.017. [16] Xu C, Lancaster J. Conversion of secondary pulp/paper sludge powder to liquid oil products for energy recovery by direct liquefaction in hot-compressed water. Water Res. 2008; 42: 157182. https://doi.org/10.1016/j.watres.2007.11.007. [17] Ma W, Du G, Li J, Fang Y, Hou La, Chen G, Ma D. Supercritical water pyrolysis of sewage sludge. Waste Manage. 2017; 59: 371-8. https://doi.org/10.1016/j.wasman.2016.10.053. [18] Xu D, Lin G, Liu L, Wang Y, Jing Z, Wang S. Comprehensive evaluation on product characteristics of fast hydrothermal liquefaction of sewage sludge at different temperatures. Energy 2018; 159: 686-95. https://doi.org/10.1016/j.energy.2018.06.191. [19] Yin F, Chen H, Xu G, Wang G, Xu Y. A detailed kinetic model for the hydrothermal decomposition process of sewage sludge. Bioresour. Technol. 2015; 198: 351-7. https://doi.org/10.1016/j.biortech.2015.09.033. [20] Castello D, Haider MS, Rosendahl LA. Catalytic upgrading of hydrothermal liquefaction biocrudes: Different challenges for different feedstocks. Renew. Energ. 2019; 141: 420-30. https://doi.org/10.1016/j.renene.2019.04.003. [21] Ghafghazi S, Sowlati T, Sokhansanj S, Melin S. Techno-economic analysis of renewable energy source options for a district heating project. Int. J. Energ. Res. 2010; 34: 1109-20. https://doi.org/10.1002/er.1637. [22] Gasafi E, Reinecke M-Y, Kruse A, Schebek L. Economic analysis of sewage sludge gasification in supercritical water for hydrogen production. Biomass Bioenerg. 2008; 32: 108596. https://doi.org/10.1016/j.biombioe.2008.02.021. 31

Journal Pre-proof [23] Tańczuk M, Kostowski W, Karaś M. Applying waste heat recovery system in a sewage sludge dryer–A technical and economic optimization. Energy Convers. Manage. 2016; 125: 121-32. https://doi.org/10.1016/j.enconman.2016.02.064. [24] Chen G, Wang X, Li J, Yan B, Wang Y, Wu X, Velichkova R, Cheng Z, Ma W. Environmental, energy, and economic analysis of integrated treatment of municipal solid waste and sewage sludge: A case study in China. Sci. Total Environ. 2019; 647: 1433-43. https://doi.org/10.1016/j.scitotenv.2018.08.104. [25] Olkiewicz M, Torres CM, Jiménez L, Font J, Bengoa C. Scale-up and economic analysis of biodiesel production from municipal primary sewage sludge. Bioresour. Technol. 2016; 214: 122-31. https://doi.org/10.1016/j.biortech.2016.04.098. [26] Xu C, Chen W, Hong J. Life-cycle environmental and economic assessment of sewage sludge treatment in China. J. Clean. Prod. 2014; 67: 79-87. https://doi.org/10.1016/j.jclepro.2013.12.002. [27] Luz FC, Rocha MH, Lora EES, Venturini OJ, Andrade RV, Leme MMV, del Olmo OA. Techno-economic analysis of municipal solid waste gasification for electricity generation in Brazil. Energy Convers. Manage. 2015; 103: 321-37. https://doi.org/10.1016/j.enconman.2015.06.074. [28] Do TX, Prajitno H, Lim Y-I, Kim J. Process modeling and economic analysis for bio-heavyoil production from sewage sludge using supercritical ethanol and methanol. J. Supercrit. Fluids 2019; 150: 137-46. https://doi.org/10.1016/j.supflu.2019.05.001. [29] Oh C-H, Lim Y-I. Process simulation and economic feasibility of upgraded biooil production plant from sawdust. Korean Chem. Eng. Res. 2018; 56: 496-523. https://doi.org/10.9713/kcer.2018.56.4.496. [30] Do TX, Lim Y-i. Techno-economic comparison of three energy conversion pathways from empty fruit bunches. Renew. Energ. 2016; 90: 307-18. http://dx.doi.org/10.1016/j.renene.2016.01.030. 32

Journal Pre-proof [31] Do TX, Lim Y-i, Cho H, Shim J, Yoo J, Rho K, Choi S-G, Park C, Park B-Y. Technoeconomic analysis of fry-drying and torrefaction plant for bio-solid fuel production. Renew. Energ. 2018; 119: 45-53. https://doi.org/10.1016/j.renene.2017.11.085. [32] Do TX, Lim Y-i, Jang S, Chung H-J. Hierarchical economic potential approach for technoeconomic evaluation of bioethanol production from palm empty fruit bunches. Bioresour. Technol. 2015; 189: 224-35. https://doi.org/10.1016/j.biortech.2015.04.020. [33] Jones S, Meyer P, Snowden-Swan L, Padmaperuma A, Tan E, Dutta A, Jacobson J, Cafferty K. Process design and economics for the conversion of lignocellulosic biomass to hydrocarbon fuels: fast pyrolysis and hydrotreating bio-oil pathway; Pacific Northwest National Laboratory, U.S. Department of Energy, 2013, NREL/TP-5100-61178. [34] Perry RH, Green DW. Perry's Chemical Engineers' Handbook: Capter 12. Psychrometry, Evaporative Cooling, and Solids Drying. 7th ed. New York: McGraw-Hill, 1999. [35] Prajitno H, Insyani R, Park J, Ryu C, Kim J. Non-catalytic upgrading of fast pyrolysis bio-oil in supercritical ethanol and combustion behavior of the upgraded oil. Appl. Energ. 2016; 172: 12-22. https://doi.org/10.1016/j.apenergy.2016.03.093. [36] Zeb H, Choi J, Kim Y, Kim J. A new role of supercritical ethanol in macroalgae liquefaction (Saccharina japonica): Understanding ethanol participation, yield, and energy efficiency. Energy 2017; 118: 116-26. https://doi.org/10.1016/j.energy.2016.12.016. [37] Bilgen S, Kaygusuz K. The calculation of the chemical exergies of coal-based fuels by using the higher heating values. Appl. Energ. 2008; 85: 776-85. https://doi.org/10.1016/j.apenergy.2008.02.001. [38] Dutta A, Sahir A, Tan E, Humbird D, Snowden-Swan LJ, Meyer PA, Ross J, Sexton D, Yap R, Lukas J. Process design and economics for the conversion of lignocellulosic biomass to hydrocarbon fuels: thermochemical research pathways with in situ and ex situ upgrading of fast pyrolysis vapors; National Renewable Energy Laboratory, U.S. Department of Energy, 2015, NREL/TP-5100-62455. 33

Journal Pre-proof [39] Kent TR, Bott CB, Wang Z-W. State of the art of aerobic granulation in continuous flow bioreactors. Biotechnol. Adv. 2018; 36: 1139-66. https://doi.org/10.1016/j.biotechadv.2018.03.015. [40] Do TX, Lim Y-i, Cho H, Shim J, Yoo J, Rho K, Choi S-G, Park B-Y. Process modeling and energy consumption of fry-drying and torrefaction of organic solid waste. Drying Technol. 2017; 754-65. https://doi.org/10.1080/07373937.2016.1211674.

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Techno-economic analysis of bio heavy-oil production from sewage sludge using supercritical and subcritical water

Truong Xuan Doa,b, Rana Mujahidc, Hyun Soo Limd, Jaekon Kime, Young-Il Lima*, Jaehoon Kimc,f,g*

*Corresponding author: Young-Il Lim ([email protected]), Jaehoon Kim ([email protected])

Highlights  Bio heavy-oil (BHO) was produced from 100 t/d sewage sludge (SS) in industrial scale  Economic feasibility was evaluated for BHO plants using super and subcritical water  Minimum fuel selling price of BHO was 0.91 $/L, higher than actual price (0.55 $/L) A BHO plant with subcritical water is profitable if SS treatment credit is >120 t/d

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