key: cord-0961644-ioe10fwh
authors: Aboelazayem, Omar; Gadalla, Mamdouh; Alhajri, Ibrahim; Saha, Basudeb
title: Advanced process integration for supercritical production of biodiesel: Residual waste heat recovery via organic Rankine cycle (ORC)
date: 2020-09-18
journal: Renew Energy
DOI: 10.1016/j.renene.2020.09.058
sha: 234ac090f8efcd33596d789b3e701d91a4c85e53
doc_id: 961644
cord_uid: ioe10fwh

Biodiesel production using supercritical methanolysis has received immense interest over the last few years. It has the ability to convert high acid value feedstock into biodiesel using a single-pot reaction. However, the energy intensive process is the main disadvantage of supercritical biodiesel process. Herein, a conceptual design for the integration of supercritical biodiesel process with organic Rankine cycle (ORC) is presented to recover residual hot streams and to generate electric power. This article provides energy and techno-economic comparative study for three developed scenarios as follows: original process with no energy integration (Scenario 1), energy integrated process (Scenario 2) and advanced energy integrated process with ORC (Scenario 3). The developed integrated biodiesel process with ORC resulted in electric power generation that has not only satisfied the process electric requirement but also provided excess power of 257 kW for 8000 tonnes/annum biodiesel plant. The techno-economic comparative analysis resulted in favouring the third scenario with 36% increase in the process profitability than the second scenario. Sensitivity analysis has shown that biodiesel price variation has significant effect on the process profitability. In summary, integrating supercritical biodiesel production process with ORC appears to be a promising approach for enhancing the process techno-economic profitability and viability.

The global energy consumption has recorded a noticeable increase during the last decades 21 and is expected to continue to rise in the foreseeable future. The demand of fossil fuels, 22

as the main source of energy, has dramatically raised along with the increasing growth of 23 population and metropolitan industrial societies. The world's heavy dependence on fossil 24 fuels has led to environmental impacts including air pollution, global warming, climate 25 change and water contaminations [1] . Fossil fuels combustion exhausts from 26 transportation vehicles and industrial burners/boilers are the main cause of air pollution. 27

It has been reported that the replacement of fossil fuels with biofuels will have a 28 significant impact on air pollution reduction and hence lead to a greener environment 29 [2, 3] . A number of researchers have highlighted the importance of public transport in 30 minimising the impact on air pollution. Other researchers have mentioned a significant 31 effect of exhaust gas filtration in improving the air quality [4, 5] . Several governments 32

have encouraged people to use bicycles as a transportation means where they have 33 announced several funding schemes i.e. cycling to work scheme in the UK [6] . 34

Recently, the global air pollution has recorded steep reduction where the environment has 35 been allowed to be self-healed. This was a consequence of a novel infectious virus, 36 COVID-19, identified in late December 2019 of which most governments have 37

introduced serious lockdown policies [7] . It has been reported that the emission of 38 nitrogen oxides (NOx), carbon monoxide (CO) and particulate matters reduced by [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] 30% [8] . Therefore, the current situation has provided a non-intended reduction in air 40 pollution, which should be continued after releasing the lockdown by decreasing the 41 fossil fuels dependency and moving towards greener renewable fuels. 42 J o u r n a l P r e -p r o o f

The search for alternative renewable and greener source of energy has been considered as 1 a vital requirement. Lignocellulosic biomass is a sustainable and renewable feedstock for 2 production of biofuels that are promising replacements for fossil fuels due to the 3 physicochemical similarities. Further, biofuels are superior to fossil fuels as being 4 renewable, non-toxic, biodegradable and producing less greenhouse gases (GHG) 5

emissions. Finally, biomass valorisation into biofuels is projected to play a key role in 6 circular bioeconomy via thermo/biochemical conversion technologies [9] [10] [11] [12] . 7

Specifically, biodiesel has received a significant interest as it could be fuelled in the 8 diesel engines without modifications [13] . Biodiesel is produced from vegetable oils, 9

animal fats and microalgae by catalytic transesterification reaction of triglycerides and 10 alcohol into fatty acids alkyl esters. Generally, edible vegetable oils have been considered 11 the main feedstock for biodiesel production. However, the food price hikes and shortages 12 due to the increasing competition with food supplies over arable lands, crops and water 13 resources. Accordingly, biofuels research has been oriented to use non-edible and waste 14 cooking oils (WCO) as an alternative non-food competitive feedstock [14] . However, the 15 main problem associated with WCO is the high acidity of the feedstock. Several pre-16 treatment steps have been developed for free fatty acids (FFA) conversion, i.e. 17 esterification and neutralisation [15, 16] . Two-steps reactions process has been developed 18

as an efficient solution where the feedstock is esterified using acidic catalysts to convert 19 FFA into biodiesel, which is followed by transesterification of triglycerides using alkaline 20

catalysts [17]. 21

Recently, non-catalytic supercritical production of biodiesel has provided an ideal 22 strategy for converting high acidity feedstock into biodiesel. It has been observed that 23 supercritical methanol is highly miscible in WCO where simultaneous esterification and 24 transesterification take place without the aid of catalysts. In addition, the process has 25 several advantages over catalytic conventional processes including high yield of 26 biodiesel, elimination of wastewater, reduction of process unit operations, simple product 27 separation and high-quality of biodiesel [18] . Several researchers have studied the 28 supercritical valorisation of high acidity feedstock into biodiesel [19, 20] . In our previous 29 study [21] , we have successfully valorised high acid value WCO into biodiesel with 30 98.8% yield and optimised the process parameters using response surface methodology 31 (RSM). We have also observed that supercritical methanolysis using low acid value 32 WCO has yielded lower biodiesel at the same process parameters than high acid value 33 WCO. We have explained that the esterification reaction has higher rate with 34 supercritical methanolysis than transesterification and hence high acidity feedstock is an 35 advantage for supercritical process [21, 22] . 36

The harsh reaction conditions and high energy consumption are considered as the main 37 disadvantages of supercritical biodiesel production. Researchers have studied lowering of 38 supercritical process parameters while achieving high yield of biodiesel using co-solvents 39

[23]. Catalytic supercritical approaches have been investigated at milder reaction 40

conditions [18] . On the other hand, researchers have applied energy integration 41 approaches to minimise the process energy requirements. Several process simulation 42 studies have been conducted on supercritical biodiesel production [24, 25] . In our 43

previous study [26] , we have designed an optimal heat exchanger network (HEN) for 44 J o u r n a l P r e -p r o o f supercritical production of biodiesel where it has resulted in lowering about 45% of the 1 process energy requirements. Ziyai et al. [27] have reported a novel process for 2 integrating biodiesel with hydrogen production unit using glycerol supercritical water 3 reforming. They have reported that the combustion of the produced hydrogen has 4 significantly reduced the process external heating requirements. In addition, they have 5 demonstrated that the produced electric energy by hydrogen combustion has exceeded the 6 process electric requirements and hence considered as process revenue. 7

Organic Rankine cycle (ORC) has been considered as a promising technology for waste 8 heat valorisation for producing electricity. It has a similar principle for the steam Rankine 9

cycle but using organic solvents with lower boiling temperatures than water, which 10 allows the heat recovery of low temperature resources. It has been reported that the 11 application of ORC for residual heat recovery has resulted in reduction of process 12 operation costs [28, 29] for gas turbine exhaust gases in a floating production storage and offloading platform 25 (FPSO). The produced electricity has covered about 21% of the electric energy 26 requirement of the plant. It has also reduced plant fuel consumption and carbon dioxide 27 emissions by 22.5%. To the knowledge of the authors, the integration of supercritical 28 biodiesel production process with ORC has not been reported yet. This article is 29 considered the first study that aims to contribute in empowering the supercritical 30 biodiesel process by valorising the residual waste heat into electric energy. 31

In this paper, a conceptual advanced process integration for supercritical production of 32 biodiesel has been implemented by recovering residual waste heat using ORC. The 33

process residual heat streams have been defined based on our previously published 34 energy integrated process [26] . An integrated HEN has been developed to exchange the 35 waste heat from the residual streams with organic Rankine solvent. By integrating waste 36 heat with ORC, not only the electrical requirements of the process are met but also 37 additional power is generated. A comprehensive analysis for three biodiesel production 38 scenarios has been conducted to highlight the processes energy requirement and techno-39 economic feasibility. In addition, the paper includes a complete study of 8 organic 40

Rankin solvents to assess their applicability to maximise power generation. Herein, the 41 considered scenarios are as follows: the original supercritical production of biodiesel 42 without energy integration (Scenario 1), the published energy integrated process 43 (Scenario 2) and the developed advanced integrated process with ORC (Scenario 3). 44 J o u r n a l P r e -p r o o f Finally, a sensitivity analysis has been performed to assess the influence of variations in 1 feedstock, biodiesel and electricity prices on the process techno-economic figures. 2

The biodiesel supercritical production process was simulated according to our previous 5 published data [26] . In summary, oil and methanol were entered to two pumps to increase 6 their pressure to approximately 200 bar. The reactants were then mixed and heated to 7

253.5 °C. The conditioned reactant mixture was then fed to a kinetic reactor with 91% 8

conversion of WCO to methyl esters (biodiesel) and glycerol. The product stream was 9 then depressurised and introduced to a flash separator to recover the vaporised unreacted 10 methanol. The liquid mixture stream of methyl esters, glycerol and methanol was then 11 directed to a distillation column to separate methanol. The distillation product stream was 12 cooled and entered a decanter to separate glycerol from methyl esters. The methyl esters 13 stream was fed to a vacuum distillation column to separate the excess triglycerides, so the 14 biodiesel product meets the EN14214 specifications. 15

The chemical components of the feedstock and the products were defined based on our 16

previous reported process design for supercritical biodiesel production [26] . The same 17 kinetic reactor was defined using the reported kinetic and thermodynamic parameters. 18

The previous reported original process was named as "Scenario 1" where all the heating 19 and cooling energy requirements were supplied using external utilities as shown in Figure  20 1. Our previous study has also developed a HEN that achieved the Pinch targets for both 21 heating and cooling energy requirements. The reported energy integrated process using 22

optimal HEN was fully simulated in this paper (including all heat-exchangers) and named 23 as "Scenario 2". Further, this paper has developed an advanced process by integrating the 24 residual heat streams with ORC and the process was fully simulated "Scenario 3". The 25 three scenarios were fully modelled and simulated using Aspen-HYSYS ® (V11) 26 commercial software (Aspen Technology Inc., USA). All the designed heat exchangers 27

were simulated and operated in the simulation environment. The full simulation of an 28 integrated design eases the process comparison and highlights the differences in external 29 utilities consumption and may provide basis for further future online-optimisation. 30 1 Figure 1 . Original supercritical production of biodiesel (Scenario 1) 2

The developed scenarios were compared for the overall electric, heating and cooling 4 energy consumptions. Further, an economic feasibility and profitability studies were 5 performed by calculating several economic indicators for each process including total 6 capital investment (TCI), annual operating cost (APC), annual total revenues (ATR), 7

annual profit (AP), payback period (PBP), net present value (NPV) and profitability 8 index (PI). The detailed equations of the mentioned indicators were comprehensively 9 described in [27] . It is worth mentioning that the products of the process are only methyl 10 esters, glycerol and electrical power (scenario 3). 11

A techno-economic analysis was performed using Aspen Process Economics Analyser ® 12 (V11) commercial software (Aspen Technology Inc., USA). The costs of the feedstock 13 and products including methanol, waste cooking oil (WCO), glycerol and methyl esters 14

(biodiesel) were defined in the software as presented in 

Based on our previous reported optimal HEN for supercritical biodiesel production 3 process, several hot streams were observed to use external cooling facilities where 4 significant heat is lost to cooling water [26] . The residual streams were identified as 5 reported in Table 2 where only streams with significant available heat energy (>250 kW) 6

were considered for utilisation. The selected residual streams for recovery were identified 7 as follows: 109, C2, 108 and 114. The total available energy of the selected residual 8 streams was reported as 4,888.25 kW. As most of the available waste energy were 9

identified by streams C2 and 108, the cold stream maximum temperature constraint was 10 set based on their inlet temperature (89 °C). Accordingly, the maximum achievable 11 temperature for the cold stream (organic Rankine solvent) was set to 79 °C. 12 

The basic organic Rankin cycle (BORC) system is composed of 4 main components 16

including turbine expander, condenser, pump and evaporator (heating source). The 17

schematic of the ORC system is depicted in Figure 2 . The evaporator was replaced in this 18 J o u r n a l P r e -p r o o f process by exchanging heat with residual streams. The evaporated solvent was then 1 introduced to the turbine expander to generate power. The expanded vapours were then 2 fed to a condenser where the fluid exchanges heat with cooling water. The fluid then 3 entered a pump to increase the pressure and then returned to the evaporator to complete 4 the cycle. 5

Alternatively, RORC has an additional heat exchanger unit to the 4 units of BORC. The 6

heat exchanger is aimed to recover the available heat of the outlet stream from the turbine 7

(HT-LP) to preheat the pressurised liquid stream (LT-HP). The application of RORC 8 reduce the required heating and cooling energies at the evaporator and condenser. Figure  9 3 provides a schematic of the RORC units and operation. Based on the available waste heat evaluation study, several constraints were applied for 3 the ORC to match the process requirements. For instance, cooling water was chosen as a 4

cooling utility and hence the outlet temperature of the ORC condenser was set to a 5 minimum temperature of 30 °C. Further, as the main residual hot streams are available at 6 net temperature of 89 °C where hereafter a maximum temperature limitation of 79 °C 7 was set for the evaporator outlet stream. The aforementioned constraints had significantly 8 narrowed the organic solvent selection process. The selected solvent should be in vapour 9

phase at elevated pressure at 79 °C and also should be in liquid phase at reduced pressure 10 at 30 °C. 11

On the other hand, the available waste heat energy from the selected residual heat streams 12 was reported as 4,888.25 kW. Hence, an independent ORC for each organic Rankin 13 solvent was simulated with an evaporator duty of 4,888 kW to identify the maximum 14 flowrate of the solvent that could achieve the energy target of the evaporator. 15

The modified cubic equation of state Peng-Robinson Stryjek-Vera (PRSV) was used as a 16

thermodynamic fluid package to calculate the properties of the ORC solvents as per 17

Equations 1-7 [36] . Aspen-HYSYS software was used to analyse the ORC performance. 18

Eight solvents have been selected for the study including Propane, Propene, iso-butane, 19

n-butane, butene, R22, Ammonia and Dimethyl ether (DME). The properties of the 20 selected solvents are presented in Table 3 [37]. 21 (3) 1

Where T c , P c andrepresent critical temperature, pressure and acentric factor, 6 respectively. 7 

The selected residual streams with significant heat energy i.e. 109, C2, 108 and 114 have 12 been integrated with a cold stream representing the organic Rankine solvent. The organic 13

Rankine solvent was defined with an inlet temperature of 31.9 °C and outlet temperature 14 of 79 °C. The temperatures have been set based on specified constraints as mentioned in 15 section 2. The available energy for the cold stream was defined as 4,844 kW (considering 16 minimum energy losses). 17

The HEN design has been developed based on Pinch technology where a composite 18 curve has been developed of the hot and cold streams as presented in Figure 4 . The Pinch 19

temperatures have been defined between 31.9 and 41.9 °C as per a reasonable assumption 20

of ΔT min of 10 °C. Accordingly, the maximum allowable cooling temperature above the 21 Pinch for the hot streams has been set to 41.9 °C. On the other hand, the maximum 1 heating temperature for cold streams below the Pinch (if any) has been set to 31.9 °C. 2

The process residual hot streams are represented in a single composite curve (shown in 3 red) while the ORC process cold stream is represented in a different composite curve 4 (shown in blue). The overlap between hot and cold composite curves illustrates the 5 available energy integration between streams. The cold stream (organic Rankine solvent) 6

was defined so it could reach its target without the aid of any external heating utility (to 7

replace the evaporator). However, further external cooling utility (cooling water) will be 8 required for hot streams to reach their targeted temperature. Using the developed 9

composite curves, the energy targets have been calculated as 0 and 217.2 kW for both 10 heating and cooling, respectively. Aspen Energy Analyzer ® commercial software (Aspen 11

Technology Inc., USA) has been used to develop the composite curves and to calculate 12 the target (minimum) energy requirement for both heating and cooling. 13 An optimal HEN has been designed based on graphical Pinch method using 6 heat 16 exchangers as shown in Figure 5 . In order to achieve the zero-heating target, the ORC 17 cold stream has been divided into three splits where each split has been heated from 31.9 18 °C to 79 °C without any external heating utility. The integration starts with developing an 19 exchanger with stream 114 as it has an inlet temperature of 80.4 °C and could not be used 20

to heat a cold stream up to more than 70.4 °C as per the applied ΔT min. Hence, it has been 21 used as a pre-heater for one of the organic Rankine solvent splits. The cooling 22

temperatures for streams 109 and 114 have been achieved using external cooling utility 23 (cooling water) with a combined cooling energy requirement of 256.5 kW. According to 24 the Pinch target of external energies, the designed HEN has achieved 100 and 117.8 % of 1 the target for heating and cooling energies, respectively. 2

The graphical Pinch method has been used to limit the trial procedures and to assess the 3 validity of the developed exchangers. The graphical Pinch method, as shown in Figure 6 , 4 has represented each exchanger as a straight line on T-T diagram. The length of each 5 exchanger line represents the heat transfer within the exchanger. In addition, the slope is 6 function of the ratio of heat capacities and flows [38] . It has been observed from Figure 6  7 that the designed exchangers are all presented at the optimal area for heat recovery 8

(above the Pinch) as explained previously by Gadalla [39] . 

The development of ORC process simulation has been commenced using selection of 6 chemical component. Eight organic Rankine solvents (working fluids) have been selected 7

for the simulation environment including propane, propene, iso-butane, n-butane, butene, 8 R22, ammonia and dimethyl ether (DME). This has been followed by selecting PRSV as 9 a thermodynamic fluid package. The system has been assumed to operate with steady-10 state conditions. In addition, several assumptions have been defined to simplify the 11 simulation as follows: 12

• Heat loss from/to the environment has been ignored. 13

• Kinetic and potential energy changes have been ignored. 14 • Pressure drop across the pipelines has been ignored. 15 • Constant efficiency for pump and turbine. ΔP across the turbine have been varied to preserve the constant set parameters. A 3 maximum allowable inlet pressure for the turbine has been set to 28 bar as reported 4

elsewhere [41] . Table 4 represents the turbine inlet and outlet conditions, solvent flowrate 5 and the turbine electric output for each solvent. 6 The inlet pressure for each solvent has been defined as the highest pressure that allows 9 the solvent to be in vapour phase at 79 °C. On the other hand, the output pressure has 10 been set based on the minimum pressure that allows the solvent to be condensed at 31.9 11

°C. It has been observed in Table 4 that n-butane, butene and iso-butane could meet the 12 process constraints and feed the turbine at relevant low pressure (<13 bar). In addition, 13

iso-butane and butene have showed the maximum power output for the process of 455 14

kW. DME has exhibited an entering turbine pressure of 20.5 bar with a relatively high-15 power output of 453.6 kW. The rest of the studied solvents including R22, propane, 16

propene and ammonia have displayed an elevated fed turbine pressure of 28 bar (the 17 maximum allowable pressure). Further, they have reported lower turbine power output 18 with a range between 319.7 -439 kW. Accordingly, butene has been selected as the 19 optimal solvent for the integrated supercritical process study. 20

The overarching aim of the development of RORC is to increase the efficiency of the 22 ORC process by integrating the available heat of the turbine outlet stream to pre-heat the 23 evaporator inlet stream [31]. This generally results in reduction of the required heating 24 and cooling energy at the evaporator and condenser, respectively. However, the present 25 work is designed to fully replace the evaporator unit with a set of heat exchangers in the 26 process. Accordingly, the pump outlet stream does not require a pre-heat as it is already 27 fully heated by energy integration with other residual process streams. 28

In particular application of RORC for the present work, a simple comparison in energy 29 reduction between BORC and RORC (presented in Figures 2 and 3) has been conducted. 30

By considering the process constrains discussed in section 2.4, the implementation of 31 RORC has resulted in decreasing the temperature of condenser inlet stream from 43.1 °C 1 (shown in Table 4 ) to 41 °C. Furthermore, this has increased the temperature of the 2 evaporator inlet stream from 31.7 °C to 33.1 °C. Accordingly, reduction in heating and 3 cooling energy requirement have been observed as 0.82% and 0.93%, respectively. It is 4 worth mentioning that the increase in temperature of pump outlet stream from 31.7 °C to 5 33.1 °C in RORC will result in decreasing the amount energy that could be 6 recovered/integrated from the biodiesel residual energy streams. This will also lead to a 7 backward increase in the external cooling energy requirement presented in Figure 5 as the 8

hot Pinch temperature will be 43.1 °C instead of 41.7 °C. Hence, streams 109 and 114 9

will be externally cooled from 43.1 °C to 25 °C. 10

Hence, for this particular application, both BORC and RORC have been observed to have 11 similar efficiency. In addition, using RORC will result in increase in the capital costs of 12 the process by installing an additional heat exchanger with no reduction in the operational 13

costs. As a result, BORC has been chosen in the present work. 14

Our previous developed HEN has been simulated in biodiesel production process by 16 introducing all the developed heat exchangers to the simulation environment and named 17

as Scenario 2 as shown in Figure 7 . Five heat exchangers have been simulated where the 18 temperature difference and the heat capacity have been defined based on the published 19 HEN [26] . Both distillation columns in the original case have been disconnected to a 20 separate column, reboiler and condenser. The disconnection was necessary to simulate 21

heat exchangers between streams in the main case with the distillation column internal 22 streams (special simulation environment for the column). The simulation has been used 23 for further energy and techno-economic analysis as described in section 3.4. 24

The new developed HEN, in the present study, between organic Rankine solvent and 25 residual hot streams of biodiesel process has been also simulated where 6 new heat 26 exchangers have been introduced to the simulation environment. In addition, the ORC 27 described in section 3.2 has been simulated to accompany the supercritical biodiesel 28

process. The ORC evaporator equipment shown in Figure 2 has been replaced with the 6 29 developed heat exchangers shown in Figure 8 . The newly developed process has included 30 11 heat exchangers as demonstrated in Figure 8 . The ORC has been operated using PRSV 31 fluid package as explained in section 2.3. 32

It is quite noticeable that the implementation of ORC to an existing process is 33 challenging, specifically for a similar case to the present study, where the evaporator has 34 been totally replaced with a set of heat exchangers. However, the conceptual design of 35 the process is promising, where it could be applied to the grassroots designs for new 36 biodiesel production plants. The energy balance of the developed scenarios has been tabulated in Tables 5-7. The  2 summation of the electric energy has been calculated by adding the consumed electric 3 power to the generated power (negative value). It has been observed (logically) that the 4 first scenario has the highest energy consumption where no energy integration exists. 5

However, the second scenario showed significant reduction of approximately 44% for 6 both heating and cooling energies as a result of energy integration. 7

In the third scenario, the residual waste heat integration with ORC has resulted in electric 8 energy generation of 455 kW from the turbine. The net process electric energy has 9

resulted in an excess of 270 kW to be considered as process revenue. In addition, the 10 process cooling energy for the third scenario has been significantly reduced resulting in 11

472.2 kW with nearly 90% reduction (without considering ORC solvent condensation). 12

However, ORC condenser itself requires approximate of 4,110 kW. Accordingly, the 13 overall process cooling energy is almost the same for both scenarios 2 and 3 as the 14 reduction in the biodiesel process cooling energy is compensated by ORC condenser. 15 Further, the heating energy is almost the same for both scenarios since the developed 16 ORC has only targeted the waste heat. However, the developed ORC integrated process 17

has resulted in generation of 270 kW instead of 165 kW consumption as described in the 18 second scenario. 19

Conceptually, the integration of supercritical production process with ORC has 20 significantly reduced the process utilities cost. However, the cost of installing the ORC 21 units in addition to 6 heat exchangers should also increase the process capital cost. 22

Hence, a comparative techno-economic analysis for the three scenarios has been 23 developed to provide a complete insight whether ORC integration would increase the 24 profitability of the process or not. 25 On the other hand, a different costing pattern has been observed for TOC for the three 18 developed scenarios. The TOC is mainly based on the cost of raw materials and the 19 process utilities. For the three scenarios, the raw materials are the same, but the utilities 20 are different as described previously in section 3.4. The first scenario has reported the 21 highest operating cost as it requires more external utilities than the other scenarios. A 22 minor difference of the TOC values of scenarios 2 and 3 referred to the electric energy 23 utility requirements as shown in Tables 6 and 7 (from section 3.4). 24

The total production of biodiesel for all scenarios is 8,000 tonnes per annum, 25 approximately 913 kg/h. which represents a revenue of 7.918 MMUSD per annum. In 26 addition, glycerol is produced with 0.16 MMUSD. Accordingly, the total revenue for 27 both first and second scenarios is 8.08 MMUSD per annum as shown in Table 8. The  28 third scenario has an additional revenue of 269.48 kW of electric energy (reported in 29 Table 7 ), which represents an additional annual revenue of 0.47 MMUSD. 30

The profitability of the developed scenarios has been checked using the AP value, NPV, 1 PI and PBP. The developed integrated biodiesel process with ORC (scenario 3) has 2

shown the maximum profitability among the other scenarios where it recorded the highest 3 AP, NPV, PI and lowest PBP. The AP value of the first scenario has shown a negative 4 value which means that the process is not profitable. However, both second and third 5 scenarios have shown AP values of 1.35 and 2.14 MMUSD/year, respectively. Thus, the 6 techno-economic analysis has proven that integrating supercritical production of 7 biodiesel with ORC has increased the process profitability. 8 A sensitivity analysis for the prices variation of the main input and outputs on the NPV of 9

the overall process has been performed. The analysis has varied the prices of WCO, 10 biodiesel and electricity about ± 30%. The results demonstrated in Figure 9A have shown 11

the negative linear effect of increasing the price of WCO on the process NPV. On the 12 other hand, the variation in biodiesel price showed the most significant variable affecting 13 the process NPV where the increase in biodiesel price has an obvious positive effect. 14 Further, the results presented in Figure 9B have shown high sensitivity of the overall 15 process with the variation effect of biodiesel price where the process become non-16 profitable (NPV equals to zero) with decrease of biodiesel prices by 11.2% and 15.1% for 17

both Scenarios 2 and 3, respectively. Finally, the effect of electricity price variation on 18 the process NPV is illustrated in Figure 9C . generation are the future routes to boost the process profitability. This article presents a novel integration approach for supercritical biodiesel process with 6 ORC in an attempt to increase the process profitability and valorise the residual process 7

heat. The process has been developed to valorise residual hot streams in a previously 8

published work using ORC. The temperature range of the ORC solvent has been defined 9 between 31 and 79 °C, based on the minimum temperature of the process residual hot 10 streams (89 °C). Eight organic Rankine solvents have been used to operate the developed 11

ORC where butene has been selected as an optimal solvent with the highest power 12 generation of 455 kW at moderate pressure scale. The developed new process (scenario 13

3) has been economically compared with previously published processes without ORC. 14 The key findings of the techno-economic comparative study are summarised below: 15

• The TCI of the first scenario has reported the lowest value due to the simplicity of 16 the process followed by second scenario that has 5 heat exchangers. 17

• The TCI of the third scenario has reported the highest value due the additional 18 cost of ORC and 6 additional heat exchangers than second scenario. 19

• TOC of the developed scenarios has varied according to consumption of the 20 utilities where the first scenario has recorded the highest value. • ATR of the first and second scenarios are almost the same as they are only based 1 on the produced biodiesel and glycerol sales unlike the third scenario that has 2 additional electrical power sales. 3

• The third scenario has resulted in net production of electricity of 257 kW for 4 8,000 tonnes/annum biodiesel production plant. 5

• The first scenario has been found to be a non-profitable process. 6

• The third scenario has provided the best economical approach with the highest 7 NPV, AP and PI. 8

In summary, the integration of supercritical biodiesel process with ORC has provided a 9 new approach to increase the process profitability. The developed approach has not only 10 provided self-sufficiency in electric energy for the process, but also produced excess 11 electric power as revenue. Future research work will include an exergoeconomic analysis 12

to provide a wider vision for the profitability of the developed approach. Further, retrofit 13

optimisation of the process HEN should be considered for better residual heat recovery. 14 CRediT AUTHOR STATEMENT 15 Biodiesel production from castor oil in Egypt: Process optimisation, kinetic study, 39 diesel engine performance and exhaust emissions analysis, Energy. 157 (2018) 40

Energy and Air Pollution

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Performance 11 analysis of supercritical ORC utilizing marine diesel engine waste heat recovery

14 Review of organic Rankine cycle for small-scale applications

Comparison between regenerative 17 organic Rankine cycle (RORC) and basic organic Rankine cycle (BORC) based on 18 thermoeconomic multi-objective optimization considering exergy efficiency and 19 levelized energy cost (LEC)

Cycle configuration 22 analysis and techno-economic sensitivity of biomass externally fired gas turbine 23 with bottoming ORC

Multi-objective optimization and exergetic analysis of a low-grade 27 waste heat recovery ORC application on a Brazilian FPSO

Study of waste heat recovery potential and 30 optimization of the power production by an organic Rankine cycle in an FPSO 31 unit

Techno-economic assessment of an energy 34 self-sufficient process to produce biodiesel under supercritical conditions

Exergetic 38 and economic comparison of ORC and Kalina cycle for low temperature enhanced 39 geothermal system in Brazil

Working-fluid selection 3 and thermoeconomic optimisation of a combined cycle cogeneration dual-loop 4 organic Rankine cycle (ORC) system for solid oxide fuel cell (SOFC) waste-heat 5 recovery

A new graphical method for Pinch Analysis applications: Heat 7 exchanger network retrofit and energy integration

A novel graphical technique for Pinch Analysis applications: 10 Energy Targets and grassroots design, Energy Convers

Maximizing ORC performance with optimal match of 13 working fluid with system design

Progress in Exergy, Energy, and the Environment

Assessment of four biodiesel production 18 processes using HYSYS.Plant

Biodiesel production from waste 21 cooking oil: 2. Economic assessment and sensitivity analysis