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Techno-Economic Evaluation of Refining of Food Supply Chain Wastes for the Production of Chemicals and Biopolymers

  • Anestis Vlysidis
  • Apostolis KoutinasEmail author
  • Ioannis Kookos
Chapter

Abstract

The development of sustainable and efficient refining of food supply chain wastes is dependent on the production of various end-products with diversifying market outlets and the identification of cost-effective processing schemes. Design and costing of proposed biorefinery concepts is essential in order to identify those processes that could be implemented on industrial scale. The successful implementation of microbial bioconversion of renewable resources for the production of chemicals and biopolymers is highly dependent on the development of cost-competitive biorefinery concepts. The recent literature on techno-economic assessment of food supply chain waste biorefining is presented. One detailed case study is presented focusing on the techno-economic evaluation of refining of orange peel wastes.

Keywords

Food waste biorefineries Process design Techno-economic evaluation Citrus processing waste 

8.1 Introduction

Although, there are uncertainties regarding the percentage of total food production that is currently lost through the whole supply chain (Parfitt et al. 2010), this has been estimated to be around 1.3 billion tones, which is approximately one third of the global production of food for human consumption (Galanakis 2012). Food waste (FW) is generated in the entire supply chain starting from agricultural production and postharvest (upstream process) to the processing of goods, distribution and consumption (downstream process) (Food Wastage Footprint 2013). In developing countries, most of FW is generated during the upstream process due to lack of infrastructure, while in developed countries the vast majority of FW is produced at the consumption stage (Parfitt et al. 2010). In 2006, EU-27 generated approximately 90 million tones of FW from the manufacturing sector and households, not including food losses from fisheries and agriculture (Monier et al. 2010). This amount accounts to 180 kg per person per year and is projected to increase up to 126 million t by 2020. Apart from the obvious economic losses in all relating sectors (agriculture, production, retailers and households) there is a significant environmental impact as it has been estimated that around 1.9 t of CO2 are produced per t of FW (Monier et al. 2010).

Due to the substantial quantities of FW generated each year worldwide, there is a global need governed from societal and economical features to re-use, re-cycle and/or re-cover these ʻlossesʼ under sustainable approaches. In recent years, the research community has focused on the valorization of FW as a renewable resource for the production of various commodity or value-added products. FW has been designated as a renewable resource that can play a significant part in the forthcoming bio-economy era as its chemical complexity fits perfectly to the concept of biorefinery development for the production of energy, chemicals and bio-based polymers (Lin et al. 2013; Koutinas et al. 2014a; Mirabella et al. 2014). This chapter focuses on the techno-economic evaluation of biorefineries using FW as renewable resource in order to assess new designs and the production of diversified end-products. A case study will be presented using food manufacturing wastes from an orange juice production factory.

8.2 Techno-Economic Assessment of Food Waste Biorefining

Biorefineries are facilities analogous to petroleum refineries that use biomass instead of crude oil for the production of various end-products including chemicals, materials, energy, fuels and biopolymers. The economic sustainability of these facilities is questioned as their end-products usually have higher production costs and cannot compete with the corresponding materials produced from petroleum. Hence, the economic evaluation of these new designs and end-products is of critical importance and need to be performed as a first step towards their successful commercialization. Various profitability criteria should be measured, most important of which are the net present value (NPV) and the internal rate of return (IRR) (Vlysidis et al. 2011). When there is not a firm market value for the obtained new products their minimum selling price (MSP), corresponding to zero NPV at the end of the life cycle of the plant, is calculated. The latter is usually assessed for different design parameters such as the capacity of the plant, the interest rate, the prices of raw materials and/or end-products and operational parameters like fermentation yields, alternative downstream processes, alternative raw materials and/or end-products (Koutinas et al. 2014a, b).

Preliminary economic studies should underline key factors that affect the profitability criteria of these new investments. Critical outcomes of these assessments should provide information regarding the stages of the process that should be modified towards the optimization of the profitability of the plant and the identification of the best available technology (Koutinas et al. 2014a). Most of the techno-economic assessments reported in the literature focus on the use of food waste and by-products coming from the manufacturing process, such as the sugarcane and dairy industries (Summers et al. 2015; Koutinas et al. 2016). These industrial streams are nowadays considered as by-products. There are also studies focusing on techno-economic assessment of valorization of food waste produced from restaurants and hotels (Han et al. 2016; Kwan et al. 2015).

Summers et al. (2015) carried out a techno-economic analysis using delactosed whey permeate for the production of renewable diesel via microbial fermentation followed by hydrolthermal liquefaction. The designed facility had a plant capacity of 1.25 million m3 of dairy liquid waste per year and it was based on lab-scale experimental results. The plant life and interest rate was assumed to be 30 years and 8%, respectively. The depreciation schedule was 7 years following the Modified Accelerated Cost Recovery System (MACRS). It was concluded that the MSP of renewable diesel production is 1.26 $/L which is higher than the average prices for soybean-derived biodiesel (1.15 $/L) and diesel (0.90 $/L). The higher MSP value was mainly attributed to the operational requirements of the yeast fermentation, the preparation of the inoculum and the intense conditions of hydrothermal liquefaction. It was estimated that the MSP of renewable diesel production could be reduced to 1.15 $/L, if the capacity of the process is increased approximately thirty times. A further reduction of up to 0.76 $/L on the MSP could be achieved via process optimization (i.e. fermentation yield and productivity as well as performance of hydrotreatment performance) (Summers et al. 2015).

Kwan et al. (2015) developed a techno-economic study on FW biorefining for the production of a spectrum of end-products such as plasticizers, lactic acid and animal feed. The FW was collected from restaurants and bakeries and was hydrolysed after grinding to small particles using enzymes produced via solid state fermentation. The FW hydrolysates were then fermented for algae production using the microalgae Chlorella pyrenoidosa. At the end of the fermentation, the lipid content of the algae was extracted so as to be used in the production of plasticizers, while lipid-free algae biomass rich in nitrogen source was used as substrate in lactic acid production via fermentation or as animal feed. Both scenarios were based on experimental results from previous studies and were designed in the software SuperPro Designer (Intelligen Inc.). The operational capacity of the plant was 1 t of food waste per day. Results from the techno-economic analysis indicated that NPV, IRR and payback period were 3.03 M$, 19% and 7.6 years, respectively, for a plant lifetime of 30 years and a discount rate of 5%. According to the sensitivity analysis, the market price of lactic acid had the most significant impact on the NPV compared to other raw-materials and end-products, accounting for approximately 30% reduction in NPV based on 10% variation in its market price (Kwan et al. 2015).

Han et al. (2016) developed a techno-economic analysis for the valorization of FW collected from a University canteen. The processing capacity of the plant was 1095 tones per year. The process included a hydrolysis stage converting FW into fermentable nutrients followed by microbial fermentation for the production of hydrogen. The hydrolysis process was carried out using crude enzymes produced via solid state fermentation. The mass and energy balances were computed using the design software Aspen Plus. The NPV of the plant was calculated for different interest rates and lifespans of the plant and it was above zero for an interest rate of 10% and a lifetime higher than 6.2 years. Although the low scale of the process decreased the profitability potential of the plant as the NPV of the investment after 15 years was around 0.44 M$, the IRR was considerably high accounting to 24.1%. Apart from H2, the pilot plant also co-produced solid biomass as animal feed (Han et al. 2016).

Koutinas et al. (2014b) have presented a techno-economic analysis for the production of microbial oil from glucose-based media. Waste or by-product streams from confectionary industries and bakeries could be employed. The capacity of the plant was 10,000 t of microbial oil production per year, while the plant operation was set at 8300 h/y. Once the microbial oil is produced by oleaginous yeast, the microbial mass is separated and dried. Cells are then disrupted mechanically and oil is separated from cell debris via a centrifugation unit using hexane. The latter is then recovered and recycled through a one-step evaporation unit. The microbial oil was then used to produce biodiesel via either direct or indirect transesterification. The mass and energy balances were calculated using the process simulation software, SuperPro Designer and UniSim (Honeywell). The cost of manufacture was largely affected by the cost of the bioreactors and was equal to $3.41 per kg microbial oil considering a zero market price of glucose. If the price of the raw material increases to $0.4/t the total production cost rises to $5.48 per kg microbial oil. Koutinas et al. (2014b) mentioned that the unitary production cost of microbial oil is significantly affected by the productivity of the microbial fermentation and the market price of the raw material used. In order to drastically decrease the manufacturing cost to around $1.76 per kg microbial oil, the productivity of the fermentation stage should be increased to 2.5 g/L/h for a zero glucose price (Koutinas et al. 2014b).

Koutinas et al. (2016) carried out techno-economic evaluation for the production of 2,3-butanediol using three different raw materials, one of which was sugarcane molasses. The process simulation software UniSim was used. Koutinas et al. (2016) conducted a sensitivity analysis for different market prices of the raw material and different plant capacities calculating each time the MSP of 2,3-butanediol production. The capacity of the plant was set at 10,000 t per year, while the plant operated for 8300 h/y. The MSP of 2,3-butanediol production was higher than 1 $/kg, which is generally regarded as the target in order to characterize a chemical production as basic or platform chemical. The MSP ranged from 2.6 to 4.8 $/kg for all raw material prices and fixed capital investments. It was stressed that the plant capacity of 10,000–40,000 t/y can be crucial as the MSP gradually drops by approximately 14%. Further capacity increase results in insignificant MSP reduction (Koutinas et al. 2016).

Another industrial FW that presents considerable interest is wine lees produced from the vinification process. Dimou et al. (2015) showed that wine lees could be used for the production of ethanol, an antioxidant-rich extract, tartaric acid and yeast cells (Fig. 8.1). The latter can be used as animal feed or for the production of nutrient supplements for microbial fermentations (Dimou et al. 2015). A techno-economic assessment conducted for a biorefinery using wine lees as renewable resource has been developed (results not published yet). The profitability of the plant utilizing the wine lees was dependent on the MSP of the antioxidant-rich fraction with respect to the plant capacity as this end-product does not currently have a firm market. A ten-fold increase from 500 to 5000 kg/h of processed wine lees can result in a significant drop of the MSP of antioxidants from 122 to 11 $/kg.
Fig. 8.1

Schematic diagram of a biorefinery using wine lees for the production of ethanol, antioxidants, tartaric acid and animal food (Dimou et al. 2015)

8.3 Case Study—Techno-Economic Evaluation of Biorefining Citrus Waste

The development of biorefineries focusing on the valorization of citrus waste first gained attention in 1940s and 1950s in the USA where juice industries were evaluating ways to give value to the huge amounts of citrus waste generated each year after the juice extraction process (Anonymous 1956; Hull et al. 1953; Van Antwerpen 1941). These studies proposed technologies to recover added-value compounds from citrus wastes such as essential oils, flavonoids and pectin as well as the production of a liquid stream called citrus molasses rich in soluble sugars (Anonymous 1956). According to FAO statistics, the year 2013 approximately 71.3 million tones of oranges were produced worldwide. Around 40% of this amount was processed in juice production and 50% of this amount was discarded as citrus peel waste (Pfaltzgraff 2014). This leads to a total annual amount of orange peel wastes equal to 14.3 million tones. The main constituents of orange peels are cellulose, hemicellulose and pectin which account to 50–70% of the dry orange peel. It also contains a fraction of soluble sugars such as xylose, glucose sucrose and fructose, 3–4% of d-limonene and 4–5% of flavonoids (Pfaltzgraff 2014). Due to the prospect of producing valuable compounds from citrus wastes, a number of techno-economic studies have been developed (Lohrasbi et al. 2010; Grohmann 2007; Zhou et al. 2007). The extraction of d-limonene is a process already employed in large scale citrus processing plants as it is used in the pharmaceutical, food and cosmetic industry. Pectin extraction is a more complicated process and it is hardly applied to orange juice factories. Pectin is used as a gelling agent in foods (Lopez et al. 2010). Flavonoids are chemical substances of low molecular weight that contain more than three phenolic hydroxides. They are abundant in nature as secondary metabolites and they are one of the most interesting groups having biological active compounds. They are used as antioxidants mainly in the pharmaceutical and cosmetic industry but they also have application in the food industry (Anagnostopoulou 2005). Figure 8.2 presents the main end-products derived from citrus wastes that have been widely investigated. In this chapter, a case study has been developed evaluating the development of a biorefinery concept using citrus waste for the production of d-limonene, energy and bioethanol. Outcomes are compared with results from similar literature-cited studies.
Fig. 8.2

Current valorization options for citrus wastes

8.3.1 Process Design

The design of the biorefinery processing orange peel waste into various end-products was performed using literature-cited results (Lohrasbi et al. 2010; Pourbafrani et al. 2010; Humbird et al. 2011), while the energy and material balances were determined using the process simulation software Unisim. The plant processes 50,000 t of orange peel waste per year which leads to an hourly flowrate of 12.5 t/h as the plant operates seasonally for 4000 h/y (approximately 5.5 months). The developed plant covers only a base case scenario for the valorization of orange peel wastes extracting the d-limonene and producing bioethanol via fermentation of free sugars as well as the hydrolysates of cellulose and hemicellulose. However, this base case scenario can be compared to more advanced biorefinery designs that extract also pectin and flavonoids. The process flow diagrams (PFDs) developed in this study for the extraction of d-limonene and the production of ethanol are shown in Figs. 8.3 and 8.4, respectively. The composition of orange peel waste (Table 8.1) has been obtained from Lohrasbi et al. (2010) and Pourbafrani et al. (2010).
Fig. 8.3

PFD for the hydrolysis of orange peel waste and the extraction of d-limonene

Fig. 8.4

PFD for ethanol production and recovery including the production of HPS from orange peel waste

Table 8.1

Composition of orange peel waste (Lohrasbiet al. 2010; Pourbafrani et al. 2010)

Component

Amount in kg/100 kg of orange peel waste

Water

80.4

Glucose

1.6

Fructose

2.4

Sucrose

0.6

Pectin

5.0

Protein

1.2

Cellulose

4.4

Hemicellulose

2.2

lignin

0.4

Limonene

1.0

Ash

0.8

The PFD for the production of d-limonene is presented in Fig. 8.3. The orange peel waste enter in a rotary cutter (M-101) through a belt conveyor (C-101) where the size of orange peel waste is reduced and the surface area available to acid hydrolysis that follows is increased. The shredded orange peel waste enter via stream 1 (12.5 t/h) to the hydrolysis reactor (R-101) where the partial hydrolysis of hemicellulose and cellulose takes place. The conversion yields achieved from cellulose and hemicellulose to the respective sugars are 50 and 60%, respectively. The composition of orange peel waste in cellulose and hemicellulose is given by Aravantinos et al. (1994) where hemicellulose is composed mainly of hexoses (60.6%). Therefore, it was considered that the hydrolysis of hemicellulose gives 60% (w/w) hexoses and 40% (w/w) pentoses according to the following stoichiometric equation:
$$ - \left( {{\text{C}}_{ 6} {\text{H}}_{ 10} {\text{O}}_{ 5} } \right)_{ 1} - \left( {{\text{C}}_{ 5} {\text{H}}_{ 8} {\text{O}}_{ 4} } \right)_{0. 8} + 1. 8\,{\text{H}}_{ 2} {\text{O}} \to {\text{C}}_{ 6} {\text{H}}_{ 1 2} {\text{O}}_{ 6} + 0. 8\,{\text{C}}_{ 5} {\text{H}}_{ 10} {\text{O}}_{ 5} $$
(8.1)
Hence, 100 kg of hemicellulose could be hydrolysed to 67.26 kg of hexoses and 44.84 kg of pentoses. Cellulose is hydrolysed into glucose. Besides polysaccharides, the orange peel waste contains also free sugars including fructose, sucrose and glucose. During the hydrolysis process, the sucrose contained in the orange peel waste is also hydrolysed to give one molecule of glucose and one molecule of fructose according to the following stoichiometric reaction:
$$ {\text{C}}_{ 1 2} {\text{H}}_{ 2 2} {\text{O}}_{ 1 1} + {\text{H}}_{ 2} {\text{O}} \to {\text{C}}_{ 6} {\text{H}}_{ 1 2} {\text{O}}_{ 6} + {\text{C}}_{ 6} {\text{H}}_{ 1 2} {\text{O}}_{ 6} $$
(8.2)

Hence, 100 kg of sucrose are hydrolysed to 52.63 kg of glucose and 52.63 kg of fructose. The differences in masses both in (8.1) and (8.2) are due to the addition of water.

The hydrolysis takes place at 150 °C by steam explosion under mild acidic conditions using 0.25% (w/w) of sulfuric acid solution. Steam explosion is carried out by providing 2.6 t/h of high pressure steam (HPS). The hydrolysis reaction lasts for 10 min and another 5 min are needed for loading and uploading the reactor. Due to fact that the hydrolysis is a batch process, a train of four reactors has been assumed. The steam is produced in a series of heat exchangers (E-103, E-104 and E-105) where process water is transformed into HPS. The superheated steam from stream 22 is produced in Area 200 by burning all the remaining solids of orange peel waste after the fermentation process. At the end of the hydrolysis process, pressure is partially released from 10.0 to 4.9 bar in a vapour-liquid separator (V-101) assuming a constant temperature of 150 °C so as to recover a gas stream comprised by d-limonene and water (stream 4) and a liquid/solid stream (stream 7) containing the produced sugars, water and the remaining solids (pectin, lignin, protein and ash). Stream 4 passes through a cooler (E-101) that condensates d-limonene and water to 25 °C. The liquid stream then enters into a decanter (V-102) where the d-limonene (stream 6) is separated from water (stream 5) as these two liquids are immiscible, forming two distinct liquid phases. Finally, the d-limonene is stored in a storage tank able to store the weekly production of d-limonene with a mass flowrate of 123.75 kg/h. Stream 5 goes into Area 200. Stream 7 is cooled down in the heat exchanger E-102 and partially in E-103 from 150 to 30 °C. Stream 9 then enters into vessel V-104 where the neutralization of the loading of the bioreactor takes place by adding a base such as caustic soda (31.2 kg/h). This vessel also acts as a holding tank before the operation of the fermentation process.

Stream 10 from Area 100 enters into the bioreactor R-201 (Area 200) together with the necessary amounts of nutrient supplements for the production of ethanol (Fig. 8.4). The fermentation time was 36 h (Humbird et al. 2011) and assuming 12 h for cleaning, preparation and loading and another 12 h for uploading, the total batch cycle time is 60 h. The number of batches per year is 67 that can be calculated by dividing the annual operating time of the plant with the duration of a single batch cycle. A seed train of five bioreactors (not included in the PFD of Fig. 8.4) with total volumes of 100.00, 10.00, 1.00, 0.1 and 0.01 m3 have been also considered in this process design. The ethanol is produced by the microorganism Zymomonas mobilis that can ferment both pentoses and hexoses into ethanol with a yield of 0.34 g/g (Humbird et al. 2011). One train of seed bioreactors will be enough to support the main ethanol bioreactor as the cycle time of each seed bioreactor is 36 h (12 h of turnaround time and 24 h of batch time). The input in each bioreactor is 14.9 t/h which includes the inoculum volume, stream 10 and the supplementary nutrients which in this case are corn steep liquor and diammonium hydrogen phosphate. These nutrients provide the necessary nitrogen and phosphorus to the microorganism. There are two output streams from the bioreactor R-201, one vapor stream (stream 16) that comes out from the tower (0.5 t/h) and passes through an absorption column where ethanol is stripped by water. The other stream is a solid/liquid stream (stream 15) that passes through a filtration unit (F-201) where all solids (yeast cells and the remaining solids of orange peel waste) are removed from the liquid. The liquid stream is then mixed with the output from the absorption column (T-201) to form stream 18. The latter enters into the distillation column (T-202). The distillate (stream 19) consists of 95% (w/w) of ethanol with a flowrate of 518.7 kg/h and the product is stored in the tank V-202 with storage capacities for one week. The solid stream (stream 17) after the filtration unit (F-201) enters into a boiler (BH-201) that can process up to 40% moisture content where the solids are burnt to produce HPS to fulfill most of the steam requirements in the hydrolysis process, but also to supply steam to the reboiler E-202. The heat produced by the boiler is 2344 kW that produces 5016 kg/h of saturated steam at 55 bar.

8.3.2 Cost Estimation

The characteristics of each equipment of the two PFDs were determined based on standard engineering procedures, while the f.o.b. cost of each unit operation was calculated using literature-cited data (Peters et al. 2003; Ulrich 1984; Turton et al. 2009). The bare module cost (CBM) was then determined using the chemical engineering plant cost index (CEPCI) and the material factor for each type of equipment. The fixed capital investment is then estimated by using the equation FCI ≈ 1.2 × Total Installed Equipment Cost. The individual cost elements relative to the estimation of the FCI are summarized in Table 8.2. The total installed equipment cost is M$13.8, which leads to a FCI of M$16.6. The most expensive unit operation is the four hydrolysis reactors, which account for the 28.6% of the total CBM followed by the boiler needed to produce 5 t/h HPS, which contributes approximately 20% of the total installed equipment cost. The bioreactor accounts for 12% of the total CBM including the agitator and coil. Finally, the neutralization reactor V-104 and the distillation column T-202 contribute around 7.34 and 7.72% of the total installed equipment cost, respectively.
Table 8.2

Equipment cost of the citrus waste biorefinery

UNIT

Description

f.o.b. cost (M$)

Source

CEPCI

FM

CBM (M$@2012)

C101

CS, 0.7 m width, 100 m length

0.180

PTW, $@2002

396

1.7

0.450

M101

CS, 12.5 t/h

0.271

JBEI, $@2008

576

2.38

0.654

R101

SS316, 1.67 m3, 4 units

4 × 0.487

JBEI, $@2008

576

2.0

3.943

V101

SS316, 1.15 m diameter, 3.45 m height

0.030

PTW, $@2002

396

2.0

0.088

V102

SS316, 1.285 m diameter, 3.85 m height

0.030

PTW, $@2002

396

2.0

0.088

V103

SS304, 25.2 m3

0.065

NREL, $@2009

522

1.8

0.130

V104

SS304, 1000 m3, includes agitator

0.453

NREL, $@2009

522

2.0

1.013

E101

SS304/CS, 1.53 m2

0.008

PTW, $@2002

396

2.2

0.027

E102

SS316/CS, 35.8 m2

0.021

PTW, $@2002

396

2.2

0.066

E103

SS316/CS, 50.6 m2

0.025

PTW, $@2002

396

2.2

0.079

E104

CS/CS, 13.2 m2

0.005

PTW, $@2002

396

2.2

0.015

E105

CS/CS, 74.8 m2

0.010

PTW, $@2002

396

2.2

0.033

Total installed equipment cost of area 100 (M$)

6.586

R201

SS304, 1000 m3, includes agitator & coil

NREL, $@2009

522

1.645

 

5th seed bioreactor 100 m3, SS304

NREL, $@2009

522

0.328

 

4th seed ferm. 10 m3, SS304, skid complete

0.081

NREL, $@2009

522

1.8

0.162

 

3rd seed ferm. 1 m3, SS304, skid complete

0.061

NREL, $@2009

522

1.8

0.122

 

2nd seed ferm. 0.1 m3, SS304, skid complete

0.040

NREL, $@2009

522

1.8

0.080

 

1st seed ferm. 0.01 m3, SS304, skid complete

0.023

NREL, $@2009

522

1.8

0.046

T201

SS316, D = 0.4 m, H = 7 m

0.036

PTW, $@2002

396

2.0

0.106

 

15 sieve trays

0.013

PTW, $@2002

396

1.0

0.019

T202

SS316, D = 0.84 m, H = 38.3 m

0.360

PTW, $@2002

396

2.0

1.065

 

57 sieve trays

0.048

PTW, $@2002

396

1.0

0.070

V201

SS316, D = 0.7 m, H = 2.1 m, horizontal

0.006

PTW, $@2002

396

2.0

0.018

V202

CS gr. C, V = 144 m3, floating roof

0.083

NREL, $@2009

522

1.7

0.158

E201

SS304/CS, 130 m2

0.025

PTW, $@2002

396

2.2

0.079

E202

SS304/CS, 8 m2

0.004

PTW, $@2002

396

2.2

0.021

E203

SS304/CS, 43 m2

0.008

PTW, $@2002

396

2.2

0.041

F201

Centrifuge, 2 kg/s solids, SS316

0.200

PTW, $@2002

396

1.7

0.500

BH201

Boiler, 5 t/h of HPS

1.513

JBEI, $@2008

576

1.8

2.758

Total installed equipment cost of area 200 (M$)

7.218

Total installed equipment cost (M$)

13.8

Fixed capital investment (M$)

16.6

Apart from the capital investment, the total production cost was also estimated. The cost of utilities (C UT ), the labour cost (C OL ), the cost of raw materials (C RM ) and the waste treatment cost (C WT ) were determined. The total production cost without depreciation was calculated based on the following empirical equation (Turton et al. 2009):
$$ TPC_{woD} = 0.18FCI + 2.73C_{OL} + 1.23\left( {C_{RM} + C_{UT} + C_{WT} } \right) $$
(8.3)
The utilities used in this case study are presented in Table 8.3. The total utilities cost is 0.15 M$/y. Due to the heat integration techniques implemented in this design the requirements in HPS were reduced to only 1.2 t/h. High energy requirements are needed in order to agitate the bioreactor. The C WT is estimated by assuming that the non-toxic wastes have a cost of disposal equal to 50 $ per 1000 m3. The wastes produced in this biorefinery are mainly from the bottom of the distillation column T-202 that ends up in stream 20 with a flowrate of 12.4 m3/h. This amount leads to an annual C WT of 2480 $/y, which is insignificant compared to the C UT . To calculate the labour cost, the number of workers required has been estimated for each unit operation based on well-known methods taken from the literature (Turton et al. 2009) and results are shown in Table 8.4.
Table 8.3

Energy requirements and calculation of the utilities cost

UNIT

Electricity (kW)

HPS (t/h)

CW (t/h)

C101

1

  

M101

70

  

A101

170

  

F201

14

  

E101

  

5.6

E102

  

65.6

E203

  

51.5

E104

 

1.2

 

TOTAL

255

1.2

122.7

Cost (M$/y)

0.061

0.080

0.008

Total utilities cost

0.150

Table 8.4

Number of workers required for each unit operation

Type of equipment

Number of units multiplied by required workers

Number of workers

Towers or vessels

8 × 0.25

2.0

Heat exchangers

8 × 0.1

0.8

Bioreactors

1 × 0.5

0.5

Boiler

1 × 0.5

0.5

Filter

1 × 0.5

0.5

Cutter

1 × 0.5

0.5

Conveyor

1 × 0.5

0.5

 

Total number of workers

5.3

The annual operating labor cost is 720,000 $/y (the annual salary of each worker is 30,000 $). The cost of raw material is calculated by multiplying the annual requirements of each raw material with its unitary cost (Table 8.5). Orange peel wastes are considered to have null price as their transportation will be minimized as the plant will be constructed in an existing orange juice factory. The rest of the chemicals needed for the hydrolysis, neutralization and fermentation process have an insignificant effect mainly due to the low amounts required. The total C RM is M$ 0.96. The requirements in corn steep liquor and diammonium hydrogen phosphate were determined so as to have 2.5 kg corn steep liquor per t broth and 0.33 kg diammonium hydrogen phosphate per m3. By using the above data and implementing (8.3), the TPCWoD was measured at M$ 5.26 per year. The revenues of the plant were calculated similarly as the C RM . The amount of ethanol produced is 2075 t/y and the amount of d-limonene is 495 t/y. As the unit price of limonene is very high compared to ethanol most of the revenues (>70.4%) comes from this source (see Table 8.6). The total revenues account for M$ 7.025. The NPV in $ and the MSP in $/kg of ethanol was then calculated for different interest rates (IR) and ethanol selling prices. Results are shown in Fig. 8.5. The NPV is above zero for interest rate values lower than 8.5% for an ethanol selling price of 1 $/kg. The IRR is higher than 10% for an ethanol selling price higher than 1300 $/t.
Table 8.5

The cost of raw materials

Material

kg/h

t/y

Unit cost $/t

Total $/y

Orange peel waste

12,500.0

50,000.0

0.0

0

H2SO4 98%

39.0

156.0

100.0

15,600

Process water

2650.0

10,450.0

0.5

5225

NaOH

31.2

125.0

400.0

50,000

Corn steep liquor

33.0

132.0

60.0

7920

diammonium hydrogen phosphate

4.4

17.4

1000.0

17,400

TOTAL CRM

96,145

   
Table 8.6

Calculation of the annual revenues of the orange peel waste biorefinery

Product

t/y

Unit price ($/t)

Revenues in M$

Ethanol

2075

1000

2,075,000

Limonene

495

10,000

4,950,000

Total revenues

7,025,000

Fig. 8.5

NPV and selling price of ethanol for different IR and IRR, respectively

8.4 Discussion and Conclusions

Currently, most of the citrus industries use their orange peels wastes for cattle feed (Rivas-Cantu et al. 2013) or dispose them as wastes without any recovery of value-added products, while very few of them extract the essential oils (Anagnostopoulou 2005). The option of using citrus wastes as animal feed provides low profits as the production process reduces significantly the overall profit due to intensive drying and the transportation cost. Apart from economic issues for not extracting the essential oils, there are also environmental concerns due to the fact that volatile compounds are emitted to the atmosphere during the drying process of the citrus waste when it is used as animal feed.

Rivas-Cantu et al. (2013) stressed the necessity to cover the technological gaps for successful hydrolysis of citrus waste by optimizing process conditions and equipment as this material differs from lignocellulosic biomass. The authors have emphasized on the improvement in the hydrolysis process regarding the enhancement of sugar production yield and the reduction of processing time by reducing the size of citrus peel particles (Rivas-Cantu et al. 2013).

Grohmann (2007) evaluated the viability of an ethanol production plant from citrus peel by implementing experimental trials in pilot scale bioreactors (0.38 and 3.78 m3) and in an industrial scale bioreactor (37.9 m3). Grohmann (2007) evaluated two options for bioconverting citrus wastes into ethanol. The first one was by enzymatic hydrolysis followed by fermentation, while the second approach involved steam pretreatment of citrus wastes followed by d-limonene removal and finally simultaneous saccharification and fermentation. The advantages of the second approach were numerous regarding both economic and technical issues. d-limonene provides an essential income on plant’s revenues, microbial inhibition is decreased as d-limonene is a toxic compound, steam pretreatment pasteurize citrus wastes and hence contamination issues are reduced. Grohmann (2007) also compared the cost of ethanol production from citrus waste with the one obtained via corn processing. Ethanol production from a citrus waste processing plant lead to a higher total income per liter (0.576 $/L contrary to 0.544 $/L from corn processing).

Zhou et al. (2007) have also carried out an economic analysis of ethanol production from citrus peel waste. The authors compared the production cost of ethanol produced from three different raw materials: starch, cellulose and citrus peels. It seems that the ethanol production cost from citrus waste (0.325 $/L) is considerably lower than the production cost of ethanol from cellulose (0.430 $/L) and only slightly higher than the production cost of ethanol from starch (0.264 $/L). The main contributor to the ethanol production cost was the cost of chemicals, waste disposals and utilities, while the plant producing ethanol from citrus waste was benefited by the high revenues obtained due to d-limonene recovery (Zhou et al. 2007).

Pourbafrani et al. (2010) carried out a laboratory study for the valorization of citrus wastes for the production of ethanol, biogas, d-limonene, pectin and animal feed. The authors first implemented a diluted acid hydrolysis in a 10 L high pressure reactor with the addition of steam. Optimum conditions were examined by the authors by conducting a central composite design. Limonene was recovered by flashing the content of the reactor after hydrolysis. The hydrolysates were then processed in a centrifugation. The solid fraction was used in the anaerobic digester for biogas production, while the liquid stream was used for pectin extraction and ethanol production. From 100 kg of citrus waste with a moisture content of 80%, 0.89 L of d-limonene and 3.88 kg of pectin were extracted and 3.96 L of ethanol and 45 m3 of methane were produced (Pourbafrani et al. 2010). The previous experimental study was developed in a process design and economic analysis without the extraction of pectin in Aspen Plus (Lohrasbi et al. 2010). Increasing the plant capacity results in decreasing ethanol production cost from around 2.5 $/L at 25,000 t/y to approximately 0.5 $/L at 400,000 t/y. Apart from the credit from d-limonene, there is also a significant income from biogas produced during the anaerobic digestion. The authors have considered a cost of raw material equal to 10 $/t due to transportation. If the facilities of the CW plant are integrated in an existing juice production plant, this cost can be reduced to zero resulting in an ethanol production cost of around 0.3 $/L for a plant capacity of 400,000 t/y (Lohrasbi et al. 2010).

All the studies presented above focusing on techno-economic evaluation of food waste valorisation, including the studies on the valorization of citrus waste, underline the necessity of using as many as possible, if not all, fractions of food waste for the production of various chemicals together with biofuels and energy. Economically viable biorefineries can be realized only if preliminary techno-economic studies illustrate key factors that affect the profitability criteria of these new investments. This chapter examines the economic sustainability of a base case scenario utilizing citrus waste for the production of d-limonene and ethanol. Also, high pressure steam is generated for the needs of the facility from the citrus residues after the fermentation process. In the citrus waste biorefinery, compounds with high added value such as d-limonene, pectin and flavonoids contained in citrus waste should be extracted first leaving the lignocellulosic fraction to be used as feedstock in the fermentation process for the production of biofuels or chemicals. The results presented in this chapter illustrate that more than 70% of the revenues are coming from d-limonene. If only bioethanol was produced, profits could be only reached for very large production capacities (i.e. higher than 200,000 t/y). Furthermore, the application of heat integration is essential in order to minimize the cost of utilities. In the proposed process, the fractions that are not used for the production of bioethanol are burnt in a boiler generating around 80% of the steam requirements of the plant. Profitability indicators are also expected to be improved if bioethanol production is replaced by chemical production via fermentation.

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Copyright information

© Springer International Publishing AG 2017

Authors and Affiliations

  • Anestis Vlysidis
    • 1
  • Apostolis Koutinas
    • 1
    Email author
  • Ioannis Kookos
    • 2
  1. 1.Department of Food Science and Human NutritionAgricultural University of AthensAthensGreece
  2. 2.Department of Chemical EngineeringUniversity of PatrasPatrasGreece

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