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An integrated strategy targeting drying and cooling unit operations to improve economic viability and reduce environmental impacts in a mango processing plant

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Abstract

An integrated strategy of replacing boiler fuel and vapour compression cooling technology in dried mango chips processing plant powered on-grid and off-grid was investigated. Three scenarios for each power setting were studied: on-grid: coal as boiler fuel and conventional vapour compression chiller (CVCC) for cooling (scenario 1), mango seed as boiler fuel and CVCC for cooling (scenario 2) and mango seed as boiler fuel and adsorption cooling system (ACS) for cooling (scenario 3). Off-grid scenarios 4, 5 and 6 corresponded to on-grid scenarios 1, 2 and 3, respectively. Greenhouse gas (GHG) emissions and economic viability for each scenario were based on material and energy balances and South African economic conditions, respectively. On-grid scenario 3 showed the greatest potential for reducing emissions, emitting 7.10 × 105 kg CO2eq per annum and had best internal rate of return (IRR) of 25.33% compared to scenarios 2 and 1 with 7.21 × 105 kg CO2eq and 7.89 × 105 kg CO2eq emissions per annum and IRR of 20.33% and 17.48%, respectively. In off-grid, scenario 6 emitted the least GHG of 6.90 × 105 kg CO2eq and had the highest IRR of 24.84% compared to scenarios 5 and 4 with 6.98 × 105 kg CO2eq and 7.67 × 105 kg CO2eq emissions per annum and IRR of 18.88% and 16.09%, respectively. However, scenarios 3 and 6 had the highest energy demand due to mango seed drying. Nevertheless, the integrated intervention shows a great potential of reducing environmental impacts and improving the economic viability of a dried mango chips processing plant by using renewable biomass fuel and ACS that utilizes boiler waste heat. Mango seed can be solar dried to reduce increased energy demand.

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Abbreviations

TS:

Total solid

TCI:

Total capital investment

CVCC:

Conventional vapour compression cooler/chiller

LCAC:

Low-cost adsorption chiller/cooler

ACS:

Adsorption chiller

\(C\) :

Equipment cost at the current year

\(C_{\text{O}}\) :

Equipment cost at some time in the past

CEPCI:

Chemical engineering plant cost index

\(C_{{p,{\text{solid}}}}\) :

Specific heat of dried product (J/kg °C)

\(C_{{p,{\text{water}}}}\) :

Specific heat of water (J/kg °C)

GWP:

Global warming potential

IRR:

Internal rate of return

\(m_{\text{fuel}}\) :

Amount of diesel fuel used by the truck (kg)

\(M\) :

Scaled-up equipment capacity

\(M_{\text{O}}\) :

Original equipment capacity

\(m_{\text{solid}}\) :

Mass of final dried product (kg)

\(m_{\text{water}}\) :

Mass of water evaporated product (kg)

NPV:

Net present value

\(P_{\text{elect}}\) :

Electrical power requirement of the equipment (kW)

\(Q_{\text{useful}}\) :

Useful fraction of the fuel energy used in the process (J)

\(Q_{\text{elect}}\) :

Electrical heat generated (J)

\(Q_{\text{dryer}}\) :

Total energy required for drying (J)

\(Q_{\text{solid}}\) :

Energy required to raise the temperature of mango chips from room temperature to the final product drying temperature (J)

\(Q_{\text{sensible}}\) :

Energy required to raise temperature of water in the mango chips to 100 °C (J)

\(Q_{\text{latent}}\) :

Latent heat of vaporization of water (J)

\(Q_{\text{fuel}}\) :

Heating value of the diesel (MJ/kg)

\(Q_{\text{trans}}\) :

Transportation energy consumed (MJ)

\(M_{\text{compost}}\) :

Mass of waste to be composted

\(t\) :

Working duration (h)

\(T_{\text{f}}\) :

Final product drying temperature (°C)

\(T_{\text{i}}\) :

Initial drying temperature (°C)

\(\eta_{\text{th}}\) :

Combustion efficiency

\(\lambda_{100}\) :

Enthalpy of vaporization of water at 100 °C (J/kg)

\(\eta\) :

Truck engine efficiency

n :

Scaling index

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Acknowledgements

Authors are grateful for the financial support by the National Research Foundation (NRF) of South Africa under the Research and Technology Fund (RTF) and the Department of Process Engineering, Stellenbosch University. The authors are also thankful to Hoedspruit Fruit Processors (South Africa) for providing the technical information needed for this study.

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Authors and Affiliations

  1. Department of Process Engineering, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa

    Aaron Dzigbor & Annie Chimphango

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  1. Aaron Dzigbor
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  2. Annie Chimphango
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Corresponding author

Correspondence to Annie Chimphango.

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Dzigbor, A., Chimphango, A. An integrated strategy targeting drying and cooling unit operations to improve economic viability and reduce environmental impacts in a mango processing plant. Clean Techn Environ Policy 21, 139–153 (2019). https://doi.org/10.1007/s10098-018-1623-2

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  • DOI: https://doi.org/10.1007/s10098-018-1623-2

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