# Modification of Conventional Sugar Juice Evaporation Process for Increasing Energy Efficiency and Decreasing Sucrose Inversion Loss

## Abstract

**:**

^{2}, and the inlet juice flow rate is 125 kg/s, the optimum modified evaporation process requires extracted steam at a pressure of 157.0 kPa. Under the condition that the fuel consumption rate is 21 kg/s, the cogeneration system that uses the optimum modified evaporation process yields 2.3% more power output than the cogeneration system that uses a non-optimum conventional cogeneration process. Furthermore, sugar inversion loss of the optimum modified process is found to be 63% lower than that of the non-optimum conventional process.

## 1. Introduction

## 2. Conventional Evaporation Process

_{h}

_{,2}) is heated in H2 and H1 to the saturation temperature (T

_{h}

_{,0}), which is 103 °C. This temperature corresponds to a pressure slightly larger than the atmospheric pressure (p

_{atm}). Juice pressure is decreased to p

_{atm}in FC before entering E1. Sugar juice and saturated steam or vapor flow from E1 to E4. The steam turbine (not shown in Figure 1) supplies extracted steam at pressure p

_{0}to E1. Vapor from E1 is sent to P, H1, and E2. Vapor from E2 is sent to H2 and E3. Vapor from E3 is sent to E4. Vapor from E4 is sent to the condenser (not shown in Figure 1). In effect i, water evaporation at pressure p

_{i}

_{+1}is caused by vapor condensation at pressure p

_{i}. Concentrated sugar juice from E4 is sent to P.

## 3. Modified Evaporation Process

_{0}) must not be lower than the minimum value that corresponds to a specified juice mass flow rate. It is possible to remove this constraint by using extracted steam instead of bled vapor for the pan stage in the modified evaporation process.

_{a}is supplied to the pan stage. The model of this process is the same as that of the conventional process with m

_{a}deleted from Equation (1). The mass flow rate of extracted steam required by the pan stage is

_{f}

_{,4}, x

_{4}, and p

_{4}of the modified and conventional evaporation processes are identical. Therefore, the values of m

_{a}of both processes are the same if p

_{a}= 150 kPa.

## 4. Performance Parameters

#### 4.1. Turbine Power Output

_{s}, p

_{s}, T

_{s}. Steam is extracted at the pressure of p

_{0}in the conventional evaporation process. The mass flow rate of extracted steam is m

_{v}

_{,0}. The extracted steam is used for evaporation in the first effect of the evaporator. The remaining steam is condensed at the pressure of p

_{c}. The mass flow rate of condensed steam (m

_{c}) is, therefore, m

_{s}− m

_{v}

_{,0}. The modified evaporation process requires not only extracted steam at the pressure of p

_{0}for evaporation in the first effect of the evaporator but also extracted steam at the pressure of p

_{a}for evaporation in the pan stage. The corresponding mass flow rates of extracted steam are m

_{v}

_{,0}and m

_{a}. The remaining steam is condensed at the pressure of p

_{c}. The mass flow rate of condensed steam (m

_{c}) is, therefore, m

_{s}− m

_{v}

_{,0}− m

_{a}.

_{f,in}, x

_{in}, and x

_{4}are the same in both the conventional evaporation process and the modified evaporation process. Moreover, both systems are assumed to consume the same amount of fuel (m

_{fuel}) in their boilers. Based on these assumptions, the only difference between both systems is turbine power output, which is expressed as

_{t}is isentropic efficiency of the steam turbine, h

_{s}is specific enthalpy at pressure p

_{s}, and temperature T

_{s}, h

_{0s}, h

_{as}, and h

_{cs}are specific enthalpies at, respectively, pressures p

_{0}, p

_{a}, and p

_{c}, and the same entropy as the inlet steam. It should be noted that m

_{a}is zero in the cogeneration system for the conventional evaporation process.

#### 4.2. Sucrose Inversion Loss

_{25}is assumed to be 6.0. The retention time (t) is proportional to the evaporator surface area (A), and inversely proportional to sugar juice mass flow rate (m

_{f}). It may be approximated by assuming that sugar juice flows through N tubes, of which diameter and length are D and L, in an evaporator vessel at the speed of V. The expression of V is

## 5. Results and Discussion

_{in}= 15%, x

_{out}= 70%, p

_{4}= 16 kPa, and T

_{h,}

_{2}= 30 °C. In each process, the total surface areas of the multiple-effect evaporator and the juice heater are, respectively, 13,000 and 2500 m

^{2}. Multiple-effect evaporators in both systems are designed to process 125 kg/s (or 450 t/h) of juice. The optimum distribution of the total evaporator surface area that maximizes the steam economy at a specified extracted steam pressure (p

_{0}) may be determined for each system.

_{1}) of 6000 m

^{2}and the second-effect area (A

_{2}) of 1200 m

^{2}, the optimum value of the third-effect area (A

_{3}) that yields the required juice mass flow rate of 125 kg/s and the maximum steam economy (SE) is 1233 m

^{2}. Figure 4b shows that, for the same value of A

_{1}, the optimum value of A

_{2}that results in maximum SE is 1251 m

^{2}. Figure 4c shows that, as A

_{1}increases, SE decreases, and first-effect pressure (p

_{1}) increases. By requiring that p

_{1}is 150 kPa, the optimum value of A

_{1}is found to be 4518 m

^{2}. The corresponding value of SE is 2.508. Therefore, the mass flow rate of extracted steam for the evaporator (m

_{v}

_{,0}) is 41.63 kg/s.

_{1}) of 4000 m

^{2}and the second-effect area (A

_{2}) of 1100 m

^{2}, the optimum value of the third-effect area (A

_{3}) that yields the required juice mass flow rate of 125 kg/s and the maximum SE is 1723 m

^{2}. Figure 5b shows that, for the same value of A

_{1}, the optimum value of A

_{2}that results in the maximum SE is 1342 m

^{2}. Figure 5c shows the optimum value of A

_{1}that results in the maximum SE is 2074 m

^{2}. The corresponding value of SE is 2.345. Since the mass flow rate of juice leaving E4 (m

_{f}

_{,4}) is 26.79 kg/s, and the mass flow rate of extracted steam for the pan stage (m

_{a}) is 13.16 kg/s, the value of m

_{v}

_{,0}is found to be 31.53 kg/s.

_{v}

_{,0}and P with p

_{0}in cogeneration systems for the conventional and modified evaporation processes that have the optimum distributions of evaporator surface areas. It can be seen that, in each system, there exists the optimum value of p

_{0}(p

_{0,opt}) that results in the maximum turbine power output (P

_{max}). In the cogeneration system for the optimum conventional evaporation process, p

_{0,opt}is 186.8 kPa, and P

_{max}is 29,286 kW. In the cogeneration system for the optimum modified evaporation process, p

_{0,opt}is 157.0 kPa, and P

_{max}is 29,442 kW. It is interesting to compare the cogeneration systems for the optimum modified evaporation process and a non-optimum conventional evaporation process, in which p

_{0}is 200 kPa. The non-optimum conventional process has the same juice processing capacity as the optimum conventional process, but it is less energy efficient. The value of SE in this process is 2.411, and the value of m

_{v}

_{,0}is 43.31 kg/s. The turbine power output of the cogeneration system that uses this process is 28,789 kW, which is 2.3% lower than the turbine power output of the cogeneration system that uses the optimum modified evaporation process. Table 1 shows simulation results of cogeneration systems for the non-optimum conventional evaporation process, the optimum conventional evaporation process, and the optimum modified evaporation process.

## 6. Conclusions

^{2}and total juice heater surface area of 2500 m

^{2}. They were designed to process 125 kg/s of inlet sugar juice. The distribution of evaporator surface area of the optimum modified evaporation process resulted in the maximum steam economy. The pressures of extracted steam supplied to the optimum modified evaporation process were chosen so that the turbine power output of the cogeneration system that used this process was maximized. According to simulation results obtained from the mathematical models developed for this investigation, extracted steam at a mass flow rate of 31.53 kg/s and a pressure of 157.0 kPa was required for the evaporator of the optimum modified evaporation process, and extracted steam at a mass flow rate of 13.16 kg/s and a pressure of 150.0 kPa was required for the pan stage of this process. The turbine power output was 29,442 kW for the cogeneration system that used the optimum modified evaporation process. This power output was 2.3% larger than the power output of the cogeneration system that used a non-optimum conventional evaporation process. Furthermore, since the pressure profile in the evaporator of the optimum modified process was lower than that of the non-optimum conventional process, sucrose inversion loss in the modified process was 63% lower.

## Funding

## Conflicts of Interest

## Nomenclature

A | heat transfer surface of evaporator, m^{2} |

A_{h} | heat transfer surface of juice heater, m^{2} |

c_{p} | specific heat capacity, kJ/kg·°C |

h | specific enthalpy, kJ/kg |

I | mass fraction of lost sugar due to inversion |

m | mass flow rate, kg/s |

P | turbine power output, kW |

p | pressure, kPa |

SE | steam economy |

T | temperature, °C |

t | retention time, min |

U | heat transfer coefficient, kW/m^{2}·°C |

x | concentration of sugar juice, % |

Greek Symbols | |

ε | heat loss coefficient in evaporator |

η_{τ} | turbine efficiency |

ρ | density, kg/m^{3} |

Subscripts | |

a | vapor to pan stage |

b | vapor to juice heater |

c | vapor from flash tank, condenser |

e | flash evaporation |

f | sugar juice |

h | juice heater |

i | effect number |

l | saturated liquid |

s | steam |

v | saturated vapor |

vl | vapor-to-liquid |

x | juice heating inside evaporator vessels |

Superscripts | |

in | inlet of an effect |

out | outlet of an effect |

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**Figure 3.**Cogeneration systems for (

**a**) the conventional evaporation process and (

**b**) the modified evaporation process.

**Figure 4.**Procedure for determining the optimum distribution of evaporator area in the conventional evaporation process driven by extracted steam at a pressure (p

_{0}) of 200 kPa: (

**a**) finding third-effect area (A

_{3}) corresponding to the inlet juice mass flow rate (m

_{f}

_{,in}) of 125 kg/s and the maximum steam economy (SE) corresponding to first-effect area (A

_{1}) = 6000 m

^{2}, and second-effect area (A

_{2}) = 1200 m

^{2}; (

**b**) finding A

_{2}that maximizes SE corresponding to A

_{1}= 6000 m

^{2}; and (

**c**) finding A

_{1}corresponding to the first-effect pressure (p

_{1}) of 150 kPa.

**Figure 5.**Procedure for determining the optimum distribution of evaporator area in the modified evaporation process driven by extracted steam at a pressure (p

_{0}) of 200 kPa: (

**a**) finding A

_{3}corresponding to the inlet juice mass flow rate (m

_{f}

_{,in}) of 125 kg/s and the maximum steam economy (SE) corresponding to A

_{1}= 4000 m

^{2}, and A

_{2}= 1100 m

^{2}; (

**b**) finding A

_{2}that maximizes SE corresponding to A

_{1}= 4000 m

^{2}; and (

**c**) finding A

_{1}that maximizes SE.

**Figure 6.**Variations with extracted steam pressure (p

_{0}) of extracted steam consumption (m

_{v}

_{,0}) and turbine power output (P) of the cogeneration systems that have the optimum distributions of evaporator surface areas for (

**a**) the conventional evaporation process and (

**b**) the modified evaporation process.

**Table 1.**Simulation results of cogeneration systems for the non-optimum conventional evaporation process, the optimum conventional evaporation process, and the optimum modified evaporation process.

Conventional EP | Optimum Modified EP | ||
---|---|---|---|

Non-Optimum | Optimum | ||

A_{1}(m^{2}) | 4695 | 6611 | 4634 |

A_{2} (m^{2}) | 4266 | 1558 | 2409 |

A_{3} (m^{2}) | 2729 | 1335 | 1932 |

A_{4} (m^{2}) | 1310 | 3496 | 4025 |

A_{h}_{,1} (m^{2}) | 80 | 469 | 1399 |

A_{h}_{,2} (m^{2}) | 2420 | 2031 | 1101 |

p_{0} (kPa) | 200.0 | 186.8 | 157.0 |

p_{1}(kPa) | 150.0 | 150.0 | 122.6 |

p_{2} (kPa) | 113.4 | 85.8 | 79.4 |

p_{3} (kPa) | 81.5 | 44.2 | 44.6 |

p_{4} (kPa) | 16.0 | 16.0 | 16.0 |

m_{f}_{,in} (kg/s) | 125.0 | 125.0 | 125.0 |

m_{v}_{,0} (kg/s) | 43.31 | 42.09 | 32.11 |

m_{a} (kg/s) | 13.16 ^{1} | 13.16 ^{1} | 13.16 ^{2} |

m_{fuel} (kg/s) | 21.00 | 21.00 | 21.00 |

P (kW) | 28,789 | 29,286 | 29,442 |

^{1}Vapor bled from the first effect at 150 kPa.

^{2}Extracted steam from turbine at 150 kPa.

**Table 2.**Comparison of sucrose inversion losses in the non-optimum conventional evaporation process, the optimum conventional evaporation process, and the optimum modified evaporation process.

Effect Number | Conventional EP | Optimum Modified EP | |
---|---|---|---|

Non-Optimum | Optimum | ||

1 | 2.95 × 10^{−3}% | 4.16 × 10^{−3}% | 1.58 × 10^{−3}% |

2 | 1.79 × 10^{−3}% | 2.93 × 10^{−4}% | 3.29 × 10^{−4}% |

3 | 6.38 × 10^{−5}% | 5.50 × 10^{−5}% | 7.46 × 10^{−5}% |

4 | 6.15 × 10^{−6}% | 1.59 × 10^{−5}% | 1.77 × 10^{−5}% |

Total | 5.38 × 10^{−3}% | 4.52 × 10^{−3}% | 2.00 × 10^{−3}% |

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**MDPI and ACS Style**

Chantasiriwan, S.
Modification of Conventional Sugar Juice Evaporation Process for Increasing Energy Efficiency and Decreasing Sucrose Inversion Loss. *Processes* **2020**, *8*, 765.
https://doi.org/10.3390/pr8070765

**AMA Style**

Chantasiriwan S.
Modification of Conventional Sugar Juice Evaporation Process for Increasing Energy Efficiency and Decreasing Sucrose Inversion Loss. *Processes*. 2020; 8(7):765.
https://doi.org/10.3390/pr8070765

**Chicago/Turabian Style**

Chantasiriwan, Somchart.
2020. "Modification of Conventional Sugar Juice Evaporation Process for Increasing Energy Efficiency and Decreasing Sucrose Inversion Loss" *Processes* 8, no. 7: 765.
https://doi.org/10.3390/pr8070765