# Energy Efficiency Analysis of the Refining Unit in Thermo-Mechanical Pulp Mill

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## Abstract

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## 1. Introduction

- A new variable, corrected refining specific energy consumption (CRSEC), is introduced and practiced to better represent the refining process’s energy efficiency.
- A MATLAB Simulink model is developed to refining energy simulation for the longer-term time interval.
- The effect of refining disturbance variables, mainly refining plate erosion, on refining motor load simulation is evaluated.

## 2. Materials and Methods

#### 2.1. Refining Process

#### 2.2. Principal Manipulated Variables

#### 2.3. Disturbance Variables

#### 2.4. Principal Operating Variables

#### 2.5. High Consistency Refiner Energy Simulation

## 3. Results and Discussion

#### 3.1. Refining Simulation Model

#### 3.2. Energy Efficiency

## 4. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Nomenclature

$MAPE$ | Mean-absolute percentage error |

CFD | computational fluid dynamic |

Variables | |

$R$ | Correlation coefficient |

${R}^{2}$ | Determination coefficient |

${C}_{i}$ | ith model coefficient |

$Ml$ | Refining motor load |

$M{l}^{old}$ | predicted refining motor load by the Basic MATLAB Simulink model |

$M{l}^{corrected}$ | corrected value of motor load by the deterioration function |

$M{l}^{measured}$ | measured value of refining motor load |

$POT$ | plate operation time |

$RH$ | Refining recovered heat in the heat recovery unit |

$ERGH$ | Energy from refining generated heat |

$RSEC$ | Refining specific energy consumption |

$CRSEC$ | Corrected refining specific energy consumption |

$DHD$ | district heating demand |

Indices | |

$i$ | model coefficients index |

$k$ | data point index |

$n$ | number of data |

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**Figure 2.**The common refiner types with pulp inlet and flow directions: (

**a**) single disc, and (

**b**) Double disc.

**Figure 5.**MATLAB Simulink toolbox model for the two-stage Thermo-mechanical pulping process (This model has been used in the case study of MPC Supervisory Control of a Two Stage Thermo-Mechanical Pulping Process, Model Predictive Control Toolbox, MATLAB R2019a).

**Figure 6.**Relationship between refining variables and primary pulp consistency (

**a**), primary motor load (

**b**), and primary refining evaporated water (

**c**). (MATLAB Thermo-mechanical pulping Simulink toolbox model).

**Figure 8.**Measured and predicted (basic model) refining characteristics for: (

**a**) short-term (

**b**) long-term analysis.

**Figure 9.**Measured and predicted (developed model) refining characteristics for long-term analysis (plate 1).

**Table 1.**Basic MATLAB Simulink model results for short- and longer-term prediction of refining motor load.

Parameter | Short-Term Analysis | Longer-Term Analysis |
---|---|---|

$MAPE$ | $1.1\%$ | $8\%$ |

${R}^{2}$ | $80\%$ | $30\%$ |

Coefficient | Min | Max |
---|---|---|

${C}_{1}$ | −1.48 | −0.65 |

${C}_{2}$ | 0.92 | 1.25 |

${C}_{3}$ | −0.00662 | −0.00232 |

${C}_{4}$ | 0.012 | 0.046 |

Parameter | Refining Motor Load (ML) | Difference% w.r.t Basic Model |
---|---|---|

$MAPE$ | $1.7\%$ | −78.75% |

${R}^{2}$ | $78\%$ | 160% |

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**MDPI and ACS Style**

Talebjedi, B.; Laukkanen, T.; Holmberg, H.; Vakkilainen, E.; Syri, S.
Energy Efficiency Analysis of the Refining Unit in Thermo-Mechanical Pulp Mill. *Energies* **2021**, *14*, 1664.
https://doi.org/10.3390/en14061664

**AMA Style**

Talebjedi B, Laukkanen T, Holmberg H, Vakkilainen E, Syri S.
Energy Efficiency Analysis of the Refining Unit in Thermo-Mechanical Pulp Mill. *Energies*. 2021; 14(6):1664.
https://doi.org/10.3390/en14061664

**Chicago/Turabian Style**

Talebjedi, Behnam, Timo Laukkanen, Henrik Holmberg, Esa Vakkilainen, and Sanna Syri.
2021. "Energy Efficiency Analysis of the Refining Unit in Thermo-Mechanical Pulp Mill" *Energies* 14, no. 6: 1664.
https://doi.org/10.3390/en14061664