# Evaluation of Jet Flooding in Distillation Column Olefins Plant on Naphtha to LPG Feed Substitution

^{*}

## Abstract

**:**

_{4}components), and pygas (pyrolysis gasoline, a mixture of benzene, toluene, and xylene), all of which are olefins. The cracking furnace and distillation columns are the primary operational units. The raw material is cracked and undergoes reactions in the cracking furnaces, while the distillation columns are responsible for separating the products. Raw material costs account for 80% of production costs. There is also the possibility of using LPG as a less expensive alternative to some of the naphtha. However, changing the raw material would affect the operability of the distillation columns and influence the yield on the cracking side. To determine the optimal naphtha substitution for LPG without causing hydraulic problems (such as jet flooding) in the distillation columns, analysis using simulation tools must be conducted. A reliability model is being developed to simulate the substitution of naphtha with other feed stocks by comparing simulation results with data from the actual plant. The LPG flow is a variable that is freely adjusted to substitute for naphtha. Simulation tools can be used to assess the effects of economically advantageous naphtha substitution for LPG without compromising plant operability. The optimum naphtha substitution rate is 21.14% from the base case, resulting in jet flooding occurring at Propylene Fractionator No. 2. By implementing this substitution, the benefits that can be obtained amount to USD 22,772.02 per hour.

## 1. Introduction

- Jet flooding: This occurs when a distillation column is operated with a high vapor load, causing liquid to be transported over the trays.
- Down comer back flood: when a distillation column is run with a substantial liquid and vapor load, liquid accumulates in the top half of the column.
- Down comer choke flood: excessive vapor flow results in liquid buildup in the trays’ down comers.
- Weeping: low vapor load results in liquid draining from the tray channel.
- Excessive pressure drops: the pressure drop across each tray should not exceed the design limit.
- Turndown ratio: it is essential to feed the distillation column within its operational capacity to maintain acceptable efficiency.

- Demethanizer: This nine-bed distillation column operates at a pressure of 5.8 kg/cm
^{2}and extracts heavier C2 compounds from methane. The top product is methane, with gauge and bottom side temperatures of −53 °C and −131 °C, respectively. - Deethanizer: A distillation column with 177 sieve trays is used to separate C
_{2}compounds (the top product) from C_{3}compounds and heavier substances (the bottom product). It operates at a pressure of 21.3 kg/cm^{2}, with top side and bottom side temperatures of −23 °C and 66 °C, respectively. - Ethylene Fractionator: With 137 sieve trays, this distillation column separates ethylene and ethane. It operates at pressures of 16.48 kg/cm
^{2}, with top side and bottom side temperatures of −35 °C and −12 °C, respectively. - Depropanizer No. 1: This distillation column, equipped with 48 sieve trays, separates C
_{3}compounds (the top product) from heavier C4 compounds (the bottom product). It operates at a pressure of 16.7 kg/cm^{2}, with a top side temperature of 44 °C and a bottom side temperature of 82 °C. - Depropanizer No. 2: Using 30 sieve trays, this distillation column separates C
_{3}compounds (the top product) from heavier C4 compounds (the bottom product). It operates at a pressure of 6.1 kg/cm^{2}, with top side and bottom side temperatures of 38.2 °C and 82 °C, respectively. - Propylene Fractionator No. 1: With 55 valve trays, this distillation column separates C
_{3}compounds from propane. It operates at a pressure of 19.7 kg/cm^{2}, with top side and bottom side temperatures of 50 °C and 58 °C, respectively. - Propylene Fractionator No. 2: Propylene and propane are separated using 149 sieve trays in this distillation column, which operates at pressures of 19.2 kg/cm
^{2}and temperatures of 46 °C (top side) and 50 °C (bottom side). - Propylene Fractionator No. 3: Propylene and propane are separated using 210 sieve trays in this distillation column, which operates at pressures of 18.3 kg/cm
^{2}and temperatures of 46 °C (top side) and 58 °C (bottom side). This column can be interchanged with Propylene Fractionator No. 1 and No. 2. - Debutanizer: This distillation column, equipped with 34 valve trays, separates C4 compounds (the top product) from C5 compounds and heavier substances (the bottom product). It operates at a pressure of 4.34 kg/cm
^{2}, with top side and bottom side temperatures of 47 °C and 116 °C, respectively.

_{h}= hole diameter, mm; $\mathsf{\sigma}$ = surface tension, mN/m (dyn/cm); ${\rho}_{G}$, ${\rho}_{L}$ = vapor and liquid densities, kg/m

^{3}; TS = tray spacing, mm; h

_{ct}= clear liquid height at froth to spray transition, mm; h

_{ct}is obtained from the Equation (2):

_{, H2O}derived from Equation (3)

^{3}liquid down flow/(h,m weir length) and ${A}_{f}$= fractional hole based on active bubbling area; for example, derived from Equation (5).

## 2. Data Input and Methods

#### 2.1. Data Input

- Distillation column data sheets, which provide information about the geometry of each column.
- Actual operating conditions of each distillation column, including pressure, temperature, flow rate, and composition. These operating conditions are derived from actual plant data.
- Naphtha composition, which serves as the basis for the study.

- d.
- Naphtha flow rate basis for study.

- e.
- Feed composition of LPG feed for substitute naphtha use for study.

- f.
- LPG flow rate basis for study.

#### 2.2. Methods

#### 2.2.1. Theory

_{ct}was subsequently obtained from Equation (3) and can be applied to calculate the percentage flood for each distillation column. This percentage indicates the extent to which the column is operating at or near its flood capacity, as calculated in Equation (7). It is important to note that the accuracy of these predictions may vary, and it is recommended to validate the results against actual plant data to ensure reliability.

#### 2.2.2. Fluid Package Selection

#### 2.2.3. Model Development

- (a)
- Ideal solution: Both vapor and liquid phases are assumed to be ideal solutions, and constant average relative volatilities are considered. This assumption simplifies the thermodynamic calculations involved in the separation process.
- (b)
- Condenser and operating conditions: The column top temperature is estimated based on the assumed condenser operating pressure. The feed and reflux streams are assumed to be at their dew point and bubble point, respectively. A total condenser is assumed for the reflux condenser.
- (c)
- Constant molal overflow: The assumption of constant molal overflow simplifies the calculation of liquid and vapor flows in the column.
- (d)
- Stage efficiency: The stages in the column are initially assumed to be 100% efficient with respect to mass transfer. However, adjustments may be made to match the simulation results with actual plant conditions.
- (e)
- Pressure drop and reboiler temperature: The pressure drop through the tower is calculated based on the sieve tray characteristics. The temperature of the reboiler is estimated based on the tower bottom pressure.
- (f)
- Stream configuration: The distillation column is assumed to have only the feed, distillate, and bottoms streams, without any other side streams.
- (g)
- Uniform composition: The liquid hold-up in the reboiler, reflux drum, and on each tray of the column is assumed to be well-mixed with uniform composition.
- (h)
- Negligible dynamics: The dynamics of the piping, reboiler, and condenser are considered negligible, implying that there are no significant time lags in the system. Vapor phase dynamics are neglected as they are much faster compared to the liquid phase.
- (i)
- Constant liquid hold-ups: The liquid hold-ups are assumed to be constant on each tray, as well as in the reboiler and reflux drums.
- (j)
- Adiabatic column: The column is assumed to be adiabatic, neglecting any heat release from components. Decay heat is also neglected in this case.
- (k)
- Actual feed composition: The feed composition to the column is obtained from actual plant operation data, ensuring that the model reflects the real-world conditions.
- (l)
- The equations for the non-equilibrium state describe liquid and heat accumulation. The equilibrium conditions are only valid at bubble point temperature. Once the bubble point temperature is reached, the equations are switched to the equilibrium state. We assumed that all the vapor entering the stage is condensed until the temperature on each stage reaches the equilibrium state.

#### 2.2.4. Model Validation

#### 2.2.5. Sensitivity Analysis Substitution of Naphtha to LPG into % Flooding

#### 2.2.6. Economic Calculation

#### Determine the Relevant Flow Rates

#### Determine the Relevant Prices

#### Determine the Utilities Cost

## 3. Results and Discussion

#### 3.1. Simulation Matching with Actual Plant Data

#### 3.2. Sensitivity Anaysis

#### 3.3. Economical Evaluation

## 4. Summary and Conclusions

## Supplementary Materials

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## Nomenclature

Greek Symbols | |

σ | surface tension, mN/m (dyn/cm) |

$\rho $ | vapor and liquid densities, kg/m^{3} |

Latin Symbols | |

Q_{L} | liquid down flow, m^{3}/h |

A_{f} | fractional hole based on active bubbling area, m^{2} |

d_{h} | hole diameter, mm |

Csb | Kister and Haas correlation for jet flooding |

AAPE | Absolute Percent Error, % |

RMS | R-squared value or root-squared-mean values |

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**Figure 1.**Olefins plant (PT Chandra Asri, 2021), as indicated in the block diagram product portfolio of olefins plant under study [5].

**Figure 4.**Parity plot of % flooding based on Equations (1)–(6) for (

**a**) Demethanizer, and (

**b**) Deethanizer column with % naphtha substitution to LPG in Table 3. The solid line correspondence to regression result and R-squared value is shown in the graph.

**Figure 5.**Parity Plot of % flooding based on Equations (1)–(6) for (

**a**) Ethylene Fractionator, and (

**b**) Depropanizer No. 1 column with % naphtha substitution to LPG in Table 3. The solid line correspondence to regression result and R-squared value is shown in the graph.

**Figure 6.**Parity plot of % flooding based on Equations (1)–(6) for (

**a**) Depropanizer No. 2, and (

**b**) Propylene Fractionator No. 1 column with % naphtha substitution to LPG in Table 3. The solid line correspondence to regression result and R-squared value is shown in the graph.

**Figure 7.**Parity plot of % flooding based on Equations (1)–(6) for (

**a**) Propylene Fractionator No. 2, (

**b**) Propylene Fractionator No. 3, and (

**c**) Debutanizer with % naphtha substitution to LPG in Table 3. The solid line correspondence to regression result and R-squared value is shown in the graph.

**Table 1.**Feed composition of LPG feed component correspondence for chemical compound in naphtha feed, based on lab sampling results.

Number of Carbons | Composition (% wt) | |||
---|---|---|---|---|

n-Paraffins | Iso-Paraffins | Naphthalene | Aromatics | |

4 | 0.22 | 2.64 | ||

5 | 25.22 | 17.94 | 4.19 | |

6 | 14.88 | 23.41 | 2.82 | 2.0 |

7 | 1.67 | 3.27 | 0.97 | |

8 | 0.57 | |||

Total | 41.99 | 47.83 | 7.01 | 3.17 |

**Table 2.**Feed composition of LPG feed component correspondence for chemical compound in LPG feed, based on lab sampling results.

Component | Unit | Specification |
---|---|---|

Propane | % w.t | <1 |

N-butane | % w.t | >73 |

Iso-butane | % w.t | <23 |

Number of Furnaces Run with Naphtha Feed | Number of Furnaces Run with LPG Feed | Flow Rate of Naphtha (t/h) | Flow Rate of LPG (t/h) | % Substitution of LPG to Naphtha |
---|---|---|---|---|

7 | 0 | 252 | 0 | 0.00 |

6 | 1 | 216 | 36 | 14.28 |

5 | 2 | 180 | 72 | 28.57 |

4 | 3 | 144 | 108 | 42.84 |

3 | 4 | 108 | 144 | 57.12 |

2 | 5 | 72 | 180 | 71.40 |

1 | 6 | 36 | 216 | 85.68 |

0 | 7 | 0 | 252 | 100.00 |

**Table 4.**Summary of column under study, Fluid Package in ASPEN HYSYS selected based on guideline of properties in each column under study [11].

Column | Fluid Package in ASPEN HYSYS |
---|---|

Demethanizer | UNIQUAC |

Deethanizer | Peng-Robinson |

Ethylene Fractionator | Peng-Robinson |

Depropanizer No. 1 | Peng-Robinson |

Depropanizer No. 2 | Peng-Robinson |

Propylene Fractionator No. 1 | SRK-Twu (Soave-Redlich-Kwong) |

Propylene Fractionator No. 2 | SRK-Twu (Soave-Redlich-Kwong) |

Propylene Fractionator No. 3 | SRK-Twu (Soave-Redlich-Kwong) |

Debutanizer | Peng-Robinson |

**Table 5.**Cost reference for economic calculation, data taken from plant data year 2022 [4].

Description | Unit | Price |
---|---|---|

Naphtha | $/ton | 835 |

LPG | $/ton | 750 |

Ethylene | $/ton | 1230 |

Propylene | $/ton | 1310 |

Mixed C4 | $/ton | 560 |

Pygas | $/ton | 621 |

Utilities Cost | $/ton product | 8.9 |

**Table 6.**Summary of assessment simulation result in ASPEN HYSYS compare with actual plant data, Fluid Package in ASPEN HYSYS selected based on guideline of properties in each column under study [11], column efficiency as trial result by following rule of thumb in distillation column operating [13], and the average absolute percent error (AAPE) to assess the goodness of fit.

Column | Fluid Package in ASPEN HYSYS | Column Efficiency (%) | AAPE (%) |
---|---|---|---|

Demethanizer | UNIQUAC | 72.87 | 0.81 |

Deethanizer | Peng-Robinson | 74.31 | 0.92 |

Ethylene Fractionator | Peng-Robinson | 71.92 | 0.77 |

Depropanizer No. 1 | Peng-Robinson | 73.14 | 0.84 |

Depropanizer No. 2 | Peng-Robinson | 73.19 | 0.95 |

Propylene Fractionator No. 1 | SRK-Twu (Soave-Redlich-Kwong) | 74.15 | 0.88 |

Propylene Fractionator No. 2 | SRK-Twu (Soave-Redlich-Kwong) | 74.92 | 1.12 |

Propylene Fractionator No. 3 | SRK-Twu (Soave-Redlich-Kwong) | 74.08 | 1.13 |

Debutanizer | Peng-Robinson | 73.12 | 1.15 |

**Table 7.**Summary of the goodness of fit using the correlation (Equations (1)–(6)) for % flooding as compared to % naphtha substitution with LPG. The goodness of fit is quantified using root-mean-squared error (RMS). In each distillation column under study, the maximum amount of % naphtha substitution with LPG when % flooding hit 100% is also presented.

Column | Maximum Percentage Naphtha Substitution to LPG (%) | RMS |
---|---|---|

Demethanizer | 38.47 | 0.94 |

Deethanizer | 31.14 | 0.90 |

Ethylene Fractionator | 29.73 | 0.84 |

Depropanizer No. 1 | 27.14 | 0.89 |

Depropanizer No. 2 | 31.25 | 0.89 |

Propylene Fractionator No. 1 | 23.97 | 0.87 |

Propylene Fractionator No. 2 | 21.14 | 0.85 |

Propylene Fractionator No. 3 | 22.73 | 0.88 |

Debutanizer | 26.87 | 0.87 |

**Table 8.**Data input for economic evaluation as required for calculating Equation (8); data calculated from validated model with limitation feed flow rate % LPG from naphtha based on minimization result of Table 7.

Data | Unit | Value |
---|---|---|

% LPG from Naphtha Max. for Substitution | % | 21.14 |

Flow Rate Naphtha | Ton/hour | 198.07 |

Flow Rate LPG | Ton/hour | 53.93 |

Flow Rate Ethylene Product | Ton/hour | 100.03 |

Flow Rate Propylene Product | Ton/hour | 55.18 |

Flow Rate Mixed C_{4′}s Product | Ton/hour | 34.98 |

Flow Rate Pygas Product | Ton/hour | 25.14 |

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**MDPI and ACS Style**

Wijanarko, A.; Hidayat, M.; Sutijan, S.
Evaluation of Jet Flooding in Distillation Column Olefins Plant on Naphtha to LPG Feed Substitution. *ChemEngineering* **2023**, *7*, 63.
https://doi.org/10.3390/chemengineering7040063

**AMA Style**

Wijanarko A, Hidayat M, Sutijan S.
Evaluation of Jet Flooding in Distillation Column Olefins Plant on Naphtha to LPG Feed Substitution. *ChemEngineering*. 2023; 7(4):63.
https://doi.org/10.3390/chemengineering7040063

**Chicago/Turabian Style**

Wijanarko, Albertus, Muslikhin Hidayat, and Sutijan Sutijan.
2023. "Evaluation of Jet Flooding in Distillation Column Olefins Plant on Naphtha to LPG Feed Substitution" *ChemEngineering* 7, no. 4: 63.
https://doi.org/10.3390/chemengineering7040063