# Heat Integration of an Industrial Unit for the Ethylbenzene Production

^{1}

^{2}

^{*}

## Abstract

**:**

_{min}is determined, which is limited by the technological conditions of the process. Additionally, two different heat pump (HP) integration options and the joint retrofit Pinch project with HP integration are under consideration. The economic analysis of each of the projects was carried out. It is shown that the best results will be obtained when implementing the joint project. As a result, steam consumption will be reduced by 34% and carbon dioxide emissions will be decreased by the same amount.

## 1. Introduction

## 2. Methods

## 3. Description of the EB Production Process

^{2}. In addition to the main reaction, a number of side reactions occur with the production of polyalkylbenzenes (di, tri, tetra-ethylbenzene). As a result of the reaction of alkylation and transalkylation, a thermodynamic equilibrium composition of the reaction products is established. The selectivity of the process and the quality of marketable products do not change with a change in temperature in the specified range.

^{2}, then returns back to the K-52; the bottom liquid of the K-62 column into the T-63 boiler, heated by steam 28 kgf/cm

^{2}, then returns back to the K-62; steam condensate from E- 83/1.2 vat liquid of column K-72 enters the boiler T-73, heated by steam 28 kgf/cm

^{2}, then returns back to K-72; benzene charge (fresh and returnable benzene) from containers E-13, E-14 and benzene-distillate from E-41, into the heat exchanger T-48 and into the heat exchanger T-48b then enters the K-42; part of the bottom liquid of the K-42 column (hot jet) is heated in the T-43 boiler, which is heated with steam 2.5 kgf/cm

^{2}, then returns back to the K-42.

## 4. Determination of the Potential for Energy Saving in the Process of EB Production

_{rec}= 312 kW. Further, using the stream data table and special software [29], composite curves were constructed for the existing EB production process, so that the projection of the overlap of cold and hot composite curves along the stream enthalpy axis was equal to the heat recuperation capacity in the existing HEN unit (Figure 3a). This graphical plot shows clearly the values of the payloads used by the hot and cold utilities process: Q

_{H}

_{min}= 4.962 kW and Q

_{C}

_{min}= 6.647 kW, respectively. The composite curve diagram also shows the Pinch location in the process streams system. The minimum temperature difference between heat carriers in the heat exchange equipment of the existing HEN for vertical heat transfer is ΔT

_{min}= 43 °C, and the Pinch is localized at the Pinch temperature of hot process streams T

_{Hp}= 136 °C and cold streams T

_{Cp}= 93 °C.

_{minopt}is observed (Figure 5).

_{rec}= 838.7 kW, the capacity of hot and cold utilities will be decreased by the same amount, i.e., to the values Q

_{H}

_{min}= 4435.3 kW and Q

_{C}

_{min}= 6119.9 kW, respectively. The Pinch in this case is localized at the Pinch temperatures of hot flows T

_{Hp}= 136 °C and cold flows T

_{Cp}= 96 °C (Figure 3b).

_{min}= 40 °C, is the limiting value with an increase in the heat recovery power in the process under consideration by the methods of classical Pinch analysis. This value is achieved when organizing heat exchange between the technological overhead stream of ethylbenzene vapor from the K-62 column and the hot jet from the K-42 column (Figure 5). The use of this stream as a hot heat carrier for other heat consumers (bottom heating of K-52, K-62, K-72) is limited by its current temperature and the condensation temperature at the initial pressure.

## 5. Integration of the Heat Pump with the EB Production Process

_{TH}= 1441 kW, and W = 250 kW, COP = 6.76.

_{TH}= 1191 kW, and W = 500 kW, COP = 3.38.

^{2}K). In addition, the heat exchange surface area is ~141 m

^{2}(reserve 25%).

## 6. Conclusions

_{2}emissions by 1.0 t/h. It should also be noted that the use of combined thermal integration of ethylbenzene production by classical Pinch analysis methods with optimal integration of a heat pump allows reducing the average steam consumption by more than 30% compared to previously performed works that used only Pinch analysis to integrate ethylbenzene production. This reconstruction option generates the largest capital out of all considered at various values of the interest rate, and its payback period is only inferior to the Pinch integration project.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## Nomenclature

Abbreviations | |

BP | boiling point |

CC | composite curves |

GCC | grand composite curves |

COP | coefficient of performance |

DPP | discount payback period |

EB | ethylbenzene |

HEN | heat exchanger network |

HP | heat pump |

IRR | internal rate of return |

NPV | net present value |

PI | profitability index |

TS | supply temperature |

TT | target temperature |

Symbols | |

CP | flowrate heat capacity (kW) |

Q_{Cmin} | requirement for cold utility (kW) |

Q_{Hmin} | requirement for hot utility (kW) |

Q_{Rec} | heat recovery (kW) |

S | heat exchange surface area of heat exchanger (m^{2}) |

T | temperature (°C) |

Greek Symbols | |

ΔH | change of stream enthalpy (kW) |

ΔT_{min} | minimum allowed temperature difference (°C) |

## Appendix A

**Figure A1.**Aspen Hysys model of ethylbenzene production. CW—cool water; K-42—azeotropic drying tower; K-52—recycle benzene stripper; K-62—rectified ethylbenzene recovery column; K-72—column for separating polyalkylbenzenes from tar; Q—compressor; T—heat exchanger.

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**Figure 2.**Schematic diagram of the unit for the production of ethylbenzene. K—distillation column; CW—cooling water.

**Figure 3.**CC of the ethylbenzene production process. (

**a**) For a process with an existing heat exchange system and ΔT

_{min}= 43 °C; (

**b**) for an integrated process and ΔT

_{min}= 40 °C; 1—hot composite curve; 2—cold composite curve.

**Figure 5.**Dependence of the discounted values on the minimum value of the driving force of heat exchange in the heat energy recovery system of the EB production process. 1—the total present value of the project; 2—the annual cost of the used useful energy; 3—the reduced value of capital investments; dashed lines are not existing values.

**Figure 7.**GCC of the EB production process. Q

_{HP}—heat output transported by the HP, W—is the power on the shaft of the HP compressor.

**Figure 10.**Schematic diagram of operation compression system for the HP integration in the first case.

**Figure 11.**Hysys model step-by-step Pinch integration and HP integration between columns K-62 and K-52.

**Figure 12.**Comparison of the main economic indicators for the projects of the EB production unit retrofit, depending on the value of the Interest rate: (

**a**) For the net present value; (

**b**) discounted payback period. 1—Pinch retrofit; 2—integration of a heat pump between columns K-62 and K-52 (case 1); 3—integration of the heat pump with the column K-62 (case 2); 4—combining Pinch retrofit and option 1.

No | Stream | Type | T_{S} (°C) | T_{T} (°C) | CP (kW/K) | ΔH (kW) |
---|---|---|---|---|---|---|

1 | Steam K-3 | Hot | 114.0 | 27.0 | 8.5 | 740.5 |

2 | Product K-3 | Hot | 114.0 | 44.0 | 8.0 | 557.0 |

3 | Ethylbenzene rectified | Hot | 99.6 | 21.0 | 1.9 | 148.2 |

4 | Steam condensate from E-93 | Hot | 115.0 | 91.0 | 8.0 | 193.6 |

5 | Benzene steam from the top K-52 | Hot | 89.1 | 38.0 | 31.2 | 1595.6 |

6 | Excess benzene from E-56 | Hot | 38.1 | 31.0 | 3.5 | 25.0 |

7.1 | Ethylbenzene rectified steam K-62 | Hot | 136.0 | 136.0 | – | 2088.9 |

7.2 | Ethylbenzene cooling | Hot | 136.0 | 99.5 | 12.2 | 446.4 |

8 | Steam PAB from K-72 | Hot | 90.2 | 42.0 | 3.0 | 146.8 |

9 | Azeotrope steam from K-42 | Hot | 76.9 | 23.0 | 5.9 | 319.0 |

10 | Distillation fluid K-42 | Hot | 92.7 | 90.0 | 37.7 | 100.0 |

11 | Hydrocarbon steam K-112 | Hot | 99.0 | 45.0 | 0.01 | 0.54 |

12 | Sour boiled water from a cube K-112 | Hot | 99.4 | 27.0 | 8.3 | 601.3 |

13 | Alkylate from E-10, E-11, E-12 | Col | 38.0 | 72.0 | 6.2 | 211.7 |

14 | Distillation fluid K-52 | Col | 153.1 | 156.0 | 578.7 | 1691.3 |

15 | Distillation fluid K-62 | Col | 189.5 | 191.3 | 1413.7 | 2441.1 |

16 | Distillation fluid K-72 | Col | 162.3 | 187.0 | 12.3 | 3303.0 |

17 | Benzene charge from E-13, E-14, E-41 | Col | 38.2 | 41.0 | 36.2 | 100.0 |

18 | Hot jet K-42 | Col | 92.7 | 95.8 | 168.3 | 527.1 |

Parameter | Value |
---|---|

Planning horizons, years | 10 |

Saving steam, payload (MW) | 0.53 |

Saving steam (t/h) | 0.90 |

Capital costs including unit and commissioning, USD | 258,503 |

NPV, USD | 956,416 |

IRR,% | 93 |

DPP, year | 3.0 |

PI | 5.0 |

**Table 3.**Comparison of the economic indicators of retrofit projects for the unit of EB production with the integration of a heat pump.

Parameter | HP Option 1 | HP Option 2 | Pinch Project + HP Option 1 |
---|---|---|---|

Planning horizons, years | 10 | 10 | 10 |

Saving steam, payload (MW) | 1.7 | 1.7 | 2.2 |

Saving steam (t/h) | 2.9 | 2.9 | 3.8 |

Capital costs including unit and commissioning, USD | 1,418,600 | 2,730,100 | 1,670,100 |

NPV, USD | 2,614,400 | 3,248,400 | 3,706,300 |

IRR,% | 49 | 34 | 58 |

DPP, year | 4.0 | 4.8 | 3.7 |

PI | 3.0 | 2.3 | 3.4 |

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**MDPI and ACS Style**

Ulyev, L.M.; Kanischev, M.V.; Chibisov, R.E.; Vasilyev, M.A.
Heat Integration of an Industrial Unit for the Ethylbenzene Production. *Energies* **2021**, *14*, 3839.
https://doi.org/10.3390/en14133839

**AMA Style**

Ulyev LM, Kanischev MV, Chibisov RE, Vasilyev MA.
Heat Integration of an Industrial Unit for the Ethylbenzene Production. *Energies*. 2021; 14(13):3839.
https://doi.org/10.3390/en14133839

**Chicago/Turabian Style**

Ulyev, Leonid M., Maksim V. Kanischev, Roman E. Chibisov, and Mikhail A. Vasilyev.
2021. "Heat Integration of an Industrial Unit for the Ethylbenzene Production" *Energies* 14, no. 13: 3839.
https://doi.org/10.3390/en14133839