Analysis on heat exchange network and available energy of wax oil hydrocracking unit optimized by pinch technology in 2017

State Key Laboratory of Fine Chemicals, Dalian University of Technology, Research and Development Center of Membrane Science and Technology, Dalian 116024, Liaoning Province; 2 Sinopec Fushun Petrochemical Research Institute, Fushun, Liaoning 113001; 3 Beijing WorleyParson Engineering Technology Co., Ltd., Beijing 100015)

Abstract: For a 1.5 million ton wax oil hydrocracking unit in a refinery, the process flow of single stage series connection+cold high pressure separation+atmospheric tower+vacuum tower+light hydrocarbon absorption tower is adopted. Based on production data, Aspen Plus software is used to simulate each unit module of the reaction part and separation part of the unit. Through parameter adjustment, the simulation results are in good agreement with the calibration data, and then the thermodynamic parameters of each stream are obtained. The energy efficiency of the heat exchanger network is analyzed by combining the pinch technology, and then the energy "bottleneck" in the process flow is found. Under the premise of not changing the main equipment of the device, the existing heat exchanger network is optimized and the energy saving scheme is obtained by simulation calculation. At the same time, the energy consumption of the heat exchanger network before and after the transformation is evaluated by using the effective energy analysis method. After optimization, the consumption of thermal utilities is 25709kW, saving 42.20% compared with the original process flow, and the consumption of cold utilities is 29863kW, saving 38.50% compared with the original process flow; In general, the transformation scheme saves 17.19kgEO/t energy consumption compared with the original process flow. Total heat exchanger network? The loss is also reduced from 13530kW to 8477kW? The loss decreased by 37.35%.

The data of propylene oxide process system is extracted under normal working conditions (we adopt design parameters), and the heat exchange equipment at the heat exchange node in the heat exchange network is simulated with Aspen plus software to correct the data and calculate the heat load at the heat exchange node. For example, the heat exchange equipment taken is the refining tower bottom liquid condenser, the thermal flow is the refining tower bottom liquid (RESIDUEI-O), and the cold flow is the circulating cooling water (WCSIN-OUT). Aspen plus software is used for modeling, and the heater heat exchange model is used.

The input quantity is the composition of thermal flow (H2O, C3H6Cl2, C3H7ClO) and its mass fraction, the inlet and outlet temperatures are 348.4 and 301.4 K, the flow rate is 0.625 t/h, and the thermal flow vaporization fraction, etc; Composition of cold flow (H2O), inlet and outlet temperatures of 299.1 and 304.6 K, vaporization fraction of cold flow, etc. The NRTL-RK method based on the non random two-phase liquid model and RK equation is selected as the physical property method. The simulation results show that the cold flow rate is 0.0304 t/h, the simulation results are basically consistent with the measured values (design parameters), and the heat load is 20.63 kW. The heat exchange equipment of each heat exchange node in the heat exchange network is simulated and corrected respectively. The average error between the simulation results and the measured values is 0.75%, which indicates the accuracy of the extracted logistics data and the feasibility of applying Aspen Plus software.

Based on the calibration report of 3.5Mt/a atmospheric and vacuum distillation unit (see Table 2), a steady state model is established by using Aspen Plus software. Through the distillation range data of each side line and the temperature distribution of the tray, it is verified that the model is highly consistent with the actual operating parameters (see Table 3), which better reflects the current actual operation of the unit and can be used for the next optimization work.

The existing heat exchange network of delayed coking unit includes 9 heat exchangers (E201 ～ E209), 3 coolers and 1 heating furnace (heater, cold flow C1 and C2 share 1 heating furnace), and 2 steam generators (ER203 and ER209). The raw material (C1) of delayed coking unit enters the heat exchange network for heating from 110 ℃, and the actual final heat exchange temperature reaches 303 ℃. The existing heat exchange network of jet fuel hydrogenation unit includes 4 heat exchangers (E301 ～ E304), 3 coolers and 2 heaters. Feed oil (C5) and circulating hydrogen (C6) of jet fuel hydrogenation unit enter the heat exchanger network for heating from 45 ℃ and 50 ℃ respectively, reaching 166 ℃ and 188 ℃ respectively. Then raw oil, circulating hydrogen and fresh hydrogen are mixed to form a mixed feed (C7), which enters the heat exchange network from 164 ℃ to 216 ℃ (the actual final heat exchange temperature), and then enters the heating furnace for heating.

The steady-state process simulation of crude oil heat exchange network is realized with Aspen plus software. The simulation results show that the initial temperature of crude oil is 55 ℃, the temperature after heat exchange with overhead oil and gas is 65.8 ℃, and the temperature before entering the primary distillation tower is 160.2 ℃. Field operation data: the initial temperature of crude oil is 55 ℃, the temperature after heat exchange with overhead oil and gas is 66.4 ℃, and the temperature before entering the primary distillation tower is 161.7 ℃. It can be seen that the simulation results are basically consistent with the actual data, and the steady-state simulation conforms to the actual working conditions on site.