*Appendix A.1 Unit A*/*B*

All retrofit proposed for the Units A and B reduce the load on furnace HTR-AB1. For the existing configuration of the included process equipment of Unit A, see Figure A1.

**Figure A1.** Existing process configuration of effected part of Unit A.

#### Appendix A.1.1 Retrofit Proposal 1A

In this retrofit proposal, the feed to furnace HTR-AB1 is pre-heated before entering heat exchanger HX-AB1. The feed is pre-heated by a process stream from Unit B, which thereby gets a lower cooling demand, reducing the load on air cooler CLR-AB. Since the heat recovery is very high in this retrofit proposal, the need for new heat exchanger area is large. The retrofit proposal is displayed in Figure A2.

**Figure A2.** Retrofit proposal 1A.

#### Appendix A.1.2 Retrofit Proposal 1B

Retrofit proposal 1B involves increased heat recovery and network complexity compared to retrofit proposal 1A. The hot stream from Unit B is in this proposal used as a heat source for a distillation column's reboiler, HX-AB3, before preheating the reactor feed in HX-AB2. The proposal is shown in Figure A3.

**Figure A3.** Retrofit proposal 1B.

Appendix A.1.3 Retrofit Proposal 1C

Retrofit proposal 1C is structurally the same as retrofit proposal 1A. The difference in this proposal is that HX-AB1 is not extended, thus changing the temperature of the hot process stream leaving HX-AB1 and reducing the fuel saving in the furnace compared to proposal 1A. The proposal is shown in Figure A4.

**Figure A4.** Retrofit proposal 1C.

#### Appendix A.1.4 Retrofit Proposal 2

Also in retrofit proposal 2, fuel gas is saved in HTR-AB1. In this case the increased pre-heating is achieved by an additional convection part in HTR-AB2, recovering more energy from the hot flue gases of that furnace. The retrofit proposal is shown in Figure A5.

**Figure A5.** Retrofit proposal 2.
