对二甲苯装置低温热回收分析

Analysis of low-temperature heat recovery in para-xylene unit

对二甲苯装置生产流程复杂,包括石脑油催化重整、芳烃抽提、歧化及烷基转移、二甲苯精馏、吸附分离和异构化等芳烃生产、转化及分离单元,能源消耗量大,对二甲苯产品综合能耗在25 GJ/t以上,一套600 kt/a PX装置未回收主要低温热达150 MW,节能增效势在必行。对对二甲苯装置主要精馏塔——抽余液塔和抽出液塔塔顶低温热的回收利用进行了分析与探讨。结合装置的情况,制定了低温热回收方案:先进行现有抽出液塔塔顶低温热的回收利用,再进行抽余液塔和抽出液塔加压操作的低温热回收利用。通过塔顶馏出物加热除氧水、塔加压操作后塔顶馏出物加热除氧水发生蒸汽等方法,大幅降低对二甲苯装置能耗,预计单位能耗可从14.2 GJ/t降低到12.4 GJ/t,提高了装置经济性能。

The para-xylene （PX） unit including naphtha catalytic reforming unit, aromatic extraction unit, disproportionation transalkylation unit, PX fractionation unit, absorbers and isomerization unit as well as the units for aromatic production, conversion and separation, etc, are complex in process and high in energy requirement. The energy required for PX production is over 25.12 GJ/t. Therefore, the energy saving to im- prove pix^fitability is an extreme necessity. The recovery and utilization of low-temperature heat from overheads of main fractionatorIextraction raffinate tower and extract tower are studied, and the following low-tempera- ture heal recovery schemes have been recommended ： The low-temperature of existing extract tower overhead is first recovered and utilized and then followed by the recovery and utilization of low-temperature heat from raffi- nate tower and extract tower through pressurized operation. In addition, the use of overhead effluent to heat deaerated water and the use of heated deaerated water from pressurized tower operation to generate steam, etc have greatly reduced the energy consumption of PX unit and improved the unit＇ s economics.