TDI生产中无压缩光气回收工艺的研究

Study of phosgene recovery system without compression in TDI production

对TDI生产中现有的光气回收工艺进行了分析,提出了无压缩机的光气回收工艺。原工艺的特点是在光气化回路压力比较高,而在脱气和气提工序压力低;从后两工序分离出的气体需要采用两级压缩的工艺来升高压力,然后进入高压吸收塔进行光气回收,回收的光气重新返回到光气化回路。光气两级压缩不仅设备投资大,而且在生产中容易发生故障,造成整个系统的波动或者是停车,危险性较大。无压缩工艺去除了压缩工序,增加了深冷器,对反应分离罐分离出来的光气进行了深冷,使大部分光气在此处冷凝为液相返回到光气化回路。剩余少量光气和脱气塔、气提塔来的光气用吸收塔进行吸收。吸收塔改用微正压操作。吸收下来的光气经泵加压后返回到光气化回路。经Aspen模拟,新工艺能够满足工艺要求,减少设备投资,并降低系统的能耗。

According to the analysis of present phosgene recovery system in TDI production, a process for phosgene recovery without compression system was proposed. The original process adopted high operation pressure in phosgenation loop and low pressure in degassing and stripping processes. The former operation condition could get a higher yield of TDI, and the latter could completely remove phosgene and HCI from crude production. The phosgene separated from degassing and stripping processes needed to increase pressure again by two-stage compressor, to meet the feed condition of high pressure absorber. The two-stage compressor is not only needing large investment, but also it is prone to mechanical failure, resulting in fluctuations of the entire system or parking. In this improved process, a deep freezer was bought in the system, which condensed most of phosgene from reaction flash separation into liquid. The remaining phosgene accompanied with the gas from degasser and HC1 stripper was absorbed by an atmospheric absorption tower. Absorbent was pressurized by pump and returned to the phosgenation loop. The compression system was reduced. The new process was simulated by Aspen Plus simulation software, and the appropriate cryogenic temperature and the amount of absorbent was obtained. It can meet the technological requirement, reduce the energy consumption, which shows this new process is feasible.