Petroleum Displacement Technology Research Center Korea Research Institute of Chemical Technology (KRICT), Daejeon 305-600, Korea.
Environ Sci Technol. 2010 Feb 15;44(4):1412-7. doi: 10.1021/es902784x.
A process model for a gas-to-liquids (GTL) process mainly producing Fischer-Tropsch (FT) synthetic oils has been developed to assess the effects of reforming methods, recycle ratio of unreacted syngas mixture on the process efficiency and the greenhouse gas (GHG) emission. The reforming unit of our study is composed of both steam reforming of methane (SRM) and carbon dioxide reforming of methane (CDR) to form syngas, which gives composition flexibility, reduction in GHG emission, and higher cost-competitiveness. With recycling, it is found that zero emission of CO(2) from the process can be realized and the required amount of natural gas (NG) can be significantly reduced. This GTL process model has been built by using Aspen Plus software, and it is mainly composed of a feeding unit, a reforming unit, an FT synthesis unit, several separation units and a recycling unit. The composition flexibility of the syngas mixture due to the two different types of reforming reactions raises an issue that in order to attain the optimized feed composition of FT synthesis the amount of flow rate of each component in the fresh feed mixture should be determined considering the effects of the recycle and its split ratio. In the FT synthesis unit, the 15 representative reactions for the chain growth and water gas shift on the cobalt-based catalyst are considered. After FT synthesis, the unreacted syngas mixture is recycled to the reforming unit or the FT synthesis unit or both to enhance process efficiency. The effect of the split ratio, the recycle flow rate to the FT reactor over the recycle flow rate to the reforming unit, on the efficiency of the process was also investigated. This work shows that greater recycle to the reforming unit is less effective than that to the FT synthesis unit from the standpoint of the net heat efficiency of the process, since the reforming reactions are greatly endothermic and greater recycle to the reformer requires more energy.
已开发出一种用于天然气制液体（GTL）工艺的过程模型，主要用于生产费托（FT）合成油，以评估重整方法、未反应合成气混合物的循环比对工艺效率和温室气体（GHG）排放的影响。我们研究的重整单元由甲烷蒸汽重整（SRM）和甲烷二氧化碳重整（CDR）组成，形成合成气，这提供了组成灵活性、减少 GHG 排放和更高的成本竞争力。通过回收，发现可以实现该过程 CO(2)的零排放，并且可以显著减少对天然气（NG）的需求。该 GTL 过程模型是使用 Aspen Plus 软件构建的，主要由进料单元、重整单元、FT 合成单元、几个分离单元和回收单元组成。由于两种不同类型的重整反应，合成气混合物的组成灵活性提出了一个问题，即为了达到 FT 合成的最佳进料组成，应该考虑回收及其分流比的影响来确定新鲜进料混合物中每个组分的流量。在 FT 合成单元中，考虑了钴基催化剂上链增长和水汽变换的 15 个代表性反应。FT 合成后，未反应的合成气混合物被回收至重整单元或 FT 合成单元或两者以提高工艺效率。还研究了分流比、回收到 FT 反应器的流量与回收到重整单元的流量之比对工艺效率的影响。这项工作表明，从过程的净热效率的角度来看，较大的回收到重整单元的效果不如回收到 FT 合成单元的效果好，因为重整反应是非常吸热的，较大的回收到重整器需要更多的能量。
