(112a) Sensitivity Analysis of Scrub Column Design in LNG Liquefaction Process

Authors: 
Zhang, L., JGC America, Inc
In the LNG liquefaction process, there are various methods for achieving the typical LNG specification and preventing the plugging or fouling before entering the cryogenic equipment. Scrub column is one of typical configuration for the heavy component removal. The scrub column removes BTX (Benzene, Toluene and Xylene) and the other heavy hydrocarbons (C5+) from natural gas to avoid freeze-up in the cold end of Main Cryogenic Heat Exchanger (MCHE) and achieve the LNG product specifications such as C5+ Content, Higher Heating Value (HHV) requirement. At meant time, it also provides the feed to Fractionation to generate refrigerant make-up and C5+ condensate product.

The scrub column is often operating near the supercritical region for improving the liquefaction efficiency. Column has huge vapour and liquid traffic difference through the column internals. The BTX and C5+ specification in overhead of column has very strict ppm level purity requirement. So, the column operation is sensitive to the feed gas composition and pressure changes. The current design is heavily dependent on the licensor or engineers’ experiences to address those uncertainties and challenges.

There are many literatures related to the sensitivity analysis of different liquefaction technologies. In the presentation, the feed gas composition and inlet pressure changes, ambient temperature variation affecting the column design will be focused. This presentation will describe how sensitivity analysis study can lower the risk of design and potentially reduce capital costs and operational costs. Systematic evaluation of those challenges will provide a path to address and resolve concerns in early stage project. Due to BTX and C5+ ppm level requirement, the accuracy of binary parameters (BIPs) among key components in thermodynamic model also plays critical role for the column simulation and design. The uncertainty of BIPs for column design will also be discussed. Due to the integration of liquefaction plant, the impacts of whole plant performance by those parameters will be presented.