(131d) On-Site Miniplant Technology: Improving the Absorption Process of Removing Aromatic Hydrocarbons by Using Biodiesel as Scrubbing Fluid

The recovery of aromatic hydrocarbons from coke oven gas by an absorption/desorption process represents one stage of the gas purification at a coking plant. Coke oven gas (COG) is a highly caloric and valuable by-product that is formed during the coking process comprising about 30-40 g/Nm³ of BTX-components (Benzene, Toluene, Xylene). Recent studies under lab conditions at the Berlin Institute of Technology have shown that the absorption capability of Biodiesel concerning BTX is up to 30% higher in comparison to the traditional industrially applied scrubbing fluid Coal Tar Oil (CTO) for generating crude benzene. In order to test the performance and the applicability of the alternative scrubbing fluid (also under industrial conditions), a flexible modular and transportable Miniplant was built at our Institute shifted afterwards to a coking plant. The Miniplant, which is mainly composed of an absorption, desorption, and distillation column, is monitored and controlled by almost 80 sensors via the DCS process control system Freelance 800F from ABB. Furthermore, the Miniplant matches any safety requirements according to ATEX II2G so as to work with flammable gases and liquids. It also comprises some sophisticated and complex emergency shutdown procedures that enables an autonomous steady state operation for several hours without attendance.

Besides the concept and design of the modern Miniplant, the performance of the alternative green scrubbing fluid will also be presented. During the experimental investigation, several advantages of biodiesel compared to the commonly used Coal Tar Oil (CTO) arose, which contribute to saving investment and operational costs in case of a change of the scrubbing fluid. First of all, the higher absorption capability could be proved on-site. Furthermore, a better product quality of crude benzene under the same conditions can be achieved even at higher temperatures at the distillation column top. Due to its higher boiling point and thermal stability, the thermodynamic parameters of biodiesel such as viscosity remained almost constant during more than 450 operating hours, although running the plant with top temperature of up to 115°C. While using CTO top temperatures of less that 90°C are need to guarantee a stable steady state plant operation. Another advantage of the higher boiling point of biodiesel is that the scrubbing fluid losses are comparably lower, which directly contributes to saving operational costs. The accessibility of biodiesel, which is widespread nearly all over the world, represents an additional advantage because CTO is only available where tar distillation is carried out.