الأبحاث

2-  Evaluation of Hydrodynamics and Absorption Efficiency of a Pilot Plant Column for Carbon Dioxide Capture

Abstract 

Greenhouse gas emissions have increased exponentially since the start of the industrial revolution. The main dominant gas is carbon dioxide which is mainly released from fuel combustion processes. Developing a process to capture the carbon dioxide emissions is crucial to avoid dramatic climate change.The absorption column is a widely used separation unit for gas emissions treatment.  This dissertation explored a wide range of carbon dioxide absorbents and the internal design options of the column to minimise the capture cost. The internal design affects the hydrodynamics of the column which has to been evaluated to maintain the operation at the optimum level. The pressure drop and flooding velocities were the main hydrodynamics properties to be analysed. Series of experiments were conducted in a pilot plant absorption column mainly to investigate the hydrodynamics of the column and its capture efficiency. The column has double packing beds of a total height of 2.8 m and a diameter of 0.3 m. The beds are equally divided into DuraPack^®glass structured packing and plastic pall ring random packing. It was observed that the pressure drop is strongly affected by the gas flowrate. By the aid of Robbins pressure drop model, the dry packing factor was determined, 30 ft^-1, for the recently released DuraPack^® packing. The Robbins model predicted the pressure drops accurately for structured packing over a wide range of flowrates. However, the predictions were insignificantly underestimated for the random packing. In the flooding evaluation, the Billet and Schultes model slightly overestimated the flooding velocities for all ranges of flowrates. The capturing experiment revealed that the removal efficiency is directly proportional to sodium hydroxide concentration. At fixed solvent flowrate, the capture efficiency increases as the gas flowrate decreases. The optimum solvent flowrate was found to be around 25 l min^-1 for all chosen values of gas flowrates. The column was also modelled in Aspen HYSYS^® to predict the capture efficiency of the column when monoethanolamine is used as absorbent. In the air capture modelling, the efficiency is similar to the sodium hydroxide. However, the capture efficiency decreases as the carbon dioxide concentration increases in the gas inlet. The maximum capture efficiency is limited at 75% for all scenarios of the current column.

 

​