Costing Research Papers - Academia.edu (original) (raw)

An absorption column is required to recover acrylic and acetic acid from the gaseous reactor effluent by contacting gas with water. Two incoming streams are handled by the column. The first is the gas stream of 5756,14 kmol/h with 0,078 % (wt./wt.) acrylic acid. It enters at a temperature of 280,50 °C and a pressure of 1,79 bar. The second stream contains processed water available from plant available at 30 °C and 1 bar and it is mixed with 500 ppm of hydroquinone inhibitor. The choice of hydroquinone as an inhibitor for this process was facilitated by its known properties to prevent polymerization of acrylic acid that is susceptible to radical-initiated polymerization (Schork, 2006). The preferred inhibitor dilution range is between 300ppm – 700 ppm (Elder J.E, 2006). The column has two exiting streams, gaseous stream and aqueous liquid stream. The gaseous stream exits at a flowrate of 5782,13 kmol/h with 390,3 ppm (wt./wt.) of acrylic acid and 23.98 ppm (wt./wt.) of acetic acid. It exits at a temperature of 70,13 °C and a pressure of 1 bar. The second exiting stream is the product stream at a total flowrate of 1576, 9 kmol/h. This stream contains 55.2 % (wt./wt.) acrylic acid (main product). It exits at a temperature of 81, 86 °C and a pressure of 1 bar. This stream is cooled to 46.5 °C prior to the LLE unit.
The product specification requires 100 000 tonnes per year of ester grade acrylic acid (minimum purity 94% (wt.) by oxidation of propylene (94% purity on molar basis). This acid product requires approximately 817.33 kmol/h of processed water. The use of packing columns is recommended for diameters less than 0.6 m (Seader, et al., 2011). The obtained diameter was 5,21 m, thus, a packed column couldn’t be chosen. Sieve trays (as opposed to bubble or valve-type trays) were chosen because of their ease of installation and lower cost compared to packed columns. The choice of sieve trays was also facilitated by their well-known design procedures, low fouling tendency and large capacity (Seader, et al., 2011). The design specifies a column with approximately 24.8 m of height, and containing 60 sieve plates. Processed water with 300 ppm of hydroquinone inhibitor is added to tray 1 (the top tray), and recycle stream is added at tray 69, one stage above the base stage. Single pass crossflow-type trays are employed for all the plates. The column operating pressure is 1 bar and the operating temperature range is from 69,85°C to 81.8 °C. A safety factor of 10% was accounted for in the design temperature and pressure. The total weight of a column vessel including the shell weight, plates and insulation is 1096,85 kN which is equivalent to 111847,55 kg. The absorption column and its associated structures (insulation, trays and vessel) are expected to cost in the region of R 8,8 million. Detailed calculations concerning the absorption column design are presented in Appendix F.