The development of simplistic and cost-effective methods for the evaluation of tray and packed column efficiencies

Lamprecht, Johannes Hendrik (2017-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH SUMMARY: Phase contacting column internals are manufactured through a series of punching, die moulding and bending. Although cost-effective on a large scale, this process is considered unfavourable for prototyping, as it is both time-consuming and expensive. This limits designer creativity and introduces extended waiting periods between the design, fabrication and evaluation phases. This translates into development timelines in excess of two years. During the evaluation stage, efficiencies are conventionally measured using hydrocarbons system at total reflux. This introduces notable constraints on the prototype packing and tray material, due to the high temperatures and pressures required for these tests. Therefore, this research project focused on the development and experimental validation of two simplistic and cost effective methods that can be used to quantify column internal efficiency. The ADIBAA (aqueous desorption of isobutyl acetate in air) and HA (Humidification of air) methods are hereby proposed for efficiency measurements in packed and tray columns respectively. For validation of both methods, two separate pilot plant facilities were designed and constructed, one at Stellenbosch University and one at an industrial research laboratory. The ADIBAA-method involved using a liquid phase limiting system to isolate the performance parameters in the liquid phase. The combination of the method and experimental setup offered rapid quantification, while remaining cost-effective and environmentally friendly. The ADIBBA-method was experimentally validated in a 400mm diameter stainless steel packed column, with a bed height of 1.1 metre. Such validation entailed (a) experimental measurement of isobutyl acetate concentrations, (b) calculation of volumetric liquid phase mass transfer coefficients and (c) comparison of these calculated coefficients with predictions by four independent correlations from literature. Agreement between the literature correlations and the newly-determined experimental data was found to be within 10%. The applicability of the ADIBAA-method, in evaluating column internal efficiencies, was confirmed through comparison of 1.5’ FlexiRings® and the equivalent Intalox® Ultra™. A quantifiable improvement of 15% was recorded in the preloading regime, in favour of the Intalox® Ultra™. Further justification of the ADIBAA-method was presented in the evaluation of 2.5’ Intalox® Ultra™ packing. The HA-method, proposed to use for tray columns, focused on the evaluation of Murphree tray efficiencies. This method offered large improvements over the constant reflux method in terms of environmental and safety considerations, while also reducing the experimental time by an order of magnitude. A rectangular tray column with respective weir and flow path lengths of 762mm and 870mm was used in the experimental evaluation. The HA-method was found to adequately quantify hydrodynamic variations in both weeping and vapour bypass. The comparative ability of the method was experimentally verified by relating a 12% open area sieve tray with two separate prototypes. The method enabled rapid evaluation and quantitatively illustrated difference in efficiencies between the prototypes. From this research, it follows that the ADIBAA- and HA- methods can indeed be used as cost-effective, simple and time-efficient methods to evaluate prospective designs of random packing and trays.

AFRIKAANS OPSOMMING: Distillasie-kolomme word industrieel vervaardig deur ’n kombinasie van buig- en ponsgreedskap. Alhoewel hierdie metodes koste-effektief is vir grootskaalse produksie, bied dit struikelblokke vir die ontwerpproses. Dit is onder meer omdat die ontwikkeling van die gereedskap en produksielyn beide tydrowend en kapitaalintensief is. Die beperkende vervaardigingstegnieke is daarvolgens geïdentifiseer as ’n moontlike knelpunt in die ontwikkeling van nuwe plate en pakking. Massa-oordrageffektiwiteit word tradisioneel geëvalueer metbehulpvan koolwaterstof-oplossings in ’n konstante-terugvloei-distillasiekolom. Dié metingsmetode vereis hoë temperatuur en druk, tesame met die gebruik van gevaarlike oplosmiddels. Daarvolgens word die gebruik van moderne en versnelde vervaardigingstegnieke grootliks ingekamp. Hierdie navorsingsprojek het dus gefokus op die ontwikkeling en eksperimentele validering van vereenvoudigde en bekostigbare alternatiewe metingsmetodes vir beide gepakte- en plaatkolomme. Die ADIBAA- (selektiewe verdamping van isobutielasetaat in lug) en die HA-metodes (verdamping van water in lug) is gevolglik ontwikkel vir gebruik in onderskeidelik gepakte- en plaatkolomme. Die ADIBAA metode fokus op die kwantifisering van vloeistoffase-mass-oordrag-koëffisiënte. Dié metode word voorgestel in stede van tradisionele konstante-terugvloei-distillasie weens spoedige kwantifisering, kostebesparings en omgewingsvriendelikhied. Die ADIBAA-metode is eksperimenteel gevalideer in ’n 400 mm-deursneekolom met ’n gepakte bedhoogte van 1,1 m. Die ooreenstemming tussen literatuur- en eksperiementele waardes was in die orde van 10%. Die bruikbaarheid van die ADIBAA-metode is bevestig deur die vergelyking van 1.5’ FlexiRings® met die ooreenstemmende Intalox® Ultra™ pakking. Daarvolgens is kwantifisserbare verbeterings in die orde van 15% opgemerk, ten gunste van die laasgenoemde. In die geval van die plaatkolom is die isotermiese verdamping van water in lug gebruik ter kwantifisering van Murphree-plaat-effektiwiteite. Eksperimentele data is daarvolgens ingesamel in ‘n reghoekige kolom met dimensies van 762 mm by 870 mm. Die voordele van dié metode sluit onder meer koste- en tydbesparing sowel as aansienlik verminderde veiligheidsrisiko’s in. Ter vergelyking van verskillende ontwerpe op grond van die metode, is bevind dat genoemsame onderskeid in Murphree-plaat -effektieiwiteite gesien kon word. Kwantiatief is verbeteringe tot en met 10% waargeneem gedurende die eksperimentele vergelykking van ’n 12% oop-area-sifplaat en ’n alternatiewe prototipe. In die lig van dié bevindinge word beide die ADIBAA- en die HA-metodes voorgestel vir gebruik tydens die aanvanklike ontwerpproses waar spoedige resultate benodig word. Die gebruik daarvan beloof om die ontwerpproses aansienlik te verkort, aangesien die prototipes nie meer aan die tradisionele vervaardigingstegnieke onderhewig is nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100887
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