Abstract

An Optimization technique has been introduced to extract the nonideal parameters of gas absorption with chemical reactions process. The gas absorption is modeled using a vigorous mass transfer theory to represent the realistic behaviors of an absorber. The formed model is a highly nonlinear iterative model which correlates the overall rate of absorption (Rv) as the function of unknown nonideal parameters, including the physical liquid mass transfer coefficient kL and the wetted interfacial area of packings av. The optimization program is developed to minimize the sum of squares of relative errors between the model predictions of Rv and the experimental data. An algorithm for finding the values of optimum parameters in this study follows a modified Levenberg-Marquardt method and an active set strategy to solve the highly nonlinear least squares problem.

A system of CO2-NaOH is chosen in this study based on available experimental data. The data were obtained from a pilot plant study of Tontiwachwuthikul. (1) Ceramic Berl Saddle packings (12.7 mm or 1/2") were used in the full length absorber in the pilot plant. Four sets of experimental data are input into an optimization program for estimation of kL and av. The conditions of the operation in the pilot plant are as follows:

  1. the concentrations of NaOH are between 1.20 kmol/m3 to 2.5 kmol/m3,

  2. liquid flow rates are at 3.75 × 10−3 and 2.64 × 10−3 m3 / m3 sec;

  3. gas flow rate is at 1.48 × 10−3kmo/l m3 sec.

The physical liquid mass transfer coefficient s is estimated at the range of 6.7 × 1010−3to 3.38 X 1010−1 m sec and the wetted interfacial area of packings av is between 110.-1 to 133.6 m2 / m3 It was found that the predictions of the model are in good agreement with the experimental data. The average absolute value of relative error is about 5.4%.

Introduction

The separation of CO2 from gas mixtures is an essential step in natural gas processing, petroleum refining and petrochemical manufacture. For the production of hydrogen ammonia and synthesis gas which are basic building blocks for the petrochemical industry, the cost of CO2 separation from their gaseous streams can be as high as 30% of the total cost depending on the feed stock. Many technologies such as cryogenic separation, membrane, adsorption and absorption have been developed to separate CO2 on an industrial scale. However chemical absorption of CO2 in liquid solutions followed by stripping of the purified gas is still the most common technology used by industries. The great majority of absorbers used for gas purification are packed, plate, or spray towers. Especially, packed tower are gaining an increasing share of the market due to the development of modern high-capacity, high-efficiency packings.(2).

Although absorption with chemical reaction has been studied for over sixty years the design of a gas absorber using reactive solvents is still largely based on experiments or " rules of thumb" (3). This is due to the scarcity of fundamental design data such as mass transfer coefficients, interfacial area or other physical-chemical properties.

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