The objective of project is to examine the removal of 1.0 % H2S from 250 SCFM landfill gas stream by a NaOH solution using a pilot-scale gas absorption column. 0.05N aqueous solution of NaOH was used to separate  CO2 from air. The 4 feet pilot-scale gas absorption column is packed with  ½-inch Raschig rings. For first section of lab, the gas flow rate kept as 1426.3 mL/s while the liquid flow rate was varied from 20,40 to 60 mL/s. The inlet of  liquid flow rates effect on the gas absorption were put under investigation to determine the parameters that help in scrubbing the highest amount of H2S that coming from a gas stream in a landfill.   NaOH aqueous solution is used as a strong base that will react with CO2 and H2S to produce a solid. CO2 was used in place of H2S since they are similar in size, and they react with NaOH in a similar way. At a constant gas flow rate, Kya increased with the increase of liquid flow rate.  As the flow rate is increased, the trend of Kya reaches 0.44 lbmole/ft^3hr from 0.435 lbmole/ft^3hr.

Background

The global warming caused by increasing emission of carbon dioxide is one of the most serious environmental problems.Investigating effects of gas flow rate and carbon dioxide composition in chemical absorption of carbon dioxide in a packed bed using sodium hydroxide, using a packed bed height of 1.2m, and diameter of  the column is 10 cm, with 1cm of Rasching ring. to calculate the flux as shown in the following equation,

dGdZ= -Nco2a [Eq (1)]

G= is superficial molar velocity of gas,

Nco2= is mass transfer flux of ,

Z = is the height of packed bed column, and it’s the specific surface area of the packing.

In addition, a molecular balance in gas phase of  gives the following differential equation.

dyco2dZ=-[NCO2(1-yCO2)]Ga           [Eq(2)]

yCO2 is the mole fraction of  at gas phase. With calculated mass transfer flux of CO2 , mass transfer coefficient determined by using the following equations:

NCO2=kL(CO2I-CO2e)  in liquid phase   [Eq (3-A)]

NCO2=kg(PCO2-PCO2I)   in gas phase         [Eq ((3-B)]

kL=is the liquid phase mass transfer coefficient of carbon dioxide (CO2)

CO2I= is the concentration of carbon dioxide at the interface

CO2e= is the equilibrium concentration of unreacted carbon dioxide in the bulk of liquid

kg =is the gas phase mass transfer coefficient of carbon dioxide,

PCO2I =is interface partial pressure of carbon dioxide.

From equation (3-A), they determined the overall mass transfer coefficient of carbon dioxide.

NCO2=kg(PCO2-PCO2e) [ Eq (3-C)]

PCO2e= is the partial pressure at equilibrium

Absorption processes can be divided into two groups, those in which the process is solely physical and the one accompanied by a chemical reaction. In gas absorption equipment design, intimate contact of the gas with the liquid is required. For data collection, the liquid flow rate was fixed as (4L/min) and changed gas flow rate in the range of (50-90 L/min) increased by 10L/min. Moreover, they changed liquid flow rate for variation. Finally, they recorded the gas concentration at inlet and outlet, and analyzed the gas sample by gas chromatography. As a result, the amount of absorption increased because there is a higher partial pressure.