Modelling And Simulation Of Gas Liquid Absorption

Proceedings of National Conference on Frontiers in Applied Sciences and Computer Technology (FACT’ 12), Dec., 6-7, 2012 Edited by Dr.R.Ponalagusamy, Dr.T.N.Janakiraman and Dr.P.J.A.Alphonse. Vol.2 PP. 10 - 15.

Modelling And Simulation Of Gas Liquid Absorption Column For SO2 Emission Control V.Priya1, C.Maheswari2, K.Krishnamurthy3, R.Parameshwaran4 1

Department of Mechatronics Engineering, Kongu Engineering College, Perundurai, Tamilnadu, India. 2 Department of Mechatronics Engineering, Kongu Engineering College, 3 School of building and mechanical sciences,Kongu Engineering College, Perundurai, Tamilnadu , India. 1 [email protected], [email protected], [email protected], [email protected]

Abstract: Main motivation of this project is to reduce the environmental effects caused due to combustion of coal that results in the emission of toxic sulphur dioxide (SO2).During coal combustion, sulphur in the coal is converted into sulphur dioxide (SO2).This sulphur dioxide (SO2) is responsible for the formation of acid rain which is one of the widespread forms of pollution all over the world that causes harmful effects to humans and environment. To minimize the adverse impacts of SO2, it must be removed from flue gas. For reduction of SO2, flue gas desulphurization (FGD) is most commonly used. The mathematical viewer is developed and simulated for a gas liquid absorption column to control the flow rate of H2O2.The model equation is developed by considering material balance around the column. The absorption rate is determined by using different concentration of sulphur dioxide with hydrogen peroxide. Hydrogen peroxide, not only absorbs the SO2 but it also produce useful by-product in the form of sulphuric acid (H2SO4). Keywords: Air pollution, Flue gas, Sulphur dioxide, Desulphurization.

1.Introduction SO2 is a colorless gas with a sharp odor produced from the burning of coal High concentrations of SO2 can have serious effects on health, but more important today is its role as a precursor to the formation of particulates, a ubiquitous threat to public health and the environment. Long-range transport of sulfuric compounds also leads to the deposition of sulfur in soils and waterways in regions distant from the source of emissions. Sulfur deposition, more commonly known as acid rain, contributes to acidification of forests and lakes.

2.Prevention Methods Emission of harmful compounds to the atmosphere caused by combustion of fossil fuels is an environmental concern all over the world. Sulfur and nitrogen oxides are among the most alarming pollutants due to their great global emission and long range transport in the atmosphere.

3.Flue-Gas Desulfurization (FGD) Flue-gas desulfurization (FGD) is a technology used to remove sulfur dioxide (SO2) from the exhaust flue gases of fossil-fuel power plants, and chemical producers of sulfur oxides. As stringent environmental

10


regulations regarding SO2 emissions have been enacted in many countries, SO2 is now being removed from flue gases by a variety of methods. The below is among the common methods used:    

Wet scrubbing using a slurry of alkaline sorbent, usually limestone or lime, or seawater to scrub gases; Spray-dry scrubbing using similar sorbent slurries; Wet sulfuric acid process recovering sulfur in the form of commercial quality sulfuric acid; Dry sorbent injection systems.

For a typical coal-fired power station, FGD will remove 95 percent or more of the SO2 in the flue gases.

4.Gas Liquid Absorption Column By means of gas liquid interface gaseous component is transformed from gas phase to liquid phase

Figure1 counter current packed tower

5.Development Of Mathematical Model The steady state process absorption of the CO2-NaOH system has been studied previously [1] where the rate of absorption, the rate of transfer of material through the gas film will be the same as that through the liquid film, and the generation for the generation for mass transfer of a component is described by equation (1) Material balance around the column: 𝐺𝐺(𝐶𝐶𝐺𝐺1 − 𝐶𝐶𝐺𝐺2 (𝑡𝑡) = 𝐿𝐿(𝐶𝐶𝐿𝐿1 (𝑡𝑡) − 𝐶𝐶𝐿𝐿2 (𝑡𝑡))

(2)

Material balance around the tank: Inlet flow rate – outlet flow rate = rate of accumulation

There four time dependent parameters and only two material balance equation. A third equation is formed by modelling 𝐶𝐶𝐿𝐿1 (𝑡𝑡) as a function of time. Schematic Gas Liquid Absorption System

11


Figure 2. Gas Liquid Absorption System Henry’s Law An equivalent way of stating the law is that the solubility of a gas in a liquid is directly proportional to the Concentration of inlet gas. 𝐶𝐶𝐶𝐶 𝐶𝐶𝐶𝐶1 (𝑡𝑡) = ′1 (3) 𝐻𝐻 𝐶𝐶𝐶𝐶1 (𝑡𝑡) = Mole fraction of solute in the liquid 𝐶𝐶𝐶𝐶1 = Concentration of inlet gas 𝐻𝐻 ′ = Henry’s law constant Mixing Tank Equation

Figure 3. Mixing Tank VdCL2 (t ) = L1CL1 (t ) + CL3 L2 (t ) − L1CL2 (t ) dt VdCL2 (t ) = L1CL1 (t ) − L1CL2 (t ) + CL3 L2 (t ) dt

12


VdCL2 (t ) = ( L1 (CL1 (t ) − CL2 (t )) + CL3 L2 (t ) dt

dCL2 (t ) ( L1 (CL1 (t ) − CL2 (t )) + CL3 L2 (t ) = dt V L1 (CL1 (t ) − CL2 (t ) + CL3 L2 (t ) CL2 (t ) = ∫ V

(4)

Material balance equation

𝐺𝐺 (𝐶𝐶𝐶𝐶2 (𝑡𝑡) − 𝐶𝐶𝐶𝐶1 ) = 𝐿𝐿(𝐶𝐶𝐶𝐶1 (𝑡𝑡) − 𝐶𝐶𝐶𝐶2 (𝑡𝑡)) 𝐶𝐶𝐶𝐶𝟐𝟐 (𝑡𝑡) − 𝐶𝐶𝐶𝐶1 =

𝐿𝐿 (𝐶𝐶𝐶𝐶1 (𝑡𝑡) − 𝐶𝐶𝐶𝐶2 (𝑡𝑡) 𝐺𝐺 𝐿𝐿

𝐶𝐶𝐶𝐶2 (𝑡𝑡) = 𝐶𝐶𝐶𝐶1 + (𝐶𝐶𝐶𝐶1 (𝑡𝑡) − 𝐶𝐶𝐶𝐶2 (𝑡𝑡)) (5) 𝐺𝐺

Simulink block for Mixing Tank Equation

Function CL_2= fcn(CL1,CL2,L2) L1=0.2; V=50; CL3=0.1; CL_2= ((L1*(CL1-CL2)+(CL3*L2)/V)); Simulink block for Wet scrubber Equation Function [CG2,CL_1,CL_12] = fcn(CL1,CL2,L2) CG1=650; CL3=0.1; K1=1; K2=1400; L1=0.2; G=50; CG2 = (CG1-((L1/G)*(CL1-CL2))); CL_1= CG1/K1; CL_12= (CG1*(CL3/L2)*K2)

13


6.Result And Discussion Flow rate Vs Removal Efficiency For different flow rates, corresponding Removal Efficiency of the acid are noted. It is known that for increasing in the flow rate of hydrogen peroxide the Removal Efficiency of the acid obtained gets increased. Hence suitable flow rate is to be chosen for better output of the acid. Flow rate Vs Removal Efficiency

Figure 4 Flow rate Vs Removal Efficiency Time Vs Outlet Concentration of 𝑺𝑺𝑺𝑺𝟐𝟐

When the time increase the outlet concentration of SO2 continuously decreases and after a certain period of increasing time the outlet concentration remains constant.

Figure5 Time Vs Outlet concentration of SO2

14


7.Conclusion From simulation work it is confirmed that, sulfur dioxide (SO2) can be converted to sulfuric acid by using Hydrogen peroxide (H2O2).By varying the flow rate of hydrogen peroxide and also by varying the concentration of sulfur dioxide. From the simulation it is concluded that the setting time period is increased by increasing the inlet concentration of SO2.The modelling approach used, provides the better performance result.

References:

[1] M.A. Olutoye and A. Mohammed ., “Modelling of a gas absotption packed column for carbon Dioxide-Sodium Hydroxide system”., AU J.T.10(2): 132-140 [2] Colle S., Vanderschuren J., Thomas D., (2008) ‘Effect of temperature on SO2 absorption into sulphuric acid solutions containing hydrogen peroxide’, Chemical Engineering and Processing: Process Intensification, 47 (9-10), pp. 1603-1608 [3] Zhou Y., Zhu X., Peng J., Liu Y., Zhang D., Zhang M. (2009), ‘The effect of hydrogen peroxide solution on SO2 removal in the semidry flue gas desulfurization process Journal of Hazardous Materials’, 170 (1), pp. 436-442, 2009 [4] Cofala, J., Amann, M., Gyarfas, F., Schoepp, Boudri,J.C., Hordijk, .,L Kroeze, C., Li Junfeng, Panwar, T.S., Gupta, S., “ cost effective control of SO2 Emissions in Asia”. , journal of Environmental Management , 2004, Vol. 72(3), pp.149-161 [5] Isabelle Liemans., Bruno Alban., Jean-pierre trainer., Diane Thomas., “SOx and NOx absorption based removel into acidic conditions for the flue gas treatment in oxy –fuel combustion”, Energy procedia 4, 2011, pp 2847-2854 [6] Steven W. Miller., “ Methods for reducing SO2 Emissions”., IEEE- IAS cement industry committee., 2004 [7] Diane Thomas ., Sandrine colle., acques vanderschurenj., “ Designing Wet Scrubbers for SO2 Absorption into Fairly Concentrated Sulfuric Acid Solutions Containing Hydrogen Peroxide” ., Chemical engineering technology., 2003 [8] S. colle., D.thomas., J. Venderschuren., “ process simulation of sulphur Dioxide abatement with H2O2 solutions in a packed column”., chemical engineering and design ,2005,83(A1):81-87

Nomenclature

CL1 (t) = concentration of SO2 in H2O2 leaving the K0 = limiting value of SO2 concentration in H2O2 solution column with time (gram mole/litter)

(gram mole/litter)

CL2 (t) = concentration of SO2 in H2O2 entering the k2 = time constant column with time (gram mole/litter)

L = Liquid flow rate (litters/sec)

CG2 (t) = concentration of SO2 in gas stream leaving V = tank volume (litters) the column with time (gram mole/litter) CG1 = concentration of SO2 in gas stream entering the column (gram mole/litter) CL3(t) = concentration of H2O2 entering the column with time (gram mole/litter) G = air flow rate (litters/sec 15