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Spray Tower Scrubber Sizing For Flue Gas Desulfurization

02 May 2018

Posted by ankur2061 in Technical

Dear All,

Today's blog entry deals with the design and sizing of a non-packed spray tower for the purpose of flue gas desulfurization.

A spray tower sizing web resource is available on the internet which has been used as a basis for the design. However this sizing routine does not provide a clear cut method for determining the gas phase mass transfer coefficient and therein comes the research I had to do to arrive at a empirical method to determine the gas-phase mass transfer coefficient based on a reference document from the EPA (Environmental Protection Agency) of the United States..

References can be referred to from the attachments below:

88288739-Process-Design-of-Spray-Chamber-or-Spray-Tower-Type-Absorber.docx (476.25KB)
downloads: 7779

9101DWOO.PDF_Dockey=9101DWOO.PDF (3.31MB)
downloads: 7658

The gas-phase mass transfer coefficient K_Ga has been referred from the second attachment (refer page 37 for the equation). This equation is a direct method to calculate the gas-phase mass transfer compared to the method utilized in the first attachment where this value is obtained in an indirect manner by comparing with an existing spray tower with given dimensions, inlet / outlet SO₂ concentrations and lime circulation rate.

If you compare the values of the gas-phase mass transfer coefficient K_Ga calculated from the indirect method in the first attachment and the empirical equation from the second attachment (EPA report) they are quite close based on a lime circulation rate of 60 m³/h as considered in the first attachment.

Combining the sizing methodology of the first attachment with the gas-phase mass transfer coefficient equation from the second attachment, I have developed an excel workbook which sizes a spray tower. The circulation rate for the limestone solution is considered as 3 liters per actual cubic meter of flue gas which is again referenced from another EPA report. The value of the gas-phase mass transfer coefficient is in turn dependent on the circulation rate through the spray tower. Higher the circulation rate, higher the value of the gas-phase mass transfer coefficient. The reference details are provided in the excel workbook itself.

The excel workbook can be downloaded from the file library with a link from the blog entry here:

https://www.cheresou...rubbing-design/

I would appreciate comments from members of "Cheresources" on my blog entry and the excel workbook.

Regards,
Ankur

8 Comments

SIVAMOORTHY

May 07 2018 03:15 AM

Thank you very much for easy calculation.

I have following queries.

For the calculation of packed column scrubber, we will consider both gas phase and liquid phase mass transfer coefficient based on whether the mass transfer is gas side or liquid side. If it is gas phase mass transfer (for example, H2S), then it is enough calculating KGA. However, for liquid phase mass transfer (CO2 absorption), we have to consider liquid phase mass transfer coefficient (KLA) also.

The question is that should we consider KLA or not in spray tower.

Also, the properties of scrubbing liquid also affect the mass transfer coefficient. These are not included in the calculations.

Please clarify for me.

Thank you very much...

ankur2061

May 07 2018 08:54 AM

Sivamoorthy,

Flue gas desulfurization means removal of SO2 / SO3 from flue gases also called as SOx. In any combustor (boiler / heater / oxidizer). H2S is oxidized to these components and the H2S levels in flue gas are negligible (ppb).

SO2 absorption is gas phase controlled in a spray tower design for flue gas desulfurization.

Current philosophy of stack gas release is to allow CO2 to be released to the atmosphere. To my knowledge CO2 absorbers use specific solvent such as MEA which have a design as tray or packed absorbers or a combination of trays and packings.

The scrubbing liquid only effects the reactivity of the flue gas with the scrubbing liquid. To optimize reactivity, the solution concentration and the limestone particle size need to be optimized for SO2 absorption. A 6-10% limestone solution is commonly employed for flue gas SO2 removal.

This particular blog entry provides a design only for non-packed spray towers for flue gas desulfurization and should not be used for any other absorber calculation.

Hope this clarifies your queries.

Regards,

Ankur.

SIVAMOORTHY

May 08 2018 04:33 AM

Dear Sir,

Yeah.. Got it..

Thank you very much..

SIVAMOORTHY

May 22 2018 04:57 AM

Dear Sir,

Why the calculation for number of gas phase transfer units, NG differs for horizontal and vertical spray tower?