HCl emissions

cemcem:

Can anybody share experiences on HCl emissions and what the influences of the process on the HCl level at the stack are?

i'm looking for an explanation why such a compound can survive up to the stack in an dusty and alkali environment...

The answer to your last question is that it is almost impossible for hydrogen chloride gas to survive in emissions from modern cement kilns.

What has often been reported as "HCl" in stack emissions (by USEPA Method 26)has been predominately ammonium chloride with small amounts of alkali chlorides. Because of this, about 10 years ago, the USEPA  introduced a new method for the determination of actual gaseous hydrogen chloride, specifically for cement plants, (Method 321 http://www.epa.gov/ttn/emc/promgate/m-321.pdf.), based on FTIR (Fourier Transform Infra-Red) spectroscopy.

See the following links for some background info;-

http://www.gcisolutions.com/CK&HCL.htm 

http://gcisolutions.com/gcitn0901.htm

http://tinyurl.com/3nzt5qz

http://www.cleanair.com/Services/Downloads/FTIRPaper.pdf

Regards,

Ted.

thanks ted!
how can we explain the process influence, e.g. i observe an increase in "HCl" if the oxygen in the kiln is low (bypass installed)

Hi,

Ammonia forms more readily under reducing conditions. It will then react  preferentially with the hot meal chlorides to form NH4Cl, which is extremely volatile at stack temperatures. (Ammonium Chloride can exist as gaseous forms above 130 deg.C)

You can tell if you have excessive ammonium chloride formation because the recondensing NH4Cl forms what is called a "detached plume" above the main stack.

This phenomenon occurs because the NH4Cl solidifies as smoky particles once the temperature of the stack exit gases falls to less than 130 deg.C, in the atmosphere. This invariably happens several meters above the stack exit, hence the so-called "detached" stack plume.

Detatched plumes will also be far more prevalent when the raw mill is off (direct mode). This is because in compound mode the ammonium salts formed can be adsorbed onto fresh raw meal coming from the raw mill, forming a small constant recirculation. However in direct mode the gaseous ammonium salts (predominately NH4Cl) go straight out the stack.

Below is a link to a US patent which claims to prevent these detached ammonium chloride plumes in cement plants;-

http://www.envirocare.com/about/pdfs/6060030_Detached_plume_abatement_method.pdf

Regards,

Ted.