Evaluation Of Industrial Sources Of Pah Emissions Under The Conditions Of Soderberg Anode Formation

Specific yields of tar and carcinogenic PAHs generated from the main technogenic sources from KrAZ when using APMP and APHP were calculated using the Methodika VAMI (1988). This method uses anode paste consumption values, the efficiency factors for all gas cleaning system devices, the permeability of the gas skirt, and the results of laboratory research into carbonisation of pitches and anode pastes based on these pitches.

As an example, Figure 4 schematically illustrates the balance of specific yields of tar and the most dangerous carcinogenic PAHs (BaA, BaP and DBA) from the main sources of the KrAZ Soderberg electrolyser when using APMP and the 'wet' gas-cleaning system. The local sources of tars containing PAHs include:

• emission from the hole during stud repositioning;

• gas escape from under the gas skirt;

• emission of the 'wet' gas-cleaning system;

• slimes during slime storage.

emission of the gas-cleaning system tar 0,9 BaA 0,035 BaP0,006 DBA 0,001

under the gas skirt tar 1,2 BaA 0,046 BaP0,007 DBA 0,002

'wet' gas-cleaning system dust of electrofilters tar 1,7 BaP 0,005

dust of electrofilters tar 1,7 BaP 0,005

slime storage: tar2,4; BaP0,008

from the hole tar 2,1

BaA 0,038 BaP0,034 DBA 0,024

ft from the hole tar 2,1

BaA 0,038 BaP0,034 DBA 0,024

tar 7,7 ±2,3 BaA 0,3 ± 0,1 BaP 0,05 ±0,01 DBA 0,01 ± 0,003

Figure 4. Specific yields of tar and carcinogenic PAHs from the main sources of the KrAZ Soderberg electrolyzer using anode paste based on medium-softening point pitch and 'wet' gas-cleaning system.

Rapid carbonisation of the studhole anode paste determines the emissions from the hole, slow carbonisation of 'dry' anode paste determines other emissions.

It is interesting to compare the specific yields of carcinogenic PAHs generated from the main local sources, i.e. from the hole during stud repositioning, gas escape from under the gas skirt and emission of the gas-cleaning system. The calculated specific yield values of tar and carcinogenic PAHs (BaA, BaP and DBA) from the main sources when using anode pastes based on MP and HP, and 'wet' and 'dry' gas-cleaning systems, are presented in Table 2.

These results indicate that the most dangerous local source of carcinogenic PAHs is emission from the open hole at the process stage of stud repositioning, which is about 60-70% of the total atmospheric emission. It stipulated low specific tar yields in aluminium production using the Soderberg technology of the Reynolds Company, Kaiser Aluminium & Chemical Corporation and other firms. In particular, when using HP-based anode paste the specific yield of BaP from the hole is 0.037 kg/t Al while the total atmospheric emission is 0.048 kg/t Al, which includes emissions from the hole, gas escape from under the gas skirt, and emissions from the 'dry' gas cleaning system. Traditionally this source has not been considered in calculations of specific yields of tar. Thus, the calculated total specific yield of tar when using APMP is 2.1 kg/t Al, excluding emissions from the hole (Table 2), which corresponds to data reported for the Krasnoyarsk aluminium plant (2.09 kg/t Al - Zhuravlev and Petushkov, 1998). When using HP, the specific tar yield is 0.9 kg/t Al excluding emissions from the hole (Table 2). There is a good correlation with data from the KrAZ-Kaiser-VAMI project (Johnson and Lobachev, 1998) - 0.39-0.65 kg/t Al. The total emission of carcinogenic PAHs in this project is reduced due to the use of the 'dry' gas cleaning system, and not due to the replacement of MP with HP.

Table 2. Specific yields (kg/t Al) of tar and carcinogenic PAHs from the main sources of technogenic waste produced by the Krasnoyarsk aluminium plant when using anode pastes based on MP (APMP) and HP (APHP).__

Technogenic emission

APMP

APHP

tar

BaA

BaP

DBA

tar

BaA

BaP

DBA

From the hole

2.1

0.038

0.034

0.024

1.5

0.049

0.037

0.017

From under the

1.2

0.046

0.007

0.002

0.8

0.048

0.009

0.002

gas skirt

From the gas

cleaning system:

'wet'

0.9

0.035

0.006

0.001

0.6

0.036

0.007

0.0016

'dry'

-

-

-

-

0.1

0.006

0.002

0.0002

A replacement of APMP with APHP in aluminium production using Soderberg cells results in a decrease in the yield of tar from all local sources. However, in this case the yield of BaP and other carcinogenic PAHs from these sources is not reduced.

Was this article helpful?

0 0

Post a comment