A fume treatment plant at Alba

A fume treatment plant at Alba

Emissions down at Alba com-plex

Improvements in fume treatment plants plus retrofitting and better designing in pow-er plants have helped Alba to achieve substantial reductions in harmful emissions

September 2015

Alba has achieved significant reductions in potline and power station emissions thanks to investments in pollution-reduction equip-ment, the company says.

“We have managed to drop our fluoride emission at the potrooms by 24 per cent in 2013 compared to 2012; this level was sustained in 2014 and there is around 11 per cent decrease for 2015 year-to-date as compared to 2014,” an Alba spokesman said.

“These reductions were achieved by improved reduction cells hooding, improvements at the Fume Treatment Plants (FTPs), im-provements of the emission monitoring systems and implementation of best operational practices,” he added.

According to the company, around 80 per cent of greenhouse gas (GHG) is emitted during power generation from the use of natu-ral gas to power its turbines. The company is concentrating on using the newer and more efficient power stations to improve relia-bility. The emission of perfluorocarbons (PFCs), which constitute a potent GHG, is controlled through best potroom practices and recently through the introduction of advanced control systems for the early detection and control of unfavourable process conditions that lead to PFCs emission.

Alba depends on online monitoring systems that use optical sensors and standard analytical testing procedures for the monitoring of potroom emissions from both stacks as well as fugitive roof emission as per EPA (US Environmental Protection Agency) require-ments.

The Intergovernmental Panel for Climate Change (IPCC) has defined PFCs as the GHG from the potroom. There are currently no international limits, rather there is a requirement for signatories of the United Nations Framework Convention on Climate Change (UNFCCC) to measure and regularly report their emission figures to the International Aluminium Institute (IAI). The IAI regularly produces reports to benchmark member companies. Alba’s current PFC emissions benchmarks are at around 60 per cent when com-pared with the same technology (Point Fed Pre-Baked) and there are continuous steps to reduce this emission by either equipment modification or practice improvements.

The main pollution abatement facilities at Alba are the dry scrubbers for the control of fluoride emission from potrooms. Howev-er, the company also has wet scrubbers for SO2 removal at its calciner plant, numerous dust collectors around the Alba facility but mainly at carbon departments and waste heat recovery at power plants and the calciner.

About the efficiency of its fume treatment plants, the spokesman said it ranged from 99.5 to 99.7 per cent depending on a particular model. “There has been a slight degradation of some of the FTP efficiency over the last few years due to the current creep project that basically results in an increase in the treated gas volume and temperature,” the spokesman asserted. However, he highlighted that modernisation is ongoing. “Recently some FTPs had an increase in filtering capacity, some had the addition of heat exchangers to cool the incoming fume charge and some had the addition of new treatment compartments.”

With regards to reductions in power generation emissions, the Alba spokesman said retrofitting and design preferences had helped, and provided some details: “The biggest reduction was achieved when Power Station 3 was retrofitted with low NOx burn-ers where the emission of NOx reduced from 450 to less than 100 mg/m3. The newer Power Station 4 was commissioned with Line 5 in 2005 and was originally of low NOx design (around 60 mg/m3).

“Power Stations 2 to 4 are using combined cycle where the waste heat from the gas turbine is used to run a steam turbine for max-imum power extraction with the same emission of CO2. We currently do not pre-treat natural gas for sulphur reduction.

“With the proposed future expansion project of Line 6 and Power Station 5, it is foreseen that Power Station 5 is highly efficient with NOx emission much lower than 50 mg/m3 and probably has provision for add-ons for further reduction if the need arises.”

Over the past decade, Alba has invested some BD22.91 million for retrofitting the existing six gas turbines in Power Station 3 with low NOx combustors which limited the NOx level in the exhaust to the stipulated level of 50 ppm.

More Stories