PROJECT DESCRIPTION
BACKGROUND
Sulphur oxides (SO2) are produced during the calcination process of magnesite, mainly from the fuel used in the combustion furnace. SO2 is classified as an atmospheric pollutant due to its contribution to acid rain, which is a significant problem in Europe and in the east coast of North America. For this reason, the magnesium oxide (MgO) industry is included within the polluting industries group, and consequently it must fulfil specific regulations. The traditional processes used to reduce the SO2 emissions are based on dry or wet desulphurisation technologies. The difference lies in the way of introducing the absorbent. Dry technologies use a solid or semi-liquid absorbent, while wet ones use an absorbent solution. The Best Available Technologies (BAT) conclusions for the production of cement, lime and magnesium oxide were approved on 26 March 2013. The BAT establishes that dry technologies can be used only if the use of wet technologies is not viable – i.e. because the efficiency in SO2 emissions reduction is higher for the wet desulphurisation process. The main problem with wet technologies is the high water consumption (5-12 m3/tonne) and the generation of a wastewater effluent with a high sulphate content.
In this context, it would be beneficial to test the viability of a ‘zero waste’ wet desulphurisation technology. The use of MgO-based reagents would give value to the effluent generated and ensure that it does not represent a risk to water contamination or present other environmental problems.
OBJECTIVES
The main goal of the project was to construct a wet desulphurisation demonstrative plant, on an industrial scale, using MgO-based reagents. This plant would treat the whole combustion gases generated (60 000 Nm3/h) in one of the magnesite calcination rotary furnaces, which is located in MAGNA industrial plant.
Specific project objectives were to:
RESULTS
The main objective of the LIFE SO2ZEROEF project was to construct a wet desulphurisation demonstrative plant, on an industrial scale, using MgO based reagents. This plant was expected to treat the whole combustion gases (60 000 Nm3/h) generated in one of the magnesite calcination rotary furnaces located in the beneficiary’s industrial plant. It aimed to reduce the SO2 emissions below a threshold of 400 mg/Nm3 using MgO slurry as an absorbent. The project has not achieved these main objectives because MAGNA was unable construct a wet desulphurisation demonstrative plant on an industrial scale due to the lack of permits. The permits needed to construct the new desulphurisation plant were still pending (IEA and building licence). Although the new technology met the requirements of the local government of Navarra regarding SO2 emissions, the effluent that would be generated by the plant was not expected to meet the required wastewater discharge limit for the Arga River.
Nevertheless, the project beneficiary decided to continue the project on a pilot plant. MAGMA considers that the wet desulphurisation technology was successfully validated on this scale, and it intends to implement the technology at its industrial plant by 2019. The main conclusion obtained from the monitoring of the pilot plant was that the wet desulphurisation technology is able to reduce the SO2 emissions from 7 000 mg/Nm3 to values below to 400 mg/Nm3. Moreover, the effluent generated in the wet desulphurisation process can be crystallised to obtain magnesium sulphate (MgSO4) waste that can be used as fertiliser.
The technology was also shown to reduce the sulphate concentration in the generated effluent to a below 500 mg/l. It furthermore reduces water consumption by 75% with respect to other wet desulphurisation technologies.
This new technology could be a feasible alternative to the traditional dry desulphurisation process to reduce the SO2 emissions, minimising the environmental impacts. Therefore, it could be fostered as a Best Available Technology (BAT) of cement, lime and magnesium oxide. The technology is in line with the European Directives (2010/75 EU, 2008/50/EC, 2001/81/EC, 2001/80/EC and Directive 93/12/EC) and the Geneva Convention on Long-Range Transboundary Air Pollution. The beneficiary intends to include this new technology in the next update of the BAT Reference Document for the Production of Cement, Lime and Magnesium Oxide, as outlined in its After LIFE+ plan.
Furthermore, the technology offers a range of social and economic benefits. The reduction of SO2 emissions will improve the air quality and minimise acid rain, and thus benefit human health, while the water quality of the Arga River will improve as a result of the reduction of the wastewater effluents. Also, the use of reagents based on MgO (waste from the current process) will lead to a reduction in the amount of waste produced. Moreover, the implantation of the new technology will improve the competitiveness of the company, due to the optimisation of the resources and the possibility of obtaining a marketable sub-product (MgSO4). New jobs could potentially be created to the benefit of the local economy.
