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The volume of waste for incineration is growing worldwide. In Europe alone, more than 80 million tons of household waste is burnt every year and this figure is set to rise significantly over the coming decade. 500 incineration plants currently treat around 30 percent of the EU’s municipal waste along with other products such as hazardous residue and sewage sludge.
The sustainability challenge of waste incineration
The combustion of waste produces nitrogen oxides such as nitric oxide (NO) and nitrogen dioxide (NO2). Untreated, these nitrogen oxides (NOx) have devastating impacts both on human health and the climate. In addition to contributing to ground-level ozone, which can trigger serious respiratory problems, they can also react to form harmful nitrate particles and acid aerosols. Furthermore, they contribute to climate change by favoring the formation of acid rain. Last but not least, they can compromise general visibility, water quality and even react to form toxic chemicals. Hence the release of NOx emissions is generally regulated by stringent guidelines and standards around the world.
Stricter emissions regulations for NOx abatement in waste incineration
The European Commission, for instance, recently published a new – and stricter – set of environmental standards for waste incineration emissions. The “Best Available Techniques (BAT) Reference Document for Waste Incineration“ set these new standards for NOx emissions to air from waste incineration processes at 120 mg/Nm³ for new plants and 150 mg/Nm³ for existing plants (daily averages respectively). These standards are referred to as BAT-associated emission levels or BAT-AELs, and they name selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) technologies among the “best available techniques”.
Limitations of SCR and SNCR for waste incineration
SCR and SNCR have a number of limitations in waste incineration operations, particularly in relation to NOx removal performance, asset economics and the operating temperature window. Both technologies require incineration plants to upgrade or alter their combustion and flue gas treatment setup. Adding SCR to an existing plant, for instance, can entail a high up-front investment and often requires a large footprint. By contrast, an SNCR unit requires a lower up-front investment but is limited in terms of its NOx removal efficiency. SNCR units only operate at high temperatures, which may incur additional operating costs for stream reheating when integrated into existing waste incineration plants. Another factor that can push up operating expenses is the catalyst used in SCR. This is prematurely consumed by particulates or dust in the flue gas and thus needs frequent replacement.
In addition, both technologies add a new chemical to the incineration plant’s inventory, namely ammonia or urea. Given that ammonia emission levels are also being tightened in Europe and elsewhere, this can present an additional emission control challenge in waste incineration.
Using the oxidative power of ozone for superior NOx removal
Linde developed a high-performance NOx removal technology that overcomes the performance, temperature and economics constraints of SCR and SNCR. LOTOX ® technology uses ozone to oxidize insoluble NOx to higher oxides that are then captured in a wet scrubber. This low-temperature process enables stable and constant NOx control – regardless of load or concentration. It is the solution of choice for customers looking for 95%+ abatement rates with low up-front investments.
Outperforming SNCR and SCR
LOTOX achieves NOx removal efficiency rates of near zero, thus clearly outperforming both SCR and SNCR in waste incineration plants. In addition, it operates at flue gas temperatures as low as 50°C (122°F), thus avoiding the reheating steps required for SCR (approx. 300°C) and SNCR (approx. 800°C). Other LOTOX highlights include a compact footprint and performance resilience in the presence of particulates in the flue gas. This resilience is particularly important when comparing LOTOX with SCR as it eliminates the operating expenses involved in frequent catalyst replacements.
The ozone required for NOx reduction is produced on site and on demand from oxygen. This means that hazardous chemicals such as ammonia do not need to be stored/handled. The ozone injection step can be integrated into existing pipework in many instances, making this an ideal option for space-constrained installations. Last but not least, LOTOX is easy to retrofit. So it can be used as an add-on to existing SNCR installations that cannot achieve sufficient NOx removal without significant ammonia slip, boosting the SNCR NOx removal performance to close to 95 percent and above.
LOTOX abatement efficiency vs SNCR and SCR
|NOx removal efficiency rates
|30 – 60
|70 – 90
Contact your local Linde representative for more information on how LOTOX can complement your waste incineration operations and contribute to a cleaner environment.