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All over the world, emissions of nitrogen oxides (NOx) are causing a wide range of health and environmental effects such as acid rain and deteriorated water quality. This explains why many countries are imposing tougher environmental restrictions on NOx emission.
Primary NOx abatement techniques are often no longer sufficient in order to comply with the more stringent NOx emission requirements. Therefore, secondary abatement techniques like selective non catalytic reduction (SNCR) or selective catalytic reduc- tion (SCR) are increasingly being considered.
FLSmidth recommends SNCR for the following reasons:
- SNCR is a proven technology in the cement industry and can be implemented virtually without affecting kiln operation.
- The capital costs of SNCR are considerably lower than those of SCR, and there is no catalyst that needs to be replaced and disposed of.
- SNCR does not require CFD modelling nor a lengthy pilot study prior to the final design. Depending on the type of refractory lining and local safety regulations, it can often be installed without stopping the kiln at all.
- SNCR causes no pressure loss and does not require standstill heating nor bypass.
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FLSmidth’s SNCR system is fully mechanised and automated. It consists of a storage system with one or more ammonia solution tanks and a pump module for filling (PMF). A pump module for reductant (PMR) supplies a number of control and measuring modules (CMMs) which control the flows of reductant to the respective groups of injection modules (IM). The control system consists of a standard FLSmidth Sub Control System (SCS) with a number of power and network distribution boxes (A0x) and a touch-screen (hu)man/machine interface (HMI). The SCS calculates the flow of reductant needed to comply with the NOx limit, provides set points for the CMMs and communicates with the central control room computer.
SNCR systems in practice
In Europe, tougher NOx limits have already forced a number of cement plants to install SNCR systems, but in many cases they have been reported unable to attain ammonia utilisation factors (AUF) above 40-45% (for each 100 moles of ammonia injected, 40-45 moles of NOx were removed). This is very low compared to the 60-75% generally obtained by the FLSmidth SNCR systems.
Two SNCR systems commissioned by FLSmidth in 2009 showed the following results:
- ILC type kiln 2,800 tpd. Using four injectors with a pressurised air consumption of merely 5 kg/h/injector, NOx emission was reduced from 1015 mg/Nm3, d, 10% O2 to 390 mg/Nm3, d, 10% O2 at an average AUF of 70%.
- SLC type kiln producing 6,300 tpd. Using a total of eight injectors, NOx emission was reduced from 1290 mg/Nm3, d, 10% O2 to 500 mg/Nm3, d, 10% O2 at an average AUF of 68% while maintaining the level of unreacted ammonia below 20 mg/Nm3, d, 10% O2.
Test results
FLSmidth’s SNCR test rigs have achieved NOx reduction figures above 95%, and NOx emission figures below 200 mg/Nm3, d, 10% O2 are often achievable. NOx emission values as low as 100 or even 50 mg/Nm3, d, 10% O2 may be achieved from kilns with ideal conditions in terms of stratifications, temperature, residence time and CO/O2 levels. However, if such NOx emission figures are to be achieved, or if the raw materials give off ammonia, it may be necessary to combine SNCR with a small amount of SCR catalyst – according to what we call the “Slip Break” concept.
SNCR technology on a solid basis
The increased use of waste fuels has led to more stringent NOx emission limits and increased use of kiln gas bypasses. In some cases, it may therefore be difficult to attain the NOx emission target without reducing the NOx emitted via the bypass – a result often considered virtually unachievable without installing an SCR system. FLSmidth, however, has developed SNCR equipment that is suitable for a bypass, and a NOx reduction of approximately 70% has been demonstrated in a full scale plant.
FLSmidth’s SNCR technology was developed by people with a solid background in power generation and “waste to energy” processes. Our capability of predicting the performance of NOx reduction through SNCR is based on more than 20 years of experience in applying this technology under the most diverse process conditions.
No matter what NOx emission standards are imposed which cannot be attained by primary abatement techniques, FLSmidth can provide comprehensive solutions complete with performance guarantees, personnel training, and full process and service support.
For more on SNCR
Two reports describing SNCR tests at two different plants:
Report A
Report B
