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How KHD helps you to permanently lower your NOX emission output with no extra operational cost

Published by
World Cement,

When it comes to cement production, it is all about efficiency and high output rates. When talking about emissions, it is a different kind of story. In more and more countries, NOX emissions and their long term restriction have become a sensitive topic for cement producers. SNCR or SCR systems are established solutions that essentially work fine. But they either come with very high investment and operational cost, or the NOX reduction is highly inefficient and brings new problems like excessive ammonia slip. It is about time for a new solution that does more and costs less!

Introducing Pyroredox from KHD. Pyroredox is a gasifying reactor that is installed between the kiln inlet chamber and the calciner in your preheater. Combined with the right process adaptions, this additional gasification loop adds retention time, but more importantly, enables a controlled separation of the chemical reactions which normally happen in the calciner. Think of the staged combustion principle used in modern emission-reducing calciners like KHD's LowNOX AF, but a significant step further.

Pyroredox forces a substoichiometric combustion by adding high amounts of fuel to the low-oxygen kiln exhaust gases. The fuel brings an abundance of carbon molecules (C) which react with the exhaust gases to form high amounts of carbon monoxide (CO). This so-called Boudouard reaction is the necessary groundwork for the actual NOX reduction.

KHD's gasifying reactor is able to leverage the full DeNOx potential of carbon monoxide, because it is individually designed for your pyro process to provide exactly the additional retention time that the carbon monoxide needs to react with and reduce the nitrous gases to form naturally occurring, harmless nitrogen (N2). Up to this point in the process only very little raw meal has been introduced to Pyroredox, because it impacts the efficiency of the NOX abatement. But when the lean gases from Pyroredox enter the calciner, it is the perfect moment to introduce the high-oxygen tertiary air and the raw meal. The following exothermal reaction is the crucial step that leads to the effective and complete calcination of the raw meal. From here on, the pyro process continues as usual.

To summarise, Pyroredox can significantly reduce NOX emissions while a plant's production level remains completely unaffected. On top of that, KHD's solution neither increases fuel demand nor power consumption! And just to reassure you, Pyroredox has no other hidden operational costs either.

It is time to talk numbers! KHD's Pyroredox is able to achieve NOX emission levels below 200 mg/Nm³. In case the regulated emission level you have to comply with is below that (100 mg/Nm³ or lower), KHD's gasifying reactor can be combined with an SNCR unit to achieve emission levels below 50 mg/N m³. In these cases, on top of the NOX reduction, KHD's reactor will also lower the reagent demand of the SNCR system and keep its ammonia slip in line. Such upgrades have already been conducted successfully by KHD in China. Pyroredox was installed in multiple plants with existing SNCR systems.

One example project that is already commissioned and in regular operation is Tianrui group's Weihui plant (5500 tpd) in the Henan province. Without Pyroredox and process optimisation the plant produced approximately 150 mg/Nm³ of NOX emissions with a constant ammonia (NH3) injection of 2.100 l/h.

Now, after months of stable operation, Pyroredox in combination with the SNCR system achieves a constant emission level 50 mg/Nm³ with an ammonia consumption of 450 l/h. That means NOX emission was reduced by more than 66% and the ammonia consumption by 78%! Just to reiterate, all that was achieved without deteriorating production capacity, power consumption or fuel demand. Moreover, it has to be said that the above stated results are achieved with just conservative adaptions to the overall process and fuel injection scenarios. Hence, the emission levels that Pyroredox can ultimately achieve are even lower!

KHD are pretty excited about this. And you should be too. Aside from the great operational results, the installation of Pyroredox is straightforward. Taking existing preconditions into consideration, the installation time for a Pyroredox gasifying reactor varies between 16 and 30 weeks (while the plant remains in operation). The subsequent connection and commissioning takes another two to four weeks and can be executed during a regular maintenance shutdown window!

NOX emissions are a serious threat for your production and our environment. Due to that, their sustainable reduction is nowadays an essential task for modern cement producers. If you are one of those, you should visit to learn more and talk to KHD to get started today.

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