Calciner Addons


Permanently reduce NOX emissions with a one-time investment and no increase in OPEX. Introducing the Pyroredox® gasifying reactor: our state-of-the-art solution for reducing harmful emissions. And if that is not enough to continue reading, the Pyroredox® also has no negative impact on clinker production capacity, fuel consumption or power demand.

Oxidizing Zone

Reducing Zone

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Tertiary air duct to Pyroredox® connection

Kiln inlet to Pyroredox® connection

Meal from penultimate cyclone to Pyroredox® and Pyroclon

Product Features

Two steps to controlling NOX. Here’s how the Pyroredox® does its job.

Product Features

Control the combustion reaction

  1. High amounts of fuel
  2. Kiln gases (low O2 content)
  3. CO-rich conditions

Installed between the kiln inlet chamber and calciner, the Pyroredox® separates reactions that usually happen together in the calciner. In doing so, it controls the formation of chemical compounds at specific points in the pyroprocess so as to influence subsequent reactions.

How does it do this? First, we feed in kiln exhaust gases, which have very low oxygen content. The resulting atmosphere contains insufficient oxygen for complete combustion of the fuel. A sub-stoichiometric combustion reaction therefore takes place, creating CO-rich conditions inside the Pyroredox® loop.

  1. High amounts of fuel
  2. Kiln gases (low O2 content)
  3. CO-rich conditions
Product Features

Good things take (extra) time

  1. CO-rich conditions
  2. CO reacts with NOX
  3. Formation of N2 and CO2
  4. Surplus of CO-rich lean gas

The second essential step is to extend fuel residency time – by about four seconds – in the CO-rich atmosphere of the Pyroredox®. This allows the CO to react with the NOX in the kiln exhaust gases and reduce them to CO2 and harmless N2 nitrogen.

After the kiln exhaust gases have been reduced, the remaining lean gas is fed into the calciner, where oxygen-rich tertiary air and raw meal are added. At this point, classic oxidation of the lean gas and tertiary air takes place in an exothermic reaction that ensures thorough calcination of the raw meal.

  1. CO-rich conditions
  2. CO reacts with NOX
  3. Formation of N2 and CO2
  4. Surplus of CO-rich lean gas
Product Features

The devil is in the details

It might sound complicated. But it boils down to one simple fact: a significant, permanent reduction in your NOX emissions. But when it comes to the details, our process experts will ensure that your Pyroredox® reactor is designed to achieve the highest possible NOX reduction potential for your specific process conditions.

It is all possible thanks to our profound process knowledge and experience, built up over generations here at KHD. So whatever the particular make-up of your kiln exhaust gases, fuels and raw meal, we will find the best Pyroredox® concept to ensure controllable and repeatable NOX emissions reduction.

Key Benefits

When it comes to NOX control, the Pyroredox® is our ultimate solution. Here’s why.

Key Benefits

Cost-effectively reduce your NOX emissions

We are sure this is obvious by now. The Pyroredox® reactor significantly and permanently lowers NOX emissions. But stay with us and let us put some numbers on this. As a stand-alone solution, Pyroredox® achieves emissions levels below 200 mg/Nm3. In combination with SNCR, emissions of <50 mg/Nm3 are easily achievable.

The NOX reduction potential of Pyroredox® plus SNCR is therefore in-line with SCR systems – but at a much lower cost. The Pyroredox® itself is a one-time investment that does not increase OPEX. And it lowers reagent costs in combined Pyroredox®-SNCR systems compared to stand-alone SNCR/SCR systems.

At one 5,500 tpd plant in China, for example, a Pyroredox® reactor with existing SNCR system reduced NOX emissions by 66 % to 50 mg/Nm3 (and 35 mg/Nm3 in an optimized fuel scenario). Ammonia reagent consumption fell by an even higher 78 % to just 400 l/h.

Key Benefits

Ready for any plant – including yours!

You can retrofit a Pyroredox® reactor to any existing plant without impacting production. Erection takes between 16 and 30 weeks and can be done while the plant continues to operate. Commissioning and final process implementation takes between two and four weeks and can be done during regular maintenance shutdown.

Still wondering if it will work for you? Let us summarize. The Pyroredox® works with all typical calciner fuels, even low-volatile alternative fuels. It has no impact on production quality or capacity, power demand or fuel consumption. Nor (as we have said before) does it raise OPEX.

Finally, depending on your local regulations, it can remove the need for investment in secondary measures – or make such solutions cheaper to implement. Which means you can meet environmental and social-licence-to-operate concerns confidently and cost-effectively. That is a lot of good things for a single one-off investment.

How it works

Fuel and kiln exhaust gases are mixed early in the process to create a CO-rich atmosphere that limits new NOX formation and reduces existing NOX to nitrogen.

  • Exhaust Gas (high NOx level)
  • Lean Gas (high CO level)
  • Tertiary Air (high O2 level)
  • Gas after combustion and calcination (low NOx, CO and O2 levels)
  1. Pyrotop®
  2. Penultimate cyclone
  3. Bottom cyclone
  4. Fuel feed
  5. Tertiary air duct
  6. Rotary liln
  7. Meal to kiln
  8. Meal to Pyroclon
  9. Meal to Pyroredox®
  10. Dust outlet to kiln inlet
  11. Pyroredox loop®
  12. Oxidizing zone

Pyroredox® loop

  • Reducing zone
  • Major amount of fuel
  • Small amount of meal
  • DeNOX reaction under optimal conditions

Pyroclon loop

  • Oxidizing zone
  • Small amount of fuel
  • Major amount of meal
  • Complete combustion of gasified reaction products


Find below an overview of successfully realized Pyroredox® projects.

Year Customer Country Size Production (tpd) – Before conversion Production (tpd) – After conversion* Preheater OEM
2022 Shanxi Beiyuan Line 2 China 4,3 x 66 3675 3975 Other supplier
2021 Baoding CUCC China 5,0 x 74 6150 6400 Other supplier
2020 Tengyue Tongli China 4,8 x 72 6000 6300 Other supplier
2020 Shanxi Xinyuan  China 4,3 x 64 3850 4400 Other supplier
2020 Jinrong 2 China 4,8 x 74 6600 6800 Other supplier
2020 Jinrong 1  China 4,8 x 74 6650 6850 Other supplier
2020 BBMG Dingxin China 4,8 x 72 5700 5800 Other supplier
2020 Yuzhou Hubo Line 2 China 5,5 x 78 8070 8500 Other supplier
2020 Yuzhou Hubo Line 1 China 4,8 x 70 6400 6500 Other supplier
2019 Satguru Cement India 3,4 x 54 2200 Humboldt preheater
2019 Guangshan Tianrui China 4,8 x 72 6000 6300 Other supplier
2019 Henan Yongan China 4,8 x 72 5700 6100 Other supplier
2019 Zhengzhou Tianrui China 6,2 x 92 12000 12000 Other supplier


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