Two steps to controlling NOX. Here’s how the Pyroredox® does its job.
Control the combustion reaction
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.
- High amounts of fuel
- Kiln gases (low O2 content)
- CO-rich conditions
Good things take (extra) time
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.
- CO-rich conditions
- CO reacts with NOX
- Formation of N2 and CO2
- Surplus of CO-rich lean gas
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.
When it comes to NOX control, the Pyroredox® is our ultimate solution. Here’s why.
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.
Discover more about how KHD technologies are reducing the environmental impact of cement on our Clean Solutions page.
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.
- Penultimate cyclone
- Bottom cyclone
- Fuel feed
- Tertiary air duct
- Rotary liln
- Meal to kiln
- Meal to Pyroclon
- Meal to Pyroredox®
- Dust outlet to kiln inlet
- Pyroredox loop®
- Oxidizing zone
- Reducing zone
- Major amount of fuel
- Small amount of meal
- DeNOX reaction under optimal conditions
- 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|
|2021||Tengyue Tongli||China||4,8 x 72||5900||5900||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||Guangshan Tianrui||China||4,8 x 72||6000||6000||Other supplier|
|2019||Xingdeng Tianrui||China||4,8 x 72||5700||6000||Other supplier|
|2019||Zhengzhou Tianrui||China||6,2 x 92||12000||12000||Other supplier|
|2018||Xingdeng Tianrui||China||4,8 x 72||5750||5800||Other supplier|
|2018||Xingdeng Tianrui||China||4,8 x 72||5750||6100||Other supplier|
|2017||Chettinad||India||5,0 x 82||7000||–||KHD (new line)|