Meeting the low-cost NOx reduction challenge
In anticipation of stricter future emissions regulations, Taiheiyo Engineering Corp has been developing various cement kiln NOx reduction technologies. The most recent breakthrough combines the company’s new NOx reduction technology with selective non-catalytic reduction to achieve significant reduction rates at low cost. By Toshiaki Hirose, Taiheiyo Engineering Corp, Japan
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Taiheiyo Engineering Corp has continued to develop its NOx
reduction technology to support cement companies in meeting
increasingly stricter NOx emission limits (© Halla Cement Corp)
The regulated limits for NOx emissions from cement kilns have become increasingly stricter and today NOx reduction is one of the key sustainability challenges for the cement industry.
Conventionally, it was believed that selective catalytic reduction (SCR) was the only way to achieve these limits for NOx emissions. However, since SCR investment and running costs are very high, the quest for a low-cost innovative NOx reduction technology has been an important goal for the cement industry.
Conventional NOx reduction technology
The first generation: Taiheiyo Two-Stage Combustion System
Taiheiyo Engineering Corp (TEC) has been commercialising its NOx reduction technology, the Taiheiyo Two-Stage Combustion System for NSP kilns, for over a decade.
This technology comprises one or two deNOx burners installed at the low oxygen area between the riser duct and the calciner, where part of the calciner fuel is combusted. So, NOx from the kiln is reduced and NOx generation is suppressed in the calciner.
![](/content/uploads/images/30b35db3-12e6-480a-8cce-e2d59ec2c2fd.jpg)
Figure 1: Taiheiyo Engineering Corp’s DeNOx System
(© Taiheiyo Engineering Corp)
By combusting ~30 per cent of calciner fuel by deNOx burners, ~10-30 per cent of NOx emissions can be reduced at the stack (depending on the number and position of the deNOx burners).
Based on this result, it was expected that NOx emissions could be reduced further by increasing the fuel to the deNOx burners. However, taking into account coating issues at the riser duct, the fuel to the deNOx burners was limited to up to ~30 per cent of calciner fuel.
The second generation: Taiheiyo DeNOx System
To increase the fuel to the deNOx burners without causing coating issues, TEC developed the Taiheiyo DeNOx System by combining the Taiheiyo Two-Stage Combustion System with the Taiheiyo Coating Solution (TCS) System.
However, even with the Taiheiyo DeNOx System, the fuel to the deNOx burners was limited to up to 50 per cent of calciner fuel (see Table 1).
Table 1: NOx reduction effect with Taiheiyo DeNOx system |
|||
|
Without NOxreduction technology |
Taiheiyo DeNOx system (deNOx burners + TCS system) |
|
Fuel rate fed to deNOx burners (%) |
0 |
50 |
66.8 |
Stack NOx reduction rate (%) |
0 |
14 |
30 |
Plastic waste feeding point |
Calciner |
Calciner |
Calciner |
Coating on the riser duct |
No issue |
No issue |
Issue |
TEC’s latest NOx reduction technology
In recent years, TEC has been developing and commercialising its TTR®-G technology to gasify plastic waste using hot meal for the efficient use of alternative fuels. The gas from the TTR®-G system contains a considerable level of hydrocarbons that are highly effective in reducing NOx as shown in the following reaction formulas:
• NO + CO → N2 + CO2
• NO + CmHn → NH3 + CO
• NH3 + O2 → NH2 + H2O
• NH2 + NO → N2 + H2O
Figure 2 provides an outline of the new NOx reduction technology.
![](/content/uploads/images/ed4a7893-1102-4f6d-8a7e-378e892b4142.jpg)
Figure 2: Taiheiyo Engineering Corp’s TTR®-G + deNOx burners combine in new DeNOx technology
(© Taiheiyo Engineering Corp)
Hot meal with a temperature of 740°C is extracted from the bottom of the second cyclone chute and enters the TTR-G system. The hot meal and plastic waste are mixed together in the system, and the mixed material (hot meal and residue of plastic waste) and flammable gas are discharged via separate routes. They are subsequently merged and fed into the riser duct.
The outlet temperature from the TTR-G system is controlled at 520°C. As all hot meal in the second cyclone from the bottom would have originally entered the calciner, the flow of hot meal is the same even if a portion of it is extracted and enters through the TTR-G system. Therefore, kiln operations are not affected.
Furthermore, the low temperature of the mixed material and flammable gas feeding to the riser duct prevent coating. Therefore, 100 per cent of the calciner fuel can be combusted by the deNOx burners. TEC also improved the design of the deNOx burners to enable the efficient mixing of the TTR-G gas and the NOx reducing agent. As a result, NOx emissions at the stack can be reduced by 40 per cent.
Table 2: NOx reduction effect with TTR®-G + deNOx burners + SNCR |
||
|
Without NOxreduction technology |
TTR®-G + deNOx burners + SNCR |
Fuel rate fed to deNOxburners (%) |
0 |
100 |
Stack NOx reduction rate (%) |
0 |
70 |
Plastic waste feeding point |
Calciner |
TTR-G |
Coating on the riser duct |
No issue |
No issue |
New NOx reduction technology + SNCR
To further develop its NOx reduction technology, TEC has combined the new NOx reduction technology (TTR-G + deNOx burners) with SNCR to achieve a NOx reduction rate of ~70 per cent. Table 2 shows the NOx reduction effect.
Lower heat demand
Table 3 shows a comparison between TTR-G and direct feeding of plastic waste to the calciner.
Table 3: comparison of heat loss between TTR®-G and direct feeding of plastic waste to the calciner |
|||||||
Plastic waste feeding point |
Plastic waste feed rate (tph) |
Specific gas volume – IDF (Nm3/kg clinker) |
Gas temperature – IDF (°C) |
Heat loss of exhaust gas (kJ/kg clinker) |
CO (ppm) |
Heat loss of unburnt CO (kJ/kg clinker) |
Total heat loss (kJ/kg clinker) |
Direct feeding to calciner |
10 |
1.74 |
341 |
891.8 |
6436 |
34.5 |
1036.2 |
TTR-G |
10 |
1.59 |
316 |
752.7 |
4519 |
22.2 |
845.6 |
Difference |
0 |
-0.14 |
-25 |
-139.1 |
-1917 |
12.3 |
190.6 |
According to Table 3, the gasification process also improved combustibility and reduced CO concentration, specific gas volume, and gas temperature at the IDF outlet. Therefore, by reducing the heat loss of exhaust gas, including unburnt CO at the IDF outlet, the reduction in heat consumption was 190.6kJ/kg of clinker (coal equivalent: 1.64 tph).
Conclusion
High NOx reduction effect
Taiheiyo Engineering Corp’s new NOx reduction technology (TTR-G + deNOx burners) and SNCR can achieve almost the same NOx reduction efficiency as SCR (see Table 4).
Table 4: NOx reduction technologies and their effectiveness |
|
NOx reduction technology |
NOx reduction rate (%) |
SNCR |
30 |
TTR-G + deNOx burners |
40 |
TTR-G + deNOx burners + SNCR |
70 |
SCR |
80 |
Furthermore, the amount of NOx-reducing agent by the new NOx reduction technology is enormous compared with the amount of NOx generated in the cement kiln. Therefore, further NOx reduction is possible by improving the mixture of the NOx-reducing agent and NOx.
In addition, a reduction in CO concentration can be confirmed due to the improved combustibility by gasification and a reduction of total hydrocarbon emissions is expected.
Low investment cost
The investment cost of the new NOx reduction technology is ~20 per cent of the investment cost of SCR.
In addition, large-scale modification of the preheater, such as increasing the volume of the calciner, is not required. The system’s installation work can be completed within a month during the maintenance period.
![](/content/uploads/images/3bf12f01-bd22-4196-9d3a-d3f5828bbb87.jpg)
The new NOx reduction technology developed by Taiheiyo Engineering Corp supports cement companies,
such as this cement plant in South Korea, in making their operations more sustainable
(© Taiheiyo Engineering Corp)
Improvement of the clinker production process
The new NOx reduction technology has several advantages, as it:
• improves combustibility
• reduces heat consumption compared with direct feeding to the calciner
• prevents coating issues
• contributes to stable operation.
The new NOx reduction technology is just one of many efforts by Taiheiyo Engineering Corp to contribute to environmental protection. The company is committed to developing and supplying the most innovative technologies and services for a green and sustainable society.
References
1 YAMAMOTO, Y (2020) ‘Drying sewage sludge with preheated raw meal’ in: ICR, September p79-80.
2 YAMAMOTO, Y (2021) ‘No time to waste’ in: WC, (6), p51-54.
3 YAMAMOTO, Y (2022) ‘Gasification technology for shredded solid waste’ in: ICR, November, p65-66.
This article was first published in International Cement Review in August 2024.