[Objective

]

To achieve low-carbon and clean combustion in large-scale coal-fired power plant boilers

this paper takes methanol as an alternative fuel and conducts numerical simulation on methanol co-firing in a 660 MW supercritical tangentially-fired coal-fired boiler. [Methods

]

A comprehensive numerical simulation method was adopted to systematically investigate the influence of different methanol blending ratios and injection positions on the combustion and emission performance of the boiler. Specifically

the methanol blending ratio was set in the range of 0～30%(with 0 as the pure coal combustion re

ference group)

and multiple typical injection positions(lower layer

middle layer

upper layer) were selected along the height of the furnace to simulate the co-combustion process. The simulation focused on analyzing the changes of in-furnace combustion characteristics(including furnace temperature distribution and burnout rate)

flue gas component distribution(including the content of H_2O

CO and CO

2

)

and pollutant emission characteristics(including NO and CH_2O). [Results

]

The overall furnace temperature decreases with the increase of the co-firing ratio due to the combined effects of the high latent heat of vaporization of methanol and the increased specific heat capacity of the flue gas caused by water vapor in the combustion products. Specifically

the temperature drops by 96 K at a 30% co-firing ratio

resulting in delayed ignition of pulverized coal

insufficient combustion

and a decrease in burnout rate. NO emissions are significantly reduced owing to the nitrogen-free nature of methanol and its inhibitory effect on thermal NO. Methanol combustion produces a small amount of formaldehyde(CH_2O)

an unconventional pollutant. As the methanol injection position moves upward

methanol comes into full contact with oxygen

leading to more complete combustion

and the combustion center is concentrated in the main combustion zone. The temperature in the primary combustion zone rises by approximately 81 K

while the temperature in the overfire air zone decreases by about 70 K. Concurrently

the strong reducing zone in the upper part of the main combustion zone leads to a significant decrease in the outlet mass concentrations of NO and CH_2O. [Conclusion

]

Considering both combustion and emission characteristics

15% is identified as the optimal co-firing ratio. At this ratio

the burnout rate is 97.51%

the outlet NO mass concentration decreases from 270.6 mg/m

3

to 216.5 mg/m

3

(a 20% reduction)

the peak CH_2O mass concentration is 1.34 mg/m

3

with an outlet mass concent

ration of 1.95×10

–4

mg/m

3

. Injecting methanol at the upper oil nozzle is the optimal configuration

where the burnout rate is 97.52%

the NO outlet mass concentration is 199.96 mg/m

3

the peak CH_2O mass concentration is 2.13 mg/m

3

and the outlet mass concentration is 1.2×10

–4

mg/m

3

.