1 STUDY OF THE KEY TECHNOLOGY OF SNCR DENITRIFICATION AND APPLICATION ON 300 MW CFB BOILERS Gao Hongpei, Lin Weirong, Wang Haitao, Han Ying, Zhang Jirui, Liu Haifeng, Liu Bin Huaneng Clean Energy Research Institute, 102209, Beijing, China, [email protected]ABSTRACT This paper describes the summarization of the key technology of denitrification and application on 300MW CFB boilers. Based on the literatures about the mechanism of NOx formation and destruction, the low NOx emission optimized control combustion experiments demonstrated the obvious denitrification effect, for the purpose to control NOx emission to be lower than 50mg/m 3 . The domestic proprietary spray guns used on SNCR system have successfully been developed with the optimized CFD technology application, the SNCR denitrification system can operate with the authorized denitrification efficiency higher than 85% and have successfully been applied on more than 50 300 MW degree CFB boilers. KEYWORDS: CFB, Denitrification, High Efficiency SNCR Technology, 300MW CFB Boilers Application 1. Introduction Circulating Fluidized Bed (CFB) boiler technology has rapidly developed in the past decades, due to its advantages in high combustion efficiency, wide fuel source, good load adjustability, low pollutant emission, and so on [1] . The boiler capacity has increased from 100 MW in the 1970s to 600 MW with Sichuan Baima Demonstration Power Plant as the first 600 MW scale unit in the world. There exist around 300 CFB units with capacity over 100 MW in China, ~57 units of which are 300 MW scale. Compared with Pulverised Coal (PC) boiler, pollutant emission is much lower in CFB boiler, but not low enough to meet the severe environmental policy. For pollutant of NOx, the original emission varies from 150~400 mg/Nm 3 , much higher than the upper limit of 50 unit for ultra-low emission. Therefore, denitrification solution seems necessary [2] . Efficient solution to control NOx emission in CFB boiler operation contains NOx formation suppression during coal combustion and post-combustion NOx removal with the aid of reductants, such as ammonia or urea. The former process lies in the optimization of boiler operation parameters while the latter is based on the denitrification reaction: NH 3 + NOx→N 2 + H 2 O. For denitrification technology, there are Selective Catalytic Reduction (SCR) and Selective Non-Catalytic Reduction (SNCR). SCR requires utilization of catalyst and is widely applied in PC boiler flue gas treatment while SNCR denitrification can directly work in flue gas without catalyst and the reaction condition, e.g., temperature (850~1150 ℃), is close to CFB flue gas. Compared with SCR denitrification, SNCR technology has advantages, such as low invest and operation cost, compact structure, simple installation and operation, rapid response, no SO 2 oxidation and so on. Nevertheless, the weak points for SNCR is still obvious, that is, low denitrification efficiency (40~60%) and high NH 3 leak [3] . In this paper, the key technology of SNCR denitrification based on urea is studied, including spray experiments/simulation, flow field observation in 300 MW scale CFB boiler as well as the SNCR
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STUDY OF THE KEY TECHNOLOGY OF SNCR DENITRIFICATION AND APPLICATION ON 300 MW CFB BOILERS
Gao Hongpei, Lin Weirong, Wang Haitao, Han Ying, Zhang Jirui, Liu Haifeng, Liu Bin
Huaneng Clean Energy Research Institute, 102209, Beijing, China, [email protected]
ABSTRACT
This paper describes the summarization of the key technology of denitrification and application on
300MW CFB boilers. Based on the literatures about the mechanism of NOx formation and destruction,
the low NOx emission optimized control combustion experiments demonstrated the obvious
denitrification effect, for the purpose to control NOx emission to be lower than 50mg/m3. The domestic
proprietary spray guns used on SNCR system have successfully been developed with the optimized CFD
technology application, the SNCR denitrification system can operate with the authorized denitrification
efficiency higher than 85% and have successfully been applied on more than 50 300 MW degree CFB
boilers.
KEYWORDS: CFB, Denitrification, High Efficiency SNCR Technology, 300MW
CFB Boilers Application
1. Introduction
Circulating Fluidized Bed (CFB) boiler technology has rapidly developed in the past decades, due to
its advantages in high combustion efficiency, wide fuel source, good load adjustability, low pollutant
emission, and so on[1]. The boiler capacity has increased from 100 MW in the 1970s to 600 MW with
Sichuan Baima Demonstration Power Plant as the first 600 MW scale unit in the world. There exist
around 300 CFB units with capacity over 100 MW in China, ~57 units of which are 300 MW scale.
Compared with Pulverised Coal (PC) boiler, pollutant emission is much lower in CFB boiler, but not
low enough to meet the severe environmental policy. For pollutant of NOx, the original emission varies
from 150~400 mg/Nm3, much higher than the upper limit of 50 unit for ultra-low emission. Therefore,
denitrification solution seems necessary [2].
Efficient solution to control NOx emission in CFB boiler operation contains NOx formation
suppression during coal combustion and post-combustion NOx removal with the aid of reductants, such
as ammonia or urea. The former process lies in the optimization of boiler operation parameters while the
latter is based on the denitrification reaction: NH3 + NOx→N2 + H2O. For denitrification technology,
there are Selective Catalytic Reduction (SCR) and Selective Non-Catalytic Reduction (SNCR). SCR
requires utilization of catalyst and is widely applied in PC boiler flue gas treatment while SNCR
denitrification can directly work in flue gas without catalyst and the reaction condition, e.g., temperature
(850~1150 ℃), is close to CFB flue gas. Compared with SCR denitrification, SNCR technology has
advantages, such as low invest and operation cost, compact structure, simple installation and operation,
rapid response, no SO2 oxidation and so on. Nevertheless, the weak points for SNCR is still obvious, that
is, low denitrification efficiency (40~60%) and high NH3 leak [3].
In this paper, the key technology of SNCR denitrification based on urea is studied, including spray
experiments/simulation, flow field observation in 300 MW scale CFB boiler as well as the SNCR
2
simulation. Then, combustion adjustment/SNCR system optimization operation is carried out for ultra-
low emission of NOx after the optimal SNCR scheme is designed and implemented.
2. Method 2.1 CFB combustion optimization
Air-staging combustion optimization is carried out on 300 MW CFB boiler (type of DG1100/17.4-II3
by Dongfang Boiler Co., Ltd, see Table 1) in Datang Wu’an Power Plant and the goal is to suppress the
formation of NOx during coal combustion and decrease the original NOx emission level. Aar, Nar and
Qnet,ar of the coal utilized is 43.4%, 0.79% and 3630 kCal/kg, respectively. Operation parameters of
primary air amount, secondary air amount, air ratio, bed temperature, etc. under load of 100%, 80% and
70% are optimized under the criteria of boiler heat efficiency and NOx emission.
Table 1 Main thermal parameters of 300 MW CFB boiler