Optimal Design and Operation of SNCR System for a 150t/h CFB Boiler and Discussion on the Measurement of Flue Gas Components

Transcription

1 Optimal Design and Operation of SNCR System for a 150t/h CFB Boiler and Discussion on the Measurement of Flue Gas Components Yang Hairui Tsinghua University 66 th IEA-FBC meeting 18-20, March, 2013 Brno, Czech Republic

2 Content 1 Background 2 Design and Operation of the SNCR System 2.1 Introduction of the 150t/h CFB Boiler 2.2 Design of the SNCR system 2.3 Performance of the SNCR system 3 Discussion on the Measurement of Flue Gas Components 3.1 Problems in the Previous Measuring Methods 3.2 Suggested Measuring Method 4 Summary

3 Background The total NOx emission of China in 2010 is ton The NOx emission from coal-fired power plants is about 79.1% in For NOx emission, the new National Emission Regulation (NER) of China is 100mg/Nm 3 (dry base, 6%O 2 ), which is more stringent than other countries & regions. NOx emissions of China in recent years [The Chinese Ministry of Environmental Protection, 2012] NOx emission regulation of several countries & regions [Q. Sheng, 2011] 1

4 Background SCR is not fit for CFB boilers Catalyst Space Cost The dust conc. of flue gas is harmful to the catalyst. Especially, the catalyst will be poisoned by the residual CaO from in-situ desulphurization. The space under economizer is not enough to place the SCR reactor. The cost of SCR is about 3~5 times more than SNCR, which will greatly weaken the advantage of CFB boilers. Considering the CFB s feature of low initial NOx emission, SNCR is preferable with the advantages of moderate denox efficiency, low cost, simplexes of installation and operation etc. The CFB cyclone is regard as a satisfying region for SNCR reaction due to the proper temperature, strong turbulence and mixing effect. 4NH 3 +4NO+O 2 =4N 2 +6H 2 O ( NH 3 as reductant ) 2CO(NH 2 ) 2 +4NO+O 2 =4N 2 +2CO 2 +4H 2 O (Urea as reductant ) 2

5 Design and Operation of the SNCR System Introduction of the 150t/h CFB Boiler Basic parameters of 5 # CFB boiler of Shengzhou thermal power plant No. Item Unit Value & Description 1 Manufacturer Taiyuan Boiler Company, China 2 Location Shengzhou, Zhejiang Province 3 Time in operation Feb, BMCR t/h Rated steam temperature o C Rated steam pressure MPa Feed water temperature o C Exit flue gas temperature o C Fuel consumption t/h Boiler heat efficiency % 91.2 Simplified drawing of 5 # CFB boiler of Shengzhou thermal power plant 3

6 Design and Operation of the SNCR System Introduction of the 150t/h CFB Boiler Proximate and ultimate analysis of the fuel Cumulative mass fraction Fuel of 5# boiler Cumulative mass fraction Slag of 5# boiler Particle size (μm) Particle size (μm) PSD of the fuel PSD of the bottom ash PSD of the fly ash(d 50 =22.271μm,d 90 =67.823μm)

7 Design and Operation of the SNCR System NO NO x (mg/nm 3 x conc. ) O 2 conc. of O sampling 2 (%) point Flow of primary air (Nm 3 /h) Load (t/h) Primary air Secondary air Introduction of the 150t/h CFB Boiler NO NO x x O Sampling 2 point O Furnace 2 Boiler load Time (h) 6 4 O 2 conc. of O furnace 2 (%) Flow of (Nm 3 /h) secondary air NO NO x (mg/nm 3 x conc. ) (kpa) Bottom p drop T of furnace bottom () Fuel consumption (t/h) NO NO x x Bottom - Upper Furnace bottom Cyclone outlet The relationship of NOx and several other parameters Fuel consumption Time (h) Upper p (kpa) drop () T of cyclone outlet 5 The NOx emission conc. in this case is greatly influenced by the O 2 conc. of the combustion zone. It is significant to decrease the initial NOx emission by combustion adjustment to reduce the burden of SNCR system.

8 Design and Operation of the SNCR System Design of the SNCR System Calculation of ammonia solution consumption No. Item Unit Value 1 Rated flow of the flue gas Nm 3 /h NSR Initial NOx emission conc. mg/nm Target NOx emission conc. mg/nm Mass fraction of ammonia solution 20% 6 Consumption of ammonia solution L/h 70 DeNOx efficiency Ammonia solution of low conc. Urea solution Ammonia solution is used as the reductant in the Shengzhou SNCR project. Considering the general NOx emission conc., the SNCR denox efficiency should be at least 70% to meet the regulation. NO x emission conc. (mg/nm 3 ) h NO x average value Risk Ammonia solution of low conc. Ammonia solution of high conc Time (h) Comparison of low conc. ammonia solution and other reductant 24h monitoring data of initial NOx emission conc. 6

9 Design and Operation of the SNCR System Design of the SNCR System Flow chart of the Shengzhou SNCR system The consumption of ammonia solution is controlled by the NOx emission conc. and the consumption of dilution water is adjusted to maintain the optimal atomization effect of nozzles. 7

10 Design and Operation of the SNCR System Design of the SNCR System Nozzles Ammonia distribution in the cyclone (2 nozzles) Basic parameters of nozzles No. Item Unit Value & Description 1 Nozzle number of each cyclone 2 2 Nozzle position Top of the cyclone inlet 3 Nozzle type Air atomizing nozzle 4 Spray speed m/s 45 5 Spray angle 40 (=2α) 6 Average atomized size μm 50 Viewing from the results of CFD simulation, though the reductant conc. in the upper zone of cyclone is rather high, the mixing effect in the flue benefits for the SNCR reaction. Compressed air Ammonia solution Simplified drawing of the spray lance 8

11 Design and Operation of the SNCR System Design of the SNCR System Injection points Nozzles Ammonia solution tank Flow distributor Pumps Injection points (Cyclone inlet) Compressed air tubes 9 Dilution water tank

12 Design and Operation of the SNCR System Performance of the SNCR System NO x emission conc. (mg/nm 3 ) Start Stop NO x (mg/m 3 ) NO x NH NH 3 (ppm) Time (h) 72h continuous running test of the Shengzhou SNCR system Ammonia solution NH 3 溶液 consumption 用量 ( L/h) (L/h) DeNOx effect test of the Shengzhou SNCR system 0 The SNCR denox efficiency could reach 80% with the NOx emission conc. of less than 80mg/Nm 3 and NH 3 slip of less than 10ppm. With the increase of NSR, the maximum SNCR denox efficiency could be over 90%, while the NH 3 slip increases sharply. 10

13 New SNCR design in 2*300MWe CFB boilers Midong 300MWe CFB boiler, Xiangjiang Provence Flue gas flow rate: Nm 3 /h (O2,6%) Nox initial con. 400mg/Nm 3, Reductant : Ammonia solution, 20%, 2640kg/h denox efficiency: >80% Comssioning: Nov. 2013

14 Discussion on the Measurement of Flue Gas Components Problems in the Previous Measuring Methods Stainless steel tube Prepositive filter Pump Water removal equipment Flue gas analyzer Schematic diagram of the previous measuring method Water 12 Some water-soluble components, such as NO 2, NH 3 and SO 2, may be absorbed during water removal process. Ash Some components, such as NO, N 2 O, may be catalytically reduced by the ash which blocks the filter, especially in the high-temperature cases (e.g. T>1000K). [I. Aarna, et al., 1997; Z. Zhao et al., 2002] NO+CO 1 N +CO NO+CO 2 N 2+CO2 2NO+C N 2 +CO 2

15 Discussion on the Measurement of Flue Gas Components Suggested Measuring Method Schematic diagram of the suggested measuring method 15 Most of the particles will be entrained into the cyclone so that much less particles will block the porous ceramics filter and react with the flue gas components. The high-temperature infrared analyzer( Fӧdisch MCA04-M is employed to eliminate the errors caused by the water removal process.

16 Summary Design and Operation of the SNCR System in 150t/h CFB boiler Ammonia solution is used as the reductant in the Shengzhou SNCR system. The SNCR denox efficiency could reach 80% with the NOx emission conc. of less than 80mg/Nm 3 and NH 3 slip of less than 10ppm. With the increase of NSR, the maximum SNCR denox efficiency could be over 90%, while the NH 3 slip increases sharply. It is recommended to decrease the initial NOx emission conc. by combustion adjustment to reduce the burden of SNCR system. There is no obvious relationship between denox and SO 2 emission found during shutting down the SNCR system. Discussion on the Measurement of Flue Gas Components Considering the influence of water and ash, there exists some problems in the previous measuring methods of flue gas components. With the high-temperature infrared analyzer and gas-solid separator, a suggested measuring method is proposed, which may solve the problems mentioned above. 16

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