Retrofit von Industriekesseln zur Brennstoffänderung und NOx- Reduzierung. Dr.-Ing. Marco Derksen

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1 Retrofit von Industriekesseln zur Brennstoffänderung und NOx- Reduzierung Dr.-Ing. Marco Derksen

2 Contents NOx formation In-furnace NOx reducing measures Application of premixed combustion Experiences in Stork test facility Conclusions 2

3 NOx formation Fuel NOx Formed by the conversion of chemically bound Nitrogen with the Oxygen in the combustion air. Formation depends on N content in the fuel and availabilty of Oxygen Thermal NOx Thermal fixation of atmospheric N2 with Oxygen at high temperatures in the combustion zone. Formation depends on the combustion air temperature Prompt NOx Result of Hydrocarbon radicals reacting with Nitrogen components like HCN, NH3 3

4 NOx versus fuel type 4

5 Techniques for in-furnace NOx reduction Low NOx burners Fuel staging staging Flue Gas Recirculation (FGR) Burner staging with Over Fire (OFA) 5

6 staging Secondary air register Primary air register Natural gas spuds Ignition burner Oil burner with flame stabilizer H2 gas spuds 1) Fuel-rich central flame 2) Mixing zone 3) Burnout zone 6

7 Fuel staging Fuel lean primary flame (A) (4) Remainder of the fuel injected into post-flame zone (B) of primary flame (A) (2) (1) (3) (A) (B) Combustion products of zone (A) and internal FGR (4) dilute post flame zone (B) (B) 1. Combustion air 2. Secondary gas 3. Primary gas 4. Flue gas A primary combustion zone B secondary combustion zone 7

8 Flue gas recirculation Fresh air Flue gases Consequences for burner design and boiler performance Very effective NOx reduction 8

9 Burner staging with over-fire air Burners fire understoichiometric (less O2 than needed for complete combustion) Remaining air supplied at top of furnace in burnout zone Specially suitable for oil combustion 9

10 Presently realized NOx values Fuel Retrofit New build Gas firing Good Very good Light fuel oil Very good Good Heavy fuel oil Good Very good Coal Very good Very good 10

11 Experiences in Stork Test facility New firing concept for Stork Impulse burner (4) Center burner is premixed (2) (B) 9MW total firing capacity of test burner (1) Lean Premix (3) (A) Up to 4MW premixed combustion possible (B) 11

Advantages of premixed combustion Premixed flame Fuel and oxidants

from fresh fuel-air mixture Products + fuel Flame front Possible

Well-known and used technique in gas turbines, household heating

12 Advantages of premixed combustion Premixed flame Fuel and oxidants are perfectly mixed prior to combustion Flame separates products from fresh fuel-air mixture Products + fuel Flame front Possible to eliminate thermal NOx Fuel Bunsen burner in premix mode Well-known and used technique in gas turbines, household heating systems Not yet applied in boilers Typical household central heating system 12

13 Experiences in Stork s test facility New burner concept for Stork Impulse burner (4) Premixing using ejectors High-quality premixing No low-velocity zones in premixing duct Employ gas-pressure energy as extra air pump o Use main air fan for remaining premix air requirement (2) (1) Lean premix (3) (A) (B) (B) Fuel Mixture Ejector 13

14 Fuel staging with lean premix Primary flame (A) is now lean, premixed flame No thermal NOx formation in primary flame New design Stork Impulse burner: (4) (2) (B) Fuel staging principle has not changed Very low NOx emissions of total flame (1) Lean premix (3) (A) Total flame principle is not changed: very little consequences for furnace (B) No enhanced risk of CO emissions in contrast to other NOx reduction measures 1. Combustion air 2. Secondary gas 3. Primary gas 4. Flue gas A primary combustion zone B secondary combustion zone 14

15 Experiences in Stork s test facility Present design (6 burner installation) Test burner (Test rig, in full operation) 15

16 Experiences in Stork s test facility Down to 0.5% O2 with negligible CO Ultimate performance: 9mg 3% O2 16

17 Conclusions In-furnace low-nox measures can reduce NOx emissions to below 50 mg/nm3 when firing Natural Gas 10 mg/nm3 NOx is possible with in-furnace measures, by taking advantage of premixed combustion with fuel staging Proven performance in Stork test furnace 10 mg/nm3, YES at optimal conditions Integration of burner and combustion chamber design necessary But: Ultra-low NOx design starts at the burner Every installation and fuel is different; Ultimate NOx reduction is every time a challenge 17

C C A. Combustion Components Associates, Inc.

C C A. Combustion Components Associates, Inc. C C A Combustion Components Associates, Inc. www.cca-inc.net About CCA CCA is a global provider of combustion control technologies to reduce NOx, particulate matter (PM), unburned carbon and CO emissions