Strategies for NOx / SOx reduction at biogas power plants using pellets. E. Stamate

Transcription

1 Strategies for NOx / SOx reduction at biogas power plants using pellets E. Stamate Department of Energy Conversion and Storage Technical University of Denmark Part-financed by the European Union (European Regional Development Fund

2 Outline Context NOx reduction mechanism Middle scale pilot tests for natural gas and biomass power plants Small size NOx/SOx PlasTEP reactor available at DTU Conclusions MOTIVATION Address the particularities of NOx/SOx reduction in biomass power plants

3 Context Estimates show that it is possible to raise Danish agricultural production of biomass for bioenergy 4-5 times through greater exploitation of straw at CHP plants, slurry for biogas, animal fat for biodiesel and by using perennial energy crops as well as grass from low-lying areas. (Ministry of Food, Agriculture and Fisheries of Denmark) Source: DONG Energy Responsibility 2012 Report. Footer 2

4 Context Source: DONG Energy Responsibility 2012 Report. Footer 3

5 Context Source: DONG Energy Responsibility 2012 Report. Footer 4

6 Context Source: DONG Energy Annual Report 2012 Footer 5

7 Introduction Ozone O 3 NOx N 2 O 5 NO+O 3 NO 2 +O 2 2NO 2 +O 3 N 2 O 5 +O 2 N 2 O 5 +H 2 O 2HNO 3 HNO 3 (aid rain) NOx High temperature burner Power plants, gas turbines incinerators, boilers, diesel, etc. Strong negative effects on the quality of air, soil and human health NOx Use the same principle to reduce the NOx under controllable conditions 95% NO (0.063 g/l) 5% NO 2 (1.260 g/l)

8 NOx reduction technologies NOx reduction technologies: - Selective catalytic reduction - Selective non-catalytic reduction - Low-temperature oxidation by ozone - Non-thermal plasma - Electron beam irradiation and several hybrid techniques None of these methods is free of trade-offs and limitations. Advantages of low temperature oxidation: - The discharge device is kept clean (the exhaust gas does not pass through the discharge reactor); - The removal rate of NO is higher comparing with direct oxidation methods which has discharge poisoning problem (occurrence of reverse reactions reforming NO and NO 2 by O radical)

9 Typical NOx reduction setup 1. Flue gas flow 2. NOx concentration 3. Inlet flue gas temperature 4. Electric power to ozone generator 5. Oxygen production 6. Oxygen consumption 7. Ozone production 8. Reactor temperature 9. ph in scrubber media 10. Temperature of scrubber media 11. Ozone concentration after scrubber 12. Temperature after scrubber 13. NOx after scrubber flue gas blower catalyst stack water 1-3 REACTOR O 2 /O 3 flow 6-7 Power ozone O 2 flow 4 generator 5 scrubber neutralizer 9 10 drain

10 Ringsted and Haslev power plants in Denmark

11 Two container arrangement O 3 room Control PC SCB NOx Reactor 500 cm Ozone generator SMO 300 S (WEDECO) : 2.64 kg O 3 controllable from 10% up to 100%

12 NO x reduction efficiency at different O 3 input Ringsted power plant (4 MW, natural gas fueled) 80 ppm NO x for the untreated flue gas, 60 o C 5 sec 20 sec Over 95% NOx reduction at 150 ppm O 3 at molar ratio O 3 /NO x = 1.875

13 Natural gas versus biomass Ringsted Diesel gas fueled; 60 o C flue gas; Negative pressure in the reactor; No big particles in the flue gas; Stable flue gas composition; Ozone input higher than 75 g/h leads to high NO x reduction. Haslev Straw fueled; 115 o C flue gas; Positive pressure in the reactor; Big residual particles (deposited on the observation windows and mesh); High fluctuations of NO x level in flue gas; Higher humidity in the reactor; Higher ozone flow input needed (over 300 g/h) for high NO x reduction; Additional problems related to water cooling, sensors, alarms, contamination.

14 Time dependence of NOx levels Concentration [ppm] Trace 1 Trace 2 Trace Time [sec] NOx [ppm] NOx SL1 NOx SL2 DT NOx =37 sec Time [sec]

15 Time delays in NOx reduction - biomass DT O3 DT NOx T 1 T 2

16 Ozone generator reaction time NOx_In Ozone level [ppm] t ox_off =21 sec t ox_on =21 sec t ox =42 sec V O3 Concentration [ppm] NOx_Out Ozone_Out Time [sec] Time [sec]

17 Delay compensated NOx removal - biomass 300 Concentration [ppm] NOx_In Nox_Out Ozone_Out Time [sec]

18 Ozone consumption and cost

19 NOX/SOx PlasTEP reactor built at DTU 6 m long reactor up to 250 SLM flue gas up to 100 g/h O 3 (air, O 2 ) NO, NO 2, O 3 sensors 7 sampling ports Controlled gas flows Gas and reactor heating Wet scrubber O 3 destroyer NOx up to ppm PC control Footer 18

20 NOX/SOx PlasTEP reactor built at DTU Footer 19

21 Mixing schemes NO 2 and O 3R as a function of O 3 IN at P 1 for all four mixing schemes for an air flow of 40 slm, ozonized air of 10 slm, slm of NO and initial values of NO=316 ppm and NO 2 =104 ppm (O 3 IN =0 ppm).

22 Time dependence Constant O 3 IN, on-off NO, NO x at P 1 and P 5 for 50 slm dry air, 0,21 slm NO, NO x _on= 411 ppm, NO_on= 304 ppm. O 3 IN =1900 ppm, Power ozone generator = 256 W.

23 DTU - pentagon DBD structure

24 Advantages for ozone injection method - Positive income from fertilizer or hydrochloric acid production. - The plasma denox process also removes formaldehyde and SO 2, so reduces the need for an oxidation catalyst on gas engine plants and reduces SO 2 taxes on biomass plants. - On biomass plants with bag filters, e.g. straw fired plants, the scrubber can utilize the latent heat in the flue gas by cooling the flue gas from e.g. 120 C to 70 C and increasing the efficiency of the CHP plant. - Some CHP or district heating plants operate with a very cold temperature of the return water, around 45 C, from the district heating system, which permits the denox plant to operate as part of a condensation step utilizing even more energy from the flue gas. - No need for storage and handling of ammonia as needed with the SCR technology.

25 Disadvantages NOx versus catalytic reduction - More complicated physical design - Need for ph regulating chemicals - Waste water issues - Space requirements - Environmental and safety aspects of producing and using ozone

26 Conclusions - NOx reduction by Ozone can be done with an efficiency higher than 95% - NOx reduction in biomass power plants needs additional settings to compensate delays in ozone delivery - A small size reactor for NOx/SOx reduction is available within the PlasTEP and PlasTEP+ projects