The Impact of Higher Hydrogen Concentrations in Natural Gas on Industrial Combustion Processes ICG 2017, Istanbul Jörg Leicher, Tim Nowakowski, Anne Giese, Klaus Görner
Power-to-gas what is it and why bother? o Renewable energy sources such as wind and solar power are being integrated into existing energy infrastructures all over the world to ever greater extents. o While this development helps to reduce overall CO 2 emissions from power generation, it also puts considerable strain on existing electricity grids, due to the intermittence of wind and solar power and the need to shift large amounts of energy from where it is being produced to where it is actually being consumed, e. g. population and industry centers. o Electricity grids can store energy only in very limited amounts: production and consumption have to be balanced continuously. Thus, technologies to store and release large quantities of energy economically are a key component for a successful transition into the low-carbon energy systems of the future. o Gases (e. g. H 2 or SNG) can easily be stored (either locally or by injection into the existing gas grids) and burned for power generation or in other applications. This is the main idea behind power-to-gas. Folie: 2
Sector coupling and power-to-gas Electricity Gas Nuclear Coal CO 2 SNG Methanation H 2 Natural gas Biomethane Wind, Solar Power-to-gas (Hydrogen production by electrolysis) H 2 CCGT (centralized) Gas-to-power CHP (de-centralized) Heat Folie: 3
Impact of hydrogen in natural gas on combustion? on pollutant emissions? *@ 25 C / 0 C Source: GWI Source: Slim, B.K., Darmeveil, H., van Dijk, G.H.J., Last, D., Pieters, G.T., Rotink, M.H., Overdiep, J.J., Levinsky, H.B., Should we add hydrogen to the natural gas grid to reduce CO2 emissions (Consequences for gas utilization equipment), 23 rd World Gas Conference, Amsterdam, The Netherlands, 2006 Folie: 4
AiF- Research Project H2 Substitution (IGF Grant No.: 18518 N) Folie: 5
Project H2-Substitution o The objective of this AiF-funded research project is to look into the effects of higher concentrations of hydrogen in natural gas on typical gas-fired thermal processing applications and to assess their impact on industrial end users. o Both CFD simulations (steady RANS) and experimental investigations in a semiindustrial test rig were carried out, using three different, commercially available process burners. o In addition to various hydrogen / natural gas blends (up to 50 vol.-% H 2 ), the effects of different combustion control strategies were investigated. o Finally, a series of CFD simulations of a glass melting furnace were carried out to visualize the effects of hydrogen admixtures and control strategies on a real-life industrial system. Folie: 6
GCV [kwh/m 3 ] Campaign setup and boundary conditions o Three commercially available industrial burners were investigated in detail: Burner I: a modular, non-premixed burner Burner II: a forced-draught burner Burner III: a flameless oxidation burner o Different mixtures of H 2 and DVGW Code of Practice G 260 a natural gas (GWI-Gas) were used. Many of the investigated fuel blends do not comply with current German German gas quality regulations. o Reference case (100 % NG): P = 120 kw λ = 1.05 no air preheating Superior Wobbe Index [kwh/m 3 ] @ 25 C / 0 C Folie: 7
Control strategies o In addition to the different NG/H 2 blends, the effects of different control strategies on the combustion behavior were looked into: Scenario I: Scenario II: Scenario III: no control intervention at all, i. e. volume flows of both fuel and air remain constant (worst case). air ratio is kept constant (excess oxygen sensor) by adjusting the air volume flow, but burner firing rate varies due to changing NCV of NG/H 2 blends. both burner firing rate and air ratio remain constant, based on advanced gas quality monitoring (best case). Independent control of volume flows for both fuel and oxidizer is required. Folie: 8
GWI 300 kw th semi-industrial test rig Left hand view Right hand view Flue gas duct Window for UV camera Cooling pipes View ports One of the investigated burners (Burner I) Air Gas Swirler Burner Tip Refractory (Al 2 O 3 ) Access ports for probes Radiant tubes Folie: 9
Impact on process parameters and flame shape (Burner I) Operational Parameters P: 120 kw / 120 kw / 120 kw λ: 1.05 / 1.05 / 1.05 T out : 1087 C / 1087 C / 1087 C P: 116 kw / 116 kw / 120 kw λ: 1.09 / 1.05 / 1.05 T out : 1058 C / 1082 C / 1083 C P: 111 kw / 111 kw / 120 kw λ: 1.14 / 1.05 / 1.05 T out : 1033 C / 1040 C / 1102 C Flame shapes based on iso-surfaces @ CO dry = 2000 ppm Scenario I Scenario II Scenario III Folie: 10
Impact on process parameters and flame shape (Burner I) Operational Parameters P: 120 kw / 120 kw / 120 kw λ: 1.05 / 1.05 / 1.05 T out : 1087 C / 1087 C / 1087 C P: 103 kw / 103 kw / 120 kw λ: 1.24 / 1.05 / 1.05 T out : 951 C / 1026 C / 1088 C P: 78 kw / 78 kw / 120 kw λ: 1.69 / 1.05 / 1.05 T out : 765 C / 941 C / 1107 C Flame shapes based on iso-surfaces @ CO dry = 2000 ppm Scenario I Scenario II Scenario III Folie: 11
Impact on efficiency and heat transfer o Efficiency is obviously always a concern when operating an industrial furnace. o Since energy balances are an integral part of any CFD simulation, the effects of higher hydrogen concentrations on heat transfer and overall efficiency of the process can be analyzed using the simulated cases. o The conventional Thermal Efficiency Factor alone is not sufficient here because it does not take into account that a specified heat flux into the load of a furnace is usually required for product quality reasons. o We therefore use an additional quantity that we call Heat Transfer Impact Factor (HTIF). It is calculated by comparing the most important heat flux in the system, the flux into the load, to the corresponding flux in the reference case, in this case, pure natural gas combustion. o Since we do not have a dedicated heat load in our rig, we use wall heat fluxes instead to determine the HTIFs. Folie: 12
Heat transfer impact factors and thermal efficiencies Burner I, 20 vol.-% H 2 in natural gas: HTIF= Q Load Q Load,Reference = Q Wall Q Wall, Reference 1 0,87 0,95 1,03 η thermal = 1 Q Flue P 0,47 0,48 0,50 0,48 Reference (GWI-Gas) Scenario I Scenario II Scenario III HTIC Thermal Efficiency Factor Folie: 13
Burner I: emissions measurements Scenario I: V gas = constant V air = constant Scenario III: P = constant λ = constant NO (@ 1 vol.-% O 2 ) = 66 ppm If these measurement data are corrected to a fixed reference oxygen value in the flue gas, NO emissions increase with increasing H 2 concentrations in the fuel. Folie: 14
Burner III (flameless oxidation): emissions measurements Scenario I: V gas = constant V air = constant Scenario III: P = constant λ = constant Increased NO X formation despite higher air ratios! The burner systems respond quite differently to higher H 2 concentrations, especially in Scenario I where volume flows are not adjusted to compensate. With Burner I, uncorrected NO X emissions drop due to increasing air ratios, while in the same scenario, NO X formation actually increases in Burner III. Folie: 15
CFD Study of a Regenerative Glass Melting Furnace Folie: 16
Regenerative glass melting furnace: 10 vol.-% H 2 in NG 100 % natural gas T out = 1562 C Scenario 1 Scenario 3 T out = 1512 C T out = 1562 C T max = 1960 C T max = 2001 C T max = 1970 C Temperature [ C] 2070 1865 1660 1455 1250 1045 840 635 430 225 20 Operating Conditions (Reference Case): P = 12 MW; λ 1.05; T air = 1,400 C Folie: 17
Regenerative glass melting furnace: 50 vol.-% H 2 in NG 100 % natural gas T out = 1562 C Scenario 1 Scenario 3 T out = 1486 C T out = 1535 C T max = 1960 C T max = 2006 C T max = 2055 C Temperature [ C] 2070 1865 1660 1455 1250 1045 840 635 430 225 20 Operating Conditions (Reference Case): P = 12 MW; λ 1.05; T air = 1,400 C Folie: 18
ΔNO [%] HTIF [%] Impact of H 2 and control scenarios on heat transfer and NO 100 99,51 101,10 Reference Case 95 93,89 94,74 90 HTIF[%]= Q glass Q glass,reference 100 85 80 Scenario 1 Scenario 3 ΔNO[%] = 10 % H2 in NG 50 % H2 in NG X NO,Case X NO,Reference Case 100 Reference Case 800 700 600 500 400 300 200 100 0 716,30 204,92 98,52 110,61 Scenario 1 Scenario 3 10 % H2 in NG 50 % H2 in NG Folie: 19
Conclusions o Power-to-gas is a promising technology to use the large storage capacities of gas infrastructures as a means to store surplus electricity from renewable sources. Large-scale deployment of power-to-gas units can lead to increasing (and locally fluctuating) hydrogen concentrations in natural gas grids. o Both CFD simulations and experiments in a semi-industrial burner test rig underline the importance of gas quality monitoring and process control technologies in this context. If these are used, the results indicate that even very high H 2 concentrations (way beyond current plans or regulations of H 2 injection) can be managed without compromising on process efficiency, product quality or pollutant emissions. o If, on the other hand, the burner systems cannot adapt to the changed fuel composition, the effects can be severe. o Further research is currently ongoing to look at more industrial applications. Folie: 20
Acknowledgment & Further Information The authors gratefully acknowledge AiF for the funding of this project (IGF Grant No.: 18518 N). We also wish to thank Mr. Oliver Stope for his valuable contributions to this project as part of his Master s Thesis at Ruhr-University Bochum, Germany. The final report of the project (in German) is available at Final Report Folie: 21
Thank you for your attention Dr.-Ing. Jörg Leicher Gas- und Wärme-Institut Essen e.v. Hafenstraße 101 45356 Essen, Germany Tel.: +49 (0) 201 3618 278 leicher@gwi-essen.de