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Making oxy-fuel combustion

Making oxy-fuel combustion 7
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Published Date:19-07-2017
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New Developments in Combustion Technology Part III: Making oxy-fuel combustion an advantage Geo. A. Richards, Ph.D. National Energy Technology Laboratory - U. S. Department of Energy 2014 Princeton-CEFRC Summer School On Combustion Course Length: 6 hrs June 22-23, 2014 Presentation Identifier (Title or Location), Month 00, 2008 This presentation Updated, expanded from 2012 CEFRC lecture: – Inherent carbon capture: chemical looping combustion (Day 1) – Step-change in generator efficiency: pressure gain combustion (Day 2) – Frontier approach (?): making oxy-fuel an efficiency advantage (Day 2) Sampling & Diagnostics RDC Flow P-gain rig NETL ‹› Making oxygen for oxy-fuel …reprise • Oxygen can be supplied today by commercial Air Separation Units (ASU) based on established cryogenic separation. • The energy needed to separate oxygen from air is significant (see below) • In conventional oxy-combustion, we dilute the purified oxygen to maintain the same boiler flame temperature as in air-combustion. 1 mole of air 0.21 moles oxygen Dilute again Air p = 1 atm with CO or steam O2 2 0.21 moles oxygen Separation p = 0.21 atm O2 Unity 0.79 moles nitrogen (ASU) 0.79 moles nitrogen p = 1 atm N2 p = 0.79 atm N2 C + O  CO 2 2 DH DG = 394 kJ/gmol (C or O 2) Reversible separation work: 6 kJ/gmol O produced In efficient powerplants we convert 2 less than ½ of DH to work. Thus200kJ/gmol O2 work produced Current actual process: 18kJ/gmol O produced 2 Roughly 1/10 of that is needed for ASU. e.g, the change in gibbs energy for ideal mixing (Sandler, Chemical Engineering Thermodynamics (1989) pp. 313. See Trainier et al., “Air Separation Unit…..” Clearwater Coal Conference, 2010. ‹› Making Oxy-fuel an Advantage • Producing pure oxygen requires a lot of energy • If one could find a way to make significant extra power because of the available oxygen, oxy-fuel would be an advantage. • Oxy-fuel already provides an advantage for process industries that benefit from high temperatures (e.g., glass making, steel). • Oxy-fuel already provides advantages in propulsion (rocket engines) • How can you make oxy-fuel an advantage for power generation? ‹› Efficiency 100 A) Existing Supercritical Pulverized Carnot w/r to 293 K 90 1 Coal (23.9MPa/866K/866K steam) 80 B) Advanced Ultra-Supercritical 70 Pulverized Coal (34.5 Mpa/1005K/1033K 1 60 steam) D 50 C) Simple Cycle Gas Turbine (as C reported, LMS 100, working fluid temp 40 2 estimated from exhaust and pressure ratio) B 30 A D) Combined Cycle Gas Turbine (as 20 reported, MPCP2(M501J), working fluid temp 10 3 estimated similar to case C) 0 0 500 1000 1500 2000 2500 Approximate combustion temperatures Oxy-fuel Combustion Temp. Working fluid temp. Temperature (K) PC Coal Combustion Temp. Working fluid temp. Note: boilers report HHV efficiency; Gas Turbine Combustion Temp. = Working fluid temp. turbines report LHV 1 Current and Future Technologies for Power Generation with Post-Combustion Carbon Capture, DOE/NETL-2012/1557 2 Gas Turbine World 2012 GTW Handbook, Vol. 29, Pequot Publishing pp74 3 Gas Turbine World 2012 GTW Handbook, Vol. 29, Pequot Publishing pp89 ‹› Efficiency Magnetohydrodynamic Power Generation • The high temperatures A Turbogenerator possible with oxy-fuel can be Hot Vapor N used to operate an MHD or Gas Brushes “topping” cycle: - + – Topping cycle power possible Moving because of the oxygen S Conductors – MHD exits to conventional Forming Coil steam boiler system External Current Field (“bottoming cycle”). B MHD Generator • How does MHD work? – Conductive, high-temperature N Electrode gases play the role of an Cathode electrical conductor moving Source of Hot, Electromotive through a magnetic field. Electrically Force Conducting Gas Motion – Generates power directly from S of Gas the moving gases. ‹› A combined cycle • For reasons that will be clear later, most MHD concepts only produce power ABOVE 2600K (which is….HOT). • Thus, it needs to be a combined cycle to extract energy from the whole temperature spectrum. Topping Work Output W T Bottoming Work Output W B Air separation Air unit High efficiency Oxygen MHD Power Unit steam boiler Fuel 2600 K combustion products MHD “topping” cycle including the oxygen production 45% efficient today best cases Example Enthalpy into the “top” = mass flow of fuel x HHV = Q h = 0.1 (10%) Work from the top : W = h Q T T T h = 0.45 (45%) B Enthalpy into the “bottom” = Q – W = Q ( 1 – h ) T T Combined Work from the bottom: W = h (Enthalpy into the bottom) = Q ( h – h h ) B B B T B Efficiency: Combined cycle efficiency: (W + W )/Q = h h – h h .1+.45 – (.1)(.45) T B T + B T B = 0.50 (50%) ‹› Past MHD topping efforts • Concept proven in both U.S. and USSR in 70s and 80s – US DOE 1978- 1993 – Electricity transferred to grid • Economic downfall : key factor being materials – Electrode damage – Seed material use MHD U25RM diffuser channel (USSR) 1970s From Petrick & Shumyatsky 1978. ‹› Direct Power Extraction The “new” MHD: making oxy-fuel an advantage New benefits, new approaches, new technology: Legacy MHD program Today Comments Oxy-fuel combustion developed for No CO capture CO Capture 2 2 capture enables MHD. Validated models for different Large demos Simulation & validation generator concepts, not demos. ASU power requirements have Pre-heated air Efficient oxygen production dropped 40% since 1990. No emissions Use oxy-fuel gas SOx and NOx control Capture GPU processing unit (GPU). Advanced magnets exist today. Magnets 6 Tesla Magnets 6 Tesla Electrode arcing could be controlled Analog electronics Solid-state inverters/control with digital devices. Simulations can compare multiple Linear generator Radial, Linear, others geometries. New channel construction Conventional manufacturing Advanced manufacturing approaches. Aspirational – use nanosecond Seeded flows New goal: injected plasma pulse discharge to ionize gas ? ‹› Related technology – combustion, ionized flames, and plasma • Non-equilibrium plasma may benefit new aspects of combustion: Starikovsky, A. Aleksandrov, N. (2013). Plasma-Assisted Ignition and Combustion, Progress in Energy and Combustion Science, Vol. 39, pp. 61-110. Ignition in demanding applications - Pulse detonation engines, gas turbine re-light, HCCI engines, others • Alternating current excitation of flames has recently demonstrated significant hydrodynamic changes in flame structures: Drews, A. M., Cademartiri, L., Chemama, M. L., Brenner, M. P., Whitesides, G. M., Bishop, K. J. M (2012). AC Electric Fields Drive Steady Flows in Flames, Physical Review E 86, pages 036314-1 to 4. “…AC fields induce steady electric winds….localized near the surface of the flame….these results suggest that ac fields can be used to manipulate and control combustion processes at a distance….” • Flame ionization can be used for sensors and diagnostics. Benson, K., Thornton, J. D., Straub, D. L., Huckaby, E. D., Richards, G. A. (2005). Flame Ionization Sensor Integrated Into a Gas Turbine Fuel Nozzle, ASME J. Eng. Gas Turbines and Power, Vol. 127, No. 1, pp. 42-48. Proposes detection of dynamics and combustion conditions with flame ionization • New propulsion concepts include plasma - MHD “bypass” or electric thrust propulsion: Schneider, S. (2011). Annular MHD Physics for Turbojet Energy Bypass, AIAA-2011-2230. Longmeier, B. W., Cassady, L. D., Ballenger, M. G., McCaskill, G. E., Chang-Diaz, F. R., Bering, E. A. (2014). Improved Efficiency and Throttling Range of the VX-200 Magnetoplasma Thruster, Journal of Propulsion and Power, Vol. 30, No. 1 pp. 123 – 132. • Non-equilibrium plasma: a key technology for the future? Plasma Science: Advancing Knowledge in the National Interest (2010). This National Academies report provides status and motivation to use plasma – including combustion applications. MHD enthalpy MHD accelerator extraction Inlet Plasma television display MHD Bypass Concept Turbo-jet ki/Plasma_display Mach 7 ‹› Fundamentals of Electromagnetics • Electric field E is a vector (units: volt/meter) • E can be described by the voltage potential V; E = - V • By convention, minus sign means E points to low voltage 2 • Magnetic Induction B is a vector (units: Tesla = voltsec/m ) F E F B Experimental observations of charge Q in electric Field E (left) and moving E Charge Q at velocity u in B (right). u Q B Q F = Q E F = Q (u x B) E B Q “Another” E Electric Force on Q Magnetic Force on Q E = F /Q u x B = F /Q E Q B Thus in 1-D E = -V/L E = E + u x B NET Q L = distance. ‹› A Simple Generator j Flowing conductive k gases i B u b R L u x B = -uB k • Gas (conductive) flows with bulk velocity u i • Magnetic filed B k is applied as shown. • The resulting “induced” electric field is –uB k • This field can drive a current flow in the external circuit. • How is this similar to a conventional generator? ‹› How Much Current Flows? Important Nomenclature Note: The current flux is proportioned to E : E (zero sub) is NET 0 applied by the external load & does not J = σ E ; σ = conductivity of media Amps/(voltmeter) NET include magnetic 2 induced field J = current flux vector Amps/meter 2 A = electrode area meter j b J = σ E = σ ( E + u x B) = σ ( E – uB) j NET 0 0 CHANNEL HEIGHT i R = b/sA is the resistance to current flow through i V the plasma – shown “oddly” disconnected since L E 0 J uB drives current in the same place. R R uB i L From E = - V E = - (V – V ) /b I 0 0 L H V H (V = Low Voltage V = High Voltage) SIMPLE GENERATOR FROM PREVIOUS PAGE L H E = (V – V ) /b = IR /b (Ohm’s Law) 0 H L L Define open circuit R  infinite, then J = 0 implies E = uB from above. L 0 Then, V = uBb (open circuit voltage) OC uBb V OC R ≡ internal resistance I = = ; i R + R b/ σ A + R i L L Note : as typical, V is a voltage difference while V and V are measured relative to ground oc H L ‹› Limiting Cases Open Circuit V L E 0 O = J = σ ( E – uB) E = uB 0 0 (V – V )/b = E = uB uB H L 0 V ≡ uBb OC V H Generating Circuit V L E 0 E uB; J = σ ( E – uB) J R R 0 0 i L uB I = V /(R +R ) oc i L V H Short Circuit V = V H L E = 0 E = (V – V )/b = O 0 J R 0 H L i R = O L uB V V OC OC I = = R + R =O R V = V i L i H L ‹› Electrical Analogy R i R V = E b L Load 0 G V = uBb OC I V IR R E Load L L 0 Define K = = = = V I (R + R ) R + R OC uB i L L i Several interpretations for K: 1. Ratio of load to O.C. voltage 2. Ratio of load resistance to total resistance 3. An efficiency (why ? Multiply by I/I  load power/total power) 4. A ratio of the “applied” field E to “generated” field uB 0 ‹› Electrical Analogy – Power Produced R i R V = E b L Load 0 G V = uBb OC I V IR R E Load L L 0 Define K = = = = V I (R + R ) R + R OC uB i L L i The power to the load is power = (current x load voltage): I = A J ; I = A s (E -uB) = A s uB ( K – 1 ) 0 V = b E = b uB K Load 0 2 2 x Power = I V; Power = Ab s u B K ( K - 1 ) 2 2 Power density = Power/(Ab) = s u B K ( K - 1 ) ‹› Next slides - overview What you just heard: J = σ (E – uB) a simple generator y 0 What you will hear next: • A complication arises from the Hall Effect …the flowing current also interacts significantly with B • Thus, we find: σ J = (E -  B E -uB) 2 x 0x e 0y I +  B e σ J = (E –uB+  B E ) 2 y 0y e 0x I +  B e • You can impose E or E by applying different electrical 0x 0y boundary conditions via electrode geometry ‹› Complications From the Hall Effect • Most MHD: charge is carried by electrons • By convention, electrons move against E • The electron current flow has an associate charge velocity u e • Must account for the interaction between u and B (Hall Effect) e j u u B B electrons i k electrons u - - + - + u u - + e - + - + + u x B Hall Effect u x B e No Current : u x B charge velocity = bulk velocity u Hall Effect “Tilts” the Field – How Much? Caution: note this is a simplification for clarity; u may not be aligned with the y-axis e ‹› Some Cyphering • The velocity of electrons in a field is u = - (E + u x B ) (i) e e net e • The mobility  is related to conductivity as n e = σ e e e • The B field is assumed independent of current flow B = B k E net,y u = - (E i + E j + u x B) e e net,x net,y e Straightforward E net,x algebra and u = u i + u j Also assume e ex ey B substitutions in equation (i). J = J i + J j x y • Notice that J = -n e u ; J = -n e u x e ex y e ey σ J = (E –  B E ) e x 2 2 net,x net,y I +  B e Nomenclature σ 3 n = electron density (per m ) J = (E +  B E ) e y net,y net,x 2 2 e I +  B e e = fundamental charge 1.602 E-19 C/electron m V  = electron mobility / E = E e s m net,x 0x E = E – u B net,y 0y ‹› The Simple Faraday Generator j y i x • The electrodes are long, continuous k z • Thus, E = 0 0x σ σ J = (E ) = (E -uB) u y y,net 0y 2 2 2 2 I +  B I +  B e e Notice that the simple generator analysis (without Hall Effect) gave (J ) = σ (E -uB) y 0y No Hall 1 Thus, the Hall Effect reduces the y- current by: 2 2 I +  B e What is the magnitude of meaning of J ? x σ σ J = (0-  BE ) = (- B E -uB) = - B J 2 2 x e net,y e 0y e y I +  B 2 2 e I +  B e The Hall effect leads to an x-current that is  B times the y-current. e How big is  B? (Next Slide) e ‹›