Energy turnaround and consequences for conventional power stations Dr.W.A. Benesch Director Energy Technologies
Steag Power plant sites A dependable energy expert for 75 years Bergkamen A 780 MW Bexbach 1 Weiher 1504 MW West 1 / 2 Voerde A/B2234 MW Walsum 9/10 1200 MW Bergkamen Bexbach / Weiher Voerde Duisburg Herne 2/3/4 960 MW Iskenderun 1/2 1,320 MW Raffineriekraftwerk 211 MW Raffinieriekraftwerk 162 MW Herne Iskenderun Köln-Godorf Leuna Lünen 6/7 507 MW Mindanao 1/2 232 MW Termopaipa IV 165 MW MKV, HKV, MHK *) 466 MW Lünen Mindanao Paipa Völklingen-Fenne hard coal coke oven gas refinery by-products 2
Oil fire The kind of fire we try to minimize in a coal fired power plant
00:00 00:30 01:00 01:30 02:00 02:30 03:00 03:30 04:00 04:30 05:00 05:30 06:00 06:30 07:00 07:30 08:00 08:30 09:00 09:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00 17:30 18:00 18:30 19:00 19:30 20:00 20:30 21:00 21:30 22:00 22:30 23:00 23:30 KW Voerde Block A MWnetto 700 Mo, 09.05.05 Lastmangel 21:02 Gen.v.N. 05:06 Gen.a.N. Öl in t / 15 min. 14 600 12 500 9,3 10 400 300 7,1 6,5 8 6 200 3,5 3,1 3,3 3,2 4 2,4 2,7 100 1,7 2 0 1,0 0,90,9 1,0 0,7 0,4 0,3 0,4 0,2 0, 0,0 0,0 0
00:00 00:30 01:00 01:30 02:00 02:30 03:00 03:30 04:00 04:30 05:00 05:30 06:00 06:30 07:00 07:30 08:00 08:30 09:00 09:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00 17:30 18:00 18:30 19:00 19:30 20:00 20:30 21:00 21:30 22:00 22:30 23:00 23:30 KW Voerde Block B MWnetto 700 Mi, 11.05.05 Lastmangel 05:30 Gen.a.N. Öl in t / 15 min. 14 600 12 500 10 400 7,7 8 300 6 200 100 0 3,2 2,6 2,3 0,8 1,0 4,3 4,0 3,1 0,1 0,0 0,2 0,1 0,3 1,5 0,1 0,3 1,5 1,2 0,1 1,1 0,80,8 0,5 0,2 4 2 0
PP Voerde 761 MW units
PP Voerde Generator rotor damages
What has changed in the German electricity market? Yearly Fluctuation of Wind in GWh Yesterday Conventional, scheduled electricity generation centralized in load centers (coal, gas, nuclear and others) Today Few or none scheduled conventional generation in load centers, Sometimes high wind and PV where generated when not needed (Solar mainly at noon, in summer more than in winter, Wind more in winter than in summer, heavy storm could be followed by calm periods) Daily Fluctuation of solar Power in % of installed Partly far away from the load centers
Quelle: VGB Kongress 2007, Lambertz 9.5.05 0:00 9.5.05 12:00 10.5.05 0:00 10.5.05 12:00 11.5.05 0:00 11.5.05 12:00 12.5.05 0:00 12.5.05 12:00 13.5.05 0:00 13.5.05 12:00 14.5.05 0:00 14.5.05 12:00 15.5.05 0:00 15.5.05 12:00 16.5.05 0:00 16.5.05 12:00 17.5.05 0:00 17.5.05 12:00 18.5.05 0:00 18.5.05 12:00 19.5.05 0:00 19.5.05 12:00 20.5.05 0:00 kwh Renewables and coal fired power station a team to adjust the volatile energy from wind Daily start up and shut down of big coal fired power stations 400000 350000 300000 250000 Increase of fluctuating renewable energy sources as well as economical requests ask for higher flexibility of modern fossil fired steam power plants 200000 150000 100000 50000 0
Flexible operation What are the goals? 1. Increase the ramp rate 2. Reduce the part load in pure coal operation to avoid frequent start ups and shut downs 3. Avoid negative consequences for the entire power plant What are the topics? Coal Storage Combustion system Water Steam Cycle DeNOx-Plant ESP Flue Gas Desulphurization Stack
Reduction of minimum load In the past Target PP 10 PP 9 PP 8 PP 7 PP 6 PP 5 PP 4 PP 3 PP 2 PP 1 0 5 10 15 20 25 30 35 40 Load [in % of net capacity, based on unit design capacity] 11
Optimization of start-up Standby time Start-up "to the point" T FD S TURB P FD F FD t Utilization of permissible stress limits of thick-walled components T Diff Actual situation p T Diff Target p Actual situation Target Start-up with the HP bypass station less open 12
Coal Storage Recommendations: Compaction in layers of coal Build heap side not to steep Adjustment of the stock pile to main wind direction Avoidance of water in the stock pile underground Regular, or as well continuous temperature monitoring Measurement in case of fire: Clear sections with hot spots (T>50 C) Spread thin and let it cool down Do not extinguish with water (s.a.) Average Content of volatile: 39,5%(waf)
Combustion system Flame shape during low-load operation Burner 21 Burner 22 Air swirler Pulverized coal pipe IR-Flame detector Air swirler Sec.- Air II Sec.-Air I One burner level (< 15% electr. capacity) Fuel oil EL + Atomizing air Exterior/interior Deflector Core air Coal dust + Primary air Flame stabilisator Secondary air I Secondary air II Burner 23 Burner 24
Combustion system Signals from Flame monitors 98 100 94 98 IR-Signal BRN21 [%] IR-Signal BRN22 [%] IR-Signal BRN23 [%] IR-Signal BRN24 [%] Low-load operation with only one burner level Influencing the signal by opening of viewing port
Combustion system Low-load operation close to electrical auxiliary station requirements Power generation = 9,9 MW (appr. 6,6% electr. capacity) => Increased CO-Emission as limiting factor 15,7 371 O 2 dry [Vol.-%] Thermal output [MW] Live steam [t/h] Power pubic grid [MW] Shut-down for Weekend outage 58,8 Power railway grid [MW] CO [mg/nm³] 9,9 0 54,8
Common use of storage capacities for high unit performance ZÜ2 ZÜ-EK m& ZÜ-EK ZÜ1 HDU Ü4 Ü3 EK3 m& EK3 HD MD+ ND G EK2 m& EK2 m& L Ü1/2 m& B EK1 m& EK1 ECO + VD FWP m& w HP-PREHEATER FEED- WATER- TANK LP-PRE- HEATER
CHP Herne IV Main Data Steam generator Benson, tower type Thermal capacity of boiler MW 1.277 Steam capacity t/h 1.584 Life steam temperature C 535 Life steam pressure bar 255 Reheater temperature C 541 Reheater pressure bar 63 Feedwater Temperature C 284 Mills Tube mill Number 3 Capacity t/h 85 Turbo generator One flow HP, Two flow MP, Two Flow LP Nominal capacity MW 383 Generator nominal capacity MVA 550 Generator nominal voltage kv 21 Feedwater pumps 2 x 50% electrical variable speed
Cold Start Up Herne IV older plot M1 M2 M3
Hot Start Up M1 M2 M3
Water Steam Cycle Start-up-/Low-load system with circulation pump Starting vessel (Sep. vessel) Superheater ZÜ Evaporator Circulation pump Atmosph. Flash tank Boiler water Flash tank Feed water tank HDpre-heater NDpre-heater Condenser Feed water pump Condensate receiver tank Heat retains in the cycle High investment costs
Water Steam Cycle Start-up-/Low-load system with intermediate flash tank Starting vessel (Sep. vessel) Superheater ZÜ Evaporator Atmosph. Flash tank Boiler water Flash tank Feed water tank HDpre-heater NDpre-heater Condenser Feed water pump Condensate receiver tank Heat economy slightly less than with circulation pump Lower investment cost in comparison to circulation pump
Water Steam Cycle Start-up-/Low-load system with atmospheric flash tank Starting vessel (Sep. vessel) Superheater ZÜ Evaporator Atmosph. Flash tank Boiler water Flash tank Feed water tank HDpre-heater NDpre-heater Condenser Feed water pump Condensate receiver tank Concerning heat economy the worst design Very low investment costs
Boiler efficiency [%] Electrical efficiency [%] Combustion System Electrical Efficiency / Boiler Efficiency 95 Boiler efficiency Electrical efficiency 50 94 45 93 40 92 91 90 89 88 35 30 25 20 15 87 86 Data from SR::EPOS-System 10 5 85 0 20 40 60 80 100 120 140 160 0 Electrical power[mw]
Source: Schreier 2011 Optimization of part load efficiency Variable speed controls
Source: Schreier 2011 Boiler Wall thickness and flexibility in case of new power station
ESP Dust separation Staub-Abscheidegrad rate in % in % A -w & Clean gas dust content acc. to Deutsch: r R e V Exponential influence of the migration velocity w as well as the spec. separation surface A/ V & 100,00 99,99 Half of the operation volume means Double of the spec. separation surface Optimisation of the separation capacity 99,98 99,97 99,96 99,95 99,94 Not the separation efficiency is limiting the low-load operation, but the insufficient combustion with unburnt carbon Fraction of unburnt coal particle increases Ash only commercial usable if C-content < 5 % 99,93 20 30 40 50 60 70 80 90 100 Blocklast in % Unit load in %
Flue Gas Desulphurization Very low flue gas velocity due to low-load operation Reverse flow in the inlet area of the scrubber Increasing slagging at the duct walls Optimisation by insertion of guide vanes or wall injection
Temperature in C Stack 115 110 105 Rauchgastemperatur Flue temperature in in stack Schornsteineinzelröhre single pipe at 50 m auf 50m Rauchgastemperatur Flue temperature in im stack Schornstein at 280 m auf 280m Wandtemperatur Wall temperature stack Schornstein at 280 m auf 280m 100 95 90 85 80 75 70 65 50 75 100 125 150 175 200 225 250 Gross capacity in MW el Lower flow velocity at low-load operation longer retention time of flue gas in stack higher heat loss of flue gas
Stack Contamination by fine dust and other products of reactions Drying-out by temperature changes Slagging and fouling Flake off and discharge of agglomerate particles at load increase
Summary Hard coal fired power stations of STEAG had been operated in the past already in mid merit order while world wide base load is typical. The current challenges of the Energy Turnaround are asking for further improvement of the technology, due to the increasing part of renewable energy conventional power plants will have frequent outages and need higher ramp rates. All components of the power plant are highly stressed by the new kind of operation. With increasing low-load operation high amounts of coal remain at the coal storage over a longer period with the risk of self ignition. The combustion system must be able to offer high flame stability also at low load without support fuel. Decreasing HP and IP temperatures accompanied by too high gradients can lead to ineligible stresses of the casings. Low overheating can lead to erosion effects by droplets in the turbine. As well the entire flue gas pass is affected.