chp technologies - npcc-misti.com

Dr. Mario Ortner Biomass CHP training1

#5 CHP technologies and cycles, basics


– (4a) Temperature – Entropy Diagram

– (4b) Enthalpie – Entropie Diagram

– (4c) Carnot Efficieny

– (4d) Cogeneration

– (4e) Steam Turbine Process, types of steam turbine

– (4f) Energy Efficiency versus Exergy Efficiency

Thermodynamic basis of the water/steam cycle



• First and Second law of Thermodynamics

• Energy = Exergy + Anergy

• Carnot efficiency: ɳ = 1 – Tc/Th

Tc..lower process temperature levelTh..upper process temperature level



vapor regionliquidregion

supercritical region

saturated region

Entropy (s) [kJ/kg.K]

Tem

pera

tur (

t) [K

]

Isobar change of state

critical point



Theoretical background – Carnot Efficiency:

Preheating Evaporation Superheating



Boiler

Condenser

Steam turbine



Process 1-2: The working fluid is pumped from low to high pressure Process 2-3: The high pressure liquid enters a boiler where it is heated at constant pressure by an external heat source Process 3-4: The dry saturated vapor expands through a turbine, generating powerProcess 4-1: The wet vapor then enters a condenser where it is condensed at a constant pressure to become a saturated liquid.


For cycles with high live steam parameter (p,T). This prevents the vapor from condensing during its expansion (limit x = 0,85) which can seriously damage the turbine blades.

Advantage: Improves the electrical efficiency of the cycle. Today for larger units with feed in tariff systems a „MUST DO“ condition

x = m_steam / m_total




• Enthalpy (h) is a measure of the totalenergy of a thermodynamic system.Dh = Dq + vDp

heat supply pressure change

technical work(boiler) (feed water pump)



s

h

isotherm



s

h

P_el: m x h x total

h

550°C; 70 bar

0,035 bar

m..massflow kg/sh..enthalpy diff. kJ/kgtotaltotal efficiencyP_el..power output kW


Thermodynamic basis of the water/steam cycle (supercritical)

s

h600°C; 300 bar

0,035 bar

reheating necessary to avoid low x value

600°C „family“


Thermodynamic basis of the water/steam cycle (hypercritical)

s

h700°C; 350 bar

0,035 bar


BAT, different CHP solutions


Advantages of Steam Turbines

• High number of rotations small units

• No pulsation forces lighter foundations in comparison to block engines

• High enthalpie differences + high mass flow high Power Output

• until 1400 Mwel

70% of all CHP are steam turbine cycles


Assessment of steam cycles

• Electrical Power to Heat Ratio (s)Default values- Back pressure turbine cycle: 0,45 (D.H); 0,30 (industrial) - Extration condensing turbine cycle: 0,45 (D.H); 0,30 (industrial)- (Combined Cycle Gas turbine plus heat recovery: 0,95(D.H);

0,75 (industrial)

• Operation mode: Electricity lead or Heat lead– Feed in tariff– Fuel price (electricity production costs)– Heat duration curve– Legal requirements (in EU: „Promotion of cogeneration based on a

useful heat demand in the internal energy market -PE 321.973/C1-C4 “)

– Definition of high efficient CHP


Important parameters (at design stage)

• Boiler efficiency (Coal): state of art arround 90%– Fuel preparation– Optimum burner design– Careful control of air supply

• Live steam temperatur (super and hyper critical; standard 500-620– 620°C)– Limited by fuel specification chemical analyses– Limited by type of boiler (benson, water tube or fire tube)– Limited by steam turbine material

• Design of steam blades (improvements considerable last 10 years)• Optimization of „cold end“ of steam turbine *)

– Air cooling versus water cooling facilities (ambient conditions)– Steam exit losses at the end of turbine

• Feedwater heating (up to 10 stages) up to 250/300°C feedwaterinlet temperature

• Electricity lead or Heat lead operation optimization of steamturbine design– Depending on electricity price versus heat price


Important parameters (at design stage)

• D.H network / heat concept (especially after FiT expires)– High total efficiency but large units sometimes far away from large heat

demand

• In countries with unbundling– RES plants have Grid Priority Load flexibility important for all other

plants


Gasturbine process

Ambient air

Heat client

Fuel

Additional fireing

To Transformer

Exhaust Gas

HeatRecoveryBoiler


Advantages & Disadvantages of different power generation options

T

s

max.T3-point (e.g. strategy Siemens..)Heat Input

ɳ = 1 – Tc/Th

Th…average temperature, heat is transfered to the system

Tc…average temperature, heat is transfered from the system

Gas turbine process

1

4

3

2



T

s

Steam turbine process

t pinch point

Steam turbine cycle

ɳ = 1 – Tc/Th





T

s

max.T3-point (e.g. strategy Siemens..)Heat Input


t pinch point

Steam turbine cycle

ɳ = 1 – Tc/Th





Gas turbine process



T

s

Reheating (e.g. strategy Alstom..)Heat Input


t pinch point

Steam turbine cycle

ɳ = 1 – Tc/Th





Gas turbine process

Dr. Mario Ortner Biomass CHP training


0

200

400

600

800

1000

1200

Steam turbinecycle

gas turbinecycle

combined cycle

ThTc

27


Biomass Cogeneration

Pressurised Circulating Fluid Bed Gasification (Sweden 1996)- 6 MWel; 9 MWth ; eta_el: 34%;

28



Circulating Fluid Bed Gasification (Demonstration England)- 8 MWel; 14 MWth ; eta_el: 31%;

29


Co- Gasification of Biomass in a Coal fired Plant (Zeltweg 1998)- 4,2 MWel; 10 MWth ; eta_el: 42%;


30


Steam Turbine Cycle, Theory

31


Typical Cogen Plant with Combustions Technology in Denmark - 9 MWel; 20 MWth ; eta_el: 26%;


32


Organic Rankine Cycle (e.g. Klosterneuburg) - 250 kW; ca. 1,8 MWth ; eta_el: 10%;


33


FBC example 20 MWel


Agenda

Fundamentals of Water Steam Cycle / Steam turbine processes








Cogeneration

What is Co-generation (Combined Heat and Power)?

-On site generation and utilization of energy in different forms simultaneously- Utilising fuel energy at optimum efficiency, cost effective and environmentally-several types of Cogenerations, primarily generate electricity and best practise use of heat- CHP reduce network losses, because situated close to client


Convential energy generation versus CHP:

Energy efficiency calculation

Heat

100 units fuel

80 units heat100 unitsfuel

Electricity

Combined heat an power

40 units electricity

100 unitsfuel

40 units electricity

40 units heat

ɳ_th = (40 + 80) / 200 = 60% ɳ_th = (40 + 40) / 100 = 80%


Agenda

Fundamentals of Water Steam Cycle / Steam turbine processes









s

totalm x gen x gearbox x stuffingbox

m.. Mechanical efficiency 0,98-0,985…gen.. Efficiency generator 0,97-0,98….gearbox Efficiency gearbox 0,98-0,99….._stuffingbox Efficiency stuffing box 0,99 – 0,995…..

Efficiency Benchmarks Steam Turbine


Different water/steam cycle designs

Two basic types:

1. Back pressure steam turbinecycle(steam pressure after turbine > 1bar)

2. Condensing steam turbine cycle(with or without turbine tap point)(steam pressure after turbine << 1bar)


Back pressure turbine


Condensing turbine



Hybrids of back pressure or condensing types:

1. Extraction turbine

2. Induction turbine



1. Back pressure steam turbine cycleP_el 50 MW

eta_el 23.2 %

eta_sum 89.4 %

mass[kg/s] h[kJ/kg]p[bar] t[°C]

251.25 58.55 1.3 60

2683.5 58.55 1.2 105

503.78 64.74 1.987 120

2752.9 1.561 2.087 142.53 515.56 64.74

80 121.49

2702.2 63.18 1.434 115.28

3507.6 64.74 70 540



2. Condensing steam turbine cycle (with or without turbine tap point)P_el 50 MW

eta_el 32.8 %


84.031 4104 1.2 20

63.116 4104 1.4 15

503.78 45.9 1.987 120

2752.9 7.009 2.087 142.53

515.56 45.9 80 121.49

2305 38.890.04247 30

3507.6 45.9 70 540



3. Extraction condensing turbineP_el 50 MW

Q_heat 10 MW

eta_el 31.1 %

eta_sum 37.3 %


2683.5 4.111 1.2 105

251.25 4.111 1.3 60

84.031 3976 1.2 20

63.116 3976 1.4 15

450.13 47.31 80 105.97

2324 37.360.04247 30

3507.6 47.31 70 540


Balance of Heat


Different water/steam cycle designs (extraction steam map)


Operation mode of steam turbines

Steam control-Controlled by steam control valves- 4 controlling methods-(1) Throtteling control

-All valves simultaneous in operation, steam pressure constant, high losses only for 15% to 30% load

-(2) Governing control-Valves opens in series; higher efficiency then (1)

-(3) Variable pressure control-Steam control valves in fixed position; control only by main steam advantages : steam temperature remains constant; poorer performance and limited load capability

-(4) Hybrid variable pressure control-Low loads varaible pressure-Increasing steam pressure increases steam turbine load governing control


Tasks of Steam Shaft Sealing System

• Avoids the steam exit (emergency issue)

• Protects bearings of hot steam and contamination of bearing oil(damage through water-oil mix)

• Avoids air break (condensor pressure!)

• Heating up the Rotor of the steam turbine with steam


Turbine oil system for slide seal ring


Steam Shaft Sealing system


Plant start up




Operation mode


Cooling Systems


Agenda

(3) Fundamentals of Water Steam Cycle / Steam turbine processes








Exergy Efficiency

Exer

gy c

onte

nt o

f hea

t in

%

• Electricity and Work: quality factor = 1• For Heat must be calculated

_ex = ex / (h1-h2)

ex = (h1-h2) – Tu (s1-s2)

s1s2


Methodology calculating the exergetic efficiency

Exergy Efficiency

*)

*)..depends on quality of heat (p;t)


Exergy Efficiency

• Example: Exergy calculation of water with t1=100°Cand 1 bar; ambient temperature (t_amb) is 15°Cex = (h1-h_amb) – Tu (s1-s2)= cp(t1-t_amb) – t_amb(s1-s2)For isobar process cp(t1-t_amb) – t_amb x cp x ln(t1/t_amb) == 4,19 (373-288) – 288 x 4,19 x ln(373/288) = 44 kJ/kg

To heat the water e.g. electrical energy = 100% exergy is necessary = h1- h_amp = cp (t1-t_amp) = 355 kJ/kg

Exergy loss = 355 – 44 = 311 kJ/kgExergy efficiency = 44/355 = 12,4% !!!!


• Comparison condensing mode and back pressure mode (steam turbine process) and heatingplant:

• (1) Condensing mode:– E = 45%– H = 0%– Exergy efficiencyx = 0,45 x 1 + 0 = 45%– Energy efficiencyth = 45%

• (2) Back pressure mode:– E = 35%– H= 50% (hotwater 100°C)– Exergy efficiency x = 0,35 x 1 + 0,50 x 0,124 = 41%– Energy efficiencyth = 35% + 50% = 85%

• (3) Heating plant:– H=90%– Exergy efficiency x = 0,90 x 0,124 = 11%– Energy efficiencyth = 90%

Exergy Efficiency


Conclusion:Which heat and power generation technologies are most suitable?

• Energy efficiency does not include the usability of the convertedenergy

• Exergy efficiency includes the quality level of the convertedenergy

• The exergy output should be maximized• Heat losses should be minimized by using CHP technologies

and waste heat utilization• High exergetic energy carriers (e.g. natural gas) should not be

used to produce low exergetic heat• the quality of the requested energy should correspond to the

quality of the used energy (if only low temperature heat, e.g. forspace heating is requested, the energy supply should beappropriate)

Exergy Efficiency


NOTE:

• EXERGY efficiency is most importantvalue not Energy efficiency Exergyefficiency has to be optimized

Exergy Efficiency


Kapitel – 1 Einführung

Biomass CHP

Biomass

65

chp technologies - npcc-misti.com

Documents