Industrial energy managementEnergy... · Type of steam boilers kettle boiler flue tube boiler fire tube boiler fire-flue- tube boiler ... sulzer type 3 main heat source to water/steam

1Industrial Energy Management

Industrial energy management

Fossil fuel power plants


Layout of power plant


Coal is primary fuel source (~40%) for electricity production

A physically heterogeneous, “combustible” sedimentary rock.

Inorganic mineral + Organic part (mainly C, O and H, with little S and N)

It is formed from decay and sedimentation of vegetal matter (Coalification)

Moisture

Volatile Matter : Compounds released in the gas phase, e.g. CH4, released after heating

Dry Carbon : Compounds that remains after heating but that can be burned

Fly ashes : Inorganic matter that are left after the combustion

Coal


Coalification : Peat ->Lignite ->Subbituminous -> Bituminous ->AnthraciteReserves: USA (27%), Russia (18%), China (13%), Australia (9%), India (7%, high rank), Germany (5%, low rank) Reserve to Prod: China (40y), USA and Russia (>200 year)

Rank of coal

Moist mineral-free basis

10000 Btu/lb ~ 23,2 MJ/kg


• Fuel composition

C H S O N Volatile Water Ashe

s

LHV

(MJ/kg

)

Heavy fuel oil 85 11 1-5 - 1 - - - 41.0

Light fuel oil 86 13 <0.1 - 0.005-

0.05

42.7

Diesel 86 14 <0.005 42.7

Gasoline 85 15 <0.002 43.5

Anthracite 90-

95

<4 1 2 1 10 5 3-10 29

Bituminous 76-

90

5-7 1 5-10 1 10-30 5-10 3-10 18-29

Submituminous 72-

76

5 1 15-25 1 30-40 10-30 3-15 8-25

Lignite 65-

72

4-7 0.2-1 15-30 0.5-1 40-48 30-70 3-15 5-20

Wood 47-

53

5-7 0-0.3 42-46 0-0.7 60-90 10-20 0-4 17-21

Dry-ash-free composition


• On the board :

Coal versus gas

kg CO2/ kWh of

thermal power

Coal (anthracite) 0.351

Coal (bituminous) 0.316

Coal (lignite) 0.331

Coal

(subbituminous) 0.329

Diesel fuel and

heating oil 0.248

Gasoline 0.241

Propane 0.213

Natural gas 0.180

Germany: ~0,67 kg CO2

per kWh electricity

Source : US Energy Administration

Enthalpies of

formation at 25°C

and 1 atm

(kJ/kmol)

C(s) 0

O2(g) 0

CH4(g) -74,850

CO2(g) -393,520

H2O(g) -241,820

H2O(l) -285,830


Burning coal in a clean way ??

Capturing the CO2 :

Flue gas separation.

• Most suited to thermal processes with high CO2

output e.g. coal

• Oxyfuel combustion – only water and CO2

Pre-Combustion separation

Coal (gasifier) -> CO+H2O (water shift) -> CO2+H2

Storing CO2 :

• Injected into the earth crust or to push crude oil out

Recycling CO2 :

• Convert CO2 and H2 (from hydrolysis) into methanol

• Dissociation and Fischer Tropsch

Energy cost increase : +25 % to +100 %.


Coal combustion

1. Pyrolysis:

Volatile components are set

free as gases (CH4, CO, H2,

HCN, ..., for T > 600 K)

2. Coke burn-up:

Surface reaction

Ci + O2 --> CO, CO2

(very slow, --> determines the

overall burning rate)

3. Gas combustion:

(fast)

similar to droplet combustion

(flame around particle or

around group of particles)

Raw coal

Coke

Typical burning times for coal (from Görner 1991 )

(lignite)

(bituminous)


Classification of firing

(following Reh 1976, from Görner 1991)

Bubbling Bed CirculatingPulverised Coal

FiringGrate Firing

Fluidized bed firing

Large coal particles(~5mm) / Smaller particles (1mm) / Fine particles (~50µm)


Type of steam boilers

kettle boilerflue tube boiler

fire tube boiler

fire-flue- tube boilerfire-flue- tube boiler

(Holland type)

angular tube boiler steep tube boilersteep tube radiation

boiler

shell boilers

water-tuber boilers

Generating steam


Fire tube boilersSource: Hoyrytys

• Generally low load <10 MW

• High inertia so can adapt load

changes

• Little maintenance and capital

investment

• P<4 MPa and no superheat :

Poor efficiency of Rankine cycle

• Mainly used for district and

industrial heating & process

steam

• Firing efficiency

Reaction chamber

12Q

Reactants RProducts P

State 1 State 2

)()( P R 25

,

25

,12

12

RP T

C

Rp

B

R

T

C

Pp

B

Pu

B

B dTTcn

ndTTc

n

nH

n

Qq

ValueHeating Lower

heat Available12 u

B

FH

q


Water-tube boilers

1 feed water inlet, 2 economizer, 3 steam drum, 4 evaporator,

5 distributor, 5 ash, 7 cóal and combustion air, 8 superheater,

9 fresh steam, 10 exhaust gas, 11 recirculation pump

12 moist separator (sediment bowl)

a: natural circulation boiler b: forced circulation boiler

once-through forced flow boiler: c: Benson type, d: sulzer type

3 main heat source to water/steam heat

exchangers :

• Economiser

• Evaporator

• Superheater

With steam drum

a. Natural circulation

b. Forced circulation

All heat exch. are in series

c. Benson type

d. Sulzer type

c and d have all Heat exc. in series


• Superheat necessary to compensate surface tension. Smaller bubbles need more superheat than larger bubbles - > instable

• Bubble inception at surface cavities

Bubble formation in pool boiling

source: Thermopedia


• A : Natural convection –single phase convection

• B: Nucleate boiling – heat transfer coefficient increases as number of site increases until Critical Heat flux, where supply of liquid is insufficient

• C: Transition boiling : Film forms with lower conductivity

• D: Film boiling : Continuous vapor-phase

Deviation from nucleate boiling

source: H. Effenberger, Dampferzeuger


Critical boiling events

1. Kind: DNB Departure from nucleate boiling, excess of critical heat flux while nucleate

boiling

2. Kind: Dryout Transition from annular flow to spray flow: steep decline of critical heat flux

3. Kind: Burnout High steam content, minimal critical heat fluxsource: H. Effenberger, Dampferzeuger


Natural circulation boiler

• Steam drum for water steam

separation

• Max steam vol. fraction ~ 20-40%

• Upper pressure limit ~ 15 Mpa

• Circulation Ratio : 1

• Can be assisted by pump for higher

pressure and/or flexibility

• High recirculation : large dimensions


Forced-circulation boilers

Air preheater

Economiser

Drum

Evapo

-rator

Circul-

ation

pumpMud drum

Superheater


• No recirculation : higher load

• Can operate at supercritical pressure

• Complex control and no buffer

Once-through boiler



Temperature curve in steam generators

tem

pe

ratu

re/ °

C

Fraction of heat transferred (%)

adiabatic combustion temperature

flue gas temperature

evaporator

rad

iati

on

zo

ne

su

pe

r h

eate

rre

he

ate

rII

pre

su

pe

r h

eate

r

reh

eat.

I

EC

O I

Air

Water :

Eco I

Eco II

Verdampfer (Evaporator)

Vorüberhitzer (Pre-superheater)

Überhitzer (superheater)

Turbine

ZÜ 1: Re-heater 1

ZÜ 2: Re-heater 2

Air:

Luvo : Air preheater

Asche trichter: Ash hopper

Brenner: Combustor

Feuerraumende: End of furnace

Strahlraume: Radiation zone

Superheaters and preheaters

Air pre-heater (Regen.)

water steam

side



ratio of transfered heat in boiler

evaporation

feedwater preheating

superheating

reheating 2ra

tio

of

heat

/ %

fresh steam pressure / bar



power plant design, air preheating

scheme for regenerative air preheaters with a) rotating heat storage mass and

b) fixed storage mass

rotating storagerotating

air hood

air inflow

air inflow

flue gas flue

gas



Regenerative Air preheater : Static heat storage – Rotating air

hood. Type Rothemühle

Rotation speed : 1 RPM

400m3/s

D=17.5 m

Heat transfer area:

~100000 m2

1. Hot air

2. Cold air

3. Combustion gases entry

4. Combustion gases exit



Regenerative Air preheater : Rotating heat storage mass. Type

Ljungström.

Rotation speed : 1-4 RPM

400m3/s

D=15 m

Heat transfer area: ~24000 m2

1. Cold air

2. Hot air

3. Combustion gases entry

4. Combustion gases exit



• Fly ashes contains variety of toxic inorganic compounds (As, Be, ….) over a

wide size range (10’s nm-100’s microns)

• Electrostatic precipitation to separate particles from flue gases.

Soot removal - Electrostatic precipitator


NOx removal – SCR and NSCR


• Form CaSO4 from CaCO3 and SO2

Flue Gas Desulphurization

273011.2012ISUT-Seminar Jörg Sauerhering

Thanks for your attention!

sources: H. Effenberger, DampferzeugerK. Kugeler, EnergietechnikT. Bohn, Band 5 Handbuchreihe Energie

Documents

Industrial energy managementEnergy... · Type of steam boilers kettle boiler flue tube boiler fire tube boiler fire-flue- tube boiler ... sulzer type 3 main heat source to water/steam