31
Applications of Biomass Drying Applications of Biomass Drying and Condensing Boilers in the and Condensing Boilers in the Process Industry Process Industry Q. Chen, K. Finney, H. Li, X. Zhang J. Zhou, Q. Chen, K. Finney, H. Li, X. Zhang J. Zhou, V. Sharifi, J. Swithenbank SUWIC, Department of Chemical and Process Engineering Sheffield University

Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

  • Upload
    others

  • View
    3

  • Download
    0

Embed Size (px)

Citation preview

Page 1: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Applications of Biomass Drying Applications of Biomass Drying and Condensing Boilers in the and Condensing Boilers in the

Process IndustryProcess Industry

Q. Chen, K. Finney, H. Li, X. Zhang J. Zhou, Q. Chen, K. Finney, H. Li, X. Zhang J. Zhou,

V. Sharifi, J. Swithenbank

SUWIC, Department of Chemical and Process EngineeringSheffield University

Page 2: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

OutlineOutline� Objectives

� Biomass Drying and Case Study

� Industrial Condensing Boilers & Heat Pumps

� Case Study: Thermal Design of a � Case Study: Thermal Design of a Condenser in a Biomass Heating Plant

– Heat exchanger design

– Cost estimation

� Conclusions

Page 3: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

ObjectivesObjectives

To investigate the feasibility of exploiting low grade

Low grade heat from process industries

To provide a value-added fuel

For district heating

� To investigate the feasibility of exploiting low grade waste heat to dry biomass fuel for power generation

� Thermal design of a condensing boiler in a large scale district heating plant, which exploits the large amount of low grade heat available from a flue gas condensing

system

Page 4: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Moisture in Biomass

Pulp & paper sludge

50%-60%

500-900

15-19

6@35%

Wood Bark

30%-60%

290 - 380

19-25

11@50%

Wood Chips

30%-55%

260 - 320

19-21

10@50%

Moisture

Bulk density (kg/m3, w.b.)

HHV (MJ/kg, d.b.)

HHV (MJ/kg, w.b.) 6@35% 11@50% 10@50%HHV (MJ/kg, w.b.)

Moisture

Bulk density (kg/m3, w.b.)

HHV (MJ/kg, d.b.)

HHV (MJ/kg, w.b.)

Milled Peat

45%-55%

300 - 400

19-21

10@50%

Sugarcane Bagasse

48%-52%

80 - 130

18.6-20.3

10@50%

Wood pellets

7%-12%

550 - 700

17-20

18.7@8%

Page 5: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Biomass drying

� Provide a value-added fuel� Ensure a constant moisture content to optimise the

combustion process– <30% for long-term storage and domestic applications– <10-30% for small-scale furnaces– <10-15% for the production of pellets or briquettes

� Drying is an energy-intensive process

StorageStorage Other Other

Raw material

53%

Personnel costs20%

Pelletising

14%

Other

4%

Investment

2%

Milling

2%

Cooling1%

Storage

4%

Raw material

53%

Personnel costs20%

Pelletising

14%

Other

4%

Investment

2%

Milling

2%

Cooling1%

Storage

4%Raw material

34%

Personnel costs13%

Pelletising

9%

Other 4%

Investment3%

Storage3%

Drying

30%

Raw material34%

Personnel costs13%

Pelletising

9%

Other 4%

Investment3%

Storage3%

Drying

30%

Page 6: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Biomass Drying – Commercial Dryers

Medium:

- Air

- Flue gas

-Steam

Rotary dryer Belt dryer Flash dryer Fluidized bed

Small particle

High corrosion

Fire risk after drying

Leakage in steam dryer

Variable particle sizes

Robust

Low temperature drying

Steam – heat recycle

Reasonable dimension

Steam – heat recycle

Uniform & low temperature

High M/H transfer

Variable particle sizes

Reasonable dimension

Robust

Larger dimension of dryer

Fire risk inside dryer

- high hazard risk

Corrosion and erosion

Blocked by long bark

Fire risk after drying

Small & uniform particle

Abrasion among particles

Leakage in steam dryer

Advantages

Disadvantages

Page 7: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Low grade thermal energy recovery by drying

biomass – Case study

40% flue gas250 oC – 450 oC;647 - 336 t/h

60% hot water90 oC; 737 t/h

Heating Sources

100 MW

Biomass

Heating Sources

40 MW

Drying

Page 8: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

.)./(

)(40 (kg/s)M wood

bdkgMJvalueheatingfuel

MWplantpowerininputpower

−=

Case study – Drying load

� Wood chips required for the 40MW power plant

� Drying load for the drying process

)MC-(MCMW(kg/s) outinwood ×=

Moisture change (wt%-wet)

initial, final (kg/s) (t/h)

0.6, 0.1 3.33 12.00

0.6, 0.2 3.00 10.80

0.6, 0.3 2.57 9.26

Page 9: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Case study – Belt dryer

Mflue , HCf,in, Tf,in

Mflue , HCf,out, Tf,out

Mwood, MCw,in, Tw,in Mwood, MCw,out, Tw,out

A Continuous Cross-Flow Belt Dryer

Page 10: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

M , T

Mflue , HCf,in, Tf,in, Hf,in Mflue , HCf,out, Tf,out, Hf,out

Mwood, MCw,in, Tw,in, Hw,in Mwood, MCw,out, Tw,out, Hw,out

Dryer

Case study: mass and heat balances

� Biomass drying by flue gas

� Biomass drying by superheated steam

MS, Ps,in, Ts,in, Hs,in

Mwat, Twat, Hwat

MS, Ps,out, Ts,out, Hs,out

Mwood, MCw,in,

Tw,in, Hw,in

Mwood, MCw,out,

Tw,out, Hw,out

Pre-heater

Dryer

R

Mflue , Tf,in

Mflue , Tf,,out

Page 11: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Case study – Heat input requirement

Drying by flue gas Drying by steam

Drying by steam Drying by steam

Page 12: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Case study – Size estimation

load

woodwood

W

MCM τ×+=

)1(A eff

Mwood: solid mass flow rates

MC: moisture content

W : solid loading (30kg/m2)

Belt Cross-sectional area:

Wload: solid loading (30kg/m2)

Heat exchanger area:

)(A exchangerheat

watf TTh

Q

−×=

τwood: solid residence time

Q: Heat transfer flow rate

h: Heat transfer coefficient

Tf: flue gas temperature

Twat: water temperature

Page 13: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Case study – Capital costs estimation

Drying by flue gas Drying by steam

Page 14: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Case study – Estimation of Profitability

Drying by flue gas

Initial MC=1.5 kg-w/kg-wood

Drying by steam

Final MC=0.1, 0.3 kg-w/kg-wood Final MC=0.1 kg-w/kg-wood

Fuel price = 14 €/MWH Fuel price = 14 €/MWH

Page 15: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Industrial Condensing Boiler

� Combustion of hydrocarbon-rich fuels yields two primary products, carbon dioxide and water vapor, entrained in the relatively inert nitrogen.

� Conventional boilers (non-condensing) transfer most of the sensible heat of flue gases to water. most of the sensible heat of flue gases to water.

� Condensing boiler is used to recover the latent heat of water vapour by cooling the flue gases to temperatures below the dew point

– Indirect contact

– Direct contact

Page 16: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Advantages of Condensing BoilersAdvantages of Condensing Boilers� Improving the overall thermal efficiency by

latent heat recovery

– Thermal efficiency can exceed 100% with reference to the lower heating value of fuel input

– Higher excess air ratio, lower partial pressure of water vapour, more sensible heat loss

80

85

90

95

100

105

110

115

120

30 50 70 90 110 130 150

Flue gas temperature, oC

Eff

icie

ncy

, %

λ=1.25

λ=1.6

λ=2.0

λ=2.4

Page 17: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Advantages of Condensing BoilersAdvantages of Condensing Boilers� Reducing flue gas emissions through

absorption in the condensate

– >90% highly dissociated inorganic matter and particles (>10µm)

– Lower but substantial fraction of fine particles

Page 18: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Technical Barriers & SolutionsTechnical Barriers & Solutions� Corrosion

– Highly corrosive condensate (H2SO4, HNO3, HNO2, NH3, HCl, salts)

– Durable, corrosion-resistant materials: widely applied in domestic condensing boilers

� Low return water temperature� Low return water temperature

– Below the dew point to allow water vapour condensation

– Large radiators & floor heating systems

– Heat pumps

Page 19: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Condensing boilers with Radiator & floor heatingCondensing boilers with Radiator & floor heating

� Return water from a heating system should be 30-50°C, well below the dew point of flue gas

A

B

� A floor heating system or large surface area radiator is required.

B

Page 20: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Condensing boilers with a heat pumpCondensing boilers with a heat pump

� A heat pump can be used between the condenser and the hot return water– Conventional electrically driven compression heat pump

– An absorption heat pump

A BA B

Page 21: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Case study: Condensing Boiler Case study: Condensing Boiler Design for a Biomass Heating PlantDesign for a Biomass Heating Plant� Objectives:

– Thermal design of the condensing boiler

– To investigate various technical and economic issues in relation to the condensing boiler applicationapplication

� Biomass heating plant– Oriketo Heating Station in Finland

– Fluidised bed boiler & flue gas condenser

– Capacity: 40MW + 12MW (condenser)

– Fuel: logging residue delivered mainly from final felling of spruce-dominant forests & residuals

Page 22: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Plant Process ParametersPlant Process Parameters

Fluidised bed boilerAir

Wood chips

ESP

Condensing boiler

Condensate

Flue gas to stack

District heating consumers

Hot water

Return waterPreheated water1

2

3 4

5

6

789

Stream No. Pressure, bar Temperature, °C Mass flow rate, kg/s Enthalpy, kJ/kg

1 1 20 5.4 -17.22 1 20 20.9 -5.15

3 1 150 26.3 146.7 (+388.4)4 1 150 26.3 146.7 (+388.4)5 1 35 23.0 10.6 (+92.1)6 16 140 111.6 590.07 16 30 111.6 128.08 16 55 111.6 231.79 1 35 3.32 42.4

Page 23: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Dimensions of the condenserDimensions of the condenser

Heat exchanger type Single tube pass, counter-current shell-and-tube

exchanger (E type shell)

Tube outside diameter, do (mm) 25.4

Tube inner diameter, di (mm) 22.9

Tube thickness, δt (mm) 1.25

Pitch, pt/do 1.75

Total tube number, N 1024

Tube layout Rotated square

Shell inner diameter, Do (mm) 2090

Shell thickness, δs (mm) 14

Baffle type Single-segmental

Baffle spacing, B (mm) 1776

Baffle cut 25%

Page 24: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Condensation CurveCondensation Curve

40

60

80

100

120

140

160

Tem

per

atu

re,

oC

Flue gas (shell side)

Return water (tube side)

Zone IZone IIZone IIIIV

A

B

CD

E

� Equilibrium vapour temperature vs. the difference of the specific enthalpy of the flue gas from the outlet

� At the boundaries of each zone, the heat

0

20

0 50 100 150 200 250 300 350 400 450

Specific enthalpy difference (h -h outlet) on the shell side, kJ/kg

Zone IZone IIZone IIIIV

Zone Boundaries Shell-side Tube-sideA 150.0 55.0B 64.3 49.3

C 50.0 37.0

D 40.0 32.0

E 35.0 30.0

At the boundaries of each zone, the heat transfer coefficients can be calculated. A mean overall heat transfer coefficient for each zone can thus be obtained

Page 25: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Thermal Design Methodology: LMTDThermal Design Methodology: LMTD

� The maximum driving force for heat transfer is generally the log mean temperature difference (LMTD) when two fluid streams are in countercurrent flow

� The true mean temperature difference of flow arrangements will differ from the logarithmic mean temperature difference by a certain factor, F, dependent temperature difference by a certain factor, F, dependent on the flow pattern and the terminal temperatures.

LMTD F Heat transfer rate, MW

Zone I 43.3 0.971 2.652

Zone II 14.0 0.865 5.757

Zone III 10.3 0.935 2.296

Zone IV 6.2 0.966 0.865

Page 26: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Heat ResistancesHeat Resistances� Thermal resistances in the tube-side (including the fluid

and fouling) are relatively small

� Shell-side resistances contribute approximately 60–90% of the total resistance

� In Zone I where no condensation occurs, the thermal resistance of the shell-side flue gas flow is dominant

� When condensation occurs, the shell-side fouling becomes a major contributor resistancebecomes a major contributor resistance

0.0E+00

2.0E-03

4.0E-03

6.0E-03

8.0E-03

1.0E-02

1.2E-02

1.4E-02

A B C D E

Th

erm

al r

esis

tan

ce,

m2K

/W

Tube-side fluid

Tube-side fouling

Tube wall

Shell-side fouling

Shell-side fluid

0.0E+00

2.0E-03

4.0E-03

6.0E-03

8.0E-03

1.0E-02

1.2E-02

1.4E-02

A B C D E

Th

erm

al r

esis

tan

ce,

m2K

/W

Tube-side fluid

Tube-side fouling

Tube wall

Shell-side fouling

Shell-side fluid

A B

Page 27: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Size and Pressure DropSize and Pressure Drop� Tube length:

– 63.3m for the stainless steel condensing boiler

– 74.8m for the condensing boiler made from carbon steel

� Heat transfer area:– 4919m2 for the stainless steel condensing boiler

– 5811m2 for the condensing boiler made from carbon steel

� Pressure drop– Tube side: 3.2 - 3.8 kPa– Tube side: 3.2 - 3.8 kPa

– Shell side: 28.4 - 34.1 kPa

0

50

100

150

200

250

300

Zone I Zone II Zone III Zone IV

Hea

t tr

ansf

er c

oef

fici

ent,

W/m

2K

Carbon steel condenser

Stainless Steel Condenser

0

5

10

15

20

25

30

35

Zone I Zone II Zone III Zone IV

Tu

be

len

gth

, m

Carbon steel condenser

Stainless Steel CondenserA B

Page 28: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Costs and ProfitabilityCosts and Profitability

Stainless steel condenser Carbon steel condenserCapital costs Boiler cost ($) 2,562,000 852,000+50,000(PP)Installed factor 1.9 2.2Installed boiler cost ($) 4,868,000 1,984,000Fan cost ($) 40,000 44,000In total ($) 4,908,000 2,028,000

O&M costsElectricity rate ($/kWh) 0.1 0.1Electricity rate ($/kWh) 0.1 0.1Electricity ($/year) 580,300 695,800Chemical treatment expense ($/m3) 0.45 0.45Condensate treatment cost ($/year) 37,600 37,600Maintenance cost factor (%) 6 6Maintenance cost ($/year) 294,480 121,680

BenefitWood chips saving (t/h) 5 5Wood chips cost ($/tonne) 60 60Fuel cost saving ($/year) 2,100,000 2,100,000

Page 29: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

Costs and ProfitabilityCosts and Profitability

�Expected lifetime:

–Carbon steel (CS) condenser: 5 years

–Stainless steel (SS) condenser: 10-15 years

0.0

2.0M

4.0M

6.0M

Carbon steel condenser

NP

V, $

Stainless steel condenser

�NPV evaluation

–CS: 2 years cash return

–SS: 5–7 years cash return

–NPV of the SS condenser is more sensitive to the interest rate

0 1 2 3 4 5 6 7 8 9 10-6.0M

-4.0M

-2.0M

NP

V, $

Years

i=5%

i=10%

i=15%

Stainless steel condenser

Page 30: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

ConclusionsConclusions� Waste flue gas and hot water (100 MW) exiting from a

process industrial plant is sufficient as the heating source for wood drying for biomass combustion in a 40MW power station boiler.

� In general, for both flue gas and steam drying, 3-4 year operation is expected to give a return on the investment at a fuel price of €14/MWh. investment at a fuel price of €14/MWh.

� The average heat flux per unit heat exchanger area in the designed condenser ranges from 1.5 to 2.5 kW/m2.

� NPV calculations showed that the choice of a carbon steel condenser ensured cash return in a relatively shorter period of time (i.e. 2 years) when compared to a stainless steel condenser ( i.e. 5 to 7 years).

Page 31: Applications of Biomass Drying and Condensing Boilers in ...research.ncl.ac.uk/pro-tem/components/pdfs/SusTEM2010_Track2_6… · Industrial Condensing Boiler Combustion of hydrocarbon-rich

AcknowledgementsAcknowledgements

Sheffield University would like to thank EPSRC Thermal Management

Consortium for the financial support for this project.

Thank You!Thank You!