02 Nigel Simms

8/13/2019 02 Nigel Simms

1/38

Energy Technology Centre

Biomass Combustion Systems:

Assessing Component Durability

and Emissions

Nigel SimmsEnergy Technology Centre

Cranfield University


2/38


Outline

Background

Potential biomass fuels

Issues

Component durability

Deposition

Corrosion

Emissions

Summary


3/38


Combustion systems Biomass only

Grate

Fluidised bed

Purpose built

Feed systems

Combustion chamber

Heat exchangers

Steam systems

Gas clean-up Scale up to ~30MWe

Biomass co-fired

Pulverised fuel

Designed for coal firing

Biomass additions of 5-20% (thermal input)

Higher steam temperatures

Scale up to 4000MWe (660 MWe units)


4/38


Fireside Steam-side

Corrosion

AllowanceOxidation

Allowance

TUBEWALL

Load Bearing

Thickness

Heat exchanger tubing cross-section through tube wall


5/38


Component life as f(corrosion rate, corrosion allowance)

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

100,000

0 10 20 30 40 50 60 70 80 90 100

Corrosion rate (m/1000 hour)

Life

(hours)

1 mm 1.5 mm

2 mm 2.5 mm

3 mm 3.5 mm

Corrosion Allowance


6/38


7/38


Flow Diagram for Component Life Modelling

Component

Specification

Operating

Conditions

Fuel Spec. &

Reactor System

Thermal Model Aerodynamic

Model

Thermochemical

Model

Transport & Deposition

Models

Mechanical

Property Data

Corrosion &

Erosion/Corrosion

Models

Life Predictions

Contaminant effects

Operating condition effects

Gas flow rate

P & T distributions

Inlet & outlet

gas P & T

Contaminant

levels & species

Particle

deposition

flux

Component design &

life criteria

Alloy

specificationDeposition flux &

composition

Metal surface

temperature

Component

Geometry

Damage

rates


8/38


Biomass fuels


9/38


Potential biomass fuels Specifically cultivated biomass

(energy crops), e.g.:

coppiced willow

miscanthus

reed canary grass

switchgrass

Waste biomass

various straws wood waste / forest residues

World traded biomass products, e.g.:

olive residues

pelletised wood almond waste

cereal co-product (CCP)

Sewage sludge, animal wastes

Miscanthus

Coppiced willow


10/38


Fuel Properties (1)

0.01

0.1

1

10

100

Wt% wet Wt% dry Wt% daf Wt% daf Wt% daf Wt% daf Wt% daf Wt% daf Wt% daf

Water

content

Ash Volatiles C H O N S Cl

Fuel parameter

%

Willow Poplar

Fir/pine/spruce Miscanthus

Wheat Olive waste

Coal


11/38


Fuel Properties (2): Minor / Trace Element Concentrations

0

5000

10000

15000

20000

25000

Al Ba Ca Fe K Mg Mn Na P Si Ti

Element

Concentration(mg/kgdry)

Willow Poplar

Fir/pine/spruce Miscanthus

Wheat Olive waste

Coal


12/38


0

2000

4000

6000

8000

10000

12000

0 5000 10000 15000 20000 25000 30000

Potassium (ppm)

Chlorine(ppm)

Sander (1997)Christensen (1998)

Review data

Wheat

Barley

Oil Seed Rape

Potassium and Chlorine Levels in Selected Biomass


13/38


Sulphur and Chlorine Contents of Fuels Delivered to Two UK Power Stations

Between 1992 and 1994 (Grey is Mean Values for UK Stations in 1983)


14/38


Evaluation of potential heat exchanger

operating conditions


15/38


Combustion heat exchanger issues - outlineGas stream characteristics

Gaseous species e.g. CO2, SO2, HCl, NOX, H2O, O2, N2 Vapour species e.g. Na, K

Particles From ash in fuel

Condensed vapour species

Gas temperature

Heat exchanger characteristics

Water / steam temperature (& pressure)

Metal temperature (& heat flux)

Deposit

rate of formation

composition Alloy used

corrosion damage rate viable life times ?

cost


16/38


Fuel combustion

Excluded minerals

Mineral inclusions

Pyrolysis

Convective transport

Char burning and

fragmentation

Vaporisation

Homogeneous nucleation

Coagulation

Mineralcoalescence and

fragmentation

Heterogeneous condensation

Fly ash 1-100mm

Reaction

Fly ash

Vapour

Fly ash 0.1-1mm

Fly ash with surface

condensation


17/38


Effect of Fuel Composition Variability

on Predicted Gas Compositions

0

200

400

600

800

1000

0 200 400 600 800 1000 1200 1400 1600 1800 2000

SOx (vpm)

HCl

(vpm)

UK Coal

Willow wood

Coal - wood

Coal - straw

Wheat straw


18/38


Deposition on Superheater Tubing

Vapour species

Condensation

onto solid particles

& aerosolsSolid particles &

aerosols

Condensation into

deposit

Coarse particles

stick

Thermophoresis of

fine particles

Water /

steam

Corrosion

Heat transfer

SOx

HCl

Vapours, SOx &HCl diffuse in

porous deposits

Vapour species

Condensation

onto solid particles

& aerosolsSolid particles &

aerosols

Condensation into

deposit

Coarse particles

stick

Thermophoresis of

fine particles

Water /

steam

Corrosion

Heat transfer

SOx

HCl

Vapours, SOx &HCl diffuse in

porous deposits

Deposition mechanisms:

Particles:

Direct inertial impaction

Thermophoresis

Eddy diffusion Brownian

Vapour:

Direct condensation

Condensation on particles


19/38


Fuel derived deposit compositionsDeposit compositions:Al-Si-O compounds

can fix Na, K if particle temperatures highenough

Ca/Mg carbonates / sulphatesNa / K sulphates / chlorides

Fe sulphates / chlorides / oxides / sulphides

Phosphates

Important factors

Minerals in fuels

Balance between elements

Corrosion aggravated by:

Low melting point deposits

High chloride deposits


20/38


Effect of fuel compositions

Dependence of deposit chlorine

content on fuel sulphur and alkali

chloride contents

(US DoE Research)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.1 1.0 10.0 100.0

Sulfur /2*Max (Alkali chloride)

DepositCl(%drybasis)

Appearance of chlorides in deposits

as a function of maximum alkali

chloride, fuel sulphur and % straw (onthermal basis)

(EU research)


21/38


Additives to reduce deposition & corrosion

Deposition / Corrosion of combustion heat exchangers in biomass-fired systems is

regarded as major issue by power plant manufacturers & operators

Vattenfalls latest solution:

dope flue gas with sulphur containing additive (= Chlorout) ahead of superheater

reduces deposition rate, chloride content of deposit and corrosion rate


22/38


Supergen Bioenergy - Pilot Scale Trials

Gas analysis

Temperature

monitoring

Gas analysis

Temperature

monitoring

Gases to

fan and

flue

Natural gas/excess air

pre-heater

Feed system

Biomass

Pulverised coal/biomass/air

or natural/fuel gas & air

Cooling

water out

Cooling

water in

Cooling

water out

Cooling

water in

Cooling

water in

Cooling

water out

Cyclone

Ash removal

system

Fluidised bedFluidised bed

Temperature

monitoring

Temperature

monitoring

Gas out

Topics being investigated include:

Fuel feeding & preparation

Characterisation of product

streams:

Gas compositions

Bulk gases

Trace species

Solids analyses

Fuel compositions

Ash / char compositions

Deposit compositions /

deposition fluxes oncooled (heat exchanger)

probes

Co-firing


23/38


Heat exchanger corrosion


24/38


Possible corrosion mechanismsin chloride / sulphate rich deposits

Fe Fe

Fe

HCl

NaCl

O2

O2

O2

SO2 + O2 + H2O

SO2 + O2

SO2 + O2Na2SO4

Na2S2O7

Na2O

NaHSO4FeCl2

Cl2

FeCl3

Fe2O3 Fe2O3

FeO

FeS

Tube

metal

Corrosion

products

Deposit

HCl


25/38


Alkali sulphate dominated corrosion regimes incombustion gases


26/38


Corrosion model requirements Cover wide range of operating environments

Different biomass fuel

Superheater / reheater, evaporator, water walls, etc

Corrosion damage (in terms of metal loss) as function of: Metal temperature

Gas composition (e.g. SOx, HCl, O2, CO2, H2O)

Deposit composition

Na, K Sulphate vs chloride

etc

Deposition flux (mg/cm2/hour)

Time Median vs maximum metal loss

Component life criteria


27/38


Corrosion data for model developmentAim: simulation of different specific environments

data on materials performance obtained using dimensional metrology

Laboratory based corrosion data generation:

Deposit re-coat test method Controlled atmosphere furnace

Test Variables Temperatures

Time

Gas composition:

simulated combustion gases

Variable SOx, HCl, O2, CO2, H2O, etc levels

Deposit composition

Simulated ash

(Na/K)Cl (Na/K)2SO4 Variable Na/K levels

Materials

Dimensional metrology before/after exposure


28/38


Controlled atmosphere corrosion furnace

Gas mixture 2

(e.g. N2-O2-SO2)Stainless steel

containment vesselAlumina

reaction tube

SamplesMass flow

Controller 2

Mass flow

Controller 1

Inert safety

gas (N2)

Safety

gas vent

Alumina tube

Alumina heat

shieldsGas mixture 3

(e.g. N2-O2)

Water

bath

De-ionised water

Trace heating

Mass flow

Controller 3

Vent

Gas clean-upsystem

Gas mixture 1(e.g. N2-HCl)


29/38


Surface scale& deposit

A1

A 2

An

B 1

B n

Internal

corrosion

To central

reference

point

Alloy

Where n = 24

Measurements

taken at equidistant

points spaced =

300m Surface scale& deposit

A1

A 2

An

B 1

B n

Internal

corrosion

To central

reference

point

Alloy

Where n = 24

Measurements

taken at equidistant

points spaced =

300m

-8000

-6000

-4000

-2000

0

2000

4000

6000

8000

-8000 -6000 -4000 -2000 0 2000 4000 6000 8000

X DIRECTION (MICRONS)

YDIRECTION

(MICR

ONS

ORIGINAL METAL CHANGE IN METAL

CHANGE IN GOOD METAL DEPOSIT & SCALE

100 micron contour

1-HAA-6

Sample Metrology & Data Analysis (1)


30/38


-100

-80

-60

-40

-20

0

0 90 180 270 360

Position around sample ()

Changeinsoundmetal(um)

Data ordered and

plotted againstprobability

Sample Metrology & Data Analysis (2)


31/38


Corrosion damage distributions for 2 Cr steel, 347HFG andAlloy 625 all at 560C, deposit D6 and gas 3


32/38


0

20

40

60

80

100

120

D0 D1 D2 D3 D4 D5 D6 D7 D8

Deposit

Corrosiondamage(m/1000hours

)

Gas 3, 560C (test 6)

Gas 3, 600C (test 3)

Sensitivity of 347HGF to changes in deposit composition andexposure temperature

(Corrosion Damage Evaluated at the 10% Probability of Damage Being Exceeded)


33/38


Correlation between Measured Predicted Corrosion Damage Rates(corrosion damage evaluated at the 10% probability of damage being exceeded)

10

100

1000

10 100 1000

Measured corrosion rate (m/1000 hours)

Predictedcorrosionrate

(m/1000hours)

2.25 Cr

1 Cr

X20

AISI 347

625


34/38


Emissions

Limits set by regulations vary by:

Plant capacity

Fuels

Policy decisions etc

Issues can include:

NOX SO

X HCl

Dust

Trace heavy metals

Etc

Range of technologies developed for:

Coal

Waste


35/38


Examples of particle removal systems

+ + +++

+ + +++

- - ---

Uncharged

particles

Electric field

Charged

particles

Gas Inlet Cleaned

Gas

Electrostatic Precipitator (ESP) Bag Filters


36/38


SummaryRange of potential biomass fuels being considered for

combustion systems

Heat exchanger durability Care is required in materials selection for biomass systems

Balance between fuel compositions, operating temperatures

(system efficiency), component life and materials costs

Predictive models being developed within SupergenBioenergy project relating exposure conditions to component

lives for biomass fired systems

Emissions

Control measured developed for other fuels (coal, waste) Appropriate technologies need to be selected to match

intended fuel / regulation


37/38


Thank you for your attention


38/38


Targets for heat exchanger steam operating temperatures andtube lifetimes from COST522 and COST538 programmes

50

50

100

20

Maximum

acceptablecorrosion rate

(m/1000 hours)

530 550

610 630

610 630

680 700

Metal

temperature

(C)

40,000

40,000

20,000

100,000

Target

lifetime

(hours)

500Waste

580Wood

580Straw

650Coal

Desired maximum

steam temperature

(C)

Fuel

Documents

02 Nigel Simms