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Low Grade Biomass – Challenges and

Opportunities

27th June 2017

Extending Biomass Fuel Capability – What are

the challenges?

Trudy Beeley

05/07/2017

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• Overview of Markinch CHP plant

• Current fuel

• Quality

• Challenges it presents

• What alternatives are there?

• Availability, quality

• Can we use it?

• Plant constraints, possible modifications

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Markinch CHP plant - location

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Markinch CHP plant – aerial view

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Markinch CHP plant - location

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Markinch CHP plant – size

> Transferred to RWE Generation UK 1st January 2016

– Plan to be operational Q3 2013, actual 2014

> Circulating fluidised bed (CFB) boiler

– Thermal capacity 168MWth

– Generator capacity 62.5 MWe

– Live steam capacity 216 t/h

– 3 gas fired package boilers – 90 t/h total

– Furnace gas temperature 850 – 900°C

– Replaceable superheater

– Capital cost >£200M

– Operational life 20 years

– Fuel – recycled and virgin wood (WID plant)

– Fuel logistics – approx 405,000 t/y (80 trucks/day)

– Staff – approximately 30

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Markinch CHP plant - Fuel

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> Fuel mix:

> Fuel supply: mainly local within a radius of 200 km

> Fuel logistics: ~ 400,000 t/year ( 80 trucks per day)

> Location advantage: near to harbour (~15 Miles): alternative

fuel supply per ship

recycled wood ~85%

virgin wood,

saw mill waste.

~15%

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GG

circulating

fluidised bed

boiler

bag house

hig

h p

ressu

re

ste

am

pip

e

air h

ea

ter

HP-

feed water

preheater

feed water tank

Tullis Russell

Papermakers

steam turbine

generator

condensate

preheater

feed water

pump

low

pre

ssu

re

ste

am

pip

e

biomass silos

biomass

unloading station

air-cooled

condenser

injection of

active carbon

air supply

sta

ck

Process flow diagram

elec. net capacity:

(53) 62.5 MW

steam output:

83 MW (=120 t/h)

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Materials handling

05/07/2017

magnetic

and oversize

seperator

silo 3

virgin wood

silo 2

recycled wood

silo 1

recycled wood

circulating fluidised bed

boiler

container for ferrous material

container for oversize material

belt conveyor

air-supported belt conveyor

chain conveor

Samson

Feeder

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Circulating Fluidised Bed combustion process has several

key advantages:-

• Additional turbulence gives more effective chemical

reactions and heat transfer.

• Lower temperatures than traditional PF units mean

lower NOx formation – CFB 760-930°C vs PF

>1200°C.

• Increased variation of fuel diet.

• Markinch boiler is a WID compliant unit – residence time

in furnace at temperature above 850°C for 2 seconds

(can burn recycled waste wood).

• Can inject CaCO3 to bed to remove SO2 from flue gas.

However boiler furnace, cyclone and ducts have to be

refractory clad to protect pressure parts from erosion

and fire side corrosion, so heat flux lower and boiler

size is much larger!

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Boiler issues: Tertiary superheater fireside corrosion and tube erosion

• Stainless steel tertiary superheater tubes in the loop seal have suffered from corrosion due to

condensation of alkali chlorides in flue gas.

• Initial thickness was 7.1mm, reduced to 4.3mm in some areas by September 2015. • Damage was very localised, may have been influenced by secondary mechanism.

Location of

initial leak

Loss of refractory, secondary washing of

membrane and adjacent tube damaged.

Fireside

corrosion

Tube

erosion

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Recycled/Recovered wood (RCF) combustion

challenges > Increased wear on fuel conveying system

> Increased risk of blockages

> Dust formation when handling

– Explosion safety

– Heavy metal content higher in dust than normal recycled wood

> Molten metal on grid (nozzles, ash removal)

> High amount of impurities in bottom ash – blockages

> High temperature corrosion due PbCl2 and KCl

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Recovered from

bottom ash screw conveyors

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What are the alternatives?

– Sewage sludge

– Oat husks

– Other husks e.g. sunflower, cocoa

– Shea meal

– Olive residues

– Carpet residues

– Poppy seed residues

– SRF and refined SRF

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Why change the fuel?

> Market forecast to tighten in 2018 with supply

stagnated and demand growing due to new

plant.

> Therefore need to increase diversity of fuels to

reduce risk and build in resilience to market

forces.

> Questions to ask…

> Can we widen the specification for the RCF?

> What can we take instead of RCF?

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What are the problems?

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Dust

Handling - segregation

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What else?

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Dust Self heating

14°C

10°C

12°C

15°C

11°C

and more

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Plant performance

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Is it feasible?

> Economics

> Can we feed the boiler?

– Materials Handling – minor modifications or only

possible with new feed system?

– Dedicated unloading, pneumatic conveying for

dustier fuels?

– Separate storage for niche fuels?

> What is the impact on boiler performance?

> Are there any safety implications?

> Are there any environmental issues? Waste still a very

sensitive area – public perception

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Extending plant capability > RCF

– Trialled fuel processed using different methods:

• Varying top size and fines content

– Results very encouraging

– Positives in terms of metal removal and fuel consistency

– Higher rejects and caution with reliability of materials handling system

– Boiler performance good

> Alternative fuels

– Oat husk blend successfully burnt

– Main issue is logistics

> Key development areas

– Reliable analysis that is fit for purpose

– Increasing flexibility of delivery of fuel to boiler

– Monitoring of boiler

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Any questions?

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