Densification

Question 1

Challenges with biomass (4)

Answer 1

Seasonal
Reliability and Quality of supply
Low density
Technical challenges

Question 2

What are some seasonal ,
challenges

Answer 2

Depends on harvesting window, may require mix of crops. Storage is needed, which may require protection to not degrade.

Question 3

Supply and quality challenges

Answer 3

Depends on yield and quality
Climate, pests, fertilisers affecting quality
Confidence in farmers (long term contracts)

Question 4

Why is density of biomass an issue? how to solve

Answer 4

transportation (vol density)
Chipping, pellting

Question 5

What are some technical challenges of biomass (4)

Answer 5

Moisture content - handling and utilisation
Ash - Corrosion, fouling, slagging
Dust - explosion hazard
Variability of supply - metals and chlorine in waste wood.

Question 6

Why is fuel handling important? problems

Answer 6

High moisture so needs drying
Milling is uneven and problematic at high moisture
Uneven and non spherical cause poor flow

Degredation of products

Question 7

How are wood chips produced?

Considerations?

Answer 7

Chopping process

used for boilers (>50kW)
Only pure wood may be used (recycled may have plastic/paints)
Hard wood requires more energy than moist

Question 8

How are wood logs produced?
Considerations

Answer 8

Split manually or hydraulic wood splitters
Most energy efficient
Non uniform so cant be used in automated boilers

Question 9

Benefits of briquettes vs logs

Answer 9

made from wood shavings and sawdust, fed into manual stoves or open fires because fo high CV and not prone to splitting or sparks.

Question 10

What are the steps in pellet production?

Answer 10

1.) Drying: 8-12% moisture
2.) Milling: Reduced/homogenises size in a hammer mill
3.) Conditioning: Addition of steam to improve adhesion
4.) Pelletisation: ring die - 10t/hr
5.) Cooling - improve durability

Question 11

Raw material factors affecting pellet production

Answer 11

Particle size - effects quality, energy consumption
Moisture: Energy consumption, quality, durability, combustion results
Lignin: Effects quality and mill lubrication
Density

Question 12

Equipment factors affecting pellet production

Answer 12

Process temperatures limit choice of raw materials
Available power affecting quality.
Pellet binders can reduce energy consumption

Question 13

Benefits of pellets vs chips

Answer 13

Clean, low ash and high volume energy density. Compact storage

Question 14

Benefits of wood chips

Answer 14

Cheaper, suitable for self production. Better suited to large industrial apps.

Question 15

Why should densification be done?

Answer 15

Cost and emission associated with transporting biomass can be reduced by transporting a dried and prepared product.

Question 16

What is torrefaction and why should it be done?

Answer 16

• Mild heating process (typically 290C for 30 mins in inert atmosphere)
• Heating values of 22-24 MJ/kg attained in 70-80% original mass.
• Hydrophobic solid produced so does not degrade in storage.

Question 17

Uses and products of biomass combustion

Answer 17

Hot gases - power stations, CHP

Question 18

Temperature range for torrefaction.
Mass loss, energy loss

Answer 18

230-290
Up to 30%, can retain up to 90%

Question 19

How is the grindability of torrefied biomasa

Answer 19

Power consumption of mills decrease and throughput increase.
Particle size distributions improve

Question 20

How does reducing water in torrefaction improve stability?

Answer 20

Becomes hydrophobic and resistant to fungal attack

Question 21

Benefits of torrefaction

Answer 21

high energy density, hydrophobicity, low degradation, excellent grinability, good combustion properties and co-firing