September 20101

Wood to Warmth – Fuel Delivery and Storage

Michael Beech

TV Energy

September 20102

Fuel Delivery & Storage

Pellets – delivery and storage

• Domestic systems: 10 or 15 kg bags of pellets can be loaded manually into an integral hopper attached to boiler

• Larger systems: 15tonne pellet tanker or larger for bulk delivery – concept similar to oil

• Size store for boiler consumption at full load and largest volume practical to allow lowest £/tonne as a bulk delivery

• Pellets can be blown into an above ground store via flexible tube, up to 30m if necessary – but the shorter the better

• Minimise bends in delivery tube to reduce pellet damage

• Fuel transfer to boiler by lightweight or flexible auger feed

September 20103

Fuel Delivery & Storage

Pellets

September 20104

Fuel Delivery & Storage

Woodchip – delivery and storageConsider carefully:

• Delivery vehicle access to fuel store• Types & sizes of delivery vehicle• Method of transfer of woodchip from delivery vehicle into

store• Storage capacity sized for boiler consumption at full load and

lowest £/tonne of woodchip (largest delivery volume practical)• Maintenance access to fuel store and boiler feed auger in

case of fuel quality problems• Ventilation within fuel store to prevent condensation causing

saturated chip

September 20105

Fuel Delivery & Storage

Type and arrangement can be determined by method ofwoodchip delivery. Common arrangements are:

Woodchip Store - 1

• Above ground, walking floor transfer, open at one end. • Vehicle can drive into storage area and tip (or offload using

moving floor) onto walking floor ladders, which transfer chip to one end towards auger feed to boiler.

• Can also accept deliveries from front loader vehicle, or direct from chipper.

• Walking floor mechanism requires significant civil works & hydraulics, therefore expensive

• Robust system if designed and installed correctly

September 20106

Fuel Delivery & Storage

Above ground store, walking floor transfer

September 20107

Fuel Delivery & Storage

Above ground store, walking floor transfer

September 20108

Fuel Delivery & Storage

Above ground store, walking floor transfer

September 20109

Fuel Delivery & Storage

Woodchip Store - 2

• Above ground store, rotary arm agitator feed to boiler, fully enclosed or part open on one side.

• Vehicle will offload from above, in through hinged/ sliding opening or hatch. Requires chip volume to be raised and tipped, front loader or scissor lift trailer are suitable.

• Use of a chip blower (trough type or integral to container vehicle) is a further alternative, though relatively slow, noisy and energy intensive.

• A vehicle ramp or bank up to one side of store can allow use of standard tipping vehicle.

September 201010

Fuel Delivery & Storage

Above ground store, rotary agitator

September 201011

Fuel Delivery & Storage

Above ground store, chip blowers

September 201012

Fuel Delivery & Storage

Above ground store, delivery methods

September 201013

Fuel Delivery & Storage

Woodchip Store – 3

• Containerised storage (Roll on roll off/ hook lift bins). A fuel store and transport container in one.

• Bins are specially designed with walking floors and connection to feed auger, part of docking station. Usually 3 docking stations required, bins ~30m3 each.

• An expensive system, requires good a deal of space, but affords clean woodfuel delivery

• Mechanisms and connections prone to damage

September 201014

Fuel Delivery & Storage

Containerised Storage

September 201015

Fuel Delivery & Storage

Woodchip Store - 4

• Below ground store: Both walking floor and rotary arm agitator systems can be designed to be below ground, allowing standard tipping vehicles/ trailers or moving floor container vehicles to be used to transfer chip into store under gravity.

• Allows simplest and quickest delivery method, wide range of vehicles and hence fuel suppliers can be used

• High excavation costs, pit needs to be waterproof.• If plant room is at ground level then woodchip feed auger must

route upwards with maximum 30deg. angle from horizontal, to connect to boiler.

September 201016

Fuel Delivery & Storage

Below ground storage

September 201017

Fuel Delivery & Storage

Below ground storage

September 201018

Fuel Delivery & Storage

Example calculation

Woodchip @ 30%MC Wood pellets

Estimated peak heat demand (winter design condition) 16.0 16.0 hours/day at full loadHeat output capacity 220 220 kWBiomass boiler seasonal effi ciency 88% 88%Woodfuel energy 3,300 4,700 kWh/tonneMaximum woodfuel input rate 250 250 kWh/hr at full load

75.8 53.2 kg/hr at full load1.21 0.85 tonnes/day

Estimated bulk density of woodfuel 0.24 0.6 kg/cu.m5.05 1.42 cubic m/day

Woodfuel delivery vehicle minimum capacity (min. storage capacity) 5 15 tonnesWoodfuel delivery vehicle type tractor/trailer pellet tanker

21 25 cubic metresNo. of days of operation at peak heat demand per delivery 4 18 daysApproximate number of deliveries required for annual heat load 18 4 /yrDepth of woodfuel store 3.0 3.0 mInternal width of woodfuel store 5.0 3.25 mInternal length of woodfuel store 5.0 3.25 mInternal volume of woodfuel store (gross) 75.0 31.7 cubic metresEstimated usable volume of woodfuel store 50.6 29.0 cubic metres

12.2 17.4 tonnesNo. of days of operation at peak heat demand 10 20 days

September 201019

Fuel Delivery & Storage

Common problems

• Storage capacity too small - requires frequent deliveries• Difficult access to fuel store – increases delivery times, smaller

than optimal capacity vehicles used• Poor design of access opening into fuel store – chip spillage• Inadequate ventilation within fuel store – condensation from

chip causes drips from roof onto top layer causing wet chip• Double handling of chip (offloading then delivering into store)• Inadequate provision made for maintenance access to fuel

store, woodchip agitator/ transfer equipment, feed augers • Fuel delivery and storage are most likely areas for failure

of biomass systems, due to poor planning and design

September 201020

Thank youmichael.beech@tvenergy.org