September 20101

Wood to Warmth – Bioenergy Appliances

Michael Beech

TV Energy

September 20102

Bioenergy Conversion

• CombustionComplete oxidation of biomassEnergy -> hot combustion gases

• GasificationPartial oxidation of biomassEnergy -> fuel gas (low heating value) + tars, particulates

• PyrolysisThermochemical conversion of biomass w/o oxygenEnergy -> bio-oil (‘fast pyrolysis’) + gas, solids(charcoal)

September 20103

Bioenergy Conversion

• Combustion (Boiler) Simple technology, heat -> water or steam viaheat exchanger. Wide range of biomass fuel types andspecifications possible, boiler designs can accommodate.

• Gasification (Gasifier)Fuel gas -> furnace or IC engine. Intermediate ‘gas’ stageaffords higher efficiency & control, often for CHP applications.Usually demands tighter biomass fuel quality.

• Pyrolysis (Pyrolyser)Bio-oil produced. Gives higher density fuel, decouplesprocess to provide energy storage (although unstable), useful forCHP. Fine, dry biomass particles usually required.

September 20104

Bioenergy Appliances

Stoves (room heater)

• Pellets or logs (coal may be substituted for more power!)

• Heat to surrounding space via radiation, + some convection

• Poor control of heat output with log stove, pellets better

• With back boiler or ‘heat bank’ - to radiators, hot water tank

• Up to 20kW possible

• Efficiency - up to 75% (cf. open fire 10 – 20%)

• £2000 - £4000 installed (w/ back boiler)

September 20105

Bioenergy Appliances

Stoves

Log stove with flow and return pipes Pellet stove feeding thermal store

September 20106

Bioenergy Appliances

Boilers

• Specific designs to accept logs, pellets or chip

• Hot water (LTHW @80deg.C) to space heating, hot water systems, industrial/ agri-processes, swimming pools etc

• Steam for direct application, process heat, CHP (large scale)

• All larger than equivalent size oil or gas boiler, plus space for

fuel store (woodfuel has low energy density vs. fossil fuels)

September 20107

Bioenergy Appliances

Log boilers

• Domestic applications mostly

• Require daily manual loading, regular cleaning

• Accumulator tank or back boiler for heat storage and output

control

• Advantage of widely available, minimally processed fuel

• Logs £120/tonne bulk delivery, typical

• Typically £7,000 - £15,000 system installed

September 20108

Bioenergy Appliances

Log boilers

With accumulator tank

September 20109

Bioenergy Appliances

Pellet boilers

• Often domestic scale, but also non-domestic applications where space or fuel delivery access is difficult (e.g. urban locations)

• Automatic ignition, compact boiler with integral hopper (small domestic) and/ or separate fuel store

• Hot water to end use, or via buffer tank for additional control

• Pellets supplied in bags (small domestic) or bulk delivery via tanker, free flowing fuel, relatively energy dense for biomass

• Bagged delivery equivalent to heating oil @ 55p/litre

• Bulk delivery equivalent to heating oil @ 40p/litre

• ~£10,000 + system installed (small domestic scale)

September 201010

Bioenergy Appliances

Pellet boilers

60kW domestic

September 201011

Bioenergy Appliances

Chip boilers

• Large domestic scale, or non-domestic applications

• Automatic ignition, bulky, with separate fuel store

• Hot water to buffer tank, or district heating network can provide buffer on larger systems

• Chip delivered via container vehicle under gravity, fuel bridges easily, low energy density

• £100/tonne or 3p/kWh typical (1/2 – 2/3 cost of LPG/ oil)

• Fuel cost variable with source, delivery quantity, distance

• Higher capital cost vs. pellet systems (boiler & fuel store)

• Lower fuel costs than pellet systems

September 201012

Bioenergy Conversion

Chip boilers - Types

• Stoker burner Compact, lower cost, fast response, low minimum output, <30%MC/ consistent fuel required

• Moving grate More bulky, higher cost, efficient combustion, higher minimum output wet/ variable fuel possible

September 201013

Bioenergy Appliances

Woodchip boilers

540kW Kob boiler 220kW Froling boiler

September 201014

Bioenergy Appliances

Woodchip boiler & feed system

500kW Endress boiler Woodchip auger feed

September 201015

Bioenergy Emissions

Emissions from combustion of woody biomass

• NOx (nitrogen oxides)Cause acid rain and smog. A by-product of completecombustion, minimised by combustion air control, control ofresidence time of flue gas, combustion temperature.

• CO (carbon monoxide), soot, hydrocarbons, tar compounds and unburned particles

Generally harmful. Arise from incomplete combustion, result insooting up of flue. Emissions must be adequately dispersed.

NOx and CO result from combustion of fossil fuels too

September 201016

Bioenergy Emissions

Emissions can be managed

• Boiler/ stove design & maintenance• Fuel specification/ control• Exhaust stack design

Adequate flue height above roof, andtermination above any roof ridge inclose proximity.

Biomass boiler/ flue supplier can assist,or consult Building Regulations Part Jfor guidance.

September 201017

Bioenergy Emissions

Permits

Regulations depend on boiler size, location and fuel type.

For boiler plant <20MW heat input using clean wood -

Under Clean Air Act 1993, a Local Authority may declare:

• Smoke Control Areas – therefore plan to use an ‘Exempt Appliance’

• AQMAs - approach LA for guidance, seek emissions information from the boiler supplier

For fuel input rate >45.4kg/hr (~135kW output with 30%MCfuel), LA will approve the flue height

September 201018

Thank youmichael.beech@tvenergy.org