Biofuel boiler technology and sizing for premise heating

Transcription

1 Centre Tecnòlogic Forestal de Catalunya, Solsona Course on Forest Biomass Installations, Biofuel boiler technology and sizing for premise heating Petri Rousku Forestry Centre Southeastern Finland

2 CONTENTS: Basic terms Determining the heating demand Sizing of a solid bio-fuel central heating system Boiler techniques Summary

3 Heating capacity demand of a building Ø= (Ø cond + Ø cond.ground + Ø vent + Ø leakair + Ø dhv )/ŋ where Ø=heating capacity (kw) Ø cond.ground = conduction capacity to ground Ø cond =conduction capacity through structures Ø vent =capacity demand caused by ventilation Ø leakair = capacity demand caused by leak air Ø dhv =capacity demand for domestic hot water ŋ= efficiency of heating equipment Energy demand is calculated equally.

4 Consider -Geographical area -Point of the compass -Special features of the structures, for e.g. 2-, 3- or 4-fold windows,... - placing on terrain (uphill, downhill, foundations partly dug in ) -Indoor heat sources - heat delivery techniques; radiators, floor heating

5

6 Nominal heating capacities of buildings in Finland New smallhouses W/r-m 3 Old smallhouses Rowhouses Old blocks-of-flats New blocks-of-flats offices hospitals Day nurseries schools theatres Churches, libraries Sports halls shops Accommodation restaurants Industrial buildings 15-25

7 Outdoor measuring temperature for heating equipment -29 o C in Finland -5 o C in Britain Nominal heating capacity figure in Spain =0,5*Finnish figure?

8 Nominal heating energy demand Take into consideration: Building age Structural insulation capability: insulation, window types and areas Automated air ventilation? ->+20 30% Heat recovery, capacity? -> % (Domestic) hot water demand normal or high? a hot water tap at full capacity takes 35 kw momentaneously Nominal energy demand alters in Finland kwh/building-m3,a

9 Sizing of a solid bio-fuel central heating system

10 Reserve heating capacity what s the reserve heating solution? oil, electricity, other biofuel system, solar, none? Usually necessary at least in Nordic conditions Building type-> 100 % heating demand may be needed to cover by reserve system

11 Present heating system/ renovation project usable as reserve power capacity? > influence on the investment economy > sensible to dimension the bio-plant for partial, basic capacity?

12

13 FUEL QUALITY what kind of biofuel: homogenous, less homogenous great/small energy content value dry/wet particle size

14 Varying

15 Fuel moisture content/ energy value

16 Fuel storages Spring discharge Rotating plate discharge

17 Hot water container or not? Evens the load alterations > enables a smaller bio-fueled boiler? > is it because of continuous hot water demand? -> higher boiler output demanded! Milder climate in Spain than in Finland > hot water demand has greater effect on the heating system

18 Push feeder floor discharge - hydraulic Fuel storages

19 Screw conveyors

20 Screw conveyors

21 Pneumatic conveyor for pellets Transfer distance >20 m Loose dust removal included in the Finnish system Suitable for every places, but more expensive than screw

22 Hot water container

23 Sizing for full heating capacity typically a new premise s bio-heating plant dimensioned for total power demand in Finland -> demand: good adjustment capability for low and high power needed, quick changes -> homogenous fuel, seasonal fuel changes possible although (high/low energy content -> )

24 For full power range Wood pellet boiler, 300 kw

25 Bio-heating plant for partial/basic load cheaper investment?, but what s the influence on /MWh (how large bioenergy (=cheap) production vs. reserve (oil etc.= expensive) energy adapts more easily on warm season use higher demand on top power endurance ->top power may be needed for e.g. 1 month = 30 d*24 h = 720 h without a break -> high temperatures continuously -> burner /grate must have mechanical, automatic ash removal especially with fuels with high energy density or high ash content!

26 Pellet burner - mechanical burner head

27 2 boilers Wood chip boiler, 140 kw, mechanical burner head Oil boiler, 100 kw

28 Some technical features of grate boilers & stoker burners

29 Stoker burner principle

30 Stoker burner, fixed burner head

31 Usually a good, industrial, standard product Efficiency factors: Smoke temperature Insulation Premise boiler Often a boiler-burner unit product

32 Grate boiler

33 Adjustment principles a. Conventional on-off feed with clock-switch: fuel and combustion air portably: feeding with top power till boiler top temperature reached - -> break on feed simple, easy to adjust, but flue gas emissions alter high power demand for electric motors of fuel feeding screws OR

34 b. Modulating fuel and combustion air feed with inverters vast adjustment possibilities, but more difficult to adjust at first quick reaction to load changes enables low fluegas emissions in every situation

35 Other things to consider Grate boilers/ stoker burners

36 secondary combustion air regulation based on fluegas O 2 content: emission level Lambda sensor Zirkonia oxygen probe

37 Pellets, briquettes High combustion temperature -> water-cooled grate recommendable

38 Other combustion techniques

39 Gasification boiler very good combustion results on different solid fuels possible operation principle: power adjusted by controlling the gasification of the fuel already present in the boiler (compare: grate boiler output controlled by the momentary fuel feed and combustion air) Power range 5 >100 %, but no sudden load changes

40

41 Primary combustion chamber + fire tube boiler the gas produced in the primary chamber is burned in a separate boiler typical for fuels with high moisture content Power range 20 >100%

42 Lengthened combustion time Turbulated combustion > very complete result

43 SUMMARY

44 Future brings Emission minimization Precise sizing Flexibility of systems Fuel quality control Multi-biofuel techniques Micro CHP