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Quality management in local biomass district heating systems
Impressions from the technical advisory
visits to UK and Slovenia
Slide 2
Bioheat Žetale – Starting situation
- Žetale is a small municipality in the east part of Slovenia with around
1500 inhabitants
- 12 farmers decided to invest in a wood biomass heating system and established a cooperative
- They prepared a survey from which they found out potential customers and their energy needs. On the base of the survey they selected a location for the district heating plant.
Slide 3
Bioheat Žetale – Let´s start!
1. Find investors / operators of the biomass district heating system
2. Inform people about project activities (Workshop)
3. Determination of the heat demand of the total densely populated catchments area
4. Creation of a scale plan, where the individual objects are identified by their heat demand
5. Creating a rough study, in terms of economic viability and feasibility of the project
6. Discussions with potential investors
7. Discussions with potential customers, to inform the public about the concrete project activities (e.g. organize information meetings)
Slide 4
Feasibility study
Analysis of future heat sales
Heating load and hours of full load operation
Investment costs
Boiler, installation, construction work, district heating grid, heat transfer stations, planning, amount of own work, boiler room, storage
Operational costs
Wood fuel
Maintenance, service contract, personal, chimney
Capital pay back, automatic alarm system, insurance, accounting & taxes
Calculation of heat price
Slide 5
District heating grid
Slide 6
Customers of heat consumption
Slide 7
Investment costs depends…
Is there an existing boiler room?
Is the boiler room large enough to accommodate a wood boiler?
Can the wood fuel be stored in the existing building?
Is it possible to attach an external fuel storage?
How can woodchips be delivered? (Enough room for a truck to turn?)
Need to put district heating pipes in streets (expensive) or soil (cheap)
Slide 8
Bioheat Žetale – Starting situation
Slide 9
Bioheat Žetale - Specific heat cost & annual total costs
Slide 10
Distribution of the specific heat costs with subsidies
Slide 11
Bioheat Žetale – Amortisation of the project
Slide 12
Ecological / efficiency evaluation of the project
Slide 13
Discussion point: Boiler size
Which solution is the best – one or two boilers ?
the installation of 2 x 200 kW would recommend instead of 1 x 400 kW, but this increases the investment costs (-> in the summer only the 200 kW boiler is in operation -> more full load hours -> less emissions and less wood fuel demand)
In contrast to the 200 kW boiler, a 400 kW boiler is available in an industrial version, which can also burns quality fuels with less quality easily
The decision for a boiler should also be made on the basis of the available fuel range
Slide 14
Slide 15
Criteria for a good boiler
References in practical applications
High efficiency (>90%)
Low emissions
Automatic cleaning of heat exchangers
Automatic ignition
Automatic ash removal
Available service (24 h/d, 365 days/a)
Slide 16
Boiler load during the heating season%
of f
ull c
apac
ity
Full capacity on 6 days
80 % of capacity on 19 days
60 % on 105 days
25 % on 40days
On 90 % of heating
days 60 % of boiler
power or less is used
35 % on 60 days
Heating days
Slide 17
Planning, tender and purchasing
Correct dimensioning of boiler, possibly peak load and backup boiler
Heat storage tank for load management and to cover peak load in the morning hours
Use standard components – no special solutions
Plants up to 150 kW with competent installer, no tenders
Slide 18
Heat storage tank
Higher efficiency of boiler operation
Fuel savings
Lower emissions
Better heating comfort
No tar depositions in chimney and boiler due to low load operation
Slide 19
Diskussion point: Heat grid I
Heat grid
- Plastic or iron: The decision is a question of a price
- Plastic tube is limited due to the pressure and
temperature (manufacturer)
- At high temperature and pressure decreases the time life
of the network
- Heating networks should not be dimensioned too large, it increases the pump electricity costs which causes heat losses
Slide 20
Always have an overall concept in mind,
Always think on a later extension of the network
(the heat network must be planned for the overall concept)
e.g. costumers decide for local heat after his existing heating system no longer work
e.g. higher prices for fossil fuels leads to a higher increase of demand
Attention: a lot of houses invest in thermal insulation (less heat demand in the future)
Diskussion point: Heat grid II
Slide 21
District heating grid: Important technical specifications
Significant temperature difference between out flowing and back flowing water (min. 30 °C)
Temperature of backflow < 40 °C most of time
hydraulic regulation of heat distribution system of customers
more than 900 kWh of heat sales per meter of grid length
High quality insulation of pipes
Small diameters of pipes
Slide 22
Discussion point: Fuel quality
Fuel quality
2x 200 kW plant: water content up to 35%, max. size pieces G50 mm (ÖNROM, G50=cross section of the wood chip is > 5 cm²)
400 kW plant: water content up to 50%, size pieces > G50 mm
Slide 23
Basic issues
Fuel quality is THE key for flawless plant operation, especially smaller plants are not suited for wet fuel !
Wet fuel (water content > 35%) can cause combustion problems, smoke emissions and energy losses
Large pieces of wood can block the screw feeder and stop operation
Slide 24
How to achieve high quality fuel ?
Before chipping: ideally 1 summer storage of trees in a pile
Use suitable wood types
Reduce impurities to a minimum
(sand and soil, stones, metal,...)
Sunny and wind exposed storage area
Short storage periods, as short as possible and as long as necessary
Chipper well maintained (sharp blades)
Slide 25
Discussion points: Back-up system
Options for a back-up system:
1) In variant 2 x 200 kW you have a boiler automatically as a reserve, provided that the fuel supply is disconnected (2 space host systems).
2) For a short time (3 - 5 h), the buffer offset a loss
3) Implement the existing gas heating system of the school into the biomass heating plant as a back up system (e.g Zetale)
Slide 26
Discussion points: Year-around system
Year-around system ?
The heating is carried out at newly installed district heating systems almost exclusively in the year-around operation
The comfort for the consumer is much higher
The heating plant can also be extended to a solar system
A year-around operation has higher net losses, because the network must be maintained all year
Slide 27
Diskussion points
Wood chip storage / delivery ?
- In the coldest month you need about 15% - 20% of the total annual demand. A to small wood chips storage in practice leads to problems.
- The wood chips delivery is done either through central wood chips storage or direct from the participating farmers.
- It is recommended to settle the wood chips by weight and water content and prevent future problems.
Slide 28
Wood chip delivery by conventional hanger: simple & cheap
Slide 29
Example
Storage next to boiler room Storage in existing cellar with
a storage filling screw
Slide 30
Examples
Storage above the boiler Storage above and beside boiler,
fuel retrieval on boiler level
Slide 31
Biomass district heating plants
Lessons learned - main technical deficiencies are:
The heat demand of consumers is overestimated
The pipeline system is oversized
Size of the storage is much bigger than necessary
Low utilisation ratio of the wood boiler
Fuel quality does not meet the quality requirements for the
Installed biomass boiler
Slide 32
Financing of Wood Energy Contracting Projects
little loan fraction
1/3 own capital, and services on own account
1/3 subsidy
1/3 connection fee
Slide 33
Just little building measures necessary (adaptation of existing heating rooms and fuel wood storerooms)
low conduction losses (less than 20%), low costs for pumping electricity
small and straightforward projects with low investment costs and risk
reasonable alternative to long distance heating projects and individual equipments
Advantages of Wood Energy Contracting Projects
Slide 34
Biomass district heating
Slide 35
Thanks for interest!
Contact
Thomas Loibnegger
Energy and Biomass
T: +43 316 8050 1407
Chamber of Agriculture and Forestry StyriaHamerlinggasse 38010 Graz - Austria www.lk-stmk.at