Quality management in local biomass district heating systems Impressions from the technical advisory visits to UK and Slovenia.

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

[email protected]

Chamber of Agriculture and Forestry StyriaHamerlinggasse 38010 Graz - Austria www.lk-stmk.at