The suitability of energy plants as fuel for power boilers

Aadu PaistTallinn University of Technology Thermal Engineering Department

2005

Content

Introduction Energy plants as fuel Typical combustion

characteristics of energy plants Firing facilities Potential of biofuels and peat

long-run

Introduction

In Estonia the role of renewables (biomass, biogas, hydro, wind) is not considerable in electricity production (about 1%)

The main fuel in electricity production is oil shale In heat generation the role wood fuels and biogas 17 % and

peat 4%

Estonia has declared to increase the share of

renewables in electricity production up to 5,1 % by the year 2012

Forest resources in Estonia

Data from Estonian Agricultural University According to last taxation data of Estonian forests we have 2,25

Mha (51,5 % from country area) forest land with growing stock of 462 mln s.m3. By ownership these are divided :

Forest district of State - 830 000 ha (37%), Private forests - 680 000 ha (30%), Forests under land reform - 710 000 ha (31%), Other State forests - 15 000 ha (1%), Other forests - 15 000 ha (1%).

Relation between State and private forests in counties vary substantially.

Energy plants as fuel

Using energy plants as fuel in boiler, furnaces of the dryers and in other combustion equipment assumes that we have sufficient knowledge of the combustion characteristics

Heterogeneous, non-prognosticated and seasonally different quality of the energy plants as fuels presumes that before we start to use energy plants we thoroughly analyse the environmental aspects, efficiency and lifetime of the combustion equipment.

Essential characteristics which we must take into consideration in the design and operation of combustion equipment are: moisture, ash content, ash-fusibility temperatures, ash composition, density and so etc.

Reed and cattail characteristics

Nr

Plant DateMoisture, Wr

%

Heating value, MJ/kg Energy content, MW·h/t

Low High Low High

1 Reed 23.10.2003 49,6 7,59 9,51 2,11 2,64

2 Reed 28.11.2003 33,7 10,76 12,5 2,99 3,47

3 Reed 28.12.2003 25,5 12,39 14,05 3,44 3,9

4 Reed 25.01.2004 18,7 13,74 15,33 3,82 4,26

5 Reed 28.02.2004 21,8 13,12 14,75 3,65 4,1

6 Reed 28.03.2004 15,9 14,3 15,86 3,97 4,41

7 Reed 28.04.2004 8,9 15,69 17,18 4,36 4,77

8 Cattail* 28.10.2003 48,4 7,65 9,47 2,12 2,63

9 Cattail ** 16.11.2003 55,9 6,18 8,09 1,72 2,25

10 Cattail ** 04.01.2004 45,7 8,18 9,97 2,27 2,77

11 Cattail ** 25.01.2004 39,4 9,41 11,12 2,61 3,09

12 Cattail ** 01.03.2004 43,9 8,53 10,3 2,37 2,86

13 Cattail *** 28.03.2004 32,6 10,74 12,37 2,98 3,44

14 Cattail **** 07.04.2004 56,6 6,05 7,97 1,68 2,21

15 Cattail **** 28.04.2004 25 12,23 13,77 3,4 3,82

Märkused:Reed – Rocca al Mare, Cattail ‑ Virtsu*, Cattail  ‑ Kuressaare**, Cattail  ‑ Jägala***, Cattail  ‑ Harku järv**** (mostly stems, leaves are fallen)

Moisture

Moisture content of reed and cattail is lower in April and May and at the same time heating value and energy content is higher (table 1, Fig 1).

The best time for storing their energy plants is late winter – early spring, to reduce energy consumption for drying.

Moisture content of cattail (table 1, Fig 2) is higher than for read, because the stalk cattail is spongy from inside, which help to keep moisture also in early spring

Seasonal changes in moisture content(read)

Changes in moisture content 10. 2003- 04.2004

49,6

33,7

25,5

18,721,8

15,9

8,9

0,0

10,0

20,0

30,0

40,0

50,0

60,0

23.10.2003 28.11.2003 28.12.2003 25.01.2004 28.02.2004 28.03.2004 28.04.2004

Date

Mo

istu

re %

Seasonal changes in moisture content (cattail)

Changes in moisture content 10. 2003-04. 2004

48,4

55,9

45,7

39,4

43,9

32,6

25

0,0

10,0

20,0

30,0

40,0

50,0

60,0

28.10.2003 16.11.2003 04.01.2004 25.01.2004 01.03.2004 28.03.2004 28.04.2004

Date

Mo

istu

re %

Fig 1. Cattail: Wr =30-40 %, Qrl=9-10 MJ/kg, Er=2,5-3,0 MWh/t, Ad=5-6 %

Combustion characteristics of read, cattail and flax.

PlantSampling

placeMoisture

Wr %

Low heating value

Qdl MJ/kg

AshAd %

Ash-fusibilitytemperatures

°C

ReadRocca al Mare

03.0316,5 18,9 3,7 > 1440

Cattail Kuressaare16.11.03

55,9 18,4 5,7 > 1440

Flax Mooste04.04

10,3 18,8 4,62 -

Ultimate analysis and chlorine content in read, cattail and flax

Plant

Ultimate analysis

Cd ,% Hd ,% Nd ,% Sd ,% Od ,% Cld ,%

Read 48,8 6,4 0,44 0,12 44,24 -

Cattail 46,7 5,68 0,76 0,2 46,66 -

Flax 46,5 6,08 0,4 0,25 52,23 0,27

Read-, Cattail- and Flax-Ash Chemical Composition

Component, %Read,

Võrtsjärv*Read,

Rocca al Mare*Cattail, Kuressaare

Flax,Mooste

SiO2 89,21 82,26 3,31 ‑

Stotal 0,4 0,63 1,82 ‑

R2O3 0,63 2,82 5,65 ‑

Fe2O3 0,29 0,61 0,51 ‑

Al2O3 0,34 2,21 5,14 ‑

CaO 5,25 5,49 56,4 ‑

MgO 1,62 1,44 10,26 ‑

K2O 1,61 0,83 4,49 1,75

Na2O 0,32 0,66 5,7 <0,01

P2O5 ‑ 1,75 ‑ ‑

*Võrtsjärve read ‑ fresh water*Rocca al Mare read – sea water 

Read and Cattail Ash-fusibility Temperatures

ParameterMullutu

read

Väikese väina read

Võrtsjärve read

CattailRocca al Mare

read

10 % ashwater solution

pH9,3 9,4 9,8 12,7 9,5

FusibilityTemperatures

Temperature rise to

1 430 oC,-

Temperature rise to 1 445 oC,

Temperature rise to 1 440 oC

-

t1, oC Shape of the

sampleunchanged

1 380 Shape of the sample

unchanged

Shape of the sample

unchanged

1 285

t2, oC 1 440 1 420

t3, oC 1 445 1 435

t4, oC >1 445

1 445, almost liquid

Combustion Characteristics. Conclusions

Combustion characteristics, structure and look of read is rather similar to straw, which is in use as fuel for energy production in many countries.

Analysis show that read as fuel is higher quality than straw, because fusibility temperatures are over 1 400 °C, for example for oats straw fluid temperature only  900 °C (high content of K2O) In winter thanks for low moisture content ,up to 15 %, heating value of the read ca 15 MJ/kg (4,2 kWh/kg) . Ash content is also similar to straw, 4 %.

Using cattail as fuel is needful additional drying or mixing with dry bio fuels.

In spring read and cattail moisture content is lowest and plants are suitable for direct burning or granulating.

Data of bio fuels and peat boilers

Number of boilers and their total capacity running on biofuels and peat

609

1080

815

903712

865

1366856

500

700

900

1100

1300

1500

1993.a1995.a1998.a2003.aYear

Num

ber o

f bo

ilers

500

700

900

1100

1300

1500

Tota

ca

paci

ty,

MW

Katelde arv Võimsus

Consumed fuel and generated heat by biofuel and peat running boilers

2790

61447099

8719

6988

4288

1897

5242

1000

3000

5000

7000

9000

11000

1993.a1995.a1998.a2003.aYearC

on

sum

ed

fuel

,TJ

1000

3000

5000

7000

9000

11000

Gen

erat

ed h

eat,

T

J

Tarbitud kütus Toodetud soojus

Boilers for pellets Technology transfer

Pellet–fed plants are usually intended for domestic heating and consist of a boiler and a closed storage for pellets. A screw feeder feeds the fuel into the hearth located in the boiler furnace see fig. Combustion air is supplied by a blower.

Fully automated combustion equipment for pellets

Boilers for big bales (Batch-fired boilers) Technology transfer

The boiler is fired with 1 bale a time. A tractor fitted the bale through a feeding grate at the front of the boiler. Capacity of the boiler smaller than 1 MW, an efficiency 75 % and CO content below 0,5 %. In Estonia has three such type of boilers

Burning bales of straw and energy plants in “cigar burner” Technology transfer

Bales of straw and energy plants possible to use for energy production in heating plants (cogeneration plants) where the bales through a feeding grate pushed to “cigar burner”. Capacity of the boilers 4 – 6 MW

Facility for burning scarified straw or energy plants Technology transfer

Pales of straw or energy plants is copped/scarified and transported to the furnace by screw conveyors or blowers. Burning of copped plants take place on the hearth, mechanical grate or in the fluidized bed. Copped/scarified energy plants possible to burn together with fossil fuels, wood chips and peat. Adequate combustion tests made on the experimental equipment in TED of TUT and Ldt Kuressaare Soojus.

Fluidized bed boiler for burning crushed fuel Technology transfer 1. Kolle

2. Tsüklon3. Ülekuumendi4. Ökonomaiser5. Katalüsaator6. Õhueelsoojendi7. Kütuse punker8. Liiva punker

Stocker burner elaborated in TED of TUT

Forecast of wood fuel supply for coming 30 years

Estonian Agricultural University

0

1000

2000

3000

4000

5000

6000

2003

2005

2007

2009

2011

2013

2015

2017

2019

2021

2023

2025

2027

2029

2031

thou

sand

m3

Harvesting residues from state forests

Harvesting residues from private forests

Traditional fuelwood from state forests

Traditional fuelwood from private forests

Potential of biofuels and peat today and long-run

Biomass and peat fuels

Pri

mary

ener

gy

pro

du

ctio

nin

2002

Th

eore

tica

lp

ote

nti

al

tod

ay

Th

eore

tica

lp

ote

nti

al

in 2

030

TWh TWh TWhFuelwood and harvestingresidues

6.310.1

4.6*

Wood pellets and briquettes 1.1 1.2 1.2Straw - 0.4–0.6 0.8–1.0*Energy plants - 9.8 9.8*Reed - 0.6 0.6Biogas 0.03 0.4 0.4*Food waste - 0.1 0.1*Black liquor 0.2 0.2 0.2*Peat fuels 1.67 8.3 8.3Total 8.1 31.1–31.3 25.8–26.0

* These bio fuels are available for cogeneration of heat and power, if needful equipment is installed.