**2. Model research**

The model research has been carried out at the Technical University of Dresden. It includes the combustion tests - Table 2. - on experimental pilot equipment - Fig. 1. , 2. with atmospheric circulating fluidized bed for coal and bio-fuels produced from the sewage sludge from WWTP (waste water treatment plant) and biomass, and thermo-analytical study of bio-fuels - Table 1. The modelling had the following aims:


Co-Combustion of Coal and Alternative Fuels 65

**fuel Water Ash C H N S Volatile** 

coal 100 0 14.0 5.2 55.0 3.86 1.03 0.70 45.8 20,599 Mixture 75 25 13.9 8.0 50.4 3.83 1.04 0.65 47.4 18,749 Mixture 50 50 12.6 11.9 45.2 3.79 0.92 0.54 50.6 16,728 Mixture 25 75 12.9 14.0 42.3 3.73 1.08 0.47 51.9 15,688 Biomass 0 100 14.6 13.7 36.6 4.31 1.34 0.24 57.8 13,291

Fig. 3. Scanning electron microscopy (SEM) of combustion residues during experiment - 85 % coal/15 % biomass. Sample 1 - fly ash from heat exchanger. Sample 3 - mixture of biofuel

**% % % % % % % % % kJ/kg**

**combustible Heating value** 

Fig. 2. CFB boiler 300 kW

Brown

**Coal Bio**

Table 1. The analysis of the fuel mixture


Fig. 1. General view on pilot plant

Laboratory studies were focused on a detailed identification of input raw materials (coal, biofuel, limestone) so that the measurements could be reproducible: 1. Raw material input analysis and dependence of combustion solid residues on raw material input. 2. Combustion inaccuracy assessment in actual unit condition (T, gaseous and solid components, velocities, modelling). 3. Balance of combustion elements choice, studying mechanisms of deposit formation and composition. 4. Verifying a redistribution model for a choice of elements between the fuel and solid by-products.



Laboratory studies were focused on a detailed identification of input raw materials (coal, biofuel, limestone) so that the measurements could be reproducible: 1. Raw material input analysis and dependence of combustion solid residues on raw material input. 2. Combustion inaccuracy assessment in actual unit condition (T, gaseous and solid components, velocities, modelling). 3. Balance of combustion elements choice, studying mechanisms of deposit formation and composition. 4. Verifying a redistribution model for a choice of elements

well as element analysis for fuel and biomass. - To perform leaching tests for combustion solid products.

measurements.

Fig. 1. General view on pilot plant

between the fuel and solid by-products.



Table 1. The analysis of the fuel mixture

Fig. 3. Scanning electron microscopy (SEM) of combustion residues during experiment - 85 % coal/15 % biomass. Sample 1 - fly ash from heat exchanger. Sample 3 - mixture of biofuel

Co-Combustion of Coal and Alternative Fuels 67

**Filter 85/15 Filter** 

result 11.6 11.4 9.1 7.6 10.3 insecurity 0.6 0.6 0.5 0.4 0.6

result 900 1,120 1,480 780 920 insecurity 60 70 90 50 60

result 8 13 13 6 7 insecurity 5 7 7 3 4

result 149 110 97 285 285 insecurity 9 7 6 18 18

result 180 147 200 96 108 insecurity 13 11 14 7 8

result 1,510 1,810 1,400 1,110 1,150 insecurity 70 80 60 50 50

result 105 78 69 201 201 insecurity 7 5 5 13 13

result 80 82 101 61 75 insecurity 6 6 8 5 6

result 100 68 68 59 66 insecurity 20 14 14 12 14

result 52 42 61 49 50 insecurity 5 4 5 4 5

result 610 1,080 1,400 550 660 insecurity 40 70 90 40 40

Result in % 16.8 8.47 5.55 6.25 0.57 Insecurity in % 0.2 0.09 0.06 0.07 0.01

Table 3. Concentration of heavy metals in pilot plant - test No.5., 6 by X-ray fluorescence

Co result 20 20 20 20 20

Hg result 5 5 5 5 5

Mo result 20 20 20 20 20

**0/100** 

**Cyclone 0/100-wet** 

**Cyclone 0/100-dry** 

**heat exchanger 85/15** 

**Sample** 

As

Ba

Cd

Cr

Cu

Mn

Ni

Pb

Sn

V

Zn

Loss of annealing

spectroscopy (mg.kg-1)

Fig. 4. Scanning electron microscopy-morphology. Sample 85/15-filter, enlargement 2000x. Sample 85/15-filter, enlargement 2500x


Table 2. Basic characteristics of the combustion tests

 Fig. 4. Scanning electron microscopy-morphology. Sample 85/15-filter, enlargement 2000x.

**Test No. 1 No. 2 No. 3 No. 4 No. 5 No. 6** 

Mpal = 159,3kg

Fuel delivery 42 kg.h-1 44 kg.h-1 53,1 kg.h-1 44 kg.h-1 42 kg.h-1 67.7 kg.h-1

output 240.3 kW 229.2 kW 246.7 kW 261 kW 222.2 kW 250 kW

in fluid bed 870 °C 850 °C 850 °C 804 °C 886 °C 800 °C

CO = 1 887 ppm

SO2 = 714 ppm

NOx = 191 ppm

Excess of air 1.18 1.32 1.083 1.1 1.154 1.189

in fly ash 0.051 0.035 0.042 0.086 0.0828 0.047

reactor 4.25 m.s-1 4.50 m.s-1 4.50 m.s-1 3.30 m.s-1 4.24 m.s-1 4.73 m.s-1

O2 = 3.2% O2 = 5.0% O2 = 1.6% O2 = 1.9% O2 = 2.8% O2 = 3.3%

75%:25% 50%:50% 25%:75% 85%:15% 0%:100%

Mpal = 180kg

CO = 1 842 ppm

SO2 = 950 ppm

NOx = 215 ppm

Mpal = 135kg

CO = 577 ppm

SO2 = 967 ppm

NOx = 195 ppm

Mpal = 203kg

Sample 85/15-filter, enlargement 2500x

100:0% mass

126 kg brown coal

Mpal = 132kg

CO = 201ppm

SO2 = 260 ppm

NOx = 197 ppm

Table 2. Basic characteristics of the combustion tests

Coal/biomass Mpal amount of fuel

Thermal

Temperature

Content of the flue gases

Unburned C

Velocity in


Table 3. Concentration of heavy metals in pilot plant - test No.5., 6 by X-ray fluorescence spectroscopy (mg.kg-1)

Co-Combustion of Coal and Alternative Fuels 69

**Place Year Type No Tph Producer Fuel System** 

1998 CFB 1 250 BC, BIO

1997 CFB 1 160 Siemens

(SES Tlmače) HC, BIO

HC/BC

(Vítkovice) BC, BIO Valmet

(SES Tlmače) BC, BIO Valmet

Alstom HC, BIO Honeywell

(SES Tlmače) HC Honeywell

HC, BC,

Wheeler BC, BIO Valmet

(Vítkovice) HC ABB

International HC, BIO ABB

Wheeler (CNIM)

Foster Wheeler (FORTUM) ABB

Siemens

Honeywell

HC, BIO Valmet

BIO Valmet

1995 CFB 1 160 Lurgi

1996 CFB 1 250 Foster

1996 CFB 1 350 EVT

1998 CFB 1 350 LURGI

2000 CFB 1 125 Lurgi

Hodonín 1996 CFB 2 170 AEE Austria Lignit,

hot cyclon 1 190

HC – hard coal, BC – brown coal, BIO – biomass , Tph – tons steam per hour - output

Sampling of flue gases from the bottom part of the fluidized bed.

Table 4. Newly-built fluid boilers with circulating fluid layer in the Czech Republic

Sampling of flue gas elements from the entire boiler can be divided into three groups:

 Sampling of flue gases from the boiler second pass up to the exit to the chimney. Sampling of flue gases from the boiler furnace, cyclones and cyclone link channels.

Štětí 1998 CFB Retrofit 1 220 Foster

Ml.Boleslav 1998 CFB 2 140 EVT

Fluidized

1996 CFB 1 160 Babcock ABB

bubble bed 10 125 Power

Ledvice 1998 CFB 1 350 ABB Alstom BC ABB

Kladno 1999 CFB 2 375 ABB Alstom HC ABB Plzeň 1999 CFB 1 180 ABB Alstom BC ABB

Třinec

Poříčí

Tisová

Zlín

Komořany

1995 - 99

Olomouc 1998 CFB without

**3.1 Flue gas elements** 

The model research verify if the alternative fuel produced from biomass and sewage sludge may be used as alternative energy source in respect of the EU legislation, and/or its other modifications (with additives, decontamination technologies) for suitable fuel, which would comply with emission limits or the proposed energy process optimizing the preparation of coal/sludge mixture for combustion in the existing power engineering equipment.

The limiting factor for sewage sludge utilization from WWTP (waste water treatment plant) in agriculture is the increased content of risk elements and also the occurrence of organic pollutants – primarily polyaromatic hydrocarbons, PCB (polyaromatic byfenyls) and AOX (adsorbable organic halid). Other alternative fuels have not these limiting conditions. The limiting factor for sludge combustion at incineration plants is water content. With regard to the fact that from 2005 the EU Directives EU expects to ban waste disposal sites with any material with content of organic substances above 10 %, it is apparent that the priority condition for sludge utilization is sludge decontamination or power engineering utilization (Loo & Kopperjan 2008). Results from tests may be evaluated as very good with the prerequisite for utilization, testing of investigated substances in real combustion units. On the basis of carried out laboratory and pilot tests one may expect good results from these real units (equipment with greater output), many of these experiments have been already performed. From the results of experiments and thermoanalytical studies it is clear that 15 % of alternative fuels – biofuels based on sludge and brown coal can be used in the large fluidized bed boilers located in the Czech Republic. The combined combustion will enable to fulfil the Czech Republic's pledge to the European Commission concerning the development of renewable energy resources by 2010.
