FUNDED BY THE Services to Technology Providershpcogenpak.org/wp-content/uploads/2015/04/Boiler... · 2018-12-10 · Bagasse is one of the easiest decomposable lingocellulose species

FUNDED BY THE EUROPEAN UNION

High Pressure Cogeneration for Sugar Sector in Pakistan

Services to Technology Providers

Training and Capacity building activities with HP boiler manufacturers

Session 2: the fuels and combustion Trainer: Frans Baltussen

Date: first half 2015



Unloading sugar cane Transport through cutter to shredder/mill house

Bagasse from mill house to boilers

Storage of surplus Bagasse

Bagasse from sugar mill



Bagasse in sugar mills

Water content wt% 46 till 52 ( some times 54)

Fibre content wt% 43 -52

Soluble solids wt% 2-6

Average density Kg/m3 150 loose

400 bailed

Proximate Analysis On Dry Basis(% of Dry Basis)

Ash wt% 2,5

Volatile wt% 85,5

Fixed carbon wt% 12

Higher heating value (HHV or GCV) Is including the latent heat

KJ/kg 9178

Lower heating value (LHV or NCV)

KJ/kg 7295

Ultimate Analysis On Dry Basis(% of Dry Basis)

C wt% 47,82

H wt% 5,85

N wt% 0,14

S wt% 0,3

Ash wt% 3,23

O (by diff) wt% 42,66

Cl wt% 0

For accurate data the fuel should be analyzed in the laboratory. By combustion calculation the following can be calculated for bagasse: • heating values, • Air requirement , • flue gas flow, • Compositions • Heat content • Adiabatic flame temperature



Bagasse in sugar mills

At stoichiometric combustion with air of 72% relative humidity the values are as follows: • Air quantity: 2,11 Nm3/kg / 2,70 kg/kg • Flue gas flow: 3,05 Nm3/kg / 3,68 kg/kg • O2 : 0 vol% • CO2 : 13,63 vol% • SO2 : 0,03 vol% • N2 : 52,74 vol% • Ar : 0,62 vol% • H2O : 32,98 vol% • Adiabatic firing temperature: 1465 C

The bagasse can be fired with an excess air of 1,35. Means 35% more air is supplied then required for stoichiometric combustion. What are the O2 and CO2 contents? • Air quantity: 1,35 * 2,11 =2,85 Nm3/kg

• Flue gas flow: 3,05 + 0,35*2,11 = 3,79 Nm3/kg

• O2 : (0,35*2,11*0,2047/3,79 ) * 100% = 3,99 vol%

• CO2 : {(0,35*2,11*0,0003) + (0,1363*3,05)}/3,79 *100%=

10,98 vol%

• H2O : {(0,35*2,11*0,0223) + (0,3298*3,05)}/3,79 *100%= 26,98 vol%

• Adiabatic firing temperature is 1264 C

• The CO content will be approx. 350 mg/Nm3 • The efficiency losses due to CO is approx. 0,175 %

For combustion air of 72% relative humidity the composition is as follows: • O2 : 20,47 vol% • CO2 : 0,03 vol% • N2 : 76,37 vol% • Ar : 0,9 vol% • H2O : 2,23 vol%



CO content during capacity test and the impact on efficiency: Based on operating data running at 141 tph HP steam

Oxygen content in flue gas: vol% wet

Measured CO content in flue gas: ppm

Eff. Loss Due to CO %

Improved eff due to less excess air (ref from 5 vol% oxygen) %

Overall improved eff. Due to less excess air. %

Additional power consumption fans KW

T stack

3,5 (n=1,3)

Estimate 600

0,3 (estimate)

1,4 1,1 -190 156

4 (n=1,35)

Approx 350

0,175 0,9 0,725 -141 158

5 (n=1,45)

Approx 152

0,075 Reference point

164

6 (n=1,59) Approx 50 0,025 -1,4 -1,375 +140 171

Impact excess air on boiler efficiency



Flue gas composition versus bagasse moisture



Heating value bagasse versus moisture content



At 30 % moisture 814,4 KW /tph steam

2% difference At 52 % moisture 830 KW /tph steam

Air /flue gas heat input versus moisture content



Fuel savings incase of bagasse drying



O2 and Co2 content and efficiency loss at higher excess air



Dewpoint of flue gasses with biomass firing

Dewpoint of water vapour in flue gasses: Water content in flue gas is based on 52% moisture in bagasse and excess air of 35%: 29 vol% Means partial pressure of H2O is approx. 0,29 bara which result in dewpoint of approx. 66 C Dewpoint of SO2/SO3 vapour in flue gasses: Sulfur content in bagasse is approx. 0,3% on dry weight basis There will be a certain conversion of SO2 into SO3 (approx. 2%) which will condense at certain temperature as H2SO4 on the tubes. The dewpoint as per formula of Ganapathy is as follows: • For 0,14% S in bagasse on wt%: 139 C • For 0,07% S in bagasse on wt%: 133 C • For 0,04% S in bagasse on wt%: 129 C • For 0,01% S in bagasse on wt%: 116 C This means there is a potential of corrosion of tubes at cold end due to condensation of sulfuric gasses. This is also observed in the flue gas air preheaters of the 25 bara boilers. This needs to be considered in the designs



Sulfur dewpoint depending on SO3 and H20 for SO3 content up to 1 Vppm



Sulfur dewpoint depending on SO3 and H20 for SO3 content from 1 up to 1000

Vppm

With S = 0,14 wt% in bagasse . SO2 = 0,14 g/Nm3 Conversion SO2 to SO3 is 2% SO3 = 2,8 Vppm



There have been hardly any studies available on bagasse based biomass decomposition. There is some know how available which makes it possible to make some assumption. Bagasse is one of the easiest decomposable lingocellulose species. Anarobic digestion is the bacterial fermentation of organice material like bagasse in oxygen free condition. It produces a gas composed of methane (CH4) and carbon dioxide (CO2). Called biogas Optimum temperature for this process is 38 C.

Biomass decomposition



Bagasse decomposition

Approx. 4,6 % reduction in LCV value per month



Other Biomass Fuels in Pakistan

1. Bagasse 2. Sugar cane Trash 3. Corncobs 4. Rice husks 5. Cotton Stalks 6. Wheat straw 7. Wheat rice

All those fuels have common: •High Volatile content •Nett Heating value on basis of ash and water free all approx the same (17,8 till 19 MJ/kg)

NOTE: • The composition can vary per season and per area. • It is necessary to send fuel to lab for analysis • The fuels can be fired on different stoker types and in fluidized bed system.

Fuels are different in: • moisture content •Ash content • Alkali content in ash • Sulfur • Chloride • density

16



Calculating heating value of biomass

A practical formula for estimation of heating value is: GCV= k (1 – m – a) KJ/kg m= moisture fraction of the fuel a= ash fraction of the fuel k= constant factor 17500 till 21000 , for bagasse it is 19605



The impact of each property of biomass



The impact of each element (ultimate analysis)



The ash formation during biomass combustion



The ash characteristics of fuels are important. Specially important are: • the alkali metals (Ca, Na, K) are important. • silica Further the sulfur and Chlorine content in the fuel is an important factor Those contents needs to be verified in the lab before deciding the best combustion and boiler system. Later in the session concerning boiler fouling we will discuss this in more detail

Chlorine, sulfur and ash characteristics

21



Characteristics of biomass

22

8.4

30

8 11

52

15 15

5.7 10

15 11

15 13 7

13 12

25 29

4.4

11.7

2

18

2.5 8

18.5 16

7.0

0.0

10.0

20.0

30.0

40.0

50.0

60.0

Moisture Content % LHV(MJ/Kg) Ash



Effect on fuel handling for solid fuels

23

2,309 1,302 2,599 1,526

2,954 1,615 2,098

20,336 23,780

0

5,000

10,000

15,000

20,000

25,000

LHV(MJ/M³)



Effect of fuel on ash handling

24

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

Ash content (Kg/Gj)

Ash content (Kg/Gj)



Elements in biomass & coal potentially

leading to corrosion and deposits.

25

0.60 0.2 0.02 0.1 0.03

0.3 0.2

7.1

0.8 0.50 0.4 0.2 0.1 0.01

0.7 0.5

1.47 1.47

0.73 0.32 0.18

2.44 2.22

0.12 0.09

0.001.002.003.004.005.006.007.008.00

Sulphur (S)%Chlorine (Cl)%K+Na%



Thank You for Your Kind Attention

Documents

FUNDED BY THE Services to Technology Providershpcogenpak.org/wp-content/uploads/2015/04/Boiler... · 2018-12-10 · Bagasse is one of the easiest decomposable lingocellulose species