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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 1: the water and steam system Trainer: Frans Baltussen
Date: first half 2015
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
Sugar processing flow chart
See next sheet
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
Sugar processing flow chart
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
The co-generation plant in sugar mill
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
The co-generation plant in existing Sugar mill configuration with 25 bara system
Boiler
Mill house
shredder
Crushing rolls
Power house Sugar
process
house
De-superheater
2,2 bara 130 C
Drying steam 4 bara,170 C
Steam bypass
PT
TT
25
bar
a,
35
0 C
PT
Bagasse
E
VSD
Boiler
PT
Bagasse
E
VSD
deaerator
E
Condensate vessel
Clean condensate 85% of input steam, 95 C
E
Contaminated condensate and steam
RO and
softening
plant
1,2 bara 105 C
E
Sugar mill own consumption
Surplus power in public grid
PT
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
The boiler is used for generating steam at 25 bara and 350 C. Efficiency of boiler is low with approx. 72% on LHV 2. The steam is used in mill house to drive the rollers and shredder. 3. The rest of the steam is used for generating electric power. A part will be used in sugar mill and surplus will be supplied in public grid. 4. Steam from all back pressure steam turbines is fed to the evaporators in the sugar process house. This steam should be slightly overheated. However not too much. 5. The sugar cane has a certain amount of cellulose. It is called bagasse. Can be used in boilers to generate the steam required.
This part will be changed into a HP cogeneration system
Bagasse in carrier
The co-generation plant in existing Sugar mill configuration with 25 bara system
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EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
1. TCD: This is the installed capacity of the sugar mill for crushing cane specified in Tons Cane per Day ( TCD) 2. Duration season: The total season of crushing is depending on the area. It is 110 till 150 days. 3. Utility factor: How much period of the total season the sugar mill have been in operation. 4. Bagasse amount: the cellulose in the sugar cane which will be used for firing in the boilers. This is mostly approx. 29 till 30,5% of the crushed cane weight. 5. Process steam demand. This is the process steam amount necessary in the process house for making the sugar. This amount depends on area and system used. The process steam amount in Sindh area is in example higher then in other parts of Pakistan. It varies from 40 to 55% of crushed cane. 6. Own electricity demand mill house plus sugar process: The drives of boiler are mostly electric, in mill house it is mostly all with steam turbine. When all are electric drive then the electric consumption is 30 till 35 KW per crushed ton of cane.
Indicators use in sugar industry:
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
Boiler used in existing sugar mills for producing 25 bara steam at 350 C
To ID fan and stack 230 C
Flue gas air preheater
Space in which sometimes a small economizer is placed
Steam drum
water drum
Bi- drum design
furnace
Dumping grate
Air supply
Bagasse spreader
superheater
Steam outlet
Bagasse supply from feeder
Fly ash arrestor
Efficiency approx. 72% on LCV
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High Pressure Cogeneration for Sugar Sector in Pakistan
HP bagasse fired boiler 140 tph 65,7 barg 485 C, single drum and self supporting
Economiser 3
evaporator
HP superheater single-drum
Flue gas Air preheater plus steam air preheater
cyclones
Economiser 1
Economiser 2
In HP cogeneration system are nowadays 2 systems used in sugar mills: • Bi-drum suspended design • Single drum self supporting design
To ID fan and stack 150 till 160 C
Desuperheating station
furnace
Dumping grate
Bagasse spreader
Efficiency approx. 87% on LCV
Over firing air
22
50
0
Boiler types – self supporting
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EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
HP bagasse fired boiler 140 tph 65,7 barg 485 C, bi-drum drum and suspended
Boiler types - suspended
Bi-drum HP superheaters
Economiser
Flue gas Air preheater
cyclones
furnace
Dumping grate
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
Steam is favored for: • Power production • Heat transfer It is a unique combination of: • High thermal capacity • High critical temperature • Wide availability • Non toxic nature It has a high thermal capacity and high expansion capabilities which makes equipment small and is a clean product. The properties of water and steam. 1. Enthalpy in KJ/kg: the internally stored energy as per unit mass of flowing stream 2. Specific entropy in KJ/kgK: is a measure of thermodynamic potential of a system in the units of energy
per unit mass and absolute pressure 3. Specific volume in m3/kg: is the volume per unit of mass
Water and steam as medium in co-generation plants
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High Pressure Cogeneration for Sugar Sector in Pakistan
The properties of water and steam are tabulated in steam tables by International Formulation Committee (IFC) which has representative of following countries: • Czech • France • Japan • Russia • UK • USA
Pressure In bara
temperature In C
Specific volume saturated water in m3/kg
Specific volume saturated steam in m3/kg
Density of saturated steam kg/m3
Enthalpy saturated water in KJ/kg
Enthalpy saturated steam in KJ/kg
Evaporation heat of water into steam in KJ/kg
Entropy of saturated water in KJ/kgK
Entropy of saturated steam in KJ/kgK
The properties of water and steam
FUNDED BY THE
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High Pressure Cogeneration for Sugar Sector in Pakistan
Steam tables with indication for particulate pressure for each temperature level the: • Specific volume • Enthalpy • entropy
Saturation line
The properties of water and steam
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
At what temperature water boils?
How steam volume decreases with increased pressure? Note: Steam is not an ideal gas so the formula P*V/T = C does not fully apply. There will be deviation of 20% higher then the actual value. i.e.: at 1 bar v” is 1,694 m3/kg and Tsat is 100 C. At 40 bara Tsat is 250,3 C and with PV/T the v” is 0,059 m3/kg. The real figure is 0,050. means approx 18% too high.
What is impact of pressure on steam condition?
Means at higher pressure the steam volume flow is much less and pipe sizes can be less.
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
E Temperature versus Enthalpy ( T – H diagram)
Enthalpy is the total energy in each kg of water and/or steam
The Enthalpy:
economizer
evaporator superheater
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High Pressure Cogeneration for Sugar Sector in Pakistan
More details given in T-H diagram
80 bar
374 C
318 C
282 C
221,2 bara
110 bara
66 bara
225 C 25 bara
1 bara
At 110 bara r=1258,7 KJ/kg
Comparison of evaporation heat
At 25 bara r=1839 KJ/kg
46% more then at 110 bara
Dryness of steam
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High Pressure Cogeneration for Sugar Sector in Pakistan
Heat load heating surfaces at different
pressures
962 1247 1345 1451
1838 1531 1406 1255
328 613 690 759
25 BARA, 350 C 66 BARA, 490 C 86 BARA, 520 C 110 BARA, 540 C
HEAT LOAD HEATING SURFACES
eco evap sup
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High Pressure Cogeneration for Sugar Sector in Pakistan
To review the heat absorbed by the heating surfaces we show the total heat versus the temperature in water/steam side and also flue gas side
Evaporator 47 ,2 MW
Evaporator 14,7 MW
Heat absorbed by heating surface Flue gas air-preheater:
13,8 MW
Flue gas air-preheater: 6 MW
25 bara, 350 C 66 bara, 485 C
The QT diagram
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High Pressure Cogeneration for Sugar Sector in Pakistan
318 C 110 bara
225 C 25 bara
1 bara
h’= 417,51 KJ/kg h’= 2675,4 KJ/kg
x dryness fraction
h= 800 KJ/kg
Dryness fraction steam: =weight of steam/total weight Or =heat supplied from boiler heating surface into water/total required evaporation heat (all per kg of water) X = (800-417,51)/2675,4 – 417,51) = 0,1694 Means 16,9 wt% is saturated steam and 83,1 wt% is water In case the dryness is 10% the specific volumes of the steam water mixture are: v = 0,9 * v’ + 0,1 * v”
Dryness of steam
Boiler pressure bara 10 25 110
Specific volume saturated water : v’
M3/kg 0,00011 0,00120 0,00149
Specific volume saturated steam: v”
M3/kg 0,1943 0,07991 0,01601
Specific volume water steam mixture with 10% dryness fraction: v
M3/kg 0,0195 0,0097 0,0029
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High Pressure Cogeneration for Sugar Sector in Pakistan
Dryness fraction steam: void fraction correlation
With low pressure large volume of steam at already low dryness fraction steam
How higher the pressure how lower the volume
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EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
Entropy is a measure of the degree of disorder within a system. The greater the disorder the higher the temperature. You cannot measure it. It is difficult to imagine this figure. It can be only calculated out of measured data. The heat input per kg and then divided by the average temperature change. In small temperature change steps In steam turbines it is used to indicate the efficiency. A perfect expansion process as in a steam turbine is with a constant entropy. See line A – B in This is a isentropic process (ideal) However this is not possible as all kind of losses will occur like leakages between wheels and friction losses. The isotropic efficiency is the hT = 100 * (hA – hF) / (hA – hB) % The power supplied to the shaft is m * (hA – hF) KW m= mass of steam per kg The power at generator terminal is minus the losses in gearbox and generator
h1
h2 h3 h4
A
B
h1= friction losses in diffusor, heat into steam h2= friction losses in wheels, heat into steam h3= friction losses at outlet, heat into steam H4= losses through seals of wheels
C D
E F
H in KJ /kg
S in KJ /kgK
The Entropy:
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High Pressure Cogeneration for Sugar Sector in Pakistan
The enthalpy versus the entropy (H- S diagram)
Also called Mollier diagram
Extraction point in sugar mill at 2,5 bara Steam temperature should be slightly superheated 5 C. Other wise the heating surface in evaporators are not working properly.
110 bara 540 C 64 bara ,
480 C
25 bara , 350 C
Isotropic efficiencies different pressure levels: At 110 bara: Isotropic eff= (3464 – 2350)/(3464 – 2090) * 100%= 80,2% Power per kg/s of steam: 1114 KW At 62 bara: Isotropic eff= (3370 – 2360)/(3370 – 2150) * 100%= 82,7% Power per kg/s of steam: 1020 KW
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High Pressure Cogeneration for Sugar Sector in Pakistan
110 bara 540 C 64 bara ,
480 C
25 bara , 350 C
Isotropic Efficiency existing steam turbine with 66% is lower then the 80 to 83% for the HP steam turbine. Means high losses
Why the existing steam turbine in sugar mill for driving the shredder and crushing rollers are
replaced by electric drives??
The flows of 15 to 30% are too high for extracting from High pressure steam turbine. Will reduce the isotropic efficiency. The steam temperature is too high at extraction point which requires de-superheating. This results in less steam over HP steam turbine.
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EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
There are 2 types of turbines: The impulse type (curtis wheel) is used in the higher pressure zones in order to minimize the leakage around the wheels The reaction turbine (parson wheel) is used in the lower pressure zones as in condensors.
Steam turbine types in co-generation plants
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High Pressure Cogeneration for Sugar Sector in Pakistan
Why the process steam should be only slightly superheated in ?
2. To minimize the condensate in steam lines which causes high energy and water losses
1. Poor heat transfer when it is superheated
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
What happen in case of throttling the steam ?
In case we extract steam from steam drum for burner or sootblowers or deaerator. The enthalpy will remain at inlet and outlet approx. the same. The valve needs to have special internals to avoid corrosion due to wet steam at smallest opening in valve
With 40 bar to 15 bar dry steam
With 110 bar to 15 bar wet steam
With 64 bar to 15 bar wet steam
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High Pressure Cogeneration for Sugar Sector in Pakistan
The Rankine cycle is used to predict the efficiency of steam turbine systems. We take the T-S diagram for reviewing the complete cycle in steam and water system of power plant
Limit the wet steam amount in wheel
Efficiency rankine cycle is: (Pturbine – Ppump)/ Qin * 100%
Ppump
P turbi
ne
Rankine Cycle
Rejected heat
TS diagram of a rankine cycle operating between pressure of 0,06 bar and 50 bar
Entropy in KJ/kgK
Heat input
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High Pressure Cogeneration for Sugar Sector in Pakistan
System with one boiler and one
condensing /extraction steam turbine
Process steam 2,2 bara, 135 C
E
Condensate return 85% at 98 C Demi water
E
Advantage Disadvantage
It is a simple Condensing wheel has low efficiency during season
Having low investment The steam turbine will have low efficiency as it will run
at 60 to70% of the steam load during off season.
When one main equipment trip then sugar mill will
shut down
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
Process steam 2,2 bara, 135 C
E
Condensate return 85% at 98 C
Demi water
E
E
System with two parallel systems each 50%
capacity and consisting each of one boiler and
one condensing/extraction steam turbine
Advantage Disadvantage
High redundancy in case same quality will be taken
for equipment as of ‘option. a’ Condensing wheel has low efficiency during season
When one unit trips then other unit can run at 50%
load
High investment costs of approx. 24% of total
investment cost because of additional boiler and
steam turbine.
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
Process steam 2,2 bara, 135 C
E
Condensate return 85% at 98 C Demi water
E
E
Advantage Disadvantage
In case back pressure trips then
condensing/extraction steam turbine can run and
plant has an output of 70% load
2nd steam turbine which result in higher investment
cost
High efficiency during season and off season High storage of bagasse
The size of boiler and steam turbine can be 12 to
14% smaller
System with one boiler and one back pressure
steam turbine for season operation and one
condensing steam turbine for off season
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
Process steam 2,2 bara, 135 C
E
Condensate return 85% at 98 C Demi water
E
E E
System with two parallel systems each 50% capacity and
consisting each of one boiler and one back pressure
steam turbine for operation during season, and one
condensing/extraction steam turbine for off season
Advantage Disadvantage
In case back pressure steam turbine trips the plant
can run still at 100% capacity.
3rd steam turbine and 2nd boiler which result in
higher investment cost.
High efficiency during season and off season High storage of bagasse
In case one boiler trips the plant can run still at 50%
capacity
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
More process steam required in relation to electric power result in higher plant efficiency
season Off-season
Minimum steam flow over condensing wheel into condensor
High losses in condensor
What is efficiency during season and off season
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
What is effect of higher pressure system
for sugar mill with its specific demands
Description Unit 66 bar (a), 485oC 110 bar (a), 540oC
Season/Off season - Season Off season Season Off season
Steam production boiler tph 149.7 103 154 108.5
Bagasse consumption tph 63.4 43.4 65.5 46.1
Bagasse consumption ton 205,416 40,387 212,220 36,167
Total hours power generation hours 3,240 982 3,240 785
Power output generator kW 26,139 24,569 30,021 28,325
Power consumption of the sugar mill,
shredder with electric drive kW 7,574 - 7,574 -
Power plant own consumption kW 2,091 2,580 2,425 2,718
Power supply to the grid kW 16,474 21,989 20,022 25,607
Total power generation MWh 53,376 21,593 64,871 20,101
Total power supply to the grid annually MWh 74,969 84,972
Annual Revenues (Based on 10,500 PKR
per MWh)
PKR
million 787.2 892.2
Power plant size MW 26.1 30
13,3 % more
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
Boiler
Process steam 2,2 bara, 135 C
E
Condensate return 85% at 98 C
Demi water
E
FG
eco stack
Steam air preheater
air
To water storage
For additional steam air pre heaters
System with one boiler and one condensing
/extraction steam turbine and air steam
preheater
Prevents corrosion in flue gas air preheater and generate more power over full season for fixed bagasse amount Approx. 5,2% in 66 and 110 bara system
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
The HP co-generation plant with steam air preheaters 66 bara
More steam over steam turbine and extracted to heat up the air. No increased losses in condenser while more energy generated
2,5 barg
9 barg
Extraction pressure control
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EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
What is effect on output of additional air
preheating with 1 additional steam air
preheater. For 66 bara
Description Unit 66 bar (a), 485oC at 45% steam demand
Steam Air Preheater
With steam preheaters
from 2.2 and 9.0 bar (a)
extraction
With steam preheaters
from 2.2 bar (a) extraction
only
Season/Off season - Season Off Season Season Off Season
Steam production boiler tph 149.7 103 147 101.5
Bagasse consumption tph 63.4 43.4 63.2 43.6
Bagasse consumption ton 205,416 42,630 204,768 43,246
Total hours power generation hours 3,240 982 3,240 992
Power output generator kW 26,139 24,569 25,855 24,458
Power consumption mill with electric drive
shredder kW 7,574 - 7,574 -
Power plant own consumption kW 2,091 2,580 2,080 2,542
Power supply to the grid kW 16,474 21,989 16,201 21,916
Total power generation MWh 53,376 21,593 52,491 21,741
Total power supply to the grid annually MWh 74,969 74,232
Annual revenue (Based on 105,00 PKR per
MWh)
PKR
million 787.2 779.4
1% more
7,8 million PKR more
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
The HP co-generation plant with steam air preheaters 110 bara
Flue gas air preheater eliminated
FUNDED BY THE
EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
Description Unit 110 bar (a), 540oC at 45% steam demand
Steam air preheaters
With steam preheaters from 2.2
and 9 bar (a) and 21 bar (a)
extractions
With steam preheaters from 2.2
bar (a) extraction only
Season/off season - Season Off Season Season Off Season
Steam production boiler tph 154 108.5 146 102
Bagasse consumption tph 65.5 46.1 64.8 44.7
Bagasse consumption ton 212,220 36,167 209,952 38,321
Total hours power
generation hours 3,240 785 3,240 857
Power output generator kW 30,021 28,325 29,032 27,206
Power consumption mill
with electric drive shredder kW 7,574 - 7,574 -
Power plant own
consumption kW 2,425 2,718 2,310 2,555
Power supply into grid kW 20,022 25,603 19,148 24,651
Total power generation MWh 64,871 20,101 62,040 21,126
Total power supply into
grid annually MWh 84,972 83,166
Annual revenue (Based on
10,500 PKR per MWh) PKR million 892.2 873.2
What is effect on output of additional air
preheating with 2 additional steam air
preheater. Total 3. For 110 bara
2,2% more
19 million PKR more
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EUROPEAN UNION
High Pressure Cogeneration for Sugar Sector in Pakistan
Extraction pressure control
The HP co-generation plant with BFW preheaters for 66 and 110 bara
More steam over steam turbine and extracted to heat up the air. No increased losses in condenser while more energy generated
Boiler
Process steam 2,2 bara, 135 C
E
Condensate return 85% at 98 C
Demi water
E
FG
eco stack
air
BFW preheaters
Take care for corrosion at cold end
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High Pressure Cogeneration for Sugar Sector in Pakistan
Thank You for Your Kind Attention