Efficient steam systems - Generation to WHR
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Transcript of Efficient steam systems - Generation to WHR
Efficient Steam Systems – Generation to Waste Heat
Recovery
Vizag – 8th December, 15
2
Fuel Prices and Calorific Value
Fuel Price (Rs./Kg) Calorific Value (Kcal/Kg)
Furnace Oil 30 10200
HSD 52 10800
Natural Gas 40 8500
Coal 7 5500
Petcoke 9 8000
Rice Husk 3.5 3200
Briquette 5.5 4000
Boiler Efficiency & Cost of Steam
Fuel Avg S:F Avg Cost of Steam (Rs./Kg)
Furnace Oil 12 2.25
HSD 13 4
Natural Gas 12 3.5
Coal 4.5 1.5
Petcoke 7 1.2
Rice Husk 3.2 1.2
Briquette 3 1.8
Optimal Steam Generation System
Meeting the process demands in a manner which is:
Copyright Forbes Marshall, 2009-
10
Steam & Condensate Loop
100% fuel
energy
80%
ste
am
3% distribution losses
77%
Process
consumption 57%
20%
Unburnt
Stack
Blowdown
Steam Generation-Boiler
House
• Criteria for Selection of Boiler
- Steam Demand : Peak /Average
load
- Steam Consumption pattern
- Fuel selection w. r. t. availability,
cost
- Feasibility of COGEN
Copyright Forbes Marshall, 2009-
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Copyright Forbes Marshall, 2009-
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Cost of operation-Solid fuel
Copyright Forbes Marshall, 2009-
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Cost of operation–Oil\Gas
fuels
Copyright Forbes Marshall, 2009-
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Measured Losses
Boiler Efficiency – Perception & Reality
86%
78%
74%
78%
70%
65%
60%
65%
70%
75%
80%
85%
90%
Oil Solid
Ideal
Indirect
Direct
8%
4% 8%
5%
Copyright Forbes Marshall, 2009-
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An increase of 2% efficiency in a 5 TPH boiler results in a saving of 53,200 liters of
oil per year !
Factors affecting boiler
efficiency
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Comparison of Efficiency Methods
• Direct Efficiency
• Useful Heat output / total heat input
• Covers all losses
• Simple to implement
• Instrument accuracy has a significant affect on final efficiency
• In Direct Efficiency
• Efficiency = 100 – Losses
• Considers Stack, Enthalpy, Radiation, Blowdown and unburnt losses
• Gives detailed break up of losses
• Not affected too much by instrument accuracy
Copyright Forbes Marshall, 2009-10
Real life scenario
• The measured efficiency of Process boilers varies a lot
Min. Avg. Max.
Direct Efficiency 61 % 72 % 82 %
Indirect Efficiency 63 % 78 % 84 %
• Efficiency is dynamic – It WILL keep on changing.
Copyright Forbes Marshall, 2009-
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What leads to variations
• Air temperature
• Fuel temperature
• Fuel pressure
• Moisture in fuel
• Loading pattern
• Changing calorific value of fuel
• Use of multiple fuels
Innovative Oil / Gas fired Boilers
Site Installations…
Site Installations…
Site Installations…
Site Installations…
Manual Fired Boilers – Limitations !!
• Indirect Efficiency Guaranteed 73 – 77%
• Typical Direct Efficiency obtained 50-55%
– More heat loss by radiation and convection during fuel feeding cycle resulting in lesser actual efficiency
– Distribution of fuel on furnace grate is uneven leading to Empty pockets and fuel overloaded pockets possible
– Operators tend to overfeed resulting in incomplete combustion
• Manual fuel feeding is laborious and time consuming
• The operator gets exposed to hot flames
• These boilers can not be designed for higher pressure beyond 28 kg/cm2.
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Observations in Manual Fired Boilers
• High stack temp of up to 249 Deg c @ 6 bar (g) causing heat carry over loss.
• High O2 percentage - ~ up 10 (charged) -19 (discharged)%
• Indirect efficiency – 65.3 % (@ 50% fix damper)
Direct efficiency–50 %
• Optimum Air : Fuel ratio is not maintained
25
26
Date Operating
hrs
Day wise Readings
Steam generation
(kg)
Avg steam load
(kg/h)
Wood consumptio
n (kg)
S:F
13/10/10 12 4355 363 1607.4 2.70
15/10/10 10 4503 450.3 1441.8 3.12
16/10/10 4 2333 584 834 2.79
26/10/10 10 4906 490.6 1790 2.74
28/10/10 10 4414 441.4 1840 2.39
30/10/10 11 6561 597 1785 3.67
*
31/10/10 12 7883 657 2050 3.84
*
1/11/10 – IInd shift
5 1892 378.4 920 2.05
AVERAGE Steam : Fuel Ratio 2.85
S:F Ratio with Manual Fired boiler
Gap Between Minimum and maximum S:F is 100% Gap between average and mimimum is 40%
Stack , 26%
Unburnt , 9.80%
Enthalpy, 11%
Radiation, 1.50% Ash, 1.75% Unaccounted,
0.25%
Losses in Percentage
Typical Break-up of Losses
• Stack Loss – Frequent Opening & closing of door ID Fan damper position same for all stages of operation of
boiler. • Unburnt Loss – Overfeeding of fuel resulting in low air for Burning which also leads to high amount of Unburnt generation. • Enthalpy Loss – Moisture in fuel & Air results in this loss. • Radiation Loss – Through Boiler Heating Surface areas – no Major control possible
Deep Dive into the Losses…..
Current Scenario
• Variety of Boiler designs like Wet Back/Semi Wet Back & Dry Back
• Converted external furnace boilers with deaerated capacity & with Big gap in efficiency
• Quality of Accessories used on Solid fired boilers ????
• No Automation provided, hence total reliance on operator skills
O2 Levels – 9 – 11% Excess Air - @70%
Furnace pressure – Between -5 to - 8 mmWC
What should we AIM for ?
Fuel Feeding practices
•The boiler operator looks at steam pressure and does the fuel feeding accordingly.
•Stoker mostly overfeeds fuel as per his convenience & Grate space. Irrespective of plant load, the grate is usually filled fully. This results in high un-burnts and stack loss
Current Operating Practices in Manual Fired boilers
Fuel Feeding practices
• After feeding, the window is closed & fuel burns incompletely for some time leading to high unburnts as can be seen from the black chimney smoke colour during feeding
• Thereafter, the fuel burns and is fed at a later stage by that time stack losses start to happen.
Current Operating Practices in Manual Fired boilers
Need Of The Hour based on Today’s Limitations in the Industry
• To provide information & Alerts – to assist the boiler operator for efficient boiler operation.
• To provide information to utility manager on – How the boiler was operated on Daily, weekly & monthly basis.
• To generate MIS so as to follow better operating practices in boiler house for reduced fuel bills
• To provide periodic maintenance alerts to enhance life of boiler & reduce on forced break downs.
With Intell
General operating practice
PHASE I: IMMEDIATELY AFTER FEEDING
• Fuel is overfed
• Bed not evenly spread
• Black/dark grey smoke
observed
• High unburnt loss (High CO
levels)
• Stack O2 levels: 0-5%
• Fuel feed optimised
• Bed is evenly spread
• Light grey/light Brown observed
• Low CO levels
• Stack O2 levels: 5-7%
4-
5
mi
nu
te
s
2-
3
mi
nu
te
s 6% Stack
O2
6% Stack
O2
With Intell
General operating practice
PHASE II: AFTER FEEDING (contd.)
• Large interval between fuel
feeds
• Uneven bed
• Greyish-white smoke observed
• Stack O2 levels: 5-10%
• High feeding frequency
• Light grey/light Brown smoke
observed
• Stack O2 levels: 6-10%
10-
14
mi
nut
es
8-
10
mi
nu
te
s 6% Stack
O2
6% Stack
O2
General operating practice
With Intell
PHASE III: AFTER FEEDING (contd.)
• High feeding frequency
• Light grey/light Brown smoke
observed
• Stack O2 levels: 8-12%
4-
5
mi
nu
te
s
2-
3
mi
nu
te
s 6% Stack
O2
6% Stack
O2
• Large interval between fuel
feeds
• Uneven bed
• White smoke observed
• High stack loss (High O2%
levels)
• Stack O2 levels: 8-18%
Furnace Draft pressure
• Boiler Furnace draft is maintained by guess-work and there is no measurement of it. Improper Boiler draft results in improper combustion and risk of back firing and increased unburnt loss.
• Manual damper adjustments are based on expertise and vigilance
Current Operating Practices in Manual Fired boilers
So what can be done go close to level of comitted Indirect Efficiency levels??
• Continuous Monitoring of Boiler parameters
• Generating Pop ups for corrective actions to be taken by boiler operator
• Provide History & trends to utility manager for the boiler operations, which can suggest a necessary change in operations of boiler
38
Intelligent Boiler
39
PLC Based HMI Display with POP UPS
Facts & Figures!! • 2% decrease in O2 leads to 4% increase in Boiler Efficiency.
• Every 6 deg C increase in Feed water temperature means 1% less fuel bill.
• 20 Deg C variation in stack temperature from optimum value means 1% increased fuel consumption
• Presence of 1% unburnt represents 2.5% excess fuel consumption.
• 3mm soot deposition on tubes increases fuel consumption by 2%
• Maintaining optimum water TDS avoids scaling, moisture carryover in steam & increase operating Efficiency.
Pop ups
1. Feed fuel
2. Close the door
3. Open damper
4. Close damper
5. Clean the tubes
6. Reduce feed
7. Stir/poke the fuel bed
8. Check condensate recovery
9. Avoid sudden loading
10. Excess steam demand
11. Possible back fire
12. Improve water quality
13. Drain mobrey
14. Mobrey not drained
15. Clean the TDS sensor
Safety
Boiler Efficiency
Good operating practices
Feed fuel
Condition:
1. Steam pressure is lesser than the set lower limit.
2. Gap between stack temperature & steam temperature is less than 50 C
3. Boiler door is closed
Condition:
Door open for more than 5 minutes.
Close the door
Possible Back-fire
Condition:
Furnace pressure goes positive
Intell – Management Tool!! • Min – Max values of
important parameters can be seen on Daily/weekly/Monthly basis
• History & Trends of two years of operation of boiler can be seen
• Data on Number of alarms generated, addressed can be seen.
Summary Screen
• Gives a summary for current day and last day of the number of alarms
occurred and how was the health associated to a particular parameter. • The heath number is an indication of the response time of the operator
Incorporate automated feeding for feeding fuel in Furnace
Feed only the required quantity of fuel
Ensure even spread of fuel over the bed
Modulation of air to fuel ratio
Control the air flow during operation cycle
47
How do we ACHIEVE this?
Automation –Need of Hour!!
Automation of –
• Fuel feeding mechanism
• Damper movement
Objective..
49
Capacity – 1/2/3/4/4.5TPH Pressures – 10.54 / 14.5 / 17.5 kg/cm2(g) Fuel – Briquette/Coal/Wood Chips
MS-HD DTB
Copyright Forbes Marshall, 2009-
10
Online Efficiency Monitoring
Copyright Forbes Marshall, 2009-
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Online Efficiency Monitoring
Copyright Forbes Marshall, 2009-
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Generation Opportunity Description
Generate steam at rated pressure Operating at lower pressure results in reduced output and carryover.
Minimize excess air Reduces the amount of heat lost up the stack, allowing more of the fuel
energy to be transferred to the steam
Clean boiler heat transfer surface Promotes effective heat transfer from the combustion gases to the
steam
Maintain high feedwater temperature High Feedwater temperature drives out dissolved oxygen
Size feedwater tank correctly As thumb rule, feedwater tank should be sized to be 1.5 times the peak
steam demand
Avoid oversizing the boiler Oversizing leads to frequent On-Off cycles in a boiler which lowers
boiler efficiency
Monitor Boiler Parameters Continuous monitoring of boiler parameters for optimized boiler
efficiency
Install heat recovery equipments (feedwater
economizers/combustion air preheaters,
blowdown heat recovery)
Recovers available heat and transfers it back to the system by
preheating feedwater or combustion air.
Similarly apart from controlling blowdown, heat can be recovered from
blowdown that is done.
FM Solid Fuel Fired Boilers
Hinged
Doors for
ease of
maintenance
FM Solid Fuel Fired Boilers
Factory
Insulation &
Cladding
FM Solid Fuel Fired Boilers
Structurals &
Platforms –
Packaged
Boiler
Feed Water
Pumps on Skid
FM Solid Fuel Fired Boilers
600 kg/ hr
Boiler
(Dryback)
FM Solid Fuel Fired Boilers
Packaged
Boiler)
FM Solid Fuel Fired Boilers
Twin Flue
Boiler
Ash Doors
FM Solid Fuel Fired Boilers
FM Solid Fuel Fired Boilers
FM Solid Fuel Fired Boilers
Individual Lines
for Feed Water
FM Solid Fuel Fired Boilers
FM Solid Fuel Fired Boilers
FM Solid Fuel Fired Boilers
Site Installations
Schreiber Dynamix Dairy Baramati
PO Date – 8th April 2013
Commissioning Date – 4th Dec 2013
Copyright Forbes Marshall, 2009-
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Steam Distribution • Pipe Sizing & Layout
- Check adequacy & recommend improvement
- Identify redundant piping & optimise layout for reduced losses.
• Insulation
- Check adequacy & estimate losses
- Recommend improvements
• Air Venting
- Identify locations
- Recommend right type, size & quantity
• Metering
- Identify locations
- Recommend right type & size.
• Trapping
- Trap survey & recommendations
- Estimation of loss through leaks
- Recommendations of trap monitoring
Steam pipe layout
Copyright Forbes Marshall, 2009-
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Steam
CORRECT
INCORRECT
Steam
Steam Mains –Condensate
drain
Copyright Forbes Marshall, 2009-
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Condensate to Steam trap
INCORRECT
Flow
Flow
CORRECT
Condensate to Steam trap
Steam
Importance of Correct Pipe
Sizing
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Insulation
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Need for Air Venting
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Air Venting….
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Copyright Forbes Marshall, 2009-
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Distribute at High Pressure This will have the following advantages:
– Smaller bore steam mains needed so less heat (energy) loss due to
smaller surface area.
– Lower capital cost of steam mains, both materials such as pipes, flanges
and support work and labour.
– Lower capital cost of insulation (lagging).
– Dryer steam at point of usage due to drying effect of pressure reduction
taking place.
– Boiler can be operated at higher pressure corresponding to its optimum
operating condition, thereby operating more efficiently.
– Thermal storage capacity of boiler increases, helping to cope more
efficiently with fluctuating loads, & a reduced risk of priming & carryover
Copyright Forbes Marshall, 2009-
10
Pressure Reducing Station
Copyright Forbes Marshall, 2009-
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Electro-pneumatic Temp
control
KE valve with PN actuator and EP5 Positioner
SX65 Controller
EL2270 Sensor
Pneumatic power and electronic intelligence
on a steam to liquid heat exchanger
Copyright Forbes Marshall, 2009-
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Trapping Issues
Not Fit For Purpose
Plant Start Up
Not in service
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Commonly Prevailing • Failed Closed
• Failed open
• Not in service
• Not fit for purpose
• Installation
Copyright Forbes Marshall, 2009-
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The cost of Leaks??
Cost of Steam Leaks….
Copyright Forbes Marshall, 2009-
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Copyright Forbes Marshall, 2009-10
Maintenance addresses only 20%!
20%
Maintenance
Procedures
40%
Improper
Selection/
Installation
20%
Site Conditions
20%
Manufacturing
Defects
Copyright Forbes Marshall, 2009-
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Steam Trap Selection Criteria
Steam Application Present type of Trap Benchmark Key Selection Factor
Steam Main Line Drain Thermodynamic (TD) Thermodynamic (TD) Quick condensate
removal
Steam Tracing for product line
Thermodynamic (TD) Balance Pressure
Thermostatic (BPT) Energy
Conservation
Copper Tracing for instrument tracing
No Traps Thermostatic (MST) Energy
Conservation
Process Heating Equipments
TD / IB / FT Mechanical (Float
Trap - FT) Process Efficiency
and time
Pump Casing Thermodynamic (TD) Thermodynamic (TD) Quick condensate
removal
Steam trap selection….
Copyright Forbes Marshall, 2009-
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Copyright Forbes Marshall, 2009-
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Compact Steam Trapping Station
Estimated weight : 13 kg 4.0 kg
Assembly Parts & Labor
5 ea. 600# rated globe or gate valves 1 ea. Line strainer
8 ea. Sch 80 nipples 16 ea 1/2’’ welds
2 ealine “tee” 1 ea. Steam trap
1 ea. elbow
CONVENTIONAL
720mm 160 mm
245mm
Modern Process Trap Assembly
TOFT Integrated design for base
and Cover PRODUCT MARKING
Aesthetic Features
Modern Float Trap Assembly
TOFT
TOFT VIEWS
Copyright Forbes Marshall, 2009-
10
Glandless Piston Valves
FEATURES
– CLASS VI, BUBBLE TIGHT SHUT-OFF
Ensures Positive Isolation
– SS REINFORCED GRAPHITE SEALING RINGS
Asbestos free Sealing rings,
– FORGED CS BODY FOR SIZES UPTO 1 ½”
Max. Pressure : 78 Kg/cm2
Max. Temperature : 427 °C
OPTIMIZING HEAT RECOVERIES
Waste Heat Recovery
• Important & unexplored area for reducing energy
• Around 20 to 50% industrial energy input is lost as
– Waste heat from hot exhaust gases
– Cooling water
– Hot liquor from equipments
Recovering waste heat provides attractive opportunity for emission free and less costly energy resource!
Copyright Forbes Marshall, 2009-
10
Condensate Recovery
To Drain!
Condensate contains 25% of
Total Energy Supplied – Using
this can make a difference
Copyright Forbes Marshall, 2009-
10
• Monetary Value
• Water Charges
• Effluent Restrictions
• No Boiler Derating
•Reduced water treatment costs
Every 6 deg increase in feed water temp from return of hot condensate & recovery of flash steam cuts your fuel bill by 1 %
As per our audit findings Average CR factor in industry is 50-60%(energy recovered still less) & very few recover Flash steam
Why Return Condensate?
Monetary values for
Condensate
Copyright Forbes Marshall, 2009-
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Higher FW Temp. leads to fuel
savings
Copyright Forbes Marshall, 2009-
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Copyright Forbes Marshall, 2009-
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• Back Pressure on Steam Traps
•Flash Steam vented
•Drop in Condensate Temp
•Electrical cost of pumping – besides pump problems
•Too many components to maintain
Conventional Method - CR
Copyright Forbes Marshall, 2009-
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Effective CR
FW Tank size matters….
Copyright Forbes Marshall, 2009-
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Illustration:
Consider 4KL of condensate at 90 deg C held up in a tank. Now even a 10 deg. C drop here means a loss of 32KL of
FO or 91tons of coal annually!
Copyright Forbes Marshall, 2009-
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Heat Content-Steam &
Condensate
Copyright Forbes Marshall, 2009-
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Thermocompressor
Copyright Forbes Marshall, 2009-
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Thermocompressor
Heat Recovery Potential
100 %
Energy
37%
utilize
d
63%
Waste
54.22%
Energy
Dye bath
Liquor
Condensate
Flash
Cooling Water
12.84% 14.85%
17.78%
Not considering losses the Process Heat Recovery in Dyeing m/c
Heat Recoveries - At a glance
Textile
Dye Liquor Heat Recovery
Cooling Water Recovery
CRP condensate Recovery
Stenter Exhaust Recovery
Vent Heat from Drum Washer
Brewery Wort vapor Heat Recovery
Wort Cooling Water Recovery
Recovering heat from Bottle Washer drain
SEP & Oil Refi
Heat from waste water boiler
Recovering heat from Bleached Oil, Neutral Oil, Crude Oil
Soap water to preheat hot water
Recovering heat from oil to generate hot water and preheat miscella
Textiles
Brewery
SEP & Oil Refinery
Dome Drain Heat Recovery
Hot water Heat Recovery
Blow through Steam Recovery
Tyre
Heat recovery from Dye liquor of Yarn Dyeing machine
At a large integrated textile mill From drain to savings
Dye liquor at 90 oC when used for heating soft water for process lead to annual savings of 21 lakhs with payback of just 2 months!!
CRP Hot Water Recovery
At a large integrated textile mill From drain to savings
Recovering the CRP hot water to heat DM water lead to savings of 1.5 Crores with payback period of 1 month!
Copyright Forbes Marshall, 2009-
10
Act fast and grow your Profits!!!
Fuel prices would continue to spiral
upwards……. & so would your losses!
Find out where you stand.
Copyright Forbes Marshall, 2009-
10
Thank you