ROADMAP FOR IMPROVING

ENERGY EFFICIENCY IN EXISTING

BOILERS
 Presented by
Muhammad Ammar Ghazanfar
Shift Engineer
Layyah Sugar Mills, Limited
Pakistan Sugar Industry
• Sugar Industry is supporting national
economy
• Playing key role in socioeconomic
development of society & country
• Sugar Industry is facing serious issues of
sustainability & opportunities
• Low & fluctuation profits have created
barrier on growth & investment
 Outlines
• Introduction
• Why Optimization is important?
• Advantages of optimization
• Increase in bagasse saving/
Power Export
• Case Study:

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 Introduction:
• Increasing cost of production
• Increase in price of bagasse
• Need to be efficient instead of new
investment
• Environmental threat
• Source of additional revenue
• Potential source of diversification

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INTRODUCTION:
• Most industries have considered doing something about
moderating their energy consumption.
• An industry with large high temperature waste heat outflows
also has a high energy saving potential, since very often the
waste heat can be utilized instead of primary energy.
• Any attempt at improving the energy efficiency of a plant
requires that,
 Energy efficiency of the individual components of
equipment must be refined.
 Manner in which the equipment is operated.
FLUE GAS TEMPERATURE.

• Flue gas temperature is a key indicator of boiler efficiency.

• It is second only to adequate air level in importance as a
parameter controlling boiler efficiency.
• Higher the flue gas temperature lowers efficiency because
more heat is lost to the stack.
FLUE GAS HEAT RECOVERY

At present 30-40% of the total heat is wasted in the

flue gases, except the boilers equipped with water
economizers and air heater, where this waste heat is
reduced to 15-20%. Following are the ways to
recover this waste heat.
• By installation of economizer.
• Increase in area of air heater.
• Installation of bagasse dryer.
Flue Gas Temperature VS Boiler Efficiency.

84.00%

82.00%
Percent Efficiency

80.00%

78.00%

76.00%

74.00%

72.00%

70.00%

68.00%
300F 350F 400F 500F 550F 600F 650F 700F

Flue Gas Temperature (F)

CASE STUDY OF ECONOMIZER PERFORMANCE FINANCIAL SAVING OF ENERGY SAVED

Capacity of Boiler TPH 80

Bagasse Consumption TPH 33.88
Steam Pressure Kg/Cm 25
Steam Temprature C 350 Fuel saving % 3.5
H.S of Economiser Sq.M 207
Flue Gas Temperature at Furnace Bagasse saving Per Hour Tons 1.186
Outlet C 270
Flue Gas Temp. at economiser Bagasse Saving Per Day Tons 28.46
Outlet C 260
Temp at A/H Outlet C 190 Fuel Saved in 120 Days Tons 3415
Feed Water Inlet Temprature C 110
Feed Water Outlet Temprature C 142
Increase in Feed Water
Temprature C 32
Fuel saving % 3.5
ECONOMIZERS

• Economizer is the waste heat recovery equipment & increases the feed
water temperature prior its entry into boiler.
• Waste heat directly substitute the cost of fuel.
• A well designed economizer can reduce the fuel consumption by 5-10%.
• About 4-10% capacity of boiler is increased by installation of economizer.
•Reduction in thermal stresses on boiler .
Bagasse : high value nowadays

Co-generation plant can generate power with a value of 5000 till 6000 PKR per tonnage.

Minus Costs of power plant variable and fixed costs.

Minus Costs for transport

Market Price Bagasse: 4000 PKR per tonnage.

Boiler efficiencies in the sugar mills are mostly between 68 and 77% on LCV basis.
Steam / bagasse ratio versus efficiency based on 52% moisture content:
• 2.2 means 79.2 % eff
• 2.1 means 75.6 % eff
Mostly seen
• 2.0 means 71.8 % eff
• 1.9 means 67 % eff
• 1.8 means 63.2 % eff

Sometime seen efficiencies below 68%

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Seen high contents of CO in flue gas and Unburned in ash
Caused mainly by:
• Leakages in flue tubes air preheater
• Overloading grate
• Poor spreading of bagasse

CO contents
• mostly 1000 to 4000 ppmv.
• Means 0.64 till 2.5% efficiency loss
• Also seen far above 10000 ppmv. Means more then 6.4% losses
• Regulation accept 800 ppmv. Losses are 0.5%
• New boilers with latest technology we run at 200 to 300 ppmv. Losses are 0.2%.

The Higher CO content indicate mostly higher unburned content in fly ash

In existing boilers seen ash samples of fly ash with 22% carbon in ash with LHV value of
1861 KJ/kg. This is seen with CO contents of approx. 300 till 1000 ppmv.

However also seen 59% carbon and LHV value of 4800 kcal/kg. The CO contents are then
6000 to far above 10000 ppmv.
Losses in efficiency are
• 1.6% on basis of 22% carbon
• 6.9 % on basis of 59% carbon
Reasons low efficiency
• Bagasse Feeding not constant.

• All feeders have different speeds

• Feeders are stopped and started in manual control

• Spreading over grate is not optimal

• Air distribution over grate is poor

• No proper over firing air system

• No control of combustion air. Mostly manual

• Leakage in flue gas air preheater. Causing bypass of air. Too less air in furnace

• Overloading of boilers above 80 tph. Sometimes 92 tph

• Poor insulation

• Many gas and air leakages in casing/ducting

• No measurement of oxygen and CO levels in flue gasses and flue gas temperatures at different locations in boiler

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Efficiency calculation in indirect way/ as per indirect method

Efficiency = 100% - losses%

What information is required to calculate the losses

Heat balance boiler

Q rad and conv

Q fuel Q nett
Boiler
Q air
Q stack

Q Blow down Q ash including unburned

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What are the losses and possible savings in 25 bar boilers

For most boilers having 75% efficiency

• 5.4 % convection and radiation losses to ambient due to poor insulation

• 4.9% by unburned losses
• 14.7 stack losses based on 195 C

New boilers have eff of 87.4 % with membrane walls and efficient combustion system and eco

• 0.8 % convection and radiation losses to ambient due to poor insulation

• 2.0% by unburned losses
• 9.8 % stack losses based on 140C and 3.5 vol % oxygen content on wet basis

With Modified existing LP boiler can efficiency improved to 84%

• 3% convection and radiation losses to ambient due to poor insulation

• 3% by unburned losses
• 10 % stack losses based on 140C

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Efficiency of new boilers is 87.4 %:
Due to new technology
• with membrane walls
• improved firing systems
• Large economizers at outlet
• With steam air preheaters

Additional annual revenues sugar mill with new boilers:

Sugar mill size

• 8000 TCD
• 50% steam demand
• Season 100 days
• Utilization 85%
• Bagasse from cane: 30%

Bagasse savings due to 87.4 % efficiency: 23808 tons annually

Market value at 4000 PKR/ton
Total annual additional revenues: 95 million PKR

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Technology provided for improving efficiency in existing LP boilers to 84%

• Feeders modified or replaced to provide continuous supply of bagasse

• Picker rollers installed to break the lumps
• Cold air fans installed to provide cold spreader air to spreaders with more impulse
• Opening in spreaders reduced
• Air pulsating dampers installed at each spreader inlet
• Air distribution baffle in hopper under grate
• Installation of large over firing nozzles in side walls above firing fed with secondary air.
• Installation of stream air preheater at FD fan outlet for heating up air to 100 C. No corrosion anymore
• Installation of large economizer at outlet of fly ash arrestor.
• Installation of venture at FD fan inlet to measure the air flow
• Full automatic control. Not only monitoring as mostly seen. Also with proper controls/logics
• Ensure the proper cyclones are installed.
• Regularly measurement of oxygen and CO and flue gas temperatures at different locations.

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 Biomass decomposition

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 lingo cellulose species.

Anaerobic digestion is the bacterial fermentation of organic 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.

The heating value can drop fast during storage.

See below graph
Approx. 4.6 % reduction in LCV value per month
Industry purchase bagasse for energy
generation.
They face much lower heating values after some
period.

This needs methods to keep heating value stable

Compressive overview

of what we have done

in existing LP boilers

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 Modification to screw feeders

Install baffle of 6 mm thick CS plate

Avoid lumps
10 mm free space
Increase size picker roller

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Modification drum type feeders:

lower gap between feeder drum and

casing

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New feeders of twin roller type with picker roller

high amount of fines supply into

spreaders

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Installation cold air spreader fan

Remove insulation

PI
4 spreaders installed
trimdamper

Spreader fan approx. 8000

m3/hr and 70 mbar

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 Pulsating air damper

Pulsating damper

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Over firing system
Mixing of CO and
unburned bagasse
particles with fresh
air above fire

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 Baffle in hopper to improve Air distribution Under grate

800
Approx 920

500 1000

Cut hole 30
Existing air distribution improved air distribution
mm in plate
and weld to
0
65

duct
ox

800 Weld at both sides to existing air duct

pr

Air distribution in hopper

Ap

Take 8 mm
thick plate of Duct approx. 920 * 650 mm
800

CS
Air duct
At hopper inlet

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Ensure spreading and air
distribution is equalized and
continuous

Same speed and equalized spreading

Control feeders fully automatic

Different speed

Equalized spreading in
depth

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Install venture for air measurement
Automatic combustion control is
accurate and excess air can be
minimized

Fans should be all on variable

speed control. High power savings
and control is accurate

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Multi cyclone

Use the right swirler

Check erosion of cyclone body and swirlers

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Improve the insulation
Insulation
wool is in
poor
condition

Not
gas
tight
Hot air Ducting to grade
At boiler roof

Steam outlet
line poor
insulated. No
thickness

At steam
leakages drum

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 leakage

Check regularly the wall temperatures of casing and insulation cladding with infra red temperature meter.
If more then 50 or 60 C then take action.
Make schedule for which parts needs to be improved after season.

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 Select the proper thickness and material

economic insulation thickness table

Rockwool isolation hard board 850
300 50
280 100
260 150
240 200
250
insulation thickness

220
300
200
350
180
400
160 450
140 500
120 550
100
80
60
40
20
0
0 50 10 0 15 0 20 0 25 0 30 0 35 0 40 0 45 0 50 0 55 0 60 0 65 0 70 0 75 0 80 0 85 0 90 0 95 0 0 00
1

diameter outside (mm)

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Insulation main steam line proper and install supports for cladding. Rain water tight.

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Thank You for Your Kind Attention