CFBC BOILER KNOWLEDGE

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steam turbine speed control governor

In a Steam Turbine system we control it's speed that is Turbine needs to rotate at fixed speed. Now if we want to add some additional load say if we want to raise its Power output, speed will tend to reduce as equivalent amount of heat energy is not available at that moment . Now at that condition we have to introduce more steam that is heat energy to increase that load maintained at the same speed. Now how that steam will be introduced in the turbine either someone has to operate the control valve or through some mechanized arrangement. that mechanized arrangement is its governing system. Which is either hydraulic or electro hydraulic . 
Now take the case of load increase as the speed of the turbine tends to decrease, in case of a fully hydraulic governing system , a pump which is mounted in the governing system through some gear arrangement at turbine main shaft receives oil and produces a fixed discharge pressure(This is your primary oil pressure) corresponding to the preset rotation per minute,  will also reduce as when the speed of the turbine reduced , the pump speed also reduced as it is coupled with gear arrangement. This reduced oil pressure will facilitate to introduce more secondary oil pressure in to the pilot valve which is through its hydraulic piston system will open steam entry valve to turbine , as more stem will enter into the turbine its speed will increase, now two phenomenon will occur simultaneously, primary oil pressure will rise as turbine speed has increased and one feedback mechanism fitted in the pilot valve will restrict pilot valve movement and controlled secondary oil will try to maintain the rated speed. 
Now it is the function of secondary oil and primary oil. 
Now how to protect the turbine if we want stop or trip the turbine when it is dangerous for the machine. This is the function of the trip oil. Trip oil generates from control oil which is through some mechanical device and through some solenoid valves are routed throughout the governing system. It has the mechanism to be drained rapidly so trip oil drains and blocks the oil passage of control oil. Mostly by spring arrangement steam stop valve(ESV) and control valve(regulating valve) stem stops to turbine. 
ANY HOW THIS ARE VERY BRIEF DESCRIPTION .

Now more sophisticated mechanism has been introduced which is electro hydraulic control . This system maintains turbine speed almost steady at all load condition with minimum variation.

Details on contact to kaacconsultant@gmail.com

CFBC BOILER

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Finance for Managers

https://www.icapb2b.gr/b2b_web/CMSContent/FINANCIAL_RATIOS.pdf

Techno commercial managers are gaining advantage day to day because

Only technicalities of machines  will not be fruitful unless it is balanced with market competencies in this cut throat environment unless with a close watch on business profitability which reflects in financial indicators. Potential engineering managers at some points of time has to focus on commercial aspects on their carrier ladder as technical aspects goes on conception and monitoring parameters will be financial results.

https://www.icapb2b.gr/b2b_web/CMSContent/FINANCIAL_RATIOS.pdf

above link is a good guide for reference of financial performances.
      

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BOILER OPERATION AND MAINTENANCE TRAINING SESSIONS . ANSWERS ARE GIVEN ON PAGE FOR THE QUERIES AT kaacconsultant@gmail.com

6 Do’s and Don’ts for Boiler
Operation
DO’S
• Maintain all instruments in good working
condition
• All equipment interlocks should always be in
line
• Maintain normal water level in steam drum
• Maintain water quality as per the recommended
limits. A table showing the DM water & drum
water quality is included at the end of this
section
• FD damper must be in smooth operating
condition
• Pressure raising from cold start must be done
as per the cold start up curve
• All the duct joints must be leak proof
• Use proper lubricant and maintain the schedule
as recommended by the manufacturers
• Operate the boiler within the recommended
operation limits
• Boiler, piping, ducts must be properly insulated
• Servicing of equipments should be done as per
the manufacturer’s schedule
• Maintain proper operation log sheets regularly
• Maintain the instrument air free from moisture
and oily matters and the pressure as
recommended
• Carry out regular cleaning of direct water level
gauge glasses of Boiler drum
• Use proper valve gland packing to avoid
leakage
• Use proper gaskets for ßange joints
• Operate the blowdown valves as per
recommendation
• In case of power failure close the steam stop
valve
• If the water level goes up above the limits
operate the intermittent blowdown valve
immediately and maintain the water level to
normal
• Maintain the feed water temperature at
Economiser inlet and ßue gas temperature at
Economiser outlet as recommended
• Use genuine spares
• Boiler surroundings and equipments must be
properly illuminated
DON’TS
• Don’t bypass any instruments and safety
interlocks
• Don’t use raw water as boiler feed water
• Don’t operate the boiler beyond the operation
limits
• Don’t leave the furnace door open while the
boiler is in operation
• Don’t mix up different lubricants
• Don’t alter the equipment maintenance
schedule
• Don’t leave the instrument control panel
unattended
• Don’t allow unauthorised persons to operate
the boiler and associated equipments.
• Do not dose chemicals into the boiler in batch
wise, they should be done on a continuous
basis
• If boiler is running under combustion control
manual mode, then while increasing load
air should be increased Þrst followed by Fuel

ENERGY PERFORMANCE ASSESSMENT OF BOILERS

1. ENERGY PERFORMANCE ASSESSMENT OF BOILERS
1.1 Introduction
Performance of the boiler, like efficiency and evaporation ratio reduces with time, due to poor combustion, heat transfer fouling and poor operation and maintenance. Deterioration of fuel quality and water quality also leads to poor performance of boiler. Efficiency testing helps us to find out how far the boiler efficiency drifts away from the best efficiency. Any observed abnormal deviations could therefore be investigated to pinpoint the problem area for necessary corrective action. Hence it is necessary to find out the current level of efficiency for performance evaluation, which is a pre requisite for energy conservation action in industry.
1.2 Purpose of the Performance Test
• To find out the efficiency of the boiler
• To find out the Evaporation ratio
The purpose of the performance test is to determine actual performance and efficiency of the boiler and compare it with design values or norms. It is an indicator for tracking day-to-day and season-to-season variations in boiler efficiency and energy efficiency improvements
1.3 Performance Terms and Definitions
1. Boiler Efficiency, η = 100 x input Heatoutput
Heat
= 100)()(x  kCals input fuel in Heat kCals output steam inHeat
2. Evaporation Ratio = nconsumptiofuelofQuantitygenerationsteamofQuantity
1.4 Scope
The procedure describes routine test for both oil fired and solid fuel fired boilers using coal, agro residues etc. Only those observations and measurements need to be made which can be readily applied and is necessary to attain the purpose of the test.
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1. Energy Performance Assessment of Boilers
1.5 Reference Standards
British standards, BS845: 1987
The British Standard BS845: 1987 describes the methods and conditions under which a boiler should be tested to determine its efficiency. For the testing to be done, the boiler should be operated under steady load conditions (generally full load) for a period of one hour after which readings would be taken during the next hour of steady operation to enable the efficiency to be calculated.
The efficiency of a boiler is quoted as the % of useful heat available, expressed as a percentage of the total energy potentially available by burning the fuel. This is expressed on the basis of gross calorific value (GCV) .
This deals with the complete heat balance and it has two parts:
�� Part One deals with standard boilers, where the indirect method is specified
�� Part Two deals with complex plant where there are many channels of heat flow. In this case, both the direct and indirect methods are applicable, in whole or in part.
ASME Standard: PTC-4-1 Power Test Code for Steam Generating Units
This consists of
�� Part One: Direct method (also called as Input -output method)
�� Part Two: Indirect method (also called as Heat loss method)
IS 8753: Indian Standard for Boiler Efficiency Testing
Most standards for computation of boiler efficiency, including IS 8753 and BS845 are designed for spot measurement of boiler efficiency. Invariably, all these standards do not include blow down as a loss in the efficiency determination process.
Basically Boiler efficiency can be tested by the following methods:
1) The Direct Method: Where the energy gain of the working fluid (water and steam) is compared with the energy content of the boiler fuel.
2) The Indirect Method: Where the efficiency is the difference between the losses and the energy input.
1.6 The Direct Method Testing
1.6.1 Description
This is also known as ‘input-output method’ due to the fact that it needs only the useful output (steam) and the heat input (i.e. fuel) for evaluating the efficiency. This efficiency can be evaluated using the formula: 100xInputHeatOutputHeatEfficiencyBoiler=
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1. Energy Performance Assessment of Boilers
BoilerFuel Input 100%+ Air Steam OutputEfficiency = Heat addition to Steam x 100Gross Heat in Fuel Flue Gas Water 100 valuecalorific Gross x rate firing Fuelenthalpy) water feed enthalpy (steam x rate flow SteamxEfficiencyBoiler−=
1.6.2 Measurements Required for Direct Method Testing
Heat input
Both heat input and heat output must be measured. The measurement of heat input requires knowledge of the calorific value of the fuel and its flow rate in terms of mass or volume, according to the nature of the fuel.
For gaseous fuel: A gas meter of the approved type can be used and the measured volume should be corrected for temperature and pressure. A sample of gas can be collected for calorific value determination, but it is usually acceptable to use the calorific value declared by the gas suppliers.
For liquid fuel: Heavy fuel oil is very viscous, and this property varies sharply with temperature. The meter, which is usually installed on the combustion appliance, should be regarded as a rough indicator only and, for test purposes, a meter calibrated for the particular oil is to be used and over a realistic range of temperature should be installed. Even better is the use of an accurately calibrated day tank.
For solid fuel: The accurate measurement of the flow of coal or other solid fuel is very difficult. The measurement must be based on mass, which means that bulky apparatus must be set up on the boiler-house floor. Samples must be taken and bagged throughout the test, the bags sealed and sent to a laboratory for analysis and calorific value determination. In some more recent boiler houses, the problem has been alleviated by mounting the hoppers over the boilers on calibrated load cells, but these are yet uncommon.
Heat output
There are several methods, which can be used for measuring heat output. With steam boilers, an installed steam meter can be used to measure flow rate, but this must be
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1. Energy Performance Assessment of Boilers
corrected for temperature and pressure. In earlier years, this approach was not favoured due to the change in accuracy of orifice or venturi meters with flow rate. It is now more viable with modern flow meters of the variable-orifice or vortex-shedding types.
The alternative with small boilers is to measure feed water, and this can be done by previously calibrating the feed tank and noting down the levels of water during the beginning and end of the trial. Care should be taken not to pump water during this period. Heat addition for conversion of feed water at inlet temperature to steam, is considered for heat output.
In case of boilers with intermittent blowdown, blowdown should be avoided during the trial period. In case of boilers with continuous blowdown, the heat loss due to blowdown should be calculated and added to the heat in steam.
1.6.3 Boiler Efficiency by Direct Method: Calculation and Example
Test Data and Calculation
Water consumption and coal consumption were measured in a coal-fired boiler at hourly intervals. Weighed quantities of coal were fed to the boiler during the trial period. Simultaneously water level difference was noted to calculate steam generation during the trial period. Blow down was avoided during the test. The measured data is given below.
Type of boiler: Coal fired Boiler
Heat output data
Quantity of steam generated (output) : 8 TPH
Steam pressure / temperature : 10 kg/cm2(g)/ 180 0C
Enthalpy of steam(dry & Saturated)
at 10 kg/cm2(g) pressure : 665 kCal/kg
Feed water temperature : 850 C
Enthalpy of feed water : 85 kCal/kg
Heat input data
Quantity of coal consumed (Input) : 1.6 TPH
GCV of coal : 4000 kCal/kg
Calculation 100)()(xGCVxqhHxQefficiencyBoiler−=η
Where Q = Quantity of steam generated per hour (kg/hr)
q = Quantity of fuel used per hour (kg/hr)
GCV = Gross calorific value of the fuel (kCal/kg)
H = Enthalpy of steam (kCal/kg)
h = Enthalpy of feed water (kCal/kg)
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1. Energy Performance Assessment of Boilers
100/4000/10006.1)85665(/10008)(xkgkCalxTkgxTPHxTkgxTPHefficiencyBoiler−=η
= 72.5%
Evaporation Ratio = 8 Tonne of steam / 1.6 Tonne of coal
= 5
1.6.4 Merits and Demerits of Direct Method
Merits
�� Plant people can evaluate quickly the efficiency of boilers
�� Requires few parameters for computation
�� Needs few instruments for monitoring
Demerits
�� Does not give clues to the operator as to why efficiency of system is lower
�� Does not calculate various losses accountable for various efficiency levels
�� Evaporation ratio and efficiency may mislead, if the steam is highly wet due to water carryover
1.7 The Indirect Method Testing
1.7.1 Description
The efficiency can be measured easily by measuring all the losses occurring in the boilers using the principles to be described. The disadvantages of the direct method can be overcome by this method, which calculates the various heat losses associated with boiler. The efficiency can be arrived at, by subtracting the heat loss fractions from 100.An important advantage of this method is that the errors in measurement do not make significant change in efficiency.
Thus if boiler efficiency is 90% , an error of 1% in direct method will result in significant change in efficiency. i.e.90 + 0.9 = 89.1 to 90.9. In indirect method, 1% error in measurement of losses will result in
Efficiency = 100 – (10 + 0.1) = 90 + 0.1 = 89.9 to 90.1
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1. Energy Performance Assessment of Boilers
The various heat losses occurring in the boiler are: BoilerFlue gas sampleSteam OutputEfficiency = 100 –(1+2+3+4+5+6+7+8) (by Indirect Method)AirFuel Input, 100%1. Dry Flue gas loss2. H2 loss3. Moisture in fuel4. Moisture in air5. CO loss7. Fly ash loss6. Surface loss8. Bottom ash lossWaterBlow down
The following losses are applicable to liquid, gas and solid fired boiler
L1- Loss due to dry flue gas (sensible heat)
L2- Loss due to hydrogen in fuel (H2)
L3- Loss due to moisture in fuel (H2O)
L4- Loss due to moisture in air (H2O)
L5- Loss due to carbon monoxide (CO)
L6- Loss due to surface radiation, convection and other unaccounted*.
*Losses which are insignificant and are difficult to measure.
The following losses are applicable to solid fuel fired boiler in addition to above
L7- Unburnt losses in fly ash (Carbon)
L8- Unburnt losses in bottom ash (Carbon)
Boiler Efficiency by indirect method = 100 – (L1+L2+L3+L4+L5+L6+L7+L8)
1.7.2 Measurements Required for Performance Assessment Testing
The following parameters need to be measured, as applicable for the computation of boiler efficiency and performance.
a) Flue gas analysis
1. Percentage of CO2 or O2 in flue gas
2. Percentage of CO in flue gas
3. Temperature of flue gas
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1. Energy Performance Assessment of Boilers
b) Flow meter measurements for
1. Fuel
2. Steam
3. Feed water
4. Condensate water
5. Combustion air
c) Temperature measurements for
1. Flue gas
2. Steam
3. Makeup water
4. Condensate return
5. Combustion air
6. Fuel
7. Boiler feed water
d) Pressure measurements for
1. Steam
2. Fuel
3. Combustion air, both primary and secondary
4. Draft
e) Water condition
1. Total dissolved solids (TDS)
2. pH
3. Blow down rate and quantity
The various parameters that were discussed above can be measured with the instruments that are given in Table 1.1.
Table 1.1 Typical Instruments used for Boiler Performance Assessment.
Instrument
Type
Measurements
Flue gas analyzer
Portable or fixed
% CO2 , O2 and CO
Temperature indicator
Thermocouple, liquid in glass
Fuel temperature, flue gas temperature, combustion air temperature, boiler surface temperature, steam temperature
Draft gauge
Manometer, differential pressure
Amount of draft used or available
TDS meter
Conductivity
Boiler water TDS, feed water TDS,
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1. Energy Performance Assessment of Boilers
make-up water TDS.
Flow meter
As applicable
Steam flow, water flow, fuel flow, air flow
1.7.3 Test Conditions and Precautions for Indirect Method Testing
A) The efficiency test does not account for:
�� Standby losses. Efficiency test is to be carried out, when the boiler is operating under a steady load. Therefore, the combustion efficiency test does not reveal standby losses, which occur between firing intervals
�� Blow down loss. The amount of energy wasted by blow down varies over a wide range.
�� Soot blower steam. The amount of steam used by soot blowers is variable that depends on the type of fuel.
�� Auxiliary equipment energy consumption. The combustion efficiency test does not account for the energy usage by auxiliary equipments, such as burners, fans, and pumps.
B) Preparations and pre conditions for testing
�� Burn the specified fuel(s) at the required rate.
�� Do the tests while the boiler is under steady load. Avoid testing during warming up of boilers from a cold condition
�� Obtain the charts /tables for the additional data.
�� Determination of general method of operation
�� Sampling and analysis of fuel and ash.
�� Ensure the accuracy of fuel and ash analysis in the laboratory.
�� Check the type of blow down and method of measurement
�� Ensure proper operation of all instruments.
�� Check for any air infiltration in the combustion zone.
C) Flue gas sampling location
It is suggested that the exit duct of the boiler be probed and traversed to find the location of the zone of maximum temperature. This is likely to coincide with the zone of maximum gas flow and is therefore a good sampling point for both temperature and gas analysis.
D) Options of flue gas analysis
Check the Oxygen Test with the Carbon Dioxide Test
If continuous-reading oxygen test equipment is installed in boiler plant, use oxygen reading. Occasionally use portable test equipment that checks for both oxygen and carbon dioxide. If the carbon dioxide test does not give the same results as the oxygen test, something is wrong. One (or both) of the tests could be erroneous, perhaps because of stale chemicals or drifting instrument calibration. Another possibility is that outside air is
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1. Energy Performance Assessment of Boilers
being picked up along with the flue gas. This occurs if the combustion gas area operates under negative pressure and there are leaks in the boiler casing.
Carbon Monoxide Test
The carbon monoxide content of flue gas is a good indicator of incomplete combustion with all types of fuels, as long as they contain carbon. Carbon monoxide in the flue gas is minimal with ordinary amounts of excess air, but it rises abruptly as soon as fuel combustion starts to be incomplete.
E) Planning for the testing
�� The testing is to be conducted for a duration of 4 to 8 hours in a normal production day.
�� Advanced planning is essential for the resource arrangement of manpower, fuel, water and instrument check etc and the same to be communicated to the boiler Supervisor and Production Department.
�� Sufficient quantity of fuel stock and water storage required for the test duration should be arranged so that a test is not disrupted due to non-availability of fuel and water.
�� Necessary sampling point and instruments are to be made available with working condition.
�� Lab Analysis should be carried out for fuel, flue gas and water in coordination with lab personnel.
�� The steam table, psychometric chart, calculator are to be arranged for computation of boiler efficiency.
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1. Energy Performance Assessment of Boilers
1.7.4 Boiler Efficiency by Indirect Method: Calculation Procedure and Formula
In order to calculate the boiler efficiency by indirect method, all the losses that occur in the boiler must be established. These losses are conveniently related to the amount of fuel burnt. In this way it is easy to compare the performance of various boilers with different ratings.
Conversion formula for proximate analysis to ultimate analysis
%C
=
0.97C+ 0.7(VM+0.1A) - M(0.6-0.01M)
%H2
=
0.036C + 0.086 (VM -0.1xA) - 0.0035M2 (1-0.02M)
%N2
=
2.10 -0.020 VM
where
C
=
% of fixed carbon
A
=
% of ash
VM
=
% of volatile matter
M
=
% of moisture
However it is suggested to get a ultimate analysis of the fuel fired periodically from a reputed laboratory.
Theoretical (stoichiometric) air fuel ratio and excess air supplied are to be determined first for computing the boiler losses. The formula is given below for the same.
a) Theoretical air required for combustion
=
100/)]35.4()}8/(8.34{)6.11[(22SxOHxCx+−+ kg/kg of fuel. [from fuel analysis]
Where C, H2, O2 and S are the percentage of carbon, hydrogen, oxygen and sulphur present in the fuel.
b) % Excess Air supplied (EA)
= 10021%%22xOO− [from flue gas analysis]
Normally O2 measurement is recommended. If O2 measurement is not available, use CO2 measurement ]%)(100[%)(]%)(%)[(79002222taatCOxCOCOCOx−− [from flue gas analysis]
Where, (CO2%)t
=
Theoretical CO2
(CO2%)a
=
Actual CO2% measured in flue gas
( CO2 )t
= CofMolesNofMolesCofMoles+2
Moles of N2
= 2222..NofWtMolfuelinNofWtNofwtMolairltheoriticainNofWt+
Moles of C
= CofWtMolecularfuelinCofWt
c) Actual mass of air supplied/ kg of fuel (AAS)
=
{1 + EA/100} x theoretical air
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1. Energy Performance Assessment of Boilers
The various losses associated with the operation of a boiler are discussed below with required formula.
1. Heat loss due to dry flue gas
This is the greatest boiler loss and can be calculated with the following formula:
L1
= 100)(xfuelofGCVTTxCxmafp−
Where,
L1
=
% Heat loss due to dry flue gas
m
=
Mass of dry flue gas in kg/kg of fuel
=
Combustion products from fuel: CO2 + SO2 + Nitrogen in fuel + Nitrogen in the actual mass of air supplied + O2 in flue gas. (H2O/Water vapour in the flue gas should not be considered)
Cp
=
Specific heat of flue gas in kCal/kg
Tf
=
Flue gas temperature in oC
Ta
=
Ambient temperature in oC
Note-1:
For Quick and simple calculation of boiler efficiency use the following.
A: Simple method can be used for determining the dry flue gas loss as given below.
a) Percentage heat loss due to dry flue gas = 100)(xfuelofGCVTTxCxmafp−
Total mass of flue gas (m)/kg of fuel = mass of actual air supplied/kg of fuel + 1 kg of
fuel
Note-2: Water vapour is produced from Hydrogen in fuel, moisture present in fuel and air during the combustion. The losses due to these components have not been included in the dry flue gas loss since they are separately calculated as a wet flue gas loss.
2. Heat loss due to evaporation of water formed due to H2 in fuel (%)
The combustion of hydrogen causes a heat loss because the product of combustion is water. This water is converted to steam and this carries away heat in the form of its latent heat.
L2
= 100fuelofGCV )} T-(T C {584 x H x 9afp2x+
Where
H2
=
kg of hydrogen present in fuel on 1 kg basis
Cp
=
Specific heat of superheated steam in kCal/kgoC
Tf
=
Flue gas temperature in oC
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1. Energy Performance Assessment of Boilers
Ta
=
Ambient temperature in oC
584
=
Latent heat corresponding to partial pressure of water vapour
3. Heat loss due to moisture present in fuel
Moisture entering the boiler with the fuel leaves as a superheated vapour. This moisture loss is made up of the sensible heat to bring the moisture to boiling point, the latent heat of evaporation of the moisture, and the superheat required to bring this steam to the temperature of the exhaust gas. This loss can be calculated with the following formula
L3
= 100fuelofGCV )} T-(T C {584 xMafpx+
where
M
=
kg of moisture in fuel in 1 kg basis
Cp
=
Specific heat of superheated steam in kCal/kgoC
Tf
=
Flue gas temperature in oC
Ta
=
Ambient temperature in oC
584
=
Latent heat corresponding to partial pressure of water vapour
4. Heat loss due to moisture present in air
Vapour in the form of humidity in the incoming air, is superheated as it passes through the boiler. Since this heat passes up the stack, it must be included as a boiler loss.
To relate this loss to the mass of coal burned, the moisture content of the combustion air and the amount of air supplied per unit mass of coal burned must be known.
The mass of vapour that air contains can be obtained from psychrometric charts and typical values are included below:
Dry-Bulb
Wet Bulb
Relative Humidity
Temp oC
TempoC
(%)
Kilogram water per Kilogram dry air (Humidity Factor)
20
20
100
0.016
20
14
50
0.008
30
22
50
0.014
40
30
50
0.024
L4
=100fuelofGCV ) T-(T xC afpxxfactorhumidityxAAS
where
AAS
=
Actual mass of air supplied per kg of fuel
Humidity factor
=
kg of water/kg of dry air
Cp
=
Specific heat of superheated steam in kCal/kgoC
Tf
=
Flue gas temperature in oC
Ta
=
Ambient temperature in oC (dry bulb)
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1. Energy Performance Assessment of Boilers
5. Heat loss due to incomplete combustion:
Products formed by incomplete combustion could be mixed with oxygen and burned again with a further release of energy. Such products include CO, H2, and various hydrocarbons and are generally found in the flue gas of the boilers. Carbon monoxide is the only gas whose concentration can be determined conveniently in a boiler plant test.
L5
= 1005744%%%2xfuelofGCVxCOCOCxCO+
L5
=
% Heat loss due to partial conversion of C to CO
CO
=
Volume of CO in flue gas leaving economizer (%)
CO2
=
Actual Volume of CO2 in flue gas (%)
C
=
Carbon content kg / kg of fuel
or
When CO is obtained in ppm during the flue gas analysis
CO formation (Mco)
=
CO (in ppm) x 10-6 x Mf x 28
Mf
=
Fuel consumption in kg/hr
L5
=
Mco x 5744*
* Heat loss due to partial combustion of carbon.
6. Heat loss due to radiation and convection:
The other heat losses from a boiler consist of the loss of heat by radiation and convection from the boiler casting into the surrounding boiler house.
Normally surface loss and other unaccounted losses is assumed based on the type and size of the boiler as given below
For industrial fire tube / packaged boiler = 1.5 to 2.5%
For industrial watertube boiler = 2 to 3%
For power station boiler = 0.4 to 1%
However it can be calculated if the surface area of boiler and its surface temperature are known as given below :
L6
=
0.548 x [ (Ts / 55.55)4 – (Ta / 55.55)4] + 1.957 x (Ts – Ta)1.25 x sq.rt of [(196.85 Vm + 68.9) / 68.9]
where
L6
=
Radiation loss in W/m2
Vm
=
Wind velocity in m/s
Ts
=
Surface temperature (K)
Ta
=
Ambient temperature (K)
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1. Energy Performance Assessment of Boilers
Heat loss due to unburned carbon in fly ash and bottom ash:
Small amounts of carbon will be left in the ash and this constitutes a loss of potential heat in the fuel. To assess these heat losses, samples of ash must be analyzed for carbon content. The quantity of ash produced per unit of fuel must also be known.
7. Heat loss due to unburnt in fly ash (%). 100fuelofGCVashfly of G.C.V xburnt fuel of kg / collectedash Total7xL=
8. Heat loss due to unburnt in bottom ash (%) 100fuelofGCVash bottom of G.C.V xburnt fuel of kg / collectedash Total8xL=
Heat Balance:
Having established the magnitude of all the losses mentioned above, a simple heat balance would give the efficiency of the boiler. The efficiency is the difference between the energy input to the boiler and the heat losses calculated.
Boiler Heat Balance:
Input/Output Parameter
kCal / kg of fuel
%
Heat Input in fuel
=
100
Various Heat losses in boiler
1. Dry flue gas loss
=
2. Loss due to hydrogen in fuel
3. Loss due to moisture in fuel
=
4. Loss due to moisture in air
=
5. Partial combustion of C to CO
=
6. Surface heat losses
=
7. Loss due to Unburnt in fly ash
=
8. Loss due to Unburnt in bottom ash
=
Total Losses
=
Boiler efficiency = 100 – (1+2+3+4+5+6+7+8)
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1. Energy Performance Assessment of Boilers
1.8 Example: Boiler Efficiency Calculation
1.8.1 For Coal fired Boiler
The following are the data collected for a boiler using coal as the fuel. Find out the boiler efficiency by indirect method.
Fuel firing rate
=
5599.17 kg/hr
Steam generation rate
=
21937.5 kg/hr
Steam pressure
=
43 kg/cm2(g)
Steam temperature
=
377 oC
Feed water temperature
=
96 oC
%CO2 in Flue gas
=
14
%CO in flue gas
=
0.55
Average flue gas temperature
=
190 oC
Ambient temperature
=
31 oC
Humidity in ambient air
=
0.0204 kg / kg dry air
Surface temperature of boiler
=
70 oC
Wind velocity around the boiler
=
3.5 m/s
Total surface area of boiler
=
90 m2
GCV of Bottom ash
=
800 kCal/kg
GCV of fly ash
=
452.5 kCal/kg
Ratio of bottom ash to fly ash
=
90:10
Fuel Analysis (in %)
Ash content in fuel
=
8.63
Moisture in coal
=
31.6
Carbon content
=
41.65
Hydrogen content
=
2.0413
Nitrogen content
=
1.6
Oxygen content
=
14.48
GCV of Coal
=
3501 kCal/kg
Bureau of Energy Efficiency 15
1. Energy Performance Assessment of Boilers
Boiler efficiency by indirect method
Step – 1 Find theoretical air requirement
Theoretical air required for complete combustion
=
100/)]35.4()}8/(8.34{)6.11[(22SxOHxCx+−+
kg/kg of coal
=
[(11.6 x 41.65) + {34.8 x (2.0413 – 14.48/8)} + (4.35 x 0)] / 100
=
4.91 kg / kg of coal
Step – 2 Find theoretical CO2 %
% CO2 at theoretical condition
( CO2 )t
= CofMolesNofMolesCofMoles+2
Where,
Moles of N2
=2222..NofWtMolfuelinNofWtNofwtMolairltheoriticainNofWt+
Moles of N2
= 1356.028016.028100/7791.4=+x
Where moles of C
=
0.4165/12 = 0.0347
( CO2 )t
=0347.01332.00347.0+
( CO2 )t
=
20.37%
Step – 3 To find Excess air supplied
Actual CO2 measured in flue gas
=
14.0%
% Excess air supplied (EA)
=]%)(100[%)(]%)(%)[(79002222taatCOxCOCOCOx−−
=]37.20100[14]1437.20[7900−−xx
=
45.17 %
Step – 4 To find actual mass of air supplied
Actual mass of air supplied
=
{1 + EA/100} x theoretical air
=
{1 + 45.17/100} x 4.91
Bureau of Energy Efficiency 16
1. Energy Performance Assessment of Boilers
=
7.13 kg/kg of coal
Step –5 To find actual mass of dry flue gas
Mass of dry flue gas
=
Mass of CO2 +Mass of N2 content in the fuel+ Mass of N2 in the combustion air supplied + Mass of oxygen in flue gas
Mass of dry flue gas
= 10023)91.413.7(1007713.7016.012444165.0xxx−+++
=
7.54 kg / kg of coal
Step – 6 To find all losses
1. % Heat loss in dry flue gas (L1)
=100)(xfuelofGCVTTxCxmafp−
=1003501)31190(23.054.7xxx−
L1
=
7.88 %
2. % Heat loss due to formation of water from H2 in fuel (L2)
=100fuelofGCV )} T-(T C {584 x H x 9afp2x+
=1003501 )} 31-(190 0.45 {584 x 0.02041 x 9x+
L2
=
3.44 %
3. % Heat loss due to moisture in fuel (L3)
=100fuelofGCV )} T-(T C {584 xMafpx+
=100fuelofGCV )} T-(T C {584 xMafpx+
L3
=
5.91 %
4. % Heat loss due to moisture in air (L4)
=100)(xfuelofGCVTTxCxhumidityxAASafp−
=1003501)31190(45.00204.013.7xxxx−
Bureau of Energy Efficiency 17
1. Energy Performance Assessment of Boilers
L4
=
0.29 %
5. % Heat loss due to partial conversion of C to CO (L5)
=1005744%%%2xfuelofGCVxCOCOCxCO+
=100350157441455.04165.055.0xxx+
L5
=
2.58 %
6. Heat loss due to radiation and convection (L6)
=
0.548 x [ (343/55.55)4 – (304/55.55)4] + 1.957 x (343 - 304)1.25 x sq.rt of [(196.85 x 3.5 + 68.9) / 68.9]
=
633.3 w/m2
=
633.3 x 0.86
=
544.64 kCal / m2
Total radiation and convection loss per hour
=
544.64 x 90
=
49017.6 kCal
% radiation and convection loss
=
49017.6 x 100
3501 x 5599.17
L6
=
0.25 %
7. % Heat loss due to unburnt in fly ash
% Ash in coal
=
8.63
Ratio of bottom ash to fly ash
=
90:10
GCV of fly ash
=
452.5 kCal/kg
Amount of fly ash in 1 kg of coal
=
0.1 x 0.0863
=
0.00863 kg
Heat loss in fly ash
=
0.00863 x 452.5
=
3.905 kCal / kg of coal
% heat loss in fly ash
=
3.905 x 100 / 3501
L7
=
0.11 %
8. % Heat loss due to unburnt in bottom ash
GCV of bottom ash
=
800 kCal/kg
Amount of bottom ash in 1 kg of coal
=
0.9 x 0.0863
=
0.077 kg
Heat loss in bottom ash
=
0.077 x 800
Bureau of Energy Efficiency 18
1. Energy Performance Assessment of Boilers
=
62.136 kCal/kg of coal
% Heat loss in bottom ash
=
62.136 x 100 / 3501
L8
=
1.77 %
Boiler efficiency by indirect method
=
100 – (L1+ L2+ L3+ L4+ L5+ L6+ L7+ L8)
=
100-(7.88 + 3.44+ 5.91+ 0.29+ 2.58+ 0.25+ 0.11+1.77)
=
100-22.23
=
77.77 %
Summary of Heat Balance for Coal Fired Boiler
Input/Output Parameter
kCal / kg of coal
% loss
Heat Input
=
3501
100
Losses in boiler
1. Dry flue gas, L1
=
275.88
7.88
2. Loss due to hydrogen in fuel, L2
=
120.43
3.44
3. Loss due to moisture in fuel, L3
=
206.91
5.91
4. Loss due to moisture in air, L4
=
10.15
0.29
5. Partial combustion of C to CO, L5
=
90.32
2.58
6. Surface heat losses, L6
=
8.75
0.25
7. Loss due to Unburnt in fly ash, L7
=
3.85
0.11
8. Loss due to Unburnt in bottom ash, L8
=
61.97
1.77
Boiler Efficiency = 100 – (L1 + L2+ L3+ L4+ L5+ L6+ L7+ L8) = 77.77 %
1.8.2 Efficiency for an oil fired boiler
The following are the data collected for a boiler using furnace oil as the fuel. Find out the boiler efficiency by indirect method.
Ultimate analysis (%)
Carbon
=
84
Hydrogen
=
12
Nitrogen
=
0.5
Oxygen
=
1.5
Sulphur
=
1.5
Moisture
=
0.5
GCV of fuel
=
10000 kCal/kg
Fuel firing rate
=
2648.125 kg/hr
Surface Temperature of boiler
=
80 oC
Surface area of boiler
=
90 m2
Humidity
=
0.025 kg/kg of dry air
Bureau of Energy Efficiency 19
1. Energy Performance Assessment of Boilers
Wind speed
=
3.8 m/s
Flue gas analysis (%)
Flue gas temperature
=
190oC
Ambient temperature
=
30o C
Co2% in flue gas by volume
=
10.8
O2% in flue gas by volume
=
7.4
a) Theoretical air required
=
100/)]35.4()}8/(8.34{)6.11[(22SxOHxCx+−+ kg/kg of fuel. [from fuel analysis]
=
[(11.6 x 84) + [{34.8 x (12 – 1.5/8)} + (4.35 x 1.5)] / 100
=
13.92 kg/kg of oil
b) Excess Air supplied (EA)
=10021%%22xOO− [from flue gas analysis]
=1004.7214.7x−
=
54.4 %
c) Actual mass of air supplied/ kg of fuel (AAS)
=
{1 + EA/100} x theoretical air
=
{1 + 54.4/100} x 13.92
=
21.49 kg / kg of fuel
Mass of dry flue gas
=
Mass of (CO2 + SO2 + N2 + O2) in flue gas + N2 in air we are supplying.
Mass of dry flue gas
=1007749.21100234.7005.03264015.0124484.0xxxx++++
=
21.36 kg / kg of oil
% Heat loss in dry flue gas
=100)(xfuelofGCVTTxCxmafp−
=10010000)30190(23.036.21xxx−
L1
=
7.86 %
Heat loss due to evaporation of water due to H2 in fuel (%)
=100fuelofGCV )} T-(T C {584 x H x 9afp2x+
Bureau of Energy Efficiency 20
1. Energy Performance Assessment of Boilers
=10010000 )} 30-(190 0.45 {584 x 0.12 x 9x+
L2
=
7.08 %
% Heat loss due to moisture in fuel
=100fuelofGCV )} T-(T C {584 xMafpx+
=10010000 )} 30-(190 0.45 {584 x0.005x+
L3
=
0.033%
% Heat loss due to moisture in air
=100fuelofGCV ) T-(T xC afpxxfactorhumidityxAAS
=10010000 ) 30-(190 x0.45 025.036.21xxx
L4
=
0.38 %
Radiation and convection loss (L6)
=
0.548 x [ (Ts / 55.55)4 – (Ta / 55.55)4] + 1.957 x (Ts – Ta)1.25 x sq.rt of [(196.85 Vm + 68.9) / 68.9]
=
0.548 x [ (353 / 55.55)4 – (303 / 55.55)4] + 1.957 x (353 – 303)1.25 x sq.rt of [(196.85 x 3.8 + 68.9) / 68.9]
=
1303 W/m2
=
1303 x 0.86
=
1120.58 kCal / m2
Total radiation and convection loss per hour
=
1120 .58 x 90 m2
=
100852.2 kCal
% Radiation and convection loss
=100125.2648100002.100852xx
L6
=
0.38 %
Normally it is assumed as 0.5 to 1 % for simplicity
Boiler efficiency by indirect method
=
100 – (L1 + L2+ L3+ L4+ L6)
=
100-(7.86 + 7.08 + 0.033 + 0.38 + 0.38)
=
100 – 15.73
=
84.27 %
Bureau of Energy Efficiency 21
1. Energy Performance Assessment of Boilers
Summary of Heat Balance for the Boiler Using Furnace Oil
Input/Output Parameter
kCal / kg of furnace oil
%Loss
Heat Input
=
10000
100
Losses in boiler :
1. Dry flue gas, L1
=
786
7.86
2. Loss due to hydrogen in fuel, L2
=
708
7.08
3. Loss due to Moisture in fuel, L3
=
3.3
0.033
4. Loss due to Moisture in air, L4
=
38
0.38
5. Partial combustion of C to CO, L5
=
0
0
6. Surface heat losses, L6
=
38
0.38
Boiler Efficiency = 100 – (L1 + L2+ L3+ L4+ L6) = 84.27 %
Note:
For quick and simple calculation of boiler efficiency use the following .
A: Simple method can be used for determining the dry flue gas loss as given below.
a) Percentage heat loss due to dry flue gas = 100)(xfuelofGCVTTxCxmafp−
Total mass of flue gas (m) = mass of actual air supplied (ASS)+ mass of fuel supplied
= 21.49 + 1=22.49
%Dry flue gas loss = %27.810010000)30190(23.049.22=−xxx
1.9 Factors Affecting Boiler Performance
The various factors affecting the boiler performance are listed below:
�� Periodical cleaning of boilers
�� Periodical soot blowing
�� Proper water treatment programme and blow down control
�� Draft control
�� Excess air control
�� Percentage loading of boiler
�� Steam generation pressure and temperature
�� Boiler insulation
�� Quality of fuel
All these factors individually/combined, contribute to the performance of the boiler and reflected either in boiler efficiency or evaporation ratio. Based on the results obtained from the testing further improvements have to be carried out for maximizing the performance. The test can be repeated after modification or rectification of the problems and compared with standard norms. Energy auditor should carry out this test as a routine manner once in six months and report to the management for necessary action.
Bureau of Energy Efficiency 22
1. Energy Performance Assessment of Boilers
1.10 Data Collection Format for Boiler Performance Assessment
Sheet 1 - Technical specification of boiler
1
Boiler ID code and Make
2
Year of Make
3
Boiler capacity rating
4
Type of Boiler
5
Type of fuel used
6
Maximum fuel flow rate
7
Efficiency by GCV
8
Steam generation pressure &superheat temperature
9
Heat transfer area in m2
10
Is there any waste heat recovery device installed
11
Type of draft
12
Chimney height in metre
Sheet 2 - Fuel analysis details
Fuel Fired
GCV of fuel
Specific gravity of fuel (Liquid)
Bulk density of fuel (Solid)
Proximate Analysis Date of Test:
1
Fixed carbon
%
2
Volatile matter
%
3
Ash
%
4
Moisture
%
Ultimate Analysis Date of Test:
1
Carbon
%
2
Hydrogen
%
3
Sulphur
%
4
Nitrogen
%
5
Ash
%
6
Moisture
%
7
Oxygen
%
Water Analysis Date of Test:
1
Feed water TDS
ppm
2
Blow down TDS
ppm
3
PH of feed water
4
PH of blow down
Flue gas Analysis Date of Test:
1
CO2
%
2
O2
%
3
CO
%
4
Flue gas temperature
OC
Bureau of Energy Efficiency 23
1. Energy Performance Assessment of Boilers
Sheet 3 – Format sheet for boiler efficiency testing
Date: ………………… Boiler Code No. …………………
S.No
Time
Ambient air
Fuel
Feed water
Steam
Flue gas analysis
Surface Temp of boiler, oC
Drybulb Temp, oC
Wet Bulb Temp, oC
Flow Rate, kg/hr
Temp
oC
Flow rate, m3/hr
Temp
oC
Flow rate,
m3/hr
Pressure
kg/cm2g
Temp
oC
O2
%
CO2
%
CO
%
Temp
0C
1.
2.
3.
4.
5.
6.
7.
8.
Boiler Supervisor Energy Manager Energy Auditor
Bureau of Energy Efficiency 24
1. Energy Performance Assessment of Boilers
1.11 Boiler Terminology
MCR: Steam boilers rated output is also usually defined as MCR (Maximum Continuous Rating). This is the maximum evaporation rate that can be sustained for 24 hours and may be less than a shorter duration maximum rating
Boiler Rating
Conventionally, boilers are specified by their capacity to hold water and the steam generation rate. Often, the capacity to generate steam is specified in terms of equivalent evaporation (kg of steam / hour at 100oC). Equivalent evaporation- “from and at” 100oC. The equivalent of the evaporation of 1 kg of water at 100oC to steam at 100oC.
Efficiency : In the boiler industry there are four common definitions of efficiency:
a. Combustion efficiency
Combustion efficiency is the effectiveness of the burner only and relates to its ability to completely burn the fuel. The boiler has little bearing on combustion efficiency. A well-designed burner will operate with as little as 15 to 20% excess air, while converting all combustibles in the fuel to useful energy.
b. Thermal efficiency
Thermal efficiency is the effectiveness of the heat transfer in a boiler. It does not take into account boiler radiation and convection losses – for example from the boiler shell water column piping etc.
c. Boiler efficiency
The term boiler efficiency is often substituted for combustion or thermal efficiency. True boiler efficiency is the measure of fuel to steam efficiency.
d. Fuel to steam efficiency
Fuel to steam efficiency is calculated using either of the two methods as prescribed by the ASME (American Society for Mechanical Engineers) power test code, PTC 4.1. The first method is input output method. The second method is heat loss method.
Boiler turndown
Boiler turndown is the ratio between full boiler output and the boiler output when operating at low fire. Typical boiler turndown is 4:1. The ability of the boiler to turndown reduces frequent on and off cycling. Fully modulating burners are typically designed to operate down to 25% of rated capacity. At a load that is 20% of the load capacity, the boiler will turn off and cycle frequently.
A boiler operating at low load conditions can cycle as frequently as 12 times per hour or 288 times per day. With each cycle, pre and post purge airflow removes heat from the boiler and sends it out the stack. Keeping the boiler on at low firing rates can eliminate the energy loss. Every time the boiler cycles off, it must go through a specific start-up sequence for safety
Bureau of Energy Efficiency 25
1. Energy Performance Assessment of Boilers
assurance. It requires about a minute or two to place the boiler back on line. And if there is a sudden load demand the start up sequence cannot be accelerated. Keeping the boiler on line assures the quickest response to load changes. Frequent cycling also accelerates wear of boiler components. Maintenance increases and more importantly, the chance of component failure increases.
Boiler(s) capacity requirement is determined by many different type of load variations in the system. Boiler over sizing occurs when future expansion and safety factors are added to assure that the boiler is large enough for the application. If the boiler is oversized the ability of the boiler to handle minimum loads without cycling is reduced. Therefore capacity and turndown should be considered together for proper boiler selection to meet overall system load requirements.
Primary air: That part of the air supply to a combustion system which the fuel first encounters.
Secondary air: The second stage of admission of air to a combustion system, generally to complete combustion initiated by the primary air. It can be injected into the furnace of a boiler under relatively high pressure when firing solid fuels in order to create turbulence above the burning fuel to ensure good mixing with the gases produced in the combustion process and thereby complete combustion
Tertiary air: A third stage of admission of air to a combustion system, the reactions of which have largely been completed by secondary air. Tertiary air is rarely needed.
Stoichiometric: In combustion technology, stoichiometric air is that quantity of air, and no more, which is theoretically needed to burn completely a unit quantity of fuel. ‘Sub-stoichiometric’ refers to the partial combustion of fuel in a deficiency of air
Balanced draught: The condition achieved when the pressure of the gas in a furnace is the same as or slightly below that of the atmosphere in the enclosure or building housing it.
Gross calorific value (GCV): The amount of heat liberated by the complete combustion, under specified conditions, by a unit volume of a gas or of a unit mass of a solid or liquid fuel, in the determination of which the water produced by combustion of the fuel is assumed to be completely condensed and its latent and sensible heat made available.
Net calorific value (NCV): The amount of heat generated by the complete combustion, under specified conditions, by a unit volume of a gas or of a unit mass of a solid or liquid fuel, in the determination of which the water produced by the combustion of the fuel is assumed to remain as vapour.
Absolute pressure The sum of the gauge and the atmospheric pressure. For instance, if the steam gauge on the boiler shows 9 kg/cm2g the absolute pressure of the steam is 10 kg/cm2(a).
Atmospheric pressure The pressure due to the weight of the atmosphere. It is expressed in pounds per sq. in. or inches of mercury column or kg/cm2. Atmospheric pressure at sea level is 14.7 lbs./ sq. inch. or 30 inch mercury column or 760mm of mercury (mm Hg) or 101.325 kilo Pascal (kPa).
Bureau of Energy Efficiency 26
1. Energy Performance Assessment of Boilers
Carbon monoxide (CO): Produced from any source that burns fuel with incomplete combustion, causes chest pain in heart patients, headaches and reduced mental alertness.
Blow down: The removal of some quantity of water from the boiler in order to achieve an acceptable concentration of dissolved and suspended solids in the boiler water.
Complete combustion: The complete oxidation of the fuel, regardless of whether it is accomplished with an excess amount of oxygen or air, or just the theoretical amount required for perfect combustion.
Perfect combustion: The complete oxidation of the fuel, with the exact theoretical (stoichiometric) amount of oxygen (air) required.
Saturated steam: It is the steam, whose temperature is equal to the boiling point corresponding to that pressure.
Wet Steam Saturated steam which contains moisture
Dry Steam Either saturated or superheated steam containing no moisture.
Superheated Steam Steam heated to a temperature above the boiling point or saturation temperature corresponding to its pressure
Oxygen trim sensor measures flue gas oxygen and a closed loop controller compares the actual oxygen level to the desired oxygen level. The air (or fuel) flow is trimmed by the controller until the oxygen level is corrected. The desired oxygen level for each firing rate must be entered into a characterized set point curve generator. Oxygen Trim maintains the lowest possible burner excess air level from low to high fire. Burners that don’t have Oxygen Trim must run with Extra Excess Air to allow safe operation during variations in weather, fuel, and linkage.
Heat transfer mediums
There are different types of heat transfer medium e.g. steam, hot water and thermal oil. Steam and Hot water are most common and it will be valuable to briefly examine these common heat transfer mediums and associated properties.
Thermic Fluid
Thermic Fluid is used as a heat transfer mechanism in some industrial process and heating applications. Thermic Fluid may be a vegetable or mineral based oil and the oil may be raised to a high temperature without the need for any pressurization. The relatively high flow and return temperatures may limit the potential for flue gas heat recovery unless some other system can absorb this heat usefully. Careful design and selection is required to achieve best energy efficiency.
Bureau of Energy Efficiency 27
1. Energy Performance Assessment of Boilers
Hot water
Water is a fluid with medium density, high specific heat capacity, low viscosity and relatively low thermal conductivity. At relatively low temperature e.g. 70oC -90oC, hot water is useful for smaller heating installations.
Steam
When water is heated its temperature will rise. The heat added is called sensible heat and the heat content of the water is termed its enthalpy. The usual datum point used to calculate enthalpy is 0oC.
When the water reaches its boiling point, any further heat input will result in some proportion of the water changing from the liquid to the vapour state, i.e. changing to steam. The heat required for this change of state is termed the 'latent heat of evaporation' and is expressed in terms of a fixed mass of water. Where no change in temperature occurs during the change of state, the steam will exist in equilibrium with the water. This equilibrium state is termed 'saturation conditions'. Saturation conditions can occur at any pressure, although at each pressure there is only one discrete temperature at which saturation can occur.
If further heat is applied to the saturated steam the temperature will rise and the steam will become 'superheated'. Any increase in temperature above saturated conditions will be accompanied by a further rise in enthalpy.
Steam is useful heat transfer medium because, as a gas, it is compressible. At high pressure and consequently density, steam can carry large quantities of heat with relatively small volume.
Bureau of Energy Efficiency 28
1. Energy Performance Assessment of Boilers
QUESTIONS
1)
Define boiler efficiency.
2)
Why boiler efficiency by indirect method is more useful than direct method?
3)
What instruments are required for indirect efficiency testing?
4)
What is the difference between dry flue gas loss and wet flue gas loss?
5)
Which is the best location for sampling flue gas analysis?
6)
Find out the efficiency by direct method from the data given below.
An oil fired package boiler was tested for 2 hours duration at steady state condition. The fuel and water consumption were 250 litres and 3500 litres respectively. The specific gravity of oil is 0.92. The saturated steam generation pressure is 7 kg/cm2(g). The boiler feed water temperature is 30o C. Determine the boiler efficiency and evaporation ratio.
7)
What is excess air? How to determine excess air if oxygen / carbon dioxide percentage is measured in the flue gas?
8)
As a means of performance evaluation, explain the difference between efficiency and evaporation ratio.
9)
Testing coal-fired boiler is more difficult than oil-fired boiler. Give reasons.
10)
What is controllable and uncontrollable losses in a boiler?
REFERENCE:
1. Energy audit Reports of National Productivity Council
2. Energy Hand book, Second edition, Von Nostrand Reinhold Company - Robert L.Loftness
3. Industrial boilers, Longman Scientific Technical 1999
www.boiler.com
www.eng-tips.com
www.worldenergy.org
Bureau of Energy Efficiency 29

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Install safety equipments for Earth leakage/Over load and Short circuit protection. Please see that wiring of your premises is done through licensed electrical contractor only as per rules. Follow up / observe all safety precautions to avoid electrical accidents. Use always ISI mark appliances, equipments, cables, wires, switches, protective devices etc. Make any construction by keeping clearance from electrical lines as prescribed in relevant act/ rules. Use proper capacity fuse wire and ensure healthy earthings at the your premises. In case of any fault / damage in our electrical lines / equipments, please inform local office immediately and don't touch any live part thereof. In case of electrical accident, turn off supply and remove person from circuit immediately. immediately. Shift person to hospital and mean while give artificial respiration and primacy treatment. Advice kids for not to climb kites from electrical lines or supports in any circumstances and to fly kites in open area away from electric lines. Keep away yourself, kids & your animals from electrical lines, supports, stays etc. Please keep yourself away from making illegal connections by "Langariya" strictly. Use rubber hand glows while work with electrical circuits / equipments. Always keep fire extinguishers in order in residential complex / commercial complex / factories. Ensure that supply is turned off in case of repairing / replacing lamps or appliances. Use separate and insulated earth wire. Keep plugs from away of children's reach. Don't keep plugs open. Please connect all appliances / equipments by 3 pin plug - sockets. Assume each circuit live until it is tested and confirmed that it is dead. Install main switch, Earth Leakage Circuit Breakers, fuses and any protective devices at easily accessible place so it can be turned off in case of any emergency. Educate your children for not to play with plugs, sockets, wires or other electrical equipments.

Don'ts .... Don'ts .... Don'ts

Don't use water for extinguishing fires in the vicinity of live electrical wiring / apparatus. Don't touch person who is in contact with live circuit but immediately cut off supply of circuit. Don't touch any electrical wires / appliances with wet hands. Don't use fuse in neutral wire. Don't overload wires / appliances. Don't insert direct wires in plug but use appropriate sockets/ pins. Don't attend any fault of our line but immediately inform our local fault center. Don't plant tree under / near electrical lines or equipments. Don't remove /damage or brake electrical lines stays, supports. Don't climb trees which are near electrical lines. Don't bind cloth hanging ropes with any electrical lines, stays, supports to avoid accidents. Don't attend any fault in your premises yourself but do it by licensed electrical contractor.

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Permits & Clearances relating to:

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- Power Evacuation transmission approvals for transmissions & distribution of power.



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To facilitate, develop & maintain relations with external agencies including:



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ABOUT CFBC TECHNOLOGY CFBC BOILER FURNACE

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Help identify the root cause of a problem.

Determine the relationship between different root causes of a problem.

One of the simplest tools; easy to complete without statistical analysis. (http://www.isixsigma.com/index.php?option=com_k2&view=item&id=1308&Itemid=200)

The“Five-Whys” are particularly useful in situations that involve human factors or interactions. They can be used outside of the Six Sigma context.



The term “Five-Whys” is not intended as a literal term. A team might need more or less than five whys to tunnel down to the root cause of a problem. When starting the process, it is important not “lead” the questioning to a preconceived “why.” (http://www.qualitytrainingportal.com/resources/problem_solving/problem-solving_tools-5whys.htm)



While the “Five-Whys” is a very useful tool, it does have some limitations. The brainstorming storming required to do “Five-Whys” is time-consuming when compared to other methods. This method can be particularly arduous for larger groups.



The results garnered from the brainstorming used in the “Five-Whys” technique may vary according to group and are difficult to reproduce. Even after the process has been followed, the root causes may not be identified. There is no means to verify that the root causes were identified. (http://www.oshatrain.org/notes/2hnotes10.html)



This post is laced with excellent resources and I have provided a link to a template that is helpful to use with this technique.



5 Whys Template

PROPERTIES OF REFRIGERANT

 Required Properties of Ideal Refrigerant:

1) The refrigerant should have low boiling point and low freezing point.

2) It must have low specific heat and high latent heat. Because high specific

heat decreases the refrigerating effect per kg of refrigerant and high latent

heat at low temperature increases the refrigerating effect per kg of

refrigerant.

3) The pressures required to be maintained in the evaporator and condenser

should be low enough to reduce the material cost and must be positive to

avoid leakage of air into the system.

4) It must have high critical pressure and temperature to avoid large power

requirements.

5) It should have low specific volume to reduce the size of the compressor.

6) It must have high thermal conductivity to reduce the area of heat transfer in

evaporator and condenser.

7) It should be non-flammable, non-explosive, non-toxic and non-corrosive.

8) It should not have any bad effects on the stored material or food, when any

leak develops in the system.

9) It must have high miscibility with lubricating oil and it should not have

reacting properly with lubricating oil in the temperature range of the system.

10) It should give high COP in the working temperature range. This is

necessary to reduce the running cost of the system.

11) It must be readily available and it must be cheap also.

Important Refrigerants:

Properties at -150C

(1) Ammonia (NH3)(R-717)

Latent heat = 1312.75 kJ/Kg

Specific volume = 0.509 m3/kg

(2) Dichloro–Difluoro methane (Freon–12) (R-12) [C Cl2 F2]

Latent heat = 162 kJ/Kg

Specific volume = 0.093 m3/kg

(3) Difluoro monochloro methane – or Freon-22 (R-22) [CH Cl F2]

Latent heat = 131 kJ/Kg

Specific Volume = 0.15 m3/kg.

The ideal refrigerant has favorable thermodynamic properties, is unreactive chemically, and safe. The desired thermodynamic properties are a boiling point somewhat below the target temperature, a high heat of vaporization, a moderate density in liquid form, a relatively high density in gaseous form, and a high critical temperature. Since boiling point and gas density are affected by pressure, refrigerants may be made more suitable for a particular application by choice of operating pressure. These properties are ideally met by the chlorofluorocarbons.




Corrosion properties are a matter of materials compatibility with the mechanical components: compressor, piping, evaporator, and condenser. Safety considerations include toxicity and flammability.



Refrigerants may be divided into three classes according to their manner of absorption or extraction of heat from the substances to be refrigerated:




Class 1: This class includes refrigerants that cool by phase change (typically boiling), using the refrigerant's latent heat.

Class 2: These refrigerants cool by temperature change or 'sensible heat', the quantity of heat being the specific heat capacity x the temperature change. They are air, calcium chloride brine, sodium chloride brine, alcohol, and similar nonfreezing solutions. The purpose of Class 2 refrigerants is to receive a reduction of temperature from Class 1 refrigerants and convey this lower temperature to the area to be air-conditioned.

Class 3: This group consists of solutions that contain absorbed vapors of liquefiable agents or refrigerating media. These solutions function by nature of their ability to carry liquefiable vapors, which produce a cooling effect by the absorption of their heat of solution. They can also be classified into many categories.

Main article: List of refrigerants

The R-# numbering system was developed by DuPont and systematically identifies the molecular structure of refrigerants made with a single halogenated hydrocarbon. The meaning of the codes is as follows:



Adding 90 to the number gives three digits which stands for the number of carbon, hydrogen and fluorine atoms, respectively.[9]

Remaining bonds not accounted for are occupied by chlorine atoms.

A suffix of a lower-case letter a, b, or c indicates increasingly unsymmetrical isomers.

As a special case, the R-400 series is made up of zeotropic blends (those where the boiling point of constituent compounds differs enough to lead to changes in relative concentration because of fractional distillation) and the R-500 series is made up of so-called azeotropic blends. The rightmost digit is assigned arbitrarily by ASHRAE, an industry organization.

For example, R-134a has 2 carbon atoms, 2 hydrogen atoms, and 4 fluorine atoms, an empirical formula of tetrafluoroethane. The "a" suffix indicates that the isomer is unbalanced by one atom, giving 1,1,1,2-Tetrafluoroethane. R-134 (without the "a" suffix) would have a molecular structure of 1,1,2,2-Tetrafluoroethane—a compound not especially effective as a refrigerant.



The same numbers are used with an R- prefix for generic refrigerants, with a "Propellant" prefix (e.g., "Propellant 12") for the same chemical used as a propellant for an aerosol spray, and with trade names for the compounds, such as "Freon 12". Recently, a practice of using HFC- for hydrofluorocarbons, CFC- for chlorofluorocarbons, and HCFC- for hydrochlorofluorocarbons has arisen, because of the regulatory differences among these groups.





R407C pressure-enthalpy diagram, isotherms between the two saturation linesR-401A is a HCFC zeotropic blend of R-32, R-152a, and R-124. It is designed as a replacement for R-12.[10]

R-404A is a HFC "nearly azeotropic" blend of 52 wt.% R-143a, 44 wt.% R-125, and 4 wt.% R-134a. It is designed as a replacement of R-22 and R-502 CFC. Its boiling point at normal pressure is -46.5 °C, its liquid density is 0.485 g/cm3.[11]

R-406A is a zeotropic blend of 55 wt.% R-22, 4 wt.% R-600a, and 41 wt.% R-142b.

R-407A is a HFC zeotropic blend of 20 wt.% R-32, 40 wt.% R-125, and 40 wt.% R-134a.[12]

R-407C is a zeotropic hydrofluorocarbon blend of R-32, R-125, and R-134a. The R-32 serves to provide the heat capacity, R-125 decreases flammability, R-134a reduces pressure.[13]

R-408A is a zeotropic HCFC blend of R-22, R-125, and R-143a. It is a substitute for R-502. Its boiling point is -44.4 °C.[14]

R-409A is a zeotropic HCFC blend of R-22, R-124, and R-142b. Its boiling point is -35.3 °C. Its critical temperatiure is 109.4 °C.[15]

R-410A is a near-azeotropic blend of R-32 and R-125. The US Environmental Protection Agency recognizes it as an acceptable substitute for R-22 in household and light commercial air conditioning systems.[16] It appears to have gained widespread market acceptance under several trade names.[17]

R-500 is an azeotropic blend of 73.8 wt.% R-12 and 26.2 wt.% of R-152a.

R-502 is an azeotropic blend of R-22 and R-115.

 Air as a refrigerant"Air cycle is not a new technology. At the turn of the century air cycle or 'cold air machines' were available from companies such as J & E Hall... These were used on board ships and by food producers and retailers to provide cooling for their food stores."[18]

Air has been used for residential,[19] automobile,[18] and turbine-powered aircraft[20][21] air-conditioning and/or cooling. The reason why air is not more widely used as a general-purpose refrigerant is the misperception that the use of air is too inefficient to be practical.[19]



Yet, with suitable compression and expansion technology, air can be a practical (albeit not the most efficient) refrigerant, free of the possibility of environmental contamination or damage,[19] and almost completely[22] harmless to plants and animals.



 

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POWER PLANT TRAINING PROGRAM

TURBINE BARRING GEAR / TURNING GEAR OPERATION


Hot turbine rotor and generator shaft is slowly rotated for uniformly cooing down rotor shafts to avoid distortion or bending. Also its operation is used when Turbine generator rotor is shut down for a prolonged period. In cold turbine periodic turning gear operation is used to rotate shaft position so that because of rotor weight hanging at bearings do not deform downwards at its centre of gravity.



Jack oil system

Turbine &Generator rotor is slightly lifted from its bearing position to reduce the starting torque requirement to rotate rotor at its initial running moment. A positive displacement pump of High pressure is used to supply oil to bearings to jack the rotor system.



Turbine Lube oil requirement

Turbine bearings are force lubricated system, in which lubricating oil is forced into the bearings to maintain lubrication requirement between static and rotating parts of bearings. Lubricating oil pump(s) are separately mounted to a lubricating oil tank which pumps oil to bearings and which is re circulated by suitable oil piping system, and its accessories. Hot oil after lubrication returns to tank which passes through a oil cooler to reduce oil temperature and again used in bearings. Suitable oil filters, suction filters, Oil injectors are the necessary arrangements to fulfill the systems certain needs of oil purifications, positive oil supply to pump suction, which is as discussed hereunder.

One oil pump (MOP) is either directly mounted or through gear arrangement at the turbine generator rotor system is used. When turbine attains its rated speed around 85% it started pumping lubricating oil in the system instead of the one placed outside(AOP), thus reducing power consumption.

As both these pump also supplies oil to Hydraulic speed control mechanism of Turbine to main Power frequency and in turn Generator Power Control system, these pumps Head development and Capacity delivered are bigger as compared to Emergency lubrication system pump(s)

Emergency Lubrication System

When in any case AC supply of the Force lubricating pump(AOP) is not available or any breakdown occurrence of the pumping unit another DC motor driven pump is used as Emergency Oil Pump which starts and starts supply of Lubricating Oil to bearings. This is an emergency measure and suitably incorporated in the system for automatic start







Over Head Oil Tank

This is also an emergency measure of Lube oil supply to bearings in which lubricating oil is continuously stored in a overhead mounted oil tank which can supply oil by gravity to bearings in case both pumps fails to supply lube oil in the rotating shaft.





Preparation of LUBE OIL SYSTEM prior to start of LUBE OIL CIRCUIT

1. Main oil tank is to be filled up with proper grade and quality of lube oil up to its optimum level as when Pump will be in service in can fill up Overhead Oil Tank also without shortfall of AOP or MOP pumping need.

2. Open Suction valve of AOP/MOP (if any)

3. Close Discharge Valve of AOP

4. Chose any one of the lube oil cooler for service by suitably opening of lube oil coolers inlet and outlet valve fully.

5. Choose any one of the duplex filter for service by suitably opening its inlet and outlet valve or changeover valve position.

6. Bearing inlet valves should be accurately opened for individual all bearings lube oil requirement, which varies.

7. Control Oil system is to be lined up by opening its isolation valve.

8 . Check all piping systems for any looseness, deformations, supporting system etc. thoroughly

9. Lineup Over head Oil tank system and its return piping circuit to bearings,

10. Open all pressure gauges impulse line, temperature gauges are working, Pressure , temperature transmitters , switches are properly working condition with all permissive, interlocks, protection circuit through DCS system.

11. Emergency Oil pump system DC Power, Battery system, Battery charger, Inverter, converter unit are healthy working condition.

10. Open Emergency DC Oil pump Suction valve

11. Close Emergency oil pump Discharge valve

12. Start Emergency Oil Pump

13. Open Discharge valve

14. After ensuring bearing oil flows are normal with pressure gauges are normal working , Pressure transmitter is showing Lube oil header pressure, Lube oil temperature are showing at local and DCS and no leakages are there, in the system.

15. Start AOP, and Open discharge valve

16. Oil header pressure will show through Local and DCS system

17. Check Overhead tank oil supply and its return.

17. All permissive are available except jack oil Pump pressure to start barring gear.

18. Line Jack oil pump discharge valves to bearings and pump discharge valve .

19. Jack Oil pump power supply is healthy

20. Start Jack oil Pump.

21. Ensure Barring Gear start permissive is available.

22. Slowly turn barring gear by hand wheel to engage its clutch mechanism and ensure Turbine freeness

23. Start barring gear, check barring current and record, Record Vibration and bearing oil pressure.

24. Main Oil temperature by adjusting cooling water supply to oil coolers. 42Deg C

TURBINE DETAILS

TURBINE BARRING GEAR / TURNING GEAR OPERATION


Hot turbine rotor and generator shaft is slowly rotated for uniformly cooing down rotor shafts to avoid distortion or bending. Also its operation is used when Turbine generator rotor is shut down for a prolonged period. Periodic turning gear operation is used to rotate shaft position so that because of rotor weight hanging at bearings do not deform downwards at its centre of gravity.



Jack oil system

Turbine &Generator rotor is slightly lifted from its bearing position to reduce the starting torque requirement to rotate rotor at its initial running moment. A positive displacement pump of High pressure is used to supply oil to bearings to jack the rotor system.



Turbine Lube oil requirement

Turbine bearings are force lubricated system, in which lubricating oil is forced into the bearings to maintain lubrication requirement between static and rotating parts of bearings. Lubricating oil pump(s) are separately mounted to a lubricating oil tank which pumps oil to bearings and which is re circulated by suitable oil piping system, and its accessories. Hot oil after lubrication returns to tank which passes through a oil cooler to reduce oil temperature and again used in bearings. Suitable oil filters, suction filters, Oil injectors are the necessary arrangements to fulfill the systems certain needs of oil purifications, positive oil supply to pump suction, which is as discussed hereunder.

One oil pump (MOP) is either directly mounted or through gear arrangement at the turbine generator rotor system is used. When turbine attains its rated speed around 85% it started pumping lubricating oil in the system instead of the one placed outside(AOP), thus reducing power consumption.

Emergency Lubrication System

When in any case AC supply of the Force lubricating pump is not available or any breakdown of the pumping unit another DC motor driven pump is used as Emergency Oil Pump which starts and starts supply of Lubricating Oil to bearings. This is an emergency measure and suitably incorporated in the system for automatic start

Over Head Oil Tank

This is also a emergency measure of Lube oil supply to bearings in which lubricating oil is continuously stored in a overhead mounted oil tank which can supply oil by gravity to bearings in case both pumps fails to supply lube oil in the rotating shaft.

Water treatment Water conditioning

Maintenance of internal and external surfaces of pressure part tubes/pipes in healthy conditions is essential to achieve high load factor and long life of any boiler. Deposition of insoluble material on internal surfaces of water and steam tubes/pipes influence heat transfer adversely and sometimes results in tube failure. Treatment of water should therefore be in its entirety that is from raw water to quality of steam in terms of impurities.


Working pressure of water and steam at different stages also significantly affect rate of reaction and solubility of chemicals used in water treatment. Higher operating pressure and temperature of boiler call for further stringent requirementand close limits of tolerance. Invariably water treatment system to ensure quality of water at feed water entry point as agreed and also take care of dosig appropriate chemicals at low pressure and high pressure in steam drum to ensure that impurities are within specified limits given in VGB or similar internationally accepted code.

Present day practice in water treatment technology suitable for the circofluid boilers generating steam at about 90 to 120 kg/cm2 G pressure and 500 deg C plus temperature is generally discussed in the following pages to serve as guidelines only.

Oxygen Corrosion Of Internal Surfaces

Carbon steel is protected by a fundamental iron water chemical reaction that forms a protective layer of magnetic iron oxide on the internal metal surfaces. A small amount of iron reacts with water unit to protective oxide film is formed. Once the film is established the film the reaction virtually stops and does not resume until the film is disturbed or removed. If the film is removed chemically or mechanically , the iron water reaction starts again to build up the protective oxide. This of course removes more iron the surface of the boiler parts and if allowed to continue will definitely thin the metal parts. It is therefore very important to maintain boiler water chemistry within close limits to prevent the chemical removal of the initial protective magnetic iron oxide film on the internal metal surfaces

The most common from of corrosion is that caused by the presence of oxygen in the water steam cycle. The most logical approach to the prevention of corrosion due to dissolved oxygen is to eliminate the entrance of oxygen to the cycle as far as possible and by expelling at the first opportunity the oxygen which has unavoidably entered the cycle.

The most common method of expelling oxygen is by de aerating the feed water from heaters to condensers.

HYDRAZINE HYDRATE AND SODIUM SULPHITE

Reation of Hydrazine with dissolved oxygen produces nitrogen and water. Even products of decomposition of hydrazine are volatile and tend to form , alkaline solutionswith water. This therefore donot increase dissolve solids content in boiler water. The reaction is of course dependant on hydrazine concentration , temperature and time. Due to the volatility of hydrazine and its decomposition at elevated temperature , only a small residual can be maintained I the boiler water. It is apparent that with this small quantity of hydrazine available only minute amounts of oxygen can be allowed to enter the boiler system.



Products of thermal decomposition at higher operating pressure of boiler are hydrogen sulphide and sulphur dioxide.. This will re dissolve at a point where condensation of steam occurs leading to acidic condition in water circuit. Hydrazine is therefore preferred as oxygen scavenger in the boiler operating in the region of 100 bars pressure.

pH Control of condensate feed water

in accordance with table 1 feed water pH should be controlled in the range of 8.5 to 9.5 to reduce iron and copper pickup in the condensate,feed water.

The most commonly used neutralizing chemicals used for controlling the pH of condensate water are Ammonia, Morpholine, Cyclohexamine, and hydrazine.

This chemicals are volatile alkalizers, which dissolved and distills with the steam and neutralize trace acids formed in the condensate. Hydrazine is included with the volatile alkalizers besides being an oxygen scavangers.It decomposes at the operating temperature of the boiler ito ammonia in accordance with the following reaction



2N2H4----------N2+H2+2NH3

Experience has shown that condensate pH, when using Hydrazine will stabilize in the range of 8.5-9.5 due to ammonia formation depending upon the residual of hydrazine maintained at the economizer inlet.

Proper pH control and selection of neutralizing chemical can only be determined by a critical study of the materials making up the condensate feed water system and on the basis of iron and copper concentration in the feed water system which would be indicative of the attackon these cycle materials.

I general a high pH due to ammonia concentration is considered more aggressive to copper bearing alloys but is more protective to carbo steel surfaces.



INTERNAL TREATMENT OF BOILER WATER

There are various methods for the internal treatment of boiler water. A blanket recommendation of any one method is not realistic. The final decision as to the type of treatment to be used in a particular boiler should be used on the raw water supply, history of condenser leakage, the percent of makeup required, the nature of the condensate returns, and other unique factors, A short summary of the recommended internal water treatment as follows

This type of treatment ivolves the addition of phosphates and caustic through the chemical feed ine to the steam drum. The caustic is added to the boiler water to maintain the pH in the range of 10.2- 11.2

The primary purpose of phosphate addition to boiler water is to precipitate the hardness constituents under the proper pH conditions. The calcium reacts with phosphates to precipitate calcium phosphate as hydroyapatite Ca10 (PO4)(OH)2. This is a flocculant tending to less adherent to boiler surfaces than simple tricalcium phosphate, which is precipitate below a pH of 10.2. also caustic reacts with magnesium to form magnesium hydroxide This precipitate is forme in presence to magnesium phosphate at a pH above 10.5 and is considered less adherent than magnesium phosphate.

At a higher pressure comparatively low phosphate residuals must be maintained in order to avoid appreciable phosphate hideout. Hideouts the term used to express the phenomenon of the partial disappearance of phosphate in the boiler wter upon increase in load and its reappearance upon load reduction. A change in phosphate concentration greater than 5 ppm as PO4 between high load and Low load is considered Hideout.