This document discusses energy management and control in boilers and fuel-fired systems. It covers topics such as boiler efficiency calculations, mass and energy balances, waste heat recovery, and energy conservation measures. Boilers and furnaces consume substantial amounts of energy to produce steam or heat industrial processes. Proper energy management is important to maximize efficiency and minimize costs. Various calculations can be performed around boiler inputs/outputs and properties to determine efficiency. Waste heat recovery and reducing excess air are effective ways to improve efficiency.

1. Energy Management & Control
in BOILERS & Fuel FIRED SYSTEMS
Boilers and fuel fired systems are widely used in industries but
consume substantial energy.
• Almost two-thirds of the fossil-fuel based energy consumed in boiler,
furnace, or other fired system,
• Energy produced during combustion of coal, fuel oil, and natural gas.
• Energy from nuclear; hydroelectric and geothermal are safe and
environment friendly.
• Mostly electric energy is produced using fuel-fired boilers.
• Unlike many electric systems, boilers and fired systems are not
inherently energy efficient.
• Energy Conservation measures include load reduction, waste heat
recovery, efficiency improvement, fuel cost reduction, and other
energy saving opportunities, and other issues related to day-to-day
operations.

2. Assumptions
•Boiler efficiency = Ratio of useful heat output to the total energy input.
•Boiler efficiencies vary from 60 to 90%, for the best solid biomass fuel boilers
•Deaerator provides feedwater free of air at its B.P. i.e., (Saturated Liquid)
and ~ 70 to 95% for oil and natural gas-fired boilers,
•Boiler efficiency = {boiler output (in BTUs) divide by boiler input (in BTUs)} x 100 .
•Temperatures and flow rates of input and output of the boiler are measured to calculate
the fuel-to-steam efficiency.
•Steam, Boiler, and Blowdown Pressure are the same.
•Combustion Efficiency = %age ratio of fuel energy, directly gained by feedwater to the
total energy supplied by the fuel.
•Blowdown Rate = %age ratio of incoming feedwater mass flow rate to rate saturated
liquid leaves the boiler at boiler pressure.
•Boiler efficiency depends upon boiler configurations & fluctuations in operation.
•Energy from motors (pumps, fans, etc.) are not considered.
•Boiler and fuel types are not considered
Calculation of the amount of fuel energy required to produce
steam in Boiler

3. •Using the Steam properties for heat :
Feed water Energy Flow = Specific Enthalpy * Mass Flow
Calculation Details
Step 1: Determine Properties of Steam Produced
•Using the Steam properties at Steam Pressure and (Temperature, Specific Enthalpy, Specific
Entropy, i.e. the Quality of steam).
•Steam Energy Flow = Specific Enthalpy * Mass Flow
Step 2: Determine Feed water Properties and Mass Flow
i. The feed water flow rate can be calculated from steam mass flow and blowdown rate :
ii. Blowdown Mass Flow = Feedwater Mass Flow * Blowdown Rate
iii. Steam Mass Flow = Feedwater Mass Flow - Blowdown Mass Flow
iv. Steam Mass Flow = Feedwater Mass Flow - Feedwater Mass Flow * Blowdown Rate
v. Feedwater Mass Flow = Steam Mass Flow / [ 1 - Blowdown Rate ]
Calculation of the amount of fuel energy required to produce
steam in Boiler

4. Step 3: Determine Blowdown Properties and Mass Flow
i. Using the calculated feed water mass flow and blowdown rate:
ii. Blowdown Mass Flow = Feedwater Mass Flow * Blowdown Rate
iii. The Specific Enthalpy is then multiplied by the Mass Flow to get the Energy Flow :
iv. Blow down Energy Flow = Specific Enthalpy * Mass Flow
Step 4: Determine Boiler Energy
•Boiler Energy = Steam Energy Flow + Blowdown Energy Flow - Feedwater Energy Flow
Step 5: Determine Fuel Energy
•Fuel Energy = Boiler Energy / Combustion Efficiency
Calculation of the amount of fuel energy required to produce
steam in Boiler

5. .
Performance test of boilers
• Several efficiencies are determined to test the performance of boilers and
fired systems.
• The basis for testing boilers is the American Society of Mechanical
Engineers (ASME) Power Test Code 4.1 (PTC-4.1-1964.)
• Two primary methods are used to determine efficiency, i.e.,
i. The input- output method, as gross thermal efficiency
ii. The heat-loss method, as “net” efficiency.
• These efficiencies include the additional energy utilized by auxiliary
equipment such as combustion air, fans, fuel pumps, stoker drives, etc. For
more information Taplin 1991.
• Combustion efficiency, like the heat losses due to the exhaust gases by
analyzing the composition of the exhaust gases, i.e., raw unburned fuel,
(CO2), (CO), (O2), N2 and other gases like NOX and SOX in the exhaust
gases depending upon %age of excess air supplied.
• Excess air is the amount of air above that is theoretically required for
complete combustion.

6. Boiler Efficiency : It is a combined result of efficiencies of different components of a boiler.
• A boiler has many sub systems whose efficiency affects the overall boiler efficiency.
• Couple of efficiencies which finally decide the boiler efficiency are-
1.Combustion efficiency
2.Thermal efficiency
• Combustion Efficiency
i. The combustion efficiency of a boiler, indicates burner’s ability to burn fuel.
ii. The two parameters which determine the burner efficiency are unburnt fuel quantities in exha
with excess oxygen.
iii. As the amount of excess air is increased, the quantity of unburnt fuel in the exhaust decrease
but decreases temperature.
iv. It is important to maintain a balance between enthalpy losses and unburnt losses.
v. Combustion efficiency is higher for liquid and gaseous fuels than for solid fuels.
• Thermal Efficiency
• This efficiency specifies the effectiveness of the heat exchanger of the boiler which actually
transfers the heat energy from fireside to water side.
• Thermal efficiency is badly affected by scale formation/soot formation on the boiler tubes.
• Boiler Efficiency does not include,
i. Any complex boiler configurations or fluctuations in operation.
ii. Energy consumed by the motors (pumps, fans, etc.).

7. Direct efficiency of boiler
Direct efficiency can be calculated using the basic efficiency formula-
η=(Energy output)/(Energy input) X 100
η = [Q (H-h)/q*GCV]*100
Where,
Q= Quantity of steam generated (kg/hr)
H= Enthalpy of steam (Kcal/kg)
h= Enthalpy of water (kcal/kg)
GCV= Gross calorific value of the fuel.
Indirect Efficiency
• The indirect efficiency of a boiler is based on the sum of individual
losses occurring from a boiler and subtracting the sum from 100%.
• All the measurable losses of a boiler include stack losses, radiation
losses, blowdown losses etc.
• This method may be implemented as the norms provided in BS845
standards.

8. Boiler Energy Consumption Calculations
• Boiler and other fired systems, e.g., furnaces and ovens,
combust fuel with air to releasing the chemical heat energy.
• To produce industrial ingredients, raw materials are heated to
initiate & to continue chemical reaction / process,
• The manufacturing process, may generate high-temperature
high-pressure steam which can be used to operate turbines to
generate electric power,
• The energy consumption of boilers, furnaces, and other fire
system is a function of load and efficiency, can be expressed as
under :
• Energy consumption = ∫ (load) × (1/efficiency) dt (1)

9. • Energy consumption = ∫ (load) × (1/efficiency) dt (1)
• Operating cost of a boiler or fired system can be determined as:
Energy cost =[ ∫ (load) × (1/efficiency) × dt ] (fuel cost) (2)
• The equations 1 and 2 are not accurate because the controlling
variables depend upon many other factors.
i. Load varies as a function of the process being supported.
ii. The efficiency varies w.r.t. load, time, weather and quality of fuel
iii. The cost may also vary due to geo-political circumstances,
• To reduce energy consumption, either reduce the load, or increase
combustion efficiency, or reduce the unit fuel energy cost, or combinations
of various options.
• Mass and energy balance presents all the data needed to design a unit or system.
• The total amount of mass and energy used and the relative contribution and indicate
each source and control the whole economy and for each individual consumption.

10. • Material and energy balances are very important in industrial
processes for the management to maximize product yields and
minimize costs
• Balance is based on fundamental laws, i.e., mass can neither be produced
nor destroyed that is, mass is conserved.
• Equally fundamental is the law of conservation of energy. Although energy
can change in form, it can not be created or destroyed
• The increasing availability of computers has meant that very
complex mass and energy balances can be resolved and manipulated
,
Importance of mass and energy Balance

11. Balance Equations
• Balance equations are used to analyze the process to determine inputs
and outputs to a system.
• Different types of balance equations are used in analysis of a boiler or
fired-system, e.g., heat balance and mass balance.
Heat Balance
• A heat balance is based on all sorts of heat energy enters and leaves a
system, assuming that
i. energy can neither be created or destroyed,
ii. Sum of input energies = sum of all output energies.
• In a simple furnace system, energy enters due to combustion air, fuel, and
mixed-air duct.
• Energy input includes condensate return, make-up water, combustion
fuel, and primary and secondary air supply.
• Energy output includes steam blowdown, exhaust gases, thermal losses ,
e.g., radiative, convective & conductive losses, ash, and other discharges
depending on the complexity of the system.

12. Mass Balance
• Mass balance is a fundamental step to find input and output quantities, combustion
efficiency and optimum air-to-fuel ratio.
• Mass balance is conducted to determine;
i. Rate of input and output of air, fuel and excess air.
ii. Water balance (steam, condensate return, makeup water, blowdown, and
feedwater.)
iii. Balance of total dissolved solids, or other impurity.
iv. Stoichiometric or chemical balance
• For complex systems, the mass and energy balance equations can be solved
simultaneously e.g., multiple equations can be solved , if equal number of unknowns.
• Such analysis helps to determine blowdown losses, waste heat recovery
potential, and other inter-dependent opportunities of energy savings.

13. Energy Conservation Measures
• Energy cost reduction opportunities can generally be classified in the
following categories:
i. Reducing load, increasing efficiency, and reducing unit energy cost.
ii. As with most energy conservation and cost reducing measures there are
also a few additional opportunities which are not so easily categorized.
iii. Table1 lists several energy conservation measures are cost effective in
various boilers and fired-systems.
KEY ELEMENTS FOR MAXIMUM EFFICIENCY
There are several opportunities for maximizing efficiency and reducing
operating costs in a boiler or other
fi red-system as noted earlier in Table 5.1. This section examines
in more detail several key opportunities for energy
and cost reduction, including excess air, stack temperature,
load balancing, boiler blowdown, and condensate
return.

14. Load Reduction Techniques
Insulation
i. —steam lines and distribution system
ii. —condensate lines and return system
iii. —heat exchangers
iv. —boiler or furnace
Repair steam leaks
• Repair failed steam straps
• Return condensate to boiler & repair condensate leaks
• Reduce boiler blowdown and flash steam losses.
• Improve feedwater and make-up water treatment
• Auto-Shut off boilers during long periods of no use
• Reduce Install stack dampers or heat traps in natural draft boilers
• Replace continuous pilots with electronic ignition pilots

15. Waste Heat Recovery (a form of load reduction)
 Utilize flash steam, if possible,
 Preheat feedwater and make-up with an economizer
 Preheat combustion air with a recuperator
 Recover flue gas heat to supplement supply of hot water, or for
space heating & to preheat boiler feed or make-up water
 Install a heat recovery system on incinerator or furnace
 Install condensation heat recovery system
i. indirect contact heat exchanger
ii. direct contact heat exchanger
Flash steam - the steam formed from hot condensate, when the pressure is reduced.

16. Efficiency Improvement
• Reduce excess air , just provide sufficient air for complete combustion.
Install combustion efficiency control system
i. Constant excess air control
ii. Minimum excess air control
iii. Optimum excess air and CO control
Optimize loading of multiple boilers
• Shut off unnecessary boilers
• Install smaller system for part-load operation
i. —Install small boiler for summer loads
ii. —Install satellite boiler for remote loads
Install low excess air burners
• Repair or replace faulty burners and replace natural draft burners with forced
draft burners
• Install firetube boilers or more efficient boiler, high-efficiency pulse
combustion, or condensing boiler.
• Clean heat transfer surfaces to reduce fouling and scale

17. WASTE HEAT RECOVERY
• Waste heat is heat that is produced by a machine, or
other process that uses energy, as a byproduct of doing
work e.g., heat from air conditioning machinery,
• Sources of waste heat include for example
i. hot combustion gases discharged to the atmosphere,
ii. Heat released from hot water flowing through pipes
into environment,
iii. Heat lost by the hot products exiting industrial
processes,
iv. heat transfer from hot equipment surfaces

18. Fuel Cost Reduction
• Switch to cheaper utility rate schedule,
• Fuel switching
i. switch to alternate or sustainable fuel resources,
ii. install multiple fuel burning capability,
iii. replace electric boiler with a fuel-fired boiler.
Switch to a heat pump
• use heat pump for
i. supplemental heat requirements
ii. baseline heat requirements
Other Opportunities to conserve energy.
• Install variable speed drives wherever needed.
• Replace boiler with alternative heating system
• Replace furnace with alternative heating system
• Install more efficient combustion air fan and its motor
• Install more efficient feed water pump and its motor
• Install more efficient condensate pump and its motor

19. WASTE HEAT RECOVERY
• Waste heat recovery - the process of “heat integration”, to reusing
heat /energy that is uselessly disposed-off or simply released into the
atmosphere.
• By recovering waste heat, plants can
i. reduce operational costs,
ii. CO2 and other emissions,
iii. Simultaneously increase energy efficiency.

20. INTRODUCTION WASTE HEAT RECOVERY
• A valuable approach to improve overall energy efficiency
by recovering or reusing "waste heat" in industrial
production
• Recovering waste heat (i.e. a cost free source of energy)
improves economic feasibility.
R&D develops technologies to optimize operational cost by;
i. utilizing heat recovery opportunities,
ii. maximize the heat recovery prospects,
iii. minimizing constraints to recover heat,

21. • Waste Stream Composition
i. Although chemical compositions do not directly influence the
quality or quantity of heat recovery process,
ii. Chemical composition of off gases/liquids may affect, design of
heat recovery system, material selection, operational costs.
iii. Flue gases may contain CO2, NOX, SOX, sulfates minerals, water
vapor, un-oxidized organics, and organic volatile chemicals,.
iv. To prevent chemical corrosion, exhaust temperatures should be
above the dew point temperature.

22. • Sources of waste heat ( e.g., combustion exhausts,
process exhausts, hot gases from drying ovens, cooling
tower water)
• Recovery Technology (e.g., regenerator, recuperator,
economizer, waste heat boiler, thermo-electric generator)
• End use for Recovered Heat (e.g. preheating boiler feed
water, raw streams, heating air for combustion, space
heating and supply of hot water etc.)

23. Thermo-economic optimization via waste
heat recovery
• Thermo-economics optimization- combined effect of
i. thermodynamic principles
ii. economic analysis,
• The process engineers must have to minimize cost by,
i. design, and maintenance of processes.
ii. to reduce thermodynamic in-efficiencies.

24. WASTE HEAT CAPTURING
• Capturing and utilizing waste heat from any source for economic benefits and to
reduce carbon footprints,
• A carbon footprint is the total amount of greenhouse gases (including carbon dioxide and
methane) that are generated by our actions.
• The average carbon footprint for a person in the United States is 16 tons, one of the highest
rates in the world. Globally, the average carbon footprint is closer to 4 tons.
• Usually, the bulk of an individual's carbon footprint will come from transportation, housing and
food.
• GHGs include CO2 (mostly emitted by humans and combustion of bio-masses,
• GHGs also include methane, nitrous oxide, and fluorinated gases, which trap heat in the
atmosphere, causing global warming.

25. • Identification of energy source (chemical, electrical,
mechanical, and etc.)
• Waste heat is used to produce steam for steam powers
plants to operate turbine for power generation, called
combined cycle system,
• Exhaust gas heat, temp. in range of 250°C-350°C from a
boilers & other biomass burners, (can be used to generate
electricity.)
• Power generation without additional fuel burring to save
energy.
Opportunities of WHR

26. • To calculate boiler efficiency, use the following
formula,
• waste heat boiler thermal efficiency.
η= 100 - (q2+q3+q4+q5+q6),
q2 flue gas losses, q3 gas incomplete combustion losses,
q4 - incomplete combustion losses, q5 heat radiation
losses and q6 slag ash physical losses.
Calculation Of Boiler Efficiency

27. Exhaust
gas heat
Waste
heat

28. Waste heat recovery (WHR) System
WHR is composed of heat recovery
component,
1. Heat recovery from combustion gases
through Recuperator.
2. Steam flow control & instrumentation
3. Electric generation and distribution
WHR systems are generally classified
into three groups based on the source
temperature,
• High (greater than 650°C)
• Medium (between 230 and 650°C)
• Low (less than 230°C
Regenerators and recuperators
• Heat exchange systems to recover heat by cycling
through heat sinks (regenerators) or through a high
temperature metallic heat exchanger (recuperators).
• Heat recovered by a regenerator or recuperator is
mostly used to preheat combustion air to a furnace.

29. METHODS TO RECOVER WASTE HEAT
Two different setups:
(1) Direct heat exchange between the waste heat source and
heat receiver;
(2) Integrating loop of heat transfer fluids to transfer
of heat from the waste heat site to utility point,

30. Factors Affecting Waste Heat Recovery Feasibility
• Heat quantity,
i. The quantity of waste heat is a function of both the temperature and
the mass flow rate of the stream,
ii. Although the quantity of waste heat available is an important
parameter, but waste heat quality is also important,
• Heat temperature/quality,
i. Temperature is a key factor to determine waste heat recovery
feasibility.
ii. The best ranges of temp. for cooling water are 40 – 90°C and flue gases
from glass melting furnaces may be up to 1,300°C.

31. Waste heat recovery (WHR) in cement plants,
• The heat recovery steam generator (HRSG) is a complex system to recover waste heat
from the exhaust of steel, iron, food, ceramic and cement industries.
• Heat recovery consists of various equipment, e.g., evaporator, super heater, economizer
and steam drum,
• The heat generated in the rotary kiln preheater (PH) and AQC (air quenching
cooler) exhaust hot gases are used to generate power.
• The potential of power generation is 25 KWh/ton to 45 KWh/ ton of clinker
production.
• Emerging technologies regarding direct use of heat for power conversion i.e.,
thermo-electric, piezo-electric, thermionic, and thermo-photo voltaic (TPV) power
generation techniques are under investigation.
• The functionality and usage of all technologies have many advantages and
disadvantages are to be evaluated before commercialization.

35. • Minimum allowed temperature,
i. The minimum temperature of waste heat influences the rate of
heat transfer between a heat source and heat sink, which
significantly effects recovery feasibility.
ii. The expression for heat transfer can be generalized by the
following equation: Q =U A ( LMTD) (W or Btu/s)
• Operating schedules, availability, and other
logistics
i. Estimation of benefits from WHR on the bases of operational
schedules.
ii. WHR system exergy efficacy based upon logistics and other
dependent and independent variables.

36. Waste Heat Recovery during Refrigeration cycle

37. Waste Heat Recovery Technologies
1. Recuperators:
 Suitable for annealing ovens, melting furnaces, incinerators and
radiant tube burners,.
 Recuperators are designed considering Heat Transfer occurs due
to radiation, convection,
 Recuperators can operate for the temperature range from 1,500 ºC
950 ºC.
2. Regenerators:
 Regenerators are frequently used with glass furnaces, coke ovens,
steel open hearth furnaces,.
 Regenerators recover heat released during combustion of gases /
biomass fuel.
 Regenerator are suitable for high temperature applications with
dirty exhausts.
 One major disadvantage is the large size and high capital cost, as
compared to recuperators

38. 3. Heat Wheels (Rotary Regenerator)
 Hot and cold gases flow through the regenerator alternatively.
 A rotating wheel is placed between two parallel ducts, one
contains hot waste gases and other contains cold gases

39. 4. Passive Air Preheater:
• Passive air preheaters are gas to gas heat recovery devices
for low to medium temperature.
• Applications include ovens, steam boilers, gas turbine
exhaust, secondary recovery from furnaces, and etc.
Two types of Passive preheaters
i. Plate type
ii. Heat pipe.
Consists of multiple
parallel plates which
separate the channels
for hot and cold gas
streams.
i. Plate type

40. 2. Heat Pipe Heat Exchanger- The heat pipe is a heat exchanger
consists of several pipes, sealed on both ends.

41. • Used to recover heat
from low to medium
temperature exhaust
gases for heating
liquids.
• Suitable to preheat
boiler feed water, hot
process liquids / water,
space heating.
5. Economizers /Finned Tube Heat Exchangers

42. • Water tube boilers are
suitable for medium to high
temperature exhaust gases
to generate steam.
• Capacity of waste heat boiler
depends on quantity and
quality of available heat.
• The steam can be used for
process heating or for power
generation.
6. Waste Heat Boilers

43. Low Temperature Energy Recovery Options and
Technologies
• High grade heat: temperature is higher than 650 °C,
• Medium Grade Heat: temp. ranges between 450°C to 650 °C,
• Low grade heat: temp. in between 150-300°C.
(Recent studies indicates about 66% low-grade waste heat is used )
• Utilization of low grade waste heat makes the processes cost
effective in industrial facilities.
• The indirect benefits are reduction in environmental pollution,
reduction in the consumption of energy for auxiliary uses and
reduction in the equipment sizes.
• WHRDs reduce the fuel consumption, which leads to
reduction in the production cost.

44. Challenges to Recover Low Temperature Waste Heat
Corrosion of the heat exchanger surface:
• Waste heat sources i.e. exhaust gases, liquids may foul the heat
transfer surfaces.
• The heat exchanger must be designed to avoid corrosive deposits
using advanced / special materials
Optimize heat transfer surfaces:
1. H.T. rate is function of “K” of the material of construction H.EX.
and ΔT i.e. temperature difference between the two streams
on each side of the heat transfer surface.
• If ΔT is low, either larger surface area will be required or material
should be selected having higher value of “K”.
Utilize low temperature heat:
• Recovering heat from low temperature streams may become
uneconomical,
• Potential end uses include domestic hot water, space heating, and
low temperature process heating.

45. Benefits of WHR
Reduction in pollution:
• WHR recovery reduces the environmental pollution levels due to
low toxic gases e.g. carbon monoxide, NOX, SOX, etc. because of
less burning of fuels.
Trade-off pay backs:
• WHR may outweigh the benefit gained in heat recovered due to
cost offset.
• Design and development of WHR systems enhance capital cost
but heat recovery significantly reduces operational cost.
Reduction in auxiliary equipment:
• Additional benefits in the form of reduction in auxiliary
equipment like electricity for fans, pumps, blowers etc.
Resource Conservation
• Precious resources are utilized efficiently and can be conserved
for future.
• WHR system eliminate the necessity of additional resource of
energy.
• WHR positively contributes to conserve energy resources.

47. Complex Engineering Problem
• Design Optimization of Waste Heat Recovery System around Cement
Rotary Kiln
• Optimal Sizing of Waste Heat Recovery Systems for Dynamic Thermal
Conditions.
• Cascade energy optimization for waste heat recovery in distributed
heat exchange systems
• Waste heat recovery emerging technologies and applications.