4.material and energy balance
TRANSCRIPT
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Material and EnergyBalance
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SyllabusMaterial and Energy balance:
Facility as an energy system
Methods for preparing process flow
Material and energy balance diagrams.
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Purpose of material and energy balance
To Assess the input, conversion efficiency, outputand losses
To quantify all material, energy and waste streams
in a process or a system To find out the difference between
calculated/designed values and measured/actualvalues thereby making it possible to identifypreviously unknownlosses and emissions
Powerful tool for establishing basis forimprovement and potential savings
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Sankey Diagram and its Use
Useful tool to represent input and output energy flow in any energy equipment or
system Visual impact on input and output losses to enable energy managers to focus on
solutions
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Flow charts
Inputs ofthe processcould include raw materials, water, steam, electricity
Process Steps should be sequentially classified
Wastes / by products could include solids, water, chemicals, energy
Output of the process is the final product produced in the plant.
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Facility as an Energy System
Raw material
Energy Facility Production Facility
Transformer
DG Set
BoilersChillers
Water Supplies
100%
Energy
Input
100%
Heat
Output
Product
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Boiler Plant System
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Cooling Tower & Cooling Water Supply System
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Guidelines for material and energy balance
While splitting up the total system, choose, simple discrete sub-systems.
Choose material and energy balance envelope such that, the number ofstreams entering and leaving, is the smallest possible.
The measurement units may include, time factor or production linkages.
Consider a full batch as the reference in case of batch operations.
It is important to include start-up and cleaning operation consumptions (of
material and energy resources (M&E).
Calculate the gas volumes at standard conditions.
In case of shutdown losses, averaging over long periods may benecessary.
Highlight losses and emissions (M&E) at part load operations if prevalent.
For each stream, where applicable, indicate energy quality (pressure,temperature, enthalpy, Kcal/hr, Kw, Amps, Volts etc.).
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Example/ Formula
i) Energy Supplied by Combustion: Q =Fuel consumed x Calorific value
ii) Energy Supplied by Electricity: Q = kWh x 860 kCals
Where, Q = thermal energy flow rate produced by electricity(kJ/h)
iii) Continuity Equation
A1V1 = A2V2v1 v2
where, V is the velocity in m/s , v is the specific volume in m3/kg andA is the cross sectional area of the pipe in m2.
iv) Heat addition/rejection of a fluid = mCp diffTemp
where, m is the mass in kg, Cp
is the specific heat in kCal/kg, DiffTempis the difference in temperature in k
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M & E Calculation Procedure
Clearly identify the problem to be studied.
Define a boundary that encloses the entire system or sub-system to be analysed.Entering and leaving mass and energy flows must be measured at the boundary.
The boundary must be chosen in such a way that:
All relevant flows must cross it, all non-relevant flows being within the
boundary.
Measurements at the boundary must be possible in an easy and accurate
manner.
Select an appropriate test period depending on the type of process and product.
Carry out the measurements.
Calculate the energy and mass flow.
Verify an energy and mass balance. If the balances are outside acceptable limits,
then repeat the measurements.
The energy release or use in endothermic and exothermic processes should be
taken into consideration in the energy balance
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Example:Heat Balance in a Boiler
Heat loss due to dry flue gas
Heat loss due to radiation &
other unaccounted loss
Steam Boiler
Dry Flue Gas Loss
Heat loss due to hydrogen in fuel
flue gas
Heat loss due to moisture in fuel
Heat loss due to unburnts in residue
Heat loss due to moisture in air
12.7 %
8.1 %
1.7 %
0.3 %
1.0 %
73.8 % Heat in Steam
100 %
Fuel
2.4 %
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Mass Balance in a Cement Plant