4.material and energy balance

7/28/2019 4.Material and Energy Balance..

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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

4.material and energy balance

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