heat recovery mechanisms

8/8/2019 Heat Recovery Mechanisms

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HEAT RECOVERYMECHANISMS

IN OPEN HEARTH PROCESS

SUBMITTED BY:

GARVMANCHANDA

08108056


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OPEN HEARTH:AN OVERVIEW

It is a very old process of steel making althoughit is being used in modified forms in some of oldinstalled plants. It consists of a flat bath withlength twice its width and covered with a roof.

The two ends Are provided with ports acting asburners and exhaust alternatively. Beneath thefurnace are laid heat regenerators in the form ofchecker works. In early furnaces producer gas

was used as fuel but nowadays a mixture ofblast furnace and coke ovengas is used as theyare readily available.


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OPEN HEARTH FURNACE


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HEAT RECOVERY:INTRODUCTION Waste heat is heat, which is generated in a process by

way of fuel combustion or chemical reaction, and thendumped into the environment even though it couldstill be reused for some useful and economic purpose.The essential quality of heat is not the amount butrather its value. The strategy of how to recover this

heat depends in part on the temperature of the wasteheat gases and the economics involved.

Large quantity of hot flue gases is generated from Openhearth Furnaces. If some of this waste heat could berecovered, a considerable amount of primary fuel couldbe saved. The energy lost in waste gases cannot be fullyrecovered. However, much of the heat could berecovered and loss minimized by adopting goodmeasures


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In Open Hearth Process the effluent gases are at atemperature of 650-700 degree Celsius's it is a hightemperature heat recovery process.

In any heat recovery situation it is essential to know theamount of heat recoverable and also its usage.

The total heat that can potentially be recovered can becalculated by the formula:

Q= V*p*Cp*delTWhere

Q is the heat content in Kcal

V is the flow rate of substance in m3/hr

P is the density of flue gas in kg/m3Cp is the specific heat of the substance in Kcal/kg degC

delT is the temperature difference in degC


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BENEFITS OF HEAT RECOVERY Direct Benefits:

Recovery of waste heat has a direct effect on the efficiency of theprocess. This is reflected by reduction in the utility consumption &costs, and process cost.

Indirect Benefits:

a)Reduction in pollution: A number of toxic combustible wastes

such as carbon monoxide gas, sour gas, carbon black off gases, oilsludge, and other plastic chemicals etc, releasing to atmosphereif/when burnt in the incinerators serves dual purpose i.e. recoversheat and reduces the environmental pollution levels.

b) Reduction in equipment sizes: Waste heat recovery reduces thefuel consumption, which leads to reduction in the flue gas produced.

This results in reduction in equipment sizes of all flue gas handlingequipments such as fans, stacks, ducts, burners, etc.

c)Reduction in auxiliary energy consumption: Reduction inequipment sizes gives additional benefits in the form of reduction inauxiliary energy consumption like electricity for fans, pumps etc..


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DEVELOPING THE HEAT RECOVERY SYSTEM

The flue gases emitting from Open Hearth

processes contain large amount of heat in them.The higher the temperature, the greater thepotential value for heat recovery.

Economic evaluation of heat recovery system:

It is necessary to evaluate the selected waste heatrecovery system on the basis of financial analysissuch as investment, depreciation, payback period,rate of return etc. In addition the advice of

experienced consultants and suppliers must beobtained for rational decision.


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COMMERCIAL HEATRECOVERY SYSTEMS

Recuperators :In a recuperator, heat exchange

takes place between the flue gases and the air

through metallic or ceramic walls. Duct or tubes

carry the air for combustion to be pre- heated,

the other side contains the waste heat stream. Arecuperator for recovering waste heat from flue

gases is shown


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Regenerator :The Regeneration which is preferable forlarge capacities has been very widely used in steelmelting furnaces. Important relations exist between the

size of the regenerator, time between reversals,thickness of brick, conductivity of brick and heat storageratio of the brick.

In a regenerator, the time between the reversals is animportant aspect. Long periods would mean higher

thermal storage and hence higher cost. Also long periodsof reversal result in lower average temperature ofpreheat and consequently reduce fuel economy.Accumulation of dust and slagging on the surfacesreduce efficiency of the heat transfer as the furnace

becomes old. Heat losses from the walls of theregenerator and air in leaks during the gas period andout-leaks during air period also reduces the heat transfer.


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A GAS REGENERATOR AND A CONVECTIVE RADIATIVE RECUPERATOR


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CONCLUSION The waste flue gases that comes out of open hearth

processes have a large potential calorific value which ifutilized properly can reduce our raw materials need to

a large extent as well as will reduce the pollution .But

the methods used should be used implied according to

various conditions like temperature of effluent gases,

Upset conditions occurring in the plant due to heat

recovery, Any other constraint, such as dew point

occurring in an equipments etc.Economic evaluation of

the process should also be considered. The various

recovery devices which can be adopted are:


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Recuperators

Regenerators

Heat wheels

There are also some other devices used

according to temperature and state of waste .


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THANK YOU

SUBMITTED BY:-GARV MANCHANDA

08108056

heat recovery mechanisms

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