Burners and combustion system for the reheat furnaces for small and medium rolling mills

Appeal to All
those Flaring
BFG!
Please rethink in High Fuel cost & Global
Warming era on need of Burners and Combustion system
for the reheat furnaces for small and Medium Rolling mills using
Lean fuels ( PG/BFG) & Rich Fuels ( Heavy Oil or NG) in
Combination Firing.
The Fuel costs are rising at much faster rate at this moment and it’s already at peak
and threatening to break records in near future.

Blast Furnace Gas (BFG) cum 1
FO/LDO combination firing at work on 65
TPH walking beam furnace. Photo Nov. 2002

&/or

Though coal costs are also rising still use of Producer gas as Industrial fuel is becoming
very popular in coal belt of INDIA.

There many plants in INDIA where they have small and Medium Blast furnaces and
their power plant projects have not come up to use BFG as fuels and hence they are
Flaring the gas.

Let’s look at what Customer (user) of Reheat furnace wants for smother
operation.

1. Uniform Soaking so that the rolling mill has no trouble and can ramp
up production to its maximum capacity at a short notice.

2. Less scale loss

3. Reliability

4. Fuel Economy.

5. Fuel flexibility when any one of the fuel is not available.

How does one achieve the above:

1. Provide adequate soaking time and also have uniform temperature
in each zone across the width / length of Charge ( Billet/ Slab)and


also have combination/ simultaneous firing capability of Rich and
lean fuels.

2. Minimise the Excess air. Control Oxygen at hearth level of ~3.5 %.

3. Use proven technology and manufacturers or else back up with
bigger supply chain of cheaper spare parts producer.

4. Do excellent excess air control over varying load &Heat as late as
practical.

5. Have all burners to fire both fuels.
What looks very easy from Theory given above is most challenging because of
following specialties of Rich Fuel (Furnace Oil) and Lean Gases ( Producer Gas or BFG).

a) Flame Temperature ( Adiabatic) of Only furnace Oil flame is ~2100 Deg C,
Flame Temperature ( Adiabatic) of Only Blast Furnace Gas flame is ~1250 Deg C &
Flame Temperature ( Adiabatic) of Only Producer Gas flame is ~1650 Deg C


b) This flame Temperature variation has serious effect on Uniform heating in soaking
zone, heating zone and has not any serious ill effect in preheating zone.

c) The Flue gas produced For One Tone charge heating in typical Reheat furnace
( 40 Liters/ Ton or 355120 Kcal/ Ton) by using Furnace Oil is ~ 545 Kg and by
Using Producer Gas is ~ 630 Kg/ Hr, which is 16% higher.

d) The Flue gas produced For One Tone charge heating in typical Reheat furnace
( 40 Liters/ To or 355120 Kcal/ Ton) by using Furnace Oil is ~ 545 Kg , by Using

Blast Furnace Gas is ~ 922 Kg/ Hr, which is 70% higher and in required
combination firing of BFG cum FO it is ~771 Kg/ Hr, which is over 40 % Higher.

e) Though our Pusher type conventional furnaces are liberally designed by
makers / Technocrat, its combustion air ductings, Recuparators and Flue Gas
ductings are very ambitiously designed (Read Grossly Undersized for COST of
Fabrication). Debottlenecking these areas is a very special challenge we need
to address case to case basis.

f) It’s just not saving Fuels / Environment but also avoiding Excessive Power use in

Its lot simple in a running plant to imagine that we will retain existing burners and
Combustion system (After all its given us the results for long time and we have spent
our Hard earned money in buying and Installing it) & only add up few Gas burners of
Equivalent capacity to give us ability to work on Gas or Oil and also Gas and Oil.

In the last decade may such retrofits have happened and the user and OEM’s have
realized the following:

• It did save lot of Capital Cost and also allowed use of any fuel.

• They did not have problems at running at lower tonnages on Gas firing (Largely
front fired system) but when they needed to Pickup load or run at peak
capacity they could not control the Oil consumptions.


• Rolling was not that easy!

What they experienced was not felt by couple of 10 /18 TPH Pusher Furnace users in
East India while using the Blast Furnace Gas ( Much leaner than producer Gas) and
used less than 15 Ltiers Furnace per Ton of Rolled steel , remaining heat coming from
BFG which they were flaring earlier. What was differently done by them is as follows:

• Use Combination firing burners at all locations – Reason: Uniform Temperature as
required in soak zone and also use of all fuels.

• Quick pick up like oil firing, still very low oil consumptions.

• Smooth Rolling- Leading to Power and spares saving.

Lest look at the way Steel is heated in Pusher Furnaces by way of Heating Curve.


The criticality is about heating uniformly in Soaking Zone and Heating Zone . With 4 or
six burners firing in Soaking Zone can we have Few Flames with Peak Temperature of
~2100 Deg C and Some Flames of ~1250 Deg C or ~1650 Deg C. The Industry tries to
convince itself of Uniform heating of the Billet with these Temperature Variations?


You will agree that the Billet is going to be heated with much larger Delta T /
Temperature Differential across its Length and also across its cross section.

Not having capacity to use Combination firing in which lean fuels gives most of the
energy to the Flame and only very little Rich Fuel ( That Too If Required) adding up the
Heat and also Boosting the Flame Temperature of Complete Envelop of Flame ensures
that you get required heat transfer ( Read as ease of heating) and also ensures that
Rich and costly fuel use is minimized.

Not doing combination firing and believing that PG and Oil flames are same is like
saying Sun and Moon Give same Heat to Earth.

Well many users/ OEM’s make you believe that its possible and they have been doing
this for years. Why not – They must be burning their midnight oil for doing the simplest
thing.

Attached illustration shows How Flame coverage (Obviously Uniform Temperature
Flames) is vital for Heating Steel.


We can easily conclude that over 10 Furnace users and couple of OEM’s in INDIA
have given the advantage of Combination firing to their furnaces and have benefited
immensely!

This short brief will encourage more and more customers to evaluate the short term
benefits verses Long term issue and help them to be the champion of eradicating
Issue of Global Warming by doing their bit for the generations of future!!

Happy working on preventing pollution (Which pays you back in tons) and preserving
the environment!!!


Burners and combustion system for the reheat furnaces for small and medium rolling mills

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