evaporative waste gas colling
DESCRIPTION
energy recoveryTRANSCRIPT
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Utilization of vaporation
Waste as ooling Systems
to ounteract Rising
nergy osts
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T
oday's primary sources of energy are oil, coal,
natural gas and nuclear. Fossil fuels like oil, natural
gas and coal represent almost 8.5 of the energy con-
sumption in the world. Renewable energy like hydro,
In conventional waste gas cooling plants,
the absorbed heat is emitted unused into
the atmosphere. This steam can be used for
various applications, such as steel degassing
or heat and power generation. Integrating
evaporation cooling plants into steel works
reduces costs and preserves natural resources.
wind, solar, biomass and nuclear energy account for the
remainder.
As we know, we depend on - and will continue to
depend on for many years to come - fossil fuels as
energy sources to produce electricity, transportation
and industrial applications. We also know that fossil
fuels will increase in cost with time, not because of
depletion but due to increased production costs, and
we know that fossil fuels produce emissions that could
harm the environment.
In view of the increasing production costs of these
fuels and the increasing global primary energy demand,
it ca.n be assumed that the cost of energy will strongly
increase in the future. Moreover, most of the industrial
countries have issued stricter environmental require-
ments in order to reduce the adverse impact on the
earth's climate thereby.
This development entails an increasing cost pressure
that will increase even further in the future, particularly
for companies in energy-intensive sectors where energy
costs represent a significant part of the produdion costs.
Therefore, the use of energy-efficient and environ-
mentally friendly technologies is already
highly important for economic success
and long-term competitiveness.
Author
Oschatz is an innovative, family-owned company that
operates globally in the fields of plant construction,
energy recovery and environmental technology. With
more than 160 years of experience, 1,200 employees, six
subsidiaries, as well as representative offices all over the
world, Oschatz is a market leader in the product areas
of iron and steel metallurgy, non-ferrous metallurgy,
environmental and chemical technologies.
Iron and steel metallurgy has had a high priority for
Oschatz for many years. In order to relieve the effects on
the environment and to recover the heat energy in waste
gases, Oschatz has developed solutions for cooling the
hot, highly dust-loaded and CO-containing waste gases
from production plants. Each plant concept is based on
customer and process-specific requirements to ensure
the highest degree of availability, operational safety and
profitability for the customer.
It is the purpose of this paper to show the benefits o
energy recovery from waste gases of furnaces using the
proven concept of steam generation on an evaporating
cooling system. Lower operating costs and a reduction
of harmful emissions to the environment are the advan-
tages of operating a more energy-efficient system.
Cooling Plants for Basic Oxygen Furnace
(BOF) Waste Gases
The first LD (BOF) steel works in the world came
onstream in Linz and Donawitz in 1952 and 1953
respectively. Since then, the process has steadily been
developed and further improved. Today, the greatest
part of the world's crude steel production is rroduced
according to the LD (Linz-Donawitz) process.
Along the LD process, the converter is filled with
fluid crude steel and a cooling fluid (scrap metal o
iron sponge). Afterward, pure oxygen is blown through
a water-cooled oxygen lance onto the iron melt. During
this blowing process, the carbon concentration of the
crude steel is reduced from approximately 4-4.5 down
to less than 0.1 . Within this process, primary gas i
produced that consists of 85-95 vol.
of CO and 15-5
vol. of CO2 during the main decarburization period.
In practice, for the design of waste gas cooling plants,
it is calculated with a primary gas analysis of 90 vol.
Josip Kasalo, Oschatz GmbH. Essen. Germany ([email protected])
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CO and 10 vol. CO2 and a primary gas temperature
of about 1,700C.
Because of the high temperatures and the highly dust-
loaded primary gases, dust removal without cooling is
not possible. Therefore, the primary gas is led through
a waste gas cooling plant downstream the converter and
is cooled to about 1,000-800C.
An additional cooling of the waste gas can be achieved
only by screen walls and/or convection cooling parts. By
means of these cooling parts that are installed in an
additional section of the cooling) stack, it is possible
to reduce the waste gas temperature lower than 600C.
After the cooling, the waste gas reaches the dedusting
system, where it is processed further, depending on the
chosen dust removal technology.
For the waste gas cooling plants, also called cooling
stacks, there are three different cooling systems:
.Evaporation cooling.
.
Pressurized water cooling closed circuit).
.
Water cooling in an open circuit.
The last mentioned cooling technology is only rarely
implemented at new plants.
In addition to the above-mentioned distinction of
the cooling system, there is another differentiation
between the converter cooling stacks, depending on the
combustion factor. Because of the high CO content in
the primary gas, it is possible, on the one hand, to com-
pletely burn the gas over-stoichiometric/stoichiometric
combustion, n 2 1.0) or, on the other hand, to cool
down the partly combusted gas under deficiency of air
under-stoichiometric combustion, n < 1.0), to remove
the dust and to store it in a gas holder.
In modern steel
works, usually the
under-stoichiometric igure
operation mode is
chosen with an intend-
ed combustion factor
of n < 0.1. Only then
can the converter gas
be recovered with the
highest possible CO
rate and be used for
other processes.
Another advantage
of the very low com-
bustion factor is the
lower amount of waste
gas in comparison to
the higher combustion
factor. By this means,
the dimensions of the
cooling stack, of the
attendant facilities and
of the dedusting sys-
tem are reduced. This
has a positive effect
on the investment and
operating costs. In Converter cooling stack. A
addition, the lifetime and E = deflection bend.
of the individual parts
of the cooling stack is significantly extended due to the
minor thermal load.
Objective
In this paper, two boiler systems
-
one based on evapo-
ration cooling and the other based on pressurized water
cooling, for the cooling of waste gases downstream from
the LD converter - are described. In addition, for each
plant, the energy supply and the consumption of feed
water and - for the plant based on evaporation cooling
-
the credits for steam are determined and described.
This data is later used as a basis for a rough calculation
of profitability.
The objective is to show that waste gas cooling plants
based on evaporation cooling have further significant
advantages, in addition to energy recovery in the form
of industrially usable steam. Compared to cooling plants
based on water cooling, they are more profitable and
environmentally friendly.
Cooling plants based on the open circuit see Figure
7) were not taken into consideration in this report. This
technology is not state of the art anymore, and therefore
outdated due to the corrosion problems on the water
and gas side, as well as its reinforced disposition to a
water-side staining.
Waste Gas Cooling Sjrstems - Cooling stacks, whether
with evaporation cooling or pressurized water cooling,
consist of basically the same components. Generally,
these are the skirt, the hood, the stationary stack and the
deflection bend Figure 1). Since the local conditions
and the available space in the steel works have to be taken
into account, other arrangements are possible as well.
LDconverter BOF), B
skirt, C
hood, D = stationary stack
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Figure
Tube-to-tube construction.
In contrast to the doublejacket cooling implemented
in the past, these components consist mainly of a tube-
to-tube or a tube-web-tube construction (Figures 2 and
3) connected to a circular or square tube wall (also
known as a panel wall or membrane wall) through
which the cooling medium flows. Round cooling stacks
have an advantage over square cooling stacks, as they are
more stable and therefore safer in case of gas-side explo-
sions. In addition, this form is less prone to sticking of
slag and other deposits.
After leaving the converter, the primary gas flows
through the skirt. It is directly installed above the con-
verter and is designed for an optimal collection of the
primary gas. By means of lifting and lowering the skirt,
the gap between the converter mouth and the cooling
stack is minimized, so that the intrusion of infiltration
air into the cooling stack is minimized and the adjust-
ment of the planned combustion factor is made easier.
The skirt is particularly important regarding the adjust-
ment of the combustion factors A - 0.05-0.l.
The outcome of the partial combustion of the prima-
ry gas is waste gas. Afterward, it reaches the hood that is
installed downstream of the skirt. At the waste gas cool-
ing plants used today, the lance dome, sublance dome
and the flux chutes are components of the hood and
are mostly connected gastight with the hood through a
flange connection.
Due to its location and form, the hood is exposed to
converter emissions and to a very high thermal load.
This entails an abrasion so that the hood has to be
repaired or replaced more frequently than the other
components of the cooling stack.
In order to keep the shutdown periods as short as
possible in case of a repair, it therefore makes sense to
separate the hood via valves from the rest of the cool-
ing system. In that way, it is assured that the hood can
quickly be removed and a replacement hood can be
installed, although the other parts of the cooling stack
are still connected to the cooling circulation.
After the hood, the waste gas is first cooled in the
stationary stack and afterward in the deflection bend.
The deflection bend forms the end of the cooling stack
before the waste gas enters the dedusting system for
further processing.
Although the components of both types of plants
are very similar, there are significant differences upon
closer inspection of the whole plant.
50 . Iron Steel Technology
Figure
Tube-web-tube construction.
Waste Gas Cooling System With Evaporation Cooling
-
Evaporation cooling applied to waste gas systems
generates steam, which can be used for many industrial
purposes, in contrast to the pressurized water cooling
system, where the energy transferred to the cooling
water is just wasted.
It could be assumed, based on a rough calculation,
that 75-80 kg of steam per ton of hot metal is generated
in a plant with evaporation cooling, giving the following
process conditions: C content on hot metal (or molten
iron) > 4 , C content on raw steel (or molten steel)
< 0.1 , combustion factor = 0.1 and waste gas outlet
temperature = approximately 950C.
Two different circuits form part of the evaporation
cooling system: the low-pressure system (LP system) and
the high-pressure system (HP system).
In a typical waste gas cooling plant, the parts that
are connected to the LP system are the skirt, the lance
dome, the sublance dome and the flux chutes. The heat
absorbed during the blowing period by the LP system is
used (in addition to the steam from the HP system) for
degassing of the demineralized water. Demineralized
water is used as makeup water to compensate for losses
and consumed steam.
The other parts of the waste cooling plant, like the
hood, the stationary stack and the deflection bend, are
connected to the HP system (Figure 4).
The circulation water, coming from the steam drum
at the HP system and the feed water tank at the LP sys-
tem, which flows through the components of the waste
gas cooling plant, is mainly in boiling condition. It
becomes partly evaporated due to the heat transferred
during the waste gas cooling process.
Afterward, the water/steam mixture of the HP system
is led by the riser piping to the steam drum, where it is
separated and the riser piping of the LP system supplies
the water steam mixture to the feed water tank.
The makeup water necessary for the replacement of
the consumed steam is delivered by means of feed water
pumps from the feed water tank to the steam drum, and
subsequently forwarded by circulation pumps to the
plant components.
More efficient waste gas cooling systems with evapo-
ration cooling are designed with several components
operated in natural circulation to reduce the power
demand on the circulation pumps (Figure 5). This has
the advantage that the quantity of circulation water,
within the forced circulation circuit, is reduced thereby,
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Figure
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igure
I
I
i
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depending on the hood and stack design arrangement.
The heat load of the waste gas transferred to the cool-
ing water is then removed by a heat exchanger system.
The circuit is then closed when the cooling water again
reaches the expansion tank (Figure 6).
Cost Comparison of Both Waste
as
ooling Plants
Basic Data for Design
-
The same metallurgical bound-
ary conditions are presumed to allow for a comparison
of the operating costs of both plant designs, where
investment costs, energy demand, demineralized water
consumption and credit for the generated steam are
taken into consideration. Tables 1-4 provide the data
for plant design. The following symbols should be con-
sidered for the tables:
.
All volumes in mn 3 or volumetric flowrates in
mn3/hour, mn3/minute or mn3/second refer to
the standard state according to DIN 1343.
.
All volumes in m3 or volumetric flowrates in m3
I
hour, m3/minute or m3/second refer to the
operation conditions.
.
nco = combustion factor = LILa, related to the
CO in the primary gas, where L = air quantity
effectively drawn in mn3/hour and La = air quan-
tity theoretically required to obtain a stoichio-
metric combustion of the CO contained in the
primary gas.
.dc/dt .= decarburization rate in C/minute,
related to the hot metal quantity per heat.
.Ch = heat.
Figure 8 shows a diagram of the thermal energy
absorbed by the boiler, the combustion factor, as well as
the decarburization rate during the blowing time.
Energy Consumption - Considering the basic data cal-
culated earlier, the energy consumption for both cool-
ing systems is shown in Table 6.
Considering the energy consumption of the plant
with pressurized water cooling (Table 7), the feed water
pumps are neglected because they are used solely for
Table 4
Table
Technical Data for the Steelmaking Process
Process
LD converter (BOF)
--
---~--
Number of BOFs
Hot metal quantity
340 t/Ch
-~
,.. ..
--- - -
Carbon content of hot metal
4.50
u-
Carbon content of crude steel
0.10
~-
------.
Decarburization rate 4.50 - 0.10
~
4.40
16 minutes
-----
---....
Heat period (tap-to-tap time)
44 minutes
--
-- -----
Max. reacting oxygen quantity
1,300 mn3/minute
--
--
- -
Table 2
Technical Data for Primary Gas Waste Gas
Temperature of primary gas 1,700 C
Analysis of primary gas: CO
CO2
90 vol.
10 vol.
Combustion factor nca
0.1
Outlet temperature of waste gas
850C
--
Table3
Technical Data for the Water Steam System
Operation pressure
Waste gas cooling plant with evaporation cooling
HP system 20-40 bar
LP system 4-8 bar
Waste gas cooling plant with pressurized water cooling
14-1 8 bar
---
A _--
-- ---
Cooling water temperature (pressurized water cooling)
at boiler inlet 105 C
at boiler outlet 150C
------------
.- ------
Calculated Values With Regard to the Gas Flow and Heat Flowrates
Primary gas flowVp' 142.000
--
166,000
-
22.5 MWh/Ch i) 81.0 GJ/Ch
Waste gas flow VA'
--
-,-- --- - ----
---
bsorbed heat flow 1' (uncontrolled at nea ~ 1.0)
120.0 MW
Absorbed heat flow 2' (controlled at nea
~
0.1)
Max. decarburization rate
98.0 MW
--
Note: The values
0.372 C/minute
and are based on a max. reacting oxygen flowrate of 1,300 mn3/hour.
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Figure 8
130
120
110
~ 100
~ 90
~ 80
: 70
.c
]
60
- 50
~ 40
30
20
10
0
01'
O2'
0
2 4
A
1,50
1,40
1,30
1,20
1,10 ~
1,00
]
0,90
6
0,80 ~
..
~
r
0,70 ~
~ 0.60 u
0.50
f
0.50
0.40 0,40
0,30 0,30
0,20
J
0,20
0.10 0.10
0,00 0.00
17
c
c
'E
~
ge,
B
5 6 7 8 9 ro n ~ M ~ ~
Blowl.. . period [ mln )
Heat diagram, A. Absorbed thermal energy by boiler system at nco = 0.1; B.
Decarburization rate (dc/dtJ; and C. Combustion factor.
Table
filling the plant and for compensating
the eventual leakage losses.
Cost Analysis - For the comparison o
both plants under the economic point
of view, the following average specific
costs/ credits are taken as a basis:
.
Electrical energy
cost
.Steam credit
. Demi-water (fully
demineralized) costs
O.08/kWh
27.6/t
6.9/t
The one-time accruing investment
costs, which have been only roughly
estimated, are shown in Table 8.
Generated Steam
Generated steam quantity approx,
Required steam for degassing
- ~-- -
n - - n
36 tICh ~ 49 t/hour
7,5 tICh ~ 10 t/hour
Delivered steam quantity (to consumers)
(the delivered steam quantity is related to the system boundaries: Inlet demi-water at feed water tank/steam
accumulator outlet and a demi-water temperature of 200 C)
28,5
t/Ch
~ 39
t/hour
Required demi-water quantity
--- -- -
- ----
- - -
28.5 t/Ch ~ 39 t/hour
Table
Energy Consumption of Waste Gas Cooling for a Plant With Evaporation Cooling
Volume flowrate
Feed water pumps:
For the design of the feed water pumps, it was consid-
ered that the full delivery is achieved only during the blowing period of 16
minutes and that, during the intermission of 28 minutes, only a minimum
flow is returned to the feed water tank.
Circulation pumps:
a HP circulation pumps:
Volume flowrate
Power consumption of HP cire. pump
Number of pumps
Elect ric motor efficiency
Energy consumption per heat
Summary
Plant component
Feed water pump
HP circulation pumps
LP circulation pumps
Total energy consumption
155 m3/hour
265 kW
Number of pumps
Power consumption of feed water pump
---
Elect ric motor eff ic iency
95
Energy consumption per heat
74 kWh/Ch
1,900 m3/hour
b LP circulation
pumps:
Volume flowrate
400 m hour
---
2 with 950 m3/hour/pump)
Number of pumps
Power consumption of LP cire. pump
57kW
60 kW
----
95
Elect ric motor eff ic iency
Energy consumption per heat
44 kWh/Ch
x 124 kWh/Ch
Energy demand
74 kWh/Ch
248 kWh/Ch
44 kWh/Ch
366 kWh/Ch
54
.
Iron & Steel Technology
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Table 7
Circulation pumps:
Volume flowrate
2,400 m3 hour
Energy Consumption of Waste Cas Cooling for a Plant With Pressurized Water Cooling Closed Circuit
Air cooled heat exchanger:
Airflow
1,300 m3 second
Power consumption of circulation pumps
240 kW
Number of pumps 2 (with 1,200
m31
hour per pump)
Elec tr ic motor eff ic iency
95
Energy consumption per heat
2 x 185 kWh/Ch
Summary:
Plant component Energy demand
Circulation pumps
370 kWh/Ch
Air-cooled heat exchanger
209 kWh/Ch
Total energy consumption
579 kWh/Ch
Table 8
Power consumption
285 kW
Energy consumption per heat
209 kWh/Ch
One-Time Accruing Investment Costs
Waste gas cooling plant with evaporation cooling
Design
Waste gas cooling stack
Steam drum
Steam accumulator
Feed water tank
HP circulation pumps
LP circulation pumps
Feed water pumps
Piping
Valves
Measuring and control equipment
Waste gas cooling plant with pressurized water cooling
Design
Waste gas cooling stack
Feed water tank
Expansion tank
Circulation pumps
Feed water pumps
Piping
Valves
Measuring and control equipment
Air-cooled heat exchanger
Note: The costs for transportation, as well as the costs for installation, are considered to be similar.
Cost Comparison - Table 9 shows the cost comparison
for each waste gas cooling plant. The credit entries are
marked with a plus sign (+) and the costs with a minus
sign (-). The cost breakdown comparison includes only
the costs that are different between both plants, being
the costs for direct capital investment, energy consump-
tion, demineralized water consumption and steam
utilization. The rest of the capital and operating costs,
like indirect costs for the capital project, amortization,
operating costs, maintenance, labor, etc., are considered
equal and are not shown on the breakdown.
General Consideration
-
The higher capital invest-
ment cost of the evaporation cooling plant compared to
the conventional pressurized cooling water plant is due
to the additional costs for valves and components, the
boiler s higher operating pressure, as well as the costs
for additional plant components like the steam drum
and steam accumulator. It is even higher if one consid-
ers the cost of the air-cooled heat exchanger needed on
the pressurized cooling water system.
However, if one considers the advantages in operating
costs, assuming that one could consume or sell the gen-
erated steam, the selection of an evaporation cooling
system is still economically recommended. It is not only
the advantage of the steam generation and use capa-
bilities of the system, but also the lower electric energy
consumption due to the combined natural/forced cir-
culation design.
Even more, if one considers that both waste gas cool-
ing systems could store a certain amount of CO gas and
receive credit for it, one could add it to the benefits
of the steam generation credit and conclude that the
returns of the evaporation cooling system are higher
than of the plant with pressurized water cooling (see
Figure 9).
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able
ost omparison for Each Waste as ooling Plant
Waste gas cooling plant with evaporation cooling
~ --~-
Investment
costs approx.
15,800,000
- -_.-
--- --
Energy consumption
Demand per heat
Specific costs
Total costs
366 kWh/Ch
0.08/kWh
- 29/Ch
---
Demand demi-water
Demand per heat
Specificcosts
Total costs
28.5 t/Ch
6.9/t
-197/Ch
- -~ -.-.
Steam utilization
Delivery per heat
Specific costs
Total credits/costs
28.5 t/Ch
27.6/t
+ 787/Ch
--.~-- ---
Credits/costs per heat
+ 561 /Ch
----
--
Annual credits/costs
Heats per year
Total credits/costs per year
7,500 Ch/a
4,207,000/a
--~-~--- --- ~- -
Waste gas cooling plant with pressurized water cooling
-----
-
---
Investment costs approx.
13,100,000
--............
Energy consumption
Demand per heat
Specific costs
Total costs
579 kWh/Ch
$0.08/kWh
-$46/Ch
-- -------
---
Demand demi-water
Demand per heat
Specific costs
Total costs
- t/Ch
- /t
- /Ch
,_. ,-.-
---
Steam utilization
Delivery per heat
Specific costs
Total credits/costs
- t/Ch
- /t
- /Ch
- 46/Ch
--
----
Credits/costs per heat
--
- ----
Annual credits/costs
Heats
per year
Total credits/costs per year
7,500 Ch/a
- 345,000/a
. _'_'T ----
-- ---
The differences between both plants in the cost/
return development become especially evident when
the plant is operated with a higher combustion factor.
One must consider that, at a high combustion factor
(nea;:: 1.0) the storage of CO gas is no longer feasible,
and at a low combustion factor (nea > 0.4) the storage
is seldom carried out due to the low calorific value. At
these two scenarios, credit is not available.
In Figure 10, for both waste gas cooling systems
without CO storage, the progress of the cost/return-
development is qualitatively shown.
As a result of the missing credits for the CO storage,
the pressurized cooling water system works primarily as
a consumer; therefore, the permanent charges affect
igure
>-
1
dY1
0
Return development for a plant with CO storage (qualita-
tively illustrated). A = plant with evaporation cooling; B =
plant with pressurized cooling water; X = time; Y = return;
dYl
=
Return development - pressurized water cooling;
dY 2
=
Return development - evaporation cooling.
56 .
Iron IS Steel Technology
the cost side negatively (Figure 10, curve B). At the
plant with evaporation cooling, the steam credit leads to
the fact that this type of plant is still economically rec-
ommended, in spite of the missing credit for CO storage
(Figure 10, curve A).
It should be also considered that a desire for a higher
combustion factor will mean an increase in the waste
gas flowrate, and therefore the complete plant needs
to have greater dimensions, resulting in higher capital
investment costs. It could be assumed that the amortiza-
tion time for a plant with steam-only utilization would
be longer than for a plant with combined energy utili-
zation, steam and CO storage. These factors should be
taken into account during the project feasibility study.
dY
dZ
x
B
Total cost/return development for a plant without CO-storage
(qualitatively illustrated). A
=
Plant with evaporation cooling
B
=
Plant with pressurized cooling water; X
=
Time; Y
=
Return; Z
=
Cost; dY
=
Return development - evaporatio
cooling; dZ = Cost development - pressurizedwater cooling
igure
10
>-
t
O.
dY2
-
N
.... X
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Evaporation Cooling Systems -
Operational Safety and Environmental
Protection
In the previous section, it was shown that evapora-
tion cooling plants have clear economic advantages
compared with pressurized cooling water plants. In
the following paragraphs, some other advantages are
described briefly.
Operational Safety - Water leakage from water-cooled
elements entering the furnace is the main source of
explosion hazard on any steelmaking plant. Therefore,
one of the requirements
for
a safe steelmaking opera-
tion is to avoid tube damages that would lead to water
leakage.
One important advantage of evaporation cooling is
the reduction of the risk of water leakage due to tube
damage. The cooling water inside the tube is under
saturation pressure in boiling condition. Therefore, the
cooling water flows through the cooling elements under
a constant temperature. Consequently, there are no dif-
ferential tensions and/or increased tension on the cool-
ing element due to a sudden increase of waste gas heat
load. Furthermore, due to the higher heat-transfer coef-
ficient, the temperature gradient between the unheated
and heated sides of the tubes would be less than in the
pressurized cooling water system. In this case, the risk
of thermal shock cracks is also reduced by the lower
tube material temperature difference in the tube wall,
whereby the lifetime of the cooling plant components
is increased.
In the event of mechanical or thermal damage during
operation, which causes a leak, the following physical
effect takes place in the evaporation cooling system: due
to the sudden expansion of the coolant and following
evaporation in the leakage point, a blocking effect
for
the coolant occurs. The quantity ofleaking water, along
with the resulting losses in such systems, is insignificant
compared to pressurized cooling water systems.
Additionally, the residual water in the system is at
boiling point; hence it is evaporated immediately by
the contact with the gas thermal load and/or furnace
radiation. Leakage of important water quantities, and
consequently risk of explosion and damage, is greatly
reduced.
These facts considerably reduce the causes for explo-
sion incidents, increasing in that way the operation
safety of the furnace.
Another advantage is that it leaves sufficient time to
the plant owner to establish a well-defined repair pro-
gram. The main root causes of damage that normally
leads to emergency shutdowns - such as damage to the
tube and cooling elements leading to water leakages,
due to thermal stress, lack of cooling, etc. - can be
eliminated to a large extent.
Environmental Protection
- Today, besides economic
efficiency and operational safety, industrial plants must
also be evaluated with regard to their environmental
impact and the sustainable use of energy.
Evaporation cooling plants recover energy in the
form of steam. Two examples are described here, show-
ing the magnitude of the energy recovered, which is
otherwise dissipated unused to the environment.
In accordance with the calculated values shown in
Table 5, the utilizable amount of steam generated has a
thermal energy content of approximately 21.5 MWh/Ch
- 28.5 t/ Ch of steam generated related to a demineral-
ized water temperature of 20C).
If we assume 7,500 heats/year and an annual power
demand of approximately 14,500 kWh per year and
household for the production of heat, this energy would
suffice to supply about 11,100 private households dur-
ing one year with heat.
Additionally, this energy amount is enough to save
approximately 14.5 x 106 m3 of natural gas Hi
= 10.5
kWh/m3) in a year, by which 32,250 t CO2 emission
factor
for
natural gas
0 2
kg/kWh) would not be emitted
into the atmosphere in a year.
Following these two examples, it quickly becomes evi-
dent that the potential of energy recovered as steam is
significant and could make a positive impact: there will
be less detrimental exhaust gas emitted into the atmo-
sphere, and energy is saved.
Summary
Based on an LD converter BOF) operation with a hot
metal capacity of 340 t/Ch and using average unit costs,
it has been shown that waste gas cooling plants with
evaporation cooling are more economically feasible
to operate due to the return received from the steam
generation and use, in addition to the CO storage
possibility, than comparable pressurized cooling water
plants. Another advantage is the fact that, due to the
heat recovery capabilities as industrially usable steam,
less fossil fuel is consumed and less CO2 is emitted into
the atmosphere.
The use of energy-efficient and environmentally
friendly technologies is proven to be highly important
for the competitiveness of companies in energy-inten-
sive sectors. Only those who efficiently protect natural
resources, the environment and our communities will
have sustainable success within the global competition.
Reference
1. http://www.stahl-online.de/wirtschafcund_politik/stahU
zahlen/start.asp,Jan. 20, 2009. ..
Thispaper was presented at AISTech 2010 - The Iron Steel Technology Conference and Exposition
Pittsburgh
Po.,
andpublishedin the ConferenceProceedings
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