Evaporative Waste Gas Colling

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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])

48 .. Iron .Steel Technology


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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

November 2010 + 49


3/10

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


5/10

igure

I

I

i


6/10

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.

November2010 5


7/10

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


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


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

95

- -----


8/10

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


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


209 kWh/Ch

One-Time Accruing Investment Costs


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


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).

November2010


9/10

able

ost omparison for Each Waste as ooling Plant


~ --~-

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

--~-~--- --- ~- -


-----

-

---

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


10/10

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

Did you find this article to be of significant relevance to the advancement of steel technology?

Ifso, please consider nominating it for the AISTHunt-KellyOutstanding Paper Award at AIST.org/huntkelly.

November 2010

7

Evaporative Waste Gas Colling

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