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Metal/iron & steel industryMeasuring system activates alarm when water

leaks into blast furnace

Leakage monitoring at the blast furnace

The measurement and control techno-logy specialists of Salzgitter Service andTechnik GmbH had to make quite aclimb in order to install a new measu-ring system for detecting leakages inblast furnace tuyeres. The task of theflowmeters was anything but simple,as even the smallest changes had to bedetected. Endress+Hauser supplied thenecessary precision devices.

The Salzgitter Corporation includes more than 80 national and international subsidiaries and associated companies. It is amongEuropes leading steel technology groups. Its approximately 18,000 employees generate over 6 billion Euro in external sales and produce

over 8 million tons of crude steel annually. In flat and profile steel products, the company numbers among the top five in Europe. In the

tubes sector, it occupies a leading global position. Its subsidiary Salzgitter Flachstahl GmbH produces high-quality special and branded

steels (flat steel, profile products, plates, tailored blanks, roof and wall elements, sheet piles) for an expanding field of applications. The

SZST Salzgitter Service und Technik GmbH also belongs to the Salzgitter group. As the service provider for Salzgitter AG, it covers the

following areas: workshop technology, service technology, occupational medicine, fire and breathing protection, education, training and

consultation, printing center and security services.

When the blast furnace is tapped and hot

iron pours out at a temperature of 1400 C

(2552 F), giving off a shower of sparks,

even the furnace operators at Salzgitter

Flachstahl GmbH continue to be fascinated

by the spectacle. The company operates

three blast furnaces in Salzgitter, Germany.

Every day, thousands of tons of coke and

iron ore enter the furnaces via the conveyor

belt. Eight to ten hours later, they flow out

of the tap hole in the form of liquid pig

iron. However, the companys employees

have no time to admire the beauty of the

pig iron production process. They are busy

controlling complex processes that help to

determine the quality of the final product.

Particularly when the iron ore is converted

to liquid pig iron in the blast furnace,

many details must be coordinated for the

high-tech steel product to meet the quality

requirements of large customers such as

those in the automotive and shipbuilding

industries.

Improved conditionsAt the Salzgitter plant, the workers at

blast furnace B now have one less detail to

worry about. For some time now, 60 high-

precision Promag 50W magnetic inductive

flowmeters from Endress+Hauser have

been in use, which allow the employees

to detect leakages in blast furnace tuyeres

more quickly than before. The subsidi-

ary Salzgitter Service und Technik GmbH

(SZST) is responsible for the project engi-

neering and installation of the ingenious

measuring system, which activates an alarm

when water enters the blast furnace. The

customers objective was to detect leakages

as quickly as possible, and then be able

to react quickly in order to minimize the

entry of water into the furnace, explains

Henning Borchers, MSR Specialist at SZST,

whose range of services includes testing,

maintaining and calibrating stationary and

non-stationary measuring instruments and

systems.

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CS 016B/11/en/10.06

71032780

Straub/INDD CS2

Instruments International

Endress+Hauser GmbH+Co. KG

Instruments International

P.O. Box 2222

79574 Weil am Rhein

Germany

Tel. +49 7621 975 02

Fax +49 7621 975 345

http://www.endress.com

info@ii.endress.com

Precision work was required by the sche-

dule for the installation of the measuring

system, which was installed directly into

the existing cooling water circuit at the

lofty height of eighteen meters (59 feet).

For the installation to be possible, the

blast furnace had to be shut down for a few

hours every six weeks, Borchers relates.

The tuyeres that need to be monitored are

actually injection nozzles in the wall of the

blast furnace. Arranged in a circle like a

belt, they blow hot blast into the furnace

at a temperature of 1200 C (2192 F).

The hot blast is generated by hot blaststoves, which burn the blast furnace gases

generated during the blast furnace process.

Each of the thirty tuyeres in blast furnace B

consists of two chambers and is equipped

with a water cooling system. Still, damage

to the tuyeres is frequent due to the strain

caused by the hot molten metal. This

causes recurring leakages, and water enters

the blast furnace as a result. Considering

the enormous volumes of pig iron invol-

ved, it is hard to imagine that a couple

of liters of water leaking into the furnace

would cause a problem. Experience shows,

however, that even small deviations fromthe optimum affect the reduction of air to

carbon monoxide that takes place in this

blast furnace zone.

Well thought outIn the past, the employees often noticed

leakages only hours later, when a gas

analysis showed that the proportion of

hydrogen in the blast furnace gas had risen.

Many aspects of operating a blast furnace

depend entirely on the experience of its

operators. When inspecting the quality

of the pig iron after tapping, they can tell

with astonishing accuracy whether moreaggregates are required by simply looking at

the grain structure. The installation of the

flowmeters now represents another step in

the direction of automation. Installed in the

flow and return pipes of the tuyeres, they

continuously measure the flow of cooling

water; they are always installed in groups of

two per tuyere.

Thanks to a new visualization program,

the computer in the furnace control room

emits audible and visible alarms as soon as

the flow difference exceeds the calculated

limit value. Defective tuyeres are thus de-

tected within minutes, and employees canisolate them from the cooling system using

sliding dampers. This sounds quite simple

in theory, but there are a few potential

complications in practice. The tiny leakages

cannot be seen with the naked eye, and

even with extremely precise magnetic

inductive flowmeters, the differences to be

detected lie in the range of the measuring

accuracy of the devices, explains Borchers.

In addition, to prevent false alarms, the

alarm is to be triggered only after a time

tolerance limit is exceeded. It took a few

optimization loops to make that work,

Borchers recalls. Today, the flows for eachtuyere are at approximately 20 cubic meters

per hour (706.7 cubic feets per hour), and a

signal is triggered if a difference of 50 liters

per hour (13.2 US gallon per hour) occurs

for longer than 90 seconds. The parameters

for these limit values can be configured by

the operator for each tuyere, allowing them

to be optimized. The return temperature

in the cooling circuit is also measured and

recorded. Endress+Hauser also supplied

the Pt 100 3-wire sensors of type TST42,

which are installed immediately next to the

flowmeters. Endress+Hauser has hooked

up a very attractive complete package forus, Borchers says in praise.

Convincing solutionAnother well thought out feature is the

connection architecture of the sensors using

PROFIBUS technology, which supports

the Promag series. The radially arranged

cabling of the sensors allows individual

cooling water pipes to be switched off when

changing devices or in case of fault, without

disabling the entire bus system. Groups

of two tuyeres (which correspond to six

measuring points) are connected via one

fieldbus distributor. This means a total of

15 fieldbus distributors whose signals are,

in turn, transmitted over PROFIBUS DP via8 DP/PA couplers and 4 DP links. Another

persuasive argument for using PROFIBUS,

is that the cabling effort decreases, thus

lowering costs, Borchers explains. For

a conventional type of connection, those

costs would be substantial. After all, there

are three measuring points per tuyere: two

flowmeters in the cooling water flow and

return pipes, and the temperature sensor in

the return pipe.

The central control of the system is handled

by Simatic PCS7, which is installed on an

industrial PC used for visualization and

data archiving. Likewise integrated into theprocess control system is the PM Open

Export add-on tool, with which the data

from the PCS 7 archives can be imported

into MS-Excel files. To show the history

of a defect, data about the relevant tuyere

for the last 90 hours can be stored in

MS-Excel. An important process control

technology function is the ability to disable

each tuyere individually, as otherwise error

messages would be generated continually

when a tuyere is uninstalled.

After a year of smooth operation, those in

charge of the project are most satisfied with

the results. The measuring devices work,and employees are able to react quickly in

case of damage to the tuyeres, without the

need for a time-consuming gas analysis.