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INTEGRATION OF BATCHWISELY PRODUCED REST STEAM IN A GRID OF DIFFERENT AND INDEPENDENT BATCH CONSUMERS

Ziel

Utilisation of rest steam.
Inside Basic Oxygen Steel Plant no. 2 the production (by converters) and consumption of steam (by the vacuum degassing installation) occur batchwisely. This is possible by buffering steam in an accumulator. There is an excess even if only one converter is producing steam.
This project consists in the integration of the steel plant grid to the general steam grid of the whole plant. Tuning of the steam supply and demand is reviewed continuously by means of a forecasting and information system. Protection of the new grid against waterhammer will also be controlled by automatic remote control.
Within the STOMOS model the production schedule plays a major role. From the production schedule steam demand and steam production within a two hour time frame are being calculated. So by a number of prints of the STOMOS model over a certain period of time, the production schedule input of the model has been compared to the actual situation of steam production and consumption within the steel-mill. Looking at the scheduled versus the actual production/consumption an accuracy window of 10 minutes has been used. Using this accuracy window the following results can be given :
number of model prints evaluated : 105
charge statistics :
more than 1 hour earlier : 7
between 40 minutes and 1 hour earlier : 2
between 20 and 40 minutes earlier : 10
between 10 and 20 minutes earlier : 15
within 10 minutes from schedule : 164
between 10 and 20 minutes later : 31
between 20 and 40 minutes later : 22
between 40 minutes and 1 hour later : 3
more than one hour later : 5
no charges : 12
The fact that the deviations bigger than 1 hour is higher then the deviation between 40 and 60 minutes might be explained by the fact that in these are caused by production disturbances. And are not according any statistical distribution law.
SUCCESS OF THE PROJECT
The surplus steam within the steel-mill normally would have been blown off. By exporting steam to the Hooogovens 16 bar steam grid, fuel within Hoogovens power plants, and therefore energy is being. The energy savings related to the surplus steam of the steel-mill are about 3.0 GJ/Metric ton. Based upon the project evaluation period annually 20,000 tonnes of steam will be exported to the grid. So annually 60,000 GJ of energy will be saved by the completion of this project.
During the evaluation period it was noticed that an number of outside events restrict steam recovery. It has shown that excess of by-product gases and a occasional low demand do restrict the steel-mill steam recovery. Since at an excess of by-product gases within power-plant no. 1. these are being converted into electrical energy generating a 16 barg steam surplus as well within the power plant. In the case of low steam demand the power plant boilers will at least generate steam at minimum load. Therefore an amount of 0.5 barg steam has to be blown off at the power plant in order to be able to recover the steel-mill excess steam.
INVESTMENT COST
In 1989 the investment costs were estimated at DFL 4.35 mln.
After the start part I connection between Steel-mill nr. 2 and the 16 bar grid the total investment costs had been estimated to Dfl 2,600,000.
The investment costs of the project as finalized had been accumulated up to Dfl 2,713,660 up to March 1993.
MAINTENANCE AND OPERATING COSTS
Since no additional duties are created by this project, the operational costs can be neglected. The maintenance costs however must be taken into consideration.
PRESENT SITUATION
On the western part of the Hoogovens area at Ijmuiden, Basic Oxygen Steel Plant No. 2 is situated. Basic Oxygen Steel plant No 2 has 3 converters with which steel can be batchwisely produced. 2 Steel converters are shaft cooled while steam producing. Even when only 1 of these 2 converters is producing steam there is a surplus of steam, which can partly be stored into 2 accumulators; the remainder is blown off.
On the other hand steam demand cannot always be met through steam storage. If so, steam for a vacuum degassing installation in the same steel plant has to be provided by an auxiliary boiler. Because of the fact that in the steel plant there is not enough demand for the steam production, the steam from the converters can preferably be used elsewhere on the Hoogovens site. This means integration of the rest steam in the 16 bar steam which is fed solely through Boilerhouse No.1. Besides, the inefficient stand by function of the auxiliary boiler will be avoided.
NEW SITUATION
The steel plant steam grid will be connected with the 16 bar steam grid with their several different and independent consumers.
Then, the remainder of the steel plant steam flows into the same grid which is also supplied by Boilerhouse No. 1. This means the mixing of two steam flows, saturated and superheated steam. To get maximum benefit of the project under safe conditions, the tuning of steam demand and supply has to be reviewed continuously by means of a forecasting and information system. The safeguarding of the new grid (no waterhammer) will be controlled by the Dispatching Centre (remote control at a distance of approx. 1.5 km) in conjunction with the steam control desk in Steel Plant No. 2.

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HOOGOVENS GROEP BV
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POSTBUS 10000
1970 Ijmuiden
Niederlande

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