TECH ADVANCES
Danieli Zero Scale Pit™
Minimizing infrastructure and rolling mill footprint, while effectively handling mill scale and cooling water
In the classic scale pit, the process waters that come into contact with the rolled / processed material are conveyed through a flume channel to a flake pit consisting of two sections.
The first section is a circular receptacle where the heavy scale settles by decantation, while the second is a rectangular tank where the water, now free from large scale, overflows and is pumped to the water-treatment plant.
The civil works (especially in the circular part) are an important part of the construction of the system because it takes at least 4-5 months to complete. Very often, this pit is the deepest excavation to be carried out, and particularly difficult and expensive when there are groundwater problems.
The ZSP, on the other hand, integrates perfectly with the technological foundations of the plant.
The equipment consists of a full, steel-collecting basin located close to the mill’s first stands to minimize excavations and flume length. Here, while the scraping chain continuously removes it, the coarser scale is deposited on the bottom of the pit. The scraping elements carry the scales through the inclined steel plane above the ground level, ejecting them into either a box or a truck.
The overflow water, now devoid of the dangerous material, is pumped into the longitudinal clarifier of the water treatment plant for final cleaning: medium-sized particles are removed by sedimentation, while oil and grease via an oil skimmer.
Danieli improved the traditional approach to contact-cooling systems for continuous casters and rolling mills to reach the same results in water cleaning, with significant CapEx savings in the entire application.
This new Danieli patent is based on a proper partition of the overall rolling mill discharge: the first part collects water discharged from both the descaler and the first roughing stands, containing the largest scales released from the strip. Then, flushing collects most of the residual water carrying small quantities of very-fine scale, which is not a concern for pumps and relevant delivery pipes.
| ZSP Solution | Conventional Scale Pit System |
|---|---|
| Water coming from the rolling mill direct cooling line are separated into different fluxes: those containing large/heavy scale are sent to the scraper conveyor packages, while those containing small/light scale are collected in a separate pit and directly pumped into the longitudinal clarifier. | All water coming from the direct rolling mill cooling line are sent to the scale pit to separate the large/ heavy scales. |
| The scraper conveyor packages, and the pumping pit are located under or next to the rolling mill, so concrete works are not particularly deep (-5 / -7 m). | The scale pit unit collecting all water from contact circuits is located outside of the building, due to the required depth (-10/-15 m). |
| The scale is continuously removed by the Dan-Dredge™ chain scrapers. | The scale accumulated in the pit is periodically removed through an automatic bucket. |