2015 - Caucaia - Brazil
Russula supplies water treatment plant in addition to the 600,000 ton/yr mill
In conjuntion with the turnkey supply of a 600,000 tpy bar and wire rod mill to Gerdau (formerly Silat), Russula supplied a water treatment plant. The plant was built on a 148 hectares greenfield site, located in the town of Primavera in Caucaia, 50 km from the northern Brazilian city Fortaleza. Russula provided all the water treatment plant equipment, including installation supervision, commissioning support and training.
Water Treatment Plant Layout
Common among most water treatment plants for the steel industry, one circuit is dedicated to the contact water and another to the non-contact water. The contact water circuit at the Gerdau plant has a volumetric flowrate of 2000 m3/hr and the non-contact water cirucit 850 m3/hr.
As the contact water circuit carries polluting materials that decrease the wear life of the rolling mill equipment, the main objectives of water treatment plants are to remove these materials and decrease the water temperature. Polluting materials are classified into sedimentary (scale and sludge) and non-sedimentary (oil and grease). The water treatment process is divided into four zones:
1) Large scale removal
Scale Pit
Large scale removal occurs in the scale pit, which is installed below ground level because the water that drags the scale, oil and grease from the rolling mill process falls into the mill flume below the foundations. Once the polluted water enters the scale pit, the larger scale particles fall to the bottom where they are removed by a clamshell bucket bi-valve ladle and deposited in an area or container to dry. The water containing fine scale, oil and grease then passes to a basin and is subsequently pumped to the decanting basins.
2) Fine scale sedimentation and oil/grease elimination
Twin decanting basins
The twin decanting basins are divided into a floculation zone and a decanting zone. The water speed is slow enough to avoid dragging the fine scale on the bottom of the decanting basin and allows the oil/grease particles to float to the surface for removal before entering the ring filters.
Sludge removal
Flocculants are added to the water to cause the suspended fine scale particles to clump together and settle to the bottom of the basin since the particles have a higher density than water. The clumped fine scale or sludge is then removed by a bridge scraper that moves along the bottom of the basin. The water and sludge is pumped into another tank that adds thickener to further separate the water from the sludge. The sludge is then pumped to the press plate filtration and the clean water recirculated back to the decanting basin.
Oil removal
The bridge scraper has a dual function in removing both the sludge and the oil and grease.It sweeps the floating oils and grease into a well where an oil skimmer belt removes the oil/grease and pumps the return water into the twin decanting basins.
3) Suspended fine scale removal
Pressure filtration
The main objective of filtration is to ensure that fine scale particles and oil that have not been removed by the decanting basin do not pass back into the rolling mill process. The ring filters consist of filter cartridges, which are compressed blocks of plastic rings. The water passes through the filter cartridge and the rings expand and rotate to force the removal of particles above the specified filter grade. The ring filter has an automatic self cleaning process that takes less than 3 minutes and consumes approximately 30m3 of water.
4) Temperature reduction
Cooling towers
The filtered, clean contact water arrives to the cooling zone via pumps from the ring filters or from the non-contact water circuit. The contact and non-contact water circuit is typically designed for a thermal decrease of 10°C.
Water Treatment Plant Construction
The water treatment plant was one of the first areas of the new greenfield and wire rod mill to be constructed. Starting in September, 2013 with the site surveying the following photos show the construction progress of the water treatment plant over the span of ten months, ready for the bar mill commissioning in March, 2015.
Greenfield construction site 600,000 tons/yr rolling mill
September, 2013
Drone shot of preliminary construction
January, 2014
Drone shot 5 months later
May, 2014
Ground shot of decanting basins
July, 2014
Decanting basins bridge scrapers
October, 2014
Drone shot ten months later from construction start
October, 2014
Reduction in Operational, Maintenance and Project Investment Costs
The Russula water treatment plant simplifies the civil engineering, construction, and occupies less space than conventional water treatment plants. This simplification yields two cost savings. First it lowers the total project investment including installation and equipment costs and second, over the long term, the Russula water treatment plant reduces the operational and maintenance costs. Due to a simplified, compact plant, fewer personnel are required to operate and maintain it.
