Considering the essential value of water for society, the steel industry endeavors to manage water sustainably at various stages of operations as well as water treatment. Key challenges are mentioned here for which solutions are invited:
RO is an established technology for water treatment when TDS reduction is desired.
The input water to RO has 1000-3000 ppm TDS. The typical TDS level in steel plant’s RO reject may vary between 10000-15000 ppm. High TDS of RO reject water makes it unsuitable for use in low end applications and it is directly sent to thermal evaporator. This leads to generation of high quantity of ZED (Zero Effluent Discharge) Salt which has no current economic value and lead to disposal challenges.
Tata Steel is looking for various solutions to tackle this critical waste to become zero waste company by 2030.
Processes offering:
In a steel manufacturing facility, iron ore and other raw materials are heated to extreme temperatures to produce molten steel. This molten steel is then processed into various products, such as sheets, coils, and structural beams. Critical processes within the plant, such as coke quenching, the intensive nitrogen bottom ash (INBA) system at blast furnaces, and laminar cooling at the hot strip mill (HSM), rely on water’s high heat capacity and efficient cooling properties to maintain process control, ensure product quality, and optimize operational efficiency.
As steel and other materials are heated to extreme temperatures during production, significant amounts of water are used to absorb and carry away this heat, preventing equipment from overheating and ensuring the integrity of the final products. Once the water absorbs heat from these high-temperature processes, it becomes too hot to reuse directly and is cooled in cooling towers. These towers cool the water by exposing it to air, facilitating heat exchange and evaporation, and the cooled water is recirculated back into the plant’s operations.
However, the extensive use of cooling towers results in significant water loss through evaporation. Few other applications like INBA, also include direct water quenching on very hot products (for granulating the slag) which convert to steam at that very instant, this converted steam is directed to atmosphere though chimneys. A significant amount of the water used in the cooling towers evaporates. Addressing water vapor losses from the cooling towers and from the processes mentioned above represents a significant opportunity for water recovery. This recovery would not only save substantial amounts of water annually but also reduce the energy required for water treatment and related processes.
The solutions should be easy to plugin with minimum change in equipment setup and allow for water recovery from steam/vapor. In some cases, the steam/vapor may have contaminants like SOx (sulfur oxides) and NOx (nitrogen oxides), as these may be picked up from the hot products like slag in some operations.
Solution of interest include:
In cooling tower operation, blowdown is the controlled process of removing a portion of concentrated water from the cooling tower system by mixing it with soft water. For this, chemicals are used to control scale, corrosion, and biological growth, ensuring efficient operation, and extending the life of the cooling system. Common chemicals include biocides (to kill microbes), corrosion inhibitors (to protect metal surfaces), scale inhibitors (to prevent mineral buildup), and pH adjusters (to maintain optimal pH levels). Other chemicals like defoamers are used to eliminate unwanted foam caused by factors such as excessive chemical dosing.
Cycle of concentration (COC) indicates how many times the water has been concentrated due to evaporation and is a key parameter for water efficiency and scaling control. Higher COC indicates less blowdown and more water savings. However, it is associated with higher risk of corrosion and scaling. Therefore, technology need to be adopted to reduce the chemical consumption and increasing the COC by reducing the blowdown.
The effluent emerging from steel industry at various stages of treatment have contaminants such as COD, ammonia, phenol, fluoride, and chloride in wastewater which are difficult to treat.
Fluoride and chloride contents present in wastewater are particularly notorious, causing corrosion and limiting the recycling of water.
Currently huge quantity of chemicals and area are involved to achieve optimum removals, and huge waste (sludge) is generated during treatment.
Water-based slag granulation is a widely implemented technique in blast furnace operations for transforming molten slag into a usable by-product while effectively managing thermal energy and environmental impact. During the ironmaking process, molten slag is generated alongside molten pig iron at temperatures ranging from approximately 1450°C to 1500°C.
To cool and solidify the slag, a process known as granulation is employed, where-in water serves as the primary cooling medium. High-pressure water jets—typically in the range of 5 to 10 m³ per ton of slag—are directed onto the flowing molten slag. This rapid quenching results in the formation of granulated slag and the simultaneous generation of saturated steam and hot water.
A portion of the water used in this process is lost as steam, which is typically released into the atmosphere. Consequently, to maintain the required cooling capacity, additional freshwater must be introduced into the system to compensate for this loss.
To enhance water efficiency and reduce freshwater consumption, solutions are invited which can help in capturing and recovering water from the saturated steam generated during the water-based slag granulation process in blast furnace operations.
The proposed solution should satisfy following criteria:
Design Requirements for Water Recovery System from Saturated Steam
The proposed water recovery system must meet the following functional and operational criteria: