Water Management and Pollution Control in Steel Plant

8/10/2019 Water Management and Pollution Control in Steel Plant

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Water Management and Pollution Control in

Steel Plant

Posted by Satyendra on Sep 4, 2013 in Articles | 0 comments

Water Management and Pollution Control in Steel Plant

An integrated steel plant incorporates a number of processes right from raw material preparation

to rolling of finish steel. All these processes need water. When the water is used in these processes it gets contaminated with pollutants in various amounts and concentrations. Typical

requirement of water in various processes in steel plant needs 100 to 200 Cum per ton of steel.

Pumping capacities for this amount of water is needed in the steel plant. The requirement of

makeup water depends on the water treatment and recirculation facilities in the plant and usually

is in the range of 2 to 4 Cum per ton of steel.

Water management in an integrated steel plant is very important for its successful operation since

the integrated steel plant needs a large amount of water for its operation. During the operation ofthe plant this water gets polluted. It is very difficult to separate water pollution control from

water management in the plant. A good water management leads to a decrease in pollution

control of water while at the same time pollution control of water needs good water

management. Good water management requires zero or minimum water discharge from the

plant. This is achieved by incorporating elaborate water treatment systems for recirculation of

water. This reduces water consumption since there is a reduction in the requirement of makeup

water. It also reduces the water pollution since the water discharge from the plant boundary

becomes nil or negligible. Further it reduces the necessity and cost of treatment of polluted

water before its discharge from the plant boundary.

Use of water
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Water has many varied uses in the iron and steel plant and the quality of water needed for each

use also vary. Further there may be one through systems and there are systems with either partial

or full recirculation of water. The important uses of water in an integrated steel plant are given

below.

Water is needed to meet the process needs. Examples are adjustment of moisture in coal

blend, wet quenching of coke, addition in sinter mix for pelletization in pelletizing drum,

spraying of water at blast furnace top for controlling top temperature, granulation of

liquid BF slag, pig casting, continuous casting, descaling of steel before hot rolling, on

line heat treatment and control of temperature in hot rolling mills and adjustment of

strength of pickling acid etc.

Water is used for conditioning of the materials for the ease in handling and transport.Examples are transport of scale in continuous casting and hot rolling, addition of water in

raw materials for dust suppression during their transport and storages, making of slurry

for pipeline transport, transport of fly ash to ash pond and its storage there etc.

Various type of gases generated during different processes are cooled, cleaned and

conditioned with water.

Water is used for heat transfer. Various equipments, rolls and shell of furnaces are cooled

by water. Both direct and indirect cooling methods are employed for this purpose.

Production of steam for process needs and for power generation purpose needs

demineralised water.

Water is used for miscellaneous cooling such as furnaces and refractories are cooled with

water before taking up of repairs and/or relining. Metal and slag spillages are cooled with

water before their transportation.

Water based mortars, runner mass and clays need water in required quantity.

Sewage and water treatment processes need addition of water for efficient treatment and

better reaction. Water is also needed for neutralizing of acidic effluents. Water is used for cleaning and washing of shop floors so that settled dust on the shop

floors can be cleaned.

Electric control rooms and tunnels are ventilated with moist air for which water sprayers

are used.


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Water is used for fire fighting purpose in a steel plant. Water is also used for drinking

water, cooler, canteens and wash rooms.

Steel plants are to maintain greenery inside the plant for the purpose of environment. This

activity needs water.

Terms used for water

Process water It is the water that comes into contact with an end product or with

materials incorporated into an end product.

Cooling water Water used exclusively for cooling. Boiler feed water It is demineralised water used in boilers for conversion into steam. Fire fighting water It is the water used for extinguishing of fires Intake water It is the water added to a system. Make up water It is the water which is added to the system to compensate for the

losses.

Effluent water It is the waste water taken out of the system. Domestic water It is also known as sanitary water and used for drinking and wash

rooms.

Service water It is the water used for shop floor cleaning and gardening and other such

uses.

Pollutants in effluent water

The following pollutants are present in the effluent water.

Colloidal and suspended solids ore and flux fines, scale, sand, fly ash, coal and coke

fines etc.

Temperature and heat Cooling water, boiler blow down etc. Oil rolling mill oils, lubricants, hydraulic oils, quenching oils, fuel oils, solvents, tar

and pitch etc.

Chemicals These consist of pickling liquor, acid sludge, caustic wash, lime, spent

ammoniacal liquor, boiler blow down and toxic chemicals etc.

Sanitary wastes waste from canteen, wash rooms, change rooms and toilets etc.


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Discharge of effluent water without treatment will cause pollution at the place of discharge and

hence adequate treatment of effluent water is necessary before its discharge from the steel plant.

Processes for effluent treatment

The following are some of the major methods commonly used for treatment of effluents.

Settling tanks A conventional settling process in rectangular or circular tanks is used for

sedimentation of suspended solids. Considering the outputs, flocculation is sometimes

used. The withdrawl of sludge is done by means of pumps or by means of a crane with

grab.

For removal of suspended solids of very fine size and varying size thickeners, clarifiers

and clariflocculators are used individually or in combination. Coagulants such as alum,

ferric chloride, ferric sulphates, poly electrolytes are used for coagulation of the

suspended solids.

For removal of heat and reduction of temperature hot water is treated in cooling pond,

spray basin or cooling towers.

Neutralization Waste water pH value is to be controlled between 6.5 to 7.5. For this

acid water with low pH values are treated with alkalis while the alkaline water with high

pH values are treated with acids. Effluent containing oils For collecting oils from effluents, conventional process of

natural floatation and skimming is used. The collection of skimmed oil is done by mobile

troughs.

Waste water from coke ovens with high biological oxygen demand (BOD) are treated

either in trickling filters or by activated sludge process. Activated sludge process with

extended aeration is more effective in reduction of BOD values. For proper microbial

decomposition, coke oven waste water needs supplementation of phosphorus to make it

balanced for nutrients. If raw sewage is avilable then addition of this sewage helps in

activated sludge process.

A typical flow sheet for water pollution control is given in Fig 1


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Fig 1 Typical flow sheet of water pollution control
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Water Management and Pollution Control in Steel Plant

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