Waste Heat Recovery Devices...

Waste Heat Recovery Devices  Industrial furnaces are used for carrying out certain processes which requires heat. Heat in the furnace is provided by (i) fuel energy, (ii) chemical energy, (iii) electrical energy or (iv) a combination of these energies. Gases which are generated during the process leaves the furnace at a temperature which is the inside temperature of the furnace and hence have a high sensible heat content. Sometimes the exhaust gases carries some chemical energy, which raises the temperature of exhaust gases further due to post combustion because of this chemical energy. The heat energy contained in the exhaust gases is the waste energy since it gets dumped in the environment. However, it is possible to recover some part of this energy if investments are made in waste heat recovery devices (WHRDs). Methods for waste heat recovery include (i) transferring heat between exhaust gases and combustion air for its preheating, (ii) transferring heat to the load entering furnaces, (iii) generation of steam and electrical power, or (iv) using waste heat with a heat pump for heating or cooling facilities. WHRDs work on the principle of heat exchange. During heat exchange the heat energy of the exhaust gases gets transferred to some other fluid medium. This exchange of heat reduces the temperature of the exhaust gases and simultaneously increases the temperature of the fluid medium. The heated fluid medium is either recycled back to the process or utilized in the production of some utilities such as steam or power etc. The benefits of WHRDs devices are multiple namely (i) economic, (ii) resource (fuel) saving, and (iii) environmental. The benefits of these devices include (i) saving of fuel, (ii) generation of electricity and mechanical work, (iii) reducing cooling needs, (iv) reducing capital investment costs in...

Energy Management in Small and Medium sized Re-rolling mills...

Energy Management in Small and Medium sized Re-rolling mills Energy consumption in small and medium sized re-rolling mills takes place in two forms namely (i) electrical energy, and (ii) fuel or heat energy. Electrical energy is used directly in main rolling process for shaping of hot billets into rolled product (rolling mill, and shears etc.), in reheating furnace (coal pulverizer, blower, and pusher etc.) and also in auxiliary (roll turning machines, pumps, man coolers, overhead crane etc.), and shop lighting. Fuel energy is used in the reheating furnace for raising the temperature of the feed material to desired temperatures (generally 1150 deg C–1250 deg C). The division of the energy in these two forms normally varies from mill to mill based on the practices employed as well facilities installed in the re-rolling mills in SME (small and medium enterprise) sector. However, the share of electrical energy in small and medium sized mill generally varies in the range 20 % to 30 %. Consumption of fuel energy takes the major share of the energy consumption and usually constitutes 70 % to 80 %. From a theoretical perspective, the energy in hot rolling is primarily determined by the requirements of reheating of feed material. The theoretical energy for deformation is only 0.02 GJ/ton (around 5000 kcal/ton), compared to 0.83 GJ/ton (around 200,000 kcal /ton) for heating billets when charged cold in the reheating furnace. Though it is not technically feasible to achieve theoretical energy consumption figures, but the energy efficiency of the rolling mill is depends upon how close it is to the theoretical consumption. Management of electrical energy consumption Out of the total electrical energy consumed by a re-rolling mill, the share of the process of rolling is in the range of around 60 %...

Rolling of Steel in a Modern Long Product Rolling Mill Jun19

Rolling of Steel in a Modern Long Product Rolling Mill...

Rolling of Steel in a Modern Long Product Rolling Mill Long product is a common name for (i) reinforcement steel bars, (ii) shaped steel bar products such as rounds, flats, squares, and hexagon etc., (iii) sectional products such as angles (equal and unequal), channels, beams, tees, and special profiles etc., and (iv) wire rods. Mills which roll long products are known as long product mills. Based on the product being rolled these mills are called, merchant bar mill, bar and rod mill, light section mill, rebar mill, light merchant mill, special bar quality (SBQ) mill, and wire rod mill etc. The product range of these mills usually consists of those shaped and sectional products whose cross-section is smaller than the cross section of the products rolled in medium and heavy section rolling mills. Wire rod mills produces steel wire rods of diameters 5 mm to 12.5 mm in coil form with the weight of the coil upto 2.5 tons. The qualities of steels being rolled in these mills can range from low carbon, mild steel, medium carbon, high carbon, and micro and low alloyed steels. The design of the long product rolling mill is required to provide right solutions for the required performance requirements which include high speed production, microstructure qualities of the product, and shortest changeover time from one product to other product etc. Large amount of flexibility is available in modern long products rolling mills. These mills are normally continuous mills consisting of three sets of rolling stands namely (i) roughing group of stands, (ii) intermediate group of stands and (iii) finishing group of stands. The input material for these mills is normally billet. A billet mill can be combined with the long product rolling mill through a roller hearth furnace in...

Air Pollution Control Devices...

Air Pollution Control Devices Air pollution control devices (APCD) are a series of devices which are used to prevent a variety of different pollutants, both gaseous and solid, from entering the atmosphere mainly out of the industrial stacks. These control devices can be separated into two broad categories namely (i) devices which control the amount of particulate matter escaping into the environment, and (ii) devices which controls the acidic gas emissions into the atmosphere. By and large the air pollutants are generated due to the combustion of fuels in the furnaces. The major combustion-generated pollutants are the oxides of nitrogen (NOx), sulphur dioxide (SO2), carbon monoxide (CO), unburned hydrocarbons, and particulate matter. The generated pollutants are carried by the exhaust gases produced during the combustion of the fuel. These exhaust gases are then normally passed through the APCDs before releasing them to the atmosphere.  The pollutants are removed, destroyed, or transformed in the control devices before the discharge of the exhaust gas into the atmospheric air. Common methods for removing the pollutants from the exhaust gases work on the following principles. Destroying pollutants by thermal or catalytic combustion, such as by use of a flare stack, a high temperature incinerator, or a catalytic combustion reactor. This technique is used when the pollutants are in the form of organic gases or vapours. During flame combustion or catalytic process, these organic pollutants are converted into water vapour and relatively less harmful products, such as carbon dioxide (CO2). Changing pollutants to less harmful forms through chemical reactions, such as converting nitrogen oxides (NOx) to nitrogen and water through the addition of ammonia to the exhaust gas in front of a selective catalytic reactor. In the technique known as ‘absorption’, the gaseous effluents are passed through scrubbers or absorbers. These contain a suitable liquid absorbent, which removes or modifies one or more...

Technology Upgradation Management in Re-rolling Mills...

Technology Upgradation Management in Re-rolling Mills Re-rolling mills in small and medium enterprise (SME) sector play an important role in meeting the demand of the finished steel in the country. These mills are crucial to the national steel economy since they are making available a large amount of finished steel in the market.  The technology adoption level of these mills is rather low and many of these mills operate with technologies which are 50 years to 60 years old. These mills operate at low level of productivities and high level of energy consumptions. The operations of these mills are mostly manual and most of the mill parameters as well as the quality of the product depend largely on the skill of the operators. Mill owners have the complete control over the management of the mill. The re-rolling mills are presently facing many problems and challenges. These include (i) shortage of skilled workers, (ii) shrinking market because of increasing competition, (iii) higher operating costs, (iv) low productivities, and (v) high energy consumption etc. The mill owners are presently not serious to solve the problems, since they are able to run the mills for at least a shift. The mill owners’ attitude towards finding solutions to the challenges being faced indicates that they are not aware of what is stored for them in the near future. The mill owners are not realizing that ignoring the major issues at this stage, can lead them, after certain period, to such a situation which will be out of their control. With the capacity expansions being implemented by integrated steel plants in India, the availability of finished steel is improving and the competition is becoming tougher as each day is passing by. The finished steel available from the integrated steel...