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...

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...

Heating of Steel in Reheating Furnace Jun01

Heating of Steel in Reheating Furnace...

Heating of Steel in Reheating Furnace Reheating furnace is important equipment in the process of hot rolling. It is the heart of any hot rolling mill. Reheating of steel is a continuous process. The steel material to be rolled is charged at the entrance of the reheating furnace. The steel material is pushed forward on the hearth of the furnace by means of a pusher machine whose ram is in direct contact with the steel material. The steel material is pre-heated, heated and soaked as it passes through pre-heating, heating and soaking zone of the reheating furnace. At the end of the soaking zone of the furnace, the steel material is discharged from the furnace by ejector for rolling in the rolling mill. The temperature of the heated steel material at the time of discharged depends on several factors and it can vary in the range of 1100 deg C to 1250 deg C. The size of the reheating furnace is normally expressed as the capacity to supply the rolling mill with sufficiently hot steel, in tons per hour. Steel materials with different material compositions, dimensions, and charging temperatures can reside in the furnace simultaneously. The reheating furnace used for heating the steel materials is normally considered to be having high energy consumption. It also emits good amount pollutants in the atmosphere because the process used for heat generation is the combustion process. Reheating process has considerable influence on the economics of the working of the rolling mill. There are usually three types of continuous reheating furnaces used in the rolling mills. These are (i) pusher type furnace, (ii) walking hearth furnace, and (iii) walking beam furnace. Pusher type furnaces have some disadvantages which includes (i) frequent damage of refractory hearth, (ii) skid marks...

Direct Iron Ore Smelting Process for Ironmaking Mar28

Direct Iron Ore Smelting Process for Ironmaking...

Direct Iron Ore Smelting Process for Ironmaking Direct iron ore smelting (DIOS) process is a smelting reduction process for the production of hot metal (liquid iron). It is a two-stage process which has been developed in Japan. It uses non-coking coal in a powder or granular form to smelt iron ore fines into liquid iron (hot metal) and hence, there is no necessity of a coke ovens plant and a sintering plant. The ore fines are pre-reduced in a fluidized bed furnace and are charged in the smelting reduction furnace along with non-coking coal and fluxes. Oxygen is blown into the smelting reduction furnace. The two stages of the DIOS process consists of (i) pre reduction of iron ore in preliminary reduction furnace (PRF), and (ii) the final reduction and melting in the smelting reduction furnace (SRF). The pre reduction of the ore is carried out in two steps utilizing the exhaust gas from the SRF. Each of the steps uses a fluidized bed reactor which is designed as a vertical furnace. The development of the DIOS process started in 1988 in Japan as a joint research project among eight iron manufacturing companies who had, prior to 1988, been studying the smelting-reduction process individually. This project was sponsored by MITI, the Japanese Ministry of International Trade and Industry. Japanese companies and Japan Iron and Steel Federation (JISF) actively supported the development of the process during the period of 1988 to 1996. Core technology study necessary for the construction of the pilot plant was done during the period 1988 to 1990. During this period core technologies were established. These core technologies include (i) an increase in the thermal efficiency of a SRF, (ii) the technology to be integrated with a PRF, (iii) the technology for...

Development of Smelting Reduction Processes for Ironmaking Mar08

Development of Smelting Reduction Processes for Ironmaking...

Development of Smelting Reduction Processes for Ironmaking Smelting reduction (SR) processes are the most recent development in the production technology of hot metal (liquid iron). These processes combine the gasification of non-coking coal with the melt reduction of iron ore. Energy intensity of SR processes is lower than that of blast furnace (BF), since the production of coke is not needed and the need for preparation of iron ore is also reduced. SR ironmaking process was conceived in the late 1930s. The history of the development of SR processes goes back to the 1950s. The laboratory scale fundamental studies on the SR of iron ore were started first by Dancy in 1951. However, serious efforts started from 1980 onwards. There have been two separate lines of development of primary ironmaking technology during the second half of twentieth century. The first line of development was centred on the BF which remained the principal process unit for the hot metal production. In general, this line of the development did not encompass any radical process changes in the furnace itself. It proceeded through a gradual evolution which involved (i) increase in the furnace size, (ii) improvement in the burden preparation, (iii) increase in the top pressure, (iv) increase of hot blast temperature, (v) bell-less charging and improvements in burden distribution, (vi) improvements in refractories and cooling systems, (vii) injection of auxiliary fuels (fuel gas, liquid fuel, or pulverized coal) and enrichment of hot air blast with oxygen (O2), and (viii) application of automation as well as improvements in instrumentation and control technology. The continued success of the ironmaking in BF reflects the very high levels of thermal and chemical efficiencies which can be achieved during the production of hot metal and the consequent cost advantages. In fact,...