Download Energy Balance and Coke Making: Environmental Implications and Solutions and more Study notes Materials Physics in PDF only on Docsity! Lecture 40: Thoughts on energy balance Content Preamble What is to be done more beyond fuel saving Key Words: Dry quenching technology, coke making, energy balance Preamble In the earlier lectures we have discussed the role of energy balance on fuel saving and hence on conservation of natural resources. Energy balance is a very powerful tool to address the issues of saving natural resources. What can be done more beyond fuel savings? Let us think. Facts about use of natural energy resources Fossil fuel based energy availability is associated with a) Discharge of CO in the environment and other harmful gases like SO , NO etc. 1 kg mole of carbon discharges 1 kg mole of CO in the environment. In other words 1 kg carbon produces 3.7 kg CO . b) Large amount of heat is carried away by the products of combustion. In metal extraction processes at high temperatures, products like liquid metal, slag, gases and coke carry a large fraction of heat. Sensible heat is the issue of concern.In this connection it is important to understand quality of heat. Quality of heat is decided by the temperature. Higher is the temperature of discharged product, higher is the quality of heat. Sensible heat in products: In thermo –mechanical processing, steel is heated to 1200 . Steel is rolled at this temperature and then cooled by water. Large amounts of emissions are discharged. In coke making coke is discharged at around 1200 and water cooled. Large amount of sensible heat is lost and as well as emission arising from water contaminants are discharged into atmosphere. Environmental pollution is a concern. Sensible heat in waste gas may not be possible to use since waste gases contain fine solid particles. However potential energy can be utilized. Energy balance and environment cleanliness Let me illustrate how energy balance can lead to environment cleanliness. Consider coke making technology. The details are discussed in lecture 27. As discussed in lecture 26, coke is an important source of chemical and thermal energy in integrated steel plants producing steel from iron ore. In fact 1 ton of steel would require around 940 kg coal (Assuming coke consumption is 500 kg/ton of hot metal), thus 10,000 tons of steel would require 6600 tons of coke (assuming 0.75 ton of steel is produced from 1ton hot metal). For annual production of few million tons of steel, Coke requirement would be very high. Let us consider coke‐coke conversion materials and heat balance. Material balance has already been discussed in lecture 27. Consider heat balance of a by‐product coke oven. The details of heat balance calculations can be seen in video lecture 40 on materials and heat balance. Heat balance is given for 1000kg coal. Heat input 818 4 10 kcal Calorific value of coke oven gas 704 10 113 10 kg cal kg. mole⁄(It is assumed that 40% of coke oven gas of calorific value is used to produce heat in coke oven) Heat out put kcal Calorific value of coke 5416x103 Calorific value of tar 351x103 Calorific value of coke oven gas 1053x103 Sensible heat in coke 305x103 Sensible heat in coke oven gas 174x103 Analysis of heat output Calorific values of coke, tar and coke oven gas can be utilized by combustion. Sensible heat in coke is notutilized since coke is wet quenched on wet quenching all sensible heat 305 coke is lost. In addition to this loss, air born coked us emissions coke are produced. Also huge water is required say around 0.5 0.6 m /ton coke. The in water are discharged in environment. 10 kcal 725 kg⁄ 50 kg ton⁄ contaminants Energy balance and technology development The above analysis puts a pressure to develop a new technology which can capture and reuse the sensible heat in coke. This new technology will also contribute simultaneously to the cleanliness of environment.