TOTAL SITE INTEGRATION IN SPONGE IRON PRODUCTION PROCESS

Abstract

In the present work energy conservation through process integration and total site integration of sponge iron processes is carried out. For this purpose three different plants of coal based sponge iron process such as Plant A, Plant B and Plant C are considered. These are based on SL/RN process which is widely and most commonly used method in coal based sponge iron production plants in India. Two strategies are proposed namely Strategy I and Strategy 2. which are applied to all the three plants. In Strategy I, concept of process integration is applied for energy conservation on all three plants individually. Preheating of kiln feed and slinger coal is done using the heat of gas exiting the ESP. preheating of kiln air is done through kiln exit sponge iron. and power generation is done through heat of waste gas coming out from ABC. In Strategy 2. concept of total site integration is applied to all three plants collectively. In this strategy kiln air is preheated with kiln exit sponge iron in each plant separately, ESP exit gas of all three plants is collected and used for preheating kiln feed and slinger coal in one of the plants. Further, ABC exit gas of all plants is collected in the same plant and used for generating electricity. For integration, stream data is collected and strategies are formulated. For each strategy hot and cold utility requirements are computed using Pinch technology. 'l'hen energy balance is applied on rotary kiln. 1-leat requirements like hot utility, sensible heat gain by coal, iron ore and air. heat for moisture removal, kiln losses, and heat of reactions are considered. The amount of coal required is calculated based on heat required inside the kiln. Using Strategies I and 2 preheating of coal, air and kiln feed is carried out where inlet temperatures of these streams change. As these streams enter to kiln at higher temperatures. these require less heat inside the kiln to reach the reaction temperature. Thus, coal requirement in the kiln also reduces as it is the only source of energy. Consequently amount of air required is also reduced. In these strategies amount of air required is calculated based on amount of coal required. Sensible heat gain requirement of air changes with change in amount of' air, which causes change in amount of coal required. For each value of coal consumption, iterations are performed to find constant amount of air required. For obtained fixed value of coal and air required, stream table is revisedand coal required is calculated again. Finally, constant amounts of coal and air are achieved. This method is different than usual method of integration because process data cannot be separated from utility data. Coal required in plant is process stream as well as utility stream which require iterations within iterations. For each strategy cost of equipment required for modification like g-s heat exchanger, ducts, ceramic filter, and boiler turbine system is calculated. Finally, strategies are compared based on amount of coal saving, water saving, capital required, profit per year, net profit, and payback period. Among these strategies, Strategy 2 is selected as the best modification which gives profit of Rs 11636.97 lakh/year and payback period of 4.20 years. It gives 32% and 97.1% savings in coal and water consumption, respectively, in comparison to existing system whereas. for Strategy I these are found as 22.2% and 96.9% only.