Integração energética aplicada a uma planta de fertilizantes visando a redução de consumo de utilidades quente e fria

Abstract

In this paper, an energy diagnosis was carried out in real fertilizer plant, located in the state of São Paulo, formed by six industrial units: 02 (two) dilute nitric acid plants, 02 (two) concentrated nitric acid plants, 01 (one) ammonium nitrate plant and 01 (one) prilling ammonium nitrate plant. This paper aimed to reduce the consumption of hot and cold utilities through the heat integration of each plant. The concept of heat integration is based on the maximization the energy efficiency of an industrial plant in order to reduce energy and fuel costs and consequently decrease the final cost of the final products, making them more competitive in the market. Although there are a vastly literature about heat integration, there are few studies of a heat integration been applied on real chemical process and there are no records about heat integration in an ammonium nitrate integrated plant, which confers the originality of this paper. Currently, about 20.5 % of the steam used in the industrial plant is imported from a neighboring plant, the estimated cost of this imported steam is approximately 5.4 million reais per year. Through the identification of the main currents involved in the process along with their respective characteristics as flow, temperature and composition, a model of a mass and energy balance was proposed to simulate the current condition of the plant to estimate the utilities consumption. The proposed model presented relative deviation of 7.6 % and 9.6 % for the hot and cold utilities respectively, which was considered as satisfactory for this paper. The heat integration was carried out through this model utilizing as premise the returning steam condensate of each plant for heating the cold process streams, in addition, the heat integration among the process streams will be carried out in the same plant when possible. For the Diluted Nitric Acid Plant II (PAND II) it was proposed to generate steam using two Heat Recovery Stem Generators. After the heat integration it was possible to confirm the possibility of reducing 100 % of the imported steam consumption and 11.4 % of the cooling water consumption, resulting in an annual economy of approximately R$ 5.6 million, representing 81.4 % of utilities costs. Through the analysis of the cash flows, an IRR value of 168.49 % was obtained with a discounted payback of 8.4 months, considering a cost of capital of 14 % for a period of 20 years and disregarding the depreciation cost of the equipment.