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Environment is a mirror which reflect our error". So, efforts continue working towards achieving technologies, which are environment friendly, and application of those in industry will lead to considerable energy conservation. Innovative Heat Exchanger is one such device which has the potential to make the Indian fertilizer industry the most efficient in the world, in terms of energy savings and reduction in the heat exchanger area. Heat exchangers are the backbone of the fertilizer industry, since the energy efficiency depends largely on how much waste heat can be recovered and reused. Further improved heat exchange in turn, conserves use of natural resources like coal, oil, gas etc.
Developed in-house by the Department of Chemical Engineering, IIT Delhi under Prof. K.D. P. Nigam, the pilot plant facility of the Innovative Heat Exchanger was recently inaugurated by Shri Ram Vilas Paswan, Union Minister of Chemicals & Fertilizers and Steel. The cost of the Pilot project is Rs. 2.46 crores and took three years of research and design to materialize.
Heat exchangers contribute to about 25 % of the equipments installed in fertilizer industry. Presently, shell and tube heat exchangers, plate type exchangers and helical pipe exchangers are in practice in the process industries. Fertilizer plants are highly energy intensive and 70 - 80% of the total production cost of Fertilizer is spent on energy alone. The Fertilizer industry reached a landmark, when it achieved about 11.20 million tons production during 1996 - 97, comprising of about 8.38 million tons of nitrogenous production and 2.82 million tons of phosphatic production. Today, the industry is not only an essential link in the food chain, but also has made its impact on the national economy. Plant designers continue to design and build ammonia plants with lower energy consumption. This has resulted in reduction of energy consumption from the earlier levels of 16 - 18 Giga Calories/Matric Tonnes to the present levels of 7.5 - 8.0 G Cal/MT of ammonia for Naptha based plants.
Energy conservation measures in Fertilizer industries have gained importance in the recent past and all new plants are constructed with the latest concept of low energy consumption. The theoretical thermodynamic heat requirement for ammonia production is about 4.47 G Cal/MT, as against the current average consumption of 8 G Cal/MT for natural gas based and 9 G Cal/ MT for oil based ammonia plants. Thus, about 3.5 G cal/MT to 4.5 G Cal /MT is lost in cooling water or ambient air through stack or radiation losses. Though all processes will have some losses of energy from the system, the potential to reduce the energy consumption is substantial.
The innovative heat exchanger consists of flatter velocity profiles and lower temperature gradient, which improves its performance. Narrower residence time and thermal time distributions can be obtained by increasing the mixing between the fluid elements of different age groups and temperatures. Innovative Heat Exchanger also finds extensive use owing to the cross-sectional mixing induced by centrifugal force. Uniform thermal environment is an extremely desirous factor for the improved performance of any heat exchanger. Presently, shell and tube heat exchangers, plate type exchangers and helical pipe exchangers are in practice in the process industries.
The idea of the innovative heat exchanger is based on the concept of centrifugal force. In the present device technique has been innovated for the effective utilization of the centrifugal force to advantage. The flow generated in this device due to curvature of a stationary surface bounding the flow changes direction continuously causing a local deflection of the velocity vector. This results in complex secondary flows, which is one of the principal features of fluid flow in this device. The new flow geometry is capable of rotating the plane of vortex formation by any angle thereby exploiting the advantage of centrifugal force. The occurrence of this phenomenon increases mixing between the fluid elements of different age groups and temperatures. This leads to considerable increase in the heat transfer coefficient.
After the technical discussion with the management and technical group in Fertilizer industry, various potential areas where this innovative heat exchanger can replace the existing heat exchangers were identified. Some of which are: In Ammonia plants:Methanator feed preheater, CO2 strip reboil/shift effluent coolers feed gas, CO2 stripper overhead trim cooler, Lean-solution cooler (Air cooler), CO2 stripper condenser air cooler, CO2 ejector steam generator, CO2 ejector steam reboiler, NH3 refrigeration condenser, Lean solution/BFW exchanger and in the Urea plants: Distillation pre-heater, HP hydrolyzer preheater and Distillation tower reboiler.
There is 15 – 20 % improvement in heat transfer with 60-70 % reduction in the exchanger area as compared to shell and tube heat exchanger. This device has two-fold advantage of intensifying the convective transfer processes (i.e. increase heat and mass transfer coefficients) and also provide increased transfer area per unit volume of space. It offers higher film coefficient (i.e. the rate at which heat is transferred through a wall from one fluid to another) and more effective use of available pressure drop result in efficient and less expensive designs. The Innovative Heat Exchanger geometry permits handling of high temperatures and extreme temperature differentials without high-induced stresses or costly expansion joints. The compact size provides a distinct benefit and ease of fabrication and its performance is substantially closer to plug flow system.
It can, not only work as a heat exchanger but also as inline mixer, separation devices and in chemical reactor. It has a variety of applications: in coiled membranes blood oxygenators, kidney dialysis devices due to their effectiveness in reducing concentration polarization, chemical reactors due to increased residence time and minimized axial dispersion, heat exchangers, cryogenic systems, bio-sensors, clean steam generators, natural gas heaters, freeze condensers, chromatographic columns, sample coolers and room heaters. (PIB Feature).
*PIB Features Unit
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