Low Grade Heat Utilisation

By Bharat Yadav

Energy is utilised in the industry in different forms such as electricity, steam, and thermal.  One of the measures of sustainability is specific energy consumption. One of the energy conservation measures is to recover and utilise low grade heat energy in some form.  Here is an overview of low grade heat utilisation.

A plant involves generation, distribution and utilisation of energy. Typical utilities include steam, electricity, compressed air, thermic fluid apart from various water and HVAC related systems.

Heat is one of the major forms of energy in thermal power plants, refineries, metal industry, fertiliser and petrochemical industry.

One of the basic outcomes of energy conservation and energy audits is identification of energy being wasted. Mere identification of waste/low grade heat energy is not sufficient unless it can be utilised in the Plant and in turn reduce some form and quantity of energy. Utilisation of low grade heat is a challenge in terms of techno-commercial viability.

Various forms of heat include steam (including flash steam), condensate, hot water, hot air, hot exhaust/flue gases, engine jacket heat, compressor jacket heat, heat of compression, thermic fluids used in different processes. Solar thermal is also one of the forms that can be utilised as alternative heat source for applications.

Low grade heat applications include HVAC, cleaning applications, vaporizer and water treatment.

Low grade heat recovery and utilisation calls for appropriate selection of heat transfer system and thermal insulation till point of application.

Proper quantification of energy is more important in case of low grade heat than for high enthalpy sources for appropriate cost benefit analysis. Operational cost analysis is main criteria for selecting an appropriate option apart from part load efficiency.

A few sources of heat energy and their likely utilisation in various Plants are indicated below:

Sr.

Application  Segment

Energy Source

Utilisation

 1 BOPP/BOPET / Polyfilm Segment with CP Plant Process Heat from Continuous Polymerization Steam / Hot Water

VAM for Process and HVAC

2 Complexes with Engine Based Power Generation Hot flue gas from exhaust of the DG/GE based CPP  Hot Water

VAM for Building HVAC

 3 IGCC / CHP  / CCPP Power Plants Steam Power Generation Enhancement during summer
4 Thermal Power Plant Excess Auxiliary Steam / Condensate/ Flash Recovery Steam VAM for HVAC of Buildings / BFW
5 POY/PFY /Nylon/Textile Plant Steam VAM for HVAC or Flash Steam for Humidification
6 Air Conditioned Spaces (Once Through System) HVAC exhaust Hot Air (Heat recovery Wheel)

HVAC

7 Chlor Alkali Plant Boiler/Steam Steam / Hot Water

VAM for Process Refrigeration;  hot  water for LPG vaporization

8 Plant with Solar Thermal Solar Thermal Hot Water for  LPG Vaporization;  Product Cleaning
9 Plant with Multi-Stage Compressors Heat of Compression HoC for Process Air Drying

TCE has a portfolio of utilisation of waste heat/low grade heat/solar heat/surplus heat for various industries including automotive industry, power plants, metal industry, petrochemicals including polyfilms, chlor-alkali, water treatment and pulp & paper.

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