Wealth from Waste Heat…
The depletion of the ozone layer, the breakages of ice chucks in Arctic oceans and the split of Delaware-sized iceberg from Antarctic shelf are the most terrific and fearful global warning on the global warming…! However, we are still busy debating on the causes and impacts of the global warming while reading those headlines…! Hence, holistic approaches and collective efforts right from the individuals, the companies and the governments are required to bring down the carbon footprints all over the world. In the USA alone one of third of the energy is discharged directly into the atmosphere in the form of heat whose energy is roughly equivalent to 4 months of its oil import.
Although the European union expects Mr. Trump to relax his stand on the Paris agreement, the fate of the agreement still looks grim and uncertain. Unless the USA takes a leading role in combating the global warming, the entire effort may go futile.
Roles of Companies…
“More than 60% of SME business owners did not think that energy efficiency was a top priority in the workplace and more than 50% did not have active measures in place to help them use their energy smarter”, says a survey result issued on 21st November, 2016 by YouGov. Another result from this survey points out that 1 in 10 SMEs perform an energy audit annually. On the other end, there are some large scale establishments such as petroleum refineries, petrochemical, chemical and smelting industries are aware of energy efficiency and implement the waste heat recovery processes in their plants.
A factory is considered to be smart not based on the information connected eco-systems, but also by the energy efficiency. Additionally, the environment should be conducive for people working inside and living outside the factory. The heat stress is becoming the most neglected occupational hazards in tropical and sub-tropical countries. The heat radiating from iron, glass and ceramic units, impairs the health of the workers because of the prolonged heat exposure. In India. 40% of the employees working in high temperature environments are affected by the heat stress.
Companies emit heat directly into the atmosphere or cool them for other use only when it is profitable for them. However, mostly the heat is discharged into the surroundings.
The heat energy is divided into three categories based on its quality. The temperature of the heat energy 500C and above, is considered as high quality heat, which is available from cement kilns (without preheat), glass oxy — fuel furnaces and glass regenerative furnaces. Medium quality of heat, i.e. temperature ranging between 200C — 500C, is available at cement kiln, lime kilns, steel blast furnaces, metal casting iron cupola, aluminium melting and aluminium smelting industries. Low quality heat sources are water / steam boilers and ethylene furnaces whose temperature are less than 150C.
It is not cost effective to convert the low quality heat. The return on investment from them is very long. Unfortunately more than 80% of the waste heat are of low quality ranging below 100C.
Through waste heat recovery (WHR) processes, the reduction of energy consumption is achieved by about 5 to 30%. A traditional heat recovery system consists of steam pipes, compressors and generators to convert heat into the electricity. Alternatively, the heat energy is directly used to preheat the other systems for increased throughput and to reduce equipment size.
Only large companies (on compulsion?), adopt them while small and medium scale industries generally ignore the waste heat owing to the cost of the WHR systems. Traditionally, power generation can be achieved mainly by Rankine cycle, Organic Rankine cycle and Kalina cycle. Organic Rankine Cycle is widely used in the temperature range of 80C to 400C and the capital cost of this system ranges from $ 1,500–3,500 / kW. The other two systems cost about $ 1,000 to 1,500 /kW. Apart from the higher capital expenditure, WHRs add costs to their maintenance and occupy large spaces.
Here come thermo-electric based waste heat recovery systems which directly convert heat into electrical energy. They are very compact and can be mounted directly onto the hotspots such as furnace walls or hot pipes. Only the heat-exchangers are technically very challenging and occupy some floor space but significantly lesser than the traditional WHRs. The downside of the thermo-electric based waste heat recovery systems is, its efficiency. It is just 7 to 10% when the available temperature is about 200C. The efficiency increases to 12% in the higher temperature ranges. But the traditional heat recovery systems provide thermal conversion efficiency of about 35%.
The waste heat recovery is a true wealth in terms of money, environment, safety and the society. The cost of implementation should be made reasonable through fresh R&Ds, advanced technologies and government incentives. Innovative project finances are available with various institutes. There are predictions that the cost of WHRs will rise due to demand after the Paris agreement which may make them mandatory for certain types of industries, is implemented.