Techniques of Waste Heat Recovery
Waste heat recovery is being more used more and more often today as it is becoming more effective, due to increasing energy prices, technological developments and a decrease in equipment costs. Heat recovery can be classified into three main strategies: recycling energy back into the process, recovering the energy for other onsite use and using it to generate electricity in combined heat and power systems. Once the system has been made as efficient as possible before using waste heat recovery, passive strategies are used. These have no significant input for operation except for auxiliary equipment such as pumps and fans. The last case is active strategies, which require some input of energy to upgrade …show more content…
These are typically used when heating liquids with the heat contained by condensates from refrigeration and air-conditioning systems.
Load preheating
Load preheating is when waste heat leaving a system is used to preheat the load entering a system. The most common has been discussed, the economizer for pre heating a boiler. Other applications use direct heat transfer between exhaust gases and solid materials entering the furnace. In aluminium casting, stack melters can replace reveberatory furnaces to reduce energy consumption, in one case it has helped reduce consumption by 47% compared to conventional furnaces. While feed water preheating is standard practice, load preheating is not as widely used. This is due to difficulties in controlling product quality, environmental issues and increased cost and complexity of building advanced furnaces. However this has received increased attention over last decade as it is seen as a source or real potential in waste heat recovery.
Low temperature energy recovery options
Not all waste heat is high in energy and other options need to be looked at to recover energy from low temperature waste sources. There are large quantities of waste heat available below 200ºC and this can be used very effectively for example one integrated steel mill in Japan installed a power generation plant with a 3.5 MW capacity using cooling water at only 98ºC.
In the case of