Reuse of Waste Heat
Returning to energy savings, one of the most significant ar- eas for achieving energy reductions is in the reuse of waste heat from many foundry processes. The reuse of waste heat can often net energy savings of 15% to 25% or more. While technologies exist for converting waste heat energy to elec- tric power (or, indirectly, compressed air), these often prove costly in terms of the required capital expenditures and ex- tended payback. A simple and less costly approach is to di- rectly recover captured waste heat for use in an area that requires heat. This can be performed by transporting heat via air-to-air, air-to-liquid, liquid-to-air, or liquid-to-liquid conversion. Taking this approach greatly simplifies the pro- cess by logically using an available heat to provide heat else- where as needed.
Several successful projects have been completed that utilize waste heat from melting operations for building heat, core drying, and/or shower water heating. With proper design, these systems can also use heat pump principles to utilize waste heat for air conditioning or chilling, to maximize the year-round benefit of the facility’s investment.
The simplest approach to reusing baghouse heat energy is the direct reintroduction of the exhausted filtered air back into the plant. This reintroduction of waste air is feasible if there are no additional gaseous pollutants in the waste air stream. The superior performance of modern baghouses and the advent of broken bag detection technology have elimi- nated the concern of reintroduction of particulates back into the workplace. In fact, well run dust collection equipment
regularly contains a lower particulate count than what may be experienced in the general workplace. Using this strategy provides a two-fold benefit, the reuse of available heat for space heating, and the reduction of the need for additional heated makeup air.
Air Handling Systems
Emissions requirements imposed on the metalcasting indus- try in the 1970s caused many foundries to put into service extensive air capture and baghouse systems. Many of these systems may have not undergone any significant redesign since their initial installation. The average foundry emis- sion system may consume 20% to 25% of the total energy usage in a foundry. In recent years, many improvements in piping, engineering, components, baghouse design, and bag materials have taken place. Our industry now has a greater understanding of the role of mass flows through ductwork, pressure drops across various components, fan and motor operating curves, and the computer monitoring and control of actuating devices.
Many systems have been put in service reusing existing fans and motors and other components, to facilitate installation cost savings. Other systems were placed within the limita- tions of existing plant layouts. These choices, which may have been the best option at the time, have resulted in higher pressure drops, wasted horsepower, and lower system effi- ciencies. We need to step back and re-evaluate the use of best engineering practices and available strategies to lower pressure drops, reduce horsepower consumed and improve system efficiencies.
Figure 3. Building heating from cupola melting process waste heat and benefit chart.
International Journal of Metalcasting/Summer 10
Figure 4. Baghouse heat recovery and benefit chart. 11
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81