Miller Magazine Issue: 119 November 2019

58 COVER STORY MILLER / NOVEMBER 2019 installation up to date and flawless. USE SOFT STARTERS AND/OR VARIABLE FREQUENCY DRIVES Direct start and star-delta starts cause higher currents, and thus waste more energy, than soft starters and variable frequency drives. A soft starter is, basically, a component that makes a motor start slowly. A VFD is a component that adjusts the power used by a motor according to the load. The soft starter is what you want if the machine will always work at the same rate, like in a roller, while the VFD is great when capacity varies, like in a belt conveyor. USE A PLC TO COORDINATE OPERATIONS Having to start and stop equipment manually means having longer times when you grain isn’t processed. You start the motors in an operation, from last to first, and you have to make sure the equipment is running in re- gime (in normal stable operation) before starting the next one. If you do it by instinct, you will naturally wait a little more than required, just because of the fear of getting a clog in the system and have your boss screaming at you. An automatic system can be calibrated to wait just the minimum, thus saving valuable time that would be other- wise wasted running machines empty. USE HIGH EFFICIENCY MOTORS AND GEAR DRIVES There are American (NEMA) and European (IEC) stand- ards that measure the efficiency of motors. Outside of the First World, there is hardly any regulation mandating for the use of high efficiency motors, but, if your utility bill is high, it doesn’t hurt to take a look at them. In any motor, there is a percentage of the power in- take that doesn’t go to moving anything, but is instead lost as heat. Inefficiencies are a result of mechanical and electrical imperfections in the motor. With a more careful design and fabrication, higher efficiencies are achieved. In the case of large motors, it could make sense chang- ing the usual squirrel cage motor and use a synchronous motor instead. These are more expensive, but are also more efficient by their very conceptual design. Higher efficiency can be achieved in the gear reduc- ers too. The efficiency in a gear drive ranges from 49% to 98%, depending on the type and the number of re- ducing stages. The selection must take into account the power, the reduction ratio and the position of the shafts, so this is something to consult with your sup- plier. The most efficient is in-line helical (95% to 98%), but it requires the input and output shafts to be aligned. The following best is helical spiral bevel, with efficien- cies between 94% and 97%. USE SUNLIGHT AS MUCH AS POSSIBLE The savings achieved by using daylight instead of electric light may be small, but they are savings anyway. So get some of the sheets in your warehouse replaced with trans- lucid sheets, and let your workers enjoy some natural light. USE INSULATION IN ALL THERMAL EQUIPMENTS The amount of energy wasted in grain dryers be- cause of poor insulation is breath taking. Not only in the machine itself, but also in the ducts and burners. Now that insulation materials are cheap and readily available, there is no excuse for not getting an up- grade in your dryer and insulating it. My preference is for rock wool, that is non flammable and non toxic, but I have used glass fibre very successfully. PREFER GAS OR FUEL OIL TO WOOD In grain dryers, fluid fuels allow for finer control and are more efficient. Wood may be cheaper, but the way you control the temperature is by mixing the hot air with cold air, wasting energy in the process. With gas, you can control the tem- perature by controlling the burner instead. If gas is too expensive in your country, you could con- sider fuel oil, which is the fraction of oil closest to tar that you can still burn. It requires a more com- plex pre-heating system because it is too viscous and heavy, but is very cheap and also easy to control. Or you may use a combined burner. This type uses a wood burner to supply a minimum of heat to the system and the supplements it with a gas burner to get to the desired temperature.