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11 November 20198 min reading

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 regime (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 otherwise wasted running machines empty.

Prof. Gustavo Sosa
Industrial Mechanical Engineer
Licensed Grain Inspector
MBA Project Management
SOSA – Engineering Consultants
In any industrial facility, the energy costs are a major issue. We have large motors, and we have a lot of them. Left unchecked, they can cause major problems in your company.

POWER FACTOR CORRECTION
Electrical power has two components. One is called active (or “true”), and it is the one you actually consume, as work performed or heat lost. The other one is called reactive, and it is just moved around, like waves in a lake. Both of them, summed in a vector, make the “apparent power”. Electrical motors are basically big rotating magnets, so they use a lot of reactive power. This is not bad or good per se, but for the electrical power companies, having too much reactive power means having to use larger components everywhere, just to accommodate something that nobody pays for. You can control this by adding capacitors in your facility, either next to the largest motors, or in a bank in the Control Station. These capacitors are “power factor correctors”. The power factor is this coefficient:

Power Factor =    (True Power)     
                           (Apparent Power)

If you correct the power factor to keep it over 90%, the electric company will reward you with a bonus in the bill.

The usual arrangement is correcting the large motors with a fixed capacitor in their power line, and also a set of variable capacitors in the facility Power and Control Room to correct the rest of the power.

SIMULTANEITY
Plan your system so the largest motors don’t work all at the same time. For example, you could have a large bin near the mill to stock the grain you process through the day. This bin is filled through a path of elevators and belts of 1000 ton/hour. On the other side of the facility, you have the reception of the incoming grain, with its own set of conveyors and also cleaners and dryers. Why not scheduling the work so you fill the “daily bin” at night and only receive grain during the day? Not only you would use smaller components to control the electric power, you also benefit of the lower costs of the electricity out of peak hours and stay in cheaper ranges of the bill.

TAKE ADVANTAGE OF THE DAILY SCHEDULE
Use electricity at the hours it is cheaper. Peak electricity use is at the hours everybody is home watching TV and having dinner, from 18:00 to 22:00, and at these hours it is the most expensive. Many electrical companies use a smart billing system that fluctuates the fee according to the hour of use. Scheduling the power intensive operations for the late night or the early morning makes a lot of sense.

TRY TO STAY AWAY OF PNEUMATICS
Pneumatic conveying uses too much power. Yes, it is the most flexible solution for flour conveying, but it is also a power hog. In some operations you won’t be able to avoid it, because a mechanical solution would be too complex, but (as much as possible) try to use mechanical conveyors and gravity. That is the reason why most mills (of any grain) use a vertical layout, letting the grain fall from one stage of the process to another.

KEEP YOUR WIRING IN GOOD CONDITIONS
Too much energy is wasted through earth leakage currents. Ask your electrician to conduct a test with an Ohmmeter. If the test says there are any ground currents, check your entire installation. Wiring insulation could have been lost or damaged. I, myself, have been guilty of using standard wiring in places exposed to rain, causing ground currents after the insulation got soaked. Or rodents may have eaten the insulation away. There are as many safety reasons as economic reasons for keeping your electrical 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 regime (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 otherwise wasted running machines empty.

USE HIGH EFFICIENCY MOTORS AND GEAR DRIVES
There are American (NEMA) and European (IEC) standards 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 intake 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 changing 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 reducers too. The efficiency in a gear drive ranges from 49% to 98%, depending on the type and the number of reducing 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 supplier. 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 efficiencies 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 translucid sheets, and let your workers enjoy some natural light.

USE INSULATION IN ALL THERMAL EQUIPMENTS
The amount of energy wasted in grain dryers because 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 upgrade 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 temperature by controlling the burner instead. If gas is too expensive in your country, you could consider fuel oil, which is the fraction of oil closest to tar that you can still burn. It requires a more complex 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.

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