Re: energy savings. VFDs save energy by eliminating losses associated with other forms of varying the amount of work the machine is doing. So for example in a centrifugal pump or fan, the work performed is the flow of water or air. If you are controlling flow by restriction, for example a valve or damper, then using a VFD instead will save significant energy COMPARED to using the valve or damper. If however you are NOT varying the flow, then the VFD will actually WASTE energy by virtue of its internal losses. You also must not equate CHANGING speed vs VARYING speed. If you need to match the processing speed to the product flow, permanently, you CHANGE the final output speed using a gear or belt system. VARYING the speed means there is some benefit to CONSTANTLY change the speed as conditions change.
The big mistake many people make is equating power with energy. Energy is power over time. On a constant torque machine like a hammer mill, if you slow it down, it simply does less work. So your "reduction rate" is the rate at which your coconut shells go from raw product to passing through your 80 mesh screen. Let's say that right now you are at 400kg/hr, so to process 800kg, it takes 270kW of power running for 2 hours, that is 540kWh of energy. If you slow it down to 1/2 speed the motor will draw 1/2 power, but the hammers strike less shells so less product is reduced and your output is 200kg/hr. Now in order to get 800kg of finished product, you consume 130kW of power, but it takes 4 hours. Still 540kWh, no energy was saved. Conversely let's say you only needed 400kg of finished product. You could run at half speed, or you could run at full speed for 1/2 the time. You don't need a VFD for that.
In some cases, reducing the speed of a reduction machine can have benefits of changing the product output. Vertical Shaft Impactor crushers for rocks are like that. Slowing down the spinning platter reduces the impact speed of the rocks, so instead of making sand, they can make gravel. That is a process benefit, but still, no direct energy savings. But I don't see how a hammer mill will react that way if your final goal is just to pass through an 80 mesh screen. You may want to rethink this. If someone is trying to sell you on energy savings, have them write out a report on EXACTLY how that is going to take place on YOUR hammer mill, then share it with us. I'd be interested in seeing how they get there. It's possible that there is something about processing coconut shells that I cannot see, we don't have a lot of those in Cailfornia.
But corn mills use hammer mills, and we have a lot of those now because of the ethanol movement, they work the same way. There have been numerous charlatan sales people pushing VFDs on corn mills around here, yet nobody has responded to my challenge if I get to the users before they buy it. Mind you, I am IN the VFD business and would have everything to gain by convincing my customers to buy my VFDs over those of the charlatans, but as an Engineer, I cannot abide by people selling lies. There is just no real energy savings to come from adding variable speed to a hammer mill that I am aware of.
"Will work for (the memory of) salami"
