diesel to electrical migration 2

[camphor]

Hi everyone,

We are planning to migrate our diesel machine to electrical motor. the diesel machine that we are using now is 10 cylinders mercy, 250HP, 3-phase, running a hammer mill machine crushing coconut shell. I estimated that if we migrate to Electrical power input it would need around 200KVA, is it safe to use 200KVA motor or do we need 250kva motor? then I am not sure whether what kind of inverter drive that I should use, will it be more power efficient in using electric supply compare to diesel machine? and if I may ask more, what else will I need beside a motor and inverter drive? and is it right if I assume that the hammer mill need a constant torque inverter drive? thanks.

 

[burnt2x]

I suggest you gather more data on the hammer mill than looking at your diesel drive. How big is your hammer mill?

 

[TheBlacksmith]

Exactly - your end goal is to power the hammer mill, so focus on its requirments.

 

[LionelHutz]

This doesn't make sense. "250hp, 3-phase" diesel engine? Does this diesel run a generator that powers an electric motor? If yes, keep the electric motor and just power it from the utility instead.

 

[DRWeig]

I think we might have a language barrier here?

camphor, please post a diagram if you can.

Best to you,

Goober Dave

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[camphor]

hi everyone, thanks for the replies.

@burnt2x : the hammer mill size is 1 meter diameter.

@LionelHutz: sorry my bad, what I meant is 250HP diesel engine, directly running the hammer mill.

@TheBlacksmith: my end goal is to convert diesel power engine to electrical power hammer mill machine, the problem is I dont know what kind of motor and inverter and anything else that I need to do that.

@DRWeig: yes, sorry for the bad english.

 

[jraef]

It's just not that simple.

You need to know the torque and speed requirements of the crusher and the limits it can handle, in particular the maximum rate of change in torque or speed that the crusher can take. Electric motors can change speed ant torque very fast, mechanical drive components may not be able to deal with that. Also, you say "inverter" several times, but do you know the consequences of varying the speed of a hammer mill? I ask because people often are sold a story of how a VFD can 'save energy", but on a hammer mill, it will not. The only possible reason for applying one is to change the end product particle size and reduction rate. For coconut shells, I don't know if that is the desired effect (but I admit, I have no idea what they are used for. Fuel?).

Be that as it may, if you do not know the actual torque requirements of the machine, you can only determine it indirectly based upon the existing power plant. You know it is 250HP, but you need to know the RPMs to determine the torque. Then once you know the torque, you can look at the torque of standard motors at their base speed to determine the HP size of the motor you need. Unfortunately this does not account for any over sizing of the engine that took place as a result of desired acceleration and step change recovery rates, but using that method, you will most likely end up with an electric motor that is LARGER than it needs to be, which is a safer bet than too small.

"Will work for (the memory of) salami"

 

[burnt2x]

What I meant when I asked about how big your mill was is the tons per hour of coconut shells it processes. Google Bond's formula on milling power draw.

 

[camphor]

@jraef: thanks for your deep explanation, few question, why cant VFD save energy in hammer mill? and what you mean by reduction rate? and yes we are told that it can save energy as well. to answer your question, we crush the coconut shell into powder around over 80 mesh, it can be used for coil powder coil production, incense stick, and vehicle brake lining.

@burnt2x: it is around 350-400 kg per hour.

 

[jraef]

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"

 

[LionelHutz]

What RPM is your mill running at? Would you want to use direct drive or have belts to match the motor speed to the mill speed?

 

[camphor]

@jraef: Many many many thanks!

 

[LionelHutz]

Jeff, you really should write it this way;

"If you are controlling flow by restriction, for example a valve or damper, then using a VFD instead can save significant energy COMPARED to using the valve or damper."

There isn't always a will save case when changing from a valve or damper to a VFD.