In my opinion, control is the most significant way to save energy in industrial plants. It is sometimes difficult to quantify and often overlooked, but if carried out correctly, it can transform your production. 

Simply put, if something is running when it is not necessary, and we use control to stop the operation, the saving is 100%. How often have you walked through a plant and seen empty conveyor belts running or just a small trickle coming off the stockpile conveyor? 

Furthermore, more than 90% of plants do not run at their full design capacity. Normally, a reserve factor has been introduced, which limits the capacity only to what is required to ensure reliability. 

Example 1

In my example case below, I have taken the theoretical power requirement for a conveyor to run at 2m / s compared to 1m / s.

In the example I used the following values:

 

  • 20m long 
  • 10-degree incline 
  • 1000mm wide 
  • Transferring 250tph 

 

At 1m / s the theoretical power is 6.61Kw and at 2m / s the theoretical power is 9.06Kw.

In summary, for the same "work done" 250 tons per hour, which are transferred from A to B, there is a 30% reduction in power requirements. 

 

All these savings and more can be recouped by better control of existing equipment. These opportunities are throughout the plant. We have successfully used the following control philosophy to automatically slow down conveyors using a PID loop system. This is achieved with the current from the drive itself or a sensor on the belt. 

 

  1. Fit a VSD to the conveyor.
  2. Instead of setting the speed on a VSD, set a target load. 
  3. Take feedback to the VSD as an analog signal about the load on the belt. Note: This could come from the VSD itself. 
  4. The drive automatically reduces/increases the speed to ensure that the load remains constant, i.e. a fully loaded belt all the time and no wasted energy driving a belt faster than it needs to. 
  5. The last step is to stop the belt if nothing is on it or comes to it. 

 

 

Another tip in the selection of conveyors is to manage the inclines throughout the plant and not move the product higher than it needs to go. Simply put, the higher the material, the harder the conveyor will work.

 

Example 2

In this example, the same figures as previously stated have been used.  

At 10 degrees incline, theoretical power is 6.61Kw and at 22.5 degrees incline, theoretical power is 9.45Kw

Some stockpile conveyors are height adjustable, and some just need to be permanently altered. 

 

#design #energy #opportunity