Cake system foreign debris screening rack

[ischgl99]

We take in cake from other wastewater treatment plants to burn in our incinerator. The cake gets dumped into a receiving bin with a series of 6 augers in the live bottom and passes pretty much anything that comes in. The problem is we get all sorts of junk in there, large rocks, bolts, pieces of metal from the trucks, etc that cause problems in our thermal drying unit.

We have looked at grinders to try and break this stuff up into small enough parts that it will not cause a problem, but none of the grinder companies have something they feel will work. We are thinking some sort of grating or bar rack where the trucks dump might be the best option. Does anyone have experience with something like this and know of something that will work?

 

[bimr]

You need a linear motion vibrating screen.

Here is a link to a manufacturer:

http://www.derrickcorp.com/webmodules/catCatalog/dtl_Product.aspx?ID=38

 

[ischgl99]

Thanks for the link, I will contact them and see if their products will fit.

 

[micalbrch]

I might have another idea in case derrickcorp will not be able to help. What is the max. particle size of stones/metal pieces you can accept and what is the typical size you discover in the cake?

 

[ischgl99]

Looking at the Derrick equipment, not sure it will work, but might be able to modify something along those lines. The cake ranges from 20-25% dry solids and can by dry and crumbly from our dewatering equipment, to a bit wet and pasty from the cake we receive from other plants.

Less then a golf ball size would probably be ok, this week we had the end of a valve wrench go through the system and cause damage in our dryer. This was about 8 inches long by 4 wide and 4 high. We have gotten belt press belts, tractor trailer parts such as handles, latches, etc.

My original idea was just putting a grating above the live bottom conveyors and let the cake extrude through, but we are concerned it might not flow through easy enough with openings small enough to catch the debris.

I appreciate any ideas you have.

 

[bimr]

The Derrick equipment is quite impressive. The videos on the website give you an idea of what can be done. In particular, the digester video shows a great piece of equipment.

This equipment has been applied on everything from trash to hog manure. Can't imagine that they don't have an installation on your waste application:

http://www.derrickcorp.com/Images/Documents/Wastewater.pdf

 

[micalbrch]

A grating above the live bottom conveyors will not work because of the reason you mentioned.

Specify the cake (solids concentration, particle size etc.) you are willing to receive from other sites and held the sites responsible for any deviation and for the consequences. Sounds simple but that is how it is done here in Europe. When I heard it the first time from a WWTP we had business with, I asked how any cake supplier can guarantee this. I was surprised when I head that it is not that difficult. Trucks are cleaned before they are filled with the cake and everybody works with caution because they are aware of the consequences.

If you had a pump between receiving bin and dryer you could install a screen in the discharge line of the pump. That is a systems that works well. But that would mean a cpl. change of your system which is too expensive.

 

[ischgl99]

I sent an inquiry into Derrick as well as another screen manufacturer I know and will see if their equipment will work here.

micalbrch, we used to have pumps in the receiving bin, HUGE problems and will never consider them again. The problems we have now are small compared to what we went through before.

Most of our customers are good about sending us debris free cake, but we do have one customer we suspect of intentionally sending their garbage. Unfortunately there is not a way to prove this since it takes 10-12 hours from receiving until it reaches the dryer and we can have 4-5 trucks in that time. We are going to send pictures of the break down to all the customers and truck drivers to remind them how important it is not to have the debris and how costly it is.

I thank you for your input and hopefully the screen manufacaturers have something that will work.