Separation of Green Waste (Biomass) and Soil

Dear All,

I am looking for some previous experience in separation of green waste (Biomass) from sand and soil. The Biomass includes grass cuttings, branches, trees, palm fronds, tree stumps, building timber, hard wood, soft wood, sand and soil.

I have discounted vibrating screens as the 20% soil and sand will compact and plug under compression.

I see two options to process 100 tph of green waste;

1. A disc screen (probably 3 screens in series in order to flip the fibrous material twice - each screen 3 metres long and 2 metres wide)

2. A long trommel screen (probably 8 metres long and 2 metres diameter)

I understand the trommel screen will have a better performance due to higher agitation (especially when the soil is wet and adhesive and needs a good knock to dislodge from the green waste), but I am worried about sticks wedging in the apertures and blocking flow through the trommel (imagine weilding a chainsaw inside a trommel screen to clear the blockage!). A disc screen will be reliable but sticky dirt may not be dislodged unless someone really understands the design of the cams and pitch of the axles.

Is there any experience out there on this one?


Tim Gilroy

Re: Separation Of Green Waste (Biomass) And Soil

Posted on 6. Dec. 2003 - 06:49


Where are you located?

Are you aware of how they surface mine bauxite in Australia? They dig up branches and tree stumps along with the weathered bauxite ore. They have to separate this type of bio-mass from the mineral. A special tyne assembly is used. Mineral and debris is passed over a rotating tyne assembly in a transfer chute system. Ore passes downward and debris is caught and rotated upward counter to ore stream flow. As it passes out of the ore stream it is discharged by gravity about 180 degrees opposite the ore flow stream. The bauxite can be sticky. There must be reasonable difference in size properties for this scheme to work - i.e. long and spindly or having a dendrite structure. Could work for everything but the grass clippings. The width of the ore strem might prove to be a challenge. We can model this using DEM.

For you to remove grass that may be of the size order of you sand and soil is a bigger problem. Can't float it?. Can't burn it? Can't blow it in a vertical column when the soil is dropped and granular stream separates allowing lighter density bio-mass to rise and collect it in a filter? A wet or sticky batch would not work.

Wish I could contribute more on the grass.

Lawrence Nordell

Conveyor Dynamics, Inc.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: phone: USA 360-671-2200 fax: USA 360-671-8450

Separation Of Sand From Biomass

Posted on 16. Dec. 2003 - 05:19

The best result you will get with upstreaming watertanks. The sand flows down, the biomass stays on top or goes up.

Maybe only a water basin with belt in the floor is enough? The floating parts and the none floating parts are separated with high accuracy.

If you want more information, contact me.

Jur Lommerts


Jansen & Heuning Bulk Handling Systems

Duinkerkenstraat 11

9723 BN Groningen

The Netherlands

tel: +31 50 3126 448

fax + 31 50 3138 018

Re: Separation Of Green Waste (Biomass) And Soil

Posted on 16. Dec. 2003 - 09:33


Thank you for your email. I have not seen what you are describing but I imagine it involves getting the biomass wet. I am burning this biomass in a powerstation boiler and had considered the use of water as detrimental to the calorific value.

If we used a separation process using water how would I dry the biomass without adding significant cost?

Do you know of any powerstations which burn biomass and use water to separate the biomass and sand/soil?

I look forward to your reply.

Best regards,

Tim Gilroy