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Dynamic Retarder Spout (DRS)

Dynamic Retarded Spout (DRS) is a patent pending grain flow retarder developed by Trimill Industrial Systems Inc. DRS effectively and gradually slows down the grain flow in gravity spouts and keeps the flow velocity low throughout the spout. This eliminates the problems caused by fast flowing grain in the gravity spouts.

Problems caused by fast flowing grain

  • Spout and elbow wear - some high throughput spout sections may have to be replaced in as few as 3 months. Spout maintenance & replacement is expensive because it requires cranes, labor, materials, and downtime.

  • Downstream equipment wear

  • Product damage (breakage) of friable products, such as corn, pulses and pellets

  • Creation of fines and dust



Gravity spouting in a grain elevator (left) and in a feed mill (center & right)

Grain velocity in gravity spouts

Grain quickly accelerates down the spout due to gravity. Table below shows the grain flow velocity in meters per second in a spout without retarders, as a function of spout inclination angle and spout length (in meters).

The cells in the table above are color coded as follows:

  • Grain flow velocity up to 6 m/s causes little or no problems.

  • Grain flow velocity between 6 and 9 m/s causes moderate problems.

  • Grain flow velocity above 9 m/s causes significant problems.

Current solutions for the high grain velocity problems

  • Spout liners: AR plate, polyurethane, ceramic tiles

  • Inline flow retarders

  • Adjustable spout ends and cushion boxes

Inline flow retarder (left) and adjustable spout end (right)

Issues with current solutions

    Spout liners

  • Lined spout typically cost significantly more than unlined spouts.

  • Spout liners do not reduce grain or pellet breakage and creation of fines.

    Flow retarders, adjustable spout ends and cushion boxes

  • Flow retarders cost much more than the spouting of equivalent length.

  • Bulky - in order to maintain grain flow capacity, flow retarders require a larger cross section than the spout, typically around 2.5 times that of the spout.

  • Limited abrasion reduction. Cushion boxes, while good at reducing abrasion wear in the downstream equipment, have no effect on the wear of the upstream spouting.

  • Minimal reduction in grain breakage and fines generation, because they allow high velocity grain-on-grain impact.

  • Can get clogged when handling dirty grain containing large pieces of foreign material, causing production stoppages due to plugged spouts.

  • Require access platforms for inspection, cleaning and maintenance.

New Solution: Dynamic Retarder Spout (DRS)

    What is DRS?

  • DRS is a patent pending type of flow retarder developed by Trimill.

  • DRS uses a series of baffle sets placed at regular intervals along the length of the spout.

  • DRS has no choke points and doesn’t create a stationary pile of material.

  • DRS typically limits the grain flow velocity to 4 to 6 m/s.

  • DRS keeps the grain in motion at all times.

  • DRS baffles fit within the existing cross section of the spout without reducing the grain flow capacity.

  • DRS baffles are easy to install in-situ in the existing spouts.

A DRS baffle set consisting of a leading (bottom) baffle and a trailing (top) baffle

    How does a DRS baffle set work?

  • DRS baffle set usually consists of two opposing baffles, one at the bottom and one at the top of the spout, in a staggered close-coupled arrangement.

  • A baffle set slows down the grain flow in 4 steps, by changing the flow direction 4 times. This is done without creating a slow-moving grain pile, and with a minimum grain-on-grain impact.

  • At each change of flow direction, the grain flow is slowed down. Typically, a baffle set reduces the grain flow velocity by 50% to 70% (the outgoing velocity is 0.3 to 0.5 times the incoming velocity).

4 stages of grain flow slowdown by a DRS baffle set

    How does a DRS spout with multiple baffle sets work?

  • Baffle sets described above are placed at regular intervals along the spout, causing the grain flow to accelerate and decelerate multiple times.

  • The spacing of the baffle set is determined so that the grain flow velocity never accelerates past the design velocity of 4 to 6 m/s (smaller spouts allow for a lower design velocity).

  • By keeping the grain flow velocity low, the grain impact on the baffles and the spout walls in places, as well as grain-on-grain impact, where the flow changes direction happen at a low grain flow velocity, causing minimal wear and material breakage.

DRS spout showing grain flow pattern and minimum and maximum grain flow velocities

    What are the advantages of DRS over the current solutions?

  • Virtually no maintenance is required

  • Greatly extended service life of spouts and elbows

  • Reduced breakage of friable bulk material and fines creation

  • Work for wide range of grain flows, from trickle flow to maximum flow

  • Self-cleaning and resistant to plugging with foreign matter

  • Fit within the existing spout cross sections without reducing the capacity

  • Can be retrofitted to the existing spouts without changing the spout geometry or configuration

  • Work in both round and rectangular spouts

  • Work in both inclined and vertical spouts

  • Have a lower capital cost than current solutions

  • Have a lower maintenance costs than current solutions.

Engineering the Dynamic Retarder Spout

Trimill has developed proprietary Grain Flow Simulator app to:

  • Design the optimum DRS baffle arrangement for any spout geometry

  • Predict the grain flow velocity distribution along the spout, with and without the DRS baffles

  • Estimate the wear distribution along the spout, with and without the DRS baffles

  • Create CAD installation drawings for the DRS baffles

Example output from the Grain Flow Simulator of a 5 meter long 12” round spout at 45° inclination, without and with DRS baffles. The grain flow velocity is color coded.
Bulk material is wheat and the grain flow is 10,000 cfh (218 t/h)

Trimill has lab tested close to 200 DRS baffle configurations on a 2” spout scale model to optimize the design and verify the model used in the Grain Flow Simulator

Installing DRS Baffles

    Installing DRS baffles in a round spout

  • In a round spout each baffle is held in place by a single bolt and nut.

  • A single hole is drilled in the spout for each baffle.

  • The baffles can be installed in the shop using a long lever to line up the baffle bolt with the hole in the spout.

  • Baffles can also be installed in situ by pulling them through the spout using a strong fishing line.

  • Baffles can also be installed through a spout inspection hatch.

Dynamic Retarder Baffles in a round spout with an optional inspection hatch.

    Installing DRS baffles in a rectangular spout

  • In rectangular spouts each baffle is held in place by a two bolts and nuts.

  • Two holes are drilled in the spout for each baffle.

  • The baffles can be installed in the shop.

  • Baffles can also be installed in situ, through the removable spout cover.

DRS Baffles in a rectangular spout

Typical Scope of Supply

Trimill's scope

  • DRS spout design and optimization, based on customer’s spout geometry and requirements

  • Custom designed and fabricated DRS baffles

  • Supervision of baffle installation, if required

  • Commissioning supervision, if required

DRS Baffles

Customer's scope

  • Installation of the DRS baffles

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