Sanitary Blenders: The DTL/Tri-Blender- A Case Study

June 3, 2014

Getting back to our product focused Tuesday posts, today’s post will take a look at a decades old technology that we still see a need for today- the DTL Sanitary Blender. We’re going to cover the theory of operation and an example of a customer we recently worked with to solve a problem they were having introducing a dry powder into a liquid.
Cutaway of the DTL Sanitary Blender
To begin, the DTL sanitary blenders are used for the incorporation of a dry ingredient into a wet one. A DTL or Tri blender basically consists of a centrifugal pump head and impeller mounted in such an orientation that the normal suction port, or inlet, is pointed upward. The inlet piping consists of a tube-within-a-tube arrangement- preventing wet-dry mixing and the prewetting phenomena.

The liquid inlet is mounted tangentially. The liquid entering the blender mixing chamber enters in the same direction the impeller is rotating. The impeller then strikes the liquid and accelerates it. Minimal splashing of liquid occurs which is how we can keep the power in the inlet tube dry. If splashing does occur, prewetting may occur and the powder tube can plug up.
The next element of the DTL blender is the discharge screen. As liquid is accelerated out of the pump chamber it strikes the blender screen creating a natural back pressure, forcing liquid back toward the eye of the impeller. This forms a hollow envelope into which the powder is introduced by the natural suction of the blender. This means that if the blender is operating properly, the inlet tube is always dry.

Now that we’ve covered the general operating parts of the DTL sanitary blender, let’s take a look at two auxiliary components that are just as important- the feed and discharge pumps. All DTL blender set ups will require a feed pump. It is important to maintain a constant flow of liquid through the blender. Constant flow helps maintain a constant vacuum. Without a constant vacuum the powder addition rates will vary.  If the blender is just running in a recirculation mode (normally pumping out of a tank, through the blender and back into the tank) a discharge pump in normally not required.

If there is a long distance of piping downstream of the blender, a discharge pump may be required.  Too much back pressure on the blender will reduce the vacuum resulting in diminished blending.  Increasing viscosity may also result in the necessity of a discharge pump.   As powders are incorporated into liquids, viscosity tends to go up, so we need to size based on the final viscosity of the product.

As the viscosity climbs, we will need a discharge pump to maintain vacuum and pump product downstream. While the blender itself is a pump, when used as a pump, back pressure climbs, and the liquid envelope collapses. Depending on the viscosity of product, either a PD or a centrifugal discharge pump can be used. For more help sizing your feed and discharge pumps, contact Holland today.

DTL Sanitary Blender Incorporated with a Stainless Steel Table Assembly

DTL Sanitary Blender Incorporated with a Stainless Steel Table Assembly

Getting back to applications we can use the DTL sanitary blender in, let’s look at a recent application a Holland Sales engineer encountered. Working with an end user, we found that their operators were having trouble lifting heavy bulk powder bags and dumping them into open top blend kettles. In addition to this physically taxing exercise, the side mount mixer they were using to incorporate the powder wasn’t functioning effectively. To solve this problem, Holland worked with the end user to size and design a DTL set up that incorporated a table station that made for more ergonomic dry ingredient addition. In addition to boosting throughput and consistency of dry ingredient incorporation, we were also able to make the operators job’s easier and plant managers job more stress free.

These practical, effective solutions are hallmarks of Holland. Contact a Holland Sales representative today to see how we can incorporate this technology into your next application.