In the industry we see more and more applications for eductor (venturi) systems. In some cases, the eductor may be used in dry bulk/gas conveying, or as in your case, dry bulk/liquid conveying. Eductor uses are not new, concept and application go back to the ‘originators’ - Bernoulli, and Venturi, et al (circa: 1700- 1800’s). Eductors have been in practical use in liquid and gas handling applications as ‘injectors’ or ‘ejectors’. These are typically low pressure devices, deriving the name from the Latin, Educere, meaning “one that leads out”. Used very often with liquids and gas motive fluids, primarily due to the fact that both gas and liquids have very predictive properties that are necessary for correct and efficient eductor design features. Venturi’s have been used in automotive carburetors for over a hundred years with good (expected) results. Using an eductor for moving a liquid (or gas) and solid from point “A” to point “B” becomes a bit more of a challenge, since the ‘motive fluid’ and the ‘conveyed material’ must be reviewed for compatibility.

Next,the convey loop is considered, such as the horizontal distance, the vertical distance, and the number of elbows, all of which will impact the pressure drop the system sees. System design for a dry bulk/liquid system thus becomes more complex. You did not indicate what your two dry bulk solids are, or their properties, so we can offer generalized comments here. Ideally, the conveyed material and motive fluid should be compatible, that is, easily mixed or soluble. An insoluble solid or liquid application may require a more aggressive approach to conveying. Assuming that the eductor system has been correctly designed to the above conditions, then the most important feature of the system becomes the dry bulk feeding equipment.

Remember: gas and liquid systems are easily designed due to the documented consistent properties of these states, and a vast amount of design knowledge is available. The motive fluid parameters are therefore known and considered. The addition of the dry bulk solids to the eductor system is very important to the overall operation of the system. Dry solids feeders should be designed so they provide an accurate, reliable, uniform, and consistent flow of solid into the eductor, in a ’starve feed’ flow pattern.

It is also preferred that when handling a dry bulk solid that the solid be easily soluble in the motive fluid. For this, ‘wetting cones’ are recommended to facilitate the introduction of solid to liquid flow stream. Eductor systems work best when the number of variations (or variables) such as dry bulk solid feed is eliminated or reduced by using state-of-the-art solids feeders. Such feed systems should be selected based on manufacturers’ experience in business, years and numbers of working applications with the dry bulk solids in question, and reliability and durability as would be applied to maintenance (how many moving parts does the feeder have to theoretically break?).

I assume you have your reasons for using propylene glycol as the motive media? This should not present any major concerns since basic properties are similar to water, and there are many eductor systems in use handling water. You may also want to contact eductor (venturi) manufacturers for their comments. There are a few good companies selling eductors for use with solids, which also have experience as well. Good luck with your application.