(582b) Concentrate Minimization: Testing of Improved Static Mixer Crystallizers for Inland Brine Management

When inland communities are evaluating potential sources for a new water supply, desalination of saline-impaired waters is often problematic due to the cost required to manage concentrate streams and the loss of precious additional water resources contained therein. Even when brine transport lines are available, incomplete desupersaturation of RO concentrate leads to precipitation and operational issues in them, which, in turn, increase their brine disposal costs. Zero-liquid discharge is an aspirational target for enabling access to these impaired waters, but it requires an economical crystallization of sparingly-soluble salts. The cost of crystallization is minimized when no additional chemicals are added/handled and the size (and complexity) of the crystallizer is low. More good water can be harvested and the volume for disposal can be lowered, if sparingly-soluble salts are crystallized and settled out, allowing for recycle to the desalination process.

The technical approach to be evaluated in this work is to use inline, static mixers (SMs) to accelerate crystal nucleation and overall desupersaturation of sparingly-soluble minerals in RO concentrate. Static mixers offer the flexibility to modify and analyze various parameters, such as the shape, size, and number of mixing elements, as well as flow characteristics including rate, energy dispersion, and pressure drop. This helps to optimize the crystallization rate.

The crystallizer is designed as a pipe with inserts in it. It is designed to allow the mixer elements to be removed and replaced easily. The static mixer crystallizer is connected to the concentrate RO stream with an intermediate surge tank and appropriate flow control can vary the residence times. Four different 3D printed shapes are S, F, R, and H; and different commercial polymer materials such as polyester, nylon, and polypropylene are tested to identify best shapes and materials to enhance the nucleation and crystallization rate.

The bench work experiments in lab with model supersaturated solution says that S and F are the better shapes (see figure) for increasing turbidity (a surrogate for desupersaturation) and thus crystal formation. The ongoing pilot test with real concentrate, containing antiscalants, will also be discussed to enhance our understanding.