Flow Reversal Technology

The need

The main limiting factor in Brackish Water RO’s recovery rate is mineral scaling. Mineral scaling is caused by precipitation of soluble salts on membrane surfaces following salt concentration rise above saturation, which then leads to membrane plugging, a common phenomenon in membrane desalination. 

Membrane plugging has a negative effect on RO operational performances such as (a) increase in energy consumption due to lower flux (b) increase in chemical cleaning frequency, plant downtime (c) overall increase in operational costs, lower membrane life and a decrease in profitability.

ROTEC Ltd. has developed an innovative desalination technology called Flow Reversal designed to be implemented in existing and new desalination facilities for brackish water and other industrial applications. Flow Reversal enables significant system performance improvements, which leads to higher profitability, savings on operational costs, and reduced environmental impact associated with desalination. ROTEC’s solution substantially improves system performance compared to standard reverse osmosis desalination systems in several ways:  increasing process recovery by 10% to 15%, dramatically reducing brine volumes required for disposal by up to 70%, and minimizing or eliminating acid/ anti-scalant chemical consumption, inhibits biofouling and more.

Flow Reversal – Basic Principal

A steady-state, Ultra-High recovery RO is achieved by applying the proprietary Flow Reversal technology. This is implemented via design changes in standard RO desalination systems whether for new or existing installations. Flow Reversal is a smart process for operating desalination systems, in which the flow direction of the saline stream in RO pressure vessel arrays is periodically switched (figure 1). By periodically switching the flow direction, the scale does not have time to form on membranes surfaces before being swept away by under-saturated feed solution conditions. The frequency of switching is dictated by the time it takes for a supersaturated solution in the concentrate to grow a population of scale particles that can allow continued scale growth (denoted the “Induction Time”). By using the effectively under-saturated feed to sweep away the beginning scale particles in the concentrate before they exceed a critical size, extensive precipitation is prevented. This approach affords to operate at much higher recoveries than can be achieved with anti-scalant alone.

Figure- Flow reversal principle – switches the connection of feed and concentrate before supersaturated solutions can precipitate from the concentrate onto the membrane Timing is determined by knowledge of feed composition and operating conditions. Scaling is prevented by the “juggler principle” – change condition to under-saturation before the supersaturated solution can precipitate.