Reinventing Nutshell Filtration

ToroJet^™, Veolia Water Technologies’ latest generation of nutshell filters, resolves the issues that have plagued them for years by integrating a shared media cleaning system at grade level. This innovation enables plant designers and operators to backwash and restore nutshell media’s retention capacity with lower capital expenses. Thanks to a simpler equipment configuration and more efficient asset utilization, ToroJet reduces operational costs while dramatically improving safety and accessibility for maintenance.

Nutshell filtration has come a long way in removing trace oil and fine solids from industrial wastewater over the last 50 years. In the energy sector, it is among the most trusted methods for oil and gas producers to minimize the environmental impact of produced water and comply with regulatory standards for injection or discharge. 

For oil and gas producers worldwide, managing and processing produced water is increasingly problematic. Tighter environmental discharge, subsurface reinjection limits, and increased water cuts due to aging oilfields, all result in growing water treatment needs.

Nutshell filters are a necessary part of the solution. However, although they are one of the most cost-effective forms of trace oil and fine solids removal, they can still be very capital-intensive and operationally demanding, particularly for the maintenance of multiple units.

Because of these high financial and operational costs, the evolution of nutshell filters has been a constant drive for more uptime and better media cleaning using less and more efficient equipment. In this regard, cleaning devices that set in motion a backwash cycle -  counterflow fluidization, recirculation, and agitation -are especially critical to restore the media’s holding capacity.

In the current “state of the art”, this media cleaning device is a pump mounted at the top of each filter vessel. Despite their all-important role in cleaning the media and restoring its retention capacity, these pumps still present operators with many challenges: a dedicated cleaning pump for each filter, potential loss of filter media, and dependence on corrective startup and labor-intensive and time-consuming maintenance routines, particularly associated with the clogging of scrubbing screens with media fines.

Conventional nutshell filters require individual fluidization pumps for each filter vessel. This is not only an inefficient use of capital for a piece of equipment that is only used for less than 5% of the time, but it also creates additional work for connecting and servicing multiple pumps over their lifetime. Although they are largely effective, their installation also requires large platforms and ladders to provide safe access and space for maintenance. Multiplied across many filters in medium and large plants, the need for a single fluidization pump and associated hardware at each filter significantly increases total plant investment and maintenance expense.

Prolonged service stops to service pumps. When fluidization pumps are damaged, servicing them is problematic because they are installed on top of filters. This location is neither practical nor convenient and cannot provide adequate accessibility, making regular maintenance and routine inspection more demanding and time-consuming.

Recurrent media loss. Filter backwashing can contribute to loss of media particles as they degrade and filter through the scrubbing screen over time. This loss, which can average up to 5% of its volume per year, leaves the media bed with inadequate filtering capacity, adding operational costs to take the filter out of service and replenish it with new media. 

Corrective startup procedures. A common occurrence when performing system startup is that of the clogging of the scrubbing screen. The consequences of this plugging are important. At a minimum, the screen’s plugging with media diminishes its scrubbing capacity, thus rendering the scrubbing screen inoperative and necessitating maintenance leading to longer startup routines.