Challenge
A refinery in Northern California was unable to meet its desired boiler feed water silica specifications on a consistent basis. The higher silica levels led to an excessive blow down requirement in the boiler system. The higher blow down rates were significantly affecting the refinery's water, chemical, and natural gas costs.
The refinery was using reverse osmosis (RO) for silica treatment and TDS reduction. However, RO membranes are limited in the amount of silica they can reject, thus often creating an excess of undesired silica in the RO permeate.
Solution
Evoqua Water Technologies recommended mobile demineralizer (MODI) trailers. Three 500 gpm MODI trailers were brought online to polish the RO permeate and reduce silica levels. Each trailer contained both a lead set of ion exchange vessels, as well as a polishing set of ion exchange vessels to ensure final water quality. A fourth trailer was supplied as a reserve for change-outs, based upon the need for replacing exhausted on-line units. The installed MODI trailer system, consisting of MT5500 units, was designed for a total of 1,500 gpm. Each trailer contains a total of six 60"-vessels, each housing 70-90 cubic feet of mixed-bed resin.
Before the polishing was implemented, the silica levels ranged between 500-1300 parts per billion (ppb). With a two-year contract and an option to extend, Evoqua Water Technologies began polishing the RO permeate to reduce the levels of silica to below 20 ppb.
This customer was able to dedicate part of a large gravel lot adjacent to the RO plant for the trailers, allowing for easy connection and change out. Mobile trailers provide customers optimum flexibility.
Results
After the installation of the MODI system, the specifications for boiler feed water were met 100% of the time. The plant no longer experienced silica upsets in its boiler system, thus optimizing its operating costs and extending the life of the boiler units.
Quick delivery and installation of the equipment also affirmed that the MODI trailers provided by Evoqua were the best choice for the customer. The trailers were installed and running within days of the contract, providing immediate results.
