REFINERIES
The following case histories and application descriptions include examples of RO, UF and crossflow microfiltration systems in the specific niches identified by the SIC codes.
Chevron
Chevron's El Segundo Refinery near Los Angeles processes crude oil into semi-finished and finished products. Demineralized water is used in all boilers operating between 300-850 psig. The largest expense associated with the ion exchange system was regeneration chemicals.
The Department of Toxic Substances Control (DTSC) in the state of California considers the high and low pH water produced during a regeneration to be hazardous waste because the pH is greater than 12.5 or less than 2.0.
An RO system was installed in the "front end" of the plant, and the economics became very attractive. Not only was water consumption reduced, but expensive chemicals were virtually eliminated.
After verifying the reliability of the system as operated by Arrowhead Industrial Water, and the quality of RO water, it was decided to completely eliminate the polishing and run the boilers on straight RO water. If needed, only a split stream of the RO product water would be polished using mobile demineralizers.
Benefits derived from RO include reduced water consumption, ability to reuse the concentrate in cooling towers, elimination of hazardous waste and elimination of stored chemicals like caustic and acid. The overriding benefit from running an RO versus ion exchange is economic.
New RO element technology has been developed that allows more surface area to be packaged into the same external dimensions as conventional elements. It was demonstrated in one of 18 trains over the past year at Chevron that 21 percent more capacity can be achieved by retrofitting conventional elements with FILMTEC® BW30-400 elements.
To meet the goal in California for reclaimed water use, major industrial plants have been put under increasing pressure to use municipal wastewater. Oil refining in particular was put under heavy pressure because it is a major industry in California with 25 refineries, where cooling tower makeup is the main water user. Reusing municipal waste water as cooling tower make-up in refinery cooling water systems can present unique challenges due to the inferior quality of the water. Following is a four stage approach for water resource management in an industrial plant.
Stage 1: Plant Audit: System characterization and water quality characterization.
Stage 2: Recycle System Design and Evaluation: Includes preliminary design calculations and, as appropriate, laboratory testing to determine experimental feasibility.
Stage 3: Pilot Testing: The most promising option identified in Stage 2 is verified and estimates of system operating parameters are further refined.
Stage 4: Implementation: A cautious approach to transitioning from well water to municipal wastewater.
This approach was used in a U.S. refinery while transitioning from well water to tertiary treated municipal plant waste water as cooling tower make-up. Transitioning to municipal waste water was preceded by the following stages:
Careful analysis of the water chemistry characteristics of this water and identification of problem contaminants (NH3, COD, Fe, Cl, TDS)
Careful consideration of approaches to deal with these contaminants using computer modeling as a tool where appropriate
Pilot evaluation to optimize the cooling water treatment program, determine expected corrosion, scaling and microbiological performance and to develop solutions to safely manage risks of using municipal wastewater.
Implementation and further optimization
Several novel on-line monitoring and control tools are available to help manage risks associated with using municipal waste water while enhancing tower operation. The use of inert fluorescent tracers, the phosphate analyzer, the azole analyzer and polymer analyzer are some examples of such techniques. In addition to on-line monitoring of water chemistry parameters and product dosages, a high level of performance monitoring of critical system parameters is essential in order to provide early warning of performance problems so that corrective measures can be implemented. The use of corraters, C-factor, U-factor, bio-fouling and deposit monitors are some examples of on-line performance monitoring. A high level of system automation (e.g. automatic blow down control, ORP monitors) enhances reliable system operation.