It takes a lot of water to run a refinery and even more to start up a cold one. Charles McCloskey
A major US East Coast refinery recently started up after a lengthy shutdown and overhaul. The refinery needed assistance in restoring the purified water flow to the facility. Engineers were called on to inspect and recommend repairs and upgrades to critical components such as the raw water clarifiers, filters and demineralization systems. The refinery was provided with a mobile reverse osmosis (RO) treatment system to furnish up to 1,500 gallons per minute of boiler feedwater required to restart operations.
Water is a critical component of the refining process, with an estimated 80 gallons of water required per barrel of oil converted. Steam is used extensively for process heating and fractionation. Copious amounts of cooling water are used in heat exchangers to condense the valuable end products of the refining process. Additional water is required for onsite electricity generation to power the facility. A cold startup of process units is very water-intensive, as returned condensate can be significantly lower, intermittent and of unreliable quality, compared to normal steady-state operations.
From idle to online.
When new owners decided to bring the idle East Coast refinery back online to meet rising market demand, water was one of the first concerns addressed by the management team. To meet the aggressive schedule for returning the plant to profitable production levels, the refinerys engineering team needed assistance. To illustrate what the refinery was looking at, as far as infrastructure goes, Fig. 1 shows the basic design of the plants water treatment system.
| Fig. 1. Basic design of plants water treatment system. |
Water for this refinery is available from multiple sources including wells, surface water and municipal supply (Table 1). Pretreatment is generally required for most waters to remove suspended solids and turbidity before further purification for process water and steam production. The first step to restoring full water flow, therefore, was a detailed engineering review of the pretreatment system.
The pretreatment system was originally designed to deliver 3,160 gpm and consisted of one cascade aerator, one flash mixer (7 ft square and 7.5 ft deep), two precipitators (each 38 ft square and 16 ft deep) and four gravity filters (each 18.51 ft wide, 21.33 ft long and 13 ft deep).
As might be expected, the equipment had undergone significant modifications over the past 55 years of operation. An evaluation team detailed the condition of the equipment and alterations in the engineering report, and provided recommendations to replace critical components. The team also reviewed operations with onsite personnel and provided suggestions to improve the efficiency, consistency and reliability of the pretreatment system. A crucial component of the evaluation was that a complete set of original equipment drawings were recovered and presented to the new operators and engineering staff. The major conclusion of the study was that, while the system had aged, it was in serviceable condition to produce the design flow rate of 3,160 gpm. By following the recommendations, the useful life of the equipment could be even further extended.
While plant personnel worked on the pretreatment system to implement the necessary changes, the timetable for the refinery restart required that at least 50% of the estimated 3,000 gpm of purified water be supplied in short order. The refinery contracted with an outside company to provide up to 1,500 gpm of treated water for boiler makeup to begin steam production.
The temporary water system consisted of the following key components:
Three bag filtration skids. Each skid was rated for 1,000 gpm. Bag filtration using 10-micron bags provided an added layer of protection against turbidity fluctuations.
Four anti-scalant feed systems. Each RO trailer had its own dedicated anti-scalant feed system.
Cartridge filtration. Cartridge filters were provided as a final filtration step prior to the RO units. Each RO unit had a housing that contained 12 30-in. cartridges.
16 RO units. Each unit had a 3:2:1-4M array and 24 8-in. x 40-in. RO membranes. The unit was capable of delivering up to 100 gpm of RO permeate at 16.4 GFD flux and 75% recovery at a temperature of 40°F. Each unit had online feed and permeate conductivity monitoring, as well as permeate and concentrate flow indicators.
Four membrane separation trailers (MSTs). Each MST housed four RO units, and provided interconnecting piping, electrical distribution, lighting and heaters.
Four mobile deionization (DI) trailers. Each trailer consisted of two cation and three anion exchange vessels, each containing 90 ft3 of resin, and one mixed bed vessel containing 60 ft3 of resin.
Within days of the go-ahead, the temporary system was up and delivering the desired water quality to the refinerys power island. The system has operated without interruption for the past six months, consistently meeting the water quality specifications (Table 2). These are critical parameters for safe operation of the onsite 1,300-psig boilers.
The next step was to restore the onsite demineralizer systems to full production capacity. Two systems are onsite: an older conventional design and a newer packed-bed system. Resin analyses indicated that significant fouling of the anion resin had occurred over time. An onsite resin cleaning service was employed to restore the capacity. Vessels were inspected, and linings and laterals were replaced as needed. Most of the cation resin was purchased and replaced. The contractor provided the engineering resources, parts and contract labor to support this effort. The contractor also provided tankering service to remove, separate and reload the resin while these tasks were completed. Work continues in this area to bring the water system up to full capacity.
Working with water treatment suppliers has enabled this refinery to go from cold to hot with nearly full water and steam production while ramping up its refining capacity. HP
| Adjusting flow for maximum recovery. |
| RO trailers are fully instrumented for efficient operation. |
| Short-term operating contracts include all |
labor, chemicals and consumables.
|The author |
Charles (Chuck) McCloskey is the director of business development for mobile and onsite services for Siemens Industry, Inc. Mr. McCloskey is a graduate of Slippery Rock University of Pennsylvania, and has been actively involved with industrial water treatment applications for the past 34 years. He is located in Hoffman Estates, Illinois.