Water. Desalination + reuse
Issue link: https://fhpublishing.uberflip.com/i/545366
PROJECTS Feed water quality is a particular challenge in the oil industry. Oil refineries typically are located on coasts and estuaries which dictates that seawater, or brackish water is the raw water source for their steam production. So they require desalination and further purification stages for their large volumes of boiler feed water to reduce its conductivity below 1µS/cm. Moreover, for refineries with a cogeneration plant, usually employing combined cycle gas turbines, the standard water quality requirement is less than 0.1µS/cm, with silica at 10 parts per billion (ppb) or below. The limits for sodium, chloride and sulphate ions can each be less than 3 ppb. Such stringent specifications are necessary to protect boiler tubes and turbine blades, operating at high temperature and pressure, from scaling and corrosion. MOvE TO COnTinuOuS dEiOnizaTiOn Running costs need to be closely controlled throughout the treatment process. This includes the potentially high energy costs of running RO lines. However, due to recent developments in CEDI it has become possible to design simpler, more energy efficient water purification systems based on RO (figure 1). The latest expansions to the water treatment scheme at Motor Oil (Hellas) Corinth Refineries provide an example of oil-sector growth in the deployment of CEDI and its benefits. As a result of these expansions the company now has the largest seawater desalination system in Greece, with a production capacity exceeding 7,000 m 3 /d and outstanding operating economics. Sychem secured the contract to design and build the desalination project, operating and maintaining it over ten years, as an addition to the refinery's existing multi stage flash (MSF)/ion exchange (IX) desalination plant. The project began with Sychem's construction of a 1,100 m 3 /d potable water unit with two-pass reverse osmosis (RO). Two expansion phases followed, based on seawater ultrafiltration (UF) and seawater reverse osmosis (SWRO) for boiler feed water production incorporating Ionpure CEDI modules: • initial construction 2007: 1,100m 3 /d (1st pass RO) – 500 m 3 /d (2nd pass RO); • expansion 2010: 3,700 m 3 /d (1st pass UF+SWRO) – 3,200 m 3 /d (2nd pass RO+CEDI); and • Expansion 2013: 3,700 m 3 /d (1st pass UF+SWRO) – 3,200 m 3 /d (2nd pass RO+CEDI). To summarize, the Sychem plant now installed and in full operation comprises the following elements: • eight multimedia filters (MMF) treating the return seawater feed; • six activated carbon filters treating the return seawater feed; • four lines of 5,000 m 3 /day seawater UF systems; • four lines of 1,800 m 3 /day seawater RO; • four lines of 1,530 m 3 /day 2nd pass RO; and • two CEDI units totalling 6,000 m 3 /d (one unit for each pair of RO lines). In the past, IX, or mixed bed deionization (MBDI) would have been the sole option for the demineralization process performed by CEDI in the Corinth refinery. However, the performance of CEDI modules has been developed such that the technology now equals, or betters what is achievable using MBDI. High-flow Ionpure VNX modules achieve greater than 95% silica removal and greater than 99.5% sodium removal from RO permeate and they can also be specified to meet a variety of stipulated feedwater and product water qualities. PaybaCk A feature of Sychem's treatment plant design is that it uses warm return seawater from the refinery's cooling system. The capacity to utilize this water, with raised temperature and high suspended solids, is created by the combination of MMF and UF in a pre-treatment stage. In addition, energy is recovered in the SWRO system, using pressure exchangers to reduce power consumption by the RO water-lubricated piston, booster pumps (figure 2). August-September 2015 | Desalination & Water Reuse | 25 | Figure 1. Schematic for CEDI. Figure 2. pressure exchangers reduce energy use in the RO booster pumps.