Industrial Double Pass RO with EDI System for Power Plant 144,000 GPD - Venezuela

Treatment Train

Pre-treatment of the well water included filtration using multi-media filters to remove sediment down to the 10-20 micron range. Coagulant specifically selected for high organic/TOC water was utilized to increase filter performance/removal. Chlorine dosing was injected prior to the feed tank, which in theory reduces the biofouling potential and more importantly oxidizes metals such as iron (to precipitate and filter out). Additional chemical injection consisted of antiscalant dosing which minimizes the precipitation of sparingly soluble sulfate salts (Calcium and Barium Sulfate) and silica oxide. Pure Aqua, Inc.’s NSF approved PA 0100 antiscalant was specifically selected based on the detailed feed water analysis. SMBS was utilized for chlorine scavenger/removal. AntiChlor 427 (Avista Tech.’s product) was proposed as a safe and convenient alternative over powdered SMBS. The chemical is dosed ‘neat’, which eliminates the handling and mixing of SMBS powder. SMBS removes chlorine more effectively than activated carbon and eliminates many of the issues associated with carbon beds including carbon fines in downstream feedwaters and bacterial growth.

While typical design for EDI consists of double pass RO or softener + RO, the feed water in this case was below 200 ppm TDS. The one pass design was able to meet the required feed water quality required for EDI, specifically hardness. Hydranautics CPA5-LD membrane was selected over a low energy membrane for increased hardness rejection. The required feed quality ‘equivalent’ to the EDI is <40 uS/cm including CO2 and silica. Note one ppm of CO2 = 2.7 ppm (equivalent conductivity). It is difficult to meet the feed specification to the EDI without pH adjustment and/or membrane degasser. Decreasing the CO2 before the EDI will decrease the load (lower amps) and improve the product quality. Pure Aqua installed a membrane degasser on the EDI skid for CO2 removal/reduction. The membrane degasser replaced the proposed design of a conventional forced air degasser (tower). It was more cost efficient, compact and decreases installation time.

Standard double pass RO design typically increases the pH above 8 in between passes for CO2 removal. Carbon dioxide in water equation is as follows; H2O + CO2 <====> H2CO3 <====> H+ + HCO3-. The carbon dioxide in water pH value will drop as the concentration of carbon dioxide increases, and conversely will increase as the bicarbonate alkalinity content increases. RO membranes will reject the bicarbonate but pass the gas (CO2), in sum, increasing the pH shifts the CO2 (gas) to bicarbonate which is then rejected. In a single pass RO design, increasing the pH of the feed would result in significant chemical (caustic) consumption. The RO permeate has no buffer and chemical consumption is therefore dramatically reduced. In addition, increasing the pH increase the scaling potential, reducing recovery.

Electrodeionization removes ions from aqueous streams using a membrane and electrical current to achieve a water quality of up to 18.6 Mega Ohms. It provides polishing of RO permeate to meet stringent product water quality specifications. Ionpure (Siemens) VNX EDI module was utilized to reduce the number of individual cells. Each VNX modules produces 50 gpm up to 80 gpm depending on the required product quality. The project consisted of two modules, 2x100%, each producing 65 gpm (72 gpm max.).

Please visit Pure Aqua’s website for your commercial and industrial water treatment

Date: September 2013

Country: Venezuela

Capacity: 144,000 GPD

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Removing contaminants present in the water help improve the efficiency of operations within the power plant. This also increases the functionality of the systems within the power plant to work at full capacity. High purity water was needed for boilers and cooling towers within the power plant.

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In 2013, Pure Aqua successfully supplied a demineralizer water system to PDVSA (Venezuelan government). The water is used for boiler feed, a new power plant currently being constructed. Pure Aqua provided packaged/skidded equipment consisting of Multi-Media Filters, Reverse Osmosis Unit and Electro-deionization System (EDI) for polishing. The industrial grade equipment consisted of all CS and stainless piping, stainless tubing, galvanized conduit, etc. (no PVC).

In 2012, an American EPC/Consulting firm representing PDVSA prequalified three (3) companies to supply demin water treatment equipment. Pure Aqua, Inc. was successfully awarded the project over two major multinational companies. While being cost efficient is always important, knowledge and responsiveness were key to securing the order. Pure Aqua Inc., is a global leader in the supply of packaged/skidded Reverse Osmosis systems. We are an OEM or system/equipment integrator specializing in membranes. The company works closely with membrane and equipment manufactures to package custom solutions. The team has over 90+ years of combined experience in Reverse Osmosis alone.

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Controls/Electrical

There was one main control panel AB Compact Logix and HMI (AB PV1000), each skid/system had point (remote) I/O, connected via Ethernet to the mail panel. The pumps were wired directly from the MCC (i.e. no local motor starters). Each pump was provided with a separate disconnect. All communication between the MCC and ancillary equipment was through Ethernet, connected to the clients DCS.

Power distribution and protection was by others. The control voltage was all 24 VDC, which is safer then 120/220 VAC, a common requirement outside the USA.

All Rosemount instruments were selected to match the rest of the power plant and required for the required HART network. Pure Aqua provided analog HART modules (point I/O) that have two analog input channels; each channel can be configured for current only or current with HART. The advantage is having one network versus separate connections/network for only the instruments.

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