By Larry Zinser
The recognition of patterns in high purity water treatment systems can help us quickly determine key sites for operation, maintenance and troubleshooting of the system, without resorting to risky and time-consuming trial-and-error methods. Recognition skill provides a mental template with which to recognize the components of a system, to understand their relationship to each other and to identify existing or potential problems. This skill can be developed quickly with focused study and practice, just like Drivers’ Training. When we first sit in the driver’s seat of an automobile, it appears as a maze of buttons and pedals. Yet after a few years of driving experience, we can sit in almost any vehicle and be able to drive it. How do we develop this skill?
When we first enter a big-box home-improvement store, it also appears as a maze—of aisles and products. After a number of visits, however, we can enter any of these stores in the country and quickly find the product we are looking for. What has happened to improve our shopping experience? The same analogy can be drawn for roadway driving signs and signals, for state building codes and many other sets of information. My purpose is to show that the same analogy can also be made with high-purity water treatment systems.
First of all, how do we develop these skills? It is a matter of patterns in form and in process. We develop a mental template of operating controls (form) and a sequence to employ these controls to operate a system (process). We also learn the procedures necessary to successful operation of a system. With experience, we instinctively know how to operate almost any system by applying these templates. Form includes the physical layout of a system; process includes the manipulation of forms in order to accomplish some goal and can then lead to accomplishment of a given task or set of steps. There are also a number of clear forms and processes in high-purity water treatment. Consider pretreatment, distribution loops and reverse osmosis units. At first glance, they all seem quite complex and unrelated. With study and practice, however, we can develop the skills to approach a high-purity system or its Process & Instrumentation Diagram (P&ID) with confidence (see Figure 1).
The first form to consider is pretreatment. Simply stated, the pretreatment system exists to adjust the quality of the raw water for its use in the primary treatment system. Consequently, on one side of the pretreatment system (the input or starting end) is the raw water, and on the other side is the primary treatment system, typically a reverse osmosis unit, a distiller or a deionizer. Raw water will flow from the raw end to the treated end. Sometimes a pump is needed at the start of pretreatment in order to help push the water through various pieces of equipment that make up the pretreatment segment. The pretreatment system is typically designed for two types of water contaminants: suspended solids and dissolved solids.
Equipment sequencing is sometimes difficult to understand. The physical dimensions of the treatment room will frequently lead to ‘creative’ plumbing patterns. In these instances, it is advisable to physically trace the flow pattern of the water from the inlet end. At each node (tee fitting), note the possible flow paths. Most frequently, the first to be targeted is suspended solids because these can foul the treatment components that follow. Typically, suspended solids are treated by either a cartridge filter system or a filter media system. If a media filter system is used, it will likely have three connections: an inlet, an outlet and an opening to a drain Drivers Training for Water Treatment Systems By Larry Zinser Figure 1. Media filters and cation exchange softening unit—photo and diagram (Photo courtesy of Mar Cor Purification) Figure 2. RO treatment system with pump and prefilter (Photo courtesy of Mar Cor Purification) Water Conditioning & Purification March 2013 Figure 3. Drawings of RO treatment system, with components to increase efficiency (see Figure 1). On most modern systems, the inlet and outlet connections are clearly marked on the equipment. After treating suspended solids, a typical pretreatment system will target dissolved solids with a cation water softener. This equipment changes the composition of dissolved solids so that they are less of a potential foulant for the primary treatment. A cation water softener is recognized by its adjacent brine tank, in addition to its inlet, outlet and drain connection (see Figure 1).
A third type of pretreatment equipment that is common to high-purity systems is the carbon filter. This equipment performs two functions: it removes chlorine (or the chloramine derivative) and it adsorbs total organic carbon (TOC). Often, multiple carbon filters will be placed in series. This is done to increase the effectiveness of the carbon in treating the water. The carbon filter is similar to the other filters with three connections. The placement of the carbon filter, vis-à-vis the water softener, is an interesting topic. Once chlorine has been removed from the water, bacteria are more likely to colonize. Therefore, if the primary intent of the high-purity system is to minimize bacteria, then the carbon filter will be placed after the softener. This way, the chlorinated water in the softener will decrease the potential for bacterial growth. However, carbon adsorbs TOC much better in water which retains hardness (i.e., unsoftened water) than soft water. Therefore, if the primary intent of the system is to minimize TOC, then the carbon filter will be placed before the water softener.
There are also common patterns within the pretreatment system. These include bypass valves, pressure gauges and test ports. Bypass valves typically appear in sets of three: an inlet shutoff and an outlet shutoff (both of which are normally opened) and a bypass valve that is normally closed (see Figure 1). These valves should be arranged so that by changing the position of all three valves, inlet water will pass directly to the outlet without going through the media tank. Although this relationship is sometimes masked by creative plumbing techniques, as noted earlier, it is instructive to trace the flow of water from node (tee fitting) to node. The other two (pressure gauges and test ports)are typically co-located between each item of equipment. Their purposes are to measure pressure drop across the equipment item and to allow sampling of treated water after each item. Consequently, it is normal to find these at each juncture between pretreatment units.
Another important pattern exists for reverse osmosis (RO) units. Because of their creative packaging within small containers, the RO template is often obscured in a maze of tubing and wires. The form and the process of ROs, however, is common and predictable (see Figure 2).
Basic RO requires a pump to generate pressure, a membrane housing to hold the RO membrane and a restricting device to generate pressure within the membrane housing. No matter how large or complex, RO systems will have these three components. Additionally, RO will have three water connections: one for the untreated water inlet, the feed (F); one for the purified product, also called permeate (P) and one for the concentrated waste to drain (C) (see Figure 2). In order to generate the necessary pressure within the membrane housing, an adjustable concentrate valve is located on the drain side of the housing, together with a pressure gauge or transducer to specify the operating pressure (see Figure 3 [A]).
In order to increase the efficiency of reverse osmosis, common additions include a concentrate stream recycle and multiple membrane housings (see Figure 3 [B]). Other components that are deemed essential to modern ROs include a normally closed solenoid (indicated by the letter S in a box) and a cartridge-type prefilter at the RO inlet, preceding the pump. The solenoid closes when the RO pump is idle in order to prevent constant water flowing to drain. The prefilter provides a final barrier to Figure 4. Drawings of RO treatment system, with cleaning measures and monitoring instrumentation Water Conditioning & Purification March 2013 contaminants that could foul the membrane surface and reduce efficiency. Pre- and post-pressure gauges (P in a circle) indicate the cleanliness of the prefilter surface (see Figure 3 [C]).
As an important cleaning measure, reverse osmosis units will frequently have a concentrate flush solenoid (see Figure 4 [D]). Finally, most reverse osmosis units will include a wide array of instruments to measure pressure, flow (F in a circle) and conductivity (C in a circle) of the three fluid connections: feed, permeate (treated water) and concentrate (to drain) (see Figure 4 [E]). These assemblies and their respective process and instrumentation diagrams (P&IDs) can become quite complex. If the reverse osmosis pattern is understood, however, this template will assist the technician in recognizing the components, in understanding their relationship to each other and in appreciating the consequences of their malfunction. This is the idea behind learning pattern recognition. It applies to most components of a high-purity water treatment system, including multiport valves, pretreatment valve nests, water storage and distribution systems and electrodeionization (EDI) systems.
Reference
Pattern recognition and reading P&I diagrams are parts of the training provided by WQA’s new High-Purity Water Education Program for Service Professionals. For more information on the Webinar-based training, please see www.wqa.org/education. The class begins in mid-April, 2013.
About the author
Larry Zinser is a Sales Engineer with Master Water Conditioning Corporation. Following an education in chemistry and a career with the US Marine Corps, Zinser now designs, builds, teaches and troubleshoots water treatment systems. His background is in commercial, industrial and residential applications and he has provided accredited technical courses throughout the country and internationally. Zinser can be reached at [email protected].