About the author: Pete Anson is senior product manager for Emerson Process Management - Rosemount Analytical. Anson can be reached at [email protected] or 800.854.8257.
Continuous water analysis of pH, conductivity and turbidity is vital to municipal and industrial plants. Given this, the use of a reliable and capable liquid analyzer is essential. With the drive toward lower budgets, instrumentation and electrical (I&E) managers may tend to select their analyzers from the range of “general use” instruments with the lowest cost. Recent developments in analyzer technology, however, call this approach into question. So-called “high-end” analyzers may contain capabilities and functions that significantly reduce costs in other areas of the plant—savings that more than offset the difference in price of the instruments. Each plant is unique, but I&E managers can determine for themselves if these added functions impact their choice of instruments. By rethinking the way some essential functions are performed in a plant, managers may determine that these pH/conductivity measuring workhorses are actually sophisticated plant machines.
Many plants require the use of a data or event logger and/or a data historian to provide an audit trail for fulfillment of regulatory requirements or to meet internal reporting policies. A standalone data logger can cost $200 to $1,000, plus installation. The latest liquid analyzers, however, may contain a built-in data logger and event logger that can capture measurement data from the process and the instrument. The integral data logger therefore can act as a local data historian. Important parameters (a dozen or more live values) can be captured from both channels every 30 seconds for 30 days in the analytical instrument. An embedded event logger records every significant process and instrument event as an audit trail. Events such as power-up, calibration, alarms and alerts are gathered based on the instrument’s real-time clock. Onboard data/event loggers:
- • Allow convenient local device access;
- • Save the cost of a separate device and installation; and
- • Allow easy methods of data upload/download for reviewing and evaluation on a PC.
These logging parameters may or may not satisfy regulatory requirements in a given arena, but having the function as a built-in capability without additional charges can meet a myriad of internal reporting requirements. A pharmaceutical company in California, for example, uses an analyzer’s data logging function to record and review crucial process changes in order to ensure batch quality.
Sophisticated high-end analyzers generally are multi-parameter instruments, meaning they can record more than one input, such as pH and conductivity, chlorine, oxygen, ozone, etc. I&E managers can combine two worlds with these instruments and use them for recording not only standard liquid measurements such as pH, but also flow, which has to be reported regularly. This approach saves the cost of additional analyzers. Outfall points often are on the periphery of the plant, and liquid analyzers can be set up as wireless devices in order to transmit flow data recorded continuously within the analyzer from these points, saving personnel time and costs.
Pulp & Paper Mill
At a pulp and paper mill in Washington state, a blow-down process at its cooling tower is required to control the concentration of the cooling water. Many plants share this kind of requirement. The pulp and paper plant uses its liquid analyzer to control this function. Control functions in sophisticated analyzers provide a range of capabilities that can save plant operators time and money. For example:
- • Bleed and feed. This supports continuous monitoring of blow-down water conductivity to determine the point of excessive concentration buildup. At a programmable maximum concentration value, dumping (bleeding) of the excessively concentrated cooling tower water is triggered using a contact relay. Subsequently, pumping (feeding) of additional makeup water chemicals is enabled to account for lost blow-down cooling water.
- • Totalizer-based relay activation. This triggers a relay at user-defined intervals based on accumulated totalized flow as volume. A typical application for totalized flow relay activation is controlling chemical dosing in reactors. A totalizer-based timer feeds chemicals for a preset period every time a programmed volume of liquid has been added to or removed from a vessel.
- • Date and time activation. This relay feature allows programming one to four relays to activate on a designated day of the week and time of day/night for an assigned interval. The relays function like sprinkler timers. The programmable time frame is two weeks. An example application for date and time activation is daily chlorine dosing in seawater-cooled condensers.
Digital communications capabilities also may be a deciding factor in the selection of a liquid measurement analyzer. Long gone are the days when these instruments were isolated islands with little need to communicate or interact with other equipment. Because commissioning new HART communication protocol devices into the plant is costly, having integrated HART communications within the instrument reduces the demand on the I&E budget by saving wiring costs, new installation costs and startup costs.
I&E managers and operators also may want to consider the need for wireless communications. If measurements must be gathered from remote locations or environments that are difficult to access, such as sump points or high towers measurements gathered at one Florida phosphate plant, the use of a wireless network can save thousands of dollars in infrastructure and reduced maintenance. When compared with the installation of copper wire, wireless saves $2,000 to $3,000 per linear foot. Some general purpose liquid analyzers also can be configured wirelessly. When the additional functions of the high-end instruments, such as data logging and control, are factored in, the value of the data being transmitted wirelessly from the remote location immediately justifies the expense of adding wireless.
Finally, the higher-end analytical instrumentation often has “bells and whistles” that immediately pay for themselves in reduced plant operating costs. For example, the simple fact that an analyzer may have a high-resolution screen that can be clearly read in any lighting environment can save personnel time and avoid frustration when attempting to read critical process values on the local screen. A simple-to-use operator interface, which walks the technician easily through setup and basic functions, avoids operator error and allows technicians with minimal training to be able to operate the equipment more easily. Because efficient instrument startup equates to fast and efficient process startup, the benefits in productivity are measurable.
The advanced capability of today’s analytical instrumentation is worth consideration by any I&E manager or plant decision-maker. The additional functionality available may allow simpler, less costly means of performing essential plant functions above and beyond liquid analysis—proving that in some cases, more is less.
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