The previous two columns probably have undermined, if not eliminated, your confidence in field testing (see “Is Online Performance Testing Accurate?” and “Trust but Verify Your Equipment.”). However, sometimes field testing is the only option. So, do you hire someone to conduct the test? Do you purchase all the testing equipment and set up the test in the field. Do you use what you have and purchase the rest, then install and run the test?
Field testing has progressed from the days when a whole cadre of people logged individual instrument data. Data logging equipment eliminates the test and timing errors when inputting manual measurements. Accurate field (or temporary) instrumentation also is available. What may be missing are points to install the instrumentation or an orientation that lends itself to accurate measurement.
When contacted to do a field test of an existing heat exchanger in the process, Jake had few details and decided to visit the plant for a closer look. He could collect the design data while there. Hopefully, the file hadn’t been purged in one of the many clean-ups of files. It even might be in their newly developed cloud.
At the site, Jake met with plant personnel and formed a plan to do the performance test. He reviewed the reason for the request; the heat exchanger created a bottleneck in the process.
First, he had one of the junior engineers look through the files. He needed the design specifications for the heat exchanger and any changes made over the years. Also, they needed the current operating requirements for the heat exchanger. From experience, Jake knew that a plant’s expectations for individual pieces of equipment change over time. Processes also change as equipment is optimized; oftentimes, these changes are not recorded.
Next, the team headed to the field to make sure the field test equipment matched the files and the process flow diagram. They scraped off years of paint to gain information from the manufacturer’s equipment tags. In some cases, the tags were buried in insulation, requiring special precautions. Finally, they compared actual equipment orientation to that shown on the flow charts to determine if any changes were made to piping.
Then, the team checked the availability of data point instrumentation in the field. They collected data on type and specifications for any installed instruments. They also defined extra test points and detailed locations for items needed.
Jake and the plant engineers then returned to the office to review the information collected. The exchanger had indeed been modified over the years. Several corrosion issues had surfaced and materials were changed to minimize the corrosion. Process conditions also had changed. Jake and the team updated the current process and instrumentation diagram to reflect the changes, then drew their own diagram for the test with all the pertinent data on it.
One of the plant engineers plugged the current design information into an HTRI model to verify they had the most up-to-date calculations. This uncovered a missing item in the equipment history; no one had checked to see how the heat exchanger would perform with the changes in process conditions. As it turned out, the heat exchanger cooling-fluid flow rate needed increased to match process conditions. They updated their working diagram, then ran the test. They also checked and confirmed availability of the extra flow.
All instrumentation, new and old, was calibrated for a secure baseline. Instead of manually logging all the data, Jake used a data-logger connected to all the field instrumentation. Jake mused at how the younger generation had missed out on all the “fun” of the old days when data logging really meant many people writing down individual readings on a multiple sheets of paper. He did not miss those days. He set process conditions to the diagram values and started a one-hour test at stable conditions.
The engineers then downloaded the information from the data loggers into their performance spreadsheet. The data loggers continued monitoring while the team evaluated the results. With the correction in flow, the heat exchanger met the new operating requirements. They also found a small amount of fouling; the team put in a work order to clean the tubes at the next opportunity.
So, field testing still has a place in the life of a plant. While it probably could be done online, the single-event activity nature of the performance test can ensure that all equipment and process data is up to date and any missing data in the equipment history or process are added to the files. It has a focus that day-to-day monitoring cannot bring. Happy energy hunting.
Earl M. Clark, PE, – Engineering Manager, Global Energy Services. Clark retired from DuPont after a career of 39 years and 11 months and joined Hudson’s Global Energy Systems Group as Engineering Manager. During his over 43 years in the industry, he has worked in nearly all aspects of the energy field; building, operating and troubleshooting energy facilities for DuPont. He began his energy career with Duke Power and Clemson University during the energy crisis in the 1970s.
Active in both, the American Society of Mechanical Engineers and the American Society of Heating, Ventilating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), Clark was chairman of ASHRAE's task group on Halocarbon Emissions and served on the committee that created ASHRAE SPG3 - Guideline for Reducing Halocarbon Emissions. He has written numerous papers on CFC alternatives and retrofitting CFC chillers. He was awarded a U.S. patent on a method for reducing emissions from refrigeration equipment. He has served as technical resource for several others.