Boilers remain a large source of energy consumption in most plants. Emerson’s Bob Sabin, whom you may recall from many earlier energy management-related posts, has some great thoughts on a recent Plant Services magazine article.
The article Boiler inspection and maintenance by Stephen Kleva provides an overview and reminder of aspects of safe and economical boiler operation, and makes a number of good points. Building on this, it occurs to me that instrumentation and control technology can be leveraged to help accomplish the goals of maintaining safety and achieving lowest possible costs.
Boiler owners sometimes overlook the value of a fully functional automated control system and a computerized asset monitoring system. Mr. Kleva notes several things regarding how problems with a boiler process can occur:
It’s important to remember that most problems don’t occur suddenly. Instead, they develop slowly over a long period of time.
Boiler logs provide a continuous record of the boiler’s operation, maintenance and testing. Because operating conditions change slowly over time, a log is the best way to detect significant changes that might otherwise go unnoticed.
“The success of any boiler log is determined by how vigilant the operator is in regularly updating it.
Most operations personnel would agree with the statements above, yet many sites do not have or do not fully maintain the equipment needed for complete monitoring and/or comprehensive performance logging. For example, it is all too common for boilers to be operated for long periods with known instrumentation problems. For a variety of reasons, these are not promptly addressed, but they certainly contribute to less than most economical operation, and sometimes play a part in a breakdown.
Today’s computer technology allows monitoring of boiler process measurements to be done consistently and automatically every minute of the year, and further, today’s tools provide alerts when a parameter trends out of normal range, changes too quickly, or exceeds a constraint. The unfortunate situation is that most sites have not implemented these asset-monitoring tools even though they are relatively inexpensive and not very complicated to apply.
Extending this, many sites have not taken advantage of computerized data logging and historical data management. Even at their best, paper logbooks provide only a minimal view of process performance. They are only one-value snapshots of process parameters at a one- or two-hour interval and they are subject to gaps in data when operations personnel are tied up with other tasks. Computer control and data historian systems monitor the process in the range of every half second, do not get interrupted, and provide a multitude of data analysis tools to observe trends, identify abnormalities, and provide the basis to drive improvement.
The article also mentions, “Optimal air-to-fuel ratio is important because a boiler requires just the right amount of oxygen to ensure efficient combustion.” Mr. Kleva goes on to relate that a control system is the tool to use to achieve optimized combustion consistently over time.
A good control system will manage efficiency over the load range of the boiler, and will be designed to work with any other boilers that are present on the site. Many (if not most) industrial sites run more than one boiler to produce required steam. A modern control implementation will calculate the cost per steam in real time per boiler, and will manage load across all available boilers in order to provide the lowest cost steam in total within applicable constraints.
While instrumentation and controls may sometimes seem to be only a necessary evil for a boiler process, they have been repeatedly proven to be a technology and tool that improves performance by supporting safe operation and optimizing the economic outcome.
Bob, thanks for adding your perspectives on the role process automation can play to this boiler maintenance article!