As I wrote in February (“Know Your System Specifications,” part of HPAC Engineering’s “Trends, Issues, and Best Practices in HVACR and Buildings 2016, Part 2”), I began my professional life as a watchstander aboard a nuclear submarine for the U.S. Navy. My job was to tour the propulsion plant and monitor equipment temperature and pressure, all with the goal of ensuring systems and components stayed within design specifications.
A modern watchstander makes effective use of automation systems and analytics, but also relies on visual (and, sometimes, auditory) observations of equipment, identifying problems early, before they have negative, perhaps cascading, effects on safety, reliability, and/or regulatory compliance.
A watchstander is not a maintenance technician. A watchstander records and reports, never disengaging from holistic systems monitoring to repair or adjust equipment. Keeping a watchstander “roving” requires organizational discipline. To not support watchstanding is to be reactive, fixing equipment as it fails, instead of looking for signs failure is imminent and acting accordingly.
The intent of this article is to promote watchstanding as a means to cost-effective boiler operation. The article is not specific to any brand of boiler, nor is it a formal operating procedure or maintenance guide. Presented are fundamental concepts associated with safe and cost-effective boiler operation and explanation of how a watchstanding strategy can be integrated with those concepts.
The focus of this article is natural-gas-fired boilers found in facility settings.
If a handwritten recording of boiler-room events is not kept, machinery history must be chronicled using a computerized maintenance-management system. Making full use of commissioning reports and knowing how a system is supposed to perform is a means to best understanding machinery conditions. A watchstander’s library is incomplete without standard operating procedures (SOPs), up-to-date manufacturer’s documents, and service records.
Understanding the energies associated with hot-water/steam production and knowing how to isolate and safely release those energies is a key aspect of good watchstanding.
The watchstander’s priorities, in order of importance, are:
- Environmental impacts.
- Operational performance.
Good watchstanding backed by good engineering simultaneously supports all three missions.
The Essence of Boilers
Watchstanders seek to simplify their working environment, be it the shop workbench, an engineering system, or even a body of knowledge. When a watchstander looks at a boiler, he or she seeks to identify major systems, with a focus on fluid conditions and energy transformations. The watchstander identifies key control points, catalogs safeties, and makes best use of equipment/operator interfaces associated with engineered components and systems.
Water and Heat
A boiler transfers heat to water to create hot water and/or steam. This requires:
- A combustion system comprised of fuel and air mixing, ignition, and exhaust; associated safety devices, such as flame monitoring; a purging system; emissions monitoring; and controls.
- A water system comprised of inlet, level control, level safeties, pressure-relief systems, and other shutdown devices.
Types of Boilers
A watchstander will tell you there are boilers that make steam and boilers that make hot water. Within the steam group, high-pressure boilers are units that produce steam at pressures greater than 15 psig. Within the water group, high-pressure boilers are units that produce water at pressures greater than 160 psig or temperatures greater than 250°F.
Boilers also are grouped according to configuration: water tube or fire tube. Water-tube boilers have water within tubes and combustion product outside the tubes. In a fire-tube boiler, the combustion process is within the tubes, with water circulating outside the tubes.
Another key differentiator of boilers is their design: condensing or non-condensing. Non-condensing boilers are standard hot-water generators that send combustion byproducts directly to atmosphere via an exhaust stack. Condensing boilers send combustion byproducts through heat exchangers. Termed exhaust economizers, these heat exchangers have flue gas on one side and incoming boiler feedwater on the other. This allows for preheating of incoming feedwater using heat from exiting exhaust, making the process of heating water much more efficient. The term “condensing” refers to the fact flue gases cool and condense as they transfer heat to incoming feedwater. With the highly corrosive nature of condensate water, exhaust-stack material and drainage plumbing must be appropriately specified by the design engineer.
Unique Aspects of Steam-Boiler Operations
With regard to steam boilers, a watchstander’s primary concerns—like those of good boiler operators for more than 100 years—are water treatment, water level, and combustion and emissions.
Water treatment. When heat-transfer surfaces become fouled, conducting heat across those surfaces becomes difficult, and operating costs escalate. Water-treatment programs preserve the ability of boiler tubes to efficiently transfer heat of combustion to water by preventing scale formation. Water-treatment programs also prevent corrosion (e.g., pitting of boiler tubes).
Water-treatment programs ensure minerals that ordinarily would affix themselves to boiler tubes are converted to a mud. This mud must be blown down on a regular basis; otherwise, it will build up at the bottom and in other critical areas, such as water-level control devices, of a boiler.
Dissolved oxygen in boiler makeup water must be removed; otherwise, it will result in oxygen pitting. Oxygen that is carried into a boiler also is managed with water-treatment chemicals.
The watchstander is responsible for making sure water-treatment instrumentation is calibrated. This ensures the proper dosages of chemicals are administered and boiler-surface blowdown is not excessive. Surface blowdown involves measuring and controlling boiler-water conductivity. Calibrating a conductivity probe best ensures the proper amount of blowdown is performed. To not blow down enough is to promote carryover of solids into steam. This is damaging to system piping and other steam loads. To blow down excessively is to waste water, energy used to reheat makeup water, and chemicals used to treat makeup water.
Water level. Boilers work by passing heat to water across tubes. If there is no water in a tube, the tube will retain the heat, overheating and failing. Low water level is the cause of most boiler failures.
Watchstanders are responsible for ensuring water-level safeties are capable of shutting down a boiler on a low-water condition, such as feedwater-pump failure. For boilers that generate steam, this involves the blowing down of water-level safety devices and the water-level sightglass once every eight hours to remove mud/solids. Performance testing of a safety involves lowering the water level at low fire. This testing should be performed on a regular basis by a qualified and certified boiler operator.
Combustion and emissions. Firing is the most crucial and dangerous aspect of boiler operation. If the firebox of a boiler is not properly pre-purged of unspent gases, an explosion can occur at ignition.
Proper mixing of fuel and air relates to not only efficient firing and efficient generation of heat, but ensuring environmental mandates related to combustion byproducts are met.
Boiler controls are designed to ensure mixing and purging are managed properly. If combustion controls and emission-control devices are not maintained appropriately, with regular monitoring and proactive management, problems will arise.
Good watchstanding practices associated with combustion controls include monitoring exhaust stacks for irregular smoke, inspecting linkages driving fuel and air-control valves, and visual monitoring of flame condition via firebox monitoring system. They also include smart interfacing with continuous emission monitoring systems. “Smart” means the boiler operator fully understands the system and which trends are normal and which are not.
Fuel valves must be monitored. Typically, these are solenoid-operated. A solenoid that is degraded may begin to vibrate and hum.
If a boiler operator notices irregularities with combustion, such as boiler pulsation or even an irregular smell at the exhaust stack, he or she needs to respond accordingly, utilizing locally produced SOPs. Procedures associated with failing emission-control systems most likely will involve regulatory reporting.
While on the subject of combustion, air intakes need to be free of substances that would cause unintended consequences if combusted. For example, avoid storing fume-emitting chemicals close to a boiler. Also, ensure the intake path, the space from which the boiler draws air, is free of obstructions.
Small Packaged Boilers
Most small packaged boilers are factory-built and tested and run “hands-off and trouble-free.” As a result, lack of familiarity with operations-and-maintenance (O&M) manuals may be more of an institutional challenge. It is important to understand a unit before it fails; otherwise, the on-site technician, who may not even know where O&M manuals are kept, will end up calling a third-party service provider, who will consume valuable time troubleshooting and effecting repairs.
Related to the monitoring of combustion equipment at a boiler is the monitoring of stack temperature. If remote temperature monitoring is not available, use an infrared gun. Great sources of baseline data are commissioning reports and emission tune-up reports.
With condensing boilers, the local operator needs to understand if and how condensate is treated and how effluent goes to drain. If condensate is not treated, the ever-inquisitive watchstander needs to research the design.
Firing-rate monitoring is the most important role of the watchstander. If a boiler is cycling on and off frequently, degradation of the unit will accelerate.
With non-condensing boilers, return-hot-water temperature must be significantly above the temperature at which condensate could be produced. Non-condensing boilers typically are not constructed of materials that can withstand the acidity of condensation.
In terms of excessive cycling and low hot-water return temperature, the needs of a facility likely will be served best by recommissioning or retrocommissioning. A good watchstander understands the boundaries between watchstanding and formal engineering. Though making simple adjustments to firing rate and other settings may seem practical, more than likely there are facilitywide or automation conditions that need to be addressed. A good recommissioning will reduce equipment degradation, improve system performance, save energy, and prevent a notice of violation from air-emissions regulators.
Regardless of application, to best ensure cost-effective, safe, regulatory-compliant operations, a watchstander is advised to focus on:
- The concept of best managing systems. This may entail use of third-party service providers and engineering consultants.
- Familiarizing himself or herself with key aspects of a boiler: the water side, combustion, and associated controls and safeties.
- Becoming familiar with and understanding “as-commissioned” conditions and, when conditions deviate, investigating and initiating the appropriate corrective response.
- Ensuring documentation and service records are accurate and up to date.
David Yancosky is a central-plant optimization-and-maintenance expert with P2S Engineering Inc. Recently, as part of a contract with a community college, he was able to improve central-plant efficiencies by 70 percent through simple optimization-and-maintenance monitoring and analysis. He can be reached at 562-497-2999 or [email protected].
Did you find this article useful? Send comments and suggestions to Executive Editor Scott Arnold at [email protected].