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A Look into the Design & Safety Features of Combustion Control Systems

With over 30 years of experience, our General Manager at Pacific Combustion Engineering, Jack Valentine, is an expert when it comes to the design of combustion control systems. In the Winter 2021 edition of Today’s Boiler, Jack discusses the features and options typical of Combustion Control Systems today. Let’s take a peek at what he had to say.

Combustion equipment safety is essential for the daily operation of facilities and safety of plant personnel. Safety protocols and mechanisms in industrial plants have improved drastically in the last century, but incidents still occur far too frequently. Because boiler systems are inherently dangerous, safety must be factored into the design of not just the boiler, but also the burner, combustion control, and the overall operation of the system.  

The Combustion Control System (CCS) on a boiler, also known as the Boiler Control System (BCS), refers to the set of instrumentation and controls that modulates the firing rate of the burner in response to load demand while maintaining the proper air/fuel ratio (AFR). It works in conjunction with the Burner Management System (BMS) that provides safeguards before, during the initial light-off of the burner, and at shutdown. The BMS also provides the flame safeties and interlocks required to keep the boiler safe during continuous operation. Depending upon the complexity of the boiler, the CCS can also provide other functions such as drum level control and draft control.  With Low NOx burners, it also controls the proper amount of flue gas recirculation (FGR) to the burner.

For the sake of simplicity, the various types of CCS described below will be for boilers firing a single fuel gas only; fuel oil and solid fuel systems add an entirely new level of complexity.

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Routine Maintenance Reminders

Routine boiler maintenance is imperative not only for safety, but also to sustain efficiency and reliability of your system. Being proactive rather than reactive is likely to increase the longevity of your boiler as well as help prevent incidents that can result in injuries, damage, or worse. Incorporating routine maintenance into your facilities day-to-day operations will prove its worth with a great deal of short- and long-term benefits.

There are certain maintenance tasks that should be performed daily, and others that should be performed periodically. Below we have provided a list of best practices to follow when putting together your routine boiler maintenance plan.

On a daily basis, you should track and keep a log of the following items:

  • Boiler pressure and temperature
  • Stack temperature, to determine operational efficiency (a well-tuned boiler should have a stack temperature range of 50 – 100 degrees above the steam or water temperature)
  • Gas pressure to the regulator, as well as downstream from it
  • Water quality and pH levels, to ensure you are meeting the recommended levels

Blowdown of the boiler (bottom blow) and water column should also be performed on a daily basis. In addition, you should observe boiler and auxiliary equipment daily to ensure proper operation and that there is no damage, leaks, or unusual behavior. 

On a weekly to monthly basis, it’s important to conduct additional visual inspections and observe the operation of certain components for areas that may need to be addressed. This includes:

  • Gauge glass
  • Fuel supply valves
  • Operating and modulating controls, water level controls
  • Flame scanner & burner flame pattern
  • High- and low-pressure switches, combustion air proving switch
  • Indicating lights and alarms

When it comes to the burner, you should inspect the valves, pilot tube, and diffuser thoroughly for any signs of wear that might call for a repair. Also, be sure to observe the entirety of the boiler system for potential hot spots (an indicator of deteriorated refractory) and again, be sure to keep an eye out for any leaks of fuel, water, or flue gas.

Lastly, there are certain items that should be performed on a semi-annual to annual basis. Many of the tasks below can be checked off during the annual inspection, when the boiler is taken offline:

  • Open access doors and inspect the fireside of the boiler
  • Inspect boiler and tubes for evidence of corrosion; clean tubes and tube sheets thoroughly
  • Examine the refractory for large cracks (greater than 1/8”) and patch as necessary
  • Conduct safety tests on the gas valves
  • Review all electrical connections for tightness, signs of wiring wear
  • Check pump alignment on all base-mount pumps

This is also a good time to fully inspect the auxiliaries that provide fuel, air, water, and chemicals to the boiler. In addition, combustion should be reset periodically with the use of a combustion analyzer, for accurate readings of NOx, CO, and O2.

While the guidelines above provide a good baseline of tasks to perform when it comes to routine maintenance, be sure to consider the boiler manufacturer’s recommendations as well.  

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Nationwide Boiler Achieves New Safety Milestone

Nationwide Boiler has achieved yet another safety milestone – 2,500 days without a loss time accident! This marks the longest length of time Nationwide has gone without an accident in our forty-four years of operation. The company maintains a shop facility of 26,000 sq.ft., used for the maintenance, repair and assembly of boiler systems and auxiliaries. Nationwide Boiler’s Experience Modification Rate (EMR), a benchmark measure used for insurance premium discounts that compares worker compensation claims to other employers of similar size operating in the same type of business, has greatly improved over the last seven years. To date, Nationwide Boiler has realized a cumulative cost savings of over three-hundred-thousand dollars as a result of the company's commitments to safety.

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Keeping it Safe - Gas Trains


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Maintenance budgets are among the first to be cut when companies need to decrease costs. Unfortunately, this means that critical equipment, such as the safety of combustion equipment, may be overlooked, specifically the testing of fuel trains.

Gas trains regulate the amount and the pressure of gas to the boiler's burners and are used to eliminate gas from entering the combustion chamber. This is achieved through a series of shut-off valves that are specifically designed to close when the combustion process occurs (through safety shutoff and blocking valves). Gas trains also include a series of pressure switches that prevent gas under pressure from entering the burner. If anything should go wrong, shutdown would occur immediately.

As crucial as gas trains are for the safety of the boiler, many facilities are unable to perform the preventive maintenance and testing work on the equipment as should be necessary to help decrease combustion incidents from occurring. John Puskar (Combustion Safety Inc.) has developed the following strategies that can help any facility to be proactive in the maintenance of fuel trains and combustion equipment. Overall, the goal of any safety program is to improve the reliability and life of boiler related equipment. These guidelines not only help to achieve those goals, but more importantly they help lead to fewer unplanned outages and improve the overall safety of plant personnel.

1. Most of the explosions and fire incidents, by far, have historically been due to human error. All of the safeties and interlock equipment in the world won't help if you attempt to bypass or jumper-out safety controls. There is no possible substitute for proper training. Training has to include mock upset and hazard recognition drills. Your site needs training even if you will have contractors doing preventive maintenance work.

2. Start-up and shutdown are your biggest risks. You need clearly written procedures that everyone understands and agrees with so that consistent, safe practices are in place with every shift and every employee.

3. Make sure that you do regular and complete interlock and fuel train valve tightness testing. Jurisdictional inspectors, even where they are mandated to be around, cannot be at your facility every day. Combustion equipment safety testing needs to be part of your organization's culture regardless of what it costs and what the perceived hurdles are. You should comply with code requirements for testing even if they are not enforceable in your area.

4. Create corporate guidelines for third party combustion equipment reviews and commissioning for newly acquired equipment or for major upgrades. Now that you see how little review and attention combustion equipment may receive from the time it's specified to when its really operating, you may want a dedicated professional review of the process.

5. Upgrade equipment for safety's sake. Do not wait for a problem and let attorneys dictate when this happens.
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