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Nationwide Boiler Steamlines Newsletter: Available Now!

Nationwide Boiler's first Steamlines Newsletter of 2021 is out and available for viewing! Read up on the latest happenings at Nationwide, industry news, technical tips, and more, including... 

Nationwide has nearly 55 years of experience responding to emergency needs, and there is no doubt that we are able and ready to dispatch equipment in a moments notice. What may come as a surprise to some is that unplanned and emergency rentals make up a smaller portion of our business than planned outages. And at times, rental boilers are used for process steam when the outage is planned by the steam supplier next door.

Since the pandemic forced many companies (including NBI) to move to a temporary remote work model, some corporations like Google, Dropbox, Facebook, and Salesforce are going all in with remote work as a permanent way of business. But is remote work for everyone, and is it the future? Hear from our President & CEO, Larry Day, for his take on the matter.

Nationwide Boiler has a purpose built rental fleet featuring firetube and watertube boilers, mobile steam plants, and boiler auxiliary equipment. Partnering with multiple distinguished companies in our industry for the storage & maintenance of this equipment allows us to offer a quick and cost effective solution when a temporary steam need arises.

More changes are upon us here in California, and at Nationwide Boiler we make it a priority to stay abreast of AQMD emission rulings that will affect our customer base. The three areas of focus at this point are the South Coast AQMD, San Joaquin Valley APCD, and San Diego APCD.

With headquarters in Indianapolis, IN, Combustion Systems, Inc. (CSI) is the exclusive Nationwide Boiler representative covering the territories of Indiana, Illinois, and most of Wisconsin. Check out this edition of our representative spotlight to learn more.  

With over 100 rental boilers currently in our inventory, we still find the need to add new units to fill in the gaps, replace sold equipment, or to boost our numbers for equipment that is often in high demand. Learn about some of the new equipment currently being built for our rental fleet.

View this current edition and past editions of our Steamlines Newsletter, on our website now!

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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.

Single Point Positioning Systems

Single Point Positioning Systems, also known as Jackshaft Systems, are the least expensive and are commonly found on smaller or older boilers.  The fuel control valve and combustion air damper are mechanically linked together and controlled by a single actuator.  This necessitates that these components are in relatively close proximity to each other.

A single loop or electromechanical controller senses steam drum pressure and will send a signal to the actuator to control the firing rate of the burner to meet the required load demand.  A common jackshaft with multiple crank arms then rotates and positions the fuel control valve(s) and air damper(s)/burner register louvers. The fuel valve typically has a characterizing cam that allows you to set the AFR over the firing range of the burner.  This system is failsafe in that in the event of a failure of the actuator, the burner will remain in the proper AFR (but frozen at that firing rate).

A major drawback to the Single Point Positioning System is that the amount of hysteresis that exists in the linkage requires that the AFR be setup with additional excess air to overcome this “slop” and keep the burner from going to a dangerously rich condition. This is also amplified by the lack of repeatability of the fuel control valve and combustion air damper positions during increasing and decreasing firing rates. As a result, the burner can never be tuned to its maximum efficiency as excess air always has to be added for safety. 

In addition, Single Point Positioning Systems will also require periodic re-tuning to compensate for the varying combustion air temperatures during the year, so it is common to retune for the summer and then again for the winter months. Due to the mechanical nature of the linkage, these systems are also prone to mechanical wear.

Parallel Positioning Systems

Parallel Positioning Systems or “Linkage-less” systems are the most common system found on newer Firetube and smaller Watertube boilers today.  The advantage of these systems is that they eliminate most of the linkage hysteresis problems found with Jackshaft Systems and allow the burner to be tuned with less excess air and therefore operate more efficiently.  They also have the advantage of being able to mount the actuators and valves in a more convenient location that makes for a much less cluttered and more serviceable burner front. This level of control is also required for most Low NOx burners.

Linkage-less systems today are provided in one of two ways: as a packaged micro-processor-based system that integrates both the BMS and the CCS, or as a PLC-based system.  They provide a separate servo or actuator for the fuel control valve, combustion air damper, and FGR control valves. Ideally, the actuators are direct coupled to either the control valve or damper thus eliminating any linkage issues. Air/fuel curves are set digitally in the CCS through either a local HMI touchscreen or laptop computer.

The CCS is responsible for keeping the air and fuel actuators in the proper synchrony and position during load swings to maintain the programmed AFR.  This is accomplished by what is commonly called “cross-limiting” through position feedback signals from the actuators to the CCS to ensure that the burner maintains the proper AFR in the event of actuator failure.  Since this system relies on consistent and repeatable fuel valve and air damper positions to maintain the AFR, the pressures must be also consistent and repeatable at the inlet of the fuel control valve and air dampers. The control signals to the actuators can be either analog (typically 4-20 mAdc), digital (typically Modbus) or a combination of both. Digital control offers the advantage of less wiring since the control and position feedback signals are combined in a single twisted pair cable that is “daisy chained” to each actuator.

Features available for systems that utilize Parallel-Positioning include Oxygen Trim, Variable Frequency Drives, and as mentioned previously, PLC-based controls.

The architecture of these systems typically allows for additional burner efficiency improvements that can be provided with flue gas oxygen trim and VFD combustion fan motor control. Oxygen Trim Systems add efficiency by correcting for combustion air density and minor BTU variances with the fuel gas that have changed from the initial burner tuning. The combustion air damper is trimmed by up to +/- 10% to adjust for these changing conditions.  The CCS is programmed to maintain the varying optimal flue gas oxygen levels that were determined at each test point during the initial burner tuning. With oxygen trim systems, it is important to budget for test gasses to periodically calibrate the oxygen analyzer, and it is recommended to check calibration at least monthly.

Variable Frequency Drives (VFD) offer the potential for electrical power savings from the combustion blower motor. A VFD works in the following manner:

- Instead of moving combustion air dampers to control flow, the speed of the fan wheel controls the flow.

- A speed reference signal is sent from the CCS to the VFD changing the electrical frequency that powers the motor, and a frequency feedback signal from the VFD to the CCS provides the required cross limit data.

The rated motor RPM is typically found at 60hz, as the frequency decreases so does the motor speed.  There is a linear relationship on fan speed to flow, but it is a square root function on the static pressure.  If the fan speed is set too low, the reduced static pressure can affect the ability of the burner to properly mix fuel and air and can result in high carbon monoxide levels.

There are also minimum frequency limits on the motor that pertain to motor cooling.  As a result, in most cases the combustion air damper actuator is still required to control air flow at the lower firing settings.

The electrical savings is realized by the significantly less motor horsepower required at low fan speeds.

PLC based systems allow the flexibility to provide other energy saving schemes such as combustion air temperature compensation. Temperature correction for combustion air is especially important on the West Coast, where ambient temperatures from morning to afternoon can easily swing 30degF or more.  For the cost of a temperature sensor, temperature correction offers the “most bang for the buck” in terms of fuel savings.

Be careful, there are many older Parallel Positioning Systems that still exist today that do not incorporate any of the safety feedback features of today’s systems.  These systems simply operate the fuel and air actuators with a common signal and do not have any cross limiting that guards against air/fuel imbalances associated with an actuator failure.  They are inherently unsafe and should be replaced with a more modern system.

Fully Metered Systems

Fully Metered Cross-Limited Systems are the most efficient and most expensive method for combustion control.  Due to the high initial cost, these systems are typically found on larger watertube boilers over 60,000 lb/hr where the potential for fuel savings makes it cost effective.  Furthermore, they are typically PLC or DCS based due to the complexity of this system.

This method utilizes mass-flow transmitters that are typically pressure and temperature compensated to measure the fuel and combustion air flows to provide a precise air/fuel ratio for the burner. The control scheme is similar to the Parallel Positioning System as described above, except the flow signals provide the primary feedback to the system.  The position feedback signals from the actuators are used in the error checking logic that guards against flow transmitter and actuator failures. The air/fuel ratio is also configured so that on increasing loads the combustion air flow leads the fuel flow and conversely on decreasing loads the fuel leads the air. 

Many Ultra-Low NOx burners will require what is described as a “double cross-limited” system, which requires a very tight control of the air/fuel ratio during load swings. This results in a very slow response to load changes, taking several minutes to go from low fire to high fire.

Draft Control

Draft or Furnace Pressure Control Systems are required when the boiler has an Induced Draft Fan, a tall stack (typically > 60ft), or a common stack for multiple boilers. Typically, an actuated breaching damper on the boiler is modulated to hold a constant pressure in the furnace.

With a PLC or DCS based system, the draft control can be enhanced by adding a feed-forward scheme in conjunction with pressure control to anticipate changing loads to start opening or closing the breaching damper. Maintaining consistent furnace pressure helps to maintain the proper burner air/fuel ratio.

Drum Level Control

Proper feedwater level control in the steam drum is critical for both the safety and operation of the boiler. If the water level is too high, the water carryover in the steam line can damage equipment in the plant.  If the water level is too low, the boiler itself can be severely damaged.  To complicate things, as the steam drum experiences a drop in pressure from a sudden increased load, the drum level will swell due to the decreased density of the water. Conversely, on a rapid decreased load, the water level will shrink.

Steam drum level is typically controlled via a feedwater control valve. There are several ways to control this valve: Single Element Control, Two Element Control, and Three Element Control.

The most common method, Single Element Control, utilizes a level transmitter on the steam drum to open and close the feedwater valve to maintain the proper level.  Various instrument technologies exist today to measure this level; the most common is pressure differential.  Single element systems work very well on boilers that have very slow load swings.  On rapidly changing loads, more sophisticated methods are required to compensate for the “shrink & swell” phenomenon.

Two Element Control adds a steam flow feed-forward signal to the drum level equation to anticipate the need for more or less feedwater based on steam flow.  Obviously as the boiler produces more steam it will also require more feedwater; the opposite is true as the steam flow decreases.  This approach works well for steam plants that only occasionally experience sudden load swings.

For steam plants that have batch steam loads or experience frequent sudden load swings, Three Element Control becomes necessary.  In this method steam flow, feedwater flow, and drum level are all included in the feedwater control equation. 

In a perfect world, as a pound of steam is released from the boiler, a pound of feedwater must be replaced into the boiler. However, blowdown losses and accuracy/repeatability/turndown issues with flow and level transmitters come into play.  The drum level component of the control scheme is used as a trimming mechanism to compensate for these issues.  The control scheme is also limited by the turndown accuracies of the steam and feedwater instruments, in general below 20% load an automatic return to single element (drum level only) control is required.

Ensuring that your Combustion Control System is configured correctly for your unique application can make a world of a difference in the overall efficiency and safety of the system. And with the advances in control technology today, there are many opportunities to increase your operating efficiency and improve overall safety through combustion control upgrades; upgrades that are much more cost effective today than just several years ago.

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Preventing Freeze Damage This Winter

It's that time of year again for our annual freeze protection reminders. As you know, winter can bring extremely cold weather conditions, especially in Canada, the Northeast, Midwest, and Upper Midwest. To reiterate what we have been saying for years, here are a few things to consider to protect your rental boiler and auxiliary equipment (deaerators, water softeners, etc.) from damage due to freezing temperatures this winter.

1. If you are renting a trailer or skid-mounted firetube or watertube boiler and installing the unit outdoors, these systems are completely exposed to the environment. User's should consider enclosing the front and/or the rear end of the boiler, or build a temporary enclosure around the entire system. An external heating source should also be used. 

2. Install the proper heat tracing (steam or electric) and insulation on all main lines and piping components, regardless of whether the boiler (or auxiliary equipment) is in operation or sitting as stand-by. This should include the following lines: 
      - Sensing lines for all transmitters
      - Primary and auxiliary low-water cut-offs
      - Water column and connected piping
      - Bottom blowdown and surface blow-off piping, depending on the length of the piping runs. These valves should also be left open. 

3. During non-operational periods, drain all sensing lines and fill these lines with alcohol or a 50/50 water/glycol solution if possible and/or practical, making sure to re-connect each line. 

4. When an extended downtime is expected, completely drain the boiler, deaerator, pumps, water softener, and all associated piping (NBI installs the drain valves on all of our equipment for this purpose), as well as all stagnant water lines. 

5. If you are renting a trailer enclosed system or have enclosed system or have enclosed the rental boiler with a structure, please make sure there is an electric power supply to the system at all times, even if the unit is out of service and fully drained. The electric heaters in the trailer or structure require power, and if the rental boiler is needed it is considerably easier to bring a heated system to service. 

6. When filling a system in cold weather, remember that water may freeze when it comes in contact with cold piping. 

7. In extremely cold areas, you should consider adding electric heaters to the trailer-enclosed systems and inside temporary enclosures. Again, it is considerably easier to bring a system in to service in a heated area. 

8. Be sure to remove snow and ice from the roof of the trailer or enclosure. The accumulation of snow or ice can lead to blocked vent lines. 

9. If the boiler or auxiliary equipment is out of service, it is important to visually inspect the equipment on a routine basis to make sure all valving, piping, and sensing lines are sound and haven't frozen and split. 

If you are renting equipment, you're most likely paying a fair amount of money for the equipment and you will want the equipment to be operational if and when needed. Take these steps and be assured that the system will be available if needed. 

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Decarbonization: What Does it Mean for the Rental Boiler Industry?

Decarbonization relates to the reduction or ultimately the extinction of greenhouse gas emissions released into the atmosphere. According to the EPA, Carbon Monoxide (CO2) makes up the vast majority of greenhouse gases released during the combustion of fossil fuels. In addition to CO2, smaller amounts of methane (CH4) and nitrous oxide (N2O) are also emitted during the combustion process. With majority of rental boilers being natural gas or oil fired, what does this mean for the future of rental boilers?

With over fifty years in the industry, Nationwide Boiler has excelled through similar hurdles. In 1995, we became the first and only rental boiler company to convert our entire fleet of watertube boilers to low NOx levels of 30 ppm. In 2001, we started actively utilizing our CataStak™ SCR system on package watertube rental boilers for ultra low NOx compliance, and in 2011 we developed the product further announcing the ammonia-free / urea-based CataStak™ SCR. These and other initiatives were accomplished with sustainability and environmental improvements in mind.

While our CataStak™ and EconoStak fuel efficiency products help the environment by reducing tons of greenhouse gas emissions, we realize the need to consider an alternate non-fossil fuel with the potential to replace the “transitional” fuel of natural gas. Luckily there are some alternate energy solutions available today, including bio-fuels, hydrogen-fired, solar, hydro, and electric.

One thing we know for certain is that the current production of steam cannot be displaced easily or quickly with these alternative energy solutions. Steam as we know it is used not only for heating, but for producing many everyday products like food, beverages, paper, plastics, pharmaceuticals, chemicals, gasoline, textiles, and electricity, to name a few.

With this growing move away from the use of fossil fuels and in California specifically, Nationwide Boiler has added an electric boiler to our rental fleet – and it is our intention to add more in the future. This provides an option for customers with excess electricity available, and a solution for customers wanting a zero emissions alternative. Our first electric boiler system has been built to provide 50 hp steam at operating pressures up to 150 psig. The system includes a factory integrated, pre-piped and wired duplex feedwater system, blowdown separator, and single-point electrical POC calling for a 480 VAC, 3 phase, 60 HZ power supply. It is a smaller package than our standard fuel-fired mobile steam plants, and it requires a much smaller available footprint for installation.

In addition to adding electric boilers to our rental fleet, Nationwide Boiler is now a California representative for Precision resistant type electric steam boilers as well as Vapor Power electrode steam boilers. We can provide new, zero-emission boiler packages to facilities interested in pursuing a non-fossil fuel fired, steam boiler alternative.

As a company, Nationwide Boiler vows to continue to identify and assess alternative and sustainable options to help improve the environment while providing the reliable steam necessary for the many industries we serve today. For more information about what we’re doing to help the environment, visit our website our give us a call at 800-227-1966.

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