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Deaerator Basics

The removal of dissolved oxygen from boiler feedwater is absolutely necessary to protect your boiler equipment from severe corrosion. To ensure trouble-free boiler operation, a good deaerator is essential.

Deaerators in industrial steam systems are mechanical devices used to remove air and other dissolved gases from boiler feedwater in order to protect the system from corrosion. Dissolved oxygen in boiler feedwater will attach to the walls of metal piping and other metallic equipment and will form oxides (rust). It also combines with any dissolved carbon dioxide to form carbonic acid that causes further corrosion. A dissolved oxygen level of 5 parts per billion (PPB) or lower is needed to prevent corrosion in most high pressure boilers, accomplished by reducing the concentration of dissolved oxygen and carbon dioxide to a level where corrosion is minimized.

The two major types of deaerators are the tray type and the spray type. In both cases, the major portion of gas removal is accomplished by spraying cold makeup water into a steam environment.

Tray-type deaerating heaters release dissolved gases in the incoming water by reducing it to a fine spray as it cascades over several rows of trays. The steam that makes intimate contact with the water droplets then scrubs the dissolved gases by its counter-current flow. The steam heats the water to within 3-5º F of the steam saturation temperature and it should remove all but the very last traces of oxygen. The deaerated water then falls to the storage space below, where a steam blanket protects it from recontamination.

Nozzles and trays should be inspected regularly to insure that they are free of deposits and are in their proper position.

Spray-type deaerating heaters work on the same general philosophy as the tray-type, but differ in their operation. Spring-loaded nozzles located in the top of the unit spray the water into a steam atmosphere that heats it. The steam heats the water, and at the elevated temperature the solubility of oxygen is extremely low and most of the dissolved gases are removed from the system by venting. The spray will reduce the dissolved oxygen content to 20-50 ppb, while the scrubber or trays further reduce the oxygen content to approximately 7 ppb or less.

During normal operation, the vent valve must be open to maintain a continuous plume of vented vapors and steam at least 18 inches long. If this valve is throttled too much, air and non-condensable gases will accumulate in the deaerator. This is known as air blanketing and can be remedied by increasing the vent rate.

For optimum oxygen removal, the water in the storage section must be heated to within 5º F of the temperature of the steam at saturation conditions. From inlet to outlet, the water is deaerated in less than 10 seconds. Call us today is you have additional questions about deaerators and how important they are to your entire system.
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The removal of dissolved oxygen from boiler feedwater is absolutely necessary to protect your boiler.
Monday, 06 July 2009 09:05
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nie one
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Wednesday, 07 August 2019 07:21
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Boiler Basics 101: Burners

The burner is the key equipment component for combustion control systems, providing the heat required for a boiler to convert water into steam. Ideally, a burner should achieve the highest degree of combustion efficiency with the lowest possible excess air. In this month’s edition of Boiler Basics 101, we will discuss the importance of burners and how they fit into the overall picture within the boiler system.

An industrial burner provides a basic function with a simple concept: it mixes fuel and air together to create combustion. Burners can be fired on various types of fuel but the most common utilized are natural gas, oil, propane and coal. In recent years, facilities have moved away from the use of coal to a more efficient and cleaner fuel like natural gas.

Regardless of the type of fuel used, the burner must perform five functions:

  1. Deliver fuel to the combustion chamber
  2. Deliver air to the combustion chamber
  3. Mix the fuel and air
  4. Ignite and burn the mixture
  5. Remove the products of combustion

Complete combustion occurs when all combustible elements and compounds of the fuel are entirely oxidized. However, with complete combustion comes harmful byproducts of combustion, including NOx and CO.

The amount of NOx and CO generated depends greatly on the burner design as well as the fuel fired. Burners with uncontrolled NOx may produce 60 ppm or more. Low NOx burners are the current standard and typically produce NOx of 30 ppm. Ultra-low NOx designs have been developed but are limited to firing on natural gas or propane. These types of burners will reduce NOx emissions to as low as 5 ppm to meet strict environmental requirements that are now common in certain parts of the country. If further NOx reduction is required, Nationwide Boiler’s CataStak™ SCR system can be utilized in conjunction with a low NOx burner.

The right burner design, along with proper combustion controls, will maximize the efficiencies of your boiler system. And as a representative of Webster Combustion, Nationwide Boiler and Pacific Combustion Engineering can help in the proper selection of your new or retrofit burner.

Be sure to check out our next Boiler Basics 101 blog to continue learning about various boiler-related topics.

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Boiler Basics 101: Evolution of the CataStak

With air emission regulations constantly changing, Nationwide Boiler has had to adopt new ways to keep up with more stringent standards. For instance, in 1995, Nationwide became the first rental boiler company to convert their fleet of watertube boilers to low NOx levels of 30 ppm. The company’s method of choice to reduce NOx emissions further led to the creation of the CataStak™, which was developed in the late 90s and since then has proven to reduce NOx emissions by as much as 99%. In addition, it can be supplied for new equipment or as a retrofit on an existing system. What were the early days of the CataStak like? What steps did it take to get to where it is now? Let’s find out in this edition of Boiler Basics 101.

It all began when Nationwide Boiler chose Selective Catalytic Reduction, or SCR technology, to be their solution to NOx compliance. They determined that SCR was the best alternative due to its reliability, ease of operation, high efficiency, and its ability to reduce emissions to single digit NOx levels. In 1999, Nationwide Boiler became the first rental boiler company to conduct an SCR field demonstration on a package watertube boiler and followed by utilizing the system heavily in their rental fleet. The enormous success of rental SCR systems suggested to company management that a market existed for a field-retrofit system for package boilers - later to be branded and trademarked in 2001 as the CataStak™ SCR System.

Fast forward to the year 2004, Nationwide began offering the CataStak for new and existing package watertube boilers to meet sub 9 ppm NOx levels. After witnessing its continual growth, Nationwide Boiler introduced a new business unit, Nationwide Environmental Solutions (NES). NES was formed with a focus on lowering overall industrial greenhouse gas emissions and increasing the operational efficiency of fired equipment. This allowed Nationwide to continually raise the bar in providing reliable solutions to meet market demand.

Nationwide later developed the urea-based CataStak as a solution for customers adverse to the stringent handling requirements of ammonia. The system utilizes common diesel exhaust fluid (DEF), a safe and readily available 32.5% liquid urea solution. It was first demonstrated on a package firetube boiler in 2011 and has since been expanded to be utilized on watertube boilers and other fired equipment. Initially, the system was offered only for permanent applications but in 2018, Nationwide became the first rental boiler supplier to provide urea-based SCR systems on a boiler rental project. The company now has a fleet of urea-based SCR systems to support the rental market.

The CataStak has come a long way and has now been installed in over 180 applications. These installations range from temporary to permanent package boilers, fired heaters, gas turbines, and heat recovery steam generators. With all of these accomplishments, the CataStak has become the standard for compliance assurance, reliability and product quality. CataStak SCR systems lead the industry with the best track record in terms of performance, and source test results often exceed current local, regional and national emissions requirements.

If you’re interested in learning more about the CataStak, our website has all the details you need to get started. And be sure to check out the previous and future Boiler Basics 101 blogs to continue learning about various boiler-related topics.

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Boiler Blog 101: Importance of a Water Softener Consequences of Hard Water

Improper water treatment is the leading cause of tube damage and poor performance in a boiler system. In this month’s edition of Boiler Basics 101, we will discuss the consequences of introducing your boiler to hard water and the importance of utilizing a water softener.

If water is not treated properly before entering the boiler, scale will begin to form due to a chemical imbalance within the tubes. Scale is defined as concentrated minerals being precipitated when the water is evaporating in a boiler. The precipitated minerals consist of a mixture of calcium, magnesium, iron, aluminum, and silica, and are often referred to as “hard minerals”. Scale is detrimental in a boiler system because it acts as an insulator and prevents proper heat transfer. This can lead to decreased boiler efficiency, costly downtime, and even premature boiler failure. Eventually, scale build-up will cause boiler tubes to overheat and rupture.

To help prevent scale and deposit formation, make-up water should be circulated through a water softener before it is fed to the boiler. A water softener is an ion exchanger designed to remove positively charged ions from hard minerals (like magnesium, calcium, and iron) and replace them with negatively charged ions. The resin beads that are inside the resin tank are negatively charged by brine, which contains salt and potassium. As the water goes through the resin tank, the positively charged ions are chemically attracted to the negatively charged resin beads. The hard minerals then stick to the resin as the water runs through the tank, thus turning the water into “soft water”. This process frees the water from these minerals before entering the boiler and decreases the risk of tube scaling and irreversible damage.

Water softening is one of the main ways to increase boiler longevity and maintain boiler performance. Nationwide Boiler’s fleet of mobile boiler rooms, steam plants, and feedwater system trailers include duplex water softening systems to ensure optimum boiler performance. We also have skid-mounted and trailer-enclosed, stand-alone water softeners available for rent or for purchase. It’s important to know that when Nationwide Boiler delivers a rental unit, it is the customer’s responsibility to maintain and supervise the water treatment and chemistry of the water entering their rental boiler.

All boilers are subject to damage if proper water treatment procedures are not followed. This is an important consideration both during operation and when the boiler is idle. To avoid damage and costly repairs, monitor water chemistry routinely and ensure that you are supplying your boiler with soft water at all times.

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