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Boilers come in all different types, sizes, and shapes and are classified by configuration of the furnace, or firesides, and the watertubes, or water holding volume. The two main boiler types consist of firetube and watertube boilers, and deciding which of the two will best fit your process needs is not as easy as it may seem. It is like comparing apples to oranges; it’s not as simple as just comparing prices for similar nameplate steam capacity, and there are some significant differences to consider.

With firetube boilers, flue gases are directed through vertical or horizontal steel tubes that are surrounded by the water for heating, and typically go through two, three, or four passes, or changes in direction. In watertube boilers, the arrangement is reversed. Instead of the water being outside the tubes, it circulates inside the tubes and is heated externally by the combustion gases. Fuel is burned inside the furnace, which heats the water in the steam-generating tubes. The water then rises to the steam drum where saturated steam is drawn from the top of the drum. The watertube boiler has some relative advantages over the firetube boiler design, which are outlined below.

Watertube boilers are safer by design and generally considered to last much longer than the firetube boiler. They are available in much larger sizes and recover faster than firetube boilers, can handle pressures up to 5000 psig, and have the ability to reach very high temperatures with the use of superheaters. Because of their inherent design, firetube boilers are not suitable for pressures above 350 psig. Also, the steam output is less than the nameplate at actual operating conditions. Watertube boilers are rated at actual operating conditions. However, from a manufacturing standpoint, firetube boilers are typically lower in cost than a comparable sized watertube boiler, the firesides are easier to clean, and the straight firetubes are easily replaceable.

Let’s not forget that there is a tremendous difference in water volume between a firetube boiler and a watertube boiler. From a cold start, the firetube boiler, due to its larger water volume, takes longer to bring up to operating temperature or pressure vs. a similar sized watertube boiler. With less water volume, a watertube boiler can follow load swings more precisely and generally has better turndown. However, one advantage that the firetube boiler does offer is that once it is up to operating pressure, it can handle a sudden upward load surge better because of the large steam disengaging area. The drawback to this feature is once you drop pressure on the firetube, it takes longer to catch back up.

The rule of thumb is that if you have a very constant and steady load that doesn’t vary much, than the firetube boiler may work well. If you have a swing or varying load, then the watertube boiler is generally a better choice.

Click here to view Nationwide Boiler's current inventory of firetube and watertube boilers available for shipment anywhere in the world!

 

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Once winter arrives it is a good time to remind our customers about how to properly prepare for freezing temperatures.  This not only applies to when a boiler is in operation, but also when a boiler is down or in transport.  The guidelines below will help get you started, but contact Nationwide Boiler if you have any further questions: 1-800-227-1967.

Freeze Protection Guidelines

Freezing conditions pose a huge risk to boiler equipment if it is not properly protected from the harsh elements. In order to ensure that your unit continues to operate while facing freezing conditions, Nationwide Boiler recommends the following:

    1. Enclose both the front and rear of the boiler area and use an external heat source to minimize freezing conditions.
    2. Install heat tracing with insulation to protect exposed stagnant water lines.
    3. Utilize an appropriate heat tracing method (electric or steam tracing) to all of your main lines and piping components. This includes the following lines which should be heat traced regardless if the boiler is in operation or not (in freezing conditions): sensing lines (steam drum to CMR, high steam and steam gauge), auxiliary low-water-cut-off, water column and level control blowdown. Depending on the length of piping runs, the main and continuous blowdown should also be heat traced.
    4. In addition to heat tracing on stagnant sensing lines, drain the lines and fill them with a 50/50 (water/glycol) solution, making sure to re-connect the line.
    5. When an extended boiler down time is expected, completely drain the boiler and stagnant water lines.



NOTE:

    • The above lines are considered stagnant lines and should be heat traced regardless if the boiler is in operation or not (freezing conditions).
    • Nationwide has also done the following in addition to heat tracing on the stagnant sensing lines: Drain line, fill with 50/50 (water/glycol) solution, re-connect line.
    • Depending on the length of piping runs, the main and continuous blowdown should also be heat traced.
    • For extended boiler down time, drain boiler and stagnant water lines completely.



Standard Enclosure

The above are recommendations; however, use sound engineering judgment calls when there are concerns of possible freeze damage to the equipment.

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Three new ultra low NOx (ULN) mobile boiler rooms have been added to Nationwide Boiler Inc’s growing fleet of rental boiler systems.  The boilers have been specifically designed, manufactured and assembled to meet the increasing demand of steam for commercial and industrial boiler users located in California and other parts of the nation who must comply with strict air emission requirements. All three units have been pre-certified to comply with permitting agencies including the South Coast Air Quality Management District (SCAQMD) and the Bay Area Air Quality Management District (BAAQMD).NBI Mobile Boiler Rooms

The three new units include a pair of 47.5 hp (200 psig) ULN boilers enclosed in 27’ single axle vans and one 650 hp (250 psig) ULN boiler enclosed in a 53’ van.  All boilers include 9 ppm gas-fired burners (with the option to fire propane fuel), deaerators, feedwater pumps, chemical treatment systems, blowdown separators and sample cooler stations.

For more information about these boiler systems and other units in our rental fleet, visit our website at www.nationwideboiler.com.

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No matter what type or size of boiler you are looking to purchase, there is always one question you must always answer when selecting a steam boiler: What is the basis for design?  Fulton Company recently published a list of 10 features you wish every boiler had.   It is important to review this list and be sure to know which attributes are most important to you and your specific application.  In addition, when selecting the right boiler provider, remember that any qualified boiler company should be able to provide you with accurate boiler specifications, performance data, and drawings, all of which will make the decision process easier and will help you along the boiler decision process.

*** With emission requirements changing everyday, it is also important to make sure that you are proactive when selecting equipment that will comply with future air regulations.  Nationwide Boiler has the most experience in selecting boiler equipment that will meet current and future NOx requirements and we developed the CataStak SCR system as a solution for ULN compliance.  Contact Nationwide Boiler today to discuss the requirements of your new or used boiler systems.  We will be happy to help. Toll free: 1-800-227-1966.

1. High Pressure Vessel Mass

The mass of the boiler will be a good indication of the amount of metal used to manufacture the pressure vessel. Mass is related to thickness and thickness is related to durability. Inherently, low mass boilers will not last as long as high mass boilers.

2. High Water Volume

Water under pressure will store steam. Higher water volume means higher stored steam. Applications where you have rapid swing loads will require a high water volume boiler design.

3. High Efficiency

We all would like to have the most efficient boiler. Efficiency, however, must be defined and compared on equal terms. Ensure boiler pressure, feed water temperature, firing rate, fuel BTU value and stack CO2 levels are all defined on the same playing field.

4. Quick Startup Times

Simply put, you want steam in a reasonable time frame. Boilers that can make steam quickly likely will have low water and low mass, which may be non-desirable features. One must also realize a quick startup will facilitate a quicker cool down. The boilers on the market today typically require 5 to 20 minutes startup time or more, depending on the size of the boiler

5. Low Footprint

Boiler room real estate is quite valuable these days and the less room a boiler occupies, the better. Be sure you take into consideration the amount of room required to perform maintenance on the boiler as part of the overall footprint.

6. Low Heat Flux and High Heating Surface Area

Heat transfer is represented by the equation

Q =m x Cp x ΔT

where m is the heating surface area.

Most heating surface area listings are for the fire-side surface area, with higher fire-side surface area values indicating higher the heat transfer efficiency. However, one also must consider the wetted heating surface area. The wetted heating surface area determines heat flux. Consequently, low wetted heating surface area can have very high heat flux, which can create higher metal temperature and increase scaling potential.

Boilers with high fire-side and high wetted heating surface areas will be the most efficient and have low heat flux.

7. Ease of Clean Out

This is a measure of effectiveness of blow down and ability to keep the pressure vessel clean.

8. Effective Turndown

This feature has a lot to do with the burner performance. Effective turndown is a measure of how low the fuel input and air can be adjusted to maintain good combustion efficiency. Some burners will turn down the fuel but leave high excess air on low fire. This will create high turndown but poor overall combustion efficiency. Look at the highest turndown level while still maintaining good combustion efficiency.

9. Ease of Maintenance

Hardly ever will a specifying engineer think about maintenance when selecting a boiler. They should. Blow down valves, stack location, feed water inlet, control panel location, tube removal, burner removal and gas piping maintenance should all be considered as criteria of boiler selection.

10. Large Steam Disengagement Area

Like heating surface area, the more steam disengagement area, the better. Higher steam disengagement area produces higher steam quality, especially for low pressure steam applications. Consequently, horizontal boilers generally will produce higher steam quality than a vertical boiler of the same output.

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