Boiler Blog | Nationwide Boiler Inc.

You may not know this, but all Nationwide Boiler rental boiler systems come standard with a non-return valve. These valves are vital to protect the boiler and other plant equipment and are required by the ASME. Let’s review the basics.

What is a non-return valve?
The main function of a non-return valve (NRV), otherwise known as stop or check valve, is to allow steam flow in one direction, and automatically prevent backflow. In other words, they prevent steam from flowing back to the main header of the boiler, or back to a boiler that has failed or is off-line.

An NRV can also be used to isolate a boiler during blowdown and shutdown, and to assist in returning a boiler to operation after any planned or unplanned maintenance.

Why are they needed?
The non-return valve is really just another safety device. Although the NRV should not be relied upon for primary shut-off, it does restrict the flow of steam back from the header into the boiler, which could be disastrous.

Per ASME standards, one NRV is required for one-boiler, high pressure applications (above 15 psig). For high-pressure applications involving multiple steam boilers with manholes that are connected to a common steam main, the steam connection from each boiler must be fitted with two stop valves. The first valve must be automatic and the second should be outside-screw-and-yoke (OS&Y).

How do they prevent backflow?
Non-return valves are flow sensitive, and rely on the steam flow to open and close. The internal disc opens and allows the flow of steam through the valve. The disc will begin to close as forward steam flow decreases or is reversed, depending on the design.

As you can see, non-return valves are critical for any steam boiler system, temporary or permanent. Be sure to check with your temporary equipment supplier to ensure that they include an NRV with their boiler rental package.

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 ?T

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.

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.

The above are recommendations; however, use sound engineering judgment calls when there are concerns of possible freeze damage to the equipment. Contact Nationwide Boiler if you have any further questions: 1-800-227-1967

Nationwide Boiler recently shipped two 70,000 lb/hr trailer-mounted boilers and one 140,000 lb/hr feedwater van to Qatar as part of Qatar Petroleum and Shell's Pearl GTL project.

We took some incredible photographs of our units being shipped on the Mignon, measuring over 227 meters in length and with a car capacity of 7,200 units. Read the complete Press Release online.

The equipment is currently in transit where it will await initial start-up services and full time operation by Nationwide Boiler. Be sure to check back later when we discuss the logistics and planning involved in shipping the units back home!