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Nationwide Boiler news and events, industry updates, technical resources and more. You hear it first on The Nationwide Boiler Blog!

Superheat Boiler Design and Performance: A Brief Overview

In the boiler industry, there are three main types of watertube boilers: D-type, O-type, and A-type (see the graphic). Boilers can be designed for either saturated or superheated steam, and they can be packaged or field-erected. Package watertube boilers are designed to be small enough for highway transportation and are factory assembled. Field-erected boilers are just as they sound; multiple components are assembled and installed in the field.

For each boiler type, there are differences in superheater design and performance. Before diving into those differences, let’s review each of the main types of watertube boilers. bw boiler types

D-type boilers have one steam drum and one lower drum, centered over each other with the furnace offset to one side. These boilers are designed with only one generating bank. 

O-type boilers also have one steam drum and one lower drum, however, they are centered over each other with the furnace in the center. These boilers are designed with two generating banks (i.e. the flue gas flow splits into the two sides at the end of the furnace). 

A-type boilers are similar to O-type and include two generating banks. The major difference is the number of drums and placement. A-type boilers include one steam drum at the top center, and two lower drums; one placed on each side of the furnace.

Saturated steam means that the steam temperature is purely dependent on the steam pressure and follows the pressure-temperature curve. For example, if the upper drum is at 150 psig, the saturated temperature would be 366°F. If the upper drum is at 300 psig, the saturated temperature would be 422°F. Saturated steam boilers will have a steam nozzle directly on the upper drum regardless of the boiler type. All of the steam produced is also collected in the upper drum.

When the design calls for superheated steam, which would be higher than the saturation temperature, an extra set of steam tubes or coils are provided and added to the heat transfer circuit in the boiler. The superheater tube bank is piped downstream of the steam drum to add heat to the saturated steam and make it superheated. 

ConvectiveOn D-Type boilers, this extra tube bank is added to the convection section (or the generating bank). This is called the convective design. The benefit of this design is the steam coils are out of the radiant heat zone of the burner (the extra heat transferred uses convection only). However, performance is not as good as radiant style superheaters which means at reduced loads, the steam temperature drops off quickly.Radiant

On O-type and A-type boilers, the extra tube bank is added at the end of the furnace. This is called the radiant design. The benefit of this design is that the performance is much better as compared to the convective style throughout the load range. However, since the heat transferred is primarily radiant heat from the burner, the superheater typically doesn’t last as long and requires more maintenance.

In today’s market, D-Type boilers are the most common. The superheat performance issues can be compensated by designing the steam for a higher temperature and then using an attemperator to control steam temperature more closely over the boiler load range. In the rental boiler industry, O-type boilers are the most common because the weight is more evenly distributed making it ideal for trailer-mounting and road transportation. Stay tuned for our next blog where we will touch on a fourth, less commonly known watertube design; the Ds-type. Ds style boilers are patented and manufactured by Superior Boiler.

As a rental boiler supplier, manufacturer’s representative and stocking distributor, Nationwide Boiler has not only sold but actually operated and maintained package watertube boilers for over 50 years. Give us a call today to learn more about what type of boiler is best for your unique application.

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Reduce, Reuse, Recycle – Rental Boiler Edition

At Nationwide Boiler, we maintain a purpose-built fleet of over 100 rental boiler systems from as small as 47.5 hp to as large as 200,000 lb/hr. We have multiple configurations including mobile, trailer-mounted boilers, complete mobile boiler rooms and mobile steam plants, skid-mounted firetube and watertube boilers, factory-integrated skid packages, and even electric boiler systems. With a rental fleet as versatile as ours, we can always find a solution when a customer comes calling.

It is not uncommon for a rental boiler to return and need repairs. A unit might need parts to be replaced, an acid cleaning or even a complete retube, but the worst-case scenario would be the need to scrap a boiler entirely due to damage beyond repair. But if a boiler is properly maintained, as we have said before, it can last a lifetime. A boiler retube can transform a system and bring it back to like-new condition. And, with so many different types of boilers in our rental fleet, we have found other ways to transform, reuse, and recycle when our equipment still has years of life left. 

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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... 

A SOLUTION TO STEAM SUPPLIER OUTAGES
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.

REMOTE WORK: IS IT THE FUTURE?
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.

GETTING TO KNOW OUR STORAGE YARDS
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.

CALIFORNIA EMISSION RULE UPDATES
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.

REP SPOTLIGHT: COMBUSTION SYSTEMS, INC.
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.  

NEW RENTAL BOILERS FOR THE FLEET
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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Addressing Common Issues Impacting Safety & Performance of Boilers

Do you work with boilers? The American Boiler Manufacturer's Association (ABMA) recently published a Boiler Installation Guide that addresses common issues impacting the safety and performance of boilers. This handy guide references eight major areas with strict codes and requirements that must be followed for proper design and installation. These areas include:

 -  Combustion Air SupplyABMA Logo Transparent
 -  Stacks and Ductwork
 -  Draft Controls
 -  Gas Train Design
 -  Combustion Tuning
 -  Safety Controls
 -  Piping and Valves
 -  Outdoor Installations

Check out the complete guide to prepare for your next boiler design and installation project. And don't forget to call Nationwide Boiler for your next temporary rental boiler project or new and used boiler needs.

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