Time-honored technology has a new luster

Today, watertube units are dominant in many industrial applications. Fire-tube units, tubeless units, and hybrid boilers have their places, but when an industrial user needs medium- or high-pressure steam, and lots of it, watertube boilers usually get the nod.

By Plant Engineering May 2, 2012

Time-Honored Technology Has a New Luster

Since the beginning of the last century, watertube boilers have been developed to meet the need for higher pressures and faster response times.

Today, watertube units are dominant in many industrial applications. Fire-tube units, tubeless units, and hybrid boilers have their places, but when an industrial user needs medium- or high-pressure steam, and lots of it, watertube boilers usually get the nod. 

Factory Packaging Brings Advantages

In the distant past, most watertube boilers were assembled at the site, including installing tubing, walls, burners and controls. For all but the very largest industrial and utility installations, those days are past. Today, boilers of up to 500,000 pounds per hour are available as completely factory-packaged units. Even larger capacities are available with packaged modular designs that require very minimal assembly at the site. Customers have the assurance that unit assembly is done to the highest standards under controlled factory conditions.

Typically, packaged boilers are inspected and hydro-tested at the plant complete with required valves, controls, and power and control wiring. In the largest units, burner assemblies and overhead drums are usually attached at the site. It merely remains for the unit to be put in place and connections made.

Range of Applications

Cleaver-Brooks is a major supplier of large, packaged watertube boilers for industrial users in the U.S. and Canada, and worldwide. Jason Jacobi is Sales Manager at Cleaver-Brooks’ Nebraska Boiler unit in Lincoln, Nebraska, and is involved in large packaged boiler sales for industrial applications. Jacobi indicates that steam from packaged industrial watertube boilers is being widely used in the petro-chemical, refinery, pulp and paper, food and beverage, chemical and pharmaceutical, and miscellaneous manufacturing segments of industry.

He points out numerous benefits of replacing an older boiler with a new packaged unit. “In my opinion, the most influential advances in boiler technology in the past 20 years have come in the forms of lower emissions, increased reliability, innovative modularization and extreme efficiency improvements.”

Eliminating Refractory

Jacobi indicates that Cleaver-Brooks has strived to eliminate the need for refractory in its industrial boilers. The benefits are reduced maintenance needed for replacing broken or missing refractory, and reduced potential for overheating of burner components while cooling. 

Improved controls are another important advancement in boiler design. Jacobi points out that precise digital control of combustion is essential to meet air emission standards as well as maintaining highly efficient steam production over a range of turn-down conditions. “Advanced metering control systems allow for tight control of the fuel-air ratio.” Applying these advanced controls on an existing boiler can also be beneficial.

Retrofits Possible, But . . .

Asked whether it is practical to put new burners and controls on an older boiler, Jacobi says, “This varies on a case-by-case basis, but in general there can be real value in retrofitting an existing boiler if it is in good condition and does not require significant pressure vessel rework.”

“However,” Jacobi cautions, “The existing pressure vessel remains, and is likely not optimized for the flame geometry and mass flows of today’s green burner systems. Drawbacks of this approach can include higher fan power consumption and possibly reduced steam capacity.” He notes that when many industrial customers start to consider a retrofit, their boiler vessels are already beyond reasonable repair. “In these cases, an entirely new state-of-the-art custom designed steam generating system offers maximum value.”

New Boiler May Be Better

This thought is echoed by Ryan Cornell at The Babcock and Wilcox Company, another major manufacturer of watertube boilers for industrial plants. He explains, “Although a customer can certainly upgrade an existing boiler with a new burner and digital controls, there are substantial costs to retrofiting a  unit in the field, as well as costs for other components that may need to be installed for emission control.”

Cornell also points out that over the last 5-10 years boilers have been redesigned to improve internal heat transfer. “The heating surface is more effective than earlier designs, which allows the manufacturer to design more compact units with higher heat release rates than were possible in the past. This allows a customer to install a unit with higher capacity and better efficiency into the same footprint as an older unit in their plant.” For plants that are undergoing operational expansion, or with crowded boiler rooms, this is attractive.

Boiler Selection

In addition to being able to operate at higher pressure than a firetube boiler, today’s boilers can produce superheated steam for applications where a “dry” high-pressure steam is desirable. 

According to Cornell, most industrial boiler manufacturers have the resources and are capable of assisting owners in making an assessment of the existing system and making recommendations for retrofit or replacement. Owners should work with consulting engineers that are familiar with industry trends. 

Design Innovations

Examples of innovations in boiler design are units by Groupe Simoneau in Quebec. According to Marc Mitchell, Director of Sales and Marketing for the company, one new feature is a proprietary design for economizers integrated within the boiler.

Speaking about the boiler replacement process, Mitchell points out that many owners need to keep their old boiler operative until the new unit is installed in order to maintain plant production. He adds, “Many will keep their old one as a backup, if they have the space, instead of dismantling it after the new one is installed.” In this case, because the unit is only infrequently operated, low boiler efficiency is not a great problem.

Finding New Opportunities

Packaged watertube boilers are being installed in interesting new ways. An example is the use of multiple very large units to generate steam to facilitate extraction of oil in Canada’s western oil sands regions. Here the steam is injected into boreholes in the oil-sand deposit to heat it and facilitate oil and water removal, either from a parallel well or by cyclical injection and liquid extraction. According to Jacobi from Cleaver-Brooks, this operation replaces earlier facilities that extracted the sand and treated it on the surface, with some attendant environmental issues.

Over the past eight years, Cleaver-Brooks has manufactured nearly 40 of the massive boilers used to generate the huge quantities of steam needed in Canada’s Athabasca Oil Sands.

“No one else in the world really needs that much steam,” Jacobi says. He notes that these boilers usually use a combination of pipeline natural gas and produced gas that comes up the well with the oil. “Regardless of the fuel, environmental regulations require that all boilers be equipped with ultra-low NOx burners to achieve Best Available Control Technology (BACT).”  

Attractive Energy Prices

Today’s comparatively low prices for natural gas for industrial use make it an easy choice for many industrial steam users. The payback for a modern boiler using natural gas can be very short. If a company is currently using another fuel, or if their existing boilers are in poor condition, now is the time to change to an efficient and reliable packaged watertube boiler firing natural gas.