Making boilers more efficient - Студенческий научный форум

XII Международная студенческая научная конференция Студенческий научный форум - 2020

Making boilers more efficient

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Making boilers more efficient.

In the boiler world, most upgrades over the years have been small innovative steps rather than anything highly revolutionary as the industry continues to improve safety and efficiency and to control emissions.

Today, efficiency is the name of the game, and recently, companies have been focusing on changing the way the burner operates on the boiler as an important way to gain greater efficiency. The result for one company has been what Alan Wedal, product manager for commercial boilers at Cleaver-Brooks Inc., Milwaukee, WI, calls the biggest major development in decades and perhaps even since World War II.

It all became possible due to advances in computer modeling within the past decade that allowed engineers to work faster, generate information from the modeling program, and test prior to building and testing new boilers.

Now, we build and test to verify. It’s not as much trial and error as before,” says Florian Wisinski, Wedal’s counterpart for industrial boilers at Cleaver-Brooks.

Oxygen Level.

The goal was to get to a constant oxygen level across the entire firing range of the boiler, which is accomplished through controls and sensors, says Wisinski.

A traditional burner typically operates at lower efficiency ratings because additional oxygen is required for the burner to fire properly, and too much “excess air,” as the added oxygen is termed, can lower boiler efficiency.

According to Cleaver-Brooks, research has shown that 15% excess air is the optimal amount to introduce into the boiler combustion process. While some boilers have been able to achieve 15% excess air at the top end of a boiler’s firing range, the challenge comes at the lower end when the boiler is operating well below its maximum capacity. That’s because most boilers tend to demand greater excess air in the lower range.

Furthermore, Wedal explains, most boilers typically operate in the lower range the vast majority of the time. “So if you can improve the efficiency at the lower firing range and you’re operating there quite a bit of the time, the overall effect can be a very good efficiency gain for the end user,” he adds.

New Design.

In what became a 24-month process from initial concept, design, and validation through testing, engineers at Cleaver-Brooks started by designing a new boiler incorporating the idea of changing the burner, says Wisinski. One critical factor was a re-design of the tubes within the boiler to increase heat transfer in the tubes. Engineers added helical ribs to the inside of the tubes, creating more turbulence of the hot flue gasses and thus more heat transfer.

But it was only with the aid of CAD (Computer Aided Design) embedded with CFD (Computational Fluid Dynamics simulation software) that engineers were able to perform extremely complex calculations on various elements of a boiler system, including analyzing problems that involve fluid flows. Calculations allowed simulation of the interaction of liquids and gases with surfaces, which in turn enabled engineers to improve the tube profile and increase heat transfer by 85% compared to a traditional bare tube.

Now that the equipment is available commercially, more than half of the boilers Wisinski is providing quotes for to prospects are using this new design, which provides between 1 percent and 5 percent greater efficiency in the lower ranges and is comparable in cost to older models.

It’s changing [the marketplace] as people learn about it and understand it,” Wedal says. “We’re seeing it replacing a lot of our older models that we had been using, driven by the efficiency gains.”

Over time, Wisinski expects this will totally replace older technology although boilers can have a long life, some as long as 50 years. The new boilers have many applications for heating buildings and for all sorts of industrial processing from food, paper and plastic manufacturers to pharmaceutical and computer chip manufacturing facilities to providing process steam at healthcare facilities and other institutions.

While efficiency was the main focus, there are additional benefits, including a reduction in emissions, savings related to using less fuel and an optimized design so that the new model typically has a much smaller footprint than older boilers for a comparable size. “There are gains on many different fronts,” says Wedal.

Installation getting easier and less expensive.

Fifty years ago, most commercial boilers were so large and clunky that they had to be sawed apart to be removed from a building when their working days were over. Today, boilers have a much leaner design, yet they’re a lot more durable.

It’s the innovations inside that are making boiler installation easier and less costly. Recent breakthroughs in variable flow technology are significantly reducing boiler installation costs. Some high-end condensing boilers can operate over a wide range of flow rates with very low pressure drop. This makes it possible to install a full flow (variable primary) system. This streamlines installation by eliminating the time and materials cost of primary/secondary (boiler/system) piping—or the need for pumps to maintain flow. Variable flow technology also makes these boilers more flexible in handling frequent fluctuations in system flow rate.

Smoother, quieter modulating combustion.

Boilers using advanced fire-tube technology deliver smoother, quieter combustion with up to 25:1 turndown. For example, a boiler can fire at its maximum of 2 million BTU/hr rate when the heat load is highest, then gradually turn down as low as 4% (80,000 BTU/hr) as load decreases.

A modulating boiler system runs very efficiently, without frequent on/off cycling. When the system is zoned, units with high turndown rapidly work to match the actual system demand. This lowers a building’s fuel bill and provides better comfort by load-matching the heat loss of the system.

Ensuring greater uptime.

Today’s most innovative boiler systems are designed to deliver reliable performance with virtually no downtime. They accomplish this by sequencing multiple boilers together so there is cascade redundancy if one unit is turned off for maintenance. For example, if the lead boiler is being serviced, cascade redundancy automatically shifts the lead role to the second sequenced boiler.

Cascade sequencing can be programmed for two types of operation: lead-lag and optimization:

With lead-lag operation, one lead boiler modulates to capacity on demand. As load increases, the system then cascades to additional lag boilers in sequence. The first-on role can shift daily, distributing equal runtimes to each boiler.

In an optimized system, all boilers fire and modulate simultaneously at the same BTU/hr input rates, maximizing thermal efficiency.

A revolution in connectivity.

The first generation of building automation system (BAS) configurations usually required a standalone mid-range computer like the IBM AS/400 to control the boilers in just one building. Now facility management have the ability to monitor and manage multiple boilers across geographic locations using an app. The key is to integrate boiler operating controls effectively with a remote connectivity app. This allows one person to manage multiple boiler plants across different time zones and locations. Once the app is loaded onto an iPhone or other smart device, the user receives a text any time there’s a change in system status. It’s now easier than ever to integrate remote connectivity tools into a BAS using Modbus and BACnet MSTP as standard equipment.

Today, facility executives are exploring Internet of Things (IoT) technology. These include innovations like “smart” lighting, and boiler manufacturers are also starting to design IoT solutions. Networked boiler plants are now serving many of the world’s leading company headquarters—and even their satellite offices around the globe. These sophisticated systems are helping reduce facility heating costs and improve performance even further.

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