Real-World Problem Solving: When the Rotary Valve is the Problem

Real-World Problem Solving: When the Rotary Valve is the Problem

Industry: Cement Manufacturing
Material: Lignite Coal
Bulk Density: 54 lbs./ft³
Particle Size: Up to 1.25″
Material Temperature: Ambient
Required Throughput: 4–6 MTPH
Duty Cycle: 24/7
Application: Coal Fired Power Plant Operation
Location: Midwest, USA

The Problem

Every day, the maintenance team at this cement plant had to clear a blocked rotary airlock feeding lignite coal into the plant’s coal fired power plant operation.

The Raymond vertical mill itself was performing as expected. The rotary airlock supplied with it was not.

The severity of the problem changed significantly with the seasons.

During the relatively dry summer months, material flow was considerably less problematic. During the wet winter months, however, rain saturated the outdoor lignite stockpile, creating a gummy, sludge-like material that did not flow freely through the conveying system.

Instead, the wet lignite coal was essentially pushed through the conveying equipment until it reached the inlet rotary valve.

That’s where the problem became critical.

The wet, sticky lignite coal would pack into and completely fill the rotor pockets. Once the pockets could no longer properly receive and discharge material, the rotary valve stopped effectively metering material into the system and throughput would fall to zero.

The plant’s maintenance team then had to manually clear the packed material from the rotor to restore production, which was a daily process during the winter months.

At first glance, replacing the valve might have appeared to be a relatively simple project.

It wasn’t.

At Precision Machine & Manufacturing, we don’t believe in simply replacing one component with another and hoping the problem goes away. Before recommending a solution, we evaluate the entire bulk material handling application: the material, required throughput, equipment configuration, available space, inlet and discharge conditions, duty cycle, and how all of those variables interact in the real world.

Because bulk material handling systems that look good on paper can perform very differently in the plant.

Understanding the Application

The first priority was understanding why the existing rotary valve was creating problems.

Several factors immediately stood out.

The Material

Lignite coal, sometimes referred to as brown coal, presented a difficult combination of material characteristics.

In this application, moisture was the critical variable.

During relatively dry conditions, the lignite coal moved through the conveying system with considerably fewer problems. When winter rain saturated the outdoor stockpile, however, the material became wet, gummy, and sludge-like.

Rather than flowing freely, the material was pushed through the conveying system until it reached the rotary valve, where it packed into and filled the rotor pockets.

Once those pockets became packed, the valve could no longer effectively meter the material and throughput could ultimately be reduced to zero.

The challenge wasn’t simply moving lignite coal.

It was reliably handling lignite coal under the worst operating conditions the plant actually experienced.

The Required Throughput

The system needed to consistently handle 4–6 MTPH.

That meant determining the correct rotary valve size based on the actual application rather than simply matching the dimensions of the existing equipment.

An undersized rotary valve can become a choke point in an otherwise properly designed material handling system, which was another issue with the existing installation.

The Available Space

Correctly sizing the replacement valve created another challenge.

The properly sized PMM Self-Cleaning Rotary Valve required more space than the existing unit, which had been integrated into the original mill configuration.

Simply removing the old valve and installing another one in the same location wasn’t an option.

Inlet and Discharge Geometry

Getting material into and out of a rotary valve is just as important as selecting the valve itself.

The replacement valve had to be positioned so material could enter it consistently and then properly discharge into the Raymond mill without creating another restriction.

But the existing conveyor, mill location, available space, and required valve orientation created a complex geometric challenge.

PMM designed the lower transition to position the Self-Cleaning Rotary Valve at a 30° angle from vertical while maintaining the required discharge path into the mill.

The upper transition presented a different challenge.

Because of the compound angles created by the conveyor feeding from above, its discharge angle, the required valve orientation, and the valve’s position relative to the mill, the upper transition could not practically be finalized before installation.

PMM worked with the plant’s maintenance team throughout the process, and together determined that the upper transition would need to be designed and fabricated in the field once the valve was lifted into its operating position.

And solving those issues led us to the most unusual part of the application.

The Engineering Challenge

The available space required PMM’s Self-Cleaning Rotary Valve Airlock to be installed at 30° from vertical—approximately 60° from horizontal.

That created an engineering question we had not encountered before:

Could the valve operate at that angle while simultaneously maintaining its airlock functionality, accurately metering the material, and consistently delivering 4–6 MTPH?

There was no value in solving the clogging problem if the new installation compromised throughput, airlock performance, or material metering.

So we went back through the application data.

Then we checked it again.

Material characteristics. Moisture conditions. Capacity. Rotor configuration. Valve construction. Inlet geometry. Discharge geometry. Available space. Operating angle.

Only after we were confident that the complete system would perform as required did we move forward.

The Engineered Solution

PMM selected our proven Self-Cleaning Rotary Valve Airlock to directly address the material-packing problem that had plagued the original valve.

The Self-Cleaning design utilizes two intermeshing rotors. As the valve operates, the rotors work together so that material is continuously cleared from the rotor pockets rather than being allowed to accumulate and pack inside them.

For wet, gummy lignite that had been completely filling the pockets of the previous rotary valve, that self-cleaning action addressed the heart of the problem.

The final installation combined the PMM Self-Cleaning Rotary Valve Airlock and PMM-designed lower transition with an upper transition designed and fabricated in the field to accommodate the compound geometry of the existing conveying equipment.

The valve still had to perform three critical functions:

• Maintain the required airlock
• Meter the lignite coal consistently
• Deliver 4–6 MTPH into the Raymond mill

But ultimately, the most important requirement was much simpler:

Prevent the wet lignite from packing the rotor pockets, eliminate the recurring rotor cleaning, and give the plant a reliable system.

Instead of repeatedly asking maintenance personnel to clean packed material from the valve on a daily basis, the objective was to make the valve clean itself.

Six Years Later

This is where the story gets interesting.

The PMM Self-Cleaning Rotary Valve eliminated the recurring rotor cleaning required by the previous valve.

But solving the immediate problem was only the beginning.

Manufactured from abrasion-resistant steel and surface-treated to increase the hardness of critical internal surfaces to nearly 60 HRC, the valve was also designed for the abrasive environment it would encounter.

Today, the valve has been operating 24 hours a day, seven days a week, for six straight years.

The plant inspects the valve annually as part of its normal maintenance program.

In those six years, the valve has required no maintenance.

It continues to consistently meter 4–6 MTPH of lignite coal into the Raymond mill and has already outlived its predecessor by at least four years—and counting.

The Bigger Lesson

It’s easy to look at an application like this and conclude that the solution was simply a better rotary valve.

It wasn’t.

The solution came from understanding the entire application.

Material characteristics mattered.

Moisture mattered.

Seasonal operating conditions mattered.

Correct sizing mattered.

Inlet and discharge geometry mattered.

Available space mattered.

The operating angle mattered.

And understanding how all of those variables interacted mattered.

Had we simply looked at the dimensions of the existing rotary valve and supplied another component that fit the same opening, we might have replaced the valve without ever solving the actual problem.

A lower acquisition cost doesn’t mean much when a component requires daily attention, increases maintenance expense, restricts production, or creates unscheduled downtime.

Buying a component and solving an application are two very different things.

Performance Builds Trust

Precision Machine & Manufacturing’s relationship with this cement plant began in 2015 with an opportunity to solve a difficult bulk material handling problem.

That successful application led to another.

And then another.

Over time, the plant began deploying PMM heavy-duty Rotary Valve Airlocks in increasingly challenging applications and replacing rotary valves from other manufacturers throughout the facility.

That’s the part of this story we’re most proud of.

Not simply that one Self-Cleaning Rotary Valve has operated successfully for six years.

It’s that performance earned enough trust for a customer to continue bringing us the problems that are hardest to solve.

When the plant’s Maintenance Manager was recently asked about the key to the plant’s success, his response was:

“Precision Machine & Manufacturing has made my plant successful!”

We appreciate the compliment!

But after nearly a decade of working together, we’d put it a little differently:

When you take the time to understand the application, engineer the right solution, and deliver measurable results, you earn the opportunity to solve the next problem.

That’s real-world problem solving!

 

Have a bulk material handling application that isn’t performing the way it should?
Talk with Precision Machine & Manufacturing about the entire bulk material handling application—not just the component.

Phone: 800-722-9841

Email: sales@premach.com