Case Study:  Process Technology Training

Case Study: Process Technology Training

Whatever it takes.

How the R. A. Ross team knowledge and experience can help you.

Process technology training provides valuable information for industrial engineering firm

“I knew some of these types, but it was new exposure for me on the other half of the list

– Todd Hess, Vice President and
Senior Designer
with Hess Engineering

Sometimes, the very solution you need for a complex process may involve a technology that you may never have heard of. Engineers are often called upon to design complicated systems in industrial and municipal processes that require a specific type of pump or piece of equipment.

That’s where R.A. Ross & Associates can help!

We’ve put together a training module covering the various types of pump technologies available today and the typical applications they are best suited for. We provided our Process Technology class during a “lunch and learn” at the well respected firm of Hess Engineering (formerly A.J. Hess & Associates) in Calvert City, KY. Hess Engineering has been around since 1984 and provides civil, mechanical, electrical, chemical engineering and project management services in Western Kentucky and surrounding areas.

Contact us today to set up your class and see what you might be missing!

Some of the types of pumps covered in our training class:

Personal Development Hours Certificate Training

We also provide a PDH (personal development hours) Certificate upon completion of the training.

Download the case study

 
Case Study: Tough pumps for tough applications

Case Study: Tough pumps for tough applications

Doing whatever it takes.

The Ross team provides tough pumps for tough applications!

If you need it, Team Ross has it!

PROBLEM/SOLUTION:
A global automotive plating company with operations in Eastern Kentucky needed some rugged pumps for a rinse water application that would be required to handle a mixture of aggressive chemicals.

The existing pumps in service couldn’t hold up to the various chemicals present in the rinse water. After review of the application, the R.A. Ross team had the perfect solution in mind; the Vanton® Chem-Gard® ANSI centrifugal pump with PVDF (Kynar) wetted materials with clean water flush to protect the seal.

Wet end components of Vanton CHEM-GARD® centrifugal pumps are injection molded of corrosion resistant polypropylene (PP), polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polyvinylidene fluoride (PVDF), ethylene chlorotrifluoroethylene (ECTFE) or other non-metallic materials that are 100% inert to the fluids being handled across the entire pH range. This eliminates the corrosion and failure associated with pumps constructed of stainless steel and other alloys, the wicking associated with fiberglass pump components and the delaminating inherent with plastic-lined metal pumps.

Application info:
Transfer of corrosive rinse water at the following rates: 100 GPM @ 40’ TDH

Vanton Chem-Gard® ANSI-Centrifugal pump model CGA-KY-3x2x8

  • Horizontal centrifugal with all fluid contact parts of homogeneous non-metallic materials, dynamically balanced keyed semi-open impeller, stainless steel shaft with wet end sleeved with PVDF (Kynar).
  • Materials of Construction PVDF / Kynar
  • Impeller Dia. 8”
  • Suction and Discharge 3” x 2” 150# flanged
  • Mechanical Seal
  • Water Jacket Standard (Seal water supply & drain required).
  • Pedestal Guard Polyethylene
  • 5 HP, 230-460 volt / 3-phase / 60-Hz, 1800 RPM, TEFC, severe duty motor mounted on an epoxy coated, steel base plate including spacer coupling and coupling guard 400 GPM @ 70’ THD

Vanton Chem-Gard® ANSI-Centrifugal pump model CGA-KY-4x3x10

  • Horizontal centrifugal with all fluid contact parts of homogeneous non-metallic materials, dynamically balanced keyed semi-open impeller, stainless steel shaft with wet end sleeved with PVDF (Kynar).
  • Materials of Construction PVDF / Kynar
  • Impeller Dia. 10”
  • Suction and Discharge 4” x 3” 150# flanged
  • Mechanical Seal
  • Water Jacket Standard (Seal water supply & drain required)
  • Pedestal Guard Polyethylene
  • 20 HP, 230-460 volt / 3-phase / 60-Hz, 1800 RPM, TEFC, severe duty motor mounted on an epoxy coated, steel base plate including spacer coupling and coupling guard

The Vanton Chem-Gard ®pump used in this case study:

  • Flows to 1150 GPM (261 m3/h)
  • Heads to 185 ft (56 m)
  • Temps to 275°F (135°C)
  • Construction: PP, PVDF

Download the case study

 

What is Suction Energy

I’ve been around for a while and have observed the parade of fashions and trends coming and going through the years. From my college days in the ’60s—miniskirts, peace signs, corduroy pants, tie-dye and paisley shirts were “groovy” and “far out.”

Now 50-plus years later, many of these faded ideas have made a resurgence, at least in some circles. Perhaps some of these fashions and trends were good ideas and some were not. In retrospect, I have few regrets of my own personal choices from the past, but I do wish I had held on to my car, a muscle car that I street raced.

Thinking back to my car from the ’60s, I typically evaluated my odds of winning or losing the race by estimating the car’s horsepower to weight ratio as compared to my opponent. Going forward in the pump business the last 50 years, end users have also pushed industrial pump manufacturers toward a similar goal—exponential horsepower increases for more head and flow—all contained within smaller and smaller pump sizes or, simply, get more with less.

Suction Energy

I have been involved with industrial rotating equipment in one way or another since those days of wearing bell-bottom jeans, and sometime in the last half century, I was also exposed to the theory of suction energy (SE). SE is a concept that explains how the momentum of the fluid entering the pump suction can potentially be an issue or not. Similar to disco music, it appeared to be a good idea at the time. Thankfully it faded quickly and, like an odd wrench in the bottom of my toolbox, I did not use it anymore, but I could not throw it away either.

I dismissed the practicality of SE in a column many years ago; however, I am seriously rethinking the decision because I am now looking at it in a different way. Many readers may not have heard of this thing called suction energy. SE is, in essence, a measurement of the liquid momentum at the impeller eye. SE, in its simplest definition, is the unit-less mathematical product of the nominal inside diameter of the pump suction nozzle (D), multiplied by the pump speed (N), multiplied by the suction specific speed (Nss). Note: The speed is revolutions per minute (rpm) and the diameter is inches.

Formula 1:
Suction Energy = D x N x Nss

A more refined definition of SE exchanges the first factor of the pump suction nozzle size for impeller inlet (eye) size (De). Note: They are frequently close to the same dimension. Specific gravity (SG) was also added to the formula and, if pumping cold water it is obviously not a factor, but if pumping hot water or a different fluid, the factor should be weighed.

Formula 2:
SE = De x N x Nss x SG

If the impeller eye diameter is unknown and cannot be determined, you may estimate it by using the following factors: For an end suction pump, multiply the suction nozzle size by 0.9, and for a horizontal split case or radial inlet pump, multiply by 0.75.

Defining Levels of SE

The results of these equations produce high numbers, and so it is common to use a form of short-hand scientific notation, but the coefficient remains as a three-place number.

  • Low SE is defined as values below the high SE levels.
  • High SE is defined as values at or above 160 x 106 for end suction pumps and 120 x 106 for split case and radial inlet pumps.
  • Very high SE is defined as values at or above 240 x 106 for end suction pumps and 180 x 106 for the split case and radial inlet pumps.

Pumps Have Boundaries

We are still not allowed to violate the laws of physics, and so this imposing goal of more with less requires improved impeller designs, higher rotating speeds and fluid velocities. Along with the benefits of more horsepower and head (generated per stage) all in a smaller box, there are caveats that require higher net positive suction head (NPSH) margins, diminished operating ranges and often more wear.

Technological advances have helped us design and manufacture better pumps since Lyndon Johnson and Richard Nixon were president, but some consequences will defiantly persist, simply to cruelly remind you of the serendipitous karma that pervades our universe.

And this brings me back to the subject of SE and the suction side portion of the pump system. Most pump manufacturers will ask for a minimum of 10 or more diameters of straight, unobstructed piping prior to the pump suction flange in a seemingly fair exchange for a trouble-free and reliable pump. This means no valves, no elbows, no tees, no strainers, no reducers and surely no flow meters. In the unfair light of the real world, the pump never gets to check off any of the boxes on this wish list of desired requirements.

Additionally, it is highly suggested that the liquid velocity in the pump suction inlet piping should be less than 10 feet per second (3 meters per second—slower is even better). This velocity requirement is also often cast aside.

To oversimplify what can be a complex design requirement at the entrance to the impeller, in a perfect world we are looking for an equalized hydraulic loading with zero pre-swirl, eddies and recirculation in the fluid as it is presented to the impeller around the entire 360-degree profile. When the SE level is low, the pump owner can often disregard many of these aforementioned requirements and still avoid the downside consequences that would normally result with these violations.

What I witness more and more with industrial applications are suction side issues that could have been avoided if the end user had paid more attention to the suction system from the dual aspects of energy (suction energy) and piping geometry.

What I frequently hear is that there is enough net positive suction head available (NPSHa) and the margins are adequate or the specific speed (Ns) and/or the Nss is in an acceptable range—so, what is the problem?

One of the remaining unaddressed issues is uneven hydraulic loading of the impeller with copious amounts of pre-swirl, recirculation and high velocities. One recent application I visited had more than six obstructions introduced in three different planes within the last 10 feet of suction piping. There was adequate NPSH margin, but the pump was in the very high range of SE and, consequently, the pump was not performing properly.

What I am ultimately trying to do is help the owner-operator have a reliable pump and operating system. I don’t know where all the boundary lines are exactly for your specific application.

Additionally, note these guidelines and guardrails are often grey areas—not black and white. There are also no flashing red warning signals for the inexperienced designer.

Another way to say all of this is: If you have adequate NPSH margins and properly selected impellers for the operating range, you still need to evaluate your total system design. The typical design will be a compromise based on best practice hydraulics on one side and the initial cost of the system on the other. What many organizations do not allow is an evaluation of pump/system reliability and the associated cost over some period of time, perhaps five to 10 years or even 20.

Look at the SE level of your system and if it is low, then perhaps you have nothing to worry about and can move on. However, if it is at a high or very high level, then I suggest that you re-examine your system design with a higher degree of due diligence regardless of the NPSH margin and the impeller geometry.

Prediction Clues

When you have pump and system issues and can’t seem to figure it out, look at the SE level and, in conjunction with that data, also consider these additional prediction factors/indicators of pump issues.

  • liquid personality: temperature, viscosity and specific gravity
  • impeller speed: watch for inlet tip speeds above 75 feet per second (above 100 for sure)
  • pipe size suction: typically the size should be one size larger than the pump itself; in some high energy cases, you may want to design even bigger
  • fluid velocity suction: looking for less than 10 feet per second at the suction
  • pipe geometry (suction side): looking for elbows or components to be far
  • from the pump suction nozzle, proposing 10 diameters
  • impeller type: dual suction/shaft through the impeller or end suction
  • impeller: number of vanes
  • impeller vanes: the absence of—or the amount of vane overlap
  • impeller: inlet incidence angle and also compare that angle to suction nozzle
  • suction specific speed (Nss) and the D2 over D1 ratio
  • specific speed (Ns)
  • NPSH margin: even with an adequate margin, operating left of the best efficiency point (BEP) can be an issue when the SE is high
  • operating point on the curve relative to the BEP

Additional Perspective

If you have a system that seems plagued with unexplained pump issues, take a look at the SE level. Professional engineer Alan Budris, who is a leading expert in the pump world and a champion of this concept, has successfully corrected system issues for clients when he persuaded end users to change to a different pump (or sometimes simply an impeller change) at a lower level of SE. This is not covered here, but there are additional tools that use the SE and NPSH margin ratios.

In a Pumps & Systems article from February 2012, Terry Henshaw, whom I respect deeply, questioned the concept of SE and suggested it was perhaps a flawed concept. Henshaw argued (and I am surely oversimplifying here) that when you algebraically compare the SE formula to NPSH, pump speed and Nss, many aspects (factors) are diminished or even eliminated. I agree with the argument as it was presented. I postulate that maybe there are ranges were SE is more important than in others?

However, my main point for this column is this: When making pump application decisions, the ultimate goal is to win. And just like on the race track from years ago, I want every competitive advantage I can garner.

-Jim Elsey

 

When NOT to use a pump for liquid transfer.

A case study in how to transfer liquified gases (propylene, in this application) using the vapor itself.

Custom-built, explosion proof Blackmer compressor package exceeded our customers expectations!*

There are challenges when transferring liquids that are vapors at atmospheric pressures. Liquids like ammonia, butadiene, propane, propylene, refrigerants, or vinyl chloride must be contained under pressure to keep them in equilibrium. Pumps, with the limited Net Positive Suction Head available (NPSHA), cavitate and can become vapor locked.

Using Blackmer HD gas compressors to compress the vapor to transfer the product is much more efficient. Transfer faster and recover much more product with the Blackmer HD compressor.

A global chemical manufacturer (and their engineering firm) asked for “Liquid transfer of propylene from a 435 lb. cylinder to a 125 gallon storage tank and transfer from the storage tank to a feed tank”. Conditions: 20F, 57 psi inlet pressure/77 psi discharge pressure; 70F, 140 psi inlet pressure/166 discharge pressure; and 100F, 210 psi inlet pressure/230 discharge pressure thus the compressor was going to see varying conditions although the differential pressures (discharge minus suction) were pretty constant at 20 psid to 26 psid.


 

Using a Blackmer compressor for liquid transfer and vapor recovery

How it works:

LIQUID TRANSFER

The compressor and 4 way valve is configured to allow the destination vessel vapor to enter the compressor where the gas is slightly compressed and discharged to the top of the source container or vessel where the gas pushes on the top of the liquid forcing the liquid up the liquid line connected to the bottom of destination vessel.

 

 

 

 

 

 

LIQUID BOIL OFF AND VAPOR RECOVERY

When nearly all the product is transferred, you are left with a small amount (heel) at the bottom. You then change the 4 way valve and other valves to allow the vapor line from the source vessel to connect to the compressor inlet and you compress that gas and push it up through the bottom of the destination vessel. As the gas travels up through the liquid, it cools and tends to condense into liquid. This operation continues until the pressure in the source vessel drops to a pre-set point (typically dictated by economics).

The compressor transfer process described is done with many liquified gases and natural gas with the same basic process steps.

As a long-time distributor for Blackmer, we were able to provide a Blackmer gas compressor package for this important application.

Our design team assembled a complete package in our Louisville facility per the customers requirements from the ground up, including a custom steel base with forklift portability, and a complete controls package for “plug and play” installation.

* Our customer asked for 15 minute liquid transfer and we did it in about 5 minutes! 

Backside of Nema 7 control panel showing Nema 7 controls which were prewired and connected to compressor and panel.

Application details:

Liquified gas transfer of propylene from 435-gal cylinder to 125-gal storage tank and transfer from storage tank to feed tank. 4 SCFM @ 77 PSIG, 166 PSIG and 231 PSIG.

Custom compressor package:

  • Blackmer heavy-duty compressor model HD082B (Blackmer’s smallest HD size) – non-lubricated, 1-stage, vertical, air cooled, single cylinder, single acting, ductile-iron construction with packing.
  • 76”x26” structural steel baseplate with V-belt drive, belt-guard, motor slide base, liquid trap, 4-way valve and strainer.
  • 3-HP, 1750 RPM, 182T frame explosion proof motor, belt drive.
  • NEMA7 Low oil pressure switch, low suction pressure switch, high discharge pressure switch, high temp switch and SS high liquid level float switch.
  • Discharge relief valve ASME.
  • Mounted and wired NEMA 7 control panel with start/stop push button, Power “on” light, Production test report and hydrostatic test @ 503 PSIG.

Blackmer heavy-duty compressor model HD082B mounted on structural steel baseplate.

 

Centrifugal Pumps | An Open and Shut Case?

I am frequently asked; should the discharge valve be open or closed when the pump is started? My answer is….it depends, but regardless the suction valve better be open.


First Things First

Let’s look at the impeller. There are many things to consider, but the primary question we want to answer today is; what is the geometry of the impeller? From that shape we will determine the range of Specific Speed (NS). Ok, I may have lost you now because I used the nerdy “Specific Speed” term, but let me explain. Just for today’s purpose, let’s focus on the directional path of the liquid and specifically how it enters and exits the impeller.

Specific Speed is a predictive indicator for the shape of the curves for head, power and efficiency.

Low Ns

If the liquid enters the impeller on a path parallel with the shaft centerline and exits the impeller at an angle 90 degrees to the shaft centerline (at a right angle) then the impeller is in the low Specific Speed range. This would be a typical radial impeller like the Summit Pump model CC-FM.

Medium Ns

If the liquid enters the impeller on a path parallel with the shaft centerline and exits somewhere close to a 45 degree angle, then the impeller is in a medium Specific Speed range. These are mixed flow or Francis-Vane type impellers.

High Ns

If the liquid enters the impeller on a path parallel with the shaft centerline and exits in a path parallel to the shaft centerline, this is a high Specific Speed impeller. This axial flow type of impeller would look similar to a boat or airplane propeller.

Plan B

Don’t know the Specific Speed (Ns) of the impeller? Ask the manufacturer.


Now for the Really Interesting Part

For low Specific Speed (Ns) pumps the Brake Horse Power (BHP) required increases as you open the discharge valve and increase the flow rate, this is a direct relationship just as you would intuitively expect. For medium Ns pumps the BHP curve and its maximum point moves back to the left some nominal amount … in the past you may have not noticed this change. Axial flow pumps, of high Ns, the BHP is near its maximum point at the lower flow rates and actually reduces as the flow rate increases. Perhaps the opposite of what you would expect? Notice how the slope of the power graph also changes when the impeller design goes from low to high specific speed.

And…Answering the Original Question

I recommend that the discharge valve be closed on the startup of low Ns pumps and to be open on high Ns pumps. Note, this is a “thumb rule” and there are numerous caveats that can and will modify the answer.

  1. If the low Specific Speed (NS) pump is of any consequential size (Flow, Head and BHP) you may need to have the discharge valve slightly open to reduce the differential pressure across the valve. This step will minimize the effort to open the valve. Some pump systems will have a bypass line for this purpose.
  2. Systems that have downstream pressure (from another source) with no check valves (or check valves that are leaking by) can force the pump to spin backwards when the discharge valve is open.
  3. If you are starting a pump that will operate in parallel with another pump(s) you need to consider check valve lift points and controlling instrumentation (PID); this is a subject too cumbersome to explain in the “Sixty Seconds” platform.
  4. Normally, high Specific Speed (NS) pumps are started with the discharge valve open to reduce the electrical load and resultant stresses on the driver. In many cases the driver may not be adequately sized (on purpose) to handle the low flow power requirements and will trip offline.

-Jim Elsey