How to fix or prevent problems with vacuum pumps

Wednesday, June 27, 2018

The problems with vacuum pumps in a carbon based vapor recovery system. How can you fix it or prevent it?

In carbon based VRU applications the one key component that makes a VRU reliable is the vacuum pump. If this device fails the VRU will be down for an extended amount of time for repairs. For this reason the selection of the correct vacuum pump is crucial for the maximum uptime.

The following will describe the current vacuum pump technology used in various vendors supplied Vapor Recovery Units (VRU):

The pictures are links to take you to an information site on that particular vacuum pump.

Control Click to open link

Liquid Ring Vacuum Pump (LRVP)

 [image]

Advantages:

• Properly maintained, service life can be expected to last 5 to 10 years.

•Operates at lower speeds.

Disadvantages:

•Requires complicated seal fluid circuit that requires constant maintenance. This includes the   correct glycol/water mixture and proper PH balance.

•Can only reach a vacuum level of-28”Hg. This is an important factor in the design of a VRU.

•Cavitation of the pump can occur if airflow through the pump is not sufficient. This will damage the LRVP.

•Requires an ASME shell and tube heat exchanger to remove the heat of compression.

•Requires a three phase separator to separate VOC condensation, glycol/water and vapor.

•Not recommended when loading ethanol. This will dilute the water/glycol mixture

•Requires 1/3 more HP than dry vacuum pump systems.

 

Rotary vane oil lubricated vacuum pump

[image]

Advantages:

 Vacuum Pump cost is lower.

Disadvantages:

•This is NOT a dry pump as it needs oil to be in contact with process fluid.

•The oil is in contact with the vapors so an oil separator on the pump discharge is needed. •The oil separator can cause problems (e.g. high pressure on pump discharge and consequent over heating of the pump) and it needs frequent maintenance (e.g. filters replacement).

•The oil used must be special type “flameproof oil”, as the Vendor indicates the pump can catch fire if the wrong oil is used. This is a big issue in Vapor Recovery application.

•The oil is in contact with the vapor so vapor contamination with oil will occur. Oil carry over from the pump will cause contamination of absorbent supply tank.

•Higher power consumption. The internal oil recycle has effect on power consumption plus higher operating temperature. 

 

Rotary screw vacuum pump:

[image]

Advantages:

•Requires less power consumption verses the LRVP or rotary vane vacuum pump.

•The rotors are not lubricated; there is no contamination of vapors or dilution of the oil

•Not effected by ethanol loading.

Disadvantages:

                  •High cost.

                  •Operates at line frequency speeds to 3,600 rpm.

                  •Must be rebuilt by the manufacture due to the tight tolerances of this pump.

                  •Due to the high operating speeds the life cycle of this pump is greatly reduced.

•Requires liquid injection in to the cavity of the pump. This can result in liquid accumulation in the pump internals and locking the pump up and damaging the seals.

•Require special synthetic oil in the gear housing that can only be supplied by the vendor or the warranty will be void.

•Not recommended in crude loading operation as the injection fluid would be crude oil. Crude oil can have contaminates that could damage the pump.

 

Wing compressor style vacuum pump (HORI):

  • [image]

•Low operating speeds. This greatly increases the service life of the pump. Aereon has put this pump in operation in 2011 with more than 60 installations now without a single failure to date.

•Uses standard 30W oil in the gear case. No special synthetic oil is required.

•Does not require liquid injecting in the cavity of the pump for cooling. It only requires air cooling (like a motor cycle) and jacket cooling on the second stage.

•Proven technology as this pump was first introduced in the 1950’s in different application but has proven itself.

•This pump can be rebuilt in the field and does not require it to be shipped back to the manufacture.

•Lower noise and vibration due to the lower operating speed.

•Comes installed on its own skid for easier field installation.

•No liquid injection in the pump cavity is required, so this pump is more suited for crude oil applications.

Disadvantages:

                  •Larger foot print.

When specifying a new VRU great consideration should be given to the type of vacuum pump chosen.

Based on Aereon’s many years in the design, construction and service of this equipment we have determined that the Wing Style Vacuum pump as built by HORI is far superior to other types of vacuum pumps available today for ease of maintenance, low vibration and long service life.

 

Now that we understand the various vacuum pump technologies, what can we do with this information on existing systems in operation today?

When should you look into a vacuum pump retrofit?

 

Maintenance Costs:

Many customers approach us to retrofit their VRU systems to new Dry Vacuum Pump (DVP) technology because the maintenance costs on the existing Liquid Ring Vacuum Pump (LRVP) or troublesome Dry Vacuum Pump that was supplied with the equipment are starting to get out of control. Do you find yourself in this scenario? Do you constantly need to change out your glycol strainers? Is your glycol diluting faster than it ever has before? Is your heat exchanger starting to plug up? Is there glycol leaking out of the seals on your vacuum pump? Are you getting called out on the weekends because of glycol low flow alarm? Man, this stuff adds up. 

The routine maintenance can really kill you too. With older VRU’s its good practice to pull that heat exchanger every 5 years (this only gets worse with time), clean and pressure test it or replace it, and open up the separator and blast it out to get rid of any sludgy buildup. It’s also helpful to flush the system with cleaning agent like Aereon’s VC-Clean to try to keep the heat exchanger from plugging up quickly once you put it back online. This kind of service is going to normally run a customer around $25,000 per year. Not to mention the down time associated with this work. Factor in glycol, sock filters and your time taking care of the VRU and you are looking at a hefty sum of money. 

Alternatively, a customer can install the correct dry vacuum pump and get rid of 99% of the headache associated with a troublesome LRVP VRU system or a troublesome dry vacuum pump. You can remove the glycol piping, heat exchanger, glycol pump, glycol filter, and even the separator if possible, and never have to worry about these things ever again. With a DVP system the only thing you need to worry about is changing the oil twice a year. No more worrying about whether you have sock filters on the shelf or spare glycol on hand in case the VRU fails. You have more time to spend working on important tasks that benefit your company instead.

Even better, Aereon’s has been operating its proprietary HORI vacuum pump (Wing Compressor) since 2011 with no failures or required overhauls. They have become the standard pump of many major oil companies and we have installed over 60 of them in the field in 2017 alone. We are projecting a 10 year life expectancy out of these pumps before they require any major service and that service is expected to cost less than $25,000. You can learn more about this vacuum pump, just control click this link and use the downloads.

Although it’s not always the case, many times a VRU can handle more vapors just by swapping out the vacuum pumps. Installing a vacuum pump with more capacity might just be the trick to getting that extra truck load or two an hour during peak loading. Let us help you determine if your VRU could be a fit for a DVP retrofit to increase its capacity so you can maximize your throughput and profits!

Emissions Requirements:

Ok, so your VRU was built in the 1980s and it’s permitted at 85mg/liter. That means that you are allowed to emit 85mg of VOCs for every liter of gasoline you load onto a truck. Did you know that the standard in some parts of the world today is 0.15mg/l? Yes, there is a ZERO and a decimal point in front of that number. That is over 500 times lower than a lot of the existing VRUs out there are permitted at. 

 

Now, no one is saying that you HAVE to take it upon yourself to lower your carbon footprint, and we won’t judge you if you don’t. But if you are feeling green, then a simple retrofit to a larger capacity pump can often lower your emissions from 85mg/l to 10mg/l, 1mg/l, 0.15mg/l or even less. This is done by just changing the vacuum pump. Usually the rest of your VRU system can remain as is. 

 

Is your tuck rack getting shutdown occasionally because your VRU is creeping up towards its emissions limit? Are you looking at picking up new contracts or new customers? Do you want to push more products, add more loading arms or add a bay? Can your VRU handle this extra throughput or are you already maxing it out? Even if you have no idea what type of loading your VRU can handle, that’s fine. Aereon can perform basic engineering studies on your VRU to help you determine a max loading capacity for your VRU under its current conditions and a max future loading capacity with different types of upgrades. 

 

 

Although it’s not always the case, many times a VRU can handle more vapors just by swapping out the vacuum pumps. Installing a vacuum pump with more capacity might just be the trick to getting that extra truck load or two an hour during peak loading. Let us help you determine if your VRU could be a fit for a DVP retrofit to increase its capacity so you can maximize your throughput and profits!