ENVIRONMENTAL PROTECTION APPLICATIONS -
COMPARISON OF DEGASSING METHODS

WHY INTERNAL COMBUSTION ENGINES DON'T LIVE UP TO THE CLAIM

Envent owns Internal Combustion Engines (ICEs) and uses them on certain LOW FLOW (< 50 CFM) jobs for soil vapor extraction. The ICEs utilize 2 Ford 460 cu/in gasoline engines. The engines start on propane. Once they are running, the carburetor suction is switched over to the storage tank. When the tank vapors get lean, propane is added to the carburetor to keep the engines running.

Many Tank Cleaner/Degasser competitors with the IC Engine System will report that vapors can be controlled with a dual system (V$) Unit at 700 cubic feet per minute (CFM) but will provide no data or flow meter or calculation to support that. Air Flow can be calculated through the engines based on the displacement in the cylinders. The engines are 460 cubic inches, so the actual flow is: 460 cc x 3,000 RPM divided by 2 (4 cycle engine) divided by 1,728 (to get to cubic feet) = 400 CFM total theoretical flow. However since a gasoline engine will flood if the fuel is too rich, a stoichiometric fuel rate must be used in the calculation. Considering that 1.5% is the lowest level for a flammable mixture of gasoline, and air and 7.7% is the highest possible, then 4.5% is typical stoichiometric flammable mixture for gasoline. Therefore 400 CFM flow x 4.5% = 25 SCFM tank vapors per engine. The operators report over 700 SCFM, but our calculations show 25 CFM is closer to the truth.

The volume of an empty 150' dia. storage tank, with a floating roof height at 6', is 106,000 SCF. At 50 CFM (dual engine unit flow rate), it will take roughly 350 hours to achieve 10% LEL (5000 ppmv - the new 1149 Rule and some). This may be why you will often see 2, 3 and 4 units on a single jobsite. It is also the reason you may see them operating while the tank is enclosed with a water washing system (like a butterworth nozzle). But wait, won't the vapors escape out the roof legs and vacuum breakers? The answer is YES.

In some cases, the operators will say, "It isn't the flow, it's the BTU combustion capability. It isn't the amount of CFM you pull from the tank" – huh? Refer to the manufacturers own data. The system can combust a maximum of 30 lbs/hr of vapor, IN IDEAL CONDITIONS. API 2568 will tell you that you have up to 67,000 lbs with only 1" of scale! See Envent's Tank Degassing information. Can it ever really get ahead of the vaporization rate with product left in the tank? Highly unlikely.

The informed tank owner will ask for the equipment data sheet and figure this out for themselves. Or ask your counterparts in California about the IC Engine used for tank degassing. Or try it out and be sure to monitor the job and use your OVA and LEL meter to check the tank vapor space before he departs. These systems have their use, but this is not it.

The IC Engine operator may tell you that it is not the flow rate that degasses tanks but the richness of the vapor stream. Huh?!? Then they may suggest that you use 2, 3 or 4 units to degas a tank. Then they may say that they can put a water cannon on the tank manway and mix the tank up while they try to degas it. Huh?!? How does the ICEngine pulling 50 CFM capture the 100-300 CFM of vapors created? The answer: It doesn't. See sizing comparison chart. Ask yourself, why are vapors billowing out the back manway or why is the plastic cover bulging outward, rather than inward? The vaporization rate of material in a 70 ft diameter tank with greater than 4 RVP (e.g., gasoline, naphtha, benzene) is much faster than the ICE could handle. For the most part ICE are not used in California where degassing tanks was first required. The ICE are primarily operated in areas where permits aren't required, Texas or new markets where the owner doesn't have the experience running these units. They will struggle and eventually come to the realization that even the cost of operating the IC is TEN TIMES (10 x) greater than hiring Envent Corporation to degas your tanks. If you think you are saving money by operating these units yourself, let Envent show you the reality. Ask these questions: What is the cost of having your tank out of service for 3 additional weeks? What is the cost per MMBTU? What is the potential cost of lingering in the explosive range for days and possibly weeks? This is a serious near miss every time you degas a tank. Is the vaporization rate greater than the unit can handle. See sizing and cost chart. If you intend to use the ICEngine for refilling or product changeovers, consider the limited CFM again. At 50 CFM, you are limited to 536 BBLS/HR. But wait, that doesn't include the vaporization rate of your material. The fact is, this unit cannot handle the refloat at any fill rate.

For Tank Refloats/Refilling Operations: The large dual engine IC Engine CAN NOT handle flows above 500 bbls/hour. Do the math. A fill rate of 500 bbls/hr = 46.8 CFM: 500 bbls/hr x 42 gallons/bbl x 1 hr/60 min x 1 cubic foot/7.48 gallons = 46.8 CFM. And this doesn't take into account the vapor loading, just the air displacement. All the rest of the vapors will escape around the seals or roof fittings. Check it for yourself. If the high volume of vapors released at the tank aren't noticed by smell, drop a probe down into the tank from the platform and you will be sure to set off alarms. We would recommend being under fresh air if you go to the platform. Believe the physics. The numbers don't lie!

Safety Issues with IC Engines: sources of ignition include the potential for the engine to back fire (just like a car); the starter solenoid, the intake manifold. Most of all, the intake is usually in the explosion range and without a detonation arrester, the risk is there to have a back flash fire that enters the tank. This first generation (1970's technology) is neither safe nor effective.

IC ENGINES WITH CONDENSER UNITS

Some claims are being made that some newer ICE Units have a condenser which makes them faster and better at processing vapors. But, is this really a "condenser" which uses a coolant medium to quench vapors by dropping the temperature to below its condensation point and changing its state from gaseous to liquid? If so, where is the coolant liquid, nitrogen, ammonia or Freon? There is none. The bigger question is, if this unit condenses the vapors and dumps them back in to the tank as the diagram shows, then the condensed liquids re-condense again to then enter the IC Engine again and condense. Is this speeding up the process or extending the process? Or is this "condenser" just a free liquid knock out pot as it seems to be which really doesn't condense any liquids…you should ask and observe for yourself.

ACTIVATED CARBON - NOT FOR DEGASSING!

Activated carbon is a technique that is used occasionally. The handling of activated carbon is a nuisance. Carbon is delivered in large boxes and has to be transferred to the carbon/plenum container. The cost of carbon is between $5 to $10 per pound considering disposal, handling, containers, etc. It may take anywhere from 8 to 12 pounds of carbon to control 1 pound of VOC. So the carbon cost may be $100,000 or more for one tank. It is not practical for degassing tanks and you run the real risk of bed fires during or after the carbon has been used.

MAGIC JUICE (SURFACTANTS & OTHER CHEMICALS)

Several manufactures of proprietary bio solvent chemicals (or anaerobic bacteria oil chomping bugs) claim their products can degas tanks by eating the vapors. These products are more or less surfactants (soap). Yes, they will emulsify oils but they certainly don't eat Volatile Organics Compounds (VOCs) in the vapor space. If you let the tank sit with this chemical in them and check the vapor space several days later, you may find the vapor concentrations are reduced -- but that is strictly through the standing losses via the legs, vacuum breakers and around the seals. Want proof?? If you have a fixed roof tank blinded off, you will see NO EFFECT from these chemicals if you check with a Flame Ionization Detector (FID) or LEL meter. It just doesn't work. If it did, we wouldn't be in business.

Some folks put these magic degassing chemicals in the front vessel of a "liquid scrubber". Well, just ask yourself, where does it go? Where does the 75,000 - 150,000 LBS of Gasoline Vapor go? If the liquid scrubber truly worked, and the VOCs really did absorb into the liquid, then the liquid would need to get changed out every 10 minutes! NOW you have a hazardous waste saturated with gasoline, chemicals, or benzene. This is not what happens. The reality is that there is only one place for the vapors to go -- out to the atmosphere or onto the carbon that always follows! Ask the proprietor where the vapors go.

In some cases, you will experience emissions immediately upon startup. What the proprietor will tell you is the chemical is giving your instrument false readings! Don't believe it. If your instrument is calibrated correctly, believe it.

Just ask a simple question -- where does it go?

The question always comes up, "I have used this and it seems to work when I have my contractor squirt the material into the tank using a manway cannon. Why is this?" The answer to this is clear and simple. When you land the roof, vapors immediately exit the roof fittings (legs, vacuum breakers, and the seals) and this is further exacerbated when you displace the vapor space inside the tank by several hundred gallons per minute (50-500 CFM) of air displacement. Fact is, if a gasoline tank is landed and left in 80 deg F atmosphere, in 5 days, the LEL will be 20-30% LEL on it's own. The vapor pressure of the gasoline will allow the gasoline to vaporize. That is why most degassing rules require that the process of emptying and degassing be a continuous, uninterrupted process.

WHEN TO USE SMALL COMBUSTORS (1000 SCFM)

Mini combustors are these little enclosed flares. Envent owns several of these and we use them for a variety of projects that require vapor control. But they are NOT effective at tank degassing when the tank is larger than 25 ft diameter.

Because the TCEQ and LDEQ have no permitting requirements and engineering review, it is up to the owner to perform his own due diligence. Many tank cleaners have purchased these Soil Vapor Extraction units and jumped into the business of degassing. These units have limited or no safety control other than a flame arrester on the front of the fire box.

The contractors who use these mini-combustor units claim they are rated around 1,000 CFM. Some contractors are so bold they claim these combustors do 2,000 SCFM. But a mini-combustor can only handle 100 CFM with a very lean input concentration of tank vapor. The volume of the fire box in the mini-combustors limits their capacity. The industry standard nominal heat load rating in a combustor firebox is 500 btu per cubic foot per minute. So if the mini-combustor firebox is 4ft x 4ft x 6ft, then the capacity is 48,000 btu/min. Gasoline has 1,389 btu/cu/ft, so in reality the mini-combustor can only do a paltry 50 CFM, not the claimed 1,000 CFM, from the storage tank. Contractors who claim they have a rate of 1,000 CFM should tell the other half of the truth which is that the vapors must be very lean, perhaps in the LEL range. High concentration will result in fire and smoke coming out of the stack. The volume of an empty 150' dia. storage tank with a floating roof at 6' is 106,000 SCFM. A mini combustor will take 150 hours to complete 4 volumes at 50 CFM.

The informed tank owner will ask the contractor for a data sheet from the combustor manufacturer that shows the design BTU rating and the combustion chamber volume. Then insist on a gas flow meter between the tank and the control device to accurately measure the inlet flow and volume. Since the volume is one of the regulation requirements for vapor control, then the flow should be measured by a meter during the tank cleaning at actual flow conditions.

Again, Envent owns and operates many of these. We have substantially modified these for safe operation in industrial settings. They are NOT Soil Vapor Extraction units. This is a picture of one of our units – above. If it looks familiar, that is because the fire box is made by the same soil vapor extraction equipment manufacturer. Tank degassing is not to be taken lightly.

As for compliance reporting, as degassing becomes more important, you will need solid reporting program with accurate and detailed reports in FULL COMPLIANCE. Does your vacuum truck or tank cleaning company do this? Tank cleaners generally have little or no concern to provide a Comprehensive Degassing Log with: PID/FID calibration records, Continuous Temperature Monitoring, Verified Flow Measuring System, Required Source Testing Reports, Residence Time Certification and Correct Stack Monitoring.

CONDENSER/REFRIGERATION UNITS

Using a closed loop condenser sounds good, but is it effective outside the laboratory? Degassing is the removal of vapors and displacement with air or nitrogen. In a closed loop system that circulates vapor at a couple hundred cubic feet per minute, that doesn't happen. Once you are done trying to capture and condense a few gallons of gasoline in the plastic container, you still have to bring in a conventional tank degassing system, like a thermal oxidizer, to achieve the new low regulatory (TCEQ, AQMD, DEP, etc.) levels of 34,000 ppm or 5,000 ppmv. Now that you have a few gallons of gasoline in a plastic tote, what do you do with that now? Is it managed as hazardous waste? Furthermore, what about the 50+ leg sleeves that are open to the atmosphere allowing breathing loses and mixing of the gasoline vapors creating a potential explosive mixture? Some of the vapors just escape through these openings. Let's hope they don't go to an area where there is an ignition source. See the Schematic labeled "Chiller/Condenser Degassing".

Here are some questions to ask any company that tells you they can condense your tank vapors:

• How does this system remove residual liquid in your tank? Does it vaporize it and then re-condense it? You can never degas tanks with residual liquid until you vaporize it all. That could take weeks.
• How do you water wash the tank during this type of condensing process? You can't. The system is not under vacuum so opening a manway and water washing will allow vapors to be pushed out the open manway. To water wash, the tank must be under substantial vacuum and negative flow of at least 500 CFM.
• How does a condenser system that operates at ambient pressure prevent vapors from escaping through the vacuum breakers, leg fittings and around the seals? It can't. Purging of these vapors out these fittings commences as soon as the pump out looses suction. The slow process of condensing vapors cant possibly keep up with the vaporization of gasoline or other volatile chemicals (gasoline has a Reid Vapor Pressure (RVP) of 6-14 psig). Use your IR Camera on the tank roof during this process and you will see.
• How do you circulate through the condenser if you only have one manway or the manway is not opposing? You can't!
• What does it cost to drag in a huge Nitrogen Pumper Truck for the coolant liquid? $15,000 - $40,000.
• Is it really a greener technology than a thermal oxidizer? Absolutely not! The power to run it comes from some where.
• How do you keep the light ends (ethane, propane, butane and pentane) from re-evaporating back in to the atmosphere? You DON'T, not at ambient conditions of 14.7 psi and 70-100 deg F.
• Does a condenser generate less Green House Gas Vapors than a Thermal Oxidizer? No. Methane from gasoline isn't condensed and goes directly to the atmosphere. Some competitors will tell you that it is ok since it is exempt. Maybe in some air districts but it is a larger contributor to green house gas damage on a lb for lb basis than CO2.
• What if your tank is under pressure (which is ALWAYS the case with a gasoline or chemical tank and certainly in the case of a pressure vessel)? As crazy as it sounds, those vapors are BLED OFF TO THE ATMOSPHERE until the pressure is at ambient. This could be a substantial volume of the vapors you are desiring to capture. Bleeding vapors to the atmosphere doesn't sound safe and certainly isn't compliant with any environmental rules.
• GREENHOUSE GASES -- If all of the light ends flash off to the atmosphere, where is the benefit to the environment or to reducing Greenhouse gas emissions?? ... and we aren't even talking about the emissions generated from the nitrogen manufacturing and delivery operation!
• Bottom line - Is it allowed by the agencies, like the TCEQ? NO, you can't source test it and it can't pull a vacuum on a tank.

It sounds interesting, but is it really practical and does it really work in practice? It may be useful for euthanizing bird flocks but for tank degassing! The technology is not sufficiently developed at this time.

ENVENT MOBILE THERMAL OXIDIZATION SYSTEM (EMTOS)

The EMTOS is the most effective means of degassing tanks. These large mobile degassing units are the fastest way to destruct your tank vapors. The combustion of vapors is 99.99% effective, documented by third party source tests and continually verified and documented during operation with continuous temperature chart recorders, Flame Ionization Detectors, Photo Ionization Detectors and Flow Meters.

The EMTOS is the only system capable of degassing tanks, pipelines and vessels in a matter of hours rather than days or weeks. See schematic labeled, “Tank Degassing Flow using EMTOS”.

Our systems can handle up to 6000 CFM of vapor and degas your tanks in hours with verifiable tank vapor space readings. A 150 foot diameter tank will degas to 10% LEL in 6-8 hours depending on sludge/scale/product. A 250 ft diameter tank will be completed in 18-24 hours.

The EMTOS is a proprietary unit engineered, designed and built by Envent engineers to provide the safest and most cost effective solution to tank degassing in the world. We have spent over a decade continuously improving the operation and safety of the EMTOS.

Envent and the EMTOS has a clear advantage over the alternatives:

• Get the tank through the explosive range rapidly and safely
• EMTOS's are the only systems HazOpped by all major oil companies
• It removes and destroys the vapors
• Only systems proven by annual source testing by 3rd party
• Cost effective; 1/10th the cost per MMBTU vs ICE and small mini combustors
• In full compliance with the agency shows up - certified reporting

This is what we do. We don't clean tanks, we don't haul wastes in vacuum trucks.