Slotted Gauge Pole Emission Control Overview
EPA Enforcement Program: On January 14, 2000, EPA gave notice of its intent to implement a program to control the emissions from slotted guide poles on external floating-roof tanks. The program was developed in cooperation with the American Petroleum Institute. On April 13, 2000, notice was published in the Federal Register implementing the program and outlining the program procedures. Companies were given until June 12, 2000 to notify EPA of their intent to participate and had until December 11, 2000 to submit their plans. A summary of this program is Appendix A. Directions on how to obtain the Federal Register notice are contained on the previous page (Table of Contents).
What are Slotted Guidepoles? Guidepoles, slotted or unslotted, are hollow poles [pipes] that are attached near the tank bottom, pass through an opening in the floating roof, and extend to the top of the tank where they are held in place by a bracket. They are used to prevent the floating roof from rotating and, when slotted, act as an opening through which the liquid may be sampled and level-gauged. Slotted guidepoles have holes or “slots” that perforate the length of the pole. The slots are essential to accurate liquid-sampling and level-gauging. With slots, the liquid in the guidepole is representative of the liquid at each level in the tank. Without slots, the liquid in the guidepole is the liquid which was forced up into the pole from the bottom of the tank. If the liquid in the guidepole is denser than the liquid which surrounds the guidepole, the level in the guidepole can be much lower than the surrounding liquid. This inaccurate level might result in the tank being overfilled. Left uncontrolled, emissions from the use of slotted guidepoles can exceed 25,000 pounds per year. But simple and inexpensive solutions exist to minimize these emissions and reduce vapor losses. EPA mandated, on April 13, 2000, what these solutions should be — see Appendix A.
Emission Loss Solutions: American Petroleum Institute testing indicates that certain equipment, some depicted in this pamphlet, installed in and/or around the slotted guidepole can practically eliminate emissions from the slotted-guidepole area without rendering it unusable for its intended purposes. The equipment can be installed while the tank is in service. Appendix “A” to this pamphlet summarizes EPA’s requirements as they were agreed to by API and EPA.
Test Limitations: The EPA specified and API testing demonstrated types of controls. The testing did not test suitability of designs for field use. API publications state that there are certain considerations that are not incorporated in its publications: “…[considerations] such as tank operation, maintenance, and safety are important in designing and selecting equipment.” When selecting equipment, to duplicate the testing results in the field, consideration must be given to the factors impacting the sealing characteristics under working conditions.
“Real World” Solutions: The solution lies in building into a seal or seal system a certain amount of durability and flexibility. Ultra Check uses flexible fabric sleeves instead of metal sleeves on its pole-sleeve-type products. This polyurethane fabric is impermeable to petroleum vapors and designed to be highly resistant to abrasive situations. It can also flex, bend, and move. Because a Pole Wiper is such an important part of any sealing system, both EnvironSeal (Figure Eight) and Safe Sleeve (Figure 9) have uniquely designed Pole Wipers that resist wear and gapping.
Ultra Check floats are detailed in Figures 11, 13, and 14 but in general they have stainless steel cable to maintain them vertically and centered in the guidepole, can come with multiple seals which are height adjustable, and, each seal-layer is itself a multi-layer design to give durability while still being flexible enough for its imperfect environment. Under EPA guidelines, the seal on the float must be at or above the pole wiper on the deck cover. Ultra Check’s “Tall Float” (Figure 13) is the only float system, to Ultra Check’s knowledge as of April 4, 2001, able to meet this requirement.
Extra Considerations About Floats: Many floats (or guide-pole plugs, as they are sometimes referred to) use chain for manual retrieval. This presents problems: As liquid rises, the chain piles unevenly on the canister, causing it to lean, breaking the seal, and allowing the chain to get caught in the guide-pole slots. Once the chain is caught, rising liquid covers the canister. This leaning causes abnormal wear on the seals and they soon wear away. Also, a chain-retrieval float is messy to handle and cumbersome to use which may cause the person, after gauging and sampling, not to put it back into the guidepole.
Even floats that have no method of retrieval, and are merely dropped down the guidepole, soon have seals which are completely worn down. The dynamic forces including gravity and product movement cause the float to wobble. The seal begins to wear as it leans and rubs against the rough guidepole wall. In a short time the seal is ineffective.
“Vapor Check” (Figure 11) and “Tall Float” (Figure 13) are designed to overcome these shortcomings, no chain is added and the cable stabilizes the float in the center of the guidepole with its seals horizontal, lightly contacting the guide-pole wall. The reel assembly makes the float easy to retrieve.
Ultra Check, Inc.—Specialist in Slotted Guide Pole Emission Controls
Since 1993, Ultra Check, Inc. has specialized in sealing systems for inside and outside the guide pole. The company is well established and accepted in this field and has patents issued or pending on several products. Ultra Check’s products are installed from Hawaii and Alaska to the East Coast, Australia, France, Scotland and Qatar. The San Francisco Bay Area Air Quality Board approved an Ultra Check pole sleeve and float as a suitable emission-control system for new tanks with slotted guide poles. A few years ago, Region IX of the federal EPA cited some petroleum companies in California for emission violations; in negotiations with these companies the EPA said an Ultra Check pole sleeve and float would be a satisfactory remedy. It was the only product authorized by name. All major petroleum companies utilize Ultra Check’s products.
Average Wind Speed of Average Wind Speed of
0 MPH-Loss: 55Gal ** 10 MPH-Loss8000 Gal **
Representation: This figure represents an unprotected, slotted guidepole area of an external floating-roof, gasoline tank (EFRGT). “Unprotected” means the guidepole has no emission-control devices except a sliding cover. API testing proved, on an unprotected tank, reducing wind speed** from 10 MPH (about the national average) to 0 MPH eliminates 99% of the emissions — from 8,000 gallons to 55 gallons of gasoline annually, per tank. **For all examples, wind speed is as measured where the guidepole meets the sliding cover.
How Does the Wind Cause 99% of the Emissions? Vapors quickly mix with clean air, but once saturated the air is relatively heavy and escapes very slowly unless forced out by the wind. When clean, wind-driven air enters through the guide-pole slots, underneath the sliding cover and around the guidepole, the vapor-in-air rapidly becomes less dense and is forced out through the other side of these openings. This fresh, wind-driven air, as it passes through the containment, quickly picks up more vapors and carries them to the atmosphere.
How to Control the Losses? In principle it is obvious and simple: (1) stop the fresh air from disturbing the vapor-in-air mixture; and (2) reduce the total space in which vapor-in-air, likely to be affected by the wind, can gather. In very basic terms, plug up the holes and cover the surface. Removing the guidepole and covering the opening or replacing the slotted guidepole with an unslotted guidepole is not practical. And, as you will see, neither are such drastic and expensive measures necessary.
Choice of Controls: API testing determined certain types of controls (see Figures 4 through 7) could be used in and around the guidepole to reduce emissions — in one case (Figure 7), by more than 99%. However, API, in its publications, clearly cautions that matters “such as tank operation, maintenance, and safety are important in designing and selecting equipment.” These considerations were not evaluated during testing. It was left up to the petroleum industry, including manufacturing specialist such as Ultra Check, to design equipment that would accomplish, on live tanks, what API proved to be effective under stagnant, laboratory conditions.
Figure 4 – Basic Emission Controls
Figure 5 – Basic Emission Controls & Float with Wiper Seal