TransAlta Utilities Corp., Calgary, Alberta, Canada, has been seeking an improved method of separating oil and water from its substation secondary containment pits. The utility discovered a way to retain the oil yet allow for the release of rainwater, reduce disposal costs and volumes, and lower maintenance costs. The utility accomplished this by installing a new drain system using imbiber beads.

Out With the Old, In With the New

The previous method required the collection of water and oil that was dripped from transformers into a sump. The sump consisted of a large underground containment tank. If the oil-detection probes detected oil in the sump, a vacuum truck would travel to the location and vacuum out the sump. The water and oil mixture was then disposed of at a licensed facility. The major drawback of this method was that maintenance of this sump system required two employees to work in a confined space, adding to maintenance difficulty and expenses as well as the costs of the trucking and disposal of the liquids.

One of the driving forces for change has been the oil-detection probes, which are located in the existing containment pits (built in early 1980s) at TransAlta's hydro sites. These probes are not as reliable as the utility would like, and they require high maintenance and give false alarms that result in overtime paid to the responding employees. Hydro managers did not believe these existing systems were the best possible solution.

The first step in finding an acceptable alternative was to identify the parameters of the required system. An internal focus group discussed the potential characteristics of an ideal system, which included no confined space requirements, low maintenance and no electrical components prone to breakdown or corrosion.

After conducting thorough research on the issue of oil/water separation devices, TransAlta personnel concluded the imbiber-bead solution would be the perfect match.

To date, the imbiber-bead technology is proving effective as an oil/water-separation device in secondary oil-containment pits around transformers and other electrical equipment. The system fits in a standard-size drain and the containment pit floor slopes toward it where oil and water flow through the system (Fig. 1). TransAlta is currently using the Imbiber Beads 1 Disc System, supplied by Imbibitive Technologies Canada Inc. (IMTECH).

This system consists of a galvanized-steel container housing that fits into an existing or newly constructed drain, a silt filter, two absorbent discs (50:50 beads to sand) and a Class III imbiber bead shutoff disc (Fig. 2). The top screen is the silt filter that captures silt and prevents it from clogging up the system (Fig. 3). Below the silt filter is the absorbent 50:50 beads-to-sand disc, which absorbs minor leaks and spills. The mixture of sand and beads allows for the absorption of minor oil leaks, while still permitting water to pass through the system and exit the drain.

Finally, a beads-only disc, otherwise known as the shutoff disc, is located beneath the 50:50 beads-to-sand disc (Fig. 4). In the event of a major spill, the beads inside this disc will absorb the oil and swell to a point that the drain will be blocked completely, thus containing the oil spill.

Low-Maintenance Benefit

Maintenance of the oil/water imbiber-bead unit is minimal. Upkeep and changing of the discs depends on the amount of rainfall and the quantity of oil leaking from the transformers. Other users of the system have indicated that, in dry climates, a set of discs can last a year without needing replacements. In wetter climates, replacements may be more frequent because a greater amount of dust can be entrained with the rainwater and siltation may occur at a faster rate. The manufacturer suggests discs be inspected quarterly for silt and regular maintenance. By capturing the silt, the silt filter extends the life of the system. In addition, a 1-inch (2.54-cm) tip is set into the concrete around the installed unit so that the water will pool or slow down slightly to allow the silt to settle out. Filling the containment pit with 1 to 2 inches (3 to 5 cm) of gravel also will help in the silt settling out of the water column. If silt is not a problem, the discs will last until the beads are soaked in oil from a spill or leaking transformer.

TransAlta has installed three imbiber-bead systems (Figs. 5, 6 and 7), with the potential for another 15 future installations. TransAlta will evaluate the three current installations over the next year to determine their effectiveness in separating oil and water in the containment pits. Reports from maintenance personnel indicate one of the main advantages of the system centers on how easy it is to inspect and change the discs. It takes 15 min to remove and replace all of the discs; the bottom shutoff disc takes the longest amount of time because between four and five clamps that hold the seal around it must be removed. The other two discs simply lift out. Compare this with the sump-vacuuming operation.

Jason Desilets is the environmental coordinator for transmission at TransAlta Utilities Corp., Calgary, Alberta, Canada, which he joined in May 1998. He has the environmental science degree from the University of Calgary as well as the environmental technology diploma from Mount Royal College in Calgary. His responsibilities include environmental assessments of transmission properties, managing remediation and reclamation projects, and evaluation of environmental technologies for the company. He is a member of the Alberta Society of Engineers and Technologists.

Truly Absorbent Beads

Imbiber beads are the only true absorbent “engineered” for organic chemicals such as gasoline, diesel/jet fuels, chlorinated solvents — 1including TCE and PCBs as well as polar compounds MEK and MIBK — in the marketplace today.

Once a compatible chemical is imbibed, (absorb and imbibe are synonymous) the beads, as opposed to adsorbents, will swell up to three times their original diameter with the compatible chemical (up to 27 volumes of solvent for each volume of the beads). No liquid can be released as a result of compression, gravitational pull, inclement weather or even if the beads were cut in half.

Conversely, with adsorbents (for example, plastic foams/fibers, peat, sand and porous clay) any one of them will release adsorbed liquids, exposing both the environment and personnel to liquid contamination and dangerous vapors. In these cases, the liquid taken up is simply distributed over the surface (external or internal) of the adsorbing material. The beads are not a thickener or a solidifier — they will not dissolve in excess liquid — and the beads cannot absorb water because they are hydrophobic.