If your plant is like most, it is doing a good job of preventing oily water waste and waste oils from escaping into the environment. But at what cost? As labor resources dwindle, operating and maintaining drainage systems, oil separators, and sometimes inadequate oil removal equipment is expensive.
Paying higher than needed costs for waste oil disposal, filtration and water treatment due to these limitations is unacceptable. How can you solve waste oil management and removal problems without breaking the budget? Read on.
PROBLEM 1: A LITTLE OIL = A BIG CLEANUP: Petroleum-based products, ranging from fuel oil and hydraulic fluid to lubricating greases and oils, are found throughout every type of power generating plant or system — coal-fired, gas-fired, hydroelectric, and nuclear. Lubrication supports bearings and moving parts in all sorts of equipment: pumps, conveyors, feeders, scrubbers, cranes, turbines, and more.
Given the hundreds of lubricant connections, bearing and hydraulic seals, and other moving components in a plant, it is inevitable that some oils will escape, finding their way into the process, cooling, or cleaning water that flows throughout a plant. Hydroelectric plants face a uniquely difficult challenge, since the high-pressure process water needed to contact and drive turbine components also tends to strip away essential lubrication.
Typically, this oily or greasy water flows to:
At any of these points, oil separation and removal is the logical first step in the water treatment process — the first step in conditioning water for recirculation, for discharge into a local waterway, or for discharge into a local sewer system. With optimal oil separation and removal practices, it is likely that you can cut costs for labor and maintenance, waste oil disposal, and secondary water treatment including filtration and chemicals. But how?
PROBLEM 2: SEPARATING A LITTLE OIL FROM A LOT OF WATER: A good oil/water separation system will result in a flow of concentrated waste oil to a collection area and a flow of oil-free water ready for secondary processing or discharge. There is a lot of equipment available to help with this process, but there are some pitfalls as well.
Stokes’ Law tells us that, given the differences between the specific gravity of oil and water, separating these two liquids is really a matter of flow rate, oil droplet size and surface area. Thus, a sump, pit or pond with sufficient surface area and a sufficient amount of time can separate oil and water very effectively. However, few plants have the space or capacity to hold large volumes of oily water for long.
To speed up this process, prefabricated grease/oil interceptors or separators are often built into drainage systems deep within plants or just outside. These separators use a variety of methods — usually baffles, plates, or tubes — to “increase the surface area” that comes into contact with the oily water. The increased contact maximizes the number of small oil droplets that will agglomerate and rise to the surface in a given period of time. These form a layer of waste oil, ready for removal. Below the oil is a layer of clean water, which flows under a baffle on its way to additional processing or discharge.
Maintenance is essential to ensure continuous removal of the accumulated waste oil layer, either from the separators themselves or the drainage sumps that feed them. If waste oil is not removed from these vessels regularly, a series of problems can occur as the waste oil layer builds up:
PROBLEM 3: REMOVING A LAYER OF OIL, WITHOUT ADDING A LAYER OF EXPENSE Once an oil layer has been separated from free water, it must be removed for recycling or disposal. Many plants use one or more of these oil removal methods, but each has costly limitations:
Absorbent materials. Absorbent mats or materials are frequently used to dam up and absorb excess oils and greases resulting from accidents or the routine operation of machinery. These materials are very effective for preventing the spread of a source leak and very efficient in terms of oil pickup. Yet, their use on large volumes of waste oil results in multiple, recurring costs that can make them impractical as an everyday solution:
Manually operated “slotted pipes.” Many separators feature a “slotted pipe,” a pipe located near the top of the vessel that has a horizontal opening. Oil is removed by turning the horizontal opening downward until it meets the floating oil layer, which drains through the pipe to a collection receptacle. These pipes work well on thick layers of oil, but cannot drain off a sheen of oil without draining off a large amount of water as well.
Vacuum truck removal. Vacuum-equipped tank trucks are used to remove waste oil from collection points at plants so that it can be transported to recycling or disposal locations. If the waste oil has been thoroughly separated, highly concentrated, and stored in an appropriate receptacle, this service can be used very efficiently. However, vacuum disposal units are often used to pump oil layers directly off of water. This results in the intake
of a significant amount free water along with the waste oil – and a significantly higher cost to your plant.
SOLUTION - AUTOMATIC OIL SKIMMING REMOVES THE OIL, AND THE EXPENSE: The best option for oil removal, automatic oil skimming, complements or replaces the other methods, while improving process efficiency and reducing costs. Available in a wide range of designs and sizes, skimmers offer versatility and efficiency, cut labor and maintenance requirements, and reduce disposal requirements. Skimmers are versatile because they can remove oil from any water holding areas including separators, sumps, ponds, lagoons, cooling towers, and more. Thanks to automatic operation, they remove oil with efficiency that equals or exceeds the best of the other methods, yet with far lower labor costs. And, they reduce disposal costs because they capture and concentrate waste oil with little or no free water.
While a wide range of skimming equipment is available, experience demonstrates that the maintenance needs of power plants require skimmers with these essential characteristics and capabilities:
SUMMARY: If your plant faces challenges with oily water management and oil removal, consider the cost saving benefits of an oil skimmer. As we have noted here, the right oil skimmer can:
Do you need automatic oil skimming? Consider: