The Basics of Oil Spill Cleanup - Chapter 8

CHAPTER 8 Separation and Disposal After oil is recovered from the water surface or from land, it must be temporarily stored, the water and debris separated from it, and the oil recycled or disposed of. Pumps are used to move the oil from one process to another. This chapter covers temporary storage, separation, and disposal, as well as the types of pumps used for oil. Storage, separation, and disposal are all crucial parts of a cleanup operation. In several major cleanups, recovery has actually stopped because there was no place to put the recovered oil. When oil is recovered, sufficient storage space must be available for the recovered product. The recovered oil often contains large amounts of water and debris that increase the amount of storage space required. Several types of specially built tanks are available to store recovered oil. Flexible portable tanks, often constructed of plastic sheeting and a frame, are the most common type of storage used for spills recovered on land and from rivers and lakes. These are available in a range of sizes from approximately 1 to 100 m3 and require little storage space before assembly. Most of these types of tanks do not have a roof, however, so rain or snow can enter the tank and vapours can escape. Rigid tanks, which are usually constructed of metal, are also available but are less common than flexible tanks. Pillow tanks, constructed of polymers and heavy fabrics, are usually used to store oil recovered on land. These are placed on a solid platform so that rocks cannot puncture the tank when full. Pillow tanks are also sometimes used on the decks of barges and ships to hold oil recovered at sea. Oil recovered on land is often stored in stationary tanks built for other purposes, and in dump trucks and modular con-tainers, lined with plastic. Recovered oil can also be temporarily stored in pits or berms lined with polymer sheets, although this open type of storage is not suitable for volatile oils. Towable, flexible tanks, usually bullet-shaped, are also used to contain oil recovered at sea. Their capacity varies but they can hold up to several tons. These tanks are also constructed of polymers, with fabric materials sometimes used as a ©2000 by CRC Press LLC Photo 73 Temporary storage requirements can be overwhelming, as shown in this photo of recovered oil in Japan. (Environment Canada) base. Since most oils are less dense than water, these tanks will float throughout the recovery process. When full, these tanks can be difficult to manoeuvre, how-ever, and they can be difficult to empty, especially if the oil is viscous and contains debris. Oil recovered at sea is often temporarily stored in barges. Many cleanup orga-nizations have barges that are used solely for storing recovered oil and lease barges for use at larger spills. Recovered oil is also stored in the holds of ships, usually using older vessels. This is more economical than using designated tanks on land especially when the recovered oil has to be stored for long periods of time until a final disposal method is found. Drums, small tanks, livestock watering troughs, and even bags have also been used to contain oil from smaller spills, both on land and at sea. Pumps Pumps play an important role in oil spill recovery. They are an integral part of most skimmers and are also used to transfer oil from skimmers to storage tanks. Pumps used for recovered oil differ from water pumps in that they must be capable of pumping very viscous oils and dealing with water, air, and debris. The three basic types of pumps used for pumping oil recovered from spills are centrifugal pumps, vacuum systems, and positive displacement pumps. The operating principles of some pumps are shown in Figure 26. ©2000 by CRC Press LLC Photo 74 Photo 75 A flexible tank can sometimes be towed at high speeds, as shown here. (Foss Environmental) Portable tanks such as this are frequently used for temporary storage of recovered oil. (Oil Spill Response Limited) Centrifugal Pumps Centrifugal pumps have a spinning vane that moves the liquid out of a chamber by centrifugal force. These pumps, which are regularly used for pumping water and ©2000 by CRC Press LLC Figure 26 Operating principles of pumps. wastewater, are not designed for use with oil and are generally not capable of dealing with material more viscous than light crudes, or with debris. They are economical and universally available, however, and are often used in oil spill cleanup operations. Vacuum Systems Vacuum systems consist of vacuum pumps and tanks mounted on a skid or truck. The vacuum pump creates a vacuum in the tank and the oil moves directly through a hose or pipe to the tank from the skimmer or the source of the oil. The oil does not go through the pump, but moves directly from its source into the tank. Vacuum systems can handle debris, viscous oils, and the intake of air or water. The vacuum tank requires emptying, however, which is usually done by opening the entire end of the tank and letting the material move out by gravity. ©2000 by CRC Press LLC Positive Displacement Pumps Positive displacement pumps are often built directly into skimmers to recover more viscous oils. These pumps have a variety of operating principles, all of which have some common schemes. Oil enters a chamber in the pump where it is pushed by a moving blade, shoe, or piston to the exit of the pump. The oil and other material with it must move through the chamber because there is no alternative passage, thus the name “positive displacement.” Photo 76 This is a close-up of one type of screw pump. (Environment Canada) The screw or auger pump is a common type of positive displacement pump. The oil drops into part of the screw and is carried to an output. Wiper blades remove oil from the auger flights to prevent it from remaining on the auger shaft. The screw pump can deal with very viscous oils and is often built into skimmers. A gear or lobe pump uses gears or lobes mounted on a shaft to accomplish the positive displacement of oil through a chamber. Neither of these pumps can handle debris or highly viscous oil. The diaphragm pump uses a flexible plate or diaphragm to move oil from a chamber. This type of pump usually requires a valve, which limits its use to material that can pass through the valve making it unsuitable for oil containing debris. A vane pump, which uses a movable metal or polymer plate to move oil in a chamber, functions in a manner similar to a centrifugal pump, but with positive ©2000 by CRC Press LLC ... - tailieumienphi.vn