Storage and Transport

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After processing, finished products have to be stored and delivered to clients, or semi - finished products stored to be finished. Although these operations are not intensive energy consuming, the significant amount of volumes involved and some specialties can be observed.

Tankage Storage tanks are used to store crude oil and intermediate process streams for further processing. Finished products are stored in tanks before transportation off site. As a matter of fact, approximately 50% of the products in a regular refinery are prepared and specified at the storage tanks by means of blending. Many tanks deal with low viscosity products at ambient temperature. However, heated storage tanks are common in refineries. They are used to store products whose viscosity properties restrict flow at normal ambient temperatures. Products heavier than diesel oil, such as heavy gas oils, lube oils and fuel oils, depending what is ambient temperature in the part of the world that the refinery is, can be stored in heated tanks. Usually tanks are heated by heating coils or bayonet type immersed heaters. Steam is normally used as the heating medium. It is common also, wherever there is immersed heating, that the tank needs to be agitated by side-located propeller agitators. Eventually external circulating heating is used for tanks, and products are mixed by means of jet mixing, where the hot return stream enters the tank through a jet nozzle. External heating is used when there is a potentially hazardous situation, if steam from the immersed heater were to leak.

Measures for energy efficiency in the tank farm are insulation of heated tanks, accurate heater design and steam feed. In the heater design of course the best fitted steam trap and best steam pressure must be selected. Needless to say that condensate recovery is also included. Use of an agitator for mixing is reinforced, instead of the common procedure of pumping around the liquids to promote the blending. This last practice spends much more energy than necessary for the mixing and is less effective, compared with what is obtained in a good blending of the products by an agitator.

Pipelines The flow offluids is an essential and rather common daily operation in a refinery. Since all fluid flows pass in a pipe to be directed or withdrawn from processes and storage tanks, it is possible to estimate that a refinery regularly has to pump more than twice the volume of the distillation throughput. Considering crude oil, all products and necessary side flows, it is easy to find out that flow power demand represents 10-15% of whole refinery energy demand. And 85% of this energy demand is supplied by electricity. Energy consumed for flow depends on fluid properties, its flow rate and also on size, length and physical characteristics of the pipe. Pipework must be designed for optimal performance and should be selected balancing some factors. Adequate flow velocity to minimize erosion in piping and fittings, pipe routing to avoid many direction changes with the presence of too many bends and curves, and an internal diameter complying to plant standard pipe diameters. Inadequate pipe sizing can cause pressure losses and increase in leaks, but while increasing pipe diameter may save energy, on the other hand, it raises investment and maintenance costs for system components. Pipe diameter doesn't influence installation costs by much, but one thing is always true, undersized pipe diameter results in unnecessary energy consumption. And once the system is installed, these costs become a fixed energy cost of the refinery.

Pipeline design and installation are strictly linked to pump selection and matching piping and pumping system is what makes energy efficiency for the set.

Another important point on pipeline is related to heating and heat recovery. As mentioned previously, oil fractions with viscosity at ambient temperature, higher then 100cP or 400 SSU, need heating to reduce its viscosity and achieve better flowing condition. To move these fluids around it is critical to keep their temperature, otherwise more friction losses appear and more energy is spent. Maintaining the pipeline at an appropriate temperature is achieved by thermal insulation and steam tracing. Tracing is included inside the insulation; this choice, while bringing extra costs to installation, makes pipe replacement or repair simpler. Steam temperature is necessarily hotter than the temperature to be maintained and all materials should withstand that temperature. Energy efficiency opportunities here are proper design, selection of adequate steam pressure and a steam trap for the tracing. The best economical thickness is calculated by a balance between energy loss and cost of insulation, including maintenance and expected life endurance of the insulation. Thicker insulation conserves energy but uses more material and installation is more expensive. Fiberglass or calcium silicates are the most usual insulation materials. An outer cover of aluminum or stainless steel provides mechanical resistance to minor damage and weatherproofing.

Ships and Barges Since a refinery deals with huge volumes of liquids, either of crude oil and products, and a significant share of costs is related to transportation options, moving bulk volumes at low cost is demanding for economical operation. Because of this, many large complexes are located on coastal or riverside sites, allowing shipment by barge or ships. Tankers and barges can be loaded and unloaded at special jetties or docks for handling petroleum products. Not unusually, particularly big tankers, the very large crude carriers known as VLCC, use submarine pipelines at deep water anchorage with floating loading facilities.

Different from pipes, that are commonly used for flows inside the refinery, ships are just meant for sending flow out to the battery limits. Compared with other means of transportation, shipping is often more energy efficient than trucks or trains.

Opportunities for energy efficiency related to the refinery in this area are linked to ship consumption while docked and the timing of loading and unloading operations. Most of the ships while docked are somehow linked to energy system of the dock that might be supplied by the refinery. The more time in overall transferring operation, the more energy is demanded. And timing is related to refinery production scheduling, ship scheduling and product loading and unloading operations. These are also impacted by details such as berth availability, and delays or constraints on the product loading system. Neglecting the coordination of this scheduling implies that more energy is likely to be spent. And this is actually just waste, because any time above the expected necessary operational time means an extra energy requirement that doesn't produce more.

Of course there are other energy efficiency opportunities over ships operation, like regulating ship engine, proper voyage speed etc., but these are beyond refinery operational ground.

Rail and Truck As crude oil is refined and more specified streams are produced, smaller volumes need to be moved. This requires other transportation means, less bulky and with more flexible delivery capacity. The common method for shipping products with these characteristics is by road or rail in suitably designed tankers.

The same comments may apply as previously on energy efficiency opportunities on ships, related to scheduling and coordination but tank storage play a decisive role on smoothing consequences since the volumes when it is dealing with tankers are much smaller than ships or barges. But another point must receive some attention when loading viscous fuels to trucks and trains: loading facilities for these products also require heating to guarantee proper viscosity for the flow. If the loading dock is located too far away from the product heated tank and from the heat source, like the steam header or boiler that feeds steam to it, there may be reasonable heat losses in this process. Installing the truck and train loading dock near to the heated tank farm and a steam source is an opportunity to reduce energy consumption.

Actually energy requirements for supplying and distribution before and after refinery boundaries represent only 2 or 3% of all cycle energy demand. That doesn' t mean it is not worthwhile because it may represent a relevant share of logistic costs for certain products.

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