Distillation columns are essential in crude oil processing, as they help to separate the various components of crude oil. They require a considerable amount of energy to operate, but with a few simple tips, you can reduce energy consumption and save on costs. Here are some tips for energy saving in crude distillation.
Design Principles
The general design principles established for many years recommend the use of more trays to reduce the required reflux, hence the load on both the reboiler and the condenser. Tower pressure drop can be minimized to avoid high flash zone temperatures and/or bottoms stripping steam rates. More stripping trays can be used to minimize stripping steam requirements. Additionally, more efficient trays or modifications to existing ones can be used in an existing crude tower.
Low Pressure Operation
Another concept that has been established and found attractive is operating the vacuum tower at low pressure. Low pressure operation in vacuum tower is attained by placing the vacuum jets directly on the tower overhead upstream of the main condensers. Since this method of operation can reduce the tower overhead pressure from approximately 60 mm Hg to about 25 mm Hg, only small amounts of steam are required in the tower to obtain the required hydrocarbon vapor pressure. By utilizing vacuum pumps instead of steam ejectors, there is a net savings in steam consumption.
Product Specifications
If all the products are exactly on specification, there is little way to reduce energy consumption through non-design modifications. However, if the products that are being produced are better than necessary, the unit performance can be optimized to save energy utility. Operations optimization and stable operations programs mean adjusting product yields, pumparounds duties, stripping steam and feed temperature such that all desired product yields and specifications are attained but not exceeded in face of disturbances and crude switches.
Over Flash
In the crude atmospheric distillation tower, it may be desirable to minimize over flash if the lower side-stream back end fractionation is not critical. Going from 3%LV over flash to 5%, a 12°F reduction in ASTM temperature is achieved. An additional 4% over flash only results in an additional 8°F approximately.
Side Stream Steam Stripping
The incremental effectiveness of steam decreases as the steam rate increase. The degree of improvement in separation with steam flow rate depends on the product cut width and where the product is withdrawn from the tower. The narrower the cut width, the less the improvement. Also, for typical crude units, stripping steam appears to have its most significant effect in the intermediate and lower parts of the tower.
Integration
The “elephant” in saving potential in crude distillation unit is attained via the proper integration between the feed and side products and the pumparounds and the wider integration between the atmospheric unit and the vacuum unit as well as the integration among these two units and the rest of the refinery units directly or indirectly.
By using these tips for energy saving in crude distillation, you can reduce energy consumption, optimize unit performance, and save on costs.
