The flow characteristics of heavy crude oils make them difficult to process with conventional refining equipment. Heating and cooling capacity is limited by the laminar flow behaviour of such crudes. The flow patterns are complex and poorly understood. Heat transfer can be of several magnitudes lower than under turbulent flow conditions encountered when processing light crudes. This results in large and expensive equipment size.
This paper explains the underlying heat transfer mechanisms for such flows, employing CFD simulations backed up by experimental research. One of the characteristics is flow stratification within the tube caused by natural convection effects, leading to a local temperature pinch with diminishing heat transfer as well as ideal fouling conditions towards the bottom of the tube crossection.
To overcome such limitations hiTRAN wire matrix tube side enhancement technology can be applied and is evaluated here. The hydrodynamic of flow in tubes equipped with this technology is changed leading to much improved heat transfer compared to pure laminar flow. Enhancement levels up to 16 times the rate of heat transfer for similar flow velocities are measured. Under design conditions, with equal allowable pressure drop compared to a empty tube designs, up to six times the rate of heat transfer is possible. This results in corresponding smaller equipment size, with substantial savings in exchanger and piping costs. In offshore applications, where equipment size and weight are the constraining factors, this technology can offer substantial benefits when processing viscous fluids.
One Installation case from the Gulf of Mexico is presented in detail. In this application heavy crude with water content is heated for further processing. Heat transfer is limited by the viscous nature of the heated and the cooled fluid, resulting in large and ineffective heat transfer equipment. By applying tube side enhancement the original plain empty tube design was reduced from 20 to 8 exchanger shells, with substantial impact on the CAPEX costs for exchanger and piping. For this particular case the hydrodynamics and heat transfer is explained in detail for the original and the final hiTRAN enhanced design.
See more of this Group/Topical: Topical 7: 19th Topical Conference on Refinery Processing