Design of a vapor recovery unit for hydrocarbon Recovery from storage tank and off-gas of a Condensate fractionation plant

Abstract

A condensate fractionation plant recycles vapors coming from the tank batteries and the fractionation column by a vapor recovery unit (VRU). Otherwise, these valuable hydrocarbons would be lost through flaring or venting. VRU is essentially a multi-stage compressor, with an intercooler and aftercooler. The VRU must be designed such that it is not over-sized or under-sized. The project examined an existing plant of 4,000 barrels/day capacity and attempted to re-design the VRU for a scenario where an additional 6,000 barrels/day will be added to the plant capacity. The major obstacle in this task is to correctly estimate the total volume of vapor to be handled. There is no facility for direct measurements, so the vapor must be estimated from correlations and by process simulation. The volume of the byproducts from the column was estimated by using software, which simulated the whole fractionation process. With the help of tank data from the site, an analytical calculation was performed to compute the amount of vapor by considering different operating conditions. Following that, a compressor for the VRU system was designed which would be appropriate to handle the volume of hydrocarbon. The benefit of using VRU from an environmental point of view was included in this work. New technologies to minimize tank vapor loss, such as the construction of floating roof tanks, were also considered. The results obtained from the calculation and simulation steps reflect actual values from the plant with minor deviation, which gave confidence in this design process. The calculations indicate that, for the proposed capacity upgradation, the required VRU compressor should have 2.65 times greater capacity in the case of fixed roof tanks. With a floating roof, the VRU would need only about 3 m3/hour additional capacity. The VRU should also prevent 103.58 tonnes/year of CO2 emission.