Question2 For a crude oil cracking process to produce gasoline from crude oil, the SO generated from the catalytic cracking unit can be removed by installing a scrubber downstream of the reactor. An alternative option is to install a hydrotreater to remove sulfur from the crude oil (Figure 2), thus reducing the sulfur content in the crude oil sent to the catalytic cracking unit. The feed hydrotreater even though it requires a much larger capital investment than a scrubber, can produce a superior return on investment for the refinery due to revenues generated from improved yields and product quality, reduced crude cost and savings from residual upgrading. The approximate costs and revenues for hydrotreaters and flue-gas scrubbers are given in Table 1 Various cases are included to show the sensitivity of the results to the crude charge. Case 1 is for the installation of flue-gas scrubbing treatment. Cases 2 and 3 are for the addition of a hydrotreater for low-nitrogen and high-nitrogen crude oil, respectively. Cases 2a and 3a are for crude with low-sulfur and low-metal contents, whereas cases 2b and 3b are for crude with high-sulfur and high-metal contents. If the scrubber and all of the hydrotreaters (Table 1) are assumed to have the same expected lifetime, it is appropriate to calculate the net present value (NPV) of each option for making economic comparison Calculate the net present values of all five options assuming an interest rate of 10%, c annually, and an equipment life of 30 years. Briefly comment on your results. Recovered sulfur Crude Hydrotreater FCCU Scrubber Flue-zases Waste slury Products Figure 2. Flow diagram of a fluid catalytic cracking unit (FCCU) with a hydrotreater or a scrubber Table 1. Economics of adding a scrubber vs. a hydrotreater to reduce SOx emissions for a 40,000 barrels/day refi SOLow-N crude hydrotreatHigh-N crude hydrotreater scrubber 2b 125 3b 100 200 Capital cost, SM Net annual revenue $M/yT * Net annual revenue- annual (sales revenue-opeating cost) (SM: million dollars) 35 75