Design and cost estimation of a fisher-tropsch gas to liquid plant using natural gas from Cabo Delgado and air blown reformers

Abstract

Natural gas, has been seen as a bridge between the fossil fuels and renewables, due to fact that natural gas is cleaner than other fossil fuels. But natural gas as such offers few utilities when compared to crude oils, so in order to take a best advantage of natural gas, different technologies can be used to convert natural gas into synthetic crude oil what gives a higher variety of products as crude oil but without sulphur and aromatics. In countries with natural gas reserves, gas to liquid has proven to be an ally to reduce the dependence on importation of crude oil products. Gas to liquid plants, from small to large scale have different cost of manufacturing involved. Different techniques can be applied to estimate the cost of manufacture, these techniques involve empirical equations for cost considering the size of equipment proposed by different books, and cost available on websites. COCO simulator was used to simulate three gases to liquid plants using the Fischer Tropsch process, and natural gas from Cabo Delgado province. Natural gas was composed mainly by methane (96.86%), hydrocarbons from ethane to decane (3.08%), and traces of benzene and toluene (0.06%), was fed to three plants at different capacities (100%, 75%, 50%) all of them following the same procedure so, prior to syngas production it was necessary to pass through an hydrotreater in order to remove the aromatics, and the Autothermal Reactor (Fired Reactor) was used to burn the higher hydrocarbons with air converting them into CO2 and H2O. For the final step converting methane into syngas gas by reacting methane with steam, what lead to a CO:H2 ratio of 1to 3, and with a high amount of nitrogen. Carbon monoxide to hydrogen ratio was adjusted with the use of a reverse water gas shift reactor. Fisher Tropsch reactor was simulated to operate at 220oC and 23 bar, in a fixed bed reactor, with no recycle of the unconverted CO and H2. The annual production obtained from the three plants simulated, in metric tons per year was 82,624.25 Plant1; 68,845.65 Plant2; 49,589.96 Plant3, of synthetic crude starting from C1 to C29 and the main by product was water, and the final cost of manufacturing was estimated to be 5,180,497,221.01USD/year Plant1; 4,124,974,247.09 USD/year Plant2 and 1,608,009,196.52 USD/year Plant3 with 10% of accuracy.