Production of a Plant Making 600,000 t/y Methanol-to-Olefin (MTO) (PDF)

Project Report from the year 2016 in the subject Chemistry - Other, , language: English, abstract: This is a part two of the Advance Process design project. Part one was a group project in which we carried out a feasibility study of Methanol to Olefin (MTO) plant. The plant is an extension of an existing Coal-chemical complex in China, which produces 1,000,000 tonnes of methanol from coal each year. In order to become more competitive in the market, we studied alternative routes of MTO process and designed the most efficient, least pollutant and safest plant. The aim of this individual project is to cover a detailed design of the C2 splitter distillation column which is the final step in the MTO process where ethylene and ethane are separated. As ethylene is one of the most popular petrochemical product and the demand for the product is continuously increasing each year. Therefore, to meet the customers demand the column was designed with 99.4% purity.

For the initial design calculation, the operating pressure of the column was chosen as 24bar. The diameter of the column was calculated to be around 1.66m for the stripping section, which was suitable for the sieve plate design. Using the AlChE method, the plate overall efficiency was obtained as 73%, which was in the range of the distillation column efficiencies, by using the plate efficiency the actual number of stages was obtained, 53 stages, with an overall height of the column as 35m. At 24bar the condenser duty of the column was calculated to be 2.66MW and reboiler duty 2.43MW. The design optimisation shows that as the pressure of the column increases, the capital cost of the column also increases due to the increase in a number of actual stages and the reflux ratio, mean taller and thicker column wall, will be required to meet the right specification and to handle the high pressure of the column. But, with the increasing pressure, the energy cost of the column decreases, as less energy will be required to condense the overhead vapour. The capital cost of the column outweighs the energy cost of the column. Therefore, the column total cost increases with the increase in column pressure. The optimum pressure, for the C2 splitter column, was chosen as 10bar. The reason being, low reflux ratio and less number of stages will be required, meaning the less capital cost of the column.