Exergoeconomic analysis of hydrogen production from plasma gasification of sewage sludge using specific exergy cost method

The plasma gasification process appears to be a relatively new technology due to its better efficiency, effectiveness and environmental friendliness. The process can essentially be used for sewage sludge treatment and energy production. In this paper, we investigate a plasma gasification process from the literature for hydrogen production analysis purposes. We use the specific exergy cost (SPECO) method to calculate exergy-related parameters and display cost flows for all streams and components. We also determine exergy destructions and their costs in a more specific form as avoidable and unavoidable exergy destructions. We consider six main components: a plasma gasification furnace, a gas cleaning, syngas compressor, two heat exchangers and a pressure swing adsorption (PSA). We calculate that the PSA has the largest exergy destruction rates with 11.66 MW, followed by the plasma gasification components with 6.55 MW. We also determine exergy efficiencies for these components. The lowest exergy efficiency is 4.43% for the PSA. It is found that the maximum exergy destruction cost rates are 338.75 and 46.92 $/h, for the PSA and plasma gasification furnace, respectively, while the unit cost of hydrogen is 208.6 $/h at the outlet of the PSA. We further investigate exergy destruction rates and investment cost rates through an extended exergy analysis and obtain that for the plasma gasification furnace, the avoidable destruction and investment costs are 15.36 and 8.06 $/h, respectively.