Integrated phosphate complex: sulfuric acid steam drives the phosphoric acid concentrator

How a Jorf Lasfar-type phosphate complex runs on its own sulfur: the sulfur-burning acid plant raises HP steam, a back-pressure/extraction turbine turns it into power, and the turbine's 3.5 bar extraction is the steam the phosphoric acid concentrator condenses — the arrangement EFMA's BAT booklet on phosphoric acid describes ("the high pressure steam that is produced in the waste heat recovery boiler is normally used to produce electric power and the low pressure exhaust steam is used for phosphoric acid vacuum concentration"). One flowsheet, the steam stream physically connected. The acid plant is sized to the wet-process-phosphoric-acid-dihydrate line: 1,500 t/d of P2O5 at that example's computed 2.80 t H2SO4 per t P2O5 is 4,200 t/d of H2SO4, burned from liquid sulfur in dry air to 10.5% SO2 (the bed-1 strength of the Bayer plant in EFMA's sulphuric acid booklet). The flame reaches 1269 K; the waste-heat boiler cools the gas to 693 K for bed 1, which exits at 885 K at 63% conversion; the superheater takes it back to 713 K for beds 2-4 (99.5% overall, the booklet's double-absorption range) and the economizer to 503 K before absorption. Boiler feedwater at 105 C makes 1.29 t of 40 bar steam per t H2SO4 — 3.62 t/t P2O5 — and that is 66% of the 5.4 GJ the sulphuric acid booklet says a tonne of acid from sulfur liberates, against 57-62% in 31 bar steam on Bayer's measured plant: the model has no casing loss (Bayer: 2-3%) and stops before absorption, whose heat goes to the acid coolers here as there. The concentrator takes the dihydrate line's 27.9 wt% P2O5 filter acid to 54.0 wt% under 0.12 bar vacuum on 1.95 t of LP steam per t P2O5, inside the booklet's 0.5-2.2 t/t. So the acid plant covers the phosphoric plant's steam with room to spare: the turbine makes 38.2 MW on what the concentrator does not need, and after the air blower, the feedwater pump and the phosphoric plant's own 150 kWh/t P2O5 (the midpoint of the booklet's 120-180) the complex exports 24.1 MW — 385 kWh per t P2O5. Sweep the extraction fraction to see the trade: every tonne of steam sent to the concentrator is power the condensing section does not make. Scope, stated rather than implied: (1) the four converter beds are two lumped adiabatic reactors with fixed conversions (63%, then the rest to 99.5% overall), not equilibrium beds, and the interpass absorption and gas reheat of a double-absorption plant are not drawn; (2) the absorber is SO3 capture, so the heat of forming H2SO4 (about a quarter of the 5.4 GJ/t) is not in the balance — it goes to cooling water in the plant too; (3) the burner's heat_of_reaction carries a correction for this package's liquid-sulfur enthalpy (Peng-Robinson treats sulfur as one atom), so the heat released is NIST-JANAF's 296.81 kJ/mol from rhombic sulfur, less the 5.08 kJ/mol to melt and heat it to 413 K; (4) the concentrator acid is a feed at the dihydrate line's filter-acid strength, not that example's reactor block, and runs on the brine package (thermo_overrides) while the gas and steam run on Peng-Robinson with IAPWS-95 for water; (5) condensate is returned to a product, not recirculated, and the boiler has no drum, blowdown or deaerator; (6) no pressure drops are drawn on the gas train.