A fuel oil is burned with air in a furnace. The combustion produces 813 kW of thermal energy, of which 65% is transferred as heat to boiler tubes that pass through the furnace. The combustion products pass from the furnace to a stack at 6500C. Water enters the boiler tubes as a liquid at 200C and leaves the tubes as saturated steam at 20 bar absolute. Calculate the rate (kg/h) at which steam is produced.