A compact gas fired steam generator comprises a water tank with designated steam separation zone, boiling zone and a solids separation zone, a burner for burning gaseous fuel with air for producing
combustion products and a flat tubular type
heat exchanger immersed in water in the water tank. The
combustion products are passing through the
heat exchanger in an indirect
heat transfer relationship with water in boiling zone thereby boiling, circulating and evaporating the water in boiling zone and in an indirect
heat transfer relationship with cold make up water passing upwardly through solids separation zone thereby preheating cold make up water and cooling
combustion products and recovering
latent heat and condensing
moisture present in
combustion products. The cooled
combustion products are discharged to outdoors and the collected condensed
moisture is discharged to drain. The produced steam is separated from the boiling water in steam separation zone, the solids present in the boiling water are separated from the circulating boiling water and accumulated in solids separation zone and the accumulated solids are cooled by the incoming cold make up water and intermittently discharged from solids separation zone by a water pump together with the incoming cold make up water to drain. The
high rate internal circulation of boiling water, the extended
self cleaning heat transfer surfaces of the flat tubular type
heat exchanger immersed in the boiling water, the
recovery of
latent heat from
flue gases and the
discharge of cooled solids with cold make up water provide an exceptionally compact steam generator with overall
thermal efficiency of up to 95% and with maintenance free unattended operation. The compact steam generator can be used in humidifying of space air in buildings, in heating of air in domestic central
air heating systems and in industrial processes requiring clean steam.