The invention relates to a tubular boiler with a heat exchange tube with at least one helical layer situated in a heat exchange chamber, and which includes a set of laterally joined spirals. The boiler includes, an inner side of the helical layer, an oven that is rigidly joined to said layer and connected to a feeder by means of which fuel is supplied. The boiler also includes an output collector for collecting ash and slag, which connects the inside of the heat exchange chamber to the outside of the boiler, and a forced-air-current generator that generates a movement of air inside the boiler and directs it to the oven. This movement of air moves the ash and slag along the at least one helical layer to the output collector.

The current invention discloses a method and apparatus for production of hot water or steam in a 4-pass firetube boiler. A waste heat stream is passed through the first and second passes of the boiler, and then routed into a furnace tube (which is the third pass of the boiler) to help suppress the flame temperature and NOx emissions from the burner. The flue gas from the third pass is then passed through the fourth pass of the boiler to transfer the heat energy to the water in the boiler.

The current invention discloses a method and apparatus for production of hot water or steam in a 4-pass firetube boiler. A waste heat stream is passed through the first and second passes of the boiler, and then routed into a furnace tube (which is the third pass of the boiler) to help suppress the flame temperature and NOx emissions from the burner. The flue gas from the third pass is then passed through the fourth pass of the boiler to transfer the heat energy to the water in the boiler.