The article presents the results of numerical researches of hydrodynamics, mixing processes and stabilization characteristics of jet and niche system of gas fuel combustion. On the basis of this system has been created the universal technology allowing more effectively use natural gas in the industry and power engineering. This article shows the results of the steam boiler DE-25 modernization which has been carried out on the basis of jet and niche technology. Study of the geometrical parameters impact on the furnace burner work plays an important role in the design of the increased heat capacity furnace burner.