Research and modernisation of TGME-444 boiler thermal circuit in order to increase its reliability and efficiency

This paper is aimed at studying the main design solutions of the TGME-444 boiler, which ensure reliable operation of heating surfaces and high economic indicators when burning fuel oil. In the Russian context, such boilers relied on fuel oil from the period 1973-1993, whereas, from 1993 to the present time, the fuel was switched to natural gas. Extensive experience of boiler operation when burning natural gas shows that, according to the temperature regime reliability of the curtain convective superheater of the drop flue gas duct, the boilers cannot operate with the loads more than ~117 kg/s (420 t/h). The reasons for the increased injections when burning natural gas are due to the project decisions on the composition of boiler heating surfaces. The main engineering solutions for the boiler thermal circuit were optimised for fuel oil as the heaviest fuel. Thus, consideration was given to the several variants of thermal circuits formed with regard to their potential implementation within existing furnace and convective gas duct configurations taking the conversion to natural gas fuel into account. These are: replacement of steam superheating furnace curtains with steam generators and inclusion of the latter in the boiler circulation cycle; increase in heat absorption of water-containing heating surfaces (under reduced injection flow) by the introduction of recirculation gases withdrawn after the economiser into the furnace. Calculations were performed using TRAKT, Hydraulics, Boiler Designer programs for thermal and hydraulic calculation of steam boilers. The results of calculated variants informed changes in the design and heat absorption of boiler reheating surfaces that significantly reduced the cost of injections and thermal upset, whereas operational reliability was able to be increased while maintaining a high-level of economic indicators. The greatest effect of reducing injection costs is achieved in cases when reheating furnace curtains are replaced by steam generating curtains, with the latter included in a boiler circulation scheme. Thus, increasing the heat absorption of water-containing heating surfaces by converting superheating furnace curtains into steam-generating curtains decreases water overheating at the economiser outlet, improving operational stability.

TGME-444 steam boiler, vortex furnace, heating surfaces, thermal absorption of water-containing and steam-generating surfaces, thermal circuit improvement