Combustion of Brown Coal, Anthracite, and Their Mixtures in High-Pressure Steam–Oxygen Mixture

Abstract

The article presents the results of a study of combusting brown coal (BC), anthracite (A), and their mixtures taken in the ratios (BC : A) equal to 7 : 3, 1 : 1, and 3 : 7 in terms of organic mass in water–oxygen fluid at the pressure р ≤ 25 MPa, which was carried out for the first time. The experiments were carried out with coals heated in the Н₂О/О₂ fluid medium at a rate of 1°С/min to 550°С and in pumping the fluid through the bed of coal mixture (BC : A = 7 : 3) and heating the reactor at a rate of 1.5°С/min to 420°С. It is shown that the coals and their mixtures are oxidized in the autoclave regime according to the thermal explosion mechanism. This facilitates almost complete combustion of organic carbon for a few tens of seconds at relatively low temperature (below 700°C). The ignition temperature and combustion dynamics of mixtures with predomination of one of coals (BC or A) in the autoclave regime are similar to the combustion characteristics of this coal; the combustion of coals with the equal content of BC and A proceeds in two stages. It has been found that in pumping the Н₂О/О₂ fluid through a bed of coal mixture, their intense combustion at 230−300°С is accompanied by the generation of combustible components and their entrainment by steam flow. The organic carbon combustion rate under these conditions is governed by the oxygen flowrate supplied into the reactor. The obtained study results can become a basis for the development of promising technologies for combustion of coals and coal enrichment waste in high pressure steam to yield a high-enthalpy heat carrier.