Examinations of the process of hard coal and biomass blend combustion in OEA (oxygen enriched atmosphere)

The benefits of oxygen enrichment have been demonstrated in a variety of industrial combustion applications, but to date no implementation of oxygen enrichment in boilers has been reported, primarily due to their already high thermal efficiencies and a very large scale of such systems, which require significant amounts of oxygen. But recently, oxygen combustion in boilers has become one of the CCS technologies which can be an effective tool for reducing greenhouse gases emissions, and oxygen enriched combustion is suitable for low-calorific fuels, including biomass. This paper analyses the use of oxygen enrichment in a furnace for co-firing of different kinds of biomass with hard coal in terms of emission and burnout impact (LOI). As a part of this research, the effect of injection oxygen mode and total oxygen concentration on the flue gas emission (SO2, NOx) and burnout from co-firing of straw and wooden biomass in different proportions (20% and 40%) with hard coal were studied. The co-firing tests were carried out in an isothermal flow reactor. One of the benefits from the OEA (oxygen enriched atmosphere) technology is more effective separation of CO2 owing to the higher CO2 concentration in the flue gas. The additional advantage of the OEA combustion technology in comparison with oxy-fuel combustion is that the OEA process needs lower O-2 purities and therefore it is cost-effective. Experimental tests on co-firing of 20% straw-hard coal blend were conducted in oxygen enriched (up to 25 and 30%) atmospheres with three variants of O-2 injection modes. NOx, SO2 emissions and burnout for the various atmospheres in the combustion chamber were studied. Moreover, co-firing tests were performed with 40% share of wooden biomass to examine the effect of the biomass share and a type on emission of NOx and SO2 in OEA. The two O-2 injection modes were investigated. In each case, the emission of SO2 increases alongside an increase of oxygen concentration in atmosphere. However, the experimental results show that stable and relatively low SO2 emission and low NOx emission can be achieved for OEA when oxygen is supplied to the primary stream of air. Also, minimal LOI (loss on ignition) is obtained for OEA I+. The supply of oxygen to the secondary oxidizer stream into the burner results in highest NOx emission only in the case of OEA30. It can be therefore concluded that both the oxygen enriched atmosphere and the O-2 injection mode affects NOx emission. (C) 2015 Elsevier Ltd. All rights reserved.