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Oxy-fuel combustion is a potential low-emission technique for energy conversion. This paper presents the results of oxy-fuel experiments under high-pressure conditions. The influence of process parameters, such as reactor pressure and temperature, on the emission of NO x , N2O, and other compounds was tested. A new oxy-fuel experimental setup is presented. The experiments were conducted using a laboratory-scale (fuel input of up to 3 kg/h) pressurized fluidized-bed combustor. The feedstock used was “Ziemowit” coal, and the tests were carried out under oxy-fuel and air-fired conditions. The temperature inside the reactor was in the range of 750–900 °C. Generally, NO x emission decreases significantly under higher pressure; however, the details of this trend depend upon the experimental conditions. The effects of pressure and temperature on NO x and N2O emissions are discussed.

An autothermal fluidized bed reactor was used to research the influence of pressure (0–2 barg) on the gasification process of different types of biomasses. The tested feedstocks were bark and lignin while softwood pellet was used as a reference fuel. A mixture of O2/CO2/H2O was used as a gasification agent. The impact of the application of CO2 on the yield of H2 in product gas was determined. Resulting product gas was characterized by a high content of CO which makes its use for applications based on chemical synthesis very difficult without extensive upgrading or supply of H2 from external sources. CO2 proved to improve carbon conversion efficiency (CCE) of the gasification process and to be an option for its chemical sequestration (negative carbon footprint). A slight modification of conventional indices used to evaluate efficiencies of gasification systems (CCE and water/carbon ratio) was proposed, to take into account the impact of the additional source of carbon fed into the reactor. The increase of system pressure led to changes in the composition of the product gas in line with predictions of Le Chatelier’s principle. The influence was predominantly visible in higher yields of CH4 and lower overall production of product gas. For higher hydrocarbons (CxHy), the trend was unclear. A set of stable gasification parameters were achieved for each pressure level and a standard gasification temperature of 850 °C, except for gasification of lignin performed at 2 barg. A proposed explanation for the problem is the combined effect of the increasing concentration of ash in the fluidized bed and its low characteristic melting temperatures. Due to the obtained experimental findings, a new ash agglomeration index was formulated.

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The idea of combustion of suspended fuels was developed in the 1980s. The largest producer and user of slurry fuels (Coal Water Slurry, CWS) is China [3]. Despite of several decades of CWS research history, investigations are still carried out to improve the parameters of disperse fuels and to improve the combustion of these fuels. The close relationship between the properties of slurry fuels and number of parameters (mainly the type and properties of the coal feedstock) generates the necessity of CWS receipts and determines for what purposes the fuel may be destined. In the case of the use of coal sludge, the resulting slurry allows for the combustion / "disposal" of coal slurry in pulverized boilers. In the case of using better quality fine coal fractions in CWS production, a slurry will be created allowing for achieving the crucial technological goal such as operation of power units with a reduced technical minimum.

In this paper some issues of the transition process from air-to oxy-combustion were investigated. Advantages of flexible combustion were described. Flexible combustion tests carried out at four European plants and five plants outside Europe of different scales of process and test parameters were presented. An analysis of the transition time from air to oxy-combustion of different laboratory and pilot scale processes was carried out. The "first-order + dead time" approach was used as a model to describe transition process. Transitional periods between combustion modes and characteristic parameters of the process were determined. The transition time depends not only on the facility's capacity but also it is impacted by specific operational parameters.