Experimental and modelling investigation of the pilot-scale oxy-fuel combustion of Victorian brown coal

Lian Zhang, Jian Zhang, Xiaojiang Wu, Jianwen Zhang, Yoshihiko Ninomiya

Research output: Chapter in Book/Report/Conference proceedingConference PaperResearch

Abstract

Victorian brown coal is the single largest source contributing to the power generation in Victoria, Australia. Due to the presence of abundant moisture, i.e. up to 70 wt%, Victorian brown coal exhibits a greenhouse gas emission rate as high as ∼1300 kg-CO2/MWh-electricity sent out in the existing air-fired power plant, relative to ∼900 kg-CO2/MWh for the Australian black coal. Oxy-fuel combustion is a cost-effective option to deliver a CO2-rich gas stream that is ready for direct CO2 sequestration, when compared with the postcombustion capture, e.g. amine absorption for CO2 recovery. As the youngest lignite in the world, Victorian brown coal is supposed to possess a variety of distinct characteristics during the oxy-fuel combustion, which are to varying extents linked with the abundant moisture within the coal matrix. On the one hand, the abundant moisture is believed to enhance coal volatile ignition delay, due to the required evaporation of it at the initial heating step for coal particles. On the other hand, once being evaporated, the steam possesses a larger specific heat capacity than nitrogen and oxygen. Its presence in the furnace thus promotes the radiative heat transfer from coal flame to flue gas, and consequently to the water in the heat exchange tubes. The use of recirculated flue gas (RFG) in place of air could further complicate these two issues, considering that CO2 also has a large specific heat capacity that is comparable to steam, whilst the adjustable oxygen concentration in the furnace is in favor of shortening the ignition time of coal particle, either dry or wet. In light of this, it is of great interest for us to investigate the oxy-fuel combustion of Victorian brown coal particularly on a pilot scale. Oxy-fuel combustion of Victorian brown coal is being carried out in a 3MW pilot-scale boiler to clarify its distinct combustion characteristics. The residual moisture in brown coal plays a critical role on the ignition delay and expansion of the flame length as well, which subsequently affects flame stability, heat-transfer in furnace and even the stability of the feeding of the pulverized coal. Through a preliminary test in the pilotscale plant, a variety of essential data for the combustion of Victorian brown coal under the oxy-fuel mode have been obtained, which are useful for the future design and optimisation of an industrial-scale oxy-fuel system and burner for Victorian brown coal. Apart from experimental investigation, the computational fluid dynamic (CFD) modeling have also carried out to confirm the remarkable influence of moisture on the combustion of this distinct low-rank coal in both air and oxy-fuel mode. As has been confirmed, 3MW pilotscale oxy-fuel combustion of Victorian brown coal has been successfully, leading to the production of 80% CO2 at the 5% air ingress in the system. The moisture in brown coal plays a crucial role on coal ignition delay and the flame stability. Upon the pilot-scale tests, the valuable data for the oxy-fuel plant and burner design for Victorian brown coal are being gained, including coal oxidation rate, heat flux and distribution in the furnace, pollutant emission, and its ash fouling and slagging propensities.

Original languageEnglish
Title of host publication30th Annual International Pittsburgh Coal Conference 2013, PCC 2013
Subtitle of host publicationBeijing, China; 15-18 September 2013
Place of PublicationPittsburgh, Pennsylvania, USA
PublisherInternational Pittsburgh Coal Conference
Pages3620-3641
Number of pages22
Volume5
ISBN (Print)9781629934389
Publication statusPublished - 2013
Event30th Annual International Pittsburgh Coal Conference 2013, PCC 2013 - Beijing, China
Duration: 15 Sep 201318 Sep 2013

Conference

Conference30th Annual International Pittsburgh Coal Conference 2013, PCC 2013
CountryChina
CityBeijing
Period15/09/1318/09/13

Keywords

  • CFD modelling
  • Moisture
  • Pilot-scale oxy-fuel combustion
  • Victorian brown coal

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