Modelling primary NOx and primary N2O of Pulverised, Fuel Combustion and Circulating Fluidised Bed Combustion (Frans van Dijen)

ehem. Bestell-Kennz.: Nein
ISBN: urn:isbn:978-3-96284-082-2
Bestell-Kennz.: B15
Erscheinungsdatum: 03.09.2018
Gewicht: 140 g

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Kurzbeschreibung

Modelling primary NOx and primary N2O of Pulverised, Fuel Combustion and Circulating Fluidised Bed Combustion

Frans van Dijen

ABSTRACT

With more stringent emission limits with time, including NOx and N2O, and due to the high costs of secondary measures for NOx emissions reduction, knowledge of primary NOx and primary N2O is very important. With this knowledge, primary NOx and primary N2O can be reduced at low costs and in this way costs for secondary measures are much reduced as well. By applying the knowledge presented, the project costs of a CFBC plant can be lower than those of a PFC plant.

Knowledge regarding primary NOx and primary N2O, and their models, is useful for operators of PFC and CFBC regarding the influence of (the change of):

  • Fuel, with PFC and CFBC
  • Lambda, with PFC and CFBC
  • Temperature, with CFBC
  • Addition of limestone to the bed, with CFBC.

Knowledge regarding primary NOx and primary N2O, and their models, is useful for suppliers of boilers, burners, etcetera, regarding the influence of (the change of):

  • Design, with PFC and CFBC
  • Fuels and fuel flexibility, with PFC and CFBC
  • Conversion of the boiler for other fuels, with PFC and CFBC
  • Developing assisting systems / software, with PFC and CFBC
  • Temperature, with CFBC
  • Addition of limestone to the bed, with CFBC.

With this thesis, the mathematical models of primary NOx of CFBC, primary NOx of PFC and primary N2O of CFBC were improved. The models are based on chemical aspects, such as thermodynamics, kinetics and reaction mechanisms.

A model regarding PFC was made. This model is based on: the furnace, the specific N-content of the fuel, the fuel ratio FR and the air-to-fuel ratio Lambda. The models regarding CFBC are based on: the furnace, the specific N-content of the fuel, the fuel ratio FR, the combustion temperature and the air-to-fuel ratio Lambda.

From a qualitative point of view, the mathematical models of primary NOx are useful, both with PFC and CFBC. From a quantitative point of view, the models of primary NOx with CFBC and PFC, and N2O with CFBC, are not satisfactory. They hold for a specific boiler only. Primary emissions of NOx and N2O of CFBC also depend on air staging, catalytic activity of the ash and/or bed material, the bed inventory, “limestone addition”, cyclone separation efficiency, flue gas residence time, etcetera, which are not (yet) modelled. In this thesis attention is especially paid to the CFBC design parameters cyclone separation efficiency, “limestone addition” and the height of the secondary air ports above the bottom, and their influence on primary NOx and primary N2O. These design parameters easily explain for the variations of primary NOx and primary N2O emissions encountered and modelled.

With CFBC, the presence of catalytically active elements, like Na, K, Fe, Mg and Ca, in the fuel, the ash and the bed material, must be considered as well, which is often not the case in literature. The addition of limestone to the bed can increase primary NOx drastically, depending on the fuel, and hence in such cases limestone addition is definitely a bad idea.

Modelling primary NOx and primary N2O of Pulverised, Fuel Combustion and Circulating Fluidised Bed Combustion (Frans van Dijen)

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