BIOS - Bioenergy
  YOUR PARTNER FOR ENERGY FROM BIOMASS AND ENERGY EFFICIENCY  
 

CFD simulations

Brochure

pdf CFD-BIOS-Keyinformation-Dec_2011.pdfCFD Key Information (2.54 MB)

For a detailed description of the working field of CFD aided dimensioning of biomass-combustion and gasification plants see:
CFD-Simulation

For an overview about objectives, fields of application and advantages of CFD simulations of biomass combustion plants and actual model developments see:

For references concerning CFD-based plant development see:

http://www.bios-bioenergy.at/en/references.html

What is CFD?

CFD (Computational Fluid Dynamics) is the spatially (and temporally) resolved simulation of flow and heat transfer processes. Flows may be laminar or turbulent, they may be reactive or occur in a multiphase system. CFD simulations thus constitute an excellent tool for process analysis as well for the design and optimisation of plants.

Basic principles and general conditions

CFD simulations are applied to solve problems in various areas, for example in the automobile and aircraft industries, the biomedical industry, electronics cooling, in chemical engineering, for turbo machinery, in combustion processes, in heat and power generation, and for heating and cooling pipes. In the field of energy technology CFD is being increasingly used for the optimisation of gas and oil burners as well as for pulverised coal furnaces.
CFD modelling of biomass combustion and gasification plants is especially difficult due to the complexity of the processes involved in the thermal conversion of solid biomass, as well as due to the turbulent reactive flow in the combustion chamber or the gasification reactor, respectively. BIOS, in co-operation with researchers of Graz University of Technology, Institute for Process and Particle Engineering, has successfully developed a CFD model especially designed for the development and optimisation of biomass grate furnaces, boilers and fixed bed gasification plants. The CFD model consists of an in-house developed empirical grate combustion model complemented with modified and lab-scale tested CFD sub-models (FLUENT code) for the turbulent reactive flue gas flow in the combustion or gasification reactor. The applicability of the CFD model, as well as the reliability of simulation results were tested at pilot-scale and industrial-scale furnaces.
The long-standing continuous co-operation of BIOS with various research institutions, such as the Institute for Process and Particle Engineering of Graz University of Technology and the Austrian biomass competence centre ‘BIOENERGY 2020+’ ensures that the employed models are kept at the forefront of scientific developments.

Goals of CFD-aided plant development

The goal of a CFD-aided plant development is an efficient technological development and conception of plants aided by a spatially and temporarily resolved simulation and visualisation of the processes in biomass combustion and gasification plants. The objectives in detail are:

For combustion plants:

  • Efficient mixing of unburned flue gas with re-circulated flue gas and efficient air staging ==> improved CO burnout, NOx reduction
  • Improved mixing of unburned flue gas with secondary air ==> efficient CO burnout, reduction of furnace and boiler volumes
  • Improved utilisation of furnace and boiler geometries ==> efficient CO burnout, reduction of furnace and boiler volumes
  • Reduction of local velocity and temperature peaks in order to reduce material erosion and ash deposit formation
  • Sensitivity analyses as a basis for the optimisation of plant control
    (e.g. influence of load, water content and air staging)

For gasification plants:

  • Optimisation of the gasification agent and the reactor geometry in order to achieve an as complete as possible gasification and low tar contents in the product gas
  • Optimisation of flow and temperature distribution in gas cleaning units
  • Assessment and optimisation of the combustion of product gas

Advantages of CFD-based plant design

CFD-based plant design brings the following advantages:

  • Reduced emissions
  • Increased plant efficiency
  • Smaller plant design
  • Increased fuel flexibility
  • Reduced material wear
  • Increased plant availabilities and operating hours
  • Reduced consumption of operating agents for SNCR units
  • Reduction of development times and costs for test runs
  • Increased reliability of plant development
  • Improved basic understanding of the processes taking place in combustion or gasification reactors

Services of BIOS BIOENERGIESYSTEME GmbH

BIOS BIOENERGIESYSTEME GmbH is an engineering company highly experienced in the field of CFD simulations of plants for thermo-chemical biomass conversion and offers the following simulation services:
CFD-based development and optimisation of plants, CFD-based monitoring (test runs plus accompanying CFD simulations) of biomass combustion plants and boilers in the small (furnaces fired with pellets, wood chips and wood logs, as well as stoves), medium and large scale:

  • Design and optimisation of
    • fixed bed and grate furnaces
    • wood log fired boilers
    • wood log fired stoves
    • pellet stoves
    • pulverised fuel furnaces
  • Design and optimisation of boiler geometries (including convective sections: resolved geometry of boiler tubes for small-scale plants and using a heat exchanger model for medium and large-scale plants)
  • Design and optimisation of nozzles for the injection of re-circulated flue gas
  • Design and optimisation of nozzles for the injection of secondary/tertiary air
  • Optimisation of air staging
  • Optimisation of pressure losses in order to support fan design
  • Reduction of local temperature peaks by cooling the combustion chamber and optimisation of operating conditions
  • Prediction of zones prone to erosion and ash deposit formation
  • Modelling of the formation of ash deposits and fine particulates in biomass fired boilers
  • Calculation of heat transfer in and the influence of deposits (slagging and fouling) on biomass fired boilers
  • Calculation of particle residence times using different methods (Lagrange and Euler) for the optimised design of primary combustion zones (NOx reduction via primary measures) and secondary combustion zones (flue gas burnout), SNCR and additive injection systems
  • High temperature equilibrium calculations for the evaluation of ash melting behaviour
  • Reduction of emissions (carbon monoxide, nitrogen oxides, fine particulate emissions)
  • Calculation of the precipitation rates of fly ash particles and ash vapours in various plant zones
  • Investigation/optimisation of the operating conditions of furnaces and boilers with regard to efficiency, plant availability, partial load operation and fuel flexibility

Further CFD applications:

  • Application of furnace models to waste incineration plants
  • Simulation of biomass gasification plants
  • Simulation of rotary cement kilns
  • Calculation of heat and pressure losses in pipe networks (e.g. district heating)
  • Simulation of cyclones (particle precipitation, erosion tendencies)
  • Simulation of filters and particle separators
  • Air conditioning simulations in boiler houses and industrial plants