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Process simulation of circulating fluidized beds with combustion/gasification of biomass

Objective



Objectives of the project

Circulating fluidized bed (CFB) is the latest generation of the reactors and is supposed to be the most promising technology for furnace capacity above 10 MW. The project addresses physical and chemical processes in CFB boiler/gasifier furnaces. The partners are from different fields of coal conversion, fluidization and bioenergy. The collaboration promotes a fast development of biomass thermoconversion technologies.

There exist a number of serious technical challenges facing the increasing market for production of heat and especially power from biomass combustion/gasification. Alkali-ash deposition and emission, tar emission, fairly high NOx emission for future strict legislation, low quality (LHV and impurities) of product gas and high cost construction/operation/maintenance of biofuel plants due to size limitation are the most severe issues with respect to boilers/gasifiers. In order to solve these problems, a model-building consortium is formed to simulate the steady state behaviour of the furnaces of atmospheric CFB boilers/gasifiers. This consortium includes boiler manufacturer, Kvaerner, an European transnational corporation. The prospective simulation model is directed at medium scale biofuel plants larger than 10 MW. It is supposed to suit small scale units and to be easily extended to use in pressurized cases in the future. Both agriculture and forest biomass, such as pinup eucalyptus, salix, cork tree, maize, straw etc. are considered, which are typical biomasses in European countries. The common important issues described above will be treated. The simulation model is evaluated against tests on a 12MW commercial CFB Boiler at Chalmers and a 0. 1MW biomass pilot-scale CFB gasified and on larger full-scale unit of 40 or 50 MW of the industrial partner if the former validation is successful.

Technical approach

Mathematic modelling has been proven as an efficient method to advance our know-how in a systematic way, and together with experimental data, create efficient tools for R&D and engineering work. The main body of the project is building up an integrated mathematical model based on available rich knowledge gained from the research of solids fuel combustion/gasification, and also based on measurements for providing necessary data input to the model. The model consists of the following aspects: fluid-dynamics of multiphase flow, and gas, solids mixings, heat transfer, combustion/gasification processes in the boilers/gasifiers, alkali compounds deposition & emission, tar and NOx NH3 HCN emissions.

The model will be evaluated in commercial/pilot CFB boilers/gasifiers. The resulting model will give the following computations: solids volumetric concentration profiles, heat transfer coefficient on the boiler membrane-wall, furnace temperature profiles, composition (including NOx and combustible) flue gas from the boiler furnaces, LHV and composition (including NH3, HCN, and Tar contents ) of gas from the gasifier furnaces, alkali-ash melting phase diagram, deposition rate and gas phase content.

Expected achievements

Physical and chemical mechanisms behind alkali-ash deposition and emission, formation and destruction of tar and NOx in combustion gasification processes will be better understood, right approaches to the solution of the knotty problems and emission reduction can be found,

Furnaces can be designed and constructed appropriately for different conditions and operating conditions including ash return, fuel preparation etc. can be varied appropriately according to the product of interest by using simulator,

Tar content will be reduced and LHV will be increased by CFB intensive reactions and more effective control of temperature distribution and optimal operation conditions,

an increasing amount of alkali laden agricultural biomass will be allowed to burn in CFB by optimal design and control of operating conditions together with additive addition,

The European industry will be provided with competent engineers capable of understanding and solving the highly complex and interdisciplinary problems facing the combustion/gasification of today and tomorrow,

Standardisation of characteristics of biomass fuels on an international basis will be achieved with respect to conversion technology and the operation conditions,

A theoretical basis is set up for reducing failures & cost in demonstration and for developing new technology.

Funding Scheme

CSC - Cost-sharing contracts
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Coordinator

Mitthögskolan
Address
2,Gaengviksvaegen 2
871 88 Haernoesand
Sweden

Participants (10)

CHALMERS UNIVERSITY OF TECHNOLOGY
Sweden
Address

412 96 Göteborg
CONSEJO SUPERIOR DE INVESTIGACIONES CIENTIFICAS
Spain
Address
1,Plaza Del Praíso 1
50071 Zaragoza
ENERGIDALEN I SOLLEFTEAA AB
Sweden
Address
9,Överste Hallströms Väg 9
881 52 Sollefteae
INSTITUTE OF MECHANICAL ENGINEERING AND INDUSTRIAL MANGEMENT
Portugal
Address
174-214,Rua Do Barroco 174/214
4465-591 Sao Mamede De Infesta
Kvaerner Pulping AB
Sweden
Address

402 75 Göteborg
NATIONAL TECHNICAL UNIVERSITY OF ATHENS
Greece
Address
42,28Th Octobriu 42
10682 Athens
SCA Graphic Paper AB
Sweden
Address

85188 Sundsvall
UNIVERSIDAD COMPLUTENSE DE MADRID
Spain
Address
S/n,avenida De La Complutense S/n Ciudad Universitaria
28040 Madrid
University of Leeds
United Kingdom
Address
Woodhouse Lane
LS2 9JT Leeds
Universität Gesamthochschule Kassel
Germany
Address
3,Kurt-vossel-strasse
34109 Kassel