Fluidised bed circulating

This paper demonstrates the technical feasibility of a plastics energy recovery plant using circulating fluidised bed technology from Ahlstrom of Finland. Full details are given of a two-phase test run conducted at Ahlstrom s pilot plant in Karhula, in order to obtain information on the process behaviour when combusting different types of plastics waste. Results are presented and conclusions drawn. 

The use of plastics as an energy source was demonstrated on a commercial scale at ICl Materials plastics manufacturing site in Dumfries, UK. This paper covers the preparation and use of pre- and post-consumer plastics as supplementary fuels in a circulating fluidised bed boiler specially designed for co-combustion with coal. Full emissions data on the 15% mixtures of individual plastics with coal are given, together with calculations of thermal efficiencies. Measurements by an independent body (British Coal Research Establishment) confirmed that the co-combustion of coal and plastic reduces some emissions compared with coal alone. Thermal efficiencies of around 80% were achieved and this heat was used effectively during the production of plastics. 7 refs. 

Energy recovery from packaging waste is discussed, with particular reference to the co-combustion of mixed plastics with other conventional fuels such as wood, coal and peat. Experimental work is described in which a project was established to evaluate the possibility of energy recovery from a circulating fluidised bed boiler using packaging from different sources as fuel. The role of sulphur in the formation of PCDD/F in the combustion process was also studied. 

Lind, Terttaliisa. Ash formation in circulating fluidised bed combustion of coal and solid biomass. 1999. 79 p. + app. 88 p. 

The majority of continuously operated crystallisers are of three basic types forced-circulation, fluidised-bed and draft-tube agitated units. 

J.S. Xiang, P. Maijanovic, Hydrodynamic model of gas-solid flow in circulating fluidised bed, Proceedings of the 7th International Conference on Bulk Materials Storage, Handling and Transportation, Newcastle, Australia, October 2001, pp. 825-832. 

A.T. Harris, R.B. Thorpe, J.F. Davidson, Stochastic modelling of the particle residence time distribution in circulating fluidised bed risers, Chem. Eng. Sci. 57 (2002) 4779-4796. 

Circulating fluidised beds (CFBs) are attracting increasing interest for both gas-solid and gas-catalytic reactions however, the operating modes in these two cases are completely different. In modelling and designing... 

Sasol Sasolburg, South Africa Initially coal, currently natural gas Fused Fe/K Precipitated Fe/K Precipitated Fe/K (spray dried) Circulating fluidised bed Multi-tubular fixed bed Slurry phase reactor 1955-ca. 1985 1955 1 1993 J 5 000... 

Sasol Secunda, South Africa Mostly coal, now supplemented by natural gas Fused Fe/K Circulating fluidised bed SAS reactor 1980 1999 1995 160 000... 

B. J. Milne, L. A. Behie and F. Berrnti, Recycling of waste plastics by ultrapyrolysis using an internally circulating fluidised bed reactor. Journal of Analytical and applied Pyrolysis, 51, 157-166, (1999). 

ABSTRACT This paper describes the main characteristics of a biomass gasification gas sampling system designed and built-up at CIEMAT to characterise the emissions from an atmospheric circulating fluidised bed gasifier when doing research on coal and biomass gasification. 

The aim of the sampling system presented here is to take samples from a circulating fluidised bed gasifier at pilot plant scale (200 Nm /h of gases are released). This one has been extensively operated as a combustor and it has recently been revamped to operate as a gasifier. Different feedstocks tike oak chips, orujillo" (a residue from the olive oil making industry), etc. will be gasified in the first studies. 

Gasification to a bubbling or circulating fluidised bed of sand must be conducted at > 800°C in order to achieve a sufficiently fast gasification. At such temperatures, the low melting potassium salts in the straw ash were found to cause bed agglomeration and breakdown of fluidisation [12],... 

ABSTRACT Ttiis communication concerns the basic principles and formulation of a model for a circulating fluidised bed (CFB) biomass gasifier. The main problems are the lot of unknowns concerning the set of kinetic equations needed and the lack of data from commercial CFB biomass gasifiers to check the model. The reacting network to be used in the model is deeply analysed. It is concluded that a self learning or self Urning adaptive model is the best solution... 

Gas mixing in a pilot scale (500 kWth) air blown circulating fluidised bed biomass gasifier... 

Actual data of gas concentration profiles in a pilot riser reactor are reported by Jiang et al. They studied ozone decomposition in a catalytic circulating fluidised bed. By applying an UV detection technique they were able to measure strong radial and axial ozone concentration gradients in their experimental set-up. It was concluded that the ozone concentration profiles are consistent with the trend exhibited by the voidage distribution in both axial and radial direction. 

To study the gas mixing capacity of circulating fluidised bed (CFB) biomass gasifiers, radial and axial gas concentration profiles have been measured and interpreted in both a hot pilot scale biomass gasifier (100 kg/hr fuel) and a cold-flow set-up. The presented pilot plant data are unique in their sort and provide new insight in radial gas mixing in a CFB riser. 

Yang Y.L, Jin Y, Yu Z.Q, Wang Z.W, Investigation on the slip velocity distributions in the riser of dilute circulating fluidised bed, Powder Technology, 75,68(1992)... 

Yang Y.L, Gautam M, Mei J.S, Gas velocity distribution in a circulating fluidised bed riser, Powder Technology, 78,221 (1994)... 

Bader R, Findlay J, Knowlton, T.M, Gaa/solids flow patterns in a 30.5 -cm-diameter circulating fluidised bed, in CFB Technology II, editors Basu P, Large J.F. 123(1988)... 

Martin M.P, Turlier P, Bernard J.R, Gas and solid behaviour in cracking circulating fluidised beds. Powder Technology, 70,249 (1992)... 

Jansen M, Cold-flow circulating fluidised bed hydrodynamics (1999), MSc. thesis University of Twente... 

The biomass fuelled IGCC demonstration plant at Vamamo consists of a 18 MW pressurised circulating fluidised bed gasifier, a 4,2 MW gas turbine and a 1,8 MW steam turbine. The low heat value gas produced in the gasifier is cooled in a gas cooler and cleaned in a candle filter at a temperature of 350-400°C before it is combusted in the gas turbine. The flue gas from the gas turbine is used for the production of steam in the heat recovery steam generator. The steam is superheated, together with steam from the gas cooler, and supplied to the steam turbine. Besides electricity, 9 MW heat for district heating purposes is produced. 

During the gasification experiments in the Vamamo 18 MWg, pressurised circulating fluidised bed (PCFB), IGCC biomass power plant, the operational pressure and temperature were around 17 bar and 950 C, respectively. The filtering unit operated at a ten erature between 300 and 400"C A variety of commercially available... 

Lind, T., Kauppincn, E.I., Jokiniemi, J.K., Maenhaut, W., and Pakkanen, T.A., Alkali metal behaviour in atmospheric circulation fluidised bed coal combustion , The Impact of Ash Deposits on Coal Fired Plants, Ed. Williamson, J. Wigley, F., (1993) Solihull, Bimiingham, UK, pp, 77-88. 

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