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THE COMBUSTION OF COAL SHALE

Objectif

To use a fluidized combustor developed by CERCHAR to increase thermal efficiency of waste shale from 2,500 to 5,000 Kj PcI/Kg. The combustor has a grill surface of 18 m2 and will produce steam at a rate of 15 T/h at 30 Bar, 300 C. The project also aims to demonstrate the technical viability of the technology, and, in particular, to:
. optimise the various component units, especially of the fluidizing
medium;
. establish operational parameters;
. establish automatic control mechanisms.
The project will meet the requirements of an industrial site and totally or partially replace a coke oven gas operated boiler. Superfluous gas will be more effectively used for the synthesis of amonia, representing energy savings of 7,000 TOE/y.
Plant assembly was completed during June, 1985. Plant commissioning began in March 1985. The following preliminary tests took place prior to firing and were completed as of June 1985, except tests on the regulating system:
. wiring inspection;
. process inlets and outlets;
. sequential tests and simulation of regulating systems;
. no-load testing of all equipment;
. checks following completion of assembly.
First shale combustion started in the third quarter of 1985.
An equivalent continuous night noise level of 51.5 dB (A) was measured prior to operation, the admissible limit being 60 dB (A). Drying of refractories proceeded in July 1985 and the first shales were burned as soon as drying was completed.
The first quarter of 1986 saw the final seting-up of the installation, adaptation of equipment and modification to basic procedures.
For example. abolition of gas injection in the fluidised grill meant that the temperature increase in both preheating burnerscould be guaranteed. Bed temperature could also be controlled in the event of combustion falling below self-ignition level. The use of burners also allows for finer regulation of combustion temperature.
However, handling difficulties with solids, and with cyclone operation have prevented continuous operation with black shales.
Essentially, the handling problem relates to the double screw feeder: this will not operate in a full pan hopper, and trials are being carried out to perfect a new mechanism. Emptying and re-cooling of ashes has also revealed handling problems with transporters and elevators. Ashes congealing on the internal partitions caused problems related to water tightness and blocking of the cyclones. As a provisional solution, and to increase the amount of the time fines spend in the reactor, a feeding spout was fitted to deliver solids to the fluidising bed and, if successful, will become a permanent feature.
Other trials involved raising bed height and were carried out to set a temperature of +/- 800 deg.C in the fluidising bed and a longer residence time. Additional trials on a hot model are to be carried out to gain information on the influence of pressure on cyclone operation. Tests were also carried out to determine the level and nature of dust in the gas, particularly at boiler entry and exit.
Work over the reporting period, was completed by analysis of raw shale samples and calcinated shale, mainly to follow changes occurring in raw materials throughout the handling process and in the ahes on the return circuit.
The project is currently in the final phase with the first shales burned in December 1985. Certain technological difficulties persist and improvements are being effected to bring about satisfactory and continuous industrial operation.
The 15 Mwth demonstration unit at Drocourt in Northern France, is the country's first for fluidized bed combustion of low calorific value coal shale.
The installation is capable of accepting various qualities, washed but otherwise untreated or prepared in any particular way. Initially the plant is comprised of the following:
. a fluidized bed calcinator of 4.8 m dia. and 18 m2 in cross-section at
the grill;
. cyclones;
. a heat recuperator for exhaust gas;
. a final scrubber.
Constructed by Framatome and based on the Cerchar process, it was conceived on the basis of a fluidization reactor equipped with a Cerchar pyramid and syphon grill, operating with shale of up to 10 mm. Fluidized bed temperature is between 850 C and 950 C, obtained by shale combustion with at least 20% excess air.
Reactor temperature is adjusted by :
. water injection, or;
. injection of coke oven gas;
. the addition of other solid fuels;
. variation of excess air.
Exhaust gas is passed through hot cyclones the introduced into a recuperation boiler for steam production used at the Drocourt factory. The gases are vented to the atmosphere after treatment in a bag filter. Hot ash extracted from the base of the bed is cooled in a counter-current cooler: recovered heat is used to increase steam production.

Appel à propositions

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Régime de financement

DEM - Demonstration contracts

Coordinateur

CERCHAR (GEGS)
Contribution de l’UE
Aucune donnée
Adresse
RUE DE LA BAUME 33
75008 Paris
France

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