SLAKING THE LIME REMAINING IN THE PARTIALLY DESULPHURATED ASHES FROM A COAL FIRED BOILER

Ziel

The Provence power station, located in Gardanne (30 km North of Marseille), burns the coal mined in the adjoining colliery to generate electricity. Due to the flame desulphuring device incorporated in the 600 MW generator (Unit 5), which began functioning in 1984, the ash removed from the boiler has a higher than average lime and sulphate content. Further, if the ash is unsaleable (to concrete or cement manufacturers), the power station will, in the medium term, be faced with the problem of stocking the waste product.
The aim of the planned project is, in fact, two-fold :
- reduce the stockpiles containing the ash removed from the power station,
- upgrade the ash for use as a cement additive.
The innovative feature of the project lies in slaking the quicklime contained in the ash while retaining the hydraulic capacities of the ash.
The process is specifically connected with:
- coal that produces ashes with a particularly high calcium sulphate content,
- flame desulphurization in the boiler, resulting in a high Ca/S ratio and, consequently, in excessive calcium that is subsequently found in the quicklime present in the fly ash.
The process is dependent on thoroughly mastering the pressure and temperature parameters required to achieve selective hydration of the quicklime in water in the liquid phase, while preventing total hydration of all the ash components, so that the product retains its hydraulic setting qualities and can be used as a binding material.
The function of the industrial pilot plant will be to investigate various types ash. The experience and know-how resulting from the trials will be applied by Charbonnages de France to other projects worldwide.
The extinguishing unit has already provided knowledge on the following aspects:
- the mass effect is irrelevant for the extinguishing process, up tothe size of the autoclave (3 tonnes),
- the flow of water into the autoclave has to be tuned with the speed of the malaxor,
- the rotating speed of the malaxing device has to be kept between precise limits to avoid projections inside the autoclave or poor mixing.
Trials have shown that no additives are required for improving the slaking procedure. Possibilities for applying the slaking procedure to other types of ash (in particular FBC) will be investigated when this type of ash is available with a high quicklime content.
The data and know-how resulting from the tests will be applied to designing an industrial size plant for treating 300000 tonnes of raw ash per year.
The highly satisfactory results have ensured the ability of the process to produce an hydraulic binder for cement.
The project is designed to implement a technique for slaking ash using heat and pressure in order to achieve hydration of the lime and non-hydration of the calcic silicates and aluminates that provide ash with its pozzolanic properties.
The project is also aimed at defining an industrial plant capable of treating up to 300000 tonnes of ash per year without running the risk of the ash solidifying during hydration.
The plant will function with the ash removed from Gardanne power station's Unit 5 generator. The industrial pilot plant has been built close to the existing storage piles on the site of the Unit 5 power station.
Slaked ash will be stocked in one of the smaller storage piles on the site.
This unit is make up of :
- a 425 tonnes storage pile; ash will be supplied via one of the existing high capacity storage piles (14500 cu.m capacity).
- a 4 cu.metre spring balance mounted bin for controlling the amount of ash injected into the autoclave.
- an 11 cu.metre autoclave equipped with :
. a 90 kW capacity, three-blade variable speed mixer,
. dual casing for circulation of a heated, pressurized fluid,
. a sphere designed to function at high pressure and temperature in a steam atmosphere,
. an auxiliary reservoir designed to function at high pressure and temperature to guarantee the equipment remains safe at high pressure,
- an 11 cu. metre spring balance mounted reception bin for the slaked ash, affording effective control of the autoclave emptying operations,
- a pneumatic conveyor unit for the slaked ash, equipped with:
. 3500 cu.metre per hr. 22 kW installed capacity, Trepaud air dryer,
. a 150 kW installed capacity conveyor air compressor,
. an automatic keyboard/screen control centre in the slaking unit.

Programm/Programme

ENG-THERMIE 1 - Programme (EEC) for the promotion of energy technology in Europe (THERMIE), 1990-1994

Thema/Themen

7.6 - ULTRA-CLEAN COALS AND WASTE MANAGEMENT (WM)

Aufforderung zur Vorschlagseinreichung

Data not available

Finanzierungsplan

DEM - Demonstration contracts

Koordinator

HOUILLERE DE BASSIN DU CENTRE ET DU MIDI

EU-Beitrag

Keine Daten

Adresse

UNITE D'EXPLOITATION PROVENCE BP 1
13590 MEYREUIL
Frankreich

Gesamtkosten