Objective
The production of CaO in the first instance for the building material industry at a competitive rate by making use of :
a) Limestone fractions which are too fine to burn in conventional kilns and therefore availble at a very competitive pricelevel.
b) Ashes from conventional power plants, which contain still a certain percentage of unburnt coal.
An installation has been completed comprises the following sections :
- storage and supply of limestone
- storage and fuel supply
- the calcining unit and auxiliary equipment: this consists of a furnace and cyclone separators in series and a syphon connected in a circuit in which the material circulates. This circulation is maintained by a gas stream generated by blowers.
The main accessories are :
- a venturi heat exchanger, forming part of the circuit and in which the limestone is injected so that heat transfer is direct
- a valve regulating the extraction of calcined product from the circulating bed
- a fluid-bed heat exchanger-cooler, subdivided into a number of sections in which heat is recovered from the end product and returned to the circulating bed system (by means of heated air) for final cooling.
For the finishing of the final product a 70 T/h wind sifter and 12 T/h ball mill is installed behind the calcining furnace. The wind sifter separates fine and coarse particlesat 90 um. Coarse fraction will be ground to fine pieces and returned to the wind sifter.
The burning of the waste in a circulating fluid bed ensures that NOx and SO2 emissions and dust, are very low. The use of coal residues in sand-lime brick results in a low leeching (e.g. of arsenic) alkaline-bound product. At a concentration of 5.2 % CaO in the end product, fly-ash concentration will amount to +/- 11.5%. Running over 4000 production hours has shown that the plant will supply 200,000 T/y of limestone.
The circulating fluid-bed is suited to the processing of high carbon and/or lime content coal residue, when calcining fine grain limestone. These limestones are available in large quantities of waste which cannot be processed in conventional shalft or rotary furnaces.
Tests have demonstrated that while the carbon in the ash is almost completely burned out, the energy recovered may be used for calcining. Limestone compounds contained in the ashes from the static fluid bed is suitable for use as a basic raw material. The system, as far as temperature and residence time are concerned, is adjustable with a high degree of flexibility. As a result the quality of the fly ash/lime is controllable.
The carbon-free mixture has proved to be an excellent binding agent for application in lime compounds (e. g. sand-lime bricks). Flue-gas waste heat is used for pre-drying of wet waste material. The innovatory aspect of the project is the application of the lime-burn process in a circulating fluid-bed using energy containing carbon residues.
The heart of the plant is a circulating fluid bed furnace with a capacity of 25T/h input feed material. A distinction is made between the feeding of wet or dry material. Wet feeding takes place above the furnace to make use of the heat, and dry feed is fed into the furnace at lower levels. Transport of the final product is by the use of a fluid bed heat-exchanger. This is constructed in such a way that the primary combustion air is preheated through the incorporated heat-exchanging surfaces. Part of the heat is transmitted to the secondary combustion air by means of direct heat exchange. Combustion gas is carried off by an air-air heat exchanger, suitable for dust-loaded gases, to a cloth filter plant.
Topic(s)
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
6104 Koningsboch
Netherlands