GB1587023A - Clinker material including pulverised fuel ash - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO CLINKER MATERIAL INCLUDING PULVERISED FUEL ASH (71) We, CENTRAL ELECTRICITY GENERATING BOARD, a British Body Corporate, of Sudbury House, 15 Newgate Street, London, EC1A 7AU, do hereby declare the invention, for which we pray that a patent may be granted to us,' and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a clinker material formed from fused pulverised fuel ash (P.F.A.).

Methods have been proposed in the past for utilising P.F.A., which is a material available in large quantities, for example from coal burning power stations, to form a lightweight aggregate by a sintering process.

P.F.A. particles are very fine particles, typically spheroids of 5 microns to 100 microns diameter, and, to form a material which can be usefully employed as an aggregate, it is known to pelletise the material and add a suitable clinkering agent.

One of the problems heretofore has been that the pellets tend to disintegrate due to the thermal shock in the sintering process. It is one of the objects of the present invention to provide an improved form of clinker material including P.F.A. and a method of making such material.

According to the present invention a method of making a clinker material comprises the steps of mixing dry P.F.A. with sewage sludge, the mixture containing 30 to 70% by weight of dry P.F.A, the balance being sewage sludge, forming pellets of the mixture, and then sintering the pellets in a furnace utilising the combustible components of the pelletised material as the source of heat.

Sludge available from a sewage works, after dewatering, commonly contains about 70% of water by weight and has a calorific value of approximately 4000 BtU/lb. (9.3 x 106 J/kg). The P.F.A. particle acts as an absorbent for the high percentage of water in the sewage sludge. The sludge forms a binder. Typically it has a fibrous structure of length 5 to 20 microns together with trace quantities of fibres of much greater length.

Because of the compatibility of the two materials, they can readily be mixed and pelletised using conventional pelletising technique, for example, by putting the mixture in a tilted drum which is rotated.

Water may be added if necessary to assist the mixing and pelletising operation. The pellets build up in this process which can be stopped when the pellets are a suitable size, for example of 5 mm. to 50 mm. diameter.

It is preferred to use 40 to 60% by weight dry P.F.A. with the balance of sewage sludge. The optimum mix may be found empirically and may typically be equal quantities by weight of P.F.A. and sludge.

In the optimum mix, there is no need to add further water, the water content of the sludge being sufficient to enable the pellets to be formed.

The pellets formed as described above are sintered in a furnace. Use is made of the heat of combustion of the combustible material present in the original sludge. The furnace may have heating means for initiating the reaction when starting up but it has been found that external heating is unnecessary once the sintering temperature has been reached. The initial deformation temperature of ash fusion of P.F.A. is in the range of 1050"C to 1150"C. Commonly sewage sludge contains of the order of 3% by weight calcium oxide which has been added as lime to assist settling in the final stage of the sewage treatment works.The calcium content of the sewage sludge reduces the initial deformation temperature by about 50 C. Such temperatures are readily reached by the self-combustion of the sludge components. The sintering process can continue until the combustion is com- plete.

This process produces an agglomerate of clinker material which may be used for example as an artificial lightweight aggregate in the manufacture of building blocks or lightweight concrete or for other constructional purposes. The aggregate may also be utilised for other purposes, for example, for horticultural uses, e.g. hydroponic cultivation systems.

The invention furthermore includes within its scope a clinker material produced by the above described process.

The following is a description of one example of the invention.

Equal weights of dry P.F.A. and sewage sludge were mixed in a pan mixer. The sewage sludge was sludge as available from a town sewage works with water partially extracted by means of a filter press. The water content of the sludge was about 70% by weight. This sludge contained about 3% by weight of calcium oxide arising from the addition of lime in the sewage treatment.

The P.F.A. consisted mainly of alumina, silica and iron oxide and had a particle size of the order of 5 to 100 microns diameter.

The mixture was transferred to a tilted rotating drum mixer constituting a pelletiser. It was not necessary, with this particular example, to add further water but water can be added at this stage if there is insufficient to give satisfactory mixing and pelletising.

In this rotating drum mixer, the P.F.A.

sludge agglomerated to form pellets and mixing was continued until these pellets ranged in size from 5 to 50 mm. diameter.

Analysis of pellets from the mixer showed an ash content of 57% by weight and water 30% by weight. The calorific value was 1290 BtU/lb. (3.0 x 106 J/kg).

These pellets were then transferred to a sintering furnace having a grate with gas burners for initial heating to the required ignition temperature. When the pellets started to burn, the oil burners were turned off and combustion was allowed to continue. After combustion was complete, the pellets were found to have fused into an agglomerate of clinker material having a density of 1200 Kg/m3.

WHAT WE CLAIM IS: 1. A method of making a clinker material comprising the steps of mixing dry pulverised fuel ash with sewage sludge, the mixture containing 30 to 70% by weight of dry pulverised fuel ash the balance being sewage sludge, forming pellets of the mixture, and then sintering the pellets in a furnace utilising the combustible components of the pelletised material as the source of heat.

2. A method as claimed in claim 1 wherein the sewage sludge contains about 70% of water by weight.

3. A method as claimed in either claim 1 or claim 2 wherein the pellets are formed by putting the mixture in a tilted drum which is rotated.

4. A method as claimed in any of the preceding claims wherein the pellets are of 5 mm. to 50 mm. diameter.

5. A method as claimed in any of the preceding claims wherein the mixture contains 40 to 60% by weight of dry pulverised fuel ash with the balance of sewage sludge.

6. A method as claimed in any of the preceding claims wherein the mixture contains equal quantities by weight of dry pulverised fuel ash and sludge.

7. A method as claimed in any of the preceding claims wherein the sintering process is continued until the combustion is complete.

8. A method of making a clinkermate- rial substantially as in the hereinbefore described example.

9. A clinker material produced by the process of any of claims 1 to 8.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. plete. This process produces an agglomerate of clinker material which may be used for example as an artificial lightweight aggregate in the manufacture of building blocks or lightweight concrete or for other constructional purposes. The aggregate may also be utilised for other purposes, for example, for horticultural uses, e.g. hydroponic cultivation systems. The invention furthermore includes within its scope a clinker material produced by the above described process. The following is a description of one example of the invention. Equal weights of dry P.F.A. and sewage sludge were mixed in a pan mixer. The sewage sludge was sludge as available from a town sewage works with water partially extracted by means of a filter press. The water content of the sludge was about 70% by weight. This sludge contained about 3% by weight of calcium oxide arising from the addition of lime in the sewage treatment. The P.F.A. consisted mainly of alumina, silica and iron oxide and had a particle size of the order of 5 to 100 microns diameter. The mixture was transferred to a tilted rotating drum mixer constituting a pelletiser. It was not necessary, with this particular example, to add further water but water can be added at this stage if there is insufficient to give satisfactory mixing and pelletising. In this rotating drum mixer, the P.F.A. sludge agglomerated to form pellets and mixing was continued until these pellets ranged in size from 5 to 50 mm. diameter. Analysis of pellets from the mixer showed an ash content of 57% by weight and water 30% by weight. The calorific value was 1290 BtU/lb. (3.0 x 106 J/kg). These pellets were then transferred to a sintering furnace having a grate with gas burners for initial heating to the required ignition temperature. When the pellets started to burn, the oil burners were turned off and combustion was allowed to continue. After combustion was complete, the pellets were found to have fused into an agglomerate of clinker material having a density of 1200 Kg/m3. WHAT WE CLAIM IS:

1. A method of making a clinker material comprising the steps of mixing dry pulverised fuel ash with sewage sludge, the mixture containing 30 to 70% by weight of dry pulverised fuel ash the balance being sewage sludge, forming pellets of the mixture, and then sintering the pellets in a furnace utilising the combustible components of the pelletised material as the source of heat.

2. A method as claimed in claim 1 wherein the sewage sludge contains about 70% of water by weight.

3. A method as claimed in either claim 1 or claim 2 wherein the pellets are formed by putting the mixture in a tilted drum which is rotated.

4. A method as claimed in any of the preceding claims wherein the pellets are of 5 mm. to 50 mm. diameter.

5. A method as claimed in any of the preceding claims wherein the mixture contains 40 to 60% by weight of dry pulverised fuel ash with the balance of sewage sludge.

6. A method as claimed in any of the preceding claims wherein the mixture contains equal quantities by weight of dry pulverised fuel ash and sludge.

7. A method as claimed in any of the preceding claims wherein the sintering process is continued until the combustion is complete.

8. A method of making a clinkermate- rial substantially as in the hereinbefore described example.

9. A clinker material produced by the process of any of claims 1 to 8.