Pilot-Scale Industrial Tests on the Use of Ash from Tomsk GRES-2 in Expanded Clay Production
Abstract Generated abstract
Pilot-scale industrial tests evaluated the use of finely dispersed ash from the Tomsk GRES-2 hydraulic ash dump as an additive in expanded clay production at the Tomsk Plant of Building Materials and Products. Dried ash, added at 15 to 20 percent of the raw granule mass before the drying drum, reduced granule moisture, formed a surface ash layer, improved thermal stability, and contributed residual carbon during firing. Compared with ordinary granules, the ash-treated material showed lower bulk density, reduced sintering into clusters, improved swelling, a higher proportion of coarse fractions, and reduced fuel-oil consumption, indicating that power-plant ash can improve product quality and process performance under the tested conditions.
Full Text
Pilot-Scale Industrial Tests on the Use of Ash from Tomsk GRES-2 in Expanded Clay Production
V. M. Vityutin, T. G. Leontyeva, A. V. Vityutin, G. G. Vergun,
B. A. Utkin, V. A. Lotov
Utilization of finely dispersed ash from thermal power plants is one of the most important problems. The present report considers the results of testing additions of ash from Tomsk GRES-2 in the production of expanded clay at the Tomsk Plant of Building Materials and Products.
The main shortcomings of the known standard method for producing expanded clay are, on the one hand, excessive destruction of the raw material in the drying drum owing to the low mechanical strength and low thermal stability of the raw pellets, caused by the high moisture content of the raw material, and, on the other hand, sintering of the expanded expanded-clay granules into cluster-like aggregates in the firing kiln as a result of the comparatively low melting temperature of swelling clay materials. Both of these shortcomings lead to deterioration in the quality of expanded-clay gravel and to a noticeable reduction in the productivity of installations in terms of finished product.
As preliminary laboratory studies have shown, introducing finely dispersed ash into the drying drum makes it possible to improve the quality of expanded clay and to increase the yield of finished product by mitigating the destructive loads during disintegration of the molded raw material.
When wet raw material is pelletized in a bed of ash, the latter plays the role of a water-absorbing medium, which leads to a reduction in the moisture content of the raw material and an increase in its thermal stability. In addition, the presence of residual carbon in the ash helps create a reducing atmosphere in the firing zone and, consequently, increases the swelling—
swelling capacity of the granules.
The pilot-scale industrial tests were carried out as follows. Fine-dispersed ash from the Tomsk GRES-2 hydraulic ash dump was dried to a residual moisture content of approximately 1.5–3%. Dry ash, in an amount of 15–20% of the weight of the raw expanded-clay blanks, was fed onto the conveyor belt (directly onto the raw granules) ahead of the drying drum. The drying regime remained unchanged.
After the drying drum, samples of granules were taken (10 minutes before the start of the experiment, samples of ordinary granules were taken). The moisture content of the ordinary expanded-clay granules was 9.7%, while the moisture content of the ash–expanded-clay granules was 8.3%. On the experimental ash–expanded-clay granules after the drying drum, the thickness of the surface ash layer was measured (under a microscope). It ranged from 0.8 to 2.2 mm.
The effect of adding ash was very clearly observed visually from the condition of the layer of granules in the swelling zone. The angle of rise of the layer increased sharply. During firing, an increase in temperature in the granule swelling zone was noticeable (the temperature of the exhaust gases increased from 960 to 990°). At the same time, a decrease in fuel-oil consumption was observed, which is explained by the presence of unburned coal in the ash. No sintering of granules into clusters was observed.
Comparative characteristics of ordinary expanded-clay and experimental ash–expanded-clay granules are given in the table.
Table
| Bulk density (average kg/m³) | Compressive strength | Class | Grain composition, % | Grain composition, % | Grain composition, % | Grain composition, % | ||
|---|---|---|---|---|---|---|---|---|
| 40–20 mm | 1–20 mm | 15–10 mm | 10–5 mm | |||||
| Experimental campaign No. 1 | Ordinary granules | 550 | 21.7 | B | 30 | 5 | 20 | – |
| Experimental campaign No. 1 | Ash–expanded-clay granules | 425 | 19.6 | A | 81 | 19 | – | – |
| Experimental campaign No. 2 | Ordinary granules | 780 | 59 | B | 11 | 70 | 1 | 18 |
| Experimental campaign No. 2 | Ash–expanded-clay granules | 450 | 21.0 | A | 69 | 31 | – | – |
The reduced quality of ordinary expanded-clay granules in trial campaign No. 2 was caused by an increased feed of raw material. When this feed was reduced, the effect of introducing ash, as was to be expected, proved still greater. Owing to the presence of residual carbonaceous matter in the ash and the creation of a weak reducing atmosphere, the swelling of the granules improved. The amount of fines decreased, and the strength of the granules increased.