NL1035564C2 - Hardened fly ash manufacturing method, involves mixing fly ash, lime and cement at elevated temperature, and granulating mixture into granules at high humidity after some time of storage - Google Patents

Abstract

The method involves mixing fly ash, lime and cement at elevated temperature, and granulating mixture into granules at high humidity after some time of storage. Binder, cement lime, and water are added to the granules and the granules are hardened.

Description

Process for producing fly ash-containing particles to be cured in air.

The invention relates to a particle-granulated mixture of fly ash and binder, lime and cement. The fly ash can come from a coal-fired power plant or from a household waste incineration. To prevent the product from tearing due to expansion of sulfur-containing compounds, the ash is mixed with lime and the required cement at elevated temperature in the presence of water. From the mixture, particles are rolled at a mixture moisture content of 22 to 26% by weight, which are then enveloped by a mixture of lower, 8 to 14%, moisture content. The granulate is stored in the air under humid conditions for some time, for example in an ash dump.

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Many methods for manufacturing fly ash-containing particles are already known.

In the Dutch patent 8200193, such particles are hardened at a temperature of 95 degrees Celsius in a silo.

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U.S. Patent 4,490,178 also describes granulate that is cured at temperatures between 85 and 212 degrees Fahrenheit.

In US patent 3192060 fly ash and lime hydrate-containing particles are encased in 3 to 5% cement. The hardening takes place in an autoclave or under atmospheric conditions.

In patent US 5,704,972 a mixture of fly ash, hydrate lime, water and another hydroxide is mentioned. The compaction takes place by treating a spread layer with a vibrating press.

Characteristic of the method according to the invention is the production of a core particle with 22 to 26% moisture by weight, which is enveloped by a mixture layer of low, 8 to 14%, moisture, which prevents particles from clumping so strongly during curing that separation into individual particles is not possible. For the formation of the wet particles, fly ash is mixed at high temperature with at least 1% by weight, calculated on the dry mixture weight, lime, 1035564 2 hot water and at least 5% cement, the mixture being steamed if necessary. Steaming also takes place in the storage silo, from which the mixture is dosed to an appropriate pelletizer. The formation of core particles takes place in a short time, after which a drier mixture is applied around the particles. The envelope layer can be of the same dry composition as the core material. The coated product is then cured at least for 25 days at the air temperature under humid conditions. Hardening can take place, for example, in the ash dump of a power plant. The fly ash 10 can be obtained directly from the coal-fired power plant, but landfill fly ash can also be processed in combination with the central ash. The method offers the possibility of converting landfill ash into a useful concrete aggregate as a substitute for gravel. If landfill ash also contains soil, then less water is needed to make the 15 core particles.

The amount of lime and the amount of cement are determined by the required strength of concrete, in which the particles will be used as a substitute for gravel. When the cement quantity is increased, the strength increases approximately linearly. The introduction of lime into the strength increase is only noticeable after long air hardening and is greater than that of cement. To achieve good grain strength within 25 days for the production of concrete mortar, granules are made with 20 kg of lime and 160 kg of cement.

1035564

Claims (4)

1. Process for the manufacture of air-cured granules, by mixing the necessary raw material mixture consisting of at least fly ash, lime and cement at elevated temperature, after which after some time of storage the mixture is granulated into granules of high humidity characterized in that in a later production phase this granulate is surrounded by a mixture of low humidity, containing at least ash in addition to binder, lime and cemen, and water. Method according to claim 1, characterized in that the moisture of the granulate to be coated varies from 22 to 26% by weight and the moisture content of the coating layer varies from 8 to 14%. Method according to claim 1, characterized in that the amount of lime is at least 1% by weight and the amount of cement is at least 5%. 20 Method according to one or more of the preceding claims, characterized in that ash is partly taken from an ash storage location. 1035564