Ground quicklime

Ground burnt lime refers to ground quicklime used for agricultural liming. 

The manufacture of hydrated lime proceeds by the slow addition of water to cmshed or ground quicklime in a premixing chamber or a vessel known as a hydrator, both of which mix and agitate the lime and water. The amount of water added is critical. Too much water makes it impossible, or too cosdy, to produce the desired dry form too Httle water leaves hydration incomplete, causing degraded quaUty, namely, chemical instabiUty and stmctural unsoundness. 

Groundnut oil, in soap making, 22 735 Ground quicklime, 75 28 production of, 75 54-56 quality control for, 75 70 uses for, 75 61-62... 

The demand for various grades and qualities of ground quicklime has grown rapidly ever since the 1950s. Particle size requirements vary from relatively coarse products used for soil stabilisation (e.g. 99 % less than 2 mm with 50 % less than 75 pm) to very finely divided products for specialist applications (e.g. more than 99 % less than 50 pm). 

All grinding systems use air to convey the ground quicklime and, although part of the air is recycled, the remainder is purged via a bag filter to remove fines and heat. This inevitably leads to a limited amount of air slaking in addition to that which already occurs in the cooling zone of the lime kiln. Under typical conditions, the measured combined water may rise from 0.5 % in the feed to 0.7 % in the ground quicklime. 

The laboratory work leading to this development is described in [20.11]. Ground quicklime is used to avoid the need to classify the product. It is mixed with a water-methanol solution, the composition and volume of which provides sufficient water for the hydration reaction and sufficient methanol to remove, by evaporation, the heat of hydration (the boiling point of methanol is 65 °C)... 

Iron and steelmaking. As mentioned above, in many industrialised countries, the major use of quicklime, including calcined dolomite, is in steelmaking. While most of the lime is in granular form, modern developments require ground quicklime. Calcined dolomite is also used for the refractory linings of the vessels. 

Delivery costs often amount to 50 % of the ex-works price, depending on the distance and mode of transport. Screened products are mainly transported in bulk using tipper trucks, which are sheeted to exclude rain and to prevent dust emission. Ground quicklime and hydrated lime are transported in air pressure discharge vehicles. Such vehicles can also be used for screened products with a top size below 20 mm. Smaller quantities are packed in intermediate bulk containers of 0.5 or 11 capacity, and in paper sacks. 

Lime spreading. The lime may be ground quicklime, powdered hydrated lime or milk of lime. It is best spread mechanically to ensure an even, controlled distribution. Hydrated lime is sometimes used when the drying action of quicklime is not required. 

The ground quicklime is stored in a bunker and discharged through a similar mechanism to that described for hydrated lime (section 26.10.2). The quicklime is hydrated using either the drum, or the silo hydration process. 

In this process, the appropriate proportions of ground quicklime and sand are placed in a rotating drum. en the raw materials are thoroughly mixed, sufficient... 

Other factors. Other components in ground quicklime, such as calcium carbonate, silica, alumina and iron oxide can be regarded as inert. From the viewpoint of the aircrete producer, the key factor is not so much their level as their variability (as that is the main cause of variability in the CaO content). As an example, it is generally easier to control the calcium carbonate to within 1 % when the average level is 3 % than when it is 6 %. 

Table 27.1. Ground quicklime used for injection systems...

While most calcium aluminate cements are produced from limestone and alumina (see section 9.5), high purity, refractory-grade material is made by at least one producer using ground quicklime as the source of calcium. The quicklime and alumina are blended and fed to a rotary kiln, where they sinter and melt at over 1500 °C. The molten calcium aluminate (about 70 % AI2O3 and 28 % CaO) is cooled in a rotating cylinder to produce a clinker, which is subsequently ground to substantially less than 90 pm [32.6]. 

Calcium is produced by the thermal reduction of lime with aluminium. High purity ground quicklime and aluminium powder are briquetted and heated in a retort to 1200 °C at a pressure of 0.1 Pa or less. Calcium vapour is formed which is condensed in a cooled section of the retort [32.16]. 

A patented process, known as the DCR process, [32.34] describes the use of coated ground quicklime to disperse mineral oils and similar substances. The coating delays the hydration of the quicklime, which subsequently carbonates. Because the organic matter is finely dispersed, it is claimed to be biodegradable. The process is reported to be suitable for the treatment of contaminated soils and sludges. 

Quicklime s high affinity for water has resulted in its use as a desiccant for both gases and organic liquids. In some applications, finely ground quicklime is used. In others, the quicklime is mixed into a paste with an inert organic liquid and possibly other components. The paste is then formed into blocks or granules and the solvent removed by evaporation. 

Finely divided products, such as ground quicklime and hydrated lime, are loaded into air pressure discharge tankers for transport. A flexible chute is used, which fits the loading hatch of the vehicle, and incorporates an extraction hood connected to a vacuum filter system. The hood removes both displaced and conveying air emerging from the hatch. 

Ground quicklime refers to powdered products produced by milling. 

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