LIME SLAKING SYSTEMS
Lime slaking is the process of converting quicklime to hydrated lime (CaO + H20 -> Ca(OH)2) with the use of water. This chemical reaction is an exothermic reaction which denotes that during the reaction, heat is expelled from the slurry which produces some steam.
Hydrated lime is used for raising the pH level, or neutralising acidic solutions, of processes within the mining and heavy industries. Hydrated lime can be purchased in dry form to be mixed into a slurry but is only economical at lower usage. With high usage of Milk of Lime (MOL) slurry it warrants capital expense upfront with large amount of savings during the life of the plant.
BHT lime slaker systems are designed and manufactured to ensure long life and reliable service in the harshest of operating environments. Clear access and easy maintenance of the lime slaking systems are key to BHT design to ensure optimal up time of the plants and reduction in safety issues.
By working with BHT for the supply of your next lime slaking system you will enjoy the following benefits;
A tailored solution, engineered to suit customer specific site requirements,
Compliance to customer engineering and manufacturing specifications,
A consultative design process utilising the latest industry standards and guidelines for process control, Australian Standards and BHT proprietary design systems,
If requested, full turn key package of the lime slaking system
Provision of 3D models to allow convenient integration into overall plant layouts to ensure accurate interface and tie-in with piping.
Operator ergonomic considerations when handling the dry quicklime and equipment for maintenance.
Quicklime Slaking/ Grinding - Benefits and Features
Lime slaking systems are the integration of numerous pieces of bulk handling equipment all modified to correctly handle quicklime and MOL slurry. The MOL slurry that has correctly sized particles and the slaking temperature within normal limits, are outputs from a correctly designed, manufactured, and commissioned slaking plant.
Options and features typically included a slaking lime plant in order of process are:
Dry quicklime storage; bulk bag breaker or silo with dust collectors and level instruments
Heavy duty screw feeders or rotary valves
Suitably size vibrating conveyors
Stainless steel vortex feed bowl with flow control valves and instruments.
Roller mounted grinding ball mills
Detention type slaker
Robust rubber lined slurry pumps; transfer or dosing pumps
Lined hydrocyclone or cyclone bank
Suitably sized wet steam scrubber
Mix tank, with agitator and level sensor, designed if need to API650,
Fully programmed field mounted control panel, if requested, compliant to Australian standards
Guarding to Australian Standards AS4024
Lime Slaking Plant Design Focus
With lime slaking there are two factors that need to be critically controlled; method of water addition, and the extraction of steam.
There are two main supply points for water into the slaking circuit; before and after the mill.
The control ratio between water and quicklime before entering the mill, at the vortex feed bowl, is highly important that it be controlled so that the water flow is neither too high or low. Having the water flow too high will result in the chemical reaction "drowning" or slowing down, while having a flow too low will result in the slurry sticking to the feed pipe, blocking the vortex feed bowl, and eventually shutting down the plant.
The water addition point at the discharge of the mill is used to dilute the slurry to an acceptable figure, as required by the client. This water further cools down the MOL slurry which should have done the majority of the slaking within the mill.
Control of the water is provided by the use of flow control valves, mag flow meters, and pressure switches.
The ball mill has two primary functions within the quicklime slaking system; firstly the reduction of quicklime / hydrated lime into smaller particles critical to the correct reaction with process, and secondly provide a rotating vessel to allow majority for the chemical reaction to occur. The two processes enhance each others functions with the grinding increase the particle surface area for better chemical reaction while the chemical reaction breaks down the particles to small sizes.
Ball mills supplied by BHT are typically roller mounted mills varying from 0.5m to 2.2 meters diameter. If diameters larger than this are required, trunnion pinion mills can be supplied from 3rd party vendors as part of the package but this increases the pricing greatly and increases delivery period, hence it maybe more effective to supply multiple stream system with smaller mills and allowing redundancy. Dependant on the size of mill and throughput required, BHT supply mills with rollers manufactured from rubber tyres or polyurethane rollers.
The lifters and liners set of the mill are manufactured from specialised rubber suited to the chemical situation and the temperature produced within. These lifters are held in position using forged T-bolts through the shell of the ball mill.
Typically ball mills are supplied with automatic greasing system to ensure that the bearings are constantly purged and free of any contaminates.
The hydrocyclone is responsible for classifying the product discharged from the ball mill to ensure that the particle requested for the process is meet. Oversized material is rejected and funneled back to the inlet of he ball mill for regrinding, the undersize is discharged to the storage tank for use. The cyclone allows the mill size to be reduced by limiting the amount of grinding needed on already correct size particles.
The typical request particle size, p80, for MOL of is usually 75 microns but finer can be achieved. Do note that decreasing the microns will increase the mill size exponentially.