Control Circuit For Wet Limestone Grinding Systems and Slaking Systems in Flue Gas Desulfurization process

Liming Minerals combines the experience and expertise of Kennedy Van Saun (KVS) and MPSI to become the world’s leading supplier of grinding systems for FGD applications. Our experience record is unrivaled with over 230 of these systems installed worldwide.

Liming offers both ball mills and the vertical mill (also named VERTIMILL™) for limestone grinding and lime slaking. Our traditional horizontal ball mill produces a consistent and highly reliable product within a closed circuit. The VERTIMILL™ presents our latest technology for FGD grinding applications. Introduced over 20 years ago, the VERTIMILL’s™ proven design provides an efficient alternative for your reagent preparation. This vertical stirred grinding mill can save up to 30% on your energy costs, has lower installation and operating costs, and operates at a reduced noise level.

Our ECO-SYSTEMS team is a group of highly competent personnel who specifically address your FGD reagent preparation needs. They understand your need for equipment which provides dependable, round-the-clock service coal-fired power stations and industrial plants require to comply with established SO2 emission standards.

Liming offers specialized services in the areas of design, analysis, and education for grinding systems. Our engineers design quality equipment for process optimization. Our test laboratory is available to aid in the development of your initial process circuit design. Additionally, it can be used for testing various reagent material sources to obtain reliable grindability data and to evaluate the variations in grinding performance. Our field engineers provide mechanical troubleshooting expertise and supervision for installation, operation, or maintenance assistance. Factory training for operators and maintenance staff can be scheduled on site at initial installation or at any time to upgrade the efficiency of your FGD reagent preparation system.

Control Circuit For Wet Limestone Grinding Systems

The control circuit of a wet grinding system controls the delivery of ground limestone slurry, on demand, to the product slurry tank from one or more grinding mills. Control methods range from manual to fully automatic utilizing Programmable Logic Controllers (PLC) or complete Distributive Control Systems (DCS).

In the automatic mode, the grinding system is controlled by the slurry level in the reagent product storage tank and the mill discharge sump. When the product tank reaches high level, the feeder stops; after a time delay, the clutch de-energizes; the mill stops grinding; feed water is shut-off; and the slurry valves are placed in the recycle position allowing the circulating load and product to flow through the piping into the mill sump tank. When the product storage tank reaches low level, the grinding system automatically starts and operates until the tank reaches high level. In a two-mill system, the product tank low-low level sends a signal which starts the standby mill.

The quality of the ground product is controlled automatically by monitoring and regulating the density of the slurry solids delivered to the cyclone classifiers. Particle size analysis of the cyclone overflow, typically 90-95% minus 325 mesh (44 microns), can be monitored continuously. By doing so, the operator has the necessary information to minimize reagent usage and maximize scrubber efficiency.

Liming Slaking Systems

The economics and technology of a particular FGD system may indicate that lime should be used instead of limestone. The lime is converted to milk-of-lime by slaking (i.e. by reacting the lime with an excess amount of water, above and beyond the stoichiometric requirements). The milkof-lime is used to treat the exhaust gas stream.

Liming offers slaking systems utilizing ball mills or the VERTIMILL™. The VERTIMILL™ operates in open circuit, while the ball mills normally include a separate classification system to control particle top size.