Best Valve Solutions for Handling abrasive and corrosive Lime Slurry
Lime is used by a large majority of the chemical process industry in either a powder or liquid form. Especially in coal fired power plant and Waste incineration power plant. Engineering and maintenance personnel often face a lot of problems before find the best on-off or control valve to handle lime slurry.
Limestone is mined from a quarry in the form of calcium carbonate (CaCO3). Then the carbon dioxide is burned off (calcining) to make calcium oxide (CaO).
calcium oxide (CaO) is ground into powder in a tower mill, a spiral classifier, or a slaker. The lime milk is used for many industrial purposes including pH control, power flue-gas cleansing or Flue gas desulfurization, calcium extraction in pharmaceutical manufacturing, and other applications. One of the most common uses of lime in the chemical process industry is pH control.
Lime slurry is extremely difficult to handle in piping systems, instrumentation, and valves because its particles are very jagged and will not dissolve, but rather merely suspended in solution. Any cracks or crevices will cause the lime particles to fall out of suspension and fill these voids. Lime further aggravates this situation when it hardens in these collection points. The lime changes its state to a solid mass of material 鈥?commonly referred to as scaling. Scaling causes a pipeline's inner diameter to become smaller and smaller. Material buildup on valve seats and other surfaces can cause the valves to freeze in position.
Tips for Lime Service
Process equipment, instrumentation, and valves selected for use in lime slurry systems should limit cavities, cracks and void areas. Even a small collection point of lime can cause equipment failure and countless hours of downtime and maintenance.
The ideal product to supplement lime slurry should be able to clean itself and break apart scale. It should also be completely free of void spaces, cracks, and cavities. A piping product installed in a lime slurry system should be full port in order to limit obstruction and potential lime slurry buildup.
An oversized actuator may improve performance while decreasing downtime as a result of sticking valves, but it will not solve all related maintenance problems. Because lime is very abrasive, it affects most ball and plug valves severely. A hard material cover such as advanced ceramic ball valves will help protect the valve against the abrasive nature of lime.
The seats also are a major concern. Again, high hardness ceramic seats are most likely the best alternative in lime applications. Ceramics seated sealing will perform better in scaling substances because they have the ability to scrape built-up material off the ball surfaces.
Most polymeric seats will not maintain durability over time in lime slurry. The scaling that occurs in these valves is like a wrecking ball to most polymeric seats. The ball or plug with scale buildup is turned through these seats, usually resulting in a short lifetime. Because ball and plug valves have cavity areas that house the ball or plug, a substantial amount of material accumulates in this void area over time. It is beneficial to install flushing ports in the valve so that the body cavity area can be cleansed water to wipe out material accumulation after each cycle. This process will help minimize material buildup in the cavity area.
It is expensive to build a ball or plug valve with the all of the previously mentioned features. The cost of a ball or plug valve equipped with these features can be five to six times the price of a traditional Teflon-seated ball or plug valve. Unfortunately, however, the performance of most Teflon-seated ball or plug valves in lime slurry is less that satisfactory.
Many manufacturers and valve users try to force their standard valves into applications in which they do not belong. Obviously, a large process plant tries to standardize products as much as possible in order to cut costs with spare parts and personnel training.
Some of Foyo鈥檚 customers tried to use soft seated ball valves or butterfly valves, but finally these valves are damaged quickly and only serviced for a short period.
It's proved that ceramic ball valves are the best choice for abrasive lime slurry.