Очистные сооружения и очистные сооружения
Sludge Treatment and Purification Plants remove the harmful substances in wastewater through active or activated sludge processes so that the water can be recycled and reused. However, a by-product of these processes is a semi-solid waste commonly known as thickened sludge which needs to be either disposed of or further recycled for use in other industries such as Anaerobic Digestion Plants or Fertiliser Production Plants.
As new processes and technological advancements are being made, there has been a reduction in the moisture content within thickened sludge meaning that the % content of dry matter is getting higher and proving more difficult to pump round the various treatment stages.
This thickened sludge also tends to have adhesive properties and often plasticises which means that conventional pumping technologies often struggle to transfer these products, leading to high costs as parts wear quicker, as well as, the affiliated costs of loss of production and plant downtime.
Typically Progressing Cavity Pumps or Rotary Lobe Pumps are typically regarded as the go to pump types for the above applications as they can handle large solids. However, these pumps have a rotating element, so will experience high levels of wear and many plants are consequently seeing high levels of Stator & Rotor / Lobe and Seal replacements.
The solution for pumps experience high wear?
A Peristaltic Pump can vastly reduce the cost of spares, the interval between failures and therefore increase plant efficiency and reliability for customers.
Peristaltic Pumps slowly compress the outside of the hose to move products through the pump. The operating principle of a Peristaltic Pump ensures that no particulates are trapped between the walls of the hose and the external rotating shoes, instead the particles will be held back for the next compression.
The speed of rotation employed in this type of pump technology is often a tenth of that used in Progressing Cavity or Lobe Pumps which means the wear experienced by the hose is also substantially less.
As you can see from the diaphragm above, the only part of the pump that comes into contact with the fluid is the hose, meaning the cost of stocking spares is drastically reduced. The simplicity of maintenance is also very popular with Maintenance Engineers as the heavy lifting machinery and extra manpower required when servicing Progressing Cavity Pumps, isn’t necessary for Peristaltic Pumps.
As Peristaltic Pumps are sealless by design they therefore don’t need complicated and often expensive sealing systems to combat fluid attack or leakages caused by dry running as they can be run dry indefinitely.
By virtue of their design they are also one of the best pumps for suction lift applications (up to 9.8 m vertically) which also means that they can be employed in areas often not suitable for traditional Self-Priming Pumps (typical max. suction lift of 6m).
High Volumetric Efficiency (+/- 0.5%) for Peristaltic Pumps is also maintained whereas this decreases over time for Progressing Cavity and Lobe Pumps due to the intrinsic wear of the stator / rotors within these pumps during use.
An Anaerobic Digestion Plant contacted Tapflo UK to reduce the amount of Stator wear, clogging & dry running they were experiencing on a Vertical Immersion Progressing Cavity Pump they had installed in one of their digester feed tanks. They inherited the pump from their plant installation company and didn’t have any lifting arrangements on site to remove the 5 m long pump from the tank.
As a result, every month or so, when the stator became too worn, they had to hire a crane to lift the pump out of the tank and replace the stator, this totalled approximately £7000. The customer purchased a 4” Peristaltic Pump which was positioned on the top of the tank and the casing for the old Progressing Cavity Pump was used as a suction lance. The plant not only experienced trouble-free operation and increased capacity but they also only had to replace the hose once a year, totalling a cost of approximately £1500.
Evacuation of Tanks
Another common problem that many plants face in the Water & Wastewater Industry is the evacuation of tanks, sumps & pits which contain fluids with elevated temperatures, solids in suspension and chemically aggressive additives. These are typically waste by-products of production lines and need to be pumped away for treatment or removal.
Traditional Submersible Pumps are not always suited to these applications as they use the water they are submerged in to cool their motors, therefore, if the fluid is higher than the recommended maximum temperature of 40ºC, the motors can overheat and fail.
Furthermore, aggressive chemical additives can have a detrimental effect on the integrity of the motor supply cables which presents a further risk of failure as well as a health and safety problem for operators.
Additionally, Surface Mounted Self Priming Pumps can also be troublesome in these applications as they are generally not recommended for priming fluids over 60ºC as the fluid can start to evaporate in the suction pipe causing the pump to dry run and cavitate which results in expensive damage to the pump’s impeller, casing and mechanical seal.
What is the alternative to emptying tanks without a submersible pump?
Two options to help handle tank, sump and pit emptying could be the Vertical Sump Pump or Cantilever. These types of pumps feature an extended shaft design which enables them to be installed into tanks, sumps & pits up to 6 m deep.
The motor is kept at the surface and therefore outside of the process media, enabling them to be used on fluid temperatures up to 200ºC! The pumps are also sealless, meaning they can be dry run indefinitely and can be fitted with Closed, Semi-Open, Channel and Vortex Impellers. As a result, they can also be used for anything from clean to fluid with solids.
Figure 4 - Vertical Immersion & Cantilever