ECS Engineering Services is to install a replacement screw pump at Wessex Water’s Avonmouth Sewage Treatment Works (STW), helping secure the capabilities of the facility for decades to come.
Avonmouth STW serves a population of about 1,000,000 people in Bristol and the surrounding towns and villages. One of its key pieces of process plant is a very large screw pump which has been in operation for around 40 years. However, it had become badly worn and effectively reached the end of its useful service life.
ECS was asked to inspect the screw pump and make some proposals for its overhaul or replacement. Jake Laughton, the ECS engineer who led the inspection says: “Much of the pump is in a serviceable condition and can be retained, however, the screw itself has reached the end of its life and needs to be replaced.”
At 21 tonnes, 20 metres long, 3.1 metres in diameter and able to pump 3,645 litres of water a second, the screw is simply enormous. ECS has arranged to have a new screw fabricated in Holland by long-standing partner company, Landustrie. Made in mild steel, a high-performance, corrosion resistant coating will give it a working life measured in decades.
“We have incorporated some important innovations,” says Jake, “including a stainless steel lower bearing, again made by Landustrie. This does not need an oil or grease feed, so is both ecologically sound and reduces the maintenance requirements – features that will pay dividends in the long run.”
The design team has evaluated the loading on the pump when it is in use and optimised all the new parts to lengthen the pump’s working life and maximise its efficiency and reliability.
Jamie Wesley, Operations Director at ECS states, “To be involved with machines of this size showcases the excellent capabilities available here at ECS, our screw pump experts have given the existing motor, gearbox and upper bearing a clean bill of health, which has helped to reduce the overall cost of the project for Wessex Water.”
MAGNA3 gets environmental certificate
In an industry first, our circulator pump now comes with an Environmental Product Declaration, documenting the product’s impact on the environment.
The footprints left by MAGNA3, in terms of energy consumption, chemical substances and emissions, have been detailed in an Environmental Product Declaration (EPD). It is the first time any pump manufacturer acquires an EPD in accordance with the European standard EN 15804.
“It is a very important step for Grundfos to be able to document towards our customers the environmental performance of our products in a standardised way,” says Mathias Høeg, Senior Life Cycle Assessment Specialist at Grundfos.
The third-party verified document, issued by independent assessors at the German Institut Bauen und Umwelt, communicates transparent, comparable information about the product’s life-cycle impact.
Having an EPD does not necessarily imply that the declared product is environmentally superior to alternatives. It simply provides facts, which are widely requested among Grundfos customers and partners.
“This area is becoming a hot topic here. As an example, with a strong focus on Nearly Zero Energy Buildings, the architect on an upcoming housing development project requires an EPD for the pumps,” says Mark O’ Sullivan, Sales Engineer at Grundfos Ireland in a sentiment echoed in various markets around the world.
More products in sight
The next step will be to obtain the EPD for even more products, which falls in line with Grundfos’ ongoing ambitions to deliver as energy-efficient and environmentally friendly products as possible and to do so in a transparent manner.
“Working with EPDs and life cycle assessment influence the way we develop new products. Environmental performance will be considered alongside other design criteria such as price and functionality. This is possible because environment as a term can now be measured and communicated in numbers and graphs,” explains Mathias Høeg.
Key questions for selecting a wastewater solids handling pump
If the liquid you’re pumping contains solids, there are a number of solids handling submersible pumps that might be appropriate for your application. To avoid clogs or burning your motor out, you need to make sure you have the right pump. There are key questions that help determine which pump will solve your problems. In this post, we’ll examine these questions so that you’re prepared when you talk with your provider.
What type of solids are you’re pumping?
Understanding the solids in your liquid helps your provider determine the right type of pump for your application. We’re focusing on wastewater, so we can assume your solids are not abrasive (abrasive solids would require a hard metal, agitator pump). Most likely, they are large and soft or long and stringy. You also need to know if the solids need to be reduced to go into your system or to discharge, or if you just need to pass them.
Large and soft solids generally need a shredder pump that will shear the materials before pumping. Long, stringy solids indicate that you’ll need a vortex pump that can pass the entire solid.
Understanding the type of wastewater is also helpful. These are generally categorized as municipal (including sewage) or industrial. While municipal wastewater is generally consistent among sites, industrial wastewater solids and contaminants often vary based on industry.
What solids loading can the pump handle?
There needs to be enough liquid either in the sump or in the system to keep solids moving with the liquid. Without enough water, the pump will clog and won’t be able to pass the solids. Most solids handling pump designs can handle approximately 5% solids by volume. If your wastewater has a higher concentration, you will likely need to add more water to the sump by changing the system to allow more water to accumulate in the sump or by adding more water to the process.
The sump pump basin size is also a factor. The basin should be sized to minimize the number of cycles per hour but cannot be so large that solids will settle instead of being brought into the pump.
How might your piping system affect the pump you need?
Understanding the design of your piping system will help your provider make sure there are no areas where the solids may settle, build up and cause clogs. This includes:
- Size of the Piping: It must be large enough to pass solids downstream, but small enough to maintain carrying velocity to prevent solids from settling out. We recommend carrying velocity of 5-7 ft./sec. for municipal wastewater applications. As the specific gravity of the solids increases, you may need to further increase the velocity to carry the solids.
- Vertical Lift: This is the height that water has to travel as it moves through your piping system. A significant vertical lift combined with an improperly sized pump can cause solids to recirculate and clog within the pump volute.
- Location of Check Valves: The check valves should be as close to the pump as possible. If too far from the pump or too high, solids can build up before reaching the valve. This causes clogging as the solids backflush into the pump. Adjusting the location of the check valve generally solves these issues.
In some instances, your provider may conduct an inspection. If the entire piping system isn’t visible, you may need to show the piping system plans or explain where and how far the piping goes. The piping connections and fittings are important too.
What is the required flow rate for your system?
The flow rate is the amount of liquid that runs through the system in a given amount of time. This and the pipe sizing determine the velocity needed to pass the solids downstream through the pipes. The flow rate also indicates the appropriate size your sump should be. An undersized sump causes the pump to cycle too frequently and burn itself up.
If you don’t know your flow rate, here are two options to help your pump provider determine it:
- Calculate the flow rate by performing a draw down test. With no water entering the sump, allow the current pump to run for as long as possible while recording the time in operation. The flow rate is the volume of liquid pumped (sump length x sump width x the change in liquid level from start to end of pumping cycle) divided by the amount of time recorded during the drawdown test.
- If you have the model number of your current pump, researching the pump’s performance curve combined with the piping system information or a pressure gauge reading in the system can help your provider calculate the flow rate.
Translating answers to the solids handling pump you need
The answers to these questions provides the information your provider needs to make a recommendation. The natures of the wastewater and solids determine the type of pump you need (i.e. shredder or vortex pump). The flow rate (and the amount of head in the system) indicates the specific pump model you need.
In addition, you may have unique circumstances to consider, especially when dealing with harsh environments. These are the types of situations in which BJM Pumps excels. We build submersible pumps to deal with rugged applications and have 35 years of experience helping customers dealing with the issues you deal with every day. Contact us or call us at 860-399-5937 to request more information or to initiate a personalized evaluation of your submersible pump needs.
New pump bearings save €28,970 per annum at energy plant
Faced with frequent failures on its centrifugal pumps for water recirculation, a large CHP (combined heat and power) plant in Romania asked NSK and its local distributor to perform an on-site pump bearings investigation. The outcome identified poor lubrication of the pump bearings as the source of the failures, with NSK recommending the adoption of sealed-for-life bearings featuring DDU seals and high-temperature grease. In total, the move has led to annual cost savings of €28,970, while simultaneously offering a significant improvement in performance.
Dreamstime Prior to switching to the NSK solution, the CHP plant was suffering bearing failures on its centrifugal pumps every three months. Analysis by NSK showed that oil was leaking from the bearings as a result of poor seal condition. With 30 pumps on site, the facility was spending a significant amount on replacement bearings, oil replenishment and maintenance. When adding the cost of downtime, it became clear that a new strategy was required.
The CHP plant asked NSK´s local distributor to assess the potential for improving the lifetime of the bearings. Considering the age of the equipment and the poor condition of the seals, a design modification to avoid the oil leaks was not considered. Instead, a trial using NSK DDU Sealed Deep Groove Ball Bearings filled with high-temperature grease was performed on three pumps. With no failures occurring after six months of operation, the decision was taken to adopt the NSK solution on all pumps. Following 12 months in service, zero failures have been recorded.
NSK´s DDU Sealed Deep Groove Ball Bearings feature high-quality, ultra-clean steel that is known to extend bearing life by up to 80%. Super-finished raceways are specially honed to minimise noise and improve lubricant distribution and life, while patented seals provide resistance to contamination in the toughest environments. Another advantage of this type of bearing is the pressed steel cage, where close-coined cage pockets and tightly controlled clearances reduce friction and ensure even distribution of the lubricant. The grease offers high temperature resistance and speed capability, with good resistance to water and contamination.
Ultimately, it is the elimination of downtime, maintenance and oil replenishment costs, as well as lower bearing costs, which have led to the calculated annual cost savings at the CHP plant.
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