Planetary gears help solve long-term odour problem
Anyone working in the UK waste water treatment industry will be familiar with the type of problems faced by Yorkshire Water at the Saltend Waste Water Treatment Works, where long-standing issues around odours disturbed the local community, most notably during the peak load season through the summer.
Announcing an investment of £30m to address these issues last October, Yorkshire Water’s improvement works are now complete – with Brevini UK being awarded a contract. For this major project, Brevini was commissioned to work on the Morgan Sindall Sweco joint venture, specifically to replace the original EIMCO rake drive system in the lamella tanks – a significant part of the whole waste water treatment plant at Saltend. With a very tight timescale, Brevini had only an 8-10 week turnaround to cover concept, design, rapid pricing, manufacture and installation on site, for a solution that would interface with existing kit at the plant.
Brevini was ideally-placed to work on such a demanding project, both in terms of engineering expertise and the breadth of the company’s product portfolio, meaning it was able to consider a number of potential solutions, before specifying and installing the final drives.
As a general rule, applications in the water industry tend towards high output torque and low (or very low) output speed requirements, which make planetary drives the optimal solution. The major exceptions to this would normally be aerators and Archimedian screw drive units but, even here, a planetary solution is suitable for a large proportion of the low-medium power ranges. Brevini offers both helical and planetary gear solutions, as well as a unique hybrid gear unit – the compact Posiplan range – which features a final helical gear stage, and one or more planetary or spiral-bevel input gear stages, and the option to fit a labyrinth oilseal.
For the Saltend project, most gear unit suppliers would consider providing a simple gear unit as a replacement – particularly given the very tight turnaround from commission to completion – as this would minimise the risk of problems with specification, design and manufacture, with an in-line planetary unit seeming the most obvious selection. However, the gear unit is only a small part of the system. There would have to be an output coupling of some form, selected to transmit the output torque required, plus supporting steelwork (which would need access ports to allow bolting the coupling). Also, it is more problematic to fit a labyrinth seal to these units, and a standard oilseal could leak lubricant into the process. Given these requirements, the apparently simple planetary solution begins to look increasingly expensive.
Drawing on its extensive experience in this sector, Brevini was able to offer a solution to cover all application requirements, on time and in budget. The Brevini drive arrangement was deemed to be far more efficient, generating the required output from a much smaller prime mover. The Brevini drive has an electric motor, a planetary gear unit, a final-stage slew-pinion and bearing, plus supportive steelwork. With no separate method of torque limitation or monitoring specified, Brevini proposed to utilise the motor supply current as the generator of the torque level. While this is, technically, the least accurate position, the total combined drive efficiency of 86% is an improvement over the original drive. Brevini offered this option in part due to the application requirement, where a normal torque-limiter wouldn’t have been suitable, in case the system might stall or be disengaged.
Once Brevini’s solution was approved, the new drives were installed safely to MS2JV requirements – delivered, installed, completed and works-tested ahead of schedule. Reflecting on the project, Andrew Baggaley, aftermarket manager at Brevini UK, commented: “We’re delighted with the success of this project. With an original brief that had a very tight deadline for completion, we needed to look at a novel solution for replacement and improvement of the original drives.
“Given the nature of the project, working with hazardous gases and other safety concerns, we worked to the highest safety standards, and the highest standards of PPE. That we were able to improve on the original specification, while still delivering ahead of schedule, is testament to the expertise of our engineers and the breadth of our range of products.
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