Many western sewage systems and plants have been in operation for at least 30 years, and some for considerably longer than that. This being an area which has not historically received much in the way of attention, probably because this has to be one of the least glamorous operational areas for pumping equipment, and also because government agencies typically control the budgets, allocation of funding for modernization is not high on the list of spending priorities.

This is a mistake as there are substantial savings to be made from modernizing the pumping systems within ageing sewage plants.

A typical modernization plan will involve three stages, depending on the type of sewage plant in operation, though the principles will usually remain the same.

Stage One – Optimizing Efficiency

Older sewage pumping plants typically use belt-driven cavity pumps with a direct drive version. Optimal efficiency is achieved not by adjusting the speed of the pump but by controlling the operating times to maximize capacity. Optimal capacity is also achieved with greater effectiveness as replacement direct drive pumping systems are used with motors with a higher energy efficiency (for best results, use EFF1 – Energy Efficiency Class 1). By using power effective motors, the increased cost of acquisition is almost immediately offset by the lower energy consumption.

Maintenance cycles are increased and costs reduced by moving from belt driven systems. Replacing a belt can almost be as costly as replacing an entire motor, and downtime is drastically reduced. By re-routing pipelines and introducing optimal design, pumping power can also be reduced as distances traveled are shortened, sometimes allowing pumps to be dispensed with entirely.

Stage Two – Optimization Through Frequency-converter Control

A similar exercise to stage one is conducted, only this time dealing with the excess sludge which is produced. Belt-driven units are replaced using frequency-converter control which will operate around the clock as sludge is directed to biological clarification systems.

There is an opportunity to introduce EFF1, power efficient motors to reduce energy consumption (typically by 10 to 15%). There are also the savings from increased reliability and decreased maintenance cycles as there are fewer mechanical components associated with them. Repair and replacement is conducted at a much faster speed, minimizing downtime and costs.

Stage Three – Final Optimization Phase – Pump Modernization

Typical installations will utilize progressing cavity pumps for the chamber filter press which separates water and solids from the sewage slurry; the solid is removed as a “cake” with the liquid component being processed further. Older installations will also use only one charge pump which leads to issues of availability during downtime and there being a failure of redundancy.

Replacing the progressing cavity pump with two pumps working together will improve efficiency and redundancy. Efficiency is improved despite two pumps being used because firstly, the original charge pump can frequently be re-engineered to fit the new design which avoids the associated cost. By simplifying the twin-charge pumps, the need to carry spare parts is also reduced.

Summary

Sewage disposal and recycling plants are typically older installations which have expanded by ad hoc additions and re-design. In many instances, pumping solutions are no longer operating efficiently and there are substantial savings in terms of operating efficiency, energy savings, maintenance savings and improved capacity and redundancy to be gained by modernizing the pump system.

Author Bio: Lawrence Reaves works with Colfax Corporation, a leading provider of fluid handling equipment such as crude oil transfer pumps and commercial marine pumps. Colfax Corporation can be found online at: ColfaxCorp.com or at their blog ColfaxCorp.com/Blog .

Category: Society
Keywords: sewage plant,sewage plant modernization,pumping systems,sewage pumping,sewage pumping plants