Hermon Pumps Control Installation

Hermon Pumps Control Installation
Client: Dwr Cymru Welsh Water
Station Name and Location: Hermon Sewage Pumping Station
No of Pumps and Installation type: Submerged in Wet-well
Operating Arrangement: Duty/standby
Date of Arfon Rewinds Installation: June 2012

 

Background

Hermon SPS was built in 1991 and is a network station serving the village of Hermon (North Wales) and its surrounding area. Located on a main sewer, it receives flows of unscreened domestic and commercial raw sewage and rainwater / storm water run-off from the village with a population in the region of approximately 200. The liquid media is transferred by the installed submersible pumps via the main pipeline, which is a distance of approximately one mile to the Malltreath Treatment Works. This includes an elevation of 50 meters.

The station has a consented flow of 15 litres/sec which must be achieved during storm conditions and, if necessary, for extended periods.

Hermon DWF No: 1 FailureLike many sewage pumping stations today, Hermon receives large quantities of fibrous material [rag] and other non-specific debris transported by the inflow, which must be pumped forward to the treatment works. This material has a history of both partially and entirely blocking the pumps, a situation most prevalent during storms and high incoming flow conditions.

To ensure that the pumps remained operational and the station continued to pass forward its consented flow; avoiding spillage into the near brook, Arfon Rewinds Operations and maintenance engineers would manually unblock pumps, sometimes for several days continuously.

With the obvious consequences of losing an operational pump due to blockage, plus the man hours expended clearing debris from impellers and volutes, partial blockages could remain for many running hours, limiting hydraulic performance, rendering the pumps inefficient, consuming excess electrical power.

 

Solution

With the main objective of alleviating the regular blockages and its associated consequences, two new N-type Flygt pumps were installed to replace the failing Flygt channel pumps along with new variable speed inverter drives, which were integrated into the existing station control.

Arfon Rewinds’ engineers took ownership for the design, installation and commissioning, which included modifications to the instrument, control and motor starter circuitry.

 

Hermon Sewage Pumping Station Data

  • Pump Type: ITT Flygt 3202.091 30kw
  • Impellor Type: ITT Flygt N-Type
  • Number of Pumps: Two (2) off
  • Variable speed Drives: Yes
  • Pass Forward Flow: 15 L/sec

 

System functionality had to provide the following key features:

  • Maintain a duty flow of 15ltrs per second
  • Clear free solids passage of 140mm
  • Improved blockage detection
  • Improved energy efficiency via inverter control

 

Before and After VSD install
Calculations

To determine an accurate performance benchmark all pumps and the wet well itself was cleaned and examined at the commencement of the project. Incoming flows and passed forward flows were calculated after carrying a series of drop tests during dry weather.

Further pressure testing was carried out on both pumps to determine the correct performance curve. Arfon engineers worked closely with ITT Flygt application engineers to ensure the correct product selections were made.

 

Method of Work and Risks

  1. Method for the project:
    • Hermon Wet WellArfon engineers to mechanically install new pumps and discharge pipework in wet well area
    • Arfon Rewinds Installed and integrated VSD Drives on existing station control.
    • Setup of VSD drives to run on existing pump units.
    • SLD Pump Ltd set up temporary over-pumping arrangement to manage flows.
    • GEWS Tankering Services provided further contingency for managing flows.
    • New pump units were commissioned on new VSDs and tests carried out on each unit.
  2. Risks Eliminated:
    • No dry weather failures leading to pollution.
    • High number of reduced manual lifting of pumps.
    • High number of callouts

 

Results and Environmental Efficiencies

Variable Speed DriveArfon Rewinds’ engineers undertook commissioning tests to determine the most efficient speed setting for the required flow and therefore minimise the power used to move the required volume of liquid. Results showed a reduced running current of 11 amps per phase, giving a reduced energy saving of approximately 20%.

In the preceding 12 months no pump failures had been recorded resulting in operational savings from reduced callouts and no required operator intervention for clearing blockages.

A reduction in pump speed also reduces operating temperatures, thus reducing wear on pump components such as all rotating components, increasing mechanical seal life cycle, increasing maintenance intervals and prolonging asset life.