Ministry Of Defence, British Army


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Introduction

In 2003 the British Army was faced with the need to make secure, independent, potable water provision for forces stationed overseas in potential combat areas. In addition need was urgent and required fast track manufacturing of robust and reliable plant. 5 mobile reverse osmosis units were required complete with pre‑treatment. To facilitate transport by standard military vehicles each plant was built into 2 standard 20’ ISO Containers.

Fast tracking

From confirmation of order the first 2 plants were delivered to the Army in 7 weeks and commissioned under simulated conditions in the UK. The 3rd and 4th plants followed 2 weeks later and the final one in 10 weeks from order.

Operating Circumstances

The raw water supply for the units could be from almost any source including inland surface water (lakes or rivers), boreholes or seawater. It was anticipated that mains power would rarely if ever be available due to the remote locations they were expected to be used in and so mobile generators would be used to power the plants. The units therefore needed to be designed with maximum flexibility and energy efficiency in mind.

Feed water description Raw Water Characteristics Operating Pressure Overall Recovery Rate Output
Feed Flow m³/h 23m³/h N/A N/A N/A
TDS <1,000ppm 4 Bar 100% (pre & post treatment only) 550m³/d
TDS <3,000ppm Up to 10 Bar 80% 440 m³/d
TDS <10,000ppm Up to 40 Bar 50% 275
TDS 10,000-45,000 Up to 80 Bar 30~45% 160~245 m³/d
Temperature °C Up to 40°C N/A N/A unchanged
Suspended Solids Up to 10ppm N/A N/A NIL

Description

1st Container Pre Treatment and Cleaning:

  • Duty / Standby sand filter feed /backwash / CIP pumps each rated 23m ³/h @ 4 bar
  • 2 x 50% sand filters for suspended solids removal. Each 1.2m diameter giving 10m/h filtration rate.
  • 1 x 100% carbon filters for free chlorine / trace hydrocarbons removal - 1.8m diameter giving 6 minutes contact time.
  • 1 x 5 micron Cartridge filter
  • 1 x CIP Tank. (feed pumps double up as CIP Pumps).

2nd Container - Reverse Osmosis / Post Treatment:

  • 1 x sulphuric acid dosing set.
  • 1 x antiscalant dosing set.
  • 1 x 100% Positive displacement high pressure pump rated 23m³/h @ up to 80 Bar complete with pulsation dampers and 75kW motor. This pump operates at fixed speed, fixed flow and variable pressure.
  • 5 x RO Pressure Vessels each containing 5 x seawater RO membranes.

Post treatment Equipment:

  • 1 x Remineralisation Vessel.
  • 1 x Sodium Hypochlorite dosing set.
  • 1 x MCC / Control panel incorporating Allen Bradley PLC.

Flexibility of Operation

In cases where the plant was to be operated on municipal or other good quality, low TDS water supplies an RO by pass facility was provided connecting the pre-treatment container directly to the post treatment processes of the 2nd container.

The RO High pressure manifolds were arranged in such a way (using spectacle plates that the array could be operated as a 3-stage, 2-stage, or a single stage array optimising recovery on low or mid range TDS feed waters.

On feedwater up to 2000TDS the array could be operated as a 3 stage (2:2:1) array at up to 80% recovery. On higher TDS feedwater – up to 20,000TDS – the array would be changed to a 2-stage (3:2) array allowing recovery of up to 65%.

Above 20,000TDS all 5 tubes would be arranged in parallel (single stage), allowing up to 40% recovery.

Once the operating regime was set up the operator would choose the exact operating recovery percentage at the HMI and thereafter the plant would operate fully automatically.

These plants have operated with great success from May 2003 to date although 2 have now been returned to the UK and are on standby for future deployments.

Project Details

Client: Ministry Of Defence, British Army

Industry: Sand and Carbon Filters, Reverse Osmosis

Application: Drinking Water Reverse Osmosis

Technologies