Hartlepool Water


Download Image

Introduction

ACWA have supplied a high capacity water treatment system to feed industrial pure-water users within the Greatham and Seal Sands area of Teeside. The system comprises a fully automated and centralised high rejection (HR) reverse osmosis (RO) system. This is connected via a 12 kilometre ring-main to supply Hartlepool Power Station and Huntsman. RO permeate supplied to Huntsman’s North Tees site is then demineralised using the latest mixed bed ion exchange technology in an additional water treatment facility. The system is linked with the nearby AWS RO system installed by ACWA at Huntsman Tioxide.

Description

The centralised design was specified by AWS in order to provide the most economical solution for current requirements but also to allow extra customers to be connected to the high-purity RO permeate ring-main supply in the future. The RO design for the new plant is based on the proven ACWA plant supplied in August 1999 and installed at Huntsman Tioxide. ACWA were selected by AWS to design, build, install, commission and maintain the new system because of their proven track-record of high quality and responsive process contracting in the membrane systems field, with over 10 years experience in UK and overseas water sectors.

The water source is a chlorinated mains supply from Anglian Water’s Dalton Pearcy Water Treatment Works in Hartlepool. This supply is relatively high in hardness and alkalinity, the maximum required feed flow to the centralised facility is 410m³/h. The RO system comprises four streams of identical equipment each rated to produce 82m³/h of pure water. The existing Huntsman Tioxide site has three further identical 82m³/h streams providing an output of 246m³/h with the whole providing a total output of 574m³/h.

Sodium bisulphite is dosed into the mains supply in order to neutralise residual free chlorine present. Dedicated dosing pumps are provided for each stream of RO in order to maintain the correct neutralisation dose of sodium bisulphite.

WATER QUALITY PARAMETERS

Each RO stream is controlled by its own control panel, driven by a PLC with local operator interface. Routine monitoring of the plant allows effective preventative maintenance to be planned and implemented by ACWA’s service engineers. This ongoing after sales service minimises operating costs and maximises membrane life and plant reliability.

The ACWA RO design works with the control system maintaining a fixed feed flow from the high pressure pump via a variable frequency drive and mag-flow meter. A second control loop maintains a fixed reject flow using a modulating valve and mag-flow meter. As the osmotic pressure of the feed supply changes due to natural variations in temperature and concentration, and as the HR RO membranes gradually foul and scale, the flows are maintained, the feed pressure being automatically adjusted to ensure a constant high-quality permeate supply. The gradual fouling and scaling of the RO system results in the need to clean-in-place (CIP) the membranes. A fully integrated and installed CIP system utilises specialist acid and alkali based chemicals, diluted with permeate and heated to 40°C, as part of the semi-automated CIP sequence. Water for Huntsman North Tees is further tested by mixed bed demineralisation ion-exchange technology using a new system installed at their site by ACWA and fed directly from the ring-main. The plant comprises three 50% streams of ion exchange followed by two 50% streams of cartridge filtration acting as a resin trap in the unlikely event of resin leakage.

The mixed bed vessels contain a combination of cation exchanging and anion exchanging resin. The cation resin has H+ ions attached that are readily exchanged for cations such as calcium and magnesium in the RO permeate fed to the plant from the centralised facility. The anion resin has OH – ions attached, to be exchanged for anions such as sulphate and chloride. The resulting H+ and OH– ions released from the resin combine to form water. The treated water produced is extremely pure with a conductivity of less than 0.2µS/cm.

The plant is normally regenerated on ‘volume throughput’ with the backup of on-line conductivity monitoring and
‘time elapsed’ adding to operator flexibility in optimising the system.

The regeneration is undertaken automatically one steam at a time on one of the three vessels utilising hydrochloric acid, caustic soda, treated water and air. Bulk storage facilities for the regeneration chemicals are provided with measure tanks installed local to the vessels. Diluted hydrochloric acid (HCL) is then passed upwards through the cation resin and diluted sodium hydroxide (NaOH) is passed downwards through the anion resin. The combined flow exits at the cation-anion resin interface via a common collection system and is transferred to the waste neutralisation system. The HCL regenerates the cation resin with H+ ions whilst the NaOH regenerates the anion resin with OH– ions. Following rinsing the vessel is put back on-line and the regeneration is complete. Demineralised water is transferred to Huntsman North Tees’ storage facility.

Project Details

Client: Hartlepool Water , Teeside

Industry: Reverse Osmosis and Ion Exchange

Application: Production of Ultra Pure Water

Technologies