 Alpheus designed, financed, built and operate an ultra pure water recycling plant which treats final effluent from a municipal sewage treatment plant using a combination of ultra filtration (UF) and reverse osmosis (RO) supplying the treated water for power generation.
Background:
 Until late 2000, the 380 MW gas turbine power station at Peterborough used mains water in its demineralisation plant for boiler-feed water production. This is a widely used process but there are significant costs associated with chemical regeneration of the de-min resins, rinse water, pumps and waste chemical and wastewater disposal. Alpheus approached the power station with a proposal to supply high purity water via an innovative membrane process, utilising sewage works final effluent as its raw water source.Process:
Following successful site trials, a 10-year BOO (Build, Own, Operate) contract was signed to supply up to 1200 m3/d of high purity water of less than 70 mS/cm to the power station. The plant was installed at the Flag Fen sewage treatment works, approximately 1 km from the power station and was commissioned in October 2000. It consists of 150 mm drum screen, microfiltration (to remove solids and mirco-organisms) and reverse osmosis (to remove c. 90% of all dissolved ions) with permeate being piped to the power station’s water storage tank. Achievements:
The water quality supplied to the power station has been excellent and massive savings have been achieved in the power station’s de-min plant operation. In addition, the plant has won a number of process and environmental awards. Water Quality Results: | Parameter | Unit | Mains Water | Membrane Plant Permeate | | pH | - | 7.6 | 5.8 | | Conductivity | uS/cm | 643 | 38.5 | | Calcium | mg/l | 95.2 | 0.8 | | Sodium | mg/l | 35.1 | 4.7 | | Total Hardness | mmol/l | 28.8 | 6.5 | | Alkalinity | mmol/l | 14.5 | 16.1 | | TOC | Mg/l | 3.2 | 0.8 | | Silica | Mg/l | 2.0 | 0.2 | | Phosphorus | mg/l | 0.7 | 0.2 |
Power Station Benefits: Greatly improved de-min plant feedwater quality 90% saving in de-min plant operating costs Interval between de-min plant regenerations increased from 530 to 7,000 m3 Bulk chemical deliveries reduced from 30 times per year to just 3 - De-min plant availability increased by nearly 20%
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