# Medway Power Station

Medway Power Station is a 735 megawatts gas-fired combined cycle gas turbine (CCGT) power station on the Isle of Grain in Kent adjacent to the River Medway, about 44 miles east of London. It started to supply electricity to the national grid in 1995.

## History

Medway Power Limited (MPL) was incorporated in September 1990. It is a joint venture company originally comprising Arlington, Virginia-based AES Corporation (trading as AES Electric) (25%) and the RECs SEEBOARD (37.5%) and Southern Electric (37.5%) (became SSE in 1998). In April 1992 MPL awarded a design, procurement and construction contract to a consortium of Europower Development Ltd and TVB Power Ltd. The contract called for a turnkey 660 MW combined cycle electricity generating plant, deliverable by 1 August 1995.
The station was built by Marubeni (Japanese), Tarmac and Kansas City-based Black & Veatch. The station is run by Scottish & Southern Energy under the name Medway Power Ltd. It was commissioned in 1995, being . In June 2002, American Electric Power (AEP) sold its SEEBOARD company to eDF, giving eDF 37.5% of the power station. SSE bought the plant from AES and eDF Energy for £242m on 3 October 2003. It is near (west of) to the Grain Power Station and next to the Thamesport.

## The Site

The station is on an 11 acre (4.45 ha) site, above the 200 year flood plain. There is a requirement that the noise at the perimeter must not exceed 65 dBA. The three turbines are contained within an acoustic enclosure in a containment building. The two exhaust stacks are 65 m tall. Stack emissions are limited to 45 ppm NOx. Cooling water is abstracted from the Medway and chlorinated. Water discharges are monitored and treated prior to discharge.

## Specification

Medway power station is a CCGT-type power station that runs on natural gas. It has two General Electric Frame 9 (9001F) gas turbines. The exhaust gas from these reaches two Nooter Eriksen heat recovery steam generators. The steam from these powers one General Electric steam turbine.

### Main plant

The operating parameters of the main generating plant are as follows.
Medway power station main plant specifications :
| Parameter | Value |
| Combustion turbine generators (CGT) ||
| Manufacturer | General Electric |
| Model | MS9001FA |
| Type | Advanced Aero Engine |
| Number of | 2 |
| Combustion chambers | 18 |
| Firing temperature | 1,288°C |
| CGT output | 228 MW at 11°C |
| CGT heat rate | 10,180 kJ/kWh |
| CGT efficiency | 35% |
| Steam turbine generator (STG) ||
| Manufacturer | Nooter/Ericsen |
| Type | Natural circulation, triple pressure, reheat type HRSG |
| Number of | 2 |
| Exhaust gases | Vented to 65 m high steel stacks at 113°C |
| STG output | 247 MW |
| STG heat rate | 7,934 kJ/kWh |
| STG efficiency | 88.7% HP isentropic, 91.8% IP/LP isentropic |
| Net output available | 682 MW |
| Net heat rate | 6,800 kJ/kWh |
| Net plant efficiency | 53% |
| Generators ||
| Manufacturer | GE |
| Model | GE 324S |
| Rating | 291 MVA / 15,000 V at 0.85 power factor |
| Type | Hydrogen cooled |
During a major upgrade project in 2012 the power station benefitted from the GE DLN 2.6 install as well as an upgrade to the excitation and turbine control system. Currently the power station operates as a two-shifting plant with approximately 20MW of black start capacity.

### Ancillary plant

Specification of the ancillary plant is as shown in the table.
Medway power station ancillary plant specifications :
| Parameter | Value |
| Step up transformers ||
| Rating | 290 MVA at 15 kV/420 kV |
| Manufacturer | GEC-Alsthom |
| Number | 3 |
| Ancillary supply | Two 20 MVA transformers for auxiliary services |
| Cooling plant ||
| Manufacturer | Hamon |
| Type | Open wet mechanical cooling tower |
| Construction | 12 cell mechanical ventilation |
| Flowrate | 612,000 litres per minute |
| Design condition | 11°C, 80% humidity |
| Heat rejection | 1.614 × 10$^9$ kJ/h heat rejection |
| Condenser ||
| Manufacturer | Senlor Thermal |
| Type | Surface condenser |
| Condensing rate | 655,000 kg/h using cooling water at 21°C |
| Back pressure main steam | 41 mm Hg A on steam turbine at 538°C at 97 barA |
| Back pressure reheat | 335°C at 28 barA for hot reheat; 260°C at 6.7 barA |
| Demineraliser ||
| Manufacturer | Glegg |
| Type | Two train two bed |
| Capacity | 4,670 l/min (maximum NOx control water injection when running on fuel oil) |
| Feed water deaerator ||
| Operating pressure | 150 mm Hg A |
| | Water storage tank |
| Fuel gas heater ||
| Manufacturer | Graham/Crane |
| Type | Water-to-gas heat exchanger |
| Number | 2 |
| Temperature rise | 27°C to 150°C |
| Auxiliary cooling ||
| Manufacturer | Allfa-Laval |
| Type | Plate heat exchangers |
| Number | 3 |
| Service | Cool auxiliary cooling loop; turbine lube oil; Generator coolers |
| Metallurgy | Titanium for saline cooling water |
| Lube oil ||
| Reservoir | 30,280 l (8,000 gals) |
| Equipment | Pumps; filters; heat exchangers |
| Fuel oil ||
| Equipment | Dual filters; 3 x 50 % pumps; 2 x atomising air compressors |
| Control system ||
| Manufacturer | Bailey |
| Type | Distributed control and information system (DCIS) |
| Facilities | Operator interface with turbines; control outputs to generators; Operator control functions; Control of equipment and process parameters |