Combined Power And Water
Jumbo desalination for Shuweihat15 March 2004
The Shuweihat phase 1 (‘S1’) project now nearing completion will be, at 1500 MW and 100 MIGD, one of the world’s largest independent water and power plants. It is the most efficient CHP generator of its type and its multi-stage flash desalination units have pushed back the barrier of size to new limits.
Shuwihat S1 is being built by a consortium of Siemens Power Generation and Fisia Italimpianti. Developers CMS Energy and International Power together own 40% on a 50/50 basis while Abu Dhabi Water and Electricity Authority holds the remaining 60% . Its major components are a 1500 MW combined cycle power station with gas as the main fuel and diesel as the backup fuel, and a large water desalination facility of the MSF type with a capacity of 100 MIGD employing the largest machines of this type ever built, Fisia’s so-called ‘Jumbo’ units.
Consortium leader Siemens is responsible for turnkey erection of the power plant and is supplying five gas turbines, two steam turbines, seven electrical generators and all the ancillary systems. Fisia Italimpianti of Italy is responsible as consortium partner for the desalination facility including the six MSF units each with a distillate capacity of 16.6 MIGD.
Shuweihat S1 is being constructed on a green field site close to Jebel Dhanna, 250 km west of Abu Dhabi city. The power and water output from the facility will be sold to the Abu Dhabi Water and Electricity Company under a 20-year off-take agreement. CMS Energy and International Power will also jointly operate the facility under a 20-year operation and maintenance agreement. The EPC contract was signed in November 2001 and full commercial operation is scheduled for the summer of 2004.
Apart from the innovative financing structure arranged by CMS Energy and International Power, one of the main successes of the project has been the very close team effort between the developers and the EPC consortium of Siemens and Fisia Italimpianti, supported by developers’ consultant/owner’s engineer PB Power and the modelling expertise of GE Enter.
During the optimisation process, each of the parties provided ideas and concepts as a basis for the optimisation process. The EPC consortium provided basic and detailed concept drafts together with performance calculations (modelling) as well as price estimations for the various alternatives and the impact in maintenance costs. After finalisation of the concept, the consortium delivered a joint proposal to the developer group.
PB Power provided additional solutions for the optimisation process and prepared the minimum functional specification (MFS) taking into account the developers’ requirements together with the EPC contractors’ standards. GE Enter provided modelling of the performance of the plant throughout the 20 years off-take period as an input to the financial modelling. The developer group produced the financial model including cost estimations for the operation of the plant.
The result of this optimisation is what consortium leader Siemens calls a comprehensively optimised total plant. In an ambient of 46°C it has guaranteed a world record heat rate of 8823 kJ/kWh for combined power and water production.
The power plant section includes two Siemens V94.3A gas turbine generator sets with 40 m bypass stacks and bypass dampers, supplying the 220 kV substation, together with three more V94.3A turbine generator sets without bypass (supplying the 400 kV substation). Each gas turbine is rated 222 MW gross at reference site conditions (46°C ambient, 42% relative humidity). Siemens is also supplying the five dual-pressure HRSGs, and the two back-pressure steam turbine generator sets, extracting power from the steam flow before exhausting to the process steam main. The steam turbines are rated at 254 MW gross and deliver power to the 400 kV substation.
The HRSGs have supplementary firing to provide a degree of control in steam production independent of the GT firing rate.
The six MSF distillers are supplied with steam from the steam turbine exhaust or from the bypass if the turbines are out of service, and return brine discharge to the outfall canal. The distilled product water is remineralised to render it drinkable and stored in six tanks with capacityfor 24 h of production. The plant includes two seawater-cooled dump condensers.
The desalination island is designed for a total gross output of 460 000 m3/day of potable water. Its MSF units were designed for this project and are the largest capacity single units ever built. They represent the most up to date form available of this technology. The design derives from experience gained in building units of increasing size in the series Al Taweelah B (1995, 6 of 12.5 MIGD), Jebel Ali K phase 1 (2000, 2 units at 10 MIGD), and Jebel Ali K phase 2 (2002, 3 units at15 MIGD).
Desalination auxiliaries include a sea water intake screening and pump house of 180 000 m3/h capacity, remineralisation plant for the full production capacity, water tanks to store 100 MIG and a product water pumping station with a delivery capacity of 120 MIGD.
During performance tests the MSF units achieved a considerably higher value for performance ratio than that given in the table; in fact all other performance parameters were also exceeded during testing.
Tablestable 1 table 2