January 2009 saw the commercial hand over of the 420 MWe TEC-2 gas-fired 1+1 multi-axis combined cycle cogeneration plant (pictured below) to Latvian utility Latvenergo.

TEC-2 is the largest and most modern CCGT in the Baltic states, as well as the biggest fossil fuelled plant in Latvia, capable of providing 20% of the country’s electricity. The plant is located in the municipality of Salaspils, on the edge of Riga, feeding power into the Latvian national grid and providing hot water for local district heating.

The new plant is located on the site of an existing multi-unit power plant, which started up over the period 1973-79. This consisted of several conventional boilers firing HFO, subsequently adapted to burn natural gas, and linked to a set of steam turbines and heat exchangers.

It was in April 2004 that Latvenergo took the decision to embark on the TEC-2 combined cycle construction (or reconstruction in Latvenergo parlance) project, making maximum use of existing facilities and infrastructure.

The contract model chosen was turnkey EPC (engineering, procurement and construction) for the building of the plant, and a further maintenance contract for the first years of operation. Colenco provided engineering support to the utility.

After an international tender process the EPC contract was awarded to Iberdrola Ingeniera y Construccion and the 12-year O&M contract to Iberdrola Operacion y Mantenimiento (IOMSA), with the plant to be connected to CMDS, Iberdrola’s monitoring, diagnosis and simulation centre, established in 2002 to support operation of its CCGT fleet.

The TEC-2 gas turbine, with a capacity of 275 MWe, is a GE 9FB – Riga being the Spanish company’s fourth CCGT project to employ this machine. The two-casing steam turbine (HP/IP and LP with four extractions for use in district heating mode), together with the condenser, have been supplied by SKODA Power, while NEM has supplied the triple-pressure-level heat recovery steam generator. The gas turbine drives a hydrogen cooled GE generator (generating at 17 kV), while a Brush air cooled generator (15.75 kV) is coupled to the steam turbine. The forced draft cooling tower was supplied by SPX, while Emerson has provided the power plant control system.

Increased efficiency

With the new 420 MWe plant in operation the total electricity generation capacity at the TEC-2 site has increased from 330 MWe to 600 MWe, following closure of some of the existing facilities. The heat output remains about the same as before, around 1140 MWt.

The electrical efficiency of the new CCGT, at 57%, is about three times that of the former technology. In cogen mode, ie during the winter, total efficiency of the CCGT (heat plus power) reaches about 88%. During the summer, the plant will work in condensing mode, producing mainly electricity. In one year, it is estimated that TEC-2 will produce about 2200 GWh of electricity (compared with the previous 820 GWh), thus helping to reduce Latvia’s dependence on imported electricity supplies.

Important issues here are the imminent closure of the Ignalina RBMK nuclear plant in Lithuania and the fall in Estonia’s production of electrical energy, which until now supplied a large quantity of power to Latvia.

The main civil works on the new CCGT began in summer 2006, and it reached base load in the summer of 2008.

The project also included provision of two substations (330 kV for the gas turbine and 110 kV for the steam turbine), as well as the construction of a connection to the existing plant for district heating hot water.

Given the climatic conditions in the area, the gas turbine, steam turbine, generators, and HRSG are housed in a building, which also accommodates the condenser (located under the steam turbine), as well as other water/steam cycle equipment.

All of the auxiliary systems not contained in the main building (treatment plant for water and effluent, gas compression station, water circulation pumping and treatment system, effluent pool, etc) are also housed in buildings or enclosures to protect them from inclement weather.

The plant has a 60 m high stack for discharge of exhaust gases, at a temperature of 84°C.

Gas and water supply

The natural gas fuel for the plant comes from Russia, via the main Latvian gas network. Latvia is blessed with substantial subterranean gas storage capacity, allowing the gas to be stored during the summer, and some of the gas consumed by the power plant in the winter months is repumped from this store.

Gas conditioning equipment ensures that gas is supplied to the turbine at a pressure of 32 bar, free of humidity and impurities, with a maximum temperature of 110°C. The incoming gas, at 15 bar, is raised to the required pressure using a MAN-supplied compressor, with an additional compressor for back-up.

The combined cycle plant consumes some 130 000 Nm3/h of gas at full load.

The untreated water for use in TEC-2 comes from the supply system of the existing power plant. The water comes from the River Daugava, which is dammed near Salaspils, about 7km from the plant, for electricity production and water supply.