Plants Amsterdam cluster
The Amsterdam cluster consists of three production units:
Hemweg 7
Hemweg 7 is a conventional gas-fired plant built in 1979. A gas turbine was added to the existing steam boiler in 1988, to increase the yield. This made Hemweg 7 a ‘combi-unit’.
The gas turbine can be used independently or in combination with the steam turbine, depending on the amount of power required. The gas turbine uses low-Nox burners, so that the plant uses fuel efficiently and complies with environmental requirements for emissions.
The plant has a ‘tangentially-fired’ boiler. This means that one or more burner houses have been installed in each of the four furnace corners. The turbine has a total of 20 burners, divided over five layers. The steam turbine consists of a high-pressure, a medium-pressure and two low-pressure turbines.
Production capacity
Hemweg 7 has a capacity of 511 megawatts. The gas turbine raises that capacity to 599 megawatts. On its own, the gas turbine has a maximum capacity of 150 megawatts.
Hemweg 8
Hemweg 8 is one of the most modern coal-fired installations in Europe. This unit was officially commissioned on 9 September 1994. It has a flue 175 meters high, resting on a foundation of 220 piles, each 25 meters long.
Operation of the plant
Hemweg 8 burns 36,000 tons of coal per week, or 1.6 million tons a year. The coal is shipped in by sea to the Amsterdam storage company (OBA) about two kilometres away. From the OBA, a long conveyor belt takes the coal to the circular coal storage field (capacity: 45,000 tons). Here a digger lifts it onto another conveyor belt that carries the coal to the mill bunkers at a rate of 1,000 tons per hour.
After the coal has been ground into coal dust, it is blown into the boiler, where it serves as fuel for an enormous fireball, at a temperature of 1,200 to 1,300°C. This temperature is needed to produce the high-pressure flow. Production continues until a flow of 550 kilos per second is pressed into the turbine at 540 to 600°C., at a pressure of 250 bar.
The steam boiler has 36 low-NOx burners, which can be used for coal or natural gas. In principle, coal is used to fire the boiler. Natural gas is needed primarily to start up the unit. At full load, coal consumption is 62.5 kg/sec or 225 tons/hour: that is ten large trucks-full. By way of comparison, if natural gas were used instead of coal at full load, consumption would be 46.5 m3/sec or 2,970 m3/min, which is the annual consumption of an average Dutch family.
Production capacity
Hemweg 8 has a net capacity of 630 megawatts. The bipolar generator has a capacity of 680 megawatts and produces an alternating current of 21 kV, 50Hz. About 50 megawatts is needed to burn the coal and the net capacity amounts to 630 megawatts, equivalent to 1,000,000 hp.
DeNOx-installation
A fine example of clean coal technology is the DeNox installation that Nuon built behind the boiler house at Hemweg 8 in 2006. This installation extracts 85% of the nitrogen oxide (NOx) from the flue gases, significantly reducing NOx emissions. Thanks to this installation, total NOx emissions are reduced by 35%.
The DeNOx installation consists of two enormous reactors, also known as catalyser layers. After the first layer, most of the NOx is converted. The second layer makes the flue gases even cleaner. If the reactor activity diminishes, a third layer can be added. A fourth layer is used only as a reserve during maintenance or malfunctions.
The reactors stand on tripods 33 metres high, which promotes smooth operations and a better airflow.
Recycling of residual products
Recovery of hazardous substances and recycling of the various residual products of burning coal makes the emissions less harmful to the environment. These residual products are:
- Bottom ash
- Fly ash
- Sulphur (SO2)
- Nitrogen dioxide (NOx)
Purmerend CHP plant
The Purmerend production unit consists of a CHP plant and an ancillary CHP unit.
Production capacity
The Purmerend CHP plant is a gas-fired steam and gas (STEG) unit with a capacity of 68 megawatts. In addition to generating electricity, the unit can produce up to 64 megawatts of heat for urban heating. The gas turbine, fitted with 384 dry low-NOx burners, ensures the lowest possible NOx emissions.
Operation of the plant
The heat released during power generation in the CHP plant is re-used for domestic households and companies. In this case, the residual heat (exhaust stream) is used for urban heating in the Purmerend municipality.
The recycling of hot water to provide heat for hundreds of thousands of homes means that it is not necessary to discharge cooled water outside, producing enormous savings. At the same time, the use of urban heating leads to a substantial reduction in CO2 emissions.
Operation of CHP
The gas turbine sends hot flue gases to a boiler where steam is formed. The heat from the residual gases from the gas turbine is converted into steam in the boiler and is used to drive the steam turbine generator. A generator is positioned between the steam turbine and the gas turbine. The generator that produces the power is driven from both sides.
Ancillary CHP unit
In order to guarantee the supply of heat, the plant uses an ancillary CHP unit and storage tanks. The ancillary unit consists of six hot water boilers and can supply extra capacity during peak demand. It can also provide for continuity if the plant itself is out of action.
While the CHP plant (gas turbine) is operational, it releases processed steam. When the gas turbine is not operational, for instance during maintenance or a malfunction, heat is supplied by ancillary boilers, where the urban heating water is heated directly with fuel. The heat that is not used is stored in the four available tanks.
In the flue gas boiler, the gases from the gas turbine release their heat to the steam system connected to the generator. The generator is connected to a transformer which, in turn, is connected to the 50 kV high voltage grid.
Operation of units
All units are operated on location by the generation operators. They are in direct contact with the plant, in order to deploy the unit as effectively as possible on the basis of demand for electricity.