Operation & Maintenance of Power Plants
available for other purposes. Tis may in fact be a profitable choice for the total system.
Residual heat One of our clients, Attero, had an A-frame condenser that was operating at a pressure of 0.07 bar with a corresponding steam temperature of 39˚C. When the temperature of the outside air was higher than 15˚C, the pressure in the condenser increased, which resulted in lower efficiency of the turbine, causing less electricity to be produced. Bronswerk developed and delivered an alternative to this system, which taps off some of the steam between the turbine and the condenser. Tis steam is used to heat water. As a result, less steam is supplied to the condenser, so less cooling air is required and the ventilators can run more slowly; this means that less driving power is required for the ventilators. Because the condenser is supplied with less steam, up to an outside air temperature of 19˚C the pressure in the condenser can remains low, so that the maximum amount of electricity can be generated for many more hours per year. In the past, this water was heated by a separate
boiler running on biogas. Tis boiler can now be taken out of service and the biogas can be sold. All in all, the economic efficiency of the entire system has greatly improved. By proposing and implementing this type of
conversion as a total project, Bronswerk’s know-how and skill were shown to great advantage and the client only needed a single supplier. Te entire project consisted of:
● Tying into the existing steam pipe such that it caused minimal pressure loss
● Designing and manufacturing a new water-cooled condenser
● Supplying the pipe section from the main steam pipe to the condenser
● Supplying the vacuum unit to extract air in the steam
● Supplying condensate pumps ● And supplying a special booster heat exchanger for proper control of the temperature.
Tis is a good example of how low-temperature waste heat can be used efficiently. Other possible applications for the efficient use
of low-temperature waste heat include: greenhouses; swimming pools; fish farms; drying food or grass or grain; seasonal soil heat.
District heating For district heating, heat is required at temperatures of up to around 100˚C. Te criteria described above show that this use of CHP will lead to much lower electrical efficiency.
Another disadvantage of district heating is that the 20
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Fig. 3. The Rive Droite Environment plant.
For this reason, our client Rive Droite Environment (Veolia Environment, Bordeaux, France) decided not to opt for this
concept.Instead, they chose to operate the turbine with a low outlet pressure in the summer allowing the maximum amount of electricity to be supplied. In the summer, there is no need for district heating.
In the winter, the outlet pressure of the turbine is increased, leading to the generation of less electricity, with greater amount of heat. When this combined heat and power plant is in winter mode, most of the steam is supplied to a shell and tube heat exchanger for the district heating. Tis heat exchanger now operates as a condenser (surface condenser). However, heat consumption is not constant in
winter, so an air-cooled condenser is used to control the system pressure in a simple manner. Tis solution was supplied complete with a vacuum system, condensate collector and return pipes. ●
For more information ✔ at
www.engineerlive.com/ipe
Jeroen van Ruitenbeek and Johan van der Kamp are with Bronswerk Heat Transfer, Nijkerk, The Netherlands.
www.bronswerk.com
heat requirement varies enormously in summer and winter and during the day and at night. Needless to say, no advantage is gained from generating electricity with a low efficiency, while on top of that only a small part of the waste heat can be used efficiently. In most systems, this disadvantage is overcome by creating an extra steam tap in the steam turbine. Tis is used to take steam from the turbine where the pressure is still high. Although this is a good technical solution, it does make the turbine design very complicated.
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