6 replies to this topic

[agorostiaga]

We are working in the design of the power island for a 50MW Solar Termal Power Plant (parabolic trough) without night mode energy storage.
The power island has a high pressure steam turbine + low pressure steam turbine + condenser system using open cycle cooling water, refrigerated with cooling towers. We are using open cycle cooling water for economic reasons, the site raw water is relatively good in quality, so only filtration is sufficient to generate make up water to the cooling water circuit. Nominal cooling water flow is 8000 m3/h.
Obviously, at night, there will be no power production, so the power island will more or less shut down. We have asked the turbine manufacturer + condenser manufacturer what should be the minimum CW flow at night. We were expecting a flow of the order of 100 m3/h to condensate the steam to the seals, which have to be fed with steam all night long.
The condenser manufacturer is telling us that the minimum cooling water flow (at night) needs to be roughly 1 m/s so as to minimise the deposits, scaling and corrosion in the AISI 304L tubes. (This is the text book answer to the problem) This tube speed, represents roughly half the operation flow, so it is a huge flow to pump at night, every day of the year.
We think that the condenser manufacturer has not realized that it is different to have a permanent low velocity in the tubes than our case, where there are two modes, a day mode with high velocuty in the tubes (2.5 m/s) and then a night mode, with a minimum flow.
I would like to know if any of the forum members has come across this issue before or has experience in the operation of such "non-continous" systems that need to be shut down at night, and how they manage the cooling water flow to the condenser at night.
Possible ideas that we have are:

• - reduce the flow at night to the minimum flow required by the seals: 100 m3/h
• - Use demin water, or soft water in the cooling water circuit.
• - Drain the condenser at night. Empty it out.
• - Dilute the cooling water inside the condenser, at night using soft water.
• - Pump 4000 m3/h at night as recommended by the condenser supplier.

I appreciate any help or experiences in this regard.

[DAS-PE]

I don't have any experience with this particular situation, but I think the lower flow rate will be OK. To keep track of how the tubes are preforming, use coupon testing in the streams and check for problems. Don't be surprised down the road if this was an incorrect decision; set up a system to know what is happening in real time. The energy savings could be significant and justify some added repair if it turns out to have a long term implications.

[marry100]

Preamble
Energy is considered a prime agent in the generation of wealth and a significant factor in economic development. Limited fossil resources and environmental problems associated with them have emphasized the need for new sustainable energy supply options that use renewable energies. Solar thermal power generation systems also known as Solar Thermal Electricity (STE) generating systems are emerging renewable energy technologies and can be developed as viable option for electricity generation in future. This paper discusses the technology options, their current status and opportunities and challenges in developing solar thermal power plants in the context of India.
India’s power scenario
India’s current electricity installed capacity is 135 401.63MW. Currently there is peak power shortage of about 10 % and overall power shortage of 7.5 %.
The 11th plan target is to add 100 000 MW by 2012 and MNRE has set up target to add 14500 MW by 2012 from new and renewable energy resources out of which 50 MW would be from solar energy. The Integrated Energy Policy of India envisages electricity generation installed capacity of 800 000 MW by 2030 and a substantial contribution would be from renewable energy. This indicates that India’s future energy requirements are going to be very high and solar energy can be one of the efficient and eco-friendly ways to meet the same.
Solar energy potential
India is located in the equatorial sun belt of the earth, thereby receiving abundant radiant energy from the sun. The India Meteorological Department maintains a nationwide network of radiation stations, which measure solar radiation, and also the daily duration of sunshine. In most parts of India, clear sunny weather is experienced 250 to 300 days a year. The annual global radiation varies from 1600 to 2200 kWh/m2, which is comparable with radiation received in the tropical and sub-tropical regions. The equivalent energy potential is about 6,000 million GWh of energy per year. Figure 1 shows map of India with solar radiation levels in different parts of the country. It can be observed that although the highest annual global radiation is received in Rajasthan, northern Gujarat and parts of Ladakh region, the parts of Andhra Pradesh, Maharashtra, Madhya Pradesh also receive fairly large amount of radiation as compared to many parts of the world especially Japan, Europe and the US where development and deployment of solar technologies is maximum.
Technical Consulting Services

[mazirra]

Hi
In solar thermal power plants the incoming radiation is tracked by large mirror fields which concentrate the energy towards absorbers. They, in turn, receive the concentrated radiation and transfer it thermally to the working medium. The heated fluid operates as in conventional power stations directly (if steam or air is used as medium) or indirectly through a heat exchanging steam generator on the turbine unit which then drives the generator. To make solar high flux, with high energetic value originating from processes occurring at the sun's surface at black-body-equivalent temperatures of approximately 5800 K usable for technical processes and commercial applications, different concentrating technologies have been developed or are currently under development for various commercial applications. Such solar thermal concentrating systems will undoubtedly provide within the next decade a significant contribution to efficient and economical, renewable and clean energy supply.
Technical Consulting Services

[mazirra]

Hi
In solar thermal power plants the incoming radiation is tracked by large mirror fields which concentrate the energy towards absorbers. They, in turn, receive the concentrated radiation and transfer it thermally to the working medium. The heated fluid operates as in conventional power stations directly (if steam or air is used as medium) or indirectly through a heat exchanging steam generator on the turbine unit which then drives the generator. To make solar high flux, with high energetic value originating from processes occurring at the sun's surface at black-body-equivalent temperatures of approximately 5800 K usable for technical processes and commercial applications, different concentrating technologies have been developed or are currently under development for various commercial applications. Such solar thermal concentrating systems will undoubtedly provide within the next decade a significant contribution to efficient and economical, renewable and clean energy supply.
Technical Consulting Services

[Iarik]

Guys,

Reading the original post, I've asked myself couple of question: isn't it too many starts/stops for the steam turbine? What about the metal fatigue due to thermal expansion/contraction of the turbine shaft, casing, blades...? Is it considered in the original design?

Just interesting to know. It doesn't look feasible to have reduced life of an extra-expensive equipment (HP and LP turbines), in order to generate max 400 MWh per sunny day (during 8 hours of operation?).

Cheers.