What effect does air ingress and fouling have on surface condensers like in a power plant?

Question

how would you test its effects and what can you do to stop it ...improving a surface condenser basically with respect to air ingress and fouling..thanks

Answer 1

Surface condensers are operated under high vacuum.

The effects of Air ingress is to decrease the vacuum (increasing pressure) and leads to back-pressure on the turbine thereby decreasing its efficiency.

It's the condensing of the steam that produces the vacuum.

(1,800 litres of steam condenses down to 1 litre of water ...a huge volume decrease.

The uncondensible gases contained in the steam are 'pulled out' of the condenser, generally by a 2 stage ejector set system thus maintaining the vacuum but may not be able to cope with air ingress.

Fouling of the tubes (internal..sea-weed, silt, sand etc), will result in decreased heat exchange and therefore, again, cause a loss of vacuum.

These condensers generally have 2 banks of condenser coils and when required, can be switched over and the fouled coil isolated and back-flushed to wash out the fouling medium. (It's otherwise a shut-down job).

Air ingress...we had a smoke generator with which we could detect the point of air ingress ..pump and valve glands, pipe flanges ...etc checked and fixed if possible. Otherwise again, a shut-down job.

The greater the vacuum the greater the Energy extracted from the steam to the turbine.

Extra Info: The water level in the surface condenser must be maintained below the level of the cooling water tubes in order to allow maximum surface area to be presented to the condensing steam. (Hence the name 'Surface Condenser').

In a condenser operating at 4"Hg pressure (26"Hg Vac), the condensate is at 65°C.

Also, the level of condensate in the ejector condensers must be maintained at a level where it keeps their atmospheric loop seals filled in order to prevent uncondensible gases returning to the surface condenser.

The condensate from the condenser is returned to the Steam Generation units for re-use. Make up, treated, Boiler Feed Water (BFW) is added to replace steam losses.

Answer 2

It would reduce efficiency.

Sand is what killed many Martian probes.  In fact a Martian sand storm blew off the accumulated sand on the rovers and gave them a new lease on life allowing their original mission to be extended from 90 days to years.

I always wondered why they didn't put windshield wipers on the solar power cells, but if the sand scratches the cell then it becomes damaged and degrades efficiency.  If there is a covering over the cells then a scratched surface is still a problem.  A better solution would be to deploy a muffin style fan and blow the sand off that way.  It might also be a good idea to install a small wind turbine for auxiliary power, unlike the sun the wind works at night.

There is a solar powered plant in the US that hasn't been on line for many years.  It works by using a field of mirrors that track the sun, to focus on a single pipe that pumps molten sodium.  The sodium stores heat very well and it takes a high temperature to melt it.  The problem is that the mirror coating was not weather proof and it has since degraded ruining the efficiency of the power plant.  Since this type of power plant uses mirrors that move sand accumulation is not a big problem, however clearly the DESIGN of materials used was a big problem you need to make sure that you use equipment that is rated for the atmosphere and temperatures that it will be working at.  For example using aluminum that won’t rust is a good idea, but steal would be a poor one.

Coal, nuclear, oil and natural gas power plants all work in the same fashion; a heat source boils water and moves it through a steam turbine.  The spinning turbine creates electrical power.  Then the water has to be cooled down, and it is done so the same way your air conditioner works; using a large stack of condensers.  If you block those condensers then you reduce the efficiency.  For home units there is a metal comb that you can use to manually re-align the vanes and clean them out.  The larger power plant variety use stronger vanes so bending is not a problem. However they have to be close enough together to keep out contaminants.  Keeping these vanes clear and keeping the water clean are two important considerations.

One common method for air chilling power plants that is also used for power plants is to build a cooling tower where the water is allowed to fall and be exposed to the air.  Although falling water does heat up slightly the action of creating a water fall exposes the maximum amount of water to the air so that it can be cooled.  This can be more efficient than using vanes to cool it.

Nuclear power plants use hot reactor water to heat a nonradioactive water source into steam so the contaminated water is not released.  Crocodiles are native to North American, but not common; they prefer warmer climates and 99% of the ones in Florida are down stream from the nuclear power plant because of this.  So heat loss to the environment equals an efficiency loss to the power plant.  Recovering that lost energy would help.  Thermocouples are never more than 10% efficient so they are not a practical idea.

The best way to design a surface condenser to increase its water cooling efficiency would be to maximize air flow.  However, you want to keep the water in a power plant near the boiling point so that it can keep powering the turbine; therefore cooling the water is only needed if you plan on dumping that water back into the environment.  This is a common practice, except for nuclear power plants.  If you did it for more power plants then you would still have to worry about cooling what ever water you do release and eventually you need to release some hot water and take in colder water.  That is why the cooling effect through surface condensers, towers or water chillers is so important.  Another environmental problem is that with an increase in water temperature some species of water life are threatened and hostile forms may be encouraged.

In the Great Lakes the zebra muscle is causing a problem by clogging the water outflow channels for the power plants, they are not native to the Great Lakes and have no predators, they also like the warmer water.  This clogging reduces efficiency and the pipes have to be manually cleaned.  A robotic method of doing that would be helpful.

A show on Nova Science NOW that was on tonight and it discussed a system to maximize air exposure to a surface area for the intake of CO2 gas.  The design used long parallel sheets, so from that you can assume that long parallel water falls of cooling water would be the best way to maximize air flow and therefore cooling.  Ideally you want to keep water flowing smoothly since turbulent water not only creates heat, but it creates resistance to the water flow.  Therefore the design of the pipe sizes for a specific water rate is important also the material has to be one that is smooth and thus promotes less turbulence.

The best way to test your design is to take the temperature of the water at various stages; mainly before you cool it and after you cool it, but also after you heat it (why waste heat by heating it too much) and after each water chilling or cooling tower to see which tower is the most efficient.  Thermocouple sensors are designed and easily calibrated to work well in these situations with no moving parts.