Hybrid Cooling in Power Generation - Has the Time Arrived?

run that by this pedestrian again in straight English

It's all about using less water to achieve the same thermal efficiency in power stations.

okay so all we have to do is slightly alter a few laws of thermodynamics then we can go to lunch?

increase airflow

BTW Fredski: she must be a big fan of yours, right?

they all are!

Agreed, though the airflow needs to be split for this to work, between a sensible heat cooling unit in the first stage and a latent heat cooling unit in the second.

I would not say alter, but rather exploit. For example, boiler stacks (even though the boiler is well over 95% "efficient" in converting heat to steam) are still quite hot with respect to the temperature necessary to drive an ammonia absorption cycle, but the actual quantity of BTU's may not be there to drive the enormous chiller needed. Thus even this would have to be augmented by other heat source such as solar (which is really only needed during the hottest parts of the day). At that is what I am "projecting" by inference. Now one must also solve the stack acid gas problem due to sulfur content of the fuel, so as not to corrode "stuff". By the way considerable condensate could indeed be formed here also.

so this isnt about saving energy or initial capital costs as much as water conservation

I would say we want to "save energy" as much as possible, and simultaneously conserve water consumption (by evaporation and blow-down). If we were only concerned with stopping water consumption altogether, we would not allow combined cycle units in arid districts at all, just simple cycle gas turbines. Never mind the heat rate penalty, just pass the "savings" onto the consumers. Same thing with dry cooling of conventional steam turbine plants where some were converted to from once through cooling in California, then the cooling towers were banned due to saline pollution of the rivers... a 16% penalty by reduction of the plant output, and a heat rate penalty on top of that.

On the other hand, we want to restore plants that are not operating at 100% full nameplate rated capacity, while at the same time changing how we cool those plants, by utilizing other "wasted" or low-grade heat sources to drive refrigeration processes.

It's about achieving a better balance between them. Capital is cheap at the moment and fossil energy is expensive [in relative terms].

Modern condensing central heating boilers work by condensing the flue vapours and running the liquids to drain, thereby recovering heat. The solution involves corrosion-resistant materials at the heat exchange surface, the rest of the way to the tip of the stack, and in the condensate pumps and pipework that get it into the drainage system.

What sewage treatment processors say about the lower pH in their incoming fluids is not recorded.

I'll have to check out Prescription for the Planet to see if Blees said anything about water consumption by the IFR nuclear reactor. I know primary cooling is by liquid sodium, but I don't remember about water consumption after the steam cycle. Tomorrow I hope.

Some nuclear power plants utilize once-through cooling from a river or large body of open water. Others have to utilize open cycle evaporative cooling (cooling tower), and most of the cooling towers you see are the natural draft cooling towers.

One question I have had is this: If compression causes an increase in temperature, shouldn't the converse also be true. Thus if one introduces a suitable draft situation where there is a bernoulli effect in the air racing past the cooling coils (presume dry cooling), would there not be a lower than ambient temperature in the local pressure depression? Surely if so, would there not be some way to exploit that?

I did not find anything on water consumption in Tom Blees' book. Will now look in Plentiful Energy by Till & Chang. But don't expect to find anything; because, upon further thought, I suspect the cooling water consumption is similar. However, fast reactors, PRISM & IFR, are much better in fuel consumption, waste production, and proliferation prevention.

On your second question, yes, but . . . Expansion does produce cooling. But I don't think you have expansion here; you have velocity which causes wind chill, but that isn't expansion. Unless I misunderstand you. Wind chill increases the cooling rate, but not the ultimate temperature.

OK, now suppose you take the same air, compress it to 120% local atmospheric pressure. It will be hot. (This also takes considerable quantities of energy)....... One could cool off this compressed air, remove the water that condenses, then expand it back to normal pressure - would there not be a refrigeration effect? Same idea by attempting to reduce the pressure of air flowing into a "zone" whatever means are available. Any air that was at normal pressure, should now be at a slightly reduced temperature due to its expansion into that space where the pressure is lower.

I did find some ARPA research at North Dakota University about an improved adsorption chiller that utilizes a liquid adsorbent, slightly different than a lithium bromide chiller. I also found nothing on machines built over about 250 tons that utilize solar heat for the evaporator in these. I am still thinking of building possibly the world's largest chiller, not to mention the world's largest solar powered chiller.

I even consider that a solar chimney with PV panels being the heat absorbing medium could provide a driving force for the chillers. Unfortunately the COP of all adsorption chillers is quite low compared to VCC chillers. I suppose one could use a little of both, maybe even using a gas turbine to drive the compressor, and the waste heat could go to the adsorption unit(s).

There is nothing new under the sun.....

The thermal and water usage questions you pose, Jimmy, have been brought up many times before.

(suggest that you investigate the terms "low-grade heat" and Cheng thermal cycle on Wikipedia...)

http://en.wikipedia.org/wiki/Cheng_cycle

http://vganapathy.tripod.com/cheng.html

It is obvious to many that rejection of powerplant waste heat to the air conserves water. Air cooled condensers have been around for decades....

Also, suggest that you investigate a little thermodynamics and the laws that govern such cycles.

I am afraid that your MBA seems to be showing through in the wording of your directives......

Thank you MJCronin for sound advice. I have more background in physical chemistry than that MBA you suggested. My directive (as worded to me) was not to find an economical substitute for our present cooling towers, rather it was to find a way to cool the plant, condense the steam without water consumption anywhere near present levels.

I understand about air cooled condensers what they can and cannot do. What I present they cannot do is allow our plant to operate anywhere near capacity at present except on cool to cold weather days. We are allowed up to approximately 3" Hg column turbine back-pressure, corresponding to approximately 115 deg. F steam turbine exhaust temperature, ostensibly the condensate temperature. If the ambient temperature is over 100 deg. F, then all bets are off as far as operating without some major modifications to the last stage of the turbine, and/or chopping off the top end of load scale, maybe even operating at all.

I also know that the largest chill plant in the world is in Dubai island with a capacity guarantee of 125,000 tons. That would just about cover our situation here for two smallish steam cycle generators total capacity about 90 MW-95MW (if our emissions at that rate are in compliance). Also important to note that when it is hot outside, the VCC, or adsorption chillers would have to absorb perhaps 80% (or more) of the heat load. I know it takes more energy to run the VCC chiller than what we would get back in the cycle. It seems like a foregone conclusion does it not, what the end result will be. Last one out of town, turn off the lights.

James, here's some specifics on the Qatar installation, the numbers are enormous:

"...The nominal 130,000 chilled water plant distributes chilled water from a central plant to individual buildings via a network of underground pipes. It has a guaranteed capacity of 125,000 tons using 23 pair of 2,500 nominal electric motor-driven centrifugal chillers. Each chiller unit is 26 feet long, 11 feet wide, and 14 feet tall, and weighs 2,500 tons.

A district chilled water plant of this size has an unquenchable thirst for water. To compensate, the IDCP is one of the first district chiller plants in the region to be equipped with a desalination plant..."

So we see that an island surrounded by the Persian Gulf needs to desalinate the water supply, and where do they get the heat for that process, from the heat rejection side of a 125,000 ton VCC chiller system!! They have what you lack, a nearly infinite heat sink.

When you're turning off the lights don't let the door hit you in the butt...

Oh, we still have a few options, but that was also said about Hobbs, NM a few years back when big oil moved regional offices out, and production in the area dropped off. Now, Hobbs, NM is in a drilling boom, and BTW there is a new combined cycle plant there producing 500 MW that utilizes dry cooling on the steam half of the cycle.

One of the responding posters MJCronin, suggested the Cheng cycle, but unless one condenses water from the exhaust stack, make-up water consumption would be about as high as a wet cooling scheme, except the water would have to be purified to high pressure boiler quality first. Polishing the quality of condensate from an exhaust stack would require some minor pretreatment adjustments of pH, etc. before polishing up to feedwater quality for the cycle. At least on that one, dry cooling makes a lot more sense, because the final temperature of the water vapor containing stream is way higher than steam turbine exhaust.

When I see terms like "high back pressure steam turbines" I immediately thought that we were talking about once-through boilers, not open cycle or combined cycle plants.

Now I see that you want to capture the condensate from the GTs exhaust, clean it up, then send it back to the turbine intake to cool the incoming air, kind of an evaporative cooler cycle (aka as the Cheng cycle).

I'm not much on the ME side of Thermodynamics, but I sense that the "expense" of condensing that water and cleaning it up for reinjection, exceeds the "cost benefit" of doing so; somehow entropy is going to rear its ugly head. Maybe it's cheaper in the long run to just move the plant to a cooler climate (the EE jokingly suggested).

No. I am convinced now that the thermodynamics are favorable. The gas turbines for this already exist, the HRSG's already exist. Now comes the stack and condenser desgin. I propose simply the following:

Stage 1 condenser: ambient pressure (stack pressure), approximately 150 °C. This is so much higher than ambient temperature (40 °C est. maximum), that a much smaller set of condensers will work, and the exhaust is now loaded with steam from steam injection plus the water vapor left over from combustion. Since we don't know the fuel quality (it could be from refuse gasification, or coal gas, or natural gas), we will assume a higher S content, that would produce a corrosive condensate. We use a controlled volume of outside air to provide initial quench to the dew point, and a centrifugal condenser (spin the exhaust air mixture) to force coalescence. This small volume is collected, neutralized, and combined with RO feed, or blended without neutralization. Stage 1 condenser is at least teflon coated.

Stage 2 condenser: Assume the next condensate is mildly corrosive, so use some high end stainless steel here. This will be a standardly designed dry condenser built for high volume (of air) throughput, high differential temperature (less surface area). Condensate formed is polished and re-routed to HRSG.

Stage 3 condenser: The exhaust has now been "washed" twice with respect to acidic compounds, so use standard stainless steel. In the final section of the HRSG we have ammonia water coils (in this example), followed by ammonia cycle evaporator, condenser, and expander. The cold ammonia vapor cools the exhaust further to extract the last bit of condensate at a sub-ambient temperature. This water could be clean enough to blend with potable water supply.

Net result: A system that burns "trash", consumes little to no water, and actually produces some net water.

James,

You may think that the thermodynamics are favorable, but the engineers at General Electric Power Systems Combined Cycle Unit don't:

"...Evaporative and mechanical chiller systems maybe used to cool gas turbine inlet air to as low as45°F / 7°C. These inlet cooling systems can achieve up to 11% capacity increase during operation at site conditions of 90°F / 32°C and30% relative humidity. Evaporative cooling and chilling systems do not improve combined-cycle plant efficiency; however, they may provide economic peak power addition during warm summer periods..."

"...While gas turbine water or steam injection can be applied to enhance plant output as well as reduce NOx emissions, plant efficiency is degraded..." (bolding added).

Granted that this isn't exactly the same technology that you're looking at, but the brochure does mention closed loop cooling to reduce water consumption as an available option.

I'm not saying that your ideas aren't valid, but when I hear about any process that produces at no-cost more of something than it consumes, those little over-unity flags start a-wavin'. TANSTAAFL...

Alan

HI Ram:

For the next 30 tons

the 1/3 acre pond of 11ft deep

had

my rewound PE 3408 dr 9 1" ID 420 ft (of 500ft bought) coils of about 7ft dia x 2 ft high of 5 stacked coil-flats, x 5 high (sid viewed like 5 plates, but 3" apart, top view each spiral of each coil-flat was 6" on center)

10 coils: each of 5 coils on a 2" line, on a 2" T from 2" lines (industrially, higher pressure drop was accepted) netted 27 tons in the summer and 31+ tons in the winter at

11 to 13ft deep pond, but on a 2ft high PVC rack, as well, held down by 24 blocks, 2-holed 8x8x16 cement. Filling with air floated for inspection. Ropes held rack in line. 50+ gpm with under 2hp Baldor on Grundfos... netted over a 14f temp differential, LW ~ 82 to 86f. Savings: 84% thermal-electrical of the bill; and no refrigeration expenses again.

The system was ~ 64 x 12ft OD with coils, on its 10 x 60ft PVC frame.

1996, operational to date; and 3 HP only upped the net cooling ~ 10%, within 94f entering fluids cooling a 100 hp cycle testing circulation once cooled by a Budzar 25 hp high efficiency chiller.

JPGT 2008

I don't think I stated anything resembling over unity heat rate (cycle efficiency). Intake cooling on gas turbines is known to reduce load to the compressor during hot ambient temperature days, allowing the operator to keep load on the turbine at the maximum. Even with wet evaporative intake cooling, there is a parasitic load, although this is rather small.

The only thing over unity I was referring to is the ability to get more water out of the cycle than you input. And that all depends on whatever parasitic load is employed in driving the condenser(s). In this case, the condenser is operating at a higher input temperature, and at ambient pressure. Very little of the water will be wasted, as long as the final exhaust temperature is near or slightly below ambient. Incrementally, this will not take as much chilling as by any VCC or adsorption device, since most of the condensation will take place before this final step.

Correct, I was only commenting on the "excess water" remark, everything else is already being done by the major vendors.

Please allow me to illustrate what I am thinking:

X = steam injected in pph to the Cheng cycle turbine.

Y = any water evaporated at intake to reduce compressor inlet temperature

Z = water equivalent of the fuel (based on hydrogen content)

TQ = Theoretical qty (pph) of water recoverable = 100% of all sources, obviously

TQ > X+Y (thus >100% of "water" input as water)

There is more water recovered than that which was initially present (not including the water equivalent of the fuel). There is an opportunity (no matter how seemingly unimportant this is, and not insubstantial) to actually "produce" net water from this cycle, but it takes cooling the exhaust to near or below ambient temperature, and that takes energy, sure. Someone else will want to do the math, and see if it's worth the tradeoff in their situation. The big concern in my neck of the desert is that water is becoming a more sought after resource, so why not exploit opportunities to eliminate water consumption, and become a water producer?

James,

The Cheng cycle is not closed, it requires makeup water; it is also not a combined cycle in the traditional sense, there is no attempt to use the waste heat to run a steam turbine. It is simply a way of recovering exhaust heat and reinserting it back into the combustors as superheated steam, there is no attempt to recapture that moisture.

Your equations might work if the the stack was some type of closed system but it's not, so capturing all of the injected and fuel-borne moisture is problematic. With stack temperatures between 100-150°C, mass flow rates approaching 600 kg/s, and H2O as a gas around 5-6%, you have quite a job condensing all that water. And don't forget that the SCR (Selective Catalytic Reduction) System for NOx control, with its carryover, is also upstream of your capture system.

The good thing is that HRSG housings tend to be very large so maybe you can get the surface areas you need through multiple passes.

Alan

A couple of additional points: (1) Cheng cycle is not STIG - in STIG, steam injection is only a few percent and injection is in the last stages of compression, but in the Cheng cycle steam injection is 150% of air mass flow, and is injected at the burner cans which are designed to handle that. Also, PT blade cooling can be changed to eliminate the use of bypass air, and use steam as direct coolant inside the blades.

There is already one process that SIEMENS has (WETEX) that claims to recover approximately 75% of the moisture from an HRSG stack. Not clear at all to me they were referring to Cheng cycle only.

(2) Advanced Cheng cycle does include the use of a combined cycle approach. This includes a duct burner in the HRSG, steam injection to the GT combuster area, and a steam turbine/condenser.

I will be working on getting estimates of some particulars about how much water vapor is available for a frame 7 GE gas turbine of large megawatt output, mass flows, etc. and present that as a table (may take me a couple days).

James,

Cheng cycle was never mentioned as STIG. My concerns with your original posting suggesting the use of mechanical/absorbtion systems to cool and condense the flue gas moisture are also mirrored in the 2005 WETEX literature:

"...At the present time, there is no practical method of extracting the usually abundant water found in the power plant stack gas. Some work has been done on using mechanical heat rejection to condense water vapor. Such systems would require massive and expensive heat rejection equipment, would be severely limited by high ambient temperatures, and would result in decreased gas turbine performance as a result of higher back pressure due to closed heat exchangers in the flow path..."

"...Water removal from the flue gas ranged from 23% to 63% by volume, with the process conditions dictating the percentage of moisture removed. Higher percentages of moisture removal required higher energy inputs for heating and cooling. However, process conditions that required little or no external heating or cooling still removed a significant volume of water from the flue gas. Figure 2 illustrates the amount of moisture available in flue gas from different types of power plants firing different fuels..."

No need for you to research the amount of water available, it's huge, nearly 1,100 gpm for a 900 MW coal plant, and referenced in the paper.

Now there's a great enhancement to combined cycle technology; in addition to 375 MW of electricity you can get approximately 36,000 gph of RO quality water to sell.

As we say around here, "What's not to like?"

Alan

Nobody said there was zero exergy lost in applying gas turbine intake cooling, or in utilization of other hybrid cooling ideas within a power plant. Certainly no one, including me, believes it possible to find enough waste energy off a boiler to drive a large ammonia-water refrigeration cycle big enough to provide low condenser back pressure with a chilled water loop.

However, in the summer when it is hot, the sun is invariably shining brightly in Lubbock, TX. Enhaced solar collectors that run at 200°C should be quite hot enough to provide the tonnage once scaled up, but probably nowhere near what "sane" people would consider cost effective. It makes much more sense to size such equipment to intake chill a gas turbine (that is not at sea level) in order to improve air density and mass flow, to recover some of the power lost by being sited at elevation of over 3300 ft. Waste heat from a compressor inter-cooler is sufficient in value to drive ammonia-water cycle. Any other energy input is minimal (pumps and fans).

All that remains is for the equipment manufacturers to get hooked up with GE and provide a package deal like that to go with the LMS-100 DLE. Then one could have a fairly efficient simple cycle plant that would actually produce 100 MWe, at 3300 ft elevation on a hot day. My estimate is it will take approximately 3000 tons chilling the intake, and there are approximately 16000 tons heat equivalent available at the turbine inter-cooler, (not talking about turbine exhaust at this point), so with a typical 0.4 COP for ammonia-water absorption chillers, there is enough to even chill the final stage 1 compressed air down to sub-ambient.

Sure would take a lot more than the 4000 ton GeoThermal near grade loop in Canada !

however, for the 1st 4 tons:

" My system works. I have been watching the tube air temperature for five years now and have some data. My lowest tube air temperature in winter is near 40º F. The highest summertime temperature was near 70º F. The air tube temperature only reached those extremes when the outside temps were excessive. The average soil temp in this part of the country is 53 degrees and my air tube temps also averaged out about the same. The deeper the tubes are buried in the ground the less fluctuations in temperature they experience. As stated earlier at 8 feet the soil temp will vary 12 degrees either side of average (41º in the winter, 65º in the summer). The tube air tracks that temperature shift.

There is no problem with mold or Radon in my system. I've tested my systems for Radon and the results indicated the tube air Radon level is the same or near that of outside air.

As indicated earlier, 90 % of the air tube design and installation is to insure that they are drained properly. As a result there are no mold problems in properly installed air tubes.

Contact Info Removed - CR4 Admin

Larry Larson

http://www.earthairtubes.com/

We have continuously operating Earth Air Tube systems that are 25 years old. The air coming through them is as fresh today as the day they were installed."

Mr. Steve Kavanaugh is reachable

Even though his largest App is smaller...

http://www.ecw.org/project.php?workid=1&resultid=464

searched from

https://www.google.com/search?ie=UTF-8&q=hybrid+kavanaugh+source&sa=Search

J:

A nearly 6000 ton Earth-Coupled ground loop At Ball State U has a showing soon

Folks like GEOCON and others called GEO PRO and HeatSpring have other workshops too

http://www.heatspring.com/courses/geo-con--muncie-indiana