How to take energy from 480F degree clean flue gas

I'm not qualified to answer this type of question , but you need to give more information. My suggestion is ;

flow rate

hours/day of gas flow(how constant is it)

reason for project

geographic location (north pole / equator !)

nearest population centre (can heat be utilized directly without conversion to electricity)

etc , etc.

I don't have time to follow this , but good luck (energy recovery is a noble cause).

This is not an uncommon thing.

Install a heat exchanger in the flue gas, and extract heat , keeping the temperature of the gases above condensation temperature, and produce steam,

Use the steam to drive a steam turbine whic in turn is connected to an electrical generator.

OLD F**T IS CORRECT. COMMONLY CALLED COGEN PLANTS.

Old FooT, would freon also be suitable for driving turbines. The traditional cycle uses steam, but must this be so? Freon certainly boils at a lower temperature, so it could be used at flue-gas temps lower than would be practical for steam, wouldn't it? I'm also thinking here of co-gen plants for lower flue and turbine "exhaust" temps where steam cycles simply aren't practical. Some solar ponds also use freon-based loops with some success, or so I've heard.

-e

To europium and others:

Freon is good. What about ammonia? It is cheap, it is "green', it is readily available and one can sure smell ammonia when a small leak occurs.

I have the time and money to investigate ALL the different alternative ways to convert the waste heat from this lime plant into electrical energy. If we can use simple technology that is easily applied to this type of coal burning facility then other facilities will be standing in line to co-gen electricity. We don't have to recycle all of their waste heat but enough of the 'easy' heat to make it worthwhile. Easy heat might be concentrating the radiant heat coming from the two huge rotary kilns (each one, close to 200 feet long) the surface temperature is 850 F 'hot end' to 480 F at the cool end.

Perhaps finned tubing could be placed in the exhaust system after the bag house to collect the heat and bring it outside to a generating device.

I have looked into stream turbine generators and I think that that type of system would be too difficult to retrofit into a coal fired plant. What about some of the new Stirling technology? What about direct heat to electric generation??? There has to be an idea out there in somebodies head that needs to be talked about.

Thank all of you for your good comments so far....keep them coming.

Scout02

Sorry but... how much is 480°F in the Système International °C?
Just kidding, I can figure that out somewhere with a conversion formula.

The point is what you wish to obtain from the waste energy. Electricity, Torque+RPM (at what RPM then?) Hot water, Chemical energy...

Flue gas, is that something like exhaust gas. Then you can also think on recovering the CO2 that it contains to increase biofuel production rate (with algae). Think of the financial aspects of not emitting CO2 into the atmosphere. There is a market for this even if the tonne of CO2 is at a bottom price right now. De Beers in South Africa has started doing this with Greenfuels Technologies Ltd. and decided to invest 372 million Euro in algae cultures.

Coming back to waste heat:
There are different things you can do with it.

One company specialised in this matter is heat2power SARL in France. I happen to be commercial director of that and we have conducted a benchmark on some 15+ different technologies to regenerate waste heat of various temperature levels. Actually we specialize in waste heat regeneration systems of various kinds. One technology in particular is the fruit of our own engineering and we aim to license the technology in the transportation sector because we managed to combine high regeneration efficiency with high specific power (which is not the case with Sterling for example), very reasonable cost and low complexity. But of course we can also help you with other technologies if they occur to be more convenient for your application.

You can find us at www.heat2power.net

Please contact me directly per email or phone and I will be happy to discuss this matter further. One thing is sure: there is a lot that can be done even at 480°F.

Ammonia? Good call!

-e

Europium mentioned Stirling Engines as a means of utilising the heat extracted through the heat exchanger. Yes, This is an ideal application for the modern Stirling technology now emerging.

we are building a chickeh house heater that uses sawdust as fuel and using the flue gas to dry the sawdust however if we coud get electricity out of the 400 degree plus flue gas it would be great

You could use a working fluid other than water, but cost & complexity go up.

If your final exhaust temp. is lower, you'd also need a taller stack, or
maybe be forced to accept parasitic fan loads to maintain draft.

"...keeping the temperature of the gases above condensation temperature..." - of H₂SO₄, about 135degC, otherwise the flue will be subject to chemical attack.

Not only creation of electricity but one can look at using the excess heat for reducing energy needs of the plant such as heating via a boiler system, pre-heating boiler water, and the list of uses goes on.

Generation of electricty is a good and noble thing to do with the otherwise wasted heat energy but it can and will most likely be very exspensive taking quite some time to recoop the cost.

Hi everybody

You can take inspiration from combined cycles which use exhaust gas turbine flue gases to feed a heat recovery steam generator (HRSG). To me freon is not common for co-generation puposes, steam is the most suitable.

The steam generated in the HRSG can be used to drive a steam turbine or to feed a district heating.

From the temperature of exhaust gases (480°F) and their composition you can determine the pressure of superheated steam. You have just to draw the cooling and heating curves of steam and flue gases and to define pinch (temperature approach say 8 F).

From the mass flow of exhaust gases and by an energy balance you can determine the mass flow of steam.

good luck

kamel

kamel writes: "To me freon is not common for co-generation puposes, steam is the most suitable."

-----

My question is really more of what makes steam more suitable. Is freon less suitable simply because it is less common, or are there real, physical reasons why this is so? Further, some flue-gas temps are simply too low to produce steam at all, but the bulk heat could be used to "fuel" a freon cycle nonetheless. Power plants are notoriously inefficient, hovering at around 34% efficiency. Surely we can do better than that.

Kind Regards,
-e

Europeum is right-I fully agree.

Water may be an intermediate heat tranferer like this:

Flue Gas will be 60% CO2 + 40% N₂

So Spray correct water flow rate onto the Exhaust (flue) Gas channel -- such that goes out mostly CO2+N2---and very little Steam + Lots of Hot water at ~95⁰C--- to the Freon or ammonia Cycle.

Idea is --avoid huge and expensive finned tube low pressure water boilers.

Freon Cycle will have to be sealed closed loop- because this is expensive and dangerous Greehouse Gas.

Ammonia cycle plants are all around--chilling /refriegerating. Can be efficiently arranged by our French friend in www.heat2power.net. Others too are active.

On top of it all ,you can earn a lot, selling CO2 gas(Dry ice) or MIG/MAG welding Gas

I think steam would be the more viable option because it is readily available, but also because you would not have to use a closed system, making it easier to implement. Freon and other options would have to be contained, while a steam system could vent directly to the atmosphere, no cooling exchangers etc. Also, it is important not to confuse temperature and heat. I can't even find data for refrigerant 134a, like freon, for 480F, and it boils at -12F... Water is 212F and data is readily available.

The real problem is ensuring that tampering with the exast gas does not interfere with the initial turbines. As long as the heat exchanger does not impede the flow - ever- the company will probably not have a problem and allow you to do it. No one has stated the actual circumstances. The turbines were probably designed to run with a relatively high efficiency, perhaps the company will not bother with the idea because the power generated would be so small by comparison. Salvaging CO2 would be difficult.

So, if you're actually planning to do this, and time and money are factors, the easiest path would be the one suggested by Old F**t. The easiest isn't always the best, but it is the most likely to actually be done and completed. Good luck.

Guest writes: "Freon and other options would have to be contained, while a steam system could vent directly to the atmosphere, no cooling exchangers etc."

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Closed-loop systems are used all the time - in nuclear-reactor-based systems. There are even loops which use sodium metal for their heat-transfer mechanism, and you and I both know these systems are not vented to the outside. What a mess that would make!

None of this is rocket science. We'll begin to put more of this waste heat to good use when the economics of generating power efficiently demand it - but only after we've wasted most of our resources first and finally stop treating Nature's pockets as being infinitely deep. Nothing quite like a crisis to get us to think for once. It's always the Same Story, Different Day. An endless litany of short-sightedness, immediate return-on-investment, and Doing Things This Way 'Cuz We've Always Done It This Way.

-e

Closed loop systems are used all the time... and that also qualifies as a way we've always done it... Nuclear subs use lead, but how is the efficience boosted by this? Scout's resources have not been established, the simplest and cheapest ways (to convert heat to mechanical energy) should not yet be cast aside.

I understand the frustration of fossil fuel power generation, but it is the #1 source in use today. Alternative energy is another question altogether.

Nuclear subs do not use lead!!!(only for shielding dumb arse) they tend to use heavy water and heat exchanges. (US) the russian I beleive where using liquid metal for transfer and sheilding(lithum i think)

Why steam? compare the cost of 100 gallons of water to 100 gallons of Freon...

Hay is cheaper than gasoline, so why isn't everyone riding horses?

Is hay cheaper than gasoline if compared on a energy output level? Lot of "bang" in a gallon of fuel.

You also have to look at standby costs. Park a car and you can turn it off. Horse keeps ticking over 24 hours a day.

There are years of experience with the use of steam for co-generation of electricity. Using freon may be possible but unless you can find some company that has experience with the process and has suitable turbines you will be facing huge development cost.

Mike Love

we'd rather stick with the good old tried and true and as the world's largest consumer of natural resources flush 66 cents out of every energy dollar down the toilet. then breathe and drink the waste products of our gross inefficiency. you're kicking a dead horse my friend. care for some sealing wax?

Given the cost of energy, it is likely that the flue gas is kept at that temperature for a reason. The most likely(since they are burning high sulfur "soft" coal) reason is that lower temperatures lead to corrosion in heat exchange equipment. If it didn't, they would preheat the combustion air with the effluent. The economics easily drive this, unless they are morons, and if they are still in business in that industry, they are not).

The difficulty in recovering low temperature(hence low value) heat is that the value of the energy put into making and maintaining the equipment is larger that the value of the energy that can be recovered. There are many "Green" concepts where this is true.

Given that the frenchman does not have the ability to convert from C to F, I would take advice from the "Energy" company that he represents with a grain of salt, along with much of the advise you gotten above. If you really want to help energy efficiency, ask the company why they don't install an air preheater for their furnace. Anything else is a waste of time, money, and energy(the kind you can measure).

Best Regards

Chemsimman

Chemismman to answer your question from another post:

The statement was something that I made up. I was always told as a child you cannot discipline a cat like you can a dog, it will only learn to fear you. I cannot guarantee it is original, it does sound like many other Zen style quotes to me.

In relation to the same statement, I once saw my neighbor smack his cat, for killing a young squirrel. It was nothing that would be classified as grievous bodily harm; Rolf Harris was not called to airlift it to Battersea, it was quite funny to watch. The cat is still up to his same antics, contributing to the estimated 275 million animals killed by cats in Britain each year (sorry this isn't an animal welfare rant either, it is an anecdote).

The below link requires a dry sense of humor, and should not be visited if you are offended by the minor use of profanities or only looking for a cat related link.

http://www.alan-partridge.co.uk/multimedia/videoclips/imalans02/s02e06/16Alan%20gets%20annoyed%20by%20someone%20saying%20that%20didn%27t%20like%20his%20book.wmv

If that does not work try the below link and select the second last clip:

http://www.alan-partridge.co.uk/multimedia/videoclips/imalans02/s02e06.htm

I apologize for disrupting this serious discussion.

Thanks. I may use the quote in other context, if that is all right.

Best Regards

Chris

It has only one meaning.

The Air Preheater route can utilize WASTE ENERGY Streams, such as flash steam from boiler surface blowdown, high temperature condensate, or high temp. fluid streams if a fluid to air option is considered.

Simply developing the finned air preheat steam or fluid coil air heater, and adjusting the combustion air fan to allow for any additional pressure drop across the air preheater may have the simple benefit of insuring that constant combustion make-up air temp. is available. This assists in proper boiler tuning, energy balance.

A simply stack gas heat recovery unit that stays clear of any exit gas temps nearing dewpoint would not be a bad option, meeting required codes and of rugged construction with some cleanable, or easily inspected/removable features which are available.

As mentioned, there has to be consideration if the total ROI for new equipment has a reasonable payback (e.g. 3 yrs or less) to accomodate the equipment capital.

Even coal pricing is increasing so the ROI's may look OK, depending on hours of operation of the equipment.

Thermal-Chemical decomposition of H2O at 800 degree F. plus 6-component catalyst with 50% kickstart by tube recapture. Basics appeared in print following Iraq War and logic was counter-threat to possible knee-jerk reaction by Oil Cartel members. Argonne National Laboratory in Illinois, USA, gave recipe details to media. Threats cooled and no more articles. Feed back partial H2 and O to reach 800 F. Balance H2 and O can offset coal use for clinker production and reduce emissions. Highest and best use.

You have the necessary conditions to use a "Working Fluid" vapor cycle generating system.

The fluid must be chosen so that the highest temperature of the collecting coils or tubes do not exceed the breakdown temperature of the fluid to be vaporized. Water may work but you must do some more research first to select your fluid.

The heat collector coil (call it the evaporator or boiler) will have to be of an un-reactive material such as stainless steel.

To be efficient you should use a regeneration type system that uses the spent fluid to raise the temperature of the input fluid.

Turbines can produce large amounts of shaft output power but require larger installations.

Piston type steam engines are not as practicable as turbines.

That is a very large amount of heat to just throw away.

Luck to you.

Scout02

While heat recovery via an exchanger and eventual steam turbine-driven power production is a standard method of cogeneration from a high-temp source, it is by no means the only use to which this currently wasted resource can be put.

Thermocouples located in the flue will produce electricity directly from a high heat source with no intermediary steps.

A Venturi tube run along the exhaust line of the kilns will produce a heat source at its minor diameter component and a cooling source at the large diameter component. Arranging take-offs at each can provide the temperature difference required to drive Sterling engines. The Stirlings can be put to a variety of uses, including running generators.

In addition to being taken off to run various mechanical devices, the heat can be stored in heat sinks (e.g. piles of igneous rocks kept in insulated underground chambers, heated by the waste kiln heat) and released for use during the cold seasons to assist in heating the kiln plant offices (and other) buildings not immediately adjacent to the kilns.

An adjacent non-commercial kiln can be built nearby, taking its heat from the lime kilns and offered as a community resource for potters.

Some of the waste heat generated can be used for hydroponic greenhouse heating of tropical food crops.

How creative do you want to be with this?

Mark

What's the efficiency of a thermocouple? They're such simple devices, but still not widely used except where they are the most viable option. Deep-space probes (Voyager, et al), for example.

-e

Consider also generating electric power through chimney effect.

As an inspiration, read the following patent: US 6201313.

Regards

Scout02 to all the great commentators;

Thanks again for all of the good ideas. The plant manger asked me to visit Tues or Wed. to take a plant tour and spend as much time as I wanted with the plant environmental engineer, asking questions. So in the near future I should have a lot more information about mass flow, percentages of different gases, temperatures at different parts of the gas stream.

I, of coarse am not a trained engineer, but I do have a good bit of curiosity and drive to see a project to completion when I decide which direction to go. So, how about making up a list of questions to ask this engineer? That might save both of us some time in the discovery process.

Sincerely,

Scout02

The question I'd be asking is why are they not already using this heat. Preheating their combustion air is an obvious and well used method of increasing efficiency. Why are they not already doing this, or are they? It's possible that the temperature of the flue gas was determined to be as low as practical back at the original design stage. 250C at ground level is not a lot lof temperature to play with. Reduce it further and possibly all sorts of corrosion issues will follow further up the stack. Possibly they'll lose a required draught.

Of course it's possible that none of this applies and there's all this energy going to waste! Interesting topic.

nutwood;

Yes, they are preheating their combustion air and they are preheating the limestone. They achieve about 25% calcine rate in the preheater. Their two stacks are very tall and I have never seen a wisp of anything come from those stacks. One would think the plant is shut down but they are burning 500 tons of coal a day!

Wed. at 9:00 am I get the grand tour and will be able to ask the environmental engineer any questions I want. Mass flow, gas mix, temperatures at different parts of the plant. Were do they feel a device could tap that energy to produce electricity?

What about giant thermoelectric devices? Produce electricity directly from the heat.

Take care.....Scout02

Traditional dissimilar-metals-type thermoelectric (Seebeck effect) devices are around 10% efficient, but semiconductors have recently been demonstrated at higher levels of efficiency, up through 18%. Here's a link to an article describing efforts in this area by MIT researchers and others. Be forewarned that this article was written (apparently) by someone who doesn't understand the technology. It is under conditions of a difference in temperature that thermoelectric devices generate power. The article speaks as if the entire device is at a uniform temperature, so it's unclear whether the temperature is of the hot side referenced to ambient or what. I'm guessing it is, but the author doesn't say so.

You might not wish to suggest a "giant" thermoelectric device on your tour, as it is far more likely that this technology would be realized in practice as large arrays of very many small TE devices in combination. For my part I pictured this single jimongous 10-storey high junction parked inside a flue!

Hope this helps.

-e

Then entropy difference(the ability to do work) of this stream is very limited. Turning the energy into mechanical work(electricity, et.al) will be a futile effort.

The reasonable disposition for this sort of energy is using it in some sort of heat integration scheme. The likelyhood that they are maximizing the preheat of their incoming streams is low, and internal use(decreasing the amount of coal used) would be the most energy efficient scheme. The devices that have beens suggested for generating electricity typically do not form enough energy in their lifetime to manufacture the device, much less pay for them.

Best Regards

Chris Becker

Re: How to take energy from 480F degree clean flue gase: Generating electricity with a supply of 480 degree F. flue gas is physically feasible but not financially practical. The most prevalent problem is generating steam from 480 degree F. flue gas, the best one can do is 35 to 40 psi saturated steam and even at that it would require a lot of heating surface, and a balanced draft device to ensure the integrity of the lime kiln operation. The small amount of electricity from a 40 psig Steam Turbine or steam engine would be very expensive.

A better use would be in a HVAC application where building heat is required in the winter and Air Conditioning in the summer. Space steam heaters could be utilized for winter heat and a Steam Chiller used for summer air conditioning. Both of these systems would function well with a 35 psig staurated steam supply. From Donnie H

Operating and tested stirling engines operate at a heater temperature of about 700 degrees C. or 1292 degrees F. in the range of a less than a kw to 55 kw. Thermal efficiency of stirling engines or power output divided by heat input is in the range of 20% to 35%.

Stirling engines will not be recommended for use with 480 F. flue gases because efficiency and power output will be very low.

Absorption refrigeration using ammonia for the production of ice or air conditioning will be very practical but COP will only be in the range of 0.5 to 0.8

As an interesting aside, it is possible to remove the evaporated alcohol from the flue gases emitted at bakeries, partly to reduce local odour problems and partly to use it as a fuel. HM Revenue and Customs scuppered a recent project proposal, by insisting that Excise Duty was paid upon the alcohol recovered, and thereby rendered the project uneconomic...

86% of HM's Revenue and Customs lackeys should be shot on the spot as an example to the other 14% and any wannabies.

-e

What an interesting World that would be...

Relax, Slack. Hyperbole.

-e

Hi, Kris is right - first consider using heat without converting it into electricity. If not - try mayby Stirling Engine - quite easy, effective and can be easyli connected with electric generator. It's much safer than steam engine.

To all who are interested, here are some numbers I found on my tour of the lime plant

today.

Here are some facts.

There are two kilns, each one is 215' long and 16' in dia.

Each kiln burns 10 ton of coal per hour. ( a railroad car holds 100 ton )

There is 26.4 million BTU / ton.

The inside temp. is 850 F at the hot end and it loses about 35F for every 25' of lenght toward the cool end. The temp of the outside skin they said would be about 480 F.

The mass-flow of gases up the stack is 100,000 dry standard cubic ft./ minute per each kiln.

The PSI of gasses at the bottom of the stack is about 30" of water column.

The temperature of gasses at the stack bottom is about 400 F.

The outside temp. of the stack bottom is about 325 F.

NOX produced per day is 9360 lbs.

NOX is 275 PPM. of the exhaust gasses.

SOX up the stacks is 150 lbs. per day.

32% of the total gasses going up the stacks is CO₂

I have very good resources where combustion technology is concerned. This is a huge amount of waste heat. Best thing would be to capture & reuse to pre-heat combustion air thereby reducing the amount of fuel input to the kilns. Realize the savings at the appliance. Simple & efficient.

The stacks exist for reasons that were important years ago and are not relevant today. Knock them down, use fans to draw & exhaust air through the kiln at gound level (if draft is required), instead of natural draft from chimenies lined with mega-tons of refractory absorbing mega heat storage & radiating substantial levels of heat from exterior surfaces as well.

Direct the 480F. gasses through a purpose built, high efficiency excahnger. Use exchanged warm air & re-direct back to the burners. Keep duct velocities below 1200 FPM. Insulate all ductwork, use mild steel up to the exhchanger & grade 316SS after that.

I have manufactured Co2 generators using flue gas as source. A system of stainless condensers, columns & reboilers along with amine as the primary liquid. Very high recovery rate & amine can be recyled over & over. In this case the company would need to find a big customer for the Co2 cuz there would be a swack of it.

Save all the space age thinking for use when the space age arrives.

Just out of curiosity, what were the reasons for the stacks that are no longer important?

I think somewhere it was mentioned that they are using a preheat system for both combustion air and product.

To Daveco & Nutwood

You are right. This plant uses recycled heat for rising the temp of both combustion air and in bringing incoming limestone up to calcine temperatures. They also heat and dry the coal used for combustion with recycled heat. In every respect they appear to be a modern plant with an eye on the bottom line. This of coarse means to be as efficient as possible in the use an reuse of heat generated in the lime kiln.

If (and I think there is ) technology out there to completely scrub the plant exhaust of co2 and other gases then the tall stacks would not be that important.

They do use a +2,000 HP fan to pull the gasses through the bag house and push the clean (of particulates) exhaust up the stacks.

Thanks for the good comments, I think we are starting to hit the right track. Good work Daveco. Keep in touch.

Scout02

TO: Scout & Nutwood

The two basic reasons for tall chimneys: 1) create draft. 2) eject soot & toxic gasses upward.

CREATING DRAFT: Tall chimneys were first required with hot water & steam boilers when the state of combustion from mixing fuel & air was limited to the "atmospheric" process. In the advent of "power fired" burners, natural draft provided by tall chimneys (in most cases) was no longer required. Today draft is only required when appliances (boilers) have hot flue gas temperatures and dilution is required to reduce gas temperature through the chimney itself. (Building Fire code reasons).

You'll find many boilers still using tall stacks and any refinements made to continue with those stacks would simply be due to code compliance. In most cases the code required height of a stack is driven by consideration to: prevailing wind, rain & snow conditions, proximity to other buildings, exhaust gas temperatures & building code, & make-up of emissions. (All of this has more to do with being a good neighbor than the actual physics of exhausting from the appliance).

look at the definition of the word "chimney" it won't take long before you find the synonym "smokestack" which brings us to point 2: (Soot) Even with much of today's modern heating equipment and refined natural gas as fuel, you'll see a ring of soot around the outside of the stack. That soot can be a real problem which in itself is a topic. Smoke & soot from chimneys was commonplace until 70% of the way through the 19th century so the implementation of tall chimneys along with the tell tale problems & gremlins still lingers today.

Inevitablely, it was found that tall chimneys which exhausted well above the roof tops helped to dissipate the smoke into the wind, minimizing soot ppm & negative impact on people and buildings nearby. Today the empasis is more on emissions and getting that straightened out first so that you can exhaust wherever without chokin out your neighbor.

IN THIS CASE: There is no reason you can't have a system that exhausts at say...150F & has corrosive makeup. If corrosion is an issue (and it will be) then design to withstand.

At this point cut to the chase and do the math to estimate the savings by reducing exhaust gas temperature at the back end. Comming up with a capital cost to install the new equipment is easy. Divide the capital cost by the monthly fuel cost savings to render a ROI. (It should look tasty to those who currently cut the fuel cheques).

I realize they are alreay preheating combustion air as you have mentioned and that's a noble effort. They may be doing that for the following reasons: 1) Dependant on the type of burners & to aid in the combustion process. 2) To aid in draft - assistance to existing fans. 3) designed to minimize corrosion.

And in so doing have nessecitated the utilization of a tall chimney / stack.

However, you have about 300-350F net extractable, and right now its being ignored! So the business of preheating is not over yet I'd say. Give me a bit of time & I'll crunch some numbers to give you a realistic fuel input reduction estimate. I think I have enuf data from youre earlier messages to carry this through.

There is no reason to have anything but perfectly clean or acceptable emmisions from any process. It's clear to me that those who hold the power to enforce positive changes, do not for very selfish reasons and of which our kids will be paying. So it's nice to see when a company takes the initiative to improve.

ps: Do they use cyclones along with the baghouse? and if so, are the cyclones upstream or downstream of the baghouse? What is the particulate load being caught at the baghouse..(Lbs / day)?

Daveco

The wheat is beginning to separate from the chaff.

I will contact the operations engineer today. From what I have been told I know that the particulate load can be variable. When they mine the rock sometimes the quality will vary a bit. This causes more dust to be formed and I suppose that is caught in the bag house.

Thanks for your serious effort to help make this plant better than it already is.

Scout02

Scout: I grew up in a wheat field, I know all about separation. It is better for one to be out standing in his field. aaahhhh

So I took a quick look and crunched the following:

Given: (Coal releases 12,300btu/Lb) and (Location elevation is 2000Ft above sealevel) and (location anmbient air temperature is 70F.) and (Actual exhaust temp is 400F.) and (Exhaust pressure after the induction fans is 20" W.C.) and (100,000SCFM Air Flow) and (lining / refractory thickness is 1.25ft) and (Fuel consumption is 24.6 Mbtu/Hr):

Mass air flow corrected for elev, temp & press = 291,424Lbs/Hr.

Net temp Available: 330F. & Cp of air is .241

Btu's Heat energy Available will be: 23,176,927 btu/hr.

System Recovery Rate: 75% (Est.)

Heat Savings you can take to the bank: 17,382,695 btu/hr.

Factor in the btu's per hour / per pound, released from coal and given the current rate of consumption at 20,833lbs/hr of fuel, you finally arrive at the lbs per hr of fuel that would be saved: = 6.78% equivalent to 1,413.2 Lbs per Hour.

Also looked at the stoichiometric air required to burn the coal and right now they are driving anywhere between 20-33% excess air through the kiln (depending on what the negative pressure actually is). Maybe they could tighten that up a bit to reduce exhaust flow. Maybe they have to do this to meet emissions I suppose eh? That could potentially be corrected by implementing better burner technology...not to sure on that one??

Air velocity through the Kiln is low at 693FPM.

It would be interesting to know what type of burners they have and whether switching to nat gas fuel is cost effective?

Good luck with this.....Daveco

If you are bunning 500 tonnes of coal you surely can afford a small electrical engineer and someone to design a small power station, my advice is dont mess about here advertise and get ppl on it straight away and save $$$$$$$ ...

To Guest,

Of coarse we could hire a group of competent EEs. But would we get original and fresh ideas, that some people in this group are more than capable of generating, I think not.

Who wants to REALLY make a contribution for a more energy efficient future? Let's hear from you!

This task of converting waste heat is just the start of turning this plant into the 'greenest' large coal fired plant in the USA if not the world. The other technologies that may be applied to this facility would actually make it a negative carbon emitter

I can't talk about that stuff because of signed 'confidentiality agreements'.

Here, on this forum, we are interested in novel ways to reclaim waste heat and convert it to electricity.

Keep those good ideas coming! "We are making a list and checking it twice".

Scout2

What diameter and hight has the stack? It seems you have a pretty good airflow there and I still vote with the chimney effect for driving "wind" turbines + induction generators.

Maybe you also have more to work on the combustion efficiency. Here is a link:

http://www.osti.gov/energycitations/servlets/purl/889826-CKC6yR/889826.PDF

"...can afford a small electrical engineer..."

-----

Experience suggests that smaller ones tend to overcompensate by having greatly enlarged large egos. Are you sure of this recommendation? (just kidding!)

-e